![FFIRS 12/06/2011 10:20:19 Page 4
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Library of Congress Cataloging-in-Publication Data
Micro and smart systems / G.K. Ananthasuresh . . . [et al.].
p. cm.
Includes bibliographical references and index.
ISBN 978-0-470-91939-2 (acid-free paper)
1. Microelectromechanical systems—Design and construction. 2. Intelligent control systems—Design and
construction. I. Ananthasuresh, G. K.
TK7875.M524 2012
621.381—dc23
2011029301
Printed in the United States of America
10 9 8 7 6 5 4 3 2 1](https://image.slidesharecdn.com/2226335-250619015800-040ad3b4/85/Micro-And-Smart-Systems-Technology-And-Modeling-1st-Edition-G-K-Ananthasuresh-10-320.jpg)
![C01 11/29/2011 9:1:12 Page 1
c
CHAPTER
1
Introduction
L E A R N I N G O B J E C T I V E S
After completing this chapter, you will be able to:
c Get an overview of microsystems and smart systems.
c Understand the need for miniaturization.
c Understand the role of microfabrication.
c Learn about smart materials and systems.
c Learn about typical applications of microsystems and smart systems.
Mythology and folk tales in all cultures have fascinating stories involving magic and
miniaturization. Ali Baba, in a story in 1001 Arabian Nights, had to say Open Sesame to
make the cave door open by itself. We now have automatic doors in supermarkets that open
as you move toward them without even uttering a word. Jonathan Swift’s fictitious British
hero, Lemuel Gulliver, traveled to the island of Lilliput and was amazed at the miniature
world he saw there. Gulliver would probably be equally amazed if he were washed ashore
into the 21st
-century world because we now have fabulous miniature marvels undreamt
of in Swift’s time. Magic and miniaturization are realities today. Arthur C. Clarke, a
famous science fiction writer, once said that ‘‘a sufficiently advanced technology is
indistinguishable from magic.’’ What makes this magic a reality? The answer lies in exotic
and smart materials, sensors and actuators, control and miniaturization. Smartness and
smallness go hand in hand. Smart systems are increasingly becoming smaller, leading to a
magical reality. Small systems are increasingly becoming smarter by integrating sensing,
actuation, computation, communication, power generation, control, and more. Like the
Indian mythological incarnation Vamana, described as being small and smart, yet able to
cover the Earth, sky, and the world beneath in three footsteps, the combination of smallness
and smartness has limitless possibilities. This book is about microsystems and smart
systems, not about magic. As Nobel Laureate physicist Richard Feynman noted in his
lectures, the laws of science as we know them today do not preclude miniaturization, and
there is sufficient room at the bottom [1, 2]. It is only a question of developing the requisite
technologies and putting them together to make it all happen. Let us begin with the need
for miniaturization.
1](https://image.slidesharecdn.com/2226335-250619015800-040ad3b4/85/Micro-And-Smart-Systems-Technology-And-Modeling-1st-Edition-G-K-Ananthasuresh-29-320.jpg)
![C01 11/29/2011 9:1:13 Page 4
are comparable to those of micromechanical structures. So, there is a subfield within
microsystems known as ‘‘bio-microelectromechanical systems’’ (bio-MEMS). Further-
more, there are reasons for miniaturizing chemical processing. Controlling process condi-
tions over a small volume is much easier than over a large volume. Hence, the efficiency of a
chemical reaction is greater in miniaturized systems. It is clear from this perspective why
living organisms are compartmentalized into micron-sized units—the cells.
Miniaturization can result in faster devices with improved thermal management.
Energy and materials requirement during fabrication can be reduced significantly, thereby
resulting in cost/performance advantages. Arrays of devices are possible within a small
space. This has the potential for improved redundancy. Another important advantage of
miniaturization is the possibility of integration of mechanical and fluidic parts with
electronics, thereby simplifying systems and reducing power requirements. Microfabri-
cation employed for realizing such devices has improved reproducibility, and devices thus
produced have increased selectivity and sensitivity, wider dynamic range, improved
accuracy and reliability.
Integrated microsystems are a collection of microsensors and actuators that can sense
their environment and react to changes in that environment by use of a microcircuit control.
Such microsystems include, in addition to the conventional microelectronics packaging,
integrated antenna structures for command signals, and microelectromechanical configu-
rations for desired sensing and actuating functions. The system may also need micropower
supply, microrelay, and microsignal processing units. Such systems with microcompo-
nents are faster, more reliable, more accurate, cheaper, and capable of incorporating more
complex and versatile functions than systems used today.
A miniaturized low-power transceiver is an excellent example of a microsystem
technology. Figure 1.3(a) shows a simplified block diagram of a transceiver and a
board-level implementation of the same consisting of several chips that are basically
components with high quality-factors such as radio frequency (RF) filters, surface
acoustic wave (SAW) intermediate-frequency (IF) filters, crystal oscillators, and
transistor circuits [3]. A possible single-chip implementation of this transceiver using
microsystems technology is shown in Fig. 1.3(b). This enables miniaturization as well
as low power consumption.
c 1.2 MICROSYSTEMS VERSUS MEMS
We have presented several reasons for miniaturization from different points of view. Let us
now examine how microsystems technology came into existence. In the late 1960s and
early 1970s, not long after the emergence of the integrated chip, researchers and inventors
in academia and industry began to experiment with microfabrication processes by making
movable mechanical elements. Accelerometers, micromirrors, gas-chromatography instru-
ments, etc., were miniaturized during this period. Silicon was the material of choice at that
time. A seminal paper by Petersen [4] summarizes these developments. Increased attention
to the microsystems field came in late 1980s when a micromachined electrostatic motor
was made at the University of California, Berkeley and Massachusetts Institute of
Technology, Cambridge. This moving micromechanical entity fascinated everyone and
showed the way forward for many other developments. The acronym MEMS was coined
during that period. However, this acronym is inadequate today because of the numerous
disciplines beyond just mechanical and electrical that have joined the league. A more
suitable term is ‘‘microsystems;’’ hence the title for this book.
4 c 1 Introduction](https://image.slidesharecdn.com/2226335-250619015800-040ad3b4/85/Micro-And-Smart-Systems-Technology-And-Modeling-1st-Edition-G-K-Ananthasuresh-32-320.jpg)
![C01 11/29/2011 9:1:13 Page 5
c 1.3 WHY MICROFABRICATION?
Microsystems technology emerged as a new discipline based on the advances in integrated
circuit (IC) fabrication processes, by which sensors, actuators and control functions were
co-fabricated in silicon. The concepts and feasibility of more complex microsystems
devices have been proposed and demonstrated for applications in such varied fields as
microfluidics, aerospace, automobile, biomedical, chemical analysis, wireless communi-
cations, data storage, and optics.
In microsystems, miniaturization is achieved by a fabrication approach similar to that
followed in ICs, commonly known as micromachining. As in ICs, much of the processing
is done by chemical processing rather than mechanical modifications. Hence, machining
here does not refer to conventional approaches (such as drilling, milling, etc.) used in
realizing macromechanical parts, although the objective is to realize such parts. As with
semiconductor processing in IC fabrication, micromachining has become the fundamental
technology for the fabrication of microsystems devices and, in particular, miniaturized
sensors and actuators. Silicon micromachining, the most mature of the micromachining
(a)
Surface
acoustic
wave
(SAW)
RF filter LNA
VCO
VCO
BPF
Mixer Mixer
IF Amp.
Baseband
processing
circuits
IF filter
Off or
on-board
antenna
Crystal
oscillator
Off-chip
Ceramic
or board
level MIC
(b)
RF filter LNA
Micromachined
filters
Micromachined
filter
Micromachined
antennas
Micromachined
resonator
VCO
VCO
BPF
Mixer Mixer
IF Amp.
Baseband
processing
circuits
IF filter
Crystal
oscillator
Figure 1.3 Integrated radio frequency transceivers: a typical application of microsystems [3]. (a) Current approaches
(shaded remarks indicate components outside the electronics die). (b) Integrated MEMS-based RF receiver on a single
chip. LNA, low noise amplifier; RF, radio frequency; VCO, voltage-controlled oscillator; IF, intermediate frequency;
BPF, bandpass filter.
1.3 Why Microfabrication? b 5](https://image.slidesharecdn.com/2226335-250619015800-040ad3b4/85/Micro-And-Smart-Systems-Technology-And-Modeling-1st-Edition-G-K-Ananthasuresh-33-320.jpg)
![C01 11/29/2011 9:1:13 Page 6
technologies, allows the fabrication of microsystems that have dimensions in the sub-
millimeter to micron range. It refers to fashioning microscopic mechanical parts out of a
silicon substrate or on a silicon substrate to make three-dimensional (3D) structures,
thereby creating a new paradigm in the design of miniaturized systems. By employing
materials such as crystalline silicon, polycrystalline silicon, silicon nitride, etc., a variety of
mechanical microstructures including beams, diaphragms, grooves, orifices, springs,
gears, suspensions, and a great diversity of other complex mechanical structures have
been conceived, implemented, and commercially demonstrated.
Silicon micromachining has been the key factor in the fast progress of microsystems in
the last decade of the 20th century. This is the fashioning of microscopic mechanical
parts out of silicon substrates and
more recently other materials. This
technique is used to fabricate such
features as clamped beams, mem-
branes, cantilevers, grooves, ori-
fices, springs, gears, chambers,
etc., that can then be suitably com-
bined to create a variety of sensors.
Bulk micromachining, which in-
volves carving out the required
structure by etching out the silicon
substrate, is the commonly used
method. For instance, a thin dia-
phragm of precise thickness in the
few-micron range suitable for inte-
grating sensing elements is very
often realized with this approach.
Figure 1.4 shows the scanning elec-
tron microscope (SEM) image of a cantilever beam of SiO2 fabricated by bulk micro-
machining (wet chemical etching) of silicon. The dimensions of this cantilever beam are
length ¼ 65 mm, width ¼ 15 mm, and thickness ¼ 0.52 mm (1 mm ¼ 106
m).
Surface micromachining is an alternate micromachining approach. It is based on
patterning layers deposited on the surface of silicon or any other substrate. This approach
offers the attractive possibility of integrating the micromachined device with micro-
electronics patterned and assembled on the same wafer. In addition, the thickness of the
structural layer in this case is precisely determined by the thickness of the deposited layer
and hence can be controlled to submicron thickness levels.
Figure 1.5 shows a schematic of a polycrystalline silicon resonating beam that can be
made by the surface micromachining technique. Note that the resonator beam is anchored
at its ends and that a gap of d ¼ 0.1 mm exists
between the resonator and the rigid beam laid
perpendicular to it. As a result, the resonator
vibrates at the frequency of the ac signal
applied to it with respect to the rigid beam
and a current flows due to the capacitance
variation with time. This current peaks when
the frequency of the input signal matches with
the mechanical resonance frequency of the
vibrating beam. Thus the resonator can be
used as a filter.
Figure 1.4 SEM image of SiO2 microcantilever beam
prepared by bulk micromachining (wet chemical
etching) of silicon.
Anchor Resonator
Rigid beam
Electrodes
Figure 1.5 Schematic of a resonator beam [4].
6 c 1 Introduction](https://image.slidesharecdn.com/2226335-250619015800-040ad3b4/85/Micro-And-Smart-Systems-Technology-And-Modeling-1st-Edition-G-K-Ananthasuresh-34-320.jpg)
![C01 11/29/2011 9:1:14 Page 8
cooled. However, what distinguishes a smart material from the rest is that we design the
material so that such changes occur in a specific manner for some defined objective to be
accomplished. Hence, the main feature that distinguishes smart materials is that they
respond significantly to some external stimuli to which most materials are unresponsive.
Furthermore, one would like to enhance such a response by at least one or two orders of
magnitude over other materials.
Both active and passive approaches have been attempted in this context. This distinction
is based on the requirement to generate power required to perform responses. Hence, an
active system has an inbuilt power source. Typically, active sensors and actuators have been
favored in designing smart structures. However, in recent years the concept of passive
smartness has come to the fore. Passive smartness can be pervasive and even continuous in
the structure. Such structures do not need external intervention for their operation. In
addition, there is no requirement for a power source. This is particularly relevant in large-
scale civil engineering structures. Passive smartness can be derived from the unique intrinsic
properties of the material used to build such structures. One common example is the shape-
memory-alloy (SMA) material embedded in aerospace composites, designed so that cracks
do not propagate. Such smart materials are discussed briefly in Chapter 2.
Besides ‘‘smart system’’ or ‘‘smart material,’’ another widely used term is smart
structure. One distinctive feature of smart structures is that actuators and sensors can be
embedded at discrete locations inside the structure without affecting the structural integrity
of the main structure. An example is the embedded smart structure in a laminated
composite structure. Furthermore, in many applications, the behavior of the entire structure
itself is coupled with the surrounding medium. These factors necessitate a coupled
modeling approach in analyzing such smart structures. The function and description of
various components of the smart system in Table 1.1 are summarized in Table 1.1 [5].
Civil engineering systems such as building frames, trusses, or bridges comprise a
complex network of truss, beam, column, plate, and shell elements. Monitoring the structural
health of bridge structures for different moving loads is an area of great importance in
increasing the structural integrity of infrastructures and has been pursued in many countries.
Damping of earthquake motions in structures is yet another area that has been taken up for
active research in many seismically active countries. Smart devices derived from smart
materials are extensively used for such applications. A bridge whose structural health can be
monitored is shown in Figure 1.7. In such a bridge, fiberoptic sensors are used as sensing
devices, whereas lead zirconate titanate (PZT) or Terfenol-D actuators are normally used for
performing actuations such as vibration isolation and control.
Table 1.1 Purpose of various components of a smart system
Unit
Equivalent in
Biological Systems Purpose Description
Sensor Tactile sensing Data acquisition Collect required raw data needed for appropriate
sensing and monitoring
Data bus 1 Sensory nerves Data transmission Forward raw data to local and/or central command
and control units
Control system Brain Command and
control unit
Manage and control the whole system by analyzing
data, reaching the appropriate conclusions, and
determining the actions required
Data bus 2 Motor nerves Data instructions Transmit decisions and associated instructions to
members of structure
Actuator Muscles Action devices Take action by triggering controlling devices/units
8 c 1 Introduction](https://image.slidesharecdn.com/2226335-250619015800-040ad3b4/85/Micro-And-Smart-Systems-Technology-And-Modeling-1st-Edition-G-K-Ananthasuresh-36-320.jpg)
![C01 11/29/2011 9:1:16 Page 10
2. Microsensors: These respond to physical and chemical signals (such as pressure,
acceleration, pH, glucose level, etc.) and convert them to electrical signals.
3. Microactuators: These convert electrical or magnetic input to mechanical forms
of energy (e.g. resonating beams, switches, and micropumps).
Microsystems integrate sensors, actuators and electronics to provide some useful
function. The ADXL50, which was released in 1991 and was Analog Devices’ first
commercial device, is an excellent example of such a microsystem. The block diagram of
this system is shown in Figure 1.8 [6]. This microsystem is based on a surface micro-
machining technology with sensing electronics integrated on the same chip as the
accelerometer. Here, the accelerometer is a sensor that responds to the acceleration or
deceleration and gives an output voltage to the control circuit, which in turn triggers an
actuator to deploy the airbag during a crash, so that the persons seated in the front seat are
protected from crashing into the front windshield or the dashboard.
1.5.1 Micromechanical Structures
Micromachining is used commercially to produce channels for microfluidic devices
and also to fabricate systems referred to as ‘‘labs on a chip’’ for chemial analysis and
analysis of biomedical materials [7]. Usually such channels are made on plastics or glass
substrates. Figure 1.9 (a) shows one such device reported in the literature [8]. Micro-
machining is also used to make a variety of mechanical structures. Figure 1.9 (b) shows an
SEM image of a silicon nanotip fabricated [9] using a ‘‘bulk micromachining’’ process.
Such microtips find applications in atomic force microscopy (AFM) technology and field
emission array for futuristic vacuum electron devices capable of operation in terahertz
frequency range [10].
Output
voltage
Preamp
Buffer
Demodulator
and low-pass
filter
Square wave
oscillator
Feedback voltage
Anchor
Polysilicon proof
mass and moving
electrodes
Fixed polysilicon
capacitor plates
Suspension
system
Figure 1.8 A schematic diagram of ADXL50 accelerometer.
10 c 1 Introduction](https://image.slidesharecdn.com/2226335-250619015800-040ad3b4/85/Micro-And-Smart-Systems-Technology-And-Modeling-1st-Edition-G-K-Ananthasuresh-38-320.jpg)
![C01 11/29/2011 9:1:17 Page 12
pressure-sensitive resistors (piezoresistors) integrated on a micromachined silicon dia-
phragm. Micromachined accelerometer is yet another device which has received consid-
erable attention from the aerospace, automobile, and biomedical industries. Figure 1.10 (b)
shows a schematic cross-sectional view of one such device. The seismic mass responds to
acceleration and deflects, thus bringing about a change in the capacitance between the mass
and the fixed electrodes. The change in capacitance is a measure of the displacement,
which in turn depends upon the acceleration.
1.5.3 Microactuators
Over the last few years, micromachined actuators such as RF switches [11], micropumps,
and microvalves [12], which can be actuated using the electrostatic or piezoelectric effect,
have been reported. In addition, electrostatically actuated tiny micromirror arrays acting as
optical switches have been developed by Lucent Technologies for fiber-optic communi-
cation [13] and as digital micromirror devices (DMDs) by Texas Instruments in projection
video systems [14]. In this section, two examples of actuators are presented to highlight the
wide range of applications of microactuators. First, a schematic diagram of the electro-
statically actuated bulk micromachined silicon micropump [12] is shown in Figure 1.11.
The diaphragm deflects upward when an actuation voltage is applied as shown and the inlet
check valve opens due to a fall in chamber pressure, thereby letting in the fluid flow into the
pump chamber. When the actuation voltage drops to zero, the diaphragm moves back to its
equilibrium position. As the chamber is now full of fluid, the pressure inside is higher than
that outside. This forces the inlet valve to close and the outlet valve to open, thus letting the
fluid flow out.
The second example is the famous electrostatically actuated micromirror array
consisting of tiny mirrors as shown in Figure 1.12. Each mirror is 0.5 mm in diameter,
about the size of the head of a pin. Mirrors rest 1 mm apart and all 256 mirrors are
fabricated on a 2.5 cm square piece of silicon. The figure on the left-hand side shows how
the tilted mirrors switch the optical signals from one fiber to another fiber. Thus, there is no
need of making an optoelectronic conversion. This arrangement gives 100-fold reduction
in power consumption over electronic switches.
Deformable diaphragm
Pump chamber
Inlet
check valve
Outlet
check valve
Pyrex
separator
Actuation
voltage
Figure 1.11 Schematic of a bulk micromachined micropump.
12 c 1 Introduction](https://image.slidesharecdn.com/2226335-250619015800-040ad3b4/85/Micro-And-Smart-Systems-Technology-And-Modeling-1st-Edition-G-K-Ananthasuresh-40-320.jpg)
![C01 11/29/2011 9:1:19 Page 14
in the intracranial pressure (ICP) monitoring system. This requires pressure sensors
of chip size less than 1 mm 1 mm; also, the packaging material must be biocompatible
as the sensor is inserted into the ventricle in the brain using a catheter through a
small hole created in the skull. In yet another application, a large number of pressure
sensors, over 500, must be laid out on each wing of an aircraft to map the pressure
across the aerofoil during the development stages of an aircraft. Similarly, in oceano-
graphic applications, depth monitoring can be done with pressure sensors designed for
a wide range of pressures and suitably packaged to protect against the corrosive sea
water. Figure 1.14 gives a broad range of applications of smart materials and
microsystems.
Furthermore, the applications of microsystems can be conveniently grouped according
to major industries as shown in Table 1.3. Though this table lists diverse applications of
smart structures [15], it should be clear to the reader that there is a significant scope for
developing radically new capabilities in this domain, and that it is only limited by the
creativity and innovativeness of the human mind.
Space
structure
Aero
structure
Medical
Vibration
noise control
Automotive
Health monitoring
Self-healing
Warning
Shape
Aerodynamic
control
Rotorcraft
Drug delivery
Tele-surgery
Damping
Wall paper
Stealth
Clutch
Civil
structure
Air bags
Shock
absorber
Adaptive structures
Smart
materials
microsystems
Figure 1.14 Applications of smart materials and microsystems.
Table 1.3 Applications of smart systems in various areas
Application
Area Microcomponent or Smart Component Purpose
Machine tools Piezoceramic transducers To control chatter and thereby improve
precision and increase productivity
Photolithography Vibration control during the process using
piezoceramic transducers
To manufacture smaller microelectronic
circuits
Process control Shape memory alloy For shape control, for example, in
aerodynamic surfaces
Health
monitoring
Fiber-optic sensors To monitor the health of fiber-reinforced
ceramics and metal-matrix composites, and
in structural composites
14 c 1 Introduction](https://image.slidesharecdn.com/2226335-250619015800-040ad3b4/85/Micro-And-Smart-Systems-Technology-And-Modeling-1st-Edition-G-K-Ananthasuresh-42-320.jpg)
![C01 11/29/2011 9:1:20 Page 15
c 1.7 SUMMARY
Miniaturization and integration of a variety of components are the key aspects of micro-
systems. Besides giving rise to compact devices and systems, miniaturization leads to the
many other benefits discussed in this chapter. Miniaturization is made possible by
microfabrication techniques. Integration of sensors, actuators and micromechanical
Application
Area Microcomponent or Smart Component Purpose
Consumer
electronics
Piezoceramic and Microaccelerometers and
rotation rate sensors; quartz, piezoceramic, and
fiber-optic gyros; piezoceramic transducers
For shake stabilization of hand-held video
cameras
Helicopters and
aircraft
Piezoceramic stack actuators; PZT and
Microaccelerometers; magnetostrictive mounts
Piezoceramic pickups and error sensors; PZT
audio resonators and analog voice coils; digital
signal processor chips
For vibration and twist control of helicopter
rotor blades, adaptive control of aircraft
control surfaces
For active noise control
Submarines Piezoceramic actuators For acoustic signature suppression of
submarine hulls
Automotive Electrochromic
Piezo yaw-axis rotation sensors (antiskid,
antilock braking); Microaccelerometer (air bag
controls)
Ceramic ultrasonic ‘‘radar’’
Piezopolymer infrared (IR) sensors; rain
monitors; occupant identification; heat,
ventilation and air-conditioning (HVAC)
sensors; air pollution sensors (CO and NOx)
For chromogenic mirrors and windows
For navigation and guidance, electronic
stability control (four- heel independent auto
braking)
For collision avoidance, parking assist
For smart comfort control systems
In buildings IR, vision and fiber-optic sensors and
communications systems
For improved safety, security and energy
control systems. Smart windows to reduce
heating, ventilation, and air-conditioning
costs
Biomechanical
and biomedical
systems
SMA and polymer gel
Piezoceramic and other ultrasonic sensors and
actuators
To develop artificial muscles, active control
of in vivo drug delivery devices (insulin
pumps)
Catheter guide wire; surgical tools; imaging
devices
Computer
industry
Piezoceramic and Microaccelerometers and
rotation rate sensors
Quartz, piezoceramic and fiber-optic gyros
Bimorph-type piezopositioner
Piezoaccelerometers
For smart read/write head micropositioners
in next-generation data storage devices
For high-density disk drives
To correct for head-motion-related read/
write errors
Note: Modified after [15].
Table 1.3 (Continued)
1.7 Summary b 15](https://image.slidesharecdn.com/2226335-250619015800-040ad3b4/85/Micro-And-Smart-Systems-Technology-And-Modeling-1st-Edition-G-K-Ananthasuresh-43-320.jpg)
![C02 12/06/2011 17:19:26 Page 18
differences among various devices and systems. Although one may not understand all the
terms, the design details, and the application areas by reading this chapter, we believe that
the material of this chapter provides motivation for learning the content presented in the
rest of the book. The chapter ends with concise descriptions of various smart materials.
The following lists the devices and systems presented in this chapter. They cover a
variety of transduction principles, fabrication processes, disciplines and applications.
Although not exhaustive, they collectively represent a sufficiently wide cross-section to
make readers familiar and comfortable with the field and its uses.
1. Silicon capacitive accelerometer.
2. Piezoresistive pressure sensor.
3. Conductometric gas sensor.
4. Fibre-optic sensors
5. Electrostatic comb-drive.
6. Magnetic microrelay.
7. Microsystems at radio frequencies
8. Portable blood analyzer.
9. Piezoelectric inkjet print head.
10. Micromirror array for video projection.
11. Micro-PCR systems
c 2.1 SILICON CAPACITIVE ACCELEROMETER
Summary
Category Sensor
Purpose Measures the acceleration of the body on which the sensor is mounted.
Key words Proof mass, suspension, capacitance
Principle of
operation
Converts displacement caused by the inertial force on the proof-mass to
a voltage signal via a change in capacitance between movable and
fixed parts.
Application(s) Automotive, aerospace, machine tools, biomedical, consumer
products, etc.
2.1.1 Overview
An accelerometer measures the acceleration of a body on which it is mounted. It becomes a tilt
sensor if it measures gravitational acceleration. Almost all types of accelerometers have a basic
structureconsistingofaninertialmass(alsocalledaproofmassoraseismicmass),asuspension,
and a transducing mechanism to convert the acceleration signal to an electrical signal.
In a capacitive accelerometer, the sensing method is capacitive in that any change in
acceleration results in a change of capacitance that is measured electronically. One of the
first micromachined accelerometers was reported in 1979 by Roylance and Angell at
Stanford University [1]. It used piezoresistive transduction and weighed less than 0.02 g in
a 2 3 0.6 mm3
package. It took over 15 years for such devices to be accepted as a
product for large-volume applications.
A wide variety of micromachined capacitive accelerometers is commercially availa-
ble today. Some of the manufacturers of this type of accelerometer are Analog Devices,
18 c 2 Micro Sensors, Actuators, Systems and Smart Materials: An Overview](https://image.slidesharecdn.com/2226335-250619015800-040ad3b4/85/Micro-And-Smart-Systems-Technology-And-Modeling-1st-Edition-G-K-Ananthasuresh-46-320.jpg)
![C02 12/06/2011 17:19:26 Page 19
Honeywell, Texas Instruments, Endevco Corporation, PCB Piezotronics, Freescale Semi-
conductors, Crossbow, Delphi, Motorola, etc. Some of these are sold for less than 500 and
some of them cost more than 50,000. This is because of the variation in performance and
the applications. Low-cost accelerometers are used in consumer applications where very
coarse resolution (even 0.1 g ¼ 0.981 m/s2
) is enough. Expensive accelerometers can
resolve 106
g or even 109
g.
2.1.2 Advantages of Silicon Capacitive Accelerometers
Silicon capacitive accelerometers have:
1. Very low sensitivity to temperature-induced drift.
2. Higher output levels than other types.
3. Amenability for force-balancing and hence for closed-loop operation.
4. High linearity.
2.1.3 Typical Applications
Typical applications of silicon capacitive accelerometers include:
1. Consumer: airbag deployment systems in cars, active suspensions, adaptive brakes,
alarm systems, shipping recorders, home appliances, mobile phone, toys, etc.
2. Industrial: crash-testing robotics, machine control, vibration monitoring, etc.
3. High-end applications: military/space/aircraft industry navigation and inertial
guidance, impact detection, tilt measurement, high-shock environments, cardiac
pacemaker, etc.
2.1.4 An Example Prototype
Figure 2.1(a) shows a photograph of a packaged, two-axis, planar, micromachined
capacitive accelerometer with the mechanical sensor element and two Application Specific
Integrated Circuit Chips (ASICs) [2]. Figure 2.1(b) shows a close-up view of the sensor
element and Figure 2.1(c) shows its schematic details. This device is one of the many
accelerometers developed in research laboratories in academia and industry and has the
same features that can be found in any capacitive accelerometer. The physical arrangement
and shapes of components differ among the different types. Materials and fabrication
processes used may also be different.
2.1.5 Materials Used
The materials used to form these devices include:
1. Single-crystal silicon to form the physical structure.
2. Silicon dioxide sandwiched in a silicon-on-insulator (SOI) wafer gives electrical
isolation.
3. Handle-layer of the SOI wafer is the substrate.
4. Gold for electrodes.
2.1.6 Fabrication Process
This is a bulk micromachining. In general, almost any microfabrication process can be
used to make an accelerometer.
2.1 Silicon Capacitive Accelerometer b 19](https://image.slidesharecdn.com/2226335-250619015800-040ad3b4/85/Micro-And-Smart-Systems-Technology-And-Modeling-1st-Edition-G-K-Ananthasuresh-47-320.jpg)
![C02 12/06/2011 17:19:42 Page 21
3. Capacitance:thecapacityofabodytoholdanelectricalcharge.Capacitanceisalsoa
measure of the amount of electric charge stored for a given electric potential. For a
two-plate capacitor, if the charges on the plates are þq and q and V is the voltage
between the plates, then the capacitance is given by C ¼ q/V. The international
standard (SI) unit of capacitance is the farad (1 farad ¼ 1 coulomb/volt).
4. Parallel-plate capacitor: a pair of parallel plates separated by a dielectric
(nonconducting substance) medium.
5. Differential capacitance arrangement: in this arrangement, there are three plates
with a movable middle plate. As the plate moves, the capacitance between one of the
pairs will increase while that of the other decreases. This gives a signal that is linearly
proportional to the applied acceleration, and hence is the preferred configuration.
6. Quality factor: a system’s quality factor, Q, describes the sharpness of the system’s
dynamic response.
2.1.8 Principle of Operation
An accelerometer can be thought of as a mass suspended by a spring. When there is
acceleration, there will be a force on the mass. The mass moves, and this movement is
determined by the spring constant of the suspension. By measuring the displacement, we
can get an estimate of the acceleration (Figure 2.2). A capacitor may be formed with two
plates of which one is fixed while the other moves [Figures 2.3(a), (b)]. In another
arrangement, the mass can move in between two plates [Figure 2.3(c)]. In all three, the
capacitance changes according to the motion caused by acceleration.
At rest
Upon
acceleration
Acceleration
x
k
a = kx/m
m
Figure 2.2 A quasi-static accelerometer model.
Motion Motion
(a) (b) (c)
Motion
Figure 2.3 Examples of simple capacitance displacement sensors: (a) moving plate; (b) variable area; and (c) moving
dielectric.
2.1 Silicon Capacitive Accelerometer b 21](https://image.slidesharecdn.com/2226335-250619015800-040ad3b4/85/Micro-And-Smart-Systems-Technology-And-Modeling-1st-Edition-G-K-Ananthasuresh-49-320.jpg)
![C02 12/06/2011 17:19:42 Page 23
2. Altitude-sensing applications: such as in aircraft, rockets, satellites, weather
balloons, where the measured pressure is converted using an appropriate formula.
3. Flow-sensing applications, manifold pressure sensing: in automobiles, etc.
2.2.4 An Example Commercial Product
Figure 2.4 shows a manifold absolute pressure (MAP) sensor commercially available from
Motorola [3]. It is used in automobiles. Its packaged form and the schematic of the die
without the outer plastic casing and fluidic fittings are shown in Figure 2.5.
2.2.5 Materials Used
The material used to form this device is single-crystal silicon.
2.2.6 Fabrication Process
Bulk micromachining with bipolar circuitry plus glass frit wafer-bonding is the fabrication
process.
2.2.7 Key Definitions
The important terms used and their definitions are:
Diaphragm: a thin sheet of a flexible material, anchored at its circumference, over
which differential pressure is applied.
Piezoresistivity: the dependence of electrical resistivity on mechanical strain. Poly-
silicon shows substantive piezoresistivity.
2.2.8 Principle of Operation
Figure 2.6 shows the cross-section and top view of a pressure sensor die. When the
diaphragm deforms due to the pressure to be measured, the resistances of the piezoresistors
change. Calculation of piezoresistive responses in real structures must take account of the
fact that piezoresistors are typically formed by diffusion and hence have nonuniform
doping. They also span a finite area on the device and hence have nonuniform stress. For a
Figure 2.4 Micromachined pressure sensor. Figure 2.5 Schematic of the packaged pressure
sensor.
2.2 Piezoresistive Pressure Sensor b 23](https://image.slidesharecdn.com/2226335-250619015800-040ad3b4/85/Micro-And-Smart-Systems-Technology-And-Modeling-1st-Edition-G-K-Ananthasuresh-51-320.jpg)
![This ebook is for the use of anyone anywhere in the United States
and most other parts of the world at no cost and with almost no
restrictions whatsoever. You may copy it, give it away or re-use it
under the terms of the Project Gutenberg License included with this
ebook or online at www.gutenberg.org. If you are not located in the
United States, you will have to check the laws of the country where
you are located before using this eBook.
Title: Book-Plates
Author: William John Hardy
Release date: October 22, 2012 [eBook #41142]
Most recently updated: October 23, 2024
Language: English
Credits: Produced by Chris Curnow, Emmy and the Online
Distributed
Proofreading Team at http://www.pgdp.net
*** START OF THE PROJECT GUTENBERG EBOOK BOOK-PLATES
***](https://image.slidesharecdn.com/2226335-250619015800-040ad3b4/85/Micro-And-Smart-Systems-Technology-And-Modeling-1st-Edition-G-K-Ananthasuresh-60-320.jpg)
![probably, therefore, to this lady that we should attribute the honour
of being the first collector of book-plates, for their own sake. No
doubt the collector of engravings admitted into his portfolios book-
plates worthy a place there as interesting engravings, for stray
examples are often found in such collections as that formed in the
seventeenth century by John Bagford, the biblioclast, which is now
in the British Museum. No doubt, too, heraldic painters or plate
engravers collected book-plates as specimens of heraldry, but this
was not collecting them as book-plates—viz. as illustrations of the
custom of placing marks of ownership in books, which, I take it, was
evidently Miss Jenkins's object.[1]
Still, though little was written on the subject of book-plates prior
to 1880, it by no means follows that for some years before that date
there had not been a considerable number of persons who took an
interest in the subject. The fact is, that the book-plate collector of
earlier days was wiser in his generation than are those of his kind to-
day. He kept his 'hobby' to himself, and was thus enabled to indulge
it economically. My father had a small collection; and I can well
remember how, as a boy, I used to help him to add to it. We used to
go to a shop in a dingy street, leading off Oxford Street, and there
select from a large clothes-basket as many book-plates as were new
to our collection. The price was one penny a piece,—new or old,
dated or undated, English or foreign, that of Bishop Burnet, or David
Garrick, or Mr. Jones, or Mr. Brown,—all alike, a penny a piece; and I
have no doubt, though I do not remember the fact, there was the
usual 'reduction on taking a quantity.' I think this shop was almost
the only one in London where you could buy book-plates at all. Well,
those days are past now; and, whilst we regret them, because book-
plate collecting is no longer an economical pursuit, we cannot allow
our regret to be unmingled with satisfaction. The would-be collector
of to-day can, if he pleases, know something about the collection he
is undertaking; he can tell when he meets with a good specimen; he
knows the points which render any particular book-plate interesting;
and he can, at least approximately, affix a date to each example he
obtains.](https://image.slidesharecdn.com/2226335-250619015800-040ad3b4/85/Micro-And-Smart-Systems-Technology-And-Modeling-1st-Edition-G-K-Ananthasuresh-75-320.jpg)
![Johannis Stearne, S.T.P. Episcopi Clogherensis.' A moment's
reflection will show that this inscription is not intended as a
declaration by the book-plate (should it ever become severed from
the book in which it was fastened) that it came out of a book
belonging to Bishop Stearne; but that it is a declaration by the book
in which the book-plate is found pasted, that that particular book is
from amongst the books of a particular library, and ought to be
restored to it. It would be as rational to call book-plates 'libri,'
because the inscription on them often begins—as in a very famous
German book-plate—'Liber Bilibaldi Pirckheimer.' It may, indeed, be
laid down as a general rule, that whatever the sentiment expressed
on a book-plate, it is clearly intended to be uttered by the book in
which the book-plate is fixed, not by the book-plate itself.
There are but two instances, quoted by Lord De Tabley, of the
inscription directly referring to the book-plate. Both are foreign, and
date about the middle of the last century. One is Symbolum
Bibliothecæ of John Bernard Nack, a citizen and merchant of
Frankfort;[2] and the other, Insigne Librorum, etc., quoted from the
work of M. Poulet Malassis. Lord De Tabley thinks that the Symbolum
of Herr Nack is simply a trade card; but he founds this conclusion on
the supposition that Herr Nack was a book-dealer, and that the
scene depicted on his book-plate was, in fact, his shop. In my
opinion, we have in this book-plate a representation of a portion of
Herr Nack's library, in which Minerva(?) is seated, using the books
thereof. A gentleman in eighteenth century dress, who may, likely
enough, be Herr Nack himself, addresses himself to the goddess,
and explains—as he points to the outer scene, which shows us ships
and merchandise—that, whilst following his trade as a merchant, he
still has time to devote some attention to literature. In any case,
these and the few other instances there may be of the inscription
referring to the book-plate and not to the book, seem hardly
sufficient to make ex libris a good name for book-plates in general.
Our ancestors, of degrees more remote than grandfather, do not
appear to have referred to book-plates at all, so we are unable to](https://image.slidesharecdn.com/2226335-250619015800-040ad3b4/85/Micro-And-Smart-Systems-Technology-And-Modeling-1st-Edition-G-K-Ananthasuresh-78-320.jpg)
![Nicholas Carew, afterwards Sir Nicholas Carew, Baronet, records
in his accounts, on the 19th February 1707, a payment for his book-
plate, which is dated in that year, as follows:—'For coat of arms
impressing, 1l. 1s. 6d.;' and a few months later is a payment 'For
300 armes, 7s. 6d.'
'The mark of my books,' is the phrase which Andrew Lumisden
applies to the book-plate engraved for him by his brother-in-law, Sir
Robert Strange, about the year 1746. The plate is an interesting
one, and by an interesting man, of whom we shall speak later on.
Lumisden thought well of it, and thus refers to the work in a letter
written from Rouen, in June 1748:—'I am very anxious to know if my
brother continues his resolution of coming to this country. If he
does, I can luckily be of use to him in the way of his business, from
the acquaintance I have of a very ingenious person, professor of the
Academy of Design here ... I show'd him, a few days ago, the mark
of my books, from which he entertains a high notion of Robie's
abilities.'
There is a curious advertisement, quoted by Thomas Moule in his
Bibliotheca Heraldica, of a certain Joseph Barber, a Newcastle-on-
Tyne 'bookseller, music and copper-plate publisher,' who, in 1742,
resided in 'Humble's Buildings.' In that year he engraved the
'Equestrian Statue of King James [II.],' which once stood in the
Sandhill Market. If a moment's digression be allowed, the history of
this statue is worth telling. On 16th March 1685, the Town Council
voted £800 for the erection of 'a figure of His Majesty in a Roman
habit, on a capering horse, in copper, as big as the figure of His
Majesty, King Charles I., at Charing Crosse, on a pedestal of black
marble.' A certain Mr. William Larson executed it; Sir Christopher
Wren expressed his approval, and everybody was very pleased, for a
year or two. But popular feeling soon changed in Newcastle, as
elsewhere, and the prevalence of sentiments which threw the king
off his throne threw his metal representation into the Tyne, where it
rested till fished out to be melted down and used to make a set of
church bells. The drawing of the luckless statue was safe in the](https://image.slidesharecdn.com/2226335-250619015800-040ad3b4/85/Micro-And-Smart-Systems-Technology-And-Modeling-1st-Edition-G-K-Ananthasuresh-81-320.jpg)
Micro And Smart Systems Technology And Modeling 1st Edition G K Ananthasuresh
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- 6. FFIRS 12/06/2011 10:20:19 Page 2
- 7. FFIRS 12/06/2011 10:20:19 Page 1 Micro and Smart Systems
- 8. FFIRS 12/06/2011 10:20:19 Page 2
- 9. FFIRS 12/06/2011 10:20:19 Page 3 Micro and Smart Systems Technology and Modeling G.K. ANANTHASURESH K.J. VINOY S. GOPALAKRISHNAN K.N. BHAT V.K. AATRE Indian Institute of Science Bangalore INDIA
- 10. FFIRS 12/06/2011 10:20:19 Page 4 VP AND EXECUTIVE PUBLISHER Don Fowley ASSISTANT PUBLISHER Daniel Sayre SENIOR EDITORIAL ASSISTANT Katie Singleton EXECUTIVE MARKETING MANAGER Christopher Ruel MARKETING ASSISTANT Ashley Tomeck SENIOR PRODUCTION MANAGER Janis Soo ASSISTANT PRODUCTION EDITOR Elaine S. Chew EXECUTIVE MEDIA EDITOR Tom Kulesa MEDIA EDITOR Wendy Ashenberg MEDIA SPECIALIST Jennifer Mullin COVER DESIGNER Wendy Lai COVER IMAGE Sambuddha Khan This book was set in Times by Thomson Digital, Noida, India and printed and bound by Courier Westford, Inc. The cover was printed by Courier Westford, Inc. This book is printed on acid free paper. 1 Founded in 1807, John Wiley Sons, Inc. has been a valued source of knowledge and understanding for more than 200 years, helping people around the world meet their needs and fulfill their aspirations. Our company is built on a foundation of principles that include responsibility to the communities we serve and where we live and work. In 2008, we launched a Corporate Citizenship Initiative, a global effort to address the environmental, social, economic, and ethical challenges we face in our business. Among the issues we are addressing are carbon impact, paper specifications and procurement, ethical conduct within our business and among our vendors, and community and charitable support. For more information, please visit our website: www.wiley.com/go/citizenship. Copyright # 2012, John Wiley Sons, Inc. All rights reserved. No part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means, electronic, mechanical, photocopying, recording, scanning or otherwise, except as permitted under Sections 107 or 108 of the 1976 United States Copyright Act, without either the prior written permission of the Publisher, or authorization through payment of the appropriate per-copy fee to the Copyright Clearance Center, Inc. 222 Rosewood Drive, Danvers, MA 01923, website www.copyright.com. Requests to the Publisher for permission should be addressed to the Permissions Department, John Wiley Sons, Inc., 111 River Street, Hoboken, NJ 07030-5774, (201)748-6011, fax (201)748- 6008, website http://www.wiley.com/go/permissions. Evaluation copies are provided to qualified academics and professionals for review purposes only, for use in their courses during the next academic year. These copies are licensed and may not be sold or transferred to a third party. Upon completion of the review period, please return the evaluation copy to Wiley. Return instructions and a free of charge return mailing label are available at www.wiley.com/go/returnlabel. If you have chosen to adopt this textbook for use in your course, please accept this book as your complimentary desk copy. Outside of the United States, please contact your local sales representative. Library of Congress Cataloging-in-Publication Data Micro and smart systems / G.K. Ananthasuresh . . . [et al.]. p. cm. Includes bibliographical references and index. ISBN 978-0-470-91939-2 (acid-free paper) 1. Microelectromechanical systems—Design and construction. 2. Intelligent control systems—Design and construction. I. Ananthasuresh, G. K. TK7875.M524 2012 621.381—dc23 2011029301 Printed in the United States of America 10 9 8 7 6 5 4 3 2 1
- 11. FFIRS 12/06/2011 10:20:20 Page 5 Dedicated to The Institute of Smart Structures and Systems (ISSS) without whose initiative and support this book would not have materialized
- 12. FFIRS 12/06/2011 10:20:20 Page 6
- 13. FPREF 11/14/2011 18:55:52 Page 7 cPreface If we trace the history of electronics technology over the last six decades, we see that the discovery of the transistor and the development of the integrated circuit (IC) are the key milestones. However, it is miniaturization and the ensuing very-large-scale-integration (VLSI) technologies that really created the electronics and computer revolutions. It is only more recently, within the last couple of decades, that the technology of miniaturization has been extended to mechanical devices and systems; we now have the microelectromechan- ical system (MEMS) revolution. Complemented by the advances in smart materials, this has led to highly application-oriented microsystems and smart systems. A microsystem is a system that integrates, on a chip or in a package, one or more of many microdevices: sensors, actuators, electronics, computation, communication, control, power generation, chemical processing, biological reactions, etc. It is now clear that the functionality of such an integrated system will not only be far superior to any other engineered system that we know at the macroscale but will also be able to achieve things well beyond what macroscale integrated systems can do. Smart microelectromechanical systems are collections of microsensors and actuators that can sense their environment and can respond intelligently to changes in that environment by using microcircuit controls. Such microsystems include, in addition to the conventional microelectronics, packaging, integrated antenna structures for command signals, and microelectromechanical structures for desired sensing and actuating functions. However, micromachined actuators may not be powerful enough to respond to the environment. Using macroscale actuators would defeat the purpose of miniaturization, cost-effective batch-processing, etc. Hence, there is a need to integrate smart material- based actuators with microsystems. This trend is currently being witnessed as this field moves beyond microsensors, which have been the main emphasis in microsystems so far. Microsystems and smart system technologies have immense application potential in many fields, and in the coming decades, scientists and engineers will be required to design and develop such systems for a variety of applications. It is essential, then, that graduating engineers be exposed to the underlying science and technology of microsystems and smart systems. There are numerous books that cover both microsystems and smart systems separately and a few that cover both. Many of them are suitable for practicing professionals or for advanced-level courses. However, they assume certain fundamentals in various topics of this multidisciplinary field and thus serve the function of a reference book rather than a primary textbook. Many do not emphasize modeling at the fundamental level necessary to be useful at the undergraduate level or for self-study by a reader with background in other disciplines. This book essentially deals with the basics of microsystem technology and is intended principally as a textbook at the undergraduate level; it can also be used as a background book at the postgraduate level. The book provides an introduction to smart materials and systems. We have tried to present the material without assuming much prior disciplinary background. The aim of this book is to present adequate modeling details so that readers can appreciate the analysis involved in microsystems (and to some extent, smart systems), thereby giving them an in-depth understanding about simulation and design. Therefore, the book will also be useful to practicing researchers in all branches of science and engineering vii
- 14. FPREF 11/14/2011 18:55:52 Page 8 who are interested in applications where they can use this technology. The book presents adequate details on modeling of microsystems and also addresses their fabrication and integration. The engineering of practical applications of microsystems provides areas for multidisciplinary research, already laden with myriad technological issues, and books presently available do not address many of these aspects in sufficient depth. We believe that this book gives a unified treatment of the necessary concepts under a single title. Anticipating the need for such a technology, the Institute of Smart Structures and Systems (ISSS), an organization dedicated to promoting smart materials and micro- systems, was established. This Institute was instrumental not only in mounting a national program and triggering RD activities in this field in India, but also in creating the required human resources through training courses and workshops. Furthermore, ISSS also initiated a dialogue with Visvesveraya Technological University (VTU), Belgaum, Karnataka, a conglomerate of over 170 Karnataka engineering colleges, to introduce an undergraduate-level course in microsystems and MEMS and to set in motion the creation of a potential syllabus for this course. The culmination of this dialogue is the present book. The material for this book has been taken from several advanced workshops and short courses conducted by the authors over last few years for faculty and students of VTU. A preliminary version of book was used at VTU colleges, where a course on microsystems was first introduced in 2009, and very helpful feedback was received from teachers of this course, who patiently used the draft to teach about 500 students at various colleges. In a sense this book has been class- and student-tested and is a substantially enhanced version of the original draft. This book has ten chapters covering various topics in microsystems and smart systems including sensors and actuators, microfabrication, modeling, finite-element analysis, modeling and analysis of coupled systems (of great importance in microsystems), electronics and control for microsystems, integration and packaging, and scaling effects in microsystems. The book also includes case studies on a few microsensor systems to illustrate the applications aspects. In the authors’ opinion, the material of the book can be covered in a standard undergraduate one-semester course. The content of Chapters 5 and 6 may be considered optional. The entire book can be covered in a single-semester postgraduate course or a two-semester undergraduate course supplemented by a design and case-study oriented laboratory. viii c Preface
- 15. FLAST 11/14/2011 19:0:41 Page 9 cAcknowledgments Any project like writing a book depends on the help, advice, and consent of a large number of people. The authors have received such help from many people and it is a pleasure to acknowledge all of them. The trigger for the book was provided by the initiative taken by the Institute of Smart Structures and Systems. The authors acknowledge their indebtedness to ISSS and its presidents, and indeed dedicate the book to ISSS. The authors would like to specially thank Prof. S. Mohan of Indian Institute of Science and Dr. A.R. Upadhya, Director, National Aerospace Laboratories, for their support and encouragement. While ISSS initiated the writing of the book, it was the support and enthusiasm of the Visvesvaraya Technological University (VTU) that sustained its writing. The authors gratefully acknowledge this support, especially from the former vice-chancellors, Prof. K. Balaveer Reddy and Prof. H.P. Khincha. A number of VTU faculty and students who attended the workshops based on the preliminary versions of the book provided the all-important feedback necessary to finalize the book. While thanking them all, the authors would like to mention in particular Prof. Premila Manohar (MSR Institute of Technology, Bangalore) and Prof. K. Venkatesh (presently at Jain University, Bangalore). In addition, the significant contributions of Prof. N.G. Kurahatti (presently at East Point College of Engineering and Technology, Bangalore), who compiled part of the contents of Chapter 3 during the initial stages of manuscript preparation, are gratefully acknowledged. The writing of the book would not have been possible without the work put in by several of our post-graduate students. Contributions of P.V, Aman, Santosh Bhargav, A.V. Harikrishnan, Shyamsananth Madhavan, Ipe Mathew, Rizuwana Parveen, Pakeeruraju Podugu, and Jayaprakash Reddy, who collected much of the information presented in Chapter 2, are gratefully appreciated. Also acknowledged for their help are: Subhajit Banerjee, Varun Bollapragada, Vivek Jayabalan, Shymasananth Madhavan, Fatih Mert Ozkeskin, Krishna Pavan, Sudhanshu Shekhar, and Puneet Singh who ran simulations and provided material for Chapter 10. Assistance given by M. S. Deepika and R. Manoj Kumar in creating some of the illustrations is also gratefully acknowledged. The authors thank all their students who read the early manuscripts of this book and provided useful feedback. The credit for the cover image goes to Sambuddha Khan. The image shows a part of the bulk-micromachined accelerometer with a mechanical amplifier developed by him as part of his PhD dissertation. ix
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- 17. FLAST02 11/14/2011 19:10:22 Page 11 cA Note to the Reader Most chapters include worked-out examples, problems given within the text, and end-of- the-chapter exercises. Some chapters also include exploratory questions marked as ‘‘Your Turn’’. They urge the reader to think beyond the scope of the book. They are intended to stimulate the interest of the reader. Acronyms and notation used in the book are included in separate lists at the beginning of the book. Additionally, a glossary of important terms appears at the end of the book. An Appendix that appears at the end of the book provides supplementary material for the convenience of the reader. Typographical oversights, technical mistakes, or any other discrepancies may please bebroughttotheattentionoftheauthorsbysendinge-mailto:suresh@mecheng.iisc.ernet.in. xi
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- 19. FLAST03 11/04/2011 17:57:48 Page 13 cAcronyms mBGA Microball-grid array mCP Microcontact printing mTM Microtransfer molding mTAS Micro-total analysis system 1D One-dimensional 2D Two-dimensional 3D Three-dimensional ADC or A/D Analog-to-digital converter AFM Atomic force microscopy APCVD Atmospheric pressure chemical vapor deposition ASIC Application-specific integrated circuits ASIC Application-specific-integrated circuit BEM Boundary element method BGA Ball-grid array BiCMOS Bipolar CMOS bio-MEMS bio-microelectromechanical systems BJT Bipolar junction transistor BSG Borosilicate glass BST Barium strontium titanate BW Bandwidth CMOS Complementary metal-oxide- semiconductor CMP Chemical–mechanical planarization CMRR Common-mode rejection ratio COC Cyclic olefin copolymer COF Chip-on-flex CPD Critical point drying CRT Cathode ray tube CTE Coefficient of thermal expansion CVD Chemical vapor deposition DAC or D/A Digital-to-analog converter DFT Discrete Fourier transform DLC Diamond-like carbon DLP Digital light processor DMD Digital Mirror Device DoD Drop-on-demand DOF Degree of freedom DRIE Deep reactive-ion etching DSP Digital signal processing EDP Ethylene diamine pyrocatechol EDM Electrical discharge machining EEPROM Erasable programmable read-only memory EGS Electronic grade silicon EMI Electromagnetic interference ER Electrorheological ETC Electro-thermal-compliant ER Electro rheological FBG Fiber Bragg grating FCC Face-centered cubic FCP Few-chip package FDM Finite difference method FE Finite element FEA Finite element analysis FEM Finite element method FFT Fast Fourier transform FPI Fabry Perot interferometer HDTV High-definition television HF Hydrofluoric HVAC Heat, ventilation, and air-conditioning I/O Input/output IBE Ion beam etching IC Integrated circuit ICP Intracranial pressure IF Intermediate frequency IR Infrared ISR Interrupt service routine LCD Liquid crystal display LED Light-emitting diode xiii
- 20. FLAST03 11/04/2011 17:57:48 Page 14 LIGA Lithographie Galvanoformung Abformung LPCVD Low-pressure chemical vapor deposition LPF Low-pass filter LSB Least significant bit LTCC Low-temperature cofired ceramics LVDT Linear variable differential transformer MAP Manifold-absolute pressure MBE Molecular beam epitaxy MCM Multichip module MCM-D Multichip module – deposited MEMS Microelectromechanical systems MGS Metallurgical grade silicon Micro-EDM Microelectrical discharge machining MMF Magneto motive force MMIC Monolithic microwave integrated circuits MOCVD Metal-organic chemical vapor deposition MOEMS Micro-opto-electromechanical systems MOS Metal-oxide-semiconductor MOSFET Metal oxide semiconductor field-effect transistor MR Magnetorheological MS Metal semiconductor nMOS n-channel MOSFETs pMOS p-channel MOSFET ODE Ordinary differential equation Op-amp Operational amplifier PCB Printed circuit board PCR polymerase chain reaction PDE Partial differential equation PBGA Plastic-ball-grid array PDMS Polydimethylsiloxane PECVD Plasma-enhanced chemical vapor deposition PFC Piezofiber composite PHET Photovoltaic electrochemical etch-stop technique PID Proportional-integral-derivative PLC Programmable logic controller PLL Phase-locked loop PMMA Polymethyl methacrylate pMOS p-channel MOSFETs PMPE Principle of minimum potential energy PSG Phosphosilicate glass PTFE Polytetra-fluoroethylene PVC Polyvinyl chloride PVD Physical vapor deposition PVDF Polyvinylidene fluoride PVW Principle of virtual work PZT Lead zirconate titanate RD Research and development RF Radio frequency RIE Reactive-ion etching RTA Rapid thermal annealing SAC Successive-approximation converter SAW Surface acoustic wave SCS Single-crystal silicon SEM Scanning electron microscope SFB Silicon fusion bonding SFEM Spectral FEM SI unit International standard unit SIP System-on-a-chip SISO Single-input–single-output SMA Shape-memory-alloy SNR Signal-to-noise ratio SOI Silicon-on-insulator SOP System-on-a-package sPROMs Structurally programmable microfluidic system SuMMiT Santia ultra multi-layer microfabrication technology TCR Temperature coefficient of resistivity UV Ultraviolet VCO Voltage-controlled oscillator VED Vacuum electron devices VLSI Very large-scale integration VPE Vapor phase epitaxy WRT Weighted residual technique XFEM Extended FEM xiv c Acronyms
- 21. FLAST04 11/15/2011 9:22:48 Page 15 cNotation There are 26 letters in the English alphabet and 24 in the Greek alphabet. Using both lower and upper case, we have 100 symbols to denote various quantities. Traditionally, every discipline reserves certain symbols for certain quantities. When we mix disciplines, as happens in interdisciplinary subjects, there are bound to be clashes: the same symbol is used for different quantities in different disciplines (e.g., R for reaction force in mechanics and resistance in electronics). We have made an effort to minimize the overlap of such quantities when they are used in the same chapter. As a result, we use nontraditional symbols for certain quantities. For example, Y is used for Young’s modulus instead of E since E is used for the magnitude of the electric field, because they both appear in the same chapter. Occasionally, we also use subscripts to relate a certain symbol to a discipline (e.g., kth for thermal conductivity). Boldface symbols are used for vectors (e.g., E for the electric field vector). The symbols in the list below are arranged in this order: upper-case English, lower- case English, upper-case Greek, and lower-case Greek, all in alphabetical order. For each symbol, boldface symbols appear first and symbols with subscripts or superscripts appear afterwards. If the same symbol is used in two different disciplines, the descriptions are separated by ‘‘OR;’’ if the same symbol is used within the same discipline, ‘‘or’’ is used. A Cross-sectional area of a bar or beam OR area of a parallel-plate capacitor or a proof mass B Magnetic flux density vector A0 Difference mode gain AC Common mode gain Bo Bond number C Capacitance OR a constant Cox Gate oxide capacitance per unit area D Coil diameter of a helical spring OR magnitude of the electric displacement vector OR diffusion constant Dn Normal component of the electric displacement vector DE Dissipated energy E Electric field vector En Normal component of the electric field ESE Electrostatic energy ESEc Electrostatic complementary energy F Force; occasionally, also the transverse force on a beam or a point force on a body Fe Electrostatic force Fd Damping force G Gauge factor H Magnetic field I Inertia in general or area of moment of inertia of a beam OR electric current Ic0 Reverse saturation current Kd Derivative controller gain KP Proportional controller gain KI Integral controller gain J Polar moment of inertia OR the magnitude of the electric current density K Bulk modulus of a material KB Boltzmann constant Kn Knudsen number KE Kinetic energy L Length or size OR inductance OR Lagrangian M Magnetization M Bending moment in a beam or a column OR mass of the proof mass MSEc Magnetostatic coenergy n Number of turns NA Acceptor dopant concentration ND Donor dopant concentration xv
- 22. FLAST04 11/15/2011 9:22:50 Page 16 No Intrinsic concentration P Axial force in a bar or a beam or a point force on a body OR magnitude of an electric polarization vector PE Potential energy Q Electric charge R Reaction force OR electrical resistance Re Reynolds number S Sensitivity SE Strain energy SEc Complementary strain energy T Torque OR temperature U Velocity vector V Volume OR vertical shear force OR voltage W Work Vth Threshold voltage Vbi Built in potential Y Young’s modulus, a material property usually denoted by a in mechanics; we use a because a is used for the magnitude of the electric field and for acceleration ^ n Unit vector usually normal to a surface and directed outward a Acceleration b Width of a beam or damping coefficient dl A differential vector tangential to a path at a point ds A differential vector normal to a surface dV Differential volume g Acceleration due to gravity OR gap in parallel- plate capacitor g0 Initial gap in parallel-plate capacitor h Convective heat transfer coefficient i Electric current k Spring constant or stiffness in general kB Boltsmann constant ke Electrical conductivity kth Thermal conductivity l Length p Perimeter OR pressure q Distributed transverse load OR electric charge qe Charge of electron r Position or distance vector ^ r Unit vector in the direction of a position or distance vector se Strain energy per unit volume t Surface force on an elastic body (also called traction) te Electrostatic force on a conductor t Time OR thickness OR force (traction) on a surface u Displacement in general or only x-displacement in 2D or 3D objects v y-displacement in 2D or 3D objects w Width OR transverse displacement of a beam or z-displacement in a 3D object D Deflection OR an increment in a quantity (if followed by another symbol) a Coefficient of thermal expansion OR a constant of proportionality xe Electrical susceptibility d Deflection OR an increment in a quantity (if followed by another symbol) 2 Normal strain e Permittivity e0 Permittivity of free space er Relative permittivity h Viscosity f Twist OR electric potential g Shear strain OR surface tension k Torsional spring constant l Wave length m Permeability mn electron mobility m0 Permeability of free space n Poisson ratio u Slope of a bent beam r Radius of curvature of a straight beam that is bent re Electrical resistivity rm Mass density se Maxwell’s stress tensor s Normal stress t Shear stress or time constant v Frequency of applied stimulus (force, voltage, etc.) vn Natural frequency (also called resonance frequency) cL Line charge density cs Surface charge density cv Volumetric charge density xvi c Notation
- 23. FTOC 12/07/2011 15:48:20 Page 17 cContents Preface vii Acknowledgments ix A Note to the Reader xi Acronyms xiii Notation xv c CHAPTER 1 Introduction 1 1.1. Why Miniaturization? 2 1.2. Microsystems Versus MEMS 4 1.3. Why Microfabrication? 5 1.4. Smart Materials, Structures and Systems 7 1.5. Integrated Microsystems 9 1.5.1. Micromechanical Structures 10 1.5.2. Microsensors 11 1.5.3. Microactuators 12 1.6. Applications of Smart Materials and Microsystems 13 1.7. Summary 15 c CHAPTER 2 Micro Sensors, Actuators, Systems and Smart Materials: An Overview 17 2.1. Silicon Capacitive Accelerometer 18 2.1.1. Overview 18 2.1.2. Advantages of Silicon Capacitive Accelerometers 19 2.1.3. Typical Applications 19 2.1.4. An Example Prototype 19 2.1.5. Materials Used 19 2.1.6. Fabrication Process 19 2.1.7. Key Definitions 20 2.1.8. Principle of Operation 21 2.2. Piezoresistive Pressure Sensor 22 2.2.1. Overview 22 2.2.2. Advantages of Piezoresistive Pressure Sensors 22 2.2.3. Typical Applications 22 2.2.4. An Example Commercial Product 23 2.2.5. Materials Used 23 2.2.6. Fabrication Process 23 2.2.7. Key Definitions 23 2.2.8. Principle of Operation 23 2.3. Conductometric Gas Sensor 24 2.3.1. Overview 24 2.3.2. Typical Applications 25 2.3.3. An Example Product Line 25 2.3.4. Materials Used 25 2.3.5. Fabrication Process 25 2.3.6. Key Definitions 26 2.3.7. Principle of Operation 26 2.4. Fiber-Optic Sensors 26 2.4.1. Overview 26 2.4.2. Advantages of Fiber-Optic Sensors 27 2.4.3. An Example Prototype 27 2.4.4. Materials Used 27 2.4.5. Fabrication Process 27 2.4.6. Key Definitions 28 2.4.7. Principle of Operation 28 2.5. Electrostatic Comb-Drive 29 2.5.1. Overview 29 2.5.2. An Example Prototype 30 2.5.3. Materials Used 31 2.5.4. Fabrication Process 31 2.5.5. Key Definitions 31 2.5.6. Principle of Operation 31 2.6. Magnetic Microrelay 32 2.6.1. Overview 32 2.6.2. An Example Prototype 33 2.6.3. Materials Used 33 2.6.4. Fabrication Process 33 2.6.5. Key Definitions 33 2.6.6. Principle of Operation 33 2.7. Microsystems at Radio Frequencies 34 2.7.1. Overview 34 2.7.2. Advantages of RF MEMS 34 2.7.3. Typical Applications 35 2.7.4. An Example Prototype 35 2.7.5. Materials Used 36 2.7.6. Fabrication Process 36 2.7.7. Key Definitions 36 2.7.8. Principle of Operation 37 xvii
- 24. FTOC 12/07/2011 15:48:20 Page 18 2.8. Portable Blood Analyzer 37 2.8.1. Overview 37 2.8.2. Advantages of Portable Blood Analyzer 39 2.8.3. Materials Used 39 2.8.4. Fabrication Process 39 2.8.5. Key Definitions 39 2.8.6. Principle of Operation 39 2.9. Piezoelectric Inkjet Print Head 40 2.9.1. Overview 40 2.9.2. An Example Product 40 2.9.3. Materials Used 41 2.9.4. Fabrication Process 41 2.9.5. Key Definitions 41 2.9.6. Principle of Operation 41 2.10. Micromirror Array for Video Projection 42 2.10.1. Overview 42 2.10.2. An Example Product 43 2.10.3. Materials Used 43 2.10.4. Fabrication Process 44 2.10.5. Key Definitions 44 2.10.6. Principle of Operation 44 2.11. Micro-PCR Systems 45 2.11.1. Overview 45 2.11.2. Advantages of Micro-PCR Systems 45 2.11.3. Typical Applications 46 2.11.4. An Example Prototype 46 2.11.5. Materials Used 46 2.11.6. Fabrication Process 46 2.11.7. Key Definitions 47 2.11.8. Principle of Operation 47 2.12. Smart Materials and Systems 48 2.12.1. Thermoresponsive Materials 49 2.12.2. Piezoelectic Materials 50 2.12.3. Electrostrictive/Magnetostrictive Materials 50 2.12.4. Rheological Materials 51 2.12.5. Electrochromic Materials 51 2.12.6. Biomimetic Materials 51 2.12.7. Smart Gels 51 2.13. Summary 52 c CHAPTER 3 Micromachining Technologies 55 3.1. Silicon as a Material for Micromachining 56 3.1.1. Crystal Structure of Silicon 56 3.1.2. Silicon Wafer Preparation 59 3.2. Thin-film Deposition 60 3.2.1. Evaporation 60 3.2.2. Sputtering 61 3.2.3. Chemical Vapor Deposition 62 3.2.4. Epitaxial Growth of Silicon 64 3.2.5. Thermal Oxidation for Silicon Dioxide 65 3.3. Lithography 65 3.3.1. Photolithography 66 3.3.2. Lift-Off Technique 68 3.4. Doping the Silicon Wafer: Diffusion and Ion Implantation of Dopants 69 3.4.1. Doping by Diffusion 70 3.4.2. Doping by Ion Implantation 72 3.5. Etching 75 3.5.1. Isotropic Etching 75 3.5.2. Anisotropic Etching 76 3.5.3. Etch Stops 81 3.6. Dry Etching 82 3.6.1. Dry Etching Based on Physical Removal (Sputter Etching) 84 3.6.2. Dry Etching Based on Chemical Reaction (Plasma Etching) 84 3.6.3. Reactive Ion Etching 85 3.6.4. Deep Reactive Ion Etching (DRIE) 87 3.7. Silicon Micromachining 89 3.7.1. Bulk Micromachining 91 3.7.2. Surface Micromachining 92 3.8. Specialized Materials for Microsystems 97 3.8.1. Polymers 97 3.8.2. Ceramic Materials 98 3.9. Advanced Microfabrication Processes 99 3.9.1. Wafer Bonding Techniques 99 3.9.2. Dissolved Wafer Process 101 3.9.3. Special Microfabrication Techniques 102 3.10. Summary 106 c CHAPTER 4 Mechanics of Slender Solids in Microsystems 111 4.1. The Simplest Deformable Element: A Bar 112 4.2. Transversely Deformable Element: A Beam 115 4.3. Energy Methods for Elastic Bodies 124 4.4. Examples and Problems 127 4.5. Heterogeneous Layered Beams 132 4.6. Bimorph Effect 135 4.7. Residual Stresses and Stress Gradients 136 xviii c Contents
- 25. FTOC 12/07/2011 15:48:20 Page 19 4.7.1. Effect of Residual Stress 137 4.7.2. Effect of the Residual Stress Gradient 140 4.8. Poisson Effect and the Anticlastic Curvature of Beams 141 4.9. Torsion of Beams and Shear Stresses 144 4.10. Dealing with Large Displacements 151 4.11. In-Plane Stresses 153 4.12. Dynamics 159 4.12.1. A Micromachined Gyroscope: Two-Degree-of-Freedom Dynamic Model for a Single Mass 160 4.12.2. A Micromechanical Filter: Two-Degree-of-Freedom Dynamic Model with Two Masses 166 4.12.3. Dynamics of Continuous Elastic Systems 171 4.12.4. A Note on the Lumped Modeling of Inertia and Damping 172 4.13. Summary 173 c CHAPTER 5 The Finite Element Method 177 5.1. Need for Numerical Methods for Solution of Equations 177 5.1.1. Numerical Methods for Solution of Differential Equations 178 5.1.2. What is the Finite Element Method? 179 5.2. Variational Principles 182 5.2.1. Work and Complementary Work 182 5.2.2. Strain Energy and Kinetic Energy 184 5.2.3. Weighted Residual Technique 185 5.2.4. Variational Symbol 190 5.3. Weak Form of the Governing Differential Equation 191 5.4. Finite Element Method 192 5.4.1. Shape Functions 193 5.4.2. Derivation of the Finite Element Equation 199 5.4.3. Isoparametric Formulation and Numerical Integration 204 5.4.4. One-Dimensional Isoparametric Rod Element 204 5.4.5. One-Dimensional Beam Element Formulation 207 5.4.6. Two-Dimensional Plane Isoparametric Element Formulation 209 5.4.7. Numerical Integration and Gauss Quadrature 210 5.5. Numerical Examples 212 5.5.1. Example 1: Analysis of a Stepped Bar (Rod ) 212 5.5.2. Example 2: Analysis of a Fixed Rod Subjected to Support Movement 214 5.5.3. Example 3: A Spring-Supported Beam Structure 215 5.6. Finite Element Formulation for Time-Dependent Problems 217 5.6.1. Mass and Damping Matrix Formulation 218 5.6.2. Free Vibration Analysis 223 5.6.3. Free Vibration Analysis of a Fixed Rod 225 5.6.4. Free-Vibration Analysis of Proof- Mass Accelerometer 229 5.6.5. Forced Vibration Analysis 230 5.6.6. Normal Mode Method 231 5.7. Finite Element Model for Structures with Piezoelectric Sensors and Actuators 233 5.8. Analysis of a Piezoelectric Bimorph Cantilever Beam 235 5.8.1. Exact Solution 236 5.8.2. Finite Element Solution 238 5.9. Summary 239 c CHAPTER 6 Modeling of Coupled Electromechanical Systems 245 6.1. Electrostatics 246 6.1.1. Multiple Point Charges 247 6.1.2. Electric Potential 248 6.1.3. Electric Field and Potential Due to Continuous Charge 252 6.1.4. Conductors and Dielectrics 253 6.1.5. Gauss’s Law 254 6.1.6. Charge Distribution on the Conductors’ Surfaces 257 6.1.7. Electrostatic Forces on the Conductors 258 6.2. Coupled Electromechanics: Statics 259 6.2.1. An Alternative Method for Solving the Coupled Problem 264 6.2.2. Spring-Restrained Parallel-Plate Capacitor 267 6.3. Coupled Electromechanics: Stability and Pull-In Phenomenon 276 Contents b xix
- 26. FTOC 12/07/2011 15:48:21 Page 20 6.3.1. Computing the Pull-In and Pull-Up Voltages for Full Models 282 6.4. Coupled Electromechanics: Dynamics 283 6.4.1. Dynamics of the Simplest Lumped Electromechanical Model 285 6.4.2. Estimating the Lumped Inertia of an Elastic System 287 6.4.3. Estimating the Lumped Damping Coefficient for the In-Plane Accelerometer 290 6.5. Squeezed Film Effects in Electromechanics 294 6.6. Electro-Thermal-Mechanics 295 6.6.1. Lumped Modeling of the Coupled Electro-Thermal-Compliant Actuators 297 6.6.2. General Modeling of the Coupled ETC Actuators 304 6.7. Coupled Electromagnet-Elastic Problem 306 6.8. Summary 308 c CHAPTER 7 Electronics Circuits and Control for Micro and Smart Systems 313 7.1. Semiconductor Devices 314 7.1.1. The Semiconductor Diode 314 7.1.2. The Bipolar Junction Transistor 317 7.1.3. MOSFET 320 7.1.4. CMOS Circuits 323 7.2. Electronics Amplifiers 325 7.2.1. Operational Amplifiers 325 7.2.2. Basic Op-Amp Circuits 327 7.3. Signal Conditioning Circuits 330 7.3.1. Difference Amplifier 331 7.3.2. Instrumentation Amplifier as a Differential Voltage Amplifier 332 7.3.3. Wheatstone Bridge for Measurement of Change in Resistance 334 7.3.4. Phase-Locked Loop 336 7.3.5. Analog-to-Digital Converter 337 7.4. Practical Signal conditioning Circuits for Microsystems 341 7.4.1. Differential Charge Measurement 341 7.4.2. Switched-Capacitor Circuits for Capacitance Measurement 343 7.4.3. Circuits for Measuring Frequency Shift 343 7.5. Introduction to Control Theory 344 7.5.1. Simplified Mathematical Description 344 7.5.2. Representation of Control Systems 345 7.5.3. State-Space Modeling 346 7.5.4. Stability of Control Systems 351 7.6. Implementation of Controllers 354 7.6.1. Design Methodology 354 7.6.2. Circuit Implementation 356 7.6.3. Digital Controllers 357 7.7. Summary 360 c CHAPTER 8 Integration of Micro and Smart Systems 363 8.1. Integration of Microsystems and Microelectronics 364 8.1.1. CMOS First 364 8.1.2. MEMS First 365 8.1.3. Other Approaches of Integration 365 8.2. Microsystems Packaging 366 8.2.1. Objectives of Packaging 366 8.2.2. Special Issues in Microsystem Packaging 367 8.2.3. Types of Microsystem Packages 369 8.2.4. Packaging Technologies 370 8.2.5. Reliability and Key Failure Mechanisms 374 8.3. Case Studies of Integrated Microsystems 375 8.3.1. Pressure Sensor 376 8.3.2. Micromachined Accelerometer 388 8.4. Case Study of a Smart Structure in Vibration Control 401 8.4.1. PZT Transducers 402 8.4.2. Vibrations in Beams 403 8.5. Summary 404 c CHAPTER 9 Scaling Effects in Microsystems 409 9.1. Scaling in the Mechanical Domain 410 9.2. Scaling in the Electrostatic Domain 413 9.3. Scaling in the Magnetic Domain 414 9.4. Scaling in the Thermal Domain 415 9.5. Scaling in Diffusion 417 9.6. Scaling in Fluids 418 9.7. Scaling Effects in the Optical Domain 420 9.8. Scaling in Biochemical Phenomena 422 xx c Contents
- 27. FTOC 12/07/2011 15:48:21 Page 21 9.9. Scaling in Design and Simulation 423 9.10. Summary 426 c CHAPTER 10 Simulation of Microsystems Using FEA Software 429 10.1. Background 429 10.2. Force-Deflection of a Tapering Helical Spring Using ABAQUS 430 10.3. Natural Frequencies of an Accelerometer in ANSYS 432 10.4. Deflection of an Electro-Thermal-Compliant (ETC) Microactuator in COMSOL MultiPhysics 436 10.5. Lumped Stiffness Constant of a Comb-Drive Suspension in NISA 438 10.6. Piezoelectric Bimorph Beam in a Customized FEA Program 440 10.7. Resonant Micro-Accelerometer in ABAQUS 442 10.8. Pull-In Voltage of an RF-MEMS Switch in IntelliSuite 444 10.9. A Capacitive Pressure Sensor in Coventorware 447 10.10. Summary 449 Appendix 451 Glossary 459 Index 463 About the Authors 473 Contents b xxi
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- 29. C01 11/29/2011 9:1:12 Page 1 c CHAPTER 1 Introduction L E A R N I N G O B J E C T I V E S After completing this chapter, you will be able to: c Get an overview of microsystems and smart systems. c Understand the need for miniaturization. c Understand the role of microfabrication. c Learn about smart materials and systems. c Learn about typical applications of microsystems and smart systems. Mythology and folk tales in all cultures have fascinating stories involving magic and miniaturization. Ali Baba, in a story in 1001 Arabian Nights, had to say Open Sesame to make the cave door open by itself. We now have automatic doors in supermarkets that open as you move toward them without even uttering a word. Jonathan Swift’s fictitious British hero, Lemuel Gulliver, traveled to the island of Lilliput and was amazed at the miniature world he saw there. Gulliver would probably be equally amazed if he were washed ashore into the 21st -century world because we now have fabulous miniature marvels undreamt of in Swift’s time. Magic and miniaturization are realities today. Arthur C. Clarke, a famous science fiction writer, once said that ‘‘a sufficiently advanced technology is indistinguishable from magic.’’ What makes this magic a reality? The answer lies in exotic and smart materials, sensors and actuators, control and miniaturization. Smartness and smallness go hand in hand. Smart systems are increasingly becoming smaller, leading to a magical reality. Small systems are increasingly becoming smarter by integrating sensing, actuation, computation, communication, power generation, control, and more. Like the Indian mythological incarnation Vamana, described as being small and smart, yet able to cover the Earth, sky, and the world beneath in three footsteps, the combination of smallness and smartness has limitless possibilities. This book is about microsystems and smart systems, not about magic. As Nobel Laureate physicist Richard Feynman noted in his lectures, the laws of science as we know them today do not preclude miniaturization, and there is sufficient room at the bottom [1, 2]. It is only a question of developing the requisite technologies and putting them together to make it all happen. Let us begin with the need for miniaturization. 1
- 30. C01 11/29/2011 9:1:12 Page 2 c 1.1 WHY MINIATURIZATION? A microsystem is a system that integrates, on a chip or in a package, one or more of many things: sensors, actuators, electronics, computation, communication, control, power generation, chemical processing, biological reactions, and more. You may find it interest- ing that this definition does not explicitly mention size other than alluding to a chip or a packaged system consisting of chips and other accessories. Miniaturization is essential in achieving this level of integration of a disparate array of components. There is no doubt that the functionality of such an integrated system will not only be far superior to any other engineered system that we know at the macroscale but will also achieve things beyond those achievable by macrosystems. Think of a big ship, an aircraft, or a power plant: they all serve one primary purpose. But a chip that integrates several components, as already mentioned, can serve multiple functions. This is one reason for miniaturization. This does not imply that we cannot integrate many things at the macro scale; it is a question of economy and to some extent functionality. Microsystems technology, by following the largely successful paradigm of microelectronics, remains economical due to the batch production of microfabrication processes. You can make plenty of things on one single silicon wafer, and thus, the cost per individual thing comes down drastically. This is another reason for miniaturization. Nothing would better illustrate this than advances in computer technology. Computing systems of today are much more powerful, have many more features, are far less power-consuming and, of course, are significantly cheaper than those available 20 or 30 years ago. Miniaturization and integration approaches have played a significant role in achieving these (see Figure 1.1). Common objects in various size scales are compared in Figure 1.2. In a lighter vein, a popular acronym for the microsystems technology is spelled MDM$: it reads millions of euros and millions of dollars! The market share of microelectromechanical systems (MEMS) has exceeded the million-dollar mark some time back and is well poised to cross the billion-dollar mark. Energy has always been a precious commodity. Today it is increasingly so because of ever-increasing demand coupled with rapidly depleting energy resources. With the human propensity for electronic gadgets, the requirements for batteries are also on the rise, triggering research efforts on high-energy miniature batteries. And the smaller the gadgets (and constituent devices), the lower the energy requirements, thus adding a further reason for miniaturizing devices and systems. There are, of course, more technical reasons for miniaturization. Some phenomena favor miniaturization. Take optics, for example. If we have a micromechanical device that Figure 1.1 Miniaturization of computer hardware technology. 2 c 1 Introduction
- 31. C01 11/29/2011 9:1:13 Page 3 can move a micron-sized component and control its movement to a fraction of a micron (the range of light wavelength visible to humans), this opens up numerous new possibilit- ies. There are already commercial products that use optical microsystems, also known as micro-opto-electromechanical systems (MOEMS). Think of the biological cells that are the basic building blocks of living organisms. They are the workshops where amazing manufacturing, assemblies and disassemblies take place most efficiently. These cells too have features, that is, size, motion, and forces, that Atoms Molecules Nanostructures Viruses Smallest microelectronic features Bacteria Biological cells Dust particles Diameter of human hair Microsystem devices Optical fibers Packaged ICs Packaged MEMS Lab-on-a-chip Plain old machines Humans Animals Plants Planes, trains, automobiles 1 nm 0.1 µm 10 µm 1 mm 100 mm 10 nm 1 µm 100 µm 10 mm 1 m Å 10 m Figure 1.2 Illustration of objects at various size scales. 1.1 Why Miniaturization? b 3
- 32. C01 11/29/2011 9:1:13 Page 4 are comparable to those of micromechanical structures. So, there is a subfield within microsystems known as ‘‘bio-microelectromechanical systems’’ (bio-MEMS). Further- more, there are reasons for miniaturizing chemical processing. Controlling process condi- tions over a small volume is much easier than over a large volume. Hence, the efficiency of a chemical reaction is greater in miniaturized systems. It is clear from this perspective why living organisms are compartmentalized into micron-sized units—the cells. Miniaturization can result in faster devices with improved thermal management. Energy and materials requirement during fabrication can be reduced significantly, thereby resulting in cost/performance advantages. Arrays of devices are possible within a small space. This has the potential for improved redundancy. Another important advantage of miniaturization is the possibility of integration of mechanical and fluidic parts with electronics, thereby simplifying systems and reducing power requirements. Microfabri- cation employed for realizing such devices has improved reproducibility, and devices thus produced have increased selectivity and sensitivity, wider dynamic range, improved accuracy and reliability. Integrated microsystems are a collection of microsensors and actuators that can sense their environment and react to changes in that environment by use of a microcircuit control. Such microsystems include, in addition to the conventional microelectronics packaging, integrated antenna structures for command signals, and microelectromechanical configu- rations for desired sensing and actuating functions. The system may also need micropower supply, microrelay, and microsignal processing units. Such systems with microcompo- nents are faster, more reliable, more accurate, cheaper, and capable of incorporating more complex and versatile functions than systems used today. A miniaturized low-power transceiver is an excellent example of a microsystem technology. Figure 1.3(a) shows a simplified block diagram of a transceiver and a board-level implementation of the same consisting of several chips that are basically components with high quality-factors such as radio frequency (RF) filters, surface acoustic wave (SAW) intermediate-frequency (IF) filters, crystal oscillators, and transistor circuits [3]. A possible single-chip implementation of this transceiver using microsystems technology is shown in Fig. 1.3(b). This enables miniaturization as well as low power consumption. c 1.2 MICROSYSTEMS VERSUS MEMS We have presented several reasons for miniaturization from different points of view. Let us now examine how microsystems technology came into existence. In the late 1960s and early 1970s, not long after the emergence of the integrated chip, researchers and inventors in academia and industry began to experiment with microfabrication processes by making movable mechanical elements. Accelerometers, micromirrors, gas-chromatography instru- ments, etc., were miniaturized during this period. Silicon was the material of choice at that time. A seminal paper by Petersen [4] summarizes these developments. Increased attention to the microsystems field came in late 1980s when a micromachined electrostatic motor was made at the University of California, Berkeley and Massachusetts Institute of Technology, Cambridge. This moving micromechanical entity fascinated everyone and showed the way forward for many other developments. The acronym MEMS was coined during that period. However, this acronym is inadequate today because of the numerous disciplines beyond just mechanical and electrical that have joined the league. A more suitable term is ‘‘microsystems;’’ hence the title for this book. 4 c 1 Introduction
- 33. C01 11/29/2011 9:1:13 Page 5 c 1.3 WHY MICROFABRICATION? Microsystems technology emerged as a new discipline based on the advances in integrated circuit (IC) fabrication processes, by which sensors, actuators and control functions were co-fabricated in silicon. The concepts and feasibility of more complex microsystems devices have been proposed and demonstrated for applications in such varied fields as microfluidics, aerospace, automobile, biomedical, chemical analysis, wireless communi- cations, data storage, and optics. In microsystems, miniaturization is achieved by a fabrication approach similar to that followed in ICs, commonly known as micromachining. As in ICs, much of the processing is done by chemical processing rather than mechanical modifications. Hence, machining here does not refer to conventional approaches (such as drilling, milling, etc.) used in realizing macromechanical parts, although the objective is to realize such parts. As with semiconductor processing in IC fabrication, micromachining has become the fundamental technology for the fabrication of microsystems devices and, in particular, miniaturized sensors and actuators. Silicon micromachining, the most mature of the micromachining (a) Surface acoustic wave (SAW) RF filter LNA VCO VCO BPF Mixer Mixer IF Amp. Baseband processing circuits IF filter Off or on-board antenna Crystal oscillator Off-chip Ceramic or board level MIC (b) RF filter LNA Micromachined filters Micromachined filter Micromachined antennas Micromachined resonator VCO VCO BPF Mixer Mixer IF Amp. Baseband processing circuits IF filter Crystal oscillator Figure 1.3 Integrated radio frequency transceivers: a typical application of microsystems [3]. (a) Current approaches (shaded remarks indicate components outside the electronics die). (b) Integrated MEMS-based RF receiver on a single chip. LNA, low noise amplifier; RF, radio frequency; VCO, voltage-controlled oscillator; IF, intermediate frequency; BPF, bandpass filter. 1.3 Why Microfabrication? b 5
- 34. C01 11/29/2011 9:1:13 Page 6 technologies, allows the fabrication of microsystems that have dimensions in the sub- millimeter to micron range. It refers to fashioning microscopic mechanical parts out of a silicon substrate or on a silicon substrate to make three-dimensional (3D) structures, thereby creating a new paradigm in the design of miniaturized systems. By employing materials such as crystalline silicon, polycrystalline silicon, silicon nitride, etc., a variety of mechanical microstructures including beams, diaphragms, grooves, orifices, springs, gears, suspensions, and a great diversity of other complex mechanical structures have been conceived, implemented, and commercially demonstrated. Silicon micromachining has been the key factor in the fast progress of microsystems in the last decade of the 20th century. This is the fashioning of microscopic mechanical parts out of silicon substrates and more recently other materials. This technique is used to fabricate such features as clamped beams, mem- branes, cantilevers, grooves, ori- fices, springs, gears, chambers, etc., that can then be suitably com- bined to create a variety of sensors. Bulk micromachining, which in- volves carving out the required structure by etching out the silicon substrate, is the commonly used method. For instance, a thin dia- phragm of precise thickness in the few-micron range suitable for inte- grating sensing elements is very often realized with this approach. Figure 1.4 shows the scanning elec- tron microscope (SEM) image of a cantilever beam of SiO2 fabricated by bulk micro- machining (wet chemical etching) of silicon. The dimensions of this cantilever beam are length ¼ 65 mm, width ¼ 15 mm, and thickness ¼ 0.52 mm (1 mm ¼ 106 m). Surface micromachining is an alternate micromachining approach. It is based on patterning layers deposited on the surface of silicon or any other substrate. This approach offers the attractive possibility of integrating the micromachined device with micro- electronics patterned and assembled on the same wafer. In addition, the thickness of the structural layer in this case is precisely determined by the thickness of the deposited layer and hence can be controlled to submicron thickness levels. Figure 1.5 shows a schematic of a polycrystalline silicon resonating beam that can be made by the surface micromachining technique. Note that the resonator beam is anchored at its ends and that a gap of d ¼ 0.1 mm exists between the resonator and the rigid beam laid perpendicular to it. As a result, the resonator vibrates at the frequency of the ac signal applied to it with respect to the rigid beam and a current flows due to the capacitance variation with time. This current peaks when the frequency of the input signal matches with the mechanical resonance frequency of the vibrating beam. Thus the resonator can be used as a filter. Figure 1.4 SEM image of SiO2 microcantilever beam prepared by bulk micromachining (wet chemical etching) of silicon. Anchor Resonator Rigid beam Electrodes Figure 1.5 Schematic of a resonator beam [4]. 6 c 1 Introduction
- 35. C01 11/29/2011 9:1:14 Page 7 Until about the 1990s, most microsystems devices with various sensing or actuating mechanismswerefabricatedusingsiliconbulkmicromachining,surfacemicromachining,and micromolding processes. More recently, 3D microfabrication processes incorporating other materials(suchaspolymers)havebeenintroducedinmicrosystemstomeetspecificapplication requirements (e.g. biomedical devices and microfluidics). It is interesting to note that almost all the microsystems devices employ one or more of the three basic structures—namely, a diaphragm, a microbridge, or a beam—that are realized using micromachining of silicon in most cases and other materials including polymers, metals, and ceramics. These three structures provide feasible designs for microsensors and actuators that eventually perform the desired task in many smart structures. The main issues with respect to implementing these structures are the choice of materials and the micromachining technologies used to fabricate these devices. c 1.4 SMART MATERIALS, STRUCTURES AND SYSTEMS The area of smart material systems has evolved from the unending quest of mankind to mimic systems of natural origin. The objective of such initiatives is to develop technologies to produce nonbiological systems that achieve optimum functionality as observed in natural biological systems and emulate their adaptive capabilities by an integrated design approach. In the present context, a smart material is one whose electrical, mechanical, or acoustic pro- perties or whose structure, composition, or func- tions change in a specified manner in responseto some stimulus from the environment. In a simi- lar way, one may envisage smart structures that require the addition of properly designed sen- sors, actuators, and controllers to an otherwise ‘‘dumb’’ structure (see schematic in Figure 1.6). As smart materials systems should mimic naturally occurring systems, the general re- quirements expected from these nonbiological systems include: 1. Full integration of all functions of the system. 2. Continuous health and integrity monitoring. 3. Damage detection and self-recovery. 4. Intelligent operational management. 5. High degrees of security, reliability, efficiency and sustainability. As one can note, the materials involved in implementing this technology are not necessarily novel. Yet the technology has been accelerating at a tremendous pace in recent years and has indeed been inspired by several innovative concepts. As mentioned earlier, the structural, physical, or functional properties of smart materials respond to some stimulus from the environment and this response should be repetitive in the sense that the same change in the environment must produce the same response. We know that even without design, most materials do respond to their environ- ment. For example, note the change in dimensions of most materials when heated or Structure Sensor Actuator Control unit Figure 1.6 Building blocks of a typical smart system. 1.4 Smart Materials, Structures and Systems b 7
- 36. C01 11/29/2011 9:1:14 Page 8 cooled. However, what distinguishes a smart material from the rest is that we design the material so that such changes occur in a specific manner for some defined objective to be accomplished. Hence, the main feature that distinguishes smart materials is that they respond significantly to some external stimuli to which most materials are unresponsive. Furthermore, one would like to enhance such a response by at least one or two orders of magnitude over other materials. Both active and passive approaches have been attempted in this context. This distinction is based on the requirement to generate power required to perform responses. Hence, an active system has an inbuilt power source. Typically, active sensors and actuators have been favored in designing smart structures. However, in recent years the concept of passive smartness has come to the fore. Passive smartness can be pervasive and even continuous in the structure. Such structures do not need external intervention for their operation. In addition, there is no requirement for a power source. This is particularly relevant in large- scale civil engineering structures. Passive smartness can be derived from the unique intrinsic properties of the material used to build such structures. One common example is the shape- memory-alloy (SMA) material embedded in aerospace composites, designed so that cracks do not propagate. Such smart materials are discussed briefly in Chapter 2. Besides ‘‘smart system’’ or ‘‘smart material,’’ another widely used term is smart structure. One distinctive feature of smart structures is that actuators and sensors can be embedded at discrete locations inside the structure without affecting the structural integrity of the main structure. An example is the embedded smart structure in a laminated composite structure. Furthermore, in many applications, the behavior of the entire structure itself is coupled with the surrounding medium. These factors necessitate a coupled modeling approach in analyzing such smart structures. The function and description of various components of the smart system in Table 1.1 are summarized in Table 1.1 [5]. Civil engineering systems such as building frames, trusses, or bridges comprise a complex network of truss, beam, column, plate, and shell elements. Monitoring the structural health of bridge structures for different moving loads is an area of great importance in increasing the structural integrity of infrastructures and has been pursued in many countries. Damping of earthquake motions in structures is yet another area that has been taken up for active research in many seismically active countries. Smart devices derived from smart materials are extensively used for such applications. A bridge whose structural health can be monitored is shown in Figure 1.7. In such a bridge, fiberoptic sensors are used as sensing devices, whereas lead zirconate titanate (PZT) or Terfenol-D actuators are normally used for performing actuations such as vibration isolation and control. Table 1.1 Purpose of various components of a smart system Unit Equivalent in Biological Systems Purpose Description Sensor Tactile sensing Data acquisition Collect required raw data needed for appropriate sensing and monitoring Data bus 1 Sensory nerves Data transmission Forward raw data to local and/or central command and control units Control system Brain Command and control unit Manage and control the whole system by analyzing data, reaching the appropriate conclusions, and determining the actions required Data bus 2 Motor nerves Data instructions Transmit decisions and associated instructions to members of structure Actuator Muscles Action devices Take action by triggering controlling devices/units 8 c 1 Introduction
- 37. C01 11/29/2011 9:1:14 Page 9 The beneficiaries and supporters of the smart systems technology have been military and aerospace industries. Some of the proof-of-concept programs have addressed struc- tural health monitoring, vibration suppression, shape control, and multifunctional struc- tural concepts for spacecrafts, launch vehicles, aircrafts and rotorcrafts. The structures built so far have focused on demonstrating potential system-level performance improvements using smart technologies in realistic aerospace systems. Civil engineering structures including bridges, runways and buildings that incorporate this technology have also been demonstrated. Smart system design envisages the integration of the conventional fields of mechanical engineering, electrical engineering, and computer science/informa- tion technology at the design stage of a product or a system. As discussed earlier, smart systems should respond to internal (intrinsic) and environ- mental (extrinsic) stimuli. To this end, they should have sensors and actuators embedded in them. Some of these devices commonly encountered in the context of smart systems are listed in Table 1.2. c 1.5 INTEGRATED MICROSYSTEMS Integrated microsystems can be classified into three major groups as follows: 1. Micromechanical structures: These are non-moving structures, such as microbe- ams and microchannels. Figure 1.7 The historic Golden Bridge built in 1881 to connect Ankleshwar and Bharuch in Gujarat, India. The inset shows the details of one-time structural health monitoring of a section of the bridge. It had 66 fiber optic strain gauges and micromachined accelerometers. Courtesy: Instrumentation Scientific Technologies Pvt. Ltd., Bangalore, www.inscitechnologies.com. Table 1.2 Some sensors and actuators used in smart systems Device Physical Quantity Example Successful Technologies Sensor Acceleration Accelerometer PZT, Microfabrication Angular rate Gyroscope Fiber optic, Microfabrication Position Linear variable differential transformer (LVDT) Electromagnetic Transducer Crack detection Ultrasonic transducer PZT Actuator Movement Thermal Shape memory alloy 1.5 Integrated Microsystems b 9
- 38. C01 11/29/2011 9:1:16 Page 10 2. Microsensors: These respond to physical and chemical signals (such as pressure, acceleration, pH, glucose level, etc.) and convert them to electrical signals. 3. Microactuators: These convert electrical or magnetic input to mechanical forms of energy (e.g. resonating beams, switches, and micropumps). Microsystems integrate sensors, actuators and electronics to provide some useful function. The ADXL50, which was released in 1991 and was Analog Devices’ first commercial device, is an excellent example of such a microsystem. The block diagram of this system is shown in Figure 1.8 [6]. This microsystem is based on a surface micro- machining technology with sensing electronics integrated on the same chip as the accelerometer. Here, the accelerometer is a sensor that responds to the acceleration or deceleration and gives an output voltage to the control circuit, which in turn triggers an actuator to deploy the airbag during a crash, so that the persons seated in the front seat are protected from crashing into the front windshield or the dashboard. 1.5.1 Micromechanical Structures Micromachining is used commercially to produce channels for microfluidic devices and also to fabricate systems referred to as ‘‘labs on a chip’’ for chemial analysis and analysis of biomedical materials [7]. Usually such channels are made on plastics or glass substrates. Figure 1.9 (a) shows one such device reported in the literature [8]. Micro- machining is also used to make a variety of mechanical structures. Figure 1.9 (b) shows an SEM image of a silicon nanotip fabricated [9] using a ‘‘bulk micromachining’’ process. Such microtips find applications in atomic force microscopy (AFM) technology and field emission array for futuristic vacuum electron devices capable of operation in terahertz frequency range [10]. Output voltage Preamp Buffer Demodulator and low-pass filter Square wave oscillator Feedback voltage Anchor Polysilicon proof mass and moving electrodes Fixed polysilicon capacitor plates Suspension system Figure 1.8 A schematic diagram of ADXL50 accelerometer. 10 c 1 Introduction
- 39. C01 11/29/2011 9:1:16 Page 11 1.5.2 Microsensors Several micromachined sensors have evolved over the last two decades. Among them the pressure sensors occupy almost 60% of the market. A schematic isometric cut-away view of a piezoresistive pressure sensor die is shown in Fig. 1.10 (a). Here, we can see the four Figure 1.9 Miniature mechanical structures showing (a) polymer mesopump; (b) silicon nanotip fabricated using bulk micromachining. (a) (b) Figure 1.10 Schematic diagrams of microsensors: (a) cut-away view of a piezoresistive pressure sensor; (b) capacitive-sensing accelerometer. (a) Piezoresistor Pad Diaphragm Pressure port Glass Glass (b) Fixed electrode Fixed electrode Seismic mass Si 1.5 Integrated Microsystems b 11
- 40. C01 11/29/2011 9:1:17 Page 12 pressure-sensitive resistors (piezoresistors) integrated on a micromachined silicon dia- phragm. Micromachined accelerometer is yet another device which has received consid- erable attention from the aerospace, automobile, and biomedical industries. Figure 1.10 (b) shows a schematic cross-sectional view of one such device. The seismic mass responds to acceleration and deflects, thus bringing about a change in the capacitance between the mass and the fixed electrodes. The change in capacitance is a measure of the displacement, which in turn depends upon the acceleration. 1.5.3 Microactuators Over the last few years, micromachined actuators such as RF switches [11], micropumps, and microvalves [12], which can be actuated using the electrostatic or piezoelectric effect, have been reported. In addition, electrostatically actuated tiny micromirror arrays acting as optical switches have been developed by Lucent Technologies for fiber-optic communi- cation [13] and as digital micromirror devices (DMDs) by Texas Instruments in projection video systems [14]. In this section, two examples of actuators are presented to highlight the wide range of applications of microactuators. First, a schematic diagram of the electro- statically actuated bulk micromachined silicon micropump [12] is shown in Figure 1.11. The diaphragm deflects upward when an actuation voltage is applied as shown and the inlet check valve opens due to a fall in chamber pressure, thereby letting in the fluid flow into the pump chamber. When the actuation voltage drops to zero, the diaphragm moves back to its equilibrium position. As the chamber is now full of fluid, the pressure inside is higher than that outside. This forces the inlet valve to close and the outlet valve to open, thus letting the fluid flow out. The second example is the famous electrostatically actuated micromirror array consisting of tiny mirrors as shown in Figure 1.12. Each mirror is 0.5 mm in diameter, about the size of the head of a pin. Mirrors rest 1 mm apart and all 256 mirrors are fabricated on a 2.5 cm square piece of silicon. The figure on the left-hand side shows how the tilted mirrors switch the optical signals from one fiber to another fiber. Thus, there is no need of making an optoelectronic conversion. This arrangement gives 100-fold reduction in power consumption over electronic switches. Deformable diaphragm Pump chamber Inlet check valve Outlet check valve Pyrex separator Actuation voltage Figure 1.11 Schematic of a bulk micromachined micropump. 12 c 1 Introduction
- 41. C01 11/29/2011 9:1:17 Page 13 c 1.6 APPLICATIONS OF SMART MATERIALS AND MICROSYSTEMS The area of smart materials and structures is an interdisciplinary field bridging the gap between science and technology and combining knowledge in physics, mathematics, chemistry, material science, electrical and mechanical engineering. Through such a technology, we can build safer cars, more comfortable airplanes, self-repairing water pipes, etc. Smart structures can help us to monitor and control the environment better and to increase the energy efficiency of devices. The applications of microsystems encompass the entire range of civilian, defense, automobile, biomedical, and consumer devices used in day-to-day life. Some of the applications areas of micromachined pressure sensors are illustrated in Figure 1.13. For instance, pressure sensors are used Fibers Reflector Tilted mirror Single fiber (a) (b) Figure 1.12 (a) Schematic of micromirrors developed by Lucent Technologies optical switches in fiber- optic communication. (b) Lucent micromirror details. Ventricle in brain Hole in skull Catheter (a) Sensor chip in a 1.2 mm diameter casing 0.7 mm diameter lead wire (b) Figure 1.13 Some application areas for pressure sensors. (a) Codman (www.codman.com) ICP microsensor showing the dimensions of the packaged transducer. (b) Mapping the pressure on aircraft wings during the development stages of the aircraft. 1.6 Applications of Smart Materials and Microsystems b 13
- 42. C01 11/29/2011 9:1:19 Page 14 in the intracranial pressure (ICP) monitoring system. This requires pressure sensors of chip size less than 1 mm 1 mm; also, the packaging material must be biocompatible as the sensor is inserted into the ventricle in the brain using a catheter through a small hole created in the skull. In yet another application, a large number of pressure sensors, over 500, must be laid out on each wing of an aircraft to map the pressure across the aerofoil during the development stages of an aircraft. Similarly, in oceano- graphic applications, depth monitoring can be done with pressure sensors designed for a wide range of pressures and suitably packaged to protect against the corrosive sea water. Figure 1.14 gives a broad range of applications of smart materials and microsystems. Furthermore, the applications of microsystems can be conveniently grouped according to major industries as shown in Table 1.3. Though this table lists diverse applications of smart structures [15], it should be clear to the reader that there is a significant scope for developing radically new capabilities in this domain, and that it is only limited by the creativity and innovativeness of the human mind. Space structure Aero structure Medical Vibration noise control Automotive Health monitoring Self-healing Warning Shape Aerodynamic control Rotorcraft Drug delivery Tele-surgery Damping Wall paper Stealth Clutch Civil structure Air bags Shock absorber Adaptive structures Smart materials microsystems Figure 1.14 Applications of smart materials and microsystems. Table 1.3 Applications of smart systems in various areas Application Area Microcomponent or Smart Component Purpose Machine tools Piezoceramic transducers To control chatter and thereby improve precision and increase productivity Photolithography Vibration control during the process using piezoceramic transducers To manufacture smaller microelectronic circuits Process control Shape memory alloy For shape control, for example, in aerodynamic surfaces Health monitoring Fiber-optic sensors To monitor the health of fiber-reinforced ceramics and metal-matrix composites, and in structural composites 14 c 1 Introduction
- 43. C01 11/29/2011 9:1:20 Page 15 c 1.7 SUMMARY Miniaturization and integration of a variety of components are the key aspects of micro- systems. Besides giving rise to compact devices and systems, miniaturization leads to the many other benefits discussed in this chapter. Miniaturization is made possible by microfabrication techniques. Integration of sensors, actuators and micromechanical Application Area Microcomponent or Smart Component Purpose Consumer electronics Piezoceramic and Microaccelerometers and rotation rate sensors; quartz, piezoceramic, and fiber-optic gyros; piezoceramic transducers For shake stabilization of hand-held video cameras Helicopters and aircraft Piezoceramic stack actuators; PZT and Microaccelerometers; magnetostrictive mounts Piezoceramic pickups and error sensors; PZT audio resonators and analog voice coils; digital signal processor chips For vibration and twist control of helicopter rotor blades, adaptive control of aircraft control surfaces For active noise control Submarines Piezoceramic actuators For acoustic signature suppression of submarine hulls Automotive Electrochromic Piezo yaw-axis rotation sensors (antiskid, antilock braking); Microaccelerometer (air bag controls) Ceramic ultrasonic ‘‘radar’’ Piezopolymer infrared (IR) sensors; rain monitors; occupant identification; heat, ventilation and air-conditioning (HVAC) sensors; air pollution sensors (CO and NOx) For chromogenic mirrors and windows For navigation and guidance, electronic stability control (four- heel independent auto braking) For collision avoidance, parking assist For smart comfort control systems In buildings IR, vision and fiber-optic sensors and communications systems For improved safety, security and energy control systems. Smart windows to reduce heating, ventilation, and air-conditioning costs Biomechanical and biomedical systems SMA and polymer gel Piezoceramic and other ultrasonic sensors and actuators To develop artificial muscles, active control of in vivo drug delivery devices (insulin pumps) Catheter guide wire; surgical tools; imaging devices Computer industry Piezoceramic and Microaccelerometers and rotation rate sensors Quartz, piezoceramic and fiber-optic gyros Bimorph-type piezopositioner Piezoaccelerometers For smart read/write head micropositioners in next-generation data storage devices For high-density disk drives To correct for head-motion-related read/ write errors Note: Modified after [15]. Table 1.3 (Continued) 1.7 Summary b 15
- 44. C01 11/29/2011 9:1:20 Page 16 structures on a single chip or package leads to novel solutions in many fields. Smart materials help in devising new types of sensors and actuators. They extend the application domain of microsensors and microactuators to integrated smart systems that can sense their environment and intelligently and spontaneously respond to external stimuli. A few representative applications discussed in this chapter provide a glimpse into the unlimited opportunities provided by the combination of micro and smart systems. c REFERENCES 1. Feynman, R.P. (1992) There’s plenty of room at the bottom, Journal of Microelectrome- chanical Systems, 1(1), 60–66. 2. Feynman, R. (1993) Infinitesimal machinery, Journal of Microelectromechanical Systems, 2(1), 4–14. 3. Nguyen, C.T.C. (1999) Frequency-selective MEMS for miniaturized low-power communi- cation devices, IEEE Transactions on Microwave Theory Techniques, 47(8), 1486–1503. 4. Petersen, K.E. (1982) Silicon as a mechanical material, Proceedings of the IEEE, 70(5), 420–57. 5. Akhras, G. (2000) Smart materials and smart systems for the future, Canadian Military Journal, 1(3), 25–31. 6. Analog Devices (1996) ADXL-50 Monolithic accelerometer with signal conditioning, Data sheet, 16 pp. 7. Nagel, D.J. and Zaghloul, M.E. (2001) MEMS: micro technology, mega impact, IEEE Circuits and Devices, 17(2), 14–25. 8. Balaji, G., Singh, A. and Ananthasuresh G.K. (2006) Electromagnetically actuated minute polymer pump fabricated using packaging technology, Journal of Physics: Conference Series, Institute of Physics Publishing, 34, 258–63. 9. Private communication, Center of Excellence in Nanoelectronics, Indian Institute of Science, Bangalore, India. 10. Ive, R.L. (2004) Microfabrication of high-frequency vacuum electron devices, IEEE Trans- actions on Plasma Science, 32(3), 1277–91. 11. Goldsmith, C.L., Yao, Z., Eshelman, S. and Denniston, D. (1998) Performance of low-loss RF MEMS capacitive switches, IEEE Microwave and Guided Wave Letters, 8, 269–71. 12. Zengerle, R., Kinge, S., Richter, M. and Riscter, A. A bidirectional silicon micropump, Proceedings of the IEEE 1995 MEMS Workshop (MEMS’95, January 29–February 2, 1995, Amsterdam, Netherlands, 19–24. 13. Bishop, D.J., Giles, C.R. and Das, S.R. (2001) The rise of optical switching, Scientific American, 88–94. 14. Hornbeck, L.J. Current status of the digital-mirror device (DMD) for projection television Applications, Technical Digest, International Electron Devices Meeting, Washington, DC, 1993. 15. Varadan, V.K., Vinoy, K.J. and Gopalakrishnan, S. (2006) Smart Material Systems and MEMS: Design and Development Methodologies, John Wiley Sons, Chichester, London, UK. 16 c 1 Introduction
- 45. C02 12/06/2011 17:19:26 Page 17 c CHAPTER 2 Micro Sensors, Actuators, Systems and Smart Materials: An Overview L E A R N I N G O B J E C T I V E S After completing this chapter, you will be able to: c Understand principles of operation of some microsensors and microactuators. c Become familiar with some microsystems. c Learn about some materials and processes used to make microsystem components and devices. c Get an overview of types of smart materials. Sensors that sense the environment and actuators that provide the force needed to cause intended actions are integral parts of many systems in general and microsystems in particular. Both sensors and actuators are transducers—devices that convert one form of energy to another form. A sensor, independent of the parameter it senses, usually provides an electrical output such as voltage or current, while an actuator, in general, reacts to electrical input in order to provide a mechanical output—usually displacement and force. In this sense and from the energy point of view, a sensor may be considered to be primarily in the electrical domain and an actuator in the mechanical domain. Sensors, actuators, electronics circuitry, power sources and packaging—which inter- faces with the environment and protects all the components enclosed by it—comprise a microsystem. At the macroscale, a car, a robot, an air-conditioning unit, a water-purification unit, a television, etc., are all systems. Similarly, there are systems made possible by micromachined components. These components are not just electrical and electronics but mechanical devices fabricated using micromachining techniques with features as small as a few microns. These micromachining techniques are extended to thermal, optical, chemical, biological and other types of devices and components, and they can be packaged with microelectronic/micromechanical components to yield special microsystems. Before we learn about fabricating, modeling, simulating, controlling and packaging of microsystems, it is useful to get a bird’s-eye view of this field. This forms the core of the chapter. We provide salient features of commonly used microsensors, actuators, and systems. All of these are presented in the same format so as to highlight the similarities and 17
- 46. C02 12/06/2011 17:19:26 Page 18 differences among various devices and systems. Although one may not understand all the terms, the design details, and the application areas by reading this chapter, we believe that the material of this chapter provides motivation for learning the content presented in the rest of the book. The chapter ends with concise descriptions of various smart materials. The following lists the devices and systems presented in this chapter. They cover a variety of transduction principles, fabrication processes, disciplines and applications. Although not exhaustive, they collectively represent a sufficiently wide cross-section to make readers familiar and comfortable with the field and its uses. 1. Silicon capacitive accelerometer. 2. Piezoresistive pressure sensor. 3. Conductometric gas sensor. 4. Fibre-optic sensors 5. Electrostatic comb-drive. 6. Magnetic microrelay. 7. Microsystems at radio frequencies 8. Portable blood analyzer. 9. Piezoelectric inkjet print head. 10. Micromirror array for video projection. 11. Micro-PCR systems c 2.1 SILICON CAPACITIVE ACCELEROMETER Summary Category Sensor Purpose Measures the acceleration of the body on which the sensor is mounted. Key words Proof mass, suspension, capacitance Principle of operation Converts displacement caused by the inertial force on the proof-mass to a voltage signal via a change in capacitance between movable and fixed parts. Application(s) Automotive, aerospace, machine tools, biomedical, consumer products, etc. 2.1.1 Overview An accelerometer measures the acceleration of a body on which it is mounted. It becomes a tilt sensor if it measures gravitational acceleration. Almost all types of accelerometers have a basic structureconsistingofaninertialmass(alsocalledaproofmassoraseismicmass),asuspension, and a transducing mechanism to convert the acceleration signal to an electrical signal. In a capacitive accelerometer, the sensing method is capacitive in that any change in acceleration results in a change of capacitance that is measured electronically. One of the first micromachined accelerometers was reported in 1979 by Roylance and Angell at Stanford University [1]. It used piezoresistive transduction and weighed less than 0.02 g in a 2 3 0.6 mm3 package. It took over 15 years for such devices to be accepted as a product for large-volume applications. A wide variety of micromachined capacitive accelerometers is commercially availa- ble today. Some of the manufacturers of this type of accelerometer are Analog Devices, 18 c 2 Micro Sensors, Actuators, Systems and Smart Materials: An Overview
- 47. C02 12/06/2011 17:19:26 Page 19 Honeywell, Texas Instruments, Endevco Corporation, PCB Piezotronics, Freescale Semi- conductors, Crossbow, Delphi, Motorola, etc. Some of these are sold for less than 500 and some of them cost more than 50,000. This is because of the variation in performance and the applications. Low-cost accelerometers are used in consumer applications where very coarse resolution (even 0.1 g ¼ 0.981 m/s2 ) is enough. Expensive accelerometers can resolve 106 g or even 109 g. 2.1.2 Advantages of Silicon Capacitive Accelerometers Silicon capacitive accelerometers have: 1. Very low sensitivity to temperature-induced drift. 2. Higher output levels than other types. 3. Amenability for force-balancing and hence for closed-loop operation. 4. High linearity. 2.1.3 Typical Applications Typical applications of silicon capacitive accelerometers include: 1. Consumer: airbag deployment systems in cars, active suspensions, adaptive brakes, alarm systems, shipping recorders, home appliances, mobile phone, toys, etc. 2. Industrial: crash-testing robotics, machine control, vibration monitoring, etc. 3. High-end applications: military/space/aircraft industry navigation and inertial guidance, impact detection, tilt measurement, high-shock environments, cardiac pacemaker, etc. 2.1.4 An Example Prototype Figure 2.1(a) shows a photograph of a packaged, two-axis, planar, micromachined capacitive accelerometer with the mechanical sensor element and two Application Specific Integrated Circuit Chips (ASICs) [2]. Figure 2.1(b) shows a close-up view of the sensor element and Figure 2.1(c) shows its schematic details. This device is one of the many accelerometers developed in research laboratories in academia and industry and has the same features that can be found in any capacitive accelerometer. The physical arrangement and shapes of components differ among the different types. Materials and fabrication processes used may also be different. 2.1.5 Materials Used The materials used to form these devices include: 1. Single-crystal silicon to form the physical structure. 2. Silicon dioxide sandwiched in a silicon-on-insulator (SOI) wafer gives electrical isolation. 3. Handle-layer of the SOI wafer is the substrate. 4. Gold for electrodes. 2.1.6 Fabrication Process This is a bulk micromachining. In general, almost any microfabrication process can be used to make an accelerometer. 2.1 Silicon Capacitive Accelerometer b 19
- 48. C02 12/06/2011 17:19:26 Page 20 2.1.7 Key Definitions The important terms used and their definitions are: 1. Proof mass: the inertial mass used in the accelerometer whose displacement relative to a rigid frame is a measure of the influence of external acceleration. 2. Suspension: the compliant structure by which the proof mass is suspended from the frame. (a) (b) (c) Figure 2.1 (a) Fabricated two-axis, planar microaccelerometer with the sensor element and two ASICs; (b) a close-up view of the sensor element; and (c) schematic of the sensor element. Courtesy: Sambuddha Khan. 20 c 2 Micro Sensors, Actuators, Systems and Smart Materials: An Overview
- 49. C02 12/06/2011 17:19:42 Page 21 3. Capacitance:thecapacityofabodytoholdanelectricalcharge.Capacitanceisalsoa measure of the amount of electric charge stored for a given electric potential. For a two-plate capacitor, if the charges on the plates are þq and q and V is the voltage between the plates, then the capacitance is given by C ¼ q/V. The international standard (SI) unit of capacitance is the farad (1 farad ¼ 1 coulomb/volt). 4. Parallel-plate capacitor: a pair of parallel plates separated by a dielectric (nonconducting substance) medium. 5. Differential capacitance arrangement: in this arrangement, there are three plates with a movable middle plate. As the plate moves, the capacitance between one of the pairs will increase while that of the other decreases. This gives a signal that is linearly proportional to the applied acceleration, and hence is the preferred configuration. 6. Quality factor: a system’s quality factor, Q, describes the sharpness of the system’s dynamic response. 2.1.8 Principle of Operation An accelerometer can be thought of as a mass suspended by a spring. When there is acceleration, there will be a force on the mass. The mass moves, and this movement is determined by the spring constant of the suspension. By measuring the displacement, we can get an estimate of the acceleration (Figure 2.2). A capacitor may be formed with two plates of which one is fixed while the other moves [Figures 2.3(a), (b)]. In another arrangement, the mass can move in between two plates [Figure 2.3(c)]. In all three, the capacitance changes according to the motion caused by acceleration. At rest Upon acceleration Acceleration x k a = kx/m m Figure 2.2 A quasi-static accelerometer model. Motion Motion (a) (b) (c) Motion Figure 2.3 Examples of simple capacitance displacement sensors: (a) moving plate; (b) variable area; and (c) moving dielectric. 2.1 Silicon Capacitive Accelerometer b 21
- 50. C02 12/06/2011 17:19:42 Page 22 c 2.2 PIEZORESISTIVE PRESSURE SENSOR Summary Category Sensor Purpose Measures the pressure, typically of gases or liquids. Key words Piezoresistivity, diaphragm Principle of operation External pressure loading causes deflection, strain, and stress on the membrane. The strain causes a change in the resistance of the material, which is measured using the Wheatstone bridge configuration. Application(s) Automotive, aerospace, appliances, biomedical, etc. 2.2.1 Overview Pressure measurement is a key part of many systems, both commercial and industrial. In most pressure-sensing devices, the pressure to be measured is applied on one side of a diaphragm and a reference pressure on the other side, thus deforming the diaphragm. This deformation is measured by measuring the change in electrical resistance due to mechani- cal strain (i.e. piezoresistivity) of the material. The deformation is then related to the pressure to estimate the latter. Many devices are available for pressure measurement at the macroscale. Liquid column gauges consist of a vertical column of liquid in a tube whose ends are exposed to different pressures. The rise or fall of the column represents the applied pressure. Piston- type gauges counterbalance the pressure of a fluid with a solid weight or a spring. A Bourdon gauge uses a coiled tube that, when it expands due to increased pressure, causes rotation of an arm connected to the tube. This motion is transferred through a linkage connected to an indicating needle. Diaphragm-type pressure sensors include the aneroid gauge, which uses the deflection of a flexible membrane that separates regions of different pressures. The amount of deflection is indicative of the pressure to be determined. The first micromachined piezoresistive pressure sensors were developed in the early 1960s; however, the first reported practical pressure sensor was in the 1980s. During the 1990s several integrated microelectromechanical pressure sensor products were launched. Pressure sensors presently constitute the largest market segment of microsystems devices. There are many industries that manufacture and sell these sensors, including Motorola, Honeywell, Freescale Semiconductors, Micro Sensor Co. Ltd, American Sensors Technologies, Inc., etc. 2.2.2 Advantages of Piezoresistive Pressure Sensors Micromachined piezoresistive pressure sensors have: 1. Compact size, making them suitable for a variety of applications, including those that use an array of such sensors to measure pressure distribution. 2. Good thermal stability, since thermal compensation can be built into the sensor. 3. Good market potential due to low cost. 2.2.3 Typical Applications Typical applications of piezoresistive pressure sensors include: 1. Direct pressure-sensing applications: such as weather instrumentation, combustion pressureinanenginecylinderoragasturbine,appliancessuchaswashingmachines,etc. 22 c 2 Micro Sensors, Actuators, Systems and Smart Materials: An Overview
- 51. C02 12/06/2011 17:19:42 Page 23 2. Altitude-sensing applications: such as in aircraft, rockets, satellites, weather balloons, where the measured pressure is converted using an appropriate formula. 3. Flow-sensing applications, manifold pressure sensing: in automobiles, etc. 2.2.4 An Example Commercial Product Figure 2.4 shows a manifold absolute pressure (MAP) sensor commercially available from Motorola [3]. It is used in automobiles. Its packaged form and the schematic of the die without the outer plastic casing and fluidic fittings are shown in Figure 2.5. 2.2.5 Materials Used The material used to form this device is single-crystal silicon. 2.2.6 Fabrication Process Bulk micromachining with bipolar circuitry plus glass frit wafer-bonding is the fabrication process. 2.2.7 Key Definitions The important terms used and their definitions are: Diaphragm: a thin sheet of a flexible material, anchored at its circumference, over which differential pressure is applied. Piezoresistivity: the dependence of electrical resistivity on mechanical strain. Poly- silicon shows substantive piezoresistivity. 2.2.8 Principle of Operation Figure 2.6 shows the cross-section and top view of a pressure sensor die. When the diaphragm deforms due to the pressure to be measured, the resistances of the piezoresistors change. Calculation of piezoresistive responses in real structures must take account of the fact that piezoresistors are typically formed by diffusion and hence have nonuniform doping. They also span a finite area on the device and hence have nonuniform stress. For a Figure 2.4 Micromachined pressure sensor. Figure 2.5 Schematic of the packaged pressure sensor. 2.2 Piezoresistive Pressure Sensor b 23
- 52. C02 12/06/2011 17:19:44 Page 24 complete representation of all effects, one should solve the Poisson equation for the electrostatic potential throughout the piezoresistor, subject to boundary conditions of applied potentials at its contacts and subject to stress induced by deformation of the structural elements. From this potential, one determines the electric field, then the current density, and finally the total current. However, because the direction of current flow is along the resistor axis and, except at the contacts, parallel to the surface, considerable simplification is possible. Furthermore, the change in resistance due to stress is small, typically 2% or less. The Wheatstone bridge used to measure the change in resistance is shown in Figure 2.7. c 2.3 CONDUCTOMETRIC GAS SENSOR Summary Category Sensor Purpose It detects and quantifies the presence of a gas, that is, its concentration. Key words Adsorption, desorption Principle of operation The principle is that a suitable catalyst, when heated to an appropriate temperature, either promotes or reduces the oxidation of the combustible gases. The additional heat released by the oxidation reaction can be detected. The fundamental sensing mechanism of a gas sensor relies on a change in the electrical conductivity due to the interaction between the surface complexes such as O , O2 , Hþ , and OH reactive chemical species and the gas molecules to be detected. Application(s) Environmental monitoring, automotive application, air conditioning in airplanes, spacecraft, living spaces, sensor networks, breath analyzers, food control applications, etc. 2.3.1 Overview Gas sensing is concerned with surface and interface interactions between the molecules on the surface and the gas molecules to be detected. Many reactions are possible on the surface of sensors, and they can be accepted as the gas-sensing transduction schemes. However, the Diaphragm R2 R4 R1 R3 Top view Cross-section Figure 2.6 Schematic of a pressure-sensing element. R2 R3 R4 R1 Vs Vo + + − − Figure 2.7 Wheatstone bridge circuit used in sensing the change in resistance of the four resistors in Figure 2.6. 24 c 2 Micro Sensors, Actuators, Systems and Smart Materials: An Overview
- 53. C02 12/06/2011 17:19:44 Page 25 dominant reaction is a reversible gas-adsorption mechanism that occurs on the sensor’s surface. The adsorbed gas atoms inject electrons into or extract electrons from the semiconducting material, depending on whether they are reducing or oxidizing, respec- tively. The resulting change in electrical conductivity is directly related to the amount of analyte present in the sensed environment, thus resulting in a quantitative determination of the concentration of the gas present in the environment. For process control and laboratory analytics, large and expensive gas analyzers are used. Micromachining simplifies this through miniaturization and also reduces the cost. The oldest sensor of this kind is the Pellister, which is basically a heater resistor embedded in a sintered ceramic pellet on which a catalytic metal (platinum) is deposited. A few other methods, such as nondispersive IR methods using pyroelectric IR sensors and solid electrolyte gas-sensing mechanisms, can also be used for sensing. Commercial gas sensors are made or sold by a number of companies such as: MICS, Applied Sensor, UST, FIS, Figaro, City Tech, New Cosmos, etc. Not all of them use microsystem technology. 2.3.2 Typical Applications Typical applications of conductometric gas sensors include: 1. Environmental monitoring. 2. Exhaust gas sensing in automobiles. 3. Air conditioning in airplanes, spacecrafts, houses, and sensor networks. 4. Ethanol for breath analyzers. 5. Odor sensing in food-control applications, etc. 2.3.3 An Example Product Line Commercial gas sensors of this type are available in the market today. Figure 2.8 shows a schematic of the sensing element of a typical sensor. 2.3.4 Materials Used The materials used for making these are films of metal oxide such as SnO2 and TiO2. 2.3.5 Fabrication Process Gas sensors are fabricated using single-crystalline SnO2 nanobelts. Nanobelts are synthe- sized by thermal evaporation of oxide powders under controlled conditions in the absence of a catalyst. (b) (a) Figure 2.8 A conductometric gas sensor die and its cross-section when isotropic etch is used to release the suspended area of the sensor element. 2.3 Conductometric Gas Sensor b 25
- 54. C02 12/06/2011 17:19:44 Page 26 2.3.6 Key Definitions The important terms used and their definitions are: 1. Conductivity: a material property that quantifies the material’s ability to conduct electric current when an electric potential (difference) is applied. It depends on the number of free electrons available. 2. Adsorption: the process of collection and adherence of ions, atoms or molecules on a surface. This is different from absorption, a much more familiar term. In absorption, the speciesenterintothebulk,thatis,thevolume;inadsorption,theystayputonthesurface. 3. Desorption: the reverse of adsorption; species (ions, atoms or molecules) are given out by the surface. 4. Combustion: a technical term for burning: a heat-generating chemical reaction between a fuel (combustible substance) and an oxidizing agent. It can also result in light (e.g. a flame). 2.3.7 Principle of Operation An active area suspended by four beams off the fixed part of the wafer is the main element of this gas sensor in Figure 2.8. The adsorption or reaction of a gas on this active surface of the semiconducting material induces a change in the density of the conducting electrons in the polycrystalline sensor element. This change in conductivity is detected using electronic circuitry. The chemical reaction can be described in four steps: 1. Preadsorption of oxygen on semiconducting material surface. 2. Adsorption of a specific gas. 3. Reaction between oxygen and adsorbed gas. 4. Desorption of reacted gas on the surface. The above process of delivering electrons between the gas and the semiconductor actually represents the sensitivity of the gas sensor. While reacting with the gas, the conductivity of the semiconductor gas sensor decreases when the adsorbed oxygen molecules play the role of the acceptor, whereas the conductivity increases when the adsorbed oxygen molecules play the role of the donor. The principle is based upon initial reversible reaction of atmospheric oxygen with lattice vacancies in the oxide and the concurrent reduction in electron concentration. This reaction generates various oxygen species according to the temperature and oxygen pressures, that is, O2, O , O2 , which can then react irreversibly with certain combustible species. Metal electrodes deposited on the top of the formed membrane that contains the active area make the measurement of the resistance of the gas-sensitive layer possible. Generally, the electrodes are located underneath the sensing film. Usually, the electrode materials are gold and platinum and, in some cases, aluminum or tungsten. c 2.4 FIBER-OPTIC SENSORS 2.4.1 Overview An optical fiber hasa plastic or glassfiber core with a cladding. It isprimarily used as a medium for transmitting light signals for communication. It can also be used to sense any quantity that 26 c 2 Micro Sensors, Actuators, Systems and Smart Materials: An Overview
- 55. Another Random Document on Scribd Without Any Related Topics
- 59. The Project Gutenberg eBook of Book-Plates
- 60. This ebook is for the use of anyone anywhere in the United States and most other parts of the world at no cost and with almost no restrictions whatsoever. You may copy it, give it away or re-use it under the terms of the Project Gutenberg License included with this ebook or online at www.gutenberg.org. If you are not located in the United States, you will have to check the laws of the country where you are located before using this eBook. Title: Book-Plates Author: William John Hardy Release date: October 22, 2012 [eBook #41142] Most recently updated: October 23, 2024 Language: English Credits: Produced by Chris Curnow, Emmy and the Online Distributed Proofreading Team at http://www.pgdp.net *** START OF THE PROJECT GUTENBERG EBOOK BOOK-PLATES ***
- 61. Book-Plates
- 62. By W. J. Hardy, F.S.A. SECOND EDITION London Kegan Paul, Trench, Trübner Co., Ltd. MDCCCXCVII First Edition published 1893 as Vol. II. of 'Books about Books.'
- 63. Preface Having vindicated in my introductory chapter the practice of collecting book-plates from the charge of flagrant immorality, I do not think it necessary to spend many words in demonstrating that it is in every way a worthy and reasonable pursuit, and one which fully deserves to be made the subject of a special treatise in a series of Books about Books. If need were, the Editor of the series, who asked me to write this little hand-book, would perhaps kindly accept his share of responsibility, but in the face of the existence of a flourishing 'Ex Libris' Society, the importance of the book-plate as an object of collection may almost be taken as axiomatic. My own interest in this particular hobby is of long standing, and happily the appearance, when my manuscript was already at the printer's, of Mr. Egerton Castle's pleasantly written and profusely illustrated work on English Book-Plates has relieved me of the dreaded necessity of writing an additional chapter on those modern examples, in treating of which neither my knowledge nor my enthusiasm would have equalled his. The desire to possess a book-plate of one's own is in itself commendable enough, for in fixing the first copy into the first book the owner may surely be assumed to have registered a vow that he or she at least will not join the great army of book-persecutors—men and women who cannot touch a volume without maltreating it, and who, though they are often ready to describe the removal of a book- plate, even from a worthless volume, as an act of vandalism, do infinitely more harm to books in general by their ruthless handling of them. No doubt, also, the decay of interest in heraldry, which is mainly responsible for the eccentricities of modern 'fancy' examples, has taken from us the temptation to commit certain sins which were at one time attractive. Our ancestors, for instance, may sometimes have outraged the susceptibilities of the heralds by using as book-
- 64. plates coats-of-arms to which they had no title. Yet their offence against the College of Arms was trivial when compared with the outrage upon common-sense committed by the mystical young man of to-day, who designs, or has designed for him, an 'emblematic' book-plate, or a 'symbolic' book-plate, or a 'theoretic' book-plate, in which the emblem, or the symbol, or the theory, is far too mystical for any ordinary comprehension, and needs, in fact, a lengthy explanation, which, however, I am bound to confess, is always very willingly given by either owner or designer, if asked for. It is, perhaps, needless to say that I am very far from including all modern book-plates under this condemnation. The names of the artists—Sir John Millais, Mr. Stacy Marks, Randolph Caldecott, Mr. Walter Crane, Miss Kate Greenaway, and others—who have found time to design, some of them only one, some quite a considerable number of really interesting marks of ownership, suffice to rescue modern book-plates from entire discredit. Here and there, too, a little-known artist, like the late Mr. Winter of Norwich, has produced a singularly fine plate. Above all, the strikingly beautiful work of Mr. Sherborn, as seen in the book-plates of the Duke of Westminster, in that of Mr. William Robinson, and in many other fine examples, forms a refreshing oasis in the desert of wild eccentricity. But the most ardent admirer of modern book-plates cannot pretend that amid the multiplicity of recent examples any school or style is observable, and as I have aimed at giving in this little hand-book an historic sketch, however unpretentious, of the different styles adopted in designing book-plates from their first introduction, I hope I may be excused for not having attempted to trace their history beyond the early years of the present century, after which no distinctive style can be said to exist. As I have said elsewhere, it has been no part of my object in writing my book to advocate indiscriminate collecting. But for those who are already collectors I have one word of advice on the subject of the arrangement of their treasures. Some enthusiasts advocate a chronological arrangement, others a genealogical, others a
- 65. topographical: and the advocates of each theory paste down their specimens in scrap-books or other volumes in adherence to their own views. Now there is a great deal to be said in favour of each of these classifications: so much, indeed, that no system is perfect which does not admit of a collection being arranged according to one plan to-day and another tomorrow—i.e. no arrangement is satisfactory which is necessarily permanent. Let each specimen be lightly, yet firmly, fixed on a separate sheet of cardboard or stout paper, of sufficient size to take the largest book-plates commonly met with. These cards or sheets may be kept, a hundred or a hundred and fifty together, in portfolios or boxes, which should be distinctly numbered. Each card or sheet should also be paged and bear the number of the portfolio to which it belongs. The collector can by this means ascertain, when he pleases, if all his portfolios contain their proper number of cards or sheets, and he can arrange his specimens according to the particular point of interest in his collection which from time to time he may desire to illustrate. In addition to this, the system of single cards has obvious advantages for the purpose of minute study and comparison. In conclusion, it only remains for me to express my warm thanks to Lord De Tabley and to Mr. A. W. Franks, C.B.; to the former for allowing me to make use, without oft-repeated acknowledgment, of the matter contained in his Guide to the Study of Book-Plates, a second, and much amplified edition of which we may hope will, before long, make its appearance; to the latter, not only for constant advice and assistance, but also for the loan from his collection of nearly all the book-plates with reproductions of which this volume is illustrated. W. J. H. 1893.
- 67. Preface to the Second Edition A few words are, perhaps, needed by way of introduction to the present revised and enlarged edition of this work. Some slips of my own have been rectified, and there has been added a considerable amount of additional information, brought to light since 1893; for much of this I am indebted to the researches of Mr. Egerton Castle, Mr. Charles Dexter Allen, Miss Norna Labouchere, and Mr. Walter Hamilton, as well as to Mr. Fincham and various other contributors to the pages of the Ex Libris Journal. During the three years that have elapsed since the first publication of my book, the ranks of those taking an intelligent interest in book-plates have been largely increased; yet they have suffered some serious losses, and foremost amongst these must be placed the death of Lord De Tabley. That he died ere the completion of the promised new edition of his Guide to the Study of Book-Plates is a matter of sincere regret to every student of the subject; all we can now hope for is that Sir Wollaston Franks—the one man really capable of bringing out a new edition of Lord De Tabley's book—will some day undertake the task. As before, I have again to express my sincere gratitude to a great number of collectors for the kindly help they have given me; and I must not pass without special thanks the kindness of Mr. Everard Green, F.S.A., Rouge Dragon, for allowing me to illustrate this preface with his own book-plate, designed and engraved for him by Mr. George W. Eve; it is in every way an excellent specimen of modern work in book-plates, being both appropriate and artistic, and, above all, rational. W. J. H. St. Albans, 1896.
- 69. Contents PAGE CHAPTER I. Introductory, 1 CHAPTER II. The early use of Book-Plates in England, 20 CHAPTER III. 'Styles' in English Book-Plates, 48 CHAPTER IV. Allegory in English Book-Plates, 72 CHAPTER V. English 'Picture' Book-Plates, 98 CHAPTER VI. German Book-Plates, 114 CHAPTER VII. The Book-Plates of France and other Countries, 135 CHAPTER VIII. American Book-Plates, 150 CHAPTER IX. Inscriptions on Book-Plates in condemnation of Book-stealing or Book-spoiling, and in praise of Study, 162
- 70. CHAPTER X. Personal Particulars on Book-Plates, 178 CHAPTER XI. Ladies' Book-Plates, 186 CHAPTER XII. The more prominent Engravers of English Book-Plates, 200 CHAPTER XIII. Odds and Ends, 216 INDEX, 231
- 71. List of Illustrations of Book-Plates Richard Towneley, 1702, Frontispiece PAGE Everard Green, Rouge Dragon. By G. W. Eve, x PLATE I. Sir Thomas Isham. By Loggan, 9 II. Francis de Malherbe, 25 III. Sir Nicholas Bacon, 27 IV. Sir Thomas Tresham, 1585, 29 V. Gore. By Burghers, 35 VI. Marriott. By Faithorne, 37 VII. St. Albans Grammar School, 41 VIII. Charles James Fox, 45 IX. Thomas Knatchbull, 1702, 51 X. Sir Thomas Hare, 1734, 61 XI. James Brackstone, 1751, 63 XII. Bishop of Kilmore, 1774, 67 XIII. Birnie of Broomhill, 71 XIV. Gift by George i. to Cambridge, 1715, 77 XV. George Lambart. By Hogarth, 80 XVI. John Wiltshire, 83 XVII. Dr. William Oliver, 85 XVIII. Dr. Thomas Drummond. By Sir R. Strange, 89 XIX. Lady Bessborough. By Bartolozzi, 93 XX. William Hewer, 1699, 101 XXI. The Record Office in the Tower of London, 105 XXII. Southey. By Bewick, 111 XXIII. Gift-Plate to Buxheim Monastery, 115 XXIV. Ebner. By Albert Dürer. 1516, 119
- 72. XXV. Paulus Speratus, 123 XXVI. 'È Bibliotheca Woogiana,' 129 XXVII. Electoral Library of Bavaria, 1618, 133 XXVIII. Charles de Sales, 139 XXIX. Amadeus Lulin. By B. Picart, 1722, 145 XXX. Michael Lilienthal, 165 XXXI. David Garrick, 169 XXXII. Lady Bath, 1671, 187 XXXIII. Countess of Oxford and Mortimer. By Vertue, 191 XXXIV. Frances Anne Hoare, 197 XXXV. Bishop Hacket. By Faithorne (Portrait), 201 XXXVI. Sir Christopher Musgrave, 205 XXXVII. Francis Carington, 1738, 207 XXXVIII. Benjamin Adamson, 1746, 209 XXXIX. William Oliver, 1751, 211 XL. Samuel Pepys. By R. White (Portrait), 217 XLI. Francis Perrault (Portrait), 219 XLII. Robert Bloomfield, 1815, 229
- 73. BOOK-PLATES
- 74. CHAPTER I INTRODUCTORY Book-plate collecting, at least in this country, is a thing of yesterday. On the Continent, particularly in France, it attracted attention sufficiently serious to induce the publication, in 1874, of a monograph on French book-plates by M. Poulet Malassis, which in the next year obtained the honours of a second edition. In England, prior to 1880, we had no work devoted to the study; but, in that year, the Honourable J. Leicester Warren—afterwards Lord De Tabley —published A Guide to the Study of Book-Plates (Ex Libris). How little was then generally known about these marks of ownership is shown by the allusions to them—very few in number—that find place in the pages of such publications as The Gentleman's Magazine or Notes and Queries: for that reason, the skilful handling of the subject by the late Lord De Tabley, and his zeal in compiling the treatise, are all the more conspicuous. One of the most useful works which has yet appeared in the journal of the Ex Libris Society—a society intended to promote the study of book-plates—is a compilation by Mr. H. W. Fincham and Mr. J. Roberts Brown, A Bibliography of Book-Plates, arranged chronologically. A glance at this compilation emphasises the truth of the statement, just made, as to the scantiness of recorded information on book-plates prior to the year 1880; it also shows what a great deal about them has been written since. Writing to Notes and Queries in 1877, Dr. Jackson Howard, whose collection is now one of the largest in England, says that he began collecting forty years before that date, and that the nucleus of his own collection was one made by a Miss Jenkins at Bath in 1820. It is
- 75. probably, therefore, to this lady that we should attribute the honour of being the first collector of book-plates, for their own sake. No doubt the collector of engravings admitted into his portfolios book- plates worthy a place there as interesting engravings, for stray examples are often found in such collections as that formed in the seventeenth century by John Bagford, the biblioclast, which is now in the British Museum. No doubt, too, heraldic painters or plate engravers collected book-plates as specimens of heraldry, but this was not collecting them as book-plates—viz. as illustrations of the custom of placing marks of ownership in books, which, I take it, was evidently Miss Jenkins's object.[1] Still, though little was written on the subject of book-plates prior to 1880, it by no means follows that for some years before that date there had not been a considerable number of persons who took an interest in the subject. The fact is, that the book-plate collector of earlier days was wiser in his generation than are those of his kind to- day. He kept his 'hobby' to himself, and was thus enabled to indulge it economically. My father had a small collection; and I can well remember how, as a boy, I used to help him to add to it. We used to go to a shop in a dingy street, leading off Oxford Street, and there select from a large clothes-basket as many book-plates as were new to our collection. The price was one penny a piece,—new or old, dated or undated, English or foreign, that of Bishop Burnet, or David Garrick, or Mr. Jones, or Mr. Brown,—all alike, a penny a piece; and I have no doubt, though I do not remember the fact, there was the usual 'reduction on taking a quantity.' I think this shop was almost the only one in London where you could buy book-plates at all. Well, those days are past now; and, whilst we regret them, because book- plate collecting is no longer an economical pursuit, we cannot allow our regret to be unmingled with satisfaction. The would-be collector of to-day can, if he pleases, know something about the collection he is undertaking; he can tell when he meets with a good specimen; he knows the points which render any particular book-plate interesting; and he can, at least approximately, affix a date to each example he obtains.
- 76. As to the morality of book-plate collecting, I suppose something ought to be said here. There is but one objection to it, but that is, undoubtedly, a serious one: taking a book-plate out of a book means the possible disfigurement and injury of the volume from which it is taken; yet, for the purpose of study and comparison, the removal is a distinct advantage. To confess this seems, at first sight, to bring collecting at all under a sweeping condemnation; and such, indeed, would be the case, were it not for the fact that damage to, or even the actual destruction of, very many books is really a matter of no consequence whatever. Book-plates are found quite as often in the worthless literary productions of our ancestors as in the worthy; and it is puerile to cavil over the removal of a book-plate from a binding which holds together material by the destruction of which the world would certainly not be the poorer. So much for the book-plates in valueless books. As regards those in valuable or interesting ones, it is certainly unwise to remove them at all. This is a golden rule which cannot be too forcibly impressed upon collectors and booksellers. The case does not occur very often; and when it does, the book itself, with the book-plate in it, can be easily fetched and placed beside the 'collection' when needed for comparison. It may happen that the book-plate in this valuable book is interesting from the fact that it belonged to some man of note, or that it is unique; if so, we have only a further reason against taking it out of the volume. The value of a very early book-plate, when preserved in the volume in which it is discovered, is lessened almost to a vanishing point if separated from that volume. Pasted into a book as a mark of ownership, it is an undoubted book-plate; whereas, if taken out and fastened into a collection of book-plates, it at once loses the proof of its original use, so essential to its value and so material to the student of book-plates. On the other hand, as I have said, there is no harm in removing, from some uninteresting and valueless volume, the book-plate of a famous man. Everybody knows that Bishop Burnet or David Garrick had plenty of what they themselves regarded as 'rubbish' in their libraries; so that Burnet's book-plate in an actually valueless volume
- 77. does not prove that the Bishop's shrewd eye ever scanned its pages, or that his episcopal hand ever held it. Besides, I know as a fact that it is a not uncommon trick for the possessor of the book-plate of some famous man to affix that book-plate in a worthless volume, and then offer the whole for sale at a price much higher than would be asked or obtained for the book-plate itself, though the value of the book may be nil! Without quarrelling with the name book-plate,—as applied to the marks of ownership pasted into books,—and without wasting time with discussion of suggestions for a better one, it may be admitted that the word is not altogether happily chosen. It perhaps suggests to the mind of the 'uninitiated' an illustration in a book rather than a mark of possession. But then at the present day there are not many 'uninitiated' amongst either buyers or sellers of books and prints, so that the inappropriateness of the name need not concern us. As to its antiquity, that is doubtful; but probably one of the earliest instances of its use, in print, occurs in 1791, when John Ireland published the first two volumes of his Hogarth Illustrated. In this work he says that the works of Callot were probably Hogarth's first models, and 'shop bills and book-plates his first performances.' Again, in 1798, Ireland refers to the 'book-plate' for Lambert the herald-painter, which Hogarth had executed. In 1823, a certain 'C. S. B.,' writing in the pages of the Gentleman's Magazine, refers to what 'are generally called' book-plates. His letter was suggested by an article—a review of Thomas Moule's Bibliotheca Heraldica—in the previous number of the magazine, the writer of which was evidently not familiar with the term book-plate as we now apply it, for he calls book-plates 'plates of arms.' We shall see, later on, that this is quite an inappropriate name; some of the most interesting and the most beautiful book-plates have nothing armorial about them. On the Continent, the term ex libris is generally applied to book- plates. This is, perhaps, even less appropriate than book-plate. It is taken from the two first words of the inscription on a great many book-plates, when the inscription is written in Latin—e.g. 'ex libris
- 78. Johannis Stearne, S.T.P. Episcopi Clogherensis.' A moment's reflection will show that this inscription is not intended as a declaration by the book-plate (should it ever become severed from the book in which it was fastened) that it came out of a book belonging to Bishop Stearne; but that it is a declaration by the book in which the book-plate is found pasted, that that particular book is from amongst the books of a particular library, and ought to be restored to it. It would be as rational to call book-plates 'libri,' because the inscription on them often begins—as in a very famous German book-plate—'Liber Bilibaldi Pirckheimer.' It may, indeed, be laid down as a general rule, that whatever the sentiment expressed on a book-plate, it is clearly intended to be uttered by the book in which the book-plate is fixed, not by the book-plate itself. There are but two instances, quoted by Lord De Tabley, of the inscription directly referring to the book-plate. Both are foreign, and date about the middle of the last century. One is Symbolum Bibliothecæ of John Bernard Nack, a citizen and merchant of Frankfort;[2] and the other, Insigne Librorum, etc., quoted from the work of M. Poulet Malassis. Lord De Tabley thinks that the Symbolum of Herr Nack is simply a trade card; but he founds this conclusion on the supposition that Herr Nack was a book-dealer, and that the scene depicted on his book-plate was, in fact, his shop. In my opinion, we have in this book-plate a representation of a portion of Herr Nack's library, in which Minerva(?) is seated, using the books thereof. A gentleman in eighteenth century dress, who may, likely enough, be Herr Nack himself, addresses himself to the goddess, and explains—as he points to the outer scene, which shows us ships and merchandise—that, whilst following his trade as a merchant, he still has time to devote some attention to literature. In any case, these and the few other instances there may be of the inscription referring to the book-plate and not to the book, seem hardly sufficient to make ex libris a good name for book-plates in general. Our ancestors, of degrees more remote than grandfather, do not appear to have referred to book-plates at all, so we are unable to
- 79. SIR THOMAS ISHAM'S BOOK-PLATE, BY DAVID LOGGAN. learn by what name they would have called them. Pepys, in 1668, speaks of going to his 'plate-maker's,' and there spending 'an hour about contriving' his 'little plate' for his books. This 'little plate' still exists, and is a characteristic one; it shows us the initials 'S. P.,' with two anchors and ropes entwined. But we shall speak again of this, and Sam's other book-plates, later on.
- 80. David Loggan, a German born, and an engraver of some note, has, in writing to Sir Thomas Isham in 1676, a no more concise name for Isham's book-plate than 'a print of your cote of arms.' Loggan, as a return for many favours, had sent Sir Thomas a book- plate designed and executed by himself. 'Sir,' he says, in the covering letter, 'I send you hier a Print of your Cote of Armes. I have printed 200 wich I will send with the plate by the next return, and bege the favor of your keind excepttans of it as a small Niew yaers Gift or a aknowledgment in part for all your favors. If anything in it be amies, I shall be glade to mend it. I have taken the Heralds painter's derection in it; it is very much used amongst persons of Quality to past ther Cotes of Armes befor ther bookes instade of wreithing ther Names.' The 'Heralds painter' was, unfortunately, wrong in his treatment of the Isham 'coat,' and so Loggan's work, artistic as it might be, could not be acceptable to Sir Thomas, to whom a mistake in the family escutcheon was no light matter. This he evidently told David, who, a few days after, writes to him again:— 'I ame sorry that the Cote is wronge; I have taken the herald's derection in it, but the Foole did give it wrong.... The altering of the plate will be very trubelsom, and therfor you will be presented with a newe one, wich shall be don without falt, and that very sudenly. And if you plase, Sir, to give thies plate and the prints to your Brothers, it will serve for them.' These Isham book-plates are really very beautiful pieces of work. A reproduction of one of them may be seen on the foregoing page. This is evidently the one first executed, the omission of the mark of baronetcy—the 'bloody hand of Ulster'—and the helmet of an esquire instead of a knight or baronet clearly constituting the blunder into which Loggan had fallen. By the kindness of Sir Charles Isham, the present baronet, I have been enabled to see a copy of the corrected design sent by Loggan, which is in all respects accurate. This was doing duty as a book-plate in a volume in which it had evidently been placed at the time it was received by Sir Thomas.
- 81. Nicholas Carew, afterwards Sir Nicholas Carew, Baronet, records in his accounts, on the 19th February 1707, a payment for his book- plate, which is dated in that year, as follows:—'For coat of arms impressing, 1l. 1s. 6d.;' and a few months later is a payment 'For 300 armes, 7s. 6d.' 'The mark of my books,' is the phrase which Andrew Lumisden applies to the book-plate engraved for him by his brother-in-law, Sir Robert Strange, about the year 1746. The plate is an interesting one, and by an interesting man, of whom we shall speak later on. Lumisden thought well of it, and thus refers to the work in a letter written from Rouen, in June 1748:—'I am very anxious to know if my brother continues his resolution of coming to this country. If he does, I can luckily be of use to him in the way of his business, from the acquaintance I have of a very ingenious person, professor of the Academy of Design here ... I show'd him, a few days ago, the mark of my books, from which he entertains a high notion of Robie's abilities.' There is a curious advertisement, quoted by Thomas Moule in his Bibliotheca Heraldica, of a certain Joseph Barber, a Newcastle-on- Tyne 'bookseller, music and copper-plate publisher,' who, in 1742, resided in 'Humble's Buildings.' In that year he engraved the 'Equestrian Statue of King James [II.],' which once stood in the Sandhill Market. If a moment's digression be allowed, the history of this statue is worth telling. On 16th March 1685, the Town Council voted £800 for the erection of 'a figure of His Majesty in a Roman habit, on a capering horse, in copper, as big as the figure of His Majesty, King Charles I., at Charing Crosse, on a pedestal of black marble.' A certain Mr. William Larson executed it; Sir Christopher Wren expressed his approval, and everybody was very pleased, for a year or two. But popular feeling soon changed in Newcastle, as elsewhere, and the prevalence of sentiments which threw the king off his throne threw his metal representation into the Tyne, where it rested till fished out to be melted down and used to make a set of church bells. The drawing of the luckless statue was safe in the
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