Review of MEMS Technology & its Applications in Various Fields

International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395-0056
Volume: 04 Issue: 06 | June -2017 www.irjet.net p-ISSN: 2395-0072
© 2017, IRJET | Impact Factor value: 5.181 | ISO 9001:2008 Certified Journal | Page 343
Review of MEMS technology & its applications in various fields
Prof. Ms. D. S. Bhade
Assistant Professor
DMIETR, Wardha, Maharashtra
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Abstract - MEMS are small integrated devices which
combine electronics, electrical as well as mechanical element
to meet the control related functional requirements such as
sensing and actuation. Basically MEMS technology believes in
Good things comes in small packet. To satisfy today’s market
demand miniaturization is the only solution. The miniaturized
devices are particularly suited for biomedical & aerospace
application due to their minute size & weight. MEMS devices
are consider to range in characteristic length from one
millimeter down to one micron-many times smaller than the
diameter of a human hair. MEMS are the integration of active
and passive element on a single silicon substrate developed
through more advanced IC processing technology. MEMS
consist of mechanical microstructures, micro sensors, micro
actuators and microelectronics, all integrated onto the same
silicon chip. Almost every smart phone is now equipped with a
MEMS accelerometer-gyroscope system. The core element in
MEMS generally consists of two principal components, sensing
or actuating element and a signal transduction unit. There
are different micro sensors developed for various application
and widely used in the society. Some of the common sensors
are biosensor, chemical sensor, optical sensors, thermal &
pressure sensors. The application of Micro Electro Mechanical
Systems (MEMS) in the biomedical field is leading to a new
generation of medical devices. In this paper we will discuss
MEMS technology and its applications in various fields.
Biomedical sensor and biosensor used for diagnostic analyses.
These sensors require a minute amount of sample and can
produce results significantly faster than the traditional
biomedical instrument, the cost of these biosensors are low as
they produced in batches and easily disposable after use.
There are many other types of micro sensors that are
available in the market. They include chemical sensors for
detecting chemicals or toxic gases such as CO, CO2, NO, O3,
and NH3 etc.
Keywords-MEMS, Micro sensor, Micro actuator, Micro
fabrication
1. INTRODUCTION
Microsystem Technology based on the advancement made
in development of IC fabrication process. MEMS technology
smartly integrate electronics, electrical &
Mechanical components on a single silicon wafer similar to
integrated circuit technology. We can say that MEMS is the
integration of active elements that is sensors, actuators and
passive electronics as well as mechanical system as sown in
figure 1.In IC fabrication technology, fabrication of 3D
mechanical components such as plate, beam, cantilever,
diaphragm, gear etc. as well as electrical components such
as inductors & capacitors are not possible, whereas MEMS
technology adapted modified micromachining techniques to
fabricate these devices. This makes it possible for MEMS
technology to realize system-on-a-chip design.
Fig-1: MEMS Devices [2]
It combines microelectronic, micromechanics & micro optics.
MEMS have been identified as one of the most promising
technologies for this century and have the capacity to
combine both industrial and consumer products by
combining silicon based microelectronics with
micromachining technology. This emerging technique has
the tremendous power to affect all our life.
Micro level dimension
Mechanical
components
Electronics
components
Electrical
components
Semicon
ductors
Insulator
Diodes
Transisto
rs
Conductors
Resistors
Capacitors
Inductors
Gear
Bearing
Diaphra
gms
Cantile
ver
Beam
Flexure
Post
Anchor
Probe

Fig-2: Components of Microsystems
2. MICRO SENSORS & MICROACTUATORS
2.1 Microsensors
Sensor is a device that converts one form of energy into
another which gives output in response to specific
measurable input. A sensor system includes the sensing
element and related signal processing hardware. The signal
processing circuit could be an amplifier, analog to digital
converter, an offset compensator etc. Sensors which are
designed by using MEMS technology are called micro
machined micro sensors or MEMS sensors. Sensors are
classified into different types depending on the nature of
signal they handle, selective material of the transducer, and
the level of signal generation. Now we will discuss some of
the commonly used MEMS sensor
i) Silicon Capacitive Accelerometer: It measures the
acceleration of the body on which it is mounted .It
converts the displacement caused by the inertial force on
the proof mass to a voltage signal via change in
capacitance between movable and fixed parts. It is mainly
used in Automotive
ii) Pressure sensors: These sensors function on the
principle of mechanical deformation and stresses of thin
diaphragms induced by the pressure. This deformation
then converted into electrical signal output with the help
of transduction unit. Pressure sensor mainly used in Flow
sensing application, Automobile, biomedical application,
aerospace, direct pressure sensing application etc.
iii) Optical sensors: These optical sensors convert
optical signal into electronic output. Micro-optical sensors
have been developed to sense the intensity of light. The
mostly used optical sensors are photovoltaic junction,
photoconductive devices, photodiodes, and
phototransistors. All these devices convert incident
photon energy into electric output. Semiconducting
material such as silicon (Si), gallium arsenide (GaAs) are
common materials used for optical sensors.
iv) Thermal sensors: A thermocouple is a transducer
used for the measurement of temperature. It consists of
two dissimilar metals, joined together at one end, called
thermocouple junction. When the temperature of this
junction is different from the temperature of other parts of
the metal an EMF is generated.
v) Chemical sensors: These sensors are used to sense
particular chemical compounds, such as various gas
species. We know that many materials are sensitive to
chemical attacks and this property of material is the basis
for many chemical sensors.
vi) BioMEMS: In Biomedicine two types of sensors are
mostly used that is biomedical sensors and Biosensors.
Biomedical sensors are used to detect biological
substances, whereas biosensors are the measuring devices
that contain biological element. These sensors usually
involve biological molecules such as antibodies or
enzymes, which interact with analyses that are to be
detected. To design and manufactures this biomems one
require the knowledge & experience in molecular biology
as well as physical chemistry in addition to engineering.
The manufacturer has to think about biological system of
patient as well as about its mobility & easy navigation for
operations.
2.2 Micro actuators
The actuator is a very important part of a microsystem that
involves motion .The process of micro movement is called
micro actuation. Micro actuators are lightweight,
conformable and precision devices. The commonly available
micro actuators are Mechanical actuators, Electrostatic
actuators, Thermal actuators and Magnetic actuators.
Electrostatic actuation is widely used in devices and
machines at micro scales. The micro actuations applications
are:
a) Actuation of micro mirrors to scan laser beams.
b) Driving of cutting tools for microsurgical applications.
c) Driving of micro pumps and valves for fluid &
gas transportation
d) Printing application
e) Spatial light modulation for display application
f) Optical signal switching
g) RF signal tuning
3. MICROFABRICATION PROCESS
Fabrication of microsystem is known as
micromachining..Materials used for micromachining are
semiconductors, metals, ceramics, polymers etc. The most
common substrate material for micromachining is silicon
because of following reason
1. Silicon is abundant, inexpensive
2. Silicon’s ability to be deposited in thin films is very
amenable to MEMS
Power Supply
Signal
transduction &
processing
uunitUnit
Sensor Actuator
Microsystem

3. High definition and reproduction of silicon device
shapes using photolithography are perfect for high
levels of MEMS precision
4. Silicon has desirable electrical & mechanical
properties required for micromachining.
MEMS devices have been fabricated using the well-known
micromachining techniques used in the integrated circuit
domain, such as: photolithography, thin film deposition by
chemical vapor deposition (CVD) or physical vapor
deposition (PVD), thin film growth by oxidation and epitaxy,
doping by ion implantation or diffusion, wet etching, dry
etching, etc. as shown in fig.3. MEMS devices have the
potential of providing significant cost advantages when
batch fabricated. The micromachining process can use the
material to form microstructures by etching directly into the
material or use structural layer. Most widely used micro
fabrication processes are bulk micromachining and surface
micromachining.
Fig-3: Basic steps involved microelectronics fabrication
3.1Bulk Micromachining: Most of the commercial
microsystem devices are fabricated using bulk
micromachining. It was first used in microelectronics in
1960s.In bulk micromachining technique, significant
amount of material is removed from silicon wafer to form
membranes, cantilever beams, different types of trenches,
holes and other types of structures. Now let’s see how to
build cantilever beam on a silicon wafer by using Bulk
Micromachining
i) Grow thick layer of silicon dioxide on silicon wafer.
ii) ii) Apply a layer of photoresist on silicon dioxide
surface.
iii) Next is the photolithography process to define
cantilever geometry.
iv) Etch out oxide in unwanted area to form cantilever
beam and expose silicon surface.
v) Do anisotropic etching to form cavity in silicon
wafer.
3.2 Surface Micromachining: In contrast to Bulk
Micromachining, Surface Micromachining build
microstructures by adding material layer on the top of the
substrate. Basic steps involved in Surface Micromachining
are:
i) Deposition & patterning of sacrificial layer mostly
silicon dioxide
ii) Deposition & patterning of structural (polysilicon)
layer.
iii)Removal of sacrificial layer.
Fig- 4: Surface Micromaching process sequence
Silicon wafer preparation
(substrate)
Thin film deposition by using PVD
or CVD
Apply layer of photo resist on it
UV exposure under aligned mask
Desired pattern development as per
mask
Etching (Remove the photoresist
from exposed area)
Remove the photoresist from exposed
area
Wafer preparation &
cleaning
Sacrificial layer deposition that
is thin dielectric insulating layer
Base patterning with primary
mask layer
Deposition of structural layer
Pattern microstructure with second
mask layer
Selective etching of sacrificial layer
Rinsing, cleaning and drying

Bulk Micromachining Surface Micromachining
Established 1960 1980
Process Maturity Well established Fairly well established
Ruggedness Structure can withstand
vibration & shock
Less rugged
Die area Large Small
IC compatibility Not fully integrated IC compatible
Structure Geometry Limited option Wide range possible
Planar Geometry Rectangular Unrestricted
Comparison between Bulk & Surface Micromachining [3]
3.3 LIGA Process: To overcome disadvantage of Bulk &
Surface Micromachining that is low geometric aspect ratio,
use of only silicon based material, LIGA process have been
used..LIGA means Lithography (Electroforming & Molding)
Fig-5: LIGA process steps [3]
LIGA process is the most expensive micro fabrication
process. The major advantages of LIGA process are, It is the
best manufacturing process than others for mass production,
with the provision for injection molding ,also it allows the
production of metallic microstructures with unlimited
aspect ratio of the microstructure geometry.
4. MICROSYSTEM PACKAGING
The purpose of microelectronics packaging is to provide
mechanical support, electrical connections, and protection
of the delicate integrated circuits from all possible attacks
by mechanical and environmental sources. It also removed
heat generated by the integrated circuits. The three levels of
microsystem packaging are: Die level, Device level & System
level packaging
Types of Microsystem Packages
i) Metal packages: Metal packages are often used for
microwave integrated circuits and hybrid circuits
because they provide excellent thermal dissipation and
excellent electromagnetic shielding.
ii) Ceramic packages: This type of packaging is popular in
microelectronics industry due to its low mass,low cost
and ease of mass production.
Fig.6.Three levels of microsystem packaging[1]
iii)Plastic packages: This packages uses resin material to
encapsulate chip. The packages are also susceptible
to cracking in humid environments during
temperature cycling This is most common type of
packaging due to its low cost.
iv) Low-temperature co-fired ceramic packages (LTCC):
These are constructed from individual pieces of thick
film sheets of ceramic& then metal lines are deposited
in each film by thick processing.
5. APPLICATION OF MEMS
MEMS technology adapts miniaturization which makes
them suitable for each & every application to makes a
system smart one. As we know the miniaturized systems
have better response time, faster analysis and diagnosis,
Deep x-ray lithography
Desired patterns on thik
photoresist
Electroplating of metal on
patterns
Metal molds
Metal
product
Plastic products by injection
molding

less power consumption etc. Now we will discuss major
application of MEMS in some industry.
A] In Automotive industry:
i) Inertial sensors have been used in Airbags and
antilock braking system for safety purpose, vehicle
dynamic control, navigation systems.
Active suspension, roll detection
ii) Pressure sensors have been used in manifold air
iii) Pressure, tire pressure management systems.
iv) Flow sensors have been used to check air intake of
Engine, air quality in cabin. Microphones have been
used for hand free calling.
B] In Health Care Industry:
i) Intrauterine pressure sensors have been used to
monitor pressure during child delivery. Also
Angioplasty pressure sensors are used to monitor
the pressure inside the balloon once it is inside the
blood vessel.
ii) Optical sensors have been used in Micro
iii) spectrometers for patient self-testing and
monitoring
iv) Microfluidic devices have been used for
insulin pump & micro needles.
C] In Telecommunication field
i) RF MEMS have been used in tunable
Capacitors and resonators for mobile phones,
Switches in base stations.
ii) Optical sensors are used in Variable optical
Attenuators, optical switching, tunable filters
D] In consumer Product
i) IR sensors are used in Cabin temperature
Control, crash prevention, anti-fog systems, seat
Occupancy, tire and break monitoring system
ii) Microfluidic devices are used in inkjet heads
iii) Microphones have been used in Mobile phones,
Note books, camcorder.
iv) Inertial sensors are used in Pedometer, game
Control, image stabilization in video cameras,
Hard disk protection
E] In Aerospace & Defense
i) RF MEMS have been used in Switches and
Tunable capacitors for radar and communications.
ii) Inertial sensors are used in Missile guidance,
Navigation, laser range finder application
iii) Pressure sensors are used in Flight control
Systems, cabin pressure monitoring, hydraulic
Systems
iv) IR sensors are used for security monitoring
6. CONCLUSION
Miniaturization is the need of today’s world, as
everything is digitized. Last few decades have shown the
growth in microelectronics industry. The boom of
microelctomechanical industry in recent years would not
have been possible without the development of
microelectronic system. .There is no doubt that for all future
innovations in every walk of human endeavor, the rapid
growth of MEMS technology plays a vital role. As per earlier
discussion we can say the multidisciplinary mature of MEMS
technology makes it suitable for each and every field that is
automobile, medical, aerospace, telecommunication,
consumer product etc.
Currently, MEMS market demands are strongly
becoming high .This technology adapted new advanced
micromachining process for fabrication of products that
meet customer requirement as well as performance. In this
paper we discuss the need of miniaturization, different
sensors and actuators used in MEMS technology. Also this
paper focuses on microfabrication process need to design
MEMS structure. The various application of microsystem
discussed in this paper clearly specify how MEMS
technology becomes an integral part of each & every field.
REFERENCES
[1]“MEMS & MICROSYSTEMS Design and Manufacture” by
Tai-Ran Hsu Mc Graw Hill Education
[2]MEMS by Nitaigour Premchand Mahalik Mc Graw Hill
Education
[3]“MICRO AND SMART SYSTEMS” by
G.K.Ananthasuresh,K.J.Vinoy,S.Gopalakrishnan,K.N.Bhat,
V.K.Atre Wiley India Pvt..Ltd..
[4] Nidhi Maheshwari, Gaurav Chatterjee,V. Ramgopal Rao
“A Technology Overview and Applications of Bio-MEMS” J.
ISSS Vol. 3 No. 2, pp. 39-59, Sept. 2014.
[5] Srinivasa Rao Karumuri.K.Girija Sravani, S. Durga
Sailaja, J.Vijay Sekhar,Y.Srinivas, Ramendu Bhattacharje,
“Micro-Electro-Mechanical-Systems (MEMS) Technology”
Scholars Research Library Archives of Applied Science
Research, 2012, 4 (1):307- 314
[6]N.Maluf,“AnIntroduction to Microelectromechanical
Systems Engineering” Artech House, Norwood, MA, 2000
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Review of MEMS Technology & its Applications in Various Fields