Micro Electromechanical System (MEMS)

Outline
 MEMS Introduction
 Sensor and its type
 Fabrication
 MEMS Manufacturing Technology
 Applications
 Conclusion
 References

What is MEMS?
 MEMS or Micro-Electro Mechanical System is a
technique of combining Electrical and Mechanical
components together on a chip, to produce a system
of miniature dimensions.

 MEMS is the integration of a number of microcomponents on a single chip which allows the
microsystem to both sense and control the
environment.

 The components are integrated on a single chip
using micro fabrication technologies.

What is a Sensor?
 A device used to measure a physical quantity(such as
temperature) and convert it into an electronic signal of
some kind(e.g. a voltage), without modifying the
environment.

 What can be sensed?
Almost Everything!!!
Commonly sensed parameters are:
 Pressure
 Temperature
 Flow rate
 Radiation
 Chemicals
 Pathogens

N
W

E
S

2 Axis Magnetic
Sensor
2 Axis
Accelerometer
Light Intensity
Sensor
Humidity Sensor
Pressure Sensor
Temperature Sensor

But why MEMS for sensors?

 Smaller in size
 Have lower power consumption
 More sensitive to input variations
 Cheaper due to mass production
 Less invasive than larger devices

Type of Sensors

Mechanical
Sensors
•
•
•
•
•

Optical
Sensors

Strain Gauges
Accelerometers
Pressure Sensors
Microphones
Gyroscopes(Rotation
Rate)

• Direct Sensors (Light
 Electronic Signal)
• Indirect Sensors (Light
 Intermediate
Energy  Electronic
Signal)
• Biological Light
Sensors

Thermal
Sensors
• Thermo mechanical
(Dimension)
• Thermo Resistive
(Resistance)
• Acoustic (Sound)
• Biological

Chemical & Biological
Sensors
• Electronic Nose
• Electronic Tongue

Fabrication
Materials used are:
 Silicon

Basic Process

 Polymers
 Metals
 Ceramics

Deposition

Patterning

Etching

Basic Process of Fabrication
 Deposition
 Deposition that happen because of a chemical reaction or physical reaction.

 Patterning
 The pattern is transfer to a photosensitive material by selective exposure to a radiation source such as
light. If the resist is placed in a developer solution after selective exposure to a light source, it will etch
away.

 Etching
 Etching is the process of using strong acid to cut into the unprotected parts of a metal surface to create
a design in.
 There are two classes of etching processes:
 Wet Etching
 Dry Etching.

MEMS Manufacturing Technology
Bulk Micromachining
Surface Micromachining
High Aspect Ratio (HAR) Silicon Micromachining

Bulk Micromachining
 This technique involves the selective removal of the
substrate material in order to realize miniaturized
mechanical components.

 A widely used bulk micromachining technique in
MEMS is chemical wet etching, which involves the
immersion of a substrate into a solution of reactive
chemical that will etch exposed regions of the
substrate at very high rates.
Etched grooves using
(a) Anisotropic etchants,
(b) Isotropic etchants,
(c) Reactive Ion Etching (RIE)

Surface Micromachining
 In surface micromachining, the MEMS sensors are formed on top of the wafer
using deposited thin film materials.

(a)

Spacer layer deposition.

(b)

Pattering of the spacer layer.

(c)

Deposition of the microstructure layer.

(d)

Patterning of desired structure.

(e)

Stripping of the spacer layer resolves final
structure.

High Aspect Ratio (HAR) Silicon Micromachining
 HAR combines aspects of both surface and bulk
micromachining to allow for silicon structures with
extremely high aspect ratios through thick layers of
silicon (hundreds of nanometers, up to hundreds of
micrometers).
 HAR MEMS technology enables a high degree of
immunity to high-frequency, high-amplitude parasitic
vibrations.

Applications in Medical Science
 Biocavity Laser : This device distinguishes
cancerous from non cancerous cells thus aiding the
surgeons in operations.

 Smart Pill :
 Implanted in the body
 Automatic drug delivery (on demand)

 Sight for the blind : MEMS based array that may
be inserted in the retina of a blind person to provide
partial sight

Applications in Marine Science
Sensing in marine environment maybe done for
various reasons:
Oil exploration and related applications
Global weather predictions
Monitor water quality for any contamination
Measure parameters detrimental to the “health” of
structures in the sea ( like oil rigs and ships )
Study of aquatic plants and animals
In military operations

Applications in Marine Military Operations
 An array of MEMS sensors spread on the ocean
floor could detect the presence of enemy
submarines.

 MEMS sensors (pressure sensors, accelerometers
etc.) are being used in anti-torpedo weapons on
submarines and ships.

 MEMS sensors in torpedoes are responsible for
 Detonating the torpedo at the right time
 Hitting the target in a crowded environment
 Prevent any premature explosion

CONCLUSION

 MEMS promises to be an effective technique of producing sensors of high quality, at lower costs.
 Thus we can conclude that the MEMS can create a proactive computing world, connected
computing nodes automatically, acquire and act on real-time data about a physical environment,
helping to improve lives, promoting a better understanding of the world and enabling people to
become more productive.

References
 X. Wang, J. Engel, C. Liu, J. Micromech. Microeng. 2003, 13, 628.
 Christian A. Zorman, Mehran Mehregany, MEMS Design and Fabrication, 2nd Ed. 2,16.
 Ms. Santoshi Gupta, MEMS and Nanotechnology IJSER, Vol 3, Issue 5,2012
 Stephen Beeby, MEMS Mechanical Sensor, PP. 7
 Lenz, J., Edelstein, A.S., "Magnetic sensors and their applications." IEEE Sensors J. 2006, 6,
631-649.
 Sinclair M J 2000 A high force low area MEMS thermal actuator Proc. 7th Intersociety Conf. on
Thermal and Thermomechanical Phenomena (Las Vegas, NV) pp 127–32
 R. Ghodssi, P. Lin (2011). MEMS Materials and Processes Handbook. Berlin: Springer.

 Chang, Floy I. (1995).Gas-phase silicon micromachining with xenon difluoride. 2641. pp. 117.

Micro Electromechanical System (MEMS)

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