Presentation on Micro Electro Mechanical System

1. MicroElectromechanical Systems
(MEMS)
Submitted by-
Sandip Paul
M.Tech VLSI Design and
MicroElectronics.

2. Contents:
• Introduction
• Components.
• Fabrication Processes.
• Manufacturing Technologies.
• Sensing and Actuation Mechanism.
• MEMS Transducer.
• MEMS Applications.
• Advantage and Disadvantages.
• Design Tools.

3. Introduction
 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.
 These devices (or systems) have the ability to sense,
control and actuate on the micro scale, and generate
effects on the macro scale.
 MEMS are Made up of components between 1-100
micrometers in size.

4. This is a physical gear and
chain. This machinery
moves and functions same
as a gear and chain to
move and function.
However, the links in the
chain are about 50 µm
long—i.e., less than the
diameter of a human hair.

5. Components:
 MEMS consist of mechanical microstructures, microsensors,
microactuators and microelectronics, all integrated onto the
same silicon chip.

6. Microelectronics:
• “brain” that receives, processes, and makes decisions
• data comes from microsensors
Microsensors:
• constantly gather data from environment
• pass data to microelectronics for processing
• can monitor mechanical, thermal, biological, chemical
optical, and magnetic readings
Commonly sensed parameters are:
• Pressure
• Temperature
• Chemicals
Fig: MEMS Pressure Sensor

7. Microstructures:
• extremely small structures built onto
surface of chip
• built into silicon of MEMS.
Microactuator:
• acts as trigger to activate external
device
• microelectronics will tell
microactuator to activate device.
Some of Microactuators are-
i) Microvalves for control of gas and
liquid flows.
ii) Micropumps to develop positive
fluid pressures.
Microvalve
Micro pump

8. Fabrication Processes
FABRICATION PROCESS
Deposition Patterning Etching
Physical Chemical Lithography Wet Dry

9. DEPOSITION:
• deposit thin film of material (mask) anywhere between a few nm
to 100 micrometers onto substrate.
MEMS deposition technology can be classified in two groups:
• physical: material placed onto substrate, techniques include sputtering and
evaporation(PVD).
• chemical: stream of source gas reacts on substrate to grow product,
techniques include chemical vapor deposition and atomic layer deposition.
substrates:
silicon, glass, quartz
thin films:polysilicon, silicon
dioxide, silicon nitride,
metals, polymers

10. PATTERNING
• Patterning of MEMS is the transfer of a
pattern into a material.
 Lithography is a widely used process
 Examples of lithography are– Photolithography,
Electron beam lithography, Ion beam lithography, Ion
track technology, X-ray lithography.

11. ETCHING
• Etching is the process of using strong acid to cut the
unprotected parts of a metal surface to create a design
in.
There are two classes of etching processes:
• Wet Etching: dipping substrate into chemical solution that
selectively removes material.
• Dry Etching: material sputtered or dissolved from substrate with
plasma or gas variations

12. MANUFACTURING TECHNOLOGIES
• MEMS Manufacturing Techniques are-
–Bulk Micromachining.
–Surface Micromachining.
–High Aspect Ratio (HAR) Micromachining.

13. Bulk Micromachining:
• oldest micromachining technology
• technique involves selective removal of substrate to produce
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.

14. Basic Process Flow of Bulk Micromachining Process
Substrate
Deposition of
masking Layer
Structuring
masking layer
front and
backside
KOH Etching of
Cavity and Wafer
through Hole
Top view of
Resulting
Structure
a) Cantilever
b) Cavity
c) Wafer through
hole
a b c

15. Surface Micromachining
• It was initiated in the 1980’s and is the newest MEMS
production technology.
• Surface micromachining involves processing above the
substrate.
• Material is added to the substrate in the form of layers of
thin films on the surface of the substrate which can act as
either Sacrificial layer or Structural layer.
 A structural layer which is a free standing structure.
 A sacrificial layer on which the Structural layer is
made

16. Basic Process Flow of Surface Micromachining
Substrate
Deposit Sacrificial layer
Structure the Sacrificial
layer
Deposit Structural layer
Structure the Structural
Layer
Release Sacrificial Layer

17. High-Aspect-Ratio Micromachining
• High Aspect Ratio Micromachining combines of both
surface and bulk micromachining to allow for silicon
structures with extremely high aspect ratios through
thick layers of silicon.
• HAR MEMS technology enables a high degree of
immunity to high frequency, high amplitude parasitic
vibrations.
• Depth of the etch can be hundreds
or even thousands of microns into the silicon substrate.

18. Sensing and actuation mechanisms
• Sensing Mechanisms:
Many Microsensors based on different sensing
principles for MEMS have been developed , such as-
chemical sensors, gas sensors, optical sensors etc.
Some of the major sensing mechanisms are-
i) Piezoresistive Sensing
ii) Capacitive Sensing

19. i) Piezoresistive Sensing:
• Piezoresistive sensing uses the
resistors varied with the external
pressing to measure such physical
parameters as pressure, force,
accelerometer, flow rate, etc.
• Resistors are usually built on a silicon
diaphragm. The deflection of the
diaphragm leads to the dimension
change of the resistors, resulting in the
resistance changing because of the
piezoresistive effect in silicon.
• Resistance of the resistors is
proportional to the external pressure.

20. Capacitive Sensing
• Capacitive sensing uses the diaphragm deformation–
induced capacitance change to convert the information of pressure, force,
etc., into the electrical signals.
• Here an electrode on the flexible diaphragm and the other one on the
substrate construct the sensing capacitor.
• The capacitive sensing was found to have
potential for higher performance than
piezoresistive sensing in applications
requiring high sensitivity, low pressure
range, and high stability. Capacitive Sensing Structure

21. Microactuation mechanism:
• Microactuators are necessary for MEMS to
perform physical functions.
• Research and development efforts have been
directed toward using different actuation
principles and designing various structures for
specific applications.
• Some the major actuation principles are-
i) Electrostatic Actuation
ii) Thermal Actuation

22. i) Electrostatic Actuation
• For a simplest parallel plate-type electrostatic
microactuator, the electrostatic force is
created by applying a voltage across two
plates that are separated by insulation layer
with certain thickness.
• Electrostatic actuation has been widely
used in microactuator developments.
• In general, electrostatic actuation is
advantageous in which the
high actuation power is snot required.
• Electrostatic actuators can be easily integrated
on a chip from the fabrication point of view
and consume less input power.

23. ii) Thermal Actuation
• Thermal actuation has been extensively used
in microactuators. Thermal actuation is based
on a broad spectrum of principles such as
mechanical thermal expansion, thermal
pneumatic etc.
• In Figure, A thermally actuated microvalve is
shown in which heaters were embedded in
the valve diaphragm.
• When the valve diaphragm is heated, the
beam expansion resulted in the upward or
downward direction of the valve diaphragm,
controlling open/off of the microvalve.
• High power consumption and the low
switching frequency are the concern for the
application of this type of microactuators.

24. MEMS Transducer:
• A transducer is a device that converts power from one form to
another for purposes of measurement or control.
MEMS Transducers are categorized as-
i) Electro-Mechanical where inputs are as in Mechanical
form and Output as Electrical signal.
ii) Thermoelectric and Thermo-mechanical, converting
heat energy into either an electrical signal or a
mechanical motion.

25. Response characteristics of transducers:
• MEMS transducers have two types of
response characteristics-
i) Static response and
ii) Dynamic response.
• This response characteristics useful for
comparing the performance of different
transducers.

26. Step Response characteristics :
• Here, a steady (static) input is applied to the transducer and the resulting steady (static)
output is measured.
• Basic static performance characteristics are illustrated in Fig.
• Here, Span or full scale input is the domain of input values over which output values
of a transducer produces with acceptable accuracy.
• Full-scale output (FSO) is the range of output values.
• A transducer is linear if the ratio of output to input is constant .

27. Dynamic Response characteristics:
• Dynamic performance characteristics are
those observed when a transducer
responds to a “dynamic” input.
• For step response Input transducer
rises (or falls) from one constant value
to a new constant value and gives a
output rising (or falling) according to
its step response.
• Output takes time to reach its new
steady state value it is called response
time. Long and short response time are
illustrated in Fig. Fig. Responses of a linear
transducer to a step input.

28. MEMS APPLICATIONS:
• In medicine:
a. Blood pressure sensor.
b. Pacemaker.
c. Miniature Surgical Instruments.
• In Automotive:
a. Internal navigation sensors
b. Fuel level and vapour pressure sensor.
c. Airbag Sensor.
• In Defence:
a. Surveillance
b. Arming systems

29. ADVANTAGES and DISADVANTAGES
• ADVANTAGES:
a. Minimize energy and materials.
b. Improved reproducibility.
c. Improved accuracy and reliability.
• DISADVANTAGES:
a. Farm establishment requires huge investments.
b. Micro-components are costly compared to macro components.
c. Design includes very much complex procedures.

30. DESIGN TOOLS :
• CAD tools- In MEMS technology, CAD is defined as a
tightly organized set of cooperating computer
programs that enable the simulation of
manufacturing processes, device operation.
• COMMERCIALLY AVAILABLE SOFTWARES:
a. Coventorware from Coventor.
b. IntelliSuite from Intellisense Inc.
c. MEMScap from MEMScap Inc.

31. THANK YOU