SEMINAR ON
MICRO-ELECTRO-MECHANICAL SYSTEMS
(MEMS)
PART-1
A.RADHAKRISHNAN
MECHANICAL ENGINEERING, CPT COLLEGE
THIRUVANANTHAPURAM
MEMS
2
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What is MEMS Technology ?
What are MEMS ?
Design
Fabrication
Applications
What is MEMS Technology?
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Micro-Electro-Mechanical Systems (MEMS) is the
integration of mechanical elements, sensors, actuators, and
electronics on a common silicon substrate through microfabrication technology.
While the electronics are fabricated using integrated
circuit (IC) process sequences (e.g., CMOS, Bipolar, or
BICMOS processes).
The micromechanical components are fabricated using
compatible "micromachining" processes that selectively
etch away parts of the silicon wafer or add new structural
layers to form the mechanical and electromechanical
devices.
What are MEMS?
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Micro-electro-mechanical
systems.
Very small mechanical
assemblies.
 Hinged plate
 Hinge close-up
Micro-Electro-Mechanical Systems (MEMS)
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MEMS promises to revolutionize nearly every product
category by bringing together silicon-based microelectronics
with micromachining technology, making possible the
realization of complete systems-on-a-chip.
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MEMS is an enabling technology allowing the development
of smart products, augmenting the computational ability of
microelectronics with the perception and control capabilities
of microsensors and microactuators and expanding the space
of possible designs and applications.
Micro-Electro-Mechanical Systems (MEMS)
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How small exactly?
The photo above shows a
silicon motor together
with a strand of human
hair.
MEMS
systems
are
measured in micrometers
(microns),
that
is,
millionths of a meter.
The diameter of human
hair is about 100
microns.
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silicon motor together with
a strand of human hair
Micro-Electro-Mechanical Systems (MEMS)
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Microelectronic integrated circuits
can be thought of as the "brains" of a
system and MEMS augments this
decision-making capability with
"eyes" and "arms", to allow
microsystems to sense and control the
environment.
Sensors gather information from the
environment
through
measuring
mechanical,
thermal,
biological,
chemical, optical, and magnetic
phenomena.
Micro-Electro-Mechanical Systems (MEMS)
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The electronics then process the
information derived from the sensors
and through some decision making
capability direct the actuators to
respond by moving, positioning,
regulating, pumping, and filtering,
thereby controlling the environment for
some desired outcome or purpose.
Because
MEMS
devices
are
manufactured using batch fabrication
techniques similar to those used for
integrated.
MEMS micromotor
Micro-Electro-Mechanical Systems (MEMS)
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Microelectromechanical systems (MEMS) consist of
extremely tiny mechanical elements, often integrated
together with electronic circuitry.
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MEMS devices are made in a similar fashion to computer
microchips. The advantage of this manufacturing process
is not simply that small structures can be achieved but
also that thousands or even millions of system elements
can be fabricated simultaneously. This allows systems to
be both highly complex and extremely low-cost.
What is Micro-engineering ?
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Microengineering refers to the technologies and practice of
making three dimensional structures and devices with
dimensions in the order of micrometers.
The two constructional technologies of microengineering are
microelectronics and micromachining.
Micro-electronics, producing electronic circuitry on silicon
chips, is a very well developed technology.
Micromachining is the name for the techniques used to produce
the structures and moving parts of microengineered devices.
What is Micro-engineering ?
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One of the main goals of Micro-engineering is to be able to
integrate microelectronic circuitry into micromachined structures,
to produce completely integrated systems (microsystems). Such
systems could have the same advantages of low cost, reliability
and small size as silicon chips produced in the microelectronics
industry.
When considering such small devices, a number of physical effects
have different significance on the micrometer scale compared to
macroscopic scales. Interest in microengineering has spawned or
renewed interest in a number of areas dealing with the study of
these effects on microscopic scales. This includes such topics as
micromechanics, which deals with the moving parts of
microengineered devices, and microfluidics, etc.
What is Micro-engineering ?
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The some of micromachining techniques that are in use / under
development.
Silicon micromachining is given most prominence, since this is one
of the better developed micromachining techniques. Silicon is the
primary substrate material used in the production microelectronic
circuitry (ie, bettersilicon chips), and so is the most suitable
candidate for the eventual production of microsystems.
The Excimer laser is an ultraviolet laser which can be used to micro
machine a number of materials without heating them, unlike many
other lasers which remove material by burning or vaporising it. The
Excimer laser lends itself particularly to the machining of organic
materials (polymers, etc).
MUMPS Design Rules
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Enclose
Cut in
Cut out
14 mandatory design rules, 4 classes
Behavior
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Displacement scales as linearly
Capacitance scales as size2
Mass scales as size3
(Forget most of what you know about electromechanical
systems).
Design Tools
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L-Edit (Tanner)
 extends SPICE for mechanical analysis.
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MEMCad (Microcosm).
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VHDL
 in the works, but not ready yet.
Silicon Wafer
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A wafer is a thin slice of
semiconductor material, such as a
silicon crystal, used in the
fabrication of integrated circuit and
other micro devices.
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The wafer serves as the substrate
for microelectronic devices built in
and over the wafer and undergoes
many micro fabrication process
steps such as doping or ion
implantation, etching, deposition
of various materials,and
photolithographic patterning.
Fabrication
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Bulk micro-machining
 etch into the substrate.
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Surface micro-machining
 build up layers above the substrate and etch.
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LIGA
 deep structures.
Bulk micro-machining
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Pressure sensing diaphragm
example.
Etch with KOH (potassium hydroxide).
Etch is anisotropic.
 stopped in (1,1,1) direction
SiC also stops etch and forms
diaphragm.
Bulk micro-machined example
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Surface micromachining
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Specifically - MUMPS (Multi-User MEMS Processes).
 MUMPS has been called “MOSIS
(Metal Oxide Semiconductor Implementation Service)
for MEMS”.
 Three poly layer process derived from
Berkeley Sensors and Actuators
Center
 Seven total material layers.
 N mask steps.
Processing Layers (micro motor)
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7 material layers/
 Isolation
(Nitride)
 conductor (poly)
 1st sacrificial (oxide)
 1st structural (poly)
 2nd sacrificial (oxide)
 2nd structural (poly)
 metal
Patterning Poly 0
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Initial layers:

substrate/nitride/poly0/
resist.
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Expose resist.
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Dissolve exposed resist.
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Etch poly0.
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Wash remaining resist.
First Sacrificial (oxide) Layer
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This layer will eventually
be dissolved. Its purpose
is to support the structural
layer (poly1) above it.
Note: all layers are
conformal.
Two timed etches - short
for dimples, longer for
anchor.
First structural (poly1) layer
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Deposit 2mm of
polysilicon.
Coat with resist,
expose.
Etch with RIE (reactive
ion etch).
2nd sacrificial (oxide) layer
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Deposit 0.75mm oxide.
Two etch steps - first
contacts poly1, second
contacts substrate.
2nd structural (poly2) layer + metal
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Deposit second poly layer.
Apply resist and etch (RIE).
Apply resist and etch.
Deposit metal, gold in
MUMPS.
Released mechanism
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Rinse in solvent to
remove resist and
overlying metal.
Micro motor
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Soak 2 minutes in
concentrated HF to
dissolve sacrificial
oxide layers.
LIGA
LIthograpie, Galvanoformung, Abformung
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LIGA is a technique that can be used to
produce moulds for the fabrication of
micromachined
components.
synchrotron source
Microengineered components can be made
from a variety of materials using this
technique, however it does suffer the
disadvantage that currently the technique
requires X-rays from a synchrotron source.
A quick introduction to mask design is provided following discussion of
techniques and structures, rather than directly following the
photolithography section. This is so that we are able to become
acquainted with the concept of creating structures by sequential
photolithography and machining steps first, which hopefully makes it
easier to understand what mask design software is trying to achieve.
LIGA
LIthograpie, Galvanoformung, Abformung
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200mm deep
structures.
Coat with thick resist.
Pattern with Xrays.
Electroplate exposed
area with Ni.
Machine to +-5mm.
Use titanium and Cu as
sacrificial layers.
Deep Reactive
Ion Etching
Photolithography Process - Steps
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UV Light
HMDS
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Resist
Mask
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1) Vapor prime
2) Spin coat
3) Soft bake
4) Alignment
and Exposure
5) Post-exposure
bake
6) Develop
7) Hard bake
8) Develop
inspect
Photolithography
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Vapour Prime
Photoresist
dispenser
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Promotes Good Photoresistto-Wafer Adhesion.
Dehydration Bake .
Primes Wafer with
Hexamethyldisilazane(HMDS).
Vacuum chuck
To vacuum
pump
Spindle
connected to
spin motor
MEMS DEVICES
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• Infrared Imager (S)
• Inertial Measurement Unit (S)
- Accelerometer
- Gyros
• Air Velocity (S)
• Pressure (S)
Vibration ring for gyros
Microbolometer,
• Chemical Species (S)
• Micromotor (A)
• Micromirror (A)
Micromirror/optical switch
Accelerometer, Analog Device