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CONTENTS
1. Overview of MEMS technology
2. History of MEMS technology
3. Miniaturization
4. Scaling laws 4.1. Scaling in Geometry
4.2. Scaling in Rigid-Body Dynamics
4.3. Scaling in Electro Static Forces
4.4. Scaling in Electro Magnetic Forces
4.5. Scaling in Electricity
4.6. Scaling in Fluid Mechanics
4.7. Scaling in Heat Transfer
5. Working Principle of MEMS 5.1. Micro Sensors
5.2. Actuators
6. Examples of MEMS devices
7. Materials used in MEMS Fabrication
8. Microfabrication Processes 8.1. Photolithography
8.2. Ion implantation
8.3. Diffusion
8.4. Oxidation
8.5. Chemical vapor deposition
8.6. Physical vapor deposition (Sputtering)
8.7. Deposition by expitaxy
8.8. Etching
9. Fabrication Methods 9.1. Bulk Micromanufacturing
9.2. Surface Micromanufacturing
9.3. LIGA Process
10. Design and simulation using FEM tools
11. Applications
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1. Overview of MEMS technology Creation of 3-dimentional structures using integrated circuits fabrication techniques
and special micromachining processes. Typically done on silicon or glass(SIO2)
wafers.
MEMS merge at Nano scale in to Nano Electro Mechanical Systems (NEMS) &
Nano technology.
MEMS are made up of components between 1 to 100 micrometer in size.
2. History of MEMS technology MEMS word introduced in 1986 i.e. in proposal submitted to DARPA (Defense
Advanced research project agency) by the center for engineering design university of
UTAH.
Thomas Edison’s first successful light bulb model done in December 1879 at
Menlo park.
In 1904, British scientist John Ambrose Fleming first showed his device famous as
“Fleming Diode” to convert an alternating current signal in to direct current
signal. The “Fleming Diode” was base on an effect that Thomas Edison used in light
bulb model i.e. “vacuum tube”.
From 1904 to 1960 many other inventors tried to improve the “Fleming Diode”, the
only one who succeeded was New York inventor Lee De Forest.
In 16 December 1947, first time a Solid State Electronic Transistor known as
“Point Contact Transistor” developed by John Bardeen and Walter Brattain at
bell laboratories led by physicist William Shockly. This group has been working
together on experiments and theories of electric field effects in solid state
materials, with the aim of replacing “Vacuum Tubes” with a smaller and less
power consuming devices. And Silicon oxidation is demonstrated in 1953 in Bell
Telephone Laboratories & with this monolithic transistors are implemented. Got
Nobel prize in 1956.
1954: Piezoresistive effect in Germanium and Silicon (C.S. Smith), this discovery
showed that silicon and germanium could sense air or water pressure better than
metal. Many MEMS devices such as strain gauges, pressure sensors, and
accelerometers utilize the Piezoresistive Effect in silicon.
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Figure 1: An Example of a Piezoresistive Pressure Sensor [MTTC Pressure Sensor]
1958: First Integrated Circuit (IC) (J.S. Kilby1958 / Robert Noyce1959) Nobel
prize in 2000. Miniaturization of electronic circuits is started with this.
Figure 2: Texas Instrument's First Integrated Circuit [Photos Courtesy of Texas Instruments]
The famous lecture “There’s Plenty of Room at Bottom” is by Richard Feynman
in 1959, from this it is clear that there is a scope for micro and nano devices to fulfill
the future social technical needs.
1959 First silicon pressure sensor demonstrated (Kulite)
1967 Anisotropic deep silicon etching (H.A. Waggener et al.)
1968 Resonant Gate Transistor Patented (Surface Micromachining Process) (H.
Nathanson, et.al.)
Figure 3: Resonant Gate Transistor
1970‟s Bulk etched silicon wafers used as pressure sensors (Bulk MicromachingProcess)
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1971 The microprocessor is invented
Figure 4: (a) The Intel 4004 Microprocessor (b) Busicom calculator
[Photo Courtesy of Intel Corporation] [Photo Courtesy of Intel Corporation]
1979, Hewlett Packard developed the Thermal Inkjet Technology (TIJ). The TIJ
rapidly heats ink, creating tiny bubbles. When the bubbles collapse, the ink squirts
through an array of nozzles onto paper and other media. MEMS technology is used to
manufacture the nozzles. The nozzles can be made very small and can be densely
packed for high resolution printing. New applications using the TIJ have also been
developed, such as direct deposition of organic chemicals and biological molecules
such as DNA.
Figure 5: Nozzles in thermal Inkjet Printer
1982 "Silicon as a Structural Material," K. Petersen
1982 LIGA process, It allows for manufacturing of high aspect ratio microstructures.
High aspect ratio structures are very skinny and tall. LIGA structures have precise
dimensions and good surface roughness.
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Figure 6: LIGA-micromachined gear for a mini electromagnetic motor[Courtesy of Sandia
National Laboratories]
1982 Disposable blood pressure transducer (Honeywell)
1983 Integrated pressure sensor (Honeywell)
1983 "Infinitesimal Machinery" R. Feynman
1985 Sensonor Crash sensor (Airbag)
1985 The "Buckyball" is discovered
1986 The atomic force microscope is invented
Figure 7: Cantilever on an Atomic Force Microscope
1986 Silicon wafer bonding (M. Shimbo)
1988 Batch fabricated pressure sensors via wafer bonding (Nova Sensor) 1988 Rotary
electrostatic side drive motors (Fan, Tai, Muller)
1991 Polysilicon hinge (Pister, Judy, Burgett, Fearing)
1991 The carbon nanotube is discovered
1992 Grating light modulator (Solgaard, Sandejas, Bloom)
1992 Bulk micromachining (SCREAM process, Cornell)
1993 Digital mirror display (Texas Instruments)
1993 MCNC creates MUMPS foundry service
1993 First surface micromachined accelerometer in high volume production (Analog
Devices)
1994 Bosch process for Deep Reactive Ion Etching is patented
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1996 Richard Smalley develops a technique for producing carbon nanotubes of
uniform diameter
1999 Optical network switch (Lucent)
2000s Optical MEMS boom
2000s Bio-MEMS proliferate
3. Miniaturization Why miniaturization?
Batch fabrication, lower cost per device,
Less energy, less material consumed,
Array of sensors possible,
Can take advantage of different scaling laws,
Integration with circuitry can reduce noise and improve sensitivity,
Reliability may improve,
Fewer defects per chip i.e. 106 defects/cm
3->1 defect for every 10
6µm
3
The ENIAC Computer in 1946 A “Lap-top” Computer in 1996
A “Palm-top” Computer in 2001
Size: 106 down
Power: 106 up
Size: 108 down
Power: 108 up
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Figure 8: Miniaturization
Micromachining has become a key technology for the miniaturization of sensors.
Miniaturization is the trend to manufacture ever smaller mechanical, optical and
electronic products and devices.
In miniaturization the main problem is satisfying the scaling laws; otherwise the
device may fail in functionality.
4. Scaling laws Why scaling is important in MEMS?
Types of scaling laws
Scaling in Geometry
Scaling in Rigid-Body Dynamics
Scaling in Electro Static Forces
Scaling in Electro Magnetic Forces
Scaling in Electricity
Scaling in Fluid Mechanics
Scaling in Heat Transfer
4.1. Scaling in Geometry: Scaling of physical size of objects. Scaling in phenomenological behavior is of both size and
material characterization.
Volume (V) and Surface (S) are two physical parameters that are frequently involved
in machine design.
Volume leads to the Mass & weight of device components.
Volume relates to both mechanical and thermal inertia, the thermal inertia is a
measure on how fast we can heat or cool a solid.
Surface is related to pressure.
If we let ℓ=linear dimension of a solid, we have:
The Volume: V α ℓ3
The Surface: S α ℓ2
S/V= ℓ-1
4.2. Scaling in Rigid-Body Dynamics:
Forces are required to make parts to move such as in the case of micro actuators.
Power is the source for generation of force.
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In the case of miniaturization one need to understand the effect of reduction in the
size on the power (P), force (F) or pressure (F) and the time (t) require to deliver
the motion.
Trimmer Force Scaling Vector
F= [ ℓF] = [
]
Weight: W α ℓ3
Pressure: P α ℓ
-2
4.3. Scaling in Electrostatic Forces:
When two parallel electric conductive plates is charged by a voltage it will creates
electric potential field.
The corresponding potential energy is, U=
=
V
2
here: o , r α ℓ0 and W, L and d ℓ
1
Therefore:
U α ℓ3
i.e. A 10 times reduction of linear size of electrodes will reduce 1000 time s in potential energy.
The Electrostatic forces: F α ℓ2
i.e. A 10 times reduction in electrode dimensions will reduce 100 times the magnitude of the
electrostatic forces.
4.4. Scaling in Electro Magnetic Forces: The electromagnetic forces are the principal actuation forces in microscale or traditional motors
and actuators.
From Faradays law: Electromagnetic force F α ℓ4
What the above scaling means is that reducing the wire length by half (1/2) would
result in reduction of F by 24 = 16 times, whereas the reduction of electrostaic force
with similar reduction of size would result in a factor of 22 = 4.
This is the reason why electromagnetic forces are NOT commonly used in MEMS
and microsystems as preferred actuation force.
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4.5. Scaling in Electricity:
Electric Resistance: R=
α ℓ
-1
in which ρ, L and A are respective electric resistivity of the material, the length and across-
sectional area of the conductor
Resistive power loss: P=
α ℓ
1
Where V is the applied voltage.
Electric field energy: U=
E
2 α ℓ
-2
where is the permeativity of dielectric , and E is the electric field strength ∝ (ℓ) − 1
Ratio of power loss to available power:
=
= ℓ
-2
From “Nanosystems,” K. Eric Drexler, John Wiley & Sons, Inc., New York, 1992 Chapter 2,
„Classical Magnitudes and Scaling Laws,‟ p. 34:
Electric Quantity Index,a in ℓa
Current, i 2
Voltage, V 1
Resistance, R -1
Capacitance, C 1
Inductance, L 1
Power, P 2
4.6. Scaling in Fluid Mechanics: Two important quantities in fluid mechanics in flows in capillary conduits:
Figure 9: Capillary Conduits
A. Volumetric Flow, Q:
From Hagen-Poiseuille‟s equation:
Meaning a reduction of 10 in conduit radius→ 104 = 10000 times reduction in volumetric flow!
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B. Pressure Drop, ΔP:
From the same Hagen-Poiseuille‟s equation, we can derive:
Scaling: A reduction of 10 times in conduit radius → 103 = 1000 times increase in pressure drop
per unit length!!
4.7. Scaling in Heat Transfer: Two concerns in heat flows in MEMS:
A. How conductive the solid becomes when it is scaling down?
This issue is related to thermal conductivity of solids.
The thermal conductivity, k to be:
B. How fast heat can be conducted in solids:
This issue is related to Fourier number defined as:
Scaling: A 10 times reduction in size → 102 = 100 time reduction in time to heat the solid.
5. Working principle of MEMS The best examples of MEMS are
5.1. Micro Sensors : Working principle of Micro Sensors is
Figure 10: Block Diagram of Basic MEMS Sensors
Input
Signa
l
Micro Sensing
Element
Transduction
Element
Output
Signal
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Example: 1. Acoustic Sensor:
Acoustic wave sensor does not related to the sensing of acoustic waves transmitted in
solids or other media, as the name implies. Primary application of these sensors is to act like
“band filters” in mobile telephones and base stations.
Figure 11: Acoustic Sensor
2 sets of “Inter digital Transducers” (IDT) are created on a piezoelectric layer
attached to a tiny substrate as shown.
Energize by an AC source to the “Input IDT” will close and open the gaps of the
finger electrodes, and thus surface deformation/stresses transmitting through the
piezoelectric material
The surface deformation/stresses will cause the change of finger electrodes in the
“Output IDT”
Any change of material properties (chemical attacks) or geometry due to torques will
alter the I/O between the “Input IDT” and “Output IDT.”
The sensing of contact environment or pressure can thus be accomplished.
Example 2: BioMEMS:
BioMEMS include the following three major areas:
(1) Biosensors for identification and measurement of biological substances,
(2) Bioinstruments and surgical tools, and
(3) Bioanalytical systems for testing and diagnoses.
A sensor for measuring the glucose concentration of a patient.
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Figure 12: Bio MEMS to measuring the glucose concentration
The glucose in patient‟s blood sample reacts with the O2 in the polyvinyl alcohol
solution and produces H2O2.
The H2 in H2O2 migrates toward Pt film in a electrolysis process, and builds up
layers at that electrode.
The difference of potential between the two electrodes due to the build-up of H2 in
the Pt electrode relates to the amount of glucose in the blood sample.
Example 3: Chemical Sensors:
Work on simple principles of chemical reactions between the sample, e.g. ,O2 and the sensing
materials, e.g., a metal.
Types:
1. Chemiresistor
2.chemicapacitor
3. chemimechanical
4.Metal oxide gas
Figure 13: Basic Block Diagram of Chemical Sensor
Example 4: Optical Sensors:
These sensors are used to detect the intensity of lights.
It works on the principle of energy conversion between the photons in the incident light
beams and the electrons in the sensing materials.
The following four (4) types of optical sensors are available:
1. photo voltaic junction
Input
Voltage or
Current
Chemically Sensitive Polyimide Change of
Resistance
Change of
Capacitanc
e
Metal Insert
Metal Electrodes
Measurand Gas
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Figure 14: photo voltaic junction
2. photoconductive device
Figure 15: photo Conductive Device
3.photo diode
Figure 16: Photo Diode
4. Photo transistors
Figure 17: Photo Transistors
Silicon (Si) and Gallium arsenide (GaAs) are common sensing materials. GaAs has
higher electron mobility than Si- thus higher quantum efficiency. Other materials, e.g.
Lithium (Li), Sodium (Na), Potassium (K) and Rubidium (Rb) are used for this purpose.
Example: 5. Pressure Sensors:
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Micro pressure sensors are used to monitor and measure minute gas pressure in
environments or engineering systems, e.g. automobile intake pressure to the engine.
They are among the first MEMS devices ever developed and produced for “real world”
applications.
Micro pressure sensors work on the principle of mechanical bending of thin silicon
diaphragm by the contact air or gas pressure.
Figure 18: Basic Pressure Sensor
The strains associated with the deformation of the diaphragm are measured by tiny
“piezoresistors” placed in “strategic locations” on the diaphragm.
These tiny piezoresistors are made from doped silicon. They work on the similar
principle as “foil strain gages” with much smaller sizes (in μm), but have much higher
sensitivities and resolutions.
Major problems in pressure sensors are in the system packaging and protection of the
diaphragm from the contacting pressurized media, which are often corrosive, erosive,
and at high temperatures.
Example: 6. Thermal Sensors:
Thermal sensors are used to monitor, or measure temperature in an environment or of an
engineering systems.
Common thermal sensors involve thermocouples and thermopiles.
Thermal sensors work on the principle of the electromotive forces (emf) generated by
heating the junction made by dissimilar materials (beads):
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Figure 19: Thermal Sensor
The generated voltage (V) by a temperature rise at the bead (ΔT) is:
V= β ΔT
where β = Seebeck coefficient:
5.2. Actuators:
Figure 20: Basic Block Diagram of Actuator
Example 1: Actuation Using Thermal Forces:
Solids deform when they are subjected to a temperature change (ΔT)
A solid rod with a length L will extend its length by ΔL = α ΔT, in which α = coefficient
of thermal expansion (CTE) – a material property.
When two materials with distinct CTE bond together and is subjected to a temperature
change, the compound material will change its geometry as illustrated below with a
compound beam:
Figure 21: Geometrical change because of heating
These compound beams are commonly used as microswitches and relays in MEMS
products.
Output
Action
Power
Supply
Micro Actuating Element
Transduction Element
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Example 2: Actuation Using Piezoelectric Crystals:
A certain crystals, e.g., quartz exhibit an interesting behavior when subjected to a
mechanical deformation or an electric voltage.
This behavior may be illustrated as follows:
Figure 22: Actuation Using Piezoelectric Crystals
6. Examples of MEMS Devices
6.1. Few examples of real MEMS products are: 1. Adaptive Optics for Ophthalmic Applications
2. Optical Cross Connects
3. Air Bag Accelerometers
4. Pressure Sensors
5. Mirror Arrays for Televisions and Displays
6. High Performance Steerable Micromirrors
7. RF MEMS Devices
8. Disposable Medical Devices
9. High Force, High Displacement Electrostatic Actuators
10. MEMS Devices for Secure Communications
6.2. MEMS devices used in Space exploration field include: 1.Accelerometers and gyroscopes for inertial navigation
2. Pressure sensors
3. RF switches and tunable filters for communication
4. Tunable mirror arrays for adaptive optics
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5. Micro-power sources and turbines
6. Propulsion and attitude control
7. Bio-reactors and Bio-sensors, Microfluidics
8. Thermal control
9. Atomic clocks
7. Materials used in MEMS Fabrication The materials used in MEMS and micro systems fabrications are
Silicon: (Symbol: Si, Atomic number: 14, Atomic mass: 28.0855 u ±
0.0003 u, Electron configuration: [Ne] 3s23p
2 , Melting point: 1,414 °C,
Atomic radius: 117.6 pm, Discoverer: Jöns Jacob Berzelius) and
Germanium: (Symbol: Ge, Atomic number: 32, Electron
configuration: [Ar] 3d10
4s24p
2 , Discovered: 1886, Melting point: 938.2 °C,
Atomic mass: 72.64 u ± 0.01 u, Discoverer: Clemens Winkler).
Single crystal silicon is the most widely used substrate material for MEMS and
microsystems.
The popularity of silicon for such application is primarily for the following reasons:
It is mechanically stable and it is feasible to be integrated into electronics on
the same substrate.
Electronics for signal transduction such as the p or n-type piezoresistive can
be readily integrated with the Si substrate-ideal for transistors.
Silicon is almost an ideal structure material. It has about the same Young‟s
modulu‟s as steel (∼2x105 MPa[Minimum tensile strength]), but is as light as
aluminum with a density of about 2.3 g/cm3 .
As such, silicon will be the principal material to be studied.
Other materials to be dealt with are silicon compounds such as:
SiO2-Silicomdioxide or Silica, It acts as a diffusion mask permitting selective diffusions
into silicon wafer through the window etched into oxide. SiO2 acts as the active gate
electrode in MOS device structure. It is used to isolate one device from another. It
provides electrical isolation of multilevel metallization used in VLSI.
SiC-silicon carbide or Carborundum
Si3N4 – Silicon Nitride
polysilicon.
Also will be covered are electrically conducting of silicon piezoresistors (N-Type, P-
Type) and piezoelectric crystals for electromechanical actuations and signal
transductions.
An overview of polymers, which are the “rising stars” to be used as MEMS and
microsystems substrate materials, will be studied too.
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8. Microfabrication Processes
8.1. Photolithography: Photolithography process involves the use of an optical image and a photosensitive film
to produce desired patterns on a substrate.
The “optical image” is originally in macro scale, but is photographically reduced to the
micro-scale to be printed on the silicon substrates.
The desired patterns are first printed on light-transparent mask, usually made of quartz.
The mask is then placed above the top-face of a silicon substrate coated with thin film of
photoresistive materials.
The mask can be in contact with the photoresistave material, or placed with a gap, or
inclined to the substrate surface:
Figure 23: Photolithography
8.2. Ion Implantation:
It is physical process used to dope silicon substrates.
It involves “forcing” free charge-carrying ionized atoms of B, P of As into silicon
crystals.
These ions associated with sufficiently high kinetic energy will be penetrated into the
silicon substrate.
Physical process is illustrated as follows:
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Figure 24: Ion Implantation
8.3. Diffusion:
Diffusion is another common technique for doping silicon substrates.
Unlike ion implantation, diffusion takes place at high temperature.
Diffusion is a chemical process.
The profile of the spread of dopant in silicon by diffusion is different from that by ion
implantation:
Figure 25: Diffusion
8.4. Oxidation: SiO2 is an important element in MEMS and microsystems. Major application of SiO2
layers or films are:
(1) To be used as thermal insulation media
(2) To be used as dielectric layers for electrical insulation
SiO2 can be produced over the surface of silicon substrates either by:
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(1) Chemical vapor deposition (CVD), or
(2) Growing SiO2 with dry O2 in the air, or wet steam by the following two chemical
reactions at high temperature:
Si (solid) + O2 (gas) → SiO2 (solid)
Si (solid) + 2H2O (steam) → SiO2 (solid) + 2H2 (gas)
Figure 26: Oxidation
9. Fabrication Methods Basic integrated circuit fabrication involves
1. Deposition 2. Lithography 3. Removal
Figure 21: IC Fabrication Process Flow
Micromanufacturing: Applying Micromachining to create 3-D structures using 2-D
processing
2D IC Process 3D structures
Micromachining
Basic Types of Micromachining:
9.1. Bulk Micromanufacturing:
Wafer
Deposition Lithography Etch
Chips
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Bulk micromanufacturing technique involves creating 3-D components by removing
materials from thick substrates (silicon or other materials) using primarily etching
method.
Etching - dry or wet etching is the principal technique used in bulk
micromanufacturing.
Substrates that can be etched in bulk micromanufacturing include:
1. Silicon. 2. SiC 3. GaAs 4. Special polymers
Less expensive in the process, but material loss is high.
Suitable for microstructures with simple geometry.
Limited to low-aspect ratio in geometry.
(a) (b)
Figure 22 : Bulk Micromachining (a) Back-side Etching (b) Front-side Etching
9.2. Surface Micromanufacturing: Surface micromachining creates 3-D microstructures by adding material to the
substrate.
Requires the building of layers of materials over the substrate.
Complex masking design and productions.
Etching of sacrificial layers is necessary – not always easy and wasteful.
The process is tedious and more expensive.
There are serious engineering problems such as interfacial stresses and stiction.
Major advantages:
Not constrained by the thickness of silicon wafers.
Wide choices of thin film materials to be used.
Suitable for complex geometry such as micro valves and actuators.
Figure 23: Surface Micromachined Structure
9.3. LIGA Process:
LIGA: Lithographie, Galvanoformung, Abformung
Form high aspect ratio structures on top of wafer
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Uses molding and electroplating
Synchrotron Radiation (X-Ray) used
Most expensive in initial capital costs.
Requires special synchrotron radiation facility for deep x-ray lithography.
• Micro injection molding technology and facility for mass productions.
• Major advantages are:
Virtually unlimited aspect ratio of the microstructure geometry.
Flexible in microstructure configurations and geometry.
The only technique allows the production of metallic microstructures.
Figure 24: LIGA Process
Feature:
Aspect ratio: 100:1
Gap: 0.25μm
Size: a few millimeters
10. Design and Simulation using FEM Tools There are many Finite Element Model Tools (FEM Tools), to design and simulate
MEMS devices.
Example:
1. Comsol Multiphysics
2. Intellisuite
3. MEMS Pro
4. HiQLAB
5. Coventor
11. Applications
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11.1. Automotive domain:
1. Airbag Systems
2. Vehicle Security Systems
3. Intertial Brake Lights
4. Headlight Leveling
5. Rollover Detection
6. Automatic Door Locks
7. Active Suspension
11.2. Consumer Domain: 1. Appliances
2. Sports Training Devices
3. Computer Peripherals
4. Car and Personal Navigation Devices
5. Active Subwoofers
11.3. Industrial Domain: 1. Earthquake Detection and Gas Shutoff
2. Machine Health
3. Shock and Tilt Sensing
11.4. Military: 1. Tanks
2. Planes
3. Equipment for Soldiers
11.5. Biotechnology: 1. Polymerase Chain Reaction (PCR) microsystems for DNA amplification and identification
2. Micromachined Scanning Tunneling Microscopes (STMs)
3. Biochips for detection of hazardous chemical and biological agents
4. Microsystems for high-throughput drug screening and selection
5. Bio-MEMS in medical and health related technologies from Lab-On-Chip to biosensor &
chemosensor.
11.6. The commercial applications include: 1. Inkjet printers, which use piezo-electrics or thermal bubble ejection to deposit ink on
paper.
2. Accelerometers in modern cars for a large number of purposes including airbag
deployment in collisions.
3. Accelerometers in consumer electronics devices such as game controllers, personal media
players / cell phones and a number of Digital Cameras.
4. In PCs to park the hard disk head when free-fall is detected, to prevent damage and data
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loss.
5. MEMS gyroscopes used in modern cars and other applications to detect yaw; e.g. to
deploy a roll over bar or trigger dynamic stability control.
6. Silicon pressure sensors e.g. car tire pressure sensors, and disposable blood pressure
sensors.
7. Displays e.g. the DMD chip in a projector based on DLP technology has on its surface
several hundred thousand micromirrors.
8. Optical switching technology, which is, used for switching technology and alignment for
data communications.
9. Interferometric modulator display (IMOD) applications in consumer electronics (primarily
displays for mobile devices).
10. Improved performance from inductors and capacitors due the advent of the RF-MEMS
technology.
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References: 1. Lectures of
Dr. Tai-Ran Hsu
Professor, Department of Mechanical Engineering
San José State University
One Washington Square
San José, California 95192-0087
Office: Engineering 117B
Telephone: (408) 924-3905
Fax: (408) 924-3995
E-mail: [email protected]
2. Lecture of
Prof. Santiram Kal,
Department of Electronics & Electrical Communication Engineering
Indian Institute of Technology, Kharagpur.