overviewof mems_2016
TRANSCRIPT
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Introduction to MEMS Technology
Dr. S. L. Pinjare
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Topics What is MEMS
Why MEMS?
How are MEMS Made
The History of MEMS
Challenges of MEMS
MEMS Applications
MEMS markets
MEMS in Action
Summary
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What is MEMS?
Micro-Electro-Mechanical Systems
Three MEMS blood pressure
sensors on a head of a pin [Photo
courtesy of Lucas NovaSensor,
Fremont, CA]
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MEMS?
MEMS - evolved from the Microelectronics revolutionMEMS or MST?
United States the technology is known as MicroElectroMechanicalSystems - MEMS
In Europe it is called Microsystems Technology MST
In Japan, Micromachines
What's in a name? ... A rose by any othername would smell as sweet.
W. Shakespeare inRomeo and Juliet
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MEMS?
MEMS is simultaneously a toolbox, a physical product, and amethodology, all in one:
It is a portfolio of techniques and processes to design and
create miniature systems.
It is a physical product often specialized and unique to a final
at the neighborhood electronics store.
MEMS is a way of making things,
reports the Microsystems Technology Office of the United
States DARPA [1].
These things merge the functions of sensing and actuation
with computation and communication to locally control
physical parameters at the microscale, yet cause effects at
much grander scales.
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MEMS?
A MEMS is a device made from extremely small parts (though a universaldefinition is lacking).
MEMS products possess a number of distinctive features.
miniature embedded systems
involving one or many micromachined components or structures.
enable higher level functions,
By themselves they may have limited utility
integrate smaller functions together into one package for greater utility
merging an acceleration sensor with electronic circuits for self
diagnostics).
cost benefits
directly through low unit pricing or indirectly by cutting service and
maintenance costs.
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MEMS as a MicroSystem
A microsystem might comprisethe following:
A sensor that inputs
information into the system;
An electronic circuit that
An actuator that responds to
the electrical signals
generated within the circuit.
Both the sensor and the actuator
could be MEMS devices in their
own right.
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MEMS?
A Micro-Electro-MechanicalSystem (MEMS) contains bothelectrical and mechanicalcomponents with characteristicsizes ranging from a few
nanometers to millimeters.
Mechanical Elements,
Sensors,
Actuators, and
Electronics
On a Common Substratethrough the Utilization ofMicrofabrication Technology.
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MEMS? Microelectronics
The microelectronics act as the"brain" of the system.
It receives data, processes it, and
makes decisions.
The data received comes from.
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MEMS? Microsensors
The microsensors act as thearms, eyes, nose, etc.
They constantly gather data
from the surrounding
environment and pass this
information on to the
microelectronics for
processing.
These sensors can monitor
mechanical, thermal,biological, chemical, optical
and magnetic readings from the
surrounding environment.
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MEMS? Microactuators
A micro actuator acts as a switchor a trigger to activate an external
device.
As the microelectronics is
processing the data received from
the microsensors, it is making
decisions on what to do based on
this data.
Sometimes the decision will
involve activating an externaldevice.
If this decision is reached, the
microelectronics will tell the
micro actuator to activate this
device.
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MEMS? Microstructures (Mechanical)
Due to the increase intechnology for micromachining,
extremely small structures can
be built onto the surface of a
chip.
These tin structures are called
micro structures and are actually
built right into the silicon of the
MEMS.
Among other things, thesemicrostructures can be used as
valves to control the flow of a
substance or as very small
filters.
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MEMS?
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MEMS device and biological
material Size Comparison
Human Hair 70 micron
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MEMS Size
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Why MEMS
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Why MEMS?
Small devices:Fast mechanical response:
tend to move or stop more quickly due to low mechanicalinertia.
Ideal for precision movements and also for rapid actuation.
Encounter less thermal distortion and mechanical vibration dueto low mass.
Have higher dimensional stability at high temperature due to lowthermal expansion.
Are particularly suited for biomedical and aerospaceapplications being minute in size.
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Why MEMS?
less spaceThis allows the packaging of more functional
components in a single device/system.
less materialMeans low cost of production and
transportation. , ,
increased selectivity and sensitivity,wider dynamic range.
minimal invasive (e.g., microfabricated
needles)Potential to integrate with circuits
The ability to fabricate array of devices
Batch fabrication
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- a r ca on
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Substrates
Planar substrates:
Single-crystal silicon,
Single-crystal quartz,
glass, and
fused (amorphous) quartz.gallium arsenide,
optoelectronic devices can be fabricated with this
material.
Wafer Sizes:300 mm (12") diameter are now standard.
450 mm (18") diameter wafers in future,
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Substrates
Pressure on MEMS fabricators to shift to increasing wafer sizesto maintain compatibility with production equipment.
MEMS fabrication obeys different economics than standard
microelectronics.
25-wafer runs of 100 mm (4") wafers to supply a full year's.
less pressure to go to larger wafer sizes.
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Silicon as a Structural materialarac er s cs o con
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Silicon
Silicon is the most important materialdriving the electronic industry.
It is being used for its electrical properties.
Now it is being used in new commercial
product not for its electronic properties but
properties.
Silicon has already revolutionalized the
way we think about electronics. The
microprocessor has permeated our life. Now this versatile material is changing
our perception of miniaturized mechanical
devices and components.
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Why Silicon?
Silicon microfabrication is the obvious
Choice for microcomponents and devices as:
It is abundantly available and inexpensive.
It can be produced and processed controllably to high purity and perfection.
Silicon is being used in MEMS because it has excellent mechanicalro erties and also the microfabrication technolo is well established.
Silicon processing is based on thin deposited films which are highly
amenable to miniaturization.
Photolithography techniques are used to define the device shapes and
patterns. It is a very precise technique and is amenable to miniaturization.
Silicon based devices and mechanical components can also be batch
produced like silicon integrated microcircuits. Thus making them
commercially viable.
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More on Silicon
Single crystal Silicon is a very
Brittle material, yielding
catastrophically rather than
deforming plastically.
However it is not as fragile as.
A 100 micron thin wafer of
silicon can be bent around a
one inch diameter cylinder.
The stress concentration leads
to fracture.
All steps should be taken to avoid
stress concentration.
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More on Silicon.
Silicon wafers:Thickness: Usually 250-500 micron,
Diameter: could be anywhere from 25 mm to 300 mm.
Tendency to cleave along certain crystallographic direction.
If there are any defects Bulk, Edge or Surface along the cleavagep anes, t e wa er can eas y rea ue to stress concentrat on
around defects.
The wafers chip due to the defects on the edge of the wafers.
The high temperature processing of the wafer and multiple thinfilm deposition can cause internal stresses due to thermal
expansion mismatch.
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Silicon Substrate(+)
It is an excellent choice for a substrate for mechanicalsensors, due to its Intrinsic mechanical stability andfeasibility of integrating electronics. (+)
Si is often preferred for thin films. It is very flat substrate
wafers. (+)
Si is more expensive than other substrates per unit area
but the cost is offset by the small size of the features. (+)
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Silicon Substrate(-)
Si as a substrate sometimes makes packaging moredifficult.(-)
For chemical sensors, Si is often just a substrate andadvantages are less clear. (-)
When the device is large or production volume is low, Siagain is not too good a choice.(-)
If there is no need for integrating electronics then Sibecomes less interesting. (-)
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Single Crystal Silicon
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Crystal Structure
Crystals are characterized by a unit cell which repeats in thex, y, z directions.
Planes and directions are defined using an x, y, z coordinate
system.
[111] direction is defined by a vector having components of, .
Planes are defined by Miller indices - reciprocals of the
intercepts of the plane with the x, y and z axes.
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Single Crystal-Unit Cell
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Crystal Structure
Silicon has the basicdiamond crystal structure two merged FCC cells offsetby a/4 in x, y and z.
100 wafers are used in
manufacturings a om c ens es are
different on 100 and 111planes their properties alsodiffer.
Etch rates: 100 etches fasterthan 111
Oxidation: 111 oxidizesfaster than 100
Defect Density: 111 has higherelectrical defects on thesurface due to presence of
dangling bonds.Dopant diffusion coefficient
and other bulk properties alsodepend on orientations.
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Angle between planes
[abc] in a cubic crystal is just a direction vector(abc) is any plane perpendicular to the [abc] vector
()/[] indicate a specific plane/direction
{}/ indicate equivalent planes/direction
Angles between directions can be determined by scalar
ax+by+cz = |(a,b,c)|*|(x,y,z)|*cos(q)
e.g.:
q =54.74;
Angles:(100) vs. (110): 45, 90 ;
(100) vs. (111): 54.74;
(110) vs. (111): 35.26, 90 , 144.74;
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con a ers
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Silicon wafer
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Silicon crystallography
Wafers commonly used for Bulk
micromachininge e c ng: an
111 not used.
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MEMS-Fabrication
Microengineering refers to the technologies and practice ofmaking three dimensional structures and devices with
dimensions in the order of micrometers.
The two constructional technologies of microengineering are
Microelectronics:
,
a very well developed technology.
Micromachining:
Techniques used to produce the structures and moving
parts of microengineered devices.
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MEMS-Fabrication
MEMS makes use of thefabrication techniquesdeveloped for the integratedcircuit industry
to add mechanical elements
such as, , ,
springs to devices.
Usually fabricated on Siliconsubstrates Source: Sandia National Laboratories
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MEMS Fabrication
Traditional mechanical means (e.g. machining, milling, drillingetc.) can not be used to shape the MEMS components due totheir extremely small size.
Microfabrication techniques based on physical/chemical meansfor IC are used as the principal fabrication techniques for
MEMS.o o ograp y or e n ng pa ern on su s ra es;
Etching for removing substrate materials;
Deposition for building thin layers onto substrates;
Epitaxy for the growth of thin films of same substrate
material;
Diffusion for introducing foreign materials into substrates;
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Silicon Micromachining
Bulk Micromachining: Buildingmicrostructure by Removingmaterials by etching
Enable better control in Z-direction, with a loss in XYflexibility.
Thus, they are useful in high
Etched pitEtched Pit
Silicon
.
Surface micromachining: : Layer bylayer additionDepositing Thin filmsonto the substrate one layer afteranother to build the 3-dimensional
geometry.Can produce planar structures (in
XY direction) with littlecontrol in Z-direction
low aspect ratio devices.
Silicon
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Bulk Micromachining:1. Anisotropic wet etch processes
2. Deep Reactive ion etching
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Bulk micromachining
is removal of a lot of material - almost the entire film thickness -to create windows, membranes, various structures
How - by etching:
Wet etching:
isotropic and undercut appears, which can be used in
anisotropic: structures defined by crystal planes
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Anisotropic Wet etching
KOH - not compatible with ICs (alkali metal such as Kcontaminates the transistors); high selectivity for different
crystal orientation: (100 : 111 = 400 : 1),
silicon nitride is a very good mask (selectivity 1000),
silicon oxide (selectivity 100), stops at p++ layers
- , ,
lower anisotropy: (100 : 111 = 35 : 1)
N2H4 (Hydrazine)- explosive
TMAH (tetra methyl ammonium hydroxide) - The etch
difference not so big: (100 : 111 = 25 : 1)
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Anisotrpic Back etching
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Control of etch depth
in order to make structures with certain dimension, it isimportant to etch the right depth; there are a few methods used
to control the etch depth:
Timing - it is the least accurate method, due to the fact that
etching rate varies very much with temperature,
concentration, etc
Anisotropic etching of V-grooves - if only small
rectangulars/windows are made, then in an anisotropic wet
etch, the etching stops when the two planes combine, making
a V-groove
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Control of etch depth
P++ doping - the etch rate is much lower in high dopedmaterial, than in undoped material, therefore if implantation
occurs in the region where etching should end, an etch stop is
created .
explanation: electrons recombine with holes, limiting the
electrons number needed for etchin .
Not IC-compatible, more process steps, lower
piezoresistive coefficient for high doping
SiO2 (or other material) can be used to stop the etching
Electrochemical etch stop - by biasing positive a n-siliconpart, the p silicon will be etched, the n-Si not etched.
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Anisotrpic Back etching
The pressure sensitive diaphragm is formed by silicon back-endBulk micromachining.
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Silicon Diaphragm
The pressuresensitive diaphragmis formed by siliconback-end Bulkmicromachining.
Four piezoresistive sense
elements are placed on a
thin crystalline silicon
membrane in Wheatstone
bridge configuration to
measure stress.
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Deep Reactive Ion etching
Dry etching: XeF2 , no plasma, rough surface
Plasma etch - 1:100 -
Deep trench etching (alternating passivation step and etching
step)o vantage: vert ca eatures,
o Disadvantage: cost of equipment
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Bulk MEMS Fabrication: DRIE
start with unpatterned wafer stack a wafer-bonded SOI(silicon on insulator)
sacrificial SiO2(1) Pattern photoresist
bulk silicon substrate
photoresist
wafer bonded Silicon
(2) DRIE vertical etch
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Bulk MEMS Fabrication: DRIE
start with unpatterned wafer stack a wafer-bonded SOI(silicon on insulator)
(3) SiO2 isotropic etch
(4) Gold evaporation
Narrow features released, Wide featuresjust undercut
Gold mirrors on top and potentially sides
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Bulk Silicon MEMS Devices
Comb-drive switch photo courtesy
IMT (Neuchatel)
Single-axis tilt-mirror photo
courtesy R. Conant, BSAC
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Surface micromachining
What is it. a sacrificial layer beneath another layer is etched (completely
removed from the final structure), thus releasing the upper
layer, which will remain connected to the wafer only in some
regions
It is called "surface" because it takes lace on the wafersurface (compared to bulk, where the whole wafer thickness
is etched)
Why is it used?
Bulk micromachining requires bigger areas due toanisotropic wet etching (the lateral etch is big)
Parts of the structure can be released and move laterally, thus
it is useful in making actuators
Can be integrated with IC
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Surface Mircomachining
Materials used low-stress film polysilicon deposited by LPCVD
it is annealed because annealing changes the type of stress
from compressive to tensile due to crystallization
(contraction), giving the possibilty to obtain stress free
Si3N4 - increased hardness
sacrificial layer - removed without etching the structural
layer
Al, photoresist, SiO2
o SiO2 is prefered because of high temp deposition,
high selectivity for HF(polysilicon)
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Suraface MIcromachining
Applications: cantileverused to sense chemicals
frequency of vibrations is measured and the mass of chemical
particles can be calculated
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Surface MicromachiningStarting from bare silicon wafer, deposit & patternmultiple layers to form a MEMS wafer
Completed MEMS wafer
~ 10 mask steps
From Cronos/JDSU MUMPS user guide at
www.MEMSRUS.com
Assembly = mechanical manipulation of structures(e.g., raising and latching a vertical mirror plate)
Various techniques used, some highly
proprietary
Release = isotropic chemical etch to remove oxidesSpecial techniques may be used to remove liquid
(e.g., critical point drying)
Diced and released MEMS device
1st O ti l MEMS d i
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Projector& DLP PROJECTOR
TM
1st Optical MEMS device
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Wafer Bonding
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is used to join irreversible two wafers together .Bonding has to be leakproof
http://81.161.252.57/ipci/courses/technology/inde_378.htm
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Wafer bonding
typesof bonding:
Fusion bonding:
first the wafer is immersed in acid to
create hydrophilic surfaces with O-H bonds t en t e sur aces are put n contact
and hydrogen bonds are created, without pressure
at the end, a high temperature treatment (800oC) is
given and the bonds become permanent bonds (water is
desorbed and strong Si-O bonds are created)
surfaces such as Si/Si, SiO2/SiO2, Si/Si3N4, etc. can be
bonded
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Anodic bonding - in this case temperature + voltage biasareused to form a strong bond between glass and silicon
The two wafers are placed on a heater and a voltage bias is
applied between them (positive at silicon, negative at the
Pyrex/glass wafer)
,
travel through the the glass wafer to the electrode, both
wafers become conductive and the electric field is
concentrated at the high-resistance area at the interface
between the wafers
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Electrostatic attractive forces pull the wafers togethercreating a strong contact, together with the temperature
(400oC), creates chemical bonds between glass and Si
(oxygen ions drift to the silicon, creating strong Si-O bonds)
Surfaces must be very clean and flat
,
be used with wafers patterned with metal,
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eutectic bonding one Si wafer has a layer of gold on top
when the two wafers are put in contact and tempereature
is raised until eutectic temperature, Au will diffuse in Si,
creating a strong alloy at the interface
pressure sensor, for example:
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History of MEMS
.Some historical stuff
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The inception of Microelectromechanical Systems (MEMS)devices occurred in many places and through the ideas and
endeavors of several individuals.
Worldwide, new MEMS technologies and applications are being
developed every day. This unit gives a broad look at some of the
milestones which have contributed to the develo ment ofMEMS as we know them today.
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1940s
1939 PN-junction semiconductor (W. Schottky)1947 Transistor (J. Bardeen, W.H. Brattain, W. Shockley)
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A transistor uses electrical current or a smallamount of voltage to control a larger change
in current or voltage.
Transistors are the building blocks of
computers, cellular phones, and all other
modern electronics.
In 1947, William Shockley, John Bardeen,
and Walter Brattain of Bell Laboratories
built the first point-contact transistor.
The first transistor used germanium, asemiconductive chemical.
It demonstrated the capability of building
transistors with semiconductive materials.
First Point Contact
Transistor and Testing
Apparatus (1947) [PhotoCourtesy of The
Porticus Centre]
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1950s
1950: Silicon Anisotropic Etchants (KOH) in BellLab
1954: Piezoresistive effect in Silicon and
Germanium (C.S. Smith)
The piezoresistive effect of semiconductor can be
several magnitudes larger than that in metals.s scovery s owe t at s con an
germanium could sense air or water pressure
better than metal .
Strain gauges began to be developed
commercially in 1958.
Kulite was founded in 1959 as the first
commercial source of silicon strain gages .
Many MEMS devices such as strain gauges,
pressure sensors, and accelerometers utilize the
piezoresistive effect in silicon.
An Example of a
Piezoresistive Pressure
Sensor
[MTTC Pressure Sensor]
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1958 First integrated circuit
Prior to the invention of the IC therewere limits on the size of transistors.
They had to be connected to wires
and other electronics.
An IC includes the transistors,
resistors, ca acitors, and wires.
If a circuit could be made all
together on one substrate, then the
whole device could be made smaller
In 1958, Jack Kilby from TexasInstruments built a "Solid Circuit
on one germanium chip: 1 transistor,
3 resistors, and 1 capacitor.
Texas Instrument's FirstIntegrated Circuit
[Photos Courtesy of Texas
Instruments]
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http://www.monolithic3d.com/blog/jack-kilby-bob-noyce-and-the-3d-integrated-circuit
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first "Unitary Circuit on a silicon chip.
The first patent was awarded in
1961 to Robert Noyce
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1959: Theres Plenty of Room at the
Bottom
Richard Feynmans Theres Plenty of Room atthe Bottom was presented at a meeting of the
American Physical Society in 1959.
The talk popularized the growth of micro and nano
technology.
Feynman introduced the possibility of manipulatingma er on an a om c sca e.
He was interested in denser computer circuitry, and
microscopes which could see things much smaller
than is possible with scanning electron microscopes.
He challenged his audience to design and build a an
electrical motor smaller than 1/64th of an inch or to
write the information from a page of a book on a
surface 1/25,000.
For each challenge, he offered prizes of $1000.
Richard Feynman
on his bongosPhoto credit: Tom
Harvey
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William McLellan's prize-winning electric motor, which
would fit inside a cube one sixty-
fourth of an inch across, is seen
next to a gnat's wing
But just two and a half months
later, William McLellan, aphysicist at the University of
California Institute of Science and
Technology, claimed the prize http://www.daviddarling.info/childrens_encyclopedia/Nanotechnology_Chapter6.html
http://www.rsc.org/chemistryworld/Issues/2009/January/FeynmansFancy.asp
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The tiny print prize took 25years to materialize and was
finally awarded in November
1985 to a Stanford grad
student named Thomas H.
Newman.shrunk the first paragraph of
A Tale of Two Cities to
1/25,000 of it's normal size,
using a beam of electrons to
scratch the surface of a thinplastic membrane.
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1960s
1962: Silicon integrated piezo actuators (O.N. Tufte,P.W.Chapman and D. Long)
1964: Harvey Nathanson from Westinghouse produced the first
batch fabricated MEMS device: a resonant gate transistor
(RGT).
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The Resonant Gate Transistor
This device joined a mechanicalcomponent with electronic
elements
The RGT was a gold resonating
MOS gate structure.
It was approximately one
millimeter long and it responded to
Resonant Gate Transistor
a very narrow range of electrical
input signals.
It served as a frequency filter for
ICs.
The RGT was the earliestdemonstration of micro electrostatic
actuators.
It was also the first
demonstration of surface
micromaching techniques.
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1965: Invention of surface micromachining; Surfacemicromachined FET accelerometer (H.C. Nathanson, R.A.
Wickstrom)
1967: Anisotropic deep silicon etching (H.A. Waggener et al.)
1968 The Resonant Gate Transistor Patented
1971 Th I i f h
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1971 The Invention of the
Microprocessor
1971, Intel publicly introduced the world's first single chipmicroprocessor -The Intel 4004
It powered the Busicom calculator
This invention paved the way for the personal computer
The Intel 4004 Microprocessor
Photo Courtesy of Intel Corporation
Busicom calculator
Photo Courtesy of Intel Corporation
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1960 and 70s 1960's and 1970s Bulk-Etched Silicon Wafers as Pressure Sensors
"Electrochemically Controlled Thinning of Silicon" by H. A. Waggener
illustrated anisotropic etching of silicon (removes silicon selectivity).
This technique is the basis of the bulk micromachining process.
Bulk micromachining etches away the bulk of the silicon substrate
leaving behind the desired geometries.
techniques such as bulk etching.
In the 1970's, a micromachined pressure sensor using a silicon diaphragm
was developed by Kurt Peterson from IBM research laboratory.
Thin diaphragm pressure sensors were proliferated in blood pressure
monitoring devices .
Considered to be one of the earliest commercial successes of
microsystems devices.
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1970s
SeventiesFirst capacitive pressure sensor (Stanford)
1977 Silicon electrostatic accelerometer (Stanford)
1979 Integrated gas chromatograph (S.C. Terry, J.H. Jerman and
J.B. Angell)
cromac ne n et ozz e
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1979 HP Micromachined Inkjet Nozzle
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.
.
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 biologicalmolecules such as DNA
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nozzlesClose-up view of a
commercial inkjet printer head
illustrating the nozzles [HewlettPackard]
Schematic of an array of
inkjet nozzlesClose
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1980s Early 1980s,
1982 Silicon as aMechanical Material (K.Petersen)
Rebirth of surfacemicromachining. Polysilicon
sacrifical layers,. (Berkeleyand Wisconsin)
1982LIGA Process(W. Ehrfeldet al.) Disposable blood pressure
transducer
1983 Integrated pressuresensor (Honeywell)
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1982 LIGA Process Introduced
LIGA is a German acronym for X-raylithography (X-ray Lithographie),
Electroplating (Galvanoformung), and
Molding (Abformung).
In the early 1980s Karlsruhe Nuclear
Research Center in German develo ed LIGA-micromachinedLIGA.
It allows for manufacturing of high aspect
ratio microstructures.
High aspect ratio structures are veryskinny and tall.
LIGA structures have precise dimensions
and good surface roughness.
electromagnetic
motor[Courtesy of
Sandia National
Laboratories]
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1980s Late 1980s
Berkeley and Bell Labs demonstrate poly-silicon surface micro-mechanism;
1986 Silicon wafer bonding (M. Shimbo)
The Beginning of MEMS CAD
Analog Devices begins accelerometer project
1986 Invention of the AFM
1988 Batch fabricated ressure sensors via wafer bondin Nova Sensor
Rotary electrostatic side drive motors (Berkeley)
Lateral comb drive (Tang, Nguyen, Howe, Berkeley)
The motors stimulating major interest in Europe, Japan, and U.S
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1986 Invention of the AFM
In 1986 IBM developed a microdevice called the atomic forcemicroscope (AFM).
The AFM maps the surface of an atomic structure by
measuring the force acting on the tip (or probe) of a
microscale cantilever.
.
It is a very high resolution type of scanning probe
microscope with a resolution of fractions of an Angstrom
Cantilever on an Atomic
Force Microscope
Rotary electrostatic side drive motors
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Rotary electrostatic side drive motors
(Berkeley
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1990sEarly Nineties:
MEMS rapidly extending to the whole world.
Research on Fabrication techniques, Design technology, CAD tools andDevices are developing quickly.
CAD Tools:
MIT, S. D. Senturia, MEMCAD1.0
Michigan, Selden Crary, CAEMEMS1.0 Techniques:
1992: Bulk micromachining (SCREAM process, Cornell)
MCNC starts the Multi User MEMS Process (MUMPS),
Sandia SuMMit Technology
Bosch Process for DRIE is Patented
Devices:
Grating light modulator invented at Stanford University (Solgaard,Sandejas, Bloom)
First micromachined hinge
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1992 Grating Light Modulator
The deformable grating lightmodulator (GLM) was introduced
by Solgaardin 1992.
It is a Micro OptoElectro
Mechanical System (MOEMS).
various applications: Display
technology, graphic printing,
lithography and optical
communications
Grating Light Valve
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http://electronicdesign.com/site-
files/electronicdesign.com/files/archive/electronicdesign.com/files/29/1498/figure_03.gif
1993 Multi User MEMS Processes
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1993 Multi-User MEMS Processes
(MUMPs) Emerges
In 1993 Microelectronics Center of North Carolina (MCNC)created MUMPs:
A foundry meant to make microsystems processing highly
accessible and cost effective for a large variety of users
A three layer polysilicon surface micromachining process
,
area to create their own design.
In 1998, Sandia National Labs developed SUMMiT IV (Sandia
Ultra-planar, Multi-level MEMS Technology 5)
This process later evolved into the SUMMiT V, a five-layerpolycrystalline silicon surface micromachining process
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Two sim le structures usin the MUMPsprocess [MCNC]
A MEMS device built using SUMMiT IV
[Sandia National Laboratories]
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Mid. 1990s
Devices
1993: Digital mirror display (TexasInstruments)
BioMEMS rapidly development
1994:Commercial surface micromachined
accelerometer (ADXL50)(Analog Devices)MEMS Design
MEMCAD2.0
Microcosm Inc. for MEMCAD
Intellisense Inc. for IntelliSuite
ISE for TCAD, SOLIDIS and ICMAT
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1993 First ManufacturedAccelerometer
In 1993 Analog Devices were the first toproduce a surface micromachined
accelerometer in high volume.
The automotive industry used this
accelerometer in automobiles for
airba de lo ment sensin . It was sold for $5 (previously, TRW
macro sensors were being sold for
about $20).
It was highly reliable, very small, andvery inexpensive.
It was sold in record breaking
numbers which increased the
availability of airbags in automobiles.
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1994 Deep Reactive Ion Etching is
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1994 Deep Reactive Ion Etching is
Patented
In 1994, Bosch, a company fromGermany, developed the Deep
Reactive-Ion Etching (DRIE)
process.
DRIE is a highly anisotropic etch
rocess used to create dee , stee -sided holes and trenches in wafers.
It was developed for micro devices
which required these features.
It is also used to excavate trenches
for high-density capacitors for
DRAM (Dynamic random-access
memory).
Trenches etched with DRIE[SEM
images courtesy of Khalil Najafi,
University of Michigan]]
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Later 1990s
DevicesBio-MEMS: Microfluidics starts with capillary electrophoresis.
-TAS (Micro-total-analysis System) vision for diagnosis,
sensing and synthesis
Optical MEMS booming and bust from 1998-2002 (Lucent)
1999 Optical network switch (Lucent)RF MEMS from 2000
Commercialization of inertial sensors (AD, Motorola)
by each company by 2002
Late 1990's Early 2000's Optics
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Late 1990 s, Early 2000 s Optics
In 1999 Lucent Technologies developed the first optical networkswitch.
Optical switches are optoelectric devices.
They consist of a light source and a detector that produces a
switched output.
communications network.
These MEMS optical switches utilize micro mirrors to switch or
reflect an optical channel or signal from one location to another.
There are several different design configurations.Growth in this area of technology is still progressing.
Late 1990's Early 2000's BioMEMS
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Late 1990 s, Early 2000 s BioMEMS
Scientists are combining sensors and actuators with emergingbiotechnology.
Applications include
drug delivery systems
insulin pumps (see picture)
arrays
lab-on-a-chip (LOC)
Glucometers
neural probe arrays
microfluidicsInsulin pump [Debiotech, Switzerland]
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2000-till today
MEMS Microphone 2005
2015: Dissolvable Micro Medical Devices
11/18/15 Thinking back to the late 1960s when scientific
researchers were envisioning using a tube made out of metal
(stent) to open up an artery, they would never have imagined we
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2006 Akustica introduces world's first digital microphone -the AKU2000
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Massive industrialisation and commercialisation.
2001 Triaxis accelerometers appear on the market.
2002 First nanoimprinting tools announced.
2003 MEMS microphones for volume applications introduced.
2003 Discera start sampling MEMS oscillators.
s c p sa es rose to near y m on.
2005 Analog Devices shipped its two hundred millionth MEMS-
based inertial sensor.
2006 Packaged triaxis accelerometers smaller then 10 mm3 are
becoming available.2006 Dual axis MEMS gyros appear on the market.
2006 Perpetuum releases vibration energy harvester.
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RF MEMS
RF switch,
OPTICAL MEMS
Micromirror array for optical switching,
BIOMEMS
Lab on a chip, Capillary Electrophoresis Analysis
MiniMed Paradigm 522 insulin pump
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Retina array:
[Courtesy of Sandia National Laboratories]
Micro-pump for insulin
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MiniMed Paradigm 522 insulin pump
The MiniMedParadigm522 insulin
pump, with sensor, transmitter and
infusion line is one of a few devices on
the market that can not only monitor a
ersons lucose levels 24/7, but candeliver insulin on an as needed basis.
Its components are
(A) an external pump and computer,
(B) a soft cannulathat delivers the
insulin,
(C) an interstitial glucose sensor, and
(D) a wireless radio device that
communicates with the
Micro-pump for insulin
[Printed with permission
from DebiotechSA]
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computer.The sensor (C) is placed under
the skin. The sensor continuously
measures glucose levels in the interstitial
fluid (the fluid between body tissues).
The measurements from the sensor are
received in real time by the wirelessradio device (D). This device sends the
readings to the computer (A) which
determines the amount of insulin needed.
The pump (A) administers that amount
into the patient via the cannula (B). TheMini-Med Paradigm computer also
stores all the data.
MiniMed Paradigm 522
insulin pump, with
MiniLinkTM] transmitter
and infusion set. [Printed
with permission from
Medtronic Diabetes]
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A therapeutic bioMEMS device
currently being tested is the artificial
retinal prosthesis called the Argus
Retinal Prosthesis System.
Artificial RetinaThe heart of the
s stem is an arti icial retina -anelectrode array placed directly on the
retina at the back of the eye. This
array duplicates the task of the
photoreceptor cells in the retina.
These cells are destroyed in retinaldiseases such as age-related macular
degeneration and retinitis
pigmentosa(RP).
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The Rapid, Automated Point-of-Care
System (RapiDx) developed by Sandia
National Laboratories is a portable
diagnostic instrument that uses mere
microlitersof a sample to measure large
panel of biomarkers.RapiDxquickly measureswith high
sensitivitydisease and toxin biomarkers
in human biological samples (e.g., blood,
saliva, urine) so that patient ailments can
be quickly diagnosed and treated.RapiDxis an ideal instrument for point-of-
care diagnostics of disease and toxin
detection in health clinics and on the field.
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S
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Summary
Since the invention of the transistor, scientists have been trying
to improve and develop new micro electro mechanical systems.
The first MEMS devices measured such things as pressure in
engines and motion in cars. Today, MEMS are controlling our
communications networks
beating hearts.
MEMS are traveling through the human body to monitor blood
pressure.
MEMS are even getting smaller. We now have nano electromechanical systems (NEMS).
The applications and growth for MEMS and NEMS are endless
Intraoc lar Press re sensor
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Intraocular Pressure sensor
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Challenges of MEMS
Challenges of MEMS
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Challenges of MEMS
The complexity of MEMS design.
Typical MEMS devices, even simple ones, manipulate
energy (information) in several energy domains. The
designer must understand, and find ways to control, complex
interactions between these domains.
does not lend it self to step-by step optimization of a design.
The high tooling costs.
A state-of-the-art silicon foundry cost the better part of $1B.
Challenges
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Challenges
Packaging
usually need to interact with the environment in some way
(e.g., pressure sensor, chemical sensor)
very diversified no standard packaging method
Testing:
nvo ves mu t p e energy oma ns
Power sources
CAD tools (interdisciplinary, usually involves several energy
domains, mechanical, electrical, thermal, etc.)
Multidisciplinary/interdisciplinary collaboration
MEMS Standards (?)
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MEMS Standards (?)
Standards are generally driven by the needs of high-volume
applications.
MEMS has roots in integrated circuit industry
But, the two market dynamics differ.
The major difference is the lack of standards in MEMS.
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The Multi-discipline nature of
MEMS technology
Natural Science:
Physics & Chemistry
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Mechanical Engineering
Machine components design.
Precision machine design.
Mechanisms & linkages.
Thermomechanicas:
Quantum physics
Solid-state physics, Scaling laws
Electrical Engineering
Power supply.
Electric systems
design in electro-
hydrodynamics.
Si nal transduction
Materials Engineering
Materials for device
components & packaging.
Materials for signal
Electromechanical
-chemical Processes
Material
Science
Physics & Chemistry
transfer, fracture mechanics.
Intelligent control.
Micro process equipment
design and manufacturing.
Packaging and assembly design.
acquisition, condition-
ing and processing.
Electric & integrated
circuit design.
Electrostatic & EMI.
.
Materials for fabrication
processes.
Process Engineering Design & control of
micro fabrication processes.
Thin film technology.
Industrial Engineering Process implementation.
Production control.
Micro packaging & assembly.
(Multidiscipline of MEMS.Slide presentation)HSU
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MEMS Applications
Automotive industry
Medical
Digital Light Projection Technology
Printing Technology
SMART Phone
MEMS Applications
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MEMS Applications
Where can you find
MEMS?
in your car
Applications in Automotive Industry
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Applications in Automotive Industry
Every new car sold has micromachined sensors on-board. Theyrange from
MAP (Manifold Absolute Pressure) engine sensors,
Accelerometers for active suspension systems,
,systems.
Flowsensors
microscanners
http://www.analog.com/library/techArticles/mems/xlbckgdr4.html
Applications in Automotive Industry
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Applications in Automotive Industry
Applications in Automotive Industry
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Applications in Automotive Industry
Micro-accelerometer
ADXL-50: surface micromachined,integrated BiCMOS (Analog Devices, 1995)
Analog Devices
Analog Devices' ADXL50 accelerometerSurface micromachining capacitive sensor
2.5 x 2.5 mm die incl. electronic controls
Cost: $30 vs ~$300 bulk sensor (93)Cut to $5/axis by 1998Replaced by 3-axis ADXL150
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Acceleration Sensors
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Acceleration Sensors
Capacitive Accelerometer
Silicon substrate
Elastic hinge Proof Mass
Spacer Force
Applications in Automotive Industry
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Micro inertia sensor (accelerometer)
Applications in Automotive Industry
Inertia Sensor for Air Bag Deployment System
(Analog Devices, Inc)
Pressure Sensors
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Capacitive Pressure Sensor
Silicon substrate
Pint
Pext
Spacer
Membrane
ForceMeasureRC time
Piezo-resistive pressure sensor
NovaSensors piezo-resistive pressure sensors Disposable medical sensor
High-pressure gas sensor(ceramic surface-mount)
Applications-Medical
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Applications Medical
Applications-Medical
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Applications Medical
Micropump
Lower 2 wafers bonded via silicon fusionbonding. Top wafer later glued.
Piezo ceramic driven by high voltage (-40V,+90V)
At 100Hz, no back pressure, average flow rate1600l/min.
Dead volume = pump chamber volume 800nl.
Average stroke volume = 260nl.
Bubble tolerant and self-priming.
Applications-Medical
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Applications Medical
BioMEMS:
Applications-Digital Light Projection
T h l
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Technology
DMD- 1st Optical MEMS device
Texas Instruments
TMDigital Light Projector
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& DLP PROJECTOR
Applications-Printing Technology
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Applications Printing Technology
Inkjet Printers
Computer read/write heads
Magnetic disk read/write head
Ink jet print head
Applications:Communications
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pp
Micro Switches for Fiber Optical Network
(Lucent Technology, Murray Hill, NJ)
Applications:Communications
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pp
MEMS Optical Switch Lucent micro-
mirror16X16 Array
Size of Each mirror:~ head of a pin
Tilts to steer lightwave signals fromone optical fiber to another
(Lucent, 1999)Part of LucentTechnologies'
WaveStartm
LambdaRouter
Communications
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MEMS Resonators, filters, Phase shifters, Reconfigurable
antennae
Consumer Electronics
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Smart Phones, Cameras
Micromachinedaccelerometer sensors arenow being used in seismicrecording, machinemonitoring, and diagnostic
-application where gravity,shock, and vibration arefactors.
The field is also widening
considerably in othermarkets.
MEMS Market
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$ 7 billion at the component level
Enable $ 100 billions market
Akustika: MEMS-based speakers
Audio ixels
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MEMS Market
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Automotive industry:
manifold air pressure sensor (Honeywell, Motorola) nearly 40 millionunits per year.
Air bag sensor (accelerometer:50 million units per year).
Anolog Devices: Accelerometer, Gyroscopes.
Medical
.Digital Light Projection Technology:
TI digital mirror display (DMD) video projection system (developmentcost ~ $1B)
Printing Technology:
Inkjet nozzles (HP, Canon, Lexmark)up to 1600 x 1600 resolution(~ 30Munits per year)
MEMS Microphones
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CAD For MEMS
MEMS Design Tools
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g
Example: Pressure Sensor Design
The design involves: Designingthe pressure sensor membrane geometry:
maximizing the sensitivity by optimizingthe membrane dimensions.The pressuresensor membrane
the si nal conditionin circuita suitable package for the device
Layout design using MEMS PRO
Simulation using ANSYS software.
Coventerware
COMSOL
MEMS+
Intellisuite
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Eg.The pressure sensor Model
in MEMSPRO
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in MEMSPRO
Meshed Model
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Meshed in Hypermesh 5.0
The deflection analysis
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In micronMaximum Deflection:3.5 micron
Stress analysis
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Maximum Stress: 424 MPa
In MPa
The Schematic of Piezoresistive Pressure
sensor
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sensor
Voltage Sensitivity Simulation
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TOP Ten Products
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As for areas of opportunity, VDC's market attractiveness index
identifies the top 10 near term opportunities in the MEMS /MST market:Micro-fluidic biochips for medical diagnostics and drug discovery
Glucose micro-fluidic monitoring sensors
Tire pressure sensors
Consumer print heads for inkjet printers
Over the counter micro-fluidic testing devices for detecting medicalconditions
Large format print heads
Devices that enable advanced automotive functions
ABS accelerometers and gyroscopes
Automobile mass airflow sensors
Microphones
RF antennas
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TOP TEN products
1. Inkjet PrinterHead
2. DMD
3.Gyro
4.Accelerometer
5. Lb on a chip
6. TPMS
7. Microphone
8. Silicon clock(resonator)
9.RF MEMS
10. Medical Pressure sensor
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The Pressure Sensor
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Silicon Cap Wafer
Silicon Substrate
Glass Plate
for support
SiliconMembrane
Fig.3. Cross section of a typical sensor die
Fig.5. TOP VIEW : Silicon Membrane wafer
Bonding padsConductor
Pattern
Piezoresistors
MEMS Pressure Sensor
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These are based on the deflection of Silicon Membrane.
Silicon Cap Wafer
Silicon Substrate
Glass Plate
Silicon
Membrane
The sensing is of two types
Capacitive
Piezoresistive
for support
Cross section of a typical sensor die
Fabrication
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Bulk micro machining in single crystal silicon and
Surface micromachining in polysilicon.
Pressure Sensor Range
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vacuum,
Low pressure (0.02 to 0.1 Atm),
Medium pressure (0.25 to 10 Atm),
High pressure (60 to more than 500 Atm).
Capacitive pressure sensors
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high sensitivity
small dynamic range
because the gap between the capacitor plates must be very
small to obtain a large capacitance.
A thin silicon diaphragm is employed with a narrow capacitive
.The silicon diaphragms have better mechanical properties,
including freedom from creep, resulting in better repeatability
than metal diaphragms.
Capacitive pressure sensors
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The sensor is formed from two glass substrates and a silicon
wafer.
The silicon wafer is sandwiched between the two glass wafers
by anodic bonding, simultaneously forming a sealed reference
cavity.
- -
to maintain the reference cavity at high vacuum. After bonding
in vacuum, the NEG can absorb the remaining gas in the
reference cavity.
Capacitive pressure sensors
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Use of a P++ (heavily doped boron) etch stop layer provides
accurate control of diaphragm thickness.
Structure of a capacitive absolute pressure sensor
P 0 100 T
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Pressure range 0-100mTorr
Can be extended to about 500 mtorr.
1. A Ultra-Sensitive, High-Vacuum Absolute Capacitive Pressure Sensor;Technical Digest of the 14th IEEE International Conference On MicroElectro Mechanical Systems (MEMS 2001), pp. 166-169, Interlaken,Switzerland, Jan. 21-25, 2001.
Working of piezoresistive sensor
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The sensing materialdiaphragm formed on a silicon substrate,
which bends with applied pressure. The
membrane defection is typically less than 1
m.
A deformation occurs in the crystal lattice of the
diaphragm because of that bending.
This deformation causes a change in the
resistivity of the material. This change can bean increase or a decrease according to the
orientation of the resistors.
Working of piezoresistive sensor
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The Piezoresistive sensor utilizes silicon strain gaugesconfigured as a Wheatstone bridge in which one or moreresistors change value when strained.
The output normalized to input pressure is known as sensitivity(mV/V/Pa), and is related to the piezoresistive coefficients.
-electronics for operation.
Due to the simple construction and their large output signal,Piezoresistive sensors take a primacy within pressure sensors.
Piezoresistive pressure sensors are available for different
nominal pressure ranges from 10mbar up to 1000 bar and cantherefore be used for different applications.
piezoresistive silicon Pressure Sensor
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Mature processing technology.
Different pressure levels can be achieved according to the
application.
Also, various sensitivities can be obtained.
Read-out circuitry can be either on-chip or discrete
Low-cost
Diaphragm
Th iti di h i
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The pressure sensitive diaphragm is
formed by silicon back-end bulkmicromachining.
Silicon diaphragms are formed byAnisotropically etching the back of asilicon wafer. Usually a square
The SEM (ScanningElectron Microscope)view of the back-side ofone of the sensor
etching in KOH or TMAH (TriMethylAmmonium Hydroide) solution.
The circular membranes can be obtainedby dry etch process.
The silicon diaphragms 5-50 microns1 micron and area 1- 100 square mm.
The size and thickness of the finisheddiaphragm depend on the pressure rangedesired.
diaphragm
Typical Piezoresistive Pressure Sensor
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Th i i ti l t (i th diff d i t )
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The piezoresistive elements (i.e., the diffused resistors) are
located on an n-type epitaxial layer of typical thickness 2-10micron. The epitaxial layer is deposited on a p-type substrate.
The aluminum conductors join the semiconductor resistors in a
bridge configuration and are attached to the bond pads for circuit
interconnection.
The resistors are placed on the
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The resistors are placed on the
diaphragm such that two experiencemechanical tension in parallel and theother two are perpendicular to thedirection of current flow.
Thus, the two pairs exhibit resistance
.pairs are located diagonally in the bridgesuch that applied pressure produces abridge imbalance.
Deformation by applied pressure causes
high levels of mechanical tension at theedges of the diaphragm. Positioning theresistors in this area of highest tensionincreases sensitivity.
The pressure
sensor chip
Al i b t t d f th k i f th
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Alumina substrates are used for the packaging of the sensor
Here the sensor is bonded on thesubstrate .The wire bonding isalso done.The alumina substrate has a hole atthe middle. This is required for
differential pressure measurementsand the air pressure is always appliedto the back side of the sensor via thishole.
The packed pressure sensor
A cap is made for the inp t press re port The electrical
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A cap is made for the input pressure port. The electrical
connections are covered with epoxy for electrical isolation.
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MEMS in ACTIONS
MEMS in Action
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MEMS in Action
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MEMS in Action
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MEM GYRO
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MEMS Directional Microphone
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Summary
We have learnt:
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We have learnt:
What is MEMS why do we need mems , how do wefabricate, what are the challenges in design, fabrication,
packaging and testing MEMS
We have reviewed current MEMS market and a few
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