Overviewof MEMS_2016

7/24/2019 Overviewof MEMS_2016

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Introduction to MEMS Technology

Dr. S. L. Pinjare

[email protected]


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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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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



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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



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Micro inertia sensor (accelerometer)


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



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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.



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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.



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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.



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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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Documents

Overviewof MEMS_2016