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SECTION 1.1 WHAT IS MEMSTECHNOLOGY?

Micro-Electro-Mechanical Systems (MEMS) is the integration of

mechanical elements, sensors, actuators, and electronics on a common silicon

substrate through microfabrication technology. While the electronics are fabricated

using integrated circuit (IC) process sequences, the micromechanical components are

fabricated using compatible "micromachining" processes that selectively etch away

parts of the silicon wafer or add new structural layers to form the mechanical and

electromechanical devices.

Microelectronic integrated circuits can be thought of as the "brains" of a

system and MEMS augments this decision-making capability with "eyes" and "arms",

to allow microsystems to sense and control the environment. Sensors gather

information from the environment through measuring mechanical, thermal, biological,

chemical, optical, and magnetic phenomena. The electronics then process the

information derived from the sensors and through some decision making capability

direct the actuators to respond by moving, positioning, regulating, pumping, and

filtering, thereby controlling the environment for some desired outcome or purpose.

Because MEMS devices are manufactured using batch fabrication techniques similar

to those used for integrated circuits, unprecedented levels of functionality, reliability,

and sophistication can be placed on a small silicon chip at a relatively low cost.


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MEMS devices are typically fabricated onto a substrate (chip) that may

also contain the electronics required to interact with the MEMS device. Due to the

small size and mass of the devices, MEMS components can be actuated

electrostatically (piezoelectric and bimetallic effects can also be used). The position of

MEMS components can also be sensed capacitively. Hence the MEMS electronics

include electrostatic drive power supplies, capacitance charge comparators, and signal

conditioning circuitry. Connection with the macroscopic world is via wire bonding

and encapsulation into familiar BGA, MCM, surface mount, or leaded IC packages.

A common MEMS actuator is the "linear comb drive" (shown above) which consists

of rows of interlocking teeth; half of the teeth are attached to a fixed "beam", the other

half attach to a movable beam assembly. Both assemblies are electrically insulated.

By applying the same polarity voltage to both parts the resultant electrostatic forcerepels the movable beam away from the fixed. Conversely, by applying opposite

polarity the parts are attracted. In this manner the comb drive can be moved "in" or

"out" and either DC or AC voltages can be applied. The small size of the parts (low

inertial mass) means that the drive has a very fast response time compared to its

macroscopic counterpart. The magnitude of electrostatic force is multiplied by the

voltage or more commonly the surface area and number of teeth. Commercial comb

drives have several thousand teeth, each tooth approximately 10 micro meters long.

Drive voltages are CMOS levels.

The linear push / pull motion of a comb drive can be converted into

rotational motion by coupling the drive to push rod and pinion on a wheel. In this

manner the comb drive can rotate the wheel in the same way a steam engine

functions!


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SECTION 3 MEMS DESCRIPTION

MEMS technology can be implemented using a number of different

materials and manufacturing techniques; the choice of which will depend on the

device being created and the market sector in which it has to operate.

SILICON

The economies of scale, ready availability of cheap high-quality

materials and ability to incorporate electronic functionality make silicon attractive for

a wide variety of MEMS applications. Silicon also has significant advantages

engendered through its material properties. In single crystal form, silicon is an almost

perfect Hookean material, meaning that when it is flexed there is virtually no

hysteresis and hence almost no energy dissipation. The basic techniques for producing

all silicon based MEMS devices are deposition of material layers, patterning of these

layers by photolithography and then etching to produce the required shapes.

POLYMERS

Even though the electronics industry provides an economy of scale for

the silicon industry, crystalline silicon is still a complex and relatively expensive

material to produce. Polymers on the other hand can be produced in huge volumes,

with a great variety of material characteristics. MEMS devices can be made from

polymers by processes such as injection moulding, embossing or stereolithography

and are especially well suited to microfluidic applications such as disposable blood

testing cartridges.

METALS

Metals can also be used to create MEMS elements. While metals do not

have some of the advantages displayed by silicon in terms of mechanical properties,

when used within their limitations, metals can exhibit very high degrees of reliability.

Metals can be deposited by electroplating, evaporation, and sputtering processes.

Commonly used metals include gold, nickel, aluminum, chromium, titanium,

tungsten, platinum, and silver


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SECTION 4 MEMSDESIGN PROCESS

There are three basic building blocks in MEMS technology, which are,

Deposition Process-the ability to deposit thin films of material on a substrate,

Lithography-to apply a patterned mask on top of the films by photolithograpic

imaging, and Etching-to etch the films selectively to the mask. A MEMS process is

usually a structured sequence of these operations to form actual devices.

SECTION 4.1 DEPOSITION PROCESSES

One of the basic building blocks in MEMS processing is the ability to

deposit thin films of material. In this text we assume a thin film to have a thickness

anywhere between a few nanometers to about 100 micrometer

MEMS deposition technology can be classified in two groups:

1. Depositions that happen because of a chemical reaction:o Chemical VaporDeposition (CVD)o Electrodepositiono Epitaxyo Thermal oxidation


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These processes exploit the creation of solid materials directly from chemical

reactions in gas and/or liquid compositions or with the substrate material. The

solid material is usually not the only product formed by the reaction.

Byproducts can include gases, liquids and even other solids.

2. Depositions that happen because of a physical reaction:o Physical VaporDeposition (PVD)o Casting

Common for all these processes are that the material deposited is physically

moved on to the substrate. In other words, there is no chemical reaction which

forms the material on the substrate. This is not completely correct for casting

processes, though it is more convenient to think of them that way.

This is by no means an exhaustive list since technologies evolve continuously.

SECTION 4.1.1 CHEMICAL VAPOR DEPOSITION (CVD)

In this process, the substrate is placed inside a reactor to which a number

of gases are supplied. The fundamental principle of the process is that a chemical

reaction takes place between the source gases. The product of that reaction is a solid

material with condenses on all surfaces inside the reactor.

The two most important CVD technologies in MEMS are the Low

Pressure CVD (LPCVD) and Plasma Enhanced CVD (PECVD). The LPCVD process

produces layers with excellent uniformity of thickness and material characteristics.

The main problems with the process are the high deposition temperature (higher than

600C) and the relatively slow deposition rate. The PECVD process can operate at

lower temperatures (down to 300 C) thanks to the extra energy supplied to the gas

molecules by the plasma in the reactor. However, the quality of the films tend to beinferior to processes running at higher temperatures. Secondly, most PECVD

deposition systems can only deposit the material on one side of the wafers on 1 to 4

wafers at a time. LPCVD systems deposit films on both sides of at least 25 wafers at a

time. A schematic diagram of a typical LPCVD reactor is shown in the figure below.


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Figure 1:Typical hot-wall LPCVD reactor.

WHEN DO WE WANT TO USE CVD?

CVD processes are ideal to use when you want a thin film with good

step coverage. A variety of materials can be deposited with this technology; however,

some of them are less popular with fabs because of hazardous by-products formed

during processing. The quality of the material varies from process to process, however

a good rule of thumb is that higher process temperature yields a material with higher

quality and less defects.

ELECTRODEPOSITION

This process is also known as "electroplating" and is typically restricted

to electrically conductive materials. There are basically two technologies for plating:

Electroplating and Electroless plating. In the electroplating process the substrate is

placed in a liquid solution (electrolyte). When an electrical potential is applied

between a conducting area on the substrate and a counter electrode (usually platinum)

in the liquid, a chemical redox process takes place resulting in the formation of a layer

of material on the substrate and usually some gas generation at the counter electrode.

In the electroless plating process a more complex chemical solution is

used, in which deposition happens spontaneously on any surface which forms a

sufficiently high electrochemical potential with the solution. This process is desirable

since it does not require any external electrical potential and contact to the substrate


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during processing. Unfortunately, it is also more difficult to control with regards to

film thickness and uniformity. A schematic diagram of a typical setup for

electroplating is shown in the figure below.

WHEN DO WE WANT TO USE ELECTRODEPOSITION

?

The electrodeposition process is well suited to make films of metals

such as copper, gold and nickel. The films can be made in any thickness from ~1m

to >100m. The deposition is best controlled when used with an external electrical

potential, however, it requires electrical contact to the substrate when immersed in the

liquid bath. In any process, the surface of the substrate must have an electrically

conducting coating before the deposition can be done.

Figure 2:Typical setup for electrodeposition.

EPITAXY

This technology is quite similar to what happens in CVD processes,

however, if the substrate is an ordered semiconductor crystal (i.e. silicon, gallium

arsenide), it is possible with this process to continue building on the substrate with the

same crystallographic orientation with the substrate acting as a seed for the

deposition. If an amorphous/polycrystalline substrate surface is used, the film will

also be amorphous or polycrystalline.


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There are several technologies for creating the conditions inside a

reactor needed to support epitaxial growth, of which the most important is Vapor

Phase E pitaxy (VPE). In this process, a number of gases are introduced in an

induction heated reactor where only the substrate is heated. The temperature of the

substrate typically must be at least 50% of the melting point of the material to be

deposited.

An advantage of epitaxy is the high growth rate of material, which

allows the formation of films with considerable thickness (>100m). Epitaxy is a

widely used technology for producing silicon on insulator (SOI) substrates. The

technology is primarily used for deposition of silicon. A schematic diagram of a

typical vapor phase epitaxial reactor is shown in the figure below.

Figure 3:Typical cold-wall vapor phase epitaxial reactor.

WHEN DO WE WANT TO USE EPITAXY?

This has been and continues to be an emerging process technology in

MEMS. The process can be used to form films of silicon with thicknesses of ~1m to

>100m. Some processes require high temperature exposure of the substrate, whereas

others do not require significant heating of the substrate. Some processes can even be

used to perform selective deposition, depending on the surface of the substrate.


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THERMAL OXIDATION

This is one of the most basic deposition technologies. It is simply

oxidation of the substrate surface in an oxygen rich atmosphere. The temperature is

raised to 800 C-1100 C to speed up the process. This is also the only depositiontechnology which actually consumes some of the substrate as it proceeds. The growth

of the film is spurned by diffusion of oxygen into the substrate, which means the film

growth is actually downwards into the substrate. As the thickness of the oxidized

layer increases, the diffusion of oxygen to the substrate becomes more difficult

leading to a parabolic relationship between film thickness and oxidation time for films

thicker than ~100nm. This process is naturally limited to materials that can be

oxidized, and it can only form films that are oxides of that material. This is the

classical process used to form silicon dioxide on a silicon substrate. A schematicdiagram of a typical wafer oxidation furnace is shown in the figure below.

SECTION 4.2 ETCHING PROCESSES

In order to form a functional MEMS structure on a substrate, it is

necessary to etch the thin films previously deposited and/or the substrate itself. In

general, there are two classes of etching processes:

1. Wet etching where the material is dissolved when immersed in a chemicalsolution

2. Dry etching where the material is sputtered or dissolved using reactive ions ora vapor phase etchant

SECTION 4.2.1 WET ETCHING

This is the simplest etching technology. All it requires is a container

with a liquid solution that will dissolve the material in question. Unfortunately, there

are complications since usually a mask is desired to selectively etch the material. One

must find a mask that will not dissolve or at least etches much slower than the

material to be patterned. Secondly, some single crystal materials, such as silicon,

exhibit anisotropic etching in certain chemicals. Anisotropic etching in contrast to


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isotropic etching means different etches rates in different directions in the material.

The classic example of this is the crystal plane sidewalls that appear when

etching a hole in a silicon wafer in a chemical such as potassium hydroxide

(KOH). The result is a pyramid shaped hole instead of a hole with rounded sidewalls

with a isotropic etchant. The principle of anisotropic and isotropic wet etching is

illustrated in the figure below.

WHEN DO WE WANT TO USE WET ETCHING?

This is a simple technology, which will give good results if you can find

the combination of etchant and mask material to suit your application. Wet etching

works very well for etching thin films on substrates, and can also be used to etch the

substrate itself. The problem with substrate etching is that isotropic processes will

cause undercutting of the mask layer by the same distance as the etch depth.

Anisotropic processes allow the etching to stop on certain crystal planes in the

substrate, but still results in a loss of space, since these planes cannot be vertical to the

surface when etching holes or cavities. If this is a limitation for you, you should

consider dry etching of the substrate instead. However, keep in mind that the cost per

wafer will be 1-2 orders of magnitude higher to perform the dry etching

If you are making very small features in thin films (comparable to the

film thickness), you may also encounter problems with isotropic wet etching, since

the undercutting will be at least equal to the film thickness. With dry etching it is

possible etch almost straight down without undercutting, which provides much higher

resolution.

Figure 4:Difference between anisotropic and isotropic wet etching.


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SECTION 4.2.2 DRY ETCHING

The dry etching technology can split in three separate classes called

reactive ion etching (RIE), sputter etching, and vapor phase etching.

In RIE, the substrate is placed inside a reactor in which several gases are

introduced. Plasma is struck in the gas mixture using an RF power source, breaking

the gas molecules into ions. The ion is accelerated towards, and reacts at, the surface

of the material being etched, forming another gaseous material. This is known as the

chemical part of reactive ion etching. There is also a physical part which is similar in

nature to the sputtering deposition process. If the ions have high enough energy, they

can knock atoms out of the material to be etched without a chemical reaction. It is

very complex tasks to develop dry etch processes that balance chemical and physical

etching, since there are many parameters to adjust. By changing the balance it is

possible to influence the anisotropy of the etching, since the chemical part is isotropic

and the physical part highly anisotropic the combination can form sidewalls that have

shapes from rounded to vertical. A schematic of a typical reactive ion etching system

is shown in the figure below.

A special subclass of RIE which continues to grow rapidly in popularity

is deep RIE (DRIE). In this process, etch depths of hundreds of microns can be

achieved with almost vertical sidewalls. The primary technology is based on the so-

called "Bosch process", named after the German company Robert Bosch which filed

the original patent, where two different gas compositions are alternated in the reactor.

The first gas composition creates a polymer on the surface of the substrate, and the

second gas composition etches the substrate. The polymer is immediately sputtered

away by the physical part of the etching, but only on the horizontal surfaces and not

the sidewalls. Since the polymer only dissolves very slowly in the chemical part of the

etching, it builds up on the sidewalls and protects them from etching. As a result,

etching aspect ratios of 50 to 1 can be achieved. The process can easily be used to

etch completely through a silicon substrate, and etch rates are 3-4 times higher than

wet etching. Sputter etching is essentially RIE without reactive ions. The systems

used are very similar in principle to sputtering deposition systems. The big difference

is that substrate is now subjected to the ion bombardment instead of the material

target used in sputter deposition.


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Vapor phase etching is another dry etching method, which can be done

with simpler equipment than what RIE requires. In this process the wafer to be etched

is placed inside a chamber, in which one or more gases are introduced. The material

to be etched is dissolved at the surface in a chemical reaction with the gas molecules.

The two most common vapor phase etching technologies are silicon dioxide etching

using hydrogen fluoride (HF) and silicon etching using xenon diflouride (XeF2), both

of which are isotropic in nature. Usually, care must be taken in the design of a vapor

phase process to not have bi-products form in the chemical reaction that condense on

the surface and interfere with the etching process.

WHEN DO WE WANT TO USE DRY ETCHING?

The first thing you should note about this technology is that it is

expensive to run compared to wet etching. If you are concerned with feature

resolution in thin film structures or you need vertical sidewalls for deep etchings in

the substrate, you have to consider dry etching. If you are concerned about the price

of your process and device, you may want to minimize the use of dry etching. The IC

industry has long since adopted dry etching to achieve small features, but in many

cases feature size is not as critical in MEMS. Dry etching is an enabling technology,

which comes at a sometimes high cost.

Figure 5:Typical parallel-plate reactive ion etching system.


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SECTION 5 FABRICATION TECHNOLOGIES

The three characteristic features of MEMS fabrication technologies are

miniaturization, multiplicity, and microelectronics. Miniaturization enables the

production of compact, quick-response devices. Multiplicity refers to the batch

fabrication inherent in semiconductor processing, which allows thousands or millions

of components to be easily and concurrently fabricated. Microelectronics provides the

intelligence to MEMS and allows the monolithic merger of sensors, actuators, and

logic to build closed-loop feedback components and systems. The successful

miniaturization and multiplicity of traditional electronics systems would not have

been possible without IC fabrication technology. Therefore, IC fabrication

technology, or microfabrication, has so far been the primary enabling technology for

the development of MEMS. Microfabrication provides a powerful tool for batch

processing and miniaturization of mechanical systems into a dimensional domain not

accessible by conventional techniques. Furthermore, microfabrication provides an

opportunity for integration of mechanical systems with electronics to develop high-

performance closed-loop-controlled MEMS.

Advances in IC technology in the last decade have brought about corresponding

progress in MEMS fabrication processes. Manufacturing processes allow for the

monolithic integration of microelectromechanical structures with driving, controlling,

and signal-processing electronics. This integration promises to improve the

performance of micromechanical devices as well as reduce the cost of manufacturing,

packaging, and instrumenting these devices.

SECTION 5.1 ICFABRICATION

Any discussion of MEMS requires a basic understanding of IC

fabrication technology, or microfabrication, the primary enabling technology for the

development of MEMS. The major steps in IC fabrication technology are:

Film growth: Usually, a polished Si wafer is used as the substrate, on which athin film is grown. The film, which may be epitaxial Si, SiO2, silicon nitride

(Si3N4), polycrystalline Si, or metal, is used to build both active or passive

components and interconnections between circuits.


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Doping: To modulate the properties of the device layer, a low and controllablelevel of an atomic impurity may be introduced into the layer by thermal

diffusion or ion implantation.

Lithography: A pattern on a mask is then transferred to the film by means ofa photosensitive (i.e., light sensitive) chemical known as a photoresist. The

process of pattern generation and transfer is called photolithography. A typical

mask consists of a glass plate coated with a patterned chromium (Cr) film.

Etching: Next is the selective removal of unwanted regions of a film orsubstrate for pattern delineation. Wet chemical etching or dry etching may be

used. Etch-mask materials are used at various stages in the removal process to

selectively prevent those portions of the material from being etched. These

materials include SiO2, Si3N4, and hard-baked photoresist.

Dicing: The finished wafer is sawed or machined into small squares, or dice,from which electronic components can be made.

Packaging: The individual sections are then packaged, a process that involvesphysically locating, connecting, and protecting a device or component. MEMS

design is strongly coupled to the packaging requirements, which in turn are

dictated by the application environment.

Figure6: Typical packaging


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SECTION 6 CURRENT CHALLENGES

MEMS and Nanotechnology is currently used in low- or medium-

volume applications. Some of the obstacles preventing its wider adoption are:

LIMITED OPTIONS

Most companies who wish to explore the potential of MEMS and

Nanotechnology have very limited options for prototyping or manufacturing devices,

and have no capability or expertise in microfabrication technology. Few companies

will build their own fabrication facilities because of the high cost. A mechanism

giving smaller organizations responsive and affordable access to MEMS and Nano

fabrication is essential.

PACKAGING

The packaging of MEMS devices and systems needs to improve

considerably from its current primitive state. MEMS packaging is more challenging

than IC packaging due to the diversity of MEMS devices and the requirement that

many of these devices be in contact with their environment. Currently almost all

MEMS and Nano development efforts must develop a new and specialized package

for each new device. Most companies find that packaging is the single most expensive

and time consuming task in their overall product development program. As for the

components themselves, numerical modeling and simulation tools for MEMS

packaging are virtually non-existent. Approaches which allow designers to select

from a catalog of existing standardized packages for a new MEMS device without

compromising performance would be beneficial.

FABRICATION KNOWLEDGE REQUIRED

Currently the designer of a MEMS device requires a high level of

fabrication knowledge in order to create a successful design. Often the development

of even the most mundane MEMS device requires a dedicated research effort to find a

suitable process sequence for fabricating it. MEMS device design needs to be

separated from the complexities of the process sequence.


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SECTION 7 APPLICATIONS

PRESSURE SENSORS

MEMS pressure microsensors typically have a flexible diaphragm that

deforms in the presence of a pressure difference. The deformation is converted to an

electrical signal appearing at the sensor output. A pressure sensor can be used to sense

the absolute air pressure within the intake manifold of an automobile engine, so that

the amount of fuel required for each engine cylinder can be computed.

ACCELEROMETERS

Accelerometers are acceleration sensors. An inertial mass suspended by

springs is acted upon by acceleration forces that cause the mass to be deflected from

its initial position. This deflection is converted to an electrical signal, which appears

at the sensor output. The application of MEMS technology to accelerometers is a

relatively new development.

Accelerometers in consumer electronics devices such as game

controllers (Nintendo Wii), personal media players / cell phones (Apple iPhone ) and

a number of Digital Cameras (various Canon Digital IXUS models). Also used in PCs

to park the hard disk head when free-fall is detected, to prevent damage and data loss.iPod Touch: When the technology become sensitive. MEMS-based sensors are ideal

for a wide array of applications in consumer, communication, automotive and

industrial markets.

The consumer market has been a key driver for MEMS technology

success. For example, in a mobile phone, MP3/MP4 player or PDA, these sensors

offer a new intuitive motion-based approach to navigation within and between pages.

In game controllers, MEMS sensors allow the player to play just moving the

controller/pad; the sensor determines the motion.


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Micro Engines

A three-level polysilicon micromachining process has enabled the fabrication ofdevices with increased degrees of complexity. The process includes three movablelevels of polysilicon, each separated by a sacrificial oxide layer, plus a stationary

level. Microengines can be used to drive the wheels of microcombination locks. Theycan also be used in combination with a microtransmission to drive a pop-up mirror outof a plane. This device is known as a micro mirror.

HOMELAND SECURITY

Homeland Security refers to protection of territory, domestic population andcritical infrastructure against external threats and aggression.

September 11 attacks and the bio-terrorism threats have made Department ofHomeland Security a focal point in defending the nation against terroristattacks.

Military Applications of MEMS

Development of agile and advanced military warfare Faster access to information in all domains

AIR, SEA & LAND

Figure 7:block model


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Multisensor Microcluster

This system includes micro-sensors for measurement of temperature, pressure,humidity and position.

Applications : Environmental Monitoring Health Monitoring

MEMS POLYCHROMATOR

Figure 8:Typical mems polychromator


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MEMS MAGNETOMETER

MEMS magnetometer coupled with wireless systems can detect tanks, trucksor terrorists with weapons hiding in caves upto depths of 100 feet.

MEMS Magnetometer sense change in earths Magnetic field without any drivecurrent

Figure 9:Typical mems magnetometer

Biometric Identification

Reliable, low cost and convenient method of uniquely identifying individualsby measuring certain physical and behavioral characteristics

This sample is then compared with the template or signature, based on thesame characteristics established as unique identity of that individual and storedin the security system

Characteristics: Finger prints, Palm prints, Retina and iris patterns, facepatterns, voice, gait.


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Electronic Tongue

MEMS Sensors act as TASTE BUDS to identify chemical Components inLiquids

Incorporates number of chemical sensors generating an electronic fingerprint ofthe tastes.

Figure 10:Typical electronic tongue

Some Other Commercial applications include:

y Inkjet printers, which use piezoelectrics or thermal bubble ejection to depositink on paper.

y Accelerometers in modern cars for a large number of purposes includingairbag deployment in collisions.

y MEMS gyroscopes used in modern cars and other applications to detect yaw;e.g. to deploy a roll over bar or trigger dynamic stability control.

y Silicon pressure sensors e.g. car tire pressure sensors, and disposable bloodpressure sensors.

y Displays e.g. the DMD chip in a projector based on DLP technology has on itssurface several hundred thousand micromirrors.

y Optical switching technology which is used for switching technology andalignment for data communications.

y Bio-MEMS applications in medical and health related technologies from Lab-On-Chip to MicroTotalAnalysis (biosensor, chemosensor).

y Interferometric modulator display (IMOD) applications in consumerelectronics. Used to create interferometric modulation - reflective display

technology as found in mirasol displays.


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MEMS IC fabrication technologies have also allowed the manufacture

of advanced memory devices (nanochips/microchips).

Figure 11:Typical structure of mems based advanced memory device

As a final example, MEMS technology has been used in fabricating

vaporization microchambers for vaporizing liquid microthrusters for nanosatellites.

The chamber is part of a microchannel with a height of 2-10 microns, made using

silicon and glass substrates

ADVANTAGES OF MEMS DISADVANTAGES OF MEMS

Minimize energy and materialsuse in manufacturing

Cost/performance advantages Improved reproducibility

Improved accuracy andreliability

Increased selectivity andsensitivity

Farm establishment requireshuge investments

Micro-components are Costlycompare to macro-components

Design includes very muchcomplex procedures

Prior knowledge is needed tointegrate MEMS devices


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SECTION 8 THE FUTURE

Each of the three basic microsystems technology processes we have

seen, bulk micromachining, sacrificial surface micromachining, and

micromolding/LIGA, employs a different set of capital and intellectual resources.

MEMS manufacturing firms must choose which specific microsystems manufacturing

techniques to invest in.

MEMS technology has the potential to change our daily lives as much as

the computer has. However, the material needs of the MEMS field are at a

preliminary stage. A thorough understanding of the properties of existing MEMSmaterials is just as important as the development of new MEMS materials.

Future MEMS applications will be driven by processes enabling greater

functionality through higher levels of electronic-mechanical integration and greater

numbers of mechanical components working alone or together to enable a complex

action. Future MEMS products will demand higher levels of electrical-mechanical

integration and more intimate interaction with the physical world. The high up-front

investment costs for large-volume commercialization of MEMS will likely limit the

initial involvement to larger companies in the IC industry. Advancing from their

success as sensors, MEMS products will be embedded in larger non-MEMS systems,

such as printers, automobiles, and biomedical diagnostic equipment, and will enable

new and improved systems.

.


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SECTION 9 CONCLUSIONS

The automotive industry, motivated by the need for more efficient safety

systems and the desire for enhanced performance, is the largest consumer of MEMS-

based technology. In addition to accelerometers and gyroscopes, micro-sized tire

pressure systems are now standard issues in new vehicles, putting MEMS pressure

sensors in high demand. Such micro-sized pressure sensors can be used by physicians

and surgeons in a telemetry system to measure blood pressure at a stet, allowing early

detection of hypertension and restenosis. Alternatively, the detection of bio molecules can

benefit most from MEMS-based biosensors. Medical applications include the detection of

DNA sequences and metabolites. MEMS biosensors can also monitor several chemicals

simultaneously, making them perfect for detecting toxins in the environment.

Lastly, the dynamic range of MEMS based silicon ultrasonic sensors have

many advantages over existing piezoelectric sensors in non-destructive evaluation, proximity

sensing and gas flow measurement. Silicon ultrasonic sensors are also very effective

immersion sensors and provide improved performance in the areas of medical imaging and

liquid level detection.

The medical, wireless technology, biotechnology, computer, automotive and

aerospace industries are only a few that will benefit greatly from MEMS.

This enabling technology allowing the development of smart products,

augmenting the computational ability of microelectronics with the perception

and control capabilities of microsensors and microactuators and expanding the

space of possible designs and applications.

MEMS devices are manufactured for unprecedented levels of functionality,

reliability, and sophistication can be placed on a small silicon chip at a

relatively low cost.

MEMS promises to revolutionize nearly every product category by bringing

together silicon-based microelectronics with micromachining technology,

making possible the realization of complete systems-on-a-chip.

MEMS will be the indispensable factor for advancing technology in the 21st

century and it promises to create entirely new categories of products.


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SECTION 10 REFERENCES

Online Resources

BSAC http://www-bsac.eecs.berkeley.edu/

DARPA MTO http://www.darpa.mil/mto/

IEEE Explore http://ieeexplore.ieee.org/Xplore/DynWel.jsp

Introduction to Microengineering http://www.dbanks.demon.co.uk/ueng/

MEMS Clearinghouse http://www.memsnet.org/

MEMS Exchange http://www.mems-exchange.org/

MEMS Industry Group http://www.memsindustrygroup.org/

MOSIS http://www.mosis.org/

MUMPS http://www.memscap.com/memsrus/crmumps.html

Stanford Centre for Integrated Systems http://www-cis.stanford.edu/

USPTO http://www.uspto.gov/

Trimmer http://www.trimmer.net/

Yole Development http://www.yole.fr/pagesAn/accueil.asp

Journals

Journal of Micromechanical Systems

Journal of Micromechanics and Microengineering

Micromachine Devices

Sensors Magazine