0018-9162/99/$10.00 © 1999 IEEE October 1999 25

Cover Feature

MEMS: The Systems Function Revolution

Information systems are no longer confined todesktops, but are rapidly becoming part of cars,personal digital assistants, and palmtop sys-tems. In this context, systems must be able notonly to compute but also to sense their physi-

cal environment and respond to it. These requirementsmove beyond even complex microelectronics, callingfor a functionality that combines electrical andmechanical components.

This new functionality is realized in microelectro-mechanical systems (MEMS). It is important to viewMEMS in this broad context. They are not about asingle application or device, nor are they defined by asingle fabrication process or material type. Rather,MEMS typify a fabrication approach that demon-strates the advantage of using multiple miniaturizedcomponents and microelectronics to design and buildintegrated electromechanical systems. Using the fab-rication techniques and materials familiar in micro-electronics as a basis, MEMS processes constructelectrical components, which provide computationalor decision-making capabilities, and mechanical com-ponents, which sense, control, and interface with themacroworld in which we live.

MEMS devices are fast becoming part of everythingfrom automobiles and fighter aircraft to printers andtelecommunications switching equipment. The “Appli-cations on the Horizon” sidebar gives a technologysample. Although MEMS devices will be a fraction ofthe cost, size, and weight of their systems, they will becritical to the systems’ operation, reliability, andaffordability.

Yet, despite their seemingly obvious advantages,MEMS are not well understood by the systems designand applications community—ironically, the ones towhom MEMS offer the greatest opportunities forenhancing system functionality. One area of confusionis how MEMS are produced and how that process dif-fers from microelectronics manufacturing. In this arti-cle, we explain similarities and differences and identify

some trends and motivations that are leading to a newsystems functionality.

FABRICATION METHODSRegardless of the fabrication process used, all

MEMS fabrication approaches share three key char-acteristics:

• Miniaturization. Small, light structures yielddevices with relatively high resonant frequencies,which in turn produce sensors and actuators withhigher operating frequencies and bandwidths.Thermal time constants, the rate at which struc-tures absorb and release heat, are shorter forsmaller, less massive structures. Unlike purelymicroelectronic devices, MEMS devices interactwith some aspect of the physical world (such aspressure, inertia, fluid flows, and light), so thereis a size below which further miniaturization actu-ally hurts operation. For example, reducing thesize (and consequently the mass) of an accelerom-eter makes it harder to detect low-g accelerations.For most MEMS applications, the size limits arethree to five times larger than for the smallestmicroelectronic device features.

• Multiplicity. Because MEMS processing uses thephotolithography methods used in integrated cir-cuit technology, you can fabricate 10,000 or amillion components as easily and quickly as youcan make one. This batch fabrication approachis critical to reducing the device’s unit cost.Additionally, multiplicity provides the flexibilitynecessary to design massively parallel, intercon-nected electromechanical systems. The design ofa digital micromirror display1 calls for an arrayabout the size of two standard postage stamps,with more than a million mirrors, each the size ofa red blood cell. Collectively, they must generatea complete, high-resolution video image. Buildingsuch a display with conventional component

Microelectromechanical systems offer unprecedented flexibility, but manysystem implementers do not grasp their advantages and abilities or howtheir fabrication differs from semiconductor manufacturing processes. Thisunderstanding is critical to MEMS commercialization.

Karen W.MarkusCronos IntegratedMicrosystems Inc.

Kaigham J.GabrielCarnegie MellonUniversity

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putin

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actic

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Applications on the HorizonMEMS devices and the smart products

they enable will increasingly determine thecommercial and military market players.MEMS will create new capabilities, makehigh-end functionality affordable in low-end systems, and extend the operationalperformance and life of existing products ina range of industries.

AutomotiveFor the past six years, the automotive

industry has used MEMS to sense and con-trol a car’s relationship to its environment,most notably to sense acceleration. His-torically, this is done using single-elementMEMS devices in automotive airbag accel-erometers. Recent MEMS developments arenow making it possible to have two-axisside-impact accelerometers, as well as ratesensors for body and braking control. Theindustry should soon see MEMS helpingcontrol the orientation and position of vehi-cles through the use of inclinometers andvehicular navigation systems. Future devel-opments will include collision avoidancesystems and smart highways that help con-trol the ever-increasing traffic flow. A nextstep beyond one- or two-axis sensing is com-plete inertial navigation units (INUs) on achip. These INUs will be composed of mul-tiple integrated MEMS accelerometers andgyroscopes. Current inertial navigation sys-tems are large, heavy, expensive, and powerconsumptive. INUs will let designers notonly augment global positioning systemreceivers to track battlefield assets but alsouse miniaturized navigation systems in auto-mobiles and personal navigation systems.

TelecommunicationsTelecommunications has a broad array

of applications, from microrelays for line-card applications to complex multifre-

quency tunable systems for wireless com-munications. The integrated circuit indus-try is heading toward system on a chip(SoC), which seeks to integrate completefunctionality on a single silicon substrate.The MEMS community has the same goal,but is taking a different approach. MEMSare being developed and designed intotelecommunications systems that will soonbe reaching the marketplace and providingan order-of-magnitude increase in perfor-mance and functionality. Some applicationsinclude optical switching networks (16 ×16 optical cross-connects, for example),such as those shown in Figure A. Othersinclude tunable capacitors, inductors, andfiltering systems for both military and com-mercial wireless receivers, base stations,and mobile phones.

MEMS communication systems are alsobeing driven by fiber-to-home managementand implementation, wavelength divisionmultiplexing (WDM) networks, and distrib-uted wireless sensing, control, and commu-nications networks for asset tracking, bordercontrol, environmental monitoring, securitysurveillance, and process and manufacturingcontrol. The leading challenge is educatingsystem implementers and SoC project lead-ers on MEMS abilities and advantages. Theease of integrating MEMS components, bothfrom a monolithic and an advanced hybridlevel, will add complementary capabilities toexisting and future SoCs.

Areas with potentialIn addition to these applications, there

are many opportunities to insert MEMSinto systems across a number of technolo-gies and products:

• Integrated fluidic systems will aidminiature chemical/biological analysisinstruments, hydraulic and pneumatic

systems, propellant and combustioncontrol, and printing technology.Applications could be DNA analysisor microturbine power sources.

• Low-power, high-resolution, small-area displays will be part of tacticaland personal information systems,providing ready access to computa-tional and visual data.

• Embedded sensors and actuators willhelp the condition-based maintenanceof machines and vehicles and pro-vide on-demand amplified structuralstrength in lower-weight weaponssystems/platforms and disaster-resis-tant building.1

• Mass data storage devices will offerstorage densities of terabytes persquare centimeter.

• Active, conformal surfaces will allowdistributed aerodynamic control ofaircraft, adaptive optics, and preci-sion parts and material handling.

• Integrated micro-optomechanical com-ponents for advanced communicationand computational systems, displays,2

and fiber-optic switches/ modulatorswill help usher in the age of all-opticalnetworking, providing the bandwidthand speed demanded by an Internet-based society.

To realize many of these potential areas,the MEMS community must build on cur-rent microelectronics design and manufac-turing processes and equipment to takeMEMS technology to higher performancelevels. For example, the sensitivities andstabilities required for INUs must be threeto four orders of magnitude better than thebest current MEMS accelerometers orgyroscopes.

For MEMS devices that must operate inhigh-temperature conditions for combus-

manufacturing and assembly methods would benearly impossible.

• Microelectronics. Integrated microelectronics givesMEMS their intelligence and allows closed-loopfeedback systems, localized signal conditioning,and the control of massively parallel actuatorarrays. Moreover, there is considerable investmentin microelectronics materials, processing, andexpertise. Because microelectronics is a key part

of MEMS, it will be easier and faster to developMEMS devices, as well as promote their accep-tance by systems designers and integrators.

Bulk micromachiningThis approach encompasses a variety of etching

procedures, based on both wet and dry chemistry, thatselectively remove material from most of the wafer.Figure 1a shows how wet chemical etching, the more

ate highly anisotropic structures in silicon. Figure 1bshows a sample structure.

Wafer-to-wafer bonding is an adjunct to bulk micro-machining technology. Bulk micromachining allowsonly the removal of material. Wafer bonding lets mate-rial be added using pressure or a combination of pres-sure and a high voltage across the wafer. Two or moremicromachined wafers (or those with prefabricatedelectronics) can be bonded. In many cases, the bondedwafers are silicon-to-silicon, but silicon-to-quartz andsilicon-to-pyrex bonds are also common. Wafer-to-wafer bonding is versatile, yields high-quality interfacesand bonds, and makes it possible to process wholewafers at a time. It is used heavily in the production ofpressure sensors and integrated fluidic systems (flowvalves and regulators, ink-jet nozzles, pumps, chemi-cal sensors, and miniature analytical instruments).

Surface micromachiningLike bulk micromachining, surface micromachin-

ing starts with a wafer. The difference is that in surfacemicromachining, the wafer itself is the substrate—theworking surface—on which multiple, alternating lay-

October 1999 27

Figure 1. How wet and dry chemical etching compare. (a)Wet bulk micromachining is limited to the rectangular andreverse-pyramid shapes allowed by silicon’s tetragonal crys-tallographic structure. (b) Deep silicon reactive ion etching, adry chemical process, allows the formation of free geometricshapes in the wafer’s plane while providing high anisotropyin the vertical dimension.

(a)

(b)

tion control, new materials are required. Becausedevices made of silicon cannot be used at temperaturesabove 150°C, such devices cannot be used directlyinside engines. MEMS devices made of new materialssuch as silicon carbide, however, will enable operationat temperatures nearly three times present limits.

References1. K.J. Gabriel, “Engineering Microscopic Machines,”

Scientific Am., 150th anniversary issue, Technology inthe 21st Century, Sept. 1995, pp. 150-153.

2. J.M. Younse, “Mirrors on a Chip,” IEEE Spectrum,Nov. 1993, pp. 27-31.

Figure A. (1) Lucent’s MEMS optical switch, with less than0.5 dB loss, fabricated through MUMPs (multiuser MEMSprocesses, a registered trademark of Cronos) program,and (2) Cronos’ latchable photonic switch component thatcan be fabricated as a single switch or as an integratedarray of individually controlled switches on a single chip.

(1)

(2)

common method, produces inverted pyramidal cavi-ties in the silicon wafer. Although it is an effective low-cost method, wet chemical etching severely limits theshape and size of structures that can be produced.

More recently, a dry chemical etch process, referredto as deep silicon reactive ion etching (DRIE), has beendeveloped for use in bulk silicon micromachining.DRIE uses the inductively coupled plasma etchingprocess developed by Robert Bosch Company to cre-

28 Computer

ers of material are deposited and etched. The processuses two main types of material: structural material,which makes up the operational structure, and sacri-ficial material, which is used to produce the spacesand gaps in the mechanical structure. Sacrificial mate-rial is removed through chemical processes at the endof the process when the devices are released. Layeringstructural and sacrificial material produces movable,suspended, or interlocked levels. Figure 2 shows theprocess steps to build a single cantilever beam.

The most common processes start with siliconwafers of the same grade and type used in microelec-tronics fabrication. They then use layers of silicondioxide as the sacrificial material and layers of poly-silicon (a deposited, low polycrystalline form of sili-con) as the structural material. Other depositedmaterials such as silicon nitride, polyimides, and alu-minum are also extensively used to provide electricallyinsulating materials, conducting materials, etchingmasks, and additional structural materials. All thesematerials are used in standard microelectronics fabri-cation and are thus usually available.

Surface micromachining is at the heart of much ofthe current scientific and commercial MEMS activitybecause it lets designers fabricate free-form, complex,and integrated electromechanical structures. Surfacemicromachining uses laminated structural and sacrifi-cial material layers, and its material etching process isinsensitive to crystalline structure (because of the etchor because the material itself is noncrystalline). MEMSdesigners can thus envision and build a wide range ofdevices and systems without inordinate constraints onmaterials, geometries, assembly, or interconnections.The only requirement on the material system is that ithave complementary structural and sacrificial materi-als (for example, metals paired with polyimides).

Having freedom in so many areas contributes

greatly to the richness, depth, and diversity of MEMSapplications.

High-aspect-ratio micromachiningBulk micromachined structures are typically only a

few hundred microns thick and suspended within thewafer’s plane. Surface micromachined structures, incontrast, are usually only five to 10 microns thick.High-aspect-ratio micromachining was developed toallow the fabrication of tall (up to centimeters), pre-cision MEMS structures with nearly vertical sides (ahigh-aspect ratio).

Like bulk and surface micromachining techniques,high-aspect-ratio micromachining uses photolitho-graphic processes, but the photoresist layers used toprovide the template for the structures are hundredsof microns to centimeters thick rather than the two tothree microns typical in the other techniques. Thesehigh-aspect-ratio templates can be produced by bothx-ray and ultraviolet (UV) lithographic processes,though the use of UV illumination, which is far moreprevalent than x-rays, limits the aspect ratio anddegree of verticality relative to the use of x-rays. X-rays are what give the plating templates their sharpedges, as Figure 3 shows.

High-aspect-ratio micromachining usually begins byexposing and developing the thick photoresist, whichleaves deep, high-aspect-ratio canyons. Electroplatingis then used to fill the canyons in the photoresist withmetal (typically nickel, but any electroplatable metalwill do) that will mold itself into the shape of the pat-terned canyons. Finally, all photoresist is removed,leaving behind metal parts with geometries defined bythe thickness of the original resist layer and the sub-micron precision exposure of x-rays.

High-aspect-ratio micromachining is not yet com-mon, although it has been particularly useful in build-ing electromagnetic MEMS because of their relativelylarge structures and high-permeability metals, whichcan be electroplated. It is also promising as an end-

Ultraviolet light

Ultraviolet light

Mask

Silicon dioxide

Silicon substrate

Window

(a) (b)

(c) (d) (e)

Polycrystallinesilicon Base Beam

Figure 2. Using surface micromachining to build a singlecantilever beam. The process begins with the sacrificialmaterial layer (silicon dioxide) being (a) patterned and (b)etched. Next, the structural material (polysilicon) isdeposited over the entire surface. The polysilicon is then (c)patterned and (d) etched in the shape of the cantilever beamand base. Finally, the polysilicon is released by (e) removingthe remaining underlying silicon dioxide. The part of the pat-terned polysilicon where the silicon dioxide was removed in(b) is attached to the substrate and forms the anchor. Theareas where the silicon dioxide was left before the releasestep create suspended structures, free to move after release.

Figure 3: Thick nickel parts formed using the LIGA high-aspect-ratio process (x-ray exposure). LIGA is a Germanacronym for lithographe, galvanoformung, and abformung,which translates to imaging, electroplating, and molding. The high precision of the x-rays creates plating templateswith extreme edge acuity (less than 0.1 micron runout over a 400-micron height).

run technology to produce high-volume, low-cost,precision piece parts and housings without conven-tional milling and machining tools.

COMPARISON TO MICROELECTRONICSAlthough MEMS fabrication uses many of the mate-

rials and processes of semiconductor fabrication, thereare important distinctions. The most significant are theprocess recipe, use of design and simulation tools, andend-stage production. Figure 4 shows key points ofcontrast. The main challenge in using semiconductorprocesses for MEMS fabrication is not in what pro-cesses and materials to use but how to use them.1

Process recipeA process recipe is the number, sequence, and type

of deposition, removal, and patterning steps used tofabricate a device. The MEMS fabrication technologythat most closely follows the microelectronics processrecipe is surface micromachining. It is also the tech-nology that uses those processes and materials at theirextremes.

Film thickness. The films typically deposited forMEMS are usually thousands to tens of thousands ofangstroms thick. In contrast, microelectronic filmsare usually hundreds to thousands of angstroms. Thethicker films in MEMS mean that the materialremoval steps or etches are necessarily deeper andtake longer. The etch profiles (shape of the side wallsin the etched features) are then harder to control andmaintain to target specification.

Topography. The successive buildup of materialfrom multiple depositions, patterning, and etchingmakes the (topographical) surface of MEMS-

processed wafers very nonplanar after only a fewprocess cycles. This has consequences for laterprocess steps. In photolithographic steps, features onprominences in the wafer will be out of focus if fea-tures in the depressions are in focus. During materialdeposition, there will be thinned areas and evenbreaks in the surface coverage, particularly at sharptransitions from prominences to depressions.

Material removal. A processing step unique toMEMS is to free or release the parts designed to move(membranes, resonating beams, tiltable mirrors) byremoving material under them. The release of themovable and structural components poses problemsthat are new to microelectronics processing. One suchproblem is the residual stress inherent in the releasedfilms. If not properly controlled, the stresses will causethe released mechanical structures to lose theirdesigned shape and orientation, making the deviceunable to perform its intended function.

Design and simulation toolsMEMS fabrication requires more design aids than

microelectronics design and production. It needs newdrawing and layout tools to generate the patterns foradding or removing material. It requires not only a rangeof modeling tools (simulators for mechanical deforma-tion, electrostatic fields, mechanical forces, electro-magnetic fields, material properties, and electronicdevice simulators) but also connective algorithms to rec-oncile and blend results from different simulators.

New algorithms. Consider a single cantilever beam(diving board) suspended above the substrate at someinitial gap, holding an electric charge. An electric fieldsimulator calculates the force from the field created

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Free-form geometries3D solid modelers

Coupled electrical, mechanical,fluidic, kinematic … analysis

Thicker films,deeper etches,

fewer steps

Remove underlyingmaterials to release

mechanical parts

Special probing, sectioning, and handlingprocedures to protect released parts

Seal some parts of devicebut expose others

Test more thanelectrical function

Multiple processing cycles

Conception ofnew device,specification

of process

Computer-aideddesign, simulation,

and layoutof device

Generation ofphysical masks or

direct-writepatterns

Depositionof

material

Patterntransfer

Removalof

material

Probetesting

Individualdie

Assemblyinto package

Packageseal

FinaltestSectioning

Figure 4. The manufacturing process flow for a typical microelectronic integrated circuit and a MEMS device. The text in boldin the diagram shows the points at which MEMS fabrication differs.

30 Computer

by the charge, which is then fed to the mechan-ical deformation simulator. The mechanicaldeformation simulator determines how theforce will bend the beam and calculates a newgap. Because the gap changed, the electric fieldswill now be different and must be recalculatedto reflect the beam’s new mechanical position.The new fields will cause new forces, which inturn will cause further deformations in themechanical structures, causing more changes inthe field, and so on. The different simulatorstransfer the device simulation results back andforth until a stable solution is reached.

For a simple MEMS device, like a cantilever and oneor two simulators, a stable solution is simple to calcu-late. As devices have more independent mechanicalcomponents, however, and multiple simulators areinvolved, the complexity of both the simulations andthe coupling grow exponentially, and a stable solutionis difficult to reach. MEMS technologists need radicallynew approaches to modeling and simulation for themany physical effects and different functions of MEMS.

Material data. The simulators also need new mod-els and data to relate process parameters to materialproperties relevant for MEMS design. Simulators andmodels are only as good as the data they are built on.The accuracy of existing microelectronic device sim-ulators is built on huge amounts of historic materialand device measurements coupled to carefully con-trolled process conditions. By knowing the relation-ship between processing conditions and the resultingmaterial parameters, microelectronics manufacturerscan control material properties, and hence, deviceyields. Understandably, microelectronic circuit de-signers were interested in properties that related tothe electronic function of the devices they were build-ing, like doping levels and dielectric constants. Butvery few reliable measurements of material proper-ties (for example, modulus, residual stress, or reflec-tivity) are relevant to MEMS production. As morematerial data and related models for MEMS devicesbecome available, simulator accuracy will increase aswill the rate of successful, first-pass MEMS designs.

Drawing and layout tools. All the tools used to makethe masks for transferring the pattern of materialdeposition or etching were developed for microelec-tronics manufacturing. They tend to draw rectangu-lar features in square grids (Manhattan geometries),which are adequate for defining the device’s electri-cal properties. New drawing and pattern layout toolsmust take into account the free-form geometries ofMEMS designs and systems.

Design-rule checkers are also needed to automati-cally detect when constraints imposed by the fabrica-tion process are violated. Obviously, different processeswould have different design constraints, requiring dif-

ferent and associated design-rule checkers. MEMS fab-rication has different checking needs than microelec-tronics. For example, it needs some way toautomatically detect designs that do not have sufficientclearance for mechanical structures to move or designsthat result in released mechanisms that will collide.

End-stage fabricationMajor differences arise during processing steps at the

end of the manufacturing cycle. The principal one—and the root of all subsequent processing differences—is the release of mechanical structures. Even after asuccessful release and sectioning, the individual diesmust now be handled and assembled into a packagewithout damaging the mechanical structures or alteringtheir properties. Further, the objective in MEMS pack-aging is different from microelectronics packaging, inwhich the device is completely sealed from its environ-ment. The whole point of a MEMS device is to interactwith the physical world, whether it is to sense or act.

MEMS require new approaches to packaging thatselectively seal and expose different parts of the deviceto its environment. In fact, a better term for “packag-ing” in this context is “interfacing.” Because eachMEMS application area involves different physicalforces and interactions, the different applicationsrequire unique solutions that are unlikely to be similarto already solved problems from other MEMS appli-cations. MEMS fluidic devices, such as ink jets andpumps, present a completely different set of interfac-ing requirements (packages must allow contact withfluids but seal other portions) compared to a MEMSoptical system (package must be transparent to wave-lengths of interest but must maintain a vacuum).

TECHNOLOGY TRENDSFigure 5 is a map of electromechanical integration

that we created to trace MEMS developments acrossapplication areas. The vertical axis is a log plot of thenumber of transistors, from one to one billion. Thehorizontal axis is a log plot of the number of mechan-ical components. We view the number of transistors asa measure of information processing ability and thenumber of mechanical components as a measure ofthe ability to perceive and control the operational envi-ronment.2

This graph places historic and current MEMSdevices and some recent advanced MEMS devices,such as Analog Device accelerometers. It also attemptsto place classes of future MEMS technologies andapplications. The region that contains many currentMEMS devices (pressure sensors, accelerometers, andso on) is a small area near the plot’s origin (lower left).Moving from this cluster, regions of higher levels ofintegrated electronics are generally to the left and top,and regions of greater numbers of mechanical com-

The release of themovable and

structuralcomponents

poses problems that are new to

microelectronicsprocessing.

ponents are to the right and top. For example, theADXL-50 accelerometer has approximately 200 tran-sistors to a single mechanical proof mass, and the dig-ital micromirror display has approximately six milliontransistors to two million mechanical micromirrors.

The higher levels of integrated electronics and thegreater number of integrated mechanical componentsrepresented by these two MEMS devices quantify thedegree of MEMS technology advancements in the pastfive years. In the context of the entire graph, the twopoints also illustrate the opportunity in MEMS rep-resented by the regions of processing, perception, andactuation integration that are just starting to beexplored. These regions guide not only advances inintegration but also the capabilities that will beenabled at those levels. For example, developing iner-tial navigation units on a chip will likely require anincrease of nearly two orders of magnitude in both thenumber of transistors and mechanical components toreach the needed device sensitivity and stability. Incontrast, the development of some fluid pumps ormicro-optomechanical devices will likely requiregreater numbers of mechanical components, but atlower levels of integrated electronics.

By merging the capabilities of sensors and actu-ators with information systems, MEMS isextending and increasing the ability to both

perceive and control the physical world. FutureMEMS applications will be driven by processes thatenable greater functionality through higher levels ofelectronic-mechanical integration and more mechan-ical components. These process developments in turnwill be paced by investments in the development ofnew materials, device and systems design, fabricationtechniques, packaging/assembly methods, and testand characterization tools.

An important step in process development is toadapt semiconductor manufacturing equipment andprocesses to MEMS requirements, such as thinnerwafers or low-stress materials. Processing steps thatare unique to MEMS will require new manufacturingequipment and processes.

With MEMS entering the market, more productionrequirements are coming to light. The MEMS com-munity must begin investing in MEMS-specific manu-facturing equipment and packaging/interfacingtechniques. Although advanced MEMS device designs,systems concepts, and fabrication processes will con-tinue to be important, advances in these MEMS-specific manufacturing resources will largely paceMEMS development, commercialization, and use. ❖

References1. K.W. Markus, “Fabrication Technology and the Chal-

lenges of Large-Scale Production,” Proc. 2nd Ann.Symp. Frontiers Eng., National Academy Press, Wash-ington, D.C., 1997, pp. 57-62.

2. A. Berlin and K.J. Gabriel, “Distributed MEMS: NewChallenges for Computation,” IEEE Computational Sci-ence & Engineering, Vol. 4, No. 1, 1997, pp. 12-16.

Karen W. Markus is vice president and chief technicalofficer at Cronos Integrated Microsystems Inc., therecent MEMS spin-off from MCNC. She founded theMEMS Technology Applications Center at MCNC in1992 and has been responsible for the developmentand technical strategy of the MEMS infrastructure.She has served on several National Research Councilcommittees related to MEMS and is a regular confer-ence speaker on MEMS commercialization challenges.She received a BSEE from the University of SouthernCalifornia and is a member of the IEEE. Contact herat markus@memsrus.com.

Kaigham J. Gabriel is a professor in Carnegie MellonUniversity’s Electrical and Computer EngineeringDepartment and Robotics Institute and co-directorof CMU’s MEMS Laboratory, where he is conduct-ing research in acoustic and biomedical applicationsof MEMS technology. He was the director ofDARPA’s Electronics Technology Office and thefounding program manager of the DARPA MEMSProgram. He received an ScD in electrical engineer-ing and computer science from the MassachusettsInstitute of Technology. He is a member of the IEEE.Contact him at kgabriel@cs.cmu.edu.

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VLSI electromechanics

Distributedstructuralcontrol

Ultrasonicimagers

Terabits/cm2

data storage Displays

RF switching,wireless

Integrated fluidicsystems

Inertial navigationon a chip

Tran

sist

ors

Cellularrobotics

Parts handling

Optical switchesand aligners

Car,consumer

Recentadvances

109

108

107

106

105

104

103

102

101

100

100 101 102 103 104 105 106 107 108 109

Mechanical components

Mostexistingdevices

ADXLfamily

Figure 5. Tracking MEMS development. In this log-log plot, the number of transistors isrelated to the number of mechanical components for MEMS devices and systems. Thenumber of transistors is a measure of information processing; the number of mechani-cal components is a measure of perception and control. The areas in green representexisting MEMS devices. The area near the origin is where most existing devices fall.The green region just above it represents the Analog Devices family of accelerometers.The light blue regions denote envisioned application areas. The dashed triangle encom-passes devices that are considered VLSI electromechanics. The amorphous nature ofthe regions is meant to convey the range of abilities within an application area.