Progress In Mems And Micro Systems Research

Progress in MEMS and Micro Systems Research Chang Liu Micro and Nanotechnology Laboratory 208 N. Wright Street Urbana, IL 61821 Phone: 217-333-4051 Fax: 217-244-6375 Email: [email protected]

Abstract

MEMS technology has revoluntionized microfabrication, and the sensors and actuators industries. What is the state of the art of MEMS applications that use ceramic materials? what are major trends of development for the MEMS field in the future? this talk will present a broad and timely overview for conference attendees that address these twoquestions.

The integrated circuit (IC) technology is the starting point for discussing the history of MEMS. In 1971, the then state-of-the-art Intel 4004 chip consisted of only 2250 transistors. Intel 286 and Pentium III processors, unveiled in 1982 and 1999, had 120,000 and 24 million transistors, respectively. IC technology developed with a level of fierceness rarely matched in other fields. The density of transistor integration has increased by two-fold every 12-18 months, following the Moore’s Law [1] after an observation made by Gordon Moore, one of the co-founders of Intel Corporation. This is a remarkable feat of ingenuity and determination because, at several points in the past several decades, there were deep concerns that the trend predicted – and in some sense, mandated – in the Moore’s Law would not continue but run into limits imposed by fundamental physics or engineering capabilities at the time. The microfabrication technology is the engine behind functional integration and miniaturization of electronics. Between the early 1960s to the middle of 1980s, the fabrication technology of integrated

circuits rapidly matured after decades of research following the invention of the first semiconductor transistor [2]. Many scientific and engineering feats we take for granted today will not be here without the tremendous pace of progress in the area of microfabrication and miniaturization. The list include the exponentially growing use of computers and the Internet, cellular telephony, digital photography (capturing, storing, transferring, and displaying), flat panel displays, plasma televisions, fuel-efficient automobiles, sequencing the entire human genome (with 3 billion base pairs) [3], rapid DNA sequence identification [4], the discovery of new materials and drugs [5], and digital warfare. The field of MEMS evolved from the integrated circuit industry. The germination of the MEMS field covers two decades (from the mid 1960’s to 1980’s), when sparse activities were carried out. For example, anisotropic silicon etching was discovered to sculpture three dimensional features into otherwise planar silicon substrates [6]. Several pioneering

researchers in academic and industrial laboratories began to use the integrated circuit processing technology to make micro mechanical devices, including cantilevers, membranes, and nozzles. Crucial elements of micro sensors, including piezoresistivity of single crystalline silicon and polycrystalline silicon, were discovered, studied, and optimized [7-9]. At this stage, the name of the field had yet to be coined. However, both bulk micromachining and surface micromachining technologies were rapidly maturing [10-12]. There are a number of notable early works. In 1967, Harvey Nathanson at Westinghouse introduced a new type of transistor called the resonant gate transistor (RGT) [13]. Unlike conventional transistors, the gate electrode of the RGT was not fixed to the gate oxide but was movable with respect to the substrate. The distance between the gate and the substrate was controlled by electrostatic attractive forces. The RGT was the earliest demonstration of micro electrostatic actuators. In the 1970s, Kurt Petersen at the IBM research laboratory, along with other colleagues, developed diaphragm-type silicon micromachined pressure sensors. Very thin silicon diaphragms with embedded piezoresistive sensors were made using silicon bulk micromachining. The diaphragm deforms under differential pressures, inducing mechanical stress that was picked up by the piezoresistors. The thin diaphragm allowed greater deformation under a given pressure differential, hence greater sensitivity compared with conventional membrane-type pressure sensors. The sensors could be micromachined in batch, therefore increasing the uniformity of performance while reducing the costs of production. Pressure sensors for applications including blood pressure monitoring and industrial control provided the earliest commercial success of MEMS technology. Today, micromachined pressure sensors are built with a variety of structures and fabrication methods. These sensors can be based on capacitive [14], piezoelectric [15], piezoresistive [16], electronics resonance [17], and optical detection [18] techniques. Advanced features for integrated pressure sensors include built-in vacuum for absolute pressure measurement [14], integrated telemetry link [19], close-loop control [20], insensitivity to contaminants [21], biocompatibility for integration into micro medical instruments [22], and use of non-silicon membrane materials (e.g., ceramics, diamonds) for functioning in harsh and high temperature environments [17, 23, 24].

Ink jet printers offer a low cost alternative to laser jet printing and nowadays provide high performance and yet affordable color photographic-quality printing. Canon discovered ink jet by thermal bubble formation (bubble jet), whereas Hewlett-Packard pioneered the technology of silicon micromachined ink jet printer nozzles in 1978. Arrays of ink jet nozzles eject tiny ink droplets (“drop on demand”), upon expansion of liquid volume by thermal bubbles (see Figure 1). The collapse of the bubble draws more ink into the ink cavity for the next firing. Color ink jet printing is achieved by dropping primary subtractive color dyes – cyan, magenta, and yellow (CMY). Silicon micromachining technology played an enabling role for the ink jet printing technology [2527]. Using silicon micromachining, ink-ejection nozzles can be made extremely small and densely populated, an important trait for realizing high printing resolution, and sharp contrast. Smallvolume cavities with equally small heaters means rapid temperature rise (during ink ejection) and fall, allowing ink jet printing to reach appreciable speed. In 1995, the number of nozzles per cartridge has increased to 300 while the average weight of ink droplet is only 40 ng. In 2004, ink jet heads are based on a variety of principles, including thermal, piezoelectric, and electrostatic forces. The volume of each drop is on the order of 10 pl, with resolution as high as 1000 dpi reached [28]. Many ink jet printers on the market today are based on the thermal ink jet principle and dispense heatresistant dyes. Alternative ink jet principles are also possible. Epson-brand ink jet printers, for example, use piezoelectric ink jet technology and special ink dyes (since they do not have to be heat resistant). The inks for piezoelectric inkjet printers dry more quickly to minimize spreading on paper and therefore produce greater resolution. Today, ink jet printers compare favorably with laser jet printing. Ink jet printers are generally cheaper although the cost of replacing ink cartridges makes ink jet printing more expensive to own and use over long periods of time. The ink jet technology is being applied beyond text and photo printing. It is now used for direct deposition of organic chemicals [29], elements for organic transistors [30], and biological molecules (such as building blocks of DNA molecules) [31].

silicon – either bulk silicon substrate (single crystalline silicon) or thin film silicon (polycrystalline silicon). These two forms of silicon were readily accessible as they were used heavily in the integrated circuit industry - bulk silicon is used as the substrate of circuitry, while polycrystalline silicon is used for making transistor gates. Threedimensional mechanical structures, such as suspended cantilevers or membranes, can be made out of bulk silicon or thin film silicon. In 1984, Petersen published a seminal paper titled “Silicon as a mechanical material” [10]. This paper was (and still is) widely quoted in the 1990s as the field expanded rapidly.

heater

nozzle

Ink reservoir

Ink drop

MEMS chip

Ink nozzles

Figure 1: Micromachined ink jet printer nozzles. (Top) Schematic side-view of an ink jet chip with fluid nozzles. (Middle and Bottom) Close-up view of a commercial inkjet printer head, and the silicon chip consisting of many nozzles. Integrated circuits on chips control nozzle firing. (File: fig1-1-1, fig1-1-2, fig1-1-3) In the late 1980s, researchers in the nascent field called micromachining mainly focused on the use of

The use of thin film silicon leads to surface micromachined mechanisms including springs, gear trains, and cranks, to name a few. In 1989, a first silicon surface micromachined micromotor driven by electrostatic forces was demonstrated by researchers at the University of California at Berkeley [32]. A polysilicon rotor, less than 120 µm in diameter and 1 µm thick, was capable of rotating at a maximum speed of 500 rpm under a three-phase, 350 V driving voltage. This motor, though with limited application at that time, brought the excitement of MEMS to the broader scientific community and the general public. Micro rotary motors based on different actuation principles, covering a wider range of scales (even down to nanometers), and with much greater achievable torque and power have been demonstrated since then [33, 34]. A few years later, the phrase Micro Electro Mechanical Systems – MEMS was introduced. It gradually became an internationally accepted name of the field. This name captured the scale (micro), practice (electro-mechanical integration) and aspiration (systems) of the new field. Two subtle facts often elude beginning readers. Many research results and products of MEMS technology are indeed components within a bigger system. The phrase embodies both a unique machining and manufacturing approach (micromachining), and a new format of devices and products. In the 1990s, the field of MEMS entered a period of rapid and dynamic growth worldwide. Government and private funding agencies in many countries throughout the world funded and supported focused research activities. Early research efforts at several companies started to bear fruits. Most notable examples include the integrated inertial sensors by Analog Devices for automotive air-bag deployment and the Digital Light Processing chip by Texas

Instruments for projection display. These two applications are discussed in the following. The ADXL series accelerometer made by Analog Devices Corporation consists of a suspended mechanical element and signal-processing electronics integrated on the same substrate. The initial development targeted the automotive market [35]. The accelerometer monitors excessive deceleration and initiate air-bag deployment in the event of a life threatening collision. The mechanical sensing element is a free-moving proof mass suspended by four support springs (Figure 2). Movable electrodes in the form of interdigitated fingers are attached to the proof mass. The fixed and moving electrodes form a bank of parallel-connected capacitors, with the total capacitance depending on the distance between the moving and fixed fingers. If an acceleration (a) is applied to the chip, the proof mass (with mass m) will move under an inertia force (F=ma) against the chip frame. This changes the finger distances and therefore the total capacitance. The minute amount of capacitance change is read using on-chip signal processing electronics. The integration of mechanical elements and electronics is critical for reducing interference noises (stemming from stray electromagnetic radiation) and avoiding parasitic capacitance associated with otherwise long conductor leads.

Figure 2: Mechanical elements of an integrated accelerometer. (Left) The proof mass is at an equilibrium position without acceleration; (right) The proof mass moves relative to the fixed fingers under an applied acceleration. (Figure name: fig1-2.jpg)

The MEMS technology offers significant advantages over then existing, macroscopic electromechanical sensors, mainly in terms of high sensitivity and low noise. The MEMS approach also decreases the costs of ownership of each sensor, mainly by eliminating manual assembly steps and replacing them with batch fabrication. Today, one can find a variety of micromachined acceleration sensors on the market based on a number of sensing principles and fabrication technologies. Accelerometers based on capacitive sensing [36, 37], piezoresistivity [38], piezoelectricity [39], optical interferometry [40] and thermal transfer [41, 42] have been demonstrated. Advanced features include integrated three axis sensing [43], ultrahigh sensitivity (nano-g) for monitoring seismic activities [44, 45], increased reliability by eliminating moving mass [42], and integrated hermetic sealing for long term stability [46]. The technology that produces the accelerometer can be modified to realize rotational acceleration sensors, or gyroscopes [47]. Due to their small sizes, MEMS inertia sensors can be inserted into tight spaces and enable novel applications, including smart writing instruments (e.g., smart pens that detect and transmit hand writing strokes to computers for character recognition), virtual reality headgears, computer mouse (Gyro mouse), electronic game controllers, running shoes that calculate the actual distance of running, and portable computers that stops the spinning of hard disks if the computer is accidentally dropped. In the information age, still images and videos are generated, distributed, and displayed in an all-digital manner to maximize quality and lower the distribution cost. Projection display is a powerful tool for digital multimedia presentation, movie theaters, and home entertainment systems. Traditional projection displays are analog in nature, based on liquid crystal display (LCD) technology. The Digital Light Processor (DLP) of Texas Instruments, a revolutionary digital optical projector [48, 49], consists of a light-modulating chip with more than 100,000 individually addressable micromirrors, called digital micro mirrors (DMD). Each mirror has an area of approximately 10x10 µm2 and is capable of tilting by +/- 7.5o. The mirror array is illuminated by a light source. Each mirror, when placed at a correct angle, reflects light towards the screen and illuminates one pixel. An array of such mirrors can form an image on a projection screen.

The schematic diagram (top view) of an individual mirror is shown in Figure 3. A mirror plate is supported by two torsional support beams and can rotate with respect to the torsion axis. According to the cross-sectional view (along A-A’ line), electrodes are located under the mirror to control its position. When one of the electrodes is biased, the mirror will be pulled toward one side by electrostatic attraction force. Because of the large number and high density of mirrors, they are addressed using a row-column multiplexing scheme. Static random addressing memory (SRAM) circuits employing 0.8-µm, double level metal CMOS technology for controlling each mirror are embedded on the silicon substrate, beneath the layer for mirrors. The DLP display offers advantages over the incumbent, transmissive LCD projection, including a higher (better) pixel fill factor, greater brightness and black level, greater contrast ratio, more efficient use of light, and stability of contrast and color balance over time. It should be noted that a successful device such as DLP is not an over-night success but a result of long-term commitment and development. In fact, the DLP was successfully launched following a string of unsuccessful earlier R&D activities at various companies, carried out in a span of 20 years.

Figure 3: Diagrams illustrating the structure and operating principles of a single DMD mirror. (Figure name: fig1-3.jpg) Today, digital micromirrors find applications beyond image projection. It is being pursued as a rapid maskless lithography technology to save the cost of mask making [50], as well as flexible, in situ DNA micro-array manufacturing using light-array assisted synthesis [51]. Advanced optical scanning mirrors, such as ones with continuous angular tuning, large displacement range, and more degrees of freedom have been developed for optical communication.[52] Besides the acceleration sensor and digital micro mirror, many new MEMS device categories were

developed in the 1990s, with varying degrees of industrial implementation presently. The MEMS technology field has undergone tremendous amount of change in the past few years. Among the most important new trends: (1) MEMS technology is being combined with nanotechnology and biomedical technologies to create a brand new categories of devices and for enabling new applications; (2) MEMS technology is moving away from using silicon and semiconductor materials exclusively. Polymer materials are being used more frequently. In recent years, silicon micromachining techniques are being rapidly augmented with new materials and processes. Silicon, a semiconductor material, is mechanically brittle. It is also expensive or unnecessary for certain applications. New materials such as polymer and compound semiconductors can fill the gap of performance. Polymer materials are being incorporated into MEMS because of their unique materials properties (e.g. biocompatibility, optical transparency), processing techniques, and low costs compared to silicon. Polymer materials that have been explored in recent years include silicone elastomers, Parylene, and polyimide, among others. Many sensors and actuators are needed to operate in harsh conditions, such as direct exposure to environmental elements, high temperature, wide temperature swing, or high shock. Delicate microstructures made of silicon or inorganic thin film materials are not suited for such applications. Several inorganic materials are being introduced for MEMS applications in harsh environments. Silicon carbide, in both bulk and thin film forms, are explored for applications including high temperature solid-state electronics and transducers [53-55]. Diamond thin films provide the advantage of high electrical conductivity and high wear resistance for potential applications including pressure sensors and scanning electron microscopy probes [23, 24, 56]. Other compound semiconductor materials including GaAs ([57-60]) are also being investigated. New material processing techniques are being developed for fabrication both on silicon substrates and other materials. New processes for MEMS include laser-assisted etching for material removal and deposition [61], stereo lithography for rapid

prototyping [62, 63], local electrochemical deposition [64], photo-electroforming [65], high aspect ratio deep reactive ion etching [61], micro milling [66, 67], focused ion beam etching [68], X-ray etching [69] [70], micro electro discharge [71, 72], ink jet printing (e.g., of metal colloids [73]), micro contact printing [74, 75], in-situ plasma [76], molding (including injection molding, [77]), embossing [78], screen printing [79], electrochemical welding [80], chemical mechanical polishing, and guided and self-directed self-assembly in two or three dimensions [81, 82]. Microfabrication processes have also been expanded to reach nanoscale resolution to realize nanoelectromechanical systems (NEMS) [63, 83]. Reliable and economical fabrication of electromechanical elements with nanoscopic feature sizes or spacing represents new challenges and methodologies. Traditional lithography does not offer sub-100-nm resolution readily, at low cost, and with parallelism. A variety of nanostructure patterning techniques, often drastically different from the photolithographic approach, are developed in the physics and chemistry communities for producing nano-meter scale patterns. Readers who are interested in exploring this class of techniques may start by reading literatures on nanoimprint lithography [84], nano whittling [85], and nanosphere lithography [86]. [1] [2] [3] [4] [5]

[6] [7] [8]

R. R. Schaller, "Moore's law: past, present, and future," in IEEE Spectrum, vol. 34, 1997, pp. 52-59. M. Riordan, "The Lost History Of the Transistor," Spectrum, IEEE, vol. 41, pp. 44-49, 2004. L. Rowen, G. Mahairas, and L. Hood, "Sequencing the Human Genome," Science, vol. 278, pp. 605-607, 1997. E. Pennisi, "BIOTECHNOLOGY: The Ultimate Gene Gizmo: Humanity on a Chip," Science, vol. 302, pp. 211, 2003. L. Peltonen and V. A. McKusick, "GENOMICS AND MEDICINE: Dissecting Human Disease in the Postgenomic Era," Science, vol. 291, pp. 1224-1229, 2001. K. E. Bean, "Anisotropic etching of silicon," IEEE Transaction on Electron Devices, vol. ED 25, pp. 1185-1193, 1978. C. S. Smith, "Piezoresistance effect in germanium and silicon," Physics Review, vol. 94, pp. 42-49, 1954. P. J. French and A. G. R. Evans, "Polycrystalline silicon strain sensors,"

It is noteworthy that the materials and technologies for microelectronics fabrication have not been standing still either. In fact, the traditional photolithography techniques and semiconductor materials associated with integrated circuits are undergoing rapidly changes in the past decade. New processing techniques such as roll-to-roll printing are being actively pursued for fast production of large area electronics, photovoltaic generators, and optoelectronics displays [87]. Organic polymer materials are being used in place of semiconductor materials for logic [30], storage [88], and optical display [89]. The future of new materials and fabrication methods is bright and exciting. Fabrication and manufacturing technologies such as micromachining, nanofabrication, and microelectronics fabrication have historically been developed in different communities with virtual disregard of each other, on independent sets of materials and substrates. As science and technology progresses towards the micro and nanoscopic dimensions, these distinct families of fabrication methods are being connected and hybridized to create powerful and transcending new fabrication methods which will enable new scientific studies and new devices.

[9]

[10] [11] [12]

[13]

[14]

Sensors and Actuators A, vol. 8, pp. 219225, 1985. F. T. Geyling and J. J. Forst, "Semiconductor strain transducers," The Bell Sysem Technical Journal, vol. 39, pp. 705-731, 1960. K. E. Petersen, "Silicon As A Mechanical Material," Proceedings of the IEEE, vol. 70, pp. 420-457, 1982. K. J. Gabriel, "Microelectromechanical systems," Proceedings of the IEEE, vol. 86, pp. 1534-1535, 1998. J. B. Angell, S. C. Terry, and P. W. Barth, "Silicon Micromechanical Devices," Scientific American Journal, vol. 248, pp. 44-55, 1983. H. C. Nathanson, W. E. Newell, R. A. Wickstrom, and J. R. D. Jr., "The Resonant Gate Transistor," IEEE Transactions on Electron Devices, vol. ED-14, pp. 117-133, 1967. A. V. Chavan and K. D. Wise, "Batchprocessed vacuum-sealed capacitive pressure sensors," Microelectromechanical

[15]

[16]

[17]

[18]

[19]

[20]

[21]

[22]

[23]

[24]

Systems, Journal of, vol. 10, pp. 580-588, 2001. A. Choujaa, N. Tirole, C. Bonjour, G. Martin, D. Hauden, P. Blind, A. Cachard, and C. Pommier, "AIN/silicon Lamb-wave microsensors for pressure and gravimetric measurements," Sensors and Actuators A: Physical, vol. 46, pp. 179-182, 1995. S. Sugiyama, M. Takigawa, and I. Igarashi, "Integrated piezoresistive pressure sensor with both voltage and frequency output," Sensors and Actuators A, vol. 4, pp. 113120, 1983. M. A. Fonseca, J. M. English, M. von Arx, and M. G. Allen, "Wireless micromachined ceramic pressure sensor for hightemperature applications," Microelectromechanical Systems, Journal of, vol. 11, pp. 337-343, 2002. N. A. Hall and F. L. Degertekin, "Integrated optical interferometric detection method for micromachined capacitive acoustic transducers," Applied Physics Letters, vol. 80, pp. 3859-3861, 2002. S. Chatzandroulis, D. Tsoukalas, and P. A. Neukomm, "A miniature pressure system with a capacitive sensor and a passive telemetry link for use in implantable applications," Microelectromechanical Systems, Journal of, vol. 9, pp. 18-23, 2000. J.-S. Park and Y. B. Gianchandani, "A servo-controlled capacitive pressure sensor using a capped-cylinder structure microfabricated by a three-mask process," Microelectromechanical Systems, Journal of, vol. 12, pp. 209-220, 2003. C. C. Wang, B. P. Gogoi, D. J. Monk, and C. H. Mastrangelo, "Contaminationinsensitive differential capacitive pressure sensors," Microelectromechanical Systems, Journal of, vol. 9, pp. 538-543, 2000. A. Gotz, I. Gracia, C. Cane, A. Morrissey, and J. Alderman, "Manufacturing and packaging of sensors for their integration in a vertical MCM microsystem for biomedical applications," Microelectromechanical Systems, Journal of, vol. 10, pp. 569-579, 2001. D. R. Wur, J. L. Davidson, W. P. Kang, and D. L. Kinser, "Polycrystalline diamond pressure sensor," Microelectromechanical Systems, Journal of, vol. 4, pp. 34-41, 1995. X. Zhu, D. M. Aslam, Y. Tang, B. H. Stark, and K. Najafi, "The Fabrication of AllDiamond Packaging Panels With Built-In Interconnects for Wireless Integrated

[25]

[26]

[27]

[28]

[29]

[30]

[31]

[32]

[33]

Microsystems," Microelectromechanical Systems, Journal of, vol. 13, pp. 396-405, 2004. C. A. Boeller, T. J. Carlin, P. M. Roeller, and S. W. Steinfield, "High-volume microassembly of color thermal inkjet printheads and cartridges," Hewlett-Package Journal, vol. 39, pp. 6-15, 1988. K. E. Petersen, "Fabriaction of an integratd planar silicon ink-jet structure," IEEE Transaction on Electron Devices, vol. ED26, pp. 191801920, 1979. J.-D. Lee, J.-B. Yoon, J.-K. Kim, H.-J. Chung, C.-S. Lee, H.-D. Lee, H.-J. Lee, C.K. Kim, and C.-H. Han, "A thermal inkjet printhead with a monolithically fabricated nozzle plate and self-aligned ink feed hole," Microelectromechanical Systems, Journal of, vol. 8, pp. 229-236, 1999. F.-G. Tseng, C.-J. Kim, and C.-M. Ho, "A high-resolution high-frequency monolithic top-shooting microinjector free of satellite drops - part I: concept, design, and model," Microelectromechanical Systems, Journal of, vol. 11, pp. 427-436, 2002. J. C. Carter, A. Wehrum, M. C. Dowling, M. Cacheiro-Martinez, and N. B. Baynes, "Recent developments in materials and processes for ink jet printing high resolution polymer OLED displays," Proceedings of the SPIE - The International Society for Optical Engineering; Organic LightEmitting Materials and Devices VI, 8-10 July 2002, vol. 4800, pp. 34-46, 2003. H. Sirringhaus, T. Kawase, R. H. Friend, T. Shimoda, M. Inbasekaran, W. Wu, and E. P. Woo, "High-Resolution Inkjet Printing of All-Polymer Transistor Circuits," Science, vol. 290, pp. 2123-2126, 2000. T. R. Hughes, M. Mao, A. R. Jones, J. Burchard, M. J. Marton, K. W. Shannon, S. M. Lefkowitz, M. Ziman, J. M. Schelter, M. R. Meyer, S. Kobayashi, C. Davis, H. Dai, Y. D. He, S. B. Stephaniants, G. Cavet, W. L. Walker, A. West, E. Coffey, D. D. Shoemaker, R. Stoughton, A. P. Blanchard, S. H. Friend, and P. S. Linsley, "Expression profiling using microarrays fabricated by an ink-jet oligonucleotide synthesizer," Nature Biotechnology, vol. 19, pp. 342-347, 2001. L.-S. Fan, Y.-C. Tai, and R. S. Muller, "ICProcessed Electrostatic Micro-motors," presented at IEEE International Electronic Devices Meeting, 1988. C. H. Ahn, Y. J. Kim, and M. G. Allen, "A planar variable reluctance magnetic

[34]

[35]

[36]

[37]

[38]

[39]

[40]

[41]

[42] [43]

[44]

micromotor with fully integrated stator and coils," Microelectromechanical Systems, Journal of, vol. 2, pp. 165-173, 1993. C. Livermore, A. R. Forte, T. Lyszczarz, S. D. Umans, A. A. Ayon, and J. H. Lang, "A High-Power MEMS Electric Induction Motor," Microelectromechanical Systems, Journal of, vol. 13, pp. 465-471, 2004. D. S. Eddy and D. R. Sparks, "Application of MEMS technology in automotive sensors and actuators," Proceedings of the IEEE, vol. 86, pp. 1747-1755, 1998. N. Yazdi, K. Najafi, and A. S. Salian, "A high-sensitivity silicon accelerometer with a folded-electrode structure," Microelectromechanical Systems, Journal of, vol. 12, pp. 479-486, 2003. N. Yazdi and K. Najafi, "An all-silicon single-wafer micro-g accelerometer with a combined surface and bulk micromachining process," Microelectromechanical Systems, Journal of, vol. 9, pp. 544-550, 2000. A. Partridge, J. K. Reynolds, B. W. Chui, E. M. Chow, A. M. Fitzgerald, L. Zhang, N. I. Maluf, and T. W. Kenny, "A highperformance planar piezoresistive accelerometer," Microelectromechanical Systems, Journal of, vol. 9, pp. 58-66, 2000. D. L. DeVoe and A. P. Pisano, "Surface micromachined piezoelectric accelerometers (PiXLs)," Microelectromechanical Systems, Journal of, vol. 10, pp. 180-186, 2001. N. C. Loh, M. A. Schmidt, and S. R. Manalis, "Sub-10 cm<sup>3 interferometric accelerometer with nano-g resolution," Microelectromechanical Systems, Journal of, vol. 11, pp. 182-187, 2002. U. A. Dauderstadt, P. H. S. De Vries, R. Hiratsuka, and P. M. Sarro, "Silicon accelerometer based on thermopiles," Sensors and Actuators A: Physical, vol. 46, pp. 201-204, 1995. A. M. Leung, Y. Zhao, and T. M. Cunneen, "Accelerometer uses convection heating changes," Elecktronik Praxis, vol. 8, 2001. S. Butefisch, A. Schoft, and S. Buttgenbach, "Three-axes monolithic silicon low-g accelerometer," Microelectromechanical Systems, Journal of, vol. 9, pp. 551-556, 2000. J. Bernstein, R. Miller, W. Kelley, and P. Ward, "Low-noise MEMS vibration sensor for geophysical applications," Microelectromechanical Systems, Journal of, vol. 8, pp. 433-438, 1999.

[45]

[46]

[47]

[48] [49]

[50] [51]

[52] [53]

[54]

[55]

[56]

[57]

C.-H. Liu and T. W. Kenny, "A highprecision, wide-bandwidth micromachined tunneling accelerometer," Microelectromechanical Systems, Journal of, vol. 10, pp. 425-433, 2001. B. Ziaie, J. A. Von Arx, M. R. Dokmeci, and K. Najafi, "A hermetic glass-silicon micropackage with high-density on-chip feedthroughs for sensors and actuators," Microelectromechanical Systems, Journal of, vol. 5, pp. 166-179, 1996. S. Lee, S. Park, J. Kim, S. Lee, and D.-I. Cho, "Surface/bulk micromachined singlecrystalline-silicon micro-gyroscope," Microelectromechanical Systems, Journal of, vol. 9, pp. 557-567, 2000. J. M. Younse, "Mirrors on a chip," Spectrum, IEEE, vol. 30, pp. 27-31, 1993. P. F. Van Kessel, L. J. Hornbeck, R. E. Meier, and M. R. Douglass, "A MEMSbased projection display," Proceedings of the IEEE, vol. 86, pp. 1687-1704, 1998. N. Savage, "A revolutionary chipmaking technique?," in IEEE Spectrum, vol. 40, 2003, pp. 18. S. Singh-Gasson, R. D. Green, Y. Yue, C. Nelson, F. Blattner, M. R. Sussman, and F. Cerrina, "Maskless fabricaiton of lightdirected oligonucleotide microarrays using a digital micromirror array," Nature biotechnology, vol. 17, pp. 974-978, 1999. "Elastomeric Organic Transistors," Science, vol. 303, pp. 1577e-, 2004. M. Mehregany, C. A. Zorman, N. Rajan, and C. H. Wu, "Silicon carbide MEMS for harsh environments," Proceedings of the IEEE, vol. 86, pp. 1594-1609, 1998. S. Tanaka, S. Sugimoto, J.-F. Li, R. Watanabe, and M. Esashi, "Silicon carbide micro-reaction-sintering using micromachined silicon molds," Microelectromechanical Systems, Journal of, vol. 10, pp. 55-61, 2001. C. R. Stoldt, C. Carraro, W. R. Ashurst, D. Gao, R. T. Howe, and R. Maboudian, "A low-temperature CVD process for silicon carbide MEMS," Sensors and Actuators A: Physical, vol. 97-98, pp. 410-415, 2002. T. Shibata, Y. Kitamoto, K. Unno, and E. Makino, "Micromachining of diamond film for MEMS applications," Microelectromechanical Systems, Journal of, vol. 9, pp. 47-51, 2000. Z. L. Zhang and N. C. MacDonald, "Fabrication of submicron high-aspect-ratio

[58]

[59]

[60]

[61]

[62]

[63]

[64]

[65]

[66]

[67]

[68]

GaAs actuators," Microelectromechanical Systems, Journal of, vol. 2, pp. 66-73, 1993. S. Adachi and K. Oe, "Chemical etching characteristics of (001) GaAs," Journal of Electrochemical Society, vol. 123, pp. 24272435, 1983. N. Chong, T. A. S. Srinivas, and H. Ahmed, "Performance of GaAs microbridge thermocouple infrared detectors," Microelectromechanical Systems, Journal of, vol. 6, pp. 136-141, 1997. N. Iwata, T. Wakayama, and S. Yamada, "Establishment of basic process to fabricate full GaAs cantilever for scanning probe microscope applications," Sensors and Actuators A: Physical, vol. 111, pp. 26-31, 2004. M. Heschel, M. Mullenborn, and S. Bouwstra, "Fabrication and characterization of truly 3-D diffuser/nozzle microstructures in silicon," Microelectromechanical Systems, Journal of, vol. 6, pp. 41-47, 1997. S. Maruo, K. Ikuta, and H. Korogi, "Forcecontrollable, optically driven micromachines fabricated by single-step two-photon microstereolithography," Microelectromechanical Systems, Journal of, vol. 12, pp. 533-539, 2003. W. H. Teh, C.-T. Liang, M. Graham, and C. G. Smith, "Cross-linked PMMA as a lowdimensional dielectric sacrificial layer," Microelectromechanical Systems, Journal of, vol. 12, pp. 641-648, 2003. J. D. Madden and I. W. Hunter, "Threedimensional microfabrication by localized electrochemical deposition," Microelectromechanical Systems, Journal of, vol. 5, pp. 24-32, 1996. C.-C. Tsao and E. Sachs, "Photoelectroforming: 3-D geometry and materials flexibility in a MEMS fabrication process," Microelectromechanical Systems, Journal of, vol. 8, pp. 161-171, 1999. C. R. Friedrich and M. J. Vasile, "Development of the micromilling process for high-aspect-ratio microstructures," Microelectromechanical Systems, Journal of, vol. 5, pp. 33-38, 1996. M. P. Vogler, R. E. DeVor, and S. G. Kapoor, "Microstructure-level force prediction model for micro-milling of multiphase materials," ASME Journal of Manufacturing Science and Engineering, vol. 125, pp. 202-209, 2003. A. A. Tseng, "Recent developments in micromilling using focused ion beam

[69]

[70]

[71]

[72]

[73]

[74]

[75]

[76]

[77]

technology," Journal of Micromechanics and Microengineering, vol. 14, pp. R15R34, 2004. A. D. Feinerman, R. E. Lajos, V. White, and D. D. Denton, "X-ray lathe: An X-ray lithographic exposure tool for nonplanar objects," Microelectromechanical Systems, Journal of, vol. 5, pp. 250-255, 1996. M. Manohara, E. Morikawa, J. Choi, and P. T. Sprunger, "Transfer by direct photo etching of poly(vinylidene flouride) using X-rays," Microelectromechanical Systems, Journal of, vol. 8, pp. 417-422, 1999. D. Reynaerts, W. Meeusen, X. Song, H. V. Brussel, S. Reyntjens, D. D. Bruyker, and R. Puers, "Integrating electro-discharge machining and photolithography: work in progress," Journal of Micromechanics and Microengineering, vol. 10, pp. 189-195, 2000. K. Takahata and Y. B. Gianchandani, "Batch mode micro-electro-discharge machining," Microelectromechanical Systems, Journal of, vol. 11, pp. 102-110, 2002. S. B. Fuller, E. J. Wilhelm, and J. M. Jacobson, "Ink-jet printed nanoparticle microelectromechanical systems," Microelectromechanical Systems, Journal of, vol. 11, pp. 54-60, 2002. J. A. Rogers, R. J. Jackman, and G. M. Whitesides, "Constructing single- and multiple-helical microcoils and characterizing their performance as components of microinductors and microelectromagnets," Microelectromechanical Systems, Journal of, vol. 6, pp. 184-192, 1997. A. J. Black, P. F. Nealey, J. H. Thywissen, M. Deshpande, N. El-Zein, G. N. Maracas, M. Prentiss, and G. M. Whitesides, "Microfabrication of two layer structures of electrically isolated wires using selfassembly to guide the deposition of insulating organic polymer," Sensors and Actuators A: Physical, vol. 86, pp. 96-102, 2000. C. G. Wilson and Y. B. Gianchandani, "Silicon micromachining using in situ DC microplasmas," Microelectromechanical Systems, Journal of, vol. 10, pp. 50-54, 2001. R.-H. Chen and C.-L. Lan, "Fabrication of high-aspect-ratio ceramic microstructures by injection molding with the altered lost mold technique," Microelectromechanical

[78]

[79]

[80]

[81]

[82] [83]

Systems, Journal of, vol. 10, pp. 62-68, 2001. X.-J. Shen, L.-W. Pan, and L. Lin, "Microplastic embossing process: experimental and theoretical characterizations*1," Sensors and Actuators A: Physical, vol. 97-98, pp. 428-433, 2002. V. Walter, P. Delobelle, P. L. Moal, E. Joseph, and M. Collet, "A piezo-mechanical characterization of PZT thick films screenprinted on alumina substrate," Sensors and Actuators A: Physical, vol. 96, pp. 157-166, 2002. R. J. Jackman, S. T. Brittain, and G. M. Whitesides, "Fabrication of threedimensional microstructures by electrochemically welding structures formed by microcontact printing on planar and curved substrates," Microelectromechanical Systems, Journal of, vol. 7, pp. 261-266, 1998. D. H. Gracias, J. Tien, T. L. Breen, C. Hsu, and G. M. Whitesides, "Forming Electrical Networks in Three Dimensions by SelfAssembly," Science, vol. 289, pp. 11701172, 2000. G. M. Whitesides and B. Grzybowski, "SelfAssembly at All Scales," Science, vol. 295, pp. 2418-2421, 2002. M. Despont, J. Brugger, U. Drechsler, U. Durig, W. Haberle, M. Lutwyche, H.

[84]

[85]

[86]

[87]

[88] [89]

Rothuizen, R. Stutz, R. Widmer, and G. Binnig, "VLSI-NEMS chip for parallel AFM data storage," Sensors and Actuators A: Physical, vol. 80, pp. 100-107, 2000. S. Y. Chou, P. R. Krauss, and P. J. Renstrom, "Imprint of sub-25 nm vias and trenches in polymers," Applied Physics Letters, vol. 67, pp. 3114-3116, 1995. Y. Zhang, K. Salaita, J.-H. Lim, and C. A. Mirkin, "Electrochemical Whittling of Organic Nanostructures," Nano Letters, vol. 2, pp. 1389-1392, 2002. A. J. Haes and R. P. V. Duyne, "A Nanoscale Optical Biosensor: Sensitivity and Selectivity of an Approach Based on the Localized Surface Plasmon Resonance Spectroscopy of Triangular Silver Nanoparticles," Journal of American Chemical Society, vol. 124, pp. 1059610604, 2002. A. Shah, P. Torres, R. Tscharner, N. Wyrsch, and H. Keppner, "Photovoltaic Technology: The Case for Thin-Film Solar Cells," Science, vol. 285, pp. 692-698, 1999. R. F. Service, "ELECTRONICS: Organic Device Bids to Make Memory Cheaper," Science, vol. 293, pp. 1746a-, 2001. C. Kim, P. E. Burrows, and S. R. Forrest, "Micropatterning of Organic Electronic Devices by Cold-Welding," Science, vol. 288, pp. 831-833, 2000.