Progress in MEMS and micro systems research

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]. Ink reservoir heater