ABSTRACT
The advances in silicon photolithographic process technology since the 1960s have led to the development of microcomponents (or microdevices) known as microelectromechanical systems (MEMS). More recently, lithographic processes have been developed to process non-silicon materials. These lithographic processes are being complemented with nonlithographic micromachining processes for fabrication of milliscale components or devices. Using these fabrication processes, researchers have fabricated a wide variety of miniaturized devices, such as acceleration, pressure, and chemical sensors; linear and rotary actuators; electric motors; gear trains; gas turbines; nozzles; pumps; fluid valves; switches; grippers; tweezers; and optoelectronic devices with dimensions in the range of a couple to a few thousand microns (for an early review, see Peterson, 1982; for recent reviews, see Muller et al., 1990; Madou, 1997; Trimmer, 1997; and Bhushan, 1998a). MEMS technology is still in its infancy and the emphasis to date has been on the fabrication and laboratory demonstration of individual components. MEMS devices have begun to be commercially used, particularly in the automotive industry. Silicon-based high-G acceleration sensors are used in airbag deployment (Bryzek et al., 1994). Acceleration sensor technology is slightly less than a $1 billion-a-year industry, dominated by Lucas NovaSensor and Analog Devices. The digital micromirror devices (DMDs) provided by Texas Instruments are large-scale, integrated spatial light modulators (Hornbeck, 1989). These use deformable mirror arrays on microflexures as part of airlineticket laser printers and high-resolution projection devices.
