ABSTRACT
With the proven record of accomplishment in very large integrated circuits (VLSI) brought about by batch-fabrication technology for electronic devices of ever-decreasing size, there is widespread enthusiasm about emerging opportunities to design mixed micromechanical and microelectronic systems. New development, based heavily on integrated-circuit-related technologies, have led to rapid progress in the development of microdynamic systems. These systems are based upon the science, technology, and design of moving micromechanical devices, and are a subclass of what is known in the U.S. as microelectromechanical systems (MEMS). The dimensions of the micromechanical devices in MEMS are typically smaller than 100 p.m. Recent rapid progress gives promise for new designs of integrated sensors, actuators, and other devices that can be combined with on-chip microcircuits to make possible high-performing, compact, portable, low-cost engineering systems. Mechanical materials for some of the microdynamic systems that have thus far been demonstrated consist of deposited thin films of polycrystalline silicon, silicon nitride, aluminum, polyimide, and tungsten among other materials. To make mechanical elements using thin-film processing, microstructures are freed from the substrate by etching a sacrificial layer of silicon dioxide. First demonstrated as a means to produce electrostatically driven, doubly supported beam bridges, this sacrificial-layer technology has proved very versatile and has been used to make, among other structures, laterally vibrating doubly folded bridges, gears, springs, and impacting microvibromotors. Recently, micromirrors that consist of multiple hinged plates which 674fold out of the surface plane in which they are formed (reaching vertical heights of millimeter dimensions) have been demonstrated. The polycrystalline silicon cross section for these mirrors is thinner than 2 μm. The mirrors can be moved using electrostatic comb drives or microvibromotors. Continued research on the mechanical properties of the electrical materials forming microdynamic structures (which previously had exclusively electrical uses), on the scaling of mechanical design, on tribological effects, on coatings, and on the effective uses of computer aids is now under way. This research promises to provide the engineering base that will exploit this promising technology.
