MOVING THE WORLD WITH SURFACE MICROMACHINING

Surface micromachining is a process whereby miniature mechanical devic es, both sensors and actuators, are made using a variation of integrat ed circuit manufacturing technology. The first surface micromachined d evice was the resonant gate transistor, demonstrated almost 30 years a go [1], consisting of a transistor with a free-standing metal cantilev er beam as the transistor gate. Polycrystalline silicon (polysilicon) surface micromachining was described over a dozen years ago [2]. Since then, numerous prototypes for sensing devices and, recently, the firs t marketable sensors [3] have been developed. Actuators, surface micro machined devices that can do work on their environment, have been more elusive. Phenomena that are inconsequential in the normal scale of th ings become dominant at sub-millimeter dimensions. Surface tension, wh ich allows a mosquito to walk on water, is one notorious example. Thes e phenomena affect ''normal'' friction and wear, which, although adequ ately controlled in large-scale machinery, must be re-examined at a fu ndamental level when considering microdevices. Despite these issues, m icroactuation with surface-micromachined devices is finally taking hol d.