Design and fabrication of movable silicon plates suspended by flexible supports

A process for fabricating silicon plates of varying thicknesses suspended by thin, flexible polyimide arms has been developed. The process uses bulk micromachining techniques and consists of four steps: a diaphragm etch from the back of the wafer; a trench etch from the front side (to define the plates); deposition and patterning of the plate support beams; and a self-aligned backside plasma etch to release the plates. The authors have used this process to fabricate square silicon plates two millimeters on a side and 7-10-μm-thick suspended by polyimide beams 500-μm long, 4-μm thick, and 100-200-μm wide. By evaporating aluminum on the topside of the plates, it was possible to deflect them electrostatically approximately 60 μm at 40 V applied voltage. These structures were designed for application as micromachined mirrors, although their sensitivity to motion and electrical and thermal isolation suggest other potential applications such as gas sensors, flow sensors, and accelerometers