FABRICATION AND CHARACTERIZATION OF SILICON MICROMACHINED THRESHOLD ACCELEROMETERS

This paper describes the development of a threshold accelerometer for sensing very high acceleration levels. The device, which is fabricated by silicon micromachining techniques, comprises an array of eight normally open switches, each having a different acceleration threshold. Each switch is a miniature silicon dioxide cantilever beam, only 2.2-mu-m in thickness, with metallization running along its length and fabricated on the surface of a silicon wafer. Under an applied acceleration, the cantilever beam deflects across a 2.5-mu-m gap and makes contact with another electrode, thus closing a switch. Electrostatic and static centrifuge testing have been performed on the devices. Closing the switches (beams 120 to 400-mu-m long and 80-mu-m wide) electrostatically with voltages in the 10 to 70 V region provides a convenient way to pre-test the beams for closure. Under static centrifuge testing, a maximum of 20 000 g was measured with a cantilever beam 180-mu-m long and 80-mu-m wide.