MEASUREMENTS OF THE MECHANICAL-BEHAVIOR OF MICROMACHINED SILICON AND SILICON-NITRIDE MEMBRANES FOR MICROPHONES, PRESSURE SENSORS AND GAS-FLOW METERS

This paper mainly presents the experimental determination of the small deflection behaviour of boron-implanted silicon-nitride and highly boron-doped silicon diaphragms for micromachined silicon subminiature microphones. The additional implantation of boron into silicon-nitride diaphragms reduces the intrinsic stress in the deposited amorphous films. The minimum detectable deflection, using a Mach-Zehnder interferometer, is about 0.02 nm for dynamic measurements (A-weighted filtering). The largest measurable deflection (where nonlinearities of the interferometer are negligible) is strongly influenced by the wavelength of the laser and is about 10 nm. Thus, applying this method to pressure sensors and ps flow meters, the pressure range is restricted. In order to achieve a high sensitivity of the measuring apparatus and a low detectable deflection amplitude a feedback configuration stabilizes the interferometer in the most sensitive operation points.