LOW-PRESSURE ACOUSTIC SENSORS FOR AIRBORNE SOUND WITH PIEZORESISTIVE MONOCRYSTALLINE SILICON AND ELECTROCHEMICALLY ETCHED DIAPHRAGMS

In this paper experimental results and theoretical considerations of a n acoustic silicon sensor for airborne sound, which is based on boron- implanted monocrystalline piezoresistors located on an electrochemical ly etched silicon diaphragm, are presented. The bandwidth of the senso r is nearly 20 kHz (full audio bandwidth), a maximum sensitivity of 80 mu V Pa-1 (bias voltage, 8 V) was achieved and a lowest equivalent no ise level of about 61 dB(A) was measured. The membrane thickness is ab out 1.3 mu m; the membrane area amounts to 1 mm(2). Furthermore, a goo d reproducibility and linearity could be obtained. The weak sensitivit y can mainly be explained by a residual inherent tensile stress in the silicon-silicon dioxide-silicon nitride layer system of the diaphragm and by the large geometric dimensions of the resistors.