Low pressure acoustic sensors for airborne sound with piezoresistive monocrystalline silicon and electrochemically etched diaphragms

TLDR: In this paper, an acoustic silicon sensor for airborne sound, which is based on boron-implanted monocrystalline piezoresistors located on an electrochemically etched silicon diaphragm, is presented.

Abstract: In this paper experimental results and theoretical considerations of an acoustic silicon sensor for airborne sound, which is based on boron-implanted monocrystalline piezoresistors located on an electrochemically etched silicon diaphragm, are presented. The bandwidth of the sensor is nearly 20 kHz (full audio bandwidth), a maximum sensitivity of 80 μV Pa −1 (bias voltage, 8 V) was achieved and a lowest equivalent noise level of about 61 dB(A) was measured. The membrane thickness is about 1.3 μm; the membrane area amounts to 1 mm 2 . Furthermore, a good reproducibility and linearity could be obtained. The weak sensitivity 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.