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The fabrication process and the properties of a capacitive silicon sensor for the detection of airborne sound are described. The device consists of two chips; one chip carries a 150-nm-thick silicon nitride membrane of 0.8×0.8 mm2 , and the second chip represents a complete back plate including the back electrode and the air gap spacer. Both chips are produced by means of an orientation-dependent etching procedure. The overall dimensions of the transducer are 1.7×2×0.6 mm3 . Measurements of the acoustic properties yield sensitivities between −60 and −90 dB re: 1 V/Pa, depending on the tension of the diaphragm. The most sensitive microphones have a frequency response extending up to 2 kHz, while the less sensitive transducers have higher cutoff frequencies.
Hohm et al. (Sun,) studied this question.