IC-Processed piezoelectric microphone

A miniature diaphragm pressure transducer having sensitivity to acoustic signals at the level of conversational speech has been fabricated by combining micromachining procedures (to produce a thin silicon-nitride diaphragm) with ZnO thin-film processing. The sensor consists of a patterned ZnO layer (which acts as a piezoelectric transducer) deposited on a thin square micromachined diaphragm made of LPCVD silicon nitride. The diaphragm, 2 µm in thickness, is the thinnest yet reported for a piezoelectric readout structure of relatively large area (3 × 3 mm
²
). The transducer shows an unamplified response of roughly 50 µV/µbar when excited by sound waves at 1 kHz with the variation of the sensitivity from 20 Hz to 4 kHz being approximately 9 dB. These results are obtained using a 0.1-mm-wide annular pattern that measures 3.6 mm in circumference.