Piezoelectric membrane acoustic devices

This paper reports the 3/spl times/3/spl times/0.003 mm/sup 3/ piezoelectric membrane acoustic device, which works as a microphone and a microspeaker. It has a 0.5 /spl mu/m thick zinc oxide (ZnO) piezoelectric thin film on a 1.5 /spl mu/m thick low stress silicon nitride membrane, made of LPCVD. The maximum deflection in the center of membrane, using laser Doppler vibrometer, is 1 /spl mu/m at 7.3 kHz with input drive 15 V/sub P-K/ (zero-peak). The output sound pressure level (SPL) of microspeaker is 76.3 dB SPL at 7.3 kHz, and 83.1 dB SPL at 13.3 kHz with input drive 15 V. The distance between reference microphone and piezoelectric microspeaker is 1 cm. The sensitivity of microphone is 0.51 mV/Pa at 7.3 kHz with noise level of 18 dB SPL.