PIEZOELECTRIC CANTILEVER VOLTAGE-TO-FREQUENCY CONVERTER

A micromachined piezoelectric cantilever acoustic device that function s as a microspeaker and a voltage-to-frequency converter has been desi gned, fabricated and tested. The 2 x 2 x 0.0047 mm(3) cantilever has a 1.3-mu m-thick zinc oxide (ZnO) piezoelectric thin film on a supporti ng layer of LPCVD low-stress silicon nitride. When measured with 8 VP- P (peak-peak) input drive, the sound pressure level (SPL) of the canti lever microspeaker output is higher than 70 dB at 5 kHz at a distance of 0.5 cm. The microspeaker also can be used as a voltage-to-frequency converter by the addition of a silicon top plate and an aluminum (Al) sputtered layer on the backside of the cantilever. The resonant frequ ency of the microspeaker is changed by the potential applied between t he top plate and the backside Al layer. As the potential is changed fr om 0 to 40 VP-P, the resonant frequency shifts down from 14.5 to 11.5 kHz. In the potential range of 15 to 25 VP-P, the frequency shift is f airly linear with the potential change and the sensitivity (frequency shift/applied potential change) is 200 Hz/V around 13 kHz. (C) 1998 El sevier Science S.A. All rights reserved.