Piezoelectric cantilever voltage-to-frequency converter

Abstract

A micromachined piezoelectric cantilever acoustic device that functions as a microspeaker and a voltage-to-frequency converter has been designed, 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 supporting layer of LPCVD low-stress silicon nitride. When measured with 8 VP-P (peak-peak) input drive, the sound pressure level (SPL) of the cantilever 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 frequency of the microspeaker is changed by the potential applied between the top plate and the backside Al layer. As the potential is changed from 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 fairly linear with the potential change and the sensitivity (frequency shift/applied potential change) is 200 Hz/V around 13 kHz. (C) 1998 Elsevier Science S.A. All rights reserved.