PIEZOELECTRIC CANTILEVER ACOUSTIC TRANSDUCER

We present a piezoelectric acoustic transducer fabricated on a bulk-mi cromachined cantilever diaphragm. Use of the cantilever as a supportin g diaphragm produces a highly sensitive microphone. In addition, when the device is driven electrically as an output transducer, a microspea ker, the relatively large deflections produce significant acoustic out put. A voltage-to-frequency converter has also been demonstrated with piezoelectric cantilever transducers. The 2 x 2 x 0.0047 mm(3) microma chined transducer has a zinc oxide (ZnO) piezoelectric thin film on a 1.5 mu m thick cantilever diaphragm, made of LPCVD low-stress silicon nitride. The measured cantilever microphone sensitivity is fairly cons tant around 3 mV mu bar(-1) in the low-frequency range below the first resonant frequency, which occurs at 1.8 kHz. The microspeaker output is approximately 100 dB SPL at 4.8 kHz and 12 VP-P (peak-peak) input d rive. The voltage-to-frequency conversion is accomplished by the addit ion of a conducting plate and an aluminum (Al) sputtered layer on the underside of the cantilever. The resonant frequency of the microspeake r is changed by the potential applied between the top conducting plate and the lower Al layer. As the potential is changed from 0 to 40 VP-P , the resonant frequency shifts down from 14.5 kHz to 11.5 kHz while t he amplitude of the output pressure is increased by 12.5 dB SPL. In th e potential range of 15 to 25 VP-P, the frequency shift is fairly line ar with the potential change and the sensitivity (frequency shift per unit applied potential change) is 200 Hz V-1 around 13 kHz.