PIEZOELECTRIC CANTILEVER MICROPHONE AND MICROSPEAKER

A micromachined piezoelectric cantilever transducer, which works both as a microphone and as a microspeaker, has been fabricated and tested, The 2000 x 2000 x 4.5 mu m(3) cantilever has a zinc oxide (ZnO) piezo electric thin film on a supporting layer of low-pressure chemical-vapo r-deposited (LPCVD) low-stress silicon nitride, A highlight of the fab rication process, which may also be relevant for other micromachined s tructures, is the technique for producing a Bat, multilayer cantilever . The measured microphone sensitivity is fairly constant at 3 mV/mu ba r in the low frequency range and rises to 20 mV/mu bar at the lowest r esonant frequency of 890 Hz. The 3 mV/mu bar sensitivity is the highes t reported to date for a microphone with a micromachined diaphragm. Wh en measured into a 2 cm(3) coupler with 4 V(zero-peak) drive, the micr ospeaker output sound pressure level (SPL) is 75 dB at 890 Hz. It incr eases to approximately 100 dB SPL at 4.8 kHz with 6 V(zero-peak) drive . The measured microphone frequency response agrees well with the resu lts of an ABAQUS simulation.