Dependence of material properties on piezoelectric microspeakers with AlN thin film

This paper reports the dependence of residual stress on the piezoelectric microspeakers that are audible in open air with high quality piezoelectric AlN thin film deposited onto Mo/Ti electrode. This successful achievement is followed by using a compressively stressed silicon nitride film as a supporting diaphragm and high quality AlN thin film with compressive residual stress (less than -100 MPa). The sound pressure level (SPL) is relatively small when we use a tensile stressed silicon nitride film, the SPL of the fabricated microspeakers that have compressively stressed composite diaphragm shows more than 60 dB from 100 Hz to 15 kHz and the highest SPL is about 100 dB at 9.3 kHz with 20 V_peak-to-peak sinusoidal input biases and 10 mm distances from the fabricated microspeakers to the reference microphone. The packaging structure enhances the low frequency characteristics significantly.