Performance of Packaged Piezoelectric Microspeakers Depending on the Material Properties

This paper presents the improved piezoelectric microspeakers that implement a packaging structure with AlN film and are made of composite diaphragms of different residual stresses. The output Sound Pressure Level (SPL) is enhanced more than 10 dB with a higher compressively stressed composite diaphragm (having -20 MPa silicon nitride film as a supporting layer) from 100 Hz to 3 kHz. The best microspeaker produces more than 100 dB SPL into open field around 3 kHz (when measured 10 mm away from the speaker that is driven with 20 V_peak-to-peak sinusoidal signal). A microspeaker with a square electrode pattern produces more uniform frequency response above 4 kHz than that with a circular electrode pattern.