On the design of piezoelectric MEMS microspeaker for the sound pressure level enhancement

Abstract

This study aims to design and realize MEMS microspeakers with high sound pressure level (SPL) for in-ear applications. On the basis of high piezoelectric coefficient PZT thin film, the proposed suspension-spring and dual-electrode designs enhance the out-of-plane displacement of central diaphragm to improve low-frequency SPL. The preliminary tests show that both proposed single-curve and dual-curve spring designs have higher low-frequency SPL than that of the reference clamped diaphragm microspeaker. Measured in the standard ear simulator systems with 2 Vpp driving voltage, the proposed dual-curve spring design demonstrates good performance at low frequencies. At the resonant frequency of 1.85 kHz, the dual-curve spring design is 28 dB SPL higher than the clamped diaphragm. In addition, from 100 Hz to 3 kHz, more than 10 dB SPL enhancement is achieved. Furthermore, the total harmonic distortion (THD) of dual-curve spring design is less than 2% in most of the audio range. Compared with the published literature of piezoelectric MEMS microspeakers, this study shows a reasonable SPL with the smallest diaphragm area of 1 mm2.