On the design of a two-way piezoelectric MEMS microspeaker based on a multi-shape cantilever array for high-frequency applications

Abstract

This study presents the design and realization of a piezoelectric MEMS microspeaker for high-frequency enhancement. Based on piezoelectric thin film actuation, designs of cantilever diaphragms are conducted by modal analysis. Under a die size of 2.5 mm (w) × 5 mm (l) × 0.4 mm (t), the diaphragms are designed to include mid-range and tweeter units with regard to the balance of radiation area and sound pressure contribution. Furthermore, the out-of-phase driving of the proposed device can ensure that the superposition of the sound pressure level (SPL) is within the target frequency range (8–13 kHz) while reducing the SPL outside the target range. In pressure-field measurements, the proposed multi-shape cantilever array can produce high average SPL (91.6 dB) in the target frequency range from 8 kHz to 13 kHz and has a low total harmonic distortion (THD) of <1.4% under a 0.707 Vrms input signal. The performance can be further improved by biasing the input signal. With a 9 V bias, the average SPL of the proposed microspeaker in the target frequency range is enhanced to 99.4 dB, and the average THD is reduced to <0.7%. In addition, the THD from 7.7 kHz to 18 kHz is below 2.5%. This study shows the great potential of piezoelectric MEMS microspeakers for in-ear applications.