Low Frequency Sound Pressure Level Improvement of Piezoelectric Mems Microspeaker Using Novel Spiral Spring with Dual Electrode

Abstract

Extending the approach in the previous work [1], this study presents a piezoelectric actuation MEMS microspeaker with novel spring design to achieve high sound pressure level (SPL) at low frequencies for in-ear applications. The soft PZT/Si unimorph springs enable larger out-of-plane displacement to enhance SPL. With the proposed spiral-spring design, longer spring length (compared with [1]) and lower resonant frequency are achieved to improve SPL at low frequencies. Moreover, the spiral spring has simple stress distribution during actuation to ease electrical routings and also increase the net driving output for piezoelectric films, thus the dual driving electrodes to increases diaphragm out-of-plane displacement and SPL is achieved. Measurements demonstrate 79.5dB SPL (72.6dB SPL for [1]) with only 2V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">pp</sub> driving voltage and 1mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> diaphragm area at 1kHz in a 3cm long canal. Furthermore, 106.8dB SPL is observed with 15V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">pp</sub> at 1.85kHz without any structure damage.