Abstract
This study presents a design to monolithically integrate audio filters in piezoelectric MEMS microspeaker to modulate frequency response and total harmonic distortion (THD). The proposed design has two major features: (1) leverage the advantages afforded by micromachining technology to integrate audio filters composed of passive (electronic) components and piezoelectric microspeaker onto a single chip; (2) the two-stage filter is implemented on the commonly ineffectively utilized anchor area of MEMS microspeaker to achieve selectable low-pass filtering effect that adequately modulate the bandwidth and reduce the THD. Measurements conducted using the standard ear simulator demonstrate that with the 1st stage filter, the upper limit of 85±5dB bandwidth of the microspeaker is extended from 2.2kHz to 2.9kHz, with 21.7% improvement in THD at subharmonic frequency and a 4.1% reduction at resonant frequency. With the 2nd stage filter, flat bandwidth is further extended to 3.7kHz. THD is improved by 38.3% at subharmonic and 4.9% at resonant frequency.