Multi-Way In-Phase/Out-of-Phase Driving Cantilever Array for Performance Enhancement of PZT MEMS Microspeaker

Abstract

This study presents a broadband piezoelectric MEMS microspeaker based on the design of cantilever array and novel driving method in Fig. 1a. Two main points are featured in this study: (1) The design of multi-way microspeaker with cantilever array: to improve the bandwidth of the microspeaker. The SPL is enlarged in selected frequency ranges contributed by the different resonant frequencies of each cantilever; (2) The out-of-phase driving of each cantilever after resonance: to prevent the sound pressure cancellation between cantilevers resulted from the 180° structural phase shift after resonance. In comparison, Fig. 1b shows two different driving approaches. Measurement results show the highest SPL of 110dB at 1540Hz in ear simulator system with a driving voltage of 2V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">pp</sub> under 4mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> diaphragm area. In addition, out-of-phase driving promises an improvement of 27dB at 3.7kHz where sound pressure cancellation took place. A broadband frequency response is obtained between 100Hz~10kHzwith an SPL of 70dB or higher with out-of-phase driving. With multi-way cantilever array design and in-phase/out-of-phase hybrid-driving, a high SPL and broadband microspeaker is realized.