Sound Pressure and Low Frequency Enhancement Using Novel PZT MEMS Microspeaker Design

Abstract

This study presents the piezoelectric MEMS microspeaker design in Fig. 1a with four triangular plates, a connection mass, and dual driving electrodes (inner and outer electrodes) to increase the sound pressure level (SPL). By integrating the microspeaker on chip, for example the array with 5 microspeakers in Fig. 1b, the SPL could be further increased. This study exhibits two merits: (1) The inner and outer electrodes on triangular plates (Fig. 1c) are driven with 180° out-of-phase to actuate the piston mode of structure to increase the SPL; (2) The connection mass synchronizes the vibration of the four plates to reduce the gap size surrounding the plates for low frequency sound pressure enhancement. Measurements show the SPL enhancement of the proposed dual electrode driving is 9.5dB as compared with the single (inner or outer) electrode driving. Measurements in the standard ear simulator indicate the presented microspeaker array has the SPL of 81.4dB at 100Hz and the SPL of 84.7dB at 1kHz. The results show that the presented design exhibits good SPL at low frequency. Moreover, the proposed microspeaker array (5 microspeakers) presents ±3dB bandwidth between 100Hz~2.1kHz, and the highest SPL of 118.1dB at 11.9kHz 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.