Capillary effect based selective sealing strategy for boosting the piezoelectric MEMS speaker performance

Abstract To address the serious acoustic performance deterioration induced by the air leakage and the asynchronous vibration in the electro-acoustic transduction structures, a novel sealing strategy is proposed targeting to one of the most widely reported piezoelectric MEMS speaker designs that consists of multi cantilever beams, in which an automatic and selective filling of the liquid polydimethylsiloxane (PDMS) to the air gaps between cantilevers under the capillary effect followed by curing is developed. In the proof-of-concept demonstration, an obvious enhancement in sound pressure level (SPL) within frequency range lower than 100 Hz after sealing is experimentally demonstrated, in which the SPL is increased by 4.9 dB at 20 Hz. At the same time, the deteriorated SPL response near the resonant frequencies of the cantilever beams (17 kHz-17.5 kHz) caused by their asynchronous vibration that is induced by the fabrication process non-uniformity is also significantly improved and a boosted SPL of around 15 dB is successfully achieved. Moreover, nearly the same SPL response as the initial counterpart in the frequency band from 100 Hz to 16 kHz and even smaller total harmonic distortion (THD) of 0.728% at 1 kHz under 40 V pp driving voltage can be obtained in the sealed devices. In comparison to the existing sealing methods, the current approach offers easy operation, low damage risk, excellent repeatability/reliability and excellent robustness advantages, and provides a promising technical solution for the MEMS acoustic devices.