A PIEZOELECTRIC MEMS SPEAKER WITH STRETCHABLE FILM SEALING

This paper reports a solution to acoustic short circuit issue of piezoelectric MEMS speakers by sealing slits between actuators with a stretchable film. Validated by simulation and experiment results, sound pressure level (SPL) at low frequency range of a speaker could be improved significantly. With 15 mu m thick stretchable film of polydimethylsiloxane (PDMS), the speaker SPL at 20 Hz increases by about 15 dB. Compared with alternative solutions of plastic film sealing, high sensitivity and resonant frequency of the speaker could be preserved since Young's modulus of the stretchable film is low enough for unconstrained bending of actuator diaphragms. The PDMS sealed MEMS speaker shows flat SPL curve at low frequency range with less than 5 dB variation from 20 Hz to 1 kHz, and excellent THD performance of lower than 1% over most of the whole audible frequency range. In addition, the PDMS sealed MEMS speaker is compatible with standard reflow process. The proposed stretchable film sealing solution is simple to implement and universally applicable to other MEMS speakers.

Automated summary

This paper presents a solution to the acoustic short circuit issue of piezoelectric MEMS speakers by sealing the slits between the actuators with a stretchable film. With the use of a 15 mu m thick stretchable film made of polydimethylsiloxane (PDMS), the speaker's sound pressure level (SPL) at 20 Hz increases by approximately 15 dB. Compared to alternative solutions using plastic film sealing, the proposed method preserves the high sensitivity and resonant frequency of the speaker due to the low Young's modulus of the stretchable film, allowing for unconstrained bending of actuator diaphragms. The PDMS sealed MEMS speaker demonstrates a flat SPL curve at low frequencies with less than 5 dB variation from 20 Hz to 1 kHz and exhibits excellent total harmonic distortion (THD) performance below 1% across most of the audible frequency range. Moreover, this PDMS sealed MEMS speaker is compatible with the standard reflow process and can be universally applied to other MEMS speakers.