High performance piezoelectric MEMS loudspeaker based on an innovative wafer bonding process

• Published in: Sensors and actuators. A. Physical. Vol. 358; p. 114413
• Main Authors: Liechti, Romain, Durand, Stéphane, Hilt, Thierry, Casset, Fabrice, Dieppedale, Christel, Colin, Mikaël
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 16.08.2023; Elsevier
• Subjects: Acoustic Sensors; Acoustics; Actuators (including ultrasonic devices); Mechanics; Physics; Acoustic Sensors; Actuators (including ultrasonic devices)
• ISSN: 0924-4247; 1873-3069
• DOI: 10.1016/j.sna.2023.114413

Despite a significant number of new structures in the past few years, MEMS loudspeaker still are not competitive in terms of performance compared to non-MEMS loudspeakers for free field applications. For industrial perspectives, a high sound pressure level on a wide frequency band is required, as well as a low total harmonic distortion. To widen the frequency range of MEMS loudspeakers, we propose to separate the actuating element from the radiating one, in order to separate design constraints to reach an optimal structure. In this paper, the lumped element model of the loudspeaker in presented, as well as the innovative manufacturing process. Finally, the computed frequency response is compared to the measured one. At the resonance, pressures as high as 110dBSPL at 1kHz and at 10mm are reported for an active surface of 36mm2, which is above the known state of the art for a loudspeaker with similar dimensions. Also, the flatness of the radiated sound pressure in a wide frequency range is closer to the ideal frequency response of loudspeakers than other MEMS loudspeakers, due to the piston mode of the moving rigid plate of the loudspeaker. The total harmonic distortion, mainly due to the nonlinearity of the piezoelectric transduction, is below 5% for reasonable sound pressure levels in the usable frequency band. The use of digital signal processing and of a dedicated packaging will allow our loudspeaker to advantageously replace the main or secondary one in smartphones. [Display omitted] •Simulation of a piezoelectric MEMS loudspeaker using a lumped element model and the two-port formulation.•Measurement of the frequency response of the manufactured loudspeaker.•Pressures of 110 dBSPLat 10 mm and at 1 kHz are reported.•Pressure response is within the tolerances of the simulated one.