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Article

Piezoelectric MEMS Acoustic Transducer with Electrically-Tunable Resonant Frequency

1
Department of Information Engineering, University of Brescia, 25123 Brescia, Italy
2
CNRS, Grenoble INP, TIMA, University Grenoble Alpes, 38000 Grenoble, France
*
Author to whom correspondence should be addressed.
Academic Editor: Jose Luis Sanchez-Rojas
Micromachines 2022, 13(1), 96; https://doi.org/10.3390/mi13010096
Received: 20 December 2021 / Revised: 3 January 2022 / Accepted: 6 January 2022 / Published: 8 January 2022
(This article belongs to the Special Issue Micromachined Acoustic Transducers for Audio-Frequency Range)
The paper presents a technique to obtain an electrically-tunable matching between the series and parallel resonant frequencies of a piezoelectric MEMS acoustic transducer to increase the effectiveness of acoustic emission/detection in voltage-mode driving and sensing. The piezoelectric MEMS transducer has been fabricated using the PiezoMUMPs technology, and it operates in a plate flexural mode exploiting a 6 mm × 6 mm doped silicon diaphragm with an aluminum nitride (AlN) piezoelectric layer deposited on top. The piezoelectric layer can be actuated by means of electrodes placed at the edges of the diaphragm above the AlN film. By applying an adjustable bias voltage Vb between two properly-connected electrodes and the doped silicon, the d31 mode in the AlN film has been exploited to electrically induce a planar static compressive or tensile stress in the diaphragm, depending on the sign of Vb, thus shifting its resonant frequency. The working principle has been first validated through an eigenfrequency analysis with an electrically induced prestress by means of 3D finite element modelling in COMSOL Multiphysics®. The first flexural mode of the unstressed diaphragm results at around 5.1 kHz. Then, the piezoelectric MEMS transducer has been experimentally tested in both receiver and transmitter modes. Experimental results have shown that the resonance can be electrically tuned in the range Vb = ±8 V with estimated tuning sensitivities of 8.7 ± 0.5 Hz/V and 7.8 ± 0.9 Hz/V in transmitter and receiver modes, respectively. A matching of the series and parallel resonant frequencies has been experimentally demonstrated in voltage-mode driving and sensing by applying Vb = 0 in transmission and Vb = −1.9 V in receiving, respectively, thereby obtaining the optimal acoustic emission and detection effectiveness at the same operating frequency. View Full-Text
Keywords: MEMS; piezoelectric; PiezoMUMPs; acoustic transducer; tunable; resonant frequency; finite element modelling MEMS; piezoelectric; PiezoMUMPs; acoustic transducer; tunable; resonant frequency; finite element modelling
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MDPI and ACS Style

Nastro, A.; Ferrari, M.; Rufer, L.; Basrour, S.; Ferrari, V. Piezoelectric MEMS Acoustic Transducer with Electrically-Tunable Resonant Frequency. Micromachines 2022, 13, 96. https://doi.org/10.3390/mi13010096

AMA Style

Nastro A, Ferrari M, Rufer L, Basrour S, Ferrari V. Piezoelectric MEMS Acoustic Transducer with Electrically-Tunable Resonant Frequency. Micromachines. 2022; 13(1):96. https://doi.org/10.3390/mi13010096

Chicago/Turabian Style

Nastro, Alessandro, Marco Ferrari, Libor Rufer, Skandar Basrour, and Vittorio Ferrari. 2022. "Piezoelectric MEMS Acoustic Transducer with Electrically-Tunable Resonant Frequency" Micromachines 13, no. 1: 96. https://doi.org/10.3390/mi13010096

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