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. 2021 Mar 5;21(5):1823.
doi: 10.3390/s21051823.

Development of Broadband High-Frequency Piezoelectric Micromachined Ultrasonic Transducer Array

Xu-Bo Wang  1 , Le-Ming He  1 , You-Cao Ma  1 , Wen-Juan Liu  1   2 , Wei-Jiang Xu  2   3 , Jun-Yan Ren  1 , Antoine Riaud  1 , Jia Zhou  1
Affiliations

Development of Broadband High-Frequency Piezoelectric Micromachined Ultrasonic Transducer Array

Xu-Bo Wang et al. Sensors (Basel). .

Abstract

Piezoelectric micromachined ultrasonic transducers (PMUT) are promising elements to fabricate a two-dimensional (2D) array with a pitch small enough (approximately half wavelength) to form and receive arbitrary acoustic beams for medical imaging. However, PMUT arrays have so far failed to combine the wide, high-frequency bandwidth needed to achieve a high axial resolution. In this paper, a polydimethylsiloxane (PDMS) backing structure is introduced into the PMUTs to improve the device bandwidth while keeping a sub-wavelength (λ) pitch. We implement this backing on a 16 × 8 array with 75 µm pitch (3λ/4) with a 15 MHz working frequency. Adding the backing nearly doubles the bandwidth to 92% (-6 dB) and has little influence on the impulse response sensitivity. By widening the transducer bandwidth, this backing may enable using PMUT ultrasonic arrays for high-resolution 3D imaging.

Keywords: PDMS; PMUT; PZT; high-frequency; micromachining; rangefinder; two-dimensional array; wide bandwidth.

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Conflict of interest statement

The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.

Figures

Figure 1
Figure 1
Schematic of backed piezoelectric micromachined ultrasonic transducers (B-PMUTs). (a) The designed structure of a single element. (b) Three-dimensional (3D) schematic of the array.
Figure 2
Figure 2
(a–i) The fabrication process of the B-PMUTs.
Figure 3
Figure 3
Microscopy pictures of B-PMUTs. (a) Top view of a part of 16 × 8 PMUTs arrays. (b) Cross-sectional SEM image of a typical element without PDMS backing. (c) Cross-sectional SEM image of the element with PDMS filling.
Figure 4
Figure 4
Laser Doppler vibrometer (LDV) setup for characterizing the PMUT performance.
Figure 5
Figure 5
The first resonance mode of the devices working under water load for (a) a control group without PDMS backing (C-PMUT) and (b) B-PMUT.
Figure 6
Figure 6
Peak displacement at the center of a B-PDMS element tested in air with a 10 ns 30 V pulse. The insert figure shows the detailed response from 2.9 to 4 µs.
Figure 7
Figure 7
Vibration response of (a) C-PMUT and (b) B-PMUT, tested in water with a 10 ns 30 V pulse. The time-domain response is shown with a red solid line, and the frequency-domain response is shown with a blue dash line.
Figure 8
Figure 8
Comparison of working frequency, pitch, and bandwidth of different types of PMUTs under fluid load. The values in the label are the bandwidths (from references) normalized to our study. The hollow square represent the results in the published literature, and the solid star represents the results given in this study.
See this image and copyright information in PMC

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