A Multi-Frequency pMUT Array Based on Ceramic PZT for Endoscopic Photoacoustic Imaging

This paper presents, for the first time, a multifrequency piezoelectric micromachined ultrasonic transducer (pMUT) array for endoscopic photoacoustic imaging applications. With a chip size of 3.5 × 3.5 mm2, the pMUT array consists of 285 pMUT elements with seven different resonant frequencies ranging from 1 MHz to 8 MHz. The pMUT array has been fabricated on a 9 µm-thick layer of ceramic PZT with high piezoelectric constants. Mechanical vibration tests have shown high voltage-to-displacement gains, e.g., 130 nm/V, 35 nm/V, and 8 nm/V for the pMUT elements at their resonances of 1.2 MHz, 3.7 MHz, and 7.8 MHz, respectively. Ultrasound signals with frequencies from 300 kHz to 8 MHz have been successfully generated and detected by a pair of fabricated pMUT arrays. Furthermore, photoacoustic imaging experiments have been conducted, demonstrating the advantages of using multi-frequency pMUT arrays to provide comprehensive photoacoustic images with high signal-to-noise ratio and high spatial resolution.