We proposed a PZT-film-based piezoelectric micromachined ultrasonic transducer (pMUT) with an I-shaped composite diaphragm to improve the sensitivity and resonant frequency of pMUTs with the same diaphragm area. The finite element method (FEM) simulation results indicated that the pMUT with an I-shaped composite diaphragm had relatively high sensitivity and resonant frequency. The pMUT with an I-shaped diaphragm had a 36.07% higher resonant frequency than a pMUT with a circular diaphragm. The pMUT with an I-shaped diaphragm had a 3.65 dB higher loop gain (loss) than a pMUT with a rectangular diaphragm. The piezoelectric layer thickness of the pMUT with an I-shaped composite diaphragm was then optimized. Maximum loop gain (loss) was reached when the piezoelectric layer thickness was 8 μm. The pMUT with an I-shaped composite diaphragm was fabricated using the MEMS method, and its performance was evaluated.

In this paper, a novel dual-mass MEMS piezoelectric vector hydrophone is proposed to eliminate the transverse effect and solve the problem of directivity offset in traditional single-mass MEMS piezoelectric vector hydrophones. The reason for the directional offset of the traditional single-mass cantilever MEMS piezoelectric vector hydrophone is explained theoretically for the first time, and the angle of the directional offset is predicted successfully. Both analytical and finite element methods are employed to analyze the single-mass and dual-mass cantilever MEMS piezoelectric vector hydrophone. The results show that the directivity of the dual-mass MEMS piezoelectric vector hydrophone has no deviation, the transverse effect is basically eliminated, and the directivity (maximum concave point depth) is significantly improved, so more accurate positioning can be obtained.

MEMS hydrophones, as critical sensors for maritime security and underwater information acquisition, have sensitive membrane structures that exhibit insufficient ability to withstand hydrostatic pressure, necessitating an overload-protection design. Based on buckling stability theory, a collaborative optimization method for overload-protection column design was proposed, integrating theoretical analysis, finite-element simulation, and process feasibility. An optimized design scheme for hydrophone overload-protection columns was established by comprehensively considering geometric buckling-resistant design, micro-gap anti-adhesion requirements, minimal impact on sensitivity, and micro/nano-fabrication constraints. The results indicate that intermediate slenderness columns with radii between 5.5 μm and 7.5 μm sufficiently meet both fabrication and operational requirements, effectively providing overload protection. Furthermore, at water depths not exceeding 382 m, the MEMS hydrophone can maintain the integrity of its membrane structure without column buckling.

In order to simultaneously improve the imaging resolution and sensitivity of piezoelectric micromachined ultrasonic transducers (pMUTs), a pMUT with an I-shaped composite diaphragm was developed in this work. Compared with the conventional rectangular diaphragm structure, the I-shaped structure is formed by removing the piezoelectric layer along the edges of the two long sides while retaining the remaining portion. By this design, the residual stress of the piezoelectric film is effectively reduced, and both the sensitivity and the resonant frequency of the pMUT are improved. Moreover, unlike existing residual-stress-releasing structures such as hole- or groove-etched structures, where the diaphragm is no longer a continuous membrane and through-thickness holes or grooves are present, only the piezoelectric layer is etched in the proposed design. Consequently, no additional packaging requirements are imposed on the composite diaphragm, and the intricate sealing issue associated with through-hole structures is circumvented. A comprehensive comparison from multiple aspects was performed between ZnO-based and AlN-based pMUTs. It was shown by simulation results that the ZnO-based pMUT was superior to the AlN-based counterpart in terms of transmitting sensitivity, receiving sensitivity, and loop gain. On this basis, the ZnO-based pMUT with an I-shaped diaphragm was successfully fabricated and characterized. The performance of the PMUT was evaluated in electronic fluorinated fluid (FC-3283). The results show that the device exhibits a resonant frequency of 10 MHz, with a transmitting sensitivity level of 173.5 dB (re 1 μPa/V), a receiving sensitivity level of −242.1 dB (re 1 V/μPa), a loop gain of −68.6 dB, and a −6 dB bandwidth of 10.65%. These results indicate that high sensitivity was achieved at a high operating frequency, providing a technical reference for the design and application of high-frequency, high-sensitivity pMUT arrays, and demonstrating considerable potential for applications in underwater detection, ultrasonic imaging, and beyond.