Abstract:

Compared to traditional bulk piezoelectric ultrasonic transducers, piezoelectric micromechanical ultrasonic transducers (PMUT) play a crucial role in various application fields due to their advantages such as small size, low power consumption, flexible frequency regulation, and the possibility of integration with CMOS. With the continuous expansion of application demands, new challenges are also posed to key performance indicators of PMUT, such as bandwidth and sensitivity. The article introduces the structure and working mechanism of PMUT, and based on the cavity fabrication methods of PMUT summarizes the fabrication processes and their advantages and disadvantages, including etching, sacrificial release, surface bonding, and silicon migration methods. The article summarizes the research status of PMUT performance optimization strategies from four aspects: piezoelectric materials, device structures, electrode excitation, and acoustic matching.

With high piezoelectric coefficient and low dielectric constant as the optimization objectives for piezoelectric materials, the performance indicators of piezoelectric materials are improved through techniques such as doping, modification, and fabrication process. Based on strategies such as vibration mode transformation, residual stress regulation, acoustic structure integration, and array layout, the PMUT structure is modified to achieve performance optimization. By configuring the static layout of PMUT electrodes and the parameters of the dynamic excitation signals, it is possible to regulate the resonance frequency, bandwidth, and sensitivity of the PMUT. Acoustic matching and encapsulation of the PMUT with external materials or structures further enhances its acoustic characteristics. Finally, this paper discusses the main challenges and future development trends faced by PMUT, to provide a reference for the future research and practical application of the technology.

Key words: piezoelectric micromechanical ultrasound transducer, fabrication process, resonant frequency, high sensitivity, wideband