Review of Fabrication Processes and Performance Optimization Strategies for Piezoelectric Micromachined Ultrasonic Transducer

Compared with conventional bulk piezoelectric ultrasonic transducers, Piezoelectric Micromachined Ultrasonic Transducers (PMUTs) play an increasingly important role in many fields due to their advantages such as small size, low power consumption, flexible frequency control, and ease of integration with CMOS processes. As application demands continue to grow, related fields have also posed new challenges to key performance metrics of PMUTs, such as bandwidth and sensitivity. The article first introduces the device structure and working principles of PMUTs. Then, based on the cavity fabrication methods, it reviews the process schemes for PMUT fabrication, including etching, sacrificial layer release, surface bonding, and silicon migration methods, along with their respective advantages and limitations. Subsequently, the research status of performance optimization strategies for PMUTs is systematically elaborated from four perspectives: piezoelectric materials, device structure, electrode excitation, and acoustic matching. Specifically, aiming for high piezoelectric coefficients and low dielectric constants, the performance of piezoelectric materials is enhanced through doping, modification, and process optimization. The PMUT structure is improved for better performance using strategies such as vibration mode control, residual stress management, acoustic structure integration, and array layout optimization. By designing the static layout of PMUT electrodes and dynamically controlling excitation signal parameters, effective regulation of resonant frequency, bandwidth, and sensitivity is achieved. In addition, acoustic matching and packaging of PMUTs using external materials or structures are discussed to further improve the acoustic performance of PMUTs. Finally, this paper discusses the major challenges and development trends in PMUT fabrication and performance optimization, providing a reference for future research and practical applications of PMUTs.