Stress Analysis Based Multi-Electrode Optimization for High-Frequency PMUTs in High-Order Mode

Piezoelectric micromachined ultrasonic transducers (PMUTs) are high-performance devices with diverse applications. As the demand for high-resolution devices grows, PMUTs are evolving to operate at higher frequencies. Most current PMUTs use the first-order vibration mode with center frequencies below 20 MHz. However, beyond this frequency, increased film stiffness leads to reduced sensitivity. High-order modes, which have higher resonant frequencies, are crucial for achieving higher frequencies. Given the significant impact of electrode design on different modes, this study presents a method for optimizing the electrode distribution of high-order modes using stress analysis. By optimizing the electrode design for the fourth-order mode, the round-trip sensitivity of PMUTs is improved by 35 dB compared to the first-order mode with optimized electrodes, and by 21 dB compared to the fourth-order mode with traditional electrodes. This enhancement significantly boosts pulse-echo imaging quality, making PMUTs more effective for high-resolution applications.