An Analytical Method for the Enhancement of Electromechanical Coupling of Piezoelectric Micromachined Ultrasonic Transducers Combined with Pre-Stress

This paper reports an analytical model to optimize the electromechanical coupling coefficient $k_t^2$ of Piezoelectric Micromachined Ultrasonic Transducers (PMUTs). The neutral axis position is adjusted by introducing a certain magnitude and polarity pre-stress to the PMUTs during the process flow, thus changing the stiffness and other key parameters. Finally, a PMUT with $k_t^2$ of 4.42% is realized under the compressive stress condition of 30MPa. The dynamic displacement of the device reached 2.34μm under 1 V
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sine wave excitation which is larger than current studies. As such, this work presents another possibility for performance optimization without increasing complexity of device design.