Nonlinearity of Piezoelectric Micromachined Ultrasonic Transducer Using AlN Thin Film

We present the nonlinearity of Aluminum Nitride (AlN)-based Piezoelectric Micromachined Ultrasonic Transducer (PMUT) utilizing Laser Doppler Vibrometer (LDV) technique. The PMUT working at resonant frequency excite the piezoelectric layer into strong nonlinear region. The nonlinear phenomena are observed, such as frequency shift and nonlinear out-of-plane displacement magnitude. A mathematic model of piezoelectric nonlinearity is employed for analyzing the nonlinear behavior, and the second order piezoelectric coefficient is obtained subsequently. Approximately 120 harmonics, which are generated by PMUT nonlinearity, are obtained experimentally under a single-tone AC signal of a relatively high-level voltage. In addition, the number of harmonics can be controlled meticulously. Three different applications are developed to utilize harmonic generations in acoustic-optical hybrid microsystem and Radio Frequency (RF) field. The observation and analysis of AlN piezoelectric nonlinearity could benefit a further understanding of PMUT based on AlN thin film. We believe the generated harmonics can be potentially used in a wide variety of applications in signal processing and modulation.