Nonlinearity Analysis of Dual-electrode Piezoelectric Micromachined Ultrasonic Transducer

We investigate the nonlinearity of Aluminum Nitride (AlN)-based dual-electrode Piezoelectric Micromachined Ultrasonic Transducer (PMUT). Various nonlinear vibration phenomena of PMUTs are observed when high a AC voltage is applied to their inner and outer electrodes, respectively. The out-of-plane displacement driving capability and the impedance of inner and outer electrodes are compared. Utilizing nonlinear effects, we observed high-order mechanical harmonics with inner electrodes and obtained high-order electrical harmonics output at the outer electrodes. The engineered PMUT exhibits a resonant frequency of 177.9 kHz, at which pronounced high-order harmonics are distinctly detectable at the outer electrode. In contrast, at non-resonant frequencies like 250 kHz, the high-order harmonic electrical signal is noticeably absent. The PMUT are more prone to exhibit nonlinear vibrations at resonance. These phenomena have the potential to be utilized in harmonic generation within acoustic-optical hybrid microsystems, sensing, and the radio frequency (RF) field.