Study on Generation Mechanism of Harmonic Nonlinear Signals in LiNbO3/SiO2/Si SAW Resonators Based on Measurement and Simulation

In this study, the harmonic nonlinearity of a piezoelectric-on-insulator surface acoustic wave (POI-SAW) resonator was theoretically and experimentally studied. First, the POI-SAW resonators on 30 degrees YX-LiNbO3/SiO2/Si layered structure with different tilted interdigital transducers (IDTs) were fabricated, and their linear and nonlinear responses were measured. An extended 3-D nonlinear model was developed using a combination of finite element method (FEM) and perturbation theory to explore the generation mechanism of harmonic nonlinear signals in such layered devices. The dominant nonlinear mechanism was extracted by fitting FEM simulation results with experimental data. Results revealed that the self-mixing of the electrostatic field was the main factor and the electromechanical coupling of the electrostatic field with the strain field was the secondary factor that affected the second harmonic response. Moreover, the transverse modes deteriorated nonlinearity, which could be improved by appropriately setting the IDT tilt angle: the second- and third-harmonic signals levels of 16 degrees tilted IDT resonator decreased by 10 and 15 dBm, respectively. Further simulation revealed that the strain fields induced by the transverse mode markedly decreased, thereby suppressing the resulting nonlinear harmonic response. This study provides insights into the generation mechanisms of harmonic nonlinear signals in surface acoustic wave (SAW) resonators on complex layered structures. These findings are of great significance for designing high-performance POI-SAW devices for radio frequency (RF) front-end circuits and their suppression.