Harmonic Nonlinearity of I.H.P. SAW Resonators Based on a Simplified 3-D FEM Model.

Linearity has become one of the most important performance parameters for radio frequency frontend (RFFE) surface acoustic wave (SAW) resonators. The simplified 3-D finite element method (FEM) (STDF) model of the transverse and longitudinal combined analysis is proposed for the first time, which realizes a more comprehensive simulation of the nonlinear harmonic response in the broadband range of incredible high-performance SAW (I.H.P. SAW) resonators, and also solves the problem that even-order harmonics cannot be accurately predicted by FEM. The contributions from transverse modes, longitudinal spurious modes, and related mechanisms are comprehensively represented. The origins and physical significance of nonlinear harmonic response peaks across different frequency bands are clarified, and the consistency between simulation and measurement results validates our conclusions. The displacement modes of the nonlinear harmonic responses are illustrated. By retaining only one nonlinear effect contribution term while removing the others, the generation mechanisms of the second-order harmonic (H2) and third-order harmonic (H3) responses are thoroughly investigated. Based on the dominant generation mechanisms, we targeted the investigation of how various structural modifications contribute to the nonlinear harmonic responses.