Stabilization of the simulation of saw devices on stratified structures: application to transverse plate mode resonators

Two approaches are investigated to model accurately the physical characteristics of plate mode devices, and more particularly of resonators. They are respectively based on finite element analysis (FEA) and on mixing FEA with a boundary integral method (FEA/BIM). In the later case, using a transfer matrix approach for the computation of the spectral Green´s function results in numerical instabilities for large layer thickness or large slowness. A new stable algorithm is described for the computation of the spectral Green´s function of a multilayer structure, that is inherently numerically stable. The main parameters of wave propagation (velocity, coupling factor, reflection coefficient) can then be estimated considering an infinite periodic structure and computing the harmonic admittance. For comparison with measurements of quartz transverse plate mode resonators, the estimated parameters can be inserted in a P-matrix model. Theory and experiments are found to comply well for both the pure FEA and the FEA/BIM approaches