Study on Loss mechanisms in SAW Resonators Using 42-LT Thin Plate by Full-3D FEM with Hierarchical Cascading Technique.

Abstract

This paper describes study of loss mechanisms in an incredible high performance surface acoustic wave (I.H.P. SAW) resonator on the 42°YX-LiTaO₃/SiO₂/Si structure. The full three-dimensional (3D) finite element method (FEM) is applied with the assistance of the hierarchical cascading technique. Excellent agreement is obtained between calculation and measurement not only for the effective electromechanical coupling factor k_eff² but also the Bode Q without inclusion of empirical loss mechanisms. Behavior of calculated Bode Q is mostly governed by the number of IDT finger pairs N_I and aperture length W. SAW field distribution is derived from the FEM result. Oblique SAW leakage is observed in the busbar region of reflectors and becomes negligible when N_I is large. From this, it is concluded that the Bode Q reduction discussed here is mainly occurred by the oblique SAW leakage caused by the in-plane diffraction. Finally, the mBVD model is applied for quantitative characterization. It is shown that the in-plane SAW diffraction can be modelled well by the mBVD model and gives significant impact only to the anti-resonance Q. Surprisingly its loss is dominant even when N_I=100.