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

This article describes the study of loss mechanisms in an incredible high-performance surface acoustic wave (IHP SAW) resonator on the 42°YX-LiTaO3/SiO2/Si structure. The full 3-D finite element method (FEM) is applied with the assistance of the hierarchical cascading technique (HCT). Excellent agreement is obtained between calculation and measurement not only for the effective electromechanical coupling factor ${k} ^{{2}}_{\text {eff}}$ but also the Bode Q without the inclusion of empirical loss mechanisms. The behavior of calculated Bode Q is mostly governed by the number of IDT finger pairs ${N} _{\text {I}}$ 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 ${N} _{\text {I}}$ 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 modified Butterworth-van Dyke (mBVD) model is applied for quantitative characterization. It is shown that the in-plane SAW diffraction can be modeled well by the mBVD model and gives significant impact only to the anti-resonance Q. Surprisingly its loss is dominant even when ${N} _{\text {I}} =100$ .