Impact of In-Plane Diffraction in Temperature Compensated Surface Acoustic Wave Resonator on SiO₂/131°YX-LiNbO₃ Structure

This article investigates impact of in-plane surface acoustic wave (SAW) diffraction on the Bode Q curve in temperature compensated (TC) SAW resonators on 131°YX-LiNbO3 (131-LN). The right figure compares measured TC-SAW resonator characteristics with theoretical ones obtained by the periodic and full 3-D finite element method (FEM). Estimated ohmic resistance is subtracted from the measured result. The result of full 3-D FEM agrees very well with the experiment even Bode Q although no additional loss is included in the simulation. Full 3-D FEM can explain Bode Q variation with the number of IDT finger pairs ( ${N} _{\text {I}}$ ) and aperture length (W) well. This means that the in-plane SAW diffraction is one of the major loss mechanisms in TC-SAW devices. Next, the piston mode design is applied to the TC-SAW structure for the removal of transverse mode resonances, and the full 3-D FEM simulation is applied for wide range of W and ${N} _{\text {I}}$ . It is shown that the TC-SAW resonators suffer significant Bode Q degradation by the in-plane SAW diffraction, and its impact is more severe than the incredible high-performance (I.H.P.) SAW case. Namely, the Bode Q of TC-SAW resonators is more sensitive to f, W, and ${N} _{\text {I}}$ than that of I.H.P. SAW resonators due to the convex SAW slowness shape on the surface.