A Dispersion-Engineered YX-LN/SIO2/Sapphire SH-SAW Resonator for Enhanced Electromechanical Coupling and Rayleigh Mode Suppression

In this work, an optimized shear-horizontal surface acoustic wave (SH-SAW) resonator based on YX-LN/SiO2/Sapphire (LNOS) functional substrate is demonstrated with a large electromechanical coupling coefficient $\left( {k_{{\text{eff}}}^2} \right)$ and high quality factor (Q), while effectively mitigating the Rayleigh SAW (R-SAW). Although the LN/SiO2 hetero acoustic stacking offers excellent acoustic energy confinement for SH-SAW operation, it generates significant R-SAW as an unintended byproduct alongside the targeted mode. Through detailed numerical simulations, we revealed that when these two modes are in close proximity, their electromechanical coupling undergoes drastic variations. Therefore, specific design ranges can be found to enhance the SH-SAW while simultaneously eliminating the $k_{{\text{eff}}}^2$ of R-SAW. As a proof-of-concept, one $k_{{\text{eff}}}^2$-enhanced design is experimentally verified, exhibiting a large $k_{{\text{eff}}}^2$ of 47%, a high Bode-Q (Qmax) of 1,000, yielding an excellent figure-of-merit $\left( {{\text{FoM}} = k_{{\text{eff}}}^2\cdot{Q_{\max }}} \right)$ of 470 at 1 GHz, with successful suppression of the R-SAW.