Harnessing Acoustic Dispersions in YX-LN/SiO2/Si SH-SAW Resonators for Electromechanical Coupling Optimization and Rayleigh Mode Suppression

In this study, we investigate the dispersive behavior of the electromechanical coupling coefficient (
${k}_{\text {eff}}^{{2}}$
) for shear-horizontal (SH) and Rayleigh surface acoustic wave (SAW) modes in a YX-LiNbO3 (LN)/SiO2/Si substrate across various wavelengths. Due to the difference in velocity dispersion between the SH and Rayleigh modes, mode coupling can be observed when these two modes operate at closely proximate frequencies, leading to a notable variation in their
${k}_{\text {eff}}^{{2}}$
. With a careful design, SH and Rayleigh modes can be tuned to achieve a mode-decoupling state for enhancing
${k}_{\text {eff}}^{{2}}$
of the SH-SAW and suppressing the presence of the Rayleigh mode in YX-LN/SiO2/Si. Consequently, a series of proof-of-concept SH-SAW resonators with wavelengths (
$\lambda $
) ranging from 1.6 to
$4.8 ~\mu \text{m}$
are fabricated. The optimized resonator with a
$\lambda $
of
$2.8 ~\mu \text{m}$
exhibits a resonant frequency of 1.064 GHz, an effective
${k}_{\text {eff}}^{{2}}$
of 47.7%, a maximum Bode-
${Q}$
of around 900, and an 18-dB rejection of spurious modes spanning from 0.5 to 3 GHz, without the presence of the Rayleigh mode.