Spectrum-Clean Dispersion-Engineered YX-LN/SiO $_{\text{2}}$ /Si Wideband SH-SAW Resonators With Crossed Interdigital Transducers

This work demonstrates the spectrum-clean shear-horizontal surface acoustic wave (SH-SAW) resonators with large electromechanical coupling coefficient ( $\textit{k}_{\text{eff}}^{\text{2}}\text{)}$ and substantial admittance ratio ( $\textit{A}_{\textit{R}}\text{)}$ in a lithium niobate on insulator (LNOI) platform in the gigahertz range. The solidly mounted LN waveguide is acoustically engineered through optimal selection of wavelength ( $\bm{\lambda}$ ) and electrode thickness for eliminating the undesired Rayleigh SAW mode while enhancing the $\textit{k}_{\text{eff}}^{\text{2}}$ of the SH-SAW. Consequently, the transverse spurious modes are suppressed using repetitive cross-interdigital transducers (X-IDT), with minimal tradeoffs to other key performance parameters. As a proof-of-concept, the SH-SAW resonators are fabricated on a 1.2-/0.5-/500- $\bm{\mu} $ m YX -LN/SiO $_{\text{2}}$ /Si functional substrate with gold electrodes, exhibiting a resonant frequency of 1.17 GHz, a $\textit{k}_{\text{eff}}^{\text{2}}$ of 43.3%, an $\textit{A}_{\textit{R}}$ of 74.3 dB, and a spectrum-clean response at $\bm{\lambda} $ of 2.6 $\bm{\mu} $ m with only a few minor spurious modes away from the main mode, offering significant potential for applications in wideband RF circuits.