Spectrum-Clean Dispersion-Engineered YX-LN/SiO₂/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 (<inline-formula> <tex-math notation="LaTeX">${k}_{\text {eff}}^{{2}}{)}$ </tex-math></inline-formula> and substantial admittance ratio (<inline-formula> <tex-math notation="LaTeX">${A}_{R}{)}$ </tex-math></inline-formula> 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 (<inline-formula> <tex-math notation="LaTeX">$\boldsymbol {\lambda }$ </tex-math></inline-formula>) and electrode thickness for eliminating the undesired Rayleigh SAW mode while enhancing the <inline-formula> <tex-math notation="LaTeX">${k}_{\text {eff}}^{{2}}$ </tex-math></inline-formula> 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- <inline-formula> <tex-math notation="LaTeX">$\boldsymbol {\mu }\text{m}$ </tex-math></inline-formula> YX-LN/SiO2/Si functional substrate with gold electrodes, exhibiting a resonant frequency of 1.17 GHz, a <inline-formula> <tex-math notation="LaTeX">${k}_{\text {eff}}^{{2}}$ </tex-math></inline-formula> of 43.3%, an <inline-formula> <tex-math notation="LaTeX">${A}_{R}$ </tex-math></inline-formula> of 74.3 dB, and a spectrum-clean response at <inline-formula> <tex-math notation="LaTeX">$\boldsymbol {\lambda }$ </tex-math></inline-formula> of <inline-formula> <tex-math notation="LaTeX">$2.6~ \boldsymbol {\mu }\text{m}$ </tex-math></inline-formula> with only a few minor spurious modes away from the main mode, offering significant potential for applications in wideband RF circuits.