10.5-GHz Coupled Longitudinal and Shear SAW Resonator with High Electromechanical Coupling Coefficient of 18%

This work presents a novel and revolutionary coupled longitudinal and shear surface acoustic wave (LS-SAW) resonator, which utilizes both e11 and e35 for piezoelectric excitation and achieves the highest electromechanical coupling coefficient (k²) of 18% at 10.5 GHz based on a LiNbO3-on-SiC (LNoSiC) substrate. By properly selecting the Euler angle (α) in the YZ plane and designing the lithium niobate thin film thickness (hLN) to the interdigital transducer (IDT) wavelength (λ) ratio of the LS-SAW resonator structure, the longitudinal and shear piezoelectric coefficients (e11 and e35) can be coupled in one mechanical vibration mode to enable such a higher k². When the Euler angle approaches -52°, the LS-SAW resonator operating at 10.5 GHz exhibits a high k² of 18% and an excellent figure of merit (FoM = k²•Qmax) of 39.2, which are both the highest among all reported high frequency SAW resonators above 7 GHz. This demonstration opens a new path to enable high-frequency (> 10 GHz) SAW resonators with high k² for next-generation 6G cmWave wireless communications.