Coupled Shear SAW Resonator with High Electromechanical Coupling Coefficient of 34% Using X-cut LiNbO3-on-SiC Substrate

In this work, a coupled shear mode surface acoustic wave (CS-SAW) resonator has been proposed and demonstrated for the first time, which utilizes both e 16 and e 34 for piezoelectric excitation and achieves exceedingly high electromechanical coupling coefficient ( k 2 ) of 34% at 5 GHz based on a LiNbO 3 -on-SiC (LNoSiC) substrate. By properly selecting the three-dimensional (3D) Euler angle (α) and designing the thickness ( h LN ) to wavelength (λ) ratio of the LiNbO 3 thin film, two piezoelectric coefficients ( e 16 and e 34 ) can be coherently coupled together in one single vibration pattern, so that the electromechanical coupling k 2 add up. When the Euler angle approaches 0°, the CS-SAW resonator operating at 5 GHz exhibits a high k 2 of 34% and an excellent figure of merit (FoM = k 2 ∙ Q max ) of 221, which are both the highest among all reported high frequency SAW resonators near or above 5 GHz. This demonstration not only greatly enhances the bandwidth of SAW filters at high frequencies, but also opens up a groundbreaking way of designing new and more complex coupled modes for a variety of applications.