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

Abstract

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 e16 and e34 for piezoelectric excitation and achieves exceedingly high electromechanical coupling coefficient (k2)} of 34% at 5 GHz based on a LiNbO3-on-SiC (LNoSiC) substrate. By properly selecting the three-dimensional (3D) Euler angle (α) and designing the thickness (hLN) to wavelength (λ) ratio of the LiNbO3 thin film, two piezoelectric coefficients (e16 and e34) can be coherently coupled together in one single vibration pattern, so that the electromechanical coupling k2 add up. When the Euler angle approaches 0°, the CS-SAW resonator operating at 5 GHz exhibits a high k2 of 34% and an excellent figure of merit (FoM = k2 · Qmax) 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.