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 LiNbO3-on-SiC (LNoSiC) substrate. By properly selecting the three-dimensional (3D) Euler angle (
$\alpha {)}$
and designing the thickness (
${h}_{\text {LN}}{)}$
to wavelength (
$\lambda {)}$
ratio of the LiNbO3 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 =
${k}^{{2}} \cdot ~{Q}_{\text {max}}{)}$
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.