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 e<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</inf> and e<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">35</inf> for piezoelectric excitation and achieves the highest electromechanical coupling coefficient (k<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup>) of 18% at 10.5 GHz based on a LiNbO<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf>-on-SiC (LNoSiC) substrate. By properly selecting the Euler angle (α) in the YZ plane and designing the lithium niobate thin film thickness (h<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LN</inf>) to the interdigital transducer (IDT) wavelength (λ) ratio of the LS-SAW resonator structure, the longitudinal and shear piezoelectric coefficients (e<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</inf> and e<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">35</inf>) can be coupled in one mechanical vibration mode to enable such a higher k<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup>. When the Euler angle approaches -52°, the LS-SAW resonator operating at 10.5 GHz exhibits a high k<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> of 18% and an excellent figure of merit (FoM = k<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup>•Q<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">max</inf>) 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 k<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> for next-generation 6G cmWave wireless communications.