Transforming Spurious into Bandwidth in cmWave Acoustic Resonators

In this work, a new kind of coupled-mode surface acoustic wave (SAW) resonator (named as S0-SH1-SAW or SSH-SAW for short) with high electromechanical coupling coefficient (k²) operating at centimeter wave (cmWave) frequencies has been proposed and demonstrated for the first time. By carefully modulating the dispersion characteristics, we successfully transform the spurious first-order shear horizontal (SH1) mode into coherent mechanical vibrations that add up to the main fundamental symmetric (S0) mode in a conventional longitudinal leaky SAW (LL-SAW) resonator. The demonstrated SSH-SAW resonator features a high k² of 26.8% and an excellent figure of merit (FoM = k² • Qmax) of 94 at 7.26 GHz on an X-50°Y LiNbO3/SiC (LNoSiC) substrate, which show record high k² and spurious-free responses when compared with conventional LL-SAW resonators for operating frequencies > 7 GHz. This work marks a brand new way of out-of-the-box thinking in terms of converting spurious mode directly into useful bandwidth in acoustic resonators.