Toward mmWave Surface Acoustic Wave Resonators in Lithium Niobate on Silicon Carbide.

Recent advancements in next-generation wireless systems have expanded the need for radio frequency front-ends (RFFEs) towards the millimeter wave (mmWave) range. This work introduces two methods targeting the efficient design of solidly-mounted surface acoustic wave (SAW) resonator architectures based on lithium niobate on silicon carbide (LN-on-SiC) hetero-acoustic waveguides for mmWave applications. The first method utilizes a longitudinal SAW (L-SAW) mode in X-cut LN to achieve a high phase velocity of 6500 m/s and a figure of merit (FoM) of 6.53 at 22.42 GHz, enabled by strong acoustic confinement and careful wavelength scaling. The second method presents a novel electrode-guided shear horizontal SAW (EG SH-SAW) mode in Y-cut LN, leveraging electrode design to confine higher-order SH modes and mitigate internal stress cancellation. The fabricated EG SH-SAW resonator achieves operation at 23.5 GHz with a coupling coefficient k² of 1.6% and a FoM of 4.16. Both methods demonstrate resonators successfully scaled towards mmWave range with high Q-factors and open the potential for future solidly-mounted frequency-scalable, high-performance acoustic devices in mm wave bands.