52-GHz Surface Acoustic Wave Resonators in Thin-Film Lithium Niobate on Silicon Carbide

This article reports a surface acoustic wave (SAW) resonator at 52 GHz with a high quality factor (Q) of 188 and a high phase velocity of 12.2 km/s, marking the first millimeter-wave (mmWave) SAW devices with high Q. Transferred 300-nm 128Y lithium niobate (LN) thin film on 4H silicon carbide (SiC) substrate is used for the acoustic platform. The dramatic frequency scaling is enabled by the high phase velocity thickness-shear mode, confined in the LN-SiC stack, due to the high stiffness and acoustic velocity of SiC. The high phase velocity of 12.2 km/s is approaching the longitudinal wave velocity of 12.5 km/s in 4H SiC. The resonator achieves electromechanical coupling ( ${k}^{{2}}$ ) of 0.5%, 3-dB series resonance Q ( ${Q}_{s}$ ) of 12, 3-dB shunt resonance Q ( ${Q}_{p}$ ) of 188, and maximum Bode Q of 154. Upon further development, the mmWave solidly mounted acoustic platform could enable various applications in signal processing, optomechanical, and quantum applications.