21.4 GHz Surface Acoustic Wave Resonator with 11,400 m/s Phase Velocity in Thin-Film Lithium Niobate on Silicon Carbide

This paper reports a surface acoustic wave (SAW) resonator at 21.4 GHz with a high phase velocity of 11.4 km/s, a feasible direction for SAW devices to continue down. Transferred 100 nm 128Y lithium niobate (LN) thin film on 4H silicon carbide (SiC) substrate is used for the acoustic platform. The SiC substrates high stiffness and acoustic velocity enable the high phase velocity thickness-shear mode to stay confined to the LN layer. The high phase velocity of 11.4 km/s is approaching the longitudinal wave velocity of 12.5 km/s in 4H SiC. The resonator achieves electromechanical coupling (k<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup>) of 3.4%, series resonance Q (Q<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</inf>) of 37, shunt resonance Q (Q<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p</inf>) of 65, and a maximum Bode Q of 70. Upon further development, a solidly mounted mmWave acoustic platform could be created utilizing this high-phase velocity mode with various applications in mmWave signal processing,