Micromachined Edge Reflection Thin-Film SAW Resonator on LiNbO₃-on-SiC

This work presents the design and experimental demonstration of a micromachined edge reflection thin-film surface acoustic wave (SAW) resonator on an X-cut LiNbO₃-on-SiC platform. Unlike conventional Bragg reflection resonators (BRRs), the demonstrated device employs etched free edges adjacent to the interdigital transducer (IDT) to provide lateral acoustic confinement without additional reflector arrays. Edge half electrodes are further used to tailor the lateral phase condition and suppress spurious modes. The representative Design I resonator exhibits an electromechanical coupling coefficient (k_t²) of 37.6% and a maximum Bode-Q of 712 at 4.64 GHz, corresponding to a figure of merit (FoM) of 267.7. Compared with BRR counterparts fabricated in the same batch, the ERR reduces the effective resonator footprint by approximately 27-37% while maintaining a comparable k_t². Measurements further show that the ERR exhibits a higher Q in most paired designs, thereby yielding an improved FoM. These results establish micromachined edge boundary engineering as an effective route toward reflector-less thin-film SAW resonators with reduced effective resonator footprints and high-Q coupling performance while also clarifying the fabrication-related trade-offs associated with etched free edge confinement.