Design and Characterization of an Ultrahigh‐Q Annular LiNbO ₃ Surface Acoustic Wave Resonator

Achieving ultrahigh‐quality factors (Q) on high‐coupling piezoelectric substrates remains a significant challenge in surface acoustic wave (SAW) technology. In this work, we designed and fabricated a novel SAW resonator on a 128° YX‐cut lithium niobate substrate utilizing a unique annular interdigital transducer geometry. This closed‐loop design creates a natural acoustic cavity that inherently suppresses diffraction loss and parasitic reflections, achieving efficient energy confinement. Radio frequency characterization of the 39.787 MHz fundamental mode confirmed a record Q factor of 17,466 within a highly compact device footprint, significantly exceeding that of conventional lithium niobate designs. To evaluate the device's stability and potential for sensing applications, we performed comprehensive thermal characterization from 30°C to 150°C. The resonator exhibited a stable temperature sensitivity of −2.425 kHz/°C with near‐perfect linearity and excellent repeatability. These results demonstrate that the proposed annular architecture effectively resolves the traditional trade‐off between electromechanical coupling and Q factor, providing a high‐performance platform for advanced acoustic devices.