Analysis and Removal of Spurious Response in SH0 Lithium Niobate MEMS Resonators

This paper reports on the analysis and removal of transverse spurious modes in shear horizontal (SH0) mode lithium niobate (LiNbO₃) laterally vibrating resonators (LVRs). A length-controlled electrode configuration that employs an optimized overlapping length between the adjacent electrodes has been developed to subdue the spurious modes. The technique modifies the stress and electric field distribution in the resonator body, consequently enabling near zero electromechanical coupling (k_t²) for the higher order transverse spurious modes. The length-controlled electrode configuration also reduces the loss at the interface between the metal electrodes and the piezoelectric layer, demonstrating a more than 2× enhancement in quality factors Q. The fabricated LiNbO₃ LVR with the length-controlled electrode configuration has shown an unprecedented spectral range (100-200 MHz) of spurious-free response, a high k_t² value of 20.1%, a Q value of 1150, and, thereby, a remarkably high figure of merit of 230.