Elimination of Spurious Modes in SH0 Lithium Niobate Laterally Vibrating Resonators

Abstract

This letter reports on a spurious mode suppression technique for the shear horizontal (SH0) mode lithium niobate laterally vibrating resonators. The concept utilizes triangular and arched edge shapes on the transversal sides of a resonant cavity to effectively distribute and scatter the acoustic waves in the inactive regions, yielding the suppression of transverse spurious modes. 2D models and 3D finite-element analyses were employed to theoretically verify the technique. For devices with the archedshape edges, complete removal of higher order transverse modes has been experimentally demonstrated with 2× enhancement for quality factor (Q). The Q enhancement arises from the improved concentration of mechanical energy under the inter-digitated transducers. The fabricated device exhibits a Q of 920, a large electromechanical coupling (k <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">t</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ) of 17.8%, and a figure of merit of 164.