Edge-narrowed IDTs for spurious mode suppression and quality factor enhancement in laterally excited bulk acoustic resonators

Spurious modes and an insufficient quality factor ( Q -factor) critically undermine the overall performance of laterally excited bulk acoustic wave resonators (XBARs), significantly limiting their efficiency and commercial viability in advanced radio frequency (RF) applications. In this work, an XBAR with edge-narrowed interdigital transducers (IDTs) is proposed to suppress spurious modes and enhance Q -factor. By narrowing electrodes at the edges, the periodicity of conventional IDTs is disrupted, and local mass-loading effect and the boundary reflection is reduced. This design effectively reduces spurious mode excitation and concentrates more energy into the first-order asymmetric (A1) mode. Experimental results show that the fabricated XBAR, based on a suspended 128° Y-cut LiNbO 3 thin film, delivers a clean frequency response. The device achieves an electromechanical coupling coefficient ( k t 2 ) of 27.8% at 3.46 GHz and a maximum Q ( Q max ) of 405. The resulting figure of merit (FOM= k t 2 × Q max ) reaches 113, highlighting its potential for high-performance RF filter applications.