A laterally excited bulk acoustic wave resonator based on LiNbO3 with reflective arrays achieving a high <i>FOM</i> of 308

This paper presents a laterally excited bulk acoustic resonator (XBAR) with reflective arrays, enabling the effective suppression of lateral acoustic leakage and enhanced energy confinement. Building upon previous studies, this work further investigates the critical design parameters of reflective arrays, specifically the optimal distance between the reflective arrays and the interdigital transducers (IDTs) and the selection of the reflective-array metal coverage at this optimal distance. Meanwhile, by systematically analyzing the key parameters of IDTs, including electrode pitch and electrode numbers, their influences on the quality factor (Q value) and spurious modes were also studied. Comparative studies with conventional XBARs and full-release air boundary XBARs further highlight the superior structural stability and performance advantages of the reflective-array design. Both simulations and experimental results confirm that the optimized configuration leverages acoustic impedance mismatch to achieve efficient reflection, effectively improving the Q value. The fabricated devices demonstrate a 2.83× increase in Bode-Q from 279 to 789 while maintaining a high electromechanical coupling coefficient (kt2) of 39.1%. The optimized XBAR further achieves excellent figures of merit FOM1 (=kt2 × Bode-Q) of 308 and FOM2 (=fs × kt2 × Bode-Q) of 10.83 × 1011 Hz, underscoring its strong potential for 5G n77-band applications.