Spurious-Mode Suppression and Efficient Design of LiTaO₃ XBAR Filters Using a FEM-COM-ABC Framework

Laterally excited bulk acoustic wave resonators (XBARs) on lithium tantalate (LiTaO₃, LT) are promising for wideband radio-frequency filters, but spurious modes and costly full-wave optimization hinder development. Limited coupling-bandwidth flexibility in commercial LT cuts motivates exploring non-standard orientations. We present a numerical framework integrating the finite-element method (FEM), coupling-of-modes (COM) theory, and artificial bee colony (ABC) optimization, emphasizing non-commercial 120° YX-LT. Hierarchical FEM screens orientation and periodic-cell response and then resolves finite aperture, busbars, and membrane boundaries. Compared with rectangular boundaries, an irregular pentagonal membrane disrupts coherent edge reflections, suppressing in-band spurious glitches and slightly enhancing effective coupling. A thickness-dependent COM model calibrated across a broad SiO₂ loading range reproduces FEM resonance and antiresonance frequencies within 1 MHz. The surrogate enables mixed-variable ABC optimization of finger-pair number, normalized aperture, and stage-specific wavelengths. Five-stage ladder filters are synthesized and verified by direct FEM reconstruction. Stage-dependent wavelengths improve simulated passband transmission and reduce ripple versus a common-wavelength baseline; COM-FEM stopband discrepancies indicate the need for full-wave verification. After calibration, ABC core search takes approximately 2.9 h without repeated full-wave solutions. This transferable framework provides a cost-effective pathway from full-wave physics to circuit-level filter synthesis on thin-film piezoelectric platforms.