Near-Spurious-Free 6.5 GHz XBARs With Dimension-Matched and Response-Averaged Electrodes

Lithium niobate (LiNbO<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub>) laterally excited bulk acoustic wave resonators (XBARs) show great potential for high-frequency, wide-bandwidth radio frequency (RF) filters. However, suppressing spurious mode responses remains a critical challenge. In this study, we demonstrate near-spurious-free 6.5 GHz Z-Y LiNbO<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> XBARs using dimension-matched and response-averaged electrodes. Dispersion analysis of traditional interdigitated transducer (IDT) electrode dimensions reveals that spurious mode response levels are minimized when the electrode width corresponds to half the wavelength of the second-order quasi-antisymmetric (QA2) Lamb mode in the electrode/LiNbO<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> plate. This result holds across a range of electrode thicknesses and exhibits weak dependence on pitch. Based on these matched IDT dimensions, we propose three novel IDT topologies that employ response-averaging strategies to further reduce spurious mode responses without compromising the first-order antisymmetric (A1) Lamb mode. The fabricated devices show good agreement with simulation results, achieving a low-spurious response and moderate performance. This work provides a systematic design framework for low-spurious-response XBARs, offering a path to more reliable and efficient next-generation wireless front-end filters. [2025-0070]