Lithium niobate-based laterally excited bulk acoustic resonator with wave-shaped electrodes and its filter

Laterally excited bulk acoustic wave resonator (XBAR) based on lithium niobate-on-insulator (LNOI) substrates has been a hotspot and is widely believed to be a potential candidate for next-generation wireless communication systems. However, it is confronted with the spurious mode issue, which can cause in-band ripples in filters. To obtain a cleaner frequency spectrum response, we propose an XBAR with a wave-shaped interdigital transducer (IDT) to suppress spurious modes. It is revealed by using a finite element method model, and spurious modes are significantly eliminated in the passband due to the non-parallel boundary of IDTs. We then experimentally verify the theoretical analyses. The wave-shaped XBAR is fabricated based on a Z-cut LiNbO3 thin film, showing a nearly spurious-free impedance response. Then a filter based on the wave-shaped XBAR is fabricated, with fewer in-band ripples, featuring a center frequency of 5.77 GHz and a 3-dB fractional bandwidth of 7.8%. This research demonstrates a potential solution for high-frequency and wideband filters based on LNOI platforms meeting 6G requirements.