19.3 GHz Acoustic Filter with High Close-in Rejection in Tri-layer Thin-Film Lithium Niobate

Abstract: Acoustic filters are preferred front-end solutions at sub-6 GHz due to their superior frequency selectivity compared to electromagnetic (EM) counterparts. With the ongoing development of 5G and the evolution toward 6G, there is a growing need to extend acoustic filter technologies into frequency range 3 (FR3), which spans 7 to 24 GHz to accommodate emerging high-frequency bands. However, scaling acoustic filters beyond 10 GHz presents significant challenges, as conventional platforms suffer from increased insertion loss (IL) and degraded out-of-band (OoB) rejection at higher frequencies. Recent innovations have led to the emergence of periodically poled piezoelectric lithium niobate (P3F LN) laterally excited bulk acoustic resonators (XBARs), offering low-loss and high electromechanical coupling performance above 10 GHz. This work presents the first tri-layer P3F LN filter operating at 19.3 GHz, achieving a low IL of 2.2 dB, a 3-dB fractional bandwidth (FBW) of 8.5%, and an impressive 49 dB close in rejection. These results demonstrate strong potential for integration into FR3 diplexers.