Lattice XBAR Filters in Thin-Film Lithium Niobate

TL;DR

This paper demonstrates lattice filters based on XBAR resonators in thin-film lithium niobate, achieving wide bandwidths and low insertion loss in a compact form factor for RF applications.

Contribution

It introduces the design and fabrication of XBAR-based lattice filters in P3F TFLN, showcasing their wide bandwidth and low loss capabilities for the first time.

Findings

Achieved 27.42% and 39.11% fractional bandwidths at ~20 GHz.

Low insertion losses of 0.88 dB and 0.96 dB.

Prototypes are smaller than 1.3 mm².

Abstract

This work presents the demonstration of lattice filters based on laterally excited bulk acoustic resonators (XBARs). Two filter implementations, namely direct lattice and layout-balanced lattice topologies, are designed and fabricated in periodically poled piezoelectric film (P3F) thin-film lithium niobate (TFLN). By leveraging the strong electromechanical coupling of XBARs in P3F TFLN together with the inherently wideband nature of the lattice topology, 3-dB fractional bandwidths (FBWs) of 27.42\% and 39.11\% and low insertion losses (ILs) of 0.88 dB and 0.96 dB are achieved at approximately 20 GHz for the direct and layout-balanced lattice filters, respectively, under conjugate matching. Notably, all prototypes feature compact footprints smaller than 1.3 mm\textsuperscript{2}. These results highlight the potential of XBAR-based lattice architectures to enable low-loss, wideband acoustic filters for compact, high-performance RF front ends in next-generation wireless communication and sensing systems, while also identifying key challenges and directions for further optimization.