Thin-Film Lithium Niobate Acoustic Filter at 23.5 GHz with 2.38 dB IL and 18.2% FBW

TL;DR

This paper presents a novel thin-film lithium niobate acoustic filter operating at 23.5 GHz with exceptionally low insertion loss and wide bandwidth, achieved through a new film stack and resonator design, enabling advanced mmWave signal processing.

Contribution

The work introduces a record-breaking millimeter-wave acoustic filter using a transferred thin-film lithium niobate on silicon with a novel intermediate layer, surpassing previous performance benchmarks.

Findings

Achieved 2.38 dB insertion loss at 23.5 GHz

Realized 18.2% fractional bandwidth

Developed a compact 0.56 mm2 filter footprint

Abstract

This work reports an acoustic filter at 23.5 GHz with a low insertion loss (IL) of 2.38 dB and a 3-dB fractional bandwidth (FBW) of 18.2%, significantly surpassing the state-of-the-art. The device leverages electrically coupled acoustic resonators in 100 nm 128{\deg} Y-cut lithium niobate (LiNbO3) piezoelectric thin film, operating in the first-order antisymmetric (A1) mode. A new film stack, namely transferred thin-film LiNbO3 on silicon (Si) substrate with an intermediate amorphous silicon (a-Si) layer, facilitates the record-breaking performance at millimeter-wave (mmWave). The filter features a compact footprint of 0.56 mm2. In this letter, acoustic and EM consideration, along with material characterization with X-ray diffraction and verified with cross-sectional electron microscopy are reported. Upon further development, the reported filter platform can enable various front-end signal-processing functions at mmWave.