Nonlinear Characterization of Thin-Film LiNbO3 Acoustic Filters

TL;DR

This paper introduces a novel nonlinear characterization methodology for high-frequency LiNbO3 acoustic filters, demonstrating substrate effects on nonlinearity and performance at millimeter-wave frequencies.

Contribution

Developed a new power-dependent S-parameters and IMD3 measurement technique for LiNbO3 filters, with experimental validation on filters on sapphire and silicon substrates.

Findings

Filters on Al2O3 showed better thermal stability and passband linearity.

In-band IIP3 exceeded 50 dBm on Al2O3 substrates.

Substrate choice significantly impacts nonlinear performance of LiNbO3 acoustic filters.

Abstract

Compact, high-performance components in millimeter-wave (mmWave) communication systems demand new acoustic filter technology at increasingly higher frequencies. Among various promising mmWave platforms, first-order antisymmetric (A1) mode laterally excited bulk acoustic resonators (XBARs) in thin-film lithium niobate (LiNbO3) have perhaps the most impressive linear performance. Despite these advances, there are few reports of nonlinear characterization of LiNbO3 filters at mmWaves. Here, we address this gap by developing a new nonlinear methodology for high-frequency filters. The result is a methodology for performing power-dependent S-parameters and third-order intermodulation (IMD3) measurements. To test our methodology, we fabricated filters on transferred single-crystal LiNbO3 films on sapphire (Al2O3) and silicon (Si) substrates with amorphous silicon (aSi) sacrificial layer. At 21.8 GHz, the filters on Al2O3 demonstrated an insertion loss of 1.48 dB, a 3 dB fractional bandwidth (FBW) of 17.7%, and in-band third-order input intercept points (IIP3) of 50.8 dBm. At 21.6 GHz, the filters on silicon demonstrated an insertion loss of 2.47 dB, a 3 dB FBW of 18.6%, and in-band IIP3 of 46.5 dBm. The nonlinear results conclusively show that thermal stability and passband distortion improved on the Al2O3 substrate, confirming that substrate selection plays a pivotal role in mitigating nonlinearity in acoustic front-end modules.