38.7 GHz Thin Film Lithium Niobate Acoustic Filter

TL;DR

This paper demonstrates a 38.7 GHz acoustic wave filter using thin-film lithium niobate, achieving high frequency operation with promising results for 5G millimeter wave applications.

Contribution

It introduces a novel high-frequency acoustic filter based on thin-film LiNbO3 resonators, pushing the operational limits into the 5G mmWave bands.

Findings

Achieved 5.63 dB insertion loss at 38.7 GHz

Realized 17.6% fractional bandwidth

Operates in 5G mmWave frequency range

Abstract

In this work, a 38.7 GHz acoustic wave ladder filter exhibiting insertion loss (IL) of 5.63 dB and 3-dB fractional bandwidth (FBW) of 17.6% is demonstrated, pushing the frequency limits of thin-film piezoelectric acoustic filter technology. The filter achieves operating frequency up to 5G millimeter wave (mmWave) frequency range 2 (FR2) bands, by thinning thin-film LiNbO3 resonators to sub-50 nm thickness. The high electromechanical coupling (k2) and quality factor (Q) of first-order antisymmetric (A1) mode resonators in 128 Y-cut lithium niobate (LiNbO3) collectively enable the first acoustic filters at mmWave. The key design consideration of electromagnetic (EM) resonances in interdigitated transducers (IDT) is addressed and mitigated. These results indicate that thin-film piezoelectric resonators could be pushed to 5G FR2 bands. Further performance enhancement and frequency scaling calls for better resonator technologies and EM-acoustic filter co-design.