Frequency Tuning of Suspended Millimeter Wave Lithium Niobate Acoustic Resonators by Ion Beam Assisted Argon Gas Cluster Etching

This paper explores the feasibility and the impact of frequency tuning suspended acoustic resonators through ion beam assisted argon gas cluster etching. To do so, groups of suspended first-order anti-symmetric (A1) mode laterally excited acoustic resonators were first fabricated in 65.2 nm thick 128° Y-cut lithium niobate (LiNbO3) and were then trimmed in equivalent time intervals. The resulting film thicknesses were 57.0 nm, 49.6 nm, and 41.7 nm. Trimmed devices were measured, and analyzed through their quality factor (Q) and resonant frequency (f). The trimmed films showed a trend of higher resonant frequencies while showing lower Q with decreasing film thickness. A key performance characteristic, the product of frequency with the quality factor of the device (fQ), a parameter describing acoustic film quality, stayed in very close proximity to its original value throughout the trimming process. Hence, frequency tuning of acoustic resonators using the proposed method has minimal effects on material quality. The proposed trimming procedure can be a crucial path towards achieving ultra-thin piezoelectric devices for signal processing and sensing applications.