5.4 GHz Acoustic Delay Lines in Lithium Niobate Thin Film with 3 dB Insertion Loss

In this work, we present the low-loss acoustic delay lines (ADLs) at 5.4 GHz, using the first-order antisymmetric (A1) mode in lithium niobate thin films. The ADLs use a single-phase unidirectional transducer (SPUDT) design with a feature size of the quarter acoustic wavelength. The fabricated miniature A1 ADLs with a feature size of 0.45 μm show a center frequency of 5.4 GHz, a minimum insertion loss (IL) of 3.0 dB, and a fractional bandwidth (FBW) of 1.6% while occupying a footprint of 0.0074 mm
²
. The simultaneously low IL and high operating frequency significantly surpass the state-of-the-art performance of ADLs. The propagation characteristics of A1 acoustic waves have also been extracted. The demonstrated performance can potentially enable low-loss, high-frequency transversal filter applications for future 5G applications in the sub-6 GHz spectrum bands.