S-band delay lines in suspended lithium niobate

Abstract

Thin-film lithium niobate is an attractive platform for GHz-frequency applications in low-power RF analog signal processing, optomechanics, and quantum devices due to its high coupling, low loss, excellent optical properties, and compatibility with superconducting quantum circuits. We demonstrate aluminum interdigitated transducers (IDTs) in this platform for horizontal shear (SH) waves between 1.2 and 3.3 GHz and longitudinal waves between 2.1 and 5.4 GHz. For the SH waves, we measure a piezoelectric coupling coefficient of 13% and 6.0 dB/mm propagation losses in delay lines up to 1.2 mm with a 300 ns delay in air at room temperature. In these high keff2 transducers, electrical loading gives rise to large reflections and resonances. Finite element method models and an experimental finger-pair sweep are used to characterize the role of resonance in these transducers, illuminating the physics behind the large motional admittances of these small-footprint IDTs.