Gigahertz Phononic Integrated Circuits on Thin-Film Lithium Niobate on Sapphire

Phononic integrated circuits that guide acoustic waves at wavelength scale offer great potential for devices in communications, sensing, and quantum technologies. Unfortunately, conventional phononic waveguides either are suspended, which prevents large-scale integration, or suffer from inefficient acoustic wave transduction. Surmounting these issues, this work implements unreleased-rib phononic circuits operating at 3.4 GHz with efficient, compact transducers in a thin-film platform of lithium niobate on sapphire. These circuits allow the authors to demonstrate mass sensing, high-quality resonators, and the characterization of low-power acoustic four-wave mixing.