High-frequency surface acoustic wave devices based on LiNbO₃/diamond multilayered structure

This research is focused on the development of a new technology for the fabrication of high-frequency surface acoustic wave (SAW) filters based on diamond and lithium niobate (LiNbO₃) materials. LiNbO₃ films are in situ deposited at 490 °C on polycrystalline diamond substrates by radio-frequency magnetron sputtering; a multistep growth process is proposed to deposit oriented LiNbO₃ films with a smooth surface. Conventional interdigital transducers are fabricated on top of the piezoelectric LiNbO₃ layer by standard optical lithography. We report experimental results for a SAW bandpass filter operating at a frequency above 2.30 GHz. We have observed that Rayleigh SAW modes are excited within this structure, with extremely high phase velocities (up to 12 000 m/s). This latter result illustrates the greatest advantage of using diamond as an acoustic substrate. It allows the fabrication of SAW devices operating in the gigahertz frequency range using standard optical lithography.