Epitaxial Aluminum Scandium Nitride Super High Frequency Acoustic Resonators

Abstract

This paper demonstrates super high frequency (SHF) Lamb and surface acoustic wave resonators based on single-crystal orientation Aluminum Scandium Nitride (AlScN) thin films grown on silicon substrates by molecular beam epitaxy (MBE). We report on the experimental frequency response and electromechanical properties of 400 nm-thick crystalline AlScN acoustic resonators with up to 12% Sc/(Sc+Al) ratio. The film thickness is optimized for operation at the SHF range, targeting emerging wireless communication standards, such as 4G LTE/5G. We report on high-performance acoustic devices that take advantage of the crystallinity, and high piezoelectric properties of 400 nm-thick epitaxial AlScN films. Our work presents enhanced effective electromechanical coupling coefficients (k <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">eff</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ) up to 5.3% and unloaded quality factors (Q <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</sub> ) of ~192 at 3-10 GHz. However, fabrication challenges due to the high-stress levels of sub-micron AlScN epi-layers grown on Si substrates remain challenging and will be discussed in this paper. [2019-0231].