Thin-Film Scandium Aluminum Nitride Bulk Acoustic Resonator with High Q of 208 and K2 of 9.5% at 12.5 GHz

This work describes sputtered scandium aluminum nitride (ScAlN) thin-film bulk acoustic resonators (FBAR) at 12.5 GHz with high electromechanical coupling <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$(k^{2})$</tex> of 9.5% and quality factor <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$(Q)$</tex> of 208, resulting in a figure of merit (FoM, <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$Q\cdot k^{2}$</tex>) of 19.8. ScAlN resonators employ a stack of 90 nm thick 20% Sc doping ScAlN piezoelectric film on the floating bottom 38 nm thick platinum (Pt) electrode to achieve low losses and high coupling toward centimeter wave (cmWave) frequency band operation. Three fabricated and FBARs are reported, show promising prospects of ScAlN-Pt stack towards cmWave front-end filters.