55.4 GHz Bulk Acoustic Resonator in Thin-Film Scandium Aluminum Nitride

Abstract

This study describes a sputtered scandium aluminum nitride (ScAlN) thin-film bulk acoustic resonator (FBAR) at 55.4 GHz. The resonator leverages the third-order symmetric (S3) mode in 37 nm Al on 85 nm Sc <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.3</inf> Al <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.7</inf> N on a 37 nm Al film stack, enabled by a new fabrication procedure. The 55.4 GHz S3 tone achieves electromechanical coupling (k <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ) of 3.8% and a 3-dB quality factor (Q) of 30, surpassing the reported state-of-the-art figure of merits (FoM, k <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ∙Q). Besides, the first-order symmetric (S1) mode at 21.0 GHz achieves k <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> of 6.4% and Q of 62. Upon further optimization of the sputtering procedure, ScAlN/AlN-based mmWave acoustic resonators will continue to be improved.