High-K² _eff High Frequency BAW Resonators Based on Single-Crystal Polarity-Inverted Al_xSc_1-xN Piezoelectric Films

Applying acoustic resonators at frequencies above 10 GHz is highly challenging due to the degradation of crystal quality in thinner piezoelectric films and the impact of parasitic parameters in ultrathin electrodes. This work presents a novel approach to fabricate bulk acoustic wave (BAW) resonators operating in the Ku band utilizing single-crystal polarity-inverted Al<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-x</inf>Sc<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</inf>N piezoelectric films. The thickness of the polarity-inverted Al<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-x</inf>Sc<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</inf>N bilayers was carefully designed to maximize the $k_{eff}^2$ of the resonator. The fabricated BAW resonator demonstrates a resonant frequency above 14 GHz, achieving a ${\text{k}}_{eff}^2$ of 9.7% and a Q factor of 439. These results highlight the significant potential of this approach for Ku-band applications, offering a promising advancement to high-frequency and wideband acoustic filter technology.