Intrinsically tunable 0.67 BiFeO₃-0.33 BaTiO₃ thin film bulk acoustic wave resonators

Intrinsically tunable 0.67BiFeO₃-0.33 BaTiO₃(BF–BT) thin film bulk acoustic wave resonators with record high tunability of 4.4% and effective electromechanical coupling coefficient of 10% are fabricated and analyzed. The analysis, based on the theory of the dc field induced piezoelectric effect with the mechanical loading by the electrodes taken into account, reveals that the enhanced parameters are associated with the inherently high BF–BT electrostriction coefficient, which is found to be 5.9x10¹⁰ m/F. The Q-factor of the BF–BT resonators is up to 220 at 4.1 GHz and is limited mainly by acoustic wave scattering at reflection from a relatively rough top interface