A High-$k_{t}{}^{2}$ Switchable Ferroelectric Al0.7Sc0.3N Film Bulk Acoustic Resonator

This work demonstrates the hysteresis behavior and temperature characterization of an AlScN Film bulk acoustic resonator (FBAR) with ∼30% $\text{Sc}/(\text{Al}+\text{Sc})$ ratio. Operating at ∼3 GHz, the as-fabricated FBAR exhibits a record high effective electromechanical coupling ($k_{t}{}^{2}$) of 18% with a mechanical quality factor ($Q_{m}$) of 328. The polarization of the FBAR can be switched from N-polar to Al-polar by using a triangular-wave signal with a peak voltage of −350 V, applied for 6 seconds at 1 kHz across a 900 nm-thick Al0.7Sc0.3N film. It is shown that the polarization switching of AlScN film not only changes the polarity of the piezoelectric coefficient (e33), but also changes the series resistance of the metal-ferroelectric-metal (MFM) stack and leads to an effective “switching” of the FBAR. The frequency response of the switchable FBAR is investigated after polarization switching during 4 cycles and at elevated temperatures up to 600 K.