Intrinsic and Extrinsic Factors Controlling Coercivity of Hafnia-based Ferroelectric Epitaxial Thin Film

Hafnia-based ferroelectric thin films are promising in integrating ferroelectricity in modern electronics due to their compatibility to silicon technology and the enhanced ferroelectric properties at the nanoscale. On the other hand, the high coercivity of ferroelectric hafnia, which is believed to originate from the unique layer structure, undermines the energy efficiency of the potential device applications. Based on epitaxial hafnia thin films grown on La_0.7Sr_0.3MnO₃/SrTiO₃ (110), we have studied the intrinsic and extrinsic factors that control coercivity. We found that coercivity is largely determined by interfacial nucleation. As an extrinsic factor, interfacial nucleation layer like amorphous Al₂O₃ can substantially enhance the nucleation rate and reduce coercivity. For the intrinsic factor, the interfacial reconstruction that leads to tetragonal phase strongly affects the nucleation rate and coercivity. More specifically, by tuning the background oxygen pressure during the film growth and the film composition, a thicker interfacial tetragonal phase can be achieved, which lowers coercivity down to below 1 V. These results suggest a route in systematically tuning coercivity of ferroelectric hafnia thin films for practical applications.