Interface-engineered ferroelectricity of epitaxial HfZrO thin films.

Ferroelectric hafnia-based thin films have attracted intense attention due to their compatibility with complementary metal-oxide-semiconductor technology. However, the ferroelectric orthorhombic phase is thermodynamically metastable. Various efforts have been made to stabilize the ferroelectric orthorhombic phase of hafnia-based films such as controlling the growth kinetics and mechanical confinement. Here, we demonstrate a key interface engineering strategy to stabilize and enhance the ferroelectric orthorhombic phase of the HfZrO thin film by deliberately controlling the termination of the bottom LaSrMnO layer. We find that the HfZrO films on the MnO-terminated LaSrMnO have more ferroelectric orthorhombic phase than those on the LaSrO-terminated LaSrMnO, while with no wake-up effect. Even though the HfZrO thickness is as thin as 1.5 nm, the clear ferroelectric orthorhombic (111) orientation is observed on the MnO termination. Our transmission electron microscopy characterization and theoretical modelling reveal that reconstruction at the HfZrO/ LaSrMnO interface and hole doping of the HfZrO layer resulting from the MnO interface termination are responsible for the stabilization of the metastable ferroelectric phase of HfZrO. We anticipate that these results will inspire further studies of interface-engineered hafnia-based systems.