Interface-engineered ferroelectricity of epitaxial Hf(0.5)Zr(0.5)O(2) 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 Hf(0.5)Zr(0.5)O(2) thin film by deliberately controlling the termination of the bottom La(0.67)Sr(0.33)MnO(3) layer. We find that the Hf(0.5)Zr(0.5)O(2) films on the MnO(2)-terminated La(0.67)Sr(0.33)MnO(3) have more ferroelectric orthorhombic phase than those on the LaSrO-terminated La(0.67)Sr(0.33)MnO(3), while with no wake-up effect. Even though the Hf(0.5)Zr(0.5)O(2) thickness is as thin as 1.5 nm, the clear ferroelectric orthorhombic (111) orientation is observed on the MnO(2) termination. Our transmission electron microscopy characterization and theoretical modelling reveal that reconstruction at the Hf(0.5)Zr(0.5)O(2)/ La(0.67)Sr(0.33)MnO(3) interface and hole doping of the Hf(0.5)Zr(0.5)O(2) layer resulting from the MnO(2) interface termination are responsible for the stabilization of the metastable ferroelectric phase of Hf(0.5)Zr(0.5)O(2). We anticipate that these results will inspire further studies of interface-engineered hafnia-based systems.