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.