Origin of the Intrinsic Ferroelectricity of HfO2 from ab Initio Molecular Dynamics

HfO2-based ferroelectric film has shown great potential for the application of ferroelectric memory due to its great advantages as compared to traditional ferroelectrics. However, the origin of the ferroelectricity of the HfO2-based ferroelectric film is still under debate. In this work, by performing ab initial molecular dynamics calculation, the phase stability and the polarization switching behavior of HfO2 were systematically studied to illuminate the intrinsic origin its ferroelectricity. Results show that, under different in-plane constraints and room temperature, the out-of-plane polarized orthorhombic ferroelectric phase Pca2(1) is always the metastable phase of HfO2. As driven by the out-of-plane electric field, HfO2 exhibits linear dielectric behavior or antiferroelectric behavior with the ferroelectric-tetragonal-ferroelectric phase transformation under in-plane compression. With the tensile strain condition, the nonferroelectric HfO2 could be transformed to be the out-of-plane polarized orthorhombic ferroelectric phase, which shows good ferroelectricity under a periodic electric field. The triggered phase transformation and ferroelectricity as modulated by the epitaxial constraint as found in this work were verified by a recent experiment and should be the intrinsic origin of the ferroelectricity of HfO2 based films.