Intrinsic ferroelectricity in Y-doped HfO₂ thin films

Ferroelectric HfO₂-based materials hold great potential for the widespread integration of ferroelectricity into modern electronics due to their compatibility with existing Si technology. Earlier work indicated that a nanometre grain size was crucial for the stabilization of the ferroelectric phase. This constraint, associated with a high density of structural defects, obscures an insight into the intrinsic ferroelectricity of HfO₂-based materials. Here we demonstrate that stable and enhanced polarization can be achieved in epitaxial HfO₂ films with a high degree of structural order (crystallinity). An out-of-plane polarization value of 50 μC cm^-2 has been observed at room temperature in Y-doped HfO₂(111) epitaxial thin films, with an estimated full value of intrinsic polarization of 64 μC cm^-2, which is in close agreement with density functional theory calculations. The crystal structure of films reveals the Pca2₁ orthorhombic phase with small rhombohedral distortion, underlining the role of the structural constraint in stabilizing the ferroelectric phase. Our results suggest that it could be possible to exploit the intrinsic ferroelectricity of HfO₂-based materials, optimizing their performance in device applications.