Intrinsic ferroelectricity in Y-doped HfO2 thin films

Ferroelectric HfO₂-based materials hold great potential for widespread integration of ferroelectricity into modern electronics due to their robust ferroelectric properties at the nanoscale and compatibility with the existing Si technology. Earlier work indicated that the nanometer crystal grain size was crucial for stabilization of the ferroelectric phase of hafnia. This constraint caused high density of unavoidable structural defects of the HfO₂-based ferroelectrics, obscuring the intrinsic ferroelectricity inherited from the crystal space group of bulk HfO₂. Here, we demonstrate the intrinsic ferroelectricity in Y-doped HfO₂ films of high crystallinity. Contrary to the common expectation, we show that in the 5% Y-doped HfO₂ epitaxial thin films, high crystallinity enhances the spontaneous polarization up to a record-high 50 µC/cm² value at room temperature. The high spontaneous polarization persists at reduced temperature, with polarization values consistent with our theoretical predictions, indicating the dominant contribution from the intrinsic ferroelectricity. The crystal structure of these films reveals the Pca2₁ orthorhombic phase with a small rhombohedral distortion, underlining the role of the anisotropic stress and strain. These results open a pathway to controlling the intrinsic ferroelectricity in the HfO₂-based materials and optimizing their performance in applications.