  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
{\mu}C/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.
