Intrinsic ferroelectricity in Y-doped HfO2 thin films

TL;DR

This study demonstrates intrinsic ferroelectricity in high-crystallinity Y-doped HfO2 thin films, achieving record polarization levels and revealing the structural basis for ferroelectric behavior, which is promising for electronic applications.

Contribution

It provides evidence of intrinsic ferroelectricity in Y-doped HfO2 films with high crystallinity, challenging previous assumptions about grain size constraints.

Findings

Record-high spontaneous polarization of 50 μC/cm2 at room temperature.

Intrinsic ferroelectricity confirmed by structural analysis and polarization persistence at reduced temperatures.

The orthorhombic Pca21 phase with rhombohedral distortion is identified as the structural basis.

Abstract

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.