Large ferroelectricity in Hf0.85Ce0.15O2−δ polycrystalline thin films via lattice expansion

Abstract

The discovery of ferroelectricity in HfO₂-based thin films has strongly energized the field of integrated semiconductor devices. To expand the physical applications of HfO₂-based thin films, it is essential to urgently enhance their ferroelectric polarization. In this work, we have synthesized Hf_0.85Ce_0.15O_2−δ thin films with a large remanent polarization of 2P_r ∼ 69 μC cm⁻², which is the maximum of all HfO₂-based polycrystal thin films. The strong increase of the remanent polarization is caused by the significant lattice expansion triggered by the increase of Ce³⁺ content, which is controlled by temperature. Due to the increase of the lattice constant in the c-axis, the unit-cell volume expands from 132.16 ų to 137.66 ų, inducing an increase in the distortion of ions along the direction of the polarization axis and leading to an increase in polarization. This finding is of significant practical importance for promoting HfO₂-based materials and their development in physical fields.