Ferroelectric memories experienced a revival in the last decade due to the discovery of ferroelectricity in HfO2-based nanometer-thick thin films. These films exhibit exceptional silicon compatibility, overcoming the scaling and integration obstacles that impeded perovskite ferroelectrics' use in high-density integrated circuits. The exact phase responsible for ferroelectricity in hafnia films remains debated with no single factor identified that could stabilize the ferroelectric phase thermodynamically. Here, supported by density functional theory (DFT) high-throughput (HT) calculations that screen a broad range of epitaxial conditions, we demonstrate conclusively that specific epitaxial conditions achievable with common substrates such as yttria-stabilized zirconia (YSZ) and SrTiO3 can favor the polar Pca21 phase thermodynamically over other polar phases such as R3m and Pmn21 and nonpolar P21/c phase. The substrate's symmetry constraint-induced shear strain is crucial for the preference of Pca21. The strain-stability phase diagrams resolve experiment-theory discrepancies and can guide the improvement of ferroelectric properties of epitaxial hafnia thin films.
@article{arxiv.2304.07057,
title = {Epitaxial ferroelectric hafnia stabilized by symmetry constraints},
author = {Tianyuan Zhu and Shiqing Deng and Shi Liu},
journal= {arXiv preprint arXiv:2304.07057},
year = {2024}
}