After decades of searching for robust nanoscale ferroelectricity that could enable integration into the next generation memory and logic devices, hafnia-based thin films have appeared as the ultimate candidate because their ferroelectric (FE) polarization becomes more robust as the size is reduced. This exposes a new kind of ferroelectricity, whose mechanism still needs to be understood. Towards this end, thin films with increased crystal quality are needed. We report the epitaxial growth of Hf0.5Zr0.5O2 (HZO) thin films on (001)-oriented La0.7Sr0.3MnO3/SrTiO3 (STO) substrates. The films, which are under epitaxial compressive strain and are predominantly (111)-oriented, display large FE polarization values up to 34 {\mu}C/cm2 and do not need wake-up cycling. Structural characterization reveals a rhombohedral phase, different from the commonly reported polar orthorhombic phase. This unexpected finding allows us to propose a compelling model for the formation of the FE phase. In addition, these results point towards nanoparticles of simple oxides as a vastly unexplored class of nanoscale ferroelectrics.
@article{arxiv.1801.09008,
title = {A rhombohedral ferroelectric phase in epitaxially-strained Hf0.5Zr0.5O2 thin films},
author = {Yingfen Wei and Pavan Nukala and Mart Salverda and Sylvia Matzen and Hong Jian Zhao and Jamo Momand and Arnoud Everhardt and Graeme R. Blake and Philippe Lecoeur and Bart J. Kooi and Jorge Íñiguez and Brahim Dkhil and Beatriz Noheda},
journal= {arXiv preprint arXiv:1801.09008},
year = {2018}
}