Abstract
Doped hafnium oxide (HfO2) ferroelectrics show great potential in next-generation memory and compute-in-memory applications due to their compatibility with advanced silicon-based technology. Typically, HfO2 shows a reverse size effect, where the polar orthorhombic phase (PO, space group Pca21) is stabilized only at thicknesses of a few nanometers. Yttrium-doped hafnium oxide (Y:HfO2) exhibits a distinct behavior, maintaining robust polarization from ultrathin films to bulk crystals. However, the mechanism enabling Y:HfO2 ferroelectricity which is critical for expanding device scalability and performance remains unclear. In this work, the multi-field stabilization mechanisms of the PO phase are systematically investigated for bulk and thin film Y:HfO2 via first-principles calculations. The synergistic effect of composite defects combined with Y dopants and tetra-coordinated oxygen vacancies (Y+VO4), strain, and electric field significantly broadens the window of thermodynamically metastable PO phase. Notably, we find that the strain requirement can be significantly relaxed with increasing concentration of Y dopants or Y+VO4 defect pairs, revealing the feasibility of achieving ferroelectricity in bulk Y:HfO2 without substrate constraints. Moreover, we demonstrate an increase in critical thickness to stabilize the PO phase in Y:HfO2 thin film compared with pure HfO2, which is ascribed to the effects of Y+VO4 defects on the surface energy. These findings clarify the key role of Y+VO4 defects in realizing thickness-unrestricted ferroelectricity in Y: HfO2 and provide critical theoretical guidance for optimizing the fabrication process of high-performance HfO2-based ferroelectric devices.
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All data supporting the findings of this study are available within the article and its Supplementary Information, and from the corresponding author upon request.
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All density functional theory calculations were performed using the commercially licensed Vienna Ab initio Simulation Package (VASP) version 6.4.3.
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Acknowledgements
Computational resources were supported by the High-Performance Computing Platform of Xidian University. In addition, the authors also sincerely acknowledge Dr. Rui Chen and Dr. Jiacheng Gao for their valuable contributions to this work. This work was supported by the National Natural Science Foundation of China (Grant Nos. 12302429, 52302151, 62504182), the National Key Research and Development Plan (2024YFA1208602), the Xidian University Cultivating New Quality Productive Forces (Grant No. QTZX25115), and the Scientific Research Innovation Capability Support Project for Young Faculty (Grant No. ZYGXQNJSKYCXNLZCXM-M22).
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Jin Huang led the investigation, data curation, and original draft preparation; Jiangheng Yang contributed to methodology and formal analysis; Shijie Jia and Junhui Wang assisted in investigation; Fei Yan, Zhipeng Wang, and Hua Chen participated in manuscript review; Jiajia Liao supervised the project and coordinated administration; Min Liao provided funding acquisition and conceptual discussions. Yichun Zhou provided software support and supervision. All authors reviewed and approved the final manuscript.
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Huang, J., Yang, J., Jia, S. et al. From ultrathin to bulk: decoding thickness-unrestricted ferroelectricity in Y:HfO2 via first-principles. npj Comput Mater (2026). https://doi.org/10.1038/s41524-026-02046-5
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DOI: https://doi.org/10.1038/s41524-026-02046-5
