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Intrinsic ferroelectricity in Y-doped HfO2 thin films

Abstract

Ferroelectric HfO2-based materials hold great potential for the widespread integration of ferroelectricity into modern electronics due to their compatibility with existing Si technology. Earlier work indicated that a nanometre grain size was crucial for the stabilization of the ferroelectric phase. This constraint, associated with a high density of structural defects, obscures an insight into the intrinsic ferroelectricity of HfO2-based materials. Here we demonstrate that stable and enhanced polarization can be achieved in epitaxial HfO2 films with a high degree of structural order (crystallinity). An out-of-plane polarization value of 50 μC cm–2 has been observed at room temperature in Y-doped HfO2(111) epitaxial thin films, with an estimated full value of intrinsic polarization of 64 μC cm–2, which is in close agreement with density functional theory calculations. The crystal structure of films reveals the Pca21 orthorhombic phase with small rhombohedral distortion, underlining the role of the structural constraint in stabilizing the ferroelectric phase. Our results suggest that it could be possible to exploit the intrinsic ferroelectricity of HfO2-based materials, optimizing their performance in device applications.

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Fig. 1: Structure characterization and ferroelectric hysteresis.
Fig. 2: Local ferroelectric switching by PFM.
Fig. 3: Temperature dependence of ferroelectric hysteresis.
Fig. 4: Structural characterization of YHO films.
Fig. 5: Results of DFT calculations for bulk undoped and 5% Y-doped HfO2.

Data availability

Source data are provided with this paper. All other data that support the findings of this study are available within the article and Supplementary Information.

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Acknowledgements

This work was primarily supported by the National Science Foundation (NSF), Division of Electrical, Communications and Cyber Systems (ECCS), under grant no. ECCS-1917635 (Y.Y., X.L., X.X., P.B., A.G., M.L, L.T. and E.Y.T.). J.L. acknowledges support from the US Department of Energy’s (DOE) (DE-SC0019173) for interdigital device fabrication. Y.Z. and Haiyan Wang acknowledge support from the NSF (DMR-2016453 and DMR-1565822) for the microscopy effort at Purdue University. The research was performed in part at the Nebraska Nanoscale Facility, National Nanotechnology Coordinated Infrastructure and the Nebraska Center for Materials and Nanoscience, which are supported by the NSF under grant no. ECCS- 2025298, as well as the Nebraska Research Initiative through the Nebraska Center for Materials and Nanoscience and the Nanoengineering Research Core Facility at the University of Nebraska–Lincoln. Sandia National Laboratories is a multimission laboratory managed and operated by the National Technology and Engineering Solutions of Sandia, a wholly owned subsidiary of Honeywell International for the US DOE’s National Nuclear Security Administration under contract DE-NA0003525. This paper describes objective technical results and analysis. Any subjective views or opinions that might be expressed in the paper do not necessarily represent the views of the US DOE or the US Government.

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Authors and Affiliations

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Contributions

The thin films were synthesized by Y.Y. with assistance from X.X. and Haohan Wang. Structure distortion and symmetry were investigated by Y.Y. and X.X. The thin-film structures with in-plane interdigital electrodes were fabricated by X.L. and J.L. Time-resolved RHEED was studied by Y.Y. and X.L. Local switching and temperature-dependent polarization were studied and analysed by P.B. under the supervision of A.G. M.L. carried out the DFT calculations under the supervision of L.T. and E.Y.T. (S)TEM experiments were conducted by Z.A. and Y.Z. under the supervision of J.S., P.L. and Haiyan Wang. The study was conceived by Y.Y., P.B. and X.X. Y.Y., P.B., M.L., E.Y.T., A.G. and X.X. co-wrote the manuscript. All the authors discussed the results and commented on the manuscript.

Corresponding authors

Correspondence to Evgeny Y. Tsymbal, Alexei Gruverman or Xiaoshan Xu.

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The authors declare no competing interests.

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Nature Materials thanks Jeffrey Eastman, Hiroshi Funakubo and Jun Hee Lee for their contribution to the peer review of this work.

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Supplementary information

Supplementary Information

Supplementary Figs. 1–21 and refs. 1–15.

Supplementary Data 1

Atomic coordinates of the HfO2 unit cell.

Source data

Source Data Fig. 1

Source data for Fig. 1b–f.

Source Data Fig. 2

Source data for Fig. 2d.

Source Data Fig. 3

Source data for Fig. 3.

Source Data Fig. 4

Source data for Fig. 4a,d,e,g–i.

Source Data Fig. 5

Source data for Fig. 5a,b.

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Yun, Y., Buragohain, P., Li, M. et al. Intrinsic ferroelectricity in Y-doped HfO2 thin films. Nat. Mater. 21, 903–909 (2022). https://doi.org/10.1038/s41563-022-01282-6

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