A rhombohedral ferroelectric phase in epitaxially strained Hf0.5Zr0.5O2 thin films

Abstract

Hafnia-based thin films are a favoured candidate for the integration of robust ferroelectricity at the nanoscale into next-generation memory and logic devices. This is because their ferroelectric polarization becomes more robust as the size is reduced, exposing a type of ferroelectricity whose mechanism still remains to be understood. Thin films with increased crystal quality are therefore needed. We report the epitaxial growth of Hf0.5Zr0.5O2 thin films on (001)-oriented La0.7Sr0.3MnO3/SrTiO3 substrates. The films, which are under epitaxial compressive strain and predominantly (111)-oriented, display large ferroelectric polarization values up to 34 μC cm−2 and do not need wake-up cycling. Structural characterization reveals a rhombohedral phase, different from the commonly reported polar orthorhombic phase. This finding, in conjunction with density functional theory calculations, allows us to propose a compelling model for the formation of the ferroelectric phase. In addition, these results point towards thin films of simple oxides as a vastly unexplored class of nanoscale ferroelectrics.

Access options

Rent or Buy article

Get time limited or full article access on ReadCube.

from$8.99

All prices are NET prices.

Fig. 1: XRD structural characterization of HZO films on LSMO-buffered 001-oriented STO.
Fig. 2: Domain configuration and symmetry.
Fig. 3: Electron microscopy characterization.
Fig. 4: Ferroelectric characterization.
Fig. 5: Theoretical calculations and proposed structure.

Data availability

The data that support the findings of this study are included in the main text and Supplementary Information.

References

  1. 1.

    Scott, J. F. Applications of modern ferroelectrics. Science 315, 954–959 (2007).

  2. 2.

    Ramesh, R. Ferroelectrics: a new spin on spintronics. Nat. Mater. 9, 380–381 (2010).

  3. 3.

    Eom, C. B. & Trolier-McKinstry, S. Thin-film piezoelectric MEMS. MRS Bull. 37, 1007–1017 (2012).

  4. 4.

    Batra, I. P., Wurfel, P. & Silverman, B. D. Phase transition, stability, and depolarization field in ferroelectric thin films. Phys. Rev. B 8, 3257–3265 (1973).

  5. 5.

    Wurfel, P. & Batra, I. P. Depolarization-field-induced instability in thin ferroelectric film-experiment and theory. Phys. Rev. B 8, 5126 (1973).

  6. 6.

    Park, M. H. et al. Ferroelectricity and antiferroelectricity of doped thin HfO2-based films. Adv. Mater. 27, 1811–1831 (2015).

  7. 7.

    Ohtaka, O. et al. Phase relations and volume changes of hafnia under high pressure and high temperature. J. Am. Ceram. Soc. 84, 1369–1373 (2001).

  8. 8.

    Ohtaka, O. et al. Phase relations and equations of state of ZrO2 under high temperature and high pressure. Phys. Rev. B 63, 174108 (2001).

  9. 9.

    Lee, C.-K., Cho, E., Lee, H.-S., Hwang, C. S. & Han, S. First-principles study on doping and phase stability of HfO2. Phys. Rev. B 78, 012102 (2008).

  10. 10.

    Shandalov, M. & McIntyre, P. C. Size-dependent polymorphism in HfO2 nanotubes and nanoscale thin films. J. Appl. Phys. 106, 084322 (2009).

  11. 11.

    Tsunekawa, S., Ito, S., Kawazoe, Y. & Wang, J. T. Critical size of the phase transition from cubic to tetragonal in pure zirconia nanoparticles. Nano Lett. 3, 871–875 (2003).

  12. 12.

    Hasegawa, H. Rhombohedral phase produced in abraded surfaces of partially stabilized zirconia (PSZ). J. Mater. Sci. Lett. 2, 91–93 (1983).

  13. 13.

    Hasegawa, H. & Hioki, T. Cubic-to-rhombohedral phase transformation in zirconia by ion implantation. J. Mater. Sci. Lett. 4, 1092 (1985).

  14. 14.

    Zhao, B., Jak, E. & Hayes, P. C. Phase equilibria in the system. J. Less Common Met. 17, 151–159 (1969).

  15. 15.

    Burke, D. P. & Rainforth, W. M. Intermediate rhombohedral (r-ZrO2) phase formation at the surface of sintered Y-TZP’s. J. Mater. Sci. Lett. 16, 883–885 (1997).

  16. 16.

    Kisi, E. H., Howard, C. J. & Hill, R. J. Crystal structure of orthorhombic zirconia in partially stabilized zirconia. J. Am. Ceram. Soc. 72, 1757–1760 (1989).

  17. 17.

    Müller, J. et al. Ferroelectric hafnium oxide: A CMOS­compatible and highly scalable approach to future ferroelectric memories. In Proc. IEEE Int. Electron Devices Meeting 10.8.1–10.8.4 (IEEE, 2013).

  18. 18.

    Starschich, S., Griesche, D., Schneller, T. & Böttger, U. Chemical solution deposition of ferroelectric hafnium oxide for future lead free ferroelectric devices. ECS J. Solid State Sci. Technol. 4, P419–P423 (2015).

  19. 19.

    Xu, L. et al. Kinetic pathway of the ferroelectric phase formation in doped HfO2 films. J. Appl. Phys. 122, 124104 (2017).

  20. 20.

    Shimizu, T., Kata, K., Kiguchi, T., Akama, A. & Konno, T. J. The demonstration of significant ferroelectricity in epitaxial Y-doped HfO2 film. Sci. Rep. 6, 32931 (2016).

  21. 21.

    Kim, S. J. et al. Large ferroelectric polarization of TiN/Hf0.5Zr0.5O2/TiN capacitors due to stress-induced crystallization at low thermal budget. Appl. Phys. Lett. 111, 242901 (2017).

  22. 22.

    Hyuk Park, M. et al. Effect of forming gas annealing on the ferroelectric properties of Hf0.5Zr0.5O2 thin films with and without Pt electrodes. Appl. Phys. Lett. 102, 112914 (2013).

  23. 23.

    Park, M. H. et al. Study on the degradation mechanism of the ferroelectric properties of thin Hf0.5Zr0.5O2 films on TiN and Ir electrodes. Appl. Phys. Lett. 105, 72902 (2014).

  24. 24.

    Hoffmann, M. et al. Stabilizing the ferroelectric phase in doped hafnium oxide. J. Appl. Phys. 118, 072006 (2015).

  25. 25.

    Florent, K. et al. Understanding ferroelectric Al:HfO2 thin films with Si-based electrodes for 3D applications. J. Appl. Phys. 121, 204103 (2017).

  26. 26.

    Böscke, T. S., Müller, J., Bräuhaus, D., Schröder, U. & Böttger, U. Ferroelectricity in hafnium oxide thin films. Appl. Phys. Lett. 99, 102903 (2011).

  27. 27.

    Starschich, S., Schenk, T., Schroeder, U. & Boettger, U. Ferroelectric and piezoelectric properties of Hf1−xZrxO2 and pure ZrO2 films. Appl. Phys. Lett. 110, 182905 (2017).

  28. 28.

    Shimizu, T. et al. Study on the effect of heat treatment conditions on metalorganic-chemical-vapor-deposited ferroelectric Hf0.5Zr0.5O2 thin film on Ir electrode. Jpn. J. Appl. Phys. 53, 09PA04 (2014).

  29. 29.

    Park, M. H., Kim, H. J., Kim, Y. J., Moon, T. & Hwang, C. S. The effects of crystallographic orientation and strain of thin Hf 0.5Zr0.5O2 film on its ferroelectricity. Appl. Phys. Lett. 104, 072901 (2014).

  30. 30.

    Shiraishi, T. et al. Impact of mechanical stress on ferroelectricity in (Hf0.5Zr0.5)O2 thin films. Appl. Phys. Lett. 108, 262904 (2016).

  31. 31.

    Materlik, R., Künneth, C. & Kersch, A. The origin of ferroelectricity in Hf1−xZrxO2: A computational investigation and a surface energy model. J. Appl. Phys. 117, 134109 (2015).

  32. 32.

    Park, M. H. et al. Surface and grain boundary energy as the key enabler of ferroelectricity in nanoscale hafnia-zirconia: a comparison of model and experiment. Nanoscale 9, 9973–9986 (2017).

  33. 33.

    Müller, J. et al. Ferroelectricity in simple binary ZrO2 and HfO2. Nano Lett. 12, 4318–4323 (2012).

  34. 34.

    Müller, J. et al. Ferroelectric Zr0.5Hf0.5O2 thin films for nonvolatile memory applications. Appl. Phys. Lett. 99, 112901 (2011).

  35. 35.

    Park, M. H., Kim, H. J., Kim, Y. J., Lee, W. & Moon, T. Evolution of phases and ferroelectric properties of thin Hf0.5Zr0.5O2 films according to the thickness and annealing temperature. Appl. Phys. Lett. 102, 242905 (2013).

  36. 36.

    Riedel, S., Polakowski, P. & Müller, J. A thermally robust and thickness independent ferroelectric phase in laminated hafnium zirconium oxide. AIP Adv. 6, 095213 (2016).

  37. 37.

    Morozovska, A. N., Glinchuk, M. D. & Eliseev, E. A. Phase transitions induced by confinement of ferroic nanoparticles. Phys. Rev. B 76, 014102 (2007).

  38. 38.

    Polking, M. J. et al. Size-dependent polar ordering in colloidal GeTe nanocrystals. Nano Lett. 11, 1147–1152 (2011).

  39. 39.

    Lu, C. H., Raitano, J. M., Khalid, S., Zhang, L. & Chan, S. W. Cubic phase stabilization in nanoparticles of hafnia-zirconia oxides: Particle-size and annealing environment effects. J. Appl. Phys. 103, 124303 (2008).

  40. 40.

    Shen, P. & Lee, W. H. (111)-Specific coalescence twinning and martensitic transformation of tetragonal ZrO2 condensates. Nano Lett. 1, 707–711 (2001).

  41. 41.

    Vollath, D., Fischer, F. D., Hagelstein, M. & Szabó, D. V. Phases and phase transformations in nanocrystalline ZrO2. J. Nanopart. Res. 8, 1003–1016 (2006).

  42. 42.

    Huan, T. D., Sharma, V., Rossetti, G. A. & Ramprasad, R. Pathways towards ferroelectricity in hafnia. Phys. Rev. B 90, 064111 (2014).

  43. 43.

    Pešić, M. et al. Physical mechanisms behind the field-cycling behavior of HfO2-based ferroelectric capacitors. Adv. Funct. Mater. 26, 4601–4612 (2016).

  44. 44.

    Garcia-Barriocanal, J. et al. Colossal Ionic conductivity at interfaces of epitaxial ZrO2:Y2O3/SrTiO3 heterostructures. Science 321, 676–680 (2008).

  45. 45.

    Lee, H. N., Christen, H. M., Chisholm, M. F., Rouleau, C. M. & Lowndes, D. H. Strong polarization enhancement in asymmetric three-component ferroelectric superlattices. Nature 433, 395–399 (2005).

  46. 46.

    Kim, H. J. et al. A study on the wake-up effect of ferroelectric Hf0.5Zr0.5O2 films by pulse-switching measurement. Nanoscale 8, 1383–1389 (2015).

  47. 47.

    Schenk, T. et al. Electric field cycling behavior of ferroelectric hafnium oxide. ACS Appl. Mater. Interfaces 6, 19744–19751 (2014).

  48. 48.

    Lyakhov, A. O., Oganov, A. R., Stokes, H. T. & Zhu, Q. New developments in evolutionary structure prediction algorithm USPEX. Comput. Phys. Commun. 184, 1172–1182 (2013).

  49. 49.

    Oganov, A. R. & Glass, C. W. Crystal structure prediction using ab initio evolutionary techniques: Principles and applications. J. Chem. Phys. 124, 244704 (2006).

  50. 50.

    Glass, C. W., Oganov, A. R. & Hansen, N. USPEX—Evolutionary crystal structure prediction. Comput. Phys. Commun. 175, 713–720 (2006).

  51. 51.

    Demkov, A. & Navrotsky, A. Materials Fundamentals of Gate Dielectrics (Springer, Dordrecht, 2005).

  52. 52.

    Béa, H. et al. Evidence for room-temperature multiferroicity in a compound with a giant axial ratio. Phys. Rev. Lett. 102, 217603 (2009).

  53. 53.

    Tinte, S., Rabe, K. M. & Vanderbilt, D. Anomalous enhancement of tetragonality in PbTiO3 induced by negative pressure. Phys. Rev. B 68, 144105 (2003).

  54. 54.

    Wojdeł, J. C. & Íñiguez, J. Ab initio indications for giant magnetoelectric effects driven by structural softness. Phys. Rev. Lett. 105, 037208 (2010).

  55. 55.

    Rabe, K. M, Ahn, C. H. & Triscone, J.-M. (eds) Physics of Ferroelectrics: A Modern Perspective (Springer,Berlin, 2007) .

  56. 56.

    Kresse, G. & Furthmüller, J. Efficient iterative schemes for ab initio total-energy calculations using a plane-wave basis set. Phys. Rev. B 54, 11169–11186 (1996).

  57. 57.

    Joubert, D. From ultrasoft pseudopotentials to the projector augmented-wave method. Phys. Rev. B 59, 1758–1775 (1999).

  58. 58.

    Perdew, J. et al. Atoms, molecules, solids, and surfaces: applications of the generalized gradient approximation for exchange and correlation. Phys. Rev. B 46, 6671–6687 (1992).

  59. 59.

    Blöchl, P. E. Projector augmented-wave method. Phys. Rev. B 50, 17953–17979 (1994).

  60. 60.

    Stokes, H. T. & Hatch, D. M. FINDSYM: Program for identifying the space-group symmetry of a crystal. J. Appl. Crystallogr. 38, 237–238 (2005).

  61. 61.

    Capillas, C. et al. A new computer tool at the Bilbao Crystallographic Server to detect and characterize pseudosymmetry. Zeitschrift Krist. 226, 186–196 (2011).

  62. 62.

    Orobengoa, D., Capillas, C., Aroyo, I. & Perez, J. M. AMPLIMODES: symmetry mode analysis on the Bilbao Crystallographic Server research papers. Appl.Cryst. 42, 820–833 (2009).

  63. 63.

    Momma, K. & Izumi, F. VESTA 3 for three-dimensional visualization of crystal, volumetric and morphology data. J. Appl. Crystallogr. 44, 1272–1276 (2011).

  64. 64.

    King-Smith, R. D. & Vanderbilt, D. Theory of polarization of crystalline solids. Phys. Rev. B 47, 1651–1654 (1993).

Download references

Acknowledgements

We are grateful to S. Volkov and F. Bertram for their help at the P08 beamline in Petra III (DESY0-Hamburg), and T. Schenk for insightful discussions about the paper. Y.W. and B.N. are grateful for China Scholarship Council and Van Gogh travel grants. P.N. acknowledges the funding received from the European Union’s Horizon 2020 research and innovation programme under Marie Sklodowska-Curie grant agreement no. 794954. P.N. and B.D. would like to acknowledge a public grant overseen by the French National Research Agency (ANR) as a part of the `Investissements d‘Avenir’ programme (grant no. ANR-10-LABX-0035, Labex Nanoscalay) and through project ANR-17-CE24-0032/EXPAND. B.D. also acknowledges Luxembourg National Research Fund under Project MULTICALOR:INTER/MOBILITY/16/11259210. H.J.Z. and J.Í. acknowledge the support of the Luxembourg National Research Fund through the PEARL (grant no. FNR/P12/4853155/Kreisel COFERMAT) and CORE (grant no. FNR/C15/MS/10458889 NEWALLS) programmes.

Author information

B.N. and Y.W. conceived the idea, and the project plan. Y.W. synthesized the films. P.N. and J.M. prepared samples for TEM, and performed the experiments, and P.N. analysed the data, under the supervision of B.J.K. and B.D. Y.W., M.S. and B.N. performed XRD and analysed the data. Y.W., S.M. and G.A. fabricated devices, tested their ferroelectric properties and analysed the data with help from A.S.E. H.J.Z. and J.Í. performed the first-principles calculations. B.J.K. and G.R.B. extensively helped in understanding the structure and symmetry of the films. P.L. and B.D. provided useful insights all along the project. Y.W., P.N., B.N. and J.Í. co-wrote the manuscript with feedback from all of the authors.

Correspondence to Beatriz Noheda.

Ethics declarations

Competing interests

The authors declare no competing interests.

Additional information

Publisher’s note: Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Supplementary information

Supplementary Information

Supplementary Notes 1–6, Supplementary Figures 1–10

Rights and permissions

Reprints and Permissions

About this article

Verify currency and authenticity via CrossMark

Cite this article

Wei, Y., Nukala, P., Salverda, M. et al. A rhombohedral ferroelectric phase in epitaxially strained Hf0.5Zr0.5O2 thin films. Nature Mater 17, 1095–1100 (2018). https://doi.org/10.1038/s41563-018-0196-0

Download citation

Further reading