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Enhancement of ferroelectricity at metal–oxide interfaces

Nature Materials volume 8, pages 392–397 (2009)Cite this article

Abstract

The development of ultrathin ferroelectric capacitors for use in memory applications has been hampered by depolarization effects arising from the electrode–film interfaces. These can be characterized in terms of a reduced interface capacitance, or equivalently an ‘effective dead layer’ in contact with the electrode. Here, by performing first-principles calculations on four capacitor structures based on BaTiO3 and PbTiO3, we determine the intrinsic interfacial effects responsible for destabilizing the ferroelectric state in ultrathin-film devices. Although it has been widely believed that these are governed by the electronic screening properties at the interface, we show that they also depend crucially on the local chemical environment through the force constants of the metal oxide bonds. In particular, in the case of interfaces formed between AO-terminated perovskites and simple metals, we demonstrate a novel mechanism of interfacial ferroelectricity that produces an overall enhancement of the ferroelectric instability of the film, rather than its suppression as is usually assumed. The resulting ‘negative dead layer’ suggests a route to thin-film ferroelectric devices that are free of deleterious size effects.

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Figure 1: Inverse local permittivity profiles for symmetric capacitor structures studied in this work.
Figure 2: Plots of Callen dynamical charges, arranged head to head and tail to tail to emphasize rapid convergence to common bulk values.
Figure 3: Schematic representation of the salient features of the Pt2–AO interface.
Figure 4: Ionic displacements induced by a small field of D=10−3 a.u. (0.455 μC cm−2).
Figure 5: Computed local properties at the BTO–Au interface.

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Acknowledgements

This work was supported by the Department of Energy SciDac programme on ‘Quantum simulations of materials and nanostructures’, grant number DE-FC02-06ER25794 (M.S. and N.A.S.), and by ONR grant N00014-05-1-0054 (D.V.). Calculations were carried out at the San Diego Supercomputer Center and at the National Center for Supercomputer Applications.

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Authors and Affiliations

  1. Materials Department, University of California, Santa Barbara, California 93106-5050, USA

    Massimiliano Stengel & Nicola A. Spaldin

  2. Department of Physics and Astronomy, Rutgers University, Piscataway, New Jersey 08854-8019, USA

    David Vanderbilt

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Correspondence to Nicola A. Spaldin.

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Stengel, M., Vanderbilt, D. & Spaldin, N. Enhancement of ferroelectricity at metal–oxide interfaces. Nature Mater 8, 392–397 (2009). https://doi.org/10.1038/nmat2429

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