Letters to Nature

Nature 430, 758-761 (12 August 2004) | doi:10.1038/nature02773; Received 12 March 2004; Accepted 22 June 2004

Room-temperature ferroelectricity in strained SrTiO3

J. H. Haeni1, P. Irvin2, W. Chang3, R. Uecker4, P. Reiche4, Y. L. Li1, S. Choudhury1, W. Tian5, M. E. Hawley6, B. Craigo7, A. K. Tagantsev8, X. Q. Pan5, S. K. Streiffer9, L. Q. Chen1, S. W. Kirchoefer3, J. Levy2 & D. G. Schlom1

  1. Department of Materials Science and Engineering, Penn State University, University Park, Pennsylvania 16802-5005, USA
  2. Department of Physics and Astronomy, University of Pittsburgh, Pittsburgh, Pennsylvania 15260, USA
  3. Naval Research Laboratory, 4555 Overlook Avenue S.W., Washington DC 20375, USA
  4. Institute of Crystal Growth, Max-Born-Strabetae 2, D-12489 Berlin, Germany
  5. Department of Materials Science & Engineering, University of Michigan, Ann Arbor, Michigan 48109-2136, USA
  6. Materials Science and Technology Division (MST-8), Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
  7. Motorola Labs, 2100 East Elliot Road, Tempe, Arizona 85284, USA
  8. Laboratoire de Céramique, Ecole Polytechnique Fédérale de Lausanne, Lausanne CH 1015, Switzerland
  9. Materials Science Division, Argonne National Laboratory, Argonne, Illinois 60439, USA

Correspondence to: D. G. Schlom1 Correspondence and requests for materials should be addressed to D.G.S. (Email: schlom@ems.psu.edu).

Systems with a ferroelectric to paraelectric transition in the vicinity of room temperature are useful for devices. Adjusting the ferroelectric transition temperature (T c) is traditionally accomplished by chemical substitution—as in BaxSr1-xTiO3, the material widely investigated for microwave devices in which the dielectric constant (epsilon r) at GHz frequencies is tuned by applying a quasi-static electric field1, 2. Heterogeneity associated with chemical substitution in such films, however, can broaden this phase transition by hundreds of degrees3, which is detrimental to tunability and microwave device performance. An alternative way to adjust T c in ferroelectric films is strain4, 5, 6, 7, 8. Here we show that epitaxial strain from a newly developed substrate can be harnessed to increase T c by hundreds of degrees and produce room-temperature ferroelectricity in strontium titanate, a material that is not normally ferroelectric at any temperature. This strain-induced enhancement in T c is the largest ever reported. Spatially resolved images of the local polarization state reveal a uniformity that far exceeds films tailored by chemical substitution. The high epsilon r at room temperature in these films (nearly 7,000 at 10 GHz) and its sharp dependence on electric field are promising for device applications1, 2.

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