Strain engineering and the ferroelectric properties of perovskite thin films grown on Si

Joseph C. Woicik, Ceramics Division

When a thin film is grown epitaxially on a substrate that has a different lattice constant, the lattice constant of the film in the in-plane direction is strained to accommodate its in-plane registry with the substrate. Due to the intrinsic coupling between polarization and strain, this substrate clamping effect may be used to engineer both the mechanical and electronic properties of complex oxide films. Here we will give two examples of how this may be realized in practice: In the first example, we will use x-ray diffraction to show how the ferroelectric c-axis of BaTiO₃ is aligned normal to the Si(001) surface by use of a BaSrTiO₃ buffer layer. In the second example, we will use a novel combination of x-ray diffraction, x-ray spectroscopy, and density functional theory to show how strain drives a ferroelectric distortion in SrTiO₃ thin films grown on Si(001) that are normally not ferroelectric at any temperature.

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