Berlin 2008 – wissenschaftliches Programm

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DS: Fachverband Dünne Schichten

DS 23: High-k Dielectric Materials - Synthesis, Properties, Applications
The posters can also be presented at Poster A on Tuesday morning (DS poster session).

DS 23.2: Poster

Mittwoch, 27. Februar 2008, 18:30–20:30, Poster C

Induced Ferroelectricity in Strained Epitaxial SrTiO3 Films on Various SubstratesEugen Hollmann, Jürgen Schubert, Rolf Kutzner, and •Roger Wördenweber — Institut für Bio- und Nano-Systeme and cni, Forschungszentrum Jülich, D-52425 Jülich

Thin films of ferroelectric materials (SrTiO3, (Ba,Sr)TiO3 and others) are currently being used to develop active microwave devices (phase shifters, tunable high-Q resonators or filters) for cryogenic and room temperatures operation. In this contribution, the impact of strain on structure and ferroelectric properties of epitaxial SrTiO3 films on various substrate materials - substrates with larger (DyScO3) and smaller (NdGaO3 and CeO2/Al2O3) in-plane lattice constant, respectively - is analyzed. It is demonstrated that the mismatch of the lattices or, alternatively, the mismatch of the thermal expansion coefficients of films and substrate impose biaxial compressive or tensile strain to the SrTiO3 films, respectively. The strain leads to a small tetragonal distortion of the SrTiO3 lattice and has a large impact of the ferroelectric properties of the films. With decreasing film thickness and at low temperatures the permittivity deviates from the *classical* Curie-Weiss behavior. The thinnest sample shows an enhancement of the dielectric constant at room temperature by up to a factor of 3. Furthermore, strain induced ferroelectricity is observed which agrees with theoretical predictions. For electric fields parallel to the film surface induced ferroelectricity is observed for SrTiO3 that is exposed to in-plane tensile strain, i.e., ferroelectricity is observed for temperatures up to 210 K and 325 K for strained SrTiO3 on CeO2/Al2O3 and DyScO3, respectively.

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