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 Substrates — Eugen 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.