Polarization Behavior in Vinylidene Fluoride-Trifluoroethylene Copolymer Thin Films

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Abstract
The polarization behavior in films of vinylidene fluoride trifluoroethylene copolymer (P(VDF-TrFE), VDF/TrFE molar content ratio of 75/25) of thickness less than 1 µm is reported. Ferroelectricity is maintained even in 0.06 µm-thick film, whose saturated polarization is as large as that for thick films (100 mC/m2). However, the crystallites are much smaller than in thick film, and the coercive field in the thin film is higher (125 MV/m) for the 0.06 µm-thick film) than that of the thick one (40 MV/m). The switching time does not follow the exponential law, but is inversely proportional to the applied field. To analyze these data, we introduce a model in which the thin film contains many defects in its crystalline phase, and the local field in the film is modulated by the defects. The observed switching behavior is consistent with the model.