Size Effect in Ferroelectric Thin Films Prepared by Atomic Layr Controlled Growth

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The dielectric properties, such as the Curie temperature, dielectric constant, coercive field and others, depend on the film thickness or the diameter of the constituent crystallites when the size reduces to sub-micron order. The purpose of this study is to clarify the origin of the size effects. Thin films of several tens to several hundreds nanometer in thickness of lead titanate and PZT were grown on silicon substrates by means of laser ablation and sol-gel technique. A platinum-coated silicon was mainly used as a substrate. Pellets of BaTiO_3 (BT), PbTiO_3 and PZT ceramics were used as the target material of the laser ablation growth.The surface of the film was investigated by a scanning electron microscope and an atomic force microscope and found to be flat with nanometer scale. The Curie temperature of very thin BT film was slightly higher than that of bulk crystal. This tendency was opposite to our expectation, the Curie temperature would shift towards low temperatures. The results show that the inner stress plays an important role in size effects. Thin films of PT grown by laser ablation was investigated by X-ray diffraction and found to be well crystallized. Film of PZT was grown on the PT layr by a sol-gel method. The film showed a large peak around 350ﾟC, very close to the Curie temperature of bulk PZT.This means the presence of PT layr is effective to proceed the crystallization of PZT film layr.Experiments on the atomic layr growth was performed in a compound semiconductor system since it was difficult to make layr by layr growth of dielectric crystals.