Preparation and Diclectric Properties of Ferroelectric BaTiO_3 Thin Films by Sol-Gel Method

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BaTiO_3 thin films have been intensively investigated for application to multilayr capacitors, ferroelectric memories, pyroelectric detectors and electrooptic devices. A number of techniques such as sputtering, vacuum evaporation, metalorganic decomposition and sol-gel methods have been used to prepare BaTiO_3 thin films. Recently, BaTiO_3 thin films that exhibit P-E hysteresis loops have been prepared by activated reactive evaporation, , pulsed laser decomposition and sol-gel methods. However, in the dielectric constant -temperaturecharacteristic curves of BaTiO_3 thim films prepared by sol-gel method, a curie peak was not observed at a temperature around 120ﾟC.In this work, BaTiO_3 thin films were prepared by sol-gel method. In order to prepare BaTiO_3 thin films with relatively large grains, the processing temperature as high as 850ﾟC was utilized, facilitating the use of Pt plate. Their crystallinity, surface morphology and electrical properties of BaTiO_3 thin films prepared on Pt … More substrate at 850ﾟC were examined.The BaTiO_3 thin films on Pt substrate exhibited a slightly coares grain microstructure with grain sizes of about 50nm. And, the microstructure of single-layr films showed inhomogeneous texture with large isolated grains of about 450nm. Increasing with the cycles of coating/heating process, fine grains as small as about 100nm seemed to grow from the surfaces of large isolated grains and, finally, thin films prepared by multiple coating/heating processes were strongly textured with fine grains. That is, the grain sizes of the top layr of the multilayr thin films were always much finer than those of the first coating.P-E hysteresis loops of BaTiO_3 thin films prepared on Pt indicated well-saturated hysteresis loops. And, these thin films prepared exhibited Pr of 3.8 and Ec of 20kV/cm at room temperature. The thin films on Pt substrate exhibited epsilonr of about 830 and tan delta of 0.04 at room temperature. And, inthese films, the curie peak was not seen at about 120ﾟC.However, broad curie peaks were observed at around 70ﾟC.The difference of the curie temperatures may be due to the effect of BaTiO_3 sizes and the microstructure. Less