Fabrication of surface barrier layer capacitor on BaTiO 3 -based composite containing particulate SiC
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Fabrication of surface barrier layer capacitor on BaTiO3 -based composite containing particulate SiC Hae Jin Hwanga) and Koichi Niihara The Institute of Scientific and Industrial Research, Osaka University, 8-1 Mihogaoka, Ibaraki, Osaka 567, Japan (Received 9 July 1997; accepted 13 October 1997)
Surface reoxidized-type barrier layer (BL) capacitors were prepared by hot-pressing BaTiO3ySiC powder mixture in argon atmosphere and subsequently oxidizing the semiconducting BaTiO3 -based composites with fine SiC particles. Dielectric properties, such as apparent relative dielectric constant, dielectric loss tangent, and Curie temperature, were investigated as a function of SiC content and oxidation procedures. Incorporating SiC particles into BaTiO3 matrix, a thin surface insulating layer was formed, which becomes thinner by increasing the SiC content. BL capacitors showing a higher capacitance than 3 3 102 nFycm2 could be successfully fabricated. The results were discussed on the basis of high resolution transmission electron microscope (HRTEM) studies. Thin oxidized layer and the resulting high capacitance were associated with the depression of oxygen diffusion due to the presence of intergranular SiC particles. The thickness of the surface layer and some dielectric properties could be controlled by the SiC content as well as oxidation temperature and time.
I. INTRODUCTION
BL (barrier layer) capacitor, which is fabricated by oxidizing only the surface or grain boundary of a semiconducting body sintered in a reduced atmosphere, possesses a higher dielectric constant (apparent dielectric constant) than commercial capacitors and have been developed to meet the high capacitance and small-size needs of low-voltage circuitry.1–3 BaTiO3 and its related BL capacitors are used as the basic gradient for many ceramic-based capacitors. According to where the barrier layer formed, BL capacitor can be classified into the following two types: surface barrier layer capacitor and grain boundary barrier layer (GBBL) capacitor. Dielectric property of the BL capacitors, in particular, apparent relative dielectric constant (k app ) significantly depends upon the thickness of the barrier layer and microstructure of the semiconducting body. Accordingly, microstructural control proves to be a decisive factor determining the dielectric properties of BL capacitors. Since both the surface’s oxidized layer and grain boundary barrier layer were formed by the oxygen diffusion via the grain boundary and/or bulk during the oxidation process, the modification of grain boundary structure results in the variation in the diffusion rate and then is very important in developing high performance BaTiO3 -based BL capacitors.
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Present address: National Industrial Research Institute of Nagoya, 1-1 Hirate-cho, Kita-ku, Nagoya 462, Japan.
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http://journals.cambridge.org
J. Mater. Res., Vol. 13, No. 10, Oct 1998
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