Dielectric properties of plasma-spray-deposited BaTiO 3 and Ba 0.68 Sr 0.32 TiO 3 thick films
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S. Sampath Department of Materials Science and Engineering, State University of New York (SUNY)-Stony Brook, Stony Brook, New York 11794 (Received 19 September 2002; accepted 20 February 2003)
The dielectric properties of high-k dielectric BaTiO3 and Ba0.68Sr0.32TiO3 thick films deposited on alumina substrates using a plasma-spray process were investigated. The as-deposited films were predominantly crystalline but contained an amorphous second phase, the amount of which depended on spray conditions. The effect of the spray conditions on crystallinity was studied and related to the dielectric properties of the films. The presence of a low dielectric constant interfacial layer in plasma-spray-deposited films was determined from the dependence of the dielectric constant on film thickness. After annealing at 500 °C for 20 h in air, the crystallinity and dielectric constant increased. Annealing was also found to affect the interfacial layer properties.
I. INTRODUCTION
Direct writing of electronic components has received considerable interest, with applications emerging in the areas of large substrate ceramic multichip modules, thick film sensors, and microwave electronics.1 One approach under development is based on thermal-spray processing. Thermal spray is a continuous and directed spray process in which particles are melted, accelerated to high velocities, and impinged on a substrate, where thin splats are formed by rapid solidification. The successive impingement of the molten particles results in accumulation of the splats and the formation of thick films (>10 m). In contrast to traditional thick film fabrication processes such as tape casting and screen-printing, which involve heat treatment, thermal spray does not require postprocess heat treatment, and hence there are reduced constraints on the choice of substrate materials. Although the main application of thermal spray coatings has been in protective barriers against wear, corrosion, and oxidation, the application field was recently extended to include the deposition of electronic materials. Mid-k dielectric materials, including alumina, spinel, and titanates, have been deposited by a plasma spray process2–4 and their dielectric properties were often comparable to sintered ceramics. High-k dielectrics have also been deposited. Unlike the mid-k dielectrics, however, high-k dielectric BaTiO3 and Ba1−xSrxTiO3 thick films prepared by a thermal spray process have shown dielectric constants of 80–500.3,5,6 This is to be compared to a J. Mater. Res., Vol. 18, No. 5, May 2003
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value of 3000 for bulk ceramics7 and 300 for sputtered films.8 The decrease in dielectric constants in thermalspray-deposited high-k dielectrics has been attributed to the presence of a low dielectric constant amorphous phase and a fine grain size structure.6 In this study, the influence of spray conditions on the crystallinity and dielectric properties was examined for BaTiO3 and Ba0.68Sr0.32TiO3 thick films prepared using a plasma-spr
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