High-Temperature Electrical Insulation Behavior of Alumina Films Prepared at Room Temperature by Aerosol Deposition and Influence of Annealing Process and Powder Impurities
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Alumina (Al2O3) is a widely used material for highly insulating films due to its very low electrical conductivity, even at high temperatures. Typically, alumina films have to be sintered far above 1200 °C, which precludes the coating of lower melting substrates. The aerosol deposition method (ADM), however, is a promising method to manufacture ceramic films at room temperature directly from the ceramic raw powder. In this work, alumina films were deposited by ADM on a three-electrode setup with guard ring and the electrical conductivity was measured between 400 and 900 °C by direct current measurements according to ASTM D257 or IEC 60093. The effects of film annealing and of zirconia impurities in the powder on the electrical conductivity were investigated. The conductivity values of the ADM films correlate well with literature data and can even be improved by annealing at 900 °C from 4.5 × 10−12 S/cm before annealing up to 5.6 × 10−13 S/cm after annealing (measured at 400 °C). The influence of zirconia impurities is very low as the conductivity is only slightly elevated. The ADM-processed films show a very good insulation behavior represented by an even lower electrical conductivity than conventional alumina substrates as they are commercially available for thick-film technology.
Keywordsaerosol deposition method (ADM) annealing guard ring impurities insulation behavior room-temperature impact consolidation (RTIC) vacuum kinetic spraying
The authors are indebted to the following persons and organizations for supporting this work: The Bavarian research foundation (Bayerische Forschungsstiftung, BFS, grant AZ-1055-12) for funding. A. Mergner (Department for Functional Materials) and M. Heider (BIMF) for SEM sample preparation and characterization and the Department of Metals and Alloys, (Prof. Glatzel) for XRD analyses (all University of Bayreuth).
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