Properties of magnetron-sputtered electrically insulating Al2O3 coatings on copper

Amorphous Al₂O₃ coatings were deposited on Cu substrates with metallic bond layers by different magnetron-sputtering processes. Such sputtering conditions as the type of discharge, target material, total pressure, sputtering gas composition and substrate temperature were varied to study the process effects on the structure and properties of the coatings deposited. The structure and general properties were found to be strongly dependent on the type of process and parameters. The breakdown voltages did not show any significant lowering as the temperature was increased from 20 to 400–500 C. The maximum temperature without formation of cracks in the Al₂O₃ coating on Cu was about 700 C. The d.c. electrical conductivities of the Al₂O₃ were similar to that of bulk Al₂O₃ at different temperatures. The results reveal the potential use of magnetron-sputtered Al₂O₃ coatings on Cu for electrical insulation and oxidation protection in different high-temperature applications, e.g. on metallic magnetohydrodynamic electrode and insulator modules.