SiO₂ and Si₃N₄ passivation layers on Y-Ba-Cu-O thin films

High-T_c Y-Ba-Cu-O superconductor thin films were passivated with thermally evaporated SiO₂ or rf magnetron sputtered Si ₃N₄. Thermal evaporation of SiO₂ on the Y-Ba-Cu-O thin-film surface did not degrade the zero resistance temperature of Y-Ba-Cu-O films. A seriously lowered zero resistance temperature of Y-Ba-Cu-O films was found if Si₃N₄ was sputtered onto the Y-Ba-Cu-O film surface. A one month exposure of the Y-Ba-Cu-O film to the environmental air did not change the T_c onset of the superconductor thin film but gave a slight decrease of T_c zero with SiO₂ as the surface passivation layer. High-frequency capacitance-voltage studies were made on metal-insulator-superconductor to investigate the interface and surface properties of Ya-Ba-Cu-O thin films. The experimental data suggested that a very thin layer semiconductor phase Y-Ba-Cu-O was produced between Y-Ba-Cu-O films and the insulator films during the deposition of the passivation film onto the Y-Ba-Cu-O surface.