High Tc Y-Ba-Cu-O Superconducting Thick Films Fabrication and Film/Substrate Interactions

Abstract

High Tc Y-Ba-Cu-O superconducting thick films having Tc at 87 K and R=O at 79 K have been successfully made by using conventional thick film screen printing technology on MgO and ZrO₂ substrates. Film/substrate interactions were examined by electron microprobe analysis as a function of starting powders, heat treatments and substrates. At processing temperatures of 950°C, Ba and Y enrich at the substrate reaction boundary layer (~ 2 μm thick) with depletion of Cu in the superconductor for all the substrates we examined. On the other hand, Cu segregates more at the interface layer than Y and Ba in films fired at 900°C. The fired film microstructures were found to vary strongly with starting powders which demonstrated quite a difference in both densification and grain growth rates. Good superconducting films were never achieved on an alumina substrate. Limited film/substrate interactions were proved to preserve superconducting integrity and to have adhesion greater than 20 newtons, which is adequate for most of microelectronic applications.