Thermal cycling of thick-film and thin-film electrical contacts on melt-processed YBCO

Results are presented from thermal cycling experiments of electrical contacts, carried out to investigate possible failure mechanisms. The contacts were of thick-film silver and thin-film gold on thick-film yttrium barium copper oxide, the latter having been previously fired onto yttria-stabilised zirconia substrates. Continuous observation was made of a dc current passing through the samples, via thin copper wires and the cycling itself was a series of thermal shocks, produced by immersion of the samples in liquid nitrogen, followed by rapid warm-up over a temperature increment of 100 K. It was found that the method of attachment of the copper wires had the greatest effect on the reliability of the deposited contacts.