Effects of sputtered SiO2 passivation layers on YBCO microbridges and step-edge junctions

High-temperature superconducting YBa2Cu3O7-delta microbridges and step-edge junctions (SEJs) were coated with SiO2 thin film by an rf magnetron sputtering technique. The effect of the coating on critical temperature T-c and critical current I-c was studied. It was found that T-c and I-c of microbridges increased as a result of the coating, by up to 3 K for T-c and up to 23% for I-c. We believe that this is due to the oxygen in the plasma penetrating into YBa2Cu3O7-delta resulting in an increase in oxygen content and restoration of the degraded microbridge edges. I-c of the SEJ, however, was found to decrease by 20-30% after deposition of SiO2 films despite no degradation in T-c. The results of ageing tests showed that SiO2 film forms a good passivation layer, protecting YBa2Cu3O7-delta him from reacting with water.