Effects of sputtered SiO sub(2) passivation layers on YBCO microbridges and step-edge junctions

High-temperature superconducting YBa sub(2)Cu sub(3)O sub(7- delta ) microbridges and step-edge junctions (SEJs) were coated with SiO sub(2) thin film by an rf magnetron sputtering technique. The effect of the coating on critical temperature T sub(c) and critical current I sub(c) was studied. It was found that T sub(c) and I sub(c) of microbridges increased as a result of the coating, by up to 3 K for T sub(c) and up to 23% for I sub(c). We believe that this is due to the oxygen in the plasma penetrating into YBa sub(2)Cu sub(3)O sub(7- delta ) resulting in an increase in oxygen content and restoration of the degraded microbridge edges. I sub(c) of the SEJ, however, was found to decrease by 20-30% after deposition of SiO sub(2) films despite no degradation in T sub(c). The results of ageing tests showed that SiO sub(2) film forms a good passivation layer, protecting YBa sub(2)Cu sub(3)O sub(7- delta ) film from reacting with water.