Passivation of YBCO dc-SQUIDs using polymerized hexamethyldisilasane

A passivation layer was developed to protect YBCO-devices like flux transformers and SQUIDs against deterioration due to moisture, atmospheric carbon dioxide and oxygen diffusion, The passivation layer is deposited by the polymerization of the silicon organic compound hexamethyldisilasane (HMDS-N) in a plasma enhanced chemical vapor deposition (PECVD) process. AFM investigations confirm that films of 100-150nm thickness cover YBCO structures without any pinholes and good step coverage, Electrical transport measurements of passivated YBCO tracks and junctions exposed to humidity and CO2 show the excellent passivation properties of the films. No degradation in the critical parameters such as the critical current Ic, the normal resistance R-n, and the flux modulation depth Delta V is observed on step edge dc-SQUIDs, Investigations of the oxygen diffusion relaxation times show that they are much larger for the passivated samples than in samples without an overlay.