Light-anodization process for high-Jc micron and submicron superconducting junction and integrated circuit fabrication

We have developed a new approach for high critical current density (J_c) small junction fabrication. The key step is light anodization that forms a thin double-layer of Al₂O₃/Nb₂O₅ oxides around the junction area and on the sidewalls of the junction. This anodization ring is a good dry-etch stop, so the via for the junction contact can be larger than the junction area. The anodization ring can also protect the junction from plasma damage during dry etching and sputtering steps; therefore, it can reduce the junction leakage current and critical-current spread. The new technique is very simple and cost effective compared with the CMP approach. It needs only one additional mask and process step. We have used the technique to fabricate high-J_c submicron Nb/Al-AlO_x/Nb tunnel junctions with very low critical-current spreads. Using this technique, we have also fabricated Nb SQUID´s and various Nb digital IC´s.