New selective anodization process for Nb Josephson junction with AlOx barrier

One of the most important factor of the superconducting tunnel junction for a particle and radiation detection is the sub-gap leakage current. An anodization of a junction edge is an effective method to reduce the sub-gap leakage current. In a new fabrication process of a Nb/Al-AlO_x-Al/Nb junction, the sputtered Al₂O₃ layers with 10 nm thickness are used as not only the protection layer for the upper surface of both the base and counter electrodes in the anodization process, but also the etching stop layer for the formation of the contact hole by reactive ion etching process.