A NB ALOX/NB TRILAYER PROCESS FOR THE FABRICATION OF X-RAY-DETECTORS/

A new Nb/AlO(x)/Nb trilayer process for X-ray detector applications ha s been developed. The process employs a movable mechanical slit which, after the sputter deposition of the base Nb electrode followed by a t hin layer of Al and its oxidation, is shifted to a second position whe re the Nb counter electrode is deposited. The overlap area of the two electrodes forms the junction area after final patterning by standard photolithography and reactive ion etching. The best junctions so far o btained have, at 4.2 K, typically a quality factor of 42 mV with a Jos epshon current density of 1200 A/cm2, and a tunneling time tau(tun) in the range of 50 to 500 ns. We discuss several aspects of this techniq ue in comparison with the selective niobium anodization process (SNAP) and the selective niobium etching process (SNEP).