New Thickness Control Process of Oxide Barrier for Nb-Based Tunnel Junctions

The Nb-based superconductor-insulator-superconductor (SIS) tunnel junctions have been broadly used in many applications. The critical current density ( ), one of the most important parameters of SIS tunnel junction, is usually controlled by the oxygen exposure ( 2) of the Al oxidation process. R. E. Miller et al. demonstrated the relation between and oxygen exposure using the SNEP process. However, the value of still varies with Nb/AlO Al/Nb deposition system, even run-to-run process. A new AuAl2/Al composite, instead of pure Al, has been used in the oxidation process. From the 2 relation, we have demonstrated the oxidation rate of AuAl2 is about 400 times lower than that of Al. Using AuAl2 layer, two advantages are observed. 1) For low tunnel junctions, the thickness of AlO , or , can be controlled easily by inserting AuAl2 layer as a blocking layer in oxidation process. 2) High quality factor tunnel junctions with 100 kA/cm are achieved by oxidation of AuAl2 layer directly.