ALL-NIOBIUM PROCESS FOR JOSEPHSON SERIES ARRAY CIRCUITS

We have developed a new fabrication process for integrated Nb/Al2O3/Nb Josephson series arrays using the selective niobium anodization proce ss (SNAP), the image reversal technique (IRT) and lift-off. To avoid c haotic behavior, the critical current of the array was decreased by po st-fabrication annealing or the in situ multilayer oxidation process. In the frequency range 70-100 GHz, the array containing 2520 junctions produced stable quantized voltage steps up to 2 V with step widths of 40-100 mu A and stability times of more than 4 h.