All-niobium process for Josephson series array circuits

We have developed a new fabrication process for integrated Nb/Al/sub 2/O/sub 3//Nb Josephson series arrays using the selective niobium anodization process (SNAP), the image reversal technique (IRT) and lift-off. To avoid chaotic behavior, the critical current of the array was decreased by post-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 /spl mu/A and stability times of more than 4 h.<
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