Improved critical-current-density uniformity by using anodization

Dept. of Electr. Eng., Massachusetts Inst. of Technol., Cambridge, MA, USA
IEEE Transactions on Applied Superconductivity (Impact Factor: 1.2). 07/2003; DOI: 10.1109/TASC.2003.813658
Source: IEEE Xplore

ABSTRACT We discuss an anodization technique for a Nb superconductive-electronics-fabrication process that results in an improvement in critical-current-density Jc uniformity across a 150-mm-diameter wafer. We outline the anodization process and describe the metrology techniques used to determine the NbOx thickness grown. In the work described, we performed critical current Ic measurements on Josephson junctions distributed across a wafer. We then compared the Jc uniformity of pairs of wafers, fabricated together, differing only in the presence or absence of the anodization step. The cross-wafer standard deviation of Jc was typically ∼5% for anodized wafers but >15% for unanodized wafers. This difference in Jc uniformity is suggestive of an in-process modification from an unknown cause that is blocked by the anodic oxide. It is interesting that small junctions do not see an improvement in Ic uniformity - apparently the anodization improves only the Jc uniformity and not the variation in junction size. Control of Jc is important for all applications of superconductive electronics including quantum computation and rapid single-flux quantum (RSFQ) circuitry.

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