Improved critical-current-density uniformity by using anodization

• Published in: IEEE transactions on applied superconductivity Vol. 13; no. 2; pp. 111 - 114
• Main Authors: Nakada, D., Berggren, K.K., Macedo, E., Liberman, V., Orlando, T.P.
• Format: Journal Article Conference Proceeding
• Language: English
• Published: New York, NY IEEE 01.06.2003; Institute of Electrical and Electronics Engineers; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Applied sciences; Circuit properties; Classical and quantum physics: mechanics and fields; Critical current; Current measurement; Design. Technologies. Operation analysis. Testing; Digital circuits; Electric, optical and optoelectronic circuits; Electronic circuits; Electronics; Etching; Exact sciences and technology; Fabrication; Integrated circuits; Josephson junctions; Metrology; Niobium compounds; Performance evaluation; Physics; Quantum computation; Quantum computing; Quantum information; Semiconductor electronics. Microelectronics. Optoelectronics. Solid state devices; Superconducting devices; Superconductivity; Critical current density; Superconducting logic circuits; Josephson junction; Quantum logic; critical-current-density; Quantum electronics; Anodization; Thickness; Quantum computation; Superconducting integrated circuits; Critical current; Current measurement; Anodizing; Manufacturing process; Measuring system; Josephson junctions; Standard deviation; Electric current measurement; Measurement method; Anodic oxide; Comparative study; Wafer
• ISSN: 1051-8223; 1558-2515
• DOI: 10.1109/TASC.2003.813658

We discuss an anodization technique for a Nb superconductive-electronics-fabrication process that results in an improvement in critical-current-density J/sub c/ uniformity across a 150-mm-diameter wafer. We outline the anodization process and describe the metrology techniques used to determine the NbO/sub x/ thickness grown. In the work described, we performed critical current I/sub c/ measurements on Josephson junctions distributed across a wafer. We then compared the J/sub c/ uniformity of pairs of wafers, fabricated together, differing only in the presence or absence of the anodization step. The cross-wafer standard deviation of J/sub c/ was typically /spl sim/5% for anodized wafers but >15% for unanodized wafers. This difference in J/sub c/ 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 I/sub c/ uniformity - apparently the anodization improves only the J/sub c/ uniformity and not the variation in junction size. Control of J/sub c/ is important for all applications of superconductive electronics including quantum computation and rapid single-flux quantum (RSFQ) circuitry.