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Conference on Precision Electromagnetic Measurements

A high quality 1-V Josephson series array developed at KRISS

Se II Park, Kyu‐Tae Kim, Rae Duk Lee

Published Dec 17, 2002• 0 citations
Publisher

Abstract

By combining the selective niobium anodization process (SNAP) and the image reversal technique (IRT) a new fabrication process of integrated Josephson series array has been developed at KRISS. The array containing 2520 Nb/Al/sub 2/O/sub 3//Nb tunnel junctions produced stable quantized voltage steps up to 2 V with stability times of more than 5-h.>

DOI
10.1109/cpem.1994.333431

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IEEE Transactions on Instrumentation and Measurement•Apr 1, 2003•3 citations
By combining the selective niobium anodization process (SNAP) and the image reversal technique (IRT) a new fabrication process of integrated Josephson series array has been developed at KRISS. The array containing 2520 Nb/Al/sub 2/O/sub 3//Nb tunnel junctions produced stable quantized voltage steps up to 2 V with stability times of more than 5-h.>
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.>
Niobium/aluminum-oxide/niobium Josephson tunnel junctions have been fabricated using electron beam evaporation to form all-metal films in a high vacuum system. A quality factor, V m (the product of the maximum dc Josephson current and the subgap resistance defined at 2 mV) between 36–37 mV, has been obtained for the best junctions of a 6 nm-thick Al layer by cooling down the surface of the base electrode for 100 minutes under a high background pressure, before the deposition of aluminum, after the formation of the base niobium electrode. An array of 80 series-connected junctions has also been fabricated using the selective niobium anodization process and the planarization process. The current-voltage characteristics of the array showed a standard deviation of the maximum dc Josephson current of 3.3%.
Developed a new fabrication process for 10-V Josephson junction series arrays (JJAs). A plasma nitridation process is employed for reducing the microwave attenuation in the Josephson microstripline. Improvements of microwave attenuation are about 2 dB for test arrays of 2000, 3000, and 4000 Josephson junctions in a single stripline. We obtained stable quantized voltage steps up to 12 V at 76.4 and 86.8 GHz with step amplitudes of more than 5 /spl mu/A and stability times of more than 5 min. The circuits used 14 648 junctions arranged in 8 parallel paths.