Internally shunted Josephson junctions with barriers tuned near the metal-insulator transition for RSFQ logic applications

Lei Yu, Raghuram Gandikota, Rakesh Singh, Lin Gu, David Smith, Xiaofan Meng, Xianghui Zeng, Theodore Van Duzer, John M. Rowell, Nathan Newman

Research output: Contribution to journalArticle

18 Scopus citations

Abstract

The fabrication of self-shunted SNS (superconductor/normal conductor/superconductor) Josephson junctions for rapid single flux quantum (RSFQ) logic could potentially facilitate increased circuit density, as well as reduced parasitic capacitance and inductance over the currently used externally shunted SIS (superconductor/insulator/superconductor) trilayer junction process. We report the deposition, fabrication, and device characterization of Josephson junctions prepared with Nb1-yTiyN electrodes and TaxN barriers tuned near the metal-insulator transition, deposited on practical large-area oxide-buffered silicon wafers. When scaled to practical device dimensions, this type of junction is found to have an I cRn product of over 0.5 mV and a critical current (I c) and normal resistance (Rn) of magnitudes suitable for single flux quantum digital circuits. A longer than expected normal-metal coherence length (ξn) of 5.8 nm is inferred from the thickness dependence of Jc at 4.2 K for junctions fabricated using a barrier resistivity of 13 mΩ cm. Although not well understood and not quantitatively predicted by conventional theories, this results in a sufficiently high Ic and IcRn to make the junctions suitable for practical applications. Similar observations of unexpectedly large Josephson coupling currents in SNS junctions have been documented in other systems, particularly in cases when the barrier is near the M-I transition, and have become known as the giant proximity effect. The temperature dependence of ξn, IcRn, and Jc are also reported. For this technology to be used in practical applications, significant improvements in our fabrication process are needed as we observe large variations in Ic and Rn values across a 100 mm wafer, presumably as a result of variations in the Ta:N stoichiometry and the resulting changes in the TaxN barrier resistivity.

Original languageEnglish (US)
Article number006
Pages (from-to)719-731
Number of pages13
JournalSuperconductor Science and Technology
Volume19
Issue number8
DOIs
StatePublished - Aug 1 2006

ASJC Scopus subject areas

  • Ceramics and Composites
  • Condensed Matter Physics
  • Metals and Alloys
  • Electrical and Electronic Engineering
  • Materials Chemistry

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