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Stacked Josephson Junctions as inductors for SFQ circuits

Published

Author(s)

Manuel C. Castellanos Beltran, David I. Olaya, Adam J. Sirois, Paul D. Dresselhaus, Samuel P. Benz, Peter F. Hopkins

Abstract

In order for Single Flux Quantum (SFQ) circuits to be scaled to densities needed for large-scale integration, typical lithographically-patterned circuit components should be made to be as compact as possible. In this work, we characterize the performance of Vertically Stacked Josephson Inductors(VSJIs) which combined with self-shunted Josephson junctions eliminate large geometrical inductors and bias resistors respec-tively. The VSJIs consist of three Josephson junctions stacked vertically and inserted into test structures which allow us to validate their potential as compact alternatives to geometrical inductors. The stacks are used in place of geometrical inductors and combined in parallel with a single ’switching’ Josephson junction (with a lower critical current). We find that even with a large difference (≥50%) in critical current between the switching junctions and stacked junctions, we must account for the nonlinearity intrinsic to the VSJI to correctly model their behavior. In order to confirm that this nonlinearity would not degrade the expected margins of SFQ circuits compared with linear, geometrical inductors we simulate two common SFQ cells including the nonlinear terms. We confirm that VSJIscould be incorporated in large-scale SFQ circuits with minimal disruption but higher circuit density
Citation
IEEE Transactions on Applied Superconductivity
Volume
29
Issue
5

Keywords

superconductor, josephson junction, niobium
Created February 11, 2019, Updated April 26, 2019