Improvement of Critical Current Density Uniformity for Interface-Modified Josephson Junctions in Single Flux Quantum Circuits

概要

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We have investigated the distribution of critical current density ($J_{\text{c}}$) for interface-modified ramp-edge Josephson junctions in high-$T_{\text{c}}$ single flux quantum (SFQ) circuits. The $1\sigma$ spread of $J_{\text{c}}$ in a toggle flip-flop test circuit with a conventional layout is 26.7% and much larger than typical values obtained for junction series-arrays. It is found that the large spread comes from the substantial dependence of $J_{\text{c}}$ on the size of base electrodes, which seems associated with a difference in their surface temperature during deposition of a counter electrode and the formation mechanism of interface-modified junctions. By employing separated base electrodes with similar size in a circuit layout, the $J_{\text{c}}$ spread was drastically reduced to 8.4%, which is almost the same as typical values for junction arrays.
2006-02-25