Semiconductor-barrier Josephson junctions for high speed digital circuits

The use of the semiconductor-barrier Josephson junction as the switching component in high-speed digital circuits is reported. The switching time of a single superconducting lead-tellurium-lead (Pb-Te-Pb) junction and the current transfer time of a memory cell using such a device as the logic switch is measured. The shortest switching time of a rather large junction is 67 ps and the current transfer time of a memory cell with loop inductance is 350 ps. These measured values are comparable with those obtained for oxide tunnel junctions with similar dimensions. Computer simulations are performed of the switching behavior of both the single junction and the memory cell. Theoretical results are in good agreement with the experimental measurements. A simple cavity model is used to analyze the self-resonances in semiconductor-barrier Josephson junctions. The cavity Q is approximately two orders of magnitude lower than that of comparable oxide tunnel junctions due to the higher damping in the semiconductor-barrier region.