9 ps Gate Delay Josephson OR Gate with Modified Variable Threshold Logic

A Josephson logic OR gate suitable for high speed logic circuits is proposed and tested. This gate has a structure modified from Variable Threshold Logic (VTL) to obtain large operating margin and small occupation area. The operating margin is calculated as ±19% for fan-out of 2, even with the critical current variation of ±20%. The circuit area is 40×60 µm2. A chain of 5-stage OR gates was fabricated. The gates had Josephson junctions of 4 µm and 7 µm diameter made with Pb-alloy technology. The minimum gate delay of 9 ps was measured using a Josephson sampler.