5.6 ps Gate Delay All Refractory Josephson OR Gate with Modified Variable Threshold Logic

The modified variable threshold logic (MVTL) OR gate has a wide operating margin of ±43% and occupies a small area of 45×65 µm2. We made this gate with all refractory material including Nb/Al-AlOx/Nb junctions and Mo resistors. A chain of 5-stage MVTL OR gate was fabricated. The junction diameters were 4 µm and 7 µm, and critical current density was 1400 A/cm2. The minimum gate delay of 5.6 ps/gate was measured using a Josephson sampler.