Ultrahigh speed direct coupled logic gate fabricated with NbN/Pb Josephson junctions.

A chain circuit of direct coupled logic gates consisting of niobium nitride (NbN)-lead (Pb) alloy electrodes has been fabricated. The junctions used were of 1.5 μm square and had a current density of 20 kA/cm2. A special sampling method with jitter of ±1.5 ps was used to precisely measure the short delay time. A minimum logic delay of 5.6 ps/gate has been obtained with a fan in=fan out=1 structure. [ABSTRACT FROM AUTHOR]