Submicron NbN/MgO/NbN Josephson tunnel junctions and their application to the logic circuit

An improved fabrication process for submicron NbN/MgO/NbN Josephson tunnel junctions has been developed. By introducing a contact layer between the junction and the wiring layer, the critical current of the wiring above the junction was considerably enhanced. A logic circuit composed of four-junction logic gates was fabricated using 0.9- mu m-square junctions. Logic delay measurement was successfully achieved with a minimum logic delay of 3.6 ps/gate and a wide operating margin of +or-17% within 50 gates.<
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