Josephson edge-junction devices using E-beam lithography

Superconducting interferometers containing up to nine lithographic levels were exposed by direct e-beam writing in a vectorscan (VS) system, The number and thickness of the layers presented a new challenge to e-beam and liftoff resist technology. A novel approach to level-to-level registration was required. In the edge-junction structure, the Josephson-junction width of typically 0.3 µm was achieved by forming the Josephson junctions on the edges of the niobium base electrode without using submicrometer lithography. Such Nb-oxide-Pb-alloy edge junctions are promising for logic and memory applications. The ruggedness of a niobium base electrode is combined with a high-current-density device having low capacitance by virtue of the small junction area.