Ultrasmall superconducting tunnel junctions

Extremely small-area superconducting Josephson junctions have been fabricated using a newly developed electron-beam lithography technique. The junctions are composed of Pb-In base electrodes and Pb counter electrodes. Areas of the junctions range from 1 to 3 × 10^-10cm². The estimated capacitance is ∼10^-15F. Junctions have been produced with resistances of ∼100 Ω which have ∼20-percent hysteresis in the critical current at a temperature of 4 K.