NB/AL-OXIDE/NB TUNNEL-JUNCTIONS FOR JOSEPHSON INTEGRATED-CIRCUITS

A new fabrication process of small Nb/Al-oxide/Nb tunnel junctions for integrated circuits is presented. Prior to making tunnel junctions of Nb/Al-oxide/Nb sandwich structure with a full wafer size, an Nb electrode layer was prepared on the wafer, whose patterns were duplicated from each junction base electrode pattern. This additional underlayer of Nb plays an important role in improving I-V characteristics, especially in the small size Nb/Al-oxide/Nb junctions. A reactive ion etching process was employed to define each junction size precisely. Using the present process, Vm equals 40 mV and Rsg/Rnn equals 26 with a critical current density of 1000 A/cm**2 have been achieved in an one-hundred 2. 5 mu m square junction array.