New fabrication process for Josephson tunnel junctions using photosensitive polyimide insulation layer for superconducting integrated circuits

Photosensitive polyimide, synthesized by block copolymerization, is expected to be an excellent insulation layer in LSI circuits in the future. This polyimide has a higher thermal resistance than those of the other organic polymers. It also has good electric properties such as a high break down voltage and a low dielectric constant. We propose a new fabrication process for the Josephson tunnel junction using a photosensitive polyimide. It is possible to simplify the fabrication process of the Josephson tunnel junction, because the photosensitive polyimide is used as the insulation layer instead of conventional inorganic insulation films without an etching process. We fabricated Nb/Al-AlOx/Nb Josephson tunnel junctions using this new process. The junctions show excellent current-voltage (I-V) characteristics with V_m values more than 80 mV.