Sub-gap leakage current of Nb/Al–AlO x–Al/Nb Josephson junction fabricated using facing target sputtering

Abstract

Nb and Al films in the Nb/AlO x /Nb junction structure have been deposited using facing target sputtering technique applied with DC power. In this sputtering technique, the γ electrons generated in the plasma are retained and reciprocated between a pair of targets and those hardly do damage to the junction interface during the deposition. A SiO 2 film has been also deposited using the same sputtering applied with RF power. An anodization process is used for the fabrication process. Fabricated junctions have indicated the I– V characteristics with small sub-gap leakage current (0.13 pA/μm 2 at 0.49 K). We think it is effective for both the facing target sputtering technique and the anodization process to obtain the junction with small sub-gap leakage current.