Development of sub-micron SNS ramp-type Josephson junctions

At PTB, a fabrication technology for sub-micron superconductor-normal metal-superconductor (SNS) ramp-type Josephson junctions has been developed which allows these junctions to be used as active elements in highly integrated circuits. Test circuits of series arrays containing up to 10000 junctions with contact areas below 0.4 μm² and of single junctions with contact areas reduced down to 0.03 μm² have been successfully realized and measured. To achieve high values of the characteristic voltage V_c , different N-layer materials, i.e. Al, PdAu and HfTi with thicknesses down to d=15 nm and different layer sequences have been investigated. Typical parameters of SNS junctions with a thickness of the HfTi N-layer of d=20nm are about j_c=470 kA/cm² and V_c=100 μV. The junctions realized allow for application in superconducting circuits