Electrical parameters of Niobium- Based Overdamped SNIS Josephson Junctions for digital applications

We have demonstrated superconductor-normal metal-insulator-superconductor Nb/Al-AlO(X)/Nb Josephson junctions developed with Al layer thicknesses between 30 and 100 nm, resulting in nonhysteretic current-voltage characteristics for critical current densities between 20 and 60 kA/cm(2). Specific capacitances ranged from 180 to 480 fF/mu m(2), depending on temperature and of barrier deposition conditions. It is shown that the high capacitance seen by the junction depends on the Josephson junction barrier but only to a least extent on the parasitic environment. Although the specific capacitance is unusually high, Stewart-McCumber parameters from 1 to 3, at 4.2 K, optimum for digital single-flux-quantum applications were obtained without external shunting. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3354090]