Properties of high-jc SINIS junctions

Nb/Al/AlO_x/Al/AlO_x/Al/Nb junctions with high critical current densities, j_c, above 20 kA/cm² were fabricated and characterized. A critical voltage of V_c=1.25 mV and small hysteresis (about 6% of the critical current) at 4.2 K were obtained for j_c=21 kA/cm². Also, devices with a modified geometry, Nb/Al/AlO_x/Al/Nb/Al/AlO_x/Al/Nb, were fabricated. In these devices, j_c≅50 kA/cm² at 4.5 K, and the temperature dependence of the critical current, I_c(T), is improved (as compared with our earlier results) in that the steep raise of I_c is shifted toward higher temperatures. We suggest a theoretical model which satisfactory describes the enhanced critical current for these SINS´NIS junctions as compared with ordinary SINIS junctions.