Properties of high-j/sub c/ SINIS junctions

Nb/Al/AlO/sub x//Al/AlO/sub x//Al/Nb junctions with high critical current densities, j/sub c/, above 20 kA/cm/sup 2/ were fabricated and characterized. A critical voltage of V/sub c/=1.25 mV and small hysteresis (about 6% of the critical current) at 4.2 K were obtained for j/sub c/=21 kA/cm/sup 2/. Also, devices with a modified geometry, Nb/Al/AlO/sub x//Al/Nb/Al/AlO/sub x//Al/Nb, were fabricated. In these devices, j/sub c//spl cong/50 kA/cm/sup 2/ at 4.5 K, and the temperature dependence of the critical current, I/sub c/(T), is improved (as compared with our earlier results) in that the steep raise of I/sub 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.