Effect of growth conditions on the electrical properties of Nb/Al-oxide/Nb tunnel junctions

We have investigated the dependence of the critical current density J/sub c/ of Nb/AlO/sub x//Nb Josephson tunnel junctions on substrate temperature T/sub s/ and oxygen exposure E (the product of oxidation time and pressure) during growth. For low O/sub 2/ exposures, J/sub c/ depended sensitively on exposure, J/sub c//spl prop/E/sup -1.6/, independent of temperature for 77 K>