Room-temperature testing for high critical-current-density Josephson junctions

This paper demonstrates that room-temperature resistance measurements can accurately predict the critical current and normal resistance of high critical-current-density junctions. We fabricated high critical-current-density (/spl sim/200 /spl mu/A//spl mu/m/sup 2/=20 kA/cm/sup 2/) Nb/Al/AlO/sub x//Nb Josephson junctions in cross-bridge Kelvin resistor (CBKR) test structures and measured their electrical characteristics both at 4.2 K and at room temperature. We developed a two-dimensional mathematical model of the CBKR test structure with two resistive wiring layers in order to characterize the effect of current crowding on the room-temperature measurements. We then used the model to remove the effect of current crowding from the room-temperature measurements and correlated the values of these measurements to the electrical properties of the junctions at 4.2 K. We also identified test-structure-design rules that guarantee current crowding is negligible.