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

This paper demonstrates that room-temperature resistance measurements can a ccurately predict the critical current and normal resistance of high critic al-current-density junctions. We fabricated high critical-current-density ( similar to 200 muA/mum(2) = 20 kA/cm(2)) Nb/Al/AlOx/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 develo ped a two-dimensional mathematical model of the CBKR test structure with tw o resistive wiring layers in order to characterize the effect of current cr owding on the room-temperature measurements. We then used the model to remo ve the effect of current crowding from the room-temperature measurements an d correlated the values of these measurements to the electrical properties of the junctions at 4.2 K, We also identified test-structure-design rules t hat guarantee current crowding is negligible.