STEP-EDGE AND STACKED-HETEROSTRUCTURE HIGH-T-C JOSEPHSON-JUNCTIONS FOR VOLTAGE-STANDARD ARRAYS

We have explored two high-transition-temperature Josephson junction te chnologies for application in voltage standard arrays: step-edge junct ions made with YBa2Cu3O7-delta and Au normal-metal bridges, and stacke d series arrays of Josephson junctions in selectively doped, epitaxial ly grown Bi2Sr2CaCu2O8 heterostructures. For both kinds of junctions, Shapiro steps induced by a microwave bias were characterized as a func tion of power. We compare the two technologies with respect to critica l current and normal resistance uniformity, maximum achievable critica l current, critical-current normal-resistance product, and operating t emperature.