Step-edge and stacked-heterostructure high-T/sub c/ Josephson junctions for voltage-standard arrays

We have explored two high-transition-temperature Josephson junction technologies for application in voltage standard arrays: step-edge junctions made with YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// and Au normal-metal bridges, and stacked series arrays of Josephson junctions in selectively doped, epitaxially grown Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub 8/ heterostructures. For both kinds of junctions, Shapiro steps induced by a microwave bias were characterized as a function of power. We compare the technologies with respect to critical current and normal resistance uniformity, maximum achievable critical current, critical-current normal-resistance product, and operating temperature. >