Nb/AlN/Nb Josephson junctions with high critical current density

We have produced Nb/AlN/sub x//Nb Josephson tunnel junctions with the aims of improving the control of critical current density J/sub c/ in the high-J/sub c/ range and exploring the possibility of high-J/sub c/ junctions with low subgap quasiparticle currents. Conventional Nb/AlO/sub x//Nb junction barriers are formed by oxidizing a thin Al overlayer on the Nb base electrode, and precise control of the oxidation process is difficult at low levels of oxygen exposure. The reactivity of Al with N/sub 2/ is very low, and AlN/sub x/ barriers are therefore formed using an N/sub 2/ plasma. We report the fabrication of AlN/sub x/ barrier junctions with J/sub c/ as large as 4 mA//spl mu/m/sup 2/ and compare their properties to Nb/AlO/sub x//Nb ones of similar J/sub c/.<
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