NB ALN/NB JOSEPHSON-JUNCTIONS WITH HIGH CRITICAL-CURRENT DENSITY/

We have produced Nb/AlNx/Nb Josephson tunnel junctions with the aims o f improving the control of critical current density J(c) in the high-J (c) range and exploring the possibility of high-J(c) junctions with lo w subgap quasiparticle current. Conventional Nb/AlOx/Nb junction barri ers are formed by oxidizing a thin Al overlayer on the Nb base electro de, and precise control of the oxidation process is difficult at low l evels of oxygen exposure. The reactivity of Al with N-2 is very low, a nd AlNx barriers are therefore formed using an an N-2 plasma. We repor t the fabrication of AlNx barrier junctions with J(c) as large as 4 mA /mu m(2) and compare their properties to Nb/AlOx/Nb ones of similar J( c).