1/f noise in high current density NbN/AlN/NbN tunnel junctions

Low frequency noise characteristics of epitaxial NbN/AlN/NbN tunnel junctions have been investigated. For all of our junctions with different current densities, the voltage noise power spectrum S_v (f) showed a frequency dependence of 1/f type. The magnitude of the S_v(f) exhibited two distinct types of dependency on the current density and AlN barrier thickness. We consider that this may result from a difference in the crystal structures of the AlN barrier by consulting with the barrier thickness dependence of tunnel barrier heights. We also estimated the 1/f noise parameter η using the Rogers and Buhrman´s empirical theory for the S_v(f), and investigated the relationship between the η and the current density J_c and the tunnel barrier thickness d_AlN. The tunnel barrier was characterized by investigating the η-d_AlN relation. It was found that the η-J_c and η-d _AlN relation in our high current density junctions, i.e, in the epitaxial tunnel junctions, are different from nonepitaxial tunnel junctions