Characteristics of NbN/AlN/NbN tunnel junctions operating at 10 K

NbN/AlN/NbN tunnel junctions and junction arrays were fabricated on single-crystal MgO and Si substrates for the basic investigation of all-NbN superconductor integrated circuits operating at 10 K. The electrical characteristics of single junctions and junction arrays were measured in a wide temperature range of 4.2-15 K. There is almost no recognizable difference in junction characteristics when the operating temperature is varied from 4.2 K to 10 K. The junctions demonstrated a very good junction quality with a high gap voltage (V-g = 4.8 mV), large IcRN products (IcRN = 2.5 mV) and a small subgap leakage current (R-sg/R-N = 6) at 10 K. NbN/AlN/NbN junction arrays were fabricated for estimating the nonuniformity of the junction parameters. I-c nonuniformity for a 200-junction array with a high current density (J(c) = 11 kA cm(-2)) was less than +/-2% (1 sigma).