Measurement of Epitaxial NbN/AlN/NbN Tunnel Junctions With a Low Critical Current Density at Low Temperature
Wei Qiu, Hirotaka Terai, Z. Wang
Superconducting qubit circuits require high quality low critical current density Josephson tunnel junctions. We have developed high quality epitaxial NbN/AlN/NbN tunnel junctions with critical current density, Jc, ranging from as low as a few A/cm2to a few tens of kA/cm2. In this work, we measured current-voltage characteristics for junctions with a Jc~ 32 A/cm2in the temperature range from 17 mK to above 6.7 K. All the junctions are in good quality and have a high gap voltage (>; 5.5 mV). We found that the junctions' sub-gap resistances were temperature dependent above 2.5 K and saturated at temperatures below 2.5 K. A junction sub-gap leakage current Irof about 23 pA was measured. The voltage noise power spectral density for 3 junctions with different sizes has been measured at the base temperature of 17 mK with the junctions biased above the gap voltage. The spectral densities clearly show 1/fbehavior at low frequency and are proportional to the junction's linear dimension.
IEEE Transactions on Applied Superconductivity•Nov 10, 2010•5 citations