Superconducting and Structural Properties of RF Magnetron Sputtered Niobium Nitride for Josephson Junctions
The material properties of rf magnetron sputtered niobium nitride prepared at a substrate temperature of 650°C have been investigated as a function of substrate rf bias. These materials exhibit a preferential crystallite orientation related to the amount of rf bias, (200) orientation for low bias and (111) for high bias. We have observed greater than expected lattice parameters of 4.46 Å for these films which we associate with a distorted fcc structure. The best films have a low temperature resistivity less than 70 µΩ-cm and transition temperatures exceeding 16 K. NbN/Si/Nb tunnel junctions have been fabricated from these films with un-oxidized hydrogenated silicon barriers using the SNAP process. These junctions have Vm values exceeding 40 mV and sum gap values ~3.9 mV. These barriers are being used in all NbN tunnel junction development.
KeywordsCounter Electrode Josephson Junction Tunnel Junction Substrate Bias Room Temperature Resistivity
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