Reactively sputtered niobium nitride thin films for Josephson integrated circuit application

The properties of sputter-deposited NbN thin films were studied under changes in various deposition conditions including nitrogen flow, substrate heating, the addition of carbon impurities, and the use of an Nb underlayer. Without the underlayer, a semiconductorlike resistive behavior above the superconducting transition temperature and a wide superconducting transition were observed in the niobium nitride films, including those with transition temperatures above 15 K. With the underlayer, metallic behavior and a sharp superconducting transition temperature depended strongly on nitrogen flow and substrate heating but weakly on carbon impurities. The authors present details on the preparation and analysis of niobium nitride thin films with and without a niobium underlayer as well as the measured film characteristics.<>