Investigation of NbTiN thin films and AlN tunnel barriers with ellipsometry for superconducting device applications

High-energy-gap superconductors with low resistive loss and high-current-density tunnel barriers are important to increasing the operating range of THz electronics. This paper describes the development of superconducting NbTiN thin films and AIN tunnel barriers using ellipsometry analysis. NbTiN thin films were deposited by reactive DC unbalanced magnetron sputtering of NbTi in argon and nitrogen plasma onto a water-cooled, grounded substrate. The effects of total sputtering pressure, gas ratio, working distance, and voltage elevation were examined. AIN tunnel barriers were formed from DC magnetron sputtered thin films with the unique use of an ICP plasma source. The results of this ellipsometry analysis, using both discrete in-situ and spectroscopic ex-situ ellipsometers, are discussed.