Source optimization for magnetron sputter-deposition of NbTiN tuning elements for SIS THz detectors

NbTiN is one of the most promising materials for use in the tuning circuits of Nb-based SIS mixers for operating frequencies above the gap frequency of Nh (approximate to 700 GHz). Device development requires stable and reproducible film properties. In this manuscript we compare the properties of NbTiN films obtained with a sputtering source using balanced and unbalanced magnetic trap configurations. This experiment shows that reducing the effectiveness of the magnetic trap by changing the magnet configuration is equivalent to reducing the sputtering pressure. We also show that it is possible to optimize the configuration of the magnetron magnets to produce stable and reproducible NbTiN films under the same gas pressure and applied power throughout the target lifetime.