Optimization of RF- and DC-sputtered NbTiN films for integration with Nb-based SIS junctions

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 Nb (/spl ap/700 GHz). We examine the properties of NbTiN films obtained using an unbalanced sputtering source in both RF and DC operating regimes. It is found that the properties of NbTiN films are strongly affected by the total pressure of the sputtering process. Films obtained under lower pressures have higher compressive stresses and lower resistivities. The best NbTiN films are obtained by DC sputtering and have a transition temperature of 14.4 K, a resistivity of 90 /spl mu//spl Omega//spl middot/cm at 20 K, and a compressive stress of -1 GPa. Films with a resistivity of 110 /spl mu//spl Omega//spl middot/cm at 20 K and a compressive stress of -0.5 GPa have been successfully used as a stripline material for Nb/Al-AlO/sub x//Nb SIS junctions on fused quartz substrates.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 Nb (/spl ap/700 GHz). We examine the properties of NbTiN films obtained using an unbalanced sputtering source in both RF and DC operating regimes. It is found that the properties of NbTiN films are strongly affected by the total pressure of the sputtering process. Films obtained under lower pressures have higher compressive stresses and lower resistivities. The best NbTiN films are obtained by DC sputtering and have a transition temperature of 14.4 K, a resistivity of 90 /spl mu//spl Omega//spl middot/cm at 20 K, and a compressive stress of -1 GPa. Films with a resistivity of 110 /spl mu//spl Omega//spl middot/cm at 20 K and a compressive stress of -0.5 GPa have been successfully used as a stripline material for Nb/Al-AlO/sub x//Nb SIS junctions on fused quartz substrates

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 Nb (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.<br/