Characterization of NbTiN Thin Films Deposited on Various Substrates

Niobium titanium nitride (NbTiN) thin films were deposited on a selection of different substrates to explore the optimum depositing condition of high-quality NbTiN thin films. The NbTiN films deposited on MgO, Al₂O₃, and fused quartz substrates showed excellent superconducting properties with a high T_C of 14.7 K, 14.5 K, 15.2 K, and low resistivity ρ_{20 K} of 55 μΩcm, 116 μΩcm, 78 μΩcm, respectively. The chemical composition, crystal structure, and relationship between superconducting properties and crystal structure were systematically investigated by changing the N₂/(Ar+N₂) ratio in sputtering gases. The lattice parameter systematically changed as N₂/(Ar+N₂) ratio was varied. We found that the superconducting properties depend on the lattice parameter, and the film with the best superconducting properties had a lattice parameter of 4.380 Å (on MgO), 4.345 Å (on Al₂O₃), 4.335 Å (on fused quartz).