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,
${\rm Al}_{2}{\rm O}_{3}$
, and fused quartz substrates showed excellent superconducting properties with a high
$T_{\rm C}$
of 14.7 K, 14.5 K, 15.2 K, and low resistivity
$\rho_{20\ {\rm K}}$
of 55
$\mu\Omega{\rm cm}$
, 116
$\mu\Omega{\rm cm}$
, 78
$\mu\Omega{\rm cm}$
, respectively. The chemical composition, crystal structure, and relationship between superconducting properties and crystal structure were systematically investigated by changing the
${\rm N}_{2}/({\rm Ar}+{\rm N}_{2})$
ratio in sputtering gases. The lattice parameter systematically changed as
${\rm N}_{2}/({\rm Ar}+{\rm N}_{2})$
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
$\hbox{\rm{\AA}}$
(on MgO), 4.345
$\hbox{\rm{\AA}}$
(on
${\rm Al}_{2}{\rm O}_{3}$
), 4.335
$\hbox{\rm{\AA}}$
(on fused quartz).