Transport properties of polycrystalline TaNx thin films prepared by DC reactive magnetron sputtering method

Abstract

We have investigated the electrical transport properties of polycrystalline tantalum nitride (TaNx) films. Various compositions of tantalum (nitride) thin films have been deposited on SiO2 substrates by reactive DC magnetron sputtering while changing the ratio of nitrogen partial pressure. The substrate temperature was maintained at 283 K during deposition. X-ray diffraction analyses indicated the presence of α-Ta and β-Ta phases in the Ta film deposited in pure argon atmosphere, while fcc-TaNx phases appeared in the sputtering gas mixture of argon and nitrogen. The N/Ta atomic ratio in the film increased ranging from 0.36 to 1.07 for nitrogen partial pressure from 7 to 20.7%. The superconducting transition temperatures of the TaNx thin films were measured to be greater than 3.86 K with a maximum of 5.34 K. The electrical resistivity of TaNx thin film was in the range of 177-577 μΩcm and increased with an increase in nitrogen content. The upper critical filed at zero temperature for a TaN0.87 thin film was estimated to exceed 11.3 T, while it showed the lowest Tc = 3.86 K among the measured superconducting TaNx thin films. We try to explain the behavior of the increase of the residual resistivity and the upper critical field for TaNx thin films with the nitrogen content by using the combined role of the intergrain Coulomb effect and disorder effect by grain boundaries.