Structure And Electrical Transport Properties Of ?-TaN Thin Films

?-TaN has received particular interest in recent years owing to their physical,chemical and mechanical properties, such as high hardness, wear resistance, chemical inertness, thermal stability and low temperature coefficient of resistance. Due to this superior properties, it is widely used as hard and wear-resistant coatings on tools,thin-films resistors and diffusion barriers in integrated circuits. In addition, ?-TaN thin films has high superconducting transition temperature(6~10.5 K), small superconducting gap(~1.24 meV) and low density of states at the Fermi energy, it has a potential application prospect in the single photon detector and normal metal-insulator-superconductor(NIS) tunnel junction devices.In this work, we systematically studied the structures, surface morphology and electrical properties of a series of polycrystalline ?-TaNxthin films, deposited on quartz glass substrates by rf sputtering method. The influence of deposition parameters on the properties of thin films were carefully studied. The electrical transport behaviors of ?-TaN thin films were also systematically discussed.Through the characterization of the structure and morphology, the films deposited at different substrate temperature are polycrystalline TaN and the mean grain sizes increase with increasing deposition temperature. As for the electrical transport properties, the films reveal superconductor-insulator granular composites characteristics below ~ 5 K. While between 10 and 30 K they show hopping transport properties appearing in metal-insulator granular films. The thermal fluctuation induced tunneling(FIT) conductive mechanism dominates the temperature behaviors of resistivities from 70 to 350 K. Our results indicate that the similarity in microstructure structures between TaN polycrystalline film and granular films is the main reason that makes TaN polycrystalline film possesses high resistivity and negative coefficient of resistivity.According to XRD and SEM characterization, the films deposited at different Npp are polycrystalline ?-TaN, the mean grain sizes decrease and crystallinity of the films declined with increasing nitrogen partial pressure. As for the electrical transport properties, below ~5 K, the superconductor-insulator granular composites characteristics disappeared gradually with increasing nitrogen partial pressure. For the films deposited at 0.2%, 0.4%, 0.94% Npp, the temperature behaviors of resistivitieswere dominated by thermal fluctuation induced tunneling conductive mechanism between 10 and 350 K, while the films deposited at 5.39%, 7.50% Npp show Mott variable range hopping(VRH) transport properties between 15 to 40 K and thermal fluctuation induced tunneling behavior above 50 K.