Korean Journal of Materials Research ISSN:1225-0562(Print) 2287-7258(Online) 한국재료학회지

Ni-C composite films were prepared by co-deposition using a combined technique of plasma CVD and ion beam sputtering deposition. Depending on the deposition conditions, Ni-C thin films manifested three kinds of microstructure: (1) nanocrystallites of non-equilibrium carbide of nickel, (2) amorphous Ni-C film, and (3) granular Ni-C film. The electrical resistivity was also found to vary from about 10₂ μΩcm for the carbide films to about 10₄ μΩcm for the amorphous Ni-C films. The Ni-C films deposited at ambient temperatures showed very low TCR values compared with that of metallic nickel film, and all the films showed ohmic characterization, even those in the amorphous state with very high resistivity. The TCR value decreased slightly with increasing of the flow rate of CH₄. For the films deposited at 200 °C, TCR decreased with increasing CH₄ flow rate; especially, it changed sign from positive to negative at a CH₄ flow rate of 0.35 sccm. By increasing the CH₄ flow rate, the amorphous component in the film increased; thus, the portion of Ni₃C grains separated from each other became larger, and the contribution to electrical conductivity due to thermally activated tunneling became dominant. This also accounts for the sign change of TCR when the filme was deposited at higher flow rate of CH₄. The microstructures of the Ni-C films deposited in these ways range from amorphous Ni-C alloy to granular structures with Ni₃C nanocrystallites. These films are characterized by high resistivity and low TCR values; the electrical properties can be adjusted over a wide range by controlling the microstructures and compositions of the films.