Influence of nanostructure on charge transport in RuO2 thin films

Abstract

Polycrystalline thin films of RuO2 were grown on fused-quartz substrates and a parametric study was carried out to probe the influence of film nanostructure on the four-point Van der Pauw resistivity and Hall coefficient. The films were grown via reactive rf magnetron sputtering of a Ru target in an Ar∕O2 plasma using deposition rates from 0.27to3.5Å∕s and substrate temperatures from 16to500°C. Room-temperature resistivities of the RuO2 films ranged from 58to360μΩcm. Upon first heating following deposition, some films showed decreasing resistivity with increasing temperature, but the resistivities also decreased upon subsequent cooling suggesting that the annealing treatment reduces the film defect density. The temperature coefficient of resistance was found to be small (<0.001K−1) in agreement with previous investigations. Hall coefficient measurements of the polycrystalline thin films demonstrated that either n-type or p-type majority carriers can be present depending on deposition conditions and the resulting nanostructure, in contrast to single-crystal RuO2, which is an n-type metal. Grain size and homogeneous strain within the films were measured by x-ray diffraction and are correlated to the majority carrier type.