Influence of Sputtering Temperature and Layer Thickness on the Electrical Performance of Thin Film Strain Sensors Consisting of Nickel-Carbon Composite

Abstract

Hybrid laminates consisting of fibre-reinforced thermoplastic films and metallic thin sheets are successively replacing thermoset based systems due to their obvious advantages of higher formability and aptitude for mass production. In order to monitor the material under operating conditions, hybrid laminates need to be equipped with smart sensor units. Artifact-free integration of commercial strain gauges into hybrid laminates is almost impossible. Therefore, a new thin film strain sensor based on a PVD sputtering process was developed.The aim of this work was to evaluate the influence of the layer thickness as well as the elevated temperature during the sputtering process on the electrical performance of Ni-C strain sensors. The Ni-C films with different layer thickness and different sputtering temperatures manufactured by means of a magnetron sputtering process were investigated for the sheet resistance and the change of temperature coefficients of resistance. In addition, Raman spectroscopy was utilized to investigate the phase development with regard to different sputtering temperatures. It can be seen that the gauge factor gets doubled while optimizing the layer thickness. When the sputtering temperature was increased, the graphitic phase formation was preferred and the impurities were reduced. These results are discussed in this paper and appropriate solution concepts are provided.