Optimization of the deposition parameters of Ni-20Cr thin films on thermally sprayed Al2O3 for sensor application

Ni-Cr (80-20 at.-%) thin films were synthesized by means of DC magnetron sputtering on thermally sprayed Al2O3 insolating coatings. In view of the application as a thin-film thermocouple, the ceramic layer provides an electrical as well a thermal insulation. The thin film must feature a good adhesion as well as a good electrical conductivity to be suitable as a thin-film thermocouple. Design of Experiments was utilized to determine if deposition parameters including the bias-voltage, heating power, and chamber pressure have a significant influence regarding critical scratch load, hardness to Young's modulus ratio, and electrical resistance. It was found out that the bias-voltage is the most important influencing factor. In order to extract the significant parameters, the morphology and topography were analyzed by means of SEM. The structural properties were obtained by means of XRD on an atomic level, using synchrotron radiation. Mechanical properties, such as the hardness and Young's modulus, as well the scratch load were evaluated using nanoindentation and a scratch-tester. To verify the findings, an optimized thin film was deposited, which showed an increased layer adhesion and a significantly lower electrical resistance.