DEGRADATION OF NICR CUNIMN/NICR FILMS ON ALUMINA SUBSTRATES/

This paper addresses the aging behaviour of NiCr/CuNiMn/NiCr triple la yers on Al2O3 ceramics at temperatures up to 200 degrees C for film th icknesses d greater than or equal to 0.5 mu m. Investigations of the f ilm structure and the increase of resistance and its temperature coeff icient during the annealing process and studies of the dependence of t his aging drift on both the film thickness and the storage temperature have been carried out. Furthermore, the film stress and the effect of substrate bending on resistance have been measured. The results can b e explained by the irregular film structure (columns and small bridges between them), which causes stress and current concentrations as well as local creeping, cracking and oxidation processes in the micro-brid ges. They are compared with such for structurally homogeneous films on silicon wafers.