Corrosion-resistant metal layers from a CMOS process for bioelectronic applications

The use of the dominant CMOS (complementary metal–oxide–semiconductor) process technology in perspective bioelectronic applications imposes severe restrictions on the materials used with respect to their stability in aqueous solutions with high concentrations of electrolytes. We report the results of a comparative study of Al:Cu, CoSi2 and TiN metal layers that were prepared within a regular CMOS process and characterized by depth-profiling with X-ray photoelectron spectroscopy (XPS) in order to determine chemical composition and contaminants. The corrosion caused by isotonic NaCl solution was investigated and the most pronounced corrosion resistance was observed for TiN layers showing only negligible conductivity degradation when exposed to high concentration of electrolytes at elevated temperature for a time span of days. In addition, TiN layer electrodes turned out to be stable in an electrochemical cell over a large potential range and a wide pH range. No electrocatalytic activity for the conversion of hexacyanoferrate or catechol has been found. It is concluded that from the different metal layers available in CMOS processing, TiN layers are best suited for biomedical electrode applications.