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A thin-film resistor out of Ni(80%)Cr(20%) for integration in a standard complementary metal-oxide-semiconductor process with a temperature coefficient of resistance (TCR) below 10 ppm/K was realized by applying a thin Ti layer underneath. The Ti-layer thickness and the temperature and duration of furnace annealing after deposition were optimized in different experiments. The combination of 5-nm Ti + 10-nm NiCr and a 30-min heat treatment at 350degC in a forming gas ambient was found to yield a sheet resistance of about 140 Omega/sq and a TCR of below 10 ppm/K. The long-term drift of the sheet resistance after 1000 h at 200degC was about 0.3%. A transmission electron microscopy analysis was conducted to investigate the structure of the film and a possible change during annealing. An Auger analysis was conducted for film surface analysis.
Date of Publication: March 2008