Development and TCR control of Nichrome thin film resistors for GaAs MMICs

Process for Nichrome resistor fabrication has been developed that gives nichrome resistors with sheet resistance Rs 40Ω/□.The alloy composition used is 80wt% Ni and 20wt% Cr. RF sputter deposition conditions, optimum for Nichrome thin film deposition with repeatable values of resistivity are reported. Comparison of results with split and normal mode of sputter deposition is also reported. The alloy composition of the deposited film is seen to depend on the purity of the sputter gas. The present deposition conditions give as-deposited NiCr films with resistivity 130μΩ-cm and TCR 85-100ppm/°C.The film resistivity and TCR are strong functions of heat cycles in the fabrication process. When subjected to heat cycles of resistor fabrication process, the film resistivity is found to drop to 104±8μΩ-cm with a rise in TCR values to 250ppm/°C.