Effects of annealing on the electrical properties of NiCr vs AlCu thin film resistors prepared by DC magnetron sputtering

NiCr is widely used in the manufacture of thin metal film resistors (TFR) in the value range 10Ω to 1MΩ because of its relatively large resistivity, low temperature co-efficient of resistance (TCR) and excellent stability of resistance. However the demand for TFR’s with ohmic values of less than 10Ω has significantly increased in recent years due to the rising demand for low-loss current sensing in many electronic products. Consequently this trend has highlighted a number of problems associated with the manufacture of lower resistance NiCr films, primarily increased film thickness and hence increase in deposition time. This paper investigates the electrical properties of AlCu as a replacement for NiCr in this lower resistance range. Films of NiCr and compositions of AlCu were prepared by DC magnetron sputtering in Ar. After deposition the films were annealed in both air and N2 atmospheres at a range of temperatures. A direct comparison of electrical characteristics of the two film systems was then performed. Results reveal that an increase in Al content produces a decrease in TCR and gives an improvement in resistance stability. A wide region of alloy composition exists where films with equivalent resistance stability and sheet resistance to NiCr can be obtained at lower deposition times.