The effect of annealing process on the performance of strain nickel–chromium thin film sensor

In order to reduce the resistance value of the sputtering thin film resistor grid and improve the adhesion of the film, a thin film sensor with the NiCr film as a sensitive layer on a 304 stainless steel substrate is annealed in the N2 environment. During the experiment, it is found that the different annealing temperatures (300 °C, 350 °C, 400 °C, 450 °C, and 500 °C) can effectively reduce the resistance value of the thin film resistor grid; the decrease is the largest at 450 °C, and the resistance value change is 1.77 kΩ. The small resistance value enables the thin film sensor to detect smaller strain and has higher measurement accuracy. The thin film has the strongest adhesion on the substrate at 350 °C and 30 min, which is about 37.5% higher than that of the sputtering state. The increase in adhesion makes the thin film less likely to crack and fall off prematurely, which can expand the measuring force range. In addition, the atomic force microscopy results demonstrate that the thin film annealed at a higher annealing temperature has higher surface roughness, which may be caused by the phenomenon of original grain clusters after annealing. In addition, the temperature coefficient of resistance value and strain sensitivity coefficient (kn) increase with the increase in the annealing temperature, with kn increasing only slightly.