The effect of the nickel and chromium concentration ratio on the temperature coefficient of the resistance of a Ni–Cr thin film-based temperature sensor

Wearable devices have become one of the most promising modern technologies due to the rapid development of network and sensor systems. Moreover, flexible sensors were researched to be applied in wearable devices. In this paper, we show a low cost and flexible temperature sensor that has high responsivity to temperature. A cylindrical PET monofilament was used as a main substrate and a Ni–Cr thin film was deposited by RF magnetron co-sputtering without a pattern. Various Ni–Cr concentration ratios were applied in this paper by altering the sputtering power of the Cr target. Increasing the concentration of Cr resulted in the variation of several characteristics such as the thickness of the Ni–Cr thin film, crystallinity, and the surface state. In addition, depositing the Ni–Cr thin film on a PET monofilament meant that the device showed resistive behavior when the temperature increased. This was proven by measuring the Temperature Coefficient of Resistance (TCR). The TCR was also measured after both repetitive bending and washing to evaluate its suitability in wearable devices. Overall, TCR showed diverse features for different Ni–Cr concentration ratios with a maximum value of 30 × 10⁻³ °C⁻¹.