Abstract
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.
Highlights
Micro–nano strain film sensor is an emerging technology with broad application prospects in the force measurement system1–4 due to the simple structure, small size, reliable performance, and low cost
The resistance value of the thin film resistor grid is the minimum at 450 ○C annealing temperature, which is 74.7% lower than the sputtering state
The prepared NiCr thin film sensor on a 304 stainless steel substrate is annealed in the N2 environment
Summary
Micro–nano strain film sensor is an emerging technology with broad application prospects in the force measurement system due to the simple structure, small size, reliable performance, and low cost. In the case of small strain, a thin film resistor grid with a large resistance value will not be conducive to the measurement of its high precision strain sensitivity. At the same time, during the tensile test, the film may crack or fall off prematurely due to insufficient adhesion on the substrate.6,7 These two phenomena could hinder the development of sensors. A thin film sensor with a NiCr film as the sensitive layer on the 304 stainless steel substrate is prepared. Scitation.org/journal/adv and mechanical properties of NiCr thin film resistor grids, such as resistance, temperature coefficient of resistance (TCR), strain sensitivity, and adhesion, are studied under different annealing conditions (300 ○C, 350 ○C, 400 ○C, 450 ○C, and 500 ○C). This work has a high reference value for the design optimization of the embedded tool-type strain film sensor in the future
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