Microstructural design for fabrication of strain sensor utilizing tungsten-doped amorphous carbon coatings

Tungsten-containing diamond-like carbon (W-DLC) coatings were fabricated with an aim of producing new strain sensor applications. W-DLC coatings with various metal concentrations were prepared by chemical vapor deposition and DC magnetron co-sputtering of a tungsten metal target. The electrical resistance was shown to be proportional to the value of compression and tensile strain. The expression ΔR/R = Kε, was applied to the experimental results in order to determine the gauge factor of each coating, and this gauge factor varied according to the metal concentration. Transmission electron microscope was employed for structural analyses and it was shown that the structure of the W-DLC coatings consisted of nanometer size grains dispersed into an amorphous carbon host matrix. The electrical properties of the W-DLC coatings were simulated using a model based on a composite insulator-metal cluster structure. These results were in agreement with the experimental ones, and a high gauge factor can be obtained with low metal concentration or increase in size of metal cluster.