Carbon based polyimide nanocomposites thin film strain sensors fabricated by ink-jet printing method

Abstract

Carbon-nanotube (CNT) and graphene-nanoplate (GNP) are two popular fillers to fabricate carbon-based nanocomposite devices. In this study, CNT-polyimide (PI) and GNP-PI nanocomposite thin film piezoresistive strain sensors were fabricated on flexible polyimide substrates and their electromechanical properties were characterized. The percolation thresholds were first determined for the two nanocomposites by investigating the volumetric conductivity as a function of filler concentration. Inkjet printing technique was employed to produce the nanocomposite devices with filler concentrations around the percolation threshold. The interdigital electrodes pre-deposited on the substrate were used for the electrical measurement of the devices. The piezoresistive sensitivity of the nanocomposite strain sensors was characterized by uniaxial tensile tests. The optimal compositions of 1.8 wt% CNT-PI and 1.4wt% GNP-PI nanocomposites were suggested for maximum gauge factors of 3.5 and 26, respectively. The temperature coefficients of resistance (TCR) for the fabricated nanocomposite thin film strain sensors were also characterized. The results demonstrate that GNP-PI nanocomposite strain sensors exhibit higher strain sensitivity than the CNT-PI counterpart. Temperature compensation is therefore necessary in practical applications of these nanocomposite strain sensors.