Electrical and Structural Properties of Inkjet-Printed Single-Walled Carbon Nanotube Thin Film, and Its Applications

Abstract

Recently, flexible and stretchable features have been introduced for the use in various devices such as sensor, thin film transistor, and organic light-emitting diode. Advance developments in terms of materials, device physics, chemistry, and mechanics allow various devices to sustain their performance under deformation. But, many researches are still required to achieve stretchable electronic devices having high performance. Among the element, it is expected that the materials have an important role and lead to high performance. A carbon nanotube is one of the promising materials for the use in the stretchable electronics due to its excellent properties resulted from unusual structure of the carbon nanotube. In addition, tunable properties using functionalized group on the tube are advantages of the carbon nanotube. So, the use of carbon nanotube in stretchable electronics has been increased using the excellent properties. However, some technical issues such as low dispersion stability, scalability, and lower properties than individual carbon nanotube remain, which should be solved. First, we used an inkjet printer to improve the low scalability. In contrast to spin coating or screen printing reported in previous paper, the inkjet printing system reduces loss of materials

this is advantage for the use of single-walled carbon nanotube that suffers from high cost. Instead of the organic solvent having toxicity, the single-walled carbon nanotube was dispersed in aqueous solution. The low dispersion stability of the single-walled carbon nanotube in the aqueous solution was solved using surfactant. The synthesized ink was printed on stretchable substrate. Well-shaped film was obtained by controlling substrate temperature, UV ozone treatment. To reduce the surfactant used for dispersion stability, two post treatments (water rinsing and nitric acid treatment) were performed. Significant results of both treatments were confirmed from conductivity and structural properties. The inkjet-printed single-walled carbon nanotube thin films exhibited excellent mechanical properties under deformation. The thin films did not lose conductivity in even high tensile strain (100%), and the conductivity was maintained in cyclic stretching test although little variation of resistance was shown. The specific phenomenon was confirmed from microstructure of the thin film, which was crack bridging of carbon nanotube. The property was demonstrated using a integration with light-emitting diode. Response of the single-walled carbon nanotube thin film on the external strain could be controlled by structural properties of the thin film without loss of durability. Inkjet-printed pre-pattern caused cracks on the thin film, which improved the response on the external strain. When the conditions of the pre-pattern were optimized, the thin film had high sensitivity, durability, linearity. The printed thin films were demonstrated by detecting human motions. Strain sensor system consists of stretchable electrode and strain sensor were fabricated using tunable response of the inkjet-printed single-walled carbon nanotube thin film on the tensile strain.