Enhanced Current Path by Circularly and Periodically-Aligned Semiconducting Single-Walled Carbon Nanotubes for Logic Circuit Device

Improving the performance of solution-processed single-walled carbon nanotube thin film transistors (SWCNT TFTs) is essential to their wide usage in next generation large-area electronic devices. However, uncontrollable tube-tube junction and random network formation from conventional solution processes of SWCNTs has limited mobility and on-current level of SWCNT TFTs. Herein, we demonstrate a facile method by switching idea of reducing coffee-ring of the conventionally solution-processed or inkjet-printed thin films. Spontaneous coffee-ring formation of the inkjet-printed droplets is found to enhance directional alignment of SWCNTs in the outer rim of the coffee-rings. The evaporation-driven capillary flow toward the rim inside induces migration of SWCNT and thus forms densely aligned SWCNT rings. Periodic connection of such rings can provide high-current path at a given voltage. Therefore, by additionally forming the periodically connected rings on a pre-established random network of SWCNT in channel area of TFTs, we significantly improved the mobility and Ion/Ioff ratio of SWCNT TFTs without degradations in other electrical parameters such as threshold voltage and subthreshold swing. We also demonstrated all-solution-processed inverters with higher voltage-gain in comparison with conventional ones.