Effects of dispersion conditions of single-walled carbon nanotubes on the electrical characteristics of thin film network transistors.

To facilitate solution deposition of single-walled carbon nanotubes (SWNTs) for integration into electronic devices they need to be purified and dispersed into solutions. The vigorous sonication process for preparing these dispersions leads to large variations in the length and defect density of SWNTs, affecting the resulting electronic properties. Understanding the effects of solution processing steps can have important implications in the design of SWNT films for electronic applications. Here, we alter the SWNTs by varying the sonication time, followed by deposition of sub-monolayer SWNT network films onto functionalized substrates. The corresponding electrical performance characteristics of the resulting field effect transistors (FETs) are correlated with SWNT network sorting and morphology. As sonication exposure increases, the SWNTs shorten, which not only affects electrical current by increasing the number of junctions but also presumably leads to more defects. The off current of the resulting transistors initially increased with sonication exposure, presumably due to less efficient sorting of semiconducting SWNTs as the defect density increases. After extended sonication, the on and off current decreased because of increased bundling and fewer percolation pathways. The final transistor properties are influenced by the nanotube solution concentration, density, alignment, and the selectivity of surface sorting of the SWNT networks. These results show that in addition to chirality, careful consideration of SWNT dispersion conditions that affect SWNT length, bundle diameter, and defect density is critical for optimal SWNT-FET performance and potentially other SWNT-based electronic devices.