High performances and low variability of semiconducting-SWCNT thin-film-transistors achieved by shortening tube lengths
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High performances and low variability of semiconducting-SWCNT thin-film-transistors achieved by shortening tube lengths Takeshi Saito1,2, Shigekazu Ohmori1,2, Kazuki Ihara2,3, Yuki Kuwahara1,2 and Fumiyuki Nihey2,3 1 Nanotube Research Center, National Institute of Advanced Industrial Science and Technology, Tsukuba, Ibaraki, 305-8565, Japan 2 Technology Research Association for Single Wall Carbon Nanotubes, Tsukuba, Ibaraki, 3058565, Japan 3 NEC Smart Energy Research Laboratories, Tsukuba, Ibaraki, 305-8501, Japan ABSTRACT The tube-length distribution in the semiconducting single-wall carbon nanotube (sSWCNT) ink extracted by the electric-field-induced layer formation (ELF) method was characterized by atomic force microscopy, which revealed that the nonionic surfactant Brij 700 adopted in ELF causes the significant and homogeneous shortening of SWCNTs compared with sodium cholate that is frequently used for the dispersion of SWCNTs as an ionic surfactant. It was found that the shortened s-SWCNTs in the semiconducting ink positively effect on the uniformity of performance among the s-SWCNT thin-film transistors. INTRODUCTION Single-wall carbon nanotubes (SWCNTs) have attracted considerable attention as a potential semiconducting material [1] in the ink applied to “printed electronics” [2] because of their excellent electronic properties, as well as their flexibility and chemical robustness. For the printed electronics of SWCNTs, various processes, such as not only the printing process itself, but also the semiconducting-ink preparation and removal of surfactants by heat and/or wet treatments are required. [3] Among these processes, recent significant advances in the extraction techniques for the ink preparation of semiconducting SWCNTs (s-SWCNTs) have improved the device performance of thin-film transistors of SWCNTs (SWCNT-TFTs). Recently, we have developed a novel separation technique, what we call the electric-field-induced layer formation (ELF) method [4], to extract high-purity s-SWCNTs ink not containing ionic surfactants. Besides the purity of s-SWCNTs, many geometrical parameters, such as the most basic parameters of tube length [5] and diameter, [6] can directly affect the device characteristics. In particular, the effect of the tube length is complicated because it influences SWCNT-TFTs in terms of some different aspects of device performance. For example, the long SWCNTs lead to a prominent high-mobility above 100 cm2V-1s-1 due to the reduction in the number of contacts and their resistance. In contrast, SWCNTs much shorter than the channel length of devices can contribute to a decrease in the error probability in the device performance, which results in the improvement of device reliability. [7] These recent reports suggest the importance of characterizing the tube length distribution in the SWCNT dispersion for the analysis of SWCNTTFT performance. Here we report the statistical analysis of the tube-length distribution in the s-SWCNT ink extracted by ELF by atomic force microscopy (AFM) observation. Furt
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