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nanotimes News in Brief

11-01 :: December 2010 / January 2011

Carbon Nanotubes // World‘s First Successful Operation of CNT-based Integrated Circuits Manufactured on Plastic Substrates

fessors Yutaka Ohno from Nagoya University in Ja- pan and Esko I. Kauppinen from Aalto University in Finland along with their colleagues have developed a simple and fast process to manufacture high quality carbon nanotube-based thin film transistors (TFT) on a plastic substrate. They used this technology to manufacture the world’s first sequential logic circuits using carbon nanotubes. Using this tech- nology, the development of high-speed roll-to-roll manufacturing processes to manufacture low cost flexible devices such as electronic paper in the future will be possible.

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In conventional solution processes, soot-like carbon nanotube material is first dispersed in liquid via sonication to purify the materials and to separate the tubes from each other. In such processes, it is diffi- cult to form homogeneous carbon nanotube films. In addition, technology has not yet been developed to completely remove the dispersant.

In contrast, using the new innovative technology, Kauppinen and his team continuously grow nano- tubes in an atmospheric pressure chemical-vapor deposition process. The nanotubes are then collected on the filter and subsequently transferred onto a po-

s part of NEDO‘s Industrial Technology Research Grant Japan-Finland collaborative project, Pro-

lymer substrate using simple gas-phase filtration and transfer processes to achieve clean, uniform carbon nanotube films (Fig. 1). It takes only a few seconds to deposit the carbon nanotubes. This process may be adaptable to high-speed roll-to-roll manufacturing systems in the near future.

In conventional solution-based carbon nanotube TFT manufacturing processes, nanotubes are dispersed using powerful ultrasound which cuts the nano- tubes and reduces their length. Due to high contact resistance between these short nanotubes and the residual impurities caused by the dispersion process, the resulting TFT mobility was approximately 1 cm2

/

Vs. Due to the doping effect caused by residual im- purities from the dispersion, the on/off ratio was only between about 104~105.

When carbon nanotube thin films are manufactured using the above gas-phase filtration and transfer pro- cesses, the tubes in the film are as clean and long as those that are grown in the synthesis processes.

Accordingly, TFTs with a high mobility of 35 cm2 /Vs

were achieved. In addition, due to precision control of the nanotube density, an on/off ratio of 6x106 was simultaneously achieved. The TFT performance is significantly higher than the performance of orga-