Flexible high-performance carbon nanotube integrated circuits

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Abstract

Carbon nanotube thin-film transistors1 are expected to enable the fabrication of high-performance2, flexible3 and transparent4 devices using relatively simple techniques. However, as-grown nanotube networks usually contain both metallic and semiconducting nanotubes, which leads to a trade-off between charge-carrier mobility (which increases with greater metallic tube content) and on/off ratio (which decreases)5. Many approaches to separating metallic nanotubes from semiconducting nanotubes have been investigated6,7,8,9,10,11, but most lead to contamination and shortening of the nanotubes, thus reducing performance. Here, we report the fabrication of high-performance thin-film transistors and integrated circuits on flexible and transparent substrates using floating-catalyst chemical vapour deposition followed by a simple gas-phase filtration and transfer process. The resulting nanotube network has a well-controlled density and a unique morphology, consisting of long (~10 µm) nanotubes connected by low-resistance Y-shaped junctions. The transistors simultaneously demonstrate a mobility of 35 cm2 V–1 s–1 and an on/off ratio of 6 × 106. We also demonstrate flexible integrated circuits, including a 21-stage ring oscillator and master–slave delay flip-flops that are capable of sequential logic. Our fabrication procedure should prove to be scalable, for example, by using high-throughput printing techniques.

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Figure 1: Carbon nanotube growth and device fabrication.
Figure 2: Mobility and on/off ratio.
Figure 3: Channel-length dependence and statistics of on/off ratio.
Figure 4: Carbon nanotube TFTs and integrated circuits on a flexible substrate.
Figure 5: Logic gates and delay flip-flops on a flexible substrate.

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Acknowledgements

This work was supported by the Industrial Technology Research Grant Program in 2008 from the New Energy and Industrial Technology Development Organization (NEDO) of Japan and the Aalto University MIDE program via the CNB-E project, and was partially supported by the Academy of Finland (pr. no. 128445).

Author information

Y.O. and E.K. conceived and designed the experiments. D.S. performed device fabrication and characterization. M.T. and Y.O. performed the growth of nanotubes. Y.T. and M.T. performed absorption measurements. A.N. and E.K. developed the floating-catalyst growth technique. D.S. and Y.O. co-wrote the paper. All authors discussed the results and commented on the manuscript.

Correspondence to Yutaka Ohno.

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