Nature Nanotechnology, Vol.6, No.3, 156-161, 2011
Flexible high-performance carbon nanotube integrated circuits
Carbon nanotube thin-film transistors(1) are expected to enable the fabrication of high-performance(2), flexible(3) and transparent(4) 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 investigated(6-11), 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 (similar to 10 mu m) nanotubes connected by low-resistance Y-shaped junctions. The transistors simultaneously demonstrate a mobility of 35 cm(2) V-1 s(-1) and an on/off ratio of 6 x 10(6). 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.