Carbon nanotube transistors could lead to inexpensive, flexible electronics

Feb 16, 2011 By Lisa Zyga feature
Carbon nanotube thin-film transistors and integrated circuits on a flexible and transparent substrate. Image copyright: Dong-ming Sun, et al. ©2011 Macmillan Publishers Limited.

(PhysOrg.com) -- Recently, researchers have been developing carbon nanotube-based thin-film transistors (TFTs) in the hopes of creating high-performance, flexible, transparent devices, such as e-paper and RFID tags. However, one of the biggest challenges holding back the transistors’ performance is a trade-off between the properties of metallic and semiconducting nanotubes that make up the transistors. In a new study, researchers have developed a new way of fabricating nanotube networks that partly overcomes this problem, and show that the nanotube networks could be used to make transistors as well as flexible integrated circuits (ICs).

The researchers, Dong-ming Sun from Nagoya University in Nagoya, Japan, and coauthors from there and Aalto University in Finland, have published their study on the fabrication of high-performance TFTs and ICs on flexible, transparent substrates in a recent issue of .

“We have shown that, without consideration of carbon nanotube chirality, the as-grown carbon nanotubes can be used to fabricate high-performance TFTs and ICs, leading to a simple and fast technique for low-cost, flexible electronics,” coauthor Yutaka Ohno of Nagoya University told PhysOrg.com. “Lightweight and flexible devices such as mobile phones and electronic paper are gaining attention for their roles in achieving a smarter and green ubiquitous information society. It is important to manufacture such devices at extremely low cost in replacing conventional paper-based media such as newspapers and magazines. Our work can provide such technology.”

As the researchers explained in their study, nanotube networks contain both metallic and semiconducting nanotubes. While a greater amount of metallic nanotubes increases the transistor’s charge-carrier mobility, it also decreases the on/off ratio.

Since both of these characteristics are important for overall transistor performance, the researchers in the new study found a way to optimize both characteristics by fabricating a nanotube network with certain unique properties. For instance, the network’s morphology consists of straight, relatively long (10 micrometers) nanotubes (30% of which are metallic) compared to other nanotube networks. The new network also uses more Y-junctions than X-junctions between nanotubes. Since Y-junctions have a larger junction area than X-junctions, they also have lower junction resistance.

The carbon nanotube film with X- and Y-junctions. Image copyright: Dong-ming Sun, et al. ©2011 Macmillan Publishers Limited.

Using this nanotube network, the researchers fabricated TFTs that simultaneously demonstrate a high charge-carrier mobility and on/off ratio, offering significantly better performance than previous nanotube-based transistors. The researchers explained that the high mobility is due to the nanotube network’s unique morphology, while the high on/off ratio can be attributed to the lower density of metallic nanotubes, which can be controlled during the fabrication process.

After building the transistors, the researchers fabricated an IC capable of sequential logic – the first such circuit based on to date. In sequential logic circuits, the output depends on both the present input as well as the history of the input, so that these circuits have storage or memory functions.

The researchers predict that, by scaling up the fabrication process and using improved printing techniques, these nanotube-based TFTs could lead to the development of large-scale, inexpensive, and flexible electronics.

“Our near-future plan is to demonstrate roll-to-roll fabrication of CNT-based TFT arrays and ICs,” Ohno said. “To do so, we need to replace all the lithographic techniques by high-throughput printing techniques. For commercialization, we have to improve the uniformity of TFT characteristics more, but we are aiming at commercializing within five years.”

Explore further: Scanning tunnelling microscopy: Computer simulations sharpen insights into molecules

More information: Dong-ming Sun, et al. “Flexible high-performance carbon nanotube integrated circuits.” Nature Nanotechnology. Advance Online Publication. DOI: 10.1038/NNANO.2011.1

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Decimatus
5 / 5 (3) Feb 16, 2011
Computer chips are starting to look awfully organic.
Mr_Frontier
5 / 5 (1) Feb 16, 2011
Perhaps coincidental that organics should become part of our models?
Jayman
3.7 / 5 (3) Feb 17, 2011
$5 disposable ebook readers?
mrbunnylamakins
not rated yet Feb 19, 2011
Name One cheap product???. They lie all the time about prices and things being cheap. Years ago when they fist developed OLED they said it was cheap to make. Yet when it came to market for TV it was they most expensive product out there.
Quantum_Conundrum
not rated yet Feb 20, 2011
Name One cheap product???. They lie all the time about prices and things being cheap. Years ago when they fist developed OLED they said it was cheap to make. Yet when it came to market for TV it was they most expensive product out there.


You don't think millionaires become millionaires by selling you things "at cost" do you? Where do you think that CEO got his $13 million per year from? The company over charges you. Many things in America, from books and computers to other electronics, have a 100% to 1000% markup above cost, and this money ends up in the owner or CEO's pocket.
Doctor_Professor
not rated yet Feb 21, 2011
I wouldn't say that OLED TVs are excessively marked-up, although it's possible. LCDs are cheap because we can produce the manufacturing technology cheaply, which allows more factories to buy the equipment, which leads to a larger supply of LCD panels. Large OLED panels, on the other hand, are probably only made in a handful of factories, and the equipment needed to produce them may have cost quite a bit as well.

Once the manufacturing technique for both the panels and the panel manufacturing equipment becomes easier and faster with less defects, we will see prices drop on OLED sets as supply rises, thanks to easier supply of the manufacturing equipment.

This is all just pure speculation on my part, but I think it makes sense.

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