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Cheaper electronics possible with new Carbon nanotube transistors

Cheaper electronics possible with new Carbon nanotube transistors

30-May-11
In recent years there has been an increase in the use of carbon nanotubes as a transistor substance. This is because of their excellent conduction potential and chemical stability.
A research team has created a quick and effortless method of making high-performance, thin-film transistors on plastic substrate.
Researchers have been developing carbon nanotube-based thin-film transistors (TFTs) in the hope of creating high-performance, flexible, transparent devices, such as e-paper and RFID tags. As per PhysOrg.com, 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). This is a study on the fabrication of high-performance TFTs and ICs on flexible, transparent substrates in a recent issue of Nature Nanotechnology, leading to a simple and fast technique for low-cost, flexible electronics. As per co author Yutaka Ohno of Nagoya University, "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. 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 carbon nanotube transistors 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. Though easy solution oriented processes have been created for making nanotube thin-film transistors, the transistors have not reached capability goals in comparison to transistors made from single nanotubes. This is because the conduction properties of the nanotubes break down during the process. The groundbreaking method relies on growing the nanotubes in atmospheric pressure gas and gathering them with a filter. The results are a thin film which is then transferred from the filter onto plastic, which is able to provide a clean film with uniformity in seconds. This new process is being made into a technology for fast roll-to-roll (R2R) manufacturing.
 
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