CNT-TFT Made With Flexographic Printing Technology

Sep 15, 2012
Tetsuo Nozawa, Nikkei Electronics
An array of CNT-TFTs. The PEN substrate measures 15 x 15cm. (photo courtesy of the Ohno Laboratory of Nagoya University)
An array of CNT-TFTs. The PEN substrate measures 15 x 15cm. (photo courtesy of the Ohno Laboratory of Nagoya University)
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A Japanese research group made a carbon nanotube (CNT)-based TFT for flexible displays, etc with a flexographic printing technology and achieved a carrier mobility as high as 112cm2/Vs.

The research group consists of Yutaka Ohno, associate professor at the School of Engineering, Nagoya University, and researchers of Bando Chemical Industries Ltd. This was announced Sept 13, 2012, at the 73rd JSAP Autumn Meeting, 2012, which runs from Sept 11 to 14, 2012, at Ehime University (lecture number: 13a-C2-5).

Flexographic printing is a kind of relief printing and uses a rubber plate or a flexible plate made of photo-curing resin. A roll of relief printing plate with patterns to be printed is made by using the photo-curing property, etc. And a roll having a porous surface (anilox roll) is used to apply water-based ink to the plate.

The printing precision of flexographic printing is slightly lower than that of gravure printing. But its throughput is much higher than those of screen printing and ink-jet printing.

The research group made the CNT-TFT with a flexographic printing technology because of its high throughput, low cost and compatibility with roll-to-roll methods.

All the processes for making the CNT-TFT take place under normal temperatures and pressures. And they use silver (Ag) nanoparticles for gate electrodes and source/drain electrodes, imide resin for gate dielectric films and CNTs for the channel layer of the TFT. Oxygen (O2) plasma is used for the patterning of CNTs under a normal pressure, but a printing technology is used to form a resist layer for it.

The CNT is made by using a gas-phase filtration/dry transfer method that Ohno's laboratory has been developing. And a PEN (polyethylene naphthalate) film is used as a substrate. The printing speed is 6.6cm per second.

The channel length, carrier mobility and on/off ratio of the CNT-TFT are 115μm, 112cm2/Vs and 104, respectively. The carrier mobility is high enough to be used for driver TFTs of displays.