A joint research group based in Tokyo, comprising of the National Institute of Advanced Industrial Science and Technology (AIST), Hitachi, and the Optoelectronic Industry and Technology Development Association, reported their major progress at a conference last month in using printing methods to fabricate organic thin-film transistors.
The group produced a 1.4-inch full-color liquid-crystal display with a resolution of 80 pixels/inch which is comparable to existing amorphous-silicon thin-film-transistor LCDs.
The display's organic TFTs use a protective layer that is printed rather than formed through costly photolithography and vacuum-deposition processes. Toshihike Kamata, group leader of the organic-semiconductor device group of AIST, reported, "We cleared the last hurdle, which is to form the protective layer by printing. Each component can be formed by printing separately at present. What we have to do is to integrate all processes by printing."
The group is aiming to develop a low cost display with quality as good as notebook screens, which is compeltely printed and costs $10.
The Japanese research group claimed to resolve two major challenges:
- the deterioration of transistors through the LC process
- high contact resistance between the organic transistor and metal electrodes for source and drain.
This was done by revising the shape of the electrodes, forming the edge of each electrode end that has contact with the organic semiconductor as a steep angle. With this shape, the transistor's resistance was lowered 20 percent, thus increasing source-to-drain current, the group said.