Mar 6, 2008
Inkjet prints transparent CNT film
Transparent conductive film for use in displays is one of the headline applications for carbon nanotubes (CNTs). The interconnected material is seen as being more robust than today's ITO electrodes and could prove a popular choice for flexible devices, but the challenge is to bring down production costs.
Fabricating a transparent CNT film typically involves a coating step followed by some kind of pattern transfer, but scientists in Korea believe that they can combine these two steps into one by using inkjet printing.
In the past, researchers have shown that inkjet printing works well with multiwalled CNTs, but this material is less attractive to display makers due to its relatively low conductivity and low bandwidth in comparison with single-walled CNTs. Unfortunately, single-walled CNTs have a tendency to agglomerate and clog the inkjet nozzle, which has put the material's high-performance potential on hold.
To get around this, the Korean team centrifuges its ink before use to remove any large particles. In addition, substrate preparation is critical. To improve the drying time of the inkjet printed drops and to promote uniform evaporation, the researchers use hydrophilic plasma-treated substrates. Heating the glass substrate to 60 °C is also beneficial and further reduces the drying time of the ink solution (CNT concentration 20 µg/ml) from 12 down to 1.6 seconds.
The researchers overprint to adjust the electrical properties of the film and to stabilize bandwidth performance. "The film's high-frequency response will be important for interconnecting electronic devices such as thin-film transistors, LEDs and MEMs," Chang-Soo Han of the Korea Institute of Machinery and Materials told nanotechweb.org.
Han and his colleagues have printed various patterns and electronic circuits on glass, glassy paper and polymer substrates. "Recently, we have achieved a line width of 46 µm and a dot pattern with a diameter of 4.12 µm after surface treatment," he added.
According to Han, the technique is also attracting interest from makers of gas sensors and the group plans to follow this up alongside its display interests.
The researchers presented their work in Nanotechnology.
About the author
James Tyrrell is editor of nanotechweb.org.