Using the same rubbery CNT-based conductor they developed a few months ago, researchers at the University of Tokyo have made a stretchable display. With the advantage of being printable, this brings us closer to cheap flexible and conformal displays.
The earlier invented flexible CNT-based conductor is now used to connect organic light-emitting diodes (OLEDs) with the organic transistors addressing each OLED pixel. With improved conductivity and stretchability, it is now possible to fold the display in half or even crumple it up without damage, and to stretch it up to 50 percent of the original shape.
A few months earlier, the flexible conductive material was used to connect organic transistors in a stretchable electronic circuit. At this stage, it was already clear that potential other applications for this flexible conductive CNT-based material are flexible displays, actuators and electronic skin for robots etc.
Stretchable mesh of transistors connected by elastic conductors that were made at the University of Tokyo. Credit: Science/AAAS.
Dr. Takao Someya, electrical-engineering professor at the University of Tokyo, and his colleagues also developed a process for making long carbon nanotubes on an industrial scale.
The used rubber is produced by a jet-process. In a first step, the carbon nanotubes are combined with an ionic liquid that contains charged molecules, and a liquid polymer. The resulting nanotube-rubber paste then has to pass a high-pressure jet, which is needed to spread the tubes in the rubber material and make them thinner without shortening.
Dr. Takao Someya says: "The longer and finer bundles of nanotubes can form well-developed conducting networks in rubbers, thus significantly improved conductivity and stretchability".
The process also increases the viscosity of the rubber material and thereby allows deposition by high-definition screen-printing. For the wire grid used to connect the transistors and the OLEDs of the flexible display, they printed 100-micrometer-wide lines using a printing mask.
In comparison with other flexible electronics the rubber-like material offers the additional advantage that complex three-dimensional objects can be covered, which opens up new possibilities for applications.
According to Someya Dai Nippon Printing is interested in commercializing this invention. With further improvements especially regarding width of the printed lines and resolution, a commercial product should be possible in five years.
To learn more attend Printed Electronics Asia 2009 or Printed Electronics USA 2009.
