In a joint project scientists from Finland and Japan have developed a process for producing thin-film transistors on plastic based on carbon nanotubes (CNTs).
The project team from Aalto University in Finland and Nagoya University in Japan has used the technology to produce sequential logic circuits, proving that CNTs can be used to make display backplanes and other flexible circuit applications.
In the project nanotubes were grown in an atmospheric pressure chemical-vapour deposition process, then collected on a filter and transferred onto a plastic substrate to achieve clean, uniform CNT films, which takes a few seconds. The next challenge for the team is to adapt the process for roll-to-roll manufacturing systems.
The research is funded by a grant from Japan's New Energy and Industrial Technology Development Organisation (NEDO).
Deposition
Conventional flexible thin-film transistors (TFT) are produced using a variety of semiconductor materials such as silicon and zinc-oxide, requiring vacuum deposition and high-temperature curing. R&D in organic semiconductors has yet to overcome low-mobility challenges and achieve good stability.
US additive printing technology provider Optomec has tested the feasibility of producing TFTs using CNTs. The company's Aerosol Jet deposition process was used to completely print all four layers of the transistor. An ultra-high operating frequency of over 5GHz and an on-off ratio of over 100 were demonstrated.
The company works with nanomaterials developers that produce conductive inks based on silver, CNTs, silicon and other nanomaterials.
Research
High-speed roll-to-roll and direct write deposition technologies can be used to develop alternative TFT processes that are more efficient and use fewer processing steps.
University of Illinois at Urbana-Champaign, working with Purdue University in the US, has also succeeded in building flexible circuits from CNTs using low-temperature processes.
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