PORTLAND, Ore. — Carbon nanotube thin films sprayed onto flexible plastic substrates can enable low-cost sensors and other flexible electronics, according researchers at the Technische Universität München (TUM, Munich). To prove the concept, a team including professor Paolo Lugli, director of the TUM Institute for Nanoelectronics; postdoctoral researcher Alaa Abdellah; and their colleagues recently fabricated a gas detection sensor on a flexible polymer substrate.
Postdoctoral researcher Alaa Abdellah at the Technische Universität München (TUM, Munich) shows a flexible carbon nanotube-based gas sensor developed there.
SOURCE: Credit: U. Benz/TUM
Carbon nanotube thin films are already being developed for a variety of applications. Stanford University recently demonstrated the world's first carbon-nanotube based computer chip.
Other semiconductor applications of carbon nanotube films are being developed at companies like Nantero Inc. (Woburn, Mass.), which recently raised additional funding for its resistive random access memory (ReRAM)
And companies like Eikos Inc. (Franklin, Mass.) and Unidym Inc. (Sunnyvale, Calif.) are developing carbon nanotube thin films as a replacement for the transparent indium tin oxide (ITO) layer on liquid crystal displays (LCDs).
The TUM research demonstration showed that carbon nanotube thin films can also function as gas sensors by providing a resistive network that shows an immediate change in impedance whenever it comes into contact with molecules of a certain kind of gas. Sensitivity for its gas-sensors, fabricated on flexible plastic substrates, was demonstrated for ammonia, carbon dioxide, and nitrogen oxide.
The low-cost fabrication method uses a robotic sprayer that should be easy to scale up for mass production to deposit carbon nanotube-based circuits on a flexible substrate.
SOURCE: Credit: U. Benz/TUM
Such carbon-nanotube based gas sensor thin films could be useful in a variety of applications, according to the researchers. For instance, inexpensive sensors could be integrated into compact air-quality monitors or even into food packaging that reads-out a freshness indicator (instead of depending on "use by" dates). The team is also developing a range of other applications for their carbon-nanotube thin films, including pressure and temperature sensors, and a new type of solar cell.
For the future, the team suggested a variety of applications involving spraying sensors onto large-scale sheets of flexible plastic or other surfaces, such as the skin of robots to provide them with a sense of touch.
The TUM researchers demonstrated two deposition processes. The first fabricates the carbon-nanotube films onto glass, then uses transfer-printing to move the carbon nanotube films onto a flexible substrate. The second directly deposits the carbon-nanotube films onto a flexible substrate using an robotic nozzle spray-on process.
The carbon nanotubes themselves were randomly oriented when sprayed-on in thin films at room temperature, yet because of their tiny size -- just nanometers in diameter but microns long -- they formed a relatively uniform conductive network. The researchers also claimed that their material could modulated with an applied voltage to create a transistor-like action.
Next, the research aims to functionalize the surface of their sensors for selective sensitivity to particular gases.
Funding was provided by the German Research Foundation (DFG), the Cluster of Excellence Nanosystems Initiative Munich (NIM), and by the Bavarian State Ministry for Science, Research and the Arts' Solar Technologies Go Hybrid initiative.