Credit: © 2008 AAAS

Rubber-like electronics that can be stretched require both mechanical robustness and electronic performance. Fully elastic circuits have been achieved by embedding the electronic components in rubber sheets and integrating them with flexible metal wires. Researchers at the University of Tokyo and research institutes in Japan have now created a rubber-like composite material that can connect semi-rigid arrays of organic transistors to form a stretchable active matrix without making the entire circuit fully elastic.

Takao Someya and colleagues1 combined an ionic liquid with millimetre-long single-walled carbon nanotubes and dispersed it in a fluorinated polymer matrix. This was then coated with silicone rubber and processed into a net-shaped structure to form an 'elastic conductor' that is flexible and tensile (can withstand tension). The composite could be uniaxially stretched by up to 110% over several cycles while maintaining its high conductivity. Continued stretching did irreversibly decrease the conductivity but it still outperformed commercial carbon particle-based conducting rubber. The success of the material depends on the compatibility and mixing ratios of the components. A small active matrix created by connecting arrays of organic transistors with the composite could withstand up to 70% stretching with negligible change in electrical characteristics because the transistors themselves were not deformed.

With this material and approach, stretchable electronics could be integrated with pressure sensors to form intelligent surfaces, such as artificial skin, to interface with humans.