A group of engineers at the University of Southern California Viterbi School of Engineering, Los Angeles, say that they are developing a flexible, energy-efficient hybrid circuit combining carbon nanotube thin film transistors with other thin film transistors. This hybrid, they say, could take the place of silicon as the traditional transistor material used in electronic chips, since carbon nanotubes are more transparent, flexible, and can be processed at a lower cost.

Hybrid CNT/IGZO circuits fabricated on a polyimide film are laminated on a polydimethylsiloxane substrate. (Credit: USC Viterbi, Chongwu Zhou)

The team developed an energy-efficient circuit by integrating carbon nanotube thin film transistors (TFT) with thin film transistors made of indium, gallium, and zinc oxide (IGZO). Since carbon nanotubes can only be viewed through a scanning electron microscope, the hybridization of carbon nanotube thin films and IGZO thin films was achieved by combining their types, p-type and n-type, respectively, to create circuits that can operate complimentarily, reducing power loss and increasing efficiency. IGZO thin film transistors were included primarily for power efficiency to increase battery life.

Potential applications for this kind of integrated circuitry are numerous, the team says, including organic light emitting diodes, digital circuits, radio frequency identification tags, sensors, and wearable electronics.

The new technology also has major medical implications. Currently, to record heart rate or brainwave data from a patient, stiff electrodes are placed on several fixed locations on the patient’s body. Using this new hybridized circuit, electrodes could be placed all over the patient’s body with just a single large but flexible object, they say.

What’s next? The team plans to build more complicated circuits using a carbon nanotube and IGZO hybrid that achieves more complicated functions and computations, as well as to build circuits on flexible substrates. They believe that carbon nanotube technology, including this new CNT-IGZO hybrid, will be commercialized in the next 5 to 10 years.