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Hybrid circuit casts a spotlight on carbon nanotubes

Posted: 18 Jun 2014  Print Version  Bookmark and Share

Keywords:carbon nanotube  silicon  circuit 

USC Viterbi School of Engineering researchers have developed a flexible, energy-efficient hybrid circuit that could take the place of silicon as the traditional transistor material used in electronic chips.

Electrical engineering professor Dr. Chongwu Zhou and USC Viterbi graduate students Haitian Chen, Yu Cao, and Jialu Zhang developed this energy-efficient circuit by integrating carbon nanotube (CNT) thin film transistors (TFT) with thin film transistors comprised of indium, gallium and zinc oxide (IGZO).

Carbon nanotubes are so small that they can only be viewed through a scanning electron microscope. This hybridisation 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. The inclusion of IGZO thin film transistors was necessary to provide power efficiency to increase battery life. If only carbon nanotubes had been used, then the circuits would not be power-efficient. By combining the two materials, their strengths have been joined and their weaknesses hidden.

The potential applications for this kind of integrated circuitry are numerous, including OLEDs, digital circuits, radio frequency identification (RFID) tags, sensors, wearable electronics, and flash memory devices. Even heads-up displays on vehicle dashboards could soon be a reality.

The new technology also has major medical implications. Currently, memory used in computers and phones is made with silicon substrates, the surface on which memory chips are built. To obtain medical information from a patient such as heart rate or brainwave data, stiff electrode objects are placed on several fixed locations on the patient's body. With this new hybridized circuit, however, electrodes could be placed all over the patient's body with just a single large but flexible object.

With this development, Zhou and his team have circumvented the difficulty of creating n-type carbon nanotube TFTs and p-type IGZO TFTs by creating a hybrid integration of p-type carbon nanotube TFTs and n-type IGZO TFTs and demonstrating a large-scale integration of circuits. As a proof of concept, they achieved a scale ring oscillator consisting of over 1,000 transistors. Up to this point, all carbon nanotube-based transistors had a maximum number of 200 transistors.

"We believe this is a technological breakthrough, as no one has done this before," said Haitian Chen, research assistant and electrical engineering PhD student at USC Viterbi. "This gives us further proof that we can make larger integrations so we can make more complicated circuits for computers and circuits."

The next step for Zhou and his team will be to build more complicated circuits using a CNT and IGZO hybrid that achieves more complicated functions and computations, as well as to build circuits on flexible substrates.

Hybrid circuit

Hybrid CNT/IGZO circuits fabricated on a polyimide film laminated on a polydimethylsiloxane (PDMS) substrate. Source: USC Viterbi





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