USC researchers print dense lattice of transparent nanotube transistors on flexible base

December 17, 2008: University of Southern California graduate students have created a clear, colorless disk, about 5 inches in diameter, that bends and twists like a playing card, with a lattice of more than 20,000 nanotube transistors capable of high-performance electronics printed upon it using a potentially inexpensive low-temperature process.

Its developers believe the prototype points the way to long sought after applications, such as affordable “head-up” car windshield displays. The lattices could also be used to create cheap, ultra thin, low-power “e-paper” displays; be incorporated into fabric that would change color or pattern as desired for clothing or wall covering; or be incorporated into nametags, signage and other applications.

The team at the USC Viterbi School of Engineering that created the new device, described and illustrated it in a paper, called “Transparent Electronics Based on Printed Aligned Nanotubes on Rigid and Flexible Structures” published in the journal ACS Nano.

Fumiaki Ishikawa and Hsiaoh-Kang Chang worked under Professor Chongwu Zhou of the School’s Ming Hsieh Department of Electrical Engineering on the project, solving the problems of attaching dense matrices of carbon nanotubes to flexible highly heat-vulnerable transparent plastic substrates. The researchers also connected them to commercial gallium nitrate (GaN) light-emitting diodes, which change their luminosity by a factor of 1,000 as they are energized.

See-through circuit makers: Hsaioh-Kang Chang, left, and Fumiaki Ishikawa, are pictured with their transparent, flexible transistor array. (Credit: USC Viterbi School of Engineering.)

“Our results suggest that aligned nanotubes have great potential to work as building blocks for future transparent electronics,” say the researchers.

Earlier attempts at transparent devices used other semiconductor materials with disappointing electronic results, enabling one kind of transistor (n-type); but not p-types; both types are needed for most applications. The critical improvement in performance, according to the research, came from the ability to produce extremely dense, highly patterned lattices of nanotubes, rather than random tangles and clumps of the material. The Zhou lab has pioneered this technique over the past three years.


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