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Low-cost technique targets flexible electronics

Posted: 21 Dec 2011 ?? ?Print Version ?Bookmark and Share

Keywords:carbon nanotube? flexible electronics? smart application?

Researchers with the U.S. Department of Energy (DOE)'s Lawrence Berkeley National Laboratory (Berkeley Lab) have created a low-cost method for developing large-scale flexible and stretchable backplanes. They used semiconductor-enriched carbon nanotube solutions that yield networks of thin film transistors with excellent electrical properties that according to them has a charge carrier mobility that is higher than organic equivalents.

To demonstrate carbon nanotube backplanes that they have produced, the researchers constructed an artificial electronic skin (e-skin) that can detect and respond to touch. They noted that the innovation can be used to advance smart devices. Among the applications that have been envisioned are electronic pads that could be folded away like paper, coatings that could monitor surfaces for cracks and other structural failures, medical bandages that could treat infections and food packaging that could detect spoilage.

flexible thin film

The flexible and stretchable thin film transistor array covering a baseball shows the mechanical robustness of this backplane material for future plastic electronic devices. Source: The University of California, Berkeley Lab.

From solar cells to pacemakers to clothing, the list of smart applications for so-called 'plastic electronics' is both flexible and stretchable. First, however, suitable backplanes must be mass-produced in a cost-effective way.

"With our solution-based processing technology, we have produced mechanically flexible and stretchable active-matrix backplanes, based on fully passivated and highly uniform arrays of thin film transistors made from single walled carbon nanotubes that evenly cover areas of approximately 56cm2," stated Ali Javey, a faculty scientist in Berkeley Lab's materials sciences division. "This technology, in combination with inkjet printing of metal contacts, should provide lithography-free fabrication of low-cost flexible and stretchable electronics in the future."

Javey is the corresponding author of a paper titled "Carbon Nanotube Active-Matrix Backplanes for Conformal Electronics and Sensors." Co-authoring this paper were Toshitake Takahashi, Kuniharu Takei, Andrew Gillies and Ronald Fearing.

With the demand for plastic electronics so high, R&D in this area has been intense for the past decade. Single walled carbon nanotubes (SWNTs) have emerged as one of the top contending semiconductor materials for plastic electronics, primarily because they feature high mobility for electronsa measure of how fast a semiconductor conducts electricity. However, SWNTs can take the form of either a semiconductor or a metal and a typical SWNT solution consists of two-thirds semiconducting and one-third metallic tubes. This mix yields nanotube networks that exhibit low on/off current ratios, which poses a major problem for electronic applications, explained Toshitake Takahashi, co-author of the paper at Berkeley Lab.

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