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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?

"An on/off current ratio as high as possible is essential for reducing the interruption from pixels in an off-state, he said. "For example, with our e-skin device, when we are pressure mapping, we want to get the signal only from the on-state pixel on which pressure is applied. In other words, we want to minimize the current as small as possible from the other pixels which are supposed to be turned off. For this we need a high on/off current ratio."

To make their backplanes, Javey, Takahashi and their co-authors used a SWNT solution enriched to be 99 percent semiconductor tubes. This highly purified solution provided the researchers with a high on/off ratio (about 100) for their backplanes. Working with a thin substrate of polymide, a high-strength polymer with superior flexibility, they laser-cut a honeycomb pattern of hexagonal holes that made the substrate stretchable as well. The holes were cut with a fixed pitch of 3.3mm and a varied hole-side length ranging from 1-1.85mm.

"The degree to which the substrate could be stretched increased from 0-60 percent as the side length of the hexagonal holes increased to 1.85mm," Takahashi indicated. "In the future, the degrees of stretchability and directionality should be tunable by either changing the hole size or optimizing the mesh design."

Backplanes were completed with the deposition on the substrates of layers of silicon and aluminum oxides followed by the semiconductor-enriched SWNTs. The resulting SWNT thin film transistor backplanes were used to create e-skin for spatial pressure mapping. The e-skin consisted of an array of 96 sensor pixels, measuring 24cm2in area, with each pixel being actively controlled by a single thin film transistor. To demonstrate pressure mapping, an L-shaped weight was placed on top of the e-skin sensor array with the normal pressure of about 15 kilo Pascals (313lbs/ft2).

"In the linear operation regime, the measured sensor sensitivity reflected a threefold improvement compared with previous nanowire-based e-skin sensors reported last year by our group," Takahashi claimed. "This improved sensitivity was a result of the improved device performance of the SWNT backplanes. In the future we should be able to expand our backplane technology by adding various sensor and/or other active device components to enable multifunctional artificial skins. In addition, the SWNT backplane could be used for flexible displays."

- Julien Happich
??EE Times


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