Transparent and Flexible Carbon Nanotube Transistors

Abstract

We report the fabrication of transparent and flexible transistors where both the bottom gate and the conducting channel are carbon nanotube networks of different densities and Parylene N is the gate insulator. Device mobilities of 1 cm 2 V -1 s -1 and on/off ratios of 100 are obtained, with the latter influenced by the properties of the insulating layer. Repetitive bending has minor influence on the characteristics, with full recovery after repeated bending. The operation is insensitive to visible light and the gating does not influence the transmission in the visible spectral range.The quest for flexible and transparent transistors has recently resulted in several noteworthy achievements. Transparent transistors have been fabricated using both polymers 1-3 and inorganic oxides. 4,5 These advances, notable in the emerging technology arena that is generally called "plastic electronics", have received wide publicity. Both, nevertheless, have significant deficiencies. The former have low mobility and the latter do not have the desired flexibility and are not easily manufacturable. These factors severely limit the application potential of the devices. Our method introduces a transistor architecture that potentially includes only two materials: carbon nanotubes (NTs) and a polymeric gate insulator. This simplicity of structure would ensure a simple manufacturing process.Carbon nanotubes, because of their excellent electronic properties, have been explored for applications as active electronic devices. Field effect transistors (FETs) with NT conducting channels have been fabricated 6,7 and their properties and operation explored.8-10 Subsequently, it has been shown 11,12 that a random network of nanotubes with an appropriate density can also act as a conducting channel in a FET configuration. This has opened up the avenue for a manufacturable device architecture. Room-temperature fabrication techniques enabling flexible transistors 13 have also been explored. It has been shown that, due to the high mobility of carbon nanotubes, a network with low sheet resistance is also transparent in the visible spectral range. 14, 15 We have fabricated, using an extremely simple spray technology, field effect transistors where carbon nanotube networks of different densities provide both the gate and the conducting channel. We find that the devices are highly transparent, that the mobility is superior to that of organic transistors, and that repeated bending does not lead to a substantial effect on the transistor characteristics. The transistor architecture, aside from having a possible impact on a new technology, represents a further step in the advancement of carbon nanotube based transistors.A schematic illustration of the FET devices that have been fabricated is shown in Figure 1 together with an optical image of one of the transistors. The devices were prepared on a sheet of polyester (PE), using purified, single walled HipCO nanotubes from CNI (used as received). Because nanotubes are hydrophobic, they stick well to th...

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