Nov 22, 2013
CNT active matrix makes flexible imager
Researchers at the University of California, Berkeley, and the Lawrence Berkeley National Laboratory have succeeded in fabricating mechanically flexible imagers using nanotube-based active-matrix backplanes. The devices, which can image in both the visible and X-ray range, could be used to make large-area flexible sensor networks for a variety of imaging applications, such as interactive surfaces and displays that can be pasted onto a host of surfaces and objects. The devices that work in the X-ray part of the spectrum might find use in portable medical imaging too.
Nanotube thin film transistors are ideal for making low-power active matrix backplanes on a wide range of substrates, including mechanically flexible plastics. Indeed, researchers have already managed to combine such backplanes with pressure sensors to make electronic “skins”, and with organic light-emitting diodes for flexible displays.
The team, led by Ali Javey, has now exploited these backplanes in another important application: large-area flexible imagers. The researchers made their devices by monolithically integrating organic photodetectors (OPDs) atop a nanotube backplane comprising an 18 x 18 pixel array. The actual size of the array is 2 x 1.5 cm.
Javey and colleagues chose OPD materials that respond to visible light for optical imaging applications. By adding a scintillator film (capable of converting incident X-rays into visible photons that are then detected by the OPDs) on top of the imager, they were also able to fabricate an X-ray light detector.
“The nanotube backplane consists of thin film transistors (TFTs) made using solution-processed semiconductor-enriched carbon nanotubes,” explains team member Zhibin Yu. “Such transistors have high mobilities of up to 50 cm2/V.s and high on-off current ratios of 106,” he told nanotechweb.org. “These values represent a significant advantage over silicon- and organic semiconductor-based devices that often have mobilities two orders of magnitude lower.”
The large-area visible light imager might be used as a new platform to develop interactive surfaces that can be laminated onto a variety of different surfaces, such as flexible plastics, and that can spatially map hand and body movements, he added. The flexible X-ray detector, for its part, might come in handy as a portable X-ray device for medical imaging applications.
The team says that it will now try to integrate a microlens array onto the pixels in its device for tuning light focus depth and increasing the sharpness of the images obtained.
The research is detailed in Nano Lett. DOI: 10.1021/nl403001r.
About the author
Belle Dumé is contributing editor at nanotechweb.org