In a few years, when people ask, "What's on the tube tonight?" they might be making an unintentional pun. That's because researchers have created a new transistor based on carbon nanotubes that could soon light up televisions and other screens.
Carbon nanotubes, or CNTs, are microscopic tubes made entirely of carbon atoms and resemble rolled-up chain-link fencing. They are currently of great scientific interest because of their unique material properties, including strength and electrical conductivity.
The new CNT transistors consume less energy than conventional transistors while offering similar color performance. The finding might pave the way for larger, sharper screens based on organic light-emitting diodes, or OLEDs, which offer key advantages over other types of displays, researchers say.
"Our device opens up a whole new realm of materials that could solve this size limitation problem," among other OLED issues, said Andrew Rinzler, a professor of physics at the University of Florida and a co-author of a paper appearing today in the journal Science.
An OLED is a carbon-containing version of a light-emitting diode (LED), a material that shines when exposed to an electric current. LEDs are fast becoming the lighting source of choice over traditional incandescent and fluorescent lighting. They also find use as backlighting in so-called LED TVs, a subset of liquid crystal display (LCD) sets, which along with plasma screens have largely replaced old-school cathode ray tubes and rear-projection TVs over the last decade.
Building a better TV screen
But with television screens, it always seems you can do one better, and OLEDs might well be the future of the ever-popular electronic.
For starters, OLEDs use about half as much energy as plasma and LCD screens. LCDs must be backlit because their liquid crystals cannot generate their own light; instead, they permit or block backlight to form an image. In OLEDs, however each pixel can shine on its own. Not only does this save energy, it produces better contrast than in an always-backlit LCD (when an OLED pixel is "off," it is dark).
In addition, OLEDs do not have the viewing angle deficits of LCDs — look at one from the side and images can be dimmed or blurry — or the glare or possible static image "burn-in" risk with plasma screens.
Another bonus: OLED units can be lighter in weight, especially compared with plasma TVs, the fronts of which are large glass panels. Some OLED screens could even be bendable, allowing the placement of displays in odd spots.
Yet OLEDs have their own problems. They rely on high voltages to make light, which eats into the screens' lifetime. Due to the difficulty of manufacturing conventional transistors uniformly, OLED screens have been limited in the size department as well. Most OLEDs today serve merely as tiny cellphone displays, and about 30 percent of OLED cellphone screens end up being scrapped due to defects, Rinzler noted.
Carbon nanotubes to the rescue
The new transistors developed by Rinzler and his colleagues address these issues that have dogged OLEDs. The transistors, for instance, do just fine on lower voltages, and can still produce bright light output of the three primary colors — red, green and blue — needed to render images.
The transistors have a vertical architecture, unlike the lateral, silicon-based transistors used in standard OLED displays. The carbon nanotubes enabled this stacked design, allowing the device to act as both a transistor driving electrical current and as a light emitter. Combining these normally separate components, and doing away with the need for other accessory parts, such as a capacitor, "could be a fairly significant benefit for manufacturers," Rinzler told TechNewsDaily.
Yang Yang, a professor of materials science and engineering at the University of California, Los Angeles who was not involved in the study, described the new transistors as "very smart."
"This is great work with very encouraging results," Yang said, "which can have significant impacts in future OLED displays."
Future development will now involve building arrays of the pixel-generating devices. The researchers also will scale down the pixels; the experimental transistors produced pixels about 1 millimeter square, while commercial, rectangular screen pixels are in the neighborhood of 300 micrometers by 200 micrometers.
Rinzler said he could see TVs on the market using the technology in as little as two to five years, "depending on how quickly large display manufacturers recognize this as an important solution for what they need."
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