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Electronic engineering

Evolution of the screen

New FED monitors generate quality images while saving energy

cenpraPrototypes of the new display being tested at CenPRA: evolution to substitute the plasma screenscenpra

Brazilian consumers have barely got used to the slim Liquid Crystal Display/LCD screens of computer monitors and sophisticated TV sets, and a new technology is already on the way. Japanese manufacturer Sony, through its Field Emission Technologies spin-off company, plans to launch, in 2009, a line of monitors based on the field emission display/FED system. This technology is characterized by a digital panel with a layer of phosphorus that produces light in the same way as the conventional cathode ray tubes/CRT) used in conventional TV sets for many years. Canon, another Japanese manufacturer, has also shown an interest in this market and recently exhibited high quality prototypes at major technology trade fairs. In Brazil, research into these screens, which can also be used in outdoor environments, is being conducted by a team from the Renato Archer Research Center (CenPRA), linked to the Ministry of Science and Technology. The two main advantages of FEDs versus current technologies – the flat LCDs, the plasma screens and the CRTs – are their low energy consumption and superior image quality.

Unlike CRTs, FEDs use nanostructured layers to emit electrons that consist of, for example, carbon nanotubes – nanometric cylinders that emit electrons very efficiently from the extremities, or through copper. These nanostructured layers are organized in the form of a matrix of pixels, the luminous points that, when juxtaposed, form the image on the screen. The light is produced in the same way as in CRTs, namely, by the number of electrons emitted over the phosphorus layer. The difference is that, unlike CRTs, which rely on electron beams based on heated filaments and a large image tube, FEDs have thin layers of different materials that add up to a thickness of no more than three millimeters. FEDs use of nanostructures rather than heated filaments to emit electrons ensures lower energy consumption. Moreover, this kind of display uses several electron emitters per image pixel. This, besides further reducing energy consumption, allows the total thickness of the device to be reduced, making it similar to any other kind of flat monitor. “The fact that this kind of monitor is slim and consumes less energy, plus the fact that the FED image quality is the same as that of the CRT, lends this technology high potential to corner the global display market,” points out Victor Pellegrini Mammana, boss of CenPRA’s Division of Information Displays and coordinator of studies in this field at the institution.

Many experts believe that FEDs will be the first example of the application of carbon nanotubes in the field of electronics; however, for this to come true, it will be necessary to overcome technological and industrial challenges. The main one is to cut the equipment’s production costs, currently higher than those of competing technologies. “LCDs nowadays are a system and not a component. LCD manufacturers have a wide range of alternatives in terms of parts and component suppliers that are part of a mature productive chain. This is why any new display technology has to show good performance at a lower cost,” explains Mammana, who created a Young Researcher project run by FAPESP, called “Development of electron emitters based on membranes.” The word membranes in this case refers to the porous structures formed by multiple layers of conducting and isolating materials, in which each pore is an image pixel.

Complementary screens
Despite the cost-related issue, he believes that a strong sign of the opportunity for FEDs in the big displays market (from 35 inches up), is the co-existence of LCD and plasma technologies in this market niche. “This shows that the two technologies are complementary in terms of price, energy consumption, image quality and durability, and no item is superior to the other for the time being. The field emission displays are an alternative that has several advantages,” he says. Canon, for example, claims that its FED technology lasts some 50 thousand hours, which is equivalent to the durability of an LCD or CRT monitor, and higher than that of plasma screens. This is a step forward in relation to the early FEDs, based on spindt technology, which had a chronic emitter durability problem. At present, the biggest technological problem associated with this new technology is the durability of the phosphorus and the existence of electrical discharges in the device. These two problems are connected with the difficulty of maintaining the quality of the vacuum inside the display. “Our group’s biggest innovation, which has already been patented, is related mostly to the new display design, which enhances the quality of the vacuum.

cenpraCopper oxide nanostructures: alternative for carbon nanotubescenpra

“The Young Researcher project is looking for a way to maintain a good vacuum, with the lowest possible pressure and a low-cost assembly,” says Mammana. This project aimed at producing innovations for wide-screen FEDs, because he believes that this is the segment with the best chance of competing with liquid crystal technology. “Wide-screen LCDs are still very expensive and will probably remain so for some time. Our chosen approach follows what most of the companies investing in FEDs, such as Motorola and Canon, are doing,” says Mammana. Regarding image quality, the performance of the field emission displays is far higher than that of conventional screens, as FEDs provide excellent color contrast – the levels of black are very good, unlike those of the LCD, which are never really black – and the speed of the images is much quicker.

As for power consumption, the advantage over LCDs is more apparent in TV monitors because, unlike FEDs, LCD screens do not produce their own light, and resort to a back light, which is usually fluorescent. On average, an LCD uses only 4% of the light generated by this back light because of the quantity of layers of materials placed in the light’s path, and that ultimately absorb this light. Additionally, when a liquid crystal screen shows a very dark image, most of the light is lost. Instead, the FED is a power-on-demand device. This means that power consumption depends on the image’s brightness, resulting in the use of less energy when the displayed image is darker. This FED characteristic is especially beneficial for application in television sets, because TV programs systematically broadcast duller images than those shown on computer monitors, for example.

Research studies, such as the one presented by Larry Weber, president of the Society for Information Display, at an event during the Latin Display Fair held last November in the city of Campinas, indicate that most of the time the luminance (the photometric size associated with the brightness of the image) of TV programs corresponds to only 20% of the maximum possible luminance. Power-on-demand technologies, such as FEDs, benefit greatly from this characteristic of TV shows.

Lower consumption
In addition to application in TV and computer monitors, the FED can also be used as the back light of LCD monitors. “This is a way of using both technologies together while attempting to cut down on the energy consumption of the TV sets with liquid crystal displays; moreover, this bypasses the problem of LCDs’ motion blur, which refers to the blurred images that form when people, animals or objects are moving on the screen,” says Mammana.

Besides demonstrating the principle of how the FEDs function based on light emitting membranes, the CenPRA team focused on designing the entire process in such a way as to make it more accessible for the industry. “The choice of the materials and processes in this kind of project should not be based only on lab performance criteria, or the resulting solutions might be totally unfeasible from the industrial point of view and then it becomes difficult to go back, once a high-cost process or material has been chosen,” says Mammana. “I’m certain that this innovation is an important element for the industrial success of the FEDs,” he emphasizes. The group also made it a point to work together with a local supplier so that they could adapt the device to products that were manufactured by established factories. “The small company which is developing the membranes for us (whose name Mammana prefers not to disclose) was very excited about this new technology and decided to invest in its development. We are also getting ready to submit a project for the Technological Innovation Program for Small Companies (now renamed the Innovative Research Program for Small and Very Small Companies / Pipe), run by FAPESP. Hopefully, that company will present an industrial process based on our multiple layers, the patent for which has already been granted in the United States,” says the researcher from CenPRA.

The Project
Development of electron emitters based on membranes
Aid Program for Young Researchers
Victor Pellegrini Mammana – CenPRA
R$ 233,906.25 and US$ 14,300.00 (FAPESP)