The big picture

Flat panel displays could be made larger, better and cheaper following a carbon nanotube breakthrough.

A breakthrough in carbon nanotube research could allow the creation of large flat panel displays with better picture quality than plasma and LCD screens but at a much lower cost.

The technology may have applications in many other areas including improved fuel and solar cells, ultra-small transistors, biotech sensors that identify pathogens in the body and environmental applications that reduce pollutants.

Researchers at Motorola’s Arizona applied research laboratory said their nano-emissive display (NED) technology could produce wall-mounted flat panel screens just a couple of centimetres deep but measuring over 125cm diagonally.

Carbon nanotubes possess unique electron emission properties. This makes them ideal for use in flat panel displays where electrons must be emitted to hit phosphor-coated pixels on a screen, making them glow and form an image.

Motorola has developed a method for growing the carbon nanotubes at the low temperatures necessary to avoid damaging the materials such as glass and transistors with which they must bond to create screens.

The company has also developed a way to place the nanotubes individually on a surface material while controlling their eventual length and diameter, enabling it to design products on a molecular level and enhance particular characteristics.

The resulting NED material can display images with optimised brightness, colour purity and resolution, said principal staff researcher Dr Ken Dean.

He said an atmosphere of carbon-based gas is seeded with a catalyst that extracts the carbon to build the nanotube: ‘As a tree grows by incorporating the carbon from CO2 in the air, so the seed here is a special catalyst material that extracts the carbon from methane gas to produce a nanotube. The seeds are less than five nanometres in diameter, which assures that we will grow nanotubes of the same diameter as the seeds.’

As the seeds do not change size with temperature, thin nanotubes can be grown at 500 degrees C in an oven using extra methane gas in a technique called hot filament chemical vapour deposition.

Other methods for producing similar sized nanotubes use temperatures of up to 1,000 degrees C, which would melt the glass on which the nanotubes must be grown.Carbon nanotubes can be grown separately, purified and then applied to the device as a solution or paste. However, this technique has disadvantages.

‘There is no control over the orientation or proximity of the nanotubes and in reality few, if any, are sticking up out of the goo to become useful electron guns,’ explained Dean.

Other types of electron guns require either expensive lithography and deposition equipment to tailor them to the optimum size, or custom electrical modification to make them uniform.

‘We use millions of miniature electron guns in place of the foot-long electron gun found in the back of typical TVs,’ said Dean. ‘Our electron guns are much shorter than the thickness of a sheet of paper, and we place many of them behind each pixel in the display.’

Viewing angle, brightness and contrast are similar to those of cathode ray systems which in turn are superior to those of conventional plasma and LCD systems.

Moreover, the nanotubes are thin and well-positioned, so little voltage is needed to extract many electrons from them, reducing the cost of the electronics required to run the system.

The company is now talking to electronics manufacturers in Asia and Europe about licensing the technology for commercialisation.

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