Science & Environment

Flexible nano-pixel screen patented

nano-pixel images Image copyright Oxford University
Image caption These images produced by the researchers were 0.07mm across - smaller than the width of human hair

Scientists have patented a new way to make ultra high-res displays that can bend and are thousandths of a mm thick.

They used a miniscule layer of a phase-change material, that flips between two chemical states when hit with current.

By sandwiching it between transparent electrodes, they made pixels just 300 nanometres across and produced images smaller than the width of human hair.

The design, published in Nature, could be useful in wearable technology, smart contact lenses or foldable screens.

According to Prof Harish Bhaskaran, who led the research at Oxford University, it will be "at least five years" before any applications appear.

But as far as Prof Bhaskaran is aware, the resolution of the images his team produced is among the highest ever achieved. "I haven't seen any other technology that approaches 100 or 200 nanometre resolution," he told the BBC.

Phase-change materials are commonly used in heat management, because they absorb or release heat in switching between an orderly, crystalline state and a more chaotic "amorphous" state. Because their optical properties change with these states as well, they have also proved useful in data storage, such as rewritable DVDs.

The key to the new design is a very thin layer of one of these materials: an alloy containing germanium, antimony and tellurium (Ge2Sb2Te5, or "GST" for short).

Instead of using GST to encode ones and zeros within the rings of a DVD, Prof Bhaskaran's team sandwiched it in between two layers of a transparent material that conducts electricity, producing a three-layered film no thicker than 0.0002mm. Then they painted a picture into the GST, pixel-by-pixel, by delivering current to different points across the film.

Electrical current causes the GST to switch states - and change colour. In this way, the researchers produced a number of microscopic images.

Image copyright Oxford University
Image caption The team produced films that were flexible and semi-transparent

They also demonstrated that the technique could produce different colour changes, by using different thicknesses for the outer layers of the sandwich.

None of the pictures move - yet - but the team has filed a patent because of the potential to develop a new generation of flexible, thin, high-resolution displays.

"The cool part about this is that the functional part is very thin," explained Prof Baskaran. "Because of that you could actually have displays that are non-intrusive, because you can keep the electronics far away."

This contrasts with current LCD displays, which require transistors immediately behind the screen to switch the colour of the pixels.

"Think of having a pen - and you can roll out your screen from inside the pen, but the electronics are contained within the pen," Prof Baskaran said.

Other mooted applications include smart glasses or contact lenses, and even synthetic retinas, if the technology could be rejigged to convert pixels of light into electrical impulses.

The design could also offer big energy savings, because the pixels would simply stay put until they need to be changed.

Image copyright Oxford University
Image caption A microscopic image of a well-known Oxford landmark, made up of 150x150 300-nanometre pixels

"Unlike most conventional LCD screens, there would be no need to constantly refresh all pixels, you would only have to refresh those pixels that actually change," said Dr Peiman Hosseini, the study's first author.

"This means that any display based on this technology would have extremely low energy consumption."

Dr Stephen Kitson runs the Bristol display technology company Folium Optics, developing other strategies for flexible, high-resolution displays, and is also a visiting professor at the University of Western England. He said the findings were promising.

"It's a really challenging area, to get something that's bright," he told BBC News. "There's a way to go, to see if they can get the dynamic range that you'd need - in other words, can you switch from really bright to really dark.

"They've got some interesting colour switches there, which is a brilliant first step."

Prof Bhaskaran agrees this is only the first stage. "We're showing that we can combine thin-film effects with a super-thin layer of phase change material, and get colour out of it," he said.

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