The size of these images is about 300 by 300 nanometres, less than the width of a human hair

Nano-pixel images pave way for super high-res displays

Oxford University researchers have discovered a technique that enables creating complex images smaller than the width of a human hair.

The technique described in the latest issue of Nature, uses tiny current to draw the images within sandwiches of phase change materials. The scientists believe it could pave way for future ultra-thin super high resolution displays.

The phase changed materials used in the study are known for being able to switch between an amorphous and crystalline state. By sandwiching a seven nanometre thick layer of those materials between two layers of a transparent electrode, the research team managed to unlock never before explored properties of the materials. As many great scientific findings in the history the discovery came rather by accident.

“We were exploring the relationship between the electrical and optical properties of phase change materials and then had the idea of creating this GST 'sandwich' made up of layers just a few nanometres thick,” said Professor Harish Bhaskaran of Oxford University's Department of Materials, who led the research. “We found that not only were we able to create images in the stack but, to our surprise, thinner layers of GST actually gave us better contrast. We also discovered that altering the size of the bottom electrode layer enabled us to change the colour of the image.'

Initially, still images were created using an atomic force microscope but the team went on to demonstrate that such tiny 'stacks' can be turned into prototype pixel-like devices. These 'nano-pixels' – just 300 by 300 nanometres in size – can be electrically switched 'on and off' at will, creating the coloured dots that would form the building blocks of an extremely high-resolution display technology.

The layers of the GST sandwich are created using a sputtering technique where a target is bombarded with high energy particles so that atoms from the target are deposited onto another material as a thin film.

'Because the layers that make up our devices can be deposited as thin films they can be incorporated into very thin flexible materials – we have already demonstrated that the technique works on flexible Mylar sheets around 200 nanometres thick,' said Professor Bhaskaran. 'This makes them potentially useful for 'smart' glasses, foldable screens, windshield displays, and even synthetic retinas that mimic the abilities of photoreceptor cells in the human eye.'

The Oxford scientists have filed a patent on the invention with the help of the university's technology commercialisation company, Isis Innovation, and are looking for prospective commercial partners to help them bring the technology further.

"We can tune our prototype 'pixels' to create any colour we want - including the primary colours needed for a display,” said Peiman Hosseini, from Oxford University's Department of Materials.

"One of the advantages of our design is that, 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. This means that any display based on this technology would have extremely low energy consumption."

The research suggests that flexible paper-thin displays based on the technology could have the capacity to switch between a power-saving 'colour e-reader mode', and a backlit display capable of showing video. Such displays could be created using cheap materials and, because they would be solid-state, promise to be reliable and easy to manufacture.

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