'Nano-pixels' pave way for thin, flexible displays

Oxford researchers, including one of Indian-origin, have created 'nano-pixels' just 100 nanometres in size that could pave the way for extremely high-resolution and low-energy thin, flexible displays for applications such as 'smart' glasses, synthetic retinas, and foldable screens.
A team led by Oxford University scientists explored the link between the electrical and optical properties of phase change materials - materials that can change from an amorphous to a crystalline state.
They found that by sandwiching a seven nanometre thick layer of a phase change material (GST) between two layers of a transparent electrode they could use a tiny current to 'draw' images within the sandwich 'stack'.

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.
"We didn't set out to invent a new kind of display," said Professor Harish Bhaskaran of Oxford University's Department of Materials, who led the research.

"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.

"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," Bhaskaran said.
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 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," he said.
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.
The research is published in the journal Nature.