Imagine having an ultra high-resolution display built directly into a pair of contact lenses. This could be the future of digital displays thanks to scientists at Oxford University, who have adapted a material currently used to store data on DVDs and transformed it into a radical new display technology.
Writing in Nature today, they say the material could usher in a new generation of displays that are thinner, lighter, with higher resolution and lower power consumption than any existing technology.
They could even be mounted on flexible or transparent surfaces, raising the possibility of applications beyond just e-readers and smartphones to things such as car windshields and contact lenses.
The development relies on the same process that turns water into ice cubes in your freezer. Many substances undergo changes in structure when they change temperature, such as going from solid to liquid, or crystalline to non-crystalline. These phase-change materials are currently used for a wide range of applications, from computer memory and rewritable DVDs to advanced forms of home insulation.
The team, led by Professor Harish Bhaskaran, was exploring other uses of phase-change materials like germanium antimony tellurium (GST), when they realized they might be able to use them to produce a colour display.
They took a single layer of GST just nanometers thick and sandwiched it between two ultra-thin layers of a transparent conductor, and stuck that on top of a mirrored surface.
The researchers predicted that by varying the thickness of one of the transparent layers, they could change the color of light that was reflected back, and by changing the phase of the GST they could switch it from one color to another. They then built a prototype to see if the material could change from grey to blue when it was heated.
"We couldn't believe it. It worked on the first attempt. So we tried it with a few other colors and it worked well," says Bhaskaran. "I've been an experimentalist for a long time, and I've never seen things work this well at the first attempt."
The researchers then used the head of an atomic force microscope to draw a monochromatic image on the surface.
They also constructed a single pixel using a transparent electrode, which is a crucial step in producing a workable display technology.
Bhaskaran says the technology has many potential advantages over existing displays. The layers of film are only nanometers thick, the display can be ultra thin and light, and once an image is drawn on screen it requires no power to keep it there.
And, because the pixels are only nanometers across, the resolution of the screen is potentially far higher than what is achievable with today's technologies, such as LCD and organic LED.
While it's still early days for the phase-change technology, Bhaskaran and his team are hopeful that it might migrate from the lab into electronics stores within several years.
"We have a patent filed and we are developing a monochrome prototype," he says. "We want to show that it can render video on a really small display to showcase the super high resolution that is possible. Hopefully that'll be done by the end of 2015. If that works, then we'll take it from there."
The technology is a highly novel use of an existing phase-change material, says Dr John Daniels, senior lecturer in materials science at the University of New South Wales. "It's an old material technology being used for a new popular application," says Daniels, who wasn't involved in the research.
However, there are still significant hurdles to overcome in turning it into a workable display technology.
"My big concern is the range of colors and contrast the technology can produce. That's the big question mark: whether they can make these materials competitive with the real market leader, which is organic LED, in terms of quality."
But he concedes that this is a fast-moving industry, and new technologies can potentially gain dominance rapidly.
"It always is a long way from the first demonstration to the first application. But this is a field where things can go from the lab to application in a very short period of time because the dollars are so big if they have something that's better than what's on the market at the moment."