10 July 2014

Nanopixel displays with 150 times higher resolution and they’re flexible, too

Oxford University's ITO/GST phase-change material nanopixel display
Researchers in England have created nanopixels that measure just 300-by-300 nanometers. Compare this to a modern smartphone with a 400 ppi display, where each pixel is about 150 times larger (about 50 microns across). Furthermore, the prototype nanopixel displays are low-power and thin and flexible. Ultimately, these nanopixels could be used in extremely high-resolution displays with billions of pixels though it might be rather hard to find a graphics card that can drive a 198000×120000 display, of course.

These nanopixels, developed by Oxford University and the University of Exeter in England, are surprisingly similar to the LCD pixels in your laptop or smartphone display. There are two transparent thin-film electrode layers of ITO (indium tin oxide), with a very thin layer of GST (germanium-antimony-tellurium) sandwiched in between. GST is a phase-change material (PCM) that is famous for its use in rewritable DVDs. In its default state GST is crystalline and transparent, but if you apply a voltage (or laser beam), it changes phase into an amorphous state that is opaque. Give it another jolt and it becomes crystalline and transparent again. You can probably see where this is going.
How the thickness of the bottom ITO layer (t) affects the pixel's reflected color
How the thickness of the bottom ITO layer (t) affects the pixel’s reflected color

Depending on the thickness of the bottom layer of ITO, a different wavelength of light is reflected (the researchers have already worked out how to create R, G, and B pixels). By changing the phase of the GST layer, the nanopixel can be turned on or off. Importantly, because PCMs “stick” until another current/laser is applied, these nanopixel displays are very power efficient much in the same way that e-ink displays don’t need to constantly refresh their pixels and can thus last days on a single charge. Finally, because the ITO and GST layers are so thin, and because they can be deposited on very thin substrates (such as 200nm Mylar), the nanopixel displays are very flexible. [doi:10.1038/nature13487 - "An optoelectronic framework enabled by low-dimensional phase-change films"]

So far, so awesome then especially if circle back to the main point: These nanopixels are really, really small. Not only are the individual ITO/GST layers measured in tens of nanometers, but the pixels themselves can be just 300nm across. In a modern 400+ ppi display (such as the Galaxy S5 or HTC One M8) you get around 400 pixels per inch, or one pixel per 0.06 millimeters. Taking into account the gaps between pixels you can’t see them, but they’re there and each pixel is around 50 micrometers (micron) across. This is 150 times larger than each of Oxford’s nanopixels.

More nanopixel display stuff

While it’s obviously a lot more complex than just multiplying current pixel counts by 150, it’s clear that smaller and more-energy-efficient pixels could definitely result in some seriously high-res displays. Add flexibility to the mix and the number of possible applications explodes foldable e-paper, windshield displays, smart glasses that actually look like smart glasses with just a thin display laminated over the lens.

A nanopixel display, showing the The Great Wave off Kanagawa by the Japanese artist Hokusai
A nanopixel display, showing the The Great Wave off Kanagawa by the Japanese artist Hokusai

David Wright, co-author of the research paper, had this to say: “Along with many other researchers around the world we have been looking into the use of these GST materials for memory applications for many years, but no one before thought of combining their electrical and optical functionality to provide entirely new kinds of non-volatile, high-resolution, electronic colour displays so our work is a real breakthrough.”

Beyond filing for a patent in case of eventual commercialization, there’s no word on what the researchers intend to do next with the technology. The appeal for a high-res, low-power, flexible display is massive but let’s see if someone creates a CPU or GPU with the processing power to drive a display with 150 times more pixels first. A 1920×1080 display has 2.07 million pixels in total; times that by 150 and you’re looking at over 311 million pixels.

Courtesy extremetech


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