Researchers at Oxford University have used a type of phase-change material to make devices whose color changes instantly in response to a small jolt of power. The materials, which are used in some types of DVDs, could lead to ultra-low-power full-color displays, according to an article describing the work in the journal Nature.
Displays made using the approach might overcome some of the drawbacks of other low-energy display technologies, such as the E-ink used in Kindle e-readers. For example, pixels can switch on and off much faster than in the e-reader, which could make it useful for displaying video.
Researchers have long known that shining a laser on phase-change materials can change their crystal structure. This, in turn, changes the way light bends when it encounters them—that’s how information is stored in rewriteable DVDs.
The Oxford researchers showed that similar optical changes can be achieved by applying a small jolt of power. They also showed that when these materials are sandwiched between two very thin layers of transparent conductive material, changes in the way light bends can also produce changes in color. Light reflects off each of the layers in different ways, canceling some wavelengths and amplifying others—green and blue light might be eliminated, leaving red, for example. Varying the thickness of the layers, or the voltage applied to the phase-change material, affects what colors each pixel in a display shows.
Unlike conventional displays, which require a constant supply of power to produce a glowing pixel, these devices maintain their color without any electricity. It’s the same energy-conserving strategy used in the e-ink displays in Kindle e-readers.
The researchers haven’t made a complete display yet. Instead, they used the ultra-sharp tip of an atomic force microscope to sketch out images by applying electricity to specific parts of the phase-change material. But in theory, the color changes could be controlled using some of the same electronics used in other types of displays.
The technology will face competition from OLED displays, which use less power than conventional LCD displays yet produce sharp, high-contrast color images. The Oxford researchers say they need to improve the contrast of their images to be competitive.