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Nanopixels Create High-Resolution Displays

August 1, 2014


Smart glasses that display real-time information with the blink of an eye, synthetic retinas, and foldable electronic tablets. These and other technologies are closer to reality thanks to a new material developed by scientists at Oxford Univ. and the Univ. of Exeter.

The new material consists of a nanoscale layer of germanium antimony tellurium alloy (Ge1Sb2Te5, GST) - a phase-change material - sandwiched between two transparent electrodes made of indium tin oxide (ITO). When an electric current is applied to the electrodes, the phasechange material switches between an amorphous phase and a crystalline phase, altering the material's color. When combined into an array, these materials act as nanopixels that can be turned on and off to create images.

"We didn't set out to invent a new kind of display," says Harish Bhaskaran, an associate professor of materials at Oxford Univ. "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 nanometers thick," he says. "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."

Using sputtering and lithography techniques, the scientists fabricated a 300-nm by 300-nm array of pixels, one layer at a time. Then they developed a model that employs a transfer matrix optical computational method to relate the thickness of each layer of the film to the optical properties of the material. By performing experiments in which they changed the thickness of each layer and measured the optical properties, the team verified the model.

"Our models are so good at predicting the results of the experiments that we can tune our prototype pixels to create any color we want - including the primary colors needed for a display," says Peiman Hosseini, a professor of materials at Oxford Univ. "One of the advantages of our design is that, unlike most conventional LCD screens, there would be no need to constantly refresh all pixels. Only those pixels that actually change would need to be refreshed, because the static pixels remain as they were," he explains. "Thus any display based on this technology would have extremely low energy consumption."

With their model in hand, the researchers "drew" images with their pixelated array using a nanoscale conductive pointer to stimulate individual pixels. Images drawn include butterflies, tigers, and ocean waves.

"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 nonvolatile, high-resolution, electronic color displays," says David Wright, a professor of engineering at the Univ. of Exeter.

The Oxford team has filed for a patent on the discovery with the help of Isis Innovation, the university's technology commercialization company.

For more stories covering the world of technology, please see HispanicBusiness' Tech Channel

Source: Chemical Engineering Progress

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