Nature 511, 206–211 (2014)

Credit: NPG

Phase-change materials such asgermanium antimony tellurium (GST), which can be rapidly switched between amorphous and crystalline states, have attracted considerable attention as candidates for inexpensive high-speed data storage. It now seems that such materials may also prove useful for constructing displays. A team from the University of Oxford and the University of Exeter have demonstrated electrically-induced colour change in ultrathin films of GST and claim that the material could be suitable as a pixel for a new type of microdisplay. By sandwiching a layer of GST, just a few nanometres thick, between two transparent electrodes made of indium tin oxide (ITO), the researchers created miniature displays from arrays of 300 × 300 nm pixels. When the GST phase is switched, the transmission of the pixel changes due to the differences in the reflectivity of the amorphous and crystalline states. Furthermore, control over the colour of the image is achieved by changing the thickness of the bottom ITO electrode, which enhances the reflectivity of specific wavelengths while suppressing others. Because the pixels are ultrathin, they are compatible with flexible surfaces. They can be used with or without a mirrored substrate and are therefore well suited for either reflective or semi-transparent configurations. The researchers expect that displays based on this technology will exhibit very low energy consumption as they do not require power when displaying a static image.