An optoelectronic framework enabled by low-dimensional phase-change films

Here stable colour changes induced by solid-state electrical switching of ultrathin films of a germanium-antimony-telluride alloy are demonstrated, adding to its established uses in data storage; possible applications include flexible and transparent displays. Smart thin-film colour displays Phase-change materials such as the alloy germanium antimony tellurium (GST) have found wide practical use in optical storage media such as rewritable DVDs. More recently, such materials are also being investigated as candidates for the next generation of electrically operated non-volatile memories. Harish Bhaskaran and colleagues now consider the possibility of combining both optical and electrical control in ultrathin phase-change films. They first demonstrate that stable colour changes can be achieved in thin films of GST and go on to showcase a range of possible applications such as flexible and transparent displays. The work offers a new type of optoelectronic framework, and while still at an early stage, it offers an intriguing promise for technological applications. The development of materials whose refractive index can be optically transformed as desired, such as chalcogenide-based phase-change materials, has revolutionized the media and data storage industries by providing inexpensive, high-speed, portable and reliable platforms able to store vast quantities of data. Phase-change materials switch between two solid states--amorphous and crystalline--in response to a stimulus, such as heat, with an associated change in the physical properties of the material, including optical absorption, electrical conductance and Young's modulus.sup.1,2,3,4,5. The initial applications of these materials (particularly the germanium antimony tellurium alloy Ge.sub.2Sb.sub.2Te.sub.5) exploited the reversible change in their optical properties in rewritable optical data storage technologies.sup.6,7. More recently, the change in their electrical conductivity has also been extensively studied in the development of non-volatile phase-change memories.sup.4,5. Here we show that by combining the optical and electronic property modulation of such materials, display and data visualization applications that go beyond data storage can be created. Using extremely thin phase-change materials and transparent conductors, we demonstrate electrically induced stable colour changes in both reflective and semi-transparent modes. Further, we show how a pixelated approach can be used in displays on both rigid and flexible films. This optoelectronic framework using low-dimensional phase-change materials has many likely applications, such as ultrafast, entirely solid-state displays with nanometre-scale pixels, semi-transparent 'smart' glasses, 'smart' contact lenses and artificial retina devices.
Author(s): Peiman Hosseini [sup.1] , C. David Wright [sup.2] , Harish Bhaskaran [sup.1] Author Affiliations: (1) Department of Materials, University of Oxford, Parks Road, Oxford OX1 3PH, UK, (2) College [...]