MD4: Phase-Change Materials and Applications

Harish Bhaskaran, University of Oxford

Novel displays, smart windows, and other optoelectronics using phase change materials

Written by Michael Lee

Harish Bhaskaran of the University of Oxford is not satisfied by the latest smartphone screen resolution. The crisp, vibrant LCD or OLED displays only represent wasted battery power – 80% of which is used to power the light that is transmitted to your eyes. Reflective displays (popularized by the Amazon Kindle) use ambient light and reflect it toward your eyes, but lack vivid colors causing a faded appearance. In order to appease consumers the color performance and resolution must match or exceed existing devices, and phase change materials like Ge₂Sb₂Ta₅ (GST) represent an efficient solution. GST can be switched between amorphous and crystalline phases by mechanical, electronic, or optical perturbations to induce a massive variation in reflected color appearance. In principle the resolution can be defined by pixels 70 nm in diameter with a reflectance greater than 70%, which is better than standard paper. Furthermore, GST can be used in transmission geometry on building windows to dynamically modulate infrared radiation to improve heating and cooling efficiency. These applications, among many more, indicate GST and other phase change materials may serve a huge variety of functions in the near future.