Implementing full color display with a simple structure
Can be applied to display and encoding optical information (HelloT, 20200716)
SNU College of Engineering announced on the 16th that the joint research team of ECE Professor Byoungho Lee, Professor Taek Dong Chung of the department of chemistry, and Professor Ho jung Sun of Kunsan National University’s department of material science and engineering developed a display device that uses a nano thin film of tungsten oxide, an electrochromic material. This development signifies a step’s advance toward the possible development of thinner display with less power consumption and manufacturing costs.
Electrochromism is a phenomenon in which the color of the material changes through an electrochemical reaction that depends on voltage. Each electrochromic material is known to attain its unique color through oxidation and reduction. In the case of tungsten oxide, a well-known electrochromic material, lithium ions are injected into the initially transparent material through a reduction voltage, and the color changes to dark blue. Its color can be returned to being transparent by extracting lithium ions through an oxidation voltage.
Intensive research has been conducted to apply this phenomenon, as it allows switching colors at a low voltage, but researchers were faced with difficulties in expressing various colors and adjusting the intensity as tungsten oxide could not change into colors other than blue.
▲Working principles of the nano optical device(above) that uses tungsten oxide film: Lithium ions are injected into or extracted from the tungsten oxide by applying oxidation and reduction voltage. Thus, the colors are changed (reflective type) or the intensity of color is adjusted (transmissive type)(below). This is an optical information encryption device that can hide and reconstruct letters through the oxidation and reduction of tungsten oxide.
Professor Byoungho Lee’s joint research team confronted this problem by combining a nanometer thin tungsten oxide film, which is approximately 1/500 the thickness of an adult hair, semiconductors, and metals to create a photonic device that can assume various colors as well as change in color.
Rather than using a complex structure, the team created a tungsten oxide structure stacked on a silicon reflector. Various colors of the reflected light were reproduced depending on the thickness. Based on the principle that the color of the reflected light changes by the oxidation and reduction voltage, the team created an optical information encryption device and confirmed the possibilities of applying this for display devices.
In addition, by combining a nanometer-thin metal with a tungsten oxide thin film, the team succeeded in producing transmissive RGB (red, green, blue) color pixels that can exhibit about 94% of the color gamut used in conventional displays and controlled the intensity by voltage. The optical device is a simple stacked structure of a thickness of less than 200 nanometers. As no voltage is required for it to sustain color, it is expected to be of great help in the development of low-cost, ultra-thin, and low-power displays.
Dr. Yohan Lee, who led the experiment, explained, “Through this research, we have come one step closer to developing full color display devices using electrochromic material. For commercialization, the key is to obtain improved reversibility and response speed.”
Research results were published online on July 6 in the international journal Nano Letters, which is published by the American Chemical Society (ACS).
Translated by: Jee Hyun Lee, English Editor of Department of Electrical and Computer Engineering, email@example.com