Seoul National University and Kunsan National University joint research team, tungsten oxide
Development of display devices using nano thin films
No voltage is needed to maintain the color.


Seoul National University College of Engineering announced on the 16th that a joint research team consisting of Professor Lee Byung-ho of the Department of Electrical and Information Engineering, Professor Jung Taek-dong of the Department of Chemistry, and Professor Sun Ho-jeong of Kunsan National University Department of Materials Science and Engineering has developed a display device using tungsten oxide ( _WO3 ) nanofilms, an electrochromic material.

Electrochromism is a phenomenon in which the color of a substance changes due to an electrochemical reaction in response to voltage, and each electrochromic material is known to possess a unique color resulting from oxidation and reduction.

In the case of tungsten oxide, a representative electrochromic material, it changes to a deep blue color when lithium ions are injected into the material through a reduction voltage while it is in a transparent state, and it can return to a transparent state by extracting the lithium ions again through an oxidation voltage.

Although much research has been conducted to utilize this phenomenon, which allows color change with low voltage, in displays, there have been difficulties in expressing various colors and controlling their intensity due to the limitation that the color cannot change to colors other than blue.

To solve these problems, Professor Lee Byung-ho's joint research team developed an optical device capable of various color reproduction and color change by combining nanometer-thick tungsten oxide thin films with semiconductors and metals.

complicationBy creating a tungsten oxide structure stacked layer upon layer on a silicon reflector without using a single structure, various colors of reflected light were reproduced according to the thickness, and an optical information encryption device was fabricated based on the principle that the color of the reflected light changes to a different color through oxidation-reduction voltage, confirming the possibility of its application as a display device.

In addition, by combining a tungsten oxide thin film with a nanometer-thick metal, we succeeded in reproducing a transmissive RGB pixel capable of expressing about 94% of the color gamut used in conventional displays and controlling its intensity with voltage.

The fabricated optical device has a simple stacked structure with a thickness of less than 200 nm and does not require voltage to maintain color, so it is expected to help in the development of low-cost, ultra-thin, and low-power displays.

Dr. Lee Yo-han, who led the experiment, explained, “Through this research, we have taken another step closer to developing full-color display devices using electrochromic materials,” adding that “securing improved device driving reversibility and response speed is key to practical application.”

Meanwhile, this study was published as an online paper on July 6 in 'Nano Letters,' an international academic journal published by the American Chemical Society (ACS).