KAIST develops ultra-thin transparent transistors for wearable displays

Picture credit: KAIST

A research group from the Korea Advanced Institute of Science and Technology (KAIST) has developed ultra-thin transistors aimed at improving the performance of electronic and wearable displays.

As the IoT era gains ground, there has been robust demand for wearable and transparent displays suited to the requirements of various fields such as augmented reality (AR) and skin-like thin flexible devices. However, the researchers argue that previous technology for flexible transparent displays has proved inadequate with challenges such as poor transparency and low electrical performance being difficult to overcome. Past research efforts aimed at using inorganic-based electronics have also faced headwinds on account of the fundamental thermal instabilities of plastic substrates to yield to the high temperature process, a key step in the fabrication of high performance electronic devices.

The research group led by Professors Keon Jae Lee and Sang-Hee Ko Park of the Department of Materials Science and Engineering, has developed ultrathin and transparent oxide thin-film transistors (TFT) for an active-matrix backplane of a flexible display by using the inorganic-based laser lift-off (ILLO) method. Professor Lee's team previously demonstrated the ILLO technology for energy-harvesting and flexible memory devices.

The research team fabricated a high-performance oxide TFT array on top of a sacrificial laser-reactive substrate. After laser irradiation from the backside of the substrate, only the oxide TFT arrays were separated from the sacrificial substrate as a result of reaction between laser and laser-reactive layer, and then subsequently transferred onto ultrathin plastics (4μm thickness). Finally, the transferred ultrathin-oxide driving circuit for the flexible display was attached conformally to the surface of human skin to demonstrate the possibility of the wearable application. The attached oxide TFTs showed high optical transparency of 83% and mobility of 40 cm^2 V^(-1) s^(-1) even under several cycles of severe bending tests.

Professor Lee said: “By using our ILLO process, the technological barriers for high performance transparent flexible displays have been overcome at a relatively low cost by removing expensive polyimide substrates. Moreover, the high-quality oxide semiconductor can be easily transferred onto skin-like or any flexible substrate for wearable application.”

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