The research team of Associate Professor Yasuaki Ishikawa and Assistant Professor Mami Fujii at the Graduate School of Materials Science, Nara Institute of Science and Technology (NAIST), in collaboration with Chief Scientist Shimpei Ono at the Central Research Institute of Electric Power Industry, achieved ultra-low voltage operation and high reliability simultaneously by introducing an ionic liquid dielectric layer in amorphous InGaZnO (IGZO) thin-film transistors (TFTs). The operation voltage and instability were suppressed less than 40% and the half, respectively, compared to IGZO TFT with a conventional silicon dioxide dielectric layer. An ionic liquid, which is ambient temperature molten salt, realizes this achievement, consequently, leading to further development of flexible and light-weight monitors.
In the field of developing transparent flexible displays, attention has recently been drawn to oxide semiconductor, IGZO, for channel material of TFT which is pixel switching device of liquid crystal or organic light emitting display. There are at least three technological challenges: Firstly, lowering of operation voltage which enables to decrease energy consumption in TFT operation; secondly, reliability under electrical and environmental stress, and thirdly low temperature process for each functional layer in order to use flexible substrate. Their research succeeded in dealing with these simultaneously by introducing an electric double layer which is produced at the interface of ionic liquid and IGZO layer which can be prepared under room temperature process. The introduced electric double layer can provide high density carriers than the conventional IGZO TFT, leading to driving the TFT under ultra-low voltage less than 40% with low instability suppressed less than the half. The researchers are expecting that this technology enables to operate transparent flexible displays without instability for long time.