An ‘aqueous route’ for the fabrication of low-temperature-processable oxide flexible transparent thin-film transistors on plastic substrates

Metal-oxide semiconductors have attracted considerable attention as next-generation circuitry for displays and energy devices because of their unique transparency and high performance. We propose a simple, novel and inexpensive ‘aqueous route’ for the fabrication of oxide thin-film transistors (TFTs) at low annealing temperatures (that is, <200 °C). These results provide substantial progress toward solution-processed metal-oxide TFTs through naturally formed, unique indium complex and post annealing. The fabricated TFTs exhibited acceptable electrical performance with good large-area uniformity at low temperatures. Additional vacuum annealing facilitated the condensation reaction by effectively removing byproduct water molecules and resulted in the activation of the In2O3 TFT at low annealing temperatures, even temperatures as low as 100 °C. In addition, we have demonstrated that the flexible and transparent oxide TFTs on plastic substrates exhibit good resistance to external gate bias stress. Metal oxide semiconductor structures can be both electrically conductive and optically transparent — an attractive combination for electronic devices. Their fabrication has typically involved the deposition of the precursors under vacuum, a method that is costly and can result in materials lacking uniformity over large surface areas. A team of researchers led by Byeong-Soo Bae at the Korea Advanced Institute of Science and Technology has alleviated these issues by devising a low-temperature fabrication route in aqueous media. Solution-based processes had been investigated, but often involved alcohol solvents that require high processing temperatures or complex and unstable precursors. An indium oxide thin film has now been prepared from an aqueous solution, at temperatures lower than 200 °C, that further served as the active layer of a fully transparent thin-film transistor. In addition, using plastic as a substrate enabled the construction of a transparent, flexible device. We propose the simple and novel ‘aqueous route’ for realizing oxide thin-film transistors (TFTs) at low annealing temperatures <200 °C with low cost. These results provide substantial progress toward solution-processed metal-oxide TFT through naturally born unique indium complex and post annealing. They exhibit acceptable electrical performance with good large-area uniformity at low temperature. The additional vacuum annealing facilitates the condensation reaction by effective removal of byproduct water molecule and activates the In2O3 TFT at low temperature, even with 100 °C annealing. Also, we have demonstrated the flexible and transparent oxide TFTs on a plastic substrate with good stability to the external gate bias stress.