Highly Stable Thin-Film Transistors for Flexible and Transparent Displays

This paper investigates the development of highly stable thin-film transistors (TFTs) for flexible and transparent displays. Structural designs and material requirements for mechanical flexibility and optical transparency, as well as several fabrication techniques used to achieve high operational stability, are investigated. In particular, a display backplane with circular amorphous-indium-gallium-zinc-oxide (a-IGZO) TFTs having electrically shorted top and bottom gates is found to exhibit better stability to electric current and mechanical bending stress than conventionally used rectangular TFTs. Additionally, hard saturation in the output characteristics of the circular a-IGZO TFTs guarantees constant drive current within a wide fluctuation margin of the input voltage, thereby eliminating the need for voltage (IR)-drop compensation circuits. Furthermore, the circular shape translates to bending direction independence and immunity to local electric field crowding at corners or channel edges. The double gate structure enables volume accumulation, which enhances operational performance and stability.