Since a short channel length increases the electric field between the source and drain, a decrease of the channel length enables the decrease of the drain voltage without the decrease of the on-current. The drain voltage should also be decreased for small operation voltage of a TFT.
Both the decrease of the thickness and increase of the dielectric constant increase the induced charge in the channel by the gate voltage, which results in a decrease of the threshold voltage of the TFT and enables the low voltage operation of the TFT. Since a TFT has a metal–insulator–metal (MIS) structure, effective ways to reduce the operation voltage are decreasing the thickness of the gate insulator and using a high dielectric-constant material. Low operation voltage is essential for low power operation because the power is inversely proportional to the square of the operation voltage.
Low power consumption is necessary for more extended applications such as internet of things (IoT) and any mobile applications. Recently, indium gallium zinc oxide (IGZO) TFTs have drawn much attention and have been applied to OLED TVs due to their low off-current, higher mobility than amorphous silicon TFTs, and lower process cost than polycrystalline silicon TFT 11. Amorphous silicon TFTs were applied to liquid crystal displays (LCDs), and low-temperature polycrystalline silicon TFTs were adopted in high-resolution LCDs and organic light emitting diode (OLED) displays. Thin-film transistors (TFTs) have been being used widely in display backplanes and studied for applications such as wearable displays, stretchable displays and sensing devices 1, 2, 3, 4, 5, 6, 7, 8, 9, 10.
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