(Invited) Highly Robust a-IGZO TFT for Foldable Displays

Abstract

The amorphous-oxide-semiconductor (AOS), particularly amorphous-indium-gallium-zinc-oxide (a-IGZO), has attracted considerable attention for applications in large-size, flexible AMOLED displays because it yields high device performance even when sputter deposited at temperatures that are compatible with plastic substrates. In particular, a-IGZO is now considered the most favorable material for designing integrated circuits used in display applications because of its mobility and processing compatibility with plastic substrates. To realize a flexible AMOLED display, the TFT backplane should be fabricated on a flexible substrate. One of challenge in making flexible AMOLED displays is the integration of driver circuits on the TFT backplane. The use of rigid external driver circuits limits the display flexibility because excessive bending may result in the detachment of/damage to the rigid external driver circuits. We have demonstrated foldable thin-film transistor (TFT) fabricated on a free-standing plastic substrate. With extreme bending machine, the repeated extreme bending stress was applied on the TFTs up to 10,000 times. If the bending stress applied along the strain perpendicularly on the channel current flow, conventional TFT characteristics degraded under extreme bending stress. In the a-IGZO TFTs with source and drain electrode splitted, no degradation could be found under the extreme bending stress. It is because in the reducing the area of metal electrode and active layer, occurring cracks by the extreme bending remarkably decreased after extreme bending up to 10,000 times. Therefore, the TFTs and TFT gate drivers perform well after repeated bendings. We will present the model to explain the experimental results.