Mobility Improvement of Amorphous Indium-gallium-zinc Oxide Thin Film Transistor by Roll-to-roll Compatible Plasma Treatment

For the mobility enhancement of amorphous indium-gallium-zinc oxide thin film transistor (a-IGZO TFT), Ar plasma treatment was proposed at room temperature under air as an economic and continuous process. Through the suggested method, the field effect mobility (μFE) improves significantly from 1.69 cm²/V·s to 4.20 cm²/V·s. The increase of oxygen vacancy (VO) and decrease of metal-oxide bonding are observed in the plasma treated device by X-ray photoelectron spectroscopy (XPS) analysis. The increased VO is thought to enhance the carrier concentration and mobility. Some of VO, however, will be an inactive and deep state in the forbidden energy gap of IGZO and deteriorate the electrical stability. To avoid this side effect, the selective Ar plasma treatment was also adapted on source/drain (S/D) contact region and threshold voltage shift under the constant positive gate bias stress was measured to decrease from 6.2 V to 4.8 V, which is similar with the untreated device of 4.4 V. In the contract region plasma device, the μFE improves also by 39.6 % to 2.35 cm²/V·s mainly due to the reduction of S/D contact resistance extracted by the transmission line method (TLM).