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Effect of the oxygen flow rate for active-layer deposition on the thermal stability of amorphous InGaZnO thin film transistors (a-IGZO TFTs) was investigated. The transfer characteristics of a-IGZO TFTs were measured at temperatures ranging from 298 to 398 K and a simple analytical model was used to relate the threshold voltage $({\rm V}_{\rm th})$ decrease with increasing temperature to the formation of the point defects in a-IGZO films. Lower oxygen flow rate for active-layer deposition was proved to improve the thermal stability of a-IGZO TFTs, as was confirmed to be due to the increase in defect formation energy with the oxygen flow rate decreasing by the related theoretical analysis and XPS measurements.

This study investigates the impact of gate bias stress with and without light illumination in a-Si:H thin film transistors. It has been observed that the I–V curve shifts toward the positive direction after negative and positive gate bias stress due to interface state creation at the gate dielectric. However, this study found that threshold voltages shift negatively and that the transconductance curve maxima are anomalously degraded under illuminated positive gate bias stress. In addition, threshold voltages shift positively under illuminated negative gate bias stress. These degradation behaviors can be ascribed to charge trapping in the passivation layer dominating degradation instability and are verified by a double gate a-Si:H device.

The amorphous indium gallium zinc oxide thin film transistors (a-IGZO TFTs) passivated by sputtered non-stoichiometric aluminum oxide (AlOx) and titanium oxide (TiOx) layers were comparatively investigated in this letter. The devices with TiOx passivation layers exhibited better long-time storage stability compared with those passivated by AlOx films. Although both a-IGZO TFTs with AlOx and TiOx showed quite stable properties for negative bias-stress tests, the device passivated by TiOx film exhibited abnormal Vth shift during positive bias-stress tests. A novel passivation-layer structure consisting of both AlOx (~15 nm, bottom side) and TiOx film (~85 nm, top side) was proposed, which could perform better than either sing layers and might be preferred in mass production of a-IGZO TFTs.

A high reliable amorphous silicon gate driver with shared dual pull-down units is proposed and fabricated for large-sized TFT-LCD applications. A special unit in the driver is designed to generate bipolar pulse bias for low-level holding TFTs to suppress the threshold voltage shift, which achieves 40.5% and 34.8% improvement compared with conventional DC and unipolar pulse bias respectively according to measurement results.

Process development of inverted-staggered amorphous InGaZnO thin-film transistors (a-IGZO TFTs) with wet-etched electrodes was employed in this paper. Five metals (Al, Cu, Ti, Ta, and Cr) as well as various etchants were comparatively investigated, indicating H2O2 based solution etched Ta films were good candidates for the wet-etched electrodes of a-IGZO TFTs. The aforementioned findings along with other improving attempts successfully established inexpensive processing steps and conditions with which stable a-IGZO TFTs were finally fabricated. The device performance was reasonably good enough (μFE of 6.0 cm2/V·s, Vth of 2.5 V, SS of 1.8 V/decade, and Ion/Ioff of 106) to meet the requirements of applications especially for small-sized flat panel displays.

Tantalum etched by H2O2 solution shows best performance to be the source/drain electrodes of inverted staggered amorphous Indium Gallium Zinc Oxide thin film transistors among the investigated five metal materials. In addition, the etching property is improved significantly by adding aqueous ammonia properly.