This study investigates the effects of bias-induced oxygen adsorption on the electrical characteristic instability of zinc tin oxide thin film transistors in different ambient oxygen partial pressures. When oxygen pressure is largest, the threshold voltages showed the quickest increase but the slowest recovery during the stress phase and recovery phase, respectively. This finding corresponds to the charge trapping time constant and recovery time constant, which are extracted by fitting the stretched-exponential equation and which exhibit a relationship with oxygen pressure. We suggest that the gate bias reduces the activation energy of oxygen adsorption during gate bias stress.

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The environment-dependent electrical performances as a function of temperature for sol-gel derived amorphous indium-gallium-zinc-oxide ͑a-IGZO͒ thin film transistors are investigated in this letter. In the ambients without oxygen, thermal activation dominates and enhances device performance. In oxygen-containing environments, mobility and drain current degrades and the threshold slightly increase as temperature increases. We develop a porous model for a-IGZO film relating to the drain current and mobility lowering due to film porosity and oxygen adsorption/penetration. It also relates to the threshold voltage recovery at high temperature owing to the varying form of adsorbed oxygen and the combination of oxygen and vacancies.

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This paper investigates the environmental effects and related adsorbent species reactions on sol-gel derived amorphous indium gallium zinc oxide thin film transistors (a-IGZO TFTs). The discrepancy between device characteristics measured in atmospheric and vacuum conditions was clarified through experiments with thermal annealing and different gas partial pressures. The measurement of a-IGZO TFTs in simulated water vapor environment was also utilized. We verified that the adsorbed water originating from the surrounding atmosphere can cause an increase in off-current and also enhance more oxygen molecule adsorption on the exposed back-channel surface, leading to more serious degradation in on-current.Recently, zinc oxide (ZnO)-based materials have been investigated as active channel layers in thin film transistors (TFTs) due to potential high transparency and large area deposition applications. [1][2][3][4][5] Compared to conventional amorphous silicon (a-Si) TFTs, amorphous indium gallium zinc oxide (a-IGZO) TFTs have similar device performance. Furthermore, they have the advantage of low manufacturing cost and a compatible process flow with conventional a-Si TFTs. 6,7 Nowadays, oxide TFTs are mainly produced by vacuum systems such as radio frequency magnetron sputtering and pulsed laser deposition. 1,4,7,8 Their high carrier mobility, low processing temperature and high transparency are advantageous for numerous applications. 9 They have also attracted interest as a backplane candidate in large-area applications on account of their highly uniform deposition. 10 Therefore, simple solution processing with high throughput and low cost is desirable for TFT fabrication. Several research groups have demonstrated sol-gel derived TFTs using ZnO, indium zinc oxide (IZO), and IGZO as active channel layers. 11,12 Their results further display that the device performance of sol-gel derived TFTs is comparable to that of vacuum-processed oxide TFTs, and demonstrate low-cost potential in mass manufacturing. In particular, a-IGZO has been widely studied for the backplane of active matrix organic light emitting diode display panels.It is well known that oxygen and water in the surrounding atmosphere affect the electrical characteristics of a-IGZO TFTs. Due to the charge transfer between the a-IGZO film and the adsorbed molecules, the adsorbed H 2 O molecules enhance the conductance, while O 2 molecules adsorbed on the oxide surface lead to a decrease in conductivity in a-IGZO thin film. 7 However, the published papers usually discuss the effect of only one gas species in the experimental environment, while the device instabilities under the coexistence of oxygen and water are rarely reported. 13,14 From the investigation of oxygen sensitivity for ZnO tetrapod sensors, Zheng et al. claimed that if water was pre-existent on the device, the oxygen sensitivity can be effectively enhanced, due to the adsorption competition of the two kinds of molecules. 15 In this paper, such competition effect on the device characteristics of a-IGZO...