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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In this work, the influence of copper on amorphous type Indium-Gallium-Zinc-Oxide (a-IGZO) thin-film transistor's (TFTs) transfer curve is studied. The I D -V G curves of a-IGZO TFTs with source/drain in the structures of Cu/Ti and Ti/Al/Ti are compared. The results show that the copper greatly deteriorates the performance of the TFTs. The presence of the copper in the channel region of the device is verified by SIMS analysis. A Cu-dipping experiment is conducted by dipping devices into the solution of CuSO 4 to confirm the role of copper in the deterioration of the I D -V G curves. The hypothesis is also verified through ATLAS device simulator.Indium-Gallium-Zinc-Oxide (a-IGZO) thin-film transistors (TFTs) have attracted great attention for the impressive transparent and high carrier mobility characteristics. They can serve in switching pixel or peripheral circuit application for active-matrix liquid crystal displays (AMLCDs) in the next generation. 1, 2 With the increase of display size, resolution, and the operating frequency in television and 3D display, Cu is applied to replace Al for the reduction of resistance loading in the signal metal bus. Many attempts have been made to incorporate Cu into the amorphous silicon TFT array fabrication. [3][4][5] The process implementation of using Cu as the source/drain (S/D) metal of a-IGZO TFT is also an interesting topic to study. However, most of the previous papers about a-IGZO TFT with the application of Cu emphasized on the contact resistance and the quality of the surface between Cu and a-IGZO. 6-10 In the present work, the influence of Cu diffusion to the electrical properties of a-IGZO TFT is observed and studied. Device and ExperimentThe experimental work was based on the bottom-gate TFT devices of back-channel-etch (BCE) structure with symmetrical S/D fabricated on the glass substrate. Shaped Ti/Al/Ti (50/200/50 nm) gate electrodes were capped with 400-nm-thick SiNx gate dielectric, which was deposited by plasma enhanced chemical vapor deposition (PECVD) at 370 • C. The active layer of 60-nm-thick a-IGZO film was deposited by DC magnetron sputtering system using a target of In:Ga:Zn = 1:1:1 in atomic ratio with the O 2 /Ar ratio about 6%. For the S/D metals, both samples of Ti/Al/Ti (50/200/50 nm) and Cu/Ti (200/50 nm) were prepared by DC sputtering at room temperature. Then, the devices are capped with passivation at 280 • C as protection layer to avoid the disturbance of outside surrounding. After that, via holes and ITO were patterned and shaped for device measurement. The final annealing step was conducted at 280 • C for 1 hour in the oven. In this study, the electrical characteristics are measured by Agilent 4156-C system at 25 • C in dark under 1 atmosphere pressure. The threshold voltage (V T ) is defined by the gate voltage (V G ) when the size-normalized drain current I D reaches 10 −9 A. The subthreshold swing (S.S) and effective field mobility (μ) are extracted at drain voltage V D = 1V. Transfer CharacteristicsFigure 1a and 1b show the electrical ...

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.