An exposure of the back channel of an indium gallium zinc oxide (IGZO) thin film transistor (TFT) to ultraviolet (UV)-activated oxygen can effectively shift the threshold voltage (V th ) of the TFT. The V th decreases linearly with the exposure time while the on-state current greatly increase with the exposure time. The exposure doesn't have a strong impact on other device parameters. The effect of the exposure on the V th is attributed to the increase in the electron concentration of the channel layer as a result of the creation of oxygen vacancies by exposure. Transparent oxide semiconductors (TOS) have attracted much attention for the application of flat-panel displays due to their high carrier mobility (>1 cm 2 /V s) and high transparency in visible range. 1-3 Amorphous indium gallium zinc oxide (a-IGZO) is one of the most attractive TOS that can be used in the next-generation active-matrix flat panel displays, because it has a few superior properties including relatively high mobility, good uniformity, low temperature process, high optical transparency, high threshold voltage stability, etc. 4,5 It has been recently reported that the threshold voltage (V th ) of a-IGZO thin film transistors (TFTs) is affected by the process parameters such as deposition pressure, target composition, channel thickness, post annealing temperature. 6,7 The oxygen content and the thickness of the a-IGZO channel layer are also reported to play an important role in the electrical characteristics including the V th of the TFTs. 8,9 The V th is determined by the electron concentration in the channel layer of the TFT, thus it is related to the oxygen vacancies which provide the free charge carriers for electrical conduction in the oxide layer. Controlling the V th is required in the TFT application; however, it is not an easy task as the oxygen vacancies can be easily generated during the fabrication processes.In the present work, we have demonstrated that the V th can be easily changed by exposing the back channel of the IGZO TFT to ultraviolet (UV)-activated oxygen. The V th of the TFT is found to be highly sensitive to the exposure to UV-activated oxygen, and a linear relationship between the V th shift and the exposure time is observed. However, the exposure does not have a large impact on other device parameters including the field-effect mobility and subthreshold swing.The IGZO TFTs were fabricated on a heavily-doped n-type Si substrate with resistivity lower than 0.001 · cm, which served as the bottom gate of the TFTs. Firstly, a 30 nm Al 2 O 3 layer was deposited onto the Si substrate by an atomic layer deposition (ALD) process to form the gate insulator. A 50 nm IGZO thin film was subsequently deposited on the Al 2 O 3 thin film layer by radio-frequency sputtering in Ar ambient at room temperature using a IGZO target (In:Ga:Zn mole ratio = 1:1:1). The IGZO thin film was then subject to the exposure to UV-activated oxygen for different durations. Photolithography process followed by wet etching was used to pattern the active ...

The effect of short-duration ultraviolet (UV) exposure on the threshold voltage (V th ) of amorphous indium gallium zinc oxide thin film transistors (TFTs) and its recovery characteristics were investigated. The V th exhibited a significant negative shift after UV exposure. The V th instability caused by UV illumination is attributed to the positive charge trapping in the dielectric layer and/or at the channel/dielectric interface. The illuminated devices showed a slow recovery in threshold voltage without external bias. However, an instant recovery can be achieved by the application of positive gate pulses, which is due to the elimination of the positive trapped charges as a result of the presence of a large amount of field-induced electrons in the interface region. V

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