| Summary: | 碩士 === 國立中興大學 === 光電工程研究所 === 106 === The amorphous Indium-gallium-Zinc-Oxide (a-IGZO) thin film transistor (TFTs) has many advantages such as lower leakage current and higher electron mobility. And they can reduce device’s size as compared with the conventional amorphous silicon ones, and have a higher aperture ratio to improve resolution, which can make mobile devices thinner and lighter, and the power consumption is also lower. Due to its large energy gap, they are widely used in transparent electronic products. However, in the display applications, it is well known that the unstable characteristics under simultaneous illumination and bias stress are an important issue. Besides, the electrical characteristics under simultaneous illumination and bias stress at high temperatures will be more unstable.
In this study, a novel measurement method is proposed to investigate the reliability of a-IGZO TFTs, which provides the time-varying characteristics of the device at different temperatures with simultaneous illumination and bias stress. In the experimental setup, a 12.5V battery is used to provide a fixed voltage difference (Vgd) between the gate and drain, and the Keithley 4200 is used to hold the drain current of 1 nA. Under the illumination and bias stress at the different temperatures, we can measure the gate voltage changing with time owing to the device’s degradation. Then we confirm the consistency between the traditional Id-Vg measurement method and Vg-t measurement one. The fitting formula is used to analyze the degradation and recovery parts of the TFT devices. We propose the further qualitative explanation for the degradation and recovery mechanisms of light-induced electron-hole pair generation and oxygen vacancy response using the principle of thermal equilibrium and Le Chatelier’s principle. These principles can reasonably explain the measuring results. The oxygen vacancy reaction model is hypothesized the main degradation and recovery mechanisms and the oxygen vacancies have different reaction life time, At higher temperature measurements, there will be more oxygen vacancies with longer life time to participate in the reaction of degradation.
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