Abnormal Behavior of Threshold Voltage Shift in Bias-Stressed a-Si:H Thin Film Transistor under Extremely High Intensity Illumination

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• 作者：Sang Youn Han ; Kyung Tea Park ; Cheolkyu Kim ; Sanghyun Jeon ; Sung-Hoon Yang ; Hyang-Shik Kong
• 刊名：ACS Applied Materials & Interfaces
• 出版年：2015
• 出版时间：July 22, 2015
• 年：2015
• 卷：7
• 期：28
• 页码：15442-15446
• 全文大小：285K
• ISSN：1944-8252

文摘

We report on the unusual behavior of threshold voltage turnaround in a hydrogenated amorphous silicon (a-Si:H) thin film transistor (TFT) when biased under extremely high intensity illumination. The threshold voltage shift changes from negative to positive gate bias direction after 鈭?0 min of bias stress even when the negative gate bias stress is applied under high intensity illumination (>400鈥?00 Cd/cm²), which has not been observed in low intensity (鈭?000 Cd/cm²). This behavior is more pronounced in a low work function gate metal structure (Al: 4.1鈥?.3 eV), compared to the high work function of Cu (4.5鈥?.1 eV). Also this is mainly observed in shorter wavelength of high photon energy illumination. However, this behavior is effectively prohibited by embedding the high energy band gap (鈭?.6 eV) of SiO_x in the gate insulator layer. These imply that this behavior could be originated from the injection of electrons from gate electrode, transported and trapped in the electron trap sites of the SiN_x/a-Si:H interface, which causes the shift of threshold voltage toward positive gate bias direction. The results reported here can be applicable to the large-sized outdoor displays which are usually exposed to the extremely high intensity illumination.