Browsing by Author "Tsai, Ming-Yen"

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Influence of an anomalous dimension effect on thermal instability in amorphous-InGaZnO thin-film transistors
(2014-10-21)
Liu, Kuan-Hsien
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Chang, Ting-Chang
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Chou, Wu-Ching
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Chen, Hua-Mao
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Tsai, Ming-Yen
This paper investigates abnormal dimension-dependent thermal instability in amorphous indium-gallium-zinc-oxide (a-IGZO) thin-film transistors. Device dimension should theoretically have no effects on threshold voltage, except for in short channel devices. Unlike short channel draininduced source barrier lowering effect, threshold voltage increases with increasing drain voltage. Furthermore, for devices with either a relatively large channel width or a short channel length, the output drain current decreases instead of saturating with an increase in drain voltage. Moreover, the wider the channel and the shorter the channel length, the larger the threshold voltage and output on-state current degradation that is observed. Because of the surrounding oxide and other thermal insulating material and the low thermal conductivity of the IGZO layer, the self-heating effect will be pronounced in wider/shorter channel length devices and those with a larger operating drain bias. To further clarify the physical mechanism, fast ID-VG and modulated peak/base pulse time ID-VD measurements are utilized to demonstrate the self-heating induced anomalous dimension-dependent threshold voltage variation and on-state current degradation. (C) 2014 AIP Publishing LLC.
Investigating Degradation Behavior of InGaZnO Thin-Film Transistors induced by Charge-Trapping Effect under DC and AC Gate-Bias Stress
(2012)
Hsieh, Tien-Yu
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Chang, Ting-Chang
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Chen, Te-Chih
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Tsai, Ming-Yen
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Chen, Yu-Te
This paper investigates the degradation mechanism of amorphous InGaZnO thin-film transistors under DC and AC gate bias stress. Comparing the degradation behavior at equal accumulated effective stress time, more pronounced threshold voltage shift under AC positive gate bias stress in comparison with DC stress indicates extra electron-trapping phenomenon occurs in the duration of rising/falling time in pulse. Contrarily, illuminated AC negative gate bias stress exhibits much less threshold voltage shift than DC stress, which suggesting the photo-generated hole does not has sufficient time to drift to the interface of IGZO/gate insulator and causes hole-trapping under AC operation. Since the evolution of threshold voltage fits the stretched-exponential equation well, the different degradation tendencies under DC/AC stress can be attributed to the different electron-and hole-trapping efficiencies, and this is further verified by varying pulse waveform.
Investigation of gate-bias stress and hot-carrier stress-induced instability of InGaZnO thin-film transistors under different environments
(2013-09-01)
Hsieh, Tien-Yu
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Chang, Ting-Chang
;
Chen, Te-Chih
;
Tsai, Ming-Yen
;
Chen, Yu-Te
This paper investigates the temperature and ambiance effects on various reliability issues for InGaZnO thin film transistors with an organic passivation layer. Hot-carrier stress and gate-bias stress are carried out under different environmental temperatures and ambient gases. The device exhibits relatively good stability under room temperture, whereas high temperature enhances degradation. Futhermore, different degradation behaviors after gate-bias stress in atmosphere and in vacuum can be attributed to gas adsorption/desorption-induced instability. Moreover, capacitance-voltage measurement techinique is utilized to analyze the degradation mechanism and to extract the density of state (DOS). The result reveals that the threshold voltage shift after both hot-carrier and gate-bias stress originates from the charge-trapping effect at the interface of gate insulator and active layer, with the extra trap states generated during stress responsible for C-V curve distortion. In addition, the asymmetric degradation behavior of gate-to-drain capacitance (Cgd) and gate-to-source capacitance (Cgs) indicates that trap states are generated near the drain side. (C) 2012 Elsevier B.V. All rights reserved.