Browsing by Author "Chen, Jian-Jie"

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An Energy-Band Model for Dual-Gate-Voltage Sweeping in Hydrogenated Amorphous Silicon Thin-Film Transistors
(2019-06-01)
Chen, Guan-Fu
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Chen, Hong-Chih
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Chang, Ting-Chang
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Huang, Shin-Ping
;
Chen, Hua-Mao
This paper clarifies the correct transmission mechanism, misattributed in the previous research, of a hydrogenated amorphous silicon thin-film transistor (a-Si:H TFT) device. Complete drain current-gate voltage (I-D-V-G) transfer characteristics including the forward and backward gate sweeps (gate voltage carried out in the OFF-state -> on-state and the ON-state -> OFF-state) are performed, and the physics models of an energy-band schematic are clearly explained. This paper reveals that the I-D-V-G curve stretch-out behavior of the subthreshold region is due to the leakage of the Poole-Frenkel region. At the Poole-Frenkel regions, electrons transfer to the drain terminal, and holes remain in the valance band of the a-Si:H bulk. The remaining holes represent the positive voltage and cause the electron barrier height lowering. This causes an increase in subthreshold current of the subthreshold region. Finally, three experiments are performed to prove the correctness of these models, and the a-Si TFTs device improvement methods will be proposed to enhance the stability and performance of product of the a-Si TFTs.
Effect of a-InGaZnO TFT Channel Thickness under Self-Heating Stress
(2019-09-18)
Tai, Mao-Chou
;
Chang, Po-Wen
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Chang, Ting-Chang
;
Tsao, Yu-Ching
;
Tsai, Yu-Lin
In this work, indium-gallium-zinc-oxide thin film transistors (IGZO-TFTs) with different channel thicknesses were compared after self-heating stress (SHS). Although TFTs with a thicker channel have higher current during stress conditions, less degradation is reported. This degradation, manifest as the threshold voltage shift in the transfer characteristics, is well described by the stretched-exponential equation. In addition, the average effective barrier height, Et, is extracted to compare the difference in degradation between both TFTs, and finds that the barrier height in the thick channel device is twice that of the thin channel device. Finally, a COMSOL simulation is performed to demonstrate the electrical difference at the gate insulator layer and confirm such phenomena. (C) 2019 The Electrochemical Society.
Improving Reliability of High-Performance Ultraviolet Sensor in a-InGaZnO Thin-Film Transistors
(2019-09-01)
Tsai, Yu-Lin
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Chien, Yu-Chieh
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Chang, Ting-Chang
;
Tsao, Yu-Ching
;
Tai, Mao-Chou
High-performance ultraviolet (UV) sensors using amorphous indium gallium zinc oxide thin-film transistors (a-IGZO TFTs) can detect I-ON/I-OFF ratio up to 10(6) and match the a-IGZO panel process. However, it has a reliability issue under long-term detection. When the top gate length of the dual gate TFT is small, it is twice as reliable as a TFT where the top gate fully covers the device. The electrical properties of the device correspond to the a-IGZO energy band, such that the top gate length was positively related to the underlying energy band diagram. The integrated systems engineering technology computer aided design (ISE-TCAD) electric field simulations show that the etch stop layer (ESL) electric field is weak in the small top gate device. This means that it is difficult for the holes to either be trapped in the ESL or to generate ionized oxygen vacancies.
Investigation of the Capacitance-Voltage Electrical Characteristics of Thin-Film Transistors Caused by Hydrogen Diffusion under Negative Bias Stress in a Moist Environment
(2019-10-30)
Chen, Hong-Chih
;
Kuo, Chuan-Wei
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Chang, Ting-Chang
;
Lai, Wei-Chih
;
Chen, Po-Hsun
In this study, the impact of moisture on the electrical characteristics of an amorphous In-Ga-Zn-O thin-film transistor (a-IGZO TFT) was investigated. In commercial applications of such TFTs, high stability and quality performance in humid environments are essential. During TFT operation under ambient moisture, the electrolysis of water molecules occurs via the tip electric field effect. Hydrogen diffuses from the etch-stop layer or back-channel into the main channel under a negative electric field. The hydrogen atoms act as shallow donors (which causes the carrier concentration in the channel to rise), causing the threshold voltage (V-TH) to shift in the negative direction. Hydrogen diffusion from the overlap of the source/drain and gate electrodes to the channel center caused by the tip electric field induces a significant barrier lowering and V-TH shifts in a short-channel device. However, under negative bias stress (NBS) in ambient moisture, the negative V-TH shift is more obvious in short- than in long-channel devices, indicating suppressed hydrogen diffusion in long-channel devices. This is attributed to the electrolysis of water by the tip electric field at the source, drain, and gate electrodes, which causes hydrogen to diffuse to the center of the channel. Here, a novel physical model of the capacitance-voltage (C-V) electrical property changes under ambient moisture is proposed, based on the early appearance of abnormalities in the C-V measurements. The electrolysis of water caused by the tip electric field and electrical abnormalities caused by hydrogen diffusion into the a-IGZO active layer are explained by this model. A secondary-ion mass spectrometry analysis shows that hydrogen content in the channel generally increases under NBS in ambient moisture. The degradation behavior due to moisture in a-IGZO is clarified. Thus, inhibiting the tip electric field may benefit future flexible-display and gas-sensing applications.