人類生活中傳統的陰極射線管CRT已幾乎被平面顯示器(LCD、OLED、PDP)所取代，顯示器產業更被評為繼半導體產業之後的全球重大產業之一。而市場上大面積的顯示面板主流為TFT-LCD(薄膜電晶體液晶顯示器)，正是使用了非晶矽薄膜電晶體為液晶顯示器的畫素開關。
a-Si TFT的製程中，主動層材料(a-Si)的光導係數較高，在光源照射下有較大的漏電流，使得畫素開關動作不完全造成顏色顯示上的問題。若在主動層製程中通入了SiF4，使主動層偏P型半導體及增加了主動層的缺陷密度，對光漏電流的有抑制效果。
又因為液晶的特性，TFT-LCD顯示器的畫素開關的驅動將會施加偏壓，形同對TFT做STRESS。因此針對SPL作DC STRESS的實驗,發現摻雜SiF4的元件比較不會劣化,可靠度較佳。
本論文主要研究a-Si:F TFT在低溫下的光漏電流變化並了解STRESS對TFT影響

Since the traditional CRT(Cathode Ray Tube) replaced by FPD(Flat Panel Display), e.g. LCD、OLED、PDP, FPD industry is regarded as the important one of global industry following Semi-conductor industry. The main stream of Large-Area Displays is TFT-LCD(Thin Film Transistor-Liquid Crystal Display) and it’s applied a-Si:H TFT (the hydrogenated Amorphous Silicon Thin Film Transistor) as pixel-switch device on LCD.
In a-Si:H TFT Cell process, the active region material(a-Si:H) with higher Photoconductivity results into higher off-state current under light illumination and that causes color performance discrepancy as incomplete On/Off operation of pixel-switch devices. As long as the introduction of F into a-Si:H modify the density of states in the gap of a-Si:H(:F), that may result the shift of the Fermi level toward the valence band edge and The density-of-states increasing. It’s effective to decrease the photo leakage current.
Due to electro-optical properties of liquid crystal(LC), to drive Pixel-switch device in TFT-LCD shall force On/Off voltage to change Twist Angle of LC is corresponding to have Stress on TFT device. According to DC Stress experiment results, it’s found TFT device with SiF4 dopant can reach better reliability.
This issue is aimed to research the photo leakage current variation of a-Si:H TFT at low temperature and ON/Off state effect by stress on TFT device.

Chinese Abstract……………………...………………………….I
English Abstract…………………………..…………………….II
Content…………………………...…………………………………….IV
Table Captions…………………………………..…………………….VII
Figure Captions………………………………………………………VIII

Chapter One - Introduction
1.1 Introduction………………………………………………………………….1
1.1.1 Overview
1.1.2 Hydrogenated Amorphous Silicon
1.1.3 Atomic Structure and the Electron Density of States
1.2 Photo leakage current mechanism…...……………………….………….....5
1.3 Some solutions for reducing photo leakage current……....……….......…..9

Chapter Two - Fabrication
2.1 Deposition of Hydrogenated Amorphous Silicon by PECVD ……….….11
2.2 Deposition of SiNx by PECVD……………….…………………………….14
2.3 Deposition of n+ Hydrogenated Amorphous Silicon by PECVD………16
2.4 Process Flow………………………………………………………………..17

Chapter Three - Apparatus and Parameters
3.1 Apparatus List………………………………………………………….…..18
3.2 Setup instruments for Current-Voltage (I-V) Measurement …...………19
3.2.1 The Room Temperature and High Temperature
3.2.2 The Low Temperature
3.3 Method of Device Parameter Extraction…………..………...……….…...21
3.3.1 Determination of the threshold voltage
3.3.2 Determination of the subthreshold swing
3.3.3 Determination of the field-effect mobility
3.4 Density of States……………………………………………………………24
3.4.1 Overview
3.4.2 Evaluation of the density of states--Activation energy method

Chapter Four –Experiments Results and Discussion
4.1 Overview of the experiments sample..........................................30
4.1.1 Characteristics
4.1.2 Relative parameters
4.2 Characteristics at Low Temperature……………………….…………..…33
4.2.1 Motivation and Experiment Steps
4.2.2 The electrical characteristics at low temperature
4.2.3 Measured with light illuminated at low temperature
4.2.4 Summary
4.3 Light Illuminated Experiment………………………….………..………..39
4.3.1 Motivation and Experiment Steps
4.3.2 A Discussion on Experiment Results
4.3.3 Summary
4.4 Reliability Experiment—DC Stress……………………………………..44
4.4.1 Motivation and Experiment Steps
4.4.2 A Discussion on Experiments Results
4.4.3 Summary

Chapter Five – Conclusion…………………………………...……..47

References..…………………………………….……………..……….48
Tables…………………………………………………………….…..56
Figures…………………………………….................……….………..57

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Chapter Two –Fabrication
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Chapter Three - Apparatus and Parameters
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Chapter Four - Experiments Results and Discussion
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