臺灣博碩士論文加值系統

Nowadays thin-film-transistor (TFT) has been widely used in flat panel displays, which is used whether in mobile phone, MP3 or LCD-TV. As the evolution with technology, flat panel display becomes larger and more sophisticated. In the development of large scale display, we need to consider the uniformity of TFT materials. In high-frequency operation (ex. 3-D screen), we have to use the material with higher mobility.

The most commonly used materials in TFT are poly-silicon and amorphous-silicon. Compared the poly-Si and a-Si with a-IGZO, the a-IGZO is considered to be the next generation of materials used in TFTs, due to the perfect uniformity and well mobility at same time. However a-IGZO TFT has several instabilities such as gate bias stress, light
illumination and oxygen adsorption effect.

Previous studies have discussed the phenomenon. However, the instabilities compared in different ambience are rarely mentioned. Now we investigate on the environment-dependent bias stress and photosensitive characteristics of a-IGZO TFT. We use Positive/Negative Bias Stress (PBS/NBS) and light-illumination in different ambience to discuss the degradation of a-IGZO TFT. We found the positive bias stress (PBS) induce the oxygen adsorption on a-IGZO surface by the increasing electron concentration. Besides, the negative bias stress didn’t not cause any degradation on a-IGZO in any kind of environment by channel carrier depletion. Although oxygen will cause the higher threshold voltage, oxygen can effectively suppress the negative threshold voltage shift caused
by photo-generated charges.

Chapter 1. Introduction & Motivation…………………………………1
1.1 Overview………………………………………………................1
1.2 a-IGZO characteristics…………………………………………...2
1.3 Instability of a-IGZO……………………………………………..4
a) Gate Bias……………………...……………………..………………….….4
b) Light Illumination………………………………………………………..4
c) Oxygen Ambience…………………………………………...……………..5
1.4 Motivation………………………………………………………..6

Chapter 2. Device Fabrication & Instrument…………………………13
2.1 Device fabrication……………………………………………….13
2.2 Instrument……………………………………………………….14
(1) Agilent HP4156C……………...…………………..…..…………….….14
(2) Agilent B2201A 14ch Low Leakage Switch Mainframe…….……..14
(3) TTP-6 Probe Station…………………..………………...……………..15
(4) ICS (Interactive Characterization Software)………………………..15
2.3 Set up instruments for I-V……………………………………….16

Chapter 3. Experiment &Result……………………………………….21
3.1 Positive Bias Stress (PBS) in different ambience……………….21
3.1.1 Result…………………………….………………………...21
3.1.2 Discussion………………………………………………….22
3.1.2.1 Vacuum……………………………………………….22
3.1.2.2 O2……………………………………………………..23
a) Oxygen adsorption mechanism without bias………………….24
b) Oxygen adsorption mechanism with PBS……………………..26
3.1.2.3 Air…………………………………………………....27
3.1.3 Summary…………………………………………………...27
3.2 Negative Bias Stress (NBS) in different ambience……………...29
3.2.1 Result………………………………………………………29
3.2.2 Discussion………………………………………………….29
3.2.2.1 Vacuum……………………………………………….30
3.2.2.2 O2……………………………………………………..30
3.2.2.3 Air……………………………………………………31
3.2.3 Summary…………………………………………………..32
3.3 Stability under illumination in different ambience………………33
3.3.1 Result………………………………………………………33
3.3.2 Discussion………………………………………………….34
3.3.2.1 Vacuum……………………………………………….34
3.3.2.2 O2……………………………………………………..35
3.3.2.3 Air…………………………………………………....36
3.3.3 Summary…………………………………………………..36

Chapter 4. Conclusion…………………………………………………56

References……………………………………………………………..58

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