臺灣博碩士論文加值系統

氫化非晶矽薄膜電晶體，目前已經被廣泛應用在各種電子產品，雖然技術日趨成熟，但隨著新興技術有機發光二極體發展而成為驅動元件，在電流驅動方面存在著許多可靠度的問題。關於非對稱式氫化非晶矽薄膜電晶體，由於非對稱的結構，我們定義通道寬度較長的結構為U型端，通道寬度較短的結構為I型端，而定義I型端為汲極時會有較大的導通電流，以及極低的漏電流，作為定電流的元件時其可靠度仍需探討。

施加電壓應力之非晶矽薄膜電晶體不穩定性:

閘極電壓愈高，能打斷愈多在通道a-Si:H與閘極絕緣層SiNx 接面的Si-H鍵，進而產生懸浮鍵，當汲極加入直流電壓做應力測試，閘極與汲極間的電位差減小，產生的缺陷也減少。在做交流訊號應力測試時，加在閘極交流訊號頻率高低，對氫化非晶矽薄膜電晶體特性衰退並無相關性，因為交流訊號下，通道內電子堆積的速度比閘極所給的交流訊號快很多。而在一個週期時間的交流訊號內，只有正電壓時間能有效產生缺陷，因此交流訊號對薄膜電晶體的影響相對比直流偏壓小。非對稱式氫化非晶矽薄膜電晶體，因為汲極與源極圖案不同，兩端在受到外加應力後，U型端的通道寬度所產生的缺陷數量比I型端的多，因此選用U型端作為電子輸出端，非對稱式氫化非晶矽薄膜電晶體會有較嚴重的退化現象。

施加定電流應力之非晶矽薄膜電晶體不穩定性:

在1µA定電流應力測試下，對稱式氫化非晶矽薄膜電晶體操作在線性區應力測試比操作在飽和區有較嚴重的退化現象，其原因為線性區下，電子在通道內能有效撞擊汲極端產生缺陷，而在飽和區下，在閘極絕緣層與矽的接面的缺陷因為閘極與汲極間產生空乏區，故沒產生缺陷，而非對稱式氫化非晶矽薄膜電晶體也有相似的情況。在線性區應力測試下，由U型端提供定電流(Is)，有較大的退化現象，其原因為等量的電子流撞擊U型端會有較多位置的Si-H鍵可以被打斷產生缺陷。我們也探討了非對稱式氫化非晶矽薄膜電晶體在線性區下10µA與1.3µA之定電流在相同閘極電壓下，定電流較小者有較大的退化現象的原因。在不同閘極電壓與不同定電流應力下，可以藉由觀察電晶體各端點之電壓，參照定電壓應力測試下之不穩定性機制，來探討定電流退化機制，有助於定電流應力下之非晶矽薄膜電晶體不穩定性機制的了解。

The hydrogenated amorphous silicon thin-film transistors (a-Si:H TFTs) were important electronic devices in many electronic products. The a-Si:H TFT technology in active-matrix liquid-crystal displays (AM-LCD) was applied to new products recent years, the active-matrix organic light emitting displays (AM-OLED). We investigated the asymmetric TFT electrical characteristics under different voltage stress and constant current stress because TFTs would be used as current driver.
The instability of voltage stress:
We made the experiments about DC stress and AC stress. The gate bias was larger, the more degradation in TFT electrical characteristics. Because larger gate bias could induce more electrons, the electrons broke the weak bond, Si-H, at the interface between a-Si and the gate insulator, and induced Si dangling bond defect. Based on this model we add the stressed bias on drain electrode to reduce the voltage between gate and drain electrodes, and the degradation of the TFTs electrical characteristics would become smaller. In AC stress, the bias stress experiment has the same result. But the degradation of AC stress showed no frequency dependence. Because the electrons would rapidly accumulate in the channel, the AC signal was not fast enough to react. Because there were different patterns of drain electrode between and source electrode in the asymmetric TFTs, the U type terminal, which has large channel width, could induce more defects. When U type terminal provided electrons, the electric characters of asymmetric TFTs had larger degradation.
The instability of constant current stress:
The symmetric TFT under 1µA constant current stress, the degradation of TFT operated in linear region was serious than that operated in saturation region. The electrons would break the Si-H bond at the interface between a-Si:H and the gate insulator when TFT operated in linear region, however, the depletion region near drain terminal deduced the electrons to impact the Si-H bond, therefore, it led to the result. We investigated that 1.3µA constant current stress had larger degradation than 10µA on electrical characteristics under the same gate bias in linear region. For the asymmetric TFT, we would explain the degradation mechanism of the constant current stress baseon the DC stress model.

致謝 i
中文摘要 ii
Abstract iii
目次 iv
表目次 vi
圖目次 vii
第一章 簡介 1
1.1 背景 1
1.2 研究動機 3
1.3 文獻探討 4
1.4 論文架構 7
第二章 基本原理介紹 8
2.1 液晶顯示器工作原理 8
2.2 有機發光二極體 10
2.3 氫化非晶矽薄膜特性 12
2.4 非晶矽薄膜電晶體 13
2.5 薄膜電晶體之各種電性參數萃取 15
2.5.1 載子移動率(mobility, μFE)和轉導(Gm)之定義 15
2.5.2 臨界電壓(Vth)之定義 16
2.5.3 導通電流(Ion)與漏電流(Ioff)之定義 16
第三章 元件介紹與實驗流程 17
3.1 元件結構 17
3.2 量測系統介紹 22
3.3 量測方法及流程 23
3.3.1 直流定電壓下之電性不穩性測試 23
3.3.2 交流訊號下之電性不穩性測試 25
3.3.3 定電流下之電性不穩性測試 27
第四章 結果與討論 29
4.1 直流定電壓下之電性不穩性測試 29
4.1.1 對稱式TFT閘極直流偏壓應力測試 29
4.1.2 對稱式TFT閘極直流偏壓下加入汲極直流偏壓應力測試 32
4.1.3 非對稱式TFT閘極直流偏壓應力測試 36
4.1.4 非對稱式TFT閘極直流偏壓下加入汲極直流偏壓應力測試 40
4.1.5 非對稱TFT閘極直流偏壓下加入源極直流偏壓應力測試 43
4.1.6 直流偏壓測試後的飽和區量測 46
4.2 交流訊號下之電性不穩性測試 49
4.2.1 對稱式TFT閘極交流訊號做應力測試 49
4.2.2 非對稱式TFT閘極交流訊號應力測試 52
4.2.3 非對稱TFT閘極交流訊號下加入汲極直流偏壓應力測試 55
4.2.4 非對稱TFT閘極交流訊號下加入源極直流偏壓應力測試 58
4.3 定電流下之電性不穩性測試 64
4.3.1 對稱式TFT定電流下操作在飽和區與線性區 64
4.3.2 非對稱式TFT不同操作區下汲極定電流1.3µA應力測試 70
4.3.3 非對稱式TFT不同操作區下源極定電流1.3µA應力測試 74
4.3.4 非對稱式TFT不同方向定電流1.3µA應力測試比較 78
4.3.5 非對稱式TFT不同操作區下汲極定電流10µA應力測試 81
4.3.6 非對稱式TFT不同操作區下源極定電流10µA應力測試 85
4.3.7 非對稱式TFT不同方向定電流10µA應力測試之比較 89
4.3.8 非對稱TFT在線性區應力測試下相同電流方向不同定電流之比較 92
4.3.9 非對稱TFT在飽和區應力測試下相同電流方向不同定電流之比較 97
4.3.10 定電流應力測試後的飽和區量測 100
第五章 結論 106
5.1 電壓應力之不穩定性 106
5.2 定電流應力之不穩定性 107
參考文獻 109

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