科技不斷進步，顯示器追求著更高解析度與大尺寸螢幕，因此隨著畫素變多與操作頻率變快，電晶體所需要的載子遷移率也跟著提高。對於金屬氧化物薄膜電晶體因其在非晶態下可維持不錯的電子遷移率，因此有潛力取代非晶矽薄膜電晶體成為新世代顯示器中主流的材料。本論文是使用a-IGZO金屬氧化物當通道材料，而IGZO是容易受光影響的材料，但主動式陣列顯示器因為無法自行發光，所以需要搭配背光源操作使用，因此電晶體會長時間處於照光的環境，再加上閘極大部分是被施予負偏壓訊號使電晶體關閉的狀態，於是本論文主要探討改變閘極覆蓋IGZO照光範圍以及雙閘極結構的電性分析，並對元件進行可靠度物理機制探討。
第一部分，討論IGZO主動層有無被金屬閘極遮蔽之基本電性量測與照光下量測的差異，觀察到在固定主動層面積下，當閘極覆蓋區域在通道長度方向短於主動層時，因為主動層兩側會受corner effect造成的尖端電場影響，使電容量測下有提早導通現象。進行照光量測時，不論主通道露出或被完全遮蔽皆會產生次臨界漏電，代表金屬閘極無法有效完全遮蔽光的穿透，且隨著主動層露出的範圍越多，光漏電的現象會越嚴重。在可靠度實驗中，發現閘極覆蓋區域小於主動層的元件，會有尖端電場所造成不均勻電洞注入的現象；而當隨閘極覆蓋範圍往通道寬度方向延伸，會使側邊電流路徑變多導致電流變大，且因為閘極往上延伸使閘極與主動層重疊區域變大所以通道電容變大，直到閘極等於或大於IGZO後重疊面積不變而通道電容成定值。照光量測下，同樣會產生次臨界漏電，且光漏電隨著元件寬度變大而變小的現象，是因為側邊電流的比例會隨著元件寬度越大而比例越小所影響。
第二部份，雙閘極結構的銦鎵鋅氧電晶體，由於接觸窗口型元件的源極和汲極有多餘的延伸電極，使得上閘極只能控制到局部的主動層，因此上/下閘極操作的量測結果並不會對稱。在不同閘極量測方式中，觀察到當雙閘極的上下閘極同時量測，因其可以同時控制整體和中間能障使得電晶體更容易關閉，所以此臨界電壓會小於只有單邊閘極的量測。可靠度實驗中，因為雙閘極同時給電壓去做應力實驗使得絕緣層電場變小不利於電洞注入，使其劣化會小於單邊閘極劣化。在不同主動層厚度的可靠度實驗，同樣有其結果，且隨主動層變厚上下閘極控制能力會變弱。

In this study, the electrical analyses and physical mechanisms of structure-depended reliability tests in InGaZnO thin film transistors are investigated. In the first part, the difference of shielded area between IGZO layer and metal gate is discussed. Under the different metal gate length devices, an abnormal rise in capacitance at the off-state in capacitance-voltage characteristics curves can be observed. It is attributed to edge effect-induced high electrical field when the length of metal gate is smaller than IGZO layer in the device length direction . Under light illumination measurement, the behaviors of subthreshold-leakage current can be observed whether the lengths of metal gate are larger than IGZO layer or not. After the negative gate bias illumination stress (NBIS), it is found that the devices which have edge effect caused the more severe hole injection into the gate insulator. However, as metal gate extends toward the device width direction, it is found that the drain current increase slightly. This is because that there are additional paths for current flowing from the side of device. Further, the channel capacitance also increases as gate extends until the width of metal gate is larger than IGZO layer. Also, these devices all show subthreshold-leakage current under light illumination measurement. However, the subthreshold-leakage current becomes smaller after normalized the drain current by device size. This is because that the ratio of side currents decreases as the device width increases.
In the dual gate structure of IGZO TFTs, the top gate can only control the partial channel due to the redundant electrode of via-contact type device. It makes the characteristics in the top and bottom gate operation are not symmetric. Under the different gate operation modes, it is found that the top and bottom gate control the entire and central channels at the same time makes transistor to be close easier and leads to smaller Vt than single gate operation. In reliability experiment, the top and bottom gate is applied simultaneously during stress makes the electric field across the gate insulators becomes smaller and lessens the degree of degradation. This phenomenon becomes unobvious as the channel thickness increases because the thicker channel thickness might reduce the gate control ability.

學位論文審定書 i
公開授權書 ii
致謝 iii
中文摘要 iv
英文摘要 vi
目錄 viii
圖目錄 x
第一章 概論 1
1.1 前言 1
1.2 非晶態氧化銦鎵鋅主動層 2
第二章、元件特性與儀器介紹 6
2.1 元件基本特性 6
2.1.1 輸出特性與轉換特性曲線 6
2.1.2 參數萃取 7
2.2 儀器介紹 9
第三章、改變氧化銦鎵鋅照光區域之效應 12
3.1 簡介 12
3.2 實驗架構 12
3.3 結果與討論 13
3.3.1 IGZO Length方向照光區域變化 13
3.3.2 IGZO Width方向照光區域變化 16
第四章、雙閘極照光負偏壓應力之效應 35
4.1 簡介 35
4.2 實驗架構 35
4.3 結果與討論 36
4.3.1 雙閘極結構之基本特性 36
4.3.2 雙閘極結構之可靠度分析 38
4.3.3 雙閘極結構之主動層厚度影響 40
第五章、結論 66
Reference 68

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