新穎式透明非晶態氧化銦鎵鋅薄膜電晶體穩定性之研究

Abstract

非晶態氧化半導體(Amorphous Oxide Semiconductors: AOSs) 具有高載子遷移率而且可低溫沉積、可撓曲、透明性以及均勻度佳等特點已受到廣泛的重視.目前被研究的氧化半導體有ITO、IZO、TiO2、ZnO、In2O3、Ga2O3、IGO、a-IGZO等.其中以透明非晶態氧化銦鎵鋅(Amorphous InGaZnO: a-IGZO)薄膜當作主動層(Active layer)的薄膜電晶體(Thin Film Transistors: TFTs),具有載子遷移率與可靠度比傳統氫化非晶矽薄膜電晶體(a-Si:H TFT)高、均勻性優於低溫複晶矽薄膜電晶體(Low Temperature Polycrystalline Silicon TFT: LTPS TFT) 而且可低溫製程,因此a-IGZO薄膜電晶體具有取代氫化非晶矽薄膜電晶體與低溫複晶矽薄膜電晶體來製作主動矩陣有機發光顯示器(Active Matrix Organic Light Emitting Display: AMOLED)的潛力.但是a-IGZO存在著一些本質上的缺點,例如對光以及環境中的水、氧很敏感進而影響元件的穩定性.然而,a-IGZO TFT長時間操作的可靠度也是需要探討.本論文主要研究a-IGZO 沒有保護層(passivation)的情況,與環境中的水、氧所影響的穩定性分析、元件長時間操作的可靠度分析與紫外光影響元件穩定性分析等三個主要方向來進行探討,以期得到改善元件穩定性的方法.從實驗結果我們發現,當沉積a-IGZO時通入氮氣(N2),可以提升元件穩定性與可靠度.以這個特性,最後我們提出新穎式雙層結構來改善元件可靠度以及紫外光對元件造成的穩定性.

Amorphous oxide semiconductors (AOSs) are attracted much attention due to high mobility, low temperature deposition, flexible,transmission, and uniformity.It has been investigated of AOSs, such as ITO, IZO, TiO2, ZnO, In2O3, Ga2O3, IGO, a-IGZO,etc. Especially,the thin film transistors (TFTs) with a-IGZO thin film as active layer perform higher mobility and better reliability than conventional hydrogenated amorphous silicon TFT (a-Si: H TFT). In addition, the uniformity of a-IGZO TFT is also superior to Low Temperature Polycrystalline Silicon TFT (LTPS TFT). Therefore, the a-IGZO TFTs have the potential to replace a-Si: H TFT and LTPS TFT forming Active Matrix Organic Light Emitting Display (AMOLED). However, a-IGZO there are some inherent defect, such as sensitive to water and oxygen in ambient and light illumination thereby affect the device stability. The device reliability under GBS also has to be considered.In this thesis, we studied the interaction between surrounding oxygen and moisture with passivation-free a-IGZO thin film transistors.Time dependence threshold voltage variation in ambient of passivation-free a-IGZO TFT and reliability are investigated. Photo-reaction of a-IGZO TFT under UV-illumination is also investigated.From the experimental results, Adding N2 gas during a-IGZO deposition can improve the device stability and reliability under GBS. Finally we successfully investigated a novel bi-layer structure which insensitive to ambient air and improve storage and reliability issue and decreased photosensitive affects under ultraviolet(UV)-light illumination.