低溫複晶矽薄膜電晶體之單位光通量漏電流特性分析

Abstract

低溫複晶矽薄膜電晶體(LTPS TFTs) 由於擁有良好的電流驅動能力，目前已被廣泛的運用在主動式矩陣液晶顯示器(AMLCD)上。另外許多高附加價值的功能像光感測器、觸控式面板、影像掃描等等，都被試著整合至顯示器電路週邊的玻璃基板上，倘若我們可以直接利用低溫複晶矽薄膜電晶體做為光偵測器而達到上述的效果的話，不僅可以降低功率的消耗，也可以簡化製程的步驟。因此低溫複晶矽薄膜電晶體的光效應是值得我們去探討的。 在此篇論文中，首先確認了光漏電流在低溫複晶矽薄膜電晶體中主要產生的區域為汲極端，之後我們進一步的去研究關於製造額外缺陷態對光效應的影響。熱載子效應(Hot Carrier effect)與自發熱(Self Heating effect)效應兩種分別提供了不同種類的缺陷，並在不同的汲極電壓下對光效應產生不同的影響。此外，我們還修正了之前所提出關於描述光漏電流行為的經驗公式，修正後新的經驗公式更能符合完整描述光漏電流在不同溫度與缺陷下的行為變化。因此我們利用新經驗公式中各個參數與缺陷態之間的變化結果，試著去提出一個簡單的模型來解釋這些不規則的光電流變化與缺陷態的關係。

Low temperature polycrystalline silicon (LTPS) thin-film transistors (TFTs) have been widely used on the active-matrix liquid-crystal displays due to the excellent current driving ability. In addition, all kinds of attempts of high added value functions like light sensor, touch panel, image scanner, etc. have been reported to integrate display circuits to peripheral area of the glass substrate. If we integrate the ambient light sensor with the same LTPS technology used to fabricate the display, the power consumption can be reduced, and the fabrication process can be simplified. Therefore, the photosensitivity of LTPS TFTs is a significant design consideration for achieving high-image-quality display panels In this thesis, first, we confirm that the photo leakage current occurs mainly on the drain side. Furthermore, photo current behaviors affected by extra defect states creation have been also investigated. Hot-Carrier and Self-Heating effects afford different types of defect states creation in the energy gap and change photo leakage current versus drain bias. Moreover, we also revise the empirical formula for ULC to provide even more accurate description of the photo induced current under the presentation of defect states and temperature. Thus, we proposed a ULC model for TFT versus the changing trend of fitting factors to explain these illumination behaviors.