非晶矽薄膜電晶體特性及可靠度之研究

Abstract

本論文探討影響非晶矽薄膜電晶體的特性的因素。包括閘極絕緣層材料與 厚度，非晶矽的材料特性和厚度，以及非晶矽層介面等，皆會對元件特性 有很大的影響。並對其可靠度加以研究，增進對非晶矽薄膜電晶體不穩定 性機構的了解，發現主要的來源有二：其一是在閘極絕緣層中以及其與非 晶矽層的介面上存在的電荷陷阱，造成截止電位的漂移；其二是在非晶矽 層中所產生的能態生成，造成元件特性在副截止電位區的變化：而缺陷池 模型的效應，亦是造成元件特性不穩定的的重要因素。此外，薄膜電晶體 結構中寄生之電容的特性及可靠度亦被探討，並建立此電容與薄膜電晶體 間的關係。 This thesis presents the factors which can affect the characteristics of the hydrogenated amorphous silicon (a-Si :H) thin film transistors (TFTs), including the gate dielectrics the a-Si:H film, and interfaces, etc. The reliability issue of these were also studied. By comparing the various behaviors of the TFTs with varied gate dielectric and a-Si:H films, it is confirmed that the instability mechanisms of the a-Si:H TFTs are charge trapping and the state creation. The charge trapping can rigidly shift the transfer characteristics of the TFTs. The state creation can degrade the subthreshold behaviors of the TFTs. The defect pool in the a-Si:H is also found to be an important instability mechanism. In addition, the reliability and characteristics of the capacitors embedded in the structure of TFTs were investigated to realize their correspondences.