- 學位論文
氫化非晶矽薄膜電晶體的正偏壓溫度不穩定性與其恢復機制
Degradation and Recovery Mechanisms of Positive Bias Temperature Instability in a-Si:H TFTs
摘要
氫化非晶矽薄膜電晶體(a-Si:H TFTs)已被廣泛的應用在平面顯示器中，作為畫素開關的重要元件，然而，隨著陣列上之電晶體數量不斷的增加，或更先進的應用中，氫化非晶矽薄膜電晶體會進一步作為驅動元件，並與顯示器周邊電路做整合。上述兩項意味著元件的電性將會受到更多因素的影響，例如不同偏壓的作用或溫度的效應等，因此元件的可靠度就顯得更加重要。 本篇研究中，我們探討正偏壓溫度不穩定性(PBTI)影響氫化非晶矽薄膜電晶體劣化的問題，我們在25、50及75℃三個不同的溫度下，進行PBTI的加壓測試，並隨時觀察及記錄測試元件的劣化情形。 研究結果發現，在PBTI的模式下，在高溫及較高的應力電壓下，元件劣化較為嚴重。造成電晶體劣化的主要原因是由於臨界電壓的升高以及次臨界擺幅的增大，還有微小的遷移率劣化，臨界電壓的偏移是由氮化矽閘極介電層之電荷攫取與非晶矽主動層中之缺陷的生成這兩種機制所造成。除了臨界電壓的變大之外，次臨界擺幅變大的原因被歸咎於非晶矽主動層中之懸鍵數量的增加所導致。 此外在本篇研究中，我們也分析了實驗數據來探討氫化非晶矽薄膜電晶體劣化的回復現象與機制，實驗的結果顯示缺陷的產生是可逆的，且恢復的情況與溫度的高低有關。
並列摘要
The hydrogenated amorphous silicon (a-Si:H) thin film transistors (TFTs) have been widely used as pixel switching element in flat panel displays. However, due to the higher density of transistors on array and for the more advanced applications, a-Si:H TFTs are now used as driving devices and integrated with the peripheral circuits on display. The above two cases means that the device electrical properties would be influence by various factors such as the bias and temperature, and thus the reliability of the components will become more important. In this study, we investigated the positive bias temperature instability (PBTI) of a-Si:H TFTs. Stress conditions were performed by grounding the drain and source, and applying positive voltages to the gate at temperatures of 25, 50 and 75 ℃. From the experimental results, it is found that the a-Si:H TFTs exhibit more serious degradation with the enhancement of temperature and stress voltage. The main source of degradation in a-Si:H TFTs is an increase in threshold voltage (VTH) and sub-threshold swing (S.S.), and minor decrease in field-effect mobility (μFE). Mechanisms responsible for the threshold voltage shift are the trapping of electrons in the silicon nitride gate insulator, and the creation of defects in the a-Si:H. However, an increase in the subthreshold swing was attributed to the generation of additional dangling bonds. Furthermore, the recovery mechanism on degraded a-Si:H TFTs is discussed by analyzed based on experimental data. The results show that defects creation is reversible and temperature dependence has also been observed.