The Studies of Low Photocurrent and High Performance Submicron Bottom Gate Polysilicon TFTs
| Autor: | Dun-Nian Yaung, 楊敦年 |
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| Rok vydání: | 2000 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 89 The characteristics of submicron polysilicon thin film transistors (TFTs) with/without some improving technologies have been investigated. It was found that narrow width effects of unhydrogenated and hydrogenated are dominated by the traps of grain boundary and channel edge, respectively; and as drain bias increases, the subthreshold swing of TFTs is decreasing due to floating-body effect which is related to grain size, drain bias and hydrogenation or not. In addition, TFTs with more traps show better punchthrough immunity. The annealing effect of donor-like traps caused by tunneling electrons/captured holes interaction is used to explain the improved characteristics of unhydrogenated TFTs under some stress conditions. However, the poststress characteristics will not to be improved if trap states have been previously removed by hydrogenation. As hydrogenation time increase, the dark current is decreased but the photocurrent is increased because the traps — generation/recombination centers have been passivated. For low power SRAM and TFT-LCD module under high illumination applications, the polysilicon TFTs should offer low leakage current and low photocurrent, respectively. Hence some improvement technologies are needed for achieving a high performance and high reliability polysilicon TFT for these special applications. Poly-channel oxidation improves the subthreshold swing, leakage current and device instability under electric stress for submicron bottom-gate polysilicon TFTs, but degrade cell stability of TFT-SRAM due to increasing voltage drop of interpoly contact. It can be solved by using a self-aligned Ti-silicide interpoly contact. Optimizing hydrogenation time and poly-channel oxidation time, polysilicon TFTs show low dark current and low photocurrent simultaneously under high illumination environment. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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