利用二維電子雲效應製作氧化鋅�氧化鋅鎵多重通道薄膜電晶體

Abstract

薄膜電晶體長久以來在液晶顯示技術上扮演著重要的角色，目前顯示技術上的發展趨勢為製作出高透光度的薄膜電晶體陣列，以提高背光使用效率。氧化鋅材料擁有寬能隙、高透光度、高載子遷移率以及可使用射頻磁控濺鍍法低溫沉積等優點，且具有潛力製作薄膜電晶體於塑膠等軟性基板上，以實現可撓性顯示器以及可撓性電路的夢想。 然而在近年來的研究中，氧化鋅薄膜電晶體依舊擁有著一些缺點，像是低工作電流、材料穩定性不足等缺點，限制其在業商業應用上的發展。因此，我們提出了使用新材料，以鎵參雜氧化鋅 (氧化鋅鎵) 製作薄膜電晶體，氧化鋅鎵擁有高載子濃度以及高穩定性，改善了工作電流同時提升元件穩定度，然而元件結構需要改變來適應氧化鋅鎵。在這裡我們試驗了不同通道層厚度以及閘極電極長度的氧化鋅鎵薄膜電晶體，並提出一套模型來解釋其物理現象。成功分析氧化鋅以及氧化鋅鎵薄膜電晶體各自最適合的元件結構，也分別展示了在此最適元件結構下，氧化鋅以及氧化鋅鎵薄膜電晶體各自優異的電特性表現。 此外，為了更進一步提高薄膜電晶體的工作電流以及反應速率，我們製作了世界上第一個可在通道層形成二維電子雲(2DEG)結構的脈衝參雜薄膜電晶體(Delta-doped TFT)，並提出模型加以說明工作原理。與本實驗室先前所從事之研究相比，此薄膜電晶體成功提高工作電流，提升開關率(On/Off ratio)，並證實可藉由通道參雜結構改變，進一步控制元件之臨界電壓(Threshold voltage)。我們相信以此結構製作之薄膜電晶體擁有世界上屬一屬二的優秀電特性。

Thin-film transistors (TFTs) have been playing an important role in the LCD display industry. The recent trend of TFTs is the transparent pixel, which can be fulfilled by using zinc oxide (ZnO) as the active layer. ZnO is the material with properties of wide bandgap, high mobility, and easy deposition by RF sputtering at room temperature. But ZnO also has some drawbacks like the low operating current level and the stability problem. We introduce the gallium doped zinc oxide (GZO) as the active layer. GZO does solve the drawbacks of ZnO above but new problems arisen. We have tried many channel thicknesses and gate sizes of ZnO and GZO TFTs in order to find the best structures of each kind of TFTs. We have successfully explained the structure differences of TFTs by use of a model. We have also fabricated the delta-doped TFTs so as to further improving of current level and response time. A model has been showed to explain the operation of devices by forming a 2-dimentional electron gas (2DEG) structure in the channel layer successfully, and the controllable threshold voltage is also proved by varying the composition of the delta-doping layer. The result of our delta-doped TFTs is much better than the previous work in our lab, and is believed to be one of the best ZnO-based TFT performances in the world.