Study of Flexible Oxide Semiconductor Thin Film Transistors for Flexible Flat Panel Display

可撓式顯示器在近幾年來開始逐漸吸引各界的關注，其具備輕量化、易攜帶等優點，例如電子紙、電子標籤，甚至是穿戴式顯示器，是目前最重要的科技發展重點之一，是下一世代最令人矚目的新產品，另外，在近幾年來環保的宣傳風潮之下，可重複性使用電子紙之研究更是蔚為風潮，不久的將來，軟性電子及顯示器的技術將在市場上有一席之地。 而氧化物薄膜電晶體具有非晶態特性下，仍能保有高載子移動率；另外，氧化物半導體在可見光區下大多為透明，可用於提升平面顯示器之開口率；顯示出氧化物半導體具有高度取代非晶矽的潛力；最重要的是，氧化物薄膜電晶體製程中並不需要高溫製程，將可應用在各種軟性基板之上。 本論文中，使用聚亞醯胺做為軟性基板，以非晶氧化鋅銦鎵做為主動層，使用全微影全蝕刻製程，製作出軟性氧化物薄膜電晶體；其中比較分析溼蝕刻以及乾蝕刻製程，對元件製作過程之影響；接著本論文提出利用蝕刻停止層，來達到乾蝕刻電極過程中，保護聚亞醯胺基板以及絕緣層不受電漿侵蝕；最後，本論文探討元件在不同曲率撓曲後之電性變化，證實這些元件在數毫米曲率半徑撓曲後，仍可正常操作。In recent years, flexible electronics have attracted a great deal of attention due to their various advantages such light weight, thin profile, and portability. Various novel applications of flexible displays, such as electronic paper, and wearable displays, are among the most significant technologies in the next generation. Moreover, the emerging conscience of environmental protection renders the reusable electronic as a viable solution. It is believed that flexible electronics and displays will appear and play an important role in the market soon. Oxide thin-film transistors (TFTs) could exhibit high mobility in the amorphous phase. In addition, their transparency in visible region can improve the pixel aperature ratio in flat-panel displays. These benefits of oxide TFTs render their highly potential to replace amorphous silicon (a-Si) TFTs. Most importantly, oxide TFTs could be fabricated at relatively low temperatures and thus are compatible with flexible electronics on plastic substrates. In this thesis, we use fully lithographic and etching processes, polyimide as the flexible substrate and the amorphous indium gallium zinc oxide (a-IGZO) as the active layer to fabricate flexible oxide TFTs. First, we analyze the effects of wet-etching and dry-etching techniques on device fabrication. Then, we demonstrate a technique of using the etch-stop layer to protect polyimide substrates and the other dielectric layers from erosion during the dry etching of electrodes. Finally, we characterize the variation of device performances after they are bended in the different bending curvatures. We show that these devices can function normally even after they are bended in the radius of curvature of a few millimeters.第一章 序論..................................1 1.1 軟性電子與顯示器發展....................1 1.1.1 軟性電子與顯示器之應用..............1 1.1.2 軟性電晶體與顯示器之發展............1 1.1.3 軟性基板介紹........................3 1.2 氧化物半導體載子傳輸特性................5 1.3 薄膜電晶體結構與操作特性................6 1.4 研究動機................................9 1.5 論文架構................................9 1.6 參考資料...............................10二章 軟性氧化物半導體薄膜電晶體之製程.....18 2.1 前言...................................18 2.2 元件製備...............................18 2.3 溼式蝕刻法定義電極圖樣.................21 2.3.1 王水蝕刻氧化銦錫...................21 2.3.2 鈦酸蝕刻鈦金屬膜...................21 2.3.3 酸液蝕刻鈦/金/鈦多層金屬膜.........22 2.4 乾式蝕刻法定義電極圖樣.................23 2.5 乾/溼式蝕刻法定義電極圖樣..............26 2.6 參考資料...............................28三章 元件特性分析與探討...................43 3.1 前言...................................43 3.2 利用溼蝕刻氧化銦錫為電極之薄膜電晶體...44 3.2.1 電晶體置於平面時之分析.............44 3.2.2 電晶體於撓曲後之分析...............45 3.3 利用乾蝕刻鈦為電極之薄膜電晶體.........46 3.3.1 電晶體置於平面時之分析.............46 3.3.2 電晶體於撓曲後之分析...............47 3.4 利用乾蝕刻鈦及溼蝕刻氧化銦鋅複合電極之薄膜電晶體..49 3.4.1 電晶體置於平面時之分析.............49 3.4.2 電晶體於撓曲後之分析...............50 3.5 參考資料...............................51四章 總結與未來展望.......................71 4.1 總結...................................71 4.2 未來展望...............................7