p型氧化亞錫半導體與薄膜電晶體之研究

Abstract

近年來氧化物薄膜電晶體受到廣泛的重視與研究，因為氧化物半導體系統具備高載子遷移率與低溫成膜能力，極有潛力成為下一世代透明軟性電子產品之關鍵材料。雖然n型氧化物半導體領域已獲得重要突破並導入量產，然而至今p型氧化物半導體與薄膜電晶體相關之研究尚稱缺乏，而其元件特性亦無法滿足實際應用。然而，p型氧化物薄膜電晶體是實現氧化物互補式金屬氧化物半導體邏輯電路與傳統有機發光二極體驅動電路不可或缺之元件，由此可知發展高效能p型氧化物薄膜電晶體是現階段最重要的挑戰。由目前已發表的文獻可知，氧化亞錫是p型氧化物半導體中最具潛力可以實現高效能p型元件的材料之一，然而其薄膜電晶體製程與元件特性尚無法相容與滿足量產需求，因此需要更深入的研究。 本論文針對氧化亞錫系統，深入探討靶材、薄膜以及元件之物理與化學特性，研發出相容於現今薄膜電晶體工業量產之靶材與製程技術。本論文之研究成果對於提升氧化亞錫材料的實際應用具有價值。 首先，我們使用適合量產之濺鍍技術搭配純氧化亞錫靶材製備p型氧化亞錫薄膜與薄膜電晶體。研究中詳細分析後退火之效應並藉由接觸電阻分析選擇適合氧化亞錫之實用金屬電極材料，接著使用此金屬電極成功製備p型氧化亞錫薄膜電晶體。第二，針對氧化亞錫靶材無法高溫燒結之缺點，我們探討可高溫燒結之高密度錫/氧化錫混合靶材，並使用此混合靶材搭配純氬氣濺鍍製程成功製備p型氧化亞錫薄膜。第三，我們更進一步使用此錫/氧化錫混合靶材搭配含氫之濺鍍氣氛成功製備具備高優選方向之純氧化亞錫薄膜與薄膜電晶體，並詳細探討氫含量比例與後退火之效應。最終，我們使用化性穩定且已廣泛應用於工業之氧化錫靶材搭配含氫還原製程氣氛製備p型氧化亞錫薄膜與薄膜電晶體，並詳細分析氫含量比例對於結晶結構、成份、表面粗糙度、光學與導電特性之影響。

Thin-film transistors (TFTs) using oxide semiconductors have been regarded as a promising next-generation TFT technology for displays and flexible electronics because of their merits in performance and production. Despite the great success in the development of n-type oxide TFTs in recent years, only few p-type oxide semiconductors were reported for TFTs and their properties and fabrication techniques are still far from practical applications. However, p-type oxide TFTs are strongly demanded in general so that low-power and high-performance complementary circuits can be realized by oxide TFTs and better compatibility with circuits of active-matrix organic light-emitting diode displays may be achieved. Among all p-type oxides reported, tin monoxide (SnO) is considered one of the most promising candidates for realizing practical p-channel devices. However, the properties of SnO-based TFTs and fabrication techniques are not yet good enough for practical applications, necessitating further studies. In this dissertation, we investigated the SnO system from the material properties to the device characteristics, and developed industry-compatible sputtering targets as well as processing techniques. The research results in this study can facilitate the practical application of SnO in the next-generation display technology. Firstly, we fabricated p-type SnO thin-films and TFTs by an industry-compatible sputtering technique with the pure SnO ceramic target as the benchmark for further study. The post-annealing effects on SnO films were studied by physical and chemical analysis, and the transmission line method (TLM) was adopted to characterize the contact resistance between SnO layers and various metal electrodes. Lastly, p-type SnO TFTs using practical metal electrodes were successfully fabricated. In view of the difficulty related to the preparation of pure SnO targets at high temperatures, we further proposed use of Sn/SnO2 mixed target for sputtering deposition of p-type SnO films. The Sn/SnO2 mixed targets can be fabricated by the high-temperature high-pressure pressing/sintering technique and have higher density and robustness more suitable for real uses. The deposited films can be tuned from pure n-type SnO2 to p-type SnO by controlling the sputtering conditions with pure Ar sputtering. Next, we further investigated sputtering deposition of p-type SnO thin films and TFTs by using the robust Sn/SnO2 mixed target and the hydrogen-containing atmosphere. The effects of the hydrogen gas ratio and post-annealing were studied. Pure polycrystalline SnO films with unified preferential orientation could be readily obtained by appropriate process conditions, and decent p-type SnO TFTs were also demonstrated. Finally, we investigated the sputtering deposition of p-type SnO using the widely used and robust SnO2 target in a hydrogen-containing reducing atmosphere. The effects of the hydrogen gas ratio on structures, compositions, optical, and electrical properties of deposited SnOx films were studied, and p-type SnO thin-film transistors using such SnO-dominant films were also demonstrated, showing the feasibility and industrial compatibility of this method.