臺灣博碩士論文加值系統

氧化銦鎵鋅(IGZO)是一種透明的n-type金屬氧化物半導體材料，主要應用於薄膜電晶體(TFT)的通道層(Channel layer)，由於其對空氣中的氧氣十分敏感的特性，又表面氧吸附是金屬氧化物半導體氣體感測機制的重要關鍵，因此也可以做為氣體感測器的感測層。
在本研究中我們使用大氣壓電漿輔助化學氣相沉積(APECVD)於二氧化矽絕緣層上沉積氧化銦鎵鋅薄膜，並使用爐管作為退火工具，量測不同製程條件下各個試片對一氧化碳的感測表現，最終開發出最佳的製程。本研究分為五個部分，首先探討不同氧化銦鎵鋅薄膜厚度對感測表現的影響，找出最佳感測厚度。第二，分別探討薄膜在氮氣與氧氣不同流量下退火的感測表現。第三，找出最佳的退火時間。第四，分別結合氮氣退火與氧氣退火的優點，開發出兩段式退火的新製程並研究出最合適的製程參數。最後我們分別比較傳統氮氣退火與新穎兩階段退火製程所製造的氧化銦鎵鋅感測器在真實環境下一氧化碳的感測能力並測試經過兩階段退火製程感測器的長時間感測穩定性。
除了一氧化碳感測量測外，我們使用掃描電子顯微鏡(SEM)觀察各種退火條件的表面影像我們發現過高的溫度或過長的時間都會使薄膜晶粒大小長大甚至有部分區域開始結晶，薄膜變更緻密且感測表面積縮小，最終導致感測效果下降。還有X-射線光電子光譜(XPS)去分析氧化銦鎵鋅感測層薄膜表面的氧鍵結情況。許多文獻指出表面氧空缺的多寡對於氣體感測的影響是至關重大的，當表面氧空缺所占的比例提高，薄膜的氣體感測能力也會提升。XPS分析顯示當使用傳統氮氣退火時，薄膜表面氧空缺比例大幅下降至為退火前的一半，金屬-氧鍵結大幅增加，雖然退火使薄膜品質變好，但必須承擔表面氧空缺大幅減少的副作用。而使用此論文提出的兩階段退火製程時，薄膜表面氧空缺比例與退火前基本維持不變，際達成薄膜退火的目的同時也克服了傳統氮氣退火的缺點。
在最後的兩種退火製程比較實驗中，使用兩階段退火的氧化銦鎵鋅薄膜相較傳統退火的薄膜，在相同工作溫度下其氣體感測能力在所有測試的一氧化碳濃度下皆大幅提升，尤其在低濃度環境下一氧化碳感測能力更是顯著地有2.5倍~3倍的提升。

Indium gallium zinc oxide (IGZO) is one kind of transparent n-type metal oxide semiconductor material which is often utilized to the channel layer of thin-film transistors (TFT). IGZO is very sensitive to oxygen in air. Since the sensing mechanism of semiconductor metal oxide materials mainly depend on oxygen adsorption on the material surface, this property makes IGZO also be utilized as gas sensing layer of semiconductor gas sensors.
In this study, we used atmospheric pressure plasma enhanced chemical vapor deposition (APECVD) system to deposit IGZO films on silicon oxide and as-deposited IGZO films were annealed in furnace. Samples which were fabricated in different conditions were exposed to carbon monoxide to measure the sensing performance. In the end we could finally develop the best process for IGZO sensors. The study is divided into five parts. First, we investigated the effect of film thickness on sensing performance and determined the best IGZO film thickness for CO sensing. Second, we studied the effects of N2 and O2 annealing with different gas flow rates on sensing performance. Third, we studied the effects of different annealing time on sensing performance. Fourth, we combined the advantages of N2 annealing and O2 annealing, and developed the brand-new two-step annealing process and determined the best annealing recipe for IGZO films. Finally, we tested the samples annealed by traditional annealing and two-step annealing in real-world environment and compared the results.
In addition to CO sensing measurements, we used Scanning Electron Microscope (SEM) to observe the surface images of different annealing conditions. The images showed that excessively high annealing temperatures and excessively long annealing time would cause the grain size grow larger, resulting in smaller sensing surface area and lower sensing effect. X-ray photoelectron spectroscopy (XPS) is also used to analysis the oxygen bonds on IGZO film surface. It was reported that high proportion of surface oxygen vacancies can enhance sensing performance of the film. From XPS analysis we discovered that when IGZO films annealed by traditional annealing process, percentage of oxygen vacancies on the surface dropped to only half of it compare to as-deposited films. On the other hand, IGZO films annealed by two-step annealing process had almost same percentage of oxygen vacancies remained on the surface. By using the two-step annealing process we developed in this study, IGZO sensing films could still get the benefit from annealing but remove the side effect. Finally, in real-world environment CO sensing test two-step annealed samples also showed much higher sensitivity than traditional N2 annealed samples.

摘 要 i
Abstract iii
致 謝 v
Contents vi
Table Captions viii
Figure Captions xi
Chapter 1 Introduction -1-
1.1 The hazards of Carbon monoxide -1-
1.2 Overview of gas sensors -3-
Chapter 2 Literature Reviews -10-
2.1 Sensing mechanism of metal oxides gas sensor -10-
2.1.1 Oxygen ionosorption model -11-
2.1.2 Oxygen vacancy model -17-
2.1.3 Short conclusion -19-
2.2 Atmospheric pressure plasma enhanced chemical vapor deposition -33-
2.3 Annealing process for IGZO as sensing layer -39-
2.3.1 Annealing temperature -40-
2.3.2 Side effect of annealing process -42-
Chapter 3 Experimental -53-
3.1 Device design -53-
3.2 Experiment processes -56-
3.3 Gas sensing measurements -59-
Chapter 4 Results and discussions -63-
4.1 CO sensing results with different thicknesses of IGZO -65-
4.2 CO sensing results with different annealing gas -71-
4.3 CO sensing results with different annealing time -77-
4.4 CO sensing results with two-step annealing -83-
4.4.1 Introduce new annealing process for IGZO sensors -83-
4.4.2 Experimental result and material analysis -84-
4.5 Comparison of two annealing processes -97-
Chapter 5 Conclusions and Future Work -110-
5.1 Conclusion -110-
5.2 Future work -115-
References -116-

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