臺灣博碩士論文加值系統

石墨烯具備許多優異性能，在未來可能取代矽甚至是金屬導體等，已在各領域被廣泛研究。對於其製程整合考量，氧化石墨烯(GO)透過氧官能基的調變，具有更多的變化性，具備良好的應用前景。本論文主要探討氧化石墨烯薄膜作為電阻式記憶體之應用，將其作為記憶體之電阻轉態層及沉積於二氧化矽(SiO2)形成疊層結構，探討元件切換特性、操作穩定性及記憶特性，並將元件置於無水氣環境下分析其切換情形，討論與大氣下之差異性。首先針對Al/GO/Al元件結構進行電性探討，發現元件具備非極性之轉態特性，但在負方向進行雙極性轉態時有較差的操作穩定性，這歸因於氧化石墨烯薄膜製程中使用含水懸浮液及烘烤步驟，造成元件在初始狀態時下電極界面處已經形成較厚的鋁氧化界面層，致使元件在負方向操作時所能儲存的氧離子受限，而表現出較差的轉態特性。在正方向操作下，鋁上電極的界面氧化與氧化石墨烯薄膜有直接的關係，因此在元件操作時能穩定的儲存與釋放氧離子，而有較穩定的轉態特性。並針對較佳特性之正方向操作進行記憶時間與耐久度測試，發現元件於正方向操作下能達到大於10^4秒的非揮發特性與超過10^3次的寫入/抹除特性表現。接著將元件置於無水氣環境下進行轉態測試，發現元件在無水環境下正負方向皆無法正常轉態，顯示出氧化石墨烯元件轉態對於水氣的依賴性。
第二部分將氧化石墨烯沉積於SiO2薄膜上，製成Cu/GO/SiO2/Pt元件結構，與控制元件Cu/SiO2/Pt於大氣下進行特性比較，發現加入GO層後，因GO本身片狀結構與內部的缺陷，能有效的限制銅離子的遷移擴散，使薄膜內部形成固定且穩定的銅金屬絲狀路徑，讓元件在操作穩定性上獲得明顯的改善，在耐久度測試下能達到3×103次以上循環轉態，超過控制元件的10^3次，且記憶時間可達到超過10^4秒，與控制元件相同。第三部分將控制元件與GO改善元件置於無水氣環境下進行比較，發現控制元件在無水氣環境下無法進行轉態，歸因於薄膜內部水分流失而無法產生銅氧化物作為銅離子源，而GO改善元件因氧化石墨烯內部富含氧官能基團，能使元件產生銅氧化物界面層作為穩定的銅離子供應源，因此元件在無水氣下仍可正常的進行電化學效應切換，且在無水氣環境下元件保持與大氣下相同之記憶時間及耐久度轉態表現。

Graphene has many advantageous properties and it has been studied for many applications. Because of process integration and various promising properties, graphene oxide (GO) also attracts much interest. This thesis investigated graphene oxide for applications of resistive random access memory (RRAM). The GO film also stacked on a SiO2 layer to be a bi-layer structure for RRAM applications. The GO RRAM device can be inversely switched by dc voltages and the related characteristics were also investigated. In addition, the influence of water vapor on the GO RRAM devices were also investigated. The first part, Al/GO/Al structure was investigated. This structure shows non-polar resistive switching behavior. However, there is some difference between the resistive switching behaviors in different polarities. Due to the process procedures, interface layer is thicker in the bottom electrode than in the top electrode. Therefore, the interface layer in the bottom electrode can store less oxygen ions than the interface layer in the top electrode; thus, the resistive switching in the negative polarity is poorer than in the positive polarity. The resistive switching in the positive polarity shows smaller switching variation, and better switching reliabilities such as long retention (>10^4 s) and good endurance (>10^3 cycles). The second part investigated the resistive switching properties of Cu/GO/SiO2/Pt structure in air. The GO film with layer structure and defects can limit Cu diffusion and thus improved the switching stability. The Cu/GO/SiO2/Pt structure has more stable resistive switching behavior than the Cu/SiO2/Pt structure. The Cu/GO/SiO2/Pt structure has long retention (>10^4 s) and good endurance (>3x10^3 cycles). The third part investigated the resistive switching properties of Cu/GO/SiO2/Pt structure in N2. Water vapor assists Cu ionization procedure from the Cu electrode into SiO2 layer. Therefore, the Cu/SiO2/Pt structure can resistively switch in air, but can not switch in N2. The GO film has lots of oxygen-related groups and thus it can help the Cu ionization in N2. Thus, the Cu/GO/SiO2/Pt structure can stably switch in N2 and also has good memory reliability.

目錄
中文摘要 I
英文摘要 III
誌謝 V
目錄 VI
圖目錄 X
表目錄 XIV
第一章 緒論 1
1-1 前言 1
1-2 研究動機與目的 2
1-3 論文架構說明 3
第二章 文獻回顧與基礎理論 4
2-1 石墨烯與氧化石墨烯介紹 4
2-2 記憶體說明與介紹 7
2-3 電阻式記憶體 9
2-4 常用於電阻式記憶體的材料 11
2-4-1 鈣鈦礦材料 11
2-4-2 二元氧化物 11
2-4-3 石墨烯與氧化石墨烯 12
2-5 電阻式記憶體操作特性 13
2-5-1 單極性切換(Unipolar switching) 14
2-5-2 雙極性切換(Bipolar switching) 15
2-6 電阻式記憶體切換機制 16
2-6-1 熱化學效應(Thermochemical reaction) 16
2-6-2 價數變換效應(Valence change effect) 19
2-6-3 電化學效應(Electrochemical reaction) 22
2-6-4 其它石墨烯相關 24
2-7 電流傳導機制 27
2-7-1 歐姆傳導機制(Ohmic conduction) 28
2-7-2 蕭特基發射傳導機制(Schottky emission) 28
2-7-3 法蘭克-普爾傳導機制(Frenkel-Poole emission) 28
2-7-4 空間電荷限制傳導機制(SCLC) 28
2-8 界面改善雙層結構 29
2-9 環境對電阻式記憶體的影響 31
第三章 實驗方法與步驟 34
3-1 實驗敘述與流程說明 34
3-2 實驗設備 35
3-2-1 旋轉塗佈機(Spin coater) 35
3-2-2 射頻磁控濺鍍機(RF magnetron sputter) 35
3-2-3 熱蒸鍍系統(Thermal evaporation system ) 36
3-3 元件製備 37
3-3-1 氧化石墨烯懸浮液(Graphene oxide suspension) 37
3-3-2 矽基板清洗 39
3-3-3 鋁(Al)電極製備 41
3-3-4 鉑(Pt)底電極製備 41
3-3-5 二氧化矽(SiO2)薄膜 42
3-3-6 氧化石墨烯(Graphene oxide)薄膜 43
3-3-7 銅(Cu)上電極製備 43
3-4 材料分析 44
3-4-1 穿透式電子顯微鏡(TEM) 44
3-4-2 雙束型聚焦離子束(DB-FIB) 44
3-4-3 拉曼光譜分析(Raman spectroscopy) 44
3-4-4 X光繞射分析(XRD) 45
3-4-5 X光光電子能譜儀分析(XPS) 46
3-5 電性量測分析 48
3-5-1 量測環境 48
3-5-2 電阻切換特性 49
3-5-3 溫度係數量測 49
3-5-4 記憶時間量測分析(Retention) 50
3-5-5 耐久度量測分析(Endurence) 50
第四章 結果與討論 51
4-1 以氧化石墨烯作為電阻切換層之基本特性與轉態機制 51
4-1-1 元件製備流程 51
4-1-2 材料與化學鍵結分析 52
4-1-3 電阻切換機制 55
4-1-4 電流傳導機制 58
4-1-5 溫度係數量測分析 61
4-1-6 切換特性分析 62
4-1-7 耐久度測試(Endurance) 71
4-1-8 記憶時間測試(Retention) 71
4-1-9 元件於無水氣環境下電性分析 72
4-2 氧化石墨烯疊層結構於大氣環境之基本特性與機制 74
4-2-1 元件製備流程 75
4-2-2 材料與化學鍵結分析 76
4-2-3 大氣環境下元件之電阻切換特性與機制 80
4-2-4 大氣環境下之電流傳導機制 84
4-2-5 大氣環境下元件之溫度係數量測分析 87
4-2-6 大氣環境下元件切換特性分析 88
4-2-7 耐久度測試(Endurance) 96
4-2-8 記憶時間測試(Retention) 96
4-3 氧化石墨烯疊層結構於無水氣環境之基本特性與機制 98
4-3-1 無水氣環境下之電阻切換特性與機制 98
4-3-2 於無水氣環境下之電流傳導機制 101
4-3-3 於無水氣環境下之溫度係數分析 103
4-3-4 於不同環境之切換特性分析 104
4-3-5 於不同環境之耐久度測試 111
4-3-6 於不同環境之記憶時間測試 112
4-3-7 氧化石墨烯改善元件轉態模型 113
第五章 結論與未來展望 115
5-1 結論 115
5-2 未來展望 118
參考文獻 119

[1]Y. Chen, B. Zhang, G. Liu, et al., "Graphene and Its Derivatives: Switching ON and OFF," Chem. Soc. Rev., vol. 41, pp. 4688-4707, May 2012.
[2]Y. Zhu, S. Murali, W. Cai, et al., "Graphene and Graphene Oxide: Synthesis, Properties, and Applications," Adv. Mater., vol. 22, pp. 3906-3924, Sep 2010.
[3]S. Eigler and A. Hirsch, "Chemistry with Graphene and Graphene Oxide-Challenges for Synthetic Chemists," Angew. Chme. Int. Ed., vol. 53, pp. 7720-7738, Jul 2014.
[4]J. S. Meena, S. M. Sze, U. Chand, et al., "Overview of Emerging Nonvolatile Memory Technologies," Nanoscale Res. Lett, vol. 9, pp. 526-558, Sep 2014.
[5]M. Zangeneh and A. Joshi, "Design and Optimization of Nonvolatile Multibit 1T1R Resistive RAM," IEEE Trans. Very Large Scale Integr. VLSI Syst., vol. 22, pp. 1815-1828, Aug 2014.
[6]P. Y. Chen and S. Yu, "Compact Modeling of RRAM Devices and Its Applications in 1T1R and 1S1R Array Design," IEEE Trans Electron Devices, vol. 62, pp. 4022-4028, Dec 2015.
[7]P. Sun, N. Lu, L. Li, et al., "Thermal Crosstalk in 3-Dimensional RRAM Crossbar Array," Sci Rep., vol. 5, p. 13504, Aug 2015.
[8]A. Janotti, X. Cui, B. Himmetoglu, et al., "Structural and Electronic Properties of SrZrO3 and Sr(Ti,Zr)O3 Alloys," Phys. Rev. B, vol. 92, p. 085201, Aug 2015.
[9]O. C. Compton and S. T. Nguyen, "Graphene Oxide, Highly Reduced Graphene Oxide, and Graphene: Versatile Building Blocks for Carbon-Based Materials," Small, vol. 6, pp. 711-723, Mar 2010.
[10]H. Deng, M. Zhang, T. Li, et al., "Nonvolatile Unipolar Resistive Switching Behavior of Amorphous BiFeO3 Films," J. Alloys Compd., vol. 639, pp. 235-238, Aug 2015.
[11]L. Zhang, H. Xu, Z. Wang, et al., "Coexistence of Bipolar and Unipolar Resistive Switching Behaviors in the Double-Layer Ag/ZnS-Ag/CuAlO2/Pt Memory Device," Appl. Surf. Sci., vol. 360, pp. 338-341, Jan 2016.
[12]Y. Li, "Conductance Quantization in Resistive Random Access Memory," Nanoscale Res. Lett, vol. 10, p. 420, Oct 2015.
[13]K. M. Kim, T. H. Park, and C. S. Hwang, "Dual Conical Conducting Filament Model in Resistance Switching TiO2 Thin Films," Sci Rep., vol. 5, p. 7844, Jan 2015.
[14]U. Russo, D. Ielmini, C. Cagli, et al., "Self-Accelerated Thermal Dissolution Model for Reset Programming in Unipolar Resistive-Switching Memory (RRAM) Devices," IEEE Trans Electron Devices, vol. 56, pp. 193-200, Feb 2009.
[15]宋柏瑋, "銅摻雜二氧化矽薄膜於電阻式記憶體特性之研究," 國立高雄應用科技大學電子工程系碩士班論文, 2010.
[16]Y. Li, X. Pan, Y. Zhang, et al., "Write-Once-Read-Many-Times and Bipolar Resistive Switching Characteristics of TiN/HfO2/Pt Devices Dependent on the Electroforming Polarity," IEEE Electron Device Lett, vol. 36, pp. 1149-1152, Nov 2015.
[17]J. Guy, G. Molas, P. Blaise, et al., "Investigation of Forming, SET, and Data Retention of Conductive-Bridge Random-Access Memory for Stack Optimization," IEEE Trans Electron Devices, vol. 62, pp. 3482-3489, Nov 2015.
[18]H. Y. Jeong, J. Y. Kim, J. W. Kim, et al., "Graphene Oxide Thin Films for Flexible Nonvolatile Memory Applications," Nano Lett., vol. 10, pp. 4381-4386, Oct 2010.
[19]H. D. Kim, M. J. Yun, J. H. Lee, et al., "Transparent Multi-level Resistive Switching Phenomena Observed in ITO/RGO/ITO Memory Cells by the Sol-Gel Dip-Coating Method," Sci Rep., vol. 4, p. 4614, Apr 2014.
[20]S. M. Sze and K. K. Ng, Physics of Semiconductor Devices, Third ed.: John wiley & sons, 2006.
[21]J. C. Wang, C. H. Chiu, and W. F. Chen, "Thickness-Optimized Multilevel Resistive Switching of Silver Programmable Metallization Cells With Stacked SiOx/SiO2 Solid Electrolytes," IEEE Trans Electron Devices, vol. 62, pp. 1478-1483, May 2015.
[22]M. Rogala, P. J. Kowalczyk, P. Dabrowski, et al., "The Role of Water in Resistive Switching in Graphene Oxide," Appl. Phys. Lett., vol. 106, p. 263104, Jun 2015.
[23]T. Tsuruoka, K. Terabe, T. Hasegawa, et al., "Effects of Moisture on the Switching Characteristics of Oxide-Based, Gapless-Type Atomic Switches," Adv. Funct. Mater., vol. 22, pp. 70-77, Jan 2012.
[24]L. Shahriary and A. A. Athawale, "Graphene Oxide Synthesized by using Modified Hummers Approach," Int. J. Renew. Energy Environ. Eng., vol. 02, pp. 58-63, Jan 2014.
[25]N. M. Huang, H. N. Lim, C. H. Chia, et al., "Simple Room-Temperature Preparation of High-Yield Large-Area Graphene Oxide," Int J Nanomedicine, vol. 6, pp. 3443-3448, Dec 2011.
[26]I. K. Moon, J. Lee, R. S. Ruoff, et al., "Reduced Graphene Oxide by Chemical Graphitization," Nat. Commun, vol. 1, p. 73, Sep 2010.
[27]A. Buchsteiner, A. Lerf, and J. Pieper, "Water Dynamics in Graphite Oxide Investigated with Neutron Scattering," J. Phys. Chem. B, vol. 110, pp. 22328-22338, Nov 2006.