臺灣博碩士論文加值系統

本研究利用鎳金屬靶進行反應性射頻磁控濺鍍製備氧化鎳薄膜，以未含金夾層氧化鎳薄膜(Al/NiO/Pt)、經氧氣氛熱處理未含金夾層氧化鎳薄膜(Al/anneal_NiO/Pt)及含金夾層氧化鎳薄膜(Al/NiO/Au/NiO/Pt)三個系統製作電阻式記憶體(RRAM)元件，由電流-電壓(I-V)及電容-電壓(C-V)特性曲線，搭配原子力顯微鏡及穿透式電子顯微鏡，嘗試了解氧化鎳電阻轉換的工作機制。
在氧化鎳的材料分析及RRAM元件電性量測方面，本研究利用穿隧式電子顯微鏡分析氧化鎳及金夾層的膜厚與微結構；利用拉塞福背向散射能譜儀及電子微探儀對氧化鎳薄膜中Ni、O原子成分進行分析；利用低掠角X光繞射儀進行氧化鎳薄膜結晶結構分析；利用四點探針及霍爾效應量測進行氧化鎳薄膜導電性質分析；利用精密半導體參數分析儀(Agilent 4156C)及電感電容電阻計量儀(Agilent 4284A)進行RRAM元件電性量測分析；最後，利用導電式原子力顯微鏡進行氧化鎳薄膜微區導電性分析。
實驗結果顯示，透過反應性射頻磁控濺鍍製備的氧化鎳薄膜，其初鍍薄膜及經熱處理後的薄膜具有多晶結構，O/Ni比值皆大於1，屬於P型半導體。但經熱處理的氧化鎳薄膜O/Ni比值會較趨近於1，且其電阻率和載子遷移率皆上升，但載子濃度大幅下降。
而三個系統的氧化鎳RRAM元件在I-V量測上，都可觀察到電阻轉換的現象。其中經熱處理後的元件，其電阻轉換成功率明顯下降。而含有金夾層的元件，藉由金夾層加入降低由高電阻態轉換至低電阻態的轉換電壓(switching voltage, Vset)， 且可降低轉換電壓值的標準差，增加元件轉換電壓的一致性。此外，三個系統在記憶時間穩定度方面，經過3600秒測試，其高電阻態與低電阻態皆能維持。三個系統RRAM元件，在高電阻態的導電機制皆屬於蕭特基發射效應，而在低電阻態的導電機制皆屬於歐姆行為。
本實驗亦量測未含金夾層氧化鎳薄膜與含金夾層氧化鎳薄膜RRAM元件的C-V特性曲線，二個系統在高電阻態的電容值皆小於低電阻態的電容值，代表於低電阻態時，薄膜內的電荷數目較高電阻態多。此外，含金夾層氧化鎳元件的高低電阻態電容值都較未含金夾層氧化鎳元件電容值高，故金夾層的加入，可能增加氧化鎳內薄膜的電荷數目。

In this research, nickel oxide(NiO) thin films were deposited by reactive sputtering from nickel(Ni) target. Resistance random access memory(RRAM) devices were fabricated using NiO film without embedded Au layer(Al/NiO/Pt), NiO film without embedded Au layer after thermal treatment in oxygen ambient(Al/anneal_NiO/Pt), and NiO film with embedded Au layer(Al/NiO/Au/NiO/Pt). The mechanism of resistive switching is explored based on the current-voltage(I-V) and capacitance-voltage(C-V) measurements of the devices, in combination with material characterization by atomic force microscopy(AFM) and transmission electron microscopy(TEM).
Thickness and micro-structure of NiO films and embedded Au layer were analyzed by using transmission electron microscopy. Rutherford Backscattering Spectrometry(RBS) and Electron Probe X-ray Microanalyzer (EPMA) were utilized to determine the composition of NiO films. The crystal structure of NiO films was identified by grazing incident angle X-ray diffraction (GIAXRD). Mobility, carrier concentration and resistivity of NiO films were determined by Hall measurement. Film resistivity of NiO films was also determined by four-point probe. The electrical properties of RRAM devices were measured by precision semiconductor parameter analyzer (Agilent 4156C) and LCR meter (Agilent 4284A). Finally, atomic force microscopy was utilized to analyze local conductivity of NiO films.
Experimental results reveal that all NiO films, before and after thermal treatment, are polycrystalline. The O/Ni atomic ratios are larger than 1, and the NiO is a P-type semiconductor. After thermal treatment at 500oC in oxygen ambient, the O/Ni atomic ratio approaches to 1. Carrier concentration is decreased, and the resistivity and mobility are increased.
Resistive switching phenomenon can be seen in all RRAM devices. Nevertheless, the device yield of resistive switching is greater for the devices without thermal treatment than the devices with thermal treatment. Switching voltage values as well as the standard deviation are both reduced for devices with embedded Au layer. In addition, current stress test indicates that the on-state and off-state maintain stable for at least 3600 seconds. The I-V conduction mechanism of all structures is ohmic at on-state, and that of all structures is Schottky emission at off-state.
RRAM devices of NiO films without and with embedded Au layer were also measured C-V curves. A distinct peak is seen in the C-V curves of all devices and the peak is larger for the device at on-state than at off-state, and it is larger for NiO with embedded Au layer than NiO without embedded Au layer. The C-V curves suggest that the number of charges in NiO is greater at on-state than at off-state. Moreover, the number of charges in NiO films increases when embedding an Au layer.

第1章 緒論 1
1-1 前言 1
1-2 研究目的與動機 2
第2章 理論基礎 3
2-1 電阻式記憶體 3
2-1-1 記憶體簡介 3
2-1-2 電阻式記憶體之電流-電壓特性曲線 4
2-2 電阻式記憶體材料種類 8
2-2-1 鈣鈦礦結構材料（Perovskite） 8
2-2-2 高分子材料 8
2-2-3 過渡金屬氧化物 9
2-3 電阻轉換機制探討 11
2-4 介電層導電機制 15
2-4-1 穿隧 (Tunneling) 15
2-4-2 熱離子發射 (Thermionic emission)或蕭特基發射 (Schottky emission) 16
2-4-3 夫倫克爾-普爾發射 (Frenkel-Poole emission) 16
2-4-4 歐姆效應 (Ohmic) 17
2-4-5 離子傳導 (Ionic conduction) 17
2-4-6 空間電荷限制電流 (Space-charge-limited current, SCLC) 18
2-5 氧化鎳基本特性介紹 21
第3章 實驗方法與步驟 25
3-1 實驗流程 25
3-1-1 濺鍍靶材 (Sputtering Target) 25
3-1-2 基板材料 (Substrate) 26
3-1-3 實驗使用氣氛 (Gas Ambient) 26
3-1-4 實驗相關藥品與耗材 27
3-2 實驗設備 28
3-2-1 薄膜濺鍍系統 (Sputtering system) 28
3-2-2 乾式熱氧化系統 (Dry Oxidation System) 30
3-2-3 熱處理系統 (Thermal Treatment System) 31
3-3 實驗流程 32
3-3-1 基材清洗 32
3-3-2 氧化鎳RRAM元件製備 32
3-3-3 氧化鎳薄膜氣氛熱處理 34
3-3-4 霍爾效應量測試片製備 34
3-4 分析儀器 38
3-4-1 表面粗度儀（α-step） 38
3-4-2 電子微探儀 ( Electron Probe X-ray Microanalyzer, EPMA ) 38
3-4-3 拉塞福背向散射能譜儀 ( Rutherford Backscattering Spectrometry, RBS ) 39
3-4-4 θ-2θ X光繞射分析儀 (θ-2θ X-ray Diffractometer, θ-2θ XRD ) 39
3-4-5 低掠角X光繞射分析儀 ( Glancing Incident Angle XRD, GIAXRD ) 40
3-4-6 四點探針 ( 4-point probe ) 40
3-4-7 霍爾效應量測系統 ( Hall effect measurement ) 41
3-4-8 精密半導體參數分析儀 ( Precision Semiconductor Parameter Analyzer ). 42
3-4-9 電感電容電阻計量儀 ( LCR meter ) 43
3-4-10 原子力顯微鏡 ( Atomic force Microscopy, AFM ) 43
3-4-11 穿透式電子顯微鏡 ( Transmission Electron Microscopy, TEM） 45
第4章 結果與討論 46
4-1 試片編號命名及試片結構 46
4-1-1 試片編號命名 46
4-1-2 RRAM試片結構 48
4-2 薄膜材料性質及電性分析 52
4-2-1 氧化鎳薄膜成分分析 52
4-2-2 氧化鎳薄膜結晶性分析 55
4-2-3 四點探針電阻率量測 60
4-2-4 霍爾效應量測（Hall effect measurement） 62
4-3 RRAM元件I-V電性量測分析 64
4-3-1 Al/NiO/Pt RRAM元件之電阻轉換性質量測 66
4-3-2 Al/NiO/Au/NiO/Pt RRAM元件之電阻轉換性質量測 75
4-3-3 RRAM元件記憶時間穩定度量測 81
4-3-4 RRAM元件介電層導電機制之分析 86
4-4 RRAM元件之C-V電性量測分析 96
4-5 AFM及TEM微結構分析 101
4-5-1 薄膜表面粗糙度及C-AFM分析 101
4-5-2 TEM顯微結構觀察 108
4-6 氧化鎳RRAM元件電阻轉換機制探討 117
第5章 結論 122
第6章 參考文獻 124

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