本實驗以溶液法製備之氧化鋅奈米顆粒 (ZnO NPs) 和磁控濺鍍的氧化鉭(TaOX) 做為電阻式記憶體元件的介電層，利用旋轉塗佈法將ZnO NPs旋塗於ITO玻璃基板上，利用物理氣相沈積法將TaOX沉積於Pt基板和ITO玻璃基板，並沉積鋁(Al)、鉭(Ta)做為上電極，製備Ta/TaOX/Pt、Ta/TaOX/ITO、Ta/ZnO NPs/ITO和Al/ZnO NPs/ITO四種電阻式記憶體元件，探討不同上電極材料或下電極材料對電阻式記憶體元件電性的影響。藉由分析TaOX-bsaed元件的電性結果，建立TaOX-bsaed元件的電阻轉換機制，並定義ITO下電極與Pt下電極的角色差異性。基於TaOX-bsaed元件的電阻轉換機制，藉以探討ZnO NPs-based元件的電阻轉換效應，試圖瞭解ZnO NPs-based電阻式記憶體元件的電阻轉換機制。
在材料分析方面，本實驗利用X光光電子能譜儀(XPS)，分析上電極與ZnO NPs介電層的界面以及介電層內部，而得知界面周遭和介電層內部的元素鍵結形態；利用穿透式電子顯微鏡(TEM)，確認電阻式記憶體元件各層薄膜的厚度及觀察ZnO NPs介電層的結晶程度。在元件電性量測方面，本實驗利用精密半導體參數分析儀(Agilent 4156C) 量測電阻式記憶體元件的電流-電壓特性曲線及阻態穩定時間。
XPS結果顯示，上電極材料在接近介電層的位置，會有上電極金屬的氧化物訊號出現，代表上電極與介電層之間有一層金屬電極氧化物的界面層。由TEM結果得知溶液法製備之ZnO NPs，其顆粒粒徑大約為3~5 nm，且每個ZnO NP均為單晶，經旋轉塗佈而堆疊出多晶的ZnO NPs薄膜。另外，實驗室之前的研究顯示，濺鍍的TaOX薄膜為非晶質態。
電性分析結果顯示，正常運作的TaOX-based元件屬於“正偏壓寫入，負偏壓抹除”的雙極性電阻轉換行為。其差異為Ta/TaOX/Pt元件可正偏壓寫入，也可以負偏壓寫入，但是只有負偏壓可以抹除，但Ta/TaOX/ITO元件只能以正偏壓寫入負偏壓抹除。ZnO NPs-based元件也屬於雙極性電阻轉換行為，但其寫入/抹除的偏壓極性不同，Ta/ZnO NPs/ITO和Al/ZnO NPs/ITO元件都只能以“負偏壓寫入，正偏壓抹除”。ZnO NPs-based元件元件具有操作電壓小之特性，從高電阻態(HRS) 轉換成低電阻態 (LRS) 的臨界電壓(VSet)約為-0.7 V，而從LRS轉換成HRS的臨界電壓(VReset) 約為+0.2 V；相較之下，TaOX-based元件的VSet和VReset均大於ZnO NPs-based元件，Ta/TaOX/Pt元件Ta/TaOX/ITO元件的VSet分別為4.85 V、1.52 V，而VReset約為-1.0 V。
藉由TaOX-based元件使用兩種下電極材料，ZnO NPs-based元件使用兩種上電極材料，獲得四組不同的電流-電壓特性曲線。透過分析元件的電流-電壓特性曲線以及XPS的結果，建立TaOX-based元件與ZnO NPs-based元件的電阻轉換機制，並推論出上電極與介電層的界面以及下電極與介電層的界面，在電阻轉換機中所扮演的重要角色。

In this study, we have prepared tantalum oxide (TaOX) thin films by reactive sputtering from tantalum (Ta) target on Pt/SiO2 and ITO/glass substrates, as well as zinc oxide nanoparticles (ZnO NPs) thin films by spin-coating with the ZnO NPs synthesized via solution process on ITO/glass substrate. In order to investigate the influences of top electrode and bottom electrode materials on the resistive switching behavior, we also deposited tantalum by reactive sputtering and aluminum by thermal evaporation as top electrodes to fabricate Ta/TaOX/Pt, Ta/TaOX/ITO, Ta/ZnO NPs/ITO, and Al/ZnO NPs/ITO resistive random access memory devices.We first analyze the I-V characteristics to construct the resistive switching mechanism of TaOX-based devices and define the difference between Pt and ITO bottom electrode. Then, on the basis of the resistive switching mechanism of TaOX-based devices, we try to develop the resistive switching mechanism of ZnO NPs-based devices.
Regarding to the material characteristics and electrical properties, X-ray photoelectron spectroscopy (XPS) is used to analyze the interface between top electrode and ZnO NPs film to acquire the chemical bonding status of the interface. The thickness of thin films in resistive random access memory devices and the crystallinity of the ZnO NPs film are examined by transmission electron microscopy. Finally, the electrical properties of resistive random access memory devices are measured by precision semiconductor parameter analyzer (Agilent 4156C).
XPS results suggest that the top electrode forms an oxide interlayer adjacent to the active layer. TEM images reveal that the solution-processed ZnO NPs film is composed of crystalline ZnO grains with random orientations, of which the grain size is around 3 to 5 nm.
The I-V measurement shows that TaOX-based devices basically perform the "positive bias set and negative bias reset" bipolar resistive switching behavior. However, Ta/TaOX/Pt device can be set by applying either positive or negative bias, but can only be reset by negative bias. In contrast, Ta/TaOX/ITO device can only be operated under the "positive bias set and negative bias reset" condition.
ZnO NPs-based devices also perform the bipolar resistive switching behavior but the switching polarity is different from that of TaOX-based devices. Both Ta/ZnO NPs/ITO and Al/ZnO NPs/ITO devices can work only under "negative bias set and positive bias reset" condition. ZnO NPs-based devices have the advantage of low operation voltages, which is about -0.7 V from HRS to LRS (VSet) and about 0.2 V from LRS to HRS (VReset). However, the operation voltages of TaOX-based devices are much larger in comparison to that of ZnO NPs-based devices. The VSet of Ta/TaOX/Pt and Ta/TaOX/ITO are 4.85 V and 1.52 V, respectively; the VReset of both TaOX-based devices are about -1.0 V.
We obtain four groups of I-V characteristic curves under different operation polarities by using two bottom electrodes in TaOX-based devices and using two top electrodes in ZnO NPs-based devices. The individual resistive switching mechanisms in TaOX-based devices and ZnO NPs-based devices are proposed based on the inter-correlation of I-V characteristic curves and XPS results. Accordingly, we have acquired that the interfaces between the top electrodes, as well as the bottom electrodes, and active layer play important roles in the resistive switching mechanism.

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