本篇論文的主題主要圍繞在電阻式記憶體(RRAM)的製作與探討，並且以尖晶石結構(spinel)的氧化鎂鎵(MgGa2O4)作為電阻切換層的材料。論文的前半部分主要透過改變氧化鎂鎵的濺鍍製程條件以及沉積五種不同上電極(鋁、鈦、鉑金、鎳、銀)的方式，探討對於基於氧化鎂鎵電阻式記憶體的影響。對於不同製程條件的氧化鎂鎵薄膜，透過X射線光電子能譜、能量色散X射線能譜、X射線繞射光譜、選區電子繞射圖、原子力顯微鏡去探討薄膜的元素組成、晶格結構、表面粗糙度。對於主要以氧空缺作為燈絲(filament)的鋁電極之電阻式記憶體。若氧化鎂鎵之製程中未摻入氧氣，會由於缺乏氧空缺而不具備電阻切換特性，鈦、鉑金雖然有電阻切換特性，但在可靠度方面表現極差。對於主要以金屬原子為燈絲組成成分的電阻式記憶體元件則在3種氧氬比 [O2/(Ar+O2)] 條件下皆具備電阻切換特性。將可靠度、操作電壓與變異性三種參數作為考量，不同電阻切換層的製程條件與不同種類的上電極，會讓電阻式記憶體個別對應到自己的優缺點。同時我們也對電阻式記憶體做記憶保存測試的量測，以氧氬比為20%的氧化鎂鎵做為電阻切換層，對應到五種不同上電極的電阻式記憶體，發現除了鉑金上電極的電阻式記憶體外，在10,000秒的測試下都能有效地保存當前的阻態。此外，透過電流電壓曲線的擬合，五種上電極的電阻式記憶體之高低阻態下，有不同的電流傳導機制。
論文的後半部則是基於前面的實驗結果作為考量，去探討三種不同方式去改善電阻切換特性。第一個實驗是以鋁電極的電阻式記憶體為架構，對於作為電阻切換層的氧化鎂鎵薄膜通以不同的熱退火溫度的處理，具有超過7000次的切換次數與降低操作電壓等優點。並透過晶體結構、元素組成以及表面粗糙度之材料分析方式，推斷元素組成比的改變為主要的原因。第二個部分則是以以鋁上電極的架構，在上電極與電阻切換層之間插入一層緩衝層(buffer layer)，金屬則選擇鈦或銀，厚度控制在5或10奈米。插入鈦的緩衝層能夠有效抑制離群值的分佈，越厚的鈦緩衝層能夠更有效地改善記憶體的變異性並維持良好的穩定度。銀緩衝層的插入則有效提升元件穩定度，分別讓記憶體可以超過3000與6000多次的切換週期。與單一的鋁上電極之RRAM相比，平均的導通電壓(VSET)縮減為2.10伏特。最後則是以鈦電極作為架構，並沉積惰性金屬(Pt)做為帽層(capping layer)，展現出集中的高電阻態(HRS)分佈與約104的開關比(ON/OFF ratio)。同時藉由改變電阻切換層的厚度，可以發現越薄的電阻切換層在低操作電壓與高電阻態有低變異量等優勢，越厚的元件則是在可靠度與開關比有較佳的表現，彼此間存在權衡(tradeoff)。

This thesis focuses on the fabrication and investigation of resistive memory (RRAM) and the MgGa2O4 is served as a resistive switching layer material. The first half of this thesis focuses on investigating the effects on the MgGa2O4 based RRAM by varying the fabrication conditions and depositing five different electrodes (aluminum, titanium, platinum, nickel, and silver). The elemental composition, crystal structure and surface roughness of the MgGa2O4 thin films are analyzed by X-ray photoelectron spectroscopy (XPS), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), selected area electron diffraction (SAED), and atomic force microscopy (AFM). For the RRAM with aluminum electrodes, the composition of filament are mainly oxygen vacancies. The RRAMs will not show resistive switching (RS) characteristics if the oxygen gas is not incorporated during the MgGa2O4 deposition owing to the deficiency of defects. Although RRAM with Ti and Pt electrode have RS behavior, they have bad performance in terms of reliability. For ECM based RRAMs, the filaments, which are mainly composed of metal atoms, have RS properties under three oxygen to argon ratios [O2/(Ar+O2)].
Through the consideration of reliability, operating voltage and variability, different RRAMs with different fabrication conditions of RS layer and different types of top electrodes have their individual merits and disadvantages. Meanwhile, we also conduct data retention test to verify the non-volatile properties of RRAM, where the RS layers are composed 20% oxygen partial pressure MgGa2O4. All the RRAMs pass the 10,000 seconds test except for the one with platinum electrode. In addition, the RRAMs with five different electrodes have different current conduction mechanisms in their high and low resistance states by I-V curve fitting.
In the second half of the thesis, based on the previous experimental results, three techniques are used to improve the resistive switching characteristics. In the first experiment, the RRAM with aluminum electrode is used as the framework. The MgGa2O4 thin films been used as RS layer are treated with different thermal annealing temperatures. The optimized RRAM achieves more than 7,000 switching cycles and lowers the operating voltage. By the material analysis of crystal structure, elemental composition, and surface roughness. We infer that the change of elemental composition is the main reason.
In the second experiment, a buffer layer is inserted between the top electrode and the RS layer in the structure of aluminum top electrode RRAM. The choice of metal is titanium or silver, and the thickness is controlled to be 5 or 10 nm. Inserting a buffer layer of titanium can effectively suppress the distribution of outliers. The thicker buffer layer can further effectively improve RRAM’s variability and maintain good reliability. The insertion of a silver buffer layer effectively improves RRAM reliability, allowing the memory to switch more than 3000 and 6000 times, respectively. The average of SET voltage (VSET) is reduced to 2.10 V compared to single Al top electrode RRAM.
Finally, the titanium electrodes RRAMs are used as the structure, and inert metal (Pt) is deposited as the capping layer. The results show a concentrated distribution of high resistance states (HRS) and favorable ON/OFF ratio about 104. By varying the thickness of the RS layer, the thinner RS layer, a lower programming voltage and more concentrated distribution of HRS are obtained. For the thicker RS layer, a better cycling endurance and a higher ON/OFF ratio are generally shown, implying the tradeoff between them.

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