本論文針對二維材料(2D materials)於電阻式隨機存取記憶體（resistive random-access memory, RRAM）和平面互連(planar interconnect)中的應用進行了全面性的探索研究。具有凡得瓦(Van der Waals)原子級層狀結構的二維材料作為不同的工作機制被應用於RRAM堆疊層中，包含:電阻切換(resistive switching)、穿隧(tunneling)和阻擋(blocking)層，並透過實驗、量測和第一原理(ab initio)模擬計算，實現和研究不同的RRAM功能。接著，通過第一原理分析，進行鋸齒形石墨烯奈米緞帶（zigzag graphene nanoribbon, ZGNR）應用於超小尺度平面互連的可行性評估。

針對在RRAM堆疊層中使用二維材料作為電阻切換層之研究，分別對具絕緣特性的多層六方氮化硼(hexagonal boron nitride, hBN)和具半導體特性的單層二硫化鉬(molybdenum disulfide, MoS2)進行探討。通過嵌入刻意氧化的氧化鈦層，為多層hBN RRAM實現了有效的雙堆疊層調製，使其呈現了增強的電阻切換特性，包含:均勻的 I–V 分佈、可控的電阻狀態、改善的記憶體窗口耐久性和較低的重置電壓(Vreset);根據實驗和理論分析，有效的雙堆疊層調製為透過硼缺陷和氧缺陷之間巨大的形成能差異所達成。接著，使用密度泛函理論（density functional theory, DFT）和非平衡格林函數（non-quilibrium Green’s function, NEGF），針對僅具原子級厚度的單層MoS2 RRAM之電阻切換機制進行研究，通過對缺陷、界面和傳輸的全面性分析，提出了黃金陽離子於MoS2缺陷處還原形成導電絲的類導電橋機制(conductive-bridge)。

而為了進一步發揮二維材料的凡得瓦原子級層狀結構的優勢，特別設計了二維材料不直接參與電阻切換的RRAM堆疊層。極薄的無選擇器電阻式記憶體(selectorless RRAM)通過使用hBN作為RRAM堆疊層內的穿隧層取得實現，分別於1/2和1/3讀取偏壓方案(bias scheme)下展現了12和23的良好非線性值;並且受益於hBN原子級厚度的優勢，selectorless RRAM的雙堆疊層總厚度降低至6.3 nm。此外，透過使用單層MoS2作為電阻切換層和氧交換層之間的阻擋層，提出了罕見的揮發性電阻式記憶體(volatile RRAM)，並對所提出的volatile RRAM進行簡單的脈衝量測，成功模仿了短期可塑性(short-term plasticity, STP)和長期增強性(long-term potentiation, LTP)的大腦學習行為。

最後，對於平面互連研究，使用DFT和NEGF對特殊的非對稱ZGNR作為平面互連實現的可行性進行評估。非對稱ZGNR的類導體線性 I–V 特性，顯示出其在未來的超小尺寸技術節點中，應用於平面互連的巨大潛力。於分析的尺寸範圍內，非對稱ZGNR呈現了與結構長寬無相依性的I–V 特性，此現象可歸因於邊緣主導的非散射傳輸和彈道輸運(ballistic transport)。而針對實現全石墨烯平面互連網路，本研究提出了特殊的閃電形ZGNR結構。

This dissertation presents a comprehensive exploration of the application of two-dimensional (2D) materials to resistive random-access memory (RRAM) and planar interconnect. 2D materials with the unique Van der Waals atomic structure are applied to RRAM stacks to realize different working mechanisms, including switching, tunneling, and blocking layers. Different RRAM functions are realized and studied through experiments and ab initio studies. Then, the feasibility of zigzag graphene nanoribbons (ZGNRs) for interconnect applications at the ultrasmall scale is evaluated through ab initio analysis.

For 2D materials serving as the switching layer within RRAM stacks, the insulating multilayer hexagonal boron nitride (hBN) and semiconducting monolayer molybdenum disulfide (MoS2) are investigated. Effective bilayer modulation is achieved for multilayer-hBN RRAM through the insertion of an intentionally oxidized titanium oxide layer. The modulated multilayer-hBN RRAM exhibits enhanced switching characteristics with considerably uniform I–V distribution, controllable resistance states, good endurance for the memory window, and low Vreset. Experimental and theoretical analyses reveal that the effective modulation is supported by the considerable formation energy difference between boron and oxygen vacancies. Next, the switching mechanism of monolayer MoS2 RRAM with an atomic-level thickness of approximately 0.67 nm is studied using density functional theory (DFT) and nonequilibrium Green’s function (NEGF). Through the comprehensive analyses of the defects, interface, and transmission, a conductive bridge-like mechanism of Au cation reduction at the defect site of MoS2 is proposed.

To further utilize the Van der Waals atomic structure of 2D materials within an RRAM stack, RRAM stacks in which the 2D materials do not directly participate in the switching are designed. A thin selectorless RRAM with an hBN layer serving as the tunneling layer within the RRAM stack is presented with a good nonlinearity of 12 under the 1/2-bias scheme and 23 under 1/3-bias scheme. The advantage of the atomic-level thickness of hBN facilitates reduction of the total thickness to 6.3 nm. Further, a rare volatile RRAM is proposed with a monolayer MoS2 serving as a blocking layer between the switching and oxygen-exchange layers. Moreover, the successful imitation of brain-learning behaviors of both short-term plasticity (STP) and long-term potentiation (LTP) through simple pulse measurements on the proposed volatile RRAM is described.

Finally, for the planar interconnect research, the feasibility of special asymmetric ZGNRs being implemented as a planar interconnect is evaluated using DFT and NEGF. The conductor-like linear I–V characteristics of the asymmetric ZGNRs demonstrate high potential to be applied to planar interconnects in future ultrasmall technology nodes. Within the analyzed geometrical sizes, the asymmetric ZGNRs exhibit width- and length-insensitive I–V characteristics, which are attributable to the edge-dominant nonscattering transport and ballistic transport, respectively. Further, a special lightning-shaped structure is proposed for completing the all-ZGNR planar interconnect network.

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