二維半導體黑磷烯之穩定性研究與其在電晶體及新興記憶體的元件應用;Stabilization of 2D Semiconductor Black Phosphorus for the Application in the Field Effect Transistor and Emerging Memory

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Title:	二維半導體黑磷烯之穩定性研究與其在電晶體及新興記憶體的元件應用;Stabilization of 2D Semiconductor Black Phosphorus for the Application in the Field Effect Transistor and Emerging Memory
Authors:	謝玉玲;Hsieh, Yu-Ling
Contributors:	機械工程學系
Keywords:	二維材料;奈米元件;黑磷烯;Two-dimensional (2D) materials;Nanodevices;Black phosphorus
Date:	2021-12-21
Issue Date:	2022-07-14 01:09:15 (UTC+8)
Publisher:	國立中央大學
Abstract:	二維材料 (2D materials) 由於其許多優越特性，包括原子尺度下仍保有的高載子遷移率、可饒性與層狀結構，已成為未來光電元件的候選材料，具備微縮與異質整合優勢。儘管許多的二維材料被廣泛探索，例如過渡金屬二硫屬化物 (TMDC)，但每種材料皆有其獨特特性與適合的多元應用，例如：黑磷烯 (BP) 是具有隨厚度變化保有直接能隙的二維材料 (0.3 eV~2 eV)，以及應用於電晶體 (FET) 有高達一千以上的電洞載子遷移率，然而，黑磷有一般環境下不穩定的材料特性，大幅限制其奈米元件的實際應用。此論文的第一部分，提出利用氟化物可有效且大面積保護少層黑磷的方法，達到超過五個月的長時效穩定性，其中有兩個關鍵因素：(1) 緻密的保護層阻隔了大氣中的水氧分子。(2) 氟化黑磷穩定了材料表面並抑制氧化。此外，藉由進一步超音波震盪過程，可獲得選擇性的氟化黑磷，並將其製作成可靠的氟化黑磷電晶體，可於一般環境下操作達到超過一周的穩定性，相比於原始黑磷電晶體更提昇大於十倍的輸出電流。第二部分探討溶液處理的黑磷奈米片並將其應用於新興記憶體，有電阻式記憶體 (RRAM) 和類神經憶阻器 (Memristor)。電阻式記憶體具有非揮發性、102的高開/關比和長達1500秒的時效性。除此之外，亦介紹利用三聚氰胺輔助液相剝離 (LPE) 二維材料的新穎方法，可有效率地剝離出高結晶品質的黑磷奈米片，並且進一步利用超分子自組裝，直接獲取黑磷奈米片連同自組裝的超分子，接著將包含黑磷奈米片的超分子製作成憶阻器與單向選擇器 (Selector)。憶阻器通過施加掃描和脈衝電壓表現出類比電阻轉換行為，並呈現增強與抑制作用行為。以及研究不同結構建構的閾值開關 (TS) 選擇器，表現高非線性達30 mV/dec，和高達104的電阻開/關比與超過 4000 秒的長時效性。更重要的是，透過擬合數據和材料鑑定，探討電阻轉換的傳輸機制，其中黑磷奈米片提供了主動層中電荷載子的傳導路徑。;Two-dimensional (2D) materials are one of the promising candidates for future optoelectronics due to their superior properties, including high field-effect mobility within atomic thickness, flexibility, and layered structure, which have benefits of scaling and hetero-integration. Although lots of 2D semiconductors have been widely explored, such as transition metal dichalcogenide (TMDC), each 2D materials have unique characteristics and are readily applied to various applications; for instance, black phosphorus (BP) is one of the 2D materials having thickness-dependent direct bandgap (0.3 eV~2 eV) and high hole mobility up to 103 cm2V-1s-1 in BP-based field-effect transistor (FET), but suffering from its great weakness of instability, which limits its practical applications on nanodevices. In the first part of this study, an effective and scalable pathway was introduced to protect few-layer BP with the hydrophobic fluorinated compound, achieving long-term stability over five months because of two key factors: (1) A condensed passivation layer which isolates the oxygen and water molecules in air. (2) Fluorination of BP which stabilizes the surface of BP to inhibit oxidation. Moreover, the selectively fluorinated BP was demonstrated through further ultrasonication process, and then fabricated for fluorinated BP FET with the reliable transistor applications in ambient conditions, presenting stabilized properties over one week and the enhanced output current larger than ten times compared to the pristine BP FET. For the second part, the solution-processed BP nanosheets were explored and applied to the emerging memory, namely resistive random-access memory (RRAM) and memristor. The RRAM exhibited the non-volatile property and high on/off ratio of 102, as well as long retention time up to 1500 s. In addition, the novel method to exfoliate highly crystalline BP by melamine-assisted liquid-phase exfoliation (LPE) was introduced, and BP nanosheets together with supramolecular assembly could be directly extracted. Afterward, the incorporated BP nanosheets with supramolecules were integrated into the memristor and unidirectional selector, where the memristor presented analog resistive switching behaviors as well as potentiation and depression by applying both voltage sweeping and pulse. The threshold switching (TS) selector constructed by different structures was also investigated, displaying the nonlinearity of 30 mV/dec, high on/off resistance ratio up to 104, and long retention time over 4000 s. Most importantly, the transport mechanisms of the memories were unveiled through fitting data and material identification where BP nanosheets served as conducting paths for the transport of charge carriers in the active layer.
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