自組裝雙親性嵌段共聚高分子摻混奈米碳球之形態及記憶體元件應用

Morphology and Memory Device Applications of Self-assembly Amphiphilic Block Copolymer:PCBM Composites

陳昭丞(Jhao-Cheng Chen)

指導教授 ： 陳文章

國立臺灣大學/工學院/化學工程學研究所/碩士(2011年)

https://doi.org/10.6342/NTU.2011.02859

摘要

高分子材料應用於記憶體元件為近年來之新興領域，相較於傳統元件因其本質特型不同而引起廣泛的研究及討論；自組裝嵌段共聚高分子摻混功能性奈米粒子所形成之奈米複合材料，由於具有特殊的奈米結構及電性，因此在記憶體元件的應用上具有極佳的潛力。本論文的主要研究目標為 (1) 製備及鑑定具有特殊結構的高分子奈米複合材料 (2) 進行記憶體元件的製備與測試並探討高分子奈米複合材料結構、形態對於記憶體元件性質之影響。
在本論文的第一部份(第二章)，為探討不同嵌段比之雙親性嵌段共聚高分子PS-b-P4VP ( f PS =0.70 (L1) 與0.26 (L2)) 摻混PCBM並進行溶液退火，所產生之自組裝奈米複合膜與其型態之鑑定。經由吸收光譜圖圖譜結果顯示，高分子嵌段P4VP會與PCBM產生弱巨分子作用力，藉此作用力可將PCBM分子分散於P4VP區塊中。因此，透過軟嵌段P4VP與PCBM分子之間的作用力以及雙親性嵌段共聚高分子之自組裝能力，而形成具有特殊電性之規則奈米結構。對於f PS =0.70之L1系統，複合膜經由氯仿飽和蒸氣退火而成功誘導出垂直排列之奈米結構，其中PCBM分子垂直分散於柱狀之P4VP區塊；對於f PS =0.26之L2系統，複合膜經由甲醇飽和蒸汽退火而誘導出水平排列之奈米結構，其中PCBM分子水平分散於P4VP區塊。這些奈米結構是藉由原子力顯微鏡、穿透式電子顯微鏡與小角度X光散射進行鑑定。
在本論文的第二部份(第三章)，即利用第一部份所製備之奈米複合膜製成記憶體元件，而所有元件皆製備成三明治堆疊結構(ITO/electroactive layer/Al)。若單純以PS-b-P4VP作為活性層，則元件只會呈現絕緣體性質而不具有雙穩態特性。對於L1複合膜系統，以含有5w% PCBM而形態為垂直排列之奈米結構做為記憶活性層，元件可表現出一次寫入與多次讀取(WORM)的記憶特性，且元件良率約90% 而窄分佈的門檻電壓約為-1.7伏特；然而，使用未經溶液退火的複合膜作為活性層，則元件良率會低於50%且門檻電壓會呈現寬廣的分佈。當活性層所含的PCBM濃度為10wt%時，則不論複合膜是否經過溶液退火元件皆呈現高電流的半導體特性。對於L2複合膜系統，使用含有5w% PCBM而形態為水平排列之奈米結構做為記憶活性層，則元件可表現出揮發性的記憶體特性，且該元件的良率約80%而窄分佈的門檻電壓約為-2.7伏特；然而，使用未經溶液退火的複合膜作為活性層，則元件的良率會低於25%且門檻電壓會呈現不規則的擾動。當活性層所含的PCBM濃度為10wt%時，則不論複合膜是否經過溶液退火元件皆呈現高電流的半導體特性。含有5%PCBM的複合膜經由溶液退火而誘導出特殊奈米結構(垂直及水平排列之形態)，其元件的電流開/關比值約為106~107左右；在一萬秒的維持時間測試中也都表現出優良的穩定性。此類奈米複合材料之雙穩態特性的元件物理機制受載子捕捉與空間電荷極限電流理論影響。本研究建立高分子奈米複合材料之形態與元件電性之關係，而本論文使用之具有特殊形態奈米複合膜在記憶體元件上之應用極具發展潛力。

關鍵字

自組裝 ； 嵌段共聚高分子 ； 奈米碳球 ； 形態學 ； 記憶體

並列摘要

As an emerging area in organic electronics, polymer memories have become an active research topic in recent years since they are likely to be an alternative or supplementary technology to the conventional memory fabrication. Nanocomposite containing self-assemble block copolymer and functional nanoparticle is one of potential candidates for memory device application owing to benefits of the self-assembly of block copolymer and the electronic characteristic of nanoparticle. Thus, this thesis mainly focuses on the fabrications, characterizations and morphologies of nanocomposites combined with their applications on memory device.
In the first part of this thesis (Chapter 2), the morphology, optical and electrochemical properties of poly (styrene-block-4-vinylpyridine) (PS-b-P4VP): [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) composite thin films are reported. Two PS-b-P4VP copolymers with different volume fraction (f PS =0.70 (L1) and 0.26 (L2)) are employed to blend with PCBM. The optical absorption results indicate that the formation of weak supramolecular interaction between the P4VP block and the PCBM makes the free PCBM molecule preferentially accumulate within the P4VP domains. Thus, the utilization of a P4VP block demonstrates a way to form electronic domains containing PCBM within block copolymer self-assembled nanostructures. Furthermore, morphologies based on PS-b-P4VP:PCBM composite thin films are identified via AFM topography, TEM micrograph and Small Angle X-ray Scattering (SAXS), which demonstrate that two specifically self-organized nanostructures based on different volume fraction of PS-b-P4VP, perpendicularly cylindrical array (L1, where PCBM molecules disperse in the cylindrical cores normally) and horizontal cylindrical array (L2, in which PCBM molecules disperse in the cylindrical corona horizontally), were successfully fabricated via solvent annealing.
In the second part of this thesis (Chapter 3), nanocomposite thin films based on PS-b-P4VP:PCBM with and without solvent annealing are used to evaluate the electronic memory device applications. All the memory devices are fabricated in the same configuration: ITO/electroactive layer/Al. No matter what the morphology is, the device is merely an insulator without bistable characteristic if the electroactive layer is a pure polymer film. For L1 composite system, electroactive layer containing 5wt% PCBM with perpendicularly cylindrical array via solvent annealing shows nonvolatile switching current-voltage (I-V) characteristics, a write-once read-many times memory (WORM), whose yield is about 90% and switch-on threshold voltage is located around -1.7 V with a narrow distribution. However, electroactive layer containing 5wt% PCBM but without solvent annealing reveals a low yield (<50%) and wide distribution of threshold voltage. The electroactive layers containing 10wt% PCBM with and without solvent annealing exhibit the characteristic of semiconductor. For L2 composite system, electroactive layer containing 5wt% PCBM with horizontally cylindrical array via solvent annealing displays a volatile static random access memory (SRAM) behavior, whose yield is about 80% and threshold voltage is located around -2.7 V with a narrow distribution. Nevertheless, electroactive layer containing 5wt% PCBM but without solvent annealing only reveals a low yield (< 25%) and lager variation of threshold voltage. The electroactive layers containing 10wt% PCBM with and without solvent annealing also exhibit as semiconductors. Both the memory devices containing 5wt% PCBM with specific morphologies, perpendicularly cylindrical array and horizontally cylindrical array, exhibit high on/off current ratios of 106 ~ 107 and long retention time of 104 second. The mechanism of the switching behaviors is based on electron-trapping with space charge limited current (SCLC) theory. The present study suggests the self-assembly nanocomposites with specific nanostructures have potential application on memory devices. The relationship between the morphologies, electronic properties and device performance were also established in this study.

並列關鍵字

Self-assembly ； block copolymer ； PCBM ； Morphology ； Memory

參考文獻

2. Li, C. P.; Wu, C. H.; Wei, K. H.; Sheu, J. T.; Huang, J. Y.; Jeng, U. S.; Liang, K. S., Adv. Funct. Mater. 2007, 17, 2283.

5. Lodge, T. P., Macromol. Chem. Phys. 2003, 204, 265.

6. Groot, R. D.; Madden, T. J., J. Chem. Phys. 1998, 108, 8713.

7. Bucknall, D. G.; Anderson, H. L., Science 2003, 302, 1904.

12. Gong, Y. M.; Hu, Z. J.; Chen, Y. Z.; Huang, H. Y.; He, T. B., Langmuir 2005, 21, 11870.