由界面電荷傳遞機制及分子奈米結構提升有機電晶體式記憶體元件特性

Enhancing the Electrical Characteristics of Organic Transistor-type Memory Devices through Interfacial Charge-Transfer Mechanism and Molecular Nanostructure

羅承慈(Chen-Tsyr Lo)

指導教授 ： 陳文章

國立臺灣大學/工學院/化學工程學研究所/博士(2016年)

https://doi.org/10.6342/NTU201600349

摘要

近年來有機記憶元件的研究成長快速，除了本身具有可撓曲、尺寸與材料結構多樣性等優勢之外，也因為兼具可溶液與連續式製程等優勢，其發展仍然持續受到關注。含有共軛機團的功能性高分子可以經由分子設計方法有系統的調控奈米結構及光電結構，是近來備受重視的電荷儲存材料之一。然而，目前對於這類材料應用在薄膜電晶體式儲存裝置中，其奈米結構與電荷儲存能力的關係尚未有足夠的探討。本文中首先利用共軛嵌段共聚高分子交聯製備具有核殼結構的奈米粒子並應用在薄膜電荷儲存層中，並進一步探討其分子設計與快閃式記憶體性質之間的關係。另一方面，側鍊中含有電子施體及受體的隨機共聚高分子可以有效提供電晶體式記憶體的操作範圍，並提供多層次快閃式的儲存容量。此外，為了和合成高分子系統比較，可以溶液法快速製備的超分子也被製備成具有相當耐久性及保存性的快閃式電荷儲存材料，提供未來相關領域的發展方向。這些研究主題將於下段開始描述。
本文的第一部分(第二章)- 共軛嵌段高分子交聯製備具有核殼結構的奈米粒子及其在有機非揮發性電晶體式記憶體元件電荷儲存層的應用-共軛嵌段高分子poly[poly(ethylene glycol)methylether methacrylate] -block-poly(2,5-dibromo-3-vinyl
thiophene) (poly(PEGMA)m-b-poly(DB3VT)n)雙親性嵌段高分子在特定的溶液條件下交聯成為具有核殼(core-shell)結構的奈米粒子，其外部殼層為高度水溶性的親水性poly(PEGMA)鏈段，內部核層為疏水性並且彼此交聯的噻吩(thiophene)或是施體受體共軛結構。經由分子設計可以藉由不同的嵌段比例製備不同尺寸的奈米粒子，並經由簡單的溶液法製備成有機電晶體式記憶體元件。研究中發現，交聯後的poly(PEGMA)77-b-poly(DB3VT)23奈米粒子具有最大尺寸的噻吩核狀結構，因此展現最佳的電洞儲存能力；另外，核層中同時具有施體受體基團的奈米粒子應用在有機電晶體式記憶體元件中，擁有雙極性的電子電洞儲存能力，展現38 V的記憶窗口、大於104秒的儲存耐久度、以及反覆讀寫至少100個迴圈。
本文的第二部分(第三章)-側鍊中含有電子施體/受體的隨機共聚高分子在有機非揮發性電晶體式記憶體元件電荷儲存層的應用及多層式儲存功能-側鍊中含有電子施體 9-(4-vinylphenyl)carbazole (VPK) 與電子受體 2-phenyl-5-(4-vinyl
phenyl)-1,3,4-oxadiazole (OXD)的隨機共聚高分子首次被應用在電晶體式記憶體元件中的薄膜電荷儲存層。對比具有同樣電子施體/受體比例的高分子摻合物，此共聚高分子特殊的結構能將側鍊中電子施體與受體之間的交互作用藉由主鏈的空間侷限下、形成適合電荷儲存及消除的薄膜奈米結構。本研究所製備的有機非揮發性電晶體式記憶體元件展現雙極性的電荷儲存能力，可以有效提升可供讀寫的操作範圍，即使在低至10 V仍可穩定讀寫，並且提供多層次快閃式的儲存容量。
本文的第三部分(第四章)-電荷轉移式超分子在有機非揮發性電晶體式記憶體元件電荷儲存層的應用-在溶液中利用電荷轉移 (charge-transfer) 快速及有效的製備超分子，並且將其應用在有機電晶體式記憶體元件中的電荷儲存層。本研究中分別將poly(4-vinylpyridine) (P4VP)與兩種不同的發色團(chromophores) 3-(dicyanomethylidene)indan-1-one (1CN-IN) 或 1,3-bis(dicyanomethylidene)indan (2CN-IN)形成超分子。兩種超分子系統之間因為化學結構的差異，製備超分子時擁有不同的電荷轉移效率。相較於1CN-IN，2CN-IN具有多一個電子受體基團(dicyanomethylene)能和P4VP作用，因此製備為薄膜電荷儲存層之後，單位面積中可以儲存較多的電子數量：利用P4VP(2CN-IN)0.30製備而成的元件展現最佳且穩定的快閃式元件效能：79 V的記憶窗口、大於107秒的穩定儲存耐久度、以及反覆讀寫至少100個迴圈。
我們的研究針對有機非揮發性電晶體式記憶體進行探討，並顯示分子設計與薄膜奈米結構對製備先進電荷儲存元件的重要性。

關鍵字

電晶體式記憶體 ； 高分子電荷儲存層 ； 奈米浮動閘極 ； 嵌段共聚高分子 ； 側鍊共軛高分子 ； 施體-受體 ； 超分子

並列摘要

Organic-field-effect-transistor (OFET) -type memory devices have been extensively studied due to their flexibility, scalability, and solution processability. Functional polymer containing semiconducting elements is considered as one of the most promising charge storage materials for organic field-effect transistors and organic-based memory devices, since it features a systematic route towards materials with novel architectures, functions, and physical properties. However, there is limited study on the correlations of the nanostructure and the electronic characteristic. In this thesis, we report the OFET memory devices using the dielectric layer of cross-linked core-shell block copolymers containing conjugating segments in the cores, and reveal the effect of both block composition and nanostructure on the memory characteristics. We further explored the random copolymers consisting of both pendant electron-donating and -withdrawing groups as charge storage layer in the OFET memory devices. In addition, for comparing with the synthetic polymer electrets, the solution-associated supramolecules are also applied in the OFET memory devices as charge storage dielectrics. The important discovery of this thesis was summarized in the follows.
1. Non-Volatile Field-Effect Transistor Memory Devices using Charge Storage Cross-Linked Core-Shell Nanoparticles as Polymer Electrets (Chapter 2): Solution processable cross-linked core-shell nanoparticles containing conjugated elements are firstly explored as charge storage materials for transistor-type (OFET) memories. These uniform nanoparticles containing cross-linked electron-donating or donor-acceptor cores presented efficient flash-type memory characteristics. The devices using donor-acceptor nanoparticles presented both electron- and hole-trapping abilities, along with the memory window of 38 V, the retention ability of over 10^4 s, and endurance of over 100 cycles.
2. Multilevel Non-Volatile Organic Transistor Memory Devices using Pendent Donor-Acceptor Random Copolymer Electrets (Chapter 3): Non-volatile transistor memories were fabricated using n-type semiconductor BPE-PTCDI and dielectric layer of non-conjugated random copolymers with pendant electron-donating 9-(4-vinylphenyl)carbazole (VPK) and electron-withdrawing 2-phenyl-5-(4-vinylphenyl)-1,3,4-oxadiazole (OXD) moieties. The pendent structure provided restricting regions with well-defined donor-acceptor interfaces, which is not happened in the case of PVPK/POXD polymer blend. The multilevel data storage and endurance characteristics obtained by applying different voltage pulses suggested that the devices using random copolymer P(VPKxOXDy) as electrets possessed ambipolar and controllable non-volatile flash-type memory behaviors even when the working voltage was as low as 10 V.
3. High-Performance Non-Volatile Transistor Memory Devices using Charge-Transfer Supramolecular Electrets (Chapter 4): Non-volatile OFET memory devices using charge-transfer (CT) supramolecules of poly(4-vinylpyridine) (P4VP) with two different chromophores, 3-(dicyanomethylidene)indan-1-one (1CN-IN) or 1,3-bis(dicyanomethylidene)indan (2CN-IN) were demonstrated. The intermolecular CT interaction effectively introduced the chromophores as charge trapping sites into the P4VP matrix, leading to a controllable flash-type memory behavior. The 2CN-IN with one more electron-withdrawing dicyanomethylene group, compared to 1CN-IN, provided a better electron-trapping ability and thus obtained a larger memory window. The device based on P4VP(2CN-IN)0.30 electret exhibited the largest memory window of 79 V with the excellent retention ability of up to 10^7 s and endurance of over 100 cycles.
Our study demonstrated the significance of interfacial charge-transfer mechanism and molecular nanostructure on the charge transporting and memory characteristics for novel organic electronic devices.

並列關鍵字

transistor-type memory ； block copolymer ； polymer electrets ； nano floating gate ； donor-acceptor ； random copolymer ； supramolecule

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