電子施體/受體高分子系統於記憶體元件之應用

Donor-Acceptor Polymer Systems for Electrical Memory Device Applications

余安棣(An-Dih Yu)

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(2013年)

https://doi.org/10.6342/NTU.2013.00257

摘要

近年來有機記憶元件由於具有可撓曲與材料結構多樣化等優勢，受到廣泛關注，鑑於傳統多晶矽光蝕刻製程已迫近其物理極限，可精準合成的有機/高分子材料被認為非常有機會反向由分子層級來設計未來電子元件。然而，分子結構與其可應用於記憶元件之電性關係尚需要更大量的研究方能釐清。 於此論文中使用了多種材料來測試記憶元件應用的可行性並藉此來增廣我們對電阻式及電晶體式記憶體材料結構、組成與元件表現上的認知。此外，可撓曲之記憶元件與其穩定性測試亦被開發，期對新世代電子元件之開發能有所裨益。
本論文之第一部分研究目標針對含有三苯胺−芘(pyrene)之電子施體-受體聚醯亞胺進行系統性研究，四組材料于合成中分別接上不等量的芘，藉以觀察分子結構調控對電阻式記憶體特性的影響。研究結果顯示，隨著含芘量由無到百分之百，元件之記憶特性由揮發式隨機存取記憶體轉變為僅可寫入一次之非揮發性記憶體，其主要影響機制推估為芘於電子施體部分造成的影響。電子施體/受體聚醯亞胺材料被廣泛報道在電場影響下會造成部分電荷轉移(charge transfer)現象，直接影響材料導電度。然而當外加電場移除，此電荷移轉現象將自然消失，造成記憶元件揮發特性。此研究加入具共軛平面的芘於電子施體處，成功使其滯留正電荷進而影響材料之揮發特性。此外，此系列以聚醯亞胺材料製備之元件為可撓曲式，撓曲檢驗的結果展現了良好之機械性質與穩定之記憶特性。
本論文第二部分藉混摻方法調控電子施體-受體聚醯亞胺材料之電阻式記憶特性，多環芳烴分子: 暈苯 (coronene) 與新穎苝衍生物N,N-bis[4-(2-octyldodecyloxy) phenyl]-3,4,9,10-perylenetetracarboxylic diimide (PDI-DO) 分別扮演電子施體與受體，混摻入施體-受體聚醯亞胺材料。研究顯示此類大型的共軛多環芳烴分子有助穩定電荷轉移(charge transfer)現象並改變材料之揮發特性，兩個不同特性之添加物對記憶行為的改變僅於驅動電壓與添加量上有些許不同，根據能階上的研究推測，新穎PDI-DO分子強烈的拉電子能力與電子親和力勝於暈苯，僅少量添加便可影響元件特性，所需之驅動電壓也較低。同時本系列之研究亦囊括元件撓曲性測試，添加物良好的分散性使元件在撓曲的情況下仍能展現良好的記憶特性不受影響。簡易的製備方法與諸多優點提供發展未來記憶元件的契機。
本論文第三部分藉超分子作用力(supramolecular interaction)分散氧化石墨烯(graphene oxide)於嵌段高分子中，均勻分散之奈米複合物以最簡單的點式三明治結構來進行其電阻式記憶特性量測，其電性展現了僅可寫入一次之非揮發性記憶體特性。此記憶元件於−1 V讀取下具有一個很高的電流開/關比值達10的五次方並於10的四次方秒滯留測試下無觀察到顯著變小。此元件可能的操作機制可理解為電場影響下複合物層中氧化石墨烯造成的電荷捕獲。當捕獲量達飽和時顯著提升元件的導電度。
本論文第四部分製備一系列以三苯胺(TPA)及六氟二酐(6FDA)為主的電子施體/受體聚醯亞胺材料製備於n型半導體(BPE-PTCDI)為基礎的電晶體式記憶體中，作為高分子電荷儲存層(polymer electret)。此系列研究中，於三苯胺處接上芘(pyrene)之聚醯亞胺高分子(PI(APAP-6FDA))在相同操作條件下具有最大的記憶窗口(memory window)與最佳的記憶保存能力(retention ability)。由於引入具有較大共軛平面之芘於電子施體(TPA)部分，較佳的電荷遷移能力成功地保存了機能性聚醯亞胺高分子內場效所致之電荷遷移複合物(charge transfer complex)，亦同時增強了此高分子之電荷儲存能力，使此高分子成為一良好的電晶體式記憶體材料。此外，以此材料製備之快閃記憶元件通過了100次寫入-讀取-抹除-讀取(WRER)記憶穩定性測試。此系列之研究成果提出一新式概念，以電子施體/受體聚醯亞胺高分子製備高穩定性有機電晶體式記憶體。
本論文第五部分亦將一系列三支聚醯亞胺材料製備於n型半導體(BPE-PTCDI)為基礎的電晶體式記憶體中，作為高分子電荷儲存層。此三支高分子具相同之電子施體二苯硫醚(diphenyl thioether)，分別連接上不具拉電子能力的丁二醯亞胺(succinimide)，電子受體之臨苯二甲醯亞胺(phthalimide)以及更強電子受體之二臨苯二甲醯亞胺(biphthalimide)。研究結果指出，不具有電子受體之高分子(PITE(BMI-BMMD))製備之電晶體式記憶體展現出僅可寫入一次之記憶體(WORM-type memory)，然而後兩支兼具電子施體與受體之高分子所製備之電晶體式記憶體則由於適當能階及電荷遷移複合物(CT complex)的產生而展現出非揮發式快閃式記憶體特性。本研究並更進一步將具有較高硫含量(即具有較高介電能力)之PITE(BMI-BMMD)高分子塗布於可撓曲之導電基板上，製備為可撓曲式電晶體式記憶體，並成功開發此記憶體可多層次寫入之“寫入-多次-讀取-多次”(WMRM)式記憶體，此元件並具備良好之撓曲穩定性，即使將元件撓曲至曲率半徑5厘米之程度，仍能維持其功能。於記憶保存能力(retention time)的測試上亦能維持超過10的五次方秒以上的良好程度，此多層寫入之可撓曲式記憶體將有助於發展未來高密度資料儲存元件的開發。

關鍵字

電阻式記憶體 ； 電晶體式記憶體 ； 高分子複合物 ； 施體-受體聚醯亞胺 ； 可撓曲記憶體

並列摘要

Organic-based memory devices have received extensive scientific interest due to their advantages of flexibility, scalability, and material variety. However, the relationships between molecular structures, donor/acceptor compositions and electrical memory characteristics have not been fully explored yet. In this thesis, several donor/acceptor polymeric systems were explored for the understanding of structural or composition effects on the electrical characteristics of resistor-type and transistor-type memory devices. Additionally, the stability of the flexible memory devices was also examined in both memory types for the development of next-generation electronics.
In the first three parts of this thesis, materials for resistor-type memory application were investigated. In chapter 2, triphenylamine–pyrene containing donor–acceptor (D-A) polyimides (PIs) on flexible poly(ethylene naphthalate) (PEN)/Al/PIs/Al cross-point devices were developed, which showed the memory characteristics changing from volatile to nonvolatile via the relative copolymer ratio. The PIs were prepared from the diamines AMTPA or pyrene-contained APAP and the dianhydride 6FDA, with relative AMTPA/APAP molar compositions of 100/0, 95/5, 90/10 and 0/100. As the APAP content increased, the memory device characteristics changed from volatile to nonvolatile behavior of flash and write once read many (WORM), since the pyrene moiety could stabilize the radical cation of the APAP moieties. In chapter 3, the PIs blended films were prepared from different compositions of PI(AMTPA-6FDA) and polycyclic aromatic compounds (p-type coronene or n-type PDI-DO). The additives of large π-conjugated polycyclic compounds stabilized the charge transfer complex induced by the applied electric field. Thus, the memory device characteristic changed from the volatile to nonvolatile behavior of flash and WORM as the additive contents increased in both blend systems. Due to the stronger accepting ability and higher electron affinity of PDI-DO than those of coronene, the PI(AMTPA):PDI-DO blend based memory devices showed a smaller threshold voltage and changed the memory behavior in a smaller additive content. Additionally, the endurance and bending cyclic measurements confirmed that the above flexible PI memory devices exhibited excellent reliability and mechanical stability. In chapter 4, bistable resistive switching characteristics collected from the nanocomposites of block copolymers (BCP) and graphene oxide (GO). A well-dispersed composite was obtained through a simple process of blending that utilizing supramolecular interaction between BCP and GO. Nonvolatile WORM memory characteristics were observed from the BCP:GO-based device. The composite could serve as charge storage material and effectively enhance the conductivity under applied bias.
In the last two parts of this thesis, polymer electrets for transistor-type memory were developed. In chapter 5, memory characteristics of n-type BPE-PTCDI-based OFET using a series of D-A polyimide electrets of PI(AMTPA-6FDA), PI(APAN-6FDA), PI(APAP-6FDA) were studied. Among the polymer electrets, the OFET memory device based on PI(APAP-6FDA) exhibited the largest memory window and the best charge retention ability due to the introduction of polycyclic arene pyrene into the electron donating moiety. With the excellent carrier delocalization, pyrene successfully enhanced the charge storage ability and sustained the CT complex for high performance nonvolatile OFET memories with electrets of D-A polyimide system. In chapter 6, a series of polyimides (PITE(BMI-BMMD), PI(APS-ODPA), and PI(APS-BPA)) were prepared for better understanding the function of CT complex in polymer electret for OFET memory. The memory characteristic changed from the WORM behavior (PITE(BMI-BMMD)) to flash (PI(APS-ODPA) and PI(APS-BPA)), due to the energetic relationships and charge transfer complex. Besides, BPE-PTCDI transistor memory devices fabricated on flexible PET substrates exhibited multilevel data storage (WMRM) characteristics since the dielectric capacity was enhanced by its high sulfur-content of PITE(BMI-BMMD). Such flexible WMRM devices could have potential applications for the next generation high-density data storage components.

並列關鍵字

Resistor-type memory ； OFET memory ； polymer composites ； donor-acceptor polyimides ； flexible memories

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