新穎聚醯亞胺高分子系統於有機場效電晶體型記憶體元件之應用

Novel Polyimides Systems for Organic Field-effect Transistor (OFET) Memory Device Applications

董磊(Lei Dong)

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(2014年)

https://doi.org/10.6342/NTU.2014.00209

摘要

與傳統矽技術相比, 有機記憶體器件由於具有可撓曲性, 溶液製程性, 廉價, 材質多樣性等優點而備受研究關注。同時，聚醯亞胺由於具有良好熱穩定性，化學穩定性和機械強度而被認為是最適合的記憶體候選材料之一。然而，聚醯亞胺之分子結構與相應的電記憶特性間的關係尚需要更多研究方能厘清。於此本論文中相繼研究探討了純受體與受體/施體聚醯亞胺高分子體系，以期對分子結構效應在電晶體式記憶體元件電性質上的影響有更深層次的認知。
在本論文第二章中，研究目標針對基於p型並五苯的非揮發性場效電晶體式記憶體元件，以新穎半共軛聚醯亞胺為儲存電荷的高分子介電層。使用的聚醯亞胺包括含有不同電子受體的二酐系列，如PI(BPDA-DAP), PI(PMDA-DAP), PI(ODPA-DAP), 以及含有不同脂肪族間隔體系統的PI(PMDA-DAH), PI(PMDA-DAD)。基於PI(BPDA-DAP)介電層的元件展現出最大的記憶儲存空間（memory window）,這是因為PI(BPDA-DAP)的分子共軛程度最大，進而導致其最低的LUMO能級。除此之外，從PI(PMDA-DAP) 到PI(PMDA-DAH)，再到PI(PMDA-DAD)，增加的間隔體長度導致記憶特性由flash到WORM型之漸變，與此同時存儲空間隨之下降。此研究表明在半共軛的聚醯亞胺高分子介電層系統中，電晶體式記憶體的記憶特性和電荷遷移等性質可籍由電子受體和間隔體的選擇而實現有效調控。
本論文第三章製備一系列以二氨基苯芴（BAPF）為電子施體的聚醯亞胺/聚醯胺高分子，並將其應用於基於p型並五苯的非揮發性場效電晶體式記憶體元件的介電層材料。合成的三種高分子除了相同的電子施體，分別含有電中性的己二酸（AC），拉電子的二苯醚四甲酸二酐(ODPA)和六氟二酐(6FDA)。相應元件之記憶特性則由EORM變為semi-flash，再變為flash。這種轉變主要源于分子能級和電荷遷移（charge transfer）之差異。基於PI(BAPF-6FDA)的元件記憶存儲空間最大，這是因為六氟單元造成的電荷分離效應強化了高分子電子捕獲之能力。與此類似，PI(BAPF-6FDA)的嚴重扭曲結構有利於穩定的電荷遷移複合物之形成，因而造成更多電子可被高分子俘獲。針對電荷遷移效應與電記憶特性間的關聯，此研究有提供一種思路：即可藉由材料的化學結構之調控而實現未來場效電晶體式記憶體不同電荷存儲能力的要求。

關鍵字

場效電晶體式記憶體 ； 高分子介電層 ； 受體 ； 施體-受體 ； 聚醯亞胺

並列摘要

Organic-based memory devices have received extensive research interest due to their advantages of flexibility, solution processability, low cost and materials variety compared to traditional inorganic silicon ones. Meanwhile, polyimide is mostly thought to be one of the best candidates for memory materials, concerning its good thermal stability, chemical resistance and outstanding mechanical strength. However, the relationships between the molecular structures of polyimides and corresponding electrical memory characteristics have not been fully explored yet. In this thesis, both single acceptor and donor/acceptor systems were explored for a better understanding of structural effects on the electrical characteristics of transistor-type memory devices.
In chapter 2, the new semi-conjugated polyimides as the charge-storage electrets for the p-type pentacene-based non-volatile field-effect transistor (OFET) memory devices, comprising different electron-accepting dianhydride moieties, PI(BPDA-DAP), PI(PMDA-DAP), and PI(ODPA-DAP), and varied aliphatic lengths, PI(PMDA-DAH) and PI(PMDA-DAD) were successfully developed. The device fabricated upon PI(BPDA-DAP) electret exhibited the largest memory window owing to its low-lying LUMO energy level resulting from the largest conjugation. Besides, the increment of aliphatic length, from PI(PMDA-DAP) to PI(PMDA-DAH) to PI(PMDA-DAD), led to a gradual switch from flash to WORM (write once read many times) type memory property, accompanied by the reduced memory window. This study demonstrated that the memory characteristics and charge mobility of the transistor memory could be effectively modulated through the adaptation of the electron accepting moiety and spacer moiety in the semi-conjugated polyimide based electrets.
In chapter 3, the nonvolatile memory characteristics of p-type pentacene-based organic field-effect transistor (OFET) using the synthesized polymer electrets PA(BAPF-AC), PI(BAPF-6FDA) and PI(BAPF-ODPA) were systematically studied. These three polymers contain identical electron-donating 9,9-Bis(4-aminophenyl)fluorene (BAPF) and different building blocks of neutral (hexanediamide (AC) ) and electron-accepting (aromatic hexafluoroisopropylidenediphthalimide (6FDA) and oxydiphthalimide (ODPA)), respectively. The OEFT memory characteristic of devices fabricated with these three polymers vary from the EORM (erase once and read many times) behavior (PA(BAPF-AC)) to semi-flash (PI(BAPF-ODPA)), and to flash (PI(BAPF-6FDA)), mainly due to the differences in energy levels and charge transfer effects. Furthermore, the memory device based on PI(BAPF-6FDA) exhibits the largest memory window, which is attributed to the strong electron-trapping facilitated by the induced charge separation effect from hexafluoropropane moiety. Similarly, the larger torsion angle of PI(BAPF-6FDA) results in the more stable charge transfer complex, leading to more electrons trapped. The present study provided an insight into the relationship between the charge transfer effect and the memory characteristic, and revealed the possible tuning strategies on the chemical structure of materials to achieve varied capabilities of storing charges for advanced OFET memory applications.

並列關鍵字

OFET memory ； polymer electret ； acceptor ； donor-acceptor ； polyimides

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