電活性高分子系統在電晶體式記憶體的應用

Abstract

近年來有機記憶元件由於具有可撓曲、尺寸與材料結構多樣化等優勢，受到廣泛關注。一個典型的記憶體元件結構為在電晶體元件的半導體層和介電層中加入一額外的電荷儲存層。然而，對於電荷儲存層結構對記憶體的影響尚未有系統的研究。在本論文中利用n型半導體奈米線製備成非揮發電晶體式的記憶體元件，並進一步探討其幾何結構對記憶體性質的影響。另一方面，也利用具有電子施體和受體的聚醯亞胺材料做為電荷儲存層，並探討因電荷轉移效應對記憶體性質的影響。此外，利用聚醯亞胺和二氧化鈦的複合物或是經由溶液製備成具有高介電常數的高分子和氧化石墨烯的複合物，將其製備成可在小電壓操作的記憶體元件。這些研究主題將於下段開始描述。 本文的第一部分(第二章)-自組裝的n型半導體奈米線對有機非揮發性電晶體式記憶體元件的影響-利用n型半導體材料(N,N’-bis(2-phenylethyl)-perylene- 3,4:9,10-tetracarboxylic diimide (BPE-PTCDI))製備成有機非揮發性電晶體式記憶體元件。尺寸較小的奈米線會引起較大的電場，導致元件有較大的記憶窗口。奈米線在矽基板上的記憶窗口可達到51V，比起薄膜形態的記憶窗口(~5V)有明顯的增加。此外，奈米線在較疏水的表面其記憶窗口可到達78V，開關電流比有2.1x104，且電荷可擁有長時間穩定的滯留時間。 本文的第二部分(第三章)-側鏈為不同重複單元噻吩共軛基團高分子於電晶體式記憶體元件應用-合成側鏈為一個或三個重複噻吩共軛基團高分子，PVT和PVTT，將其製備成電晶體式記憶體元件電荷儲存層。PVTT和PVT相比具有較大扭轉角度，進而阻礙了半導體層的排列，而導致較差的電荷遷移率。此外，PVTT有較高的最高佔據分子軌域，讓較多的電荷轉移至此電荷儲存層，而擁有較大的記憶體窗口。 本文的第三部分(第四章)- 含有噻吩(Thiophene)和硒酚(Selenophene)單元的電子施體/受體聚醯亞胺材料在電晶體式記憶體元件電荷儲存層的應用- n型半導體材料製備成電晶體式記憶體元件的主動層，並利用含有噻吩(Thiophene)和硒酚(Selenophene)單元的聚醯亞胺材料(PI(APSP-6FDA)和PI(APST-6FDA))做為電荷儲存層。其中，因PI(APSP-6FDA)有較高的最高佔據分子軌道和硒酚的重原子效應，讓較多的載子被注入並停留在此電荷儲存層中，因此以PI(APSP-6FDA)為電荷儲存層有較大的記憶窗口(81V)。 本文的第四部分(第五章)-具有高介電常數的電子施體/受體聚醯亞胺材料在電晶體式記憶體元件電和儲存層的應用-利用含有4,4′-diamino-4〃-cyano -triphenylamine (TPA-CN)單元的聚亞醯胺材料(PI(6FDA-TPA-CN), PI(DSDA- TPA-CN), and PI(BTDA-TPA-CN))作為電晶體式記憶體的電荷儲存層。由於PI(6FDA-TPA-CN)有較高的偶極矩和較大的扭轉角，導致較穩定的電荷遷移複合物(charge transfer complex) ，而讓PI(6FDA-TPA-CN)做為電荷儲存層時擁有較大的電荷記憶窗口到達84V。 本文的第五部分(第六章)- 聚醯亞胺和二氧化鈦的複合材料在電晶體式記憶體元件電和儲存層的應用-利用PI(F-ODPA)和PI(3S-ODPA) 聚醯亞胺材料或聚醯亞胺和二氧化鈦形成的複合物做為記憶體的電荷儲存層。由於PI(F-ODPA)含有芴的共軛基團有利於電荷的儲存引起較大的記憶窗口(8.6V)，此外，隨著二氧化鈦含量的增加(高達20wt%)，較易引起電荷遷移其記憶窗口也有增加的趨勢。 本文的第六部分(第七章) –高介電常數的高分子和氧化石墨烯的複合物在撓曲式電晶體式記憶體元件的應用-利用簡易的溶液製備方式製備高分子聚甲基丙烯酸(PMAA)和氧化石墨烯(GO)的複合物，應用在可撓曲的記憶體元件。利用聚甲基丙烯酸和氧化石墨烯(GO)產生氫鍵，進而有效分散化石墨烯。此元件可在小電壓下操作且擁有很長的電荷停留時間，可承受應力反覆至少100個迴圈。 我們的研究顯示出奈米表面形態或具有電子施體/受體的結構對製備成一先進的電荷儲存元件的重要性。

Organic-based memory devices have received extensive scientific interest due to their advantages of flexibility, scalability, and material variety. A typical configuration of OFET memory devices is a conventional transistor with an additional charge storage layer ( named as the electret) between a semiconductor layer and dielectric layer. However, there is no systematic study on the above structure effects. In this thesis, we report the nonvolatile transistor memory device characteristics of n-type organic semiconducting nanowires, and reveal the geometry effects on memory characteristics. We further explored the effects of donor-acceptor charge transfer of polyimide electrets on the memory characteristics. In addition, high dielectric constant PI/TiO2 and polymer/graphene oxide (GO) composites as charge-storage dielectrics for the low-voltage nonvolatile memory devices were also investigated. The following summarize the important discovery of this thesis. 1. Self-Assembled Nanowires of Organic N-type Semiconductor for Nonvolatile Transistor Memory Devices (Chapter 2): Organic nonvolatile transistor-type memory devices using self-assembled nanowires of n-type semiconductor, N,N’-bis(2-phenylethyl)-perylene-3,4:9,10-tetracarboxylic diimide (BPE-PTCDI). The BPE-PTCDI nanowires with small diameters induced high electrical field and resulted in a large memory window (the shifting of the threshold voltage). The value of BPE-PTCDI nanowire based memory devices on the bare substrate could reach 51 V, which was significantly larger than that (~ 5 V) of thin film. The memory window was further enhanced to 78 V with the on/off ratio of 2.1x104 and the long retention time (104 s), using the hydrophobic surface. 2. Nonvolatile Organic Field-Effect Transistor Memory Devices Using Polymer Electrets with Different Thiophene Chain Lengths (Chapter 3): Synthesis of poly(5-hexyl-2-vinylthiophene) (PVT) and poly(5-Hexyl-5”-vinyl-2,2’:5,2” -terthiophene) (PVTT) as charge storage electrets for memory devices using BPE-PTCDI. The mobility of the memory device using PVTT electret was significantly smaller compared with that of PVT because its large torsional angle hindered the molecular packing of BPE-PTCDI. Besides, the highest HOMO energy level of PVTT facilitated the charges transfer from BPE-PTCDI and led to the largest memory window of 81V. 3. Thiophene and Selenophene Donor-Acceptor Polyimides as Polymer Electrets for Nonvolatile Transistor Memory Devices (Chapter 4): Nonvolatile memory characteristics of n-type BPE-PTCDI-based organic field-effect transistors (OFET) using the polyimide electrets of poly[2,5-bis(4-aminophenylenesulfanyl) -selenophene-hexafluoroisopropylidenediphthalimide] (PI(APSP-6FDA)), poly[2,5-bis(4-aminophenylenesulfanyl)-thiophene-hexafluoroisopropylidene -diphthalimide] (PI(APST-6FDA)), and poly (4,4’-oxydianiline-4,4’ -hexafluoroisopropylidenediphthalic anhydride) (PI(ODA-6FDA)). The device with PI(APSP-6FDA) exhibited the largest memory window because the highest HOMO energy level and heavy-atom effect facilitated the charges transferring from BPE-PTCDI and trapping in the PI electret. 4. Nonvolatile Transistor Memory Devices using High Dielectric Constant Polyimides Electrets (Chapter 5): The memory characteristics of pentacene-based OFET using polyimide electrets of PI(6FDA-TPA-CN), PI(DSDA-TPA-CN), and PI(BTDA-TPA-CN), consisted of electron-donating 4,4′-diamino-4〃 -cyanotriphenylamine (TPA-CN) and different electron-accepting dianhydrides The higher dipole moment and larger torsion angle of PI(6FDA-TPA-CN) resulted in the more stable charge transfer complex and accompanied with the largest memory window of 84 V of the fabricated device. 5. Nonvolatile Transistor Memory Devices Based on High-k Electrets of Polyimide/TiO2 Hybrids (Chapter 6): Novel nonvolatile memory behaviors of BPE-PTCDI-based OFET using the new polyimides (PIs), (poly[9,9-bis(4-(4-amino-3-hydroxyphenoxy)phenyl)fluorene-oxydiphthalimide]) PI(F-ODPA) and (poly[4,4’-bis(4-amino-3-hydroxyphenylthio)diphenyl sulfide -oxydiphthalimide]) PI(3S-ODPA) and their PI/TiO2 hybrids as electrets were reported. The OFET memory device derived from PI(F-ODPA) with π-conjugated fluorene moiety exhibited larger memory window (8.6V), and could be further enhanced by introducing TiO2 (up to 20wt%) into the PIs. 6. High-k Polymer/Graphene Oxide Dielectrics for Low-Voltage Flexible Nonvolatile Transistor Memories (Chapter 7): Solution-processable nonvolatile transistor memories on flexible ITO-PEN substrate were demonstrated using the electrets of poly(methacrylic acid) (PMAA) and graphene oxide (PMAA-GO) composites. The hydrogen bonding interaction effectively dispersed GO sheets in the high-k PMAA matrix. Besides, the fabricated transistor memories have a low operation voltage, a large threshold voltage shift, a long retention ability of up to 104 s, and good stress endurance of at least 100 cycles. Our study revealed the significance of the nano-morphology and donor/acceptor structure of the electrets on the OFET memory characteristics for advanced data storage applications.