星狀高分子及其電子施體授體摻合物應用於非揮發有機電晶體式記憶體元件之電荷儲存層

Abstract

非揮發有機電晶體式記憶體由於具備可應用於可撓曲式電子元件的潛力，因此近來備受關注。記憶體元件儲存電荷的能力來自其”電荷儲存層”，故調控介電層的電荷儲存情況視為重要的課題。然而其他文獻對星狀介電致動高分子和其混摻材料應用於介電儲存層部分尚未有完整的探討，故於本研究去探討側鏈有芴系或三苯胺的共軛基團之星狀高分子與N型富勒烯(PCBM)的混摻材料在電晶體式記憶體元件之電氣性質。茲介紹如下： 於第二章，使用側鏈具有芴系基團的星狀高分子P(StFl)4混摻有機小分子富勒烯(PCBM)系統制備pentacene (p-type)為基礎的電晶體式記憶體並探討其電氣性質。由於其P(StFl)4 為低介電常數材料，故足以致使介面有較大的注入電場，並使元件具有記憶體可操作範圍的特質。該電子施體授體摻合物在電晶體型記憶體元件內可視為電子/電洞儲存點。從實驗證實該摻合物可有效轉移負電荷並提升元件主動層通道的載子遷移率(1.04 cm2V-1s-1)，記憶體的可操作範圍達35.59V，高低導電態的電流比高於106且性能操作可重覆讀寫循環操作可達一百次以上。另外，本研究也針對摻合物之介電儲存層所致的電荷轉移提出機制解釋。 於第三章，使用側鏈具有三苯胺基團的星狀高分子N(PTPMA)3混摻有機小分子富勒烯(PCBM)系統制備駢苯衍生物(BPE-PTCDI, n-type)為主動層的電晶體式記憶體並探討其電氣性質。由於三苯胺基團為電子施體，並具有穩定正電荷的性質，當將有機小分子富勒烯摻入介電層，記憶體元件會從原先的一次寫入-多次讀取(WROM)的記憶體性質轉變成快閃記憶體(flash type memory)。 經寫入(writing)及抹除(erasing)操作下，該元件呈現較大且可逆的記憶體操作範圍，顯示有機小分子富勒烯擁有儲存負電荷的能力之重要性，高低導電態亦能夠長時間維持(> 104 s)，並也能長時間重覆讀寫操作(> 140 cycles)。 由上述實驗結果證實，將星狀高分子及其電子施體授體摻合物應用於有機電晶體式記憶體之介電層不僅提升載子遷移率亦可展現高性能記憶體表現。

Organic nonvolatile transistor memory devices have attracted extensive research interest for flexible electronics in recent years. The function of charge storages arises from the chargeable gate dielectrics, an additional polymer dielectric (electret) layer between a semiconductor layer and gate contact. However, the electrets of star-branched electroactive polymers and their donor-acceptor blends have not been fully explored yet. In this thesis, we explore the transistor memory devices using electrets of star-branched polymers with pendent conjugated fluorene or triphenylamine group and their [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) blends, as described in the following: 1. Nonvolatile Transistor Memories of Pentacence Using the Electrets of Star-branched Styrene-Fluorene Polymers and Their PCBM Blends (chapter 2): Pentacene based nonvolatile transistor memory devices are studied using the electrets of hole-transporting four-armed star polymers of polystyrene para-substituted oligofluorenes (P(StFl)4) and their blends with electron-transporting PCBM. The low dielectric constant of P(StFl)4 leads to the greater loaded electric field and results in a memory window. The donor-acceptor blends of P(StFl)4 with [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) are used to realize the hole/electron storage in OFET memory devices. The hole mobility and memory windows are improved up to 1.04 cm2 V-1 s-1 and 35.59 V, respectively, using the electrets of the PCBM:P(StFl)4. The responding ON and OFF currents of the devices are maintained over 100 cycle with a high ON/OFF current ratio of 106. The charge storage mechanism is proposed for PCBM:P(StFl)4 based memories, including carrier trapping and tunneling effect under a gate electric field. 2. Nonvolatile Organic Transistor Memory Devices Using Electrets of Star-Shaped poly[4-(diphenylamino)benzyl methacrylate]/PCBM Blends(chapter 3): The organic nonvolatile transistor memory devices of the n-type semiconductor, N,N’-bis(2-phenylethyl)-perylene-3,4:9,10-tetracarboxylic diimide (BPE-PTCDI), are prepared using the blends of three-armed star-shaped poly[4-(diphenylamino)benzyl methacrylate] (N(PTPMA)3) and organic compounds (PCBM, TIPS-pen, Ferrocene) as electret. As utilized the N(PTPMA)3/PCBM blends, the device turns to a flash type memory with increased PCBM composition and could be operated repeatedly based on the tunneling process. The large shift of the reversible transfer curves and hysteresis after gate bias indicates the significance of electron charge storage. According to this mechanism, we also carried out the comparative study of the electret of N(PTPMA)3/TIPS-pen and N(PTPMA)3/Ferrocene to explore the effect of organic compounds in terms of energy-band diagram. And the data-storage types of memory could be adjusted by electrets of blends and further selecting the organic compound. In addition, all memory devices exhibit nice stability of long retention over 104 s and optimized ones could maintain the repeat cycle over 140 times for write-read-erase-read (WRER) or highly stable read-out current for WORM characteristics. The above results demonstrate that the electrets using star-shaped polymers and their donor-acceptor blends can enhance the carrier mobility and memory window for high-performance nonvolatile OFET memories.