非揮發有機場效電晶體記憶體由隔離金屬奈米粒子空間上排列在奈米結構之微胞雙塊共聚物薄膜所組成

Abstract

本研究的目的是開發新的塊狀高分子/金屬奈米複合材料之非揮發性有機場效應電晶体記憶體應用。首先，我們製作了p-型通道非揮發性的有機場效效應電晶体 (OFET) 記憶體，其利用含有不對稱 PS-b-P4VP 雙塊共聚合物層中，分別包含有高和低功函數的金屬奈米粒子在這親水性與親油性塊段中。我們選擇這高度非對稱雙塊共聚物 PS56k-b-P4VP8k 作為聚合物電滯体去創造記憶體窗口，以及使用不同功函數 ex-situ 合成的金屬奈米粒子來調整記憶體窗口，對於任何 p 或 n 通道的應用。非揮發 OFET 記憶體元件含有不對稱 PS56k-b-P4VP8k 層中，嵌有高功函數的鉑奈米顆粒 (5.65 eV) 在 P4VP 親水塊段中，其轉移曲線表現出正的臨界電壓漂移和大的記憶體窗口 (約27伏特)。與此相反，相對應非揮發 OFET 記憶體元件含有嵌入低功函數 (4.26 eV) 的銀奈米粒子，其轉移移曲線表現出負的臨界電壓漂移和一個較小的記憶體窗口 (大約19伏特)。這種方法提供了一種通用的方法對於具有相同的處理過程，來製造 p 型或可能的 n 型通道非揮發性有機場效應電晶体 (OFET) 記憶體元件。第二，討論非揮發性有機場效應電晶體記憶體元件，含有共聚物 (PS56k-b-P4VP8k) 層當作電荷儲存層時，具有 聚(4 -乙烯基吡啶)-核 (P4VP-core), 聚苯乙烯-殼 (PS-shell) 之微胞奈米結構厚度對於記憶體寬度以及電洞遷移率之影響，並以原子力顯微鏡與同步輻射光源，探討該層和電子通道層之奈米結構，分析其與記憶體性質之間的關係。例如，當 PS56k-b-P4VP8k 層厚度連續從 60 奈米改變至 27 奈米時，記憶體寬度從 7.8 V 改變至 21 V，增加為原來的 2.5 倍。使用同步輻射光源低掠角小角X光散射 (GISAXS) 與低掠角廣角X光散射 (GIWAXS) 分別去探測奈米結構微胞的 PS56k-b-P4VP8k 與直接定位在 PS56k-b-P4VP8k 層頂端之并五環 (Pentacene) 分子的堆疊。利用此方式，我們能夠去破解這雙層結構之特性與連接它們的效應在具有類似結構元件之記憶成果。藉由 GISAXS 與 GIWAXS 可觀察到在 PS56k-b-P4VP8k 層中，微胞與微胞之間的距離與橫向排列方式會隨著聚苯乙烯-殼的厚度而有所改變，當厚度增加時， 聚苯乙烯-殼在橫向距離減少，使得記憶體的開閥電壓偏移量受到影響。再者，發現在 PS56k-b-P4VP8k 層上作為電子通道層的并五環會受到 PS56k-b-P4VP8k 層之結構而影響其分子堆疊方向以及晶粒大小，進一步影響電洞遷移率。這些結果顯示出，要調整記憶體中寬度以及電洞遷移率，改變電荷儲存層中雙塊式高分子薄膜厚度和微胞奈米結構會是個簡單且有效的方式。最後地，金屬奈米顆粒陣列在雙塊共聚物中空間排列，具有許多潛在的應用在 OFET 型記憶體元件中。在這個研究中，我們採用一個捕集方法，其中我們使用 PS56k-b-P4VP8k，一個高度不對稱的雙塊共聚物具有球形微胞形態，分別地，包入各種數目之一相法合成的十二烷硫醇鈍化銀 (DT-Ag) 與固定數目之配位基交換吡啶包覆金 (Py-Au) 的奈米粒子進入到聚苯乙烯 (PS) 和聚(4 -乙烯基吡啶) (P4VP) 塊段中。我們定這些金屬奈米粒子在所述奈米結構的雙塊共聚物之堆疊特徵，我們使用倒晶格空間同步加速器低掠角小角X射線散射 (GISAXS) 以及原子力顯微鏡與穿透射電子顯微鏡在真實空間中。銀奈米顆粒在聚苯乙烯塊段中的堆疊取決於它們所屬的含量，這是我們在恆定旋轉塗佈速率下，通過調節改變複合物溶液濃度所得。在塊狀共聚物薄膜內銀和金奈米顆粒的二維交替等級排列，當 Py-Au 奈米粒子進入聚(4 -乙烯基吡啶)塊段中，以及從低濃度溶液 (0.1 wt%) 旋轉塗佈成較薄的薄膜後是被增強的，主要是由於 DT-Ag 奈米粒子會延著 Py-Au/P4VP 核的周圍去累積;當 Py-Au 奈米粒子進入到聚(4 -乙烯基吡啶)區域時，透過旋轉塗佈在較高濃度的溶液 (0.5 wt%)，在超過臨界 DT-Ag 奈米粒子的重量比 (c) 為 0.8，該二維交替等級排列是降低的，其中對 DT-Ag 奈米粒子在真實空間中會沿著 z 軸通過旋轉 20o 再排列，主要是由於在聚苯乙烯區域內 DT-Ag 奈米粒子的過飽合。

The objective of this thesis is to develop new BCP/metal NP nanocomposites for non-volatile organic field-effect transistor memory applications. First of all, we fabricated p-channel–type non-volatile organic field-effect transistor (OFET) memory devices featuring an asymmetric PS-b-P4VP diblock copolymer layer incorporating high– and low–work-function metal nanoparticles (NPs) in the hydrophilic and hydrophobic blocks, respectively. We chose the highly asymmetric diblock copolymer PS56k-b-P4VP8k as the polymer electret to create the memory windows, and used the different work functions of the ex situ–synthesized metal NPs to tune the memory window for either p- or n-channel applications. The transfer curves of non-volatile OFET memory devices incorporating an asymmetric PS56k-b-P4VP8k layer embedded with high–work-function Pt NPs (5.65 eV) in the P4VP block exhibited a positive threshold voltage shift and a large memory window (ca. 27 V). In contrast, the transfer curves of the corresponding non-volatile OFET memory devices featuring embedded low–work-function (4.26 eV) Ag NPs exhibited a negative threshold voltage shift and a smaller memory window (ca. 19 V). This approach provides a versatile way to fabricate p- or possibly n-channel–type non-volatile OFET memory devices with the same processing procedure. Second, OFET memory devices incorporating the copolymer PS56k-b-P4VP8k layer, which features a thickness-dependent micellar nanostructure (P4VP-core, PS-shell), as a charge trapping layer can exhibit tunable memory windows for p-channel applications. For instance, the memory window increased substantially from 7.8 V for the device incorporating 60-nm-thick PS56k-b-P4VP8k layer to 21 V for the device incorporating 27-nm-thick layer, an increase of more than 2.5 times. Using simultaneous synchrotron grazing-incidence small-angle X-ray scattering (GISAXS) and grazing-incidence wide-angle X-ray scattering (GIWAXS) to probe the nanostructured micellar PS56k-b-P4VP8k layer and the pentacene layer positioned directly on the top of the copolymer layers, respectively, we were able to elucidate the structural characteristics of the bilayer and to correlate their effects on the memory performances of devices with similar architectures. For the PS56k-b-P4VP8k layers, we found that the inter-micelle distance and their lateral arrangements depended on the layer thickness: the thickness of the PS shells in the lateral direction decreased upon increasing the layer thickness, as did the memory window for the OFET device that incorporates the PS56k-b-P4VP8k layers, a strong dependence of the threshold voltage shifts (i.e., memory window) on the distance between the micelles; Additionally, for the molecular packing of the pentacene layer positioned on the copolymer layer, we found that the PS56k-b-P4VP8k layers affected not only the orientation of the pentacene molecules but also their grain sizes, thereby affecting the hole mobility of the memory devices. These results suggest that tuning the micellar nanostructure of the block copolymer thin film that was used as a trapping layer can be a simple and effective way for optimizing the memory window and affecting the hole mobility of OFET memory devices. Finally, the spatial arrangement of metal nanoparticle (NP) arrays in block copolymers has many potential applications in OFET-type memory devices. In this study, we adopted a trapping approach in which we used a monolayer thin film of PS56k-b-P4VP8k—a highly asymmetric diblock copolymer having a spherical micelle morphology—to incorporate various amounts of one-phase-synthesized dodecanethiol-passivated silver (DT-Ag) NPs and a fixed amount of ligand-exchanged pyridine-coated gold (Py-Au) NPs into the polystyrene (PS) and poly(4-vinylpyridine) (P4VP) blocks, respectively. We characterized the packing of these metal NPs in the two blocks of the nanostructured diblock copolymer using reciprocal-space synchrotron GISAXS as well as atomic force microscopy and transmission electron microscopy in the real space. The packing of the Ag NPs in the PS block was dependent on their content, which we tuned by varying the concentrations in the composite solution at a constant rate of spin-coating. The two-dimensional hierarchical arrangement of Ag and Au NPs within the BCP thin films was enhanced after the addition of the Py-Au NPs into the P4VP block and after spin-coating a thinner film from lower solution concentration (0.1 wt%), due to the DT-Ag NPs accumulating around the Py-Au/P4VP cores; this two-dimensional hierarchical arrangement decreased at a critical DT-Ag NP weight ratio (c) of 0.8 when incorporating the Py-Au NPs into the P4VP domains through spin-coating at higher solution concentration (0.5 wt%), where the DT-Ag NPs realigned by rotating 20° along the z axis in the real space, due to oversaturation of the DT-Ag NPs within the PS domains.