奈米金屬/導電高分子核/殼粒子於非揮發性有機記憶體元件的應用研究

鄭峻宇

指導教授 ： 韓建中

國立清華大學/理學院/化學系/碩士(2010年)

摘要

近來我們利用自行開發的同步還原與取代反應(concurrent reduction and substitution，CRS)合成聚苯胺衍生物Pani-SBu (poly(aniline-co-butylthioaniline))，並且在共溶劑(cosolvent)系統下誘導Pani-SBu生成微胞模版進而還原Ag離子形成核-殼(core-shell)結構型態的Ag/Pan-SBu奈米粒子。在本篇論文中，我們首次嘗試把此新結構型態的奈米粒子應用於有機記憶體中的記憶核心，在探討的過程裡我們曾利用旋轉塗佈(spin-coating)的方式製成元件中的主動層(active layer)，而在電性量測的實驗中我們發現到元件在正偏壓施加至臨界電壓(threshold voltage，Vth)時會由高電阻態(off-state)轉換至低電阻態(on-state)，且再施加負偏壓時元件則回到原狀態(off-state)，另外亦發現到奈米粒子於主動層中的濃度與整體元件表現出的開關比(on/off ratio)具有其正相關性；此外我們改變了沉積奈米粒子的方式，選用滴鑄塗佈(drop-casting)把奈米粒子沉積於陽極上，並於此層之上建構一PVP高分子緩衝層(buffer layer)以改善奈米粒子與陰極界面的不平整度，而由電性量測的結果得知其元件確實具有較優異的表現；另一方面我們由混摻不同數量的PVP高分子於奈米粒子層的實驗，進一步去探討奈米粒子之間的介電層厚度對整體元件的臨界電壓之影響，而我們發現到當奈米粒子之間介電層厚度增加時，其臨界電壓值也會隨之提高；最後我們也利用X-光光電子能譜儀(XPS)來分析並討論元件可能的電阻轉換機制，由分析結果我們了解到當元件在正偏壓的施加下，由高電阻態轉換至低電阻態時，奈米粒子中的殼層高分子Pani-SBu，其主鏈上的N原子會轉為部分帶正電荷，而核心金屬Ag則是部分帶負電荷，因此我們推論在電阻轉換的過程中是由Pani-SBu上的N原子提供電子給核心金屬Ag，進而提高主動層內可移動之自由載子(free carrier)的數目，其轉換機制屬於予體受體間電荷轉移(Donor-Acceptor charge transfer)。

關鍵字

聚苯胺 ； 非揮發性有機記憶體

並列摘要

In this thesis we describe a nonvolatile memory device based on the introduction of silver/ poly(aniline-co-butylthioaniline) (Ag/Pani-SBu) core/shell nanoparticles (NPs) as the active layer. About the deposition of the nanoparticles, we have already tried both of the spin-coating and drop-casting fabrication method. In spin-coating method, we find the device will switch from off-state to on-state as the applying voltage is beyond the threshold voltage, and it can be turned off by applying opposite voltage. Besides, the ON/OFF current ratio increases as the concentration of NPs in the device increases. In drop-casting method, we use polyvinylpyrrolidone(PVP) as a top-cast buffer layer to reduce the roughness between NPs layer and cathode(Al), as illustrated experimental of devices D1 to D4. On the other hand, we also discuss whether the thickness of dielectric layer between NPs influences the threshold voltage of the device by mixing PVP polymer into NPs layer. The result indicated that as the addition amount of PVP increased, the threshold voltage of the device became higher. Furthermore, we use X-ray photoelectron spectroscopy (XPS) to analyze and investigate the possible resistance-switching mechanism. The result shows that, during the switching-on stage, the Pani-SBu shell is more positively charged while the Ag core is more negatively charged. This XPS result suggests the resistance-switching mechanism of the device is donor-acceptor charge transfer.

參考文獻

[1]　T. Mikolajick, “Materials for Information Technology: Devices, Interconnects and Packaging”, Springer London Publisher 2005

[2]　D. Frohman-Bentchkowsky, Appl. Phys. Lett. 1971, 18, 332

[3]　R. H. Fowler, L. Nordheim, Proc. R. Soc. London. A. 1928, 119, 173

[6]　J. T. Evans, R. Womack, IEEE Journal of Solid-State Circuits 1988, 23, 1171

[7]　葉林秀、李佳謀、徐明豐、吳德和，”磁阻式隨機存取記憶體技術的發展—現在與未來” 物理雙月刊 2004, 26, 607