以陽極氧化鋁輔助合成奈米碳管場發射陣列之研究

Abstract

場發射顯示器一直是眾人認為最有潛力的奈米碳管商品，其需要的場發射源便是擁有高度準直的奈米碳管。奈米碳管最為人所詬病的即是排列紊亂及缺乏方向性，本實驗利用熱蒸鍍鋁之兩階段陽極氧化處理，在矽基材上製備出高規則排列的陽極氧化鋁奈米孔洞作為模板，並利用電化學電鍍法沉積觸媒於陽極氧化鋁孔洞內，利用電子迴旋共振化學氣相沉積法，以氫氣與甲烷為製程氣體合成奈米碳管陣列。由於奈米碳管的成長受到模板孔洞的限制與外加偏壓或電漿自我偏壓的影響，因而具有優異的準直性，且由於電子迴旋共振化學氣相沉積法有較低的合成速率，奈米碳管的長度可利用成長時間做調控。本實驗則利用改變電鍍觸媒時間的長短，固定前處理和成長時間，得到不同奈米碳管之管束密度，奈米碳管密度在鋁膜上隨時間增加而降低；在陽極氧化鋁模板上隨時間增加而增加。此外，本實驗使用兩種方法製備奈米碳管三極體結構，在陽極氧化鋁模板的輔助下，三極結構內的奈米碳管具獨立性、準直性與密度可控性，此外本實驗亦直接在4吋晶圓上以陽極氧化鋁為模板輔助合成奈米碳管，本研究之奈米碳管三極體結構易大面積製備，有利於與半導體製程技術整合，可促進碳管相關商品及場發射顯示器技術的發展。最後奈米碳管陣列的場發射特性亦為矚目焦點，此性質為奈米碳管做為場發射源的重要考量之一，本實驗對不同密度的奈米碳管做場發射量測，並加以做定性與定量分析，包括掃描式電子顯微鏡、穿透式電子顯微鏡拉曼光譜儀等。

For the practical field emission display (FED) applications, growth of vertically aligned carbon nanotubes (CNTs) as field emitters is very essential. However, with the traditional synthesis methods, CNTs usually show poor arrangement and disordered direction. To grow CNTs as field emitters for FED applications, we utilize nanoporous anodic aluminum oxide (AAO) with highly ordered pore channels to template the growth of CNT field emitter arrays. The AAO template is prepared by two-step anodization of the Al film on the silicon substrate. After electro-deposition of the Co catalyst on the bottom of the AAO pore channel, multiwall CNTs were synthesized in electron-cyclotron-resonance chemical-vapor-deposition (ECR-CVD) system using the gas mixture of CH4 and H2. CNTs thus prepared were highly aligned because the nanopore channels of the AAO template constrained the CNTs growth along the axis of the pore channels, and CNTs overgrown out of the pore surface remained in the vertical growth direction due to the applied DC bias and the plasma self-bias under the ECR plasma condition. The growth rate of CNTs in the AAO template by ECR-CVD is considerably low, and therefore, the tube length can be suitably controlled by tuning the growth time. In addition, the CNTs tube number density was found to be a function of the Co electro-deposition time. The number of CNTs extending out of AAO nanopores increases linearly with the Co electro- deposition time. On the contrary, the tube number density of CNTs on the Al film decreases with reducing the Co electro-plating time. The field emission property of CNT arrays was investigated in an electrical measurement system under a vacuum condition of 10-6 torr. The electrical measurement showed that the field emission of the AAO-CNT emitter arrays followed Fowler-Nordheim (F-N) field emission behavior. In this work, the carbon nanotube field emission triode was fabricated by two methods, which will be described in the thesis. With the assistant of the AAO template, the mono-dispersed CNTs array in triode structures showed good alignment and well controlled tube number density. The fabrication methods of the CNT-triode structure used in our research are suitable for large-area substrates. The large-area fabrication capability is essential for the implementation of this AAO-CNT triode structure in the FED technology for industrial purpose.