利用陽極氧化鋁製備奈米結構電子場發射源

Abstract

過去數十年來，冷陰極電子場發射元件應用在平面顯示器及微波真空微電子技術的潛力受到了許多的注意，其中又以Spindt型場發射體最被學術界廣泛的研究。本研究利用奈米多孔性的陽極氧化鋁薄膜作為模板輔助製備奈米場發射結構之規則陣列，其奈米場發射結構包含兩種型態:其一為TiN奈米柱之場發射陣列；其二為披覆氧化銥電鍍膜之Si奈米尖錐陣列。 高規則場發射陣列結構之製備是以TiOx奈米點陣列作為奈米遮罩(nanomask)，而TiOx奈米點陣列可直接由鋁及氮化鈦雙層薄膜之陽極氧化處理獲得，並藉由陽極氧化鋁膜之高規則孔洞分佈侷限TiOx奈米點陣列之排列。 TiN奈米柱之場發射陣列的製備，是先在矽基材上依序沉積TiN與Al膜，再經由陽極氧化處理獲得TiOx奈米點。利用其TiOx奈米點陣列作為nanomask，以活性離子往下蝕刻TiN基材，即能製備出與陽極氧化鋁膜之相同孔洞分佈的TiN奈米柱之規則陣列。而TiN奈米柱陣列在移除掉頂部的TiOx nanomask之後，其頂端會呈現有環狀尖銳形貌的結構。在真空度為10-6torr環境下量測TiN奈米柱陣列之場發射性質，發現其場發射陣列具有低起始電壓，以及非線性F-N圖形之場發射特性。我們認為其非線性之場發射特性歸因於頂端之環狀尖銳形貌先產生場發射電流的關係。 Si奈米尖錐陣列與TiN奈米柱陣列有相似之製備方式，其中的差異在於TiN的厚度較薄。在移除掉上層的陽極氧化鋁膜後，在高密度電漿之活性離子蝕刻系統中先以TiOx奈米點陣列作為nanomask，對TiN層進行離子性蝕刻，接著以殘留的TiN奈米柱陣列作為nanomask，並使用不同的蝕刻氣體對Si層進行離子性蝕刻，即能製備出Si奈米尖錐陣列。為了使場發射源具有較穩定的場發射特性，以脈波電鍍法沉積IrO2至Si奈米尖錐表面上。場發射源的尖端半徑及形貌取決於電鍍條件，如脈波波形、週期、操作電流。我們並研究披覆氧化銥電鍍膜之Si奈米尖錐陣列的場發射特性，發現其奈米結構與純Si奈米尖錐相較之下，有較好的場發射性能。

For the past two decades, electron field emission devices have attracted much attention because of their potential applications for cold cathode flat panel display and vacuum microwave devices. Among various electron field emitters, the Spindt type microfabricated emitter has been extensively investigated for applications of the cold cathode field emitter. In this study, we fabricated highly ordered nanostructured field emitter array using porous anodic aluminum oxide (AAO) as the template. Two types of nanostructured field emitters were prepared: the titanium nitride (TiN) nanopillar emitter array and the iridium oxide (IrO2) coated Si nanocone emitter array. In order to fabricate ordered emitter array, a TiOx nanodot array was first prepared as the nanomask for subsequent fabrication of nanoemitters. The AAO template was used to regulate the formation arrangement of the TiOx nanomaks, with which nanoemitters were then fabricated using conventional integrated circuit process technology. For fabrication of the TiN nanopillar emitter array, TiN and Al were sequentially sputter-deposited on the Si substrate followed by electrochemical anodization of the film stack, thereby the TiOx nanodot array was produced. After reactive-ion-etching the underlying TiN layer using the TiOx nanodots as the mask, TiN nanopillars can be formed with a pattern arrangement in compliant with the AAO pattern. The TiN nanopillars had a ridge-shaped edge on the top after the removal of the TiOx nanomasks. Field emission characteristics of the TiN nanopillar array were studied under a vacuum condition of 10-6 torr. The TiN nanopillars emitters had a very low turn-on voltage while the Fowler-Nordheim plot showed a nonlinear field-emission behavior. The nonlinearity was ascribed to that the ridge-shaped top edge produced field emission before the rest of the emitting area. For fabrication of Si nanocone emitters, similar processes were performed as the fabrication processes of the TiN nanopillars excepted for the thinner thickness of the TiN film. After removal of the AAO template, the TiOx nanodots and the remanent TiN thin film were subject to reactive-ion-etching processes, and the formed TiN nanopillars were used as the mask to prepare the Si nanocone array in a high-density-plasma-reactive-ion-etching (HDP-RIE) system. In order to obtain chemically stable field emitters with a high field-emission efficiency, IrO2 was deposited on the Si nanocones by pulsed anodic electrodeposition. The tip radius and the sharpness of the field emitter were highly dependent on the electrodeposition conditions, such as the pulse waveform, period and the applied current. Field emission characteristics of the IrO2 coated Si nanocone array were also studied, and showed a better field emission performance than that of the bare Si nanocone emitter array.