新穎場發射材料與元件結構之研究

Abstract

本論文主要針對場發射材料與元件結構為主題作深入之探討。就傳統金屬場發射元件而言，本論文提出了一種新穎的煙囪狀場發射陣列，利用物理氣相沉積技術，濺鍍金屬薄膜而行成煙囪狀場發射陣列，不但有效地提昇了場發射陰極之場發射面積，同時，高深寬比之場發射尖端亦可藉由控制薄膜沉積之厚度得到，不需藉由複雜的斜角蒸度或者是高溫的氧化削尖製程，達到了簡化製程之目的。實驗結果亦驗證了煙囪狀場發射陣列相較於傳統尖錐狀場發射陣列具有更佳之場發射特性；此外改良式煙囪狀場發射陣列亦被提出來改善煙囪狀場發射金屬薄膜的中空結構造成的一些缺點，而改良式煙囪狀場發射三極陣列亦被成功地製造，並且展現了優異的場發射特性。 在於新穎場發射材料的合成部分，我們利用微波電漿輔助化學氣相沉積系統，藉由控制催化層厚度來成長不同形態的奈米碳管；而我們亦探討不同催化金屬層(鐵、鈷、鎳)對於奈米碳管的合成所造成的影響。此外由場發射的測試中可以發現，奈米碳管具有非常優異的場發射特性，而密度較高的奈米碳管因為電場之遮蔽效應(screening effect)使得其場發射特性並不因其具有較高密度之場發射源而變好。為了進一步改善奈米碳管之場發射特性，我們亦提出了利用準分子雷射處理來改變奈米碳管之密度以降低電場之遮蔽效應，實驗結果證實在適當的條件之下，奈米碳管之場發射起始電場可以大幅降低，而場發射電流亦可大幅增加。 此外，我們亦提出了有效控制奈米碳管密度的成長方法，藉由沉積一層非催化金屬層於催化金屬上，奈米碳管的密度可被有效地控制，而實驗結果亦表示優異的場發射特性可藉由調變奈米碳管之密度而得到。 為了符合場發射顯示器低電壓操作的目的，我們利用一控制閘極來製造奈米碳管之發射三極元件，我們以半導體製程技術縮小了元件的尺寸，並利用選擇性成長奈米碳管的技術，以控制奈米碳管成長長度的方式來製作場發射三極元件，順利地將閘極操作電壓降低到30 伏特；而為了更進一步降低閘極操作電壓，我們亦利用一偏移閘極，來有效降低奈米碳管與閘極之距離，以增加了閘極之控制力，來達到更低電壓操作之目的。

Novel field emission materials and devices are synthesized and fabricated in this thesis. For conventional metal field emission materials, chimney shape field emission array was proposed. Metal emitters with high aspect ratio can be obtained by controlling the thickness of the sputtering deposited metal film on the Si neck as the field emitter, the emission area was increased effectively to produce more emitter redundancy. The fabrication process was also simplified because no oxidation sharpening or high vacuum oblique physical vapor deposition was required to produce sharp features. The experimental results suggested that excellent field emission properties can be achieved from chimney shape field emission arrays as compared to cone shape field emission arrays. Modified chimney shape field emission arrays were also proposed to modify the physical construction of the chimney shape emitters, and the modified chimney shape triodes were fabricated to exhibit excellent triode properties. For the synthesis of novel field emission materials, carbon nanotubes (CNTs) with various morphologies have been synthesized using microwave plasma-enhanced chemical vapor deposition (MPCVD) by controlling the thickness of the catalyst film. The growth behaviors of CNTs with different catalysts (e.g. Fe, Co, Ni) were also discussed. The fabricated CNTs emission arrays showed excellent field emission properties, however, the field emission properties of the high density CNTs degraded for the screening effect of the electric field. To improve the field emission properties of the CNTs, a novel post treatment process via excimer laser was proposed. The results depicted the field emission properties can be upgraded with proper excimer laser treatment conditions. Additionally, a novel process was proposed to synthesize the CNTs with controlled density to exhibit excellent field emission properties. By applying an inactive layer on the catalyst layer during CNTs growth, the density of nanotubes can be controlled by varying the inactive layer thickness The CNTs triode structures with an extraction gate were proposed to achieve the low voltage modulation. CNTs triodes with reduced gate diameter were fabricated by the semiconductor fabrication process and the selective growth of CNTs with controlled length. The turn-on gate voltage was reduced to 30 V. To further reduce the gate voltage, an offset-gate CNTs triode structure was also proposed to reduce the distance between gate and the CNTs to enhance the controllability of the gate and the low turn-on gate voltage as low as 13 V was successfully achieved.