在過渡金屬元素及相關化合物之奈米材料應用中，鎢(W) 系金屬奈米線因具有較低之電子親和力及良好的化學穩定性與極佳的導熱性質，且因具有較高之韌性及較大之機械強度，強固不易脫落與可靠性高，於發射源材料應用上為CNT 材料外另一極具潛力之替代材料。本論文旨在進行之製備氧化鎢(WOx) 奈米線及其於低電壓場發射元件之相關應用研究。
於場發射元件應用架構設計方面，係以黃光微影技術後輔以物理濺鍍法定義出圖案化之純鎢濺射薄膜結構(tungsten/SiO2/Si, W-SOI)，而後分別利用電流熔斷法或是黃光微影技術於通道處形成水平式側向短間距結構，再輔以適化的熱退火處理製程進行選擇性鎢基奈米線成長的新穎技術開發，藉由自組式成長鎢基奈米線良好的高寬比，大幅提升場發射之電特性，期能降低啟動電壓使此元件可於低電壓操作，達到低功率消耗與增加最大電流值之輸出特性表現。
本研究中主題之一，是藉由黃光微影技術定義不同間距圖案化之鎢基側向短間距結構，並以700 oC、750 oC與800 oC等三種熱退火溫度成長鎢基奈米線，藉由調變退火溫度控制鎢基奈米線之長度，以精確控制間距之距離；在最適化退火溫度750℃/ 30 min/ N2 60 sccm參數製作短間距元件，其啟動電壓為28.9V(@62 μA)以達低電壓操作範圍，且在具有量產之優勢，運用於低電壓操作真空微電子元件有相當潛力。
另一主題為藉由簡易且低成本的電流熔斷法於圖案化之純鎢薄膜通道處形成短間距結構，其藉由薄膜本身電阻之自熱效應於圖案化的純鎢薄膜通道處進行電流熔斷，並以最適化熱退火製程(800℃/ 30 min/ N2 60 sccm)對試片進行選擇性鎢基奈米線之成長；此電流熔斷法可取代一般黃光微影之製程技術，且其優越的場發射特性是藉由金屬氧化鎢奈米線(W18O49)本身之發射行為所主導，其啟動電壓為26.9 V(@62 μA)且其電流值可達8 mA(@ 80.2 V)。
以黃光微影方式製備上閘極結構，經過黃光微影定義3 m間距之試片經過熱退火溫度750 oC時，由實驗可知外加Vg 電壓有助於調變啟動電壓，其最佳化之量測結果啟動電壓與值分別為61.1 V(@62 μA)與290；且若固定Vd增加(10 V ~ 120 V)時，其轉移電導(gm)亦隨之增加(5.3×10-10 A/V ~ 1.1×10-5 A/V)，由此可驗證藉由外加閘極偏壓可改善其轉移電導，進而改善其場發射特性。
以黃光微影方式製備下閘極結構，此試片外加Vg 電壓有助於調變啟動電壓，其最佳化之量測結果啟動電壓與值分別為11.9 V(@62 μA)與1236；且隨著定值Vd增加(5 V ~ 40 V)時，其轉移電導亦隨之增加(3.2×10-8 A/V ~ 2.3×10-4 A/V)，由此可驗證藉由外加下閘極偏壓可大幅改善其轉移電導，進而改善其場發射特性；若比較上閘極結構，下閘極外加相同的閘極電壓時，其改變的幅度變化更大。
利用簡易而成本低廉之電流熔斷法或是可量產而可精確控制其間距之黃光微影技術製備水平式二極元件；或是應用於三極結構中以上閘極式和下閘極式控制其電子傳輸軌跡使啟動電壓下降，及增強因子增加，使場發射特性提升，而達到低電壓操作之範圍，未來運用在低電壓操作真空微電子元件具有其相當大的潛力。

Nanotubes and nanowires of different material have attracted much attention in the field emission area. Recently, we have developed a simple method for the self-synthesis of tungsten oxide nanowires (TONWs) for field emission device using the sputtering deposition and thermal annealing. To expand its application into low operation voltage vacuum electronics, a lateral nano-gap structure with TONWs were fabricated on tungsten/SiO2/Si structures using current fusing method or photolithography with thermal annealing.
In my experiment, photolithography and DC sputtering were employed for the deposition of a patterned tungsten film on SOI (i.e., SiO2/Si) structure. Using current fusing technique, lateral nano-gaps were obtained for the tungsten thin film (50 nm in thickness). After thermal annealing in nitrogen ambient at 700~850℃ for 30 minutes, self-synthesized TONWs grew over two parts of the annealed tungsten films and the device fabrication processes were finished.
In the other experiment, photolithography and DC sputtering were employed for the deposition of a lateral nano-gaps tungsten thin film (50 nm in thickness) on SOI structure. After thermal annealing in nitrogen ambient at 700~800℃ for 30 minutes, self-synthesized TONWs grew over two parts of the annealed tungsten films and the device fabrication processes were finished. TONWs were with a typical length and diameter of 150 ~ 700 nm and 20 ~ 35 nm, respectively. TONWs crystalline were W18O49(010) obtained and utilized as the surface-conduction electron-emitters (SCEs).
It is found that current fusing samples annealed at 800oC exhibited good field emission characteristics with an emission current intensity up to 8 mA(@80.2 V) and a turn-on voltage intensity of 26.9 V(@62 μA).And photolithography samples annealed at 750oC exhibited good field emission characteristics with an emission current intensity up to 2.61 mA(@98.4 V) and a turn-on voltage intensity of 28.9 V(@62 μA).
Photolithography for the fabrication of low operation voltage horizontal 2-terminal vacuum electronic devices has been utilized. Based on the experimental results, external applied positive top-gate voltage (Vg) could help to drain emission current. As applying top-gate structure in horizontal 2-terminal devices, Von was reduced from 62.7 V to 61.1 V, Imax was enhanced from 2.1 mA to 2.58 mA, and  was thus increased from 238 m-1 to 290 m-1. Meanwhile, as applying bottom-gate structure in horizontal 2-terminal devices, Von was reduced from 62.5 V to 11.9 V, Imax was enhanced from 1.95 mA to 2.2 mA, and  was thus increased from 185 m-1 to 1236 m-1.
Both my research of FE characteristics with the laterally grown TONWs operated at low voltages will be presented and analyzed. It is expected that TONWs with sub-micron can be potential candidate for low operation voltage vacuum electronics in the near future.

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