陽極氧化鋁模版法製作奈米結構材料及其電子場發射特性研究

Abstract

本實驗的實驗目的是製作出高規則性的奈米陣列結構，並探討其場發射性質。本實驗是藉由陽極氧化鋁(AAO)之高規則孔洞分佈薄膜作為模板，控制TiOx奈米點之排列位置，並利用TiOx奈米點陣列作為nanomask蝕刻下面的基材，製作出高規則性排列之奈米陣列結構，這些利用AAO薄膜作為模板，開發出來的場發射奈米結構包括：TiN奈米柱、Si奈米尖錐、Si奈米尖錐包覆一層□a-C layer 與Si 奈米尖錐電鍍一層氧化銥。 實驗方法是在矽晶元上依序沉積TiN與Al薄膜，經由陽極氧化處理後得到TiOx奈米點，利用TiOx奈米點作為nanomask，以活性離子蝕刻（RIE）系統蝕刻下面的TiN基材。TiN奈米柱有與AAO孔洞相同的陣列結構。而TiN奈米柱在移除掉頂部的TiOx nanomask之後，其頂端會呈現有環狀尖銳形貌的結構。TiN奈米柱因為具有高深寬比與頂端環狀凸起結構，有利於降低場發射時的起始電壓。實驗發現在這種結構下，場發射的起始電場為1.6 V/um。並從F–N plot 計算出，在這種環狀凸起結構下，對場發射增強因子有∼26%的貢獻。本實驗也用相同的方式製作出Si奈米尖錐； TiN薄膜經由陽極氧化處理後，得到與AA0孔洞排列相同的TiOx奈米點。藉由TiOx nanomask蝕刻下面的Si基材，可製作出Si奈米尖錐。本實驗並用微波電漿氣象化學沉積法，利用自生（in-situ）的方式，在Si奈米尖錐上沉積厚度約~5 nm 的□a-C layer。從Raman 與 Auger 得知這層□a-C layer是含有大量的奈米級的石墨結晶。這層奈米級的石墨結晶與尖錐形的幾何形狀，有助於得到較大的場發射增強因子。為了在電場作用下得較好的熱穩定性，本實驗利用脈衝電流的方式電鍍IrO2奈米顆粒在Si奈米尖錐上。IrO2奈米顆粒的大小約小於5 nm，並且均勻分佈在Si奈米尖錐上。由於IrO2/Si奈米尖錐擁有小的區率半徑與較低的功函數，比Si奈米尖錐有更好的場發射特性。

Fabrication of highly ordered nanostructures and investigation on the corresponding field emission characteristics were engaged with nanoporous anodic aluminum oxides (AAO) as templates to regulate the formation arrangement of TiOx nanodot arrays, which were consequently employed as nanomasks to etch TiN layers and the underlying layers to manufacture nanostructures of highly ordered arrangements. Nanostructures developed by AAO templates included TiN nanopillars, Si nanotips, amorphous carbon coated silicon nanotips and IrO2 electrodeposited on Si nanotips for field emitter applications. Sequential deposition of TiN and Al on Si substrates and the successive electrochemical anodization of film stacks fabricated TiOx nanodot arrays to be used as masks to reactive-ion-etch (RIE) the underlying TiN layers. TiN nanopillars arranged in a compliant pattern with AAO had a ridge-shaped edge on the top after the removal of TiOx nanomasks. TiN nanorods with a high aspect ratio and the protruding top edge, of which the field enhancement effect was evaluated by the ellipsoidal cylinder model, showed a low turn-on voltage of 1.6 V/um. An underestimation by around 26% was found for comparison with the enhancement factor derived from the Fowler-Nordheim (F-N) plot. Similar processes were performed for Si nanotips. During the preparation of well-ordered AAO pore channel arrays, underlying TiN layers were anodically oxidized as well in the late stage of the AAO anodization to form titanium oxide nanomasks for Si nanotip fabrication. Well-ordered Si nanotip arrays were produced as a result of the arrangement pattern transfer of AAO pore channel arrays to Si substrates with titanium oxide nanomasks by the plasma etch in the MPCVD system. a-C layers about 5 nm thick and rich in nanocrystalline graphitic carbons according to Raman and Auger electron spectroscopies were in-situ deposited on Si nanotips during the MPCVD process. Nanocrystalline graphitic carbons in the coating and the sharp tip shape improved Si nanotips as excellent field emitters with a large field enhancement factor. In order to obtain thermally stable field emitters with high field-emission efficiency, well dispersed IrO2 nanoparticles with a uniform size distribution below 5 nm were deposited on ordered Si nanotips by bipolar pulse electrodeposition. Small curvature and lower work function assured IrO2/Si nanotips to be superior to bare Si nanotips in field emission performance in terms of the turn-on field and the field enhancement factor.