鑽石薄膜在場效發射矩陣上的應用與特性研究

Abstract

場發射矩陣和陰極射線管有相同的工作原理，但它能製成非常的平 且薄，卻不需要如液晶顯示器的背光設計，而是採低壓射擊陣列激發磷質 照光螢幕，具有高解析度，而對比程度卻較液晶顯示器大，且不受環境溫 度所影響，耗電也比背光式之液晶顯示器要低。本實驗利用化學氣相沉積 法(chemical vapor deposition, CVD)，利用本實驗室所開發的甲烷－二 氧化碳系為反應氣體源，在矽的場發射矩陣上沉積鑽石膜或非鑽石碳膜， 來探討鑽石膜在FED元件上應用的可能性。 經實驗結果顯示，利用甲 烷-二氧化碳做反應氣體源時，鑽石膜之品質隨甲烷濃度的上昇變差，其 成份漸趨向於類鑽石碳組織(Diamond-like carbon)或偏向石墨組織( Graphite)。其中電性最佳的組織是屬類鑽石碳膜組織(Diamond-like carbon)，因此缺陷數目和非鑽石碳組織在場發射電流中扮演重要角色。 此外，本實驗也採用二階段(two-step)薄膜沉積法，改善場發射矩陣尖 錐(tip)被覆鑽石膜的外觀之形態與電性之效果，並比較直接成長法(一階 段 one-step)。實驗結果發現，使用此二種方法所得的薄膜品質相似，不 同之處在於使用二階段成長法所得的薄膜顆粒較細，因此電流要比一階段 直接成長法高，其原因可能在於較多微細結晶粒子和缺陷造成負電子親和 力增強並提供較多的電子，以致於提高了場發射電流值(Ie)。另外我們也 以附加偏壓二階段成長法(BEN two-step)在場發射矩陣尖錐上沉積鑽石膜 ，其外觀形態和未覆蓋的純矽尖錐相比較，並沒有明顯的變化，看起來非 常的尖，且分析發現在矽的尖錐表面覆蓋有一層非常薄的DLC覆膜，而場 發射電流達342 uA且較穩定。 為了有效提高場發射電流，以亞磷酸 三甲酯(P(OCH3)3)以及硼酸三甲酯(B(OCH3)3)為摻雜源（dopant source ）來製作摻雜鑽石覆膜被覆在矽場發射矩陣上。經電性測試結果顯示，摻 雜磷和硼的鑽石覆膜其場發射電流都比未摻雜的鑽石覆膜場發射電流大， 而摻雜磷的鑽石覆膜尖錐矩陣場發射電流比未摻雜的高40倍。其原因推測 可能是摻磷鑽石膜有較好的導電特性及缺陷密度所致。 Cold-cathode FEAs operate on the same principle as the Cathode-raytube (CRT), but rather than using a bulky high- voltage electron gun, FEAs use an array of low-voltage electron emitters to excite light-emitting phosphors that illuminate that screen.It was found that thereis a effect of various carbon films on the electron emission(Ie) properties.Polycrystalline diamond thin films and/or other amorphous carbon films have been successfully coated on the apex surface of Si field emitter arrays (FEAs) using microwave plasma-enhanced chemical vapor deposition (MPCVD). The reactive gases used in deposition were the mixture of CH4-CO2.The deposition rate increases with the increasing CH4 concentration in the CH4-CO2 mixture, it was gradually to become diamond-like carbon (DLC) and/or graphite. Generally, the best emission capability was observed from the diamon-like carbon films on FEAs. It is clear that the defacts and graphite inclusions play a very significant effect on emission current. On the other hand, polycrystalline diamond films was deposited on FEAs using two-step deposition method (two-step) in our work.In order to improve the surface morphologies and emission current of the diamond-clad FEAs. To compare with one-step deposited diamond films by using SEM and Raman, there have similar morphology surfaces. It is difficultthat there are smaller grains on the two-step one,s surface than one-step ones.It suggests that electron emission increaded from two-step ones are the presence of a negative electron affinity (NEA) provided by hydrogen terminated diamond ｛111｝planes. Using Bias-enhanced(BEN) two-step method deposited diamond films on FEAs. This conformal coating does not significantly change the original shapes of Si tips thereby results in a very sharp thin-DLC-clad Si tip array. The Ie of BEN two-step coated DLC-Si tips array was 432 mA and more stability. In order to increas the emission current of diamond-clad tips, we are the first one to fabricate the P-doped and B-doped diamond-cladSi FEAs were trimethyl phosphite (P( OCH3)3) and trimethyl borate (B(OCH3)3) vapor was introduced into the CO2-CH4 gas mixtures as dopant sources.The final result were that the emission current characteristics of the undoped diamond-clad tips were further enhanced by the in situ doping of phosphorus or boron. The emission current of P-doped diamond- clad Si FEAs is 40 times larger than that of undoped ones. To compare with B-doped diamond-clad Si FEAs, the P-doped ones show a better emission current.The real reasons could be resulted from the higher electron conductivity and defect densities of P- doped diamond films.