錐形鑽石場效發射矩陣之製作與特性

Abstract

場效發射矩陣的工作原理和陰極射線管相同，但它並沒有笨重的高壓 電子槍，製成非常的平且薄，也不需要如液晶顯示器的背光設計，而是採 低壓射極陣列激發磷質照光螢幕，具有高解析度，所產生的對比程度較液 晶顯示器為低，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。而鑽石因具有負電子親和力所以較一般的金屬鍍層在相同的工作電壓 下會大大提供工作電流。因此，鑽石應用在場效發射陣列將是未來研究發 展上的主流。 本實驗利用微波電漿化學氣相沈積法，(microwave plasma chemical vapor deposition, MPCVD)，藉由鑽石粉末懸浮液超音 波震盪之前處理以提高成核密度，並以甲烷－氫氣系為反應氣體源，在倒 錐形矽基板上沈積鑽石膜，經過去除矽基板後即可得到錐形鑽石陣列。沈 積後的鑽石尖錐以掃描式電子顯微鏡(SEM)、拉曼(Raman)光譜儀、傅利葉 轉換紅外線光譜儀(FTIR)、歐傑電子光譜儀(AES)與光電子化學分析儀( XPS)觀察、鑑定與分析其表面形態、品質及鍵結型式。 經實驗結果顯 示，場效發射陣列的電流－電壓值(Ie-Va)與鑽石膜的品質有很大的關係 。改變沈積參數時，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 電流值也變的較大，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) 與三階段(three- step)薄膜沉積法，比較高濃度甲烷應用在場發射矩陣鑽石尖錐的表面和 內部，實驗結果發現高濃度應用於表面比應用於內部有較低的發射門檻 值(threshold)。兩種沈積法在高電壓(1080 V)的最大電流值相當，皆比 一階段直接成長法(one-step)高，其原因可能在於非結晶性碳組織或石墨 提供較多的電子，所以造成其電性(場發射電流值，Ie)改善不少。 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）來製作鑽石尖錐發射矩陣。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一 千倍。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。 Cold-cathode FEAs operate on the same principle as the Cathode-ray tube ( 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 the screen. Cold-cathode FEAs produce far brighter contrast displays than liquid crystal displays ( LCDs ), are insensitive to temperature, and consume substantially less power than backlit LCDs such as active- and passive-matrix displays. Diamond is considered to be one of the most appropriate material for the solid-state electron emitter, because diamond ( 111 ) has a negative or at least very small electron affinity. A diamond field emitter array has been fabricated by using microwave plasma-enhanced chemical vapor deposition ( MPCVD ). Diamond was grown on an inverted pyramidal-shape Si substrates, which were fabricated with standard photolithography and anisotropic etching technique, followed by removal of the substrate. The reactive gases used in deposition wer the mixture of CH4-H2. Scanning electron microscopy ( SEM ), Raman spectroscopy, fourier transform infrared spectroscopy ( FTIR ), Auger electron spectroscopy ( AES ), X-ray photoelectron spectroscopy ( XPS ) were used to examine the morphology, crystallity, bonging type and quality of the as-deposited diamond film. Our results indicate the deposition rate increases with the increasing CH4 concentration in the CH4-H2 mixture, it was gradually to become diamond-like carbon ( DLC ) and/or graphite. The best emission capability was observed from the lower quality diamond tips. It is clear that the defects 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 and three-step with different CH4 concentration deposition method in our work. In order to improve the emission current of diamond tips. To compare with one-step deposited diamond films, their emission current were higher more than one-step deposition, the emission current threshold of the surface defects on diamond tips was lower than that of the defects with diamond tips. In order to increase the emission current of diamond tips, we used (B(OCH3)3) and (P(OCH3)3) as dopant sources. The result were that the emission current of the undoped diamond tips were further enhanced by the in situ doping of boron and phosphorus. The emission current of P-doped diamond tips was 1000 times larger than that of undoped ones. The reasons could be resulted from the higher electron conductivity and defect densities of doped diamond tips.