低溫製程之奈米碳管場發射背光模組和利用三極結構增進均勻性之研究

Abstract

此篇論文主題之一為研究多層催化金屬在低溫下合成柱狀結構之奈米碳管場發射陣列來進行場發射，同時探討其應用於背光源之可靠度和均勻性。依據之前本實驗室之研究，利用多層式的催化金屬可以有效的降低製程所需的溫度，利用共鍍合金催化金屬的方式可以提升碳管的可靠度。所以本實驗將結合兩者的優點，嘗試多層共鍍催化金屬在低溫下合成柱狀結構之奈米碳管的研究。經過量測發現以鈷鈦共鍍在鋁上(鈷-鈦/鋁)可以在550℃得到最佳柱狀結構的碳管，其碳管的場發射起始電場為3.6 V/μm，在6 V/μm的電場之下其電流密度為1272 μA/cm2，另外可以在6.7 V/μm高電場之下維持2小時擁有變動值小於7%的優異可靠度，其在1平方公分的總面積之下擁有發光均勻性的改善。然而在探討成長時間對於其特性的影響之後，近一步發現在成長時間是90分鐘時，其碳管高度大約是8 μm時，可以得到最佳之場發射特性，起始電壓為3.5 V/μm，而在6.7 V/μm固定電場下2小時的電流衰減度低於0.1%，由材料分析可以獲知若成長時間超過90分鐘會造成非結晶相增加，而使場發射特性變差。此外，由於利用微影方式，可以控制柱體密度和調變柱體間的間距，來降低電場遮蔽效應，所以當碳管直徑為6 μm且高度為8 μm時，獲得在間距9 μm附近為最佳的場發射特性。 為了符合場發射低電壓操作的目的，所以製造利用閘極控制的奈米碳管之場發射三極元件，碳管方面利用在低溫合成催化金的技巧，且利用三極結構的電子束發散來增進背光元件的均勻性，經由多次的模擬所得到最佳結構的參數:閘極到發射源距離為2 μm，閘極和發射源的高度皆為1 μm。透過實驗獲知操作電壓可降至43 V，且經由發光測試確認均勻性之改善。未來在大面積場發射平面背光源的運用上，藉由此低溫成長之最佳發光均勻性的結構，具有製程簡單以及成本便宜的優勢下，因此本研究所提結構與技術將具有相當大之應用潛力。

In this research, we studied on the pillar-like CNT field emission arrays synthesis with co-deposited multilayer catalyst at low temperatures and try to improve their uniformity and reliability by testing as field emission backlight units (FE-BLUs). According to our group’s previous researches, we could effectively decrease the growth temperature of CNTs by utilizing multilayer catalyst and remarkably improve the reliability of CNTs by utilizing co-deposited catalysts. Firstly, we combined these two techniques to preparing co-deposited multilayer catalyst for synthesis of pillar-like CNTs at low temperatures. As a result, CNTs grown with catalysts of co-deposited Co and Ti on Al (Co-Ti/Al) showed the best morphology and field emission properties, which revealed a low turn-on field (~3.6 V/μm), a high current density of 1272 μA/cm2 under 6V/μm electric field, and superior short-term stability with current variation below 7% under the electric field of 6.7 V/μm in 2 hours. In addition, the photo luminescent image of 1cmx1cm pillar patterns illuminated uniformly. Secondly, we obtained an optimum growth time was determined to be 90 min for synthesis of the pillar-like CNTs at 550℃. Height of CNTs was about 8 μm, which revealed a low turn-on field of 3.5 V/μm, and excellent reliability was shown by the degradation of current below 0.1% under the electric field 6.7 V/μm in 2 hours. Based on the material analysis, the amorphous carbon would increase with increasing the growth time, and then the field emission characteristics became worse. Thirdly, we utilized photolithography to pattern different spacings between the pillar-like CNTs for finding out the optimum field emission characteristics by the compromising between screening-effect and emission area. Accordingly, the optimum electrical characteristics for the pillar-like CNTs with the pillar diameter of 6 μm and the pillar height of 8 μm would happen at the inter-pillar spacing of about 9 μm, which exhibited good electrical characteristics. Finally, we utilized triode-typed CNT field emission array to reduce the operation voltage, and the beam spreading to improve the emission uniformity. The optimum parameters of the triode field emission device were obtained according to the simulations, the gate-to-emitter length was 2 μm, and the vertical distance between gate and CNTs was 1 μm. And experimental results and the resultant driving voltage was as low as 43 V. In future, this structure is promising for the applications in a planar backlight because of the large-area uniformity and simple fabrication process with low cost.