藉由多層催化金屬於低溫成長奈米碳管之場發射顯示器之研究

Abstract

由於要將奈米碳管應用於玻璃基板之場發射顯示器以降低成本，且達到大面積面板之製作，因此便需要在低於玻璃熔點(~570℃)的溫度環境下，以化學氣相沉積法(chemical vapor deposition)的方式來成長奈米碳管。本論文是利用Thermal CVD於低溫成長奈米碳管，但相較於PECVD，MPCVD與ECRCVD等方法，利用Thermal CVD於低溫成長奈米碳管的成長速率太慢，但Thermal CVD具有下列幾項優點: (1)throughput高 (2) 不需在真空下操作 (3)操作簡單，只需控制升降溫，不用擔心plasma damages (4) 可靠度高 (5) 低成本。除了利用成長機台的考慮外，催化金屬的組合也是決定性的因素之一，我們希望催化金屬層能有效形成奈米顆粒，形成奈米顆粒後就有兩項優點: (1) 當顆粒尺寸越小時，奈米現象越顯著，如: 表面積增大與表面活性增強 (2) 當顆粒尺寸越小時，催化金屬的熔點會大幅下降，則有利於低溫成長奈米碳管。經過許多實驗驗證，多層催化金屬層(multilayer catalyst films)極具有上述兩項優勢，不論在碳管的morphology和 field emission properties上均表現優異。利用多層催化金屬層所成長的奈米碳管具有表面擴散的高活性成長機制，在最佳化的多層催化金屬所成長的低溫奈米碳管，展現了優異的場發射特性: 低起始電場(turn on field) 3.81V/um 及高場發射電流(current density) 8mA/cm2。除此之外，它在低電場下(3.75V/um) ，也擁有均勻性高的發亮能力，對於未來背光面板的市場有相當大的貢獻。 在金屬閘極控制的三極結構方面，整個結構均是在低溫製成下完成(~500℃) 。控制金屬閘極側吃的深度和奈米碳管的長度，進而達到增加陽極電流的控制能力並減少閘極的漏電流。 最後，我們利用上述最佳化的多層催化金屬層在低溫(500℃)下於玻璃基板(sodalime glass)上成長奈米碳管，得到了相當優異的場發射特性。 經過我們的研究，目前已經可以利用熱化學氣相沉積法(thermal CVD)，並配合多層催化金屬層，在低溫的環境下成長密度均勻的奈米碳管。同時我們也將其應用在玻璃基板上製造場發射顯示器，如能配合適當的三極結構，加強閘極控制能力，相信將對於場發射顯示器有所改善，並期待在未來大尺寸且高解析度奈米碳管場發射顯示器的誕生。

In order to decrease the costs and improve the uniformity of CNT-FEDs, the CVDs process is necessary for the synthesis of CNTs on glass substrate at a low temperature below the melting point of glass (~570℃). In this thesis the thermal CVD was employed to synthesize CNTs at low temperature (500℃). Compared to PECVD, MPCVD, and ECRCVD, thermal CVD possess some advantages, including (1) high throughput,(2) no need for vacuum operation,(3) easy heating control without plasma damages,(4) high reliability, and (5) low cost. Except the consideration of CVD methods, the combination of catalyst metals is a crucial factor in the low temperature CNT growth. We wished the catalyst metals could transform into uniform nanoparticles prior to CNT growth. The formation of nanoparticles possesses two advantages: (1) nano-phenomenon as particle size decreases and (2) lower melting point of catalyst particles as particle size decreases. Under the proofs of many experimental results, multilayer catalyst films possessed the above two advantages. Especially the 20A Co/20A Cr/100A Al was the best candidate for multilayer catalyst films. Its CNTs had great performance no matter the morphology and field emission properties of CNTs. In addition, CNTs using optimum multilayer catalyst films had the high active surface diffusion mechanism and showed the superior field emission characteristics, including low turn on field (3.81V/um) and high current density (8mA/cm2). Besides, CNTs using multilayer catalyst films had the uniform luminescent images at 3.75 v/um so that its performance will be realized in the backlight unit applications. For the gated controlled triode structure, the whole structures were fabricated at 500℃. By controlling the depth of side etching of metal gate and the length of CNTs, the ability of increasing anode currents and reducing gate leakage currents could be realized. Finally, CNTs were grown on sodalime glass substrate at low temperature by utilizing multilayer catalyst films as described above and the excellent field emission properties could be obtained. The uniform CNT films were grown successfully at low temperature with the multilayer catalyst films by thermal CVD. Simultaneously, CNTs were grown on glass substrate for the application of field emission display. We think that the field emission display will be developed if a proper gate structure is combined with the glass substrate. Then, we expect that a large size field emission display with higher resolution will be fabricated in the future.