Modeling of the Integrated Magnetic Focusing and Gated Field-Emission Device with Single Carbon Nanotube

Abstract

場發射顯示器是一種前瞻性平面顯示器，自從奈米碳管被發現並被證實可以成功應用在真空電子源後。奈米碳管場發射顯示器已變成未來顯示器發展趨勢。目前，場發射顯示器法展上的重大限制在於電子束從場發射極放射出來的發散角度很大，此結果會嚴重地限制顯示解析度，在這篇論文裡，我們利用三維粒子式模擬法對以奈米碳管作為場發射極之三極體場發射結構做元件模擬，研究以新型垂直磁場聚焦方式對於電子束聚焦效果的影響，此方法乃利用外加的線圈或永久磁鐵於場發射元件外部，對內部產生一個垂直向下方向的穩定磁場，利用電子在空間中會沿著磁場方向螺旋行進的簡單原理，對從陰極針尖擴散出來的電子束達到聚焦效果。此外，我們也模擬傳統的四極體結構(除了控制場發射針尖產生電子束的閘極外，另有一個聚焦電極於閘極上方以聚集電子束) ，我們比較兩者的結果發現，以新型垂直磁場聚焦的方式會比傳統電透鏡式聚焦之四極體結構具有更好的電子束聚焦能力，換而言之即具有更好的解析度，另外我們也發現以磁場聚焦方式，也可以免去傳統四極體存在閘極漏電流或因聚焦電極之遮蔽現象造成整體場發射電流降低的問題。

An integrally gated single carbon nanotube (CNT) field emitter with a magnetic focusing is proposed and simulated using a parallelized Poisson’s equation solver, coupled with the ray tracing of electrons, on an unstructured tetrahedral adaptive mesh. The magnetic focusing for the electrons can be achieved by a vertically downward magnetic focusing field (-Bz) through the use of either external solenoids or permanent magnets around the field-emission array. The simulation results are compared with those conventional tetrode-type field emitters using an electrostatic focusing structure. The results reveal that the magnetic focusing design can promise much higher emission current while a smaller or comparable spot size results at the anode. The proposed magnetic focusing can also possibly reduce the complexity of the fabrication of the field emitter. Noticeably, a distribution, similar to the Airy function, showing the dependence of the spot size at the anode on the magnetic flux intensity, is obtained. Thus, under the suitable magnetic focusing condition, it is possible that we can produce well-defined microelectron sources for many field emission applications such as novel parallel electron beam lithography or field emission displays.