Description FIELD EMISSION DEVICE WITH COATING LAYER AND METHOD FOR FABRICATING THE SAME [1] Technical Field [2] The present invention relates to a field emission device provided in a display device or the like and used as an electron emission source, and more particularly, to a field emission device with a coating layer which is capable of improving the low voltage operation and the emission characteristics by coating a carbonaceous matter on a carbon nano tube, and a method for fabricating the same.

[3] Background Art [4] Generally, a field emission device is used as an electron emission source of a display device, a lighting device, a backlight unit, etc. This field emission device is a display device in which, if a strong electric field is formed in an emitter, cold electrons are emitted, move in vacuum, and collide with a fluorescent film, thereby, an Image is formed by lighting a fluorescent substance.

[5] In the conventional field emission device, there is a possibility that residual gas particles in vacuum may be ionized by collision with electrons and gas ions may collide with a micro-tip and damage it. Besides, there is a drawback that the life span and performance of the field emission device is deteriorated since fluorescent particles fall off and pollute the micro-tip.

[6] Therefore, as means for solving the drawback of the field emission device, proposed was the method of forming a carbon nano tube on a substrate for the purpose of improving the field emission characteristics using a physically and chemically stable carbon nano tube. Especially, the method of forming a carbon nano tube includes the method of directly growing a carbon nano tube on a substrate using chemical vapor depcsition (CVD) and the method of screen printing using a paste.

[7] By the way, the degree of vacuum in the panel (chamber) of a field emission device is gradually decreased with the passage of time, and ionized ions, which ionized by collision with residual gases, sputter (ion collision) an electron emission source and an outgassing occus, thereby the device is damaged and the life span is reduced. Thus, in order to prevent such a deterioration of the degree of vacuum, a getter is mounted to remove residual gases, but the aforementioned problem still exists.

[8] Disclosure of the Invention [9] Therefore, an object of the present invention is to provide a field emission device with a coating layer which is capable of improving the low voltage operation and the emission characteristics by coating amorphous diamond on a carbon nano tube, and a method of making the same.

[10] To achieve the above object, there is provided a field emission device with a coating layer according to the present invention, wherein the coating layer is formed on the outer surface of a carbon nano tube.

[11] Furthermore, the coating layer is formed by preserving carbon containing methane or ethylene for 10 to 60 minutes under a pressure of 40 to 70 Torr in a hydrogen atmosphere in the temperature range from 200 to 500iÆC, with a carbon nano tube to be coated being housed in a coating apparatus.

[12] Brief Description of the Drawings [13] The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention.

[14] In the drawings: [15] Fig. 1 is a view showing a frame format of a field emission device according to the present invention; [16] Fig. 2 is a SEM photograph of the field emission device according to the present invention; [17] Fig. 3 is a graph comparatively showing the field emission characteristics of the field emission device according to the present invention; and; and to the prior art [18] Fig. 4 is a photograph comparatively showing a field emission image of the field emission device according to the present invention.

[19] Best Mode for Carrying Out the Invention [20] Hereinafter, a preferred embodiment of the present invention will be described in detail.

[21] Fig. 1 is a view showing a frame format of a field emission device according to the present invention. Fig. 2 is a SEM photograph of the field emission device according to the present invention. Fig. 3 is a graph comparatively showing the field emission characteristics of the field emission device according to the present invention. Fig. 4 is a photograph comparatively showing a field emission image of the field emission device according to the present invention characteristic of a coating layer 20 formed on the outer surface of a carbon nano tube 10.

[22] First, the present invention is to minimize the damage caused by arcing at a high voltage and reduce the work function of electrons to make an electron emission easier by forming a coating layer 20 on the outer surface of a carbon nano tube 1Q preferably at the end thereof.

[23] At this time, the coating layer 20 is a material having the characteristics such as electron affinity, chemical stability, thermal stability, and high hardness, etc. It is preferable that the coating layer 20 is made of a carbonaceous matter having a lower work function, such as amorphous diamond, diamond like carbon, carbon fiber, boron nitride, aluminum nitride, gallium nitride, graphite or the like, individually or in a combination thereof.

[24] Further, as the method of coating the coating layer 2Q sputtering, electron beam or laser deposition, chemical vapor deposition, cathodic arc deposition or the like is suitable. The thickness of the coating layer 20 is preferably 1 to lOnm.

[25] This range is set in view of the geometrical shape of an electron emission source.

The higher the aspect ratio of the geometrical shape is, that is, the sharper the tip of the electron emission source is, the better the electron emission gets, because if the coating thickness is too large, the aspect ratio becomes lower.

[26] Meantime, the process of forming a coating layer using plasma chemical vapor deposition will be described. Amorphous diamond (work function: 1-3eV) is coated on the surface of an emitter at a thickness from 1 to lOnm by preserving for 10 to 60 minutes under a pressure of 40 to 70 Torr in a hydrogen atmosphere and a gas (hydrogen content: 0. 1-0. 5 wt%) contained carbon, such as methane or ethylene, with a coating apparatus set to the temperature range between 200 and 500iÆC.

[27] Although the coating layer formation process has been described with respect to plasma chemical vapor deposition and amorphous diamond, it will be readily apparent that other coating methods and coating materials falling in the range of the above de- scription are contemplated as being within the scope of the present invention, as defined by the following claims.

[28] The operating procedure of the present invention will be described. A coating layer 20 is formed at the end of a carbon nano tube 10 and mounted or printed on a display device (not shown), and then if a voltage more than a predetermined level (threshold voltage: turn on voltage) is applied to the display device, an electric field is formed around the tip, whereby electrons start being emitted from the carbon nano tube 10.

[29] In this case, it is judged that the coating layer 20 prevents the damage caused by the residual gases and the outgassing caused upon a heat treatment being adsorbed and collided with the carbon nano tube 10 in the display device.

[30] Fig. 2 shows a comparison of SEM photographs of the prior art and the present invention. <BR> <BR> <P>[31] In a comparative example (where no coating layer is formed), the diameter ( ? ? ) of<BR> the carbon nano tube is 1 to 5nm, and the diameter ( ? ? ) of the carbon particle is 60 to 70nm, while in the present invention (where a coating layer is formed) the diameter <BR> <BR> ( ? ? ) of the carbon nano tube is 10 to 20nm.<BR> <P>[32] At this time, it can be seen that the diameter ( ? ? ) of the carbon nano tube of this invention has grown at least twice larger as compared to the comparative example.

[33] Fig. 3 is a graph showing the field emission characteristics of the prior art and of the present invention. It can be seen that in the comparative example (where no coating layer is formed), the threshold voltage (turn on voltage) is about 2 V/um, while in the present invention the threshold voltage has reduced to about 1.5 V/um.

[34] Further, it can be seen that the emission current of this invention has become better about twice or more at the same voltage as compared to the comparative example, and there is hardly any damage caused by arching even at a high voltage (more than 3kV).

[35] Fig. 4 is a view comparatively showing field emission images of the prior art and of the present invention.

[36] It can be seen that in the comparative example (where no coating layer is formed), about 8mA of an emission current is generated at 1.5 kV, while in the present invention (where a coating layer is formed) about 20 mA of an emission current is generated at 1.5 kV.

[37] This is because the coating layer 20 coated on the carbon nano tube 10 is formed of material having a low work function to thus increase the field electron emission efficiency and the coating layer 20 is overally uniformly coated.

[38] Conclusively, as shown in Figs. 2 to 4, the field electron emission efficiency has increased since the material at the sharp tip of the electron emission source is made of material having a low work function, the coating layer has become overally uniform by means of coating, and the damage caused by collision with residual gas atoms and ions is reduced by means of the coating layer.

[39] Industrial Applicability [40] As described above, according to the field emission device with a coating layer and the method of making the same, a coating layer is formed on the outer surface of a carbon nano tube to thus prevent the damage of the carbon nano tube caused by arching. By this, the emission characteristics of the field emission device are improved, the life span thereof is lengthened, and the current density of the field emission device is relatively increased to thus improve the brightness.