Field emission devices using carbon nanotubes and method thereof

[0002] The invention relates generally to a field emission device using carbon nanotubes. More particularly, the present invention relates to a vacuum field emission device using carbon nanotubes grown in a direction parallel to a substrate.

[0003] Emission of electrons in the field emission device is greatly varied depending on the structure of a device, the materials constituting a cathode and the shape of the cathode. Presently, the structure of the field emission device may be classified into a diode type consisted of a cathode and an anode, and a triode type consisted of a cathode, a gate and an anode. The triode type structure can be driven with low voltage compared to the diode type since it applies an electric field to the cathode and its neighboring gate in order to emit electrons. Further, the triode type can control easily the current applied into its gate as well as anode. However, there is a problem that the manufacturing of the triode type is not easy due to its complicated structure.

[0004] The materials constituting the cathode include a metal, silicon, diamond, diamond like carbon, carbon nanotube, etc. If the carbon nanotube is used as the cathode materials, a good field emission device could be obtained due to a high field emission characteristic and a high chemical and mechanical stability of the carbon nanotubes. If a field emission device is manufactured using the carbon nanotubes as the cathode, it can be easily applied to a microwave vacuum device, a flat display device, etc.

[0005] The field emission device using the carbon nanotube emitter, which has been attempted so far, employs a field emission emitter. The field emission emitter is manufactured by a process in which carbon nanotube is grown using arc discharge or laser vaporization method and then coated it on a substrate using a thick film process, or a process in which after depositing catalyst metal on a main board, the carbon nanotubes are grown in a vertical direction to the main board. In case of the latter, it is possible to manufacture the device using a semiconductor process. However, as the carbon nanotubes grown randomly are irregular in length, it is difficult to make uniform device. Also, there exists a problem in a vacuum packaging peculiar to the conventional field emission display. Further, there is a problem in the adhesion stability of the tube since the structure of the device becomes three-dimensional. In addition, there is a problem that application to subsequent semiconductor processes is made difficult due to existence of a space between the tubes.

[0006] The present invention provides a method of manufacturing a field emission display using an edge emitting for improving subsequent semiconductor processes, in a way that a metal catalyst is selectively deposited at the side walls of the pattern so that carbon nanotubes can be grown in a direction parallel to the catalyst metal and the grown carbon nanotubes are attached on a basic material by a coating process.

[0007] According to the present invention, a field emission device using carbon nanotubes is disclosed, including a non-conductive substrate 110 acting as a basic material, a cathode electrode 151 formed on the non-conductive substrate 110, a transparent upper plate 180 and an anode electrode is characterized in that it comprises an insulating layer 140 stacked on a portion of the cathode electrode 151, for electrically isolating the cathode electrode 151 from the anode electrode, the portion neighboring to the anode electrode on the an upper portion of the cathode electrode 151; a conductive metal catalyst 120 coated at least at a portion of sidewall opposite to the anode electrode on the sidewall of the insulating layer 140; and a carbon nanotube emitter 130 grown in the direction parallel to the non-conducting substrate 110 from the surface of the metal catalyst 120, wherein the metal catalyst 120 electrically connects the carbon nanotube emitter 130 and the cathode electrode 151.

[0008] Also, a method of manufacturing a field emission device using carbon nanotubes is disclosed that includes the steps of forming a cathode electrode 151 on a non-conductive substrate 110 acting as a basic material through patterning; forming an insulating layer 140 for an electrical isolation on the cathode electrode 151 while exposing a portion of the cathode electrode 151; selectively coating a metal catalyst 120 on the exposed portion of the cathode electrode 151 at one side wall of the insulating layer 140; growing at least one carbon nanotube emitter 130 adhered to the metal catalyst 120 and in a direction parallel to the non-conductive substrate 110; and forming a fluorescent thin film 160 at a point spaced by a given distance with the carbon nanotube emitter 130 on the non-conductive substrate 110.

[0009] The aforementioned aspects and other features of the present invention will be explained in the following description, taken in conjunction with the accompanying drawings, wherein:

[0010] FIG. 1 is a simplified view of a diode-type emission device using carbon nanotubes as an emitter and using a fluorescent thin film as an anode according to one embodiment of the present invention;

[0011] FIG. 2 is a diagram showing a field emission characteristic of the carbon nanotube emitter 130 grown by thermal chemical vapor deposition method in the field emission device shown in FIG. 1; and

[0012] FIGS. 3athrough 3fare processional cross-sectional views illustrating a method of manufacturing a field emission device according to one embodiment of the present invention.

[0013] A field emission device using carbon nanotubes and method thereof according to one embodiment of the present invention will be described in detail with reference to accompanying drawings.

[0014] FIG. 1 shows a simplified structure of a diode-type emission device using carbon nanotubes as an emitter and using a fluorescent thin film as an anode according to one embodiment of the present invention.

[0015] The field emission device shown in FIG. 1 comprises an insulating substrate 110, a cathode electrode 151 an anode 160, an insulating layer 140 for electrically isolating the cathode electrode 151 and the anode 160 neighboring to the cathode electrode 151, and carbon nanotube emitter 130 grown parallel to the substrate 110. If the device is packaged, it may be used as a cathode driving field emission device.

[0016] Also, the anode 160 uses a fine-patterned fluorescent thin film. If a spacer 170 for maintaining vacuum, a transparent electrode 152 and a transparent upper plate 180 are packaged in vacuum, a field emission display can be implemented. At this time, as fluorescent material excited by field emission electrons is confined by difference in refractive index between media, an edge emitting phenomenon is generated in a vertical direction than a horizontal direction to the substrate, thereby accomplishing a high efficiency characteristic of the emitting light. This is because the fluorescent thin film acts as a waveguide of the emitting light as well as the fluorescent materials. Also, in order to increase light efficiency in a vertical direction to the substrate, a method, by which a reflecting layer 190 may be deposited on the substrate before the fluorescent thin film is deposited.

[0017] Further, as the distance between the cathode 151 and the anode 160 can be controlled by the length of the grown carbon nanotubes and the pattern, it is possible to manufacture a diode field emission device which can be driven at low voltage.

[0018] Meanwhile, the metal catalyst 120 causes a catalyst action in a reaction in which carbon nanotubes are grown, wherein transfer metals such as Ni, Fe, Co, etc. and alloys of them may be used.

[0019] Also, the spacer 170 is located between the lower plate and the upper plate, electrically isolates them and acts to prevent contacting the upper plate and the lower plate.

[0020] FIG. 2 is a diagram showing a field emission characteristic of the carbon nanotube emitter 130 grown by thermal chemical vapor deposition method in the field emission device shown in FIG. 1.

[0021] As can be seen from FIG. 2, the carbon nanotube emitter 130 is turned on at about 1 V/μm and represents an emission current of 80 mA/cm²at about 3V/μm. That is, in case of the field emission device, as the distance between the carbon nanotube emitter 130 and the anode 160 as a fluorescent material can be freely controlled, when the distance between the two electrodes is maintained at about 1 μm, it can be driven at about 3 V.

[0022] In case of a conventional fluorescent material, the greater the energy of collided electrons is the greater its emitting efficiency. As the distance between the cathode 151 and the emitter 130 is narrower, the energy of electrons to be emitted is low but the high current can be compensated. Also, since the luminescent body acts as a waveguide to the light, loss of the luminescent efficiency due to low voltage can be compensated. Further, in order to increase the light efficiency in a vertical direction, a method may be employed by which the reflecting layer 190 is coated on the substrate 110 before depositing a fluorescent thin film. It is preferred to use as the reflecting layer 190 an aluminum thin film, which is usually employed.

[0023] In addition, if the field emission device consisted of the anode electrode 151 separated by a given distance with the carbon nanotube emitter 130 grown horizontally is packaged, this device may be applied to a low-voltage microwave power device which can drive the cathode. Since the carbon nanotube emitter 130 emits electrons at a low voltage, there are advantages that it has a good field emission characteristic and it can be easily manufactured into a cathode driving diode vacuum tube.

[0024] FIGS. 3athrough 3fare processional cross-sectional views illustrating a method of manufacturing a field emission device according to one embodiment of the present invention.

[0025] As shown in FIG. 3a, the cathode electrode 151 is formed on the basic material (substrate 110) by a patterning process. At this time, the distance between the patterns can be maintained at a desired distance between the cathode and the emitter using a semiconductor process.

[0026] In FIG. 3b, the insulating layer 140 is deposited to expose a portion of the cathode electrode 151.

[0027] Next, as shown in FIG. 3c, the metal catalyst 120 is entirely deposited on the insulating layer 140 in which the insulating layer 140 and the carbon nanotubes can be selectively grown by the metal catalyst 120. Then, as shown in FIG. 3d, the insulting layer 140 and the carbon nanotubes are etched with only the sidewall of the insulating layer 140 and the metal catalyst 120 on the cathode electrode 151 being left.

[0028] Alternatively, the metal catalyst at the sidewall may be selectively coated on one sidewall of the pattern through metal thin film deposition process. In order to selectively deposit the metal catalyst on the sidewall, a metal thin film is first deposited in the thickness of several nanometers, as shown in FIG. 3dand then the metal catalyst is left only at one sidewall through a selective etching process. Alternatively, a glancing angle metal thin film deposition process may be employed.

[0029] The metal catalyst 120 manufactured thus makes an electrical contact with the cathode electrode 151 on the substrate 110. At this time, the area of the sidewall can be freely controlled depending on the amount of the current required for the device through patterning process. Meanwhile, the thickness of the sidewall must be several nanometers or fewer so that the carbon nanotubes can be selectively grown at the sidewall in a horizontal direction. If the thickness of the sidewall is thick, as the carbon nanotube can be grown vertically as well as horizontally, it is advantageous to subsequent process that the thickness of the sidewall is thinner.

[0030] Thereafter, as shown in FIG. 3e, the carbon nanotubes 130 are induced to grow in parallel to the surface of the substrate 110 by thermal chemical deposition method or plasma chemical deposition method. At this time, although the length of the carbon nanotube 130 is irregular, the length can be made regular by growing the carbon nanotubes 130, coating a non-conductive protection film (e.g., silicon-on-glass) and applying lithography and etching processes.

[0031] Next, as shown in FIG. 3f, if a semiconductor process is freely applied to manufacture the luminescent thin film 161, the distance between the end of the carbon nanotube 130 cathode and the luminescent body anode electrode can be constantly maintained.

[0032] The present invention has been described with reference to a particular embodiment in connection with a particular application. Those having ordinary skill in the art and access to the teachings of the present invention will recognize additional modifications and applications within the scope thereof.

[0033] It is therefore intended by the appended claims to cover any and all such applications, modifications, and embodiments within the scope of the present invention.

[0034] As mentioned above, in case of a field emission device using carbon nanotubes horizontally grown presented in the present invention, there is an advantage that manufacturing can be made easier since it can employ a conventional semiconductor planar technology without development of additional process technologies.

[0035] Further, in case of using a carbon nanotube emitter and a luminescent thin film, there is an advantage that it is possible to manufacture a low voltage driving and high fine emission display.