JP3686400B2 - Cathode electrode and manufacturing method thereof - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a cathode electrode in which a field emission type electron emission material is arranged on a surface of a conductor substrate, and a method for manufacturing the same.
[0002]
[Prior art]
As an electron emission source of a light source tube typified by a fluorescent display tube or a field emission display (FED), it has been proposed to use a cathode electrode having a field emission type electron emission material. FIG. 4 is a cross-sectional view schematically showing an electrode structure of a conventional light source tube using a cathode electrode having a field emission type electron emission material. As shown in FIG. 4, the conventional light source tube has an anode electrode 430 arranged in parallel to face the cathode electrode 410 in a vacuum envelope (not shown), and the cathode electrode 410 and the anode electrode 430 are arranged in parallel. A grid electrode 420 is disposed between the cathode electrode 410 and the anode electrode 430 in parallel.
[0003]
The cathode electrode 410 is composed of a conductor substrate 411 and a field emission electron emission material 412, and a field emission electron emission material 412 such as a carbon nanotube is disposed on the surface of the conductor substrate 411 facing the grid electrode 420. . The grid electrode 420 includes a mesh part 420a having an electron passage hole and a peripheral part 420b that holds the mesh part 420a. The anode electrode 430 is formed of a metal thin film formed to a thickness that allows the electrons emitted from the cathode electrode 410 to pass therethrough, and the phosphor film 440 is disposed on the surface opposite to the cathode electrode 410.
[0004]
In this electrode structure, the grid electrode 420 functions as an electron extraction electrode (control electrode) that extracts electrons from the cathode electrode 410. That is, when a high voltage is applied to the cathode electrode 410 so that the grid electrode 420 has a positive potential, electrons are emitted from the field emission electron emission material 412 by a strong electric field formed in the vicinity of the cathode electrode 410. Field electron emission occurs, and electrons are extracted from the cathode electrode 410. The electrons extracted from the cathode electrode 410 that have passed through the mesh portion 420 a of the grid electrode 420 are further accelerated by the positive high voltage applied to the anode electrode 430, pass through the anode electrode 430, and pass over the anode electrode 430. It collides with the adhered phosphor film 440. As a result, the phosphor film 440 is excited by electron impact and emits light in a color corresponding to the phosphor.
[0005]
Here, electrons extracted from the cathode electrode 410 pass through the mesh portion 420a of the grid electrode 420 and flow into the anode electrode 430 (anode current), and some electrons flow into the grid electrode 420 (grid). Current). The electrons flowing into the grid electrode 420 do not contribute to the light emission of the light source tube. Further, there are grid currents caused by electrons colliding with the mesh part 420a and those caused by electrons colliding with the peripheral part 420b.
[0006]
When the cathode electrode 410 and the grid electrode 420 are installed in parallel, equipotential lines between the cathode electrode 410 and the grid electrode 420 are also distributed substantially in parallel. Then, since electrons are drawn toward the grid electrode 420 perpendicular to the equipotential lines, they are drawn from the cathode electrode 410 toward the grid electrode 420 in the vertical direction, collide with the peripheral portion 420b, and reach the grid electrode 420. There are inflowing electrons. That is, the electrons colliding with the peripheral portion 420b become a grid current and do not contribute to light emission of the light source tube. The presence of such electrons reduces the ratio of the anode current to the total current including the grid current and the anode current (hereinafter, this ratio is referred to as the current distribution ratio), thereby reducing the light emission efficiency of the light source tube, and hence the light emission luminance. Cause it.
[0007]
In order to solve this problem, a cathode electrode shown in FIG. 5 has been proposed. FIG. 5 is a cross-sectional view schematically showing an electrode structure of a conventional light source tube using a cathode electrode with improved current distribution ratio. The electrode structure in FIG. 5 is different from that in FIG. 4 in that the cathode electrode 510 has a dome-shaped protrusion 510 a protruding in the direction of the grid electrode 520. According to the cathode electrode 510, electrons are easily emitted at the top of the convex portion 510a having a short distance from the grid electrode 520 because the electric field strength is strong. However, as the distance from the top of the convex portion 510a toward the periphery increases, And the electric field strength is also weakened, so that electrons are hardly emitted.
[0008]
For this reason, even if the cathode electrode 510 and the grid electrode 520 are arranged so that the dome peripheral portion 510b of the cathode electrode 510 faces the peripheral portion 520b of the grid electrode 520, extraction of electrons from the dome peripheral portion 510b is suppressed. Therefore, electrons that collide with the peripheral portion 520b of the grid electrode 520 and flow into the grid electrode 520 are reduced, so that the grid current can be reduced and the current distribution ratio can be improved.
[0009]
[Problems to be solved by the invention]
However, the light source tube using the cathode electrode shown in FIG. 5 has a problem that electrons spread over a wider range than the mesh portion 520a of the grid electrode 520. That is, electrons tend to be emitted in a direction perpendicular to the equipotential line between the cathode electrode 510 and the grid electrode 520, but when the cathode electrode 510 has a convex shape toward the grid electrode 520, the cathode electrode 510 And the grid electrode 520 have a gentle convex shape projecting in the direction of the grid electrode 520, that is, have an inclination facing outward with respect to the grid electrode 520. Since it is emitted from the top of the electrode 510 with a velocity component in a direction away from the axis perpendicular to the grid electrode 520, the diffusion continues even after passing through the mesh portion 520a of the grid electrode 520, and from the area of the mesh portion 520a Will spread further. For this reason, the emitted electrons collide with the anode electrode 530 in a wider range than the mesh portion 520a, and the light emitting region of the phosphor film 540 is expanded. As a result, the density of electrons flowing into the peripheral portion is smaller than that in the central portion of the light emitting region, resulting in a phenomenon that the uniformity of light emission is reduced and the contour of the light emitting pattern is blurred.
[0010]
In addition, in a light source tube in which a spacer or an envelope is arranged in the vicinity of a display pixel such as an FED, a part of electrons that have passed through the mesh portion 520a of the grid electrode 520 diffuses and collides with the spacer or the envelope. Then, a phenomenon in which a plurality of secondary electrons are emitted from these occurs. As a result of the emission of a plurality of secondary electrons, the spacers and the envelope are charged, and the trajectory of the electrons is disturbed, further impairing the uniformity of light emission.
The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a cathode electrode that improves the current distribution ratio and suppresses the diffusion of emitted electrons, and a method for manufacturing the cathode electrode.
[0011]
[Means for Solving the Problems]
In order to solve the above-described problems, the present invention provides an anode electrode having a phosphor film attached in a vacuum envelope, and a field emission type electron emission material on the surface of a conductor substrate disposed opposite to the anode electrode. In the cathode electrode of the light source tube, the conductor having at least one arranged cathode electrode and at least one grid electrode arranged between the anode electrode and the cathode electrode so as to be separated from both the anode electrode and the cathode electrode and substantially parallel to each other. The substrate is characterized by having at least one dome-like convex portion protruding in the direction of the grid electrode, and the convex portion having at least one crater-like concave portion at the top. The cathode electrode may have at least one hole in place of the concave portion at the top of the convex portion. In addition, one configuration example of the cathode electrode is a nanotube-like fiber in which the field emission type electron emission material is made of carbon.
[0012]
The cathode electrode is made of a conductor substrate having a field emission type electron emission material disposed on the surface, the conductor substrate has a dome-like projection protruding in the direction of the grid electrode, and the projection has a crater shape on the top. Since there is a recess or hole, the grid electrode is placed in parallel to face the surface where the projection of the cathode electrode is formed, and a high voltage is applied so that the grid electrode side is a positive voltage between the cathode electrode and the grid electrode. Is applied, the electric field concentrates on the edge of the concave portion or hole forming the end at the top of the convex portion of the cathode electrode closest to the grid electrode. This makes it difficult for electrons to be emitted from places other than the edge of the concave portion or the hole even at the top of the convex portion of the cathode electrode, so that the grid current is reduced and the diffusion of the emitted electrons is difficult to occur.
[0013]
The manufacturing method of the present invention is a manufacturing method of a cathode electrode in which a field emission type electron emitting material is arranged on the surface of a conductive substrate, and the conductive substrate containing a metal that forms a nuclei of nanotube-shaped fibers made of carbon is formed on the conductive substrate. A metal film made of a predetermined metal that does not form nanotube-like fibers covering both surfaces and at least one through hole that is disposed on one side of the conductor substrate and that penetrates the metal film and exposes the substrate surface is exposed in plan view. A material gas containing a gas composed of a carbon compound at a predetermined concentration in a step of forming at least one recess disposed in the center of the substrate surface, and a conductor substrate in which the metal film, the through-hole, and the recess are formed Heating in an atmosphere and maintaining at a predetermined temperature, growing nanotube-like fibers made of carbon on the exposed substrate surface, and forming a carbon film having nanotube-like fibers; It characterized by a step of projecting the area where the carbon film is formed by returning made a conductor substrate to room temperature in a dome shape. In this case, the metal constituting the conductive substrate is iron or an alloy containing iron. In addition, as the predetermined metal that does not form the nanotube-like fiber, for example, aluminum, nickel, copper, or the like is used.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a partial cross-sectional view of an FED provided with a cathode electrode according to the present embodiment. As shown in FIG. 1, the FED includes a glass substrate 101, a cathode electrode 110 disposed on the glass substrate 101 in contact with the glass substrate 101, and a grid disposed at a predetermined distance above the cathode electrode 110. The electrode 120, the anode electrode 130 disposed above the grid electrode 120 at a predetermined distance, the phosphor film 140 disposed above and in contact with the anode electrode 130, and the glass substrate 101. And a transparent windshield 102 having a phosphor film 140 fixed to the surface facing the glass substrate 101. The glass substrate 101 and the windshield 102 are internally provided with a cathode electrode 110, a grid electrode 120, and an anode electrode. A vacuum envelope including 130 and the phosphor film 140 is formed.
[0015]
The cathode electrode 110 has a band-like shape in plan view, and has a plurality of dome-like convex portions 110a protruding in the direction of the grid electrode 120, and each convex portion 110a has a crater-like concave portion 110b at the top. FIG. 2 is a cross-sectional view schematically showing the structure of the cathode electrode according to the present embodiment. As shown in FIG. 2, the cathode electrode 110 includes a conductive substrate 111 having a plurality of dome-shaped convex portions 110 a each having a crater-shaped concave portion 110 b formed on the top thereof, and each convex portion 110 a of the conductive substrate 111. A field emission electron emission material 112 disposed on the surface and the surface of each recess 110b, and a metal film 113 disposed on a flat portion on one surface side of the conductor substrate 111 and on the other surface side.
[0016]
In this embodiment, the conductor substrate 111 is made of iron or an alloy containing iron, which is a metal serving as a production nucleus of nanotube-like fibers made of carbon. Here, the thickness of the conductive substrate 111 is, for example, 0.05 to 0.20 mm, the height of the dome-shaped convex portion 110a is, for example, 0.02 to 0.20 mm, and the depth of the crater-shaped concave portion 110b is For example, it is half the thickness of the conductor substrate 111. The field emission electron emission material 112 is made of a nanotube-like fiber made of carbon such as carbon nanotube. This nanotube-like fiber forms a carbon film and covers the surface of the convex portion 110a and the surface of the concave portion 110b of the conductor substrate 111. The metal film 113 prevents the formation of carbon nanotube-like fibers other than the regions to be the convex portions 110a and the concave portions 110b of the conductor substrate 111 in the step of forming the carbon-like nanotube fibers by the thermal CVD method described later. For example, it is made of any one of aluminum, nickel, and copper, which is a metal on which carbon nanotube-like fibers made of carbon are not formed.
[0017]
The grid electrode 120 has a band shape in plan view, and is provided with a mesh portion 120a having an electron passage hole in a region facing the convex portion 110a of the cathode electrode 110, and is opposed to the dome peripheral portion 110c of the cathode electrode 110. The peripheral portion 120b of the grid electrode 120 is provided in the region to be processed. The anode electrode 130 and the phosphor film 140 are formed in a strip shape so as to correspond to the grid electrode 120 on a one-to-one basis.
[0018]
In the present embodiment, in order to control lighting of each pixel of the FED arranged in a matrix, the cathode electrode 110 and the grid electrode 120 formed in a planar view are respectively arranged in rows and columns of the matrix orthogonal to each other. It arrange | positions so that it may respond | correspond, and each row | line | column and each column are comprised so that a cathode power supply and grid power supply which are each arrange | positioned outside the vacuum envelope can be connected. The anode electrode 130 is configured to be connectable to an anode power source disposed outside the vacuum envelope.
[0019]
A first insulating spacer 103 is disposed between the cathode electrodes 110 to hold the grid electrode 120 at a predetermined distance from the cathode electrode 110 and to insulate the cathode electrodes 110 from each other. Between the grid electrodes 120, a second insulating spacer 104 is disposed that separates the anode electrode 130 from the grid electrode 120 by a predetermined distance and insulates between the grid electrodes 120 and between the anode electrodes 130. The members constituting the FED are the same as the members used in the conventional FED except for the cathode electrode 110, and thus the description thereof is omitted.
[0020]
Next, electron emission of the cathode electrode according to this embodiment will be described with reference to FIG. A grid electrode 120 is disposed opposite to the surface of the cathode electrode 110 where the dome-shaped protrusion 110a is formed, and a high voltage is applied between the cathode electrode 110 and the grid electrode 120 so that the grid electrode 120 side has a positive voltage. Is applied, the electric field concentrates on the edge portion of the concave portion 110b formed at the top of the convex portion 110a of the cathode electrode 110 having the shortest distance from the grid electrode 120. While electrons are emitted more from the grid electrode 120, electrons are less likely to be emitted from the side surface portion of the convex portion 110 a that is away from the grid electrode 120 and from the vicinity of the bottom portion of the concave portion 110 b.
[0021]
For this reason, since electrons do not spread over a wider range than the mesh part 120a of the grid electrode 120, a phenomenon in which the light emission uniformity is reduced and a phenomenon in which the outline of the light emission pattern is blurred are suppressed. Further, the dome peripheral portion 110c of the cathode electrode 110 facing the peripheral portion 120b of the grid electrode 120 has no nanotube emission made of carbon as an electron emission source, so that there is no electron emission, and the peripheral portion 120b of the grid electrode 120. As a result, the electrons flowing into the grid electrode 120 due to collision can be almost eliminated, so that the grid current can be reduced and the current distribution ratio is improved. The concave portion 110b formed in the vicinity of the top of the dome-shaped convex portion 110a of the cathode electrode 110 can be formed so that the peripheral edge thereof has a circular shape in a plan view, but is not limited to a circular shape. It can also be square. Further, a hole may be provided in place of the concave portion at the top of the cathode electrode 110 formed in a dome shape.
[0022]
Next, an example of a manufacturing method of the cathode electrode 110 according to this embodiment will be described with reference to FIG. FIG. 3 is an explanatory view schematically showing a manufacturing process of the cathode electrode according to the present embodiment. First, as shown in FIG. 3A, a substrate 301 made of iron or an alloy containing iron is prepared. The reason why the substrate 301 is made of iron or an alloy containing iron is that nanotube-like fibers made of carbon can be formed by a thermal CVD method only for iron or an alloy containing iron.
[0023]
Here, when using iron, industrial pure iron (99.96Fe) is used, but the purity is not particularly required, and may be, for example, 97% or 99.9%. Moreover, as an alloy containing iron, for example, stainless steel such as SUS304, 42 alloy, 42-6 alloy, or the like can be used, but is not limited thereto. In this embodiment, a thin plate of 42-6 alloy having a thickness of 0.05 to 0.20 mm was used for the substrate 301 in consideration of production cost and availability.
[0024]
Next, as illustrated in FIG. 3B, a metal film 302 of any one of aluminum, nickel, and copper is formed on the entire surface of the substrate 301 except for a region where a convex portion on one surface side of the substrate 301 is formed. In this embodiment, the metal film 302 is formed so that the exposed area of the substrate surface in a substantially circular shape remains in a matrix at intervals corresponding to the pixel pitch of the FED. Here, the reason why the metal film 302 of any one of aluminum, nickel, and copper is formed on the entire surface of the substrate 301 is that the nanotube-like fiber made of carbon is not formed on the metal film 301 by the thermal CVD method. is there. These metal films 302 can be formed by a known plating method or vapor deposition method.
[0025]
After the formation of the metal film 302, as shown in FIG. 3C, a crater-shaped recess 301a is formed at the center of the region where the individual protrusions are formed. In this embodiment, the substrate 301 is etched, and a substantially circular crater is formed so that the depth is about half of the thickness of the substrate 301 in the center of the region where the substrate surface is exposed in each approximately circular shape. Form. Note that the method of forming the recess 301a is not limited to etching. For example, when the pixel size and the pixel pitch are large, the recess 301a may be mechanically processed. In addition, a crater-shaped recess 301 a may be formed before the metal film 302 is formed on the substrate 301.
[0026]
Next, as shown in FIG. 3D, the substrate 301 that has undergone the steps of FIGS. 3A to 3C is placed in a reaction furnace 303 constituted by, for example, a quartz tube, and the reaction furnace 303. A thermal CVD process is performed in which the substrate 301 is heated by the heater 304 in a state where the source gas and the hydrogen gas (carrier gas) are supplied from one of them. As the source gas, a C _{1 to} C ₃ hydrocarbon gas such as carbon monoxide, acetylene, ethylene, ethane, propylene, propane, or methane gas may be used, and the flow rate may be about 20 to 2000 sccm. The heating temperature of the substrate 301 may be about 700 to 1000 ° C. By performing the above thermal CVD process for 10 to 60 minutes, a carbon film 305 having nanotube-like fibers made of carbon is formed on the exposed surface of the substrate 301.
[0027]
A nanotube-like fiber made of carbon, which is a field emission electron-emitting material, is a substance composed of carbon having a thickness of about 2 nm to less than 1 μm and a length of about 1 μm to less than 100 μm. Single-walled carbon nanotubes with a five-membered ring formed at the tip of the cylinder and multiple graphite layers nested in a multilayer structure, and each graphite layer is closed in a cylindrical shape It may be a carbon nanotube having a structure, a hollow graphite tube having a disordered structure and a defect, or a graphite tube in which carbon is packed in a tube. Moreover, these may be mixed.
[0028]
In the process where the thermal CVD process is completed and the temperature of the substrate 301 returns to room temperature, the region of the substrate 301 in which the carbon film 305 having nanotube-like fibers made of carbon is formed is deformed, as shown in FIG. Thus, a dome-shaped convex portion 305a is formed. Such a dome-shaped convex portion 305a is formed because the carbon film 305 formed on the exposed surface of the substrate 301 and the substrate material are greatly different in thermal expansion coefficient, and thus expanded due to the high temperature in the thermal CVD process. It is considered that a difference in shrinkage occurs between the carbon film 305 formation region on one surface side and the other surface side of the carbon film 305 formation region in the process of returning the substrate 301 to room temperature, and deformation like bimetal occurs.
[0029]
Through the above steps, the field emission electron emission material is disposed on the conductive substrate, and the dome-shaped convex portion having the crater-shaped concave portion formed at the top is formed. According to this manufacturing method, the dome-shaped convex portion is formed by the formation of a nanotube-like fiber made of carbon, which is a field emission type electron emission material, so that the dome-shaped convex portion is formed by press molding as in the past. There is no need to do. For this reason, even if it is a case where the fine electron emission part difficult by press molding like FED is requested | required, it is possible to form a convex part.
[0030]
In this embodiment, since the cathode electrode used for the FED is taken as an example, it has been described as having a plurality of convex portions serving as electron emission portions, but there may be one convex portion. Moreover, although the cathode electrode provided with one concave portion on the top of the convex portion of the cathode electrode has been described as an example, the number of concave portions provided on the top of the convex portion is not limited to one, and the area of the concave portion is reduced. A plurality of them may be provided. In this case, since the electron emission region can be made more uniform, it can be expected that the emission uniformity is further improved.
[0031]
Further, in the manufacturing process, the substrate may be sized so that all cathodes of the FED can be formed, and the slit may be formed between the cathode electrodes in the process of etching the recess. In this case, if the slit forming portion is etched from both sides of the substrate, the slit can be formed simultaneously with the formation of the recess. As a result, all the cathodes of the FED can be manufactured simultaneously from a single substrate, and the manufacturing process is simplified.
[0032]
Since the cathode electrode according to this embodiment is manufactured by the manufacturing process described above, the metal film covers the portions other than the convex portions, but this metal film may not be provided. In addition, the carbon nanotube-like fibers are not arranged on the flat part of the convex part forming surface, but since the flat part is farther from the grid electrode than the convex part, there is less possibility of electrons being emitted. Nanotube fibers made of carbon may be arranged on the flat portion.
[0033]
【The invention's effect】
As described above, the cathode electrode of the present invention has a field emission type electron-emitting material disposed on the surface of a conductor substrate, and the conductor substrate has at least one dome-shaped protrusion protruding in the direction of the grid electrode. Since the convex portion has at least one crater-shaped concave portion or hole at the top, the electric field concentrates on the edge portion of the concave portion or hole forming the end portion at the top of the convex portion of the cathode electrode. Electrons are less likely to be emitted from locations other than the edge portion. As a result, electrons withdrawing from the cathode electrode can be prevented from colliding with the periphery of the grid electrode that does not contribute to light emission of the light source tube, and the grid current can be suppressed, thereby increasing the current distribution ratio of the light source tube. As a result, an effect of improving the light emission luminance of the light source tube is obtained. Further, since electrons are not easily diffused in order to prevent electrons from being drawn out from the side surface portion of the convex portion of the cathode electrode, it has an effect of improving the light emission uniformity and suppressing the blurring of the contour of the light emission pattern.
In addition, according to the manufacturing method of the present invention, since the dome-shaped convex portion is spontaneously formed at the formation position of the nanotube-shaped fiber made of carbon on the conductor substrate, an effect of simplifying the manufacturing process can be obtained. .
[Brief description of the drawings]
FIG. 1 is a partial cross-sectional view of an FED including a cathode electrode according to an embodiment.
FIG. 2 is a cross-sectional view schematically showing the structure of a cathode electrode according to an embodiment.
FIG. 3 is an explanatory view schematically showing a manufacturing process of the cathode electrode according to the embodiment.
FIG. 4 is a cross-sectional view schematically showing an electrode structure of a conventional light source tube using a cathode electrode having a field emission type electron emission material.
FIG. 5 is a cross-sectional view schematically showing an electrode structure of a conventional light source tube using a cathode electrode with an improved current distribution rate.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 101 ... Glass substrate, 102 ... Windshield, 103, 104 ... Insulating spacer, 110, 410, 510 ... Cathode electrode, 110a, 305a, 510a ... Convex part, 110b, 301a, 305b ... Concave part, 110c, 510b ... Perimeter part of dome 111, 411, 511 ... conductive substrate, 112, 412, 512 ... field emission electron emission material, 113, 302 ... metal film, 120, 420, 520 ... grid electrode, 120a, 420a, 520a ... mesh part, 120b, 420b, 520b ... peripheral part, 130, 430, 530 ... anode electrode, 140, 440, 540 ... phosphor film, 301 ... substrate, 303 ... reactor, 304 ... heater, 305 ... carbon film.

Claims (5)

In a vacuum envelope, an anode electrode having a phosphor film attached thereto, a cathode electrode in which a field emission type electron emission material is arranged on the surface of a conductor substrate arranged to face the anode electrode, the anode electrode and the cathode In a cathode electrode of a light source tube having at least one grid electrode disposed between and substantially parallel to and spaced from both the anode electrode and the cathode electrode,
The conductor substrate has at least one dome-shaped protrusion protruding in the direction of the grid electrode;
The cathode has at least one crater-like recess recessed in a direction facing the grid electrode at the top. The cathode electrode according to claim 1.
The convex portion has at least one hole in place of the concave portion at the top thereof. The cathode electrode according to claim 1 or 2,
The cathode electrode, wherein the field emission type electron emission material is a nanotube-like fiber made of carbon. A method of manufacturing a cathode electrode in which a field emission type electron emission material is disposed on a surface of a conductive substrate,
A metal substrate made of a predetermined metal that does not form the nanotube-like fibers covering both surfaces of the conductive substrate including a metal serving as a nucleus of the nanotube-shaped fiber made of carbon, and the metal disposed on one side of the conductive substrate. Forming at least one through hole having a substantially circular shape in plan view that penetrates the film and exposing the substrate surface, and at least one recess disposed in the central portion of the exposed substrate surface;
The conductor substrate in which the metal film, the through hole, and the recess are formed is heated in a material gas atmosphere containing a gas composed of a carbon compound at a predetermined concentration to be held at a predetermined temperature, and exposed. Growing nanotube-like fibers made of carbon on the substrate surface, and forming a carbon film having the nanotube-like fibers;
And a step of projecting the region on which the carbon film is formed into a dome shape by returning the conductive substrate on which the carbon film is formed to room temperature. In the manufacturing method of the cathode electrode according to claim 4,
The method for producing a cathode electrode, wherein the metal constituting the conductive substrate is iron or an alloy containing iron.

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