JP2003272517A - Cathode and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a cathode having an excellent electron emission characteristic and capable of suppressing a dispersion of the relation between the impressed voltage and the obtained emission (current vs. voltage characteristic) even in the case a plurality of such cathodes are used. <P>SOLUTION: The first electrode 2 is formed on a base board 1, and a resin layer 13 containing CNT is provided on the first electrode 2. The surface of the resin layer 13 containing CNT is polished by a polishing tape (polishing means 5) while that surface of the resin layer 13 where the polishing tape 5 is in contact and the surface of the board 1 are held parallel. Then an insulating layer 6 is formed and subjected to baking at 500°C in the open air atmosphere so as to decompose the resin component of the resin layer 13 for exposing the CNT, and an electron emission part 3 is formed to generate an electron source 4, and finally a second electrode 7 consisting of a thin metal plate is bridged on the insulating layer 6, and the intended cathode is accomplished. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cathode manufacturing method using a carbon nanotube (hereinafter referred to as CNT) and a cathode.

[0002]

2. Description of the Related Art In recent years, flat panel displays have been actively developed, and liquid crystal, plasma displays, organic EL
Various types of image display devices have been developed and partially put into practical use. Among them, an FED (Field E) using a cold cathode equipped with a micron-sized micro electron emitting portion is used.
The mission display (CRT) is a CRT (Cathode Ray) which is still the mainstream of image display devices.
(Tube) has been attracting attention as a thin display device can be realized while maintaining the features such as high brightness, wide viewing angle, long life and fast response. There are various types of cold cathodes, but the FED that applies the cold cathode using CNTs that can form the electron emission portion by a simple process such as screen printing without the need for fine processing recently is the most practical. Began to think.

[0003] CNT is a columnar structure in which carbon atoms are regularly arranged in a hexagonal shape and connected in a mesh form into a cylindrical shape, and an electric field is concentrated at the minute tip of this CNT to emit electrons. By obtaining it, the electron emission portion can be formed. As the CNT, a single-walled nanotube (SWCNT) having a single cylinder and a multi-walled nanotube (M) having concentric cylinders having different diameters are stacked.
WCNT), but in any case, it is an extremely thin tube having a diameter of a cylinder of several tens nm and a length of several tens μm to several hundreds μm.

FIG. 6 is an explanatory view of a cathode disclosed in Japanese Patent Application Laid-Open No. 2000-90813, wherein 51 is a substrate, 52 is a first electrode, 54 is an electron emitting portion, and is attached to the first electrode 52. The particles 53 containing a carbon material having a hexacarbon ring structure containing CNT or graphite as a main component are formed, and the surfaces of the particles 53 are etched by plasma or the like to cause a part of the CNT to pop out. There is. 55 is a second electrode, and the first electrode 52 and the insulating layer 56.
The electron emission from the particles 53 is started by applying a predetermined potential difference between the first electrode 52 and the first electrode 52. Since the size of the particles 53 varies,
When the distance between the uppermost part of the particle 53 and the second electrode 55 necessary for obtaining electron emission varies, and the electron emitting portion is applied to, for example, an FED having an electron emitting portion for each pixel,
Since a plurality of electron emitting portions are required, the emission characteristics of each electron emitting portion vary.

As a method of suppressing the above-mentioned variation, for example, in Japanese Patent Laid-Open No. 11-329312, a bundle of columnar graphite in which CNTs are aggregated with the longitudinal directions thereof oriented in the same direction as an emitter is formed, and the side surfaces thereof are perpendicular to the longitudinal direction. It is disclosed that the tip of the CNT is aligned by irradiating a laser beam on it to cut a bundle of CNTs. In addition, Japanese Patent Laid-Open No. 2000-2
No. 23004 discloses that an ingot of a composite material in which CNTs are dispersed is formed, and the amount of CNT in the ingot cut and exposed on the surface is increased by polishing the surface of the ingot, and then a metal is removed from the surface of the ingot. Techniques for removing CNTs to project CNTs from the surface of the ingot and then assembling them into a device and for spin-coating emitters precoated with a solder layer with CNTs are disclosed.

[0006]

When the electron emitting portion is formed by concentrating the electric field on the minute tip of the CNT to emit electrons as described above, it is desirable that the tip of the CNT be as sharp as possible. Further, if the tip of the CNT is opened without being terminated, the electron emission characteristic is improved. However, as disclosed in Japanese Patent Application Laid-Open No. 11-329312, in the method of melting and aligning the tips of CNTs with a laser beam in order to flatten the surface of the electron emitting portion,
The tip of the CNT is often bound by high heat, and there is a problem that sufficient characteristics of the CNT cannot be obtained.

A method of cutting a bundle of CNTs with the above laser beam (Japanese Patent Laid-Open No. 11-329312)
A case will be described in which the electron emitting portion 54 of FIG. 6 (Japanese Patent Laid-Open No. 2000-90813) is used as a method for flattening the uppermost portion of the particles 53. FIG. 6 (JP 2000-
In the electron emission portion 54 shown in Japanese Patent No. 90813), when the uppermost portion of the particle 53 is cut with a laser beam to be flattened, the laser beam used for the cutting and the substrate 51 must be precisely parallel to each other. This is because when the electron emitting portion 54 is applied to the FED, a plurality of the electron emitting portions are required, and moreover, in order to obtain the uniform emission brightness of the FED, the electron emission of the plurality of electron emitting portions is made constant. This is because it is necessary to keep the distance between the uppermost portion of each particle 53 of each electron emitting portion 54 and the second electrode 55 constant for that purpose. However, in order to realize the above-mentioned precise parallelism, a highly accurate manufacturing apparatus is required, and it takes a long time to set the parallelism, which causes a problem that throughput cannot be increased.

Further, when a plurality of electron-emitting portions arranged in a plane are irradiated with a laser beam from the lateral direction, the electron-emitting portions closer to the laser beam incident side are sequentially cut off, so that they are located at a farther position. When the electron emitting portion is cut, the height of the electron emitting portion near the incident side becomes low due to residual heat of the laser beam passing therethrough. for that reason,
There has been a problem that the relationship between the applied voltage and the obtained emission (current-voltage characteristic) greatly varies between the plurality of cathodes on the FED plane.

Further, in the case of using an ingot of a composite material in which CNTs are dispersed in Japanese Patent Laid-Open No. 2000-223004, there is a problem that a process of incorporating an electron emitting portion on a substrate after manufacturing is required and miniaturization becomes difficult. there were.

The present invention has been made in order to solve the above problems, is excellent in electron emission characteristics, and even when a plurality of electron emission characteristics are used, variations in the relationship between applied voltage and obtained emission (current-voltage characteristics). It is an object of the present invention to obtain a cathode in which is suppressed and a manufacturing method thereof.

[0011]

A first cathode manufacturing method according to the present invention comprises an electron source comprising an electron emitting portion containing carbon nanotubes provided on a first electrode provided on a substrate, and A method of manufacturing a cathode, comprising: a first electrode and a second electrode that is provided via an insulating layer and applies a potential difference between the first electrode and the first electrode; A step of providing a resin layer containing carbon nanotubes on the electrodes; a step of polishing the surface of the resin layer so that the distance between the surface of the resin layer and the second electrode becomes uniform; The method includes a step of thermally decomposing and removing the resin component to expose the carbon nanotubes to obtain an electron source, and a step of providing a second electrode via the first electrode and an insulating layer.

A second method for manufacturing a cathode according to the present invention comprises an electron source having an electron emitting portion containing carbon nanotubes provided on a first electrode provided on a substrate, and insulating the first electrode from the electron source. A method for producing a cathode, comprising: a second electrode which is provided via a layer and which applies a potential difference between the first electrode and the first electrode, wherein carbon nanotubes are attached to the first electrode provided on the substrate. A step of providing a resin layer containing, a step of exposing the carbon nanotubes by thermally decomposing and removing the resin component of the resin layer, and impregnating the exposed carbon nanotube groups with water glass and firing, with the water glass The step of adhering the carbon nanotubes to the first electrode is performed, and the surface of the carbon nanotubes is polished and electrically charged so that the intervals between the surface of the carbon nanotubes and the second electrode are aligned. Obtaining a source, a method comprising the step of providing a second electrode over the first electrode an insulating layer.

The first cathode according to the present invention includes an electron source having an electron emitting portion containing carbon nanotubes provided on a first electrode provided on a substrate, the first electrode and an insulating layer. And a second electrode that applies a potential difference between the first electrode and the first electrode, the electron source has a surface polished with the first electrode provided on the substrate, The part comprises an electron emitting part containing carbon nanotubes attached to the first electrode with water glass.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiment 1. 1 (a)-
(E) is a process drawing which shows the manufacturing method of the cathode of the 1st Embodiment of this invention in order of process, In the figure, 1 is a board | substrate and 2 is 1st
Electrode, 13 is a resin layer containing CNT, 3 is an electron emitting portion, 4 is an electron source, 5 is a polishing means, 6 is an insulating layer, and 7 is a second layer.
, And 8 are openings. First, the first electrode 2 is formed on the substrate 1 in a stripe shape with a pitch of usually several mm (FIG. 1A). As the first electrode 2, for example, a metal electrode such as silver, aluminum, gold, or copper, or a transparent electrode such as ITO or tin oxide can be used. As a forming method, a thick film forming method such as screen printing or a thin film forming method such as vapor deposition or sputtering can be used.

Next, a resin layer 13 containing CNT is provided on the first electrode 2 by the following procedure {FIG. 1 (b)}. First, butyl carbitol (manufactured by Wako Pure Chemical Industries) and butyl carbitol acetate (manufactured by Wako Pure Chemical Industries, Ltd.) were mixed at a ratio of 3: 1, and ethyl cellulose having a degree of polymerization of 200 (manufactured by Hercules Co., Ltd.) was dissolved in the solution. To make a solution called a vehicle. A CNT and a dispersant (trade name: Homogenol L-18, manufactured by Kao Soap Co., Ltd.) are dispersed and mixed in the above vehicle to prepare a screen printing paste.
The weight ratio is 8: 2. The dispersant is CNT.
To 0.01% by weight. CNT is an arc discharge or thermal CVD (Chemical Vapor Depos).
Ition). A screen printing mask using a stainless mesh with a mesh opening number 250 is prepared, and the paste is used to form a resin layer 13 containing CNTs by screen printing, and then 120
° C Dry in air. Resin layer 1 containing CNT
3 are isolated on the first electrode 2 in a shape such as a quadrangle or a circle, and are formed at the same pitch as the first electrode.

Next, mechanical polishing is adopted as the polishing means 5, a polishing tape of No. 1000 is used, and the substrate 1 is fixed and the polishing tape 5 is moved so that the resin layer 13 containing CNTs.
The surface is polished {Fig. 1 (c)}. At this time, the polishing tape 5 is adjusted so that the surface in contact with the resin layer 13 containing CNT and the moving direction thereof and the surface of the substrate 1 are parallel to each other. When polishing, the polishing tape 5 may be fixed and the substrate 1 may be moved, or the substrate and the polishing tape may be moved simultaneously.

Next, an insulating layer 6 having a height of about 30 μm is formed between the resin layers 13 containing CNTs by screen printing {FIG. 1 (d)}. As the paste used at this time, for example, ethyl cellulose is dissolved in terpineol (manufactured by Wako Pure Chemical Industries, Ltd.), and lead borosilicate glass and alumina powder are dispersed and mixed in the solution. The component ratio is 1 to 5 wt% of ethyl cellulose, 25 to 3 of terpineol
The range is 0 wt%, lead borosilicate glass powder 35 to 40 wt%, and alumina powder 30 to 40 wt%. Height 30
In order to obtain a thickness of .mu.m, printing is repeated 2-3 times, and after the printing is completed, it is dried in an atmosphere of 120.degree.

Then, it is fired at 500 ° C. in an air atmosphere to obtain C
The resin component such as ethyl cellulose of the resin layer 13 containing NT is decomposed to expose the CNT to form the electron emitting portion 3, the electron source 4 is obtained, and the low melting point glass of the insulating layer 6 is fixed. In this embodiment mode, the formation of the insulating layer and the CN
Although the thermal decomposition of the resin component of the resin layer containing T was performed at the same time, it may be performed separately.

Finally, a second electrode 7 made of a thin metal plate is cross-linked on the insulating layer 6 to produce a cathode {FIG. 1
(E)}. The second electrode 7 has the same stripe pitch as that of the first electrode 2 and has a plurality of slits in the direction orthogonal to the first electrode 2, and the opening 8 is provided immediately above the electron emitting portion 3. It is provided.

FIG. 2 is a block diagram of an image display device using the cathode obtained in this embodiment. In the figure, 31 is a rear substrate (corresponding to the substrate 1 in FIG. 1), 32 is a spacer, and 33 is a spacer. The front substrate, 35 is a phosphor screen, and 39 is an opening. That is, the rear substrate 31, the spacer 32, and the translucent front substrate 33 are vacuum-tightly sealed, and the stripe-shaped first electrode 2, the electron-emitting portion 3, and the insulating layer 6 are formed on the inner surface of the rear substrate 31. And a second electrode 7 having a plurality of slits in the direction orthogonal to the first electrode 2 is formed, and a cathode is formed on the inner surface of the front substrate 33 so as to face the cathode. The surface 35 is formed. As the cathode composed of the electron source 4 including the first electrode 2 and the electron emitting portion 3 and the second electrode 7, the cathode obtained by the manufacturing method of the present embodiment was used. The phosphor screen 35 is composed of one set (two for green), which are painted in red, blue, and green phosphors and arranged in a square pattern. One image display element is composed of 4 pixels or more. In addition,
Vacuum exhaust is performed from an exhaust hole (not shown) formed in the back substrate 31 through an exhaust pipe (not shown), and after the vacuum exhaust, the exhaust pipe is chipped off.

In the image display device configured as described above, when a DC or AC voltage of hundred and several tens of volts is applied to the second electrode 7 with respect to the first electrode 2, it is included in the electron emitting portion 3. In the CNTs, the electric field is concentrated on the portion where the tip of the tube faces the second electrode 7 side, and electrons are emitted. The emitted electrons pass through the opening 39 formed in the second electrode 7 and are applied at several kV, are accelerated toward the phosphor screen 35, and excite the phosphor to emit light. At this time, since the surface of the electron emitting portion 3 is made uniform in height by polishing in the above manufacturing method, the distance between the surface of the electron emitting portion 3 and the second electrode 7 is made uniform in all the cathodes. , The electron emission characteristics are the same. Therefore, when a voltage is sequentially applied to the slit-shaped second electrode for display, the same amount of electrons is always emitted from all the cathodes with respect to the applied voltage, and the electrons are excited and emitted. The amount of light emitted from the phosphor is also the same, and all the pixels in the image display element show the same light emission intensity. That is, the uniformity of the emission brightness of the image display element is improved.

FIG. 3 is a characteristic diagram showing the relationship between the applied voltage and the obtained emission (current-voltage characteristic) in each cathode manufactured according to the present embodiment in the image display device shown in FIG. Mediums a1, b1 and c1 respectively show the emission characteristics of the above-mentioned cathode, although the emission emission current from the cathode when a predetermined voltage is applied is minimum, average and maximum. As shown in FIG. 3, since the surface of the electron emitting portion 3 is made uniform in height by polishing, the distance between the surface of the electron emitting portion 3 and the second electrode 6 is made uniform between the electrodes. It is shown that the variation of the current-voltage characteristics in each electron source is small.

FIG. 4 is a characteristic diagram showing the relationship between the degree of vacuum and the emission half-life in an atmosphere where a cathode is generally used. As shown in the figure, the emission half-life increases as the degree of vacuum increases. In particular, it can be seen that there is a large change in the vacuum degree region of 1 × 10 ⁻⁶ . The vacuum degree in the image display device shown in FIG. 2 obtained by evacuation using the cathode of the present embodiment was 1 × 10 ⁻⁸ , and the emission half-life was about 5000 hours. On the other hand, when a solder layer is used in the image display device, the degree of vacuum is 5 × 10 ⁻⁶ ,
The emission half-life is 2 hours, and the degree of vacuum inside the device is lowered by soldering, which shortens the life.

As the image display device, a third electrode for converging electrons may be provided between the second electrode of the cathode and the phosphor screen of this embodiment. The same effect can be obtained with an image display device using a cathode manufactured according to the second embodiment described below.

Embodiment 2. In the first embodiment, the manufacturing is performed in the same manner as in the first embodiment up to the step shown in FIG. Then, it is fired at 500 ° C. in the atmosphere to thermally decompose the resin component contained in the electron emitting portion.

Separately from this, an aqueous solution prepared by mixing water glass {trade name: Okajil B, manufactured by Tokyo Ohka Co., Ltd.} and barium acetate is prepared. In the above aqueous solution, the concentration of water glass is 20 wt% and the concentration of barium acetate is 0.4 w
Mix to t%. This solution is impregnated into the CNTs remaining after the thermal decomposition. At this time, the dropping amount is adjusted so that the aqueous solution spreads over the entire surface of the electron emitting portion. Finally, after drying in an air atmosphere at 120 ° C, 4
Baking at 50 ° C. in the atmosphere.

After that, similarly to the step shown in FIG. 1C of the above-mentioned embodiment, the surface of the electron emitting portion is polished by fixing the substrate and moving the polishing tape by using the polishing tape of No. 1000. . Hereinafter, FIG. 1D of the above embodiment,
In the same manner as the step shown in (e), spacer formation and second
Install the electrodes.

The cathode constructed as described above has the same effect as that of the first embodiment. Further, since the resin component is thermally decomposed after polishing in the first embodiment, the flatness of the surface of the electron emitting portion may be worse than that during polishing due to generation of combustion gas when the resin component is decomposed. In, the flatness at the time of polishing can be maintained. In addition, in the present embodiment, the carbon nanotubes of the electron emitting portion are firmly adhered to the first electrode by the water glass, so that the carbon nanotubes can be prevented from falling off. Therefore, there is an effect that the CNT is prevented from dropping during operation and a short circuit is prevented, and a stable cathode is obtained.

In the first and second embodiments, the electron emitting portion containing CNT is formed by screen printing, but other methods such as gravure printing and flexo printing may be used. Furthermore, the polishing described in this embodiment can be performed even when the electron emitting portion containing CNT is formed by using a method such as CVD.

Comparative Example 1. The image display device shown in FIG. 2 is manufactured in the same manner as in Embodiment 1 except that the cathode obtained by flattening using the conventional laser is used in the above Embodiment 1, and the cathode of this device is manufactured. When the relationship between the applied voltage and the obtained emission (current-voltage characteristic) was measured, the characteristics shown in FIG. 5 were obtained. FIG. 5 is a characteristic diagram showing the relationship between the applied voltage and the obtained emission (current-voltage characteristic) in each cathode of the image display device. In the figure, a2, b2, and c2 are each a predetermined voltage at the cathode. The emission characteristics of the emission current from the cathode when applied are the minimum, average, and maximum. As shown in FIG. 5, since the distance between the surface of the electron emitting portion and the second electrode 7 varies among the electrodes, it is shown that the current-voltage characteristics of the electron sources vary widely.

[0031]

According to the first method of manufacturing a cathode of the present invention, the first electrode provided on the substrate is provided with an electron emitting portion containing carbon nanotubes, and the first electrode is provided. A method for producing a cathode, comprising a second electrode provided via an insulating layer and applying a potential difference between the first electrode and the first electrode, wherein carbon nanotubes are provided on the first electrode provided on the substrate. A step of providing a resin layer to be contained, a step of polishing the surface of the resin layer so that the distance between the surface of the resin layer and the second electrode is uniform, and a thermal decomposition of the resin component of the resin layer after polishing. A method comprising removing the carbon nanotubes to expose the carbon nanotubes to obtain an electron source and providing the second electrode with the first electrode and the insulating layer interposed therebetween is excellent in electron emission characteristics Even when used, the applied voltage and the obtained emission ® down relationship - there is an effect that the variation of (current-voltage characteristics) can be suppressed.

A second method of manufacturing a cathode according to the present invention comprises an electron source having an electron emitting portion containing carbon nanotubes provided on a first electrode provided on a substrate, the first electrode and an insulating layer. A method of manufacturing a cathode, comprising: a second electrode which is provided via a first electrode and which applies a potential difference between the first electrode and the first electrode, wherein the first electrode provided on the substrate contains carbon nanotubes. A step of providing a resin layer, a step of exposing the carbon nanotubes by thermally decomposing and removing the resin component of the resin layer, impregnating the exposed carbon nanotube groups with water glass and baking the carbon nanotubes with the water glass. The step of adhering the nanotubes to the first electrode and the electron source by polishing the surface of the carbon nanotubes so that the distance between the surface of the carbon nanotubes and the second electrode becomes uniform. In obtaining step and the method comprising the step of providing the second electrode through the insulating layer and the first electrode,
The electron emission characteristics are stable and excellent, and even when a plurality of electron emission characteristics are used, variations in the relationship between the applied voltage and the obtained emission (current-voltage characteristics) are suppressed.

In the first cathode of the present invention, the first electrode provided on the substrate is provided with an electron source having an electron emitting portion containing carbon nanotubes, the first electrode and the insulating layer. In a cathode provided with a second electrode that applies a potential difference between the first electrode and the first electrode, the electron source, the first electrode provided on the substrate, the surface is polished,
The main part is composed of the electron emitting part containing the carbon nanotubes attached to the first electrode with water glass, and the electron emitting property is stable and excellent, and the voltage to be applied can be obtained even when used in plural. This has the effect of suppressing variations in the emission relationship (current-voltage characteristics).

[Brief description of drawings]

FIG. 1 is a process chart showing a method of manufacturing an electron source according to a first embodiment of the present invention in the order of steps.

FIG. 2 is a configuration diagram of an image display device using the cathode obtained in the present embodiment.

FIG. 3 is a characteristic diagram showing a relationship (current-voltage characteristic) between applied voltage and obtained emission in each cathode manufactured according to the present embodiment.

FIG. 4 is a characteristic diagram showing the relationship between the emission half-life of the cathode and the degree of vacuum.

FIG. 5 is a characteristic diagram showing a relationship (current-voltage characteristic) between applied voltage and obtained emission in each cathode of an image display device using a conventional cathode.

FIG. 6 is an explanatory diagram of a conventional cathode.

[Explanation of symbols]

1 substrate, 2 first electrode, 3 electron emitting portion, 13 C
Resin layer containing NT, 4 electron source, 5 polishing means, 6
Insulating layer, 7 Second electrode.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Akihiko Hosono             2-3 2-3 Marunouchi, Chiyoda-ku, Tokyo             Inside Ryo Electric Co., Ltd. (72) Inventor Tomohide Shen             2-3 2-3 Marunouchi, Chiyoda-ku, Tokyo             Inside Ryo Electric Co., Ltd.

Claims (3)

[Claims] 1. An electron source comprising an electron emitting portion containing carbon nanotubes, which is provided on a first electrode provided on a substrate, and the first electrode, which is provided via an insulating layer. A method of manufacturing a cathode comprising a second electrode for applying a potential difference between the electrode and the electrode, comprising the step of providing a resin layer containing carbon nanotubes on the first electrode provided on a substrate; The step of polishing the surface of the resin layer so that the distance between the surface of the resin and the second electrode becomes uniform, and the resin component of the resin layer is removed by thermal decomposition after polishing to expose the carbon nanotubes to expose the electron source. And a step of providing a second electrode via the first electrode and an insulating layer. 2. An electron source comprising an electron emitting portion containing carbon nanotubes, which is provided on a first electrode provided on a substrate, and the first electrode, which is provided via an insulating layer. A method of manufacturing a cathode comprising a second electrode for applying a potential difference between the electrode and the electrode, comprising the step of providing a carbon nanotube-containing resin layer on the first electrode provided on the substrate, A step of thermally decomposing and removing the resin component of the layer to expose the carbon nanotubes; and a step of impregnating the exposed carbon nanotube groups with water glass and firing the carbon nanotubes with the water glass.
And a step of polishing the carbon nanotube surface to obtain an electron source so that the distance between the surface of the carbon nanotube and the second electrode becomes uniform.
A method of manufacturing a cathode, comprising the step of providing a second electrode via the first electrode and an insulating layer. 3. An electron source provided with an electron emitting portion containing carbon nanotubes on a first electrode provided on a substrate, the first electrode and an insulating layer, and the first electrode provided on the first electrode. In a cathode provided with a second electrode for applying a potential difference between the electrode and the electrode, the electron source has a first electrode provided on a substrate and a surface polished so that the backbone is the first electrode. A cathode comprising an electron emitting portion containing carbon nanotubes attached by water glass.