JP2005071863A - Manufacturing method of field emission type cold cathode, field emission type cold cathode, and field emission type picture display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enhance the adhesiveness of a cathode layer and a lower part electrode in a field emission type cold cathode used for an FED or the like, and to obtain stable conduction. <P>SOLUTION: This cathode layer of the field emission type cold cathode is formed by a process A in which the lower part electrode is formed on a glass substrate, a process B in which a carbon material is dispersed in a silica sol solution containing conductive minute particles, a process C in which the silica gel solution is heat-treated, a process E in which the carbon material of which the silica gel layers formed in the process C are fixed are dispersed in a solvent to form paste or a slurry, and a process F in which the paste or the slurry is applied to the lower electrode and heat-treated at a first prescribed temperature. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a field emission cold cathode used in, for example, a field emission display (hereinafter referred to as “FED”), a manufacturing method thereof, and a field emission image display element. More specifically, the present invention relates to a cathode layer of a field emission cold cathode constituted by carbon nanotubes and the like, and a manufacturing method thereof.

  In recent years, there has been an increasing demand for thinning image display devices, and field emission type image display elements such as FEDs have been proposed as thin image display devices in addition to plasma displays and liquid crystal displays. Hereinafter, the structure of a general field emission image display element will be described with reference to FIGS. 1 and 9. FIG. 1 is a partially enlarged view of a field emission type image display device. In FIG. 1, a lower electrode 2 is formed in a stripe shape on a glass substrate 1. The lower electrode 2 is made of indium tin oxide (hereinafter referred to as “ITO”), aluminum, silver, or the like fixed on the glass substrate 1 by a printing method or a vapor deposition method. On the lower electrode 2, a cathode layer 3 mainly composed of a carbon material such as a carbon nanotube is formed. Further, an upper lead electrode 5 is disposed at a position several μm to several tens μm away from the glass substrate 1 through a spacer 4 installed on the glass substrate 1. The upper lead electrode 5 is provided with an opening 5a at a position intersecting the lower electrode 2 in plan view. The field emission type cold cathode 6 is constituted by using the glass substrate 1, the lower electrode 2, the cathode layer 3, the spacer 4, and the upper lead electrode 5 as main components. Further, the upper glass substrate 7 is disposed at a position away from the upper extraction electrode 5 by a predetermined distance via a spacer (not shown). A transparent anode electrode 8 and a phosphor film 9 made of an inorganic metal material such as ITO are provided on the surface of the upper glass substrate 7 facing the upper extraction electrode 5. FIG. 9 is a partially enlarged view of the II cross section of FIG.

  Next, a method for driving the field emission cold cathode will be described. When different potentials are applied to the lower electrode 2 and the upper extraction electrode 5, electrons are emitted from the cathode layer 3. The emitted electrons pass through the opening 5 a of the upper extraction electrode 5 and travel toward the upper glass substrate 7. Then, the electrons flow toward the anode electrode 8 to which a voltage is applied, and cause the phosphor 9 to emit light when reaching the anode electrode 8. A desired image is formed by such an operation, and the image is displayed through the upper glass substrate 7.

  As described above, the cathode layer 3 is formed mainly of carbon nanotubes. The carbon nanotube is composed of a graphene sheet in which carbon atoms are regularly arranged, and has a cylindrical shape with a high aspect ratio such as a diameter of several to several tens of nm and a length of several tens of μm. Since the carbon nanotube has such a high aspect ratio, electric field concentration is likely to occur at the tip portion, and a current having a high emission density can be obtained from the tip portion. Furthermore, since carbon nanotubes have the advantage of high physical and chemical stability, they are used as a material for forming a cathode layer of a field emission cold cathode.

  By the way, since the carbon nanotubes constituting the cathode layer 3 are carbon, the adhesion with the lower electrode 2 formed of an inorganic metal material is low, and usually both are merely in contact with each other. Therefore, the contact resistance between the two becomes very large, and the resistance distribution is not uniform. As a result, conduction between the lower electrode 2 and the cathode layer 3 becomes unstable, and it becomes difficult to obtain a current with a high emission density and a current with little fluctuation.

  Further, when a potential difference is generated between the lower electrode 2 and the upper extraction electrode 5, a part of the carbon nanotubes constituting the cathode layer 3 separated from the lower electrode 2 due to the induced electrostatic attraction force are formed on the upper extraction electrode. 5 may cause a screen defect by short-circuiting between the upper and lower electrodes. Therefore, in order to improve the adhesion between the lower electrode 2 and the cathode layer 3, for example, a method for forming a cathode layer as described in the following patent document has been proposed.

JP 2002-190247 A JP 2003-59391 A JP 2001-31955 A

  The method for forming a cathode layer described in Patent Document 1 does not dare to carry out a purification process for removing particulate impurities that is normally performed on carbon nanotubes produced by the arc method. Then, this particulate impurity is used as a filler to improve the adhesion between the cathode layer and the lower electrode.

  However, particulate impurities obtained by the arc method are mainly carbon-based impurities such as particulate graphite and amorphous carbon, that is, carbon. Therefore, even if these carbon-based impurities are used as fillers, sufficient adhesion between the cathode layer and the lower electrode made of an inorganic metal material cannot be ensured, and carbon nanotubes are peeled off by electrostatic attraction. Is not enough to prevent.

  The cathode layer forming method described in Patent Document 2 is a method using electrophoresis. That is, after carbon nanotubes are attached to the lower electrode made of aluminum or gold by electrophoresis, heat treatment is performed in an oxygen-free atmosphere, and the dissolved lower electrode is infiltrated into the cathode layer to improve adhesion. It is a method to secure.

  However, in this method, in order to melt the lower electrode, it is necessary to heat to a temperature of 670 to 800 ° C. for aluminum and 1100 to 1200 ° C. for gold. Under such a high temperature, there is a possibility that the glass substrate 1 holding the lower electrode is deformed or cracked in the field emission cold cathode having the structure shown in FIG.

  In addition, Patent Document 3 describes a method for forming a cathode layer, which is different from the method described in Patent Document 2, using an electrophoresis method. First, a holding layer made of a polysilane film containing semiconductor or conductive particles is provided on the lower electrode, and the polysilane film is irradiated with ultraviolet rays to dissociate bonds between Si atoms inside the polysilane film. In this method, carbon nanotubes are arranged and embedded in the dissociated portion by electrophoresis, and then heat-cured.

  When the cathode layer is formed by this method, sufficient adhesion between the cathode layer and the lower electrode can be ensured. However, the bond dissociation energy between Si atoms is several hundred KJ / mol at a low estimate. Therefore, very large energy is required to cause bond dissociation between Si atoms in an amount necessary to hold the carbon nanotube. Therefore, for example, when stationary ultraviolet light such as a high-pressure mercury lamp is used for bond dissociation between Si atoms, irradiation time of several hours or more is required, resulting in poor productivity. On the other hand, when laser light with a high photon density is irradiated, processing in a short time becomes possible. However, in order to irradiate high-photon density laser light, equipment such as a large oscillator is required, and conditions such as the irradiation position and irradiation time need to be accurately controlled, so that productivity may also deteriorate. There is sex.

  The present invention has been made to solve the above-described problems, and in forming a cathode layer of a field emission cold cathode using a carbon material, a simple method that does not require a large facility, It is an object of the present invention to provide a field emission cold cathode capable of ensuring adhesion to the cathode layer, a method for manufacturing the field emission cold cathode, and a field emission image display element.

This invention
Forming a lower electrode on the glass substrate;
Step B of dispersing a carbon material in a silica sol solution containing conductive fine particles;
Step C of heat-treating the silica gel solution;
Step E, in which the carbon material produced by Step C and having the silica gel layer fixed on the surface is dispersed in a solvent to produce a paste or slurry;
And a step F of applying a paste or slurry on the lower electrode and performing heat treatment at a predetermined first temperature.

  The present invention includes a step of forming a lower electrode on a glass substrate, a step of dispersing a carbon material in a silica sol solution containing conductive fine particles, a step of heat-treating the silica gel solution, and a surface generated by the heat treatment. Dispersing the carbon material with the silica gel layer fixed in a solvent to produce a paste or slurry, and applying the paste or slurry onto the lower electrode and heat-treating it at a predetermined temperature to form a cathode layer. Therefore, a field emission type cold cathode having high adhesion between the lower electrode and the cathode layer can be obtained.

Embodiment 1 FIG.
In the present invention, a carbon nanotube having a silica gel layer containing conductive fine particles fixed on its surface is used as a material for forming the cathode layer on the lower electrode.
Hereinafter, the present invention will be specifically described with reference to the drawings showing embodiments thereof.

  FIG. 1 is a diagram showing a structure of a field emission type image display device according to Embodiment 1 of the present invention, and FIG. 2 is a partially enlarged view taken along a line II in FIG. The basic structure of the field emission cold cathode according to the first embodiment is the same as that of the conventional field emission cold cathode. However, it differs in that the cathode layer 3 is formed using carbon nanotubes having a silica gel layer containing conductive fine particles fixed on the surface thereof. Therefore, the manufacturing method of the cathode layer 3 is demonstrated below.

First, carbon nanotubes are dispersed in a silica sol solution containing conductive fine particles. Next, this silica sol solution is heat-treated to fix a silica gel layer containing conductive fine particles on the surface of the carbon nanotubes. Further, this carbon nanotube is heated, and a part of silanol group of the silica gel layer is dehydrated and crosslinked to form a SiO ₂ film on a part of the surface. Next, the carbon nanotubes are dispersed in a polar solvent to produce a paste or slurry. After the produced paste or slurry is applied on the lower electrode, the cathode layer and the lower electrode are bonded by heat treatment. Before forming the cathode layer, it is necessary to form a lower electrode on which the cathode layer is placed.
Details will be described below.

  First, a method for manufacturing the lower electrode 2 will be described. The lower electrode 2 is formed in a stripe shape on the glass substrate 1 by using an inorganic metal material such as ITO, aluminum, silver, or the like, using a vapor deposition method, a printing method, or the like (step A). In addition, this process A should just be performed before the process of apply | coating the paste or slurry mentioned later on the lower electrode 2, and as long as it is before application | coating of a paste or slurry, before and after the other process mentioned later is not ask | required. FIG. 3 is a partially enlarged view of the lower electrode 2 formed by this process.

  Next, the manufacturing method of the cathode layer 3 is demonstrated. First, the carbon nanotube 3a which becomes the main component of the cathode layer 3 is manufactured by an arc method or the like. In addition, the manufacturing method of a carbon nanotube may be methods other than the arc method. The cathode layer 3 may be made of a carbon material other than carbon nanotubes, such as diamond or graphite nanofibers having a diameter larger than that of the carbon nanotubes. Hereinafter, description will be made using carbon nanotubes.

  Next, the carbon nanotubes 3a produced by the arc method or the like are dispersed in a silica sol solution containing the conductive fine particles 3b using an ultrasonic dispersion method or the like (step B). For the conductive fine particles 3b, metal oxides such as ITO, antimony tin oxide (ATO) and ruthenium oxide, metal fine particles such as gold, silver, copper and nickel, and titanium nitride and magnesium fluoride are used. The particle diameter of the conductive fine particles 3b is, for example, about several nm to several tens of nm. In addition, alcohol may be mixed as a solvent in the silica sol solution, and an organic dispersant may be added to promote the dispersion of the carbon nanotubes 3a in the silica sol solution. Further, the timing of mixing the conductive microparticles 3b into the silica sol solution in the step B may be before the carbon nanotubes 3a are put into the silica sol solution, and the carbon nanotubes 3a and the conductive microparticles 3b are mixed at the same timing. Also good.

  Next, the silica sol solution produced in the process B is heated to deposit and fix the silica gel layer 3c containing the conductive fine particles 3b on the surface of the carbon nanotube (process C). In addition, the heat processing in the process C may be a processing which can confirm that the residue after a heating is visually dried.

Here, the paste may be prepared by using the carbon nanotubes produced in the process C as they are, but the silica gel layer 3c at the time when the process C is completed may not have a sufficient growth of silanol bridges. . Therefore, there is a possibility that the silica gel layer 3c and the conductive fine particles 3b are peeled from the carbon nanotubes 3a due to the shearing force generated during the paste or slurry mixing operation in the step E described later. In order to prevent this peeling, the carbon nanotubes produced in Step C are heat-treated at, for example, about 200 ° C. for about 20 minutes. By this treatment, a part of the silanol group (—Si—O—H) of the silica gel layer 3 c fixed on the surface of the carbon nanotube 3 a is crosslinked by dehydration polymerization (—Si—O—Si—), and the surface of the silica gel layer A SiO ₂ film 3c is formed on a part of the substrate (step D). FIG. 4 is a view showing the carbon nanotube produced by the process D.

  The heating temperature at which the reaction of the dehydration polymerization in step D is promoted is 150 ° C. or higher. On the other hand, when heated at a temperature of 250 ° C. or higher, the dehydration polymerization reaction proceeds excessively, and the amount of silanol groups related to dispersibility in a polar solvent and adhesion to the lower electrode 3 described later decreases. Therefore, the heating temperature in the process D is desirably 150 ° C. or higher and 250 ° C. or lower.

  Next, a paste or slurry to be applied on the lower electrode 2 is prepared using the carbon nanotubes manufactured in the process D (process E). For example, the composition of the carbon nanotube produced in Step D is 7%, the composition of ethyl cellulose as an organic binder for adjusting the viscosity of the paste is 6%, the composition ratio of butyl carbitol as a polar solvent is 8%, and the composition is butyl carbitol. Similarly, butyl carbitol acetate as a polar solvent is produced by mixing each with a composition ratio of 79%. Moreover, the slurry whose viscosity is lower than that of the paste is produced by adjusting the amount of the organic binder.

  In general, a carbon material such as a carbon nanotube has a small polarity and a dispersibility in a polar solvent is very small. However, since the silica gel layer 3c having a silanol group is fixed on the surface of the carbon nanotube produced through the process C, the dispersibility in the polar solvent in the process E is very good.

  Next, the paste or slurry produced in the step E is applied on the lower electrode 2, and a heat treatment is performed at a temperature of about 120 ° C. to 150 ° C. for about 10 minutes (step F). By the process F, for example, due to dangling bonds, a highly polar portion existing on the surface of the lower electrode 2 and a silanol group possessed by the silica gel layer 3c fixed on the surface of the carbon nanotube 3a are adsorbed and coordinated. Therefore, the adhesion between the lower electrode 2 and the cathode layer 3 is improved as compared with the conventional case.

  Further, after Step F, for example, heating is performed at about 350 ° C. for about 20 minutes, the organic binder is removed, and the silica gel layer 3c is dehydrated and solidified, thereby firing the cathode layer 3 on the lower electrode 2 (Step G). ). FIG. 5 is a diagram showing the cathode layer 3 formed by the process G, and is a partially enlarged view of FIG. As shown in FIG. 5, the cathode layer 3 includes a carbon nanotube 3a and a silica sol layer 3c containing conductive fine particles 3b. The cathode layer 3 has a thickness of several μm to several tens of μm.

  Furthermore, the coupling | bonding of the lower electrode 2 and the cathode layer 3 in the process G is demonstrated using FIG. 6A shows a state where the paste is applied to the lower electrode 3, and FIG. 6B shows a state after firing. In (a), the cathode layer 3 is merely placed on the lower electrode 2, but the lower electrode 2 is formed with the silanol groups of the silica gel layer in the cathode layer 3 by heating and firing. The inorganic metal material (Me) is chemically bonded (-Si-O-Me). Thereby, the adhesiveness between the lower electrode 2 and the cathode layer 3 is improved.

  After that, the spacer 4 is set on the glass substrate 1, and the upper lead electrode 5 is disposed on the spacer 4 (Step H). The upper lead electrode 5 is provided with an opening 5a at a position where the lower electrode 2 intersects in plan view.

  A field emission type cold cathode is manufactured by the process A to the process H as described above.

  Next, the results of the evaluation test of the adhesion between the lower electrode 2 and the cathode layer 3 and the evaluation test of the field emission performance, which were performed on the field emission cold cathode manufactured by the above-described process, are shown. The evaluation object is the first evaluation object manufactured through all the processes from the process A to the process H, and as a comparison object, in the process B, the conductive sol solution is not added to the silica sol solution. The second evaluation object manufactured through the process A to the process H except for the process B, and the paste or slurry using the carbon nanotubes manufactured in the process A as it is without using the silica sol solution. The third evaluation target is manufactured (process E ′) and then manufactured through processes F, G, and H.

  Therefore, in the second evaluation object, there are no conductive fine particles in the silica sol layer, and in the third evaluation object, there is no silica sol layer on the surface of the carbon nanotube.

FIG. 7 shows an outline of a field emission image display element and a current measurement system when a field emission performance evaluation test is performed. As shown in FIG. 7, for each evaluation object, a field emission type screen display element in which five lower electrodes 2 a to e and five cathode layers 3 a to e each having a size of 2 mm × 2 mm are formed. Installed in a vacuum chamber of about 2.67 × 10 ⁻⁴ Pa, and when a predetermined voltage, for example, 400 V is applied to the upper extraction electrode 4, the gap between the lower electrode 2 and the ground generated by electrons emitted from the cathode layer 3 The current value (hereinafter referred to as “cathode current value”) Ic was measured. Therefore, the larger the cathode current value Ic, the better the field emission performance.

  The adhesion evaluation test between the lower electrode 2 and the cathode layer 3 is performed when a constant load is applied to a sapphire needle having a tip R of φ0.05 mm and the surface of the cathode layer 3 is scratched at a speed of 0.5 mm / sec. The measurement was performed by measuring the minimum load value at which peeling of the cathode layer 3 occurred.

The results of the field emission performance evaluation test and the results of the adhesion evaluation test between the lower electrode 2 and the cathode layer 3 are shown in FIG.
First, the results of field emission performance will be described. Both the first evaluation object and the second evaluation object have a very large cathode current value Ic and a small variation compared to the third evaluation object. This is because both the first evaluation object and the second evaluation object are chemically bonded to the silanol group of the silica gel layer in the cathode layer 3 and the inorganic metal material constituting the lower electrode 2. 3 and the lower electrode 2 are improved in adhesion, and the state of conduction between them can be stably secured. Furthermore, since the first evaluation object includes conductive fine particles in the silica gel layer, the cathode current value Ic is higher than that of the second evaluation object. On the other hand, the third evaluation object is different from the first and second evaluation objects in that there is no silica gel layer containing a silanol group in the cathode layer 3, so the adhesion between the cathode layer 3 and the lower electrode 2 is low, The state of conduction becomes unstable. Therefore, the cathode current value Ic decreases and the variation also increases. Furthermore, in some measurement objects, the cathode layer 3 was peeled off from the lower electrode during the field emission performance evaluation test, so that the cathode current value Ic could not be measured.

  Next, the result of the adhesion evaluation test will be described. As described in the explanation of the field emission performance evaluation test, since the first and second evaluation objects have a silica gel layer having a silanol group in the cathode layer 3, the inorganic metal material constituting the silanol group and the lower electrode 2 is used. Can be bonded chemically to improve adhesion, and therefore, a better measured value than that of the third evaluation object can be obtained. On the other hand, since the 3rd evaluation object does not have the chemical bond of a silanol group and a metal, evaluation of adhesiveness is a very low value. In this evaluation test, the second evaluation object in which no conductive fine particles are present has higher adhesion than the first evaluation object in which conductive fine particles are present.

In the first embodiment, the cathode layer 3 is formed by applying the paste or slurry on the lower electrode 2, drying and firing after the lower electrode 2 is formed. A method may be employed in which the solution is prepared without adding a binder in Step E, the cathode layer is formed by a spin coating method, and then the shape of the cathode layer 3 is adjusted by a blast method or the like.
Further, the shape of the lower electrode 2 may be a shape other than the stripe shape.

  In addition, since it is necessary to remove the organic binder, the heating temperature in Step G was set to about 350 ° C., but the reaction itself from the state of FIG. 6A to the state of FIG. Progress. Therefore, when the paste is prepared without containing the organic binder, it may be heated at a temperature of 150 ° C. or higher after Step F (Step G ′).

It is a figure of the field emission type image display element in Embodiment 1 of this invention. It is sectional drawing of the field emission type image cold cathode in Embodiment 1 of this invention. It is a figure explaining the manufacturing method of the lower electrode in Embodiment 1 of this invention. It is a figure explaining the manufacturing method of the carbon nanotube in Embodiment 1 of this invention. It is a figure explaining the cathode layer in Embodiment 1 of this invention. It is a figure explaining the manufacturing method of the cathode layer in Embodiment 1 of this invention. It is a figure explaining the measurement system of the evaluation test in Embodiment 1 of this invention. It is a figure explaining the result of the evaluation test in Embodiment 1 of this invention. It is sectional drawing of the conventional field emission type cold cathode.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Glass substrate 2 Lower electrode 3 Cathode layer 4 Spacer 5 Upper extraction electrode 6 Field emission type image cold cathode 7 Upper glass substrate 8 Transparent electrode 9 Phosphor

Claims (5)

Forming a lower electrode on the glass substrate;
Step B of dispersing a carbon material in a silica sol solution containing conductive fine particles;
Step C of heat treating the silica gel solution;
A step E of producing a paste or slurry by dispersing the carbon material produced by the step C and having a silica gel layer fixed on the surface in a solvent;
And a step F of applying the paste or slurry on the lower electrode and performing heat treatment at a predetermined first temperature. After step F
Furthermore, the process G which heat-processes at predetermined | prescribed 2nd temperature.
The method of manufacturing a field emission cold cathode according to claim 1, comprising: After step C and before step E,
The method for producing a field emission cold cathode according to claim 1 or 2, further comprising a step D of heating the carbon material formed on the surface and having a silica gel layer fixed thereon. A glass substrate;
A lower electrode formed on the glass substrate;
A cathode layer containing a carbon material formed on the lower electrode and having a silica gel layer containing conductive fine particles fixed on the surface;
A field emission cold cathode, comprising: an upper lead electrode disposed at a predetermined distance from the cathode layer. A field emission image display device comprising the field emission cold cathode according to claim 4.

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