CN1221965A

CN1221965A - Cathode used in electron gun

Info

Publication number: CN1221965A
Application number: CN98102178A
Authority: CN
Inventors: 朱圭楠; 崔钟书; 金润昶
Original assignee: Samsung Electron Devices Co Ltd
Current assignee: Samsung SDI Co Ltd
Priority date: 1997-12-30
Filing date: 1998-05-27
Publication date: 1999-07-07
Anticipated expiration: 2018-05-27
Also published as: CN1141729C; KR19990058910A; JPH11204021A; KR100268243B1

Abstract

The invention relates to a cathode for electron gun to attain a long service life under a high current density load by maintaining an after-diffusion route especially for a reducing element contained in the base metal and smoothly generating a barium free radical. A metallic layer mainly composed of nickel is formed on top of a base metal mainly composed of nickel and formed to contain at least one type of a reducing element, an alkaline earth metal oxide layer at least containing barium is formed on top of the metallic layer.

Description

Cathode for electron gun

The present invention relates to a cathode for an electron gun used for a cathode ray tube, and more particularly, to a cathode for an electron gun which ensures a diffusion path of a reducing element contributing to the generation of barium radicals and can realize a long life under a high current density load.

A cathode ray tube is a device which accelerates electrons emitted from an electron gun with ahigh voltage, then sinks (1) the electrons on a phosphor of a screen, and emits light by excitation of the phosphor to display an image.

Fig. 6 shows a general structure of a cathode for an electron gun for electron emission in such a cathode ray tube. In the figure, a heater (heater)4 is provided inside a sleeve (sleeve)2, a cap-shaped base metal 6 containing a small amount of a reducing element such as silicon (Si) and magnesium (Mg) and mainly containing nickel (Ni) is provided thereon, and an electron-emitting material layer 8 mainly containing an alkaline earth metal oxide containing at least barium is provided thereon.

The oxide cathode thus provided uses heat generated from the heater as an energy source, and the metal oxide and the reducing metal react with each other to emit thermal electrons by the barium radicals generated therein. The electron emission capability of the cathode for an electron gun depends on the amount of barium radicals present in the metal oxide. However, in recent years, since cathode ray tubes tend to be highly refined and enlarged, development of cathodes capable of supplying barium radicals for a long time at a high current density has been demanded.

In a prior application of the present applicant, korean laid-open patent publication No. 96-15634 discloses a cathode in which an electron-emitting material layer containing an alkaline earth metal oxide contains both a lanthanum (La) compound and a magnesium (Mg) compound, or further contains a lanthanum-magnesium composite compound, to suppress the evaporation consumption of barium radicals.

However, as shown in FIG. 7, the cathode is formed of a base metal 6 and an electron-emitting material layer 8An intermediate layer 10 consisting of a reaction product is formed between the interfaces of (A) and (B) at 2 to 3A/cm²The high current density of (2) causes a reductionin lifetime.

The intermediate layer 10 is formed by the reaction of barium oxide thermally decomposed from barium carbonate, which is a metal oxide contributing to the generation of barium radicals for electron emission, and silicon and magnesium as reducing agents.

(1)

(2)

The barium radicals generated by the reaction formula 1and the reaction formula 2 contribute to electron emission, but follow it like MgO and Ba₂SiO₄Such a product has the intermediate layer 10 formed at the interface between the base metal 6 and the electron-emitting material layer 8.

The intermediate layer 10 thus formed serves as a barrier layer, and hinders the late diffusion of the reducing agent contained in the base metal 6, thereby making it difficult to cause a reaction of generating barium radicals requiring the reducing agent, and thus shortening the life of the cathode. Further, the intermediate layer 10 has a high resistance, and thus obstructs the flow of electron emission current, thereby limiting the density of the current that can be emitted.

On the other hand, Japanese patent application laid-open No. 3-257735 discloses a cathode for an electron gun in which a metal layer having the same or lower reducibility as that of silicon or magnesium but higher reducibility than nickel is provided between a base metal and an electron emitting material layer, a rare earth metal oxide is contained in the electron emitting material layer, and a reaction product is decomposed by the rare earth metal oxide, so that the reducibility element in the metal layer contributes to the generation of barium radicals.

However, the cathode generates bariumradicals and further forms additional reaction products, and although the performance is stable in the initial stage of use, the lifetime of the cathode rapidly decreases with the passage of time.

The purpose of the present invention is to ensure a late diffusion path of a reducing agent contained in a base metal, thereby smoothly generating barium radicals and achieving a long life under a high current density load.

The present invention provides a cathode for an electron gun comprising a metal layer containing nickel or nickel-zirconium as a main component and provided on an upper surface of a base metal containing nickel as a main component and at least one kind of reducing metal, and an electron-emitting material layer containing an alkaline earth metal oxide layer containing at least barium provided on the upper surface of the metal layer.

The metal layer of the present invention is obtained by coating nickel or nickel-zirconium on a base metal and heat-treating it or by adhering nickel or nickel-zirconium powder thereto, and is provided so as to have a particle diameter smaller than the average particle diameter of the base metal.

The present invention also includes a structure in which a second electron emitting material layer containing a lanthanum compound and a magnesium compound or a lanthanum-magnesium composite compound is provided on the electron emitting material layer, the lanthanum compound and the magnesium compound being contained in an alkaline earth metal oxide containing at least barium.

With the above configuration, in the present invention, the intermediate layer as a reaction product is effectively dispersed in the metal layer composed of particles smaller than the base metal particles, the intermediate layer forming a high resistance layer is prevented from being formed, the path of the reducing metal is ensured, the late diffusion is facilitated, the barium radical forming reaction required for the reducing metal is continuously maintained, and 2 to 3A/cm of the barium radical forming reaction is realized²Long life under high current density load.

The brief description of the drawings is as follows:

FIG. 1 is a sectional view of a cathode for an electron gun according to an embodiment of the present invention.

FIG. 2 is an enlarged cross-sectional view of a main part of a cathode for an electron gun according to an embodiment of the present invention.

FIG. 3 shows life characteristics of a cathode for an electron gun according to an embodiment of the present invention.

FIG. 4 is a cross-sectional view of a cathode for an electron gun according to another embodiment of the present invention.

FIG. 5 shows life characteristics of a cathode for an electron gun according to another embodiment of the present invention.

Fig. 6 is a sectional view of a cathode for an electron gun according to the related art.

Fig. 7 is an enlarged sectional view of a cathode for an electron gun according to the related art.

The symbols are illustrated as follows:

6 base metal

8 electron-emitting substance layer

10 intermediate layer

12 metal layer

80 nd 2 electron emitting substance layer

The best embodiments for carrying out the present invention are described below with reference to the accompanying drawings. For reference, in the description of the present invention, the same reference numerals are used for the same portions as those described with reference to the drawings referred to in the related art, for clarity.

Example 1

The cathode for an electron gun according to one embodiment of the present invention shown in fig. 1 is provided at an upper opening of a sleeve 2 having a heater 4 provided therein, and includes a cap-shaped base metal 6 containing Ni as a main component and a small amount of a reducing metal such as Si or Mg.

A metal layer 12 made of pure Ni or Ni-Zr is provided on the base metal 6, and an alkaline earth metal oxide containing at least barium, a ternary carbonate (Ba, Sr, Ca) CO, is provided on the upper portion thereof₃Or binary carbonate (Ba, Sr) CO₃An electron-emitting substance layer 8.

In this example, in the case of generating barium radicals, as a means for dispersing reaction products of BaO and Si with Mg accumulated at the interface between the base metal 6 and the electron-emitting material layer 8, the metal layer 12 composed of fine particles of pure Ni or Ni — Zr is provided at the interface.

As shown in fig. 2 in an enlarged scale, the metal layer 12 of the present example is provided so as to have a particle diameter smaller than the average particle diameter of the base metal 6, and since the diffusion paths of the reducing element contained in the base metal 6 are dispersed, the reaction of BaO, Si, and Mg proceeds at a plurality of sites in the particles of the metal layer 12, the intermediate layer 10 among the reaction products is dispersed and accumulation is suppressed, and the diffusion of Si and Mg as the reducing element proceeds smoothly, thereby contributing to the generation of barium radicals. The metal layer 12 contains pure Ni or Ni — Zr as a component, and does not form an intermediate layer as a reaction product compared with the conventional W-coated metal layer, as in the case of the base metal 6.

Therefore, the metal layer 12 of the present embodiment is obtained by providing Ni or Ni-Zr with a thickness of 200 to 20000 angstroms on the base metal 6 by sputtering (sputtering), and performing heat treatment at 700 to 1100 ℃ in an inert atmosphere or a vacuum atmosphere to allow alloying and diffusion between the base metal 6 and the metal layer 12.

The thickness of the metal layer 12 is preferably 200 to 20000 angstroms, and if 200 angstroms or less, the thickness is too thin to ensure the path of the reducing element, while if 20000 angstroms or more, diffusion of the reducing metal is inhibited. On the other hand, the thickness of the metal layer 12 in this embodiment is 3000 to 10000 angstrom, which is the best mode.

On the other hand, the metal layer 12 of the present embodiment is provided on the base metal 6 coated with Ni or Ni-Zr powder. The compounding method can be realized by physical, chemical, and mechanical methods such as a spray (spray) method, a printing method, an electrodeposition method, and a metal salt solution method.

On the metal layer 12 thus formed, a ternary carbonate or a binary carbonate having a thickness of 20 to 80 μm is formed by a usual spraying method, so that the total thickness of the cathode in this embodiment is 200 μm or less.

Example 2

The cathode for an electron gun according to example 2 of the present invention provides a scheme of replacing the electron-emitting substance layer of example 1 with the 2 nd electron-emitting substance layer.

Referring to FIG. 1, this example is described in which an alkaline earth metal oxide containing at least barium is provided on a metal layer 12 made of pure Ni or Ni-Zr as a ternary carbonate (Ba, Sr, Ca) CO₃Or binary carbonate (Ba, Sr) CO₃The 2 nd electron-emitting material layer 80 containing both a lanthanum compound and a magnesium compound or further containing a lanthanum-magnesium composite compound.

The lanthanum compound and the magnesium compound or the lanthanum-magnesium compound inhibit the evaporation of barium radicals and enable the continuous supply of barium radicals, and the lanthanum compound and the magnesium compound or the lanthanum-magnesium compound are preferably 0.01 to 1 wt% of the carbonate.

When the content is 0.01 wt% or less, the effect of suppressing barium radicals is very small during driving, and when the content is 1 wt% or more, the electron emission characteristics during initial driving are lowered.

Therefore, according to the present embodiment, at the same time as the effective dispersing action of the metal layer 12 to the intermediate layer 10, the evaporation of barium radicals generated by the reaction of BaO with Si and Mg is suppressed by the 2 nd electron-emitting substance layer 80, thereby preventing sintering of the metal oxide.

The metal layer 12 of this embodiment is obtained by coating Ni or Ni-Zr with a thickness of 200 to 20000 angstroms on the base metal 6 and heat-treating the coating in an inert atmosphere or a vacuum atmosphere so that the coating can be alloyed and diffused between the base metal 6 and the metal layer 12. The metal layer 12 of this embodiment is provided on the base metal 6 by coating Ni or Ni-Zr powder.

On the metal layer 12 thus formed, a second electron-emitting material layer 80 containing a lanthanum compoundand a magnesium compound in a ternary carbonate or a binary carbonate or further containing a lanthanum-magnesium composite compound is applied by spraying to a thickness of 20 to 80 μm, and the total thickness of the cathode in this embodiment is not more than 200 μm.

The cathode for electron gun of the present example was assembled to a cathode ray tube, and the life thereof was examined, and the results are shown in FIG. 3. In the figure, A is a cathode of the present example in which a metal layer 12 having a thickness of 3000 to 5000 angstroms is provided in a carbonate containing 0.5 wt% of a lanthanum-magnesium compound. In the figure, B is an oxide cathode in which the carbonate contains 0.5 wt% of a lanthanum-magnesium compound and the metal layer 12 is not provided. In the figure, C is a conventional oxide cathode.

The lifetime test is carried out by measuring the decrease of electron emission current in a state of continuous 6000 hours of driving, and applying a current of 2000-3000 μ A to each cathode. As a result, the cathode for an electron gun of the present invention has a remarkably improved life characteristic at a high current as compared with B, C of the prior art. Specifically, the present invention maintained 90% of the initial current value even after 6000 hours of driving at a high current density.

Example 3

As shown in FIG. 4, the cathode for an electron gun according to example 3 of the present invention is such that a metal layer 12 made of pure Ni or Ni-Zr is provided on a base metal 6, an electron-emitting material layer 8 made of a ternary carbonate or a binary carbonate containing at least barium is provided thereon, and a 2 nd electron-emitting material layer 80 containing both a lanthanum compound and a magnesium compound or further containing a lanthanum-magnesium composite compound is further provided thereon.

In this example, it is considered that in example 2, the reducing element composed of Ni or Ni — Zr promotes the reduction of the barium radical at the same time as the reducing element contained in the base metal 6, and the evaporation of the barium radical proceeds excessively.

In this example, as a means for dispersing a reaction product of BaO and Si or Mg thermally decomposed from a carbonate accumulated at the interface between the base metal 6 and the electron-emitting material layer 8, a metal layer 12 composed of pure Ni or Ni-Zr is provided between the interfaces.

In the present example, as a means for suppressing the evaporation and consumption of barium radicals in the electron emitting material layer 8, the No. 2 electron emitting material layer 80 containing a lanthanum compound and a magnesium compound or a lanthanum-magnesium composite compound in an amount of 0.01 to 1 wt% in the carbonate is provided.

Therefore, the metal layer 12 of this embodiment is obtained by coating Ni or Ni-Zr with a thickness of 200 to 2000 angstroms on the base metal 6, and heat-treating the coating in an inert atmosphere or a vacuum atmosphere to alloy and diffuse between the base metal 6 and the metal layer 12. Here, the thickness of the metal layer 12 of the present embodiment is preferably 200 to 2000 angstroms in consideration of the thickness of the electron emitting material layer 8 and the 2 nd electron emitting material layer 80 provided thereon, and the most preferred embodiment is 400 to 1200 angstroms. On the other hand, the metal layer 12 of the present embodiment is formed by adhering Ni or Ni-Zr powder to the base metal 6.

An electron-emitting material layer 8 of ternary carbonate or binary carbonate having a thickness of 20 to 80 μm is coated on the metal layer 12 thus formed, and a 2 nd electron-emitting material layer 80 of 20 to 80 μm containing both a lanthanum compound and a magnesium compound in the ternary carbonate or binary carbonate or further containing a lanthanum-magnesium composite compound is further coated thereon so that the total thickness does not exceed 200 μm, thereby manufacturing the cathode for an electron gun of the present embodiment.

The cathode for an electron gun of the present embodiment is assembled to a cathode ray tube, and the life thereof is examined, as shown in FIG. 5. In the figure, D is a metal layer 12 having a thickness of 400 to 1200 angstroms, an electron emitting material layer 8 is formed thereon, and a cathode of the present embodiment containing 0.5 wt% of a carbonate of a lanthanum-magnesium compound is further formed thereon. In the figure, E represents a conventional oxide cathode.

The lifetime test is carried out by measuring the decrease of electron emission current in a state of continuous 6000 hours of driving, and applying a current of 2000-3000 μ A to each cathode. As a result, the cathode for an electron gun of the present invention has a remarkably improved life characteristic at a high current as compared with the conventional art. Specifically, the present invention maintained 95% of the initial current value even after 6000 hours of driving at a high current density.

The cathode of the present invention shows a tendency that the maximum cathode current increases as the time elapsed from the maximum cathode current (maximum current emitted from the cathode under a certain condition) at the initial stage of driving becomes longer.

As shown in the above embodiments, the cathode for electron gun according to the present invention substantially solves the problems of the prior art. That is, the present invention has a structure in which a metal layer made of fine particles is provided between a base metal containing a reducing element and an electron-emitting material layer made of a carbonate, and a reaction product generated when barium radicals are generated is dispersed, thereby ensuring a late diffusion path of the reducing element and realizing continuous emission of barium radicals.

Further, the present invention contains both of a lanthanum compound and a magnesium compound or a lanthanum-magnesium composite compound in the electron emitting material layer, or provides a 2 nd electron emitting material layer containing both of a lanthanum compound and a magnesium compound or a lanthanum-magnesium composite compound, and thus can suppress the evaporation consumption of barium radicals.

Thus, according to the invention, the electron emission is carried out via the metal layer and the electron-emitting substance layer or the No. 2 electron emitterThe interaction of the emitter layer can sustain the emission of barium free radical and suppress the evaporation consumption, thereby the concentration of barium free radical is 2-3A/cm²The effect of improving the life characteristics can be obtained even under a high current density load.

In addition, the oxide cathode of the present invention maintains a long life at a high current density, but has a practical utility to replace an expensive immersion cathode which is difficult to manufacture.

On the other hand, the present invention is not limited to the above-described preferred embodiments, and various modifications can be made by anyone having ordinary knowledge in the field to which the present invention pertains within the scope of the summary claimed in the patent claims.

Claims

1. A cathode for an electron gun, comprising a base metal containing nickel as a main component and at least one reducing metal, and a metal layer containing nickel as a main component provided on the base metal, wherein an electron-emitting material layer containing an alkaline earth metal oxide layer containing at least barium is provided on the metal layer.

2. The cathode for an electron gun according to claim 1, wherein the metal layer is composed of nickel or nickel-zirconium.

3. The cathode for an electron gun according to claim 1 or claim 2, wherein the metal layer is obtained by coating nickel or nickel-zirconium on the base metal and heat-treating it.

4. The cathode for an electron gun according to claim 3, wherein the metal layer is composed of particles smaller than the average particle diameter of the base metal.

5. The cathode for an electron gun according to claim 1 or claim 2, wherein the metal layer is provided by adhering nickel or nickel-zirconium powder on the base metal.

6. The cathode for an electron gun according to claim 5, wherein the metal layer is composed of particles smaller than the average particle diameter of the base metal.

7. The cathode for an electron gun according to claim 1, wherein the metal layer has a thickness of 200 to 20000 angstroms.

8. The cathode for an electron gun according to claim 1, wherein the electron-emitting substance layer contains both a lanthanum compound and a magnesium compound, or further contains a lanthanum-magnesium composite compound.

9. The cathode for an electron gun according to claim 8, wherein the metal layer is composed of nickel or nickel-zirconium.

10. The cathode for an electron gun according to claim 8 or claim 9, wherein the metal layer is obtained by coating nickel or nickel-zirconium on the base metal and heat-treating it.

11. The cathode for an electron gun according to claim 10, wherein the metal layer is composed of particles smaller than an average particle diameter of the base metal.

12. The cathode for an electron gun according to claim 8 or claim 9, wherein the metal layer is provided by adhering nickel or nickel-zirconium powder on the base metal.

13. The cathode for an electron gun according to claim 12, wherein the metal layer is composed of particles smaller than an average particle diameter of the base metal.

14. The cathode for an electron gun according to claim 8, wherein the metal layer has a thickness of 200 to 20000 angstroms.

15. The cathode for an electron gun according to claim 1, wherein a 2 nd electron-emitting material layer containing both a lanthanum compound and a magnesium compound or a lanthanum-magnesium composite compound is provided in an alkaline earth metal oxide containing at least barium on the electron-emitting material layer.

16. The cathode for an electron gun according to claim 15, wherein the metal layer is composed of nickel or nickel-zirconium.

17. The cathode for an electron gun according to claim 15 or claim 16, wherein the metal layer is obtained by coating nickel or nickel-zirconium on the base metal and heat-treating it.

18. The cathode for an electron gun according to claim 17, wherein the metal layer is composed of particles smaller than an average particle diameter of the base metal.

19. The cathode for an electron gun according to claim 15 or claim 16, wherein the metal layer is provided by adhering nickel or nickel-zirconium powder on the base metal.

20. The cathode for an electron gun according to claim 19, wherein the metal layer is composed of a particle group having a smaller average particle diameter than the matrix metal.

21. The cathode for an electron gun according to claim 15, wherein the metal layer has a thickness of 200 to 2000 angstroms.