JPH0233822A - Cathode for electron tube - Google Patents

Abstract

PURPOSE:To ensure the long lifetime of an electron tube cathode by applying a rare earth metal and the like to the inner side of a grid formed with the deposition of an alkaline earth metal oxide containing Ba on a substrate and dispersing the deposit with an electron shock for the deposition thereof to an electron emission substance layer. CONSTITUTION:The ternary carbonate of Ba, St and Ca is used as a suspension and this suspension is sprayed to a substrate 7 mainly composed of Ni and preliminarily made to contain a reducing element such as Si and Mg. Thereafter, an electron emission substance layer 8 is deposited on the substrate 7 via a decomposition process from carbonate to oxide and an activating process for reducing a part of the oxide. Furthermore, in a cathode for an electronic tube, the electron emission substance layer 8 is heated with a heater 9 up to the predetermined temperature after the finish of the aforesaid decomposition and activation processes, and the predetermined direct current voltage is applied between a cathode 1 and a grid 4 for the control of an electron beam. According to the aforesaid constitution. a scandium metal film 6 is subjected to an electron shock and dispersed for deposition on the electron emission substance layer 8. Also, the scandium metal is dispersed even internally.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a cathode for an electron tube used in a double cathode ray tube image pickup tube for TV and the like.

[Conventional technology]

FIG. 3 shows the structure of the vicinity of the cathode of an electron gun used in a conventional double picture tube for TV. (1)
is a cathode, (2) is a shield provided on the outer periphery of this cathode, and (4) is an electron beam control grid, in which a small hole (5) is made.

(8) is a ceramic structure, which is provided between the shield (2) and the electron beam control grid (4) and has a cathode (1).
and the electron beam control grid (4) are fixed. Electrons emitted from the cathode (1) pass through the small hole (5) and are emitted as an electron beam. Figure 2 schematically shows the structure of the cathode, where (γ) is a bottomed cylindrical base mainly composed of nickel and containing trace amounts of reducing elements such as silicon (Si) and magnesium (Iso); ) is this substrate (γ
), at least barium (Ba)
(9) is a heater (9) disposed within the base (γ); This is for emitting thermoelectrons from the electron emitting material layer (8) by heating.

In the electron tube cathode configured in this way, the base (γ)
The electron emissive material layer (8) is deposited on the substrate as follows. First, alkaline earth metals (Ba, Sr.

A suspension consisting of the ternary carbonate of Oa) is applied to the bottom upper surface of the substrate (A) and heated by a heater (9) during the evacuation process. At this time, the alkaline earth metal carbonate turns into an alkaline earth metal oxide. Thereafter, by reducing a part of the alkaline earth metal oxide and activating it to have semiconducting properties, an electron emitting material layer made of the alkaline earth metal oxide ( 8) is formed by adhesion.

In this activation step, a part of the alkaline earth metal oxide reacts as follows. Reducing elements such as silicon and magnesium contained in the base (γ) move to the interface between the alkaline earth metal oxide and the base (γ) by diffusion and react with the alkaline earth metal oxide. . for example,
If barium oxide (Bad) is used as the alkaline earth oxide, it reacts as shown in the following formulas (1) and (2).

BaO+ 1/2Si = Ba + 1/ZSiOz
Song --- (1) EaO+ Mg = Ba +
MgO --- (2) As a result of this reaction, the substrate (a)
A part of the alkaline earth metal oxide deposited on the top is reduced and becomes an oxygen-deficient semiconductor, and the cathode temperature is 700~
An electron emission of 0.5-0.8 A/crl will be obtained at an operating temperature of 800°C.

However, in the above cathode for an electron tube, the electron emission is 0.5~
A current density of 0.8 A/-J or more cannot be obtained.

The reason for this is that when a part of the alkaline earth metal oxide is subjected to a reduction reaction, as is clear from equations (1) and (Z) above, the relationship between the substrate (γ) and the alkaline earth metal oxide layer is A composite oxide layer (intermediate layer) such as SiO2, MgO, EaO, 5i02, etc. is formed at the interface, and this intermediate layer becomes a high resistance layer and impedes the flow of current. □ Reducing element (81, Mg '1
It is thought that this is because a sufficient amount of barium is not produced because it prevents barium from diffusing to the surface side of the electron emitting material layer (8). In other words, during electron tube operation, the substrate (γ
) and the vicinity of the interface between the electron emitting material layer (8), especially the substrate (γ)
Since the intermediate layer is segregated at a position approximately 10 μm inside the electron emitting material layer (8) from the nickel crystal grain boundary near the surface and the interface, current flow and reducing elements toward the surface of the electron emitting material layer (8) occur. There was a problem in that the diffusion of electrons was hindered, and sufficient electron emission characteristics under high current density could not be obtained.

On the other hand, Japanese Patent Application No. 60-229303 discloses that 0.01 to 0.5% by weight of a rare earth metal is contained in a substrate, so that during activation when an electron emitting material layer is deposited on the substrate. , when carbonates of alkaline earth metals decompose,
Alternatively, it prevents the oxidation of the substrate when barium oxide undergoes a dissociation reaction during operation as a cathode, and
The diffusion of the reducing element contained in the substrate into the electron emitting material layer is moderately controlled, and an intermediate layer made of a composite oxide of the reducing element is concentrated near the interface between the substrate and the electron emitting material layer. Techniques have been shown to prevent this from occurring and to disperse the intermediate layer within the electron emissive material layer. In other words, this second conventional electron tube cathode has an excellent property of having little emission deterioration during high current density operation of about 1 to 3 A/j because the intermediate layer is dispersed. It is.

However, even in this case, it exceeds 3A/,l.
For example, when operating at a high current density of 4 A/d, there is a problem in that emission deterioration is large. Furthermore, a special application was made in 1986-16.
In the application No. 0851, the second
Similar to the prior art example, a technique has been proposed in which the intermediate layer is dispersed while preventing the substrate from becoming acidic. In this case, even with high current density operation of 4A/c, 4 or more,
Emission deterioration can be reduced.

[Problem to be solved by the invention]

However, in such conventional cathodes for doji tubes, when operated at a high current density of 4 A/cW1 or more after going through the normal activation process, the effect of suppressing the evaporation of Norium may not be sufficient. Therefore, the deterioration of emissions may be large, and the activation time must be long.

This invention was made to solve the above problems, and in high current density operation of 4A/1 or more,
It is an object of the present invention to obtain a cathode for an electron tube which is always effective in suppressing barium evaporation and has stable emission characteristics over a long period of time. A rare earth metal or a compound is coated on the inner surface of the electron beam control grid, and is attached to the electron emitting material layer of the cathode by the electron beam from the cathode.

[Effect]

In this invention, the rare earth metal or compound attached to the electron emitting material layer prevents the formation of an intermediate layer consisting of a composite oxide of a reducing element in the vicinity of the interface between the substrate and the electron emitting material layer. However, the intermediate layer is dispersed within the electron emitting material layer, and the attached rare earth metal or compound suppresses the evaporation of barium.

〔Example〕

An embodiment of the present invention will be described below with reference to FIGS. 1 and 4. In FIG. 4, a scandium metal film (6) is formed inside the electron beam control grid (4). In FIG. 1, (γ) is a substrate whose main component is nickel, and the substrate (A) contains Sl.

Contains reducing elements such as lvlg. (8) is an electron-emitting material layer deposited on the bottom upper surface of the substrate (γ) and containing at least barium, and also containing an alkaline earth metal oxide containing strontium and/or calcium as a main component.

In this electron tube cathode, first, a ternary carbonate of barium, strontium, and calcium is made into a suspension. .1wt%) onto the substrate (A) by spraying to a thickness of approximately 80 microns, and then, as in the conventional method, the decomposition process from carbonate to oxide and a part of the oxide are applied. The electron emitting material layer (8) is deposited on the substrate (γ) through an activation process of reducing the .

Further, in this electron tube cathode, after the above decomposition/activation process is completed, the electron emitting material layer (8) is heated to about 8,000 yen by heating with a heater (9), and the cathode (1) and the electron beam control grid (4) are heated. ), apply a DC voltage of about 100V between the two. As a result, the scandium metal film (6) receives an electron bombardment, scatters, adheres to the electron emitting material layer (8), and also diffuses inside.

Figure 5 shows the change in emission current when a diode vacuum tube was created using this electron tube cathode and a life test was conducted by operating it at a current density of 4.3 A/, -d. The results were shown. In the figure, curve A is an electron tube cathode in which a scandium metal film (6) is formed on the inner surface of an electron beam control grid (4), and the electron tube cathode has undergone the above process. The curved line does not have the scandium metal film (6), that is, it uses a conventional electron tube cathode.

The reason why this invention provides superior characteristics compared to the conventional one is considered to be due to the following reasons. The particles attached to the electron emitting material layer (8) diffuse into the interior along with the operation of the electron tube cathode to a depth of approximately 20 tm from the surface of the substrate (γ). On the other hand, the reducing agent S1 and Mg in the substrate (a) diffuse to the surface in the opposite direction to the ferrule, react with BaO on the surface, and create free substances, but also form bases 5103.

This hsioa is called an intermediate layer and inhibits the reaction of the reducing agent with BaN. However, in the present invention, since the intermediate layer is separated by Sc present on the surface layer of the substrate (γ), the reducing agent S1 can further move into the electron emitting material layer and contribute to electron emission.

In addition, in the above, the electron beam control grid (4)
A scandium metal film was applied to the metal, including yttrium, lanthanum, cerium, praseodymium, neodymium, samarium, gadolinium, scandium, dysprosium, holmium, and erbium.

A similar effect can be obtained by using at least one species selected from thulium. In addition to metals, there are also oxides.

Various compounds such as nitrides may also be used.

〔Effect of the invention〕

As described above, in this invention, an alkaline earth metal oxide containing at least barium is deposited on a substrate made of N1, a rare earth metal or a compound is coated on the inside of an electron beam control grid, and this is applied by electron bombardment. By scattering the particles and attaching them to the electron emitting material layer, it is possible to reliably achieve a long life under operation at a high current density of 4 A/i or more.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing a cathode for an electron tube according to an embodiment of the present invention, FIG. 2 is a sectional view showing a conventional cathode for an electron tube, FIG. 3 is a view showing the vicinity of the cathode of a conventional electron gun, and FIG. The figure shows the vicinity of the cathode according to the present invention, and FIG. 5 is a diagram showing the relationship between life test time and emission current. In the figure, (]) is the substrate, and (2) is the electron emitting material layer. In each figure, the same reference numerals indicate the same or equivalent parts.

Claims (1)

[Claims] It comprises a cathode in which an electron-emitting material layer made of an alkaline earth metal alloy containing at least barium is deposited on a substrate made of nickel as a main component, and an electron beam control grid installed in front of the cathode. A rare earth metal or compound is coated on the cathode side surface of the electron beam control grid, and the electron beam emitted from the cathode collides with the electron beam control grid, and the rare earth metal or compound is scattered by this collision. A cathode for an electron tube, characterized in that a metal or a compound is attached to the electron emitting material layer.