JPS6288240A - Cathode for electron tube - Google Patents

Abstract

PURPOSE:To stabilize an electron emitting property, by providing a rare earth metal film of a prescribed thickness between a base and an electron emitting substance layer to disperse a composite oxide layer of a reducing element into the electron emitting substance layer. CONSTITUTION:A rare earth metal film 12 made of Sc, Y or the like and having a thickness of 6mu or less is provided on a base 1 made of Ni as the main constituent and containing a reducing element such as Si. An electron emitting substance layer 2 made of a Ba-containing alkaline earth metal oxide as the main constituent is provided on the film 12. With this constitution, an intermediate layer of a composite oxide is prevented from being made in a concentrated manner on and near the boundary of the base 1 and the layer 2 at a high electrical current density. This results in stabilizing an electron emitting property for a long period of time.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to an electron tube cathode used in a TV double-loud tube, and more particularly to an improvement in an electron emissive material layer.

[Conventional technology]

Figure 2 shows a cathode used in a conventional double picture tube for TVs. A bottomed cylindrical base made of nickel,
(2) is deposited on the top surface of the bottom of this substrate and contains at least barium (Ba), and also contains strontium (Sr).
) or/and an electron emitting material layer made of an alkaline earth metal oxide containing calcium (Oa); (3) is a heater disposed within the base (1) to heat the electron emitting material layer (2 ) to emit thermionic electrons.

In the electron tube cathode configured in this way, the base (1)
The electron emitting material layer (2) is deposited on the substrate as follows. First, alkaline earth metals (Ha * 8
A suspension consisting of carbonate of 'rr Ca ) was added to the substrate (1
) and heated by a heater (3) during the vacuum 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 ( 2) is coated.

In this activation step, some of the alkaline earth metal oxides react as follows.

That is, reducing elements such as silicon and magnesium contained in the substrate (1) move to the interface between the alkaline earth metal oxide and the substrate (1) 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+ 1/28i=Ba+1/2SiOt
・++−+・(1) BaO+Mg =Ba+MgO
--(21) As a result of this reaction, a part of the alkaline earth metal oxide deposited on the substrate (1) is reduced and becomes an oxygen-deficient semiconductor, which operates at a shade temperature of 700 to soo'a. This means that an electron emission of 0.5 to 0.8 A/d can be obtained at a temperature of 0.5 to 0.8 A/d. However, in the case of an electron tube cathode formed in this way, the electron emission is 0.6 to 0.8 A/d. It is impossible to obtain a current density higher than that.The reason is as follows.In other words, when a part of the alkaline earth metal oxide is subjected to a reduction reaction, from the above equations (1) and (2), As is clear, 8 io, , MgO or BaO is present at the interface between the substrate (1) and the alkaline earth metal oxide layer.
, l9i0. A composite oxide layer (intermediate layer) is formed,
This intermediate layer becomes a high-resistance layer and obstructs the flow of current.The intermediate layer also prevents the reducing elements in the substrate (1) from diffusing toward the surface of the electron emitting material layer (2). It is believed that barium (Ba) is not produced.

In addition, as a conventional cathode for electron tubes, JP-A-59-209
No. 41 discloses a structure similar to that shown in Fig. 2 described above, in which the thickness of the substrate (1) is made thinner in order to obtain the rapid action of the cathode, and the individual turbidity of the reducing agent during the life of the cathode is reduced. Prevention and basics (1)
In order to prevent the strength from decreasing, the substrate (1) is coated with lanthanum such as LaNi, La, 0. It is shown that it is dispersed in the form of .

[Problem that the invention seeks to solve]

In the electron tube cathode constructed in this way, during operation, the nickel crystal grain boundary near the interface between the substrate (1) and the electron emitting material layer (2), especially near the surface of the substrate (1), and the
Since the above-mentioned intermediate layer is segregated at a position inside the electron-emitting material NI (2) of about 0 μm, the flow of current and the diffusion of reducing elements toward the surface of the electron-emitting material layer (2) are impeded, and under high current density. There was a problem that sufficient electron emission characteristics could not be obtained.

In addition, in the case of the latter, since LaNi and La, 0° are contained during the production of the substrate (1) whose main component is nickel, the LaNi and La in the substrate (1) are
Variations in the gOs content were likely to occur.

This invention has been made in view of the above-mentioned points, and prevents the formation of an intermediate layer made of a composite oxide in a concentrated manner near the interface between the substrate and the electron emitting material layer under high current density. The purpose of this invention is to obtain a cathode for an electron tube that has stable emission characteristics over a long period of time and has high productivity and reliability.

[Failure to solve the problem]

The cathode for an electron tube according to the present invention has an electron emitting material layer mainly composed of an alkaline earth metal oxide containing at least barium formed on a nickel-based substrate on which a rare earth metal film is previously formed with a thickness of 6 μm or less. It is formed by adhering to the surface.

[Effect]

In this invention, when a rare earth metal having a thickness of 6 μm or less formed on a substrate mainly composed of Ni is activated when an electron emitting material layer is deposited on the substrate, carbonic acid of the alkaline earth metal is activated. This prevents oxidation of the substrate when the salt decomposes or when barium oxide undergoes a dissociation reaction during operation as a cathode, and also prevents the diffusion of reducing elements contained in the substrate into the electron emitting material layer. Appropriate control prevents the formation of an intermediate layer made of a composite oxide of a reducing element near the interface between the substrate and the electron emitting material layer, and disperses the intermediate layer within the electron emitting material layer. It is something that makes you

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to FIG. In the figure, @ is a rare earth metal film such as scandium or yttrium formed on the top surface of the bottom of the substrate (1), and (2) contains at least barium deposited on the rare earth metal film (6). Alkaline earth metal oxide OXl containing strontium or/and calcium
This is an electron-emitting material layer whose main component is

Next, in the cathode for an electron tube configured in this way, a rare earth metal film (2) and an electron emitting material layer (2) are applied to the base (1).
). First, a ternary carbonate of barium, strontium, and calcium is mixed with a predetermined amount of a binder and a solvent to create a suspension. This suspension is sprayed to a thickness of approximately 80 microns onto a substrate (1) whose main component is nickel, on which a rare earth metal film (2) of 6 μm or less has been formed on the top surface of the bottom using an electron beam evaporator or the like. Apply and then, like the conventional one,
After a decomposition process from carbonate to oxide and an activation process to reduce a part of the oxide, the electron emitting material layer (2) is converted into a substrate (
1).

Various cathodes for electron tubes were created using various thicknesses of the rare earth metal films formed by this method, diode vacuum tubes were created using these cathodes for electron tubes, and life tests were conducted at various current densities. As a result of examining the change in emission current, the results shown in Figure 3 were obtained. Figure 8 shows the current density of a conventional television cathode of 0.664/cr! O3, 1x (z, o5A/
cl! Life characteristics and rare earth metal film of an electron tube cathode in which a rare earth metal film of various thicknesses is formed on a substrate (1) and then an electron emitting material layer (2) is formed on top of the rare earth metal film when operated at t) This figure shows the relationship with the life characteristics of a conventional example having an electron emitting material layer (2) on a substrate (1) on which no electron emitting material is formed. As is clear from FIG. 8, the device of this example, in which the rare earth metal layer is formed on the substrate (1) with a thickness of 6 μm or less, has less emission deterioration during high current density operation than the conventional example. I'll fist you.

In order to investigate in detail the effect of forming a rare earth metal layer on the substrate (1) in this way, the experimental results shown in Fig.
After measuring the emission current for 000 hours, the cross-sections of the conventional product and the electron tube cathode having an electron emitting material layer (2) with a 2 μm 8C layer (6) formed on the substrate (1) were analyzed using an electron beam X-ray microanalyzer. Analysis was performed by (EPMA). As a result, in the conventional product under high current density operation, near the interface between the substrate (1) and the electron emitting material layer (2),
Sin at the grain boundaries in the substrate (1).

A layer of MgO and a composite oxide thereof is formed, and an electron emitting material FIJ (approximately 10
It was found that a BaO-8io complex oxide layer was formed at the μ position. The above-described 8i0t MgO layer and BaO Sin layer suppress the diffusion rate of S i and Mg, which are reducing agents, from the substrate (1) into the electron emitting material layer (2), and are highly insulating. This obstructs the flow of current and eventually leads to damage due to dielectric breakdown within the electron emitting material.

On the other hand, in the cathode for an electron tube having an electron emitting material (2) in which an SC layer made of a rare earth metal is formed on a substrate (1), which is the present embodiment, the reducing agent contained in the substrate (1) is S i , Mg is averagely distributed,
Unlike the conventional example described above, there are almost no peaks of these reducing agents near the interface between the substrate (1) and the electron emitting material layer (2). This is considered to be due to the following reasons. In other words, when carbonates of alkaline earth metals decompose into oxides during activation, or when BaO etc. cause a dissociation reaction during cathode operation,
This is thought to be due to the fact that the rare earth metal prevents oxidation of the substrate (1). For example, when the rare earth metal is scandium (Be), the reaction is expressed by the following equations (4) and (6).

(Sc layer surface) ・・・・・・・・・(4) B, 10→B
a+0 (Conventional example of ¥PL radiation-resistant material)
Ni+0→Ni0 (Ni surface) ・・・・・・・・・(5) (present invention)
28C+80→SC,03 (Be layer surface)...
...(6) Therefore, as is clear from the above equations (3) and (5), the lifetime of the electron tube cathode having the electron emitting material layer (2) that does not contain rare earth metal oxides is In the initial stage, the nickel oxide already formed at the interface between the substrate (1) and the electron emitting material N(2) reacts with the reducing agent 8i, Mg in the substrate (1), resulting in the formation of SiO, MgQ.
, are formed in the outermost layer of the interface and in the grain boundaries in its vicinity.

Therefore, the electron emitting material layer (Si, Mg, which is a reducing agent)
2) Diffusion into the above 8i0. , is rate-determined by the MgO oxide layer, and the sites for reactions (1) and (2) are formed near the oxide layer.

Therefore, especially when operating at high current densities, (1) (2)
) reaction takes place actively, and the reducing agent produces oxide 8 io
, , MgO is generated in a concentrated manner near the oxide layer, and as the reactions (1) and (2) progress, the diffusion of reducing elements 8i and Mg into the electron emitting material layer is further suppressed. Emissions drop significantly.

On the other hand, a rare earth metal layer according to an embodiment of the present invention is applied to a substrate (1).
In an electron tube cathode having an electron emitting material layer (2) formed thereon, a rare earth metal is reacted with COl and O generated by the dissociation reaction of BaC0 or BaO to form a rare earth metal oxide, and the substrate is The reducing elements Si and Mg prevent the oxidation reaction of nickel in (1).
1) does not form an oxide layer at or near the grain boundaries, and easily diffuses into the electron emitting material.
The reaction sites of ) are formed at grain boundaries in the electron emitting material layer (2), and the reaction sites are located in more dispersed locations than in the conventional example. Furthermore, since the rare earth metal oxide formed near the surface of the rare earth metal layer moderately controls the rate of diffusion of the reducing element into the electron emitting material, it is stable and good even after long-term high current operation. Emission characteristics can be maintained.

Furthermore, since a part of the rare earth metal is dissolved in Ni, the effect of strengthening the adhesion between the rare earth metal layer and the Ni substrate (1),
It also has the effect of suppressing embrittlement of the Ni substrate. The effect is remarkable when the thickness of the rare earth metal layer is 6 μm or less. Thickness is 6
If it exceeds μm, 1 of Sl+Mg from Ni substrate (1)
Diffusion into the radioactive material becomes insufficient, resulting in a decrease in emission characteristics.

In addition, if the thickness of the rare earth metal layer is 6 μm or less,
After 00 hours of operation (current density 2.05 A/m2), there was no peeling phenomenon from the electron emitting material layer (2) or the rare earth metal layer (a). Incidentally, the frequency of the peeling phenomenon in a conventional electron tube cathode having an electron emitting material layer (2) not containing a rare earth metal oxide was 80 degrees.

In the above examples, the rare earth metals include Sc,
Although the explanation has been made using Sc and Y, similar effects can be obtained with other rare earth metals, especially Sc.

The effect was remarkable in Y/Ce.

〔Effect of the invention〕

As described above, in this invention, a 6μ
A rare earth metal layer is formed with a thickness of 0.0 m or less, and an electron emitting material whose main component is an alkaline earth metal oxide containing at least barium is deposited on top of the rare earth metal layer. It has the effect of realizing a long life under high current density operation that is 2 to 4 times that of conventional cathodes that are not formed, and that a highly reliable cathode for electron tubes can be formed.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing an embodiment of the present invention, FIG. 2 is a sectional view showing a conventional cathode for an electron tube, and FIG. 3 is a diagram showing the relationship between rare earth metal thickness and emission current characteristics. In the figure, (1) is a base body, and (2) is an electron emitting material layer. In each figure, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] A rare earth metal film having a thickness of 6 μm or less is formed on a substrate whose main component is nickel, and an electron emitting material layer whose main component is an alkaline earth metal oxide containing at least barium is formed on the rare earth metal film. A cathode for an electron tube characterized by the following.