JPH05266783A - Cathode for electron tube - Google Patents

Abstract

PURPOSE:To obtain an electron tube cathode with emission characteristics stabilized for a long time and high productivity and high reliability. CONSTITUTION:A substrate 1, which is mainly composed of nickel and which includes reduced elements, is coated by an electron emission material layer 2, which is mainly composed of alkaline earth metal oxide at least including barium and which includes rare earth metal oxide at 0.1-20 weight%. This substrate 1 coated with the electron emitting material layer 2 is used as a cathode for a television set to be operated at a high density of current within a range of 1.32A/cm<2>-2.64A/cm<2>.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cathode for an electron tube used in a TV cathode ray tube and the like, and more particularly to improvement of an electron emissive material layer.

[0002]

2. Description of the Related Art FIG. 2 shows a cathode used in a conventional TV cathode ray tube or image pickup tube.
Is a bottomed cylindrical substrate made of nickel as a main component containing a trace amount of reducing elements such as silicon (Si) and magnesium (Mg).
Is deposited on the top surface of the bottom of this substrate and contains at least barium.
An electron emitting material layer 3 made of an alkaline earth metal oxide containing (Ba) and additionally containing strontium (Sr) and / or calcium (Ca) is a heater 3 disposed in the substrate 1.
The above is for emitting thermoelectrons from the electron emitting material layer 2 by heating.

In the electron tube cathode thus constructed, the electron emitting material layer 2 is deposited on the substrate 1 in the following manner. First, alkaline earth metals (Ba, S
A suspension of a carbonate of r, Ca) is applied to the substrate 1 and heated by the heater 3 during the vacuum evacuation process. At this time, the alkaline earth carbonate is converted to an oxide of an alkaline earth metal. After that, a part of the alkaline earth metal oxide is reduced and activated so as to have a semiconductor property, so that the electron emitting material layer 2 made of the alkaline earth metal oxide is coated on the substrate 1. It's dressed up.

In this activation step, a part of the alkaline earth metal oxide is reacted as follows.
That is, the 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, barium oxide (B
If it is aO), it reacts as in the following equations (1) and (2).

[0005]

[Chemical 1]

As a result of this reaction, a part of the alkaline earth metal oxide deposited on the substrate 1 is reduced to become an oxygen-deficient semiconductor, and the cathode temperature is 700 to 800 ° C.
An electron emission of 0.5 to 0.8 A / cm ² will be obtained.
However, the electron tube cathode thus formed cannot take out a current density of electron emission of 0.5 to 0.8 A / cm ² or more. The reason is as follows. That is, when a part of the alkaline earth metal oxide is subjected to a reduction reaction, SiO ₂ , MgO or BaO is formed at the interface between the substrate 1 and the alkaline earth metal oxide, as is clear from the above equations (1) and (2). A composite oxide layer (intermediate layer) made of SiO ₂ is formed, and this intermediate layer serves as a high resistance layer to prevent current flow, and the intermediate layer serves to reduce the reducing element in the substrate 1 to the electron emitting material layer 2 Sufficient barium (B
It is considered that a) is not generated.

A conventional cathode for an electron tube is disclosed in
In JP-A-59-20941, the same structure as that of FIG. 2 described above is used, and the plate thickness of the substrate 1 is made thin in order to obtain the fast motion of the cathode, and the suspension of the reducing agent during the life is prevented. For the purpose of preventing the strength of the substrate 1 from decreasing, lanthanum is added to the substrate 1 as LaNi ₅ and
Dispersed inclusions in the form of La ₂ O ₃ are shown.

[0008]

In the cathode for an electron tube having such a structure, during operation, from the nickel crystal grain boundary near the interface between the substrate 1 and the electron-emitting substance layer 2, especially near the surface of the substrate 1 and the above interface. Since the above-mentioned intermediate layer is segregated at a position inside the electron emitting material layer 2 by about 10 μm, current flow and diffusion of the reducing element to the surface side of the electron emitting material layer 2 are hindered,
There is a problem that sufficient electron emission characteristics cannot be obtained under high current density. Further, in the latter case, when LaNi ₅ and La ₂ O are produced when the substrate 1 containing nickel as a main component is manufactured.
_{Since 3} was contained, variations in the content of LaNi ₅ and LO ₂ O ₃ in the substrate 1 were likely to occur.

The present invention has been made in view of the above points, and it is possible to concentrate formation of an intermediate layer composed of a composite oxide in the vicinity of the interface between a substrate and an electron emitting material layer under a high current density. It is an object of the present invention to obtain a cathode for an electron tube which is prevented, has stable emission characteristics for a long time, and has high productivity and reliability.

[0010]

A cathode for an electron tube according to the present invention is an electron-emitting substance containing, as a main component, an alkaline earth metal oxide containing at least barium, and containing 0.1 to 20% by weight of a rare earth metal oxide. A layer containing nickel as a main component and deposited on a substrate containing a reducing element, and having a thickness of 1.32 A / cm ² ~
It was operated at a high current density within the range of 2.64 A / cm ² . Further, the cathode for a television is used as the cathode for the electron tube.

Further, the cathode for an electron tube according to the present invention is
A substrate containing 0.3 to 20% by weight of a rare earth metal oxide component, the rare earth metal oxide containing at least one of scandium oxide or yttrium oxide, an electron-emitting substance layer containing nickel as a main component and a reducing element. It is deposited on the top. Furthermore, an electron emitting material layer containing 0.3 to 15% by weight of a rare earth metal oxide component is formed on a substrate containing nickel as a main component and a reducing element containing at least one of silicon and magnesium. It was made.

[0012]

In the present invention, 0.1 to 20% by weight of the rare earth metal oxide contained in the electron-emitting substance layer is an alkaline earth metal oxide during activation when the electron-emitting substance layer is deposited on the substrate. Of the reducing element contained in the substrate into the electron-emitting substance layer while preventing the reaction of the substrate to be oxidized when the carbonate of is decomposed or when barium oxide causes a dissociation reaction during the operation as a cathode. The diffusion layer is appropriately controlled to prevent the intermediate layer composed of the complex oxide of the reducing element from being intensively formed in the vicinity of the interface between the substrate and the electron emitting material layer, and the intermediate layer is formed in the electron emitting material layer. It is to disperse.

[0013]

【Example】

Example 1. An embodiment of the present invention will be described below with reference to FIG. In the figure, 2 is an alkaline earth metal oxide deposited on the upper surface of the bottom of the substrate 1, containing at least barium, and further containing strontium and / or calcium.
11 as the main component, 0.1 to 20% by weight of scandium oxide,
An electron emitting material layer containing a rare earth metal oxide 12 such as yttrium oxide.

Next, in the electron tube cathode thus constructed, a method of depositing the electron-emitting material layer 2 on the substrate 1 will be described. First, ternary carbonate of barium, strontium and calcium, and scandium oxide powder. Alternatively, a desired weight% of yttrium oxide powder (weight% assuming that all the ternary carbonates become oxides) is added and mixed to prepare a suspension. This suspension was applied by spraying on a substrate 1 containing nickel as a main component to a thickness of about 80 μm, and thereafter, as in the conventional case, the decomposition process from carbonate to oxide and a part of the oxide. The electron emissive material layer 2 is applied to the substrate 1 through an activation process of reducing the.

The rare earth metal oxide (Sc ₂ O ₃ , Y) contained in the electron-emitting material layer 2 deposited by the method described above is used.
Various cathodes for electron tubes with various contents of ₂ O ₃ ) were made, and a cathode vacuum tube was made using this cathode for electron tubes,
As a result of conducting a life test at various current densities and examining changes in the emission current, the results shown in FIGS. 3 and 4 were obtained. Figure 3
Has a current density of 0.66 A / cm ² as a conventional TV cathode.
5 wt% Sc when operated at 3.1 times (2.05 A / cm ² ).
₂ O ₃ -containing electron emitting material cathode 2 for electron tube cathode, 12 wt% Y ₂ O ₃ containing electron emitting material layer 2 electron cathode cathode life characteristics and rare earth metal oxide 3 shows the relationship with the conventional life characteristics of the electron emitting material layer 2 that does not contain any element. As is clear from FIG. 3, the rare earth metal oxide-containing material of the present embodiment is less susceptible to emission deterioration at high current density operation than the conventional one.

Further, FIG. 4 shows Sc ₂ O which is a rare earth metal oxide.
_{In the} cathode for an electron tube having the electron emitting material layer 2 in which the addition ratios of ₃ and Y ₂ O ₃ are variously changed, the current density is 0.66 A / cm ² (1
, And a life test was conducted under conditions where the current density was 2, 3, and 4 times, and the relationship between the current density and the ratio of the emission current at 6000 hours to the initial emission current was shown. .. As can be seen from FIG. 4, when the rare earth metal oxides Sc ₂ O ₃ and Y ₂ O ₃ are added in an amount of 0.1% by weight or more, there is an effect of preventing a decrease in emission under high current density operation. Not shown, Sc ₂ O ₃ , Y ₂ O ₃
This effect was confirmed up to the addition rate of 20 wt%. Next, the addition ratio of Sc ₂ O ₃ which is a rare earth metal oxide is 0.1, 1,
The cathode having the electron-emitting substance layer 2 of 5, 10, 20, 25% by weight, which was changed to 6 kinds, was incorporated into each TV cathode ray tube, and a TV cathode ray tube was produced through a predetermined process.

FIG. 5 is a graph showing the measurement results of the initial electron emission current characteristics, in which the vertical axis represents the maximum cathode current and the horizontal axis represents the scandium oxide addition ratio. As is clear from FIG. 5, when the addition ratio of scandium oxide exceeds 20 wt%, the initial reduction of electron emission current becomes remarkable. That is, if the addition rate of these rare earth metal oxides Sc ₂ O ₃ and Y ₂ O ₃ exceeds 20% by weight, stable emission of the emission current is required unless a new aging is performed after the manufacturing process. Was difficult and impractical. Therefore, the electron emitting material layer 2
The content of the rare earth metal oxide in is required to be in the range of 0.1 to 20% by weight. Especially 0.3 to 15% by weight
Within the range, the above-mentioned effects were remarkable.

In order to investigate in detail the effect of containing the rare earth metal oxide in the electron emitting material layer 2 as described above, after measuring the emission current at 6000 hours in the experimental result of FIG. The cross section of the cathode for an electron tube having the electron emitting material layer 2 containing Sc ₂ O ₃ was analyzed by an electron beam X-ray microanalyzer (EPMA), and the results shown in FIGS. 6 and 7 were obtained. FIG. 6 shows experimental results of a cathode for an electron tube having an electron emitting material layer 2 containing no conventional rare earth metal oxide, and as is clear from FIG. In the vicinity of the interface with the emissive material layer 2, the reducing agents contained in the substrate 1, Si and Mg, are segregated, and this segregation state is on the substrate 1 side from the interface between the substrate 1 and the electron emissive material layer 2. Approximately 3 to 5 μm from the depth of about 5 μm and the above interface to the electron emitting material layer 2.
The peaks of the reducing agents, Si and Mg, were simultaneously confirmed at the position of, and Si was further transferred to the electron emitting material layer 2 side from the above interface.
The largest peak was observed at 13 μ.

Although not shown, these in the electron emitting material
The presence of Ba peaks was also confirmed at the same positions as the Mg and Si peak positions. Since these Si, Mg, and Ba peaks almost coincide with the oxygen peak, it is considered that these metals exist as oxides or complex oxides. further,
It was confirmed that a small amount of Si was present in the substrate 1. As described above, in the conventional product operating at high current density, SiO ₂ , MgO and a composite oxide layer of these are formed in the crystal grain boundary in the substrate 1 near the interface between the substrate 1 and the electron emitting material layer 2. Was
Further, from the above interface to the position of the electron emitting material layer 2, BaO,
It can be seen that a composite oxide layer of MgO and SiO ₂ is formed. The above-mentioned SiO ₂ · MgO layer and BaO · SiO ₂ layer are reducing agents from the inside of the substrate 1 to the inside of the electron emitting material layer S.
In addition to suppressing the diffusion rate of i and Mg, the high insulation hinders the flow of current and eventually causes wear due to dielectric breakdown in the electron emitting material.

On the other hand, in the cathode for an electron tube having the electron emitting material layer 2 containing Sc ₂ O ₃ which is the rare earth metal oxide of the present embodiment, the substrate is as shown in FIG. The reducing agents Si and Mg contained in 1 are dispersed evenly, and these reducing agents exist near the interface between the substrate 1 and the electron-emitting substance layer 2 as in the conventional example shown in FIG. The peak of the agent does not exist at all. This is considered to be due to the following reasons. In other words, when the alkaline earth metal carbonate is decomposed into an oxide during activation, or when BaO or the like undergoes a dissociation reaction during the operation of the cathode for an electron tube, the rare earth metal oxide is used as the substrate 1.
It is thought that this is due to the prevention of the oxidation of

For example, it is considered that the rare earth metal oxide is caused by preventing the base 1 from being oxidized. For example,
The reaction when the rare earth metal oxide is scandium oxide (Sc ₂ O ₃ ) is as shown in the following equations (4) and (6).

[0022]

[Chemical 2]

Therefore, as is clear from the above equations (3) and (5),
In the cathode for an electron tube having the electron emitting material layer 2 containing no rare earth metal oxide, in the substrate 1 and the nickel oxide already formed at the interface between the substrate 1 and the electron emitting material layer 2 at the beginning of the life. Reacting with Si and Mg, which are reducing agents, to form SiO ₂ .MgO ₂ in the outermost layer of the interface and in the grain boundaries in the vicinity thereof. Therefore, reducing agents such as Si and Mg
Diffusion into the electron-emitting substance layer 2 is controlled by the SiO ₂ .MgO ₂ oxide layer, and the sites of the reactions 1 and 2 are formed in the vicinity of the oxide layer.

Therefore, particularly when operating at a high current density, the reactions (1) and (2) are actively carried out and the oxides produced by the reducing agent are used.
SiO ₂ · MgO is generated concentrated near the oxide layer,
As the reactions of (1) and (2) proceed, the diffusion of reducing elements Si and Mg into the electron-emitting material is further suppressed, and the reduction in emission becomes remarkable.

On the other hand, in the cathode for an electron tube having the electron emitting material layer 2 containing the rare earth metal oxide according to the embodiment of the present invention, the rare earth metal oxide in the electron emitting material layer 2 is the nickel of the substrate 1. Since the oxidation reaction is prevented, the reducing elements Si and Mg do not form an oxide layer at or near the crystal grain boundaries in the substrate 1, and easily diffuse into the electron emitting material layer. (2) The reaction site of (2) is formed at the grain boundary in the electron emitting material layer 2, and the reaction site is located more dispersedly than in the conventional example.

Furthermore, since the rare earth metal oxide in the electron emitting material layer 2 appropriately controls the diffusion of the reducing element into the electron emitting material layer, it is stable and good even after operation for a long time under high current density. It can maintain excellent emission characteristics. Therefore, the addition of less than 0.1% by weight of the rare earth metal oxide is insufficient in the effect of suppressing the formation of the oxide layer of SiO ₂ .MgO in the vicinity of the grain boundaries of the substrate 1, and the emission characteristics start to deteriorate. Further, if it is added in an amount of more than 20% by weight, the function of suppressing the diffusion of the reducing element in the electron emitting substance becomes large, and aging for a long time is necessary for the stable extraction of the emission current.

In the range of addition of 0.1 to 20% by weight of rare earth metal oxide, the solid solution phenomenon of rare earth metal in the substrate 1 was confirmed, and after operation for 6000 hours (current density 2.05 A /
There was no peeling phenomenon of the electron emitting material layer 2 from the substrate 1 in cm ² . Incidentally, the occurrence frequency of the peeling phenomenon was 30% in the cathode for an electron tube having the electron emitting material layer 2 containing no conventional rare earth metal oxide.

In the above examples, Sc ₂ O ₃ and Y ₂ O ₃ were used as rare earth metal oxides, but other rare earth metal oxides have similar effects, but The effect was remarkable in Sc ₂ O ₃ , Y ₂ O ₃ , and Ce ₂ O ₃ . As described above, according to the present invention, the cathode can be manufactured under substantially the same manufacturing conditions as the conventional one, and the dispersion state of the rare earth metal oxide can be controlled relatively easily.

[0029]

As described above, the present invention mainly comprises an alkaline earth metal oxide containing at least barium, which is deposited on a substrate containing a reducing element or a substrate containing at least one of silicon and magnesium. Since the electron emitting material layer as a component contains 0.1 to 20% by weight of a rare earth metal oxide, and the rare earth metal oxide is at least one of scandium oxide or yttrium oxide , the rare earth metal oxide is Electron emitting material
2 to 4 times that of the conventional one not included in the layer, that is, 1.32 A / cm ² (= 0.66 × 2) to 2.64 A / cm ² (= 0.66)
The effect of achieving a long life under high current density operation of (4) and obtaining a highly reliable cathode for an electron tube, which is inexpensive and has few restrictions on production. Further, when it is used as a cathode for a television, it can be used at the same operating temperature as that of a conventional oxide cathode, so that it does not newly affect the thermal deformation of the cathode component in the cathode ray tube for TV. Therefore, a highly reliable cathode can be obtained.

[Brief description 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.

FIG. 3 is a characteristic diagram showing a relationship between a life test time and an emission current.

FIG. 4 is a characteristic diagram showing a relationship between a current density and an emission current ratio.

FIG. 5 is a characteristic diagram showing the relationship between the scandium oxide content and the maximum cathode current.

FIG. 6 is a characteristic diagram showing a result of measuring a cross section of the device of FIG. 2 after measuring the emission current at 6000 hours by EPMA.

FIG. 7 is a characteristic diagram showing the result of measurement of the device of FIG. 1 in the same manner as in FIG.

[Explanation of symbols]

 1 substrate 2 electron emitting material layer

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Kinjiro Sano, No. 1 Baba Institute, Nagaokakyo, Kyoto Prefecture Mitsubishi Electric Corporation, Kyoto Works (72) Toyoichi Kamada, No. 1, Baba Institute, Nagaokakyo, Kyoto Mitsubishi Electric Corporation Inside the Kyoto Works

Claims (4)

[Claims] 1. A main component of which is composed of nickel and which contains, on a substrate containing a reducing element, an alkaline earth metal oxide containing at least barium as a main component and 0.1 to 20% by weight of a rare earth metal oxide component. A cathode for an electron tube, which is formed by depositing an electron emission material layer and is operated under a high current density in the range of 1.32 A / cm ^{2 to} 2.64 A / cm ² . 2. The main component is nickel, the alkaline earth metal oxide containing at least barium is contained as a main component on a substrate containing a reducing element, and 0.1 to 20% by weight of a rare earth metal oxide component is contained. A cathode for an electron tube, which is used as a cathode for a television operated under a high current density in the range of 1.32 A / cm ^{2 to} 2.64 A / cm ² by depositing an electron emission material layer. 3. A substrate comprising nickel as a component, a reducing element-containing substrate, an alkaline earth metal oxide containing at least barium as a main component, and 0.3 to 20% by weight of a rare earth metal oxide component. A cathode for an electron tube, wherein an electron emitting material layer in which the rare earth metal oxide is at least one of scandium oxide or yttrium oxide is deposited. 4. A main component is nickel, and an alkaline earth metal oxide containing at least barium is contained as a main component on a substrate containing a reducing element containing at least one of silicon and magnesium. A cathode for an electron tube, wherein an electron emission layer containing a component of the rare earth metal oxide is formed by deposition.