JPH03230445A - Cathode for electron tube - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an electron tube cathode used in a TV cathode ray tube or the like, and particularly relates to an improvement in an electron emissive material layer.

[Conventional technology]

Figure 5 is a vertical cross-sectional view showing a conventional cathode.
(2) is deposited on the bottom upper surface of this substrate (1) and contains at least barium (Ba) and strontium (
An electron emitting material layer made of an alkaline earth metal oxide containing Sr) and/or calcium (Ca); (3) is a heater (3) disposed within the base (1); This layer is for emitting thermoelectrons from the layer (2).

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, a suspension consisting of ternary carbonates of alkaline earth metals (Ba, Sr, Ca) is applied to the bottom upper surface of the substrate (1) and heated by the heater (3) 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 ( 2) is formed by adhesion.

In this activation step, a part of the alkaline earth metal oxide reacts as follows. In other words, reducing elements such as silicon and magnesium contained in the substrate (1) diffuse and move to the interface between the alkaline earth metal oxide and the substrate (1), and react with the alkaline earth metal oxide. do. 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+ 1/2S 1=Ba+ 1/2S i
02-(1) B a O+ M g = B a
+ M g O-(2) As a result of this reaction, the substrate (1)
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~
0.5-0.8A/Crn' at operating temperature of aoo'c
This results in an electron emission of .

However, with this cathode for electron tubes, 0.5 to 0.8 A/
There was a problem in that electron emission at a current density higher than crn' could not be extracted for a long time.

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 the above equations (1) and (2), the relationship between the substrate (1) and the alkaline earth metal oxide layer is A complex oxide layer (intermediate layer) such as SiO2, MgO or BaO-5i02 is formed at the interface, and this intermediate layer becomes a high resistance layer and impedes the flow of current. It is thought that this is because a sufficient amount of barium (Ba) is not generated because it prevents the reducing elements (Si, Mg) therein from diffusing to the surface side of the electron emitting material layer (2). In other words, during electron tube operation, the base (1)
The intermediate layer is segregated near the interface between the electron emitting material layer (2) and the nickel grain boundary near the surface of the substrate (1), and approximately 10 μm inside the electron emitting material layer (2) from the interface. Since the flow and the diffusion of the reducing element toward the surface of the electron emitting material layer (2) are hindered, there is a problem in that sufficient electron emission characteristics cannot be obtained under high current density.

On the other hand, Japanese Patent Application Laid-Open No. 62-88241 discloses that by containing 0.01 to 0.5% by weight of a rare earth metal in the substrate, activation is achieved when an electron emitting material layer is deposited on the substrate. Sometimes, when alkaline earth metal carbonates decompose,
Alternatively, during operation as a cathode, it prevents the oxidation reaction of the substrate when barium oxide causes a dissociation reaction, and moderately controls the diffusion of the reducing element contained in the substrate into the electron emitting material layer. A technology has been demonstrated that 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, and disperses the intermediate layer within the electron emitting material layer. In the second conventional electron tube cathode, since the intermediate layer is dispersed, the electron tube cathode exhibits little emission deterioration even when operated at a high current density of about 1 to 2 A/c rn'. A cathode is obtained.

Furthermore, JP-A No. 62-22347 discloses that by containing 0.1 to 20% by weight of a rare earth metal oxide in the electron emitting material layer, oxidation of the substrate is prevented as well as the second conventional example. A technique of dispersing the intermediate layer has been shown, and in this third conventional example as well, 2 A /
A cathode for a cathode ray tube with little emission deterioration can be obtained even under high current density operation of cr rn'.

[Problem to be solved by the invention]

However, in such a conventional cathode for an electron tube, when operating at a high current density of 2 A/cm' or more, barium evaporates significantly due to Joule heat caused by the current flowing through the electron emitting material layer, and electrons are There was a problem in that the radiation characteristics could deteriorate.

This invention was made to solve the above-mentioned problems, and even in high current density operation of 2 A/Crn' or more, the generation of Joule heat due to the current flowing through the electron emitting material layer is small, and the electron emission is suppressed. The purpose of this invention is to obtain a cathode for an electron tube with little deterioration in radiation characteristics.

(Means for Solving the Problems) A cathode for an electron tube according to the present invention includes a substrate mainly composed of nickel containing a reducing element, and an alkaline earth metal oxide containing at least barium deposited on the substrate. The main component is 0.05 to 5% by weight of RB group, III b
a second layer containing one of the metal elements of group VB and group VB or an oxide thereof; and a second layer deposited on the second layer and consisting mainly of an alkaline earth metal oxide containing at least barium. It is equipped with three layers.

[Effect]

Of the three layers forming the electron emitting material layer, the first layer generates free barium necessary for electron emission, and this free barium adheres to the third layer, which is the outermost layer, and contributes to electron emission. In addition, the second layer increases the conductivity within the electron emitting material layer to reduce electrical resistance, reduce generation of Joule heat, reduce barium evaporation, and reduce deterioration of electron emission characteristics.

[Embodiments of the Invention] Hereinafter, an embodiment of the invention according to claim 1 will be described based on FIG. 1, which is a sectional view. (1) is a substrate whose main component is nickel, and this substrate (1) contains a reducing agent such as Si or Mg.

(7) is an electron emitting material layer deposited on the upper bottom surface of the base (1), and is composed of three layers. The first layer (4) deposited on the substrate (1) is a ternary oxide of barium, strontium and calcium containing 4% by weight of scandium oxide. A second layer (5) deposited on the first layer (4).
) is a ternary oxide of barium, strontium, and calcium containing 1% by weight of copper. 2nd layer (5)
The third layer (6) deposited on top is a ternary oxide of barium, strontium and calcium.

This electron emissive material layer (7) is deposited and formed in the following manner.

First, a ternary carbonate of barium, strontium, and calcium and 4% by weight of scandium oxide are mixed together with lacquer, a solvent, etc. to create a suspension, and this suspension is sprayed onto the substrate (1). The first layer (4) is formed by coating by a method and then drying.

First, ternary carbonate of barium, strontium, and calcium and 1% by weight of fine powder of metallic copper (Cu) are mixed together with lacquer, solvent, etc., and this suspension is applied to the first layer (4).
) and then dried to form a second layer (5).

Next, a suspension of ternary carbonates of barium, strontium, and calcium mixed with lacquer, solvent, etc. is applied onto the second layer (5), dried, and then the third layer (5) is coated.
Form layer (6).

Next, this cathode is assembled into an electron tube, heated by a heater during the evacuation process, and the first layer (4) to the third layer (6) are formed.
An electron-emitting material layer (7) is formed by converting barium, strontium, and calcium carbonates in the oxide into oxides.

In this example, the average thickness of each of the first layer, second layer, and third layer is 30 μm.

They were 0.2 μm and 50 μm.

A diode vacuum tube was created using this electron tube cathode, and 2.5
FIG. 2 shows the results of a life test conducted at a current density of A/am'. Characteristic a in the figure represents the characteristic of this example, or characteristic of the second example in which the second layer contains 1% by weight of silver (Ag) instead of copper, and characteristic C indicated by the broken line represents the characteristic of this example. The characteristics of the conventional example of only one layer containing 4% by weight of scandium oxide in the electron emitting material shown in Japanese Patent Application No. 62-22347 are shown, and the cathodes of the first and second examples are as follows:
It can be seen that there is less deterioration in emission current compared to the conventional cathode.

FIG. 3 is an electron emission characteristic diagram of the third and fourth embodiments of the present invention, where the characteristic d is the characteristic of the third embodiment, and the second layer (5
) containing 1.0% by weight of indium (In). Further, the characteristic e is the characteristic of the fourth embodiment, and the characteristic e is the characteristic of the fourth embodiment.
Layer (5) contains 1.0% by weight of thallium (TIl).

FIG. 4 is an electron emission characteristic diagram of the fifth and sixth embodiments of the present invention, where the characteristic f is the characteristic of the fifth embodiment, and the second layer (
5) containing 1% by weight of antimony (sb). Further, the characteristic g is the characteristic of the sixth embodiment, and the characteristic g is the characteristic of the second layer (
5) containing 1.0% by weight of bismuth (Bi).

As can be seen from Figures 3 and 4, the third to sixth
In the cathode of the embodiment, the deterioration of the emission current is reduced compared to the conventional example (characteristic C), similar to the first and second embodiments shown in FIG.

In addition, in each of the above examples, 4% by weight was contained in the first layer (4).
Scandium oxide of 0.05 to 5.0 was contained.
By containing scandium oxide in the first layer (4), the base (1) and
It is possible to suppress the formation of an intermediate layer such as BaO-5iOz that is formed over the course of operation time at the interface with the electron emitting material layer (7).

Further, in each of the above embodiments, the second layer (5) includes IB group, I
Although 1.0% by weight of metal elements of Group II B and VB groups were contained, the effect of reducing the electrical resistance of the electron emitting material layer (7) within the range of 0.01 to 5.0% by weight was It was also observed in metallic elements and their oxides.

In addition, if it exceeds 5.0% by weight, the electron emitting material layer (7)
This is not preferable because the sintering progresses.

In this way, the second layer (5) contains IB group, IIIB group, V
The reason why the electrical resistance of the second layer (5) is reduced by containing the B group element is that the IB group element can have a monovalent or divalent valence, and the III B group element can have a monovalent or divalent valence. value,
This is thought to be because elements of the VB group can have a valence of 3 or 2, and the elements of the VB group can have a valence of 3, 5gfJ, or 4, and free electrons exist.

(Effects of the Invention) The cathode for an electron tube according to the present invention includes a base made of nickel containing reducing elements such as silicon and magnesium, and 0.05 to 5% by weight of scandium oxide deposited on the base. A first layer mainly composed of an alkaline earth metal oxide containing barium, and 0.01 to 5.0% by weight of IB group, Xia II B group, or a second layer mainly composed of an alkaline earth metal oxide containing barium and one of group VB metal elements or its oxide; and an alkali containing barium deposited on the second layer. It is characterized by having an electron emitting material layer composed of a third layer mainly composed of an earth metal oxide, and the electrical resistance of the electron emitting material layer is reduced by the second layer. Since the evaporation of barium due to Joule heat can be reduced, an electron tube cathode with less emission deterioration can be obtained even when operated at a high current density of 2 A/crn'' or more.

[Brief explanation of drawings]

FIG. 1 is a longitudinal cross-sectional view of one embodiment of the present invention, FIGS. 2 to 4 are diagrams showing electron emission characteristics of different embodiments of the present invention, and FIG. 5 is a longitudinal cross-section of a conventional cathode for an electron tube. It is a diagram. (1)...Substrate, (4)...First layer, (5)...
...Second layer, (6)...Third layer, (7)...Electron emitting material layer. In each figure, the same reference numerals indicate the same or equivalent parts.

Claims (3)

[Claims] (1) A base made of nickel containing reducing elements such as silicon and magnesium, and an alkaline earth metal oxide containing barium and containing 0.05 to 5% by weight of scandium oxide deposited on this base. A first layer as a main component and 0.01 to 5% by weight deposited on this first layer.
a second layer mainly composed of an alkaline earth metal oxide containing barium and one of the group IB, group IIIB, or group VB metal elements or its oxide; A cathode for an electron tube, comprising a third layer mainly composed of an alkaline earth metal oxide containing deposited barium. (2) The IB group element is copper or silver, the IIIB group element is gallium, indium, or thallium, and the V
2. The cathode for an electron tube according to claim 1, wherein the B group element is arsenic, antimony or bismuth. (3) The average thickness of the first layer is 10 μm or more and 90 μm or less, the average thickness of the second layer is within the range of 0.01 to 2 μm, and the average thickness of the third layer is 10 μm or more and 80 μm. The cathode for an electron tube according to claim 1, wherein the average thickness of the first layer and the third layer is 50 μm or more and less than 150 μm.