JPS59203343A - Impregnated cathode - Google Patents

Abstract

PURPOSE:To improve emitted current characteristics in the low temperature area by providing a uniform layer consisting of fine W powder, scandium oxide, and electron emission material on the surface of a cathode. CONSTITUTION:In an impregnated cathode that is used in a CRT, image pickup tube, etc, an impregnated cathode 9 to which SC2O3 is added is formed by filling a porous W substrate and an air hole section with an electron emitting material consisting of scandium oxide and barium oxide. A layer 10 consisting of fine W powder, SC2O3, and electron emitting material is formed on the surface of such a cathode 9. The particle diameter of the W powder used in the layer 10 ranges from 0.1mum to 2mum. As a result, the electric emission can be improved in the low voltage area and the high current density of a cathode material can be attained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to cathode materials for cathode ray tubes, image pickup tubes, etc., and particularly to a high-performance impregnated cathode that can provide high electron emission.

[Background of the invention]

The saturation current density of a normal impregnated cathode is 3 to 4 at 1ooor.
A/. It is 2. On the other hand, the saturation current density of the impregnated cathode containing SC oxide is IOA/cn2 at 800C.
The value of is obtained. However, the impregnated cathode with SC oxide has a low emission current value with respect to the extraction voltage in the space charge limited region (A, Van Oostrom,
Appl, 5urf, Sci, 2.1979°1
73), it is difficult to use at low temperatures and has not been put into practical use.

[Purpose of the invention]

An object of the present invention is to improve the emission current characteristics of an impregnated cathode containing SC oxide in a low temperature region.

[Summary of the invention]

The impregnated cathode containing SC oxide has the drawback that non-uniform SC oxide precipitates are formed on the surface at operating temperatures, resulting in non-uniform surface states and difficulty in emitting electrons in a low electric field region. The present invention provides a uniform layer of fine W powder, scandium oxide, and electron-emitting material on the surface of an impregnated cathode containing SC oxide, making the surface level uniform and enabling high electron emission. The place has its characteristics.

Various methods can be considered for producing the above-mentioned uniform layer of fine W powder, scandium oxide, and electron-emitting material. A uniform layer of powder, scandium oxide, and electron-emitting material can be created.

[Embodiments of the invention]

Examples of the present invention will be described in detail below.

Example 1 FIG. 1 shows a cross-sectional view of a conventional impregnated cathode containing 5C203. 1 is a W grain, 2 is one 8 C20i grain, and 3 is an electron emitting material. The W grains have a grain size of 5 to 110A1.

Normal impregnation method (heated at 1700CX for 2 minutes in H2 stream)
It was impregnated into a porous body of w-sc2o3 prepared in advance. The saturation current characteristics of this 5C203-added impregnated cathode were measured and compared with a conventional impregnated cathode and an Os-coated impregnated cathode, and the results are shown in FIG.

4 is a characteristic of a normal impregnated cathode, 5 is a characteristic of an Os-coated impregnated cathode, and 6 is a characteristic of an impregnated cathode added with 5C203. Adding 5C203 to the impregnated cathode significantly improves the saturation current density. However, the 5C203-added impregnated cathode has the drawback of low emission current under low extraction voltage. FIG. 3 shows the results of plotting the current emitted from the cathode at a temperature of 800 C using the square root of the extraction voltage, using an MO plate as the anode and setting the distance between the cathode and the anode to 1. No. 7 shows the characteristics of an 8Cx03-added impregnated cathode, and it can be seen that the emission current is low under a low extraction voltage. This is the result when the surface structure of the impregnated cathode is such that a fine W powder layer is provided on the surface of 5c2os or wall hole segregation, as shown in FIG. The W powder layer has a particle size of 0.1 to 1 μm, which is smaller than the particle size of the underlying W substrate, which is 5 to 10 μm.
It consists of fine particles, and its thickness is 0.5 μm to 2 μm.
And so. It can be seen that this 5CzOa-added impregnated cathode in close contact with W powder has a high emission current even under a low extraction voltage. This is because when a fine W powder layer is provided on the surface of an impregnated cathode with SC, O3 added, the underlying SC20, components and electron-emitting substances are absorbed into the pores of the fine W powder layer at high operating temperatures. Penetrate,
This is thought to be due to the formation of a uniform layer of W grains, 5C203, and electron emitting material on the surface. A schematic diagram of this structure is shown in FIG. Reference numeral 9 is an impregnated cathode containing 5C203, and 10 is a layer consisting of fine W powder, 5C203, and an electron-emitting substance that is in close contact with the surface. If the particle size of the W powder is less than 0.1 μm11, local grain growth of the W powder will occur during sintering at high temperatures, and the relationship between the emission current and voltage will change to the characteristic 7 in Figure 3. It has declined.

If the grain size of the W grains is 2 μm or more, it will be too close to the primary grain size of the underlying impregnated cathode, making it difficult to uniformly disperse the W grains. The desired results were not achieved.

Example 2 The fine W powder described in Example 1 was replaced with a W film coating layer. The W film was produced by a normal sputtering method and had a film thickness of 0.1 to 5 μm. When we measured the characteristics of the 5C203-added impregnated cathode coated with this W film, we found that the saturation current density had the characteristic 6 in Figure 2, and the emission current-voltage relationship had the characteristic 8 in Figure 3. Ta. This is because the W film produced by the sputtering method is a polycrystalline material with a size of 0.05 to 0.2 μm, so when it is heat-treated, 5c203 and the electron-emitting substance diffuse from the underlying impregnated cathode, as shown in Figure 4. This is because a surface structure with good uniformity as shown in Figure 3 was formed. Therefore, it is understood that the 5C203-added impregnated cathode coated with a W film also emits high electrons under a low extraction voltage. When the film thickness is less than 0.1 μm, the W film coverage is insufficient, and when it is more than 5 μm, the aging time required to stabilize the characteristics is too long, and in either case, desired results could not be obtained.

[Effects of the Invention] According to the present invention, electron emission in the low voltage region of an impregnated cathode added with SC can be enhanced, and it can contribute to increasing the current density of cathode materials such as cathode ray tubes and image pickup tubes.

[Brief explanation of drawings]

Figure 1 is a longitudinal cross-sectional view of an impregnated cathode with 5C203 added.
The figure is a saturation current characteristic diagram of an impregnated cathode made by a conventional method and a 5C203-added impregnated cathode, Fig. 3 is a relationship between emission current and extraction voltage for a conventional 5C203-added impregnated cathode and the cathode of the present invention, and Fig. 4 The figure is a longitudinal cross-sectional view of the υ-shaped cathode of the present invention. 1... Tungsten grains, 2... Scandium oxide particles, 3... Electron-emitting material, 4... Saturation current characteristics of conventional impregnated cathode, 5... Saturation current characteristics of osmium-coated impregnated cathode , 6...5 Saturation current gravity of C203-added impregnated cathode, 7...5 Relationship between emission current and voltage of C203-added impregnated cathode, 8... Relationship between emission current and voltage of impregnated cathode of the present invention , 9...5 Expansion and disconnection of C203-added impregnated cathode (Fig. 2, Fig. 3, 1-7o core j2 [

Claims (1)

[Claims] 1. In an impregnated cathode consisting of a porous W substrate and scandium oxide and barium oxide electron-emitting substances filled in the pores, fine W powder and scandium powder are formed on the surface of the cathode. An impregnated cathode characterized by providing a uniform layer of an oxide and an electron-emitting substance. 2.-The impregnated cathode according to claim 1, wherein the fine W powder has a particle size in the range of 0.1 μm to 2 μm.