JPH0528906A - Sc-compound impregnated type cathode - Google Patents

Abstract

PURPOSE:To provide an Sc-compound impregnated type cathode which is high in current density and excellent in the uniformity of the distribution of electron emission. CONSTITUTION:An Sc-compound impregnated type cathode wherein a layer 1 made from a compound of W and Sc is provided on the electron-emission side surface of a cathode base of multicore structure in which spaces among a bundle of high-density metallic thin wires each formed mainly of W are impregnated with an electron-emitting material 3 composed mainly of Ba oxide, the direction of the bundle of metallic thin wires being parallel to that in which electrons are emitted. The use of the Sc-compound impregnated type cathode provides an electron beam with higher current density and less chromatic abberation as compound with those by conventional Sc-compound impregnated type cathodes, while greatly shortening the manufacturing process of an electron tube.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a Sc-based impregnated cathode used in electron tubes such as display tubes, cathode ray tubes, and image pickup tubes, and in particular, Sc-based impregnation with high current density and excellent uniformity of electron emission distribution. Shaped cathode.

[0002]

2. Description of the Related Art Impregnated cathodes are regarded as promising cathodes for large-sized color picture tubes and high-definition cathode ray tubes because they can obtain high current density currents. As shown in FIG. 2, the conventional impregnated cathode is made of tungsten.
The electron-emitting material (barium (B
It is basically impregnated with an oxide containing a), usually a mixture of BaO and Al ₂ O ₃ ) 3, but W and scandium oxide (Sc ₂ O ₃ ) or W on the cathode surface.
It is known that the electron emission characteristics are further improved by coating the thin film 1 made of Sc ₂ W ₃ O ₁₂ and Sc ₂ W ₃ O ₁₂ (for example, Applied Surface Science, Vol. 26).
(1986) pp. 173-195; Applied Surface Science 2
6 (1986) pp.173-195). Further, as a patent application relating to the Sc-based impregnated cathode, there is JP-A-61-91821.

Sc-based impregnated cathodes have a low work function surface, which is
Ba produced by the reaction between a porous body and an electron-emitting substance
It is said that this is due to the function of a monoatomic layer consisting of Sc and O on the surface. If the cathode temperature at which a current density of 10 A / cm ² is obtained is defined as the operating temperature of the cathode, the work function of the basic type impregnated cathode is about 2.0 eV,
For the operating temperature of 1100-1200 ℃, the Sc-type impregnated cathode has a work function of about 1.2 eV and an operating temperature of 850-900 ℃.

[0004]

However, the conventional
In the case of the Sc-based impregnated cathode, as described in the above paper, there is a large non-uniformity in the electron emission distribution from the cathode, it is difficult to form a uniform space charge layer on the cathode surface, and chromatic aberration occurs in the electron beam. There was a problem of causing. This non-uniformity of the electron emission distribution uses a porous body made of W as the underlayer, and most of the pores on the surface of the W porous body are closed pores, and the evaporation of Ba from the inside is not always necessary. This is caused by the non-uniform supply of Ba due to the lack of holes. Furthermore, in the case of the Sc-based impregnated cathode, the lateral diffusion of Ba in the coating layer is slow and the dispersion in the lateral direction is slow.There are a large amount of Ba component (low work function region) and a small amount of Ba component (high work function region). ) And are likely to occur.

An object of the present invention is to solve the problems of the prior art and to provide a Sc-based impregnated cathode having a high current density and an excellent electron emission distribution uniformity.

[0006]

[Means for Solving the Problems] The above object is to make the direction of a wire bundle consisting of high-density metal thin wires containing W as a main component parallel to the direction of electron emission, and the Ba oxide as a main component in the gap between the wire bundles. This can be achieved by using a Sc-based impregnated cathode in which a layer composed of W and a Sc compound is provided on the surface on the electron emission side of a cathode substrate having a multi-core structure impregnated with the electron-emitting substance.

The above Sc compounds include Sc ₂ O ₃ and Sc ₂ W ₃
Any one selected from O ₁₂ and Sc ₆ WO ₁₂ or a mixture thereof is effective. In addition, W and Sc above
The effect is further improved by mixing Ba or a Ba compound in the layer composed of the compound. It should be noted that particularly remarkable effects are observed when the thickness of the layer is in the range of 10 to 1000 nm and the ratio of Sc to W is in the range of 1 to 10%.

The pellet used as the cathode substrate can be prepared by the following procedure. That is, a high-density W thin wire bundle can be prepared by arranging a large number of W thin wires in a cylinder made of a metal or an organic material, and then compressing the wire by a drawing method or a hydrostatic pressing method. At this time, if a bundle of W thin wires is made to contain a substance having a low melting point, it can be made more stable. Also, long W
Sintering of fine wires can be achieved by passing an electric current in the longitudinal direction of the W wire bundle in a vacuum, hydrogen, or an inert gas atmosphere and heating by energization. At this time, the low melting point substance evaporates and disappears. Further, an electron emitting substance containing Ba oxide as a main component is attached to the outer periphery of the bundle of W thin wires prepared above, and the current is heated again to impregnate the voids of the W thin wire bundle with the electron emitting substance, and finally, A cathode pellet can be obtained by slicing the obtained W thin wire bundle into vertical slices in the bundle direction. In the above, the diameter of the W thin wire is 5 to 30 μm, the sintering temperature is 1800 to 2200 ° C, and the impregnation temperature is 1600.
~ 1900 ° C is appropriate.

[0009]

[Function] In the case of the conventional Sc-based impregnated cathode, as described above, Ba is not uniformly supplied and the surface diffusion rate of Ba in the coating layer is slow, so that the Ba component concentration is high. However, in the case of the above-mentioned configuration of the present invention, Ba generated inside the cathode by the reaction between the W thin wire and the Ba oxide linearly passes through the void portion of the W thin wire bundle. Since it is possible to reach the surface, the Ba is uniformly and highly concentrated in the coating layer. When the coating layer contains a Ba source from the beginning, a surface monolayer consisting of Ba, Sc, and O is formed immediately before Ba is supplied from the cathode base, so activation is not possible. Lower temperatures and shorter activation times can be achieved.

The technique of using a tungsten wire bundle impregnated with an electron emitting substance as a cathode or a cathode substrate has already been disclosed in Japanese Patent Publication No.
-17222, JP-A-58-34540, JP-A-61-277126, etc., the manufacturing process is complicated and mass production is not possible, and especially the electron emission characteristics are improved. Since there is no such thing, mass production and practical use have not been realized so far, but by using the cathode of the present invention,
It was possible to fully realize the effect of using the tungsten wire bundle impregnated with the electron-emitting substance and to easily realize the cathode exhibiting the excellent electron-emission distribution.

[0011]

EXAMPLES The Sc-based impregnated cathode of the present invention will be specifically described below with reference to examples.

[0012]

Example 1 FIG. 1 is a cross-sectional view showing a schematic structure of a Sc-based impregnated cathode of the present invention, in which the flux direction of a high-density flux consisting of W thin wires 2 is parallel to the electron emission direction, and the gap between the fluxes is It has a multi-core structure impregnated with the electron emission material 3,
It is shown that the layer 1 composed of W and the Sc compound is provided on the surface on the electron emission side.

Next, a method of producing the cathode of the present invention will be described. 3A and 3B are views showing a method for producing a high-density W thin wire bundle, in which (A) shows a case by the drawing method and (B) shows a case by the hydrostatic pressing method. First of all, regarding (A), a W fine wire 6 having a diameter of 10 μm is inserted into a tantalum (Ta) cylinder 5 having a diameter of 2 mm, a length of 250 mm and a wall thickness of 50 μm up to a density of about 50%, and then a wire drawing die. 7 is used to narrow the diameter to 1.5 mm, and then the compressed W thin wire bundle is taken out from the Ta-made cylinder 5. In case of (B), Ta cylinder 5
After the W thin wire 6 is inserted, vacuum sealing is performed, the W thin wire 6 is placed in a high pressure container 8 and pressurized by a pressurizing pump 9 to form. In these cases, the W thin wire bundle 6 is previously made of copper.
(Cu) or tin (Sn) or other low melting point substance is contained, or after forming a bundle of thin wires using W thin wires coated with Cu or Sn, the wire drawing method or hydrostatic pressing method is used. By compressing with this method, a W wire bundle with a uniform W wire distribution and high density can be stably created.

Then, the W thin wire bundle 6 obtained as described above is linearly attached to the electrode 10 for electric heating, as shown in FIG. 4, and in vacuum, in hydrogen or in an inert gas atmosphere. A W fine wire porous body having a porosity of 17 to 30% was obtained by heating at a temperature of 1800 to 2200 ° C. for 3 to 5 hours with an electric heating power source 11. At this time, as shown by the arrow in the drawing, the thin wire bundle can be prevented from loosening due to thermal expansion by pulling in the longitudinal direction of the wire bundle or by pulling while twisting. In addition, the low melting point substance used when the above-mentioned wire bundle is created evaporates and disappears at this stage. Next, as shown in FIG. 5, 4BaCO ₃ · Al ₂ O ₃ was formed around the W thin wire porous body 6.
・ CaO 2 electron-emitting substance 12 is deposited to a thickness of about 100 μm.
The electron-emitting substance was impregnated into the W wire porous body by heating by heating to ~ 1900 ℃. Finally, 0.5 mm perpendicular to the direction of the W wire bundle
Mechanical cutting was performed at intervals to complete the cathode base.

The Sc-based coating layer 1 was formed by using a high-frequency magnetron sputtering apparatus, targeting a Sc plate having Sc ₂ O ₃ pellets on a W plate, and performing sputtering in an Ar atmosphere of 4 Pa. It was prepared by depositing a thin film having a thickness of 300 to 500 nm on the surface of the base. At this time, the weight ratio of Sc / W in the coating layer was 1 to 10%.

The evacuated to ¹⁰ ~ ⁹ ~10 ~ 10 Torr installed the impregnated cathode that was created in the ultra high vacuum chamber as described above, after aging for 1150 ° C. 4 h, the cathode was 850 ° C. The electron emission distribution was measured while being heated.
The electron emission distribution was measured at a distance of 300 μm in front of the cathode.
By placing an anode plate having 25 μm square small holes, applying +300 V to the cathode, reading the electron flow passing through the small holes with a Faraday cup, and scanning the anode plate parallel to the cathode. It was FIG. 6 shows the electron emission distribution 13 of the Sc-impregnated cathode of the present invention, and the electron emission distribution 13 of the conventional Sc-impregnated cathode.
In the figure shown in comparison with FIG. 14, the value of the current density is a value obtained by dividing the measured current value by the area of the anode small hole. From the results shown in the figure, it can be seen that the cathode of the present invention has a higher absolute value than the cathode of the conventional structure and exhibits an electron emission characteristic which is remarkably excellent in uniformity.

[0017]

[Embodiment 2] FIG. 7 shows a coating layer provided on the cathode base described in Embodiment 1, in which BaO and Sc ₂ O ₃ pellets are arranged on a W plate using a high frequency magnetron sputtering apparatus. As a target, sputtering is performed in an Ar atmosphere of 4 Pa, and the thickness of 300 to 5 is applied on the cathode base.
It is the figure which showed the result of having investigated the effect of Ba doping which acts on the electron emission characteristic of a cathode by forming a coating layer thin film of 00 nm. The weight ratio of Sc / W and Ba / W in the film is 1-10, respectively.
% And 5-20%. The horizontal axis of the figure represents the elapsed heating time, and the vertical axis of the current density represents the value measured at the cathode temperature of 850 ° C. with the cathode heating temperature of 1150 ° C. From the results of this figure, it takes 6 hours for the current density to reach saturation in the case of the Sc-based coating layer 15 without Ba doping, whereas
It is known that the Ba-doped Sc-based coating layer 16 reaches saturation in about 1 hour, which shows that the activation time is significantly shortened.

[0018]

Example 3 In Examples 1 and 2, Sc ₂ O ₃ pellets alone or Sc ₂ O ₃ pellets and Ba were used as sputter targets.
The example of using O pellets was described above.
When Ba alone is used instead of BaO or other Ba compounds such as BaH ₂ or BaN ₂ , the above S
Similar results were obtained when Sc alone or other Sc compounds such as Sc ₂ W ₃ O ₁₂ and Sc ₆ WO ₁₂ were used instead of c ₂ O ₃ . In this case, Sc and
It is desirable that the weight of Ba is in the range of 1 to 10% and 1 to 20%, and the film thickness is in the range of 10 to 1000 nm.

[0019]

[Embodiment 4] When a fine wire of W-Re alloy or W-Mo alloy having a large tensile elongation is used in place of the W fine wire used in the above-mentioned example, the high density fine wire sintered body is more stable. It was confirmed that the same effect can be obtained with the formation.

[0020]

EFFECTS OF THE INVENTION By using a Sc-impregnated cathode as the cathode of the present invention, the problems of the prior art can be solved, and a Sc-based system with high current density and excellent electron emission distribution uniformity can be obtained. An impregnated cathode could be provided. Further, by using the Sc-based impregnated cathode of the present invention in a cathode ray tube or an image pickup tube, an electron beam having a higher current density and less chromatic aberration can be obtained as compared with the case of using a conventional Sc-based impregnated cathode. The process was also shortened significantly.

[Brief description of drawings]

FIG. 1 is a sectional view showing a schematic structure of a Sc-based impregnated cathode of the present invention.

FIG. 2 is a cross-sectional view showing a schematic configuration of a conventional Sc-based impregnated cathode.

3A and 3B are views for explaining a method for producing a high-density W thin wire bundle, in which (A) shows a case of a drawing method and (B) shows a case of a hydrostatic pressing method.

FIG. 4 is a diagram for explaining a sintering method of a W wire bundle.

FIG. 5 is a view for explaining a method of impregnating a W wire bundle with an electron emitting substance.

FIG. 6 Sc-impregnated cathode of the present invention and conventional Sc
The figure which compared and showed the electron emission distribution with the system impregnation type cathode.

FIG. 7 is a diagram showing the effect of shortening the activation time by Ba doping of a Sc-based impregnated cathode surface coating layer.

[Explanation of symbols]

1 ... Layer composed of W and Sc oxide, 2 ... W thin wire, 3 ...
Electron emitting material, 4 ... W porous body, 5 ... Ta cylinder, 6 ... W
Fine wire bundle, 7 ... Drawing die, 8 ... High-pressure container, 9 ... Pressurizing pump, 10 ... Electrodes for electric heating, 11 ... Power source for electric heating,
12 ... Electron emission material, 13 ... Electron emission distribution of Sc-based impregnated cathode of the present invention, 14 ... Electron emission distribution of prior art Sc-based impregnated cathode, 15 ... Present invention having Sc-based coating layer without Ba doping Activation curve of cathode, activation curve of the cathode of the present invention having a Sc-based coating layer doped with 16 ... Ba.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Hajime Tanuma             1-280, Higashi Koikekubo, Kokubunji, Tokyo             Central Research Laboratory, Hitachi, Ltd. (72) Inventor Hayato Amano             1-280, Higashi Koikekubo, Kokubunji, Tokyo             Central Research Laboratory, Hitachi, Ltd. (72) Inventor Tomio Yaguchi             1-280, Higashi Koikekubo, Kokubunji, Tokyo             Central Research Laboratory, Hitachi, Ltd. (72) Inventor Emiko Yamada             1-280, Higashi Koikekubo, Kokubunji, Tokyo             Central Research Laboratory, Hitachi, Ltd.

Claims (7)

[Claims] 1. A wire bundle consisting of high-density metal thin wires containing tungsten (W) as the main component is parallel to the electron emission direction, and electrons containing barium (Ba) oxide as the main component are placed in the gap between the wire bundles. A Sc-based impregnated cathode characterized in that a layer composed of W and a scandium (Sc) compound is provided on the surface of the cathode substrate having a multi-core structure impregnated with an emissive substance on the electron emission side. 2. A large number of W thin wires are arranged in a cylinder made of metal or an organic substance, and compressed by a drawing method or a hydrostatic pressing method to form a bundle of high density W thin wires. A method for producing a high-density W fine wire sintered body characterized by performing high-temperature sintering in a vacuum, hydrogen, or an inert gas atmosphere while pulling in a direction or pulling while twisting. 3. The bundle of W thin wires is a bundle containing a low melting point substance in advance, or is coated with a low melting point substance.
Using a bundle of W wires, compress it by drawing or isostatic pressing to create a bundle of high density W wires, and then sinter it in a vacuum, hydrogen or inert gas atmosphere at high temperature.
The method for producing a high-density tungsten fine wire sintered body according to claim 2, wherein the low melting point substance is evaporated. 4. A high-density W produced by the method according to claim 2.
An electric current is passed in the longitudinal direction of the bundle of fine wire sintered bodies to sinter them by an electric heating method, and then Ba
After depositing an electron-emitting substance whose main component is an oxide,
A method for producing cathode pellets, characterized by heating again by energizing to impregnate the W thin wire voids with an electron-emitting substance, and then slicing the W thin wire bundle perpendicularly to the bundle direction. 5. A Sc-based impregnated cathode, characterized in that a thin film of W and Sc oxide or a thin film of scandium tungstate is provided on the upper surface of the cathode pellet prepared by the method of claim 4. 6. The Sc-based impregnated cathode according to claim 5, wherein Ba or a Ba-containing compound is contained in the thin film of W and Sc oxide or the thin film of scandium tungstate. 7. An electron tube using the impregnated cathode according to any one of claims 1 to 6.