JPH07147132A - Manufacture of impregnated cathode - Google Patents

Abstract

PURPOSE:To manufacture an impregnated type cathode with a short activating time and good reproducibility by forming the coating film of the electron emitting surface of a cathode by a spattering method having tangusten or molybdenum metal and scandium metal as spatter target. CONSTITUTION:In a basic impregnated cathode 1, a porous body formed by pressing and sintering powder of W is impregnated with an impregnating agent in which BaO, CaO, and Al2O3 are mixed in 4:1:1 by heating and fusing to 1900 deg.C in hydrogen atmosphere. A coating film containing W and Sc is formed on the upper surface of the cathode 1. As the spatter target, a one having small pieces 3 of Sc metal arranged on an W metal plate 2 is used. The composition in the film is regulated by increasing or decreasing the small pieces 3, and argon is used as the spatter gas. When heated to 1150 deg.C in a vacuum vessel and activated, Sc is taken almost in the metal state, and satisfactory electron emitting characteristic can be provided with good reproducibility.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an impregnated cathode suitable for cathode ray tubes such as cathode ray tubes and image pickup tubes, and more particularly, an impregnated cathode having a surface coating film layer containing scandium for exhibiting good electron emission characteristics. In particular, the present invention relates to a method for producing a coating film.

[0002]

2. Description of the Related Art Impregnated cathodes are cathodes capable of high current density operation, and are essential cathodes for high output electron tubes, especially for cathode ray tubes to achieve high brightness and high definition. The basic structure of the impregnated cathode is a heat-resistant porous substrate made of tungsten, mainly composed of BaO, and Al ₂ O ₃ and Ca.
O is impregnated by heating and melting O in a hydrogen atmosphere or in a vacuum. This melt impregnated material is commonly referred to as the impregnant.

The impregnated cathode is constantly heated to about 1000 ° C. during operation, and the heat resistant porous substrate and the impregnating agent react with each other to release Ba. Ba is supplied to the cathode surface by diffusion and is adsorbed on the cathode surface, that is, the tungsten substrate together with O supplied from the inside of the cathode or the atmosphere inside the electron tube. Thus, when the adsorption layer composed of Ba and O is formed on the metal surface, the work function of the metal surface is substantially lowered, and the electron emission is facilitated. This is the principle of operation of the impregnated cathode, and detailed consideration therefor can be found in, for example, Journal of Physics D: Applied Physics, Vol. 15 (1982), No. 15.
19 to 1529 (J. Phys. D: Appl. Phys., 15 (1
982) 1519-1529).

The impregnated cathode has a small electric resistance because the electron emission portion is basically a metal. Therefore, the impregnated cathode does not cause cathode deterioration due to decomposition of the cathode material itself due to Joule heat generation, unlike an electrically high resistance oxide cathode using an alkaline earth metal carbonate as a raw material. Therefore, the impregnated cathode can operate at a higher current density than the oxide cathode.

However, while the impregnated cathode can operate at high current density, it needs to be operated at a higher temperature than the operating temperature of about 750 ° C. for oxide cathodes. In the case of the impregnated cathode having the above-mentioned basic structure, it is necessary to heat it to about 1100 ° C. to obtain a current density of 10 A / cm ² .

Therefore, the impregnated cathode has been improved for the purpose of reducing the operating temperature. For example, an impregnated cathode in which osmium is coated on the surface of the impregnated cathode having the above-mentioned basic structure has been developed, and its operating temperature has been lowered to about 1000 ° C. In this regard, I, E,
E-Proceeding, Volume 128, Part 1, Number 1 (1981), pages 19-32 (IEE Pro
c., 128, Pt1, No1 (1981) 19-32).

Further, the impregnated cathode coated with a thin film containing scandium together with a refractory metal such as tungsten or molybdenum can operate at the above current density at 900 ° C. Hereinafter, this is referred to as a Sc-coated impregnated cathode, which is described in US Pat. No. 4,626,470.
And Japanese Journal of Applied Physics, Vol. 27, No. 8 (1988), No. 14
Pages 11 to 1414 (Jpn. J. Appl. Phys. 28, No. 8
(1988) 1411-1414).

When the refractory metal of the coating film is selected as tungsten, the coating film of the Sc coating type impregnated cathode is a sputtering target composed of tungsten metal and scandium oxide or scandium tungstate by a sputtering film forming method. Is used to form a film. The coating film formed using the sputter target is an amorphous film containing tungsten, scandium, and oxygen at the time of film formation. When this is heated to about 800 ° C. or higher, tungsten metal and scandium tungstate crystallize. When the cathode is further heated to 1000 ° C. or higher for activation of the cathode, barium is supplied to the coating film from the tungsten porous portion containing barium oxide, which is scandium tungstate or other scandium oxide. Is assumed to be reduced to produce scandium. It is considered that the generated scandium and other barium that has not been used for the reduction reaction form a monomolecular layer on the outermost surface of the cathode together with oxygen, and the work function is lowered to enable good electron emission. Regarding these, Japanese Journal of Applied Physics, Vol. 27, No. 3 (198
9 years) 490 to 494 (Jpn. J. Appl. Phy
s.28, No. 3 (1989) 490-494).

As described above, in order to exhibit good electron emission characteristics of the Sc-coated impregnated cathode, atomic scandium forming a monomolecular layer is necessary, and conventionally, reduction reaction requires a reduction reaction. Was needed. Therefore, activation of the Sc-coated impregnated cathode requires heating at a temperature of 1150 ° C. for 5 to 10 hours. Further, in order to obtain the electron emission characteristics of the cathode stably and with good reproducibility, it is necessary to adjust the amount of oxygen contained in the coating film by forming the coating film. The amount of oxygen contained in the coating film depends on the sputtering gas pressure, gas flow rate, and sputtering power, which are sputtering deposition conditions, because scandium oxide is decomposed during sputtering.
Further, since the scandium oxide is a powder, even if it is press-molded to have a high density, water and atmospheric components are likely to be contained in the pores when exposed to the atmosphere, and these are released during sputtering and the sputtering conditions are likely to change. The above is the same when molybdenum is used as the refractory metal of the coating film.

[0010]

As described above, for the purpose of lowering the operating temperature of the impregnated cathode, the scandium-containing coating film formed by the sputtering film formation method is a sputtering target which is a raw material for the coating film. Conventionally, scandium oxide has been used. Therefore, it was necessary to cause a reduction reaction of scandium oxide for activation, and it took a long time for activation. Further, the amount of oxygen in the coating film is likely to change depending on the sputtering conditions, and it is difficult to reproduce the electron emission characteristics well.

It is an object of the present invention to provide good electron emission characteristics with good reproducibility and shorten the activation time in a Sc-coated impregnated cathode, and to provide a manufacturing method therefor. .

[0012]

The above object can be achieved by the following means. That is, the manufacturing method of the Sc-coated impregnated cathode of the present invention is characterized in that the coating film is formed by the sputter film forming method and scandium metal and tungsten metal or molybdenum metal are used as the sputtering target.

[0013]

As described above, when scandium oxide such as scandium oxide or scandium tungstate is used as the sputtering target, the scandium in the coating film becomes scandium oxide. On the other hand, when scandium metal is used as the sputtering target, scandium contained in the coating film is almost taken in in a metallic state. Therefore, the reduction reaction of scandium oxide is not required at the time of activation, and the amount of oxygen contained in the film does not change under the sputtering conditions, and good electron emission characteristics can be obtained with good reproducibility.

[0014]

EXAMPLE FIG. 1 shows an example of a method for producing a coating film for a Sc-coated impregnated cathode of the present invention. The figure schematically shows the arrangement of the sample (basic-type impregnated cathode) and the sputtering target in the sputtering apparatus, and the configuration of the sputtering target.

The Sc-covered impregnated cathode is formed by forming a covering film containing W and Sc on the upper surface of the basic impregnated cathode 1 having a basic structure. The basic type impregnated cathode 1 is obtained by pressing and sintering tungsten powder and then impregnating it with an oxide containing BaO as a main component, that is, an impregnating agent. In this example, BaO, CaO, and Al ₂ O ₃ were used as the impregnating agent in a ratio of 4:
A mixture of 1: 1 was used. Then, this impregnating agent was heated and melted at 1900 ° C. in a hydrogen atmosphere to impregnate a tungsten sintered body, that is, a porous body. The size and shape of the basic type impregnated cathode used in this example are 1.2 mm in diameter,
It is a cylindrical pellet having a thickness of 0.4 mm.

In the present embodiment, this film was coated by the sputter film forming method, and at this time, as the sputter target, a small piece 3 of scandium metal was placed on the tungsten metal plate 2. The composition of scandium in the coating film can be adjusted by increasing or decreasing the number of scandium metal pieces 3. Argon was used as the sputtering gas. In this example, the scandium of the coating film was adjusted to about 20 at%,
The film thickness was about 100 nm. And in the vacuum container 11
Activation was carried out by heating at 50 ° C., and the emission current and its heating change were measured.

FIG. 2 shows the electron emission characteristics of the impregnated cathode of this embodiment shown in FIG.
And the characteristics of a cathode formed by a sputtering target using scandium oxide 32. The horizontal axis is the heating time at 1150 ° C in the vacuum vessel, and the vertical axis is 850 ° C.
The amount of emission current at. The measurement was performed by disposing the anode at a distance of 7 mm from the cathode and applying a voltage of 4 kV to the anode. From FIG. 2, it took about 8 hours to activate the cathode 8 produced by the conventional film forming method, but in the cathode 7 having the coating film produced by using the sputter target of this example, the cathode 8 was activated in about 2 hours. It can be seen that excellent electron emission characteristics are exhibited. Figure 2
Is a typical example of the cathode manufactured in this example, and the reproducibility of its electron emission characteristics is very good.

FIG. 3 shows another embodiment of the structure of the sputter target in the manufacturing method of the present invention. In this embodiment, the sputter targets are separate tungsten metal target 21 and scandium metal target 3.
It consists of 1. The composition of scandium in the coating film is adjusted by adjusting the power applied to each target.
Alternatively, it can be adjusted by alternately performing sputtering of tungsten and scandium and adjusting the respective sputtering times.

In the above embodiment, the impregnating agent is Ba.
A mixture of O, CaO, and Al ₂ O ₃ in a ratio of 4: 1: 1 was used, but it is clear that the same effect can be obtained with 5: 3: 2 and other compositions. Furthermore, although tungsten has been described as a constituent element of the coating film in addition to scandium, this is a metal whose work function decreases due to monolayer adsorption and which can withstand a high temperature of 1150 ° C. or higher for a long time. However, molybdenum can be used similarly to tungsten. Further, it does not matter if it contains both molybdenum and tungsten, and thus the tungsten target shown in the above embodiment may be molybdenum metal or a mixture or alloy of molybdenum metal and tungsten metal.

[0020]

According to the method of manufacturing the impregnated cathode of the present invention, the activation time of the Sc-coated impregnated cathode is shortened, and the reproducibility of electron emission characteristics is improved without sensitively depending on the sputtering conditions. be able to.

[Brief description of drawings]

FIG. 1 is an explanatory view of a sputter target of a method for manufacturing an impregnated cathode of the present invention.

FIG. 2 is an explanatory diagram showing heating time dependence of electron emission characteristics of a Sc-coated impregnated cathode manufactured according to the present invention.

FIG. 3 is an explanatory view of a sputter target of another embodiment of the present invention.

FIG. 4 is an explanatory view of a sputter target in a manufacturing method of a conventional example.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Basic type impregnation type cathode, 2 ... Tungsten metal or molybdenum metal, or their mixture or alloy, 3 ... Scandium metal, 4 ... Flow of ionized sputtering gas, 5 ... Target knocked out by collision of sputtering gas material.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toshiaki Kusunoki 1-280, Higashi Koikekubo, Kokubunji City, Tokyo Inside the Central Research Laboratory, Hitachi, Ltd. (72) Inventor Tadashi Narusei, 1-280 Higashi Koikekubo, Kokubunji City, Tokyo Hitachi, Ltd. (72) Inventor Emiko Yamada 1-280, Higashi Koigokubo, Kokubunji, Tokyo

Claims (1)

[Claims] 1. A coated impregnated cathode having a coating film containing tungsten and / or molybdenum and scandium on the electron emission surface of a so-called impregnated cathode obtained by impregnating a porous tungsten substrate with an oxide containing barium. A method for producing an impregnated cathode, characterized in that the coating film is formed by a sputter film forming method using a sputter target composed of one or both of tungsten metal and molybdenum metal and scandium metal. .