JPH03250529A - Manufacture of impregnated cathode - Google Patents

Abstract

PURPOSE:To have stable electron emission in good performance for a long period of time under a low temperature by forming a thin film consisting of a specified substance over the electron emitting surface under certain conditions, wherein the electron emitting surface is obtained by impregnation of an electron emitting substance. CONSTITUTION:A porous base body consisting of a high melting point metal such as W or Mo is impregnated with an electron emitting substance, and over the electron emitting surface thus obtained, a thin film is formed which consists of admixture of W with at least one of Sc, Y, Al, Ca or oxide of a metal chiefly containing them. The formation of such a film is accomplished by; (i) sputtering in the atmosphere in which W is not oxidized, but only metal such as Sc etc., is oxidated, of (ii) by first sputter forming the film and then heating it in H or in an atmosphere containing H. Accordingly W is in substantially perfect metal state in the film, and the oxide of metal such as Sc is held in substantially perfect oxidated state, and thus a good electron emitting characteristic is obtained.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to the production of an impregnated cathode used as a high current density cathode in electron tubes, etc., and particularly relates to the manufacture of an impregnated cathode that is used as a high current density cathode in electron tubes, etc. The present invention relates to a method for manufacturing an impregnated cathode that exhibits characteristics.

[Prior Art] An impregnated cathode has a thin film made of a high melting point metal and Sc or an oxide of Sc or both on the electron emitting surface of a porous substrate of a high melting point metal (for example, w) impregnated with electron emitting properties. Compared to conventional impregnated cathodes with thin films of O3 or Ir, it is possible to operate at temperatures of 100°C or higher, and it is said to be more resistant to ion bombardment than conventional impregnated cathodes with Sc added. This is a groundbreaking cathode (Japanese Patent Application Laid-Open No. 13526/1986).

The above cathode is supplied with Ba from the underlying substrate during operation, and a low work function monomolecular layer consisting of Ba, Sc, and O is formed on the surface of the substrate, and exhibits good electron emission characteristics.

[Problems to be Solved by the Invention] However, in rare cases, the above cathodes have extremely low electron emission characteristics, or even if the initial electron emission characteristics are good, they deteriorate in a short period of time. There was a problem of poor quality stability due to the occurrence of

An object of the present invention is to provide a method for manufacturing an impregnated cathode that can exhibit good and stable electron emission characteristics at low temperatures over a long period of time by solving the problems of the prior art described above.

[Means for Solving the Problems] The above object is to impregnate a porous substrate made of a high melting point metal such as W or Mo with an electron emitting substance, and inject W, Sc, Y, Al, or Ga onto the sonoelectron emitting surface. In the production of an impregnated cathode formed by forming a thin film consisting of at least one selected from the group consisting of neutral metals or a mixture of these and a metal oxide, (1) (a) W does not oxidize. The above Sc
In an atmosphere that can oxidize only the metals such as Sc, etc., a thin film consisting of the above mixture is formed by sputtering W and the oxide thereof on the electron emitting surface, or (b) By forming a thin film made of W or a mixture of a metal oxide mainly composed of W and an oxide of a metal such as Sc on the electron emitting surface by sputtering or the like, and then heating it in hydrogen or an atmosphere containing hydrogen. This can be achieved by forming a thin film made of the above mixture.

[Operation] The reason why the electron emission characteristics are unstable in the prior art is as follows.
For example, when a mixed film of W, Sc, and 03 is formed by sputtering with argon (Ar) gas,
Sc during film formation, 0. loses oxygen (0) by the bombardment of Ar ions and enters the film in a metallic state, while W partially incorporates this 0 and enters the film as an oxide, resulting in a composition of Ba, Sc, and O. This is due to the fact that the structure and composition of the monomolecular layer deviate from the optimal range that provides a low work function.

As a sputtering gas, Ar and 0.0% were used instead of Ar. If a mixed gas with W is used, the amount of Sc entering the film in a metallic state will be reduced, but at the same time, the amount of W entering the film as an oxide will increase, so the instability of electron emission characteristics will not be improved.

Also, instead of W and Sc, O, W and Sc, W, O,
When a mixed film is formed by sputtering , and with Ar gas, the instability of the electron emission characteristics is somewhat reduced, but this is not sufficient to improve the wood quality.

On the other hand, by adopting the methods (a) and (b) above, it is possible to reduce the amount of the oxidized metal such as Sc to almost completely in the thin film formed on the cathode electron emitting surface. As a result, good electron emission characteristics can be stably maintained over a long period of time.

[Example] Hereinafter, the method for manufacturing an impregnated cathode of the present invention will be specifically explained using Examples.

Example 1 FIG. 1 is a cross-sectional view showing the schematic structure of an impregnated cathode manufactured by the method of the present invention, which is composed of a porous body made of high melting point metal (W) 2 with a porosity of 20 to 25%. A cathode substrate 1 whose pores 3 are impregnated with Ba-Ca aluminate, and a W-Sc, O, thin film 5 formed on the surface of the cathode substrate 1.
, a cup 4 made of Mo to which the cathode base 1 is attached and fixed by laser welding or brazing, and a sleeve 6 made of Ta fixed to the outer periphery of the cup 4 by laser welding.
and a heater 9 inserted into the sleeve 6.

Here, the above W-Sc, 0. The thin film 5 is Ar 6X1
0-”Torr%Ht2X10-’Torr, H,0
W and Sc in a mixed gas atmosphere of 3XIO-'Torr,
O, and were formed by sputtering simultaneously on the surface of the cathode substrate j.

Regarding the impregnated cathode having the above configuration, the saturation current density was measured by applying a high voltage pulse with a pulse width of approximately 5 μs and a frequency of +00H2 to the anode using a diode method. the result,
The impregnated cathode manufactured by the manufacturing method of the present invention has an average of +1 at a cathode temperature of 900° Cb (brightness temperature).
The lowest value of A/cm was 8 A/cut. On the other hand, an impregnated cathode manufactured by the conventional technique, that is, W and Sc in an Ar gas atmosphere or a mixed gas atmosphere of Ar and 0. For the cathode with a thin film formed by sputtering, an average of 9 A/g and a lowest of 3 A/ci were obtained.

Example 2 In manufacturing an impregnated cathode having the same structure as in Example 1, after the cathode substrate 1 impregnated with Ba-Ca aluminate was attached and fixed to the cup 4, approximately 3% of the cathode substrate 1 was applied to the surface of the cathode substrate 1. WO containing Sc, O,.

Sc, 0. The thin film was deposited by sputtering and then heated at 1150° C. for 30 minutes in a hydrogen atmosphere with a dew point of −25° C. to form a W-Sc sail thin film 5.

Further, a sleeve 6 was placed around the outer periphery of the cup 4 and fixed by laser welding to complete the cathode structure.

Using the cathode having the above configuration, a pulse width of 5 μm was applied to the anode using the diode method in the same manner as in Example 1.
A high voltage pulse with an s1 frequency of 100 Hz was applied to measure the saturation current density. As a result, the impregnated cathode manufactured by the method of this example could be used under the same conditions as above.
The average result was +0A/cnt, and the lowest one was 8A/cm.

In the above embodiment, an example was explained in which the cathode has a thin film made of W, Sc, and O. However, instead of W, Mo, Os, Ir, Re, Ru, or an alloy mainly composed of these, W-Mo, is used. , W-Os, W-
Even if 1r, W-Re, W-Ru, etc. are used, Sc,
O, instead of Y2O2, Al, O,, Ga, 0. , etc., exactly the same results were obtained. In addition, as the atmosphere for sputtering, He, Ne, Kr, and X were used instead of Ar in the mixed gas of Ar, Hl, and 11.0%.
Similar results were obtained when using e.

In addition, in reducing the oxide film in the above hydrogen atmosphere, if the dew point of hydrogen (corresponding to the water vapor content) exceeds 0°C, the electron emitting substance in the cathode substrate will change in quality, resulting in deterioration of the electron emission characteristics. Therefore, it is desirable that the dew point of hydrogen is at least O'C or lower. Note that an inert gas such as nitrogen (N) gas or Ar gas may be further added to the same atmosphere.

In addition, if the reduction temperature is lower than 700°C, W will not be reduced sufficiently, and if it exceeds 1600°C, the electron-emitting substance in the cathode substrate will be altered and the electron-emitting properties will deteriorate.
A range of 00 to 1600°C is suitable.

[Effects of the Invention] As described above, by using the method of the present invention as the method of manufacturing an impregnated cathode, the problems of the prior art can be solved and the cathode can be produced in a good and stable manner for a long time at low temperatures. A method for producing an impregnated cathode capable of exhibiting electron emission properties could be provided.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing a schematic structure of an impregnated cathode manufactured by the manufacturing method of the present invention. 1... Cathode base, 2... High melting point metal (W)
, 3... Hole, 4... MO cup,
5... W-Sc, O, thin film, 6... Ta sleeve, 7... W core wire, 8... Alumina coating, 9... Heater

Claims (1)

[Claims] 1. A porous substrate made of a high-melting point metal such as W or Mo is impregnated with an electron-emitting substance, and the electron-emitting surface is coated with W and
In manufacturing an impregnated cathode in which a thin film is formed of at least one selected from Sc, Y, Al, and Ga, or a mixture of these and a metal oxide, W is not oxidized and the above-mentioned An impregnated cathode characterized in that a thin film made of the above mixture is formed by sputtering W and the above-mentioned metal such as Sc or its oxide on an electron emitting surface in an atmosphere that can oxidize only the metal such as Sc. Production method. 2. A porous substrate made of a high melting point metal such as W or Mo is impregnated with an electron-emitting substance, and the electron-emitting surface is coated with W and
In the production of an impregnated cathode, which is formed by forming a thin film made of at least one selected from Sc, Y, Al, and Ga, or a mixture of these and a metal oxide, W is applied to the electron emitting surface of the impregnated cathode. Alternatively, by forming a thin film consisting of a mixture of an oxide of a metal mainly composed of W and an oxide of a metal such as the above-mentioned Sc, and then heating it in hydrogen or an atmosphere containing hydrogen, A method for manufacturing an impregnated cathode, which comprises forming a thin film made of a mixture of Sc and an oxide of a metal such as Sc.