JPS60170136A - Impregnated cathode - 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 [Field of Application of the Invention] The present invention relates to an impregnated layer cathode used in electron tubes such as cathode ray tubes and image pickup tubes.

[Background of the invention]

The impregnated layer cathode is a high current density cathode, and is seen as a promising cathode for improving the performance of electron tubes.

The impregnated layer cathode has a structure in which a porous substrate is impregnated with an electron-emitting substance made of a Ba compound. Although the impregnated layer cathode has high electron emission ability, it has the disadvantage of high operating temperature. Its operating temperature is more than 400° C. higher than that of the currently commonly used coated oxide cathode. When mounting in a tube due to the high operating temperature, the electrode must be changed to a high-melting point metal material, and the cathode must be replaced with Ba.

A large amount of BaO evaporates and adheres to the electrodes, causing grid emissions and adversely affecting the bulb characteristics. Furthermore, it is very difficult to design a heater that can withstand heating the impregnated layer cathode for a long time. In the research and development of impregnated layer cathodes, lowering the operating temperature is the most important issue. As a method of lowering the operating temperature, the surface of the cathode is coated with high work function Os, I.
A common method is to increase the electron emission ability and lower the operating temperature by coating with a metal such as r or Ru. According to this method, the operating temperature of the impregnated layer cathode can be lowered by about 100°C. However, compared to coated oxide cathodes, the temperature is still 300°C or more, which is an obstacle to practical application.

[Purpose of the invention]

An object of the present invention is to provide an impregnated cathode which can be put into practical use by lowering the operating temperature of the impregnated cathode.

[Summary of Shinmei]

In order to achieve the above object, the impregnated cathode according to the present invention has S on the surface of the cathode. This is an impregnated cathode with a very thin (Ba, sC=O) composite compound layer formed at the same time or after coating.

The impregnated cathode has a structure in which a porous heat-resistant substrate is impregnated with an electron-emitting substance. W is generally used as the porous heat-resistant substrate, but Mo, Re, and other high-melting point metals are used in the form of two single alloys or a mixture of two or more types. Electron-emitting materials generally include Ba3 AQ 206 compounds as a base, Cab, and SrO.

Oxides such as MgO, ZrO2, and Y203 are added and used. The electron emitting material is heated and melted and impregnated into the pores of the porous substrate. The impregnation is carried out by heating and melting in a non-oxidizing atmosphere such as an H2 atmosphere or a vacuum, thereby producing an impregnated cathode. The impregnated cathode 1 has a cup-shaped barrier layer 2
．． It is combined with a sleeve 3 and a heating heater 4 and mounted in a tube (FIG. 1). However, in this state, the operating temperature is too high, so it is generally recommended to lower the operating temperature.
That is, in order to improve the electron emission characteristics, the surface of the cathode is coated with a film of Os, Ir, Ru, Re, or an alloy containing these having a high work function.

By coating such metals, the operating temperature can be reduced to approximately 1
00°C and can be used at about 1000°C. Furthermore, a similar effect can be obtained by mixing a metal with a high work function, that is, the above-mentioned metal, into the porous substrate. Currently, practical tests are being actively conducted using the impregnated cathode with a lower operating temperature.

In order to lower the operating temperature of the impregnated cathode, various metals other than those described above were coated and the electron emission characteristics were measured. While conducting detailed experiments on Sc, it was discovered that electron emission characteristics can be greatly improved when the surface of the cathode is coated with Sc very thinly. The impregnated cathode of the present invention will be described in detail below. There are some restrictions on improving electron emission characteristics by coating with Sc. The porous substrate of the impregnated cathode must be made from W powder or an alloy powder or mixed powder containing W as a main component.

Further, the electron-emitting material impregnated into the pores of the porous substrate may be one that has been used in conventional impregnated cathodes.

That is, nao and AQ 203. Cab.

It may be a compound or a mixture with one or more oxides selected from SrO, MgO, ZrO2, and Y203. The most common compositions are 4BaO-AQ203.CaO and 5Ba0.2A12203.3CaO. Impregnation with the electron-emitting substance is carried out by heating and melting in a non-oxidizing atmosphere such as an F7 atmosphere or a vacuum. After impregnation, excess electron-emitting material is removed to produce an impregnated cathode. The impregnated cathode of the present invention is obtained by further forming a (Ba, Sc, O) composite compound layer on the surface of the cathode. (Ba, 5c=0)II
The Jt compound layer is formed by depositing Sc on the surface of the cathode in vacuum, and then heating the impregnated cathode to 860° C. or higher, which is suitable for electron emission (Ba).

Sc, 0) A composite compound layer is formed. Also (Ba, S
c, O) The composite compound layer can also be formed by heating the impregnated cathode to 800° C. or higher and depositing Sc. Since SC has a high vapor pressure, it can be deposited by resistance heating. An electron beam evaporation method or the like may also be used. The deposition rate is preferably slow, preferably 20 persons/n+j, n or less. (Ba
, Sc, O) The thickness of the composite compound layer was about 5 to 100 mm, which had a very large effect. Therefore, the Sc coating thickness should be 100 Å or less. Although the composition ratio of the (Ba, Sc, O) composite compound layer has not been determined, the Auger spectrum shown in Figure 2 was obtained by Auger analysis, and when the composition ratio deviated significantly from this composition ratio, the electron emission characteristics also deteriorated. .

Figure 3 shows the electron emission characteristics 8 to 13 when the Sc deposited film thickness is used as a parameter, and when the Sc deposited film thickness exceeds 100, it tends to be lower than the Os coated impregnated cathode property 7. . The same figure also shows the characteristics of the conventional impregnated cathode 6 and the electron emission characteristics of the ○S-coated impregnated electrode 7. On the surface of the impregnated cathode (
13a, Sc.

O) The impregnated cathode of the present invention with a composite compound layer formed thereon was able to operate at a temperature about 200°C lower than that of an uncoated impregnated cathode and about 100°C lower than that of an Os-coated impregnated cathode. (B a , S c-,, O) The formation mechanism of the composite compound is not clear, but since Sc is very active, Sc evaporated from the evaporation source combines with O in the atmosphere, and Ba and O on the surface of the cathode combine. Combines with BaO and is suitable for electron emission (
Ba, Sc.

○) It is considered that a composite compound layer is formed.

In order for this (Ba, Sc, 0) composite compound layer to exhibit high electron emission characteristics, the substrate on the surface of the underlying cathode must be W or W.
must be the main component. It is thought that high electron emitting ability is exhibited due to the interaction between W and the (Ba, Sc, O) complex compound. The operating temperature can be lowered by approximately 200°C compared to a conventional impregnated cathode, and approximately 100°C lower than a COs-coated impregnated cathode.
This was advantageous in that the evaporation of excess a, BaO, etc. from the cathode was reduced, and the life of the heater was extended.

According to the present invention, as explained above, by forming a (Ba, Sc, O) composite compound layer on the surface of the cathode having W as the base, the operating temperature can be significantly lowered. By lowering the operating temperature by 100 to 200 degrees Celsius, the evaporation rate of Ba and BaO can be lowered by about 1 to 22 orders of magnitude (B
a, the evaporation energy of BaO is ~3.2 eV).

The impregnated cathode according to the invention is a conventional impregnated cathode, Os
It can be said that this is an impregnated cathode that has better properties than a coated impregnated cathode.

[Embodiments of the invention]

Hereinafter, the present invention will be explained by examples.

4BaO・AQ203・Ca was applied to a porous W substrate with a porosity of 23% using W powder with a particle size of 5 μm in a hydrogen atmosphere.
A conventional impregnated cathode was prepared in advance by melting and impregnating an electron emitting material having a composition ratio of O.

This impregnated cathode has an ultimate vacuum level < 5 x 10 = To
rr vacuum vessel. In the vacuum chamber, an anode was also placed at the same time so that the SC evaporation source and electron emission characteristics could be measured. Sc vapor deposition was performed by resistance heating using a W boat. The deposition rate at that time was 5.10゜20.50 people/w
I changed it to in. Further, the electron emission characteristics were measured using a diode type tube consisting of an anode and a cathode, and by applying a pulse voltage and measuring the current emitted at that time. The evaluation was performed by examining the relationship between the saturation current density and cathode temperature at zero electric field from the relationship between voltage and emission current.

Note that when placing the cathode in a vacuum container, as shown in FIG. 1, the barrier layer 2. A combination of a Ta sleeve 3 and a W heater 4 for heating was used.

During Se deposition, the cathode temperature was set to room temperature and 800°C.

Those deposited at room temperature were heat-treated at 800° C. x 5 ml after deposition. Further, the Sc deposited film was determined while considering the electron emission characteristics. In most cases there were up to 300 people. When the deposition rate was high, the composition of the formed (Ba, Sc, O) composite compound layer deviated from the composition that showed high electron emission ability. The deposition rate was preferably 20 people/min or less. No difference in characteristics due to cathode temperature was observed during Sc deposition.

Figure 3 shows the Sc deposition rate of 5 persons/min and the cathode temperature of 800°C.
The effect of the thickness of the Sc deposited film on the electron emission characteristics was observed when the following conditions were met. At 100 Å or less, the properties exceeded those of the Os-coated impregnated type. In terms of operating temperature, it is approximately 200°C lower than the conventional impregnated cathode 6, and approximately 1°C lower than the Os-coated impregnated electrode 7.
Can be lowered by 00℃. Fig. 2 shows the Auger spectrum obtained when the cathode surface was subjected to Auger analysis after being taken out from the vacuum container when the Sc film thickness was 20 mm. Almost the same spectra were shown in other cases, with (Ba, Sc) on the cathode surface.

0) It can be seen that a composite compound layer was formed.

〔Effect of the invention〕

As described above, according to the present invention, an impregnated cathode surface having a cathode surface mainly composed of W or W is coated with Sc, and (B
a, Sc, O) By forming a composite compound layer, the operating temperature can be lowered by about 200°C and O
sThe impregnated cathode has excellent properties such as being able to operate at a temperature approximately 100°C lower than the coated impregnated electrode, and as a result of lowering the operating temperature, the evaporation rate of Ba and BaO from the cathode can be reduced by one to two orders of magnitude. Obtained.

[Brief explanation of the drawing]

Figure 1 is an assembly diagram of the impregnated cathode, barrier layer, sleeve, and W heater. Figure 2 shows the surface of the impregnated cathode of the present invention.
FIG. 3 is a diagram showing an Auger spectrum of a Ba, Sc, O) composite compound layer, and is a diagram comparing a conventional impregnated cathode with an impregnated cathode according to the present invention. ■...Impregnated cathode, 2...Barrier layer, 3...Sleeve, 4...Heater, 6...Characteristics of conventional impregnated cathode, 7...Characteristics of O8 coated impregnated cathode ,8,9,10,
11° as 1st

Claims (1)

[Claims] (2) On the surface of an impregnated cathode consisting of a porous substrate mainly composed of W or W and an electron-emitting substance impregnated into the pores of the porous substrate (Ba, Sc, O). An impregnated layer cathode characterized by having a composite compound layer. 2. The thickness of the above (Ba, Sc, O) composite compound layer is 5
The impregnated layer cathode according to claim 1, characterized in that the number of the impregnated layer cathodes is 100 to 100 people.