JPH0426032A - Impregnation type 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 [Fields of Application in "Industry" 2] The present invention relates to an impregnated cathode used in electron tubes such as cathode ray tubes, image pickup tubes, and moving tubes. This article relates to an impregnated cathode that can provide high density and long life.

[Prior art] Impregnated cathodes are made of tungsten (W) or molybdenum (
The basic structure is that the pores of a heat-resistant porous substrate made of materials such as Hechi) are impregnated with an electron-emitting substance whose main component is barium (Ba), but this basic + M structure does not work. The temperature is too high to be practical.

As a method of lowering the operating temperature, for example,
2] As described in Publication No. 343, the cathode surface is generally coated with an osmium (Os)-ruthenium (Ru) base metal, but even with this method, the operating temperature is approximately 1000°C. This was a major obstacle to promoting practical application.

As a method of further lowering the operating temperature, JP-A No. 6]-1
As described in Japanese Patent No. 3526, there is a method of coating the surface of the cathode with a mixed thin film of W and scandium (Sc) oxide instead of the 0s-Ru alloy. According to this method, high electron emission performance (emission characteristics) can be obtained, and the operating temperature can be lowered by 10 (1") by 150° C. compared to the first method.

[Problems to be Solved by the Invention] However, although the impregnated cathode coated with a mixed thin film of the above-mentioned oxide and Sc oxide has a lower operating temperature, its emission life is slightly shorter than that of a conventional cathode, and it cannot be put into practical use. There was a problem at the top.

An object of the present invention is to provide an impregnated cathode that can operate at low temperatures, has a high current density, and has a long life by solving the problems of the prior art described above.

[Means for Solving the Problems] The above object is to provide a heat-resistant porous substrate, an electron-emitting substance mainly composed of Ba impregnated into the pores of the substrate, and at least W provided on the surface of the substrate. In an impregnated cathode comprising a mixed thin film of an oxide containing W and Sc, this can be achieved by forming a mixed thin film in which the above mixed thin film of W and an oxide containing W and Sc is provided in an island shape.

In particular, the mixed thin film has a remarkable effect when it occupies 50 to 90% of the cathode surface area.

[Operation] FIG. 2 shows a schematic cross-sectional view of a conventional impregnated cathode provided with a mixed thin film 8 made of W and an oxide containing W and Sc. Here, by applying electricity to the heater 6 to heat the cathode, the heat-resistant porous substrate] and the electron-emitting substance 2 react with each other in the base-impregnated cathode pellet 3 to generate free Ba. The generated free Ba diffuses into the thin film 8, and a part of it reacts with the metal 1 and the oxide containing Sc to generate free Sc.

When the oxide containing W and Sc is composed of Sc, W, O,, Sc, IJ, o, I reacts with Ba, and Sc is generated according to the formula below, and diffuses within the thin film 8. reaches the cathode surface.

Sc, W, 0. , +3Ba :> 3BaWO4+2
Sc-(1) Also, B that did not participate in the above reaction
a diffuses through the thin film 8 and reaches the cathode surface. Ba and Sc that have reached the cathode surface in this way combine with oxygen generated by thermal decomposition of the electron-emitting substance 2 and oxygen in the atmosphere.
A (Ba, Sc, 0)''f5A platform layer with a thickness of a monomolecular layer to several molecular layers is formed on the surface of the cathode.The formation of this composite layer reduces the electron emission work function of the cathode to 1.2e.
V (the work function in the absence of the composite layer is approximately Q, Qe
V), the electron emission ability is greatly improved, which makes it possible to significantly lower the operating temperature of the cathode.

Here, in order to maintain the above electron emission ability over a long period of time, it is necessary to continue forming a (Ba, Sc, 0) composite layer with a low work function, but the amount of Ba supplied from the base cathode pellet 3 must be decreases in proportion to the square root of the elapsed operation (heating) time, and Ba and S diffused on the cathode surface decrease.
The residence time of c on the cathode surface is shorter for ii′lj.

Therefore, at the initial stage of operation, the amount of Ba supplied to the thin film 8 is large;
While forming Sc, enough a is generated to reach the cathode surface, but as the operating time passes, the amount of Ba diffused to the cathode surface decreases, causing the compositional balance of the (Ba, Sc, O) composite layer to collapse. , the electron emission ability decreases. (
The surface of the cathode with reduced electron emission ability has an extremely low Ba concentration).

Therefore, B r+ from the base covert pellet 3 to the cathode surface
The electron emitting ability of the cathode can be maintained over a long period of time by having a configuration that allows easy supply of Ba. It is sufficient to have a configuration that can reach W, W and S, as shown in Figure 1.
The mixed thin film 7 is formed of an island-shaped mixed thin film consisting of an oxide containing c, and Ba is supplied not only by diffusion through the thin film 8, but also by surface diffusion. Even if the total Ba supply amount decreases, the necessary and sufficient amount of a can be supplied to the cathode surface, thereby making it possible to form and maintain a (Ba, Sc, O) composite layer for a long time. .

It has been experimentally found that an effect is exhibited when the ratio of the island-shaped mixed thin film 7 to the surface area of the cathode is in the range of 50 to 90%.

[Example] Hereinafter, the impregnated cathode having the structure of the present invention will be specifically explained using Examples.

The fabrication of the impregnated cathode of the present invention will be explained with reference to FIG. 1, which is a schematic cross-sectional view showing the general structure of the impregnated cathode of the present invention. That is, first, W powder with an average particle size of 5- is press-molded, pre-sintered in a hydrogen atmosphere, and main sintered in a vacuum to produce a heat-resistant porous substrate 1 with a porosity of 28%. Furthermore, 4BaO-Ca
A substrate-impregnated cathode pellet 3 was prepared by melting and impregnating an electron-emitting material 2 having a composition of O-AI, O, in a non-oxidizing atmosphere (in hydrogen or vacuum). Then,
The pellet 3 was inserted into a cup-shaped barrier layer 4 made of MO, and a sleeve 5 made of MO containing a heater 6 was further inserted and fixed to form a cathode body.

Next, using a device capable of simultaneous sputtering of multiple materials, two types of W, SC, W, and Oll were sputtered as sputter targets, and the openings were several tens of square meters and the pore size was 30.
Using a mesh-like mask of 50.70.90%, the area occupancy rate is 30.50.70.90 respectively on the pellet 3 surface.
% island-like mixed thin film was prepared. Note that a sample without using a mask (corresponding to an area occupation rate of 100%) was also produced at the same time. Here, sputtering is performed by first evacuating the inside of the apparatus to approximately 3XIO-'Pa, and then flowing argon gas (
30sec, atmosphere at this time 4 X 10-' Pa
) After that, with the pressure adjusted to 1 OPa by the main valve of the device exhaust system, the cathode body was cooled with water and heated with W.
is DC (direct current) sputtering, Sc, W, 0. , is R
The thickness of the mixed thin film 7 is 50 mm by F (high frequency) sputtering.
~looonm and Sc, W, 0 in the thin film
．． The sputtering power and time were adjusted so that the amount of sputtering was 18 to 33% by weight. In addition, Sc, W, 0.
When the weight ratio of Sc and W was determined by solution emission spectroscopy (ICPS) for the mixed thin film 7 containing 18 to 33% by weight of Sc/W, Sc/W was in the range of 0.02 to 0.04.

Below, the thickness of the mixed thin film is 200 nm, and the composition is W-25%.
The characteristics obtained for the cathode in the case of Sc, W, and Ol will be explained.

Figure 3 shows that the cathode sample prepared as described above was exposed to the anode after activation at 1150°C for 4 hours in a diode arrangement consisting of an anode and a cathode placed in a high vacuum chamber of the order of 10-"Pa. 9 obtained by applying a positive pulse voltage
FIG. 3 is a diagram showing the relationship between the saturation current density at 00'C and the area ratio occupied by the island-shaped mixed thin film. This result shows that the electron emission ability does not decrease when the occupied area ratio is 70% or more, and only decreases by about 10% even when the area ratio is 50%, but decreases to about half when the area ratio is 30%. Therefore, if the occupied area ratio of the mixed thin film is 50% or more, operation at 900°C is possible, and it can be called a low-temperature operation type cathode.

In addition, Figure 4 is a diagram showing the change in electron emission (emission current) over time during operation, where the vertical axis represents the emission current value when the initial emission current is set as 100, and the horizontal axis represents the single time period of 1000 hours. This is the elapsed operation time, and the occupied area ratio of the mixed thin film is shown as a parameter. This result shows that by providing the mixed thin film in the form of islands, the emission current can be maintained over a long period of time, resulting in a significantly longer life.

Furthermore, Figure 5 shows the results of Auger analysis of the cathode surface at the initial stage of operation and after 10,000 hours of operation for a cathode with a mixed thin film occupation area ratio of 70% and a cathode with 100% (conventional cathode). FIG.

From this result, a low work function (Ba, Sc, 0
) Compared with the composite layer surface (a), the conventional structure 1 (triode surface (c) after 10,000 hours of operation clearly lacks Ba (l(a, Sc, 0)) and the composition of the composite layer It can be seen that the 1!2 pole surface of the mixed thin film of the present invention with an occupied area ratio of 70% remains in almost the same state as the initial state (a) even after 10,000 hours of operation (b), indicating that the balance has been disrupted. Moreover, from this, it can be seen that the decrease in the emission current as the operating time of the conventionally configured cathode elapses is due to insufficient supply of Ba from the underlying cathode pellet to the cathode surface.

[Effects of the Invention] As described above, by making the impregnated cathode into an impregnated cathode having the structure of the present invention, W and W and Sc are added to the surface of the cathode.
By creating an impregnated cathode in which a mixed thin film made of an oxide containing
) It has been possible to provide a long-life impregnated cathode that can form and maintain a composite layer for a long time, and can maintain an emission current for a much longer time than conventional cathodes. Furthermore, by easily forming a (Ba, Sc, 0) composite layer with a low work function, the operating temperature can be lowered by 100 to 150°C compared to a conventional impregnated cathode, and therefore Ba and BaO from the surface of the shade tree can be reduced. The evaporation rate of 1~
Since the size can be reduced by 1.5 orders of magnitude, it has been possible to obtain an impregnated shade that can significantly reduce the occurrence of deterioration of tube characteristics due to grid emission and the like. moreover,
By lowering the operating temperature, the reliability of the cathode heater has been improved and power consumption has also been reduced.

[Brief explanation of drawings]

Fig. 1 is a schematic cross-sectional view showing the general structure of the impregnated cathode of the present invention, Fig. 2 is a schematic cross-sectional view showing the general structure of the impregnated cathode of the prior art, and Fig. 3 is the mixed thin film occupied area ratio and temperature at 900°C. Figure 4 is a diagram showing the relationship with the saturation current density, Figure 4 is a diagram showing a comparison of the change in emission current over time during operation between an impregnated cathode with the structure of the present invention and an impregnated cathode with a conventional configuration, and Figure 5 is a diagram showing the change in emission current over time during operation. FIG. 3 is a diagram showing a comparison of the cathode surface values in the initial stage of operation and after 10,000 hours of operation for an impregnated cathode having an inventive structure and an impregnating cathode having a conventional structure. l...Heat-resistant porous substrate, 2...Electron emitter τ'1,
:3... base impregnated cathode pessitite, 4. barrier layer, 5.
...Sleeve, 6.Heater, 7.Island-like mixed thin film, 8..;Kongo thin film 9 agent Seribuji
Ogawa) play; noj, --(<
10) 11hi 174'F (4θ Kuta! Synopsis 1 enemy 1
(kh) Diagram 1000-Jie Sou Ou: Zu: Kool N-(e)

Claims (1)

[Claims] 1. A heat-resistant porous substrate, an electron-emitting substance mainly composed of Ba impregnated into the pores of the substrate, and at least W, W and Sc provided on the surface of the substrate. In an impregnated cathode consisting of a mixed thin film of oxides, the above W and W and Sc
An impregnated cathode characterized in that the mixed thin film of oxides containing the above is provided in an island shape. 2. The impregnated cathode according to claim 1, wherein the mixed thin film of W and oxide containing W and Sc occupies 50 to 90% of the surface area of the cathode.