JPH01213934A - Cathode of electron tube - Google Patents

Abstract

PURPOSE:To suppress exhaustion of Ba in high current density operation by covering a base with a layer containing chiefly oxidated alkali earth metal incl. at least barium and also oxidated rare earth metal in specific wt.%, and thereover forming a BaO layer. CONSTITUTION:A base 1 consisting of Ni as main component is covered with an electron emitting substance layer 2 containing chiefly oxidated alkali earth metal 11 incl. at least barium and also oxidated rare earth metal 12 in 10-50wt.%, and over this mixture layer 2 a BaO layer 13 of 200nm thick or less is formed. This enables sufficient conduction of dissociation of the oxidated rare earth metal 12 in the electron emitting substance layer 2 and solid solution phenomenon of the rare earth metal in the Ni base 1. Thereby the amount of Ba supply to the surface of cathode is increased, Ba evaporation suppressed, and high current density operation over 4A/cm<2> made practicable.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to an electron tube cathode used in a di-braun tube for TV, and particularly relates to an improvement of an electron emissive material layer.

[Conventional technology]

Figure 2 shows the cathode used in conventional di-cathode ray tubes for TVs. A bottomed cylindrical base consisting of (2)
is deposited on the top surface of the bottom of this substrate and contains at least barium (&), and also contains strontium (Sr) or/
and an electron emitting material layer consisting of an alkaline earth metal oxide containing calcium (Ca) and a rare earth metal oxide of 0.1 to 20% by weight; (3) is a heater disposed within the base (1); In (3), the above electron emitting substance 1 (2) is heated.
This is to cause thermionic electrons to be emitted from the

In the electron tube cathode configured in this way, the base (1)
The electron emitting material HE (2) is deposited on the substrate as follows. First, alkaline earth metals (Ba, S
A suspension consisting of a carbonate of R, Ca) and, for example, 4% by weight of scandium oxide (5ctOs) is applied to the substrate (1) and heated by a heater (3) during the evacuation step.

At this time, the alkaline earth metal carbonate turns into an alkaline earth metal oxide. Thereafter, by reducing a part of the alkaline earth metal oxide and activating it to have semiconducting properties, an electron emitting material layer ( 2) is coated.

In this activation step, some of the alkaline earth metal oxides react as follows.

That is, reducing elements such as silicon and magnesium contained in the substrate (1) move to the interface between the alkaline earth metal oxide and the substrate (1) by diffusion and react with the alkaline earth metal oxide. For example, if barium oxide (Bad) is used as the alkaline earth oxide, it reacts as shown in the following formulas (1) and (2).

2BaO+1/2Si =Ba+1/2Ba, SiO,
...-”-(1) BaO layer Mg = Ba + MgO・
・−=−・・ (2) As a result of this reaction, the generated Ba diffuses to the surface of the electron emitting material layer and forms an impurity level in BaO, or is adsorbed to the surface of the alkaline earth metal oxide. This lowers the work function and enables current density operation of 0.5 to 2.01'y'crd at an operating temperature of 700 to 800° C. at the cathode temperature. Here, in the cathode for an electron tube formed in this way, due to the effects of Sc, O, in the electron emitting material layer, the letters Ba, Si shown in the above formula (1) and (2)
The formation of intermediate layers such as n, MgO, etc. is suppressed, and the reaction between the reducing agent and BaO is performed stably for a long period of time during the life, and the above-mentioned high jji flow density operation can be realized.

[Problem to be solved by the invention]

In the electron tube cathode constructed in this way, the current density is 2. When OA//c11t is exceeded, the electron emitting material layer is severely consumed by Joule heat, and sufficient life characteristics cannot be obtained only by the effect of Sc, 03 described above.

This invention was made to solve the above-mentioned problems, and aims to reduce the consumption of Ba to 1% in a TTF tube cathode in which Ba consumption is suppressed in high current density operation of 4A/cIIt or higher. .

[Means to solve the problem]

The cathode for an electron tube according to the present invention has a layer mainly composed of an alkaline earth metal oxide containing at least barium and containing a rare earth metal oxide of 10 to 10% by weight, on a substrate mainly composed of nickel. Furthermore, a BaO layer of 2001 m or less is formed on top of the BaO layer.

[Effect]

In this invention, the dissociation of the rare earth metal oxide in the electron emitting material layer and the solid solution phenomenon of the rare earth metal in the nickel base material are sufficiently carried out, so that the formation of the above-mentioned intermediate layer is reduced.
It becomes possible to increase the amount of Ba supplied to the cathode surface. In addition, the rare earth metal oxide in the electron emitting material layer has a large Ba evaporation suppressing effect, with 4A/cI! ! High current density operation as described above becomes possible. Furthermore, by providing a BaO layer of 200 nm or less on the upper layer of the cathode, Sc
, O, and the rare earth metal oxide composition that requires long-time aging to form Ba or BaO on the layer does not require long-time aging.

[Embodiments of the invention]

An embodiment of the present invention will be described below based on FIG. 1. In the figure ζ, (2) is deposited on the upper surface of the bottom of the substrate (1), contains at least barium, and also contains strontium or/and calcium as a main component, and contains 10~ This is a mixed oxide layer containing a rare earth metal oxide (2) such as scandium oxide or yttrium oxide in a weight percent of the total weight, and a layer (6) made of BaO is formed on top of the mixed oxide layer.

Next, we will explain how to deposit the electron emissive material layer (2) on the substrate (1) in the cathode for an electron tube constructed in this way. A desired weight % of scandium oxide powder, for example 30 weight % (weight % assuming all of the above ternary carbonates become oxides) is added and mixed to prepare a suspension. This suspension is applied by spraying onto a substrate (1) mainly composed of nickel to a thickness of approximately PDZ chrome, and then
The cathode was installed in a sputtering device and a B layer with a thickness of 50 nm was installed.
An aO film is formed, and the electron emitting material layer (2) is attached to the substrate (1) through a decomposition process from carbonate to oxide and an activation process to reduce a portion of the oxide, as in the conventional case. It is something to be covered with.

Figure 3 shows the emission current when a diode vacuum tube was made using the electron tube cathode of the example and a life test was performed by operating it at a current density of 4.3 A/d, in comparison with the conventional example described above. This shows the results of examining changes in . This example shows excellent one-mission characteristics.

Such effects of the present invention can be obtained from Sc, Ba on O5 particles, or 5c20. Ba or BaO from a complex compound of and BaO
This is thought to be due to the fact that the evaporation of Ba on the alkaline earth metal oxide particles or the evaporation of the alkaline earth metal oxide itself is sufficiently small.

Moreover, since a BaO film is formed on the top layer, a Ba-BaO layer with a low work function is formed from the beginning of the life, so the S
Although it has a large amount of c, O, and fi, it does not require a long aging time. The thickness of the BaO layer is preferably 200 nm or less,
Good initial characteristics and life characteristics were obtained with a thickness of Machiniba to mnm.

In addition, the weight ratio of rare earth metal oxide in the electron emitting material is 1
If it is less than 0%, the effect of suppressing the formation of the intermediate layer is insufficient,
If it exceeds W%, long-term aging is required even if a BaO layer is present, which poses significant practical limitations.

In the above example, 5CtO8 was used as the rare earth metal oxide, but similar effects could be obtained with other rare earth metal oxides.
O3* Y2O3p Ce, 0. d) The effect was remarkable for j L'.

〔Effect of the invention〕

As described above, the present invention includes an electron emitting material layer mainly composed of an alkaline earth metal oxide containing at least barium, which is deposited on a substrate and contains lO to ω% by weight of a rare earth metal oxide. At the same time, 20
Since a BaO layer with a thickness of 0 nm or less was formed, 4 A/
This has the effect of providing a highly reliable cathode for an electron tube that is inexpensive, has few restrictions on manufacturing, and has a long life when operating at a high current density higher than crIt.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing an embodiment of the present invention, FIG. 2 is an emission characteristic diagram of a cathode for an electron tube according to the embodiment, and FIG. 3 is a sectional view of a conventional cathode for an electron tube. In the figure, (1) is a base body, and (2) is an electron emitting material layer. In each figure, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] A layer mainly composed of an alkaline earth metal oxide containing at least barium and containing 10% to 50% by weight of a rare earth metal oxide is deposited on a substrate mainly composed of nickel. BaO with a thickness of 200 nm or less
A cathode for an electron tube characterized by forming a layer.