JPH0247055B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an oxide cathode, and more particularly to an oxide cathode with high current density, long life, and excellent electron emission characteristics.

The oxide cathode is usually made of, for example, nickel (Ni
For example, a mixture of barium carbonate (BaCO ₃ ), calcium carbonate (CaCO ₃ ), strontium carbonate (SrCO ₃ ), etc., mixed in an appropriate ratio, is sprayed onto the cathode substrate, such as a cathode substrate (noted as ). After the carbonate of BaCO ₃ and CaCO ₃ is thermally decomposed into oxides of barium oxide (BaO) and calcium oxide (CaO), electron emission is performed. It's set.

In the conventional usage of oxide cathodes, the oxide cathodes manufactured by this method were fully satisfactory, but in recent years, oxide cathodes have also been subjected to severe use that requires high current density and longer lifespan. Increasingly, conventional oxide cathodes are no longer necessarily satisfactory. As a means of obtaining such an oxide cathode with high current density and long life,
Research has been conducted on the use of a Ni-based cathode substrate alloyed with Ba added, for example, in the Institute of Electronics and Communication Engineers Technical Research Report Electronic Devices ED78-33.
It has been announced. In other words, by mixing a reducing agent such as Ba into the cathode substrate, which is mainly made of Ni,
In the intermediate layer that forms on the cathode substrate side of the electron radioactive material
This is based on the theory that leaching Ba reduces the resistance of the intermediate layer, improving electron emission characteristics and extending life. The current characteristics of this Ni-Mg base alloy and the Ni-Ba-Mg base alloy alloyed with Ba are plotted on a logarithmic scale with the vertical axis as Js/T ^5/4 (Js: saturation current density A/cm ² , T: The above-mentioned document shows that when expressed as 1/T on the horizontal axis (absolute temperature), it becomes as shown in FIG. 2, and by alloying Ba, the current characteristics are improved by about 1.4 times. However, it is very difficult to form a solid solution of metallic Ba in Ni, and at most 0.3%
It is only possible to encapsulate Ba in the Ni matrix. Although it has been demonstrated that even at this level of content, significant improvements in properties are achieved, the major drawback is that such materials are extremely hard and difficult to process, resulting in process cracks, being unable to be rolled, and being difficult to process in a vacuum. In addition to poor workability in that the annealing process must be carried out in parallel, it also has the disadvantage that complex shapes cannot be molded using small cathodes. Furthermore, in cathodes made of such materials, solid solution Ba is precipitated on the heater side, which is the back side of the electron emitting surface covered with oxide, and electrons are emitted toward the heater side, causing a gap between the cathode and the heater. The insulation deteriorates and adversely affects characteristics such as noise, so in order to prevent this, it is necessary to take measures such as adding an isolation plate to the back surface of the cathode substrate to prevent electron emission.

The present invention was developed in view of these drawbacks, and it is possible to easily form a small cathode with a complicated shape. Moreover, Ba is contained inside the cathode substrate to improve electron emission characteristics and lifetime, and to improve other characteristics. The purpose is to provide an oxide cathode that does not cause deterioration. Specifically, Ba is embedded in a thickness of 0.1 to 2 μm on the electron emitting surface side of the cathode substrate using an ion implantation method. This will be explained in detail in the drawings below. do.

FIG. 1 is a process diagram showing a process for manufacturing an oxide cathode according to an embodiment of the present invention. . First, as shown in FIG. 1a, after welding the cathode substrate 1 and the cathode sleeve 2, a concave surface is formed on the cathode substrate 1 as shown in FIG. 1b. The purpose of forming this concave surface is to make it easier for the electron beam to converge on a certain point. Depending on the desired shape of the beam, a concave surface may not necessarily be necessary; on the other hand, there may be cases where various concave surfaces are required. There is also. Next, as shown in FIG. 1c, Ba ions are implanted into the electron emitting surface of the cathode substrate 1 using an ion implantation device. This ion implantation device is a well-known device used for implanting impurities into ordinary semiconductors, and as an ion source, organic barium or the like may be used instead of metallic barium. In this case, Ba ion implantation is
10 ¹¹ to 10 ¹⁴ ions/cm ² is sufficient, and the depth of implantation into the Ni plate is at most 0.1 μm to 2 μm from the energy given to the ions, and the implanted Ba ions lose energy. Becomes a Ba atom. Since the thickness of the cathode substrate 1 is usually about 0.1 to 0.3 mm, Ba is implanted only in the very surface area of the cathode substrate 1, but the purpose of this buried Ba is to lower the intermediate resistance layer. Therefore, it is necessary to contribute only to the surface of the cathode substrate 1, and there is no fear of electron emission from the back surface of the cathode substrate 1, which is rather preferable. Next, oxide 3 is applied to the electron emitting surface of the cathode substrate 1 as shown in FIG. For example, it is attached by spraying. Next, as shown in FIG. 1e, by inserting the heater 4 into the cathode sleeve 2, a normal oxide cathode can be formed.

In the above example, Ba is embedded in the electron emitting surface of the cathode after the cathode shape is formed, but in this way, oxide can be attached to the surface of the cathode embedded with Ba before it becomes contaminated. Although it has the advantage of being able to do so, if you consider cleaning it by chemical treatment or heat treatment before oxide spraying, even if you do ion implantation in the large blank state before forming the cathode substrate, Ba will only be implanted on the surface. Therefore, there is no disadvantage that processing is difficult in forming the cathode shape later, and there is an advantage that it is easy to form a plate shape during ion implantation. Further, such ion implantation can be mass-produced and can be done economically at a sufficiently low cost.

As explained above, according to the present invention, since Ba is embedded only in the surface of the cathode substrate, there is no effect on the process of forming the cathode, and there is no electron emission toward the heater side on the back surface of the cathode substrate, and there is no effect between the cathode and the electrode. It is possible to obtain an oxide cathode that significantly improves electron emission characteristics and lifespan without adversely affecting properties such as insulation resistance, and allows the oxide cathode to be used in harsh applications such as high current density operation. There is.

[Brief explanation of the drawing]

Fig. 1 is a cross-sectional view showing the cathode manufacturing process according to an embodiment of the present invention, and Fig. 2 is a Ni-Ba alloy formed by alloying a Ni-Mg base alloy with Ba according to the Technical Research Report ED78-33 of the Institute of Electronics and Communication Engineers. FIG. 3 is a diagram comparing current characteristics with that of an Mg-based alloy. 1... Cathode substrate, 2... Cathode sleeve, 3...
oxide.

Claims (1)

[Scope of Claims] 1. In an oxide cathode that emits electrons by depositing an oxide on one surface of the cathode substrate, which is the electron emitting surface, the one surface of the cathode substrate is coated with an oxide by an ion implantation method.
An oxide cathode characterized by having barium embedded at a depth of 0.1 to 2 μm.