JPS6054734B2 - thermionic emission cathode - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a thermionic-emitting cathode, particularly a thermionic-emitting cathode whose main material is a boride having a calcium hexaboride type structure.

Borides having a calcium hexaboride type structure, such as lanthanum hexaboride LaB6, have a small work function and are generally used.

However, when this thermionic-emitting cathode chip is operated at high temperatures, a chemical reaction occurs with normal supporting metals such as tungsten and tantalum, causing weathering of the thermionic-emitting cathode chip and embrittlement of the supporting metal. It was difficult to operate stably for long periods of time.

To overcome this difficulty, the heating structure does not come into contact with the thermionic-emitting cathode chip, and the support of the thermionic-emitting cathode chip is realized by a structure equipped with a cooler, thereby preventing the chemical reaction. There is a proposal (Japanese Patent Publication No. 45-40576), but such a proposal would have a complicated structure, and in places where a thermionic emission cathode is normally used, such as an electron microscope cathode or an electron tube cathode, the power consumption during heating would be too low. is small, usually less than 10 watts. Therefore, the above structure has the disadvantage that the heating power is too large. The present invention aims to provide an excellent thermionic emission cathode that solves these drawbacks.

That is, the present invention provides a thermionic emission cathode using a boride chip having a calcium hexaboride type structure, in which a vapor deposited layer of a substance that is difficult to react with the cathode is formed on one end of the chip, and a layer of a material that is difficult to react with the cathode is formed between the substance that is difficult to react with the cathode and a supporting metal. This is a thermionic emission cathode formed by laminating a vapor-deposited layer of a mixture and a vapor-deposited supporting metal layer, and further joining the vapor-deposited supporting metal layer and an electrode via a supporting metal wire. The present invention will be explained in more detail below.

As described above, the present invention provides a support metal vapor deposition layer (hereinafter referred to as a support metal) on one end of a boride (hereinafter referred to as boride) chip having a calcium hexaboride type structure, a vapor deposited layer of a substance that does not easily react with the boride (hereinafter referred to as a reaction barrier layer), and a support metal deposited layer (hereinafter referred to as a reaction barrier layer). The feature is that a vapor deposited layer (hereinafter referred to as a mixture layer) made of a mixture of these is provided between the boride chip and the boride chip. Moreover, since there is a mixture layer, the hot cathode does not crack even when subjected to thermal cycles of 100(0) or more, and has excellent heating efficiency.

To explain this according to the drawings, FIG. 1 is a cross-sectional view of a thermionic emission material in which a reaction barrier layer and a supporting metal layer are deposited on one end of a boride chip having a calcium hexaboride type structure.

1 is a boride chip, 2 is a reaction barrier layer, 3 is a mixture layer,
4 is a supporting metal layer.

FIG. 2 is an explanatory diagram showing an example of the use of the product of the present invention, in which the above-mentioned layers are deposited on a thermionic emission cathode chip by sputtering, and then the supporting metal layer and the electrode are connected via a supporting metal wire. The electrodes are attached to a support base.

5 is a ceramic support base, 6 is an electrode, and 7 is a support metal wire. A thermionic emitting cathode chip as shown in FIG. 1 can be used as a thermionic emitting cathode as shown in FIG. Targets for the barrier layer include materials that are difficult to react with borides and supporting metals, have a melting point of 1900C or higher, and have an equilibrium vapor pressure of 10-5T0rr at 1600'C.
Any of the following can be used, but among borides, niobium boride NbB2, zirconium boride ZrB2,
Hafnium boride HfB2, tantalum boride TaB2, carbides include tantalum carbide TaC, zirconium carbide Zrc
lNitrides include zirconium nitride, ZrNl, tantalum nitride, and T.
Particularly preferred is aN. ．． In addition, as supporting metal targets, tantalum, Tal, tungsten, W1, niobium, Nb
Particularly preferred is molybdenum MO. Next, forming a deposited layer by sputtering is generally performed by glow discharge under an inert atmosphere.

The sputtering method uses a straight chi sputtering device and high frequency RF.
There is a method using a sputtering device. ■The sputtering equipment is placed in a vacuum chamber with the target and substrate facing each other.
The cathode is a target, the anode is a substrate holder, and when a DC voltage of several kilovolts is applied between the electrodes, a glow discharge is generated between the electrodes. When the glow discharge occurs, argon plasma is formed in the discharge space, and argon ions in the plasma are accelerated by the cathode potential drop and collide with the target cathode surface, sputtering and vaporizing the target surface.

The sputtered particles evaporated in this way are deposited on the opposing substrates to form a thin film. If a conductive target is not used, an x sputtering device is sufficient, but if a conductive target is not used, an RF sputtering device is used. The RF sputtering equipment becomes sputtering incident ions10
When an inert gas (Ar gas) of about -21'0rr is introduced into the sputtering chamber and a high frequency of several KV (13.56MH2) is applied to the sputtering space that is grounded to the target electrode, glow discharge occurs in the sputtering chamber. It is configured as follows. Electrons and Ar+ ions in the plasma generated by the glow discharge alternately collide with the target due to the applied high frequency voltage. In high-frequency discharge, impact ionization is effectively performed because electrons travel back and forth between electrodes due to the high-frequency electric field.

When starting vapor deposition, first sputtering the surface of the substrate with argon gas cleans the surface of the substrate and improves adhesion.

Furthermore, the strain stress caused by the difference in thermal expansion coefficient between the reaction barrier layer and the supporting metal layer can be alleviated by simultaneously depositing the reaction barrier material and the supporting metal material in the middle by sputtering. Although the examples describe HB6 single crystals, the method of the present invention can be applied to other borides, such as hexaboride single crystal thermionic emitting cathodes such as barium boride, yttrium boride, europium boride, and gadolinium boride. It can also be applied to

It can also be applied to a thermionic emitting cathode made of a polycrystalline sintered body formed by a hot-breathing method or the like. The present invention will be explained below with reference to Examples.

Example 1 TaN and Ta are used as sputter targets, 3×1
Sputter deposition was carried out in an argon atmosphere of 0-3T0rr under conditions of an accelerating voltage of 5KV.

The material to be sputtered was a LaB8 single crystal chip, and the tip of the chinobu was covered with aluminum foil to prevent deposits from adhering to it because it was used as a thermionic emission material. First of all, Ta
N3 powder was sputter deposited to form a film with a thickness of 50μ, and the following 3
In the confusion, Ta<! :． TaN was also sputter deposited to form a 50μ thick film. Next, sputter deposition of only Ta was performed three more times to form a film with a thickness of 50 μm. The obtained hot cathode was joined to the W wire by spot welding, and the temperature at the tip of the single crystal tip was 1600°C and 50CJIi! under a vacuum of 0-5T0rr. Although it was heated for f
B: No change was observed in the single crystal part.

For comparison, a thermal cycle test was conducted on the cathode prepared in Example 1 of Japanese Patent Application No. 52-116864 (Japanese Patent Publication No. 116864/1983) and the cathode prepared in Example 1. The results are shown in the table. The thermal cycle test was repeated by heating at 1600° C. for 1 hour, cooling, and then leaving at room temperature for 3 times. The method for manufacturing the hot cathode of the comparative example is as follows.

A paste consisting of TiB2 powder, cellulose nitrate, and butanol to form a reaction barrier layer is coated on the lower side surface of the chip made of LaB6 to a thickness of about 60 microns, and after it is sufficiently dried, a refractory metal is further applied on top of it. A paste consisting of W powder, cellulose nitrate and butanol forming a layer was applied to a thickness of about 40 microns.

This chip was heated at 1800C in an argon atmosphere for 1
Sintered and baked. On the refractory metal layer of the LaB6 chip having the obtained three-layer structure on its side surface, a W wire was bonded and fixed as a supporting metal by spot welding to form an LlB6 cathode. Example 2 As a sputter target, TaB,
Sputter deposition was performed on a LaB6 single crystal under the same conditions as in Example 1 using and W.

That is, TaB2 was directly sputter deposited on the LaB6 single crystal for 30 minutes (thickness 50μ), and then TaB2 was deposited for 30 minutes.
and W were simultaneously deposited (thickness: 50 μm) at a ratio of 1:1. Next, sputter deposition of only W is performed 3 times.
It was carried out in the interim. The cathode thus obtained was bonded to a Ta wire by spot welding, heated under a vacuum of 3 x 10-5 T0rr for 308 minutes so that the tip temperature of the LaB6 single crystal tip reached 1700°C, and then rapidly cooled to room temperature. Immediately, the heating cycle was repeated 100 times, but there was no change in the LlB6 single crystal portion. The product of the present invention can provide a thermionic emission cathode that operates with low power, has a long life, has excellent electron emission characteristics, and is resistant to cooling and heating. Vapor deposition by sputtering forms a dense thin film with extremely good adhesion to the substrate compared to normal vacuum vapor deposition.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a thermionic emitting cathode chip according to an embodiment of the present invention; FIG. 2 is an explanatory diagram of the product of the present invention.

Claims (1)

[Claims] 1. In a thermionic emission cathode using a boride chip having a calcium hexaboride type structure, at one end of the chip there is a vapor deposited layer of a substance that does not easily react with the boride, and a layer of a substance that does not easily react with the boride and a support metal. A thermionic emission cathode formed by laminating a vapor-deposited layer of a mixture of the above and a vapor-deposited supporting metal layer, and further joining the vapor-deposited supporting metal layer and an electrode via a supporting metal wire. 2 Substances that are difficult to react with are niobium boride, zirconium boride,
The thermoelectron according to claim 1, which is hafnium boride, tantalum boride, a boride selected from tantalum carbide, a carbide selected from zirconium carbide, zirconium nitride, and a nitride selected from tantalum nitride. Emitting cathode. 3. The thermionic emitting cathode according to claim 1, wherein the supporting metal is one or more metals selected from tantalum, tungsten, niobium, and molybdenum.