JPH04206416A - 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] [Industrial Application Field] The present invention relates to an impregnated cathode used in electron tubes such as display tubes, cathode ray tubes, image pickup tubes, and traveling wave tubes, and in particular, to obtain high current density in low-temperature operation. This invention relates to an impregnated cathode that can be used as an impregnated cathode.

[Prior Art] An impregnated cathode is a cathode that can obtain a high current density, and is a cathode that is seen as a promising cathode for improving the performance of electron tubes, especially achieving higher definition and higher brightness. .

An impregnated cathode basically has a structure in which the pores of a heat-resistant porous material made of tungsten are impregnated with an oxide containing barium, usually a compound consisting of BaO, CaO1, and Al, ○. It is known that electron emission characteristics can be improved by coating the surface with a thin film made of tungsten and scandium tungstate (SC, W, 01.). The scandium compound-coated impregnated cathode forms a monoatomic layer consisting of Ba, Sc, and O on the surface of the coating film by heating. It is believed that the formation of this monoatomic layer lowers the work function of the cathode surface and improves the electron emission characteristics. If the cathode temperature at which an initial current of IOA/cm' is obtained is defined as the operating temperature of the cathode, then the work function of an impregnated cathode without a coating layer on the cathode surface is approximately 2.
OeV and operating temperature are 1100-1200'C, whereas the scandium compound coated impregnated cathode has a work function of about 1.2eV and operating temperature is 850-900'C.

Ba, which constitutes the surface monoatomic layer, is generated by a thermal reaction between tungsten and barium oxide, which constitute a heat-resistant porous material, as shown in the following formula (1), and thermally diffuses in the coating film to reach the cathode surface. It has been reached.

W+2Ba3AI, 0. -+3Ba+BaW○, +2B
a, Al, 04-=・(1) Ba by the reaction of formula (1)
Since the formation of Ba occurs within the pores of the heat-resistant porous material, the concentration of Ba on the surface of the coating film has a distribution that reflects the shape of the porous material. The Ba'jIt degree of the part in contact with is higher than the Ba concentration of the other part.In the scandium compound-coated impregnated cathode,
Possibly due to changes in the surface work function due to Ba concentration, the intensity of emitted electrons appears to be non-uniform as compared to other impregnated cathodes such as metal-coated cathodes7. Regarding the emission current distribution of the cathode,
E.E., Transactions on Electronics, Vol. 36 (1989), pp. 209-214 (IEEE, Trans, Electr.
on Devices, 36 (1989) pp, 20
9-214), 'discussed. In addition, the Japanese Journal of Applied Physics, Vol. 28 (1,989), pp. 490 to 494 (J
pn.

J, Appl, Phys, 28 (1989)
pp, 490-494).

[Problem to be solved by the invention] As described above, tungsten and scandium tungstate are applied to the surface of the impregnated shade, which has a structure in which the pores of a heat-resistant porous body made of tungsten are impregnated with an oxide containing barium. In the conventional impregnated cathode coated with a scandium compound, non-uniformity is observed in the emission current distribution on the cathode surface. For this reason, the range of kinetic energy of the emitted electrons widens, causing problems in terms of focusing characteristics when mounted on a cathode ray tube, which has been an obstacle to practical application.

An object of the present invention is to solve the problems of the conventional scandium compound-coated impregnated cathode and to provide an impregnated cathode that can be put to practical use.

[Means for Solving the Problems] In order to achieve the above object, a thin metal film with a high melting point is provided on the surface of an impregnated cathode in which the pores of a heat-resistant porous body are impregnated with an oxide containing barium. A thin film containing tungsten and scandium tungstate was provided. In particular, the metal thin film mentioned above is ruthenium.

When the main component is at least one selected from rhodium, rhenium, osmium, and iridium, and
The effect is remarkable when the scandium tungstate is any one of 3C, w, o, and Sc, Wo, and 2, or a mixture of both. Further, remarkable effects are observed when the thickness of the metal thin film is in the range of 10 to 11,000 nm, and when the thickness of the thin film containing tungsten and scandium tungstate is in the range of 10 to 11,000 nm.

[Function] A thin metal film with a high melting point is provided on the surface of an impregnated cathode in which the pores of the heat-resistant porous body of the present invention are impregnated with an oxide containing barium, and a thin film containing tungsten and scandium tungstate is further provided. When the impregnated cathode is heated, tungsten and barium-containing oxide react in the pores of the porous body to generate Ba. Ba generated by this reaction diffuses through the coating film, reaches the cathode surface, and forms a surface monoatomic layer. Since the concentration distribution in the in-plane direction becomes uniform while the Ba metal thin film force is diffused, the Bafi degree on the surface is uniform, and a uniform emission current distribution is achieved.

Ruthenium, rhodium, and rhenium have a high melting point and do not react with Ba.

It is effective to use at least one selected from osmium and iridium as the main component. Furthermore, if the thickness of the metal thin film is less than 10 nm, it is insufficient to uniformize the Ba concentration by diffusion, and if it is more than 11,000 nm, it becomes difficult to supply Ba to the cathode surface by diffusion.
It is effective if it is in the range of 0On.

In addition, if the thickness of the thin film containing tungsten and scandium tungstate is less than 10 nm, the coating will be incomplete, and if it is more than 11,000 nm, it will be difficult to supply Ba to the cathode surface by diffusion. OOOn
It is effective if it is within the range of m.

In addition, as scandium tungstate, Sc ~'303. and Sc, WO1
, or a mixture of both is effective.

Example C] The production of the impregnated shade of the present invention will be described with reference to FIG. A porous body 1 with a porosity of 30% was produced by press-molding tungsten powder with a particle size of 5 μm and then sintering it in a vacuum. This substrate was impregnated with an oxide 2 having a composition of 4Ba◯.CaO.Al, O by heating in a hydrogen atmosphere to produce a base-impregnated cathode 3.

Next, a cup 4 and a sleeve 5 made of molybdenum were produced, and a base-impregnated cathode 3 was inserted into the cup 4 to produce a cathode body.

Next, using a high frequency magnetron sputtering device that can continuously form a multilayer film using a plurality of targets, an osmium plate, Sc, W, 01. A coating film was formed on the surface of the base-impregnated cathode 3 of the cathode body using two types of tungsten plate targets on which pellets were arranged. First, an osmium film 6 is formed to a thickness of 500 nm, and then a thin film 7 containing W, Sc, W, 0,3 is formed to a thickness of 300 nm.
It was formed with a thickness of . W and Sc, W, 01. Thin film 7 containing
Regarding this, the composition of the thin film was adjusted by changing the number of SC, W2O3, and pellets, and the weight ratio of Sc in the thin film was set to 3%. The discharge gas used was argon, and sputtering was performed while cooling the cathode body with water.

Regarding the impregnated type ink of the present invention produced as described above, in a diode arrangement using an anode having a small hole with a diameter of 25 μm provided in an ultra-high vacuum container, while applying a positive high voltage pulse voltage to the anode, The emission current distribution was measured by moving the anode horizontally with respect to the cathode surface and detecting the value of the current flowing through the small holes. The measurement result (a) was measured using W and Sc on the above cathode body 3 for comparison.
The results are shown in FIG. 2 along with measurement results (b) for a conventional scandium compound-coated impregnated cathode provided with a thin film of W, O, etc. The horizontal axis in FIG. 2 shows the position within the cathode surface, and the vertical axis shows the emission current. Heater 8 is used to heat the cathode.
The measurement was carried out by applying current to the cathode while maintaining the cathode surface temperature at 850°C. From the results shown in the figure, it can be seen that while the conventional cathode has a large emission current distribution, the emission current distribution of the cathode of the present invention is almost uniform, and that a uniform emission current distribution has been achieved. Recognize.

In the above embodiment, the case where the metal thin film was an osmium film with a thickness of 500 nm was explained, but instead of osmium, ruthenium, rhodium, rhenium, or
Even when iridium is used, the thickness of the thin film is 10
~11000n is effective in making the emission current distribution uniform, especially when the thickness of the metal thin film is 300~800n.
This effect is remarkable when it is expressed as nm. Further, as scandium tungstate, Sc, W, 01. Also when using Sc6WO12 instead of Sc6WO12 or a mixture of both, the thickness of the metal thin film is 10 to 11000 nm.
Within this range, it is effective in making the emission current distribution uniform.

Further, the cathode of the present invention explained in the above example was mounted on a cathode ray tube. A cathode ray tube using the impregnated cathode of the present invention had superior focusing characteristics compared to a cathode ray tube using a scandium compound-coated impregnated cathode with a conventional structure when the same electron gun was used. .

[Effects of the Invention] According to the present invention, an impregnated cathode is formed by providing a thin film of a high-melting point metal such as osmium on the surface of a base impregnated undercoat, and further providing a thin film containing tungsten and scandium tungstate. By doing so, it becomes possible to make the emission current distribution significantly more uniform compared to conventional impregnated cathodes.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing the schematic structure of the impregnated cathode of the present invention;
FIG. 2 is a diagram showing the emission current distribution in the impregnated cathode of the present invention and the conventional impregnated cathode. 1... Heat-resistant porous body, 2... Oxide containing barium, 3... Substrate impregnated cathode, 4... Cup, 5...
Sleeve, 6...O8 thin film, 7...W and Sc, W,
Thin film containing O, 8... Heater.

Claims (1)

[Claims] 1. In an impregnated cathode having a structure in which a heat-resistant porous body and its pores are impregnated with an oxide containing barium, a high melting point metal thin film is provided on the cathode surface, and tungsten An impregnated cathode characterized by being provided with a thin film containing scandium acid. 2. The metal thin film mentioned above is made of ruthenium, rhodium, rhenium,
The impregnated cathode according to claim 1, characterized in that the main component is at least one element selected from osmium and iridium. 3. The impregnated cathode according to claim 1 or 2, wherein the metal thin film has a thickness in the range of 10 to 1000 nm. 4. The above scandium tungstate is SC_2W_3
The impregnated cathode according to any one of claims 1 to 3, characterized in that it is one of O_1_2 and Sc_6WO_1_2, or a mixture of both. 5. The impregnated cathode according to claim 1, wherein the thin film containing tungsten and scandium tungstate has a thickness in the range of 10 to 1000 nm.