JPH0696662A - Electronic tube cathode - Google Patents

Abstract

PURPOSE:To stabilize electron emission characteristics by forming a thin film comprising W and Sc (oxide), and a metal (compound) selected from Pt, Ir and Rh on the electron emission surface of an electronic tube cathode. CONSTITUTION:The cavity 3 of a porous cathode base body 1 comprising a high-fusion point metal 2 (e.g. tungsten) is impregnated with an electron emission material (e.g. barium-calcium-aluminate). Then, the base body 1 is fitted in a molybdenum cup 4 and a tantalum sleeve 6 is provided around the external surface of the cup 4, thereby fabricating an electron tube cathode. In this case, a thin film 5 comprising tungsten, scandium (oxide), and at least one metal selected from platinum, iridium and rhodium or an allay thereof is formed on the electron emission surface of the cathode. According to this construction, such a grid electrode for the electron gun of a cathode-ray tube as capable of stably providing electron emission characteristics for a long time at low temperature operation can be provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cathode constituting an electron gun used in a cathode ray tube, and more particularly to an impregnated cathode for an electron tube suitable for a cathode ray tube used for a monitor of a color picture tube or a terminal device.

[0002]

2. Description of the Related Art An electron tube such as a color cathode ray tube is still in the mainstream as a monitor of a television broadcast reception or an information processing device because of its fine image reproducibility. Figure 2
2 is a cross-sectional view showing a color cathode ray tube as an example to explain the structure of this type of electron tube, in which 20 is a face panel, 21 is a funnel, 22 is a neck connected to the funnel, 23 is an anode terminal, and 24 are many. , 25 is an electron gun for emitting three electron beams, 26 is a deflection yoke, 27 is an electron beam, 28 is a phosphor layer arranged in a mosaic pattern, and 29 is an internal magnetic shield.

In FIG. 1, the face panel 20, the funnel 21 and the neck 22 constitute a vacuum container, and the electron gun 25 is housed in the neck 22.
A shadow mask 24 having a large number of apertures facing the phosphor layer 28 at a predetermined interval is suspended on the inner skirt portion. The funnel 21 has an inner wall on which a conductive film is evenly applied to a part of the neck 22, and the conductive film is applied to the inside of the funnel 21 and the outer surface of the funnel, and Funnel 21
And a positive electrode terminal 23 provided so as to penetrate through a part thereof, and a deflection yoke 26 is mounted on the outer wall from the funnel 21 to the neck 22.

On the inner surface of the face panel 20, red,
Green and blue phosphors are applied in the form of stripes or dot mosaics, and the three electron beams 27 emitted from the electron gun 25 are selected by the shadow mask 24 to impact each phosphor, This is made to emit light.
FIG. 3 is a schematic diagram for explaining an example of the electrode configuration of the electron gun for a cathode ray tube. The cathodes K are three parallel electron beam generators in an in-line arrangement, the first grid electrode 30, and the second grid electrode 31, The third grid electrode 32, the fourth grid electrode 33, the fifth grid electrode 34, the sixth grid electrode 35, and the cup electrode 36 serving as an anode.

In the figure, the cathode K and the respective grid electrodes 30, 31, 32, ... Anode 36 are embedded in a pair of multi-form glass 37 which are insulators and fixed at a predetermined interval in the tube axis direction. . In this type of electron gun, a so-called impregnated cathode is often used because of its stable electron emission capability and long life.

A conventional impregnated cathode is disclosed in, for example, Japanese Patent Laid-Open No.
As disclosed in JP-A-1-13526, a heat-resistant porous substrate impregnated with an electron emitting material and tungsten (W) and scandium (Sc) or an oxide of scandium on the electron emitting surface of the porous substrate. Alternatively, it has a structure in which a thin film composed of the both is formed. This type of impregnated cathode has an operating temperature of 100 ° C. or more lower than that of the impregnated cathode having a thin film of osmium (Os) or iridium (Ir) that has been used up to now, and the scandium up to that time. It has an epoch-making property that it can withstand ion bombardment as compared with the impregnated cathode of addition.

This type of impregnated cathode is supplied with barium (Ba) from an underlying substrate during its operation, whereby a monolayer of low work function consisting of barium, scandium and oxygen (O) is formed on the electron emission surface. Are formed and good electron emission characteristics are obtained.

[0008]

However, in the impregnated cathode according to the above-mentioned prior art, although it is rare, the electron emission characteristic is extremely low, or even if the initial electron emission characteristic is good, it takes a short time. There were some drawbacks, such as deterioration of the product. It is an object of the present invention to provide a cathode for an electron tube which can solve the above-mentioned drawbacks of the prior art and can stably obtain a good electron emission characteristic at a low temperature operation for a long time.

[0009]

In order to achieve the above object, the present invention provides a cathode for an electron tube comprising a porous cathode substrate made of a refractory metal impregnated with an electron emitting substance, and the electron emitting surface of the cathode. And a thin film of tungsten, either or both of scandium and scandium oxide, and at least one metal selected from platinum, iridium, and rhodium, or a compound thereof.

[0010]

The reason why the electron emission characteristic of the impregnated cathode according to the prior art is extremely deteriorated is that the amount of oxygen taken into the film during the formation of the thin film is larger or smaller than the optimum range. This is because it is difficult to form a low-work function monolayer composed of barium, scandium, and oxygen.

On the other hand, with the above-mentioned structure of the present invention, platinum (Pt), iridium (Ir),
Addition of at least one metal selected from rhodium (Rh) or a compound thereof promotes formation of the above-mentioned low work function monomolecular layer. This makes it possible to avoid the deterioration of the electron emission characteristics described above.

[0012]

Embodiments of the present invention will now be described in detail with reference to the drawings. FIG. 1 is a side view of a broken main part for explaining the structure of one embodiment of a cathode for an electron tube according to the present invention, in which 1 is a cathode substrate, 2 is a refractory metal, 3 is a hole,
4 molybdenum cup, the W-Sc ₂ -O ₃ -Pt film 5, 6 tantalum sleeve, 7 tungsten wire, 8
Is an alumina layer, and 9 is a heater.

In the figure, the cathode substrate 1 has a porosity of 2
It is composed of tungsten as the refractory metal 2 of 5%, and in the holes 3 thereof, barium, which is an electron emitting substance, is formed.
Calcium - aluminate (BaO-CaO-Al ₂ O
₃ ) is impregnated. This cathode substrate 1 is mounted in a molybdenum (Mo) cup 4 and fixed by laser welding or brazing.

On the surface of the cathode substrate 1, a W—Sc ₂ O ₃ —Pt thin film 5 containing about 3% scandium oxide (Sc ₂ O ₃ ) and about 0.2% platinum (Pt) is sputtered. Formed by. Further, a sleeve 6 made of tantalum (Ta) is arranged on the outer periphery of the molybdenum cup 4 and fixed by laser welding to complete the cathode assembly.

A heater 9 composed of a tungsten core wire 7 coated with an alumina layer 8 is inserted into the sleeve 6 of the cathode assembly thus obtained, and thermionic emission is obtained from the cathode surface by heating. Using the cathode configured as described above, the anode 35
A high voltage pulse having a pulse width of about 5 μm and a frequency of 100 Hz was applied to and the saturation current density was measured.

As a result, the electron emission characteristics of the cathode of this example were equivalent to those of the conventional cathode in which platinum was not added to the thin film formed on the cathode surface.
In the case of the cathode having the conventional structure, it was observed that the electron emission characteristic was extremely low at a rate of 1 out of 7 lots or deteriorated in a short time. On the other hand, in the case of the cathode having the structure of the present embodiment, none of the above-mentioned ones having low characteristics was generated.

In the above embodiment, platinum is added to the thin film, but the same applies to iridium and rhodium. The amount of platinum, iridium, and rhodium added may be 10 ppm or more in order to sufficiently stabilize the electron emission characteristics. In addition, if the platinum, iridium, and rhodium are added in too large amounts, the initial electron emission characteristics may be adversely affected. Therefore, the addition amount is 1
It is preferably 0% or less.

[0018]

As described above, by using the impregnated cathode according to the present invention, the extremely low electron emission characteristics and the deterioration of characteristics in a short time operation, which are problems that the prior art has, are caused. It is possible to provide a cathode for an electron tube that eliminates the occurrence of the electron emission, maintains low temperature operation, and maintains stable electron emission characteristics for a long time.

[Brief description of drawings]

FIG. 1 is a side view showing a broken main part of a structure of an embodiment of a cathode for an electron tube according to the present invention.

FIG. 2 is a cross-sectional view showing a color cathode ray tube as an example for explaining the structure of an electron tube.

FIG. 3 is a schematic diagram illustrating an example of an electrode configuration of an electron gun for a cathode ray tube.

[Explanation of symbols]

1 cathode substrate 2 refractory metal 3 holes 4 molybdenum cup 5 W-Sc ₂ -O ₃ -Pt film 6 tantalum sleeve 7 tungsten wire 8 alumina layer 9 heaters 20 face panel 21 neck 23 anode terminal 24 which is connected with the funnel 22 funnel Shadow mask with a large number of apertures 25 Electron gun for emitting three electron beams 26 Deflection yoke 27 Electron beam 28 Phosphor layer arranged in mosaic 29 Internal magnetic shield K Cathode 30 First lattice electrode 31 Second lattice electrode 32 Third grid electrode 33 Fourth grid electrode 34 Fifth grid electrode 35 Sixth grid electrode 36 Cup electrode which is an anode

Claims (1)

[Claims] 1. A cathode for an electron tube, comprising a porous cathode substrate made of a refractory metal impregnated with an electron emitting substance, wherein tungsten and scandium or scandium oxide or both are provided on an electron emitting surface of the cathode. A lattice electrode for an electron gun for a cathode ray tube, comprising a thin film made of at least one metal selected from platinum, iridium and rhodium or a compound thereof.