JPH11345559A - Cathode for electron tube - Google Patents

Abstract

(57) [Problem] To provide an electron tube cathode having excellent convergence performance and excellent drive characteristics. In an electron tube cathode, an electron emitting material layer (5) formed on a substrate (1) has a smaller diameter than the opening diameter of the opening below the opening of the grid electrode (6). It has a protruding projection 8, and the height of the projection 8 is 10 μm or more.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cathode for an electron tube, and more particularly to a cathode in an electron gun for a cathode ray tube used for a CRT, an electron microscope, an electron beam exposure apparatus and the like.

[0002]

2. Description of the Related Art FIG. 5 shows a cathode (cathode) for an electron tube used for a cathode ray tube or a picture tube for a television disclosed in Japanese Patent Publication No. 64-5417, for example. ), A base composed mainly of nickel and containing a trace amount of a reducing element such as magnesium (Mg), and 2 a cathode sleeve made of nichrome or the like.
Is applied to the substrate 1 and contains at least barium;
In addition, the electron-emitting material layer 3 mainly containing an alkaline earth metal oxide 4 containing strontium or calcium and containing a rare earth metal oxide such as scandium oxide in an amount of 0.1 to 20% by weight. With the heater arranged,
Heat electrons are emitted from the electron emitting material layer 5 by heating. Reference numeral 6 denotes a grid electrode adjacent to the electron emitting material layer 5. The surface of the electron emitting material layer of the cathode configured as described above does not have any intended irregularities,
It is flat.

[0003]

FIG. 6 is a cross-sectional side view near the cathode showing the electron trajectory of electrons emitted from the cathode having the electron emission material layer of the conventional structure. In the figure, G1, G2, and G3 are first, second, and third grid electrodes, respectively, and 7 is an electron orbit of electrons emitted from the cathode. From this figure, it can be seen that electrons emitted from the vicinity of the central axis have an intersection far from the cathode, but electrons emitted from a place away from the central axis have an intersection at a short distance from the cathode. In the conventional cathode, the intersection of the electrons emitted from a position away from the central axis does not coincide with the intersection of the electrons emitted from the vicinity of the central axis. This causes a problem that the convergence performance is not improved.

The present invention has been made to solve the above problems, and has as its object to provide a cathode for an electron tube having good convergence performance and excellent drive characteristics.

[0005]

According to a first aspect of the present invention, there is provided a cathode for an electron tube, wherein an electron emitting material layer formed on a substrate is provided under the opening of the grid electrode. It has a diameter smaller than the diameter and has a convex portion protruding from the peripheral portion.

The electron tube cathode according to the second configuration of the present invention is the same as the first configuration, except that the height of the projection is 10 μm.
m or more.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1 Hereinafter, Embodiment 1 of the present invention will be described with reference to FIG. In the figure, reference numeral 1 denotes a base composed mainly of nickel and containing a trace amount of a reducing element such as silicon (Si) and magnesium (Mg); The heater 5 is provided on the base 1 and contains at least barium, and further contains, as a main component, an alkaline earth metal oxide 4 containing strontium or calcium, and 0.01 to 25% by weight of scandium oxide. An electron emitting material layer containing a rare earth oxide such as yttrium oxide. Numeral 8 denotes a projection provided on a part of the electron emitting material layer 5 corresponding to the electron emission portion. The projection 8 has a diameter smaller than the opening diameter of the opening below the opening of the grid electrode 6, and It is a protruding projection.

FIG. 2 shows a conventional television having the above-configured cathode for an electron tube mounted on a normal television set and completed through a normal exhaust process.
9 shows convergence performance of an RT in comparison with a conventional example. Here, the thickness of the entire electron emitting material layer 5 according to the first embodiment is 100 μm, the height of the projection 8 of the electron emitting material layer 5 is 20 μm, and the surface diameter of the projection 8 is 200 μm. did. As the electron emitting material layer 5, an alkaline earth metal oxide containing scandium oxide of 7% by weight was used, and the projections 8 were formed by pressurizing portions other than the projections serving as electron emission portions. The phosphor used was a green phosphor entirely, and a beam emitted from one cathode was scanned through an aperture. The distance between the apertures is approximately 0.25 mm, and the diameter of the aperture opening is 0.1 mm.
It is about 05 mm. One cathode beam scans one line along the opening, then jumps two lines,
Scan the next aperture line. Therefore, the lines of light appearing on the phosphor should be at 0.75 mm intervals. FIG. 2 schematically shows the state. In the case where a conventional cathode is used (FIG. 2B), the above-mentioned situation is not observed even if the scanning is performed in any way, and the emission lines at 0.25 mm intervals are not obtained. Can be seen. This indicates that the beam diameter is 0.5 mm or more. On the other hand, when the cathode of the present embodiment was used (FIG. 2A), light emitting lines were observed at 0.75 mm intervals. This indicates that the beam diameter of the present embodiment is 0.45 mm or less. Therefore, it can be said that the convergence performance of the embodiment is improved as compared with that of the conventional example.

One of the causes of such excellent characteristics of the electron tube cathode according to the present embodiment is considered as follows. That is, the electrons emitted from a place away from the center of the electron emission, which is a factor of deteriorating the convergence performance, are projected to the projections 8.
It is considered that the convergence performance is improved by reducing or no longer being emitted by providing.

In the present embodiment, an oxide cathode is used, but W is formed by depositing tungsten on a substrate.
A similar effect can be obtained with a vapor deposition type cathode or an impregnated type cathode. Further, in the present embodiment, the convex portion 8 is formed by pressurizing. However, the periphery of the convex portion may be removed by laser, or masking may be performed by forming a mask when forming the electron emitting material layer. It may be formed.

Embodiment 2 FIG. 3 is a simulation result showing the relationship between the height of the projection 8 and the amount of emission emission in a region other than the projection in the electron tube cathode having the configuration of FIG. Assuming that the height of the projection is 10 μm, the amount of electrons is reduced by 50% from the amount of the surface of the projection. Regarding the convergence performance, the effect appears when the protrusion is 10 μm or more, and the effect becomes remarkable when the protrusion is 40 μm or more. If it is 40 μm or more, the effect does not change. Therefore, the height of the projections of the electron emitting material layer is suitably 10 μm or more, preferably 40 μm.

In the first and second embodiments, the electron emitting material layer 5 is formed on the entire surface of the substrate, and the projection 8 protrudes below the opening of the grid electrode. However, the electron emission material layer may be formed only in the lower part of the opening of the grid electrode on the base body and only in the convex part having a diameter smaller than the opening diameter of the opening and protruding from the surrounding base body. Also in this case, the height of the projection is 10 μm or more, preferably 40 μm.
m is appropriate.

Embodiment 3 FIG. 4 shows that the height of the convex portion is 40.
9 is a simulation result showing a relationship between a drive voltage and an emission current at μm. The normal emission current is 300 μA or less, but in this range, the drive voltage for obtaining the same emission current is lower than in the conventional example. This is probably because the cut-off voltage (the voltage at which electrons start to be emitted from the cathode) decreases due to the provision of the protrusions.

[0014]

As described above, according to the first structure of the present invention, the electron emitting material layer formed on the substrate is provided below the opening of the grid electrode with the opening diameter of the opening. Because it has a smaller diameter and has a protruding part that protrudes from the peripheral part,
The number of electrons emitted from the peripheral portion is reduced, and the convergence characteristics are improved. Further, the provision of the convex portion lowers the cut-off voltage, and thus has an effect of obtaining a device having good drive characteristics.

Further, according to the second configuration of the present invention, since the height of the projections is set to 10 μm or more in the first configuration, there is an effect that good convergence performance can be obtained.

[Brief description of the drawings]

FIG. 1 is an enlarged sectional view showing the vicinity of a cathode of an electron gun according to a first embodiment of the present invention.

FIG. 2 is a diagram showing the convergence performance of the cathode for an electron tube according to the first embodiment of the present invention in comparison with a conventional one.

FIG. 3 is a diagram showing a relationship between a height of a convex portion and an emission current in a peripheral portion according to the second embodiment of the present invention.

FIG. 4 is a diagram showing a relationship between drive voltage and emission current according to a third embodiment of the present invention.

FIG. 5 is an enlarged sectional view showing the vicinity of a cathode of a conventional electron gun.

FIG. 6 is a cross-sectional side view near the cathode, showing an electron trajectory of electrons emitted from the conventional cathode.

[Explanation of symbols]

Reference Signs List 1 base, 2 cathode sleeve, 3 heater, 4 alkaline earth metal oxide, 5 electron emitting material layer, 6 grid electrode, 7 electron orbit, 8 convex portion.

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Hiroyuki Teramoto 2-3-2 Marunouchi, Chiyoda-ku, Tokyo Mitsubishi Electric Corporation

Claims (2)

[Claims] 1. An electron tube cathode having an electron emitting material layer formed on a substrate, wherein the electron emitting material layer is provided below the opening of the grid electrode close to the electron emitting material layer. A cathode having a diameter smaller than the opening diameter of the above, and having a projection protruding from a peripheral portion. 2. The cathode for an electron tube according to claim 1, wherein the height of the projection is 10 μm or more.