JPH0785807A - Electron gun - Google Patents

Abstract

PURPOSE:To reduce a so-called halo at the time of high current by restricting grid emission. CONSTITUTION:A heater 1, a cathode 3 which is heated by the heater 1 and emits electron, and grid electrodes G1, G2 for guiding the electron from the cathode 3 in one direction are arranged on the same axis in an electron gun, and the grid electrodes G1, G2 are formed of conductive plate, on which an electron transmission hole is provided with the axis serving as its central axis. The electron emitting region of the cathode 3 is formed in a region with the axis serving as its central axis, and has an area smaller than those of the electron transmission holes P1, P2 of the grid electrodes G1, G2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electron gun, and in particular,
Regarding the improvement of the cathode.

[0002]

2. Description of the Related Art An electron gun used for a cathode ray tube or the like comprises a heater, a cathode which is heated by the heater to emit electrons, and a grid electrode which guides the electrons from the cathode in one direction.

The heater, the cathode, and the grid electrode are arranged on the same axis, and the grid electrode is formed by a conductive plate having an electron transmission hole centered on the axis.

As the cathode, for example, an impregnated cathode is used. This impregnated cathode is formed by impregnating a porous tungsten (W) substrate with an aluminate compound composed of BaO, CaO and Al ₂ O. ing.

In such an impregnated type cathode, Ba reacts with the compound impregnated in the pores and W as the metal substrate to diffuse Ba to form a monoatomic layer on the substrate surface. As a result, the work function of the substrate surface is lowered, and thermionic emission is likely to occur.

Therefore, the impregnated cathode has a long life and a large operating current density because the evaporated Ba is replenished from the inside of the substrate.

[0007]

However, the electron gun having such a structure has the Ba vaporized from the cathode.
Remains attached to the grid electrode, and in combination with the fact that the grid electrode is heated to a high temperature by the radiant heat from the cathode, there remains a problem that electrons are emitted.

Such a phenomenon is called grid emission, and has been a cause of deteriorating the quality of the display screen.

Further, there is a problem that the so-called halo becomes large in the electron beam emitted from such an electron gun, and the image resolution of the display surface on which an image is displayed by the electron beam is easily deteriorated.

Here, the halo means a skirt portion having a low current density which is spread around a portion (core) having a high current density at the center of the electron beam.

Therefore, the present invention has been made under such circumstances, and an object of the present invention is to suppress the grid emission and reduce the so-called halo at high current. To provide.

[0012]

In order to achieve such an object, the present invention basically comprises a heater, a cathode which is heated by the heater to emit electrons, and an electron from the cathode. In an electron gun composed of a conductive plate in which a grid electrode for guiding in one direction is arranged on the same axis, and the grid electrode has an electron transmission hole having the axis as a central axis,
The cathode is characterized in that the electron emission region is formed in a region having the axis as the central axis and has an area smaller than the electron transmission hole of the grid electrode.

[0013]

In the electron gun constructed as described above, the area of the cathode formation region is larger than the area of the grid electron transmission hole in the relationship between the cathode formation region and the grid electron transmission hole positioned on the same axis. It is small in size.

Therefore, since the evaporation region of Ba from the cathode serves as an electron transmission hole of the grid electrode, it is extremely difficult to adhere to the grid electrode (the conductive plate surface excluding the electron transmission hole). Therefore, the grid emission can be significantly suppressed.

Further, since the electron emission from the cathode is not emitted from a portion far away from the central axis, the so-called halo generated by the electron emission from the portion can be reduced.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 2 is a general schematic view of an electron gun to which the present invention is applied.

In the figure, the cathode K is adapted to be heated by the heater 1, and thermoelectrons are emitted from the surface of the cathode pellet 3. The electrons are controlled by the grid electrode G1 and are accelerated by the grid electrodes G2 and G3 to become an electron beam.

Then, this electron beam is applied to the grid electrode G.
3, the phosphor screen 2 by the action of the electrostatic main lens formed by the grid electrode G4 and the grid electrode G5.
It is designed to be focused on the surface.

The electron beam is deflected by the action of a magnetic field formed by a deflection yoke (not shown) provided outside the cathode ray tube, and is scanned on the phosphor screen 2 so that the electron beam is scanned. An image corresponding to the intensity of the electron beam is displayed.

FIG. 1 is a sectional view showing an embodiment of the structure of the cathode K and its vicinity.

In the figure, first, molybdenum (Mo)
There is a sleeve 4 formed by stacking an inner sleeve 4A and an outer sleeve 4B, which are cylindrical bodies, on each other.
The inner sleeve 4A is closed at its end on the grid electrode G side. The cathode pellet 3 is fixedly mounted on the central surface of the closed portion on the grid electrode G side.

The cathode pellet 3 is a so-called impregnated cathode and is formed by impregnating a porous tungsten (W) substrate with an aluminate compound composed of BaO, CaO and Al ₂ O. .

The outer sleeve 4B is closed at the end on the grid electrode G side similarly to the inner sleeve 4A, but a hole is formed in the center thereof so that the cathode pellet 3 can be positioned in this hole. It has become. As a result, the cathode pellets 3 are arranged so as to be exposed from the outer sleeve 4B.

The sleeve 4 has such a double structure in order to accurately align the central axes of the other members, as will be described later.

The inner sleeve 4A is the outer sleeve 4
It is fixed to B and the outer sleeve 4B is fixed to a member (not shown) through the support wire 7 and the support 8.

A heater 1 is built in the sleeve 4, and a terminal of the heater 1 is drawn out from an open end which is the other end of the sleeve 4.

Then, the cathode K constructed in this way
A first grid electrode G1 and a second grid electrode G2 are sequentially arranged on the cathode pellet 3 side, and the first grid electrode G1 and the second grid electrode G2 are fixed to a bead glass (not shown).

The first grid electrode G1 and the second grid electrode G2 are each formed of a conductive plate having electron transmission holes P1 and P2 formed therein.

Electron transmission holes P1 of the first grid electrode G1,
The electron transmission holes P2 of the second grid electrode G2 are circular transmission holes of the same diameter, which are positioned on the same axis, and the cathode pellet 3 is positioned on the extension of the axis.

Here, in this embodiment, in particular, the cathode pellet 3 is formed in a region having the axis as the central axis and has an area smaller than the electron transmission hole P1 of the grid electrode G1. .

Next, the axial alignment at the time of assembling the electron gun thus constructed will be described with reference to FIGS. 3 and 4.

Step 1. (FIG. 3) FIG. 3 is a diagram showing the axial alignment of the outer sleeve 4B, the first grid electrode G1, the second grid electrode G2, etc., with the bead (not shown) inserted in the axial alignment rod 10 respectively. Fix on glass.

In this case, the central axes of the transmission hole 6 of the outer sleeve, the electron transmission hole P1 of the first grid electrode G1, the electron transmission hole P2 of the second grid electrode G2, etc. can be made coaxial. Like

Step 1. (FIG. 4) Outer sleeve 4B after removing the axis-aligning rod 10
The inner sleeve 4A is inserted and fixed therein.

The inner sleeve 4A is formed in relation to the outer sleeve 4B, and the cathode pellets 3 are fixedly mounted at the positions corresponding to the transmission holes 6 formed in the outer sleeve 4B.

The electron gun constructed as described above has the cathode pellet 3 and the grid electrode G positioned on the same axis.
The area of the cathode pellet 3 is smaller than the area of the electron transmission hole P1 of the grid electrode G1 in relation to the first electron transmission hole P1.

Therefore, Ba from the cathode pellet 3
Since the evaporation region of the grid electrode G1 is smaller than the electron transmission hole P1 of the grid electrode G1, the grid electrode G1 (the electron transmission hole P1
It becomes extremely difficult to adhere to the surface of the conductive plate except 1). Therefore, the grid emission can be significantly suppressed.

Further, since the electron emission from the cathode pellet 3 is not emitted from a portion far away from the central axis, the so-called halo generated by the electron emission from the portion can be reduced.

FIG. 5 is a diagram showing the trajectory of electrons emitted according to the distance (vertical axis) from the central axis of the cathode pellet 3.

As is apparent from this figure, the electrons radiated from the vicinity of the central axis of the cathode pellet 3 are focused at a position (for example, X position) distant from the cathode pellet 3. Electrons emitted from a position 0.2 mm away from the central axis of the cathode are focused at a position (for example, a position Y) located at a short distance from the cathode.

From this, it is understood that the smaller the diameter of the cathode pellet 3, the more the generation of halo can be reduced.

FIG. 6 is a sectional view showing another embodiment of the structure of the cathode K and its vicinity.

The cathode shown in FIG. 6 is a so-called CDP.
(Controlled Porosity Dispenser: Impregnated type with controlled porosity) It is called a cathode.

A cathode pellet 20 is placed on the entire area of the closed surface of the sleeve 4 on the grid electrode G side, and a cap 9 made of molybdenum (Mo) is fixed to the sleeve 4 so as to cover the cathode pellet 20. ing.

Then, the grid electrode G of the cap 4
The micropore group 15 is formed on the side surface. Each micropore of the micropore group 15 has a diameter of, for example, about 3 μm and has an interval of about 10 μm from adjacent micropores.

The support by the support wire 7 is carried out by the cap 9 arranged as an outer frame of the sleeve 4.

The cathode thus constructed can be formed by aligning the porous structure of the metal substrate (cap 9) by, for example, laser processing, and barium is supplied through this porous structure, so that stable electrons can be obtained. Emission characteristics can be obtained.

In this embodiment, in particular, the center of the region where the micropore group 15 is formed coincides with the central axis of the transmission hole P of the grid electrode G and the electron transmission hole P of the grid electrode G is formed. Is smaller than the diameter of.

FIG. 7 is a view as seen from the grid electrode side G in FIG. 6, which is coaxial with the electron transmission hole P of the grid electrode G and has a diameter smaller than the transmission hole P and a group of micro holes 15 on the cap surface. Are formed.

Therefore, in forming the microhole group 15, the electron transmission hole P of the grid electrode G is used as a reference, so that the microhole group 15 can be easily formed coaxially and to a predetermined diameter by laser processing, for example. it can.

FIG. 8 is an explanatory view showing an embodiment of a method of manufacturing the electron gun constructed as above. Cap 9,
The grid electrode G is aligned in the same manner as shown in FIG. 4 (in this case, the alignment of the cap 9 with respect to the grid electrode G does not need to be strict), and then the cap 9 is finely aligned by laser processing or the like. The hole group 15 is formed.

Further, the sleeve 4 to which the cathode pellet 20 is fixed is inserted into the cap 9 to fix the sleeve 4 and the cap 9 together.

In each of the above-mentioned embodiments, the shape of the electron emission region of the cathode is circular in any of them, but the present invention is not limited to this, and other shapes (ellipse, square, etc.) are used. It is needless to say that the same effect can be obtained even with ().

Further, although the impregnated cathode has been described in the above-mentioned embodiments, it can be applied to a so-called oxide cathode in which an oxide of an alkaline earth metal (for example, BaO) is applied to a metal substrate. Needless to say.

[0055]

As is apparent from the above description,
According to the electron gun of the present invention, it is possible to suppress grid emission and reduce so-called halo at high current.

[Brief description of drawings]

FIG. 1 is a view showing an embodiment of an electron gun according to the present invention, and is a cross-sectional view showing its cathode and its peripheral portion.

FIG. 2 is a schematic view showing an embodiment of an electron gun according to the present invention.

FIG. 3 is a process of axis alignment in the electron gun shown in FIG. FIG.

4 is a step of axis alignment in the electron gun shown in FIG. FIG.

FIG. 5 is an explanatory diagram showing an effect of the electron gun according to the present invention.

FIG. 6 is a view showing another embodiment of the electron gun according to the present invention,
It is sectional drawing which showed the cathode and its periphery.

7 is a configuration diagram viewed from the grid electrode side in the diagram shown in FIG.

8 is an explanatory diagram showing an example of a method of manufacturing the electron gun shown in FIG.

[Explanation of symbols]

 K cathode G grid electrode P electron transparent hole 3, 20 cathode pellet 9 cap 15 micropore group

Claims (1)

[Claims] 1. A heater, a cathode that emits electrons when heated by the heater, and a grid electrode that guides electrons from the cathode in one direction are arranged on the same axis, and the grid electrode has a central axis about the axis. In the electron gun including a conductive plate having an electron transmission hole formed therein, the cathode has an electron emission region formed in a region having the axis as a central axis and is smaller than the electron transmission hole of the grid electrode. An electron gun characterized by having an area.