Electron Gun of an Image Display Apparatus

1. TECHNICAL FIELD

The present invention relates to an electron gun of a flat type image display apparatus to be used in a field for an image information display apparatus, utilizing thermoelectron emission.

2. BACKGROUND ART

At present, cathode ray tubes are mainly used as display apparatus for color televisions. Conventional cathode ray tubes, however, have a disadvantage that they are very long in depth in comparison with screen size. Consequently, fabrication of a small depth television receiver has been impossible. Recently, an EL (electro luminescence) display apparatus, a plasma display apparatus, a liquid crystal display apparatus, and the like have been developed as a flat type image display apparatus. However their quality and performance in luminance, contrast and color reproducibility are not satisfactory and they are not practicable. If used at all, they have very limited purposes.

In order to display a color television image on a flat type image display apparatus using an electron beam, an image display apparatus for the television is developed, wherein a screen of the image display apparatus is divided in plural sections in the vertical direction, electron beams of the respective sections are deflected vertically to display plural lines, moreover, the screen is divided in plural sections in the horizontal direction, fluorescent substance for red (R), green (G) and blue (B) of the respective sections radiate in turn, and intensities of the electron beams emanated on the fluorescent substance of R, G, B are controlled by color video signals, there by to display a color television image as a whole.

The image display apparatus comprises, as will be described hereinafter, plural line cathodes, a group of electrodes of a vertical convergence electrode, vertical deflection electrodes, electron beam flow control electrodes, for converging, deflecting and accelerating the electron beams emitted from the above-mentioned line cathodes, a horizontal convergence electrode, horizontal deflection electrodes and an electron beam acceleration electrode between an anode and a rear electrode.

In the above-mentioned image display apparatus, the constitution of an electron gun, in a broad sense, consists of a rear electrode, the line cathode, the vertical convergence electrode, the vertical deflection electrode, the electron beam flow control electrode, the horizontal convergence electrode, the horizontal deflection electrode and the electron beam acceleration electrode. More narrowly, the rear electrode, the line cathode and the vertical convergence electrode among the above-mentioned group of electrodes is referred to as the electron gun. The electron gun in the present invention means the narrow configuration referred to above.

The conventional configuration of the electron gun is shown in FIG. 1. The rear electrode 1 has a function of ejecting forward the electron beam which is emitted from the line electrode 2 as an electron beam source, and is formed by a glass plate, a transparent conductive film 1a is formed on its surface opposing to the line electrode 2 by evaporation of, for example, oxidized tin and oxidized indium. The line cathode 2 is stretched horizontally, the plural line cathodes are provided in a vertical direction with a suitable interval (the four line cathodes are shown in FIG. 1). These line cathodes 2 are made of, for example, a tungsten line wherein its diameter is 15-30 micron and oxidized cathode substance of oxidized barium, oxidized strontium and oxidized calcium are coated on the surface thereof by, for example, electrodeposition. The vertical convergence electrode 3 is formed by a etched thin metal plate which is 0.1-0.2 mm in thickness and is made of 426 alloy (Ni: 42%, Cr: 6%, Fe: 52%), or the like, and a film of several micron of silver, platinum, gold or the like is formed on its surface by evaporation or wet plating. The vertical convergence electrode 3 extracts the electron beam emitted from the line cathode 2 forward and converge it.

However, in the above-mentioned configuration,

(1) As shown in FIG. 1, fabrication of the rear electrode 1 was difficult because its shape was complicated and high precision was required.

(2) There is defects that the shape of the vertical convergence electrode 3 is changed by heat radiated from the line cathode 2, and furthermore, electric charges arise thereon due to electrons emitted from the line cathode 2, and an electric field in the electric gun become unstable, thereby making uneveness of luminance on the anode surface of the image display apparatus.

A main object of the present invention is to constitute an electron gun of an image display apparatus which is improved in a configuration which is easy to fabricate.

Other object of the present invention is to stabilize an electric field in the electron gun, and is to prevent uneveness of luminance on a surface of an anode of the image display apparatus.

A rear electrode part of the electron gun is constituted by a flat plate type rear electrode which is provided with a conductive film on the surface and is arranged keeping a predetermined distance from the plural line cathodes and plural spacers which are disposed between the plural line cathodes, wherein respective one ends are fixed on the rear electrode and conductive films are formed on their surfaces, thereby the above-mentioned objects of the present invention are achieved.

More specifically, the electron gun of the image display apparatus embodying the present invention comprises plural line cathodes which are disposed in parallel with each other with a given interval, therebetween the flat plate type rear electrode which has a conductive film on the surface and is disposed with a constant distance from the line cathodes, plural spacers which are disposed between the plural line cathodes, respective one end of which being fixed on the rear electrodes and a conductive film being formed on each surface. Plural convergence electrodes for converging the electron beams emitted from the line electrodes.

FIG. 1 is the cross-sectional view showing the configuration of the conventional electron guns.

FIG. 2 is an exploded perspective view showing a whole configuration of flat type image dispaly apparatus.

FIG. 3 and FIG. 4 are a cross-sectional view and a perspective view showing configurations of electron guns in an embodiment of the present invention.

FIGS. 5-8 are cross-sectional views of other embodiments of the present invention.

A fundamental configuration of a flat type image display apparatus using an electron gun of the present invention is elucidated on the base of FIG. 2. As shown in the drawing, a glass enclosure 11, a rear electrode parts 12, 13, line cathodes 2 as sources of electron beams, vertical convergence electrodes 3, 3', vertical deflection electrodes 4, electron beam flow control electrodes 5, a horizontal convergence electrode 6, horizontal deflection electrodes 7, a horizontal convergence electrode 6', electron beam acceleration electrodes 8, an anode 9, and glass enclosure 10, 11 are disposed from rear to front in the above-mentioned order. All the components are enclosed in the glass enclosure 10 and 11, and the glass enclosure is evacuated.

The line cathodes 2 are horizontally stretched and disposed to emit horizontally and linearly distributed electron beams. Plural line cathodes 2 are provided with appropriate intervals (although only four line cathodes are shown in FIG. 2). These line cathodes are made by a tungsten line wherein oxide cathode substance is coated on the surface. As will be described later line cathodes are controlled to emit the electron beam during a predetermined time period in turn from the upper line cathode.

The rear electrode parts 12, 13 produce a voltage potential inclination between the vertical convergence electrode 3 and itself, suppress the emission of the electron beams from the line electrodes except the above-mentioned line electrode which is controlled to emit the electron beam during a predetermined time period, and emit emitted electron beam only in frontward direction.

The vertical convergence electrode 3 is formed in that by a conductive plate which has horizontal long slits 3a on positions opposing to the respective line cathodes 2, and the electron beams emitted from the line cathode 2 are taken out through the slits 3a, and are converged to a vertical direction. The vertical convergence electrode 3' serves the same function.

Plural vertical deflection electrodes 4 are horizontally disposed at a center between the respective slits 3a, and the respective vertical deflection electrodes are formed by a insulation substrate with conductive members on both an upper and a lower surface thereof. A vertical deflection voltage is applied across the two conductive members and the electron beams are vertically deflected.

The electron beam flow control electrodes 5 are formed by a rectangular conductive plate with a longitudinal long slit 5a thereon, and plural ones thereof are arranged in parallel at a predetermined interval. This respective electron beam flow control electrode 5 horizontally divides the electron beam to every one picture element to be taken out it, and its flow rate is controlled by video signals for displaying respective picture elements. For this purpose, the conductive plates for control electrodes are electrically isolated from each other. In order to display a color image, the respective picture elements are displayed by three color fluorescent substances, R, G and B, and the respective video signals for R, G and B are applied to the respective electron beam flow control electrode 5 in turn.

The horizontal convergence electrode 6 is formed by a conductive plate wherein plural vertically elongated slits 6a are disposed on positions opposing to the slits 5a of the electron beam flow control electrodes 5, horizontally divided electron beams for the respective picture elements are converged horizontally and is made to be fine electron beams. The horizontal convergence electrode 6' serves the same function.

The horizontal deflection electrodes 7 are disposed on center positions of the respective slits 6a and are formed by plural rectangular conductive plates which are electrically isolated from each other, horizontal deflection voltages are applied across the respective conductive plates, the electron beams for the respective picture elements are horizontally deflected, and the respective fluorescent substances of R, G and B on the anode 9 are irradiated thereby in turn to radiate lights. The range of the deflection, in this example, is equal to a width of one picture element for each electron beam.

The electron beam acceleration electrode 8 are formed by plural conductive wires which are horizontally disposed at similar positions of the vertical deflection electrodes 4, and accelerate the electron beams as they impinge on the anode 9 with sufficient energy.

The back surface of the anode 9 are coated with the fluorescent substances which radiate lights by irradiation of the electron beams, and furthermore, a metal back layer is added thereon (not shown).

FIG. 3 and FIG. 4 show a configuration of the electron gun in an embodiment of the present invention in simplified manner. Referring to FIG. 3 and FIG. 4, the rear electrode part of the electron gun is configured as being divided into a flat plate 12 and spacers 13 made of glass plates. The electron gun which surround the line cathodes are formed by the flat plate type rear electrode 12 wherein a conductive film 12a is formed on one surface, a glass spacers 13 wherein both edges 13b of a surface which contact with the vertical convergence electrode 3 are chambered to isolate it from the vertical convergence electrode 3 and a conductive films 13a are formed on the whole surface of the opposite surface of the spacer 13 in order to keep conductivity with the rear electrode 12, and it is advantageous in quality, function and fabrication.

The line cathodes 2 are surrounded by the flat plate rear electrode 12 and the glass spacers 13, and the potential of the rear electrode 12 can be equalized with the glass spacer 13, and a uniform electric field can be maintained. Since the vertical convergence electrode 3 is electrically connected with a transparent conductive film 13c of the glass spacer 13, even if the vertical convergence electrodes 3 are deformed by heats of the line cathodes 2 the same potentials are maintained, and the uniform electric field can be maintained.

Referring to FIG. 5, both upper and lower end parts 13b of the glass spacers 13 are chambered, thereby the vertical convergence electrode 3 is isolated from the glass spacer 13 and the glass spacer 13 is isolated from the flat plate rear electrode 12, and impression of identical potential is prevented. In FIG. 6, in a similar manner shown in FIG. 5, only both edge parts 13b of a contacting part of the glass spacer 13 and the vertical convergence electrode 3 are chambered and are isolated, and the transparent conductive films 13a are evaporated so as not to make a contact to the rear electrode 12 from electrical conduction with the conductive film 13a on the glass spacer 13. Therefore, though the effect in FIG. 6 is identical with that in FIG. 5, their methods in manufacturing are different from each other. In this embodiment, since the transparent conductive film 13a is formed on the surface of the glass spacer 13 opposing to the line cathode 2, a generation of electric charges which are induced on the surface of the glass spacer 13 made of glass as dielectric substance by electron beam emitted from the line cathode 2 is prevented, and the electric field in the inside of the electron gun is stabilized, hence it is possible to cancel unevenness of luminance on the anode surface of the image display apparatus. Furthermore, even if the vertical convergence electrode 3 made of 426 metal alloy thin plate of 0.1-0.2 t is deformed by heat of the line cathode 2, the electric field inside of the electron gun can be stabilized, since the transparent films 13a are formed on the contacting part of vertical convergence electrode 3 and glass spacer 13a in both the embodiments as shown in FIG. 5 and FIG. 6 and the identical potentials can be maintained.

In embodiments as shown in FIG. 7 and FIG. 8, the transparent conductive films 13a are formed on the surfaces of the glass spacers 13 opposing to the line cathodes 2, and the electric charges which are induced by the electron beam emitted from the line cathodes 2, on the surfaces of the dielectric glass spacres 13 can be suppressed thereby. Especially in the embodiment of the FIG. 8, the transparent conductive films 13a are formed on the whole surfaces of the glass spacers 13, and the electric charge of the glass spacers 13 which are induced by the electron beam emitted from the line cathodes 2 can be made to uni-potential over the whole surfaces of the glass spacers 13.

The embodiments as shown in FIG. 7 and FIG. 8, are the configuration of the electron gun which is used in case that the vertical convergence electrodes 3 and the rear electrodes 12 are thick in thickness and have high stiffness, and they do not make a deformation due to the heat radiated from the line cathodes 2, and the conductive films 13a on the surfaces of the glass spacers 13a are formed on a desirable area by using appropriate masking material in a deposition process.

As is made clear by the above-mentioned elucidation, in the present invention, the problem in fabrication is settled by the simplified configuration of the electron gun. Generation of electric charge is prevented by providing the transparent conductive films on the surfaces of glass spacers opposing to line cathode. In addition, the electric field is stabilized, dissolution of unevenness of luminance on the surface of an anode of the image display apparatus is realized, and as a result, a long time stability in quality of the image display apparatus and reliability are greatly improved and can be secured, and the effect in practical use is noticeable.