GB2309822A

GB2309822A - Electron gun for color CRT

Info

Publication number: GB2309822A
Application number: GB9701978A
Authority: GB
Inventors: Hak-Cheol Yang; Neung-Yong Yun; Seok-Bong Son; Seong-Keun Park
Original assignee: Samsung Display Devices Co Ltd
Current assignee: Samsung SDI Co Ltd
Priority date: 1996-01-30
Filing date: 1997-01-30
Publication date: 1997-08-06
Also published as: GB9701978D0; DE19703238A1; TW329531B; KR100349901B1; KR970060323A; JPH09213232A

Description

ELECTRON GUN FOR COLOR CRT 2309922 The present invention relates to an

electron gun for a color cathode ray tube (CRT), and more particularly, to an electron gun for a color CRT employing an improved triode.

In general, as shown in FIG. 1, of the accompanying drawings, a CRT includes a panel 10 having a phosphor film (not shown) and a funnel 20 sealed to the panel 10 and having an electron gun 30 in a neck portion 21 thereof and a deflection yoke 23 around a cone portion 22 thereof. In the CRT having such a structure, an electron beam produced from the electron gun 30 is deflected by the deflection yoke 23 and lands on the phosphor film of the panel 10 thereby to form an image.

FIG. 2 of the accompanying drawings shows an example of the electron gun 30 for emitting an electron beam. As shown in the drawing, the electron gun 30 includes a cathode structure 31 which forms a triode,' a control electrode 32, a screen electrode 33, and a focus electrode 34 and a last accelerating electrode 35 which are sequentially installed from the screen electrode 33 and form an electron lens. As shown in FIG. 3 of the accompanying drawings, a typical indirectly heated cathode is employed as the cathode structure 31, which includes a sleeve 31a, a base metal 31c coupled to an end portion of the sleeve 31a and of which the upper surface is coated with an electron-emitting material 31b, and a heater 31d for heating the electron-emitting material 31b, which is installed inside the sleeve 31a.

1 In the operation of the electron gun 30 having such a structure, when a predetermined voltage is applied to the heater 31d of the cathode structure 31 and the respective electrodes, electrons are emitted from the electron-emitting material 31b and concurrently electron lenses are formed between the electrodes 32 to 35. Thus, the electron beam is focused and accelerated while passing through the electron lenses towards the phosphor film.

As shown in FIG. 4 of the accompanying drawings, in the conventional electron gun for a color CRT, the triode used for emitting electrons and controlling the emitted electrons does not provide a constant density of current of the electron beam emitted from the cathode structure 31 due to the degree of encroachment of the electric field of the control electrode 32 toward the cathode structure 31. In FIG. 4, the X axis represents the distance from the center of a hole through which the electron beam passes and the Y axis represents the current density of the electron beam.

Such a non-uniform current density for the electron beam provides a non-constant charge repulsing force being applied to the electron beam proceeding toward the phosphor film in accordance with a position thereof. Thus, the electron beam is deteriorated due to the inconsistent charge repulsing force so that the sectional shape of the electron beam is distorted when focused at the phosphor film.

Also, in another conventional electron gun using a field emitter as the cathode structure of the triode the effect of the triode according to the encroachment of the electric field

2 of the control electrode still exists although the density of current generated from the field emitter is constant.

Further, in the above-described conventional electron gun, when an incident angle of the electron beam emitted from the triode to a main electron lens formed between the focusing electrode and the last accelerating electrode is increased, the electron beam is deteriorated due to the effect of spherical aberration at the main lens.

To overcome such disadvantages, a pre-focus lens exhibiting a very strong electrical field is disposed before the main electron lens in order to reduce the incident angle of the electron beam toward the main electron lens. However, the aberration of the lens in such a case is the sum of the aberrations of the pre-focus lens and the main lens. Thus, when the intensity of the electrical field of the pre-focus lens is increased in order to reduce the aberration of the main electron lens, the radius of the electron beam is enlarged due to the effect of the aberration of the pre-focus lens rather than that of the main electron lens.

It is an object of the present invention to provide an electron gun for a color CRT which reduces the effect of the aberration of a pre-focus lens with respect to an electron beam produced from the electron gun so that deterioration of the electron beam can be prevented.

According to the present invention there is provided an electron gun for a color cathode ray tube comprising: a cathode structure including a field emitter for emitting an electron beam, and a focus electrode and a last accelerating

3 electrode, successively installed from the cathode structure, for forming a main electron lens for focusing the electron beam emitted from the field emitter of the cathode structure.

It is preferable that, in use, the voltage applied to the last accelerating electrode is relatively higher than the voltage applied to the focus electrode, and that the diameter of the field emitter is 51100 to 5/10 the diameter of an electron beam passing hole in the focus electrode.

Embodiments of the present invention will now be described by way of example with reference to the accompanying drawings, in which:

FIG. 1 is a sectional view generally illustrating a CRT; FIG. 2 is a plan view partially illustrating the electron is gun of a conventional color CRT; FIG. 3 is a sectional view illustrating the cathode structure employed in the electron gun shown in FIG. 2; FIG. 4 is a graph showing the density of current according to the passing radius of an electron beam in the conventional electron gun; FIG. 5 is a graph showing the charge repulsing force according to passing radius of an electron beam in the conventional electron gun; FIG. 6 is a sectional view illustrating an electron gun for a color CRT according to an embodiment of the present invention; FIG. 7 is a sectional view illustrating a cathode structure shown in FIG. 6; FIG. 8 is a graph showing the density of current 4 according to passing radius of an electron beam in the electron gun according to an embodiment of the present invention; FIG. 9 is a graph showing the charge repulsing force according to the passing radius of an electron beam in the electron gun according to an embodiment of the present invention; FIG. 10 is a diagram showing the path of an electron beam in the electron gun according to an embodiment of the present invention; FIG. 11 is a view showing the path of an electron beam which passes through an electron lens formed between a cathode structure and a focus electrode in the electron gun of an embodiment of the present invention; FIG. 12 is a view showing the path of an electron beam which passes through an electron lens formed between a cathode structure and a last accelerating electrode in the electron gun of an embodiment of the present invention; FIG. 13 is a graph showing a change in the diameter of the electron beam according to the radius of a field emitter forming a cathode structure in the electron gun of an embodiment of the present invention, and

FIG. 14 is a graph showing the change in the diameter of the electron beam according to current in the electron gun according to an embodiment of the present invention.

Referring to FIG. 6, an electron gun for a color CRT according to an embodiment of the present invention comprises a cathode structure 50 for emitting electrons, a focus electrode 61 for focusing an electron beam emitted from the cathode structure 50, and a last accelerating electrode 62.

The cathode structure 50 includes a field emitter 51 which is an electron emitting source and fixed to a bead glass 70.

As shown in FIG. 7, the field emitter 51 comprises a base substrate 51a made of silicon, a plurality of metal tips 51b made of molybdenum as a major component, which is formed on the upper surface of the base substrate 51a, and a conductive layer 51c for applying a predetermined voltage to metal tips 51b. Also, an insulating layer 51d made of S'02 'S formed around metal tips 51b, and a metal layer 51f having a gate 51e to expose the metal tip 51b, is formed on the upper surface of the insulating layer 51d. Since the current applied to a single metal tip 51b installed on the base substrate 51a is approximately 80-10OnA, a current of 1m.A or more, which is enough to excite the phosphor film, can be obtained when there are over 10,000 metal tips.

It is preferable that the diameter of the field emitter

51 is about 5/100 to 5110 that of an electron beam passing hole 61a (in FIG. 6) in the focus electrode 61. The field emitter can have a shape which is vertically-elongate or horizontally-elongate to compensate for the section of the electron beam which lands on the phosphor screen. The voltage applied to the focus electrode 61 is relatively lower than that applied to the last accelerating electrode 62.

The operation of an embodiment of the electron gun for a color CRT according to the present invention, will now be described with reference to FIGS. 6 and 7.

6 When a predetermined voltage is applied to the focus electrode 61 and the last accelerating electrode 62 of the electron gun, a main electron lens is formed between both electrodes. When a predetermined voltage is applied to a metal tip 51b and the metal layer 51f of the cathode structure 50, an electron beam is produced from the metal tip 51b. The emitted electron beam is focused and accelerated while passing through the main electron lens, deflected by a deflection yoke (not shown), and lands on the phosphor film (not shown) thereby to excite phosphorous material thereon.

In accordance with the electron gun for a color cathode CRT operating as above, since electrons are emitted from a plurality of metal tips 51b of the field emitter 51, the current density of the emitted electron beam is constant as shown in FIG. 8. Accordingly, since the current density of the electron beam emitted from the field emitter 51 is constant, the charge repulsing force represented by the square of the current density is uniform as shown in FIG. 9. Thus, it is possible to reduce deterioration of the electron beam.

Referring to FIGS.10, 11 and 12, the electron beams emitted from the plurality of field emitters 51 of the cathode structure 50 (see FIG. 6) proceed in parallel before passing through the electron beam passing hole 61a. However, as the electron beams pass through the electron beam passing hole 61a, the electron beams are deflected to have a larger incident angle by an electron lens 100 which is formed between the cathode structure 50 and the focus electrode 61 and then is incident upon a main electron lens 200. In FIGS. 11 and 7 12, reference numeral 300 indicates the path of the electron beam. At this time, the incident angle can be decreased by reducing the diameter of the field emitter 51. That is, since the incident angle of the electron beam passing the electron lens is affected proportionally by the diameter of the electron beam which passes the electron lens, in addition to the intensity of an electric field of the electron lens, the incident angle can be decreased by reducing the diameter of the field emitter 51, thereby reducing aberration of the main electron lens 200.

Actually, the current applied to the field emitter 51 is in proportion to the square of the radius of the field emitter 51. Thus, reducing the diameter of the field emitter 51 in an effort to reduce the aberration of the main electron lens 200 has its limitation. However, when the diameter of the field emitter 51 is increased in consideration of the current, the incident angle is increased since the electron beam is affected by the electron lens 100. Accordingly, the aberration of the main electron lens 200 increases again.

According to experiments by the present inventor, the aberration of the main electron lens can be reduced when the diameter of the field emitter 51 is about 5/100 to 5110 the diameter of the electron beam passing hole 61a (see FIG. 6) formed in the focus electrode 61.

As described above, with embodiments of the electron gun of the present invention, the process and cost for manufacturing an electron gun can be reduced since the control electrode and the screen electrode of the triode are not 8 necessary. Also, as shown in FIG. 13, the reduction rate of the diameter of the electron beam according to the reduction of the diameter of the field emitter is much greater. For instance, when the diameter of the field emitter is set to be lmm, the diameter of the electron beam can be reduced by 25% or more.

Furthermore, referring to FIG. 14, since the electron gun according to the present invention has no control or screen electrodes to form the triode, there is no encroachment of the electric field from the screen electrode making the emission density of the electron beam uniform. Thus, there is less change in the diameter of the electron beam according to the change in current, and particularly, the diameter change rate of the electron beam according to the current change can be curtailed by 30% compared to the conventional electron gun.

The present invention is not limited to the preferred embodiment described above, and it will be apparent that variations and modifications by those skilled in the art can be effected within the scope of the present invention.

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Claims

CLAIMS:

1. An electron gun for a color cathode ray tube comprising: a cathode structure including a field emitter for emitting an electron beam, and a focus electrode and a last accelerating electrode, located successively from said cathode structure, for forming a main electron lens for focusing the electron beam emitted from the field emitter of said cathode structure.

2. An electron gun for a color cathode ray tube as claimed in claim 1, wherein the diameter of said field emitter is 51100 to 5/10 the diameter of an electron beam passing hole in said focus electrode.

3. An electron gun for a color cathode ray tube as is claimed in claim 1, wherein, in use, the voltage applied to said last accelerating electrode is relatively higher than the voltage applied to said focus electrode.

4. An electron gun for a color cathode ray tube substantially as herein described with reference to Figure 6 with or without reference to any of Figures 7 to 14 of the accompanying drawings.

5. An electron gun for a color cathode ray tube substantially as herein described with reference to Figure 7 of the accompanying drawings.

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