Flat display

Abstract: Invention subject is a thin type image display device for displaying an image by emitting light from a fluorescer with irradiation of electron beams thereto. The device has a cathode panel (3) between a front panel (1) and a back panel (2) in such a manner that a space (4) exist between the cathode panel (3) and the back panel (2), wherein through holes (10) for diffusion of getters are formed in the cathode panel (3) to maintain the image quality at the center of a display screen, or the cathode panel (3) is supported by getters to maintain a required pressure, hence attaining a higher image quality even on a large-sized display screen. A gate electrode (6) may be composed of a getter material.

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thin type image display device for use in a video apparatus such as a color television receiver. 2. Description of the Prior Art Relative to a system for realizing a thin type color television receiver for example, there is proposed an image display device wherein a cathode serving as an emission source is disposed in a thin vacuum panel assembly composed of a front panel and a back panel, and electron beams are emitted from such cathode to excite a fluorescent member to thereby display a desired image. In such known device, a getter is employed for adsorbing residual gases (inclusive of gases generated from component elements) so as to maintain a proper pressure in the vacuum panel assembly. Since it is impossible to provide such getter in any portion corresponding to the effective screen area, the getter is placed mostly in a peripheral region between the front panel and the cathode outside of the effective screen area. However, if the getter is disposed in the periphery of the effective screen area, the portion other than the effective screen area is dimensionally increased to consequently reduce the substantial effective screen with another disadvantage relative to diminution of the gas adsorption effect at the center of the screen, hence raising a problem with regard to deterioration of the image quality. To the contrary, if the portion other than the effective screen area is minimized, it is impossible to contain a sufficient amount of the getter required for maintaining the proper pressure to eventually fail in attaining a satisfactory image quality. There is known another conventional thin type image display device as disclosed in Japanese Patent Laid-open No. Sho 60 (1985)-101844, wherein a space is formed between a cathode and a back panel, and some getter is contained in such space. In the above device where the getter is disposed between the cathode and the back panel, a sufficient area of the effective screen can be ensured, and also a required amount of the getter can be contained for maintaining a proper pressure. In the device mentioned, however, the getter is disposed behind the cathode on the reverse side with respect to the front panel where out-gases are generated mostly, so that the out-gases at the center of the display screen cannot be adsorbed instantaneously due to the impediment induced by the cathode. Consequently it becomes impossible to maintain the proper pressure in the vacuum panel assembly, and there occurs deterioration of the cathode as well. Furthermore the image quality is degraded at the center of the screen to eventually fail in attaining a higher image quality. There also exists a disadvantage that a satisfactory vacuum pressure withstanding capability is not achievable since the cathode is supported merely at the outer periphery thereof. The above device is so constituted that the cathode is supported via a glass plate from behind by means of U-shaped spring members disposed at four corners of the back panel. However, such structure is not exactly suited for ensuring a pressure withstanding capacility, and the cathode is prone to be broken as the pressure in the vacuum panel is rendered high particularly in a large-sized display screen. OBJECTS AND SUMMARY OF THE INVENTION It is an object of the present invention to provide an improved thin type image display device capable of containing a sufficient amount of getter for maintaining a required pressure, wherein the image quality can be maintained at the center of a display screen so that a superior image quality is attainable even on a large-sized screen. Another object of the present invention is to provide an improved thin type image display device wherein out-gases are adsorbable instantaneously and a low pressure can be maintained. And a further object of the present invention resides in providing an improved thin type image display device which ensures a superior vacuum pressure withstanding capability even in a large-sized display screen. According the present invention, there is provided an image display device having a cathode panel between a front panel and a back panel in such a manner that a space is existent between the cathode panel and the back panel, and some getter is contained in such space, wherein a plurality of through holes are formed in the cathode panel. In this image display device, a space is existent between a back panel and a cathode panel disposed opposite to a front panel, so that a sufficient amount of getters for maintaining a required pressure can be contained in such space. Furthermore, a plurality of through holes for diffusion of gases are formed in the cathode panel to realize adsorption of residual gases at the center of a display screen via such through holes, thereby attaining a superior image quality even on a large-sized display screen. In an embodiment of the present invention, there is provided an image display device of the above mentioned type, wherein the cathode panel is supported in the space by a plurality of getters. In this image display device, a space is existent between a back panel and a cathode panel disposed opposite to a front panel, so that a sufficient amount of getters for maintaining a required pressure can be contained in such space. Furthermore, the cathode panel is supported in such space by a plurality of getters, so that the pressure applied to the cathode panel is dispersed by the getters to consequently prevent breakage of the cathode panel. The above and other features and advantages of the present invention will become apparent from the following description which will be given with reference to the illustrative accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a sectional view of an exemplary image display device embodying the present invention; Fig. 2 is an enlarged sectional view of principal components in the device of Fig. 1; Fig. 3 is a partially cutaway enlarged perspective view of principal components in an exemplary cathode panel composed of extremely small cold cathodes; Fig. 4 is a sectional view of another exemplary image display device embodying the present invention; Fig. 5 is an enlarged sectional view of principal components in the device of Fig. 4; Fig. 6 is a sectional view of a further exemplary image display device embodying the present invention where a cathode panel is supported by getters; Fig. 7 is an enlarged sectional view of principal components in the device of Fig. 6; Figs. 8 and 9 illustrate modifications of the image display device shown in Fig. 6; and Figs. 10 and 11 are schematic perspective views showing other examples of the cathode panel. DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. As shown in Figs. 1 through 3, the image display device in a first embodiment includes a cathode panel 3 serving as an emission source and disposed in a vacuum receptacle which comprises a front panel 1 and a back panel 2 of glass. The front panel 1 has, on its inner wall 1a, fluorescent stripes in the colors of, for example, red (R), green (G) and blue (B), thereby forming a fluorescent display screen (not shown). Meanwhile the back panel 2 is joined to the front panel 1 in a state where the two panels are sealed up, and an internal space surrounded with the front panel 1 and the back panel 2 is evacuated. The cathode panel 3 is interposed between the fornt panel 1 and the back panel 2, and electron beams emitted from the cathodes provided on the cathode panel 3 are irradiated to the fluorescent display screen of the front panel 1. The cathode panel 3 is disposed opposite to both the front panel 1 and inner walls 1a, 2a of the back panel 2, in such a manner that a space 4 is existent between the cathode panel 3 and the inner wall 2a of the back panel 2. The space 4 is used for containing getters (not shown) composed of an alloy of Ba, Ti or Zn for adsorbing gases generated from component elements (such as undermentioned extraction electrodes 6 and so forth) which are formed on the cathode panel 3. The space 4 is so defined as to have adequate dimensions for receiving a suffiecient amount of the getter to maintain a required pressure. The cathode panel 3 in this embodiment has a multiplicity of extremely small cold cathodes arrayed as illustrated in Fig. 2. There are included cathodes 5 each serving as an emission source, extraction electrodes 6 for extracting electron beams from the cathodes 5, the cathode lines 7 for supplying potentials (potential signals) to the cathodes 5, and isolation layers 8 for isolating the extraction electrodes 6 from the cathode lines 7. Such components are arranged on a base plate 9 by a semiconductor manufacturing process. The cathodes 5 are composed of molybdenum, tungsten or lanthanum hexaboride (La B₆) for example and are shaped into extremely small conical projections each having a diameter of 1.0 micron or less. And such cathodes 5 are arrayed on the base plate 9 correspondingly to individual fluorescent dots provided on an inner wall la of the front panel 1. The extraction electrodes 6 for extracting electron beams from the cathodes 5 are formed on the isolation layers 8 which are so shaped as to surround the cathodes 5 arcuately. The extraction electrodes 6 are formed in a manner to constitute a matrix structure by the cathode lines 7 provided between the cathodes 5 and the base plate 9. Therefore, when potential signals are supplied to the cathode lines 7 provided under the cathodes 5 in the cathode panel 3, electron beams are extracted from the tips of the cathodes 5 by the extraction electrodes 6. The electron beams can be selectively emitted from the cathodes 5 by selective operation of the extraction electrodes 6 and the cathode lines 7. In the cathode panel 3 so constituted as mentioned above, a plurality of getter-diffusing through holes 10 are formed for effectively exerting the action of getters, as shown in Figs. 4 and 5. The through holes 10 are positioned in suitable positions of the front panel 1 corresponding at least to the effective screen area, in such a manner as to pierce through the extraction electrodes 6, the isolation layers 8, the cathode lines 7 and the base plate 9 sequentially in the direction of depth. Consequently any residual gases at the center of the screen in the front panel 1 are adsorbed via the through holes 10 by the getters provided in the space 4 between the back panel 2 and the cathode panel 3. In particular, since the field emission cathodes employed in this embodiment are prone to be harmfully affected by gas-induced contamination, the image quality is degraded unless satisfactory gas adsorption effect is achieved over the entire surface of the screen, and therefore the through holes 10 formed in the cathode panel 3 are effective to avert such a problem. In the image display device of the constitution mentioned, electron beams emitted from the tips of the cathodes 5 operated selectively are irradiated to the fluorescent stripes formed on the inner wall 1a of the front panel 1. And individual fluorescence dots of the fluorescent stripes at the irradiated spots are caused to emit light to thereby form a color image. In this stage, some gases are generated from the extraction electrodes 6 and so forth provided on the cathode panel 3, but such gases are adsorbed via the through holes 10 in the cathode panel 3 by the getters provided in the space 4 between the cathode panel 3 and the back panel 2. Accordingly, in the image display device of the present invention, the image quality can be maintained the center of the screen to eventually realize a higher image quality in the entire screen area. Further in the device of the present invention where getters are provided between the cathode panel 3 and the back panel 2, a sufficient amount of the getters can be contained to thereby maintain a proper pressure in the vacuum receptacle. In a further embodiment of the present invention, as shown in Figs. 6 and 7, a plurality of cylindrical getters 11 sufficient in amount for maintaining a required pressure are received in the space 4. More specifically, such getters 11 are placed in contact with both the inner wall 2a of the back panel 2 and the back surface 3a of the cathode panel 3 in a manner to support the cathode panel 3. The getters 11 are so disposed as to uniformly disperse any pressure applied to the cathode panel 3, thereby preventing breakage of the cathode panel 3. Accordingly, even when the pressure in the vacuum receptacle is rendered high in accordance with a dimensional increase of the display screen, it is still possible to completely support the cathode panel 3, hence preventing breakage of the cathode panel 3 with certainty. In addition to the above, some auxiliary members 11' of round bars or the like may be provided at the respective centers of cylindrical getters 11, as illustrated in Fig. 8. In such a structure, the vacuum pressure withstanding capability can further be enhanced. In a modification, as shown in Fig. 9, getter-diffusing through holes 10 for effectively exerting the action of the getters 11 may be formed at suitable positions in the cathode panel 3 corresponding to the effective screen area. Then any residual gases generated in the center portion of the screen area are adsorbed by the getters 11 via the through holes to consequently improve the image quality at the center of the display screen. In the image display device of the present invention mentioned, a variety of changes and modifications may be contrived within the scope not departing from the inventive concept thereof. For example, in place of the extremely small cold cathodes used for emitting electron beams in the above embodiment, it is possible to employ a cathode panel composed of semiconductor elements as illustrated in Fig. 11. The cathode panel in the above modification comprises a back electrode 12, filament cathodes 13, a first grid electrode 14, vertical deflection electrodes 15, signal modulation electrodes 16 and a horizontal deflection electrode 17, as illustrated in Fig. 10. In the cathode panel mentioned above, a matrix is constituted by a plurality of filament electrodes 13 disposed horizontally at predetermined vertical intervals and a plurality of signal modulation electrodes 16 disposed vertically at predetermined intervals, so as to control the electron beams emitted from the filament cathodes 13. Further in the above cathode panel, the vertical deflection system is constituted by, e.g., 15 pairs of vertical deflection electrodes 15 arranged correspondingly to the filament cathodes 13; while the horizontal deflection system is constituted by, e.g., 200 pairs of horizontal deflection electrodes 17 arranged correspondingly to the signal modulation electrodes 16. When different negative pulse voltages are sequentially applied to the filament cathodes 13 in the cathode panel of the above-described constitution, the potential at the first grid electrode 14 is rendered positive relatively, and a positive electric field is generated in the periphery of each filament cathode 13, so that the band-shaped electron beam is emitted toward the first grid electrode 14. Such band-shaped electron beam is advanced via the through hole formed in the first grid electrode 14 and is thereby divided into electron beams equal in number to the through holes. Thereafter such divided electron beams are vertically converged at the same time to be vertically deflected and then are emitted to the fluorescent stripes on the front panel 18, thereby causing the individual fluorescent dots to emit light therefrom. In a further modification, it is also possible to employ a cathode panel composed of semiconductor elements as illustrated in Fig. 11. The cathode panel in Fig. 11 is so constituted that a bias source 21 is provided for applying a bias between a p-type substrate 19 and an n-type impurity region 20, and also a signal source 23 is provided for applying a gating voltage between the n-type impunity region 20 and a gate electrode 22 disposed via an insulator layer 25 of silicon dioxide. In the cathode panel mentioned above, a bias is applied between the p-type substrate 19 and the n-type impurity region 20, and gating is executed by the n-type impurity region 20 and the gate electrode 22, so that electrons are emitted from a p-n junction 24 which is thin as 10 nm or so. The emission of electrons is controlled by the signal source 23.

Claims: An image display device having a cathode panel (3) between a front panel (1) and a back panel (2) in such a manner that a space (4) is existent between the cathode panel (3) and the back panel (2), and some getter is contained in such space, characterized in that a plurality of through holes (10) for diffusion of gases are formed in said cathode panel (3). An image display device as claimed in claim 1, wherein said cathode panel (3) is supported by a plurality of getters (11) in said space.

Inventors: INOUE JUNICHI C O SONY CORPORA, NAKAYAMA AKIRA C O SONY CORPOR, YAMAMOTO MASANOBU C O SONY COR, INOUE, JUNICHI, C/O SONY CORPORATION, NAKAYAMA, AKIRA, C/O SONY CORPORATION, YAMAMOTO, MASANOBU, C/O SONY CORPORATION
Applicants: SONY CORP, SONY CORPORATION
Application year: 1991
Main classification: H01J31
IPC codes: H01J29, H01J31