Image-forming apparatus and fabrication method therefor

Details Image-forming apparatus and fabrication method therefor Image-forming apparatus and fabrication method therefor

1999-09-02

2002-12-03

Patel, Nimeshkumar D. (Department: 2879)

Electric lamp and discharge devices

With getter

Electrode includes getter, supports getter, or is connected...

C313S553000, C313S554000

Reexamination Certificate

active

06489720

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to image-forming apparatuses having a vacuum and a fabrication method therefor.
2. Description of the Related Art
In a so-called image-forming apparatus in which a phosphor in an image display member is irradiated with an electron beam emitted from an electron source so that the phosphor emits light to display an image, the inside of an envelope having the electron source and the image display member must be kept at a high vacuum. This is because of the fact that if gases are generated in the envelope and the pressure is increased, the electron source is adversely affected depending on the type of gases, and the amount of electron emission is decreased. Thus, a bright image cannot be displayed.
The generated gases are ionized by the electron beam, and the ionized gases collide with the electron source because they are accelerated by an electric field and may damage the electron source. Furthermore, in some cases, a discharge may take place in the envelope, resulting in the apparatus breaking.
Generally, the envelope of an image-forming apparatus includes a plurality of glass components. In such a case, the components are joined to each other by glass frit or the like. Once the joining is completed, the pressure is maintained by a getter placed in the envelope. As such a getter, in a typical CRT, an alloy having Ba as a major constituent is employed. In the evacuated envelope, in which joining has been completed, the alloy is heated by passing an electric current or by high frequency irradiation so that an evaporated film is formed on the inner wall of the envelope, and thus gases generated inside are adsorbed and high vacuum conditions are maintained. For this purpose, an evaporative getter having a clean metal surface, such as Ba, is employed, which adsorbs evaporated gases by heating in a vacuum.
However, in a flat-display image-forming apparatus using an electron source in which many electron-emitting elements are disposed on a flat substrate, that has been recently under development, in comparison with the CRT, the ratio of the volume of the envelope to the area of the inner wall of the envelope emitting gases is substantially decreased. In the case of the comparable generation of gases, the pressure inside the envelope increases, and its adverse effect may become rather serious.
In the CRT, since the envelope has an ample inside wall surface in which the electron source or the image display member are not placed, the getter as described above can be mounted thereon by evaporation or the like. In the flat image-forming apparatus using electron-emitting elements, most of the inside surface area of the envelope is occupied by the electron source and the image-forming member. Therefore, if a getter as the evaporated film adheres thereto, inconveniences such as a short circuit may occur, and thus the position in which the getter is mounted is strongly restricted.
Generally, a spot such as a corner of the envelope is used for forming the getter film so that the getter material does not adhere to the region occupied by the image-forming member and the electron source (hereinafter referred to as “an image display region”). If the display area is increased more than a certain amount, it is not possible to secure an area of the evaporated getter film sufficient for the amount of emission gases in the envelope.
In order to overcome the above and to secure a sufficient area of the getter film, a method is disclosed in Japanese Patent Laid-Open No. 5-151916, in which, as shown in
FIG. 2A
, a wire getter
1008
is stretched tightly in the exterior of an image display region between a phosphor
1006
and a field emission element
1007
which are opposed to each other in an envelope
1005
, for example, in the periphery of the envelope
1005
, and by using the wire getter
1008
, a getter film
1009
is formed by evaporation on the inner wall of the periphery. Another method is disclosed in Japanese Patent Laid-Open No. 4-289640, in which, as shown in
FIG. 2B
, on the side of a space between a faceplate
1014
(an image display member) and a rear plate
1012
(an electron-source substrate) constituting an envelope, a getter chamber
1015
having a getter material
1018
for forming a getter film in the envelope is attached. Alternatively, another method is disclosed in Japanese Patent Laid-Open No. 1-235152, in which a given space is provided between an electron-source substrate and a rear plate of an envelope, and a getter film is formed therein.
Additionally, in the thin (flat) image-forming apparatus, when the generation of gases in the vacuum envelope is treated, the pressure is easily increased locally. With respect to an image display apparatus having an electron-source substrate and an image display member, in an evacuated envelope, gases are generated in the image display region irradiated with an electron beam and by the electron source itself.
In the conventional CRT, since an image display member and an electron source are separated and there is a space between them for forming a sufficient getter film smoothly, gases generated from the image display member are widely diffused before reaching the electron source and a portion thereof is adsorbed by the getter film, and thus the pressure is not extremely increased at the electron source. Since a getter film is also provided around the electron source, the pressure is not strongly increased locally.
However, in the thin image-forming apparatus, since an image display member and an electron-source substrate are placed closely, gases generated from the image display member reach the electron source before being sufficiently diffused, resulting in a local pressure increase. In particular, in the center of the image display region, a higher local pressure increase is observed in comparison with the periphery, because the distance to the getter film is longer than the distance between the image display region and the electron-source substrate, and the gases cannot be diffused to the region where the getter film is formed. Therefore, the generated gases are ionized by electrons released from the electron source and are accelerated by an electric field formed between the electron source and the image display member, and thus the electron source may be broken or damaged.
In view of the above, a thin image-forming apparatus provided with a specific structure, that is, an image-forming apparatus in which a getter material is disposed in the image display region so that the generated gases are immediately adsorbed, is also disclosed. For example, in accordance with an apparatus disclosed in Japanese Patent Laid-Open No. 4-12436, with respect to an electron source having a gate electrode for supplying electrons for an electron beam, the gate electrode is composed of a getter material, and a field emission electron source having a conical protrusion as a negative electrode and a semiconductor electron source having a pn junction are described as examples. In accordance with a method disclosed in Japanese Patent Laid-Open No. 63-181248, with respect to a flat panel display having a structure in which an electrode, such as a grid, for controlling an electron beam is disposed between a cathode (negative electrode) group and a faceplate in an evacuated envelope, a getter material film is formed on the controlling electrode.
In U.S. Pat. No. 5,453,659, a structure is disclosed in which a getter is formed in the interstices of phosphors in the form of stripes on an image display member (anode plate). In this case, the getter is electrically isolated from the phosphors and a conductor which is electrically connected thereto, and the getter is activated by the irradiation with electrons emitted from the electron source by applying an appropriate electric potential, or by heating the getter by passing an electric current.
Meanwhile, in a thin image-forming apparatus, it is desirable to simplify the structure and fabrication method in view of production technology,

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