Image forming apparatus

Details Image forming apparatus Image forming apparatus

1999-09-08

2002-07-16

Patel, Vip (Department: 2879)

Electric lamp and discharge devices

With luminescent solid or liquid material

Vacuum-type tube

C313S292000, C313S496000, C313S497000

Reexamination Certificate

active

06420824

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an image forming apparatus having electron emission elements and spacers in a vacuum envelope.
2. Description of the Related Art
Flat panel displays of large areas have been the focus of much research and development in recent years.
In general, an image forming apparatus using electrons is equipped with an envelope for maintaining a vacuum, electron sources and their drive circuitry for emitting electrons, an image forming member having phosphors or the like for emitting light owing to electron bombardment, accelerating electrodes for accelerating electrons toward the image forming member, and a high-voltage power supply for the accelerating electrodes. Further, in an image forming apparatus using a flat envelope as in the manner of a flat-panel display having a large screen area, there are cases where supporting columns (spacers) are disposed within the envelope as structures resistant to atmospheric pressure.
Two types of elements, namely thermionic cathode elements and cold cathode elements, are known as electron emission elements for constructing the electron sources mentioned above. Examples of cold cathode elements are surface-conduction electron emission elements, electron emission elements of the field emission type (abbreviated to “FE” below) and metal/insulator/metal type (abbreviated to “MIM” below).
An example of the surface-conduction electron emission element is described by M. I. Elinson, Radio. Eng. Electron Phys., 10 (1965). There other examples as well, as will be described later.
The surface-conduction electron emission element makes use of a phenomenon in which an electron emission is produced in a small-area thin film, which has been formed on a substrate, by passing a current parallel to the film surface. Various examples of this surface-conduction electron emission element have been reported. One relies upon a thin film of SnO
2
according to Elinson, mentioned above. Other examples use a thin film of Au [G. Dittmer: “Thin Solid Films”, 9.317 (1972)]; a thin film of In
2
O
3
/SnO
2
(M. Hartwell and C. G. Fonstad: “IEEE Trans. E.D. Conf.”, 519 (1975); and a thin film of carbon (Hisashi Araki, et al: “Vacuum”, Vol. 26, No. 1, p. 22 (1983).
FIG. 45
is a plan view of the element according to M. Hartwell, et al., described above. This element construction is typical of these surface-conduction electron emission elements. As shown in
FIG. 45
, numeral
3001
denotes a substrate. Numeral
3004
denotes an electrically conductive thin film comprising a metal oxide formed by sputtering and is formed into a flat shape resembling the letter “H” in the manner illustrated. The conductive film
3004
is subjected to an electrification process referred to as “electrification forming”, described below, whereby an electron emission portion
3005
is formed. The spacing L in
FIG. 45
is set to 0.5~1 mm, and the spacing W is set to 0.1 mm. For the sake of illustrative convenience, the electron emission portion
3005
is shown to have a rectangular shape at the center of the conductive film
3004
. However, this is merely a schematic view and the actual position and shape of the electron emission portion may be represented in other ways.
In the above-mentioned conventional surface-conduction electron emission elements, especially the element according to Hartwell, et al., generally the electron emission portion
3005
is formed on the conductive thin film
3004
by the so-called “electrification forming” process before electron emission is performed. According to the forming process, a constant DC voltage or a DC voltage which rises at a very slow rate on the order of 1 V/min is impressed across the conductive thin film
3004
to pass a current through the film, thereby locally destroying, deforming or changing the property of the conductive thin film
3004
and forming the electron emission portion
3005
, the electrical resistance of which is very high. A fissure is produced in part of the conductive thin film
3004
that has been locally destroyed, deformed or changed in property. Electrons are emitted from the vicinity of the fissure if a suitable voltage is applied to the conductive thin film
3004
after electrification forming.
Known examples of the FE type are described in W. P. Dyke and W. W. Dolan, “Field Emission”, Advance in Electron Physics, 8.89 (1956), and in C. A. Spindt, “Physical Properties of Thin-Film Field Emission Cathodes with Molybdenum Cones,” J. Appl. Phys., 47, 5248 (1976).
A typical example of the construction of an FE-type element is shown in
FIG. 46
, which is a sectional view of the element according to Spindt, et al., described above. The element includes a substrate
3010
, emitter wiring
3011
comprising an electrically conductive material, an emitter cone
3012
, an insulating layer
3013
and a gate electrode
3014
. The element is caused to produce a field emission from the tip of the emitter cone
3012
by applying an appropriate voltage across the emitter cone
3012
and gate electrode
3014
.
In another example of the construction of an FE-type element, the stacked structure of the kind shown in
FIG. 46
is not used. Rather, the emitter and gate electrode are arranged on the substrate in a state substantially parallel to the plane of the substrate.
A known example of the MIM type is described by C. A. Mead, “Operation of Tunnel Emission Devices,” J. Appl. Phys., 32, 646 (1961).
FIG. 47
is a sectional view illustrating a typical example of the construction of the MIM-type element. The element includes a substrate
3020
, a lower electrode
3021
consisting of a metal, a thin insulating layer
3022
having a thickness on the order of 100 Å, and an upper electrode
3023
consisting of a metal and having a thickness on the order of 80~300 Å. The element is caused to produce an emission from the surface of the upper electrode
3023
by applying an appropriate voltage across the upper electrode
3023
and lower electrode
3021
.
Since the above-mentioned cold cathode element makes it possible to obtain an electron emission element at a lower temperature in comparison with a thermionic cathode element, a heater for applying, heat is unnecessary. Accordingly, the structure is more simple than that of the thermionic cathode element, and it is possible to fabricate elements that are more slender. Further, even though a large number of elements are arranged on a substrate at a high density, problems such as fusing of the substrate do not readily arise. In addition, the cold cathode element differs from the thermionic cathode element in that the latter has a slow response speed because it is operated by heat produced by a heater. Thus, an advantage of the cold cathode element is a quicker response speed.
For these reasons, extensive research into applications for cold cathode elements is being carried out.
By way of example, among the various cold cathode elements, the surface-conduction electron emission element is particularly simple in structure and easy to manufacture and therefore is advantageous in that a large number of elements can be formed over a large area. Accordingly, research has been directed to a method of arraying and driving a large number of elements, as disclosed in Japanese Patent Application Laid-Open No. 64-31332, filed by the applicant.
Further, applications of surface-conduction electron emission elements that have been researched are image forming devices such as image display devices and image recording devices, as well as charged beam sources, etc.
As for applications to image display devices, research has been conducted with regard to such devices using, in combination, surface-conduction type electron emission elements and phosphors which emit light in response to irradiation with an electron beam, as disclosed, for example, in the specifications of U.S. Pat. No. 5,066,833 and Japanese Patent Application Laid-Open (KOKAI) Nos. 2-257551 and 4-28137 filed by the present applicant. The image display device us

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