Image forming apparatus with spacer

Details Image forming apparatus with spacer Image forming apparatus with spacer

1998-04-08

2001-08-21

Patel, Ashok (Department: 2879)

Electric lamp and discharge devices

With luminescent solid or liquid material

Vacuum-type tube

C313S292000, C313S336000, C313S351000, C313S496000, C313S497000

Reexamination Certificate

active

06278233

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an image forming apparatus such as an image display apparatus using an electron source.
2. Description of the Related Art
Two types of elements, namely hot 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, 1290, (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. 17
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. 17
, 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. 17
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 are not necessarily represented faithfully here.
In 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 crack 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 crack 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. 18
, 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. 18
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. 19
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 a field emission from the surface of the upper electrode
2023
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 hot cathode element, a heater for applying heat is unnecessary. Accordingly, the structure is simpler than that of the hot 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 hot 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 using the combination of the surface-conduction type electron emission elements and phosphors is expected to have characteristics superior to those of the conventional image display device of other types. For example, in comparison with a liquid-crystal display device that has become so popular in recent years, the above-mentioned image display device emits its own light and therefore does not require back-lighting. It also has a wider viewing angle.
A method of driving a number of FE-type elements in a row is disclosed, for example, in the specification of U.S. Pat. No. 4,904,895 filed by the present applicant. A planar-type display apparatus reported by Meyer et al., for example, is known as an example of an application of an FE-type element to an image display apparatus. [R. Meyer: “Recent Development

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