Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
1998-03-23
2003-06-17
Mengistu, Amare (Department: 2673)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C313S309000, C315S169100
Reexamination Certificate
active
06580407
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an electron-beam generating device having a plurality of matrix-wired cold cathode elements and to a method of driving the device. The invention further relates to an image forming apparatus to which the electron-beam generating device is applied, particularly a display apparatus using phosphors as image forming members.
2. Description of the Related Art
Two types of elements, namely thermionic cathode elements and cold cathode elements, are known as electron emission elements. 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 Ellinson, 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: “Shinkuu”, Vol. 26, No. 1, p. 22 (1983).
FIG. 1
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. 1
, numeral
3001
denotes a substrate. Numeral
3004
denotes an electrically conductive thin film comprising a metal oxide formed by sputtering. The conductive film
3004
is subjected to an electrification process referred to as “energization forming”, described below, whereby an electron emission portion
3005
is formed. The spacing L in
FIG. 1
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 represented faithfully here.
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 “energization 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 energization 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. 2
, 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. 2
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. 3
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
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 at a lower temperature in comparison with a thermionic cathode element, a heater for applying heat is unnecessary. Accordingly, the structure is simpler than that of the thermionic cathode element and it is possible to fabricate elements that are finer. 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 apparatus such as image display apparatus and image recording apparatus, charged beam sources, etc.
As for applications to image display apparatus, research has been conducted with regard to such an apparatus 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. 5,066,883 and Japanese Patent Application Laid-Open (KOKAI) Nos. 2-257551 and 4-28137 filed by the present applicant. The image display apparatus 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 apparatus of other types. For example, in comparison with a liquid-crystal display apparatus that have become so popular in recent years, the above-mentioned image display apparatus 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 flat-type display apparatus reported by Meter et al., for example, is known as an example o
Asai Akira
Suzuki Hidetoshi
Suzuki Noritake
Yamano Akihiko
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Mengistu Amare
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