Electric lamp and discharge devices: systems – Plural power supplies – Plural cathode and/or anode load device
Reexamination Certificate
1999-09-03
2001-06-12
Vu, David (Department: 2821)
Electric lamp and discharge devices: systems
Plural power supplies
Plural cathode and/or anode load device
C315S169100, C313S336000, C345S074100
Reexamination Certificate
active
06246178
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an electron source having a plurality of electron emitting devices, and an image forming apparatus using the electron source for forming images.
Lately, various efforts have been made in research and development of a thin and large screen display apparatus. The inventor of the present invention has been studying the use of cold cathode as an electron source in a thin and large screen display apparatus.
Conventionally, two types of devices, namely thermionic and cold cathode devices, are known as electron emitting devices. Examples of cold cathode devices are surface-conduction-type emitting devices, field-emission-type devices (to be referred to as FE-type devices hereinafter), and metal/insulator/metal type emission devices (to be referred to as MIM-type devices hereinafter).
A known example of the surface-conduction-type emitting devices is described in, e.g., M. I. Elinson, Radio. Eng. Electron Phys., 10, 1290 (1965) and other examples to be described later.
The surface-conduction-type emitting device utilizes a phenomenon in which electron emission is caused in a small-area thin film formed on a substrate, by providing a current parallel to the film surface. The surface-conduction-type emitting device includes devices using an Au thin film (G. Dittmer, “Thin Solid Films”, 9,317 (1972)), an In
2
O
3
/SnO
2
thin film (M. Hartwell and C. G. Fonstad, “IEEE Trans. ED Conf.”, 519 (1975)), and a carbon thin film (Hisashi Araki, et al., “Vacuum”, Vol. 26, No. 1, p. 22 (1983)), and the like, in addition to an SnO
2
thin film according to Elinson mentioned above.
FIG. 22
is a plan view of the surface-conduction-type emitting device according to M. Hartwell et al. as a typical example of the structures of these surface-conduction-type emitting devices. Referring to
FIG. 22
, reference numeral
3001
denotes a substrate; and
3004
, a conductive thin film made of metal oxide formed by sputtering. This conductive thin film
3004
has an H-shaped plane pattern, as shown in FIG.
22
. An electron emitting portion
3005
is formed by performing an electrification process (referred to as an energization forming process to be described later) with respect to the conductive thin film
3004
. Referring to
FIG. 22
, the spacing L is set to 0.5 to 1 mm, and the width W is set to 0.1 mm. The electron emitting portion
3005
is shown in a rectangular shape at the center of the conductive thin film
3004
for the sake of illustrative convenience, however, this does not exactly show the actual position and shape of the electron emitting portion.
In the above surface-conduction-type emitting device by M. Hartwell et al., typically the electron emitting portion
3005
is formed by performing the electrification process called energization forming process for the conductive thin film
3004
before electron emission. According to the energization forming process, electrification is performed by applying a constant or varying DC voltage which increases at a very slow rate of, e.g., 1 V/min, to both ends of the conductive thin film
3004
, so as to partially destroy or deform the conductive thin film
3004
or change the properties of the conductive thin film
3004
, thereby forming the electron emitting portion
3005
with an electrically high resistance. Note that the destroyed or deformed part of the conductive thin film
3004
or part where the properties are changed has a fissure. Upon application of an appropriate voltage to the conductive thin film
3004
after the energization forming process, electron emission occurs near the fissure.
Known examples of the FE-type devices are described in W. P. Dyke and W. W. Dolan, “Field Emission”, Advance in Electron Physics, 8,89 (1956) and C. A. Spindt, “Physical properties of thin-film field emission cathodes with molybdenum cones”, J. Appl. Phys., 47,5248 (1976).
FIG. 23
is a cross-sectional view of the device according to C. A. Spindt et al. as a typical example of the construction of the FE-type devices. Referring to
FIG. 23
, reference numeral
3010
denotes a substrate;
3011
, an emitter wiring comprising an electrically conductive material;
3012
, an emitter cone;
3013
, an insulating layer; and
3014
, a gate electrode. The device is caused to produce 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 device, the stacked structure of the kind shown in
FIG. 23
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. 24
is a sectional view illustrating a typical example of the construction of the MIM-type device. Referring to
FIG. 24
, reference numeral
3020
denotes a substrate;
3021
, a lower electrode consisting of metal;
3022
, a thin insulating layer having a thickness on the order of 100 &OHgr;; and
3023
, an upper electrode consisting of metal and having a thickness on the order of 80 to 300 &OHgr;. The device is caused to produce 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 device makes it possible to obtain electron emission at a lower temperature in comparison with a thermionic cathode device, a heater for applying heat is unnecessary. Accordingly, the structure is simpler than that of the thermionic cathode device and it is possible to fabricate devices that are finer. Further, even though a large number of devices are arranged on a substrate at a high density, problems such as fusing of the substrate do not easily occur. In addition, the cold cathode device differs from the thermionic cathode device in that the latter has a slow response because it is operated by heat produced by a heater. Thus, an advantage of the cold cathode device is the quicker response.
For these reasons, extensive research into applications for cold cathode devices is being carried out.
By way of example, among the various cold cathode devices, the surface-conduction-type emitting device is particularly simple in structure and easy to manufacture and therefore is advantageous in that a large number of devices can be formed over a large area. Accordingly, research has been directed to a method of arraying and driving a large number of the devices, as disclosed in Japanese Patent Application Laid-Open No. 64-31332, filed by the present applicant.
Further, applications of surface-conduction-type emitting devices that have been researched are image forming apparatuses such as an image display apparatus and an image recording apparatus, charged beam sources, and the like.
As for applications to image display apparatus, research has been conducted with regard to such an image display apparatus using, in combination, surface-conduction-type emitting devices and phosphors which emit light by colliding with electrons, 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 emitting devices 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 has become so popular in recent years, the above-mentioned image display apparatus is superior since it 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 devices 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 app
Alemu Ephren
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Vu David
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