Electric lamp and discharge devices – Discharge devices having a thermionic or emissive cathode
Reexamination Certificate
1999-06-22
2002-08-27
Patel, Nimeshkumar D. (Department: 2879)
Electric lamp and discharge devices
Discharge devices having a thermionic or emissive cathode
C313S238000, C313S292000, C313S495000, C313S496000
Reexamination Certificate
active
06441544
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an electron beam apparatus and also to an image-forming apparatus such as display apparatus that can be realized by using it.
2. Related Background Art
There have been known two types of electron-emitting device; the hot cathode type and the cold cathode type. Of these, the cold cathode type refers to devices including surface conduction electron-emitting devices, field emission type (hereinafter referred to as the FE type) devices and metal/insulation layer/metal type (hereinafter referred to as the MIM type) electron-emitting devices.
Examples of surface conduction electron-emitting device include one proposed by M. I. Elinson, Radio Eng. Electron Phys., 10, 1290, (1965) as well as those that will be described hereinafter.
A surface conduction electron-emitting device is realized by utilizing the phenomenon that electrons are emitted out of a small thin film formed on a substrate when an electric current is forced to flow in parallel with the film surface. While Elinson proposes the use of SnO
2
thin film for a device of this type, the use of Au thin film is proposed in [G. Dittmer: “Thin Solid Films”, 9, 317 (1972)] whereas the use of In
2
O
3
/SnO
2
and that of carbon thin film are discussed respectively in [M. Hartwell and C. G. Fonstad: “IEEE Trans. ED Conf.”, 519 (1975)] and [H. Araki et al.: “Vacuum”, Vol. 26, No. 1, p. 22 (1983)].
FIG. 19
of the accompanying drawings schematically illustrates a typical surface conduction electron-emitting device proposed by M. Hartwell. In
FIG. 19
, reference numeral
3001
denotes a substrate. Reference numeral
3004
denotes an electroconductive thin film normally prepared by producing an H-shaped thin metal oxide film by means of sputtering, part of which eventually makes an electron-emitting region
3005
when it is subjected to an electrically energizing process referred to as “energization forming” as will be described hereinafter. In
FIG. 19
, the thin horizontal area of the metal oxide film separating a pair of device electrodes has a length L of 0.5 to 1 [mm] and a width W of 0.1 [mm]. Note that, while the electron-emitting region
3005
has a rectangular form and is located at the middle of the electroconductive thin film
3004
, there is no way to accurately know its location and contour.
For preparing surface conduction electron-emitting devices including those proposed by M. Hartwell et al., the electroconductive film
3004
is normally subjected to an electrically energizing process, which is referred to as “energization forming”, to produce an electron-emitting region
3005
. In the energization forming process, a constant DC voltage or a slowly rising DC voltage that rises typically at a rate of 1V/min. is applied to given opposite ends of the electroconductive film
3004
to partly destroy, deform or transform the thin film and produce an electron-emitting region
3005
which is electrically highly resistive. Thus, the electron-emitting region
3005
is part of the electroconductive film
3004
that typically contains a gap or gaps therein so that electrons may be emitted from the gap. Note that, once subjected to an energization forming process, a surface conduction electron-emitting device comes to emit electrons from its electron emitting-region
3005
whenever an appropriate voltage is applied to the electroconductive film
3004
to make an electric current run through the device.
Examples of FE type device include those proposed by W. P. Dyke & 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. 20
of the accompanying drawings illustrates in cross section a typical FE type device. Referring to
FIG. 20
, the device comprises a substrate
3010
, an emitter wiring
3011
, an emitter cone
3012
, an insulation layer
3013
and a gate electrode
3014
. When an appropriate voltage is applied between the emitter cone
3012
and the gate electrode
3014
of the device, the phenomenon of field emission appears at the top of the emitter cone
3012
.
Apart from the multilayer structure of
FIG. 20
, an FE type device may also be realized by arranging an emitter and a gate electrode on a substrate substantially in parallel with the substrate.
MIM devices are disclosed in papers including C. A. Mead, “Operation of tunnel-emission Devices”, J. Appl. Phys., 32,646 (1961).
FIG. 21
illustrates a typical MIM device in cross section. Referring to
FIG. 21
, the device comprises a substrate
3020
, a lower metal electrode
3021
, a thin insulation layer
3022
as thin as 100 angstroms and an upper electrode having a thickness between 80 and 300 angstroms. Electrons are emitted from the surface of the upper electrode
3023
when an appropriate voltage is applied between the upper electrode
3023
and the lower electrode
3021
of the MIM device.
Cold cathode devices as described above do not require any heating arrangement because, unlike hot cathode devices, they can emit electrons at low temperature. Hence, the cold cathode device is structurally by far simpler than the hot cathode device and can be made very small. If a large number of cold cathode devices are densely arranged on a substrate, the substrate is free from problems such as melting by heat. Additionally, while the hot cathode device takes a rather long response time because it operates only when heated by a heater, the cold cathode device starts operating very quickly. Therefore, studies have been and are currently being conducted on cold cathode devices.
For example, since a surface conduction electron-emitting device has a particularly simple structure and can be manufactured in a simple manner, a large number of such devices can advantageously be arranged on a large area without difficulty. As a matter of fact, a number of studies have been made to fully exploit this advantage of surface conduction electron-emitting devices. Studies that have been made to arrange a large number of devices and drive them effectively include the one described in Japanese Patent Application Laid-Open No. 64-31332 filed by the applicant of the present patent application.
Applications of surface conduction electron-emitting devices that are currently being studied include charged electron beam sources and electron beam apparatuses such as image displays and image recorders.
U.S. Pat. No. 5,066,883, Japanese Patent Application Laid-Open Nos. 2-257551 and 4-28137 also filed by the applicant of the present patent application disclose image display apparatuses realized by combining surface conduction electron-emitting devices and a fluorescent panel that emits light as it is irradiated with electron beams. An image display apparatus comprising surface conduction electron-emitting devices and a fluorescent panel can be highly advantageous relative to comparable conventional apparatuses such as liquid crystal image display apparatuses that have been popular in recent years because it is of a light emissive type and does not require a backlight to make it glow.
On the other hand, U.S. Pat. No. 4,904,895 of the applicant of the present patent application discloses an image display apparatuses realized by arranging a large number of FE-type devices. Other examples of image display apparatus comprising FE-type devices include the one reported by R. Meyer [R. Meyer: “Recent Development on Microtips Display at LETI”, Tech. Digest of 4th Int. Vacuum Microelectronics Conf., Nagahama, p.p 6-9 (1991)].
Japanese Patent Application Laid-Open No. 3-55738 also filed by the applicant of the present patent application describes an image display apparatus realized by arranging a large number of MIM-type devices.
Of the known image-forming apparatus comprising electron-emitting devices, those of a flat type are attracting attention and expected to replace display apparatus of the cathode ray tube type becaus
Ando Yoichi
Mitsutake Hideaki
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Patel Nimeshkumar D.
Quarterman Kevin
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