Electric lamp and discharge devices – With luminescent solid or liquid material – Vacuum-type tube
Reexamination Certificate
1998-09-28
2001-05-29
Patel, Ashok (Department: 2879)
Electric lamp and discharge devices
With luminescent solid or liquid material
Vacuum-type tube
C313S309000, C313S336000, C313S351000, C313S497000, C313S311000
Reexamination Certificate
active
06239547
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an electron-emitting source which is arranged in vacuum and emits electrons upon application of the voltage, and a method of manufacturing the same.
Electron-emitting sources are used in an electron gun as a constituent component of the picture tube of, e.g., a television. Such an electron gun (cathode) has a basic arrangement like the one shown in
FIG. 14
in which an electron-emitting layer
1402
is formed at the closed distal end of a cathode cylinder
1401
. The cathode cylinder
1401
incorporates a heater
1403
.
The cathode cylinder
1401
is made of high-purity Ni doped with a reducing agent such as magnesium or silicon, and has a thickness of about 0.1 mm. The electron-emitting layer
1402
is made of a so-called ternary oxide of barium oxide, calcium oxide, and strontium oxide. When the electron-emitting layer
1402
is heated to about 800° C. by the heater
1403
, barium is mainly reduced and liberated. The free barium moves toward the surface of the electron-emitting layer
1402
to facilitate electron emission. Emitted electron beams are collected by a first grid
1404
and focused on a phosphor screen
1409
via a second grid
1405
, a third grid
1406
, a fourth grid
1407
serving as a focusing electrode, and a fifth grid
1408
(FIG.
14
B).
In this manner, the electron-emitting source is used in vacuum. Such electron-emitting sources are used in not only the electron gun of the picture tube but also a vacuum fluorescent display apparatus. This display apparatus is an electron tube using emitted light obtained by bombarding electrons emitted by the electron-emitting source against the phosphor within a vacuum vessel having at least one transparent end. In many cases, the vacuum fluorescent display apparatus employs a triode structure having a grid for controlling the movement of electrons. In the vacuum fluorescent display apparatus, a cathode called a filament has conventionally been used for the electron-emitting source, and thermoelectrons emitted from the cathode are bombarded against the phosphor to emit light.
Such fluorescent display apparatuses include an image tube constituting the pixel of a large-screen display apparatus. The arrangement of an electron-emitting source used in the image tube will be described with reference to FIG.
15
.
The respective components of the image tube are stored in a cylindrical glass valve
1501
constituting a vacuum vessel. The glass valve
1501
incorporates a cathode structure
1510
serving as an electron-emitting source. The cathode structure
1510
has the following arrangement. A back electrode
1512
is formed at the center of a ceramic substrate
1511
. A filament cathode
1513
is fixed above the back electrode
1512
at a predetermined interval. An elliptical grid housing
1514
having a mesh portion
1514
a
is mounted on the ceramic substrate
1511
to cover the back electrode
1512
and the filament cathode
1513
. The mesh portion
1514
a
spherically projects toward a phosphor screen (not shown) arranged inside the glass valve
1501
.
The image tube having this arrangement emits electrons from the cathode structure
1510
in the following manner. A predetermined voltage is applied to the filament cathode
1513
to emit thermoelectrons. A negative voltage with respect to the filament cathode
1513
is applied to the back electrode
1512
. A positive voltage with respect to the filament cathode
1513
is applied to the grid housing
1514
. Then, an electron beam is emitted from the mesh portion
1514
a
of the grid housing
1514
. The electron beam lands on a phosphor screen (not shown) to cause the phosphor screen to emit light.
As described above, thermoelectron emission using an electron-emitting substance is basically adopted in a conventional electron-emitting source used in an apparatus such as a picture tube or a vacuum fluorescent display apparatus using emission by the phosphor upon bombardment of electrons. The electron-emitting substance is made of a so-called ternary oxide of barium oxide, calcium oxide, and strontium oxide. Barium in this ternary oxide is consumed upon reaction with gas during use, and thus the tube is always replenished with barium from the electron-emitting layer. However, barium replenishment is insufficient even if a large current is flowed to emit many electrons. In addition, the electron-emitting substance is heated by electron emission but deteriorated by heat.
Oxides constituting the electron-emitting substance are very unstable in air. For this reason, in manufacturing a conventional electron-emitting source, an electron-emitting layer is first formed from so-called carbonates such as barium carbonate, calcium carbonate, and strontium carbonate, incorporated in a vacuum vessel together with other components, and oxidized while the vacuum vessel is evacuated and aged. Accordingly, manufacturing the conventional electron-emitting source requires many steps.
The electron flow emitted by the conventional electron-emitting source greatly depends on the temperature of the electron-emitting source. If the temperature of the electron-emitting source varies depending on the place, the electron flow also varies.
The conventional electron-emitting source is made of the electron-emitting substance, as described above. However, this substance is weak with respect to the gas produced in the vacuum vessel of the vacuum fluorescent display apparatus and may deteriorate within a short time.
In short, the conventional electron-emitting source suffers the problems of a cumbersome manufacturing process, variations in emitted current flow, low environmental resistance, and a weak structure.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a resistant electron-emitting source which can emit a larger number of electrons and can be easily manufactured.
To achieve the above object, according to an aspect of the present invention, the electron-emitting source is made of carbon nanotubes formed from a columnar graphite layer. The carbon nanotubes may be formed from a multilayer graphite column whose tip is open. In general, a plurality of carbon nanotubes aggregate to a needle-like structure.
With this structure, electrons can be emitted from the tips of the carbon nanotubes upon application of the voltage to the carbon nanotubes in vacuum.
According to another aspect of the present invention, the electron-emitting source is constituted by fixing the carbon nanotubes to the substrate with a conductive adhesive.
With this structure, electrons can be emitted from the tips of the carbon nanotubes upon application of the voltage to the carbon nanotubes via the substrate in vacuum.
According to still another aspect of the present invention, the electron-emitting source is constituted by recessing the substrate, and filling the recess with a plurality of carbon nanotubes.
With this structure, electrons can be emitted from the tips of the carbon nanotubes upon application of the voltage to the carbon nanotubes via the substrate in vacuum.
According to still another aspect of the present invention, a paste obtained by dispersing, in a conductive viscous solution, a plurality of needle-like structures each made of an aggregate of carbon nanotubes is prepared. A pattern of this paste is formed on the substrate. Portions except for the needle-like structures are removed from the surface of the pattern by a predetermined amount to at least partially expose the needle-like structures, thereby manufacturing an electron-emitting source in which the carbon nanotubes are fixed to the substrate. The portions except for the needle-like structures are removed by laser irradiation or plasma processing.
With this processing, the needle-like structures can be exposed. By laser irradiation, the portions of the needle-like structures except for the carbon nanotubes can be removed to expose the electron-emitting tips.
According to still another aspect of the present invention, a paste obtained by dispersing, in a condu
Morikawa Mitsuaki
Nagasako Takeshi
Saito Yahachi
Uemura Sashiro
Yotani Junko
Blakely & Sokoloff, Taylor & Zafman
Ise Electronics Corporation
Patel Ashok
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