Electric lamp and discharge devices – With luminescent solid or liquid material – Vacuum-type tube
Reexamination Certificate
2001-09-12
2004-01-27
O'Shea, Sandra (Department: 2875)
Electric lamp and discharge devices
With luminescent solid or liquid material
Vacuum-type tube
C313S309000
Reexamination Certificate
active
06683408
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electron-emitting device for emitting electrons by the application of a voltage, an electron source and an image-forming apparatus employing the electron-emitting device.
2. Related Background Art
Conventionally, two types of electron sources, a thermionic cathode electron source and a cold cathode electron source are known as an electron-emitting device. The cold cathode electron source includes a field emission (hereinafter referred to as FE) electron-emitting device, a metal/insulator layer/metal (hereinafter referred to as MIM) electron-emitting device, a surface conduction electron-emitting device and the like.
As examples of the FE electron-emitting device, those disclosed in W. P. Dyke & W. W. Dolan, “Field Emission”, Advance in Electron Physics, 8, 89 (1956), C. A. Spindt, “Physical Properties of thin-film field emission cathodes with molybdenium cones”, J. Appl. Phys., 47,5248 (1976) and the like are known.
As examples of the MIM electron-emitting device, those disclosed in C. A. Mead, “Operation of Tunnel-Emission Devices”, J. Apply. Phys., 32,646 (1961) and the like are known.
In addition, in recent examples, Toshiaki Kusunoki, “Fluctuation-free electron emission from non-formed metal-insulator-metal (MIM) cathodes fabricated by low current anodic oxidation”, Jpn. J. Appl. Phys. Vol. 32 (1993) pp. L1695, Mutsumi Suzuki et al., “An MIM-Cathode array for Cathode Luminescent Displays”, IDW '96, (1996) pp. 529 and the like are studies.
As examples of the surface conduction electron-emitting device, there are those described in an Elinson report (M. I. Elinson, Radio Eng. Electron Phys., 10 (1965)) or the like. This surface conduction electron-emitting device utilizes a phenomenon that electron emission is caused by flowing a current to a thin film with a small area, which is formed on a substrate, in parallel with the surface of the film.
As the surface conduction electron-emitting device, one using an SnO
2
thin film described in the above-mentioned Elinson report, one using an Au thin film (G. Dittmer, Thin Solid Films, 9,317 (1972)), one using an In
2
O
3
/SnO
2
thin film (M. Hartwell and C. G. Fonstad, IEEE Trans. ED Conf., 519 (1983)) and the like are reported.
SUMMARY OF THE INVENTION
However, in the case of the above-mentioned conventional art, there are problems as described below.
In order to apply an electron-emitting device to an image-forming apparatus, an emission current for causing a phosphor to emit light with sufficient luminance is required. In addition, a diameter of an electron beam irradiated on a phosphor is required to be small for making a display high in definition. Moreover, it is important that the electron-emitting device can be manufactured easily.
As an example of the conventional FE electron-emitting device, a Spindt type electron emitting-device is shown in FIG.
13
. In
FIG. 13
, reference numeral
1
denotes a substrate,
4
denotes a cathode electrode layer (low potential electrode),
3
denotes an insulating layer,
2
denotes a gate electrode layer (high potential electrode),
5
denotes a microchip and
6
denotes an equipotential surface.
When a bias is applied between the microchip
5
having a curvature r and the gate electrode layer
2
, electrons are emitted from the tip of the microchip
5
and heads for an anode. An amount of the emitted electrons is determined by a work function of a distance d between the gate electrode layer
2
and the tip of the microchip
5
, a gate voltage Vg and a material of an emitting portion. That is, it is an element for determining performance of a device to manufacture it with good control of the distance d between the gate electrode layer
2
and the microchip
5
.
A general manufacturing process of the Spindt type electron-emitting device is shown in FIG.
14
.
The manufacturing process will be described along this figure. First, the cathode electrode layer
4
made of Nb or the like, the insulating layer
3
made of SiO
2
or the like and the gate electrode layer
2
made of Nb or the like are stacked in this order on the substrate
1
made of glass. Thereafter, a circular opening (fine hole) perforating through the gate electrode layer
2
and the insulating layer
3
is formed by a reactive ion etching method (FIG.
14
A).
Then, a sacrifice layer
7
made of aluminum or the like is formed on the gate electrode layer
2
by diagonal evaporation or the like (FIG.
14
B).
A microchip material
8
such as molybdenum is deposited by a vacuum evaporation method on the structure formed as described above. Thus, the deposit on the sacrifice layer
7
stuffs the inside of the opening as deposition advances, and the microchips
5
are formed in a conical shape inside the opening (FIG.
14
C).
Lastly, the sacrifice layer
7
is dissolved, whereby the microchip material
8
is lifted off to complete a device (FIG.
14
D).
However, it is difficult for such a manufacturing method to manufacture the device with good control of the above-mentioned distance d, and an amount of emission current varies for each device. In addition, it is likely that a metal piece or the like generated during the lift-off causes short-circuit of the microchip
5
and the gate electrode layer
2
. In this case, if a voltage is applied between the microchip
5
and the gate electrode layer
2
at the time of driving, heat is generated in a shorted part to cause destruction of the shorted part and the part around it. Thus, an effective emission area is reduced.
If the electron-emitting device is applied as, for example, an image-forming apparatus, variation of an amount of emission current for each device causes unevenness of luminance, which makes an image extremely unsightly.
Moreover, in this example, since electrons are emitted from one emitting point, if a density of emission current is increased in order to cause the phosphor to emit light, thermal destruction of the electron-emitting region is induced, which limits a life of the FE device. In addition, ions existing in the vacuum intensively may sputter the tip of the microchip, thereby reducing the life of the device.
Further, electrons emitted into the vacuum usually advances perpendicular to the equipotential surface
6
. However, in the configuration as shown in
FIG. 13
, since the equipotential surface
6
is formed in a hole along the microchip
5
, electrons emitted from the tip of the microchip
5
tend to spread.
In addition, when spreading is caused in the emitted electrons in this way, a part of the emitted electrons is absorbed in the gate electrode layer
2
, whereby an amount of electrons reaching the anode is reduced. The amount of electrons absorbed in the gate electrode layer
2
tends to increase as the distance d is reduced.
In order to overcome such drawbacks of the FE device, various examples have been proposed as individual solutions.
As an example for preventing spreading of electron beams, there is an example in which focusing electrodes
9
are disposed above the electron-emitting region as shown in FIG.
15
.
FIG. 15
is a view showing a configuration of an FE device with focusing electrodes. In this example, emitted electron beams are focused by a negative potential of the focusing electrodes
9
. A process that is more complicated than the above-mentioned manufacturing process is required in this example, which causes increase in manufacturing costs.
As an example of reducing an electron beam diameter without disposing a focusing electrode, there is a method that does not involve formation of a microchip such as the Spindt type. For example, there are technologies disclosed in Japanese Patent Application Laid-open No. 8-096703, Japanese Patent Application Laid-open NO. 8-096704, Japanese Patent Application Laid-open No. 8-264109, U.S. Pat. No. 5,939,823, U.S. Pat. No. 5,989,404 and the like.
These disclosed technologies have advantages that flat equipotential surfaces are formed on an electron emitting surface and spreading of electron beams bec
Canon Kabushiki Kaisha
Dong Dalei
Fitzpatrick ,Cella, Harper & Scinto
O'Shea Sandra
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