Electric lamp and discharge devices: systems – Plural power supplies – Plural cathode and/or anode load device
Reexamination Certificate
2001-05-29
2003-09-23
Wong, Don (Department: 2821)
Electric lamp and discharge devices: systems
Plural power supplies
Plural cathode and/or anode load device
C313S309000, C313S497000
Reexamination Certificate
active
06624589
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electron emitting device, an electron source, and an image forming apparatus.
2. Related Background Art
Conventionally, two types of electron sources (cathodes), that is, a thermionic and a cold cathode have been known as the electron emitting device. As the cold cathode, there are a field emission type (hereinafter referred to as an FE type) electron emitting device, a metal/insulating-layer/metal type (hereinafter referred to as an MIM type) electron emitting device, a surface conduction type electron emitting device, or the like.
As examples of the FE type, 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 molybdenum cones”, J. Appl. Phys., 47, 5248 (1976), and the like have been known.
As examples of the MIM type, the one as disclosed in C. A. Mead, “Operation of Tunnel-Emission Devices”, J. Appl. Phys., 32, 646 (1961), and the like have been known.
Also, as 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 have been studied.
As examples of the surface conduction type, there are the ones as described in Elinson's report (M. I. Elinson, Radio Eng. Electron Phys., 10 (1965)), and the like. This surface conduction type electron emitting device is realized by utilizing the phenomenon that electrons are emitted out of a small area thin film formed on a substrate when a current is made to flow in parallel with the film surface. As the surface conduction type electron emitting device, the device using an SnO
2
thin film described in the above Elinson's report, a device using an Au thin film (G. Dittmer. Thin Solid Films, 9, 317 (1972)), a device 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, have been reported.
SUMMARY OF THE INVENTION
When the electron emitting device is applied to the image forming apparatus (in particular, the display), it is necessary to obtain an emitting current for causing a phosphor to emit light with a sufficient intensity. Also, for high minuteness of the display, it is desired that a diameter of an electron beam to be irradiated into the phosphor is small. Also, it is important to make the manufacturing easy.
As an example of a conventional FE type, a so-called “spindt type” electron emitting device is shown in FIG.
29
. In
FIG. 29
, reference numeral
1
denotes a substrate,
4
denotes a cathode electrode layer (lower potential electrode),
3
denotes an insulating layer,
2
denotes a gate electrode layer (higher 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 end of the microchip
5
toward an anode. An amount of emitting electron is determined by the distance “d” between the gate electrode layer
2
and the end of the microchip
5
, a voltage Vg between the gate electrode and the microchip, a work function of an emitting region material (microchip), and the like. Namely, that the device is manufactured by controlling the distance “d” between the gate electrode layer
2
and the microchip
5
is a factor for determining the performance of the device.
A general manufacturing process of the Spindt type electron emitting device is shown in
FIGS. 30A
to
30
D. The manufacturing process will be described through those drawings. 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 laminated in this order on the substrate
1
made of glass or the like. Then, a circular minute hole which penetrates the gate electrode layer
2
and the insulating layer
3
is formed by a reactive ion etching method (FIG.
30
A).
After that, a sacrificial layer
7
made of aluminum or the like is formed on the gate electrode layer
2
by oblique evaporation or the like (FIG.
30
B).
A microchip material
8
such as molybdenum is deposited in the structure formed thus by a vacuum evaporation method. Here, the minute hole is filled with the deposition on the sacrificial layer by the progress of deposition. Thus, the microchip
5
is conically formed in the minute hole (FIG.
30
C).
Finally, the sacrificial layer
7
is dissolved to lift off the microchip material
8
. Thus, the device is completed (FIG.
30
D).
However, in such a manufacturing method, it is difficult to control the distance “d” with high repeatability. Thus, there is the case where a variation in an amount of emitting current between devices is produced by a variation in the distance “d”. Also, if the device is driven with the state that a short circuit occurs between the microchip
5
and the gate electrode layer
2
through a piece of metal or the like which is produced by the lift off, there is the case where heat is generated in the shirt circuit region and thus a discharge breakdown occurs in the shirt circuit region and its surrounding. In this case, an effective electron emitting region is decreased. Thus, in an image forming apparatus (in particular, a display) using a plurality of devices having the above variation in an amount of emitting electrons, an unevenness of brightness occurs. Thus, the apparatus becomes a low performance as the display.
Further, in the Spindt type device, electrons are emitted from an extremely narrow region. Thus, when an emitting current density is increased in order to cause the phosphor to emit light, there is the case where a thermal breakdown of the electron emitting region (microchip) is induced, and thus the life of the device is limited. Also, these is the case where the end of the microchip is intensively sputtered with ions present in a vacuum, and thus the life of the device is shortened.
Note that electrons emitted to the vacuum are carried along the direction orthogonal to an equipotential surface. However, in the structure as shown in
FIG. 29
, the equipotential surface
6
is formed in the hole along the outer shape of the microchip
5
. Thus, the electrons emitted from the end of the microchip
5
tend to spread. Since a portion of the emitted electrons is absorbed into the gate electrode layer
2
, an amount of electrons which reach the anode is decreased. When the distance “d” is shortened, an amount of electrons absorbed in the gate electrode layer
2
tends to increase.
In order to overcome such faults, various examples have been proposed.
As an example for preventing the diffusion of an electron beam, there is one that a focusing electrode
9
is located over the electron emitting region.
FIG. 31
is a structure view of an FE type device with the focusing electrode. In this example, the emitted electron beam is focused with the potential of the focusing electrode
9
. However, this example requires a further complicated process than the above manufacturing process, and thus increase in a manufacturing cost occurs.
As an example for reducing the diameter of an electron beam without locating the focusing electrode, there is the one described in Japanese Patent Application Laid-Open No. 8-264109. This structure is shown in FIG.
32
. In this example, in order to emit electrons from a thin film
10
located in a hole, since a flat equipotential surface
6
a
is formed on an electron emitting surface, the diffusion of the electron beam becomes small. However, in this example, since the electron emitting region is present in the hole and the gate electrode layer
2
is located over the electron emitting surface as conventionally, a potential distribution
6
b
correlated with
Kitamura Shin
Osada Yoshiyuki
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Lee Wilson
Wong Don
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