Electric lamp and discharge devices – Discharge devices having an electrode of particular material
Reexamination Certificate
1999-06-24
2003-05-27
Patel, Vip (Department: 2879)
Electric lamp and discharge devices
Discharge devices having an electrode of particular material
C313S309000, C313S495000, C313S336000, C313S351000
Reexamination Certificate
active
06570305
ABSTRACT:
BACKGROUND OF THE INVENTION
(1) Field of the Invention
The present invention relates to a field emission electron source for emitting electrons from the cathode as well as relating to a fabrication process thereof. Detailedly, the invention relates to a field emission electron source which enables a low voltage, heavy current, stable configuration as well as relating to a fabrication process thereof.
(2) Description of the Prior Art
Recently, there has been marked progress in the fabrication technology for field emission electron sources that emit electrons in a high electric field, with the development of micro fabrication technology used in the field of integrated circuits or thin films. In particular, field emission electron source devices having highly miniaturized, field emission cold cathodes have been proposed. The emission field cold cathode of this type of electron source device is a most essential electron emission device, being one of the main parts constituting a micro-miniature electron tube of a triode type or micro- miniature electron gun.
FIGS. 1A
to
1
F show a fabrication method of a typical field emission electron source, which is disclosed, in Japanese Patent Application Laid-Open Hei 5 No.94,762.
First, an n-Si substrate
11
is thermally oxidized forming an ioxide film
15
on the surface thereof (FIG.
1
A). Then, a circular cap
15
a
is formed after a photo process (FIG.
1
B). When this substrate with the cap is dry etched, substrate
11
is etched with the portion beneath cap
15
being eroded from the underside so that a conical Si projection
11
a
is formed (FIG.
1
C). Then, the substrate in this condition is thermally oxidized again forming an oxide film
12
a
(FIG.
1
D). This oxide film
12
a
finally serves as an insulating film
12
between a cathode
10
and a gate
13
and also functions to keep the tip pointed. Next, gate electrode
13
is formed by oblique vapor deposition rotating around axis of rotation
16
(FIG.
1
E), then the silicon oxide is etched by hydrofluoric acid to remove cap
15
a
and expose cathode tip
10
to thereby complete the intended field emission electron source (FIG.
1
F).
FIG. 2
is an operational circuit diagram for operating this device. In a vacuum, an anode electrode
9
is arranged over cathode
10
of this field emission electron source with voltages applied between cathode
10
and gate
13
and between cathode
10
and anode
9
. By this arrangement, the electric field between cathode
10
and gate
13
concentrates upon the pointed cathode end, causing cathode
10
to emit electrons forming a emitter portion, whereby electrons are drawn into the vacuum by the field emission tunnel effect.
These devices are very unstable at present, so that the obtainable current is low. If a large current is attempted, an excessive current flows through the cathode, finally, explosive meltdown and hence destruction could occur from Joule heat.
As an improvement against this, Japanese Patent Application Laid-Open Hei 3 No.220,337 offers deposition of a chemically stable, resistive material over the cathode surface. This method permits low voltage operation. However, if a heavy current is tried, the resistance of the resistive material generates heat so that there is a fear that the cathode tip's temperature be raised and a meltdown occur. Therefore, this method involves a risk of the device being destroyed, resulting in unsuitability as a heavy-current device.
Japanese Patent Application Laid-Open Hei 5 No.274,998 has proposed formation of a gold thin film over the cathode tip surface using a focused ion beam. This method, however, needs large-scale equipment for generating the focused ion beam. Further, use of a precious metal such as gold sharply raises the fabrication cost of the device, making it difficult to realize a low-cost device.
U.S. Pat. No. 5,038,070 discloses a configuration shown in
FIG. 3
, in which three layers of metal films
51
,
52
and
53
form cathodes
54
with hollows
55
therein. For fabrication, the three layers of metal films are formed on a substrate having concavities and then the substrate is removed to thereby form projections of the metal films. However, since the cathode is formed of thin films, even though it is of three layers, there is a concern that the pointed end of the cathode would rise in temperature and melt down if a heavy current flows. Therefore, this method also has a risk of the device being destroyed, resulting in unsuitability as a heavy-current device.
SUMMARY OF THE INVENTION
The present invention has been devised in order to solve the above problems and it is therefore an object of the present invention to provide a stable, field emission electron source and a fabrication method thereof, wherein a heavy current can be assured with a low voltage, by coating the cathode tip by inexpensive, physical vapor deposition or sputtering vapor deposition.
In order to achieve the above object, the present invention is configured as follows:
In accordance with the first aspect of the present invention, a field emission electron source comprises:
a cathode made up of a substrate for emitting electrons;
a gate electrode for drawing electrons from the cathode; and
an insulating film for insulating the gate electrode and the cathode, and is characterized in that a metallic material having a lower resistance than that of the cathode substrate is coated as the first layer over the substrate surface, and then another material having a lower work function than that of the substrate is coated as the second layer over the surface of the first layer of metallic material.
In accordance with the second aspect of the present invention, the field emission electron source having the above first feature is characterized in that at least one selected from Mo, W, Ta, Nb, Hf, Zr and Ti is used as the first layer of metallic material and as least one selected from HfC, ZrC and TiC is used as the second layer of material having a low work function is used.
In accordance with the third aspect of the present invention, the field emission electron source having the above first feature is characterized in that the first layer of metallic material is formed with a film thickness of 5 nm or more.
In accordance with the fourth aspect of the present invention, the field emission electron source having the above second feature is characterized in that the first layer of metallic material is formed with a film thickness of 5 nm or more.
In accordance with the fifth aspect of the present invention, the field emission electron source having the above first feature is characterized in that the second layer of material having a low work function is formed with a film thickness of 3 nm or more.
In accordance with the sixth aspect of the present invention, the field emission electron source having the above second feature is characterized in that the second layer of material having a low work function is formed with a film thickness of 3 nm or more.
In accordance with the seventh aspect of the present invention, the field emission electron source having the above third feature is characterized in that the total film thickness of the first layer of metal material and the second layer of material having a low work function is equal to or smaller than 30 nm.
In accordance with the eighth aspect of the present invention, the field emission electron source having the above fourth feature is characterized in that the total film thickness of the first layer of metal material and the second layer of material having a low work function is equal to or smaller than 30 nm.
In accordance with the ninth aspect of the present invention, the field emission electron having the above fifth feature is characterized in that the total film thickness of the first layer of metal material and the second layer of material having a low work function is equal to or smaller than 30 nm.
In accordance with the tenth aspect of the present invention, the field emission electron source having the above sixth feature is characterized in t
Inoue Yoshio
Uda Keiichiro
Urayama Masao
Yano Seiki
Patel Vip
Sharp Kabushiki Kaisha
Williams Joseph
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