Electric lamp and discharge devices: systems – Plural power supplies – Plural cathode and/or anode load device
Reexamination Certificate
2000-10-17
2003-06-24
Wong, Don (Department: 2821)
Electric lamp and discharge devices: systems
Plural power supplies
Plural cathode and/or anode load device
C313S310000, C445S050000
Reexamination Certificate
active
06583578
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a field emission-type electron source for emitting electron beams by means of electrical field emission and to a manufacturing method thereof.
2. Description of the Prior Art
The inventors of the present application have already proposed a field emission-type electron source having an electrically conductive substrate, a thin metal film (surface electrode) and a strong electric field drift layer interposed between the conductive substrate and the thin metal film. The strong electric field drift layer, through which electrons injected thereto from the conductive substrate can drift, is formed by rapidly and thermally oxidizing a porous polycrystalline semi conductor layer (for example, a polycrystalline silicon layer which was made porous, namely a porous polysilicon layer) by means of a rapid thermal oxidation (RTO) process.
For example, as shown in
FIG. 9
, a field emission-type electron source
10
′ (hereinafter, merely referred to “electron source
10
′”) is provided with an n-type silicon substrate
1
as the conductive substrate. On the main surface of the n-type silicon substrate
1
, a strong electric field drift layer
6
(hereinafter, merely referred to “drift layer
6
”) composed of an oxidized porous polycrystalline silicon layer (porous polysilicon layer) is formed. On the drift layer
6
, a surface electrode
7
′ composed of a thin metal film is formed. In addition, on the back surface of the n-type silicon layer
1
, an ohmic electrode
2
is formed.
Where the electron source
10
′ shown in
FIG. 9
is used, the surface electrode
7
′ is disposed in a vacuum circumstance while a collector electrode
21
is disposed so as to face the surface electrode
7
′, as shown in FIG.
10
. Then a DC voltage Vps is applied between the surface electrode
7
′ and the n-type silicon substrate
1
(ohmic electrode
2
) in such a manner that the surface electrode
7
′ has a positive electrical potential against the n-type silicon substrate
1
. On the other hand, a DC voltage Vc is applied between the collector electrode
21
and the surface electrode
7
′ in such a manner that the collector electrode
21
has a positive electrical potential against the surface electrode
7
′. Thus the electrons injected into the drift layer
6
from the n-type silicon substrate
1
drift through the drift layer
6
, and then emitted outward from the surface electrode
7
′ (chain lines in
FIG. 10
showing flows of the electrons e
−
emitted from the surface electrode
7
′). Therefore it may be preferable that the surface electrode
7
′ is composed of a material having a smaller work function.
In the electron source
10
′, the current flowing between the surface electrode
7
′ and the ohmic electrode
2
is referred to “diode current Ips”. On the other hand, the current flowing between the collector electrode
21
and the surface electrode
7
′ is referred to “emitted electron current Ie”. The larger the ratio of the emitted electron current Ie to the diode current Ips (Ie/Ips) becomes, the higher the electron-emitting efficiency becomes. In the electron source
10
′, even if the DC voltage Vps applied between the surface electrode
7
′ and the ohmic electrode
2
is such a lower one as about 10 to 20V, the electrons can be emitted. According to the electron source
10
′, the electron-emitting property less depends on the degree of the vacuum. In addition, a popping phenomenon does not occur when the electrons are emitted. In consequence, the electrons can be stably emitted with higher electror-emitting efficiency.
As shown in
FIG. 11
, it may be considered that the drift layer
6
includes at least polycrystalline silicon columns
51
, thin silicon oxide films
52
, fine crystalline silicon particles
63
of nanometer order scale and silicon oxide films
64
acting as insulating layers. The thin silicon oxide films
52
are formed on the surfaces of the polycrystalline silicon columns
51
. The fine crystalline silicon particles
63
are interposed among the polycrystalline silicon columns
51
. The silicon oxide films
64
, each of which has the thickness smaller than the crystalline particle diameter of the fine silicon particle
63
, are formed on the surfaces of the fine crystalline silicon particles
63
.
That is, in the drift layer
6
, it may be considered that the surface portion of each of the grains is made porous while the inner portion (core) of the grain maintains a crystalline state. Therefore the most part of the electrical field, which is applied to the drift layer
6
, may be applied to the silicon oxide films
64
. In consequence, the injected electrons are accelerated among the polycrystalline silicon columns
51
by the strong electric field applied to the silicon oxide films
64
, and then drift in the direction of the arrow A in
FIG. 11
(upward in
FIG. 11
) toward the surface of the drift layer
6
. Thus the electron emitting efficiency may be improved. Hereupon, it may be considered that the electrons, which have reached the surface of the drift layer
6
, are hot electrons so that they easily tunnel the surface electrode
7
′, and then are emitted into the vacuum circumstance. The thickness of the surface electrode
7
′ may be set to about 10 to 15 nm.
Meanwhile, in order to improve the electron emitting efficiency of the above-mentioned electron source
10
′, it is necessary to restrain the electrons from scattering in the surface electrode
7
′. Therefore the surface electrode
7
′ is required to have characteristics as follows. That is, the surface electrode
7
′ must restrain the electrons from scattering in the thin metal film thereof. In addition, it must have higher adhesion with the under layer (drift layer
6
in the above-mentioned case) not so as to cause its peeling during the photolithography process, the annealing process or the like. So it may be suggested such an electron source in that the surface electrode
7
′ is composed of a first metal layer formed on the drift layer
6
and a second metal layer formed on the first metal layer, the two layers being stratified (stacked) together. Hereupon the first metal layer is composed of a metal material with higher adhesion while the second metal layer is composed of a metal material in which the electrons less scatter. In the above-mentioned electron source, however, it may be caused such a disadvantage that the electrons highly scatter in the surface electrode
7
′ as same as the case that the surface electrode
7
′ is composed of only one metal material in which the electrons highly scatter so that the electron emitting efficiency may be lowered, because the electrons highly scatter in the metal material with higher adhesion (probability of scattering being larger). In addition, it may be caused such a disadvantage that if the surface electrode
7
′ is peeled off from the drift layer
6
during the manufacturing process thereof, its yield is lowered to increase its cost while its stability for the lapse of time and reliability may be lowered. The above-mentioned disadvantages may occur also in other field emission-type electron sources, for example, such as a MIM (Metal Insulator Metal) type one or a MOS (Metal Oxide Semiconductor) type one.
SUMMARY OF THE INVENTION
The present invention, which has been achieved to solve the above-mentioned problems, has an object to provide an inexpensive field emission-type electron source having good stability for the lapse of time, in which the deterioration of electron emitting efficiency due to scattering of the electrons is less, and to Provide a manufacturing method of the field emission-type electron source.
A field emission-type electron source (hereinafter, merely referred to “electron source”) according to the present invention which is performed to achieve the above-mentioned object, includes an e
Aizawa Koichi
Hatai Takashi
Honda Yoshiaki
Ichihara Tsutomu
Komoda Takuya
Alemu Ephrem
Greenblum & Bernstein P.L.C.
Matsushita Electric & Works Ltd.
Wong Don
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