Electric lamp and discharge devices – With envelope – Having base and connector
Reexamination Certificate
2000-10-17
2004-07-20
Patel, Ashok (Department: 2879)
Electric lamp and discharge devices
With envelope
Having base and connector
C313S497000
Reexamination Certificate
active
06765342
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 under influence of an electric field and also to a method of manufacturing the same.
2. Description of the Prior Art
Of the various field emission-type electron sources known in the art, a Spindt-type electrode such as disclosed in, for example, U.S. Pat. No. 3,665,241 has been well known. The Spindt-type electrode includes a substrate having a multiplicity of emitter chips of a generally triangular pyramid shape arranged on one surface thereof, emission holes through which respective tips of the emitter chips are exposed to the outside, and gate layers disposed in an insulated relation to the emitter chips. When the Spindt-type electrode is in use, electrons are emitted in vacuum from the tips of the emitter chips through the emission holes upon application of a high voltage to the gate layers then serving as negative electrode relative to the emitter chips.
It has, however, been found that the Spindt-type electrode does not only require a complicated manufacturing process, but difficulty has hitherto been encountered to tailor the emitter chips of the generally triangular pyramid shape to precise dimensions. Accordingly, when it comes to application of the field emission electron source to, for example, a planar light emitter or a flat display, the Spindt-type electrode is incapable of being manufactured in a large format with a sufficiently large surface area for electron emission.
The Spindt-type electrode has an additional problem in that the electric field tends to converge so as to concentrate on the tips of the emitter chips. Accordingly, where the degree of vacuum around and adjacent the tips of the emitter chips is so low as to permit residue gas to drift around the tips of the emitter chips, the residue gas tends to be positive ionized by the electrons emitted and the resultant positive ions would subsequently collide against the tips of the emitter chips. Once this occurs, the tips of the emitter chips are damaged (for example, as a result of the ion bombardment), resulting in reduction in stability and efficiency of the current density of the electrons emitted and also reduction in lifetime of the emitter chips.
Accordingly, in order to substantially eliminate a possible of occurrence of those problems, the Spindt-type electrode has to be used in a highly evacuated atmosphere (for example, about 10
−5
to about 10
−6
Pa), and, for this reason, the use of the Spindt-type electrode tends to result in increase of cost and handling difficulty.
To substantially eliminate the problems inherent in the Spindt-type electrode, the field emission-type electron sources of a type utilizing MIM (Metal Insulator Metal) and MOS (Metal Oxide Semiconductor) have been suggested. As the nomenclature indicates, the MIM electron source makes use of a metal-insulator-metal laminar structure whereas the MOS electron source makes use of a metal-oxide film-semiconductor laminar structure. In these field emission-type electron sources, the insulator film or the oxide film is required to have a relatively small thickness in order for the electron emission efficiency to be increased (i.e., in order for an increased mass of electrons to be emitted). However, the excessively smaller the film thickness of the insulator film or the oxide film, the more often dielectric breakdown may occur when a voltage is applied between upper and lower electrodes of the laminar structure. Accordingly, in the suggested field emission-type electron sources, the extent to which the film thickness of the insulator film or the oxide film can be reduced is limited. In view of the foregoing, the suggested field emission-type electron sources requires means to be taken to avoid any possible dielectric breakdown and, therefore, a problem is often encountered in sufficiently increasing the electron emission efficiency (electron extracting efficiency).
On the other hand, the Japanese Laid-open Patent Publication No. 8-250766 discloses a field emission-type electron source (a semiconductor element for emission of cold electrons) including, in order to increase the electron emission efficiency, a monocrystalline semiconductor substrate such as, for example, silicon substrate having one surface region anodized to define a porous semiconductor layer (a porous silicon layer) which is in turn overlaid by a metal thin-film. Application of a voltage between the semiconductor substrate and the metal thin-film results in emission of electrons.
However, in the field emission-type electron source disclosed in the above mentioned Japanese publication, a material for the substrate is limited to a semiconductor and, therefore, difficulty has hitherto been encountered in providing an electron source of a large surface format at a reduced cost. Also, this known field emission-type electron source is susceptible to a so-called popping phenomenon, accompanied by a varying quantity of electrons emitted. For this reason, application of this known field emission-type electron sources to a planar light emitter or a flat display would result in a pattern of uneven distribution of light.
In the Japanese Patents No. 2987140 (Japanese Patent Application No. 10-272340) and No. 296684 (Japanese Patent Application No. 10-272342), the inventors of the present invention have suggested the field emission-type electron source of a type wherein the porous polycrystalline silicon layer is oxidized by the use of a rapid thermal oxidation technique. Oxidation of the porous polycrystalline silicon layer by the use of the specific technique results in formation, between the electroconductive substrate and the metal thin-film, of a strong electrical field drift layer in which electrons injected from the electroconductive substrate can drift.
By way of example, as shown in
FIG. 16
, the field emission-type electron source (hereinafter, merely referred to “electron source”)
10
′ includes an electroconductive substrate that is defined by an n-type silicon substrate
1
. The n-type silicon substrate
1
has a major surface, with a strong electrical field drift layer (hereinafter, merely referred to “drift layer”)
6
formed on the major surface of the silicon substrate
1
. The metal thin-film identified by
7
is formed on the drift layer
6
as a surface electrode. An ohmic electrode
2
is formed on the back surface of the silicon substrate
1
.
As shown in
FIG. 17
, the electron source
10
′ when in use is disposed in a highly evacuated envelope together with a collector electrode
21
. confronting the surface electrode
7
. A direct current voltage Vps is applied between the surface electrode
7
and the silicon substrate
1
(specifically, the ohmic electrode
2
) so that the surface electrode
7
can be held at a positive potential relative to the silicon substrate
1
. On the other hand, a direct current voltage Vc is applied between the collector electrode
21
and the surface electrode
7
so that the collector electrode
21
can be held at a positive potential relative to the surface electrode
7
. When the direct current voltages Vps and Vc are applied in the manner described above, electrons injected from the silicon substrate
1
into the drift layer
6
drift within the drift layer
6
and are then emitted through the surface electrode
7
(Single-dotted lines in
FIG. 17
indicate flow of electrons e
−
emitted through the surface electrode
7
.) Accordingly, it is considered desirable that the surface electrode
7
employed in the electron source
10
′ is made of a material having a low work function.
The current flowing between the surface electrode
7
and the ohmic electrode
2
is generally referred to as a diode current Ips. On the other hand, the current flowing between the collector electrode
21
and the surface electrode
7
is generally referred to as an emitted electron current Ie. The higher the ratio (Ie/Ips) of the emitted electron current Ie re
Aizawa Koichi
Hatai Takashi
Honda Yoshiaki
Ichihara Tsutomu
Komoda Takuya
Greenblum & Bernstein P.L.C.
Matsushita Electric Work, Ltd.
Patel Ashok
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