Electric lamp and discharge devices – Discharge devices having a thermionic or emissive cathode
Reexamination Certificate
2003-05-15
2004-09-14
Patel, Nimeshkumar D. (Department: 2879)
Electric lamp and discharge devices
Discharge devices having a thermionic or emissive cathode
C313S496000
Reexamination Certificate
active
06791248
ABSTRACT:
DETAILED DESCRIPTION OF THE INVENTION
1. Field of the Invention
This invention relates to a field emission electron source for emitting electrons due to the field emission using a semiconductor material without heating and a method of manufacturing the same. More particularly, the present invention relates to a field emission electron source applicable to a planar light emitting apparatus, a display apparatus, and a solid vacuum device, and a method of producing the same.
2. Prior art
As field emission electron sources, those using the so-called Spindt type electrode such as disclosed in, for example, U.S. Pat. No. 3,665,241 are well known. The Spindt type electrode comprises a substrate having a multitude minute emitter chips of a triangular pyramid shape disposed thereon and gate layers that have emission holes through which tips of the emitter chips are exposed and are insulated from the emitter chips. In this structure, a high voltage is applied in a vacuum atmosphere to the emitter chips as negative electrode with respect to the gate layer, electron beams can be emitted from the tips of the emitter chips through the emission holes.
However, the production process of the Spindt type electrode is complicated and it is difficult to make a multitude of emitter chips of a triangular pyramid shape with high accuracy and hence, difficult to make a device of large emission area when applying this technology to, for example, a planar light emitting apparatus or a display apparatus. Also with the Spindt type electrode, since the electric field is concentrated on the tip of the emitter chip, emitted electrons ionize various residual gases into positive ions where the degree of vacuum is low and the residual gas exists in the vicinity of the tips of the emitter chips. Therefore, the positive ions impinge on the tip of the emitter chips and eventually damage the tips of the emitter chips, resulting in such problems that the current density and efficiency of the emitted electrons become unstable and the service life of the emitter chips decreases. Thus, the Spindt type electrode has such a drawback that the atmosphere in which it is used must be pumped to a high degree of vacuum (10
−5
Pa to 10
−6
Pa) in order to avoid the problems described above, resulting in higher cost and difficult handling.
In order to overcome the drawback described above, field emission electron sources of MIM (Metal Insulator Metal) type and MOS (Metal Oxide Semiconductor) type have been proposed. The former is a field emission electron source of a planar configuration having a laminated structure of metal-insulation film-metal and the latter is the same structure one of a metal-oxide film-semiconductor. However, it is necessary to reduce the thickness of the insulation film or the oxide film in order to improve the electron emitting efficiency to thereby increase the number of electrons emitted with these types of field emission electron sources, while making the insulation film or the oxide film too thin may lead to dielectric breakdown when a voltage is applied between the upper and lower electrodes of the laminated structure described above. Thus there has been such a problem that, in order to avoid the dielectric breakdown of the insulator film, the electron emitting efficiency (pullout efficiency) cannot be made too high because there is a limitation on the reduction of the thickness of the insulation film or the oxide film.
A different field emission electron source has recently been proposed in Japanese Patent Kokai Publication No. 8-250766. According to this publication, the field emission electron source is made by using a single-crystal semiconductor substrate such as a silicon substrate, forming a porous semiconductor layer (a porous silicon layer, for example) by anodization of one surface of the semiconductor substrate, and forming a surface electrode made of a thin metal film on the porous semiconductor layer. A voltage is adapted between the semiconductor substrate and the surface electrode to cause the field emission electron source (semiconductor cold electron emitting device) to emit electrons.
However, in the structure disclosed in Japanese Patent Kokai Publication No. 8-250766, there is such a drawback that the popping phenomenon is likely to occur during electron emission. In the field emission electron source in which the popping phenomenon is likely to occur during electron emission, the unevenness in amount of electrons emitted is likely to occur. Thus, when this type of field emission electron source is used in a planar light emitting device and a display apparatus, there is such a drawback that the light is not emitted uniformly.
Then, the inventors studied whole-heartedly the above drawbacks and found out that in the field emission electron source as disclosed in Japanese Patent Kokai Publication No. 8-250766, since a porous silicon layer formed by making the entire surface of the single crystal substrate on the principal surface side porous constructs a strong electric field drift layer into which electrons are injected, the strong electric field drift layer has a heat conductivity lower than that of the crystal substrate and the field emission electron source has a high thermal insulating characteristics, which results in that the temperature of the substrate rises relatively largely when voltage is applied and current is flown. Further the inventors found out that electrons are thermally excited and electrical resistivity of the single-crystal semiconductor substrate decrease when the temperature of the substrate increases, accompanied by increase of the amount of electrons emitted. Therefore, this structure is susceptible to the popping phenomenon during electron emission leading to unevenness in amount of electrons emitted.
Based on the above findings, the present invention has been accomplished. That is, the object of the present invention is to provide a field emission electron source capable of achieving a stable emission of electrons with high efficiency at a low cost and a method of producing the same.
THE SUMMARY OF THE INVENTION
In order to achieve the above-mentioned object, according to a first aspect of the present invention, there is provided a field electron source comprising an electrically conductive substrate having principal surfaces; a strong electric field drift layer formed on one of the principal surfaces of said electrically conductive substrate and a surface electrode made of a thin electrically conductive film which is formed on said strong electric field drift layer, wherein a voltage is applied to said surface electrode used as a positive electrode with respect to said electrically conductive substrate, thereby electrons injected from said electrically conductive substrate being drifted in said strong electric effect drift layer and emitted through said surface electrode, characterized in that said strong electric field drift layer comprises at least a) semiconductor crystal regions formed in a manner to stand up vertically on said principal surface of the electrically conductive substrate and b) semiconductor micro-crystal regions having nano-structures intervened between the semiconductor crystal regions coated with an insulating film which has a thickness smaller than the crystal grain size of said semiconductor micro-crystal region and is formed on the surface of the semiconductor micro-crystal. Therefore, 1) the dependency on the degree of vacuum of the electron emission characteristic is low and no popping phenomenon occurs during the electron emission. Also the electrons can be emitted with a high stability and a high efficiency. 2) As the electrically conductive substrate, the semiconductor substrate such as a single-crystal silicon substrate and the substrate such as a glass substrate with a conductive film formed thereon can be used, in which case it is made possible to achieve larger emission area and lower production cost than in the case of using the conventional porous semiconductor layer and of the Spindt-type electrode, as
Aizawa Koichi
Ichihara Tsutomu
Komoda Takuya
Koshida Nobuyoshi
Greenblum & Bernstein P.L.C.
Matsushita Electric & Works Ltd.
Patel Nimeshkumar D.
Quarterman Kevin
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