Electric lamp and discharge devices – Discharge devices having a thermionic or emissive cathode
Reexamination Certificate
2000-04-21
2002-12-24
Patel, Nimeshkumar D. (Department: 2879)
Electric lamp and discharge devices
Discharge devices having a thermionic or emissive cathode
C313S311000, C313S34600R, C445S024000, C445S050000, C445S051000
Reexamination Certificate
active
06498426
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a field emission-type electron source using semiconductor materials, for emitting electron beams by means of electrical field emission, and to a manufacturing method thereof, the electron source being applied to a plane light-emitting apparatus, a display, a solid vacuum device and so on.
2. Description of the Prior Art
As a field emission-type electron source, conventionally, there has been known a Spindt-type electrode which is disclosed, for example, in the U.S. Pat. No. 3,665,241 and so on. The Spindt-type electrode is provided with a substrate on which many emitter chips of triangular pyramid shape are disposed, and a gate layer having emitting holes for exposing apexes of the emitter chips to the outside, the gate layer being disposed so as to be insulated to the emitter chips. The Spindt-type electrode can emit electron beams from the apexes of the emitter chips to the outside through the emitting holes by applying high voltage between the emitter chips and the gate layer under a vacuum atmosphere in such a manner that the emitter chips act as negative electrodes against the gate layer.
However, in the Spindt-type electrode, there exists such a problem described below. That is, the manufacturing process of the electrode is complicated, and further it is difficult to construct many emitter chips of triangular shape with higher efficiency. In consequence, if it is applied, for example, to a plane light-emitting apparatus, a display and so on, it may be difficult to enlarge the area of the electron-emitting surface.
Meanwhile, in the Spindt-type electrode, there exists also such another problem described below. That is, in the Spindt-type electrode, the electrical field converges to the apexes of the emitter chips. In consequence, if the degree of vacuum around the apexes of the emitter chips is lower so that residual gas exists thereabout, a part of the residual gas is ionized by the emitted electron beams to become positive ions. Because the positive ions collide to the apexes of the emitter chips, the apexes of the emitter chips suffer damages (for example, damages due to ion impacts). Therefore, the current density and efficiency of the emitted electrons may become unstable, or the lives of the emitter chips may be shortened.
In order to prevent the above-mentioned disadvantages, the Spindt-type electrode is required to use under a higher vacuum atmosphere (about 10
−5
Pa to about 10
−6
Pa. In consequence, there may occur such a disadvantage that the cost for sealing it with higher vacuum or for maintaining the higher vacuum, may be increased.
In order to improve the above-mentioned disadvantages, a field emission-type electron source of MIM (Metal Insulator Metal) type or MIS (Metal Insulator Semiconductor) type has been proposed. The former is a flat field emission-type electron source having a laminated structure of (metal)—(insulator film)—(metal) The latter is a flat field emission-type electron source having a laminated structure of (metal)—(insulator film)—(semiconductor). In order to elevate the electron-emitting efficiency of the above-mentioned type of field emission-type electron source (namely, in order to emit more electrons), it is necessary to decrease the thickness of the insulator film. However, if the insulator film becomes thinner to excess, it is feared that dielectric breakdown is caused when voltage is applied between the upper and lower electrodes of the laminated structure. Because there is a certain restriction on decreasing the thickness of the insulator film as described above, there may exist such a problem that its electron-emitting efficiency (electron extracting efficiency) can not be elevated so much.
Moreover, in recent years, as disclosed in the Japanese Laid-Open Patent Publication No. 8-250766, there has been proposed another field emission-type electron source (semiconductor element for emitting cold electrons), in which a porous semiconductor layer (porous silicon layer) is formed by performing anodic oxidation to a surface of a monocrystalline semiconductor substrate such as a silicon substrate or the like, and further a thin metal film is formed on the porous semiconductor layer. In the field emission-type electron source, electrons are emitted by applying voltage between the semiconductor substrate and the thin metal film.
However, in the field emission-type electron source described in the Japanese Laid-Open Patent Publication No. 8-250766, it is difficult to enlarge the area of the electron-emitting surface, because the monocrystalline semiconductor substrate is an essential constructive element. In consequence, it may not be suitable for applying to an apparatus which requests an electron source having a large electron-emitting surface area, such as a flat display apparatus. Meanwhile, in the Japanese Laid-Open Patent Publication No. 9-259795, there is disclosed a construction for achieving a flat type display based on the invention disclosed in the Japanese Laid-Open Patent Publication No. 8-250766.
In each of the above-mentioned field emission-type electron sources, electrons are emitted due to the electrical field produced by applying voltage to the both surfaces of the porous semiconductor layer. In this case, the porous semiconductor layer is composed of many fine pores and the remaining silicon particles while differing from the above-mentioned MIM or MIS. Hereupon, the porosity is 10 to 80%, while the inner diameter of each of the fine pores is 2 to several nm. In the above-mentioned Publication, there is such a description that because the number of atoms in the remaining silicon particles is several tens to several hundreds, an electron emitting phenomenon may be expected due to the quantum size effect. Meanwhile, in the Japanese Laid-Open Patent Publication No. 9-259795, there is such a description that because the electron emission occurs at a position which is very near with the surface of the porous semiconductor layer, it is desirable that the thickness is thinner, in consequence the practically usable range of the thickness may be 0.1 to 50 &mgr;m.
However, in the field emission-type electron source described in the Japanese Laid-Open Patent Publication No. 8-250766 or Japanese Laid-Open Patent Publication No. 9-259795, an electron popping phenomenon may be easily caused and further the amount of electrons emitted within the same plane may be easily dispersed. In consequence, if the electron source is applied to a plane light-emitting device or a display, There may occur such a disadvantage that the brightness dispersion or flicker of the screen may grow larger. Meanwhile, when the electron source is applied to the plane light-emitting device or the display, it is necessary to increase the amount of the emitted electrons. Hereupon, if it is intended to increase the amount of the emitted electrons by decreasing the thickness of the porous semiconductor layer, the above-mentioned disadvantages may grow much larger.
SUMMARY OF THE INVENTION
The present invention, which has been performed to solve the conventional problems described above, has an object to provide a field emission-type electron source, in which the popping phenomenon or in-plane dispersion of the emitted electrons hardly occurs while the amount of the emitted electrons and the electron-emitting efficiency are higher together, and to provide a manufacturing method of the electron source.
A field emission-type electron source according to the present invention which is preformed to achieve the above-mentioned object, includes (i) a conductive substrate, (ii) a semiconductor layer formed on a surface of the conductive substrate, at least a part of the layer being made porous, and (iii) a conductive thin film formed on the semiconductor layer, wherein (iv) electrons injected into the conductive substrate are emitted from the conductive thin film through the semiconductor layer by applying voltage between the conductive thin film and the conductive subs
Aizawa Koichi
Hatai Takashi
Honda Yoshiaki
Ichihara Tsutomu
Komoda Takuya
Matsushita Electric & Works Ltd.
Patel Nimeshkumar D.
Santiago Mariceli
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