Image display apparatus and method of fabrication thereof

Abstract: An image display apparatus comprising an insulating substrate (1) having electron sources (13) controlled by X-Y matrix electrodes (10, 11) and a face plate (4) coated with a phosphor material in opposed relationship with the substrate is disclosed. An electron source at each intersection of the X-Y matrix control electrondes is made up of a plurality of cold cathodes (2) connected to an X-control electrode (10) and a plurality of gate electrodes (3) connected to a Y-control electrode (11) opposed to the cold cathodes in the same plane, and the electron source is formed on the substrate surface on other than the X- and Y-control electrodes. A voltage applied between the cold cathodes and gate electrodes arranged in opposed relations on the same surface causes a high electric field of about 10⁷ V/cm at the forward end of the cold cathodes leading to an electron emission. A part of electrons thus emitted enters the anodes directly. Another part of electrons flow into the opposed gate electrodes to generate secondary electrons in the surface of the gate electrodes. The secondary electrons thus generated are accelerated by the positive voltage (anode voltage) applied to the phosphor surface of the opposed face plate and bombarded on the phosphor material, which is thus illuminated.

Description: The present invention relates to a thin image display apparatus using a plurality of cold cathodes. A number of thin display apparatuses comprising a plurality of cold cathodes arranged two-dimensinally for displaying an image using X-Y matrix electrodes have been disclosed in the related art (cf. EP-A-0172089). Such a known thin display apparatus, as shown in Fig. 5A, has a substrate with the surface thereof formed of a plurality of cold cathodes of field emission type in a density as high as 10⁶ to 10⁷ units/cm². As shown in Fig. 5B, these cathodes are formed on an X electrode 22 as one part of the matrix electrodes on the surface of a substrate 21, on which a Y electrode 24 is formed as the other part of the matrix electrodes together with an insulating layer 23. A minute aperture 25 one µm to 1.5 µm in diameter is formed in the Y electrode at each inter-section of the X-Y electrodes, and the insulating layer 23 is etched. A substrate assembly thus formed is rotated, while a high melting point metal such as tungsten or molybdenum is diagonally deposited by evaporation thereby to form a conical cold-cathode tip 26. After forming the cold cathodes, the metal layer on the surface not wanted is removed to produce a plurality of electron sources of cold cathodes of thin film field emission type. These X-Y matrix electron sources are arranged in opposed relationship with a face plate 27 coated with a phosphor material 28 to configure an image display apparatus. This image display apparatus, which comprises as many as more than 1000 minute electron sources in each pixel, generally has a uniform characteristic in spite of possible variations in the characteristics of individual minute electron sources, thus producing a comparatively uniform brightness over the whole screen. The aforementioned image display apparatus with its satisfactory characteristics, however, has not yet found practical applications due to the facts that a complicated production process makes the production cost high and that it is difficult to fabricate uniform cold cathodes of field emission type over an area required for a display apparatus. Another reason is that the laminated structure of the X-control electrode (cold cathode) and Y-control electrode (gate electrode) through an insulating layer therebetween leads to a large electric capacity, resulting in a heavy load imposed on a drive circuit. The present invention eliminates these disadvantages by providing a thin image display apparatus comprising an insulating substrate having two-dimensionally arranged electron source units controlled by X-Y matrix control electrodes and a face plate coated with a phosphor material and arranged in opposed relationship with the insulating substrate, wherein the said electron source unit corresponding to each intersection of X-Y matrix control electrodes includes a cold planar field emission cathode connected to an X-control electrode and a planar gate electrode connected to a Y-control electrode opposed to the cold cathode in the same plane, the electron source units being formed in the part of the substrate surface not occupied by the X- and/or Y- control electrodes. Upon application of a voltage between the cold cathode and the gate electrode arranged in opposed relationship with each other on the same surface in the manner mentioned above, a high electric field of approximately 10⁷ V/cm is formed at the forward end of the cold cathode and electrons are emitted. A part of the electrons thus emitted enters the anode directly. Another part of the electrons flow into the opposite gate electrode thereby to generate secondary electrons in the surface of the gate electrode. The secondary electrons thus generated are accelerated by a positive voltage (hereinafter called the "anode voltage") applied to the phosphor face of the opposed face plate and bombarded on the phosphor material to emit light. The apparatus according to the present invention in which a plurality of cold cathodes of planar field emission type are formed on the surface of an insulating substrate defined by X-control electrodes and Y-control electrodes, has the advantages (1) that the electric capacity between the electrodes is extremely reduced (to 1/20 to 1/30 of the related art), (2) that the production cost is low since cold cathodes and gate electrodes are capable of being formed at the same time, and (3) that crosstalks are very small. Fig. 1 is a partial sectional view of an image display apparatus according to an embodiment of the present invention. Fig. 2 is a sectional view of the essential parts of an electron source section according to the same embodiment. Fig. 3 is a plan view schematically showing an electrode arrangement according to the same embodiment. Fig. 4 is a perspective view of the essential parts of two-dimensional electron sources as configured according to another embodiment of the present invention. Figs. 5A and 5B are a perspective view and an enlarged perspective view of the essential parts respectively of a matrix display apparatus of electric field emission type related to the present invention. A partial sectional view of an image display apparatus according to the present invention is shown in Fig. 1. The image display apparatus comprises a glass substrate 1 having an electron source for electric field emission at each intersection of X-Y matrix electrodes, and a face plate 4 coated with phosphor material in opposed relationship with the glass substrate 1. The glass substrate 1 has cold cathode 2 and gate electrodes 3 arranged face to face on the surface. When a positive voltage of, say, 100 V is applied to the gate electrodes 3 with respect to the cold cathodes 2, electron beams 7 are emitted. A part of electrons thus emitted flows into the gate electrodes 3, while the other part is accelerated by a high voltage of, say, 500 V applied to an anode 5 and hits a phosphor surface 6 thereby to cause the phosphor to emit light. An enlarged perspective view of an electron source is shown in Fig. 2. A multiplicity of sawtoothed protrusions 8 are formed in the surface of the cold cathode 2 opposed to the gate electrode 3. Further, the surface of the glass substrate 1 has a recess 9 between the cold cathode 2 and the gate electrode 3 to facilitate formation of a high electric field at the forward end of the cold cathode 2. Fig. 3 shows a part of the electrode arrangement. X-control electrodes X₁, X₂, X₃, ... X n and Y-control electrodes Y₁, Y₂, Y₃, ... Y n make up matrix control electrodes. A plurality of electron sources 13 are formed on the substrate surface defined by these control electrodes. Each electron source 13, which is configured as shown in Fig. 2, includes a cold cathode 2 connected to an X-control electrode and a gate electrode 3 connected to a Y-control electrode. This construction of the electron sources 13 not overlaid on the X- or Y-control electrodes is a reduction of 1/20 to 1/30 of the area required by the prior art for superposing the electrodes on each other through an insulating layer. As a result, the probability of short-circuiting between electrodes due to a pinhole in the insulating layer and the electric capacity are decreased to 1/20 to 1/30. Now, a method of fabricating two-dimensional electron sources will be explained. A film of a metal as nickel is deposited by evaporation to the thickness of 0.5 µm over the whole surface of the glass substrate, and formed in stripes by photolithography. The electrodes are formed to the width of 0.1 mm. An SiO₂ film as thick as 1 µm is deposited as an insulating layer by the CVD process, and a part of the insulating film over an X-control electrode is removed to form a window for allowing connection to a cold cathode. Further, a tungsten film is deposited by evaporation to a thickness of 0.2 µm and a cold cathode 2, a gate electrode 3 and a Y-control electrode are formed simultaneously by photolithography. The Y-control electrode is made as wide as 0.5 mm. The protrusions of the cold cathode are set at an interval of 2 µm from the gate electrode. There are approximately 500 protrusions 8 per electron source unit (which correspond to one pixel). As the next process, the whole substrate is immersed in a buffer etching solution to form a recess 9 at the forward end of the cold cathode as shown in Fig. 2. The electrode material for forming an X-control electrode is not limited to nickel metal, but may preferably take the form of aluminum, titanium, gold-chromium alloy or other metal material which has a high adhesion with the glass substrate and is low in resistivity. Also, a silver electrode or a gold electrode may be formed by a screen printing process or the like. The SiO₂ film used as an insulating layer may be replaced by another material of high insulation characteristic such as SiN, SiO or Al₂O₃. Instead of tungsten, on the other hand, tantalum, molybdenum or an alloy or carbide thereof having a high melting point may be used as the material of the cold cathode with equal effect. In this way, a glass substrate having electron sources units 13 in the number of 480 x 660 arranged in matrix are disposed in opposed relations with a face plate coated with a ZnO:Zn phosphor material at intervals of 0.3 mm, and the surrounding parts are sealed with frit glass of a low melting point. The resulting assembly is evacuated to produce an image display apparatus with a screen size of 25,4cm (10 inches). When a voltage of 150 V is applied to the Y-control electrodes (video signal modulation electrodes) as against the X-control electrodes (vertical scanning electrodes), an electron emission current of about 10 µA is produced for each pixel. In place of the ZnO:Zn phosphor material used according to the present embodiment, the three primary colors of red, green and blue may be arranged in stripes to produce a color image. An electrode configuration of a two-dimensional electron source according to another embodiment is shown as a perspective view in Fig. 4. Stripe electrodes 10 having a width of 0.1 mm and thickness of 3 µm are formed by the screen printing method on the surface of the glass substrate 1. As the next step, frit glass of low melting point is laid to a thickness of 1 µm by screen printing at intersections of the stripe electrodes 10 and Y-control electrodes to form an insulating layer 12. In similar fashion, Y-control electrodes 11 having a width of 0.05 mm and thickness of 1 µm are formed in stripes. Further, a cold cathode material WSi₂ is formed by sputtering over the whole surface, and cold cathodes 2 and gate electrodes 3 are formed at the same time by photolithograhy. As shown in Fig. 4, the cold cathodes 2 and the gate electrodes 3 are engaged in the form of comb teeth engaged with each other, and the sides of these electrodes opposed to each other are arranged in parallel to the X-control electrodes (perpendicular to the longitudinal direction of the Y-control electrodes). This arrangement causes emitted electron beams to widen somewhat along the longitudinal direction of the Y-control electrodes but not substantially along the perpendicular direction thereof. As a result, electron beams are prevented from hitting the phosphor material corresponding to adjacent Y-control electrodes, so that what are called crosstalks rarely occur, thus producing a high-definition image display apparatus. In particular, color mixing is effectively prevented in a color image display apparatus configured by three-color phosphor materials in stripes. In this way, a glass substrate 1 making up a two-dimensional electron source and a face plate coated with a phosphor material are sealed with each other in opposed relations and evacuated in the same manner as in the first embodiment thereby to produce an image display apparatus, which is capable of displaying a clear image substantially free of crosstalks like the first embodiment.

Claims: An image display apparatus comprising an insulating substrate (1) having two-dimensionally arranged electron source units (13) controlled by X-Y matrix control electrodes (10, 11) and a face plate (4) coated with a phosphor material and arranged in opposed relationship with the insulating substrate, wherein the said electron source unit corresponding to each intersection of the X-Y matrix control electrodes includes a cold planer field emission cathode (2) connected to an X-control electrode (3) and a planar gate electrode (3) connected to a Y-control electrode opposed to the cold cathode in the same plane, the electron source units being formed in the part of the substrate surface not occupied by the X-and/or Y-control electrodes. An image display apparatus according to Claim 1, wherein a multiplicity of protrusions (8) are formed at the part of the cold cathode opposed to the gate electrode. An image display apparatus according to Claim 1, wherein at least a part of the insulating substrate (1) at the forward ends of the protrusions of the cold cathode is removed. An image display apparatus according to any one of Claims 1 to 2, wherein the cold cathodes and gate electrodes are formed in the fashion of comb teeth engaged with each other. An image display apparatus according to Claim 4, wherein the sides of the electrodes opposed to each other are perpendicular to the longitudinal direction of the Y-control electrode. A method of fabricating an image display apparatus according to Claim 1, comprising the steps of forming X-control electrodes in stripes on the surface of an insulating substrate, forming an insulating layer and forming cold cathodes, gate electrodes and Y-control electrodes at the same time by photolithography. A method of fabricating an image display apparatus according to Claim 1, comprising the steps of forming X-control electrodes and Y-control electrodes, depositing a film of cold cathode material over the whole surface, and forming cold cathodes and gate electrodes simultaneously by photolithography.

Inventors: NONOMURA KINZOU, OKAJIMA MICHIO, SAKIYAMA KAZUYUKI, WATANABE MASANORI, NONOMURA, KINZOU, OKAJIMA, MICHIO, SAKIYAMA, KAZUYUKI, WATANABE, MASANORI
Applicants: MATSUSHITA ELECTRIC IND CO LTD, MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD.
Application year: 1989
Main classification: H01J31
IPC codes: H01J1, H01J31