Display device having a thin film electron source array

The invention provides a display device using thin film type electron sources having a structure that can be formed in a simple manufacturing process. A lower electrode, a protective insulating layer and an interlayer film are formed on a cathode substrate. An upper bus electrode made from a laminated film of a metal film lower layer and a metal film upper layer is provided further on the interlayer film. A film of an upper electrode of a thin film type electron source for each pixel constituted by an insulating layer serving as an electron accelerating layer on the lower electrode and the upper electrode is formed on two stripe electrodes of the upper bus electrode in that pixel and another upper bus electrode in an adjacent pixel by sputtering. Then, the upper electrode is separated by self-alignment due to a setback portion of the metal film lower layer and an appentice of the metal film upper layer of the corresponding upper bus electrode. Thus, a thin film type electron source separated in accordance with each pixel is formed.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a self-emitting flat panel type display device, and particularly relates to a display device using thin film type electron source arrays.

2. Description of the Related Art

An FED (Field Emission Display) using micro cold cathodes that can be integrated is known as one of self-emitting flat panel type display devices using thin film type electron source arrays. The cold cathodes of FED are categorized into field emission type electron sources and hot electron type electron sources. The former includes Spindt type electron sources, surface conduction type electron sources, carbon-nanotube type electron sources, and the like. The latter includes thin film type electron sources of an MIM (Metal-Insulator-Metal) type comprised of a metal-insulator-metal lamination, an MIS (Metal-Insulator-Semiconductor) type comprised of a metal-insulator-semiconductor lamination, a metal-insulator-semiconductor-metal type, and the like.

As the MIM type electron source, for example, an MIM type electron source disclosed in JP-A-7-65710 or JP-A-10-153979 is known. As the metal-insulator-semiconductor type electron source, an MOS type electron source reported in J. Vac. Sci. Technol. B11 (2) p. 429–432 (1993) is known. As the metal-insulator-semiconductor-metal type electron source, an HEED type electron source reported in High-Efficiency-Electro-Emission Device, Jpn. J. Appl. Phys., Vol. 36, p. L939 or the like is known, an EL type electron source reported in Electroluminescence, OYO-BUTURI, Vol. 63, No. 6, p. 592 or the like is known, or a porous silicon type electron source reported in OYO-BUTURI, Vol. 66, No. 5, p. 437 or the like is known. Incidentally, the MIM type electron source is disclosed in each of those documents.

FIG. 1is a view for explaining the structure of an MIM type electron source and the principle of operation thereof. InFIG. 1, the reference numeral11represents a lower electrode;13, an upper electrode;12, an insulating layer; and23, a vacuum atmosphere. In the vacuum atmosphere, a driving voltage Vd is applied between the upper electrode13and the lower electrode11so as to set the electric field in the insulating layer12to reach about 1–10 MV/cm. In this event, electrons e−near the Fermi level in the lower electrode11penetrate a barrier due to a tunneling phenomenon, so as to be injected into a conducting band of the insulating layer12as an electron accelerating layer. Hot electrons formed thus flow into a conducting band of the upper electrode13. Of the hot electrons, ones reaching the surface of the upper electrode13with energy not smaller than a work function φ of the upper electrode13are released to the vacuum23.

It is desired that thin film type electron source arrays applied to a display device or the like can be manufactured with a simple structure and in a simple process in order to attain reduction in cost. A photolithographic method (also referred to as a photo-etching method) is conventionally used for processing thin film type electron sources. However, an exposure device used in a photolithographic process (also referred to as a photo-process simply) is expensive. In addition, associated processes required before and after the photolithographic process, such as coating with resist, pre-baking, exposure, development, post-baking, removing, and cleansing, are long, and the process cost thereof is high.

In contrast, if resist can be printed by screen printing or the like, the cost of the manufacturing apparatus can be reduced. In addition, since the resist can be patterned directly, the processes required before and after the photolithographic process, such as coating, pre-baking and development, can be omitted so that the process cost can be reduced. However, the resist patterning accuracy using the printing method is incommensurably lower than the accuracy using the photo-etching method. Thus, there is a problem in application of the printing method to processing of conventional thin film type electron sources.

When a pattern involving the accuracy of pattern matching in only one lengthwise or crosswise direction is used, the processing accuracy in the resist patterning can be loosened and the printing method can be applied easily in comparison with a pattern involving the accuracy of pattern matching in both the lengthwise and crosswise directions. In the present invention, such a shape involving the accuracy of pattern matching in only one direction is referred to as “stripe shape” in the sense that the shape needs accuracy in only one dimension. In addition, an electrode having a stripe shape pattern is referred to as “stripe electrode”. That is, the stripe electrode is a linear electrode having a width with a structure having no hole, no convex portion, no concave portion, no curved portion, etc. intentionally formed in the electrode.

Particularly, when a printing method such as screen printing, dispenser printing, inkjet printing or transfer printing is used as the patterning method, the stripe electrode is preferred because the stripe electrode is a little affected by deterioration of the patterning accuracy caused by stretch of a screen, a blur of printed resist, or the like.

BRIEF SUMMARY OF THE INVENTION

In order to reduce manufacturing cost of a display device, an object of the present invention is to provide a thin film type electron source using a stripe electrode easy to process in an image display area involving a pattern matching process, and to provide a display device using such thin film type electron sources at a low cost.

In order to attain the foregoing object, according to the present invention, an electron accelerating layer of a thin film electron source is put between two adjacent stripe electrodes, and an upper electrode is divided by self-alignment so as to attain pixel separation in the thin film electron source.

A thin film electron source can be produced using a stripe electrode easy to pattern for each sub-pixel. Further, an upper electrode can be processed by self-alignment. Thus, a display device can be obtained at a low cost.

DETAILED DESCRIPTION OF THE INVENTION

First Embodiment

A first embodiment of the present invention using MIM electron sources will be described with reference toFIGS. 2A–2CtoFIGS. 10A–10CandFIG. 11.FIGS. 2A–2Cto10A–10C are diagrams for explaining manufacturing steps of an MIM electron source forming one picture element in the first embodiment of a display device according to the present invention. The steps are illustrated in turn inFIGS. 2A–2CtoFIGS. 10A–10C.FIGS. 2A–10Aare plan views of one picture element.FIGS. 2B–10Bare sectional views taken on line A–A′ inFIGS. 2A–10Arespectively.FIGS. 2C–10Care sectional views taken on line B–B′ inFIGS. 2A–10Arespectively. Incidentally, one picture element (also referred to as “pixel”) here means a unit picture element for color display. Each picture element is comprised of a plurality of sub-picture elements (hereinafter referred to as “sub-pixels”) displaying different primary colors respectively. In this embodiment, the sub-picture elements include three primary color sub-picture elements of red, green and blue.

First, as shown inFIGS. 2A–2C, a metal film which will be made into lower electrodes11is formed on an insulating substrate (cathode substrate)10of glass or the like. Aluminum (Al) or an aluminum alloy (Al alloy) is used as the material of the lower electrodes11. The reason why Al or an AL alloy is used is that a high-quality insulating film can be formed by anodization of these materials. In this embodiment, an Al—Nd alloy doped with 2% by atomic weight of neodymium (Nd) is used. For example, a sputtering method is used for forming the film of the lower electrodes11. The film thickness is set at 300 nm. After forming the film, stripe-shaped lower electrodes11are formed by a patterning step and an etching step (seeFIGS. 3A–3C).

The electrode width of each lower electrode11varies according to the screen size and resolution of the display device, but is set substantially as large as the alignment pitch of its sub-pixels (about 100–200 μm). The film of the lower electrodes11is etched, for example, by wet etching with a mixed aqueous solution of phosphoric acid, acetic acid and nitric acid. Since the lower electrodes11have a wide and simple stripe shape, an inexpensive printing method can be used for patterning resist for electrode processing. A screen printing method is used in this embodiment. Not to say, a comparatively inexpensive photo-etching process such as proximity exposure can be used instead. Thus, reduction in cost can be attained in comparison with exposure using a stepper, a projection aligner or the like.

Next, a protective insulating layer14and an insulating layer12are formed for limiting each electron emitting portion to thereby prevent an electric field from concentrating on an edge of each lower electrode11. First, a resist film25is applied to the portion which will bean electron emitting portion on each lower electrode11, so that the lower electrode11is masked with the resist film25. The portion which is not masked with the resist film25is anodized to be selectively thick so as to form the protective insulating layer14(FIGS. 4A–4C). The resist film25used in this step has a shape as an electron accelerating layer. It is therefore desired that the processing accuracy is higher than that of the electrodes. To this end, the resist film25is patterned not in a printing method but in a photolithographic process using proximity exposure in this embodiment. When the anodization is performed with a formation voltage of 100V, the protective insulating layer14is formed with a thickness of about 136 nm.

Next, the resist film25is removed, and the remaining surface of each lower electrode11is anodized. For example, when the formation voltage is 6V, the insulating layer12is formed with a thickness of about 10 nm on the lower electrode11(FIGS. 5A–5C).

Next, an interlayer film15is formed, and a metal film for forming upper bus electrodes20as feed lines to upper electrodes13is formed on the interlayer film15, for example, in a sputtering method (FIGS. 6A–6C). For example, a silicon oxide film, a silicon nitride film, a silicon film or the like may be used as the interlayer film15. In this embodiment, a silicon nitride film is used, and the film thickness is set at 100 nm. The interlayer film15serves to fill up possible pinholes in the protective insulating layer14formed by anodization so as to secure insulation between each lower electrode11and each upper bus electrode.

The metal film serving as the upper bus electrodes20has a structure of a lamination of a metal film lower layer16and a metal film upper layer18. For example, an Al—Nd alloy may be used for the metal film lower layer16, and various metal materials such as copper (Cu) or chromium (Cr) may be used for the metal film upper layer18. In this embodiment, an Al—Nd alloy is used as the material of the metal film lower layer16, and Cu is used as the material of the metal film upper layer18.

Subsequently, the metal film upper layer18is processed into a stripe shape crossing each lower electrode11by patterning of resist using screen printing and an etching process. Stripe electrodes of the metal film upper layer18are formed so that one stripe electrode is formed in one pixel (FIGS. 7A–7C). Incidentally, other stripe electrodes adjacent to the stripe electrode illustrated by the metal film upper layer18are not shown inFIG. 7A(the same thing will be applied to the following embodiments).

Subsequently, the metal film lower layer16is processed into a stripe shape crossing each lower electrode11by patterning of resist using screen printing and an etching process. Stripe electrodes of the metal film lower layer16are also formed so that one stripe electrode is formed in one pixel (FIGS. 8A–8C). At that time, the position of a resist film26printed is shifted in parallel with each stripe electrode of the metal film upper layer18formed inFIGS. 7A–7C, so that the resist film26projects from the metal film upper layer18on one side (left side inFIG. 8C) of each stripe electrode of the metal film lower layer16so as to form a projecting portion26A. Etching is suppressed by covering the metal film lower layer16with the projecting portion26A so that a contact portion16A for securing connection with a corresponding upper electrode13which will be formed in a subsequent step and will be described with reference toFIGS. 10A–10Cis formed. On the opposite side (right side inFIG. 8C), an appentice18A is formed in the metal film upper layer18so as to serve as a mask with which a setback portion16B for separating the upper electrodes13will be formed by over-etching of the metal film lower layer16in a subsequent step. Thus, each upper bus electrode20(the laminated film of the metal film lower layer16and the metal film upper layer18) for feeding power to each upper electrode13can be formed.

Subsequently, as shown inFIGS. 9A–9C, the interlayer film15is processed to open each electron release portion. The electron release portion is formed in a part of the space surrounded by one lower electrode11in that pixel and two stripe-shaped upper bus electrodes20(the illustrated upper bus electrode20and another not-illustrated upper bus electrode20adjacent thereto) crossing the lower electrode11. Patterning of resist at that time is performed using proximity exposure because the pattern is a hole pattern. In addition, etching processing can be performed by dry etching using etching gas, for example, having CF4or SF6as a chief component (FIGS. 9A–9C).

Finally, a film of the upper electrodes13shown inFIGS. 10A–10Cis formed. Although various methods can be adopted as the method for forming the film, sputtering from above the interlayer film15is used in this embodiment. For example, a laminated film of iridium (Ir), platinum (Pt) and gold (Au) is used as the film of the upper electrodes13, and the thickness of the film is set at 6 nm. Incidentally, the film thickness is not limited thereto. In this event, each upper electrode13is cut on one side (right side inFIG. 10C) of the adjacent stripe-shaped upper bus electrode20by the appentice of the metal film upper layer18thereof, so as to be separated in accordance with each pixel. On the other hand, on the other side (left side inFIG. 10C) of the stripe-shaped upper bus electrode20, the film serving as the upper electrode13is formed continuously without disconnection to cover the interlayer film15or the insulating layer12due to the contact portion of the metal film lower layer16. Thus, a structure to feed power to the electron source is arranged. The same thing about the formation of the film serving as the upper electrodes13is applied to the following embodiments that will be described later.

FIG. 11is a partially enlarged schematic plan view for explaining the structure of the first embodiment of the display device according to the present invention. Incidentally, parts having the same functions as those inFIG. 1andFIGS. 2A–2Cto10A–10C are denoted by the same reference numerals correspondingly. This display device is constituted by a display panel in which a cathode-side substrate10(hereinafter also referred to as “cathode substrate10”) and a display-side substrate100(hereinafter also referred to as “fluorescent screen substrate100”) are laminated to each other (the same thing is applied to the following embodiments). Incidentally, inFIG. 11, the fluorescent screen substrate100is illustrated only partially in order to avoid complication, and parts of constituent members of the fluorescent screen formed in the internal surface of the fluorescent screen substrate100are shown on the cathode substrate10. The fluorescent screen is formed out of red phosphor111, green phosphor112and blue phosphor113sectioned by a black matrix120in order to increase the contrast. In addition, a film of an anode to which a high voltage of several kV is applied is formed in the internal surface of the fluorescent screen substrate100. Incidentally, the anode is not shown inFIG. 11(the same thing is applied to the following embodiments).

For example, Y2O2S:Eu(P22-R), ZnS:Cu,Al(P22-G) and ZnS:Ag,Cl(P22-B) may be used as the red, green, and blue phosphors respectively for forming the fluorescent screen. The black matrix120is formed in the internal surface of the display-side substrate100so as to surround the circumference of each color phosphor to thereby separate the color phosphor from the other adjacent phosphors.

The cathode substrate10and the fluorescent screen substrate100are laminated to each other through high-strength spacers30for supporting the panel against the atmospheric pressure. Each of the spacers30is made of plate-like glass or ceramics given conductivity in order to prevent electrostatic charge. The spacers30are disposed on the metal film upper layer18forming the upper bus electrodes20of the cathode substrate10, so as to be hidden under the black matrix120of the fluorescent screen substrate100. The lower electrodes11are connected to a signal line circuit50for supplying display signals (display data) to pixels, and the upper bus electrodes20formed out of a laminated film of the metal film lower layer16and the metal film upper layer18are connected to a scanning line circuit60for supplying selection signals to the pixels. In each thin film type electron source configured thus, a voltage applied to a scanning line constituted by the upper bus electrode20is in a range of from several V to several tens V, which is sufficiently lower than the potential of the fluorescent screen to which a voltage of several kV is applied. Thus, potential substantially as low as the ground potential can be applied to the cathode side of each spacer30. Accordingly, the upper bus electrode20made from a laminated film of the metal film lower layer16and the metal film upper layer18can be also used as a spacer electrode. In this embodiment, the upper bus electrode20is also used as a spacer electrode.

As is obvious fromFIG. 11, in the circuit connection portion where connection is established between each lower electrode11and the signal line circuit50and between each upper bus electrode20and the scanning line circuit60outside the image display area corresponding to the area where the upper electrodes13are formed, the terminal pitch of each electrode typically differs from that in the image display area. Since there is no electron source in the circuit connection portion, pattern matching is not necessary. Therefore, each electrode in the connection portion does not have to have a stripe shape. Thus, the electrode in the connection portion can be processed in a printing method with low patterning accuracy, and typically does not have to be formed into a stripe shape.

In addition, as is obvious fromFIG. 11, each thin film type electron source in an end portion of the image display area, that is, each thin film type electron source in the upper end row inFIG. 11in this embodiment has no adjacent pixel on the upper side. Thus, pixel separation using two stripe electrodes is not required.

In such a manner, in the cathode structure of the display device according to this embodiment, each of the lower electrodes11serving as signal lines (data lines) and the upper bus electrodes20(laminated film of the metal film lower layer16and the metal film upper layer18) serving as both scanning lines and spacer electrodes is formed out of one simple stripe electrode in one sub-pixel within the image display area. Further, the cathode structure has a function capable of separating the upper electrodes13by self-alignment. Thus, the electrodes can be formed even by use of an inexpensive and low-accuracy patterning method such as a printing method.

Second Embodiment

Next, a second embodiment of the present invention using MIM electron sources by way of example will be described with reference toFIGS. 2A–2Cto6A–6C,FIGS. 12A–12Cto15A–15C andFIG. 16.FIGS. 12A–12Cto15A–15C are diagrams for explaining steps for manufacturing an MIM electron source forming one picture element in the second embodiment of the display device according to the present invention. The steps are shown in turn alongFIGS. 2A–2CtoFIGS. 6A–6CandFIGS. 12A–12Cto15A–15C.FIGS. 12A–15Aare plan views of one picture element.FIGS. 12B–15Bare sectional views taken on line A–A′ inFIGS. 12A–15Arespectively.FIGS. 12C–15Care sectional views taken on line B–B′ inFIGS. 12A–15Arespectively. In addition,FIG. 16is a partially enlarged schematic plan view for explaining the structure of the second embodiment of the display device according to the present invention. Incidentally, parts having the same functions as those in the drawings of the aforementioned embodiment are denoted by the same reference numerals correspondingly.

First, a lower electrode11, a protective insulating layer14and an insulating layer12are formed and an interlayer film15, a metal film lower layer16and a metal film upper layer18(18′) are formed thereon in the same manner as the steps shown inFIGS. 2A–2Cto6A–6C in the description of the first embodiment. Subsequently, the metal film upper layer18(18′) of an upper bus electrode20is processed into stripe electrodes crossing the lower electrode11by patterning of resist using screen printing and an etching process. Thus, two stripe electrodes are formed in one pixel (FIGS. 12A–12C).

Subsequently, the metal film lower layer16of the upper bus electrode20is processed into stripe electrodes (metal film lower layers16and16′) crossing the lower electrode11by patterning of resist using screen printing and an etching process (FIGS. 13A–13C). At that time, as shown inFIG. 13C, the position of a resist film26printed is shifted in parallel with the stripe electrode of the metal film upper layer18formed inFIGS. 12A–12C, so that the resist film26projects from the metal film upper layer18on the insulating layer12side (left side inFIG. 13C) so as to form a projecting portion26A on one (metal film lower layer16) of the stripe electrodes. Due to the projecting portion26A, a contact portion16A for securing connection between the upper electrode13and the metal film lower layer16as will be formed in a subsequent step and as will be described with reference toFIGS. 15A–15Cis formed in the metal film lower layer16.

On the opposite side (right side inFIG. 13C) to the insulating layer12, an appentice18A is formed in the metal film upper layer18so as to serve as a mask with which the metal film lower layer16is set back by over-etching. A setback portion16B formed thus in the metal film lower layer16serves to separate an upper electrode13which will be formed by sputtering in a subsequent step. Thus, an upper bus electrode20(a laminated film of the metal film lower layer16and the metal film upper layer18) for feeding power to the upper electrode13can be formed in each pixel. On the other hand, in the other metal film upper layer18′ serving as a stripe electrode disposed on the left side ofFIG. 13C, the metal film lower layer16′ is over-etched both on the insulating layer12side and on the opposite side thereto. Thus, the metal film lower layer16′ is set back so that an appentice is formed on each side of the metal film upper layer18′. This appentice serves as a mask for separating the upper electrode13which will be formed by sputtering in a subsequent step as will be described later with reference toFIGS. 15A–15C. Incidentally, this electrode (upper bus electrode20constituted by the metal film lower electrode16′ and the metal film upper portion18′) finally serves as a spacer electrode21(FIG. 16) on which the spacers30are disposed.

Subsequently, the interlayer film15is processed to open electron emission portions. Each electron emission portion is formed in a part of a crossing portion of the space surrounded by one lower electrode11in that pixel and two stripe-shaped electrodes (the upper bus electrode20constituted by the metal film lower layer16and the metal film upper layer18and the spacer electrode21constituted by the metal film lower layer16′ and the metal film upper layer18′) crossing the lower electrode11. The processing of opening the electron emission portions can be performed by dry etching using etching gas, for example, having CF4or SF6as a chief component (FIGS. 14A–14C).

Finally, a film of the upper electrode13shown inFIGS. 15A–15Cis formed. A sputtering method is used for forming the film by way of example. For example, a laminated film of Ir, Pt and Au is used for the film of the upper electrode13, and the thickness of the film is set at 6 nm. In this event, the upper electrode13is cut by the appentices of the metal film upper layers18and18′ of the two stripe electrodes (the upper bus electrode20and the spacer electrode21), so as to be separated in accordance with each pixel. On the other hand, on the insulating layer12side of the upper bus electrode20, the film serving as the upper electrode13is connected without disconnection due to the contact portion16A of the metal film lower layer16. Thus, a structure to feed power over the interlayer film15and the insulating layer12is arranged.

FIG. 16is a partially enlarged schematic plan view for explaining the structure of the second embodiment of the display device according to the present invention. A fluorescent screen made from a black matrix120for increasing the contrast, red phosphor111, green phosphor112and blue phosphor113is formed in the internal surface of a fluorescent screen substrate100. For example, Y2O2S:Eu(P22-R), ZnS:Cu,Al(P22-G) and ZnS:Ag,Cl(P22-B) may be used as the red, green and blue phosphors respectively for forming the fluorescent screen. The black matrix120is formed in the internal surface of the display-side substrate100so as to surround the circumference of each color phosphor to thereby separate the color phosphor from the other adjacent phosphors. In addition, a film of an anode to which a high voltage of several kV is applied is formed in the internal surface of the fluorescent screen substrate100.

The spacers30are disposed on the spacer electrode21of the cathode substrate10so as to be hidden under the black matrix120of the fluorescent screen substrate100. Each lower electrode11is connected to a signal line circuit50, and each upper bus electrode20(laminated film of the metal film lower layer16and the metal film upper layer18) is connected to a scanning line circuit60. Each laminated film of the metal film lower layer16′ and the metal film upper layer18′ serves as a spacer electrode21, which is typically grounded.

As is obvious fromFIG. 16, in the circuit connection portion where connection is established between each lower electrode11and the signal line circuit50and between each upper bus electrode20and the scanning line circuit60outside the image display area corresponding to the area where the upper electrodes13are formed, the terminal pitch of each electrode typically differs from that in the image display area. Since there is no electron source in the circuit connection portion, pattern matching is not necessary. Therefore, each electrode in the connection portion does not have to have a stripe shape. Thus, the electrode in the connection portion can be processed in a printing method with low patterning accuracy, and typically does not have to be formed into a stripe shape.

In addition, as is obvious fromFIG. 16, each thin film type electron source in an end portion of the image display area, that is, each thin film type electron source in the upper end row inFIG. 16in this embodiment has no adjacent pixel on the upper side. Thus, pixel separation using two stripe electrodes is not required.

In such a manner, in the cathode structure of the display device according to this embodiment, each of the lower electrodes11serving as signal lines (data lines), the upper bus electrodes20(laminated film of the metal film lower layer16and the metal film upper layer18) serving as scanning lines, and the spacer electrodes21(laminated film of the metal film lower layer16′ and the metal film upper layer18′) is formed as one simple stripe electrode. Further, the cathode structure has a function capable of separating the upper electrodes13by self-alignment. Thus, the electrodes can be formed even by use of an inexpensive and low-accuracy patterning method such as a printing method.

Third Embodiment

Next, a third embodiment of the display device according to the present invention using MIM electron sources by way of example will be described with reference toFIGS. 2A–2Cto6A–6C,FIGS. 17A–17Cto20A–20C andFIG. 21.FIGS. 17A–17Cto20A–20C are diagrams for explaining steps for manufacturing an MIM electron source forming one picture element in the third embodiment of the display device according to the present invention.FIGS. 17A–20Aare plan views of one picture element.FIGS. 17B–20Bare sectional views taken on line A–A′ inFIGS. 17A–20Arespectively.FIGS. 17C–20Care sectional views taken on line B–B′ inFIGS. 17A–20Arespectively. In addition,FIG. 21is a partially enlarged schematic plan view for explaining the structure of the third embodiment of the display device according to the present invention. Incidentally, parts having the same functions as those in the drawings of the aforementioned embodiments are denoted by the same reference numerals correspondingly.

First, a lower electrode11, a protective insulating layer14and an insulating layer12are formed and an interlayer film15, a metal film lower layer16and a metal film upper layer18are formed thereon in the same manner as the steps shown inFIGS. 2A–2Cto6A–6C in the first embodiment.

Subsequently, the metal film upper layer18is processed into stripe electrodes crossing the lower electrode11by patterning of resist using screen printing and an etching process. Thus, three stripe electrodes (metal film upper layers18,18′ and18″) are formed in one pixel (FIGS. 17A–17C).

Next, the metal film lower layer16is formed into stripe electrodes (metal film lower layers16,16′ and16″) crossing the lower electrode11by patterning of resist using screen printing and an etching process (FIGS. 18A–18C). At that time, in the same manner as in the aforementioned embodiments, the positions of resist films26and26′ printed are shifted in parallel with the stripe electrodes of the metal film upper layers18′ and18″, formed inFIGS. 17A–17C, so that the resist films26and26′ project from the metal film upper layers18′ and18″ on the insulating layer12side respectively so as to form projecting portions on two stripe electrodes (metal film lower layers16′ and16″) having an insulating layer12put therebetween. Each projecting portion will serve as a contact portion for securing connection with an upper electrode13in a subsequent step.

The insulating layer12is put between the metal film lower layers16′ and16″. On the other side of the metal film lower layer16′,16″, opposite to the insulating layer12, an appentice is formed with the metal film upper layer18′,18″ as a mask so as to serve as a mask with which the metal film lower layer16′,16″ will be over-etched to separate the upper electrode13in a subsequent step. Thus, two upper bus electrodes (a laminated film of the metal film lower layer16′ and the metal film upper layer18′ and a laminated film of the metal film lower layer16″ and the metal film upper layer18″) for feeding power to the upper electrode13can be formed. On the other hand, an appentice is formed on each side of the other stripe electrode (a laminated film of the metal film lower layer16and the metal film upper layer18) with the metal film upper layer18as a mask so as to serve as a mask for separating the upper electrode13. This electrode finally serves as a spacer electrode21on which spacers are disposed.

Subsequently, the interlayer film15is processed to open electron emission portions (FIGS. 19A–19C). Each electron emission portion is formed in a part of a crossing portion of the space surrounded by one lower electrode11in that pixel and two stripe-shaped electrodes (one is a laminated film of the metal film lower layer16′ and the metal film upper layer18′ and the other is a laminated film of the metal film lower layer16″ and the metal film upper layer18″) crossing the lower electrode11and forming contact portions16′A and16″A. Etching the interlayer film15to thereby open the electron emission portions can be performed by dry etching using etching gas, for example, having CF4or SF6as a chief component.

Finally, a film of the upper electrode13is formed as shown inFIGS. 20A–20C. A sputtering method is used for forming the film by way of example. For example, a laminated film of Ir, Pt and Au is used as the film of the upper electrode13, and the thickness of the film is set at 6 nm. In this event, the upper electrode13is cut by the appentices in the outside of the two upper bus electrodes (the laminated film of the metal film lower layer16′ and the metal film upper layer18′ and the laminated film of the metal film lower layer16″ and the metal film upper layer18″) having the contact portions16′A and16″A formed therein respectively as shown inFIGS. 19A–19C, and by the appentice on each side of the spacer electrode21(the laminated film of the metal film lower layer16and the metal film upper layer18) so as to be separated in accordance with each pixel. On the other hand, on the insulating layer12side, the film serving as the upper electrode13is connected without disconnection due to the contact portions16′A and16″A of the metal film lower layers16′ and16″. Thus, a structure to feed power over the interlayer film15and the insulating layer12is arranged.

FIG. 21is a partially enlarged schematic plan view for explaining the structure of the third embodiment of the display device according to the present invention. A fluorescent screen made from a black matrix120for increasing the contrast, red phosphor111, green phosphor112and blue phosphor113is formed in the internal surface of a fluorescent screen substrate100. For example, Y2O2S:Eu(P22-R), ZnS:Cu,Al(P22-G) and ZnS:Ag,Cl(P22-B) may be used as the red, green, and blue phosphors respectively for forming the fluorescent screen. The black matrix120is formed in the internal surface of the display-side substrate100so as to surround the circumference of each color phosphor to thereby separate the color phosphor from the other adjacent phosphors. In addition, a film of an anode to which a high voltage of several kV is applied is formed in the internal surface of the fluorescent screen substrate100.

This embodiment is different from the first embodiment in that each electron release portion is not close to the spacer electrode21constituted by the metal film lower layer16and the metal film upper layer18. Accordingly, it is easy to position the spacer30, and it is also easy to increase the open area ratio of each phosphor. Further, an enough distance can be secured between the spacer30and the thin film type electron source. Thus, there is an advantage that the electron inflow to the spacer30is reduced so that the spacer30becomes difficult to charge.

The lower electrodes11are connected to a signal line circuit50, and the upper bus electrodes (a laminated film of the metal film lower layer16′ and the metal film upper layer18′ and a laminated film of the metal film lower layer16″, and the metal film upper layer18″) are connected to a scanning line circuit60. The spacer electrode21comprised of a laminated film of the metal film lower layer16and the metal film upper layer18is typically grounded.

As is obvious fromFIG. 21, in the circuit connection portion outside the image display area corresponding to the area where the upper electrodes13are formed, the terminal pitch of each electrode typically differs from that in the image display area. Since there is no electron source in the circuit connection portion, pattern matching is not necessary. Therefore, each electrode in the connection portion does not have to have a stripe shape. Thus, the electrode in the connection portion can be processed in a printing method with low patterning accuracy, and typically does not have to be formed into a stripe shape.

In such a manner, in the cathode structure according to this embodiment, each of the lower electrodes11, the upper bus electrodes20and the spacer electrode21is formed as one simple stripe electrode. Further, the cathode structure has a function capable of separating the upper electrodes13by self-alignment. Thus, the electrodes can be formed even by use of an inexpensive and low-accuracy patterning method such as a printing method. Further, the cathode structure is advantageous in view of the positioning of the spacers30and the increased open area ratio of the fluorescent screen.

Fourth Embodiment

Next, a fourth embodiment of the present invention using MIM electron sources by way of example will be described with reference toFIGS. 2A–2Cto5A–5C,FIGS. 22A–22Cto27A–27C andFIG. 28.FIGS. 22A–22Cto27A–27C are diagrams for explaining steps for manufacturing an MIM electron source forming one picture element in the fourth embodiment of the present invention.FIGS. 22A–27Aare plan views of one picture element.FIGS. 22B–27Bare sectional views taken on line A–A′ inFIGS. 22A–27Arespectively.FIGS. 22C–27Care sectional views taken on line B–B′ inFIGS. 22A–27Arespectively. In addition,FIG. 28is a partially enlarged schematic plan view for explaining the structure of the fourth embodiment of the display device according to the present invention. Incidentally, parts having the same functions as those in the drawings of the aforementioned embodiments are denoted by the same reference numerals correspondingly.

First, a lower electrode11, a protective insulating layer14and an insulating layer12are formed in the same manner as the steps shown inFIGS. 2A–2Cto5A–5C in the first embodiment. Next, as shown inFIGS. 22A–22C, an interlayer film15and a metal film are formed, for example, in a sputtering method or the like. The metal film serves as an upper bus electrode which will be a power feeder to upper electrodes13and a spacer electrode on which spacers will be disposed. For example, a silicon oxide film, a silicon nitride film, a silicon film or the like may be used as the interlayer film15. In this embodiment, a silicon nitride film is used, and the film thickness is set at 100 nm. The interlayer film15serves to fill up possible pinholes in the protective insulating layer14formed by anodization, so as to secure insulation between each lower electrode11and each upper bus electrode.

In this embodiment, the upper bus electrode is formed as a three-layer laminated film in which Cu as a metal film intermediate layer17is inserted between a metal film lower layer16and a metal film upper layer18. The laminated film is not limited to such a three-layer laminated film, but may include four or more layers. A metal material high in oxidation resistance, such as Al, chromium (Cr), tungsten (W) or molybdenum (Mo), an alloy containing those materials, or a laminated film of those materials may be used for the metal film lower layer16and the metal film upper layer18. Incidentally, in this embodiment, an Al—Nd alloy is used for the metal film lower layer16and the metal film upper layer18. Alternatively, a five-layer film using a laminated film of Cr, W, Mo or the like and an Al alloy as the metal film lower layer16, a laminated film of Cr, W, Mo or the like and an Al alloy as the metal film upper layer18, and high-melting metal for films in contact with Cu of the metal film intermediate layer17may be used. In this case, the high-melting metal serves as a barrier film in the heating step in the manufacturing process of the display device, so that alloying of Al and Cu can be suppressed. Thus, such a five-layer film is effective particularly in reducing in resistance.

When only the Al—Nd alloy is used, the film thickness of the Al—Nd alloy is set so that the metal film upper layer18is thicker than the metal film lower layer16, and Cu of the metal film intermediate layer17is as thick as possible in order to reduce the wiring resistance thereof. In this embodiment, the thickness of the metal film lower layer16is set at 300 nm, the thickness of the metal film intermediate layer is set at17, 4 μm, and the thickness of the metal film upper layer18is set at 450 nm. Incidentally, Cu of the metal film intermediate layer17may be formed by electroplating or the like as well as sputtering.

In the case of the five-layer film using high-melting metal, it is particularly effective that a laminated film in which Cu is inserted between pieces of Mo and which can be wet-etched with a mixed aqueous solution of phosphoric acid, acetic acid and nitric acid, is used as the metal film intermediate layer17in the same manner as Cu. In this case, each Mo film into which Cu is inserted is set to be 50 nm thick, and the Al alloy films as the metal film lower layer16and the metal film upper layer18having the metal film intermediate layer17put therebetween are set to be 300 nm thick and 50 nm thick respectively.

Subsequently, the metal film upper layer18is processed into a stripe shape crossing the lower electrode11by patterning of resist using screen printing and an etching process, as shown inFIGS. 23A–23C. In this etching process, for example, wet etching with a mixed aqueous solution of phosphoric acid and acetic acid is used. Since nitric acid is not added to the etchant, Cu is not etched but only the Al—Nd alloy can be selectively etched.

Also in the case of the five-layer film using Mo, when nitric acid is not added to the etchant, Mo and Cu is not etched but only the Al—Nd alloy can be selectively etched. In this embodiment, one piece of the metal film upper layer18is formed in each pixel in the same manner as in the first embodiment, but two pieces may be formed in the same manner as in the second embodiment.

Subsequently, using the same resist film as it is, or using the Al—Nd alloy of the metal film upper layer18as a mask, Cu of the metal film intermediate layer17is wet-etched, for example, with a mixed aqueous solution of phosphoric acid, acetic acid and nitric acid (FIGS. 24A–24C). The etching rate of Cu in the etchant of the mixed aqueous solution of phosphoric acid, acetic acid and nitric acid is much higher than that of the Al—Nd alloy. Thus, only Cu of the metal film intermediate layer17can be etched selectively. Also in the case of the five-layer film using Mo, the etching rate of Mo and Cu is much higher than that of the Al—Nd alloy. Thus, only the three-layer laminated film of Mo and Cu can be etched selectively. Alternatively, an ammonium persulfate aqueous solution or a sodium persulfate aqueous solution is also effective in etching Cu.

Subsequently, the metal film lower layer16is processed into a stripe shape crossing the lower electrode11by patterning of resist using screen printing and an etching process (FIGS. 25A–25C). The etching process is performed with a mixed aqueous solution of phosphoric acid and acetic acid. At that time, the position of a resist film26printed is shifted in parallel with the stripe electrode of the metal film upper layer18formed inFIGS. 23A–23C, so that the resulting metal film lower layer16projects from the metal film upper layer18on one side (left side ofFIG. 25C) so as to form a contact portion16A for securing connection with the upper electrode13in a subsequent step. On the other side (right side ofFIG. 25C) of the metal film lower layer16, over-etching is performed with the metal film upper layer18and the metal film intermediate layer17as a mask so as to set back the metal film lower layer16as if an appentice is formed in the metal film intermediate layer17. Thus, a setback portion16B is formed.

The appentice of the metal film intermediate layer17serves to separate the film of the upper electrode13formed in a subsequent step. At that time, since the metal film upper layer18is made thicker than the metal film lower layer16, the metal film upper layer18can be left on Cu of the metal film intermediate layer17even after the etching of the metal film lower layer16. Thus, the surface of Cu can be protected so that the oxidation resistance can be secured in spite of use of Cu, and the upper electrode13can be separated by self-alignment, while an upper bus electrode20for feeding power to the upper electrode13can be formed. In the case where the five-layer film having Cu put between pieces of Mo is used as the metal film intermediate layer17, Mo can suppress the oxidization of Cu even if the Al alloy of the metal film upper layer18is thin. Thus, it is not always necessary to make the metal film upper layer18thicker than the metal film lower layer16.

Subsequently, the interlayer film15is processed to open electron emission portions. Each electron emission portion is formed in a part of a crossing portion of the space surrounded by one lower electrode11in the pixel and two upper bus electrodes (one is a laminated film of the metal film lower layer16, the metal film intermediate layer17and the metal film upper layer18and the other is a laminated film of the metal film lower layer16, the metal film intermediate layer17and the metal film upper layer18in a not-shown adjacent pixel) crossing the lower electrode11. This etching can be performed by dry etching using etching gas, for example, having CF4or SF6as a chief component (FIGS. 26A–26C).

Finally, a film of the upper electrode13is formed. A sputtering method is used for forming the film in this embodiment. For example, a laminated film of Ir, Pt and Au is used as the film of the upper electrode13, and the thickness of the film is set at 6 nm. In this event, the upper electrode13is cut by the setback portion16B of the metal film lower layer16based on the appentice structure of the metal film intermediate layer17and the metal film upper layer18on one side (right side inFIG. 27C) of the two upper bus electrodes (the laminated film of the metal film lower layer16, the metal film intermediate layer17and the metal film upper layer18) having an electron emission portion put therebetween. On the other side (left side inFIG. 27C) of the two upper bus electrodes, the film serving as the upper electrode13is connected to the upper bus electrode (the laminated film of the metal film lower layer16, the metal film intermediate layer17and the metal film upper layer18) without disconnection due to the contact portion16A of the metal film lower layer16. Thus, a structure to feed power to the electron release portion is arranged (FIGS. 27A–27C).

FIG. 28is a partially enlarged schematic plan view for explaining the structure of the fourth embodiment of the display device according to the present invention. In the same manner as in the aforementioned embodiments, a black matrix120for increasing the contrast, red phosphor111, green phosphor112and blue phosphor113are formed in a fluorescent screen substrate100. For example, Y2O2S:Eu(P22-R), ZnS:Cu,Al(P22-G) and ZnS:Ag,Cl(P22-B) may be used as the red, green and blue phosphors respectively. The black matrix120is formed in the internal surface of the display-side substrate100so as to surround the circumference of each color phosphor to thereby separate the color phosphor from the other adjacent phosphors. In order to avoid complication of the drawing, the black matrix and the phosphors of the respective colors are shown in only a part of the image display area. In addition, a film of an anode to which a high voltage of several kV is applied is formed in the internal surface of the fluorescent screen substrate100.

The spacers30are disposed on the upper bus electrode20of the cathode substrate10so as to be hidden under the black matrix120of the fluorescent screen substrate100. Each lower electrode11is connected to a signal line circuit50, and each upper bus electrode20is connected to a scanning line circuit60. In each thin film type electron source configured thus, a voltage applied to the upper bus electrode20serving as a scanning line is in a range of from several V to several tens V, which is sufficiently lower than a voltage of several kV to be applied to the anode of the fluorescent screen substrate100. Thus, potential substantially as low as the ground potential can be applied to the anode side of each spacer30.

As is obvious fromFIG. 28, in the circuit connection portion outside the image display area corresponding to the area where the upper electrodes13are formed, the electrode terminal pitch of the lower electrodes11or the upper bus electrodes20typically differs from that in the image display area. Since there is no electron source in the circuit connection portion, pattern matching is not necessary. Therefore, each electrode terminal in the connection portion does not have to have a stripe shape. Thus, the electrode terminal in the connection portion can be processed in a printing method with a low patterning accuracy and typically does not have to have a stripe shape.

In addition, as is obvious fromFIG. 28, each thin film type electron source in an end portion of the image display area (each thin film type electron source in the upper end row inFIG. 28in this embodiment) has no adjacent pixel. Thus, pixel separation using two stripe electrodes as in the image display area is not required.

In such a manner, in the cathode structure forming the display device according to this embodiment, due to the structure of a laminated film in which low-resistance Cu wiring is put between pieces of an Al alloy, Cr or the like having oxidization resistance, the upper electrode13can be processed by self-alignment, and the upper bus electrode (laminated film of the metal film lower layer16, and the metal film intermediate layer17and the metal film upper layer18) prevented from deteriorating even in a sealing step can be produced. Thus, a voltage drop due to the wiring resistance of the display device can be suppressed. Particularly when a five-layer laminated film structure in which high-melting metal such as Mo is inserted between an Al alloy and Cu is used, alloying reaction between Al and Cu can be prevented so that the wiring resistance can be kept low specially.

In addition, due to the thick upper bus electrode (laminated film of the metal film lower layer16, and the metal film intermediate layer17and the metal film upper layer18), the thin film type electron sources can be prevented from being mechanically damaged by the spacers bearing the atmosphere.

Fifth Embodiment

Next, a fifth embodiment of the present invention using MIM electron sources by way of example will be described with reference toFIGS. 2A–2Cto5A–5C,FIGS. 22A–22Cto27A–27C,FIGS. 29A–29CandFIG. 30.FIGS. 29A–29Cshow a step for manufacturing an MIM electron source forming one picture element in the fifth embodiment of the display device according to the present invention.FIG. 29Ais a plan view of one picture element.FIG. 29Bis a sectional view taken on line A–A′ inFIG. 29A.FIG. 29Cis a sectional view taken on line B–B′ inFIG. 29A. In addition,FIG. 30is a partially enlarged schematic plan view for explaining the structure of the fifth embodiment of the display device according to the present invention. Incidentally, parts having the same functions as those in the drawings of the aforementioned embodiments are denoted by the same reference numerals correspondingly.

First, steps until forming the film of an upper electrode13are performed in the same manner as that in the description ofFIGS. 2A–2Cto5A–5C andFIGS. 22A–22Cto27A–27C in the fourth embodiment. Subsequently, a paste containing a metal material such as silver (Ag) and a glass material is printed on an upper bus electrode (a laminated film of a metal film lower layer16, a metal film intermediate layer17and a metal film upper layer18) in a screen printing method, a dispenser method, an inkjet method or the like, so as to form a thick film electrode22. The thick film electrode22can be made about 10–20 μm thick enough to reduce the wiring resistance and absorb the pressure from spacers. Further, the conductive properties of the thick film electrode22prevents the spacers from being charged, while the spacers can be fixed firmly by baking the glass contained in the thick film electrode22. The thick film electrode22is baked in a high temperature process when sealing is secured between the thick film electrode22and the fluorescent screen substrate100after the thick film electrode22is dried. Thus, low resistance and bonding with the spacers are attained (FIGS. 29A–29C). The formation of the film of the upper electrode13is performed in the same manner as in the aforementioned embodiments.

FIG. 30is a partially enlarged schematic plan view for explaining the structure of the fifth embodiment of the display device according to the present invention. In the same manner as in the aforementioned embodiments, a black matrix120for increasing the contrast, red phosphor111, green phosphor112and blue phosphor113are formed in a fluorescent screen substrate100. For example, Y2O2S:Eu(P22-R), ZnS:Cu,Al(P22-G) and ZnS:Ag,Cl(P22-B) may be used as the red, green and blue phosphors respectively. The black matrix120is formed in the internal surface of the display-side substrate100so as to surround the circumference of each color phosphor to thereby separate the color phosphor from the other adjacent phosphors. In order to avoid complication of the drawing, the black matrix and the phosphors of the respective colors are shown in only a part of the image display area. In addition, a film of an anode to which a high voltage of several kV is applied is formed in the internal surface of the fluorescent screen substrate100.

The spacers30are disposed on the thick film electrode22formed on the cathode substrate10so as to be hidden under the black matrix120formed in the fluorescent screen substrate100. Each lower electrode11is connected to a signal line circuit50, and each thick film electrode22is connected to a scanning line circuit60. In each thin film type electron source configured thus, a voltage applied to the thick film electrode22serving as a scanning line is in a range of from several V to several tens V, which is sufficiently lower than a voltage of several kV to be applied to the anode of the fluorescent screen. Thus, potential substantially as low as the ground potential can be applied to the cathode side of each spacer.

As is obvious fromFIG. 30, in the circuit connection portion outside the image display area corresponding to the area where the upper electrodes13are formed, the electrode terminal pitch of the lower electrodes11or the upper bus electrodes20typically differs from that in the image display area. Since there is no electron source in the circuit connection portion, pattern matching is not necessary. Therefore, each electrode terminal in the connection portion does not have to have a stripe shape. Thus, each electrode terminal in the connection portion can be processed in a printing method with a low patterning accuracy and typically does not have to have a stripe shape.

In addition, as is obvious fromFIG. 30, each thin film type electron source in an end portion of the image display area (each thin film type electron source in the upper end row inFIG. 30in this embodiment) has no adjacent pixel. Thus, pixel separation using two stripe electrodes as in the inside of the image display area is not required.

In such a manner, in the cathode structure forming the display device according to this embodiment, due to the thick film paste of Ag or the like printed on the upper bus electrode, a voltage drop due to the wiring resistance of the display device can be suppressed. In addition, the thick film electrode22is thick enough to absorb the pressure of each spacer30. Thus, each thin film electron source can be prevented from being mechanically damaged by the spacer30.