Method of bonding display substrates by application of an electric current to heat and melt a bonding material

After sealing layers are formed on peripheral edge parts of a front substrate and a rear substrate, the front substrate and the rear substrate are disposed to be opposed to each other. Current paths are formed in the sealing layers, and power supply is begun. An electric current, which reaches a maximum current value after a current-increasing period of 10% or more of an entire power-supply time, is supplied for a perdetermined time period. The sealing layers are heated and melted by the power supply, and peripheral parts of the front substrate and rear substrate are joined.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a manufacturing method and a manufacturing apparatus for a flat image display device including a pair of substrates which are opposed to each other and are attached to each other at their peripheral edge parts.

2. Description of the Related Art

In recent years, various image display devices have been developed as next-generation light-weight, small-thickness display devices, which will take the place of cathode-ray tubes (hereinafter, referred to as CRTs). Such image display devices include liquid crystal displays (LCDS) which control the intensity of light by making use of alignment of liquid crystal, plasma display panels (PDPs) which cause phosphors to emit light by ultraviolet of plasma discharge, field emission displays (FEDs) which cause phosphors to emit light by electron beams of field-emission-type electron emitting elements, and surface-conduction electron-emitter displays (SEDs) which cause phosphors to emit light by electron beams of surface-conduction-type electron emitting elements.

The FED or SED, for example, generally comprises a front substrate and a rear substrate that are opposed to each other across a predetermined gap. These substrates have their respective peripheral portions joined together by a sidewall in the form of a rectangular frame, thereby forming a vacuum envelope. A phosphor screen is formed on the inner surface of the front substrate. Provided on the inner surface of the rear substrate are a large number of electron emitting elements for use as electron emission sources, which excite the phosphors to luminescence.

A plurality of support members are provided between the rear substrate and the front substrate in order to support an atmospheric-pressure load acting on these substrates. The rear substrate-side potential is substantially set at a ground potential, and an anode voltage is applied to the phosphor surface. Electron beams, which are emitted from the electron emitting elements, are applied to red, green and blue phosphors of the phosphor screen, and cause the phosphors to emit light. Thereby, an image is displayed.

According to the FED or SED constructed in this manner, the thickness of the display device can be reduced to about several millimeters, so that the device can be made lighter in weight and thinner than CRTs that are used as displays of existing TVs or computers.

For the FED, for example, various manufacturing methods have been examined to join the front substrate and the rear substrate that constitute the envelope by means of the sidewall in the form of a rectangular frame. In general, a sintering material such as frit glass is filled between the two substrates and the side wall, and the sintering material is heated and sintered in a furnace. Thus, the substrates and the side wall are coupled to form the envelope. In an example of the basic procedure, a structure, in which the rear substrate and side wall are coupled by fusion, is prepared in advance, and the front substrate is joined to this structure.

However, when frit glass is sintered, unnecessary gas is produced. The gas remains in the sealed envelope after fusion, and the gas causes a problem when the inside of the envelope is evacuated later to a high vacuum level. Jpn. Pat. Appln. KOKAI Publication No. 2002-319346, for instance, discloses another method. In this method, a low-melting-point sealing material, such as indium, is filled between the front substrate and rear substrate. Then, current is supplied to the sealing material in a vacuum apparatus, and the sealing material itself is heated and melted by the resulting Joule heat to seal substrates together (hereinafter referred to as “electric heating”). According to this method, only the sealing material can be heated up to high temperatures and melted. Thus, a long time is not needed to heat and cool the substrates, and the substrates can be joined to form the envelope in a short time.

In the case of the electric heating, however, it is necessary to supply current so as to stably melt the sealing material. If the sealing material is not stably melted, the time for melting the sealing material varies from envelope to envelope, and stable coupling of the substrates cannot be carried out. If the electrically conductive sealing material is excessively heated, such problems arise that the sealing material may be broken due to heat or a crack may occur in the substrates. Conversely, if the sealing material is not sufficiently melted, the coupling of the substrates becomes deficient, and such problems arise that the air-tightness for maintaining vacuum deteriorates or the vacuum state of the envelope cannot be kept. Under the circumstances, in the prior art, a DC current of 100 A is supplied to the entire sealing material, and heating/melting is carried out for about one minute. Thereby, the sealing material is stably melted. On the other hand, 10 to 20 minutes are needed for cooling. In order to improve mass-productivity, there has been a demand for a further decrease in sealing time.

Although the time for melting and cooling the electrically conductive sealing material can be reduced by increasing the value of the constant current, the increase in current value leads to frequent occurrence of sparks between the sealing material and the electrode, between the electrode and the apparatus-side electrode contact, or between the sealing layers, and there arises the problem that the sealing layer cannot stably be melted.

In addition, in the above-described manufacturing method, only one side of the substrate, to which the indium is applied, is heated by the power-supply heating, resulting in a difference in temperature between the front and back surfaces of the substrate. Consequently, such a warp occurs on the substrate that the surface, on which the indium is applied, becomes convex. In this case, after cooling, the corner portions of the envelope become thicker than the central parts of the side portions of the envelope. If the envelope becomes partly thick, such problems arise that the air-tightness for vacuum deteriorates, the relative position between the electron source and phosphor layer is displaced at the corner part, and the envelope cannot easily be attached to the cabinet.

BRIEF SUMMARY OF THE INVENTION

The present invention has been made in consideration of the above-described problems, and the object of the invention is to provide a manufacturing method for an image display device, which enables a quick and stable sealing work of an electrically conductive sealing material.

According to an aspect of the invention, there is provided a method of manufacturing an image display device having an envelope including a front substrate and a rear substrate, the method comprising: forming a sealing layer by disposing an electrically conductive sealing material on a peripheral edge part of at least one of the front substrate and the rear substrate; disposing the front substrate and the rear substrate such that the front substrate and the rear substrate are opposed to each other; forming a current path in the sealing layer, beginning power supply to the sealing layer, and supplying an electric current, which reaches a maximum current value after a current-increasing period of 10% or more of an entire power-supply time, for a predetermined time period; and heating and melting the sealing layer by the electric current supply and bonding the peripheral parts of the front and rear substrates together with the molten sealing layer.

According to another aspect of the invention, there is provided a method of manufacturing an image display device having an envelope including a front substrate and a rear substrate, the method comprising: forming a sealing layer by disposing an electrically conductive sealing material on a peripheral edge part of at least one of the front substrate and the rear substrate; attaching to the sealing layer a pair of electrodes which supply power for heating and melting the sealing layer, and forming a current path for the power supply in the sealing layer; disposing the front substrate and the rear substrate such that the front substrate and the rear substrate are opposed to each other, and pressing the front substrate and the rear substrate toward each other; beginning power supply to the sealing layer via the electrodes in the state in which the front substrate and the rear substrate are pressed; supplying an electric current, which reaches a maximum current value after a current-increasing period of 10% or more of an entire power-supply time, for a predetermined time period; and heating and melting the sealing layer by the power supply to bond a peripheral part of the front substrate and a peripheral part of the rear substrate to each other.

According to another aspect of the invention, there is provided a method of manufacturing an image display device having an envelope including a front substrate and a rear substrate which are disposed to be opposed to each other and are joined at peripheral parts thereof, the method comprising: forming sealing layers on the front substrate and the rear substrate by disposing electrically conductive sealing materials on peripheral edge parts of mutually opposed surfaces of the front substrate and the rear substrate; attaching, to each of the sealing layer of the front substrate and the sealing layer of the rear substrate, a pair of electrodes which supply power for heating and melting the associated sealing layer, and forming current paths for the power supply in the sealing layer of the front substrate and the sealing layer of the rear substrate; beginning power supply to the sealing layers via the electrodes, and supplying an electric current, which reaches a maximum current value after a current-increasing period of 10% or more of an entire power-supply time, for a predetermined time period; heating and melting the sealing layer of the front substrate and the sealing layer of the rear substrate by the power supply; pressing the front substrate and the rear substrate toward each other in the state in which the front substrate and the rear substrate are opposed to each other; and bonding the peripheral parts of the front substrate and rear substrates to each other.

According to the manufacturing method for the image display device with the above structure, an electric current, which has such a gentle curve that the current reaches a maximum current value after a current-increasing period of 10% or more of the entire power-supply time, is supplied to the electrically conductive sealing material for a predetermined time period, thus heating/melting the sealing material and carrying out the sealing process. Thereby, the maximum current value for heating/melting is set at a value twice as high as a value in the prior art. Hence, even in the case where the power-supply time for heating is reduced, the occurrence of spark can surely be avoided, and the current can stably be supplied to the sealing layer. Thereby, the sealing layer can be formed with uniform thickness over the entire periphery, and the sealing work can stably be performed in a short time while the entire substrate is kept at low temperatures.

According to still another aspect of the invention, there is provided a method of manufacturing an image display device having an envelope including a first substrate and a second substrate which are opposed to each other with a gap and are joined at peripheral parts thereof, a sealing layer which is disposed along a peripheral edge part on an inner surface of at least one of the first substrate and the second substrate and contains an electrically conductive material, and a plurality of pixels provided within the envelope, the method comprising:

forming a sealing layer by disposing an electrically conductive sealing material along a peripheral edge part on an inner surface of at least one of the first substrate and the second substrate; disposing the first substrate and the second substrate such that the first substrate and the second substrate are opposed to each other in a state in which one of the first substrate and the second substrate is supported, and then supplying power to the sealing layer to heat and melt the sealing material and sealing together peripheral parts of the first and second substrates; and pushing corner portions of the other of the first and second substrates toward the one of the first and second substrates during or after the power supply to correct warp of the substrate.

According to an aspect of the invention, there is provided an apparatus for manufacturing an image display device having an envelope including a first substrate and a second substrate which are disposed to be opposed to each other with a gap and are coupled at peripheral parts thereof, a sealing layer which is disposed along a peripheral edge part on an inner surface of at least one of the first substrate and the second substrate and contains an electrically conductive material, and a plurality of pixels provided within the envelope, the apparatus comprising:

a support mechanism which supports the first substrate and the second substrate that are opposed to each other, in a state in which one of the first and second substrates is supported; a power-supply mechanism which supplies power to the sealing layer disposed on said at least one of the substrates; and a pushing mechanism which pushes corner portions of the other of the first and second substrates toward the one of the substrates to correct warp of the substrate.

DETAILED DESCRIPTION OF THE INVENTION

An FED, which is an image display device, and a manufacturing method of the FED according to a first embodiment of the present invention will now be described in detail with reference to the accompanying drawings.

As shown inFIG. 1toFIG. 4, the FED includes a front substrate11and a rear substrate12, each of which is formed of a rectangular glass plate. The front substrate11and rear substrate12are disposed to be opposed to each other with a gap of 1 to 2 mm. The rear substrate12has a greater size than the front substrate11. Peripheral edge parts of the front substrate11and rear substrate12are attached via a rectangular-frame-shaped side wall18, thereby forming a flat, rectangular vacuum envelope10in which a vacuum is maintained.

A plurality of plate-shaped support members14are provided within the vacuum envelope10in order to support an atmospheric pressure load acting on the front substrate11and rear substrate12. The support members14extend in a direction parallel to one side of the vacuum envelope10, and are arranged at predetermined intervals in a direction perpendicular to the one side of the vacuum envelope10. The support members14are not limited to plate-shaped ones, and may be columnar ones.

A phosphor screen16which functions as an image display surface is formed on the inner surface of the front substrate11. As shown inFIG. 4, the phosphor screen16is constructed by arranging red, green and blue phosphor layers R, G and B and a black light absorption layer20which is located between these phosphor layers. The phosphor layers R, G and B extend in a direction parallel to the one side of the vacuum envelope10, and are arranged at predetermined intervals along a direction perpendicular to the one side of the vacuum envelope10. As shown inFIG. 3, a metal back17formed of, e.g. aluminum, and a getter film27formed of, e.g. barium are successively stacked on the phosphor screen16.

A number of electron emitting elements22, which emit electron beams, are provided on the inner surface of the rear substrate12as electron emitter sources for exciting the phosphor layers of the phosphor screen16. These electron emitting elements22are arranged in columns and rows in association with pixels. Specifically, an electrically conductive cathode layer24is formed on the inner surface of the rear substrate12, and a silicon dioxide film26having many cavities25are formed on this electrically conductive cathode layer. Gate electrodes28which are formed of, e.g. molybdenum or niobium are formed on the silicon dioxide film26. Conical electron emitting elements22, which are formed of, e.g. molybdenum, are provided in the cavities25on the inner surface of the rear substrate12. As shown inFIG. 1, many wiring lines23for supplying potential to the electron emitting elements22are provided in a matrix on the inner surface of the rear substrate12, and end portions thereof are led out to the peripheral edge part of the vacuum envelope10.

In the FED with the above-described structure, video signals are input to the electron emitting elements22and gate electrodes28which are formed in a simple matrix scheme. When the electron emitting elements22are regarded as a reference, a gate voltage of +100 V is applied at a time of maximum luminance. In addition, a voltage of +10 kV is applied to the phosphor screen16. Thereby, electron beams are emitted from the electron emitting elements22. The magnitude of electron beams from the electron emitting elements22is modulated by the voltage of the gate electrodes28. The electron beams excite the phosphor layers of the phosphor screen16and cause the phosphor layers to emit light, thereby displaying an image.

Since a high voltage is applied to the phosphor screen16, as described above, a high-strain-point glass is used as plate glasses for the front substrate11, rear substrate12, side wall18and support members14. As will be described later, the rear substrate12and side wall18are sealed together by a low-melting-point glass19such as frit glass. The front substrate11and side wall18are sealed together by a sealing layer21including indium (In) as an electrically conductive low-melting-point sealing material.

The FED includes a plurality of, for example, a pair of electrodes30. These electrodes are attached to the envelope10in a state in which the electrodes are electrically connected to the sealing layer21. These electrodes30are used as electrodes for supplying power to the sealing layer21.

As shown inFIG. 2,FIG. 3andFIG. 5, each of the electrodes30is formed by bending a copper plate with a thickness of, e.g. 0.2 mm as an electrically conductive member. Specifically, the electrode30is bent in a substantially U-shaped cross section, and integrally comprises a mounting portion32, a body portion34which extends from the mounting portion and serves as a current path to the sealing layer, a contact portion36which is located at an extension end of the body portion and is capable of contacting the sealing layer, and a flat electrically conductive portion38which is formed of back surface parts of the mounting portion and body portion. The mounting portion32integrally includes a clamping portion which is bent in a clip-like shape. The mounting portion32clamps a peripheral edge part of the front substrate11or rear substrate12, and thus can be attached thereto. A horizontal extension length L of the contact portion36is set at 2 mm or more. The body portion34is formed in a strip shape and extends obliquely upward from the mounting portion32. Thus, the contact portion36is positioned higher than the mounting portion32and body portion34in the vertical direction.

As shown inFIG. 1toFIG. 3, each electrode30is attached in a state in which the electrode30is resiliently engaged with, for example, the rear substrate12of the vacuum envelope10. Specifically, each electrode30is fitted to the vacuum envelope10in a state in which the peripheral part of the rear substrate12is resiliently clamped by the mounting portion32. The contact portion36of each electrode30is electrically connected to the sealing layer21. The body portion34extends outward of the vacuum envelope10from the contact portion36, and the electrically conductive portion38is opposed to the side surface of the rear substrate12and is exposed to the outer surface of the vacuum envelope10. The paired electrodes30are provided at two diagonally spaced-apart corners of the vacuum envelope10and are disposed symmetric with respect to the sealing layer21.

Next, a method of manufacturing the FED with the above-described structure is described in detail.

To start with, the phosphor screen16is formed on a plate glass which becomes the front substrate11. Specifically, a plate glass having the same size as the front substrate11is prepared, and a phosphor stripe pattern is formed on the plate glass by a plotter machine. The plate glass, on which the phosphor stripe pattern is formed, and the plate glass for the front substrate are placed on a positioning jig and are set on an exposure table. In this state, exposure and development are carried out to form the phosphor screen on the glass plate which becomes the front substrate11. Then, a metal back17is laid over the phosphor screen16.

Subsequently, the electron emitting elements22are formed on the plate glass for the rear substrate12. Specifically, a matrix-shaped electrically conductive cathode layer24is formed on the plate glass. An insulation film of a silicon dioxide film is formed on the cathode layer by, e.g. thermal oxidation, CVD or sputtering. On this insulation film, a metal film of, e.g. molybdenum or niobium for forming gate electrodes is formed by, e.g. sputtering or electron-beam evaporation deposition. Then, a resist pattern, which has a shape corresponding to gate electrodes to be formed, is formed on the metal film by lithography. Using the resist pattern as a mask, the metal film is etched by wet etching or dry etching, and the gate electrodes28are formed.

Thereafter, using the resist pattern and the gate electrodes28as a mask, the insulation film is etched by wet etching or dry etching, and thus cavities25are formed. After the resist pattern is removed, electron-beam evaporation deposition is carried out on the surface of the rear substrate12in an inclined direction at a predetermined angle. Thereby, a peeling layer of, e.g. aluminum or nickel is formed on the gate electrodes28. Further, a material for forming cathodes, such as molybdenum, is vertically deposited on the surface of the rear substrate12by electron-beam evaporation deposition. Thus, the electron emitting elements22are formed in the cavities25. Then, the peeling layer, together with the metal layer formed thereon, is removed by a lift-off method.

Subsequently, the side wall18and support members14are sealed on the inner surface of the rear substrate12by a low-melting-point glass19in the atmospheric air. As shown inFIG. 6AandFIG. 6B, indium is coated with a predetermined width and thickness on the entire periphery of a sealing surface of the side wall18, thereby forming a sealing layer21a, and also indium is coated with a predetermined width and thickness on the entire periphery of a sealing surface of the front substrate11, which is opposed to the sealing surface of the side wall18, thereby forming a sealing layer21b. The sealing layers21aand21bare applied to the sealing surfaces of the side wall18and front substrate11by, for example, a method in which molten indium is applied to the sealing surfaces, or a method in which solid indium is placed on the sealing surfaces.

Subsequently, as shown inFIG. 7, the paired electrodes30are attached to the rear substrate12to which the side wall18is attached. In this case, each electrode30is attached such that the contact portion36does not contact the sealing layer21aand is opposed to the sealing layer with a gap. It is necessary to provide a pair of electrodes30with a positive (+) polarity and a negative (−) polarity on the substrate, and it is desirable to equalize the lengths of the current paths of the sealing layers21aand21bthrough which current is supplied in parallel between the paired electrodes. The paired electrodes30are mounted at two diagonally opposed corners of the rear substrate12, and the lengths of the sealing layers21aand21b, which are positioned between the electrodes, are set to be substantially equal on both sides of each electrode.

After the electrodes30are mounted, the rear substrate12and front substrate11are spaced apart with a predetermined distance and are opposed. In this state, the resultant structure is put in a vacuum process apparatus. For example, a vacuum process apparatus100shown inFIG. 8is used. The vacuum process apparatus100includes arranged chambers, that is, a load chamber101, a baking/electron-beam cleaning chamber102, a cooling chamber103, a getter film evaporation deposition chamber104, an assembly chamber105, a cooling chamber106, and an unload chamber107. A power supply unit120, which outputs a DC power for heating and melting the sealing layers21aand21b, and a computer200which controls the power supply unit120are connected to the assembly chamber105. Each chamber of the vacuum process apparatus100is constructed as a process chamber that is capable of carrying out a vacuum process. When the FED is manufactured, all the chambers are evacuated. These process chambers are connected via gate valves, etc., which are not shown.

The front substrate11and rear substrate12, which are opposed with a predetermined distance, are first introduced into the load chamber101. After the load chamber101is evacuated, the front substrate11and rear substrate12are transferred to the baking/electron-beam cleaning chamber102.

In the baking/electron-beam cleaning chamber102, the various members are heat up to 350° C. to 400° C., and a surface-adsorbed gas on the front substrate11and rear substrate12is released. At the same time, electron beams are emitted from an electron beam generating unit (not shown), which is attached to the baking/electron-beam cleaning chamber102, to the phosphor screen surface of the front substrate11and to the electron emitting element surface of the rear substrate12. In this case, the electron beams are deflected and scanned by a deflecting device, which is mounted on the outside of the electron beam generating unit. Thereby, the entire phosphor screen surface and electron emitting element surface are subjected to electron-beam cleaning.

In the baking step, the sealing layers21aand21bare once melted by heat and have fluidity. However, the contact portion36of each electrode30is not in contact with the sealing layer21a,21b, and is opposed to the sealing layer21a,21bwith a gap. Thus, the molten indium is prevented from flowing out of the rear substrate12via the electrode30.

The front substrate11and rear substrate12, which have been subjected to baking and electron-beam cleaning, are delivered to the cooling chamber103, and cooled down to temperatures of about 120° C. Then, the front substrate11and rear substrate12are transferred to the getter film evaporation deposition chamber104. In the evaporation deposition chamber104, a barium film is deposited by evaporation as the getter film27on the outside of the metal back17. The barium film can prevent the surface thereof from being contaminated with oxygen or carbon, and the active state can be maintained.

The front substrate11and rear substrate12are then delivered to the assembly chamber105. As shown inFIG. 9, in the assembly chamber105, the front substrate11and rear substrate12are disposed to be opposed to each other and are held on hot plates131and132in the assembly chamber. The front substrate11is fixed to the upper-side hot plate131by a fixing jig129in order to prevent the front substrate11from dropping.

While the temperatures of the front substrate11and rear substrate12are maintained at about 120° C., the front substrate11and rear substrate12are moved toward each other and pressed under a predetermined pressure. The substrates are moved by a method in which both the front substrate11and rear substrate12are moved toward each other, or by a method in which one of the front substrate11and rear substrate12is moved so that the front substrate11and rear substrate12approach each other.

By pressing the front substrate11and rear substrate12under a predetermined pressure, the sealing layer21bon the front substrate11side and the sealing layer21aon the rear substrate12side are put in contact, the contact portion36of each electrode30is clamped between the sealing layers21aand21b, and each electrode30is electrically connected to the sealing layers21aand21b. At this time, since the contact portion36has a horizontal length of2mm or more, the contact portion36can stably contact the sealing layers21aand21b. It is possible to coat indium on the contact portion36of electrode30in advance. In this case, better contact and electrical conduction between the contact portion36and the sealing layers21aand21bcan be achieved.

In this state, as shown inFIG. 10, power output terminals40of the power supply unit120are electrically connected to the paired electrodes30. Then, a DC current is supplied in a constant current mode from the power supply unit120to the sealing layer21aon the side wall18side, and to the sealing layer21bon the front substrate11side. By the power supply, the sealing layers21aand21bare heated and the indium is melted.

In the first embodiment, at the time of heating/melting by power supply to the sealing layers21aand21b, an electric current, which has such a gentle curve that the current reaches a maximum current value (constant current value) after a current-increasing period of 10% or more of the entire power-supply time during a power-supply transition period, and which has a maximum current value of 200 amperes or more, is supplied for a predetermined time period, thereby heating/melting the sealing layers21aand21b.

The heating/melting process by the power supply to the sealing layers21aand21bin this case is explained with reference toFIG. 11. In the power supply unit120, a constant current source121generates a predetermined constant current of, e.g. about 200 to 400 amperes. A power supply output control unit122controls an output constant current from the constant current source121, and has a function of controlling a transition current. In accordance with a control command CS from the computer200(or a pressing state detection signal of a substrate pressing mechanism in the assembly chamber105), the power supply output control unit122outputs, for a predetermined time period, a current (Io) which has, as shown in the Figure, such a gentle curve that the current reaches a maximum current value (constant current period) after a current-increasing period of 10% or more of the entire power-supply time, and which has a maximum current value of 200 amperes or more. Current paths, along which current passes through the sealing layers21aand21bin this case, are designated by ia and ib in the Figure. In the example of the coated sealing layers in this embodiment, the sealing layer21bis coated on the front substrate11, and the sealing layer21ais coated on the rear substrate12. Thus, the output current is divided into four components, that is, currents ia and ib flowing in the sealing layer21aand currents ia and ib flowing in the sealing layer21b. Accordingly, if the maximum current value (Io) is 280 amperes, a 70 ampere constant current is equally supplied as each of ia and ib to the sealing layer21aduring a constant current period tb.

In the present embodiment, during the power-supply transition period until reaching the maximum current value (Io), the output current value is gradually increased. Thereby, occurrence of spark is prevented under the condition that the current value that is necessary for heating/melting is set at a higher value.

FIGS. 12A,12B,12C, and12D show examples of the current waveform in the power-supply transition period (current-increasing period) until reaching the maximum current value (Io). InFIG. 12A, a transition current (TI) is linearly varied during the current-increasing period (ta), that is, the power-supply transition period until reaching the maximum current value (Io), that is, the constant current period (tb). The current-increasing period (ta) is set at 10% or more of the entire power-supply period (ta+tb). According to this setting, the output control unit122executes output control of the transition current.

In the example shown inFIG. 12B, the current-increasing period (ta), that is, the power-supply transition period until reaching the maximum current value (Io), is set at 50% or more of the entire power-supply period. During this period, the transition current (TI) is varied in a curve. In the example shown inFIG. 12C, the transition current (TI) is varied in an S-curve during the current-increasing period (ta), that is, the power-supply transition period until reaching the maximum current value (Io). In the example shown inFIG. 12D, the transition current (TI) is varied stepwise during the current-increasing period (ta), that is, the power-supply transition period until reaching the maximum current value (Io).

FIGS. 13 and 14show examples of power supply in a plurality of kinds of heating/melting process modes in which the supplied current reaches the predetermined constant current value after the above-described current-increasing period (Ti).FIG. 13shows an example of power supply of the constant current in the pressing/heating mode in which the sealing layers21aand21bare heated and melted in the state in which the substrates (front substrate11and rear substrate12) are pressed on each other. In this case, the sealing layers21aand21b, which are being pressed, are heated/melted by the above-described equally divided currents from the single power supply.

FIG. 14shows an example of power supply of the constant current in the heating/pressing mode in which the front substrate11and rear substrate12are pressed toward each other in the state in which each of the sealing layer21bcoated on the front substrate11and the sealing layer21acoated on the rear substrate12is heated/melted. In this case, the sealing layers21aand21bare heated/melted in a simultaneous, parallel fashion by separate power supplies or by a single power supply.

As described above, in the assembly chamber105, at the time of heating/melting by power supply to the sealing layers21aand21bcoated on the front substrate11side and rear substrate12side, an electric current, which has such a gentle curve that the current reaches a maximum current value after a current-increasing period of 10% or more of the entire power-supply time, and which has a maximum current value of 200 amperes or more, is supplied for a predetermined time period, thereby heating/melting the sealing layers21aand21b. The peripheral part of the front substrate11and the side wall18are sealed together by the sealing layers21aand21bwhich are heated and melted.

The front substrate11, side wall18and rear substrate12, which are sealed in the above-described step, are cooled down to normal temperature in the cooling chamber106, and are taken out from the unload chamber107. Thereby, the vacuum envelope10of the FED is completely fabricated.

If necessary, the pair of electrodes30may be removed after the fabrication of the vacuum envelope10is completed.

According to the above-described manufacturing method of the FED, at the time of heating/melting by power supply to the sealing layers21aand21bcoated on the front substrate11side and rear substrate12side, an electric current, which has such a gentle curve that the current reaches a maximum current value after a current-increasing period of 10% or more of the entire power-supply time, and which has a maximum current value of 200 amperes or more, is supplied for a predetermined time period, thereby heating/melting the sealing layers21aand21b. The peripheral part of the front substrate11and the side wall18are sealed together by the sealing layer21which is heated and melted. Thereby, the time needed for the sealing work in the manufacturing process can be reduced, and the drawback, such as spark, can be avoided and a current for stable heating/melting can be supplied to the sealing layer21. Hence, the sealing work can be carried out in a short time period before the entire substrate is unnecessarily heated, and the sealing work can be performed efficiently and quickly. Since the electrically conductive low-melting-point sealing material, which forms the sealing layer, can stably and exactly be melted in a predetermined power-supply time, quick and exact sealing can be carried out without causing cracks, etc. in the sealing layer21.

Therefore, the FED, which has good mass-productivity and can obtain a stable and excellent image, can be manufactured at low cost.

In the above-described embodiment, the current-increasing control at the initial stage of power supply is not limited to the examples shown inFIG. 11toFIG. 14. Various modifications and applications can be made in the method in which current paths are formed in the sealing layer and the power supply to the sealing layer is begun, and an electric current, which reaches a maximum current value after a current-increasing period of 10% or more of the entire power-supply time, is supplied for a predetermined time period. In the embodiment, each electrode30integrally comprises the clip-like clamping portion functioning as the mounting portion. Alternatively, as shown inFIG. 15andFIG. 16, each electrode30may include a separate clip41functioning as the clamping portion. Specifically, the electrode30includes a contact portion36, a body portion34and a flat base portion39, which are integrally formed by bending a plate material. The mounting portion of the electrode30is constituted by the base portion39and a separate clip41. The clip41clamps the base portion39and a peripheral edge part of the substrate, that is, a peripheral edge part of the rear substrate12in this example, and thereby the electrode30is attached to the rear substrate12.

Next, a method of manufacturing an FED, according to a second embodiment of the invention is described. In the second embodiment, the parts common to those in the first embodiment are denoted by like reference numerals, and a detailed description thereof is omitted.

To start with, like the first embodiment, the phosphor screen16is formed on a plate glass which becomes the front substrate11as a first substrate. Then, a metal back layer17is laid over the phosphor screen16. The electron emitting elements22are formed on a plate glass for the rear substrate12which is a second substrate.

Subsequently, the side wall18and support members14are sealed on the inner surface of the rear substrate12by a low-melting-point glass19in the atmospheric air. As shown inFIG. 17AandFIG. 17B, indium is coated with a predetermined width and thickness on the entire periphery of a sealing surface of the side wall18, and a sealing layer21ais formed. Similarly, indium is coated in a rectangular-frame shape with a predetermined width and thickness on the entire periphery of a sealing surface of the front substrate11, which is opposed to the side wall18, and a sealing layer21bis formed.

Subsequently, as shown inFIG. 18, two pairs of electrodes30aand30bare attached to the rear substrate12to which the side wall18is attached. Each of the electrodes is formed by bending a copper plate with a thickness of, e.g. 0.2 mm as an electrically conductive member. Each electrode integrally comprises a mounting portion32which clamps a peripheral part of the rear substrate12and thus can be attached thereto, a tongue portion35which contacts a power supply electrode to be described later, and a contact portion36which can contact the sealing layer21. The electrodes30aand30bare attached to the corner portions of the rear substrate in the state in which the peripheral edge part of the rear substrate12is resiliently clamped by the mounting portions32. In this case, the contact portion36of each electrode30a,30bis put in contact with the indium formed on the side wall18, and the electrode is electrically connected to the sealing layer21a.

The electrodes30a,30bare used as electrodes for supplying power to the sealing layers21aand21b. It is necessary to provide the paired electrodes30a,30bwith a positive (+) polarity and a negative (−) polarity on the substrate, and it is desirable to equalize the lengths of the current paths of the sealing layers through which current is supplied in parallel between the paired electrodes. The paired electrodes30aare mounted near two diagonally opposed corners of the rear substrate12, and the lengths of the sealing layers, which are positioned between the electrodes30a, are set to be substantially equal on both sides of each electrode. Similarly, the paired electrodes30bare mounted near the other two diagonally opposed corners of the rear substrate12, and the lengths of the sealing layers, which are positioned between the electrodes30b, are set to be substantially equal on both sides of each electrode.

After the electrodes30a,30bare mounted, the rear substrate12and front substrate11are spaced apart with a predetermined distance and are opposed. In this state, the resultant structure is put in the above-described vacuum process apparatus100.

The front substrate11and rear substrate12, which are opposed with a predetermined distance, are first introduced into the load chamber101. After the load chamber101is evacuated, the front substrate11and rear substrate12are delivered to the baking/electron-beam cleaning chamber102. In the baking/electron-beam cleaning chamber102, the various members are heat up to 300° C., and a surface-adsorbed gas on each substrate is released. At the same time, electron beams are emitted from the electron beam generating unit (not shown), which is attached to the baking/electron-beam cleaning chamber102, to the phosphor screen surface of the front substrate11and to the electron emitting element surface of the rear substrate12. In this case, the electron beams are deflected and scanned by the deflecting device which is mounted on the outside of the electron beam generating unit. Thereby, the entire phosphor screen surface and electron emitting element surface are subjected to electron-beam cleaning.

The front substrate11and rear substrate12, which have been subjected to the electron-beam cleaning, are delivered to the cooling chamber103, and cooled down to temperatures of about 120° C. Then, the front substrate11and rear substrate12are transferred to the getter film evaporation deposition chamber104. In the evaporation deposition chamber104, a barium film is deposited by evaporation as the getter film27on the outside of the metal back17. The barium film can prevent the surface thereof from being contaminated with oxygen or carbon, and the active state can be maintained.

The front substrate11and rear substrate12are then delivered to the assembly chamber105. As shown inFIG. 19, in the assembly chamber105, hot plates131and132are disposed to be opposed to each other with a gap. A vertically movable stage134is provided under the hot plate132. A plurality of support pins133are vertically disposed on the stage134. A spring138is attached to an extension end of each support pin133. Each support pin133is slidably passed through a through-hole formed in the hot plate132. The support pins133can support the rear substrate12at their distal ends. The support pins133and stage134are vertically driven by a motor135that is provided on the outside of the assembly chamber105. The stage134, support pins133and motor135constitute a driving mechanism, and also constitute, together with the hot plates131and132, a support mechanism. On the outside of the assembly chamber105, a load cell139which measures a pressure acting on the substrates is disposed via bellows140.

As shown inFIG. 19toFIG. 21, two pairs of power supply electrodes137, which contact the tongue portions35of the electrodes30aand30bmounted on the rear substrate12, are provided at end portions of the hot plate132. Each power supply electrode137is electrically connected to the power supply unit120via a power supply line136. Data relating to current and voltage which are supplied to the power supply electrodes137from the power supply unit120via the power supply line136, and data relating to pressure, which is output from the load cell139, are input to the computer200. The power supply electrodes137and power supply unit120constitute a power supply mechanism.

As is shown inFIG. 19andFIG. 20, an elevation plate145is provided on the outside of the assembly chamber105. A motor141is connected to the elevation plate145. The hot plate132is connected to the elevation plate145via a plurality of shafts142and bellows143. By driving the motor141, the hot plate132can be raised/lowered in a direction toward/away from the other hot plate131. The hot plate132, motor141, shafts142, elevation plate145and power supply electrodes137constitute a pushing mechanism, and each power supply terminal constitutes a pushing section.

The front substrate11and rear substrate12, which are transferred to the assembly chamber105, are first positioned and fixed on the associated hot plates131and132. The front substrate11and rear substrate12are heated and kept at about 120° C. by the hot plates. After the front substrate11is positioned downward, the entire surface of the front substrate11is attracted and fixed by the hot plate131by a conventional electrostatic attraction technique, and the front substrate11is prevented from dropping.

After the front substrate11and rear substrate12are mutually aligned, the motor135is driven to raise the stage134and support pins133. The rear substrate12is supported by the support pins133and moved toward the front substrate11. The rear substrate is pressed on the front substrate under a predetermined pressure. In this case, the degree of warp and the amount of the formed indium vary from substrate to substrate, but the springs138provided at the distal ends of the support pins133can cancel such variation. Thus, any kind of substrate can stably be pressed. By the pressing, the contact portions36of the electrodes30aand30bare clamped between the sealing layers21band21aon the front substrate11side and rear substrate12side, and the respective electrodes are put in electrical contact with the sealing layers21aand21bof both substrates at the same time. In this case, the pressure acting on the rear substrate12is measured by the load cell139and the measured value is input to the computer200.

Thereafter, as shown inFIG. 20andFIG. 21, the motor141is driven to push the hot plate132upward, and the power supply electrodes137are brought into contact with the electrodes30aand30bfrom the lower side. In this state, a DC current of140A is output from the power supply unit120to the paired electrodes30a, and thus the current is supplied in a constant current mode to the sealing layers21aand21bvia the power supply line136, power supply electrodes137and electrodes30a. Thereby, the indium is heated and begins to melt. When the indium is melted to a certain degree, the supply of the DC current of140A is switched to the other paired electrodes30band the current is supplied for the same time period. By this alternate power supply, the entire indium can uniformly be melted. Since the pressure is applied to the rear substrate12as described above, if the indium melts, the rear substrate12is pushed toward the front substrate11until the support members14provided on the rear substrate completely contact the inner surface of the front substrate11.

After the power supply for the predetermined period is finished, a signal indicating the end of power supply is sent from the computer200to the power supply unit120, and the power supply to the sealing layer is stopped. For several minutes thereafter, the pressing state is maintained. Thus, the indium is cooled and solidified, and the front substrate11and side wall18are sealed together by the sealing layer21. Thereby, the vacuum envelope10is formed.

In addition, during the power supply, or after the end of the power supply and before the solidification of the indium, the motor141is driven for slight upward pushing and the power supply electrodes137push the electrodes30aand30bupward. Thereby, the four corner portions of the rear substrate12are pushed toward the front substrate11via the electrodes30aand30b, and the warp of the rear substrate12due to the power-supply heating of the sealing layer is corrected. No warp occurs on the front substrate11since the front surface thereof is attracted and held by the hot plate131. Therefore, the warp of the substrate can be prevented and the vacuum envelope10with uniform thickness can be obtained.

After the sealing, the vacuum envelope10is transferred to the cooling chamber106and is cooled down to normal temperature, and is then taken out from the unload chamber107. Thus, the FED is completely manufactured. The electrodes30a,30bmay be removed after the sealing.

According to the above-described manufacturing method and manufacturing apparatus of the FED, the surface-adsorbed gas can sufficiently be released by the combination of the baking and electron-beam cleaning, and the getter film with high adsorption performance can be obtained. Since the sealing can be completed in a short time period by the power-supply sealing using the indium, the manufacturing method and manufacturing apparatus with excellent mass-productivity can be obtained. During the power-supply heating of the sealing layer or after the power-supply heating, the four corner portions of the rear substrate12are pushed and the warp of the rear substrate12is corrected. Thereby, the vacuum envelope with uniform thickness can be obtained. Hence, high air-tightness for vacuum can be maintained over the entire periphery of the vacuum envelope, and the relative position between the electron emitting elements and the phosphor layer can exactly be set over the entire region. Furthermore, when the vacuum envelope is to be attached to a cabinet, etc., the assembly performance can be improved.

In the second embodiment, the power supply is executed in the state in which the front substrate and rear substrate are pressed on each other and the sealing layers are put in contact. Alternatively, after the sealing layer of the front substrate and the sealing layer of the rear substrate are supplied with power and heated and melted, the substrates may be pressed toward each other and sealed together. In this case, the two pairs of electrodes are mounted on the rear substrate, and one pair of electrodes are formed such that their contact portions contact the rear substrate-side sealing layer and the other pair of electrodes are formed such that their contact portions contact the front-substrate-side sealing layer.

In the second embodiment, the electrodes30aand30bare pushed upward by the power supply electrodes137. Alternatively, the corner portions of the rear substrate may directly be pushed by a pushing mechanism that is separately provided on the assembly chamber105.

The present invention is not limited directly to the embodiments described above, and its components may be embodied in modified forms without departing from the spirit of the invention. Further, various inventions may be made by suitably combining a plurality of components described in connection with the foregoing embodiments. For example, some of the components according to the foregoing embodiments may be omitted. Furthermore, components according to different embodiments may be combined as required.

In the first and second embodiments, the sealing layers of indium are provided on both the rear substrate side and front substrate side. Alternatively, the sealing layer may be provided on one of the rear substrate side and front substrate side, and in this state the front substrate and rear substrate may be sealed together.

The sealing material is not limited to indium, and may be any other sealing material with electrical conductivity. In general, in the case of metal, a sharp variation occurs in resistance value when the phase of the metal changes, and thus the metal is usable as sealing material. For example, an electrically conductive low-melting-point material, which is usable in place of indium, may be an elemental metal selected from the group consisting of In, Ga, Pb, Sn and Zn, or an alloy including at least one element selected from the group consisting of In, Ga, Pb, Sn and Zn. In particular, it is preferable to use an alloy including at least one element selected from the group consisting of In and Ga, an In metal, or a Ga metal. A low-melting-point sealing material including In or Ga has good wettability with a glass substrate that is formed mainly of SiO2, and is particularly suitable when the substrate, on which the low-melting-point sealing material is to be disposed, is formed of a glass that is formed mainly of SiO2. Preferable low-melting-point sealing materials are an In metal and an alloy including In. Examples of the alloy including In are an alloy including In and Ag, an alloy including In and Sn, an alloy including In and Zn, and an alloy including In and Au. A metal including at least one of In, Sn, Pb, Ga and Bi is usable.

The side wall of the envelope may be formed integral with the rear substrate or front substrate in advance. Needless to say, the outer shape of the vacuum envelope and the structure of the support members are not limited to the above-described embodiments. A matrix-shaped black light absorption layer and phosphor layer may be formed, and sealing may be carried out by aligning columnar support members each having a cross-shaped cross section with the black light absorption layer. A pn-type cold-cathode element or a surface-conduction-type electron emitting element may be used as the electron emitting element. In the above-described embodiments, the substrates are coupled in the vacuum atmosphere, but the invention is applicable in other atmospheric environments.

The present invention is applicable not only to FEDs, but also to other image display devices, such as SEDs and PDPs, and to image display devices in which a high vacuum is not created within envelopes.