Patent Application
20090251041
1. Field of the Invention
The present invention relates to an electron beam display in which an external light reflection has been suppressed.
2. Description of the Related Art
As for image display apparatuses such as a CRT, the realization of a further larger size of a display screen is demanded and studies to realize it are vigorously being performed. In association with the realization of the large size, it is an important object to realize a thin size, a light weight, and low costs. However, in the CRT, since an electron accelerated by a high voltage is deflected by a deflecting electrode and phosphor on a face plate is excited, if the screen size is enlarged, a depth is necessary in principle and it is difficult to realize the thin size and the light weight. As an image display apparatus which can solve the above problems, the inventors et al. have studied with respect to a surface conduction electron-emitting device and an image display apparatus using the surface conduction electron-emitting devices.
In recent years, various kinds of units for improving image characteristics such as luminance and contrast in a thin-type image display apparatus (flat panel display) have been proposed.
Patent Document 1 {Japanese Patent Application Laid-Open No. 2006-004804 (corresponding U.S. Patent Application Publication No. US-2005-0280349)} discloses such a technique that an occupation area of a black matrix is set to a value within a range of 60% to 95%, a metal film is formed on the black matrix, an aperture and a plurality of small holes are provided for the black matrix, and extracting efficiency of light is improved.
Patent Document 2 (Japanese Patent Application Laid-Open No. H11-339683) discloses a phosphor screen surface including: a black matrix film; a light reflecting film formed on the black matrix film; a phosphor film; and a rear light reflecting film (metal back). According to the invention of Patent Document 2, the light extracting efficiency is improved by a structure of the metal back.
Although both of the image display apparatuses disclosed in Patent Documents 1 and 2 mentioned above intend to improve the extracting efficiency of the light from the phosphor, in recent years, it is demanded to further improve display characteristics.
To improve a contrast of a bright portion, it is necessary to increase an occupation ratio of the black matrix, that is, decrease an aperture ratio. However, if the aperture ratio is merely decreased, light emission of the phosphor is obstructed and the light extracting efficiency deteriorates.
It is, therefore, an object of the present invention to provide an electron beam display in which light extracting efficiency from phosphor and a bright-portion contrast have been improved.
To accomplish the above object, an electron beam display according to the present invention has: an electron source; a metal back; and a phosphor dot which is disposed in opposition to the electron source through the metal back and emits light responsive to an irradiation with an electron beam emitted from the electron source. The electron beam display according to the present invention further has a face plate having a black member which is disposed in opposition to the electron source through the phosphor dot and has an aperture in a region in which the phosphor dot is formed. In such an electron beam display, a region irradiated with the electron beam emitted from the electron source is not larger than the phosphor dot, a part of the black member is disposed in the region irradiated with the electron beam, and at least a part of the aperture is disposed outside of the region irradiated with the electron beam.
According to the present invention, the light extracting efficiency from the phosphor and the contrast of the bright portion can be improved.
Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.
An exemplary embodiment of the present invention will be described hereinbelow.
An electron beam display of the present invention incorporates a field emission type electron beam display (FED), a surface conduction electron-emitting display (SED), a cathode ray tube display (CRT), and the like. Particularly, the FED and SED are forms which are desirable to apply the present invention from a viewpoint that an electron beam can be easily irradiated (converged) to a desired position. As an electron-emitting source which is used in the FED, a spint type, an MIM type, a carbon nanotube type, a ballistic electron surface emitting (BSD) type, and the like can be mentioned.
As an embodiment of the present invention, an electron beam display using surface conduction electron-emitting devices will be described as an example with reference to
In the diagrams, a plane direction of the face plate 1 is set to the XY directions and a direction of a gap between the face plate 1 and a rear plate 9 provided with electron-emitting devices 10 is set to the Z direction.
The face plate 1 is provided with: phosphor 2 to which the electron beam is irradiated and emits the light; a black member 3; and a metal back 4. As a material of the face plate 1, in order to allow the light emitted from the phosphor to pass through and observe the transmitted light, a transparent insulating substrate is desirably used and plate glass such as soda-lime glass is desirably used. Besides, glass with a high strain point which is used in the field of a PDP (Plasma Display Panel) or the like is also desirably used.
The phosphor 2 is a material which emits the light by being irradiated by the electron beam and forms an image. A phosphor dot 20 is constructed by a plurality of phosphor particles 2. As phosphor 2, powdery phosphor which emits the light by an electron beam excitation such as P22 phosphor which is used in the CRT is desirably used. As a material similar to such a material, thin film phosphor which is produced by being directly formed onto the face plate 1 is also desirably used. Particularly, the P22 phosphor can be desirably used because it has excellent light-emitting color, light-emitting efficiency, color balance, and the like owing to the development of the CRT. The phosphor 2 is formed by a screen printing method, a photolithography method, an ink-jet method, or the like. Particularly, the screen printing method is desirably used from a viewpoint of a material using efficiency.
The black member 3 is also called a black matrix, a black stripe, or the like and is provided in order to raise a bright-portion contrast by absorbing the external light and prevent color mixture of the phosphor. In the black member 3, a plurality of apertures 8 are formed in a region where the phosphor dot 20 has been formed. As a black member 3, carbon black, a paste containing a black pigment and a glass frit with a low melting point, or the like is used. The black member 3 is formed by the screen printing method, photolithography method, or the like. Particularly, a black member obtained by mixing a photosensitive resin to the paste containing the black pigment and the glass frit with the low melting point is desirably used because patterning can be easily performed.
To improve the bright-portion contrast, it is necessary to increase an occupation ratio of the black member 3, that is, decrease an aperture ratio. However, if the aperture ratio is merely decreased, the light emission of the phosphor is obstructed. It is, therefore, required to reduce the light-shielding and raise the extracting efficiency of the light as much as possible. The improvement of the light extracting efficiency will be described hereinlater.
The metal back 4 is a member provided to apply an accelerating voltage for accelerating an electron emitted from the rear plate 9 and reflect the light emitted in the direction of the rear plate 9 in the light emitted from the phosphor 2 to the face plate 1 side. In the metal back 4, since it is necessary to improve reflectance of the light while reducing an energy loss of the accelerated electron beam as much as possible, a thin-film-like metal is desirably used. As a metal back 4, aluminum which can reduce the energy loss of the electron is particularly desirably used. The metal back 4 is formed by using a filming method, a transfer method, or the like which is well known in the CRT. Particularly, the filming method using a resin intermediate film is desirably used because the reflectance of the metal back 4 can be improved.
The electron-emitting devices (electron source) 10 are provided on the rear plate 9 disposed in opposition to the face plate 1.
Subsequently, the electron beam emitted from the electron-emitting device (electron source) 10 will be described. The electron beam emitted from the electron-emitting device 10 flies as illustrated by the trajectory 5, is irradiated to the phosphor dot 20 on the face plate 1, and a light-emitting region by the electron beam is obtained.
The region irradiated with the electron beam will now be described.
Depending on the phosphor which is used, there is a case of occurrence of such a phenomenon that the more what are called gamma characteristics, that is, a current density that is excited is increased, the more light-emitting efficiency decreases and a luminance saturation occurs. In such a case, the irradiation intensity profile of the electron beam and the light-emitting intensity profile do not coincide strictly. However, it is an object of the present invention to efficiently extract the light emitted from the phosphor. The region obtained from the region of the half of the peak in the light-emitting profile is set to an electron beam irradiating region 6. However, when a plurality of apertures 8, which will be described hereinlater, are arranged in this instance, there is a case where it is difficult to observe the light-emitting profile from the outside of the face plate 1. In such a case, the electron beam irradiating region 6 is obtained by the following method and a plurality of apertures are arranged for the region 6.
(1) The profile which can be observed from a plurality of apertures 8 is measured.
(2) A prediction profile of the electron beam which is presumed from a shape of the electron-emitting source, a shape of the rear plate, the accelerating voltage, and the like is measured.
(3) A beam profile is measured by using the face plate in which the apertures are large or the black member 3 does not exist.
In order to efficiently extract the light from the phosphor 2 as an object of the present invention, it is necessary to pay attention to the light-emitting intensity in the phosphor 2.
A size of electron beam irradiating region 6 is smaller than a size of pixel 7 (there is also a case where it is called a sub-pixel) and the electron beam is irradiated to the almost fixed region. In the electron beam display of the fixed pixel type, since the electron beam irradiating region 6 is smaller than the pixel 7, it is necessary to consider the light extracting method. In the CRT, the electron beam is deflected by a deflecting coil and scanned, thereby displaying an image. Therefore, the electron beam is irradiated to the whole pixel in the direction in parallel with the scanning direction. In the CRT having a shadow mask or the like, however, there is a case where the electron beam irradiating region 6 is limited. In such a case, the present invention can be also desirably used. That is, the present invention can be desirably used so long as such an electron beam display that the position/region of the electron beam which is irradiated to the face plate is limited to a certain portion.
Subsequently, a method of improving the light extracting efficiency when a plurality of apertures 8 are formed will be described.
A plurality of apertures 8 are formed to extract the light emitted by the irradiation of the electron beam mentioned above. First, an effect which is obtained by providing the plurality of apertures will be described with reference to
A light beam from phosphor 2a which has emitted the light by the irradiation of the electron beam mentioned above is shown by an arrow in each diagram. The emitting direction of the light beam from the phosphor 2a is isotropic. The phosphor 2a in the phosphor 2 is phosphor which is not located just under the aperture 8 but exists at a position hidden by the black member 3.
In the example illustrated in
In such a construction, the light beams (shown by arrows which progress to the left from the phosphor 2a) emitted in the direction toward the aperture 8 are scattered and reflected by the phosphor 2 and the metal back 4 and most of the light beams can be emitted from the aperture 8. However, in the case of the light beams (shown by arrow which progress to the right from the phosphor 2a) emitted to the side opposite to the aperture 8, even they are scattered and reflected by the phosphor 2 and the metal back 4, the light beams are difficult to reach the aperture 8. Even if the light beams reached the aperture 8, the light has been attenuated due to the scattering and reflection of the considerable number of times.
As illustrated in
In the example illustrated in
In such a construction, the light beams (shown by arrows which progress to both of the right and left from the phosphor 2a) emitted from the phosphor 2a are liable to reach the aperture 8 before the light is attenuated by the scattering and reflection. In this manner, it is desirable that both of the right and left sides of the phosphor 2a, in other words, the light-emitting portions are arranged at the sandwiched positions in the X direction in the aperture 8.
As illustrated in
In the example illustrated in
In such a construction, the light beams emitted from the phosphor 2a are liable to reach the aperture 8 in any of the X and Y directions. The number of apertures 8 is not always limited to the plural number but the aperture 8 may be formed in a continuous coupled form.
Subsequently, shapes and positions of the apertures 8 for the electron beam irradiating region as a feature of the present invention will be described.
In the embodiment in which the electron beam irradiating region 6 is smaller than the phosphor dot 20, by using the following construction, the light extracting efficiency and the bright-portion contrast can be improved.
As mentioned above, in order to improve the light extracting efficiency, it is required that the aperture 8 exists outside of the region where the light emission is performed. For this purpose, it is constructed so that at least a part of the aperture 8 is located outside of the electron beam irradiating region 6.
In order to improve the bright-portion contrast, it is necessary to increase the occupation ratio of the black member 3 which can absorb the external light, that is, decrease the aperture ratio. For this purpose, it is constructed so that a part of the black member 3 is located in the electron beam irradiating region 6.
Specific examples of such a construction will be described hereinbelow.
As a first construction, there is considered a construction in which the aperture 8 is divided into a plurality of apertures and at least one of the divided apertures 8 is arranged outside of the electron beam irradiating region 6 so as to sufficiently surround the electron beam irradiating region.
As examples of such a construction, constructions illustrated in (a) to (f) in
(a) in
A length in the longitudinal direction of the rectangular aperture 8 is longer than the minor axis of the elliptical electron beam irradiating region 6.
By forming such apertures 8 in the black member 3, the apertures 8 are made to exist outside of the light-emitting region and the occupation ratio of the black member 3a which can absorb the external light is increased, thereby enabling the aperture ratio to be reduced. That is, the light extracting efficiency can be improved and the bright-portion contrast can be improved.
(b) in
(c) in
Although (d) in
According to such a layout of such an aperture 8, as illustrated in
(e) in
(f) in
Subsequently, as a second construction, a construction in which such an aperture as to include the electron beam irradiating region 6 is presumed and the black member 3 is arranged in the electron beam irradiating region 6 is considered in place of the first construction having the divided aperture shapes.
(g) in
(h) in
(i) in
Further, a construction of the aperture portion necessary to further improve the light extracting efficiency (layout of the black member, reflecting member, and aperture) will be described.
The light beam emitted from the phosphor which has performed the light emission by the electron irradiation is repetitively subjected to
(1) scattering in the phosphor,
(2) reflection by the metal back, and
(3) reflection by the black member
and is emitted from the aperture to the observer side. In order to reduce the attenuation amount of the light beam as much as possible, therefore, a method whereby light absorption amounts in the phenomena of (1) to (3) are reduced as much as possible and a method whereby distances at which the phenomena of (1) to (3) occur are shortened are considered. Among (1) to (3), the light absorption amount is largest in the phenomenon of (3).
Therefore, as illustrated in
As a reflecting member 11, a member such as a metal film which performs a mirror reflection or a white colored member using a white colored material such as ceramics which performs a diffuse reflection can be used.
In the case of using the metal film as a reflecting member 11, a metal having a high reflectance can be used and silver, aluminum, nickel, platinum, rhodium, or the like can be desirably used. Particularly, aluminum is desirable because it is cheap, a reflectance is high, and it is also suitable for the photolithography. As a method of producing the reflecting film of the metal by laminating onto the black member 3a, a vacuum evaporation depositing method, a transfer method, a plating method, a screen printing method, or the like can be mentioned. As a patterning method, the photolithography, transfer method, screen printing method, or the like can be mentioned. In the case of the screen printing method, a material obtained by mixing microflakes of metal pieces into a paste form is used. Particularly, a method whereby the metal film formed by the vacuum evaporation depositing method is formed in the portion other than the aperture by the photolithography can be desirably used because of easiness of processes.
Subsequently, the case of using the white colored member as a reflecting member 11 will be described. The white colored member is a member having a high diffusion reflectance. It is assumed here that the member whose diffusion reflectance is equal to 50% or more is used as a white colored member. By laminating the white colored member onto the black member 3a, the high reflectance can be obtained irrespective of the surface state of the black member 3a serving as an underground. As a material of the white colored member, ceramics such as alumina, zirconia, or titania, barium sulfate which is used for the diffusion reflecting plate, or the like can be mentioned. As a method of forming the white colored member, the photolithography, screen printing method, transfer method, or the like using a member obtained by forming a paste from the above material can be mentioned. Among them, particularly, the photolithography using the photosensitive paste of the ceramics can be desirably used because of easiness of processes.
The black member 3a and the reflecting member 11 can be also simultaneously patterned. The whole surface is previously coated with the material of the black member 3a and, subsequently, the surface is formed as a film or coated with the material of the reflecting member 11. By preliminarily mixing a photosensitive material into those materials and photosensing and developing them in a lump, they can be collectively patterned. Therefore, particularly, the laminate structure of the black member 3a and the reflecting member 11 can be desirably formed.
Either a mode to form the metal film onto the black member 3a or a mode to form the white colored member can be properly selected according to the surface state of the black member 3a. If the black member 3a is flat, the metal film by which the mirror reflection can be obtained can be desirably used. When the black member 3a is not flat, even if the metal film is formed onto the non-flat black member 3a, a glossy surface cannot be obtained and the reflectance decreases. In such a case, it is desirable to use the white colored member such as ceramics or the like in which the high reflectance can be obtained irrespective of the surface state of the black member 3a as mentioned above.
Subsequently, a method of improving the light extracting efficiency by shortening a distance until the light is extracted will be described. Naturally, although it is most desirable that the aperture exists in the light-emitted portion, the aperture ratio cannot be reduced by such a construction. However, if the distance (distance between the apertures; length of light-shielded member) of the portion which is light-shielded by the black member 3a is short, since the number of times of the scattering in this portion is decreased, an attenuation ratio of the light can be reduced.
A shape suitable to shorten the distance of the portion which is light-shielded by the black member 3a will now be described with reference to
In the example illustrated in
The light beams emitted in the other directions also reach the aperture by relatively short distances. In addition, since the aperture ratio can be easily reduced, an effect of raising the bright-portion contrast is large.
In order to improve the bright-portion contrast, particularly, it is desirable to form the aperture 8 into a rectangle of a large aspect ratio (that is, the black member 3a also has a rectangular shape of a large aspect ratio). Naturally, when a distance L of the light-shielded portion is too long, even if the light-shielded portion is set into a rectangle of a large aspect ratio, the effect decreases. Therefore, it is desirable that the distance L of the black member 3a lies within a certain range. If it is sufficient that a degree of reduction in aperture ratio is small, the shape as illustrated in (h) in
Subsequently, a relation between the distance L of the black member 3a and the film thickness of the phosphor 2 will be described.
Since the light beam from the phosphor 2 which has been excited by the electron beam and emitted the light is isotropically radiated, it has an extent of a certain degree. The light beam is mainly concerned with the film thickness of the phosphor dot 20 made of the phosphor 2 and is spread to a distance (XY directions) which is about five times as large as the film thickness. Therefore, if the distance L of the black member 3a is equal to or larger than five times as large as the film thickness of the phosphor dot 20, since almost all of the light beams are certainly reflected by the black member 3a, the light extracting efficiency decreases. It is, therefore, desirable that the distance L of the black member 3a is equal to or less than five times as large as the film thickness of the phosphor 2.
Subsequently, the relation between the aperture ratio and the bright-portion contrast will be described. When the aperture ratio is too large, the effect of improving the bright-portion contrast decreases. However, if the aperture ratio is set to be too small, the light extracting efficiency decreases.
The effect of improving the bright-portion contrast starts to appear from a point where the aperture ratio in the electron beam irradiating region 6 is equal to about 90% and it appears typically when the aperture ratio is smaller than 70%. If the aperture ratio in the electron beam irradiating region 6 is smaller than 30%, the light extracting efficiency decreases. If it is smaller than 20%, the luminance is too low. Therefore, by setting the aperture ratio to a value within a range from 20% or more to 90% or less, desirably, a range from 30% or more to 70% or less, the bright-portion contrast can be desirably improved.
When the aperture ratio is equal to 30%, the luminance decreases to about 60%. When the aperture ratio is set to a value less than 30%, the luminance becomes too dark. On the contrary, if the aperture ratio is equal to about 70%, the effect of improving the bright-portion contrast decreases to about 30%.
The present invention has specifically been described above with respect to the electron beam display using the surface conduction electron-emitting devices. The present invention can be also desirably used in a display using other electron-emitting devices. When the other electron-emitting devices are used, an irradiating region of the electron beam according to them is formed. In the case of the spint type, the irradiating region is formed by a number of spots. In the case of a CRT using the shadow mask, a sharp current density profile having a shape almost similar to that of the aperture portion of the shadow mask is obtained. In this instance as well, by deciding the aperture shape in order to improve the bright-portion contrast for the electron beam irradiating region, the bright-portion contrast can be remarkably improved.
The present invention will be described in detail hereinbelow by showing specific Examples.
In this Example, the electron beam display having the black member illustrated in
First, a method of manufacturing the face plate 1 showing the feature of the present invention will be described.
<Step 1: Formation of Black Member>
An annealing process is executed to an upper surface of a soda-lime glass substrate and the upper surface is cleaned. After that, the whole surface is coated with a black paste serving as a black member 3 so as to have a thickness of 5 μm. In this Example, carbon black in which a sensitizer has been mixed is used as a black paste. After the coating, an exposure is executed so as to have such a shape as to have a plurality of apertures 8 per subpixel as illustrated in
<Step 2: Formation of Reflecting Member>
Subsequently, a film of aluminum is formed as a reflecting member 11 onto the whole surface by the vacuum evaporation depositing method so as to have a thickness of 300 nm. Then, the whole surface is coated with a photoresist and an exposure is performed so that the resists of the portions of the apertures 8 are removed. After that, the resists of the portions of the apertures 8 are removed by a development, the aluminum film is removed by etching, and thereafter, the remaining resists are exfoliated.
<Step 3: Formation of Phosphor>
Subsequently, the phosphor 2 of RGB are formed by the screen printing method. The P22 phosphor made by Kasei Optonix, Ltd. are used as phosphor 2; that is, red P22RE3 (Y202S), green P22GN4 (ZnS: Cu, Al), and blue P22B2 (ZnS: Ag, Cl) are used. A mean diameter of each phosphor 2 is equal to 7 μm and they are formed so that an average film thickness of the phosphor dot 20 is equal to 15 μm. After that, the baking is performed at 450° C.
<Step 4: Formation of Metal Back>
Subsequently, the metal back 4 is formed by using the filming method which is well known in the field of the CRT. After the resin intermediate film was formed, a film of aluminum is formed by the vacuum evaporation depositing method so as to have a thickness of 100 nm. After that, the baking is performed at 450° C. and the resin intermediate film is removed.
<Step 5: Formation of Vacuum Vessel>
The face plate 1 is produced through the foregoing steps and combined with the rear plate 9, thereby forming a vacuum vessel. The operation as an electron beam display was confirmed. A description about the producing methods of the rear plate 9 and the electron-emitting devices 10 is omitted here.
A construction of the surface conduction electron-emitting devices used in the embodiment will now be described.
A luminance of the manufactured electron beam display is measured, so that it is equal to 450 cd/m2. A diffusion reflectance at an illuminance in the room of 300 1× is measured, so that it is equal to 3%. A bright-portion contrast is equal to about 300.
Example 2 relates to an example in which the white colored material is used as a reflecting member 11. Since a shape of aperture 8, producing methods of the phosphor 2 and the metal back 4, and the like are similar to those in Example 1, their description is omitted.
<Formation of Black Member and Reflecting Member>
An annealing process is executed to a soda-lime glass substrate and the substrate is cleaned. After that, the whole surface is coated with a black paste serving as a black member 3 so as to have a thickness of 5 μm. In this Example, a paste obtained by mixing a sensitizer, a binder resin, a black pigment, and a glass frit of a low melting point is used as a black paste.
Subsequently, the whole surface is coated with a white paste so as to have a thickness of 5 μm. In this Example, a paste obtained by mixing a sensitizer, alumina, and a glass frit of a low melting point is used as a white paste.
After the white paste was laminated and coated, a drying is performed, an exposure is executed so as to have a desired shape, and a development is performed, thereby obtaining the pattern as illustrated in
Subsequently, the phosphor and the metal back are formed by a method similar to that of Example 1.
A luminance of the manufactured electron beam display is measured, so that it is equal to 420 cd/m2. A diffusion reflectance at an illuminance in the room of 300 1× is measured, so that it is equal to 3%. A bright-portion contrast is equal to about 280.
(Comparison)
Subsequently, as a Comparison, the black member 3 formed with the aperture 8 which covers the whole electron beam irradiating region 6 illustrated in
A luminance of the manufactured electron beam display is measured, so that it is equal to 500 cd/m2. A diffusion reflectance at an illuminance in the room of 300 1× is measured, so that it is equal to 6%. A bright-portion contrast is equal to about 170.
While the present invention has been described with reference to exemplary embodiments, it is to be understood that the present invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.
This application claims the benefit of Japanese Patent Application No. 2008-097025, filed Apr. 3, 2008, which is hereby incorporated by reference herein in its entirety.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2008-097025 | Apr 2008 | JP | national |
