BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a cross-sectional view of three-electrode surface discharge type of plasma display panel of the prior art.
FIG. 2 is a cross-sectional view of a plasma display panel of a first embodiment.
FIG. 3 is an overhead view showing the production process of a second substrate.
FIG. 4 is an overhead view showing the production process of a second substrate.
FIG. 5 is an overhead view in which display electrodes are superimposed on the second substrate of FIG. 4.
FIG. 6 is an overhead view of a third substrate.
FIG. 7 is a different overhead view of a third substrate.
FIG. 8 is a cross-sectional view of a plasma display panel of a second embodiment.
FIG. 9 is an overhead view of a first substrate of a second embodiment.
FIG. 10 is a different overhead view of a first substrate of as second embodiment.
FIG. 11 is an overhead view showing display electrodes 11 and address electrodes ADD superimposed on a matrix-like barrier 16 of FIG. 10.
FIG. 12 is a cross-sectional view of a plasma display panel of a third embodiment.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The following provides an explanation of embodiments of the present invention with reference to the drawings. However, the technical scope of the present invention is not limited to these embodiments, but rather extends to the matters described in the scope of claim for patent and matters equivalent thereto.
FIG. 1 is a cross-sectional view of a three-electrode surface discharge type of plasma display panel of the prior art. Display electrodes 11, comprised of a transparent electrode 12 and a bus electrode 13 of a highly conductive metal (three-layer structure of Cr/Cu/Cr) superimposed thereon, a dielectric layer 14 covering the display electrodes 11, and a protective layer 15 comprised of MgO covering the dielectric layer 14, are formed on a side of a discharge space of a front side glass substrate 10.
On the other hand, address electrodes ADD, which intersect with the display electrodes 11 and form unit emission regions at the locations of those intersections, a dielectric layer 22 covering the address electrodes ADD, and a barrier 24, in the form of stripes or in the form of a matrix comprised of vertical walls and horizontal walls, are formed on a side of the discharge space of a back side substrate 20. This barrier 24 demarcates the unit emission regions and prevents discharge interference between adjacent unit discharge regions.
Phosphors 26 in the three colors of red, green and blue (RGB) are provided on the dielectric layer 22 of the back side substrate 20 and on the side of the barrier 24. The phosphors 26 are formed by coating a paste in which a phosphor powder is mixed with a vehicle onto the surface of the back side substrate 20 on which the barrier 24 is formed, and baking after volatilizing the vehicle by high-temperature treatment to leave only the phosphor powder.
In the plasma display panel of FIG. 1, an address discharge is generated between the display electrodes 11 and the address electrodes ADD during an address period, and an electrical charge generated by the discharge accumulates on the surfaces of the dielectric layer 14 and the protective layer 15. During a sustain discharge period following the address period, a voltage is alternately applied between adjacent display electrodes, and a sustain discharge is repeated by using a wall electric charge accumulated during the address period. As indicated with the upward arrows, light emitted by the phosphors is output towards the front side substrate as a result of ultraviolet light generated during the discharge generation exciting the phosphors resulting in emission of light. A desired brightness can be displayed according to the number of these sustained discharges.
As shown in FIG. 1, since phosphors 26 are provided on the back side substrate, and the sustain discharge accounting for the majority of the plasma discharge is a surface discharge occurring between the display electrodes of the front side substrate, phosphors 26 are not directly subjected to ion bombardment during discharge. Even so, since the phosphors 26 are exposed in the discharge space, ion bombardment during plasma discharge cannot be completely avoided. In particular, phosphors 26 in the vicinity of the apex of the barrier 24 are susceptible to ion bombardment generated by sustain discharge between the display electrodes. Thus, this causes deterioration of the phosphors and shortening of the panel lifetime.
In addition, although the phosphor paste is coated by a printing method and so forth followed by high-temperature treatment, since the vehicle (such as a resin, organic solvent or plasticizer) in the paste cannot be completely removed, aging is carried out by applying a high voltage after the panel has been formed. This aging step leads to increased costs.
FIG. 2 is a cross-sectional view of a plasma display panel of a first embodiment. Although the constitution of the front side first substrate 10 is the same as in FIG. 1, a characteristic of this first embodiment is that the back side second substrate 20 in which the address electrodes ADD are formed separates the phosphors 36 from the discharge space surrounded by the barrier 24 and the upper and lower substrates 10 and 20. As a result, the phosphors 36 are not subjected to ion bombardment during plasma discharge, deterioration of the phosphors over time is inhibited, and the lifetime of the panel can be extended.
A third substrate 30 is provided adhered on the opposite side of the second substrate 20 from the discharge space. Recesses 32 are formed in the third substrate 30 at locations corresponding to the unit emission regions, and phosphor powders are filled into these recesses 32. However, these recesses 32 may also be provided on the back side of the second substrate 20, and in either case, the second substrate 20 and the third substrate 30 are adhered with the phosphors 36 interposed therebetween. Since phosphor powders can be filled into the recesses 32, it is not necessary to coat a phosphor base followed by high-temperature treatment as in the prior art, thereby making it possible to eliminate the need for the aging step responsible for increasing production costs.
In the example of a constitution of FIG. 2, the second substrate 20 is comprised of a transparent substrate which allows transmission of ultraviolet light generated by plasma discharge as well as transmission of light emitted by the phosphors in the form of visible light, and the barrier 24 is provided on the second substrate 20 for demarcating the unit emission regions. In addition, since the phosphors 36 are provided on the back side of the second substrate 20, a dielectric layer comprised of a glass material having a low melting point is not provided for covering the address electrodes ADD.
Moreover, a secondary electron emission layer 26 comprised of MgO is formed on the lateral surface of the barrier 24. The protective layer 15 on the side of the first substrate 10 is also an MgO layer, and these layers 15 and 26 emit secondary electrons in response to ion bombardment during plasma discharge. Thus, emission efficiency is improved by increasing the emission level of secondary electrons during discharge to either lower the effective discharge voltage or increase the amount of emitted light if the discharge voltage is the same. In other words, by providing the phosphors on the back side of the second substrate 20, the secondary electron emission layer 26 comprised of MgO can be formed on the barrier 24.
In addition, a reflective layer 34 such as Cr or Cu is formed on the inner surfaces of the recesses 32 of the third substrate into which phosphor powder is filled. Since a comparatively large number of phosphor powders 36 are filled into the recesses 32 and the light emitted by those phosphors is reflected by the reflective layer 34, emitted light can be efficiently guided to the front side, thereby making it possible to enhance emission efficiency.
The address electrodes ADD formed on the surface of the second substrate 20 are formed from a transparent electrode material so as to enable emitted light to be transmitted from the phosphors. For example, this transparent electrode material may be ITO, SnO2 or Ga2O3. Ultraviolet light transmitting holes HOLE are formed in the centers of the address electrodes ADD to allow transmission of ultraviolet light. Ultraviolet light is guided to the phosphors 36 located directly below through these center holes HOLE, while derivation to the phosphors 36 of unit emission regions adjacent thereto in the diagonal direction is inhibited.
In the plasma display panel shown in FIG. 2, since the structure of the first substrate 10 is the same as that of the example of the prior art shown in FIG. 1, an explanation of the production process thereof is omitted. The production processes of the second substrate 20 and the third substrate 30 are explained with reference to overhead views.
FIG. 3 and FIG. 4 are overhead views showing the production process of the second substrate 20. First, the barrier 24 in the form of a plurality of stripes is formed on the surface of the second substrate 20 comprised of a transparent resin substrate by direct etching of regions other than the barrier 24 by a method such as laser forming or chemical etching. Alternatively, the barrier 24 may also be formed by applying a thick coating of a glass paste having a low melting temperature to the second substrate 20 comprised of a transparent glass substrate or resin substrate, forming multiple stripe pattern by sand blasting using a mask film, and then baking at a high temperature. This state is shown in the overhead view of FIG. 3. The solid lines of the barrier 24 indicate the bottom surfaces, while the broken lines indicate the apical surfaces, and unit emission regions are formed in the regions interposed by the barrier 24.
Next, as shown in FIG. 4, the address electrodes ADD comprised of the above-mentioned transparent electrode material are formed between the barriers 24. These address electrodes are formed by either sputtering the transparent electrode material onto the entire surface of the substrate followed by forming into stripes using ordinary lithography technology, or by sputtering with a mask having striped passage pattern arranged on the upper surface of the substrate to form the address electrodes in a striped pattern. Square holes HOLE for allowing transmission of ultraviolet light are then formed at the locations corresponding to the unit emission regions of the address electrodes ADD.
Although not shown in the drawings, a secondary electron emission layer comprised of MgO is formed on the side walls and apices of the barrier. This layer is preferably formed in the same manner as the address electrodes either by sputtering MgO over the entire surface followed by allowing it to remain on the barrier by ordinary lithography technology, or by sputtering MgO with a mask having a striped passage pattern arranged on the upper surface of the substrate.
In the present embodiment, a dielectric layer which covers the address electrodes ADD is not formed. In the example of the prior art of FIG. 1, as a result of providing the dielectric layer 22, a glass paste layer for forming a barrier thereon can be patterned by sandblasting. In other words, the dielectric layer 22 has the function of protecting the address electrodes during sandblasting as well as the function of improving adhesion between the substrate and the barrier when the mask film of the sandblasting step is peeled off. In the present embodiment however, since it is necessary to radiate ultraviolet light onto the phosphors on the back of the second substrate 20, it is preferable to not provide such a dielectric layer to prevent attenuation of the ultraviolet light.
FIG. 5 is an overhead view in which display electrodes are superimposed on the second substrate of FIG. 4. This drawing shows the relationship between the unit emission regions at the locations where the display electrodes and the address electrode intersect, and the ultraviolet transmission holes HOLE of the address electrodes. The display electrodes 11 are composed transparent electrodes 12 and bus electrodes 13 formed overlapping the central portions thereof. The regions in opposition to the transparent electrodes 12 and interposed by the barrier 24 correspond to the unit emission regions. The ultraviolet transmission holes HOLE of the address electrodes ADD are formed at those locations overlapping these unit emission regions.
FIG. 6 is an overhead view of the third substrate. This third substrate 30 is a glass substrate or resin substrate, and the recesses 32 are formed in a striped pattern at the locations corresponding to the unit emission regions. This striped pattern conforms to the regions between the stripes of the barrier 24 as shown in FIG. 2 and FIG. 3. In addition, in the case the third substrate 30 is a resin substrate, it can be laminated with the second substrate 20 with an adhesive, and grooves for applying that adhesive are formed around the third substrate 30.
Grooves for applying a sealant are also formed by directly etching the substrate for the recesses 32 as well. This direct etching process is carried out by laser forming or chemical etching. The depth of the recesses 32 into which the phosphors are filled is, for example, preferably about 100 to 300 μm.
Reflective layers are then formed on the inner surfaces of the recesses 32. These reflective layers are formed by sputtering a reflective film over the entire surface of the third substrate 30 followed by patterning while leaving only the inner surfaces of the recesses 32 by ordinary lithography technology. Alternatively, a reflective layer material may be sputtered only on the insides of the recesses with a mask fixed on the third substrate 30. Subsequently, three colors (RGB) of phosphor powders are filled into the recesses 32 in which the reflective layer has been formed. A dispensing method or blade method is preferably used for filling. Here, a phosphor paste like that of the example of the prior art is not used.
FIG. 7 is a different overhead view of the third substrate. In the example of FIG. 7, after having been formed by a direct etching process in the third substrate 30, the recesses 32 are patterned as a plurality of rectangles arranged in the form of a matrix instead of a striped pattern. These rectangular recesses 32 are formed at locations matching the unit emission regions where the display electrodes and the address electrodes of the first and second substrates intersect. Thus, these rectangular recesses 32 also match the ultraviolet transmission holes HOLE formed in the address electrodes ADD. Reflective layers are then formed on the inner surfaces of the recesses 32 and phosphor powders are filled therein.
FIG. 8 is a cross-sectional view of a plasma display panel in a second embodiment. This plasma display panel differs from that of the first embodiment shown in FIG. 2 in that a barrier 16, which demarcates the unit emission regions, is formed on the first substrate 10, and a combination protective layer/secondary electron emission layer 15 comprised of MgO is formed on the surfaces of a dielectric layer 14 and the barrier 16. Other aspects of this second embodiment are the same as the first embodiment.
The display electrodes 11 comprised of the transparent electrodes 12 and the bus electrodes 13 are formed on the transparent first substrate 10, and the dielectric layer 14 is formed covering the display electrodes 11. The barrier 16, in the form of a striped pattern or a matrix pattern composed of horizontal walls and vertical walls, is formed on the dielectric layer 14, and an MgO layer 15 is formed on the dielectric layer 14 and the barrier 16.
Only the address electrodes ADD are formed on the transparent second substrate 20. The third substrate 30, in which phosphor powders have been filled into the recesses 32, is adhered to the back side of the second substrate 20. The reflective layer 34 is formed on the inner surfaces of the recesses 32 so as to guide light emitted from the phosphors to the front side.
Since the phosphors 36 are separated from the discharge space by the second substrate 20, in this second embodiment as well, the phosphors are not subjected to ion bombardment accompanying discharge, and the lifetime thereof can be extended. In addition, since the phosphor powders are filled into the recesses 32, it is not necessary to use a phosphor paste, and an aging step of stabilizing brightness is also not required.
In addition, emission efficiency is improved due to the combination protective layer/secondary electron emission layer 15 comprised of MgO, and emission efficiency is further improved by the reflective layer 34 on the inner surfaces of the recesses 32.
Since the phosphors are provided on the third substrate 30 in this second embodiment, a dielectric layer covering the address electrodes ADD is not required to be provided, and ultraviolet light is prevented from being attenuated during discharge. In addition, since the phosphors are provided in the third substrate 30, it is not necessary to provide the barrier 16 on the second substrate and provide phosphors on the side walls thereof. Therefore, in this second embodiment, the degree of freedom of the barrier pattern is improved by providing the barrier 16 on the first substrate.
In other words, in the case of forming the barrier on the second substrate 20, a glass paste is applied after forming the address electrodes ADD, and the glass paste is patterned by sandblasting followed by baking at a high temperature. In the case of sandblasting, it is necessary to cover the address electrodes ADD with a dielectric layer for the purpose of protecting the address electrodes and so forth. However, if this dielectric layer is provided, ultraviolet light is attenuated thereby resulting in the risk of said ultraviolet light being unable to adequately reach the phosphors of the third substrate. Therefore, the barrier is formed on the first substrate and the dielectric layer on the address electrodes is eliminated since it is no longer necessary to form the barrier on the second substrate accompanying formation of the phosphors in the third substrate.
FIG. 9 is an overhead view of a first substrate in the second embodiment. Although the display electrodes 11 and the dielectric layer 14 are formed on the first substrate 10, these are not shown in FIG. 9. The barrier 16 is shown to have a striped pattern in FIG. 9. In the same manner as previously described, the solid lines indicate the lower sides of the barrier, while the broken lines indicate the apices. Unit emission regions are located between the stripes of the barrier 16.
FIG. 10 is a different overhead view of a first substrate in the second embodiment. In this example, the barrier 16 has a matrix pattern comprised of walls in the vertical direction and walls in the horizontal direction, barrier 16 demarcates the unit emission regions C in four directions, and completely separates adjacent unit emission regions C.
FIG. 11 is an overhead view showing the display electrodes 11 and the address electrodes ADD superimposed on the matrix-like barrier 16 of FIG. 10. The transparent electrodes 12 of two adjacent display electrodes 11 are arranged in opposition to unit emission regions C demarcated by the matrix-like barrier 16, and the bus electrodes 13 of the display electrodes 11 are arranged so as to overlap the barrier 16 extending in the horizontal direction. As a result, there is no opaque material to block the unit emission regions C demarcated by the barrier 16, and numerical aperture can be increased. In addition, the ultraviolet transmission holes HOLE of the address electrodes ADD are also arranged at locations corresponding to the unit emission regions C.
The overhead views of the third substrate in this second embodiment are the same as those of FIG. 6 and FIG. 7.
FIG. 12 is a cross-sectional view of a plasma display panel of a third embodiment. This third embodiment differs from the second embodiment in that the recesses 32 are formed on the opposite side of the second substrate 20 from the discharge space, the reflective layers 34 are formed on the lateral surfaces thereof, and phosphor powders 36 are filled into the recesses 32. Reflective layers 34 are formed on the third substrate 30 at locations corresponding to the phosphors 36. In addition, although the barrier 16 is formed on the first substrate 10 in the same manner as the second embodiment, it may also be formed on the second substrate. Other structures are the same as in the first and second embodiments.
As has been explained above, according to the present embodiment, since the phosphors are separated from the discharge space by the second substrate, the lifetime of the phosphors can be extended, and since the phosphors are filled into recesses in the third substrate or the second substrate, an aging step required when using phosphor paste is not required. In addition, since a reflective layer is provided around the phosphors and an MgO layer is provided on the barrier as well, effective emission efficiency is improved.
Patent Application
20080018249
