# Patent

## Title
Method of manufacturing a colorant-added upper dielectric layer for a PDP display

## Abstract

A front substrate for a plasma display panel (PDP) and an associated fabrication method are provided. An upper dielectric layer of the front substrate includes a colorant, which causes the dielectric layer to also act as a color filter. The resulting front substrate enhances at least one of color temperature, color purity, and/or contrast without increasing complexity or cost.

## Background
This application is a Continuation Application of application Ser. No. 11/264,021 filed Nov. 2, 2005, which in turn is a Continuation Application of application Ser. No. 10/760,454 filed Jan. 21, 2004, which issued into U.S. Pat. No. 6,992,336 on Jan. 31, 2006. The disclosures of the previous applications are incorporated by reference herein.


BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a plasma display panel (PDP) and, more particularly, to a front substrate of the PDP and its fabrication method.
2. Description of the Background Art
In general, with the development and growing spread of in an information processing system, an importance of a next-generation multimedia display device as a visual information transmission means is increasing. Especially, because a conventional CRT (Cathode Ray Tube) fails to go with the recent tendency aiming at a large and flat screen, researches on an LCD (Liquid Crystal Display), an FED (Field Emission Display), a PDP (Plasma Display Panel), and an EL (ElectroLuminesence) are actively ongoing.
As a self-emission display device using a plasma gas discharge, the PDP is advantageous in that it can be enlarged in size, its picture quality is excellent and an image response speed is fast.
In addition, the PDP receives an attention in the market as a wall-mounted display device together with the LCD or the like.
A discharge cell of a three-electrode AC surface discharge type PDP having such characteristics will now be described with reference to FIG. 1.
FIG. 1 illustrates a structure of a general three-electrode AC surface discharge type PDP.
As shown in FIG. 1, the general three-electrode AC surface discharge PDP is constructed such that a front substrate 10 and a back substrate 20 are coupled and a discharge gas is injected therebetween.
The front substrate 10 includes: an upper glass substrate 11; transparent electrode 12 and bus electrode 13 formed on the glass substrate; an upper dielectric layer 14 formed entirely on the transparent and bus electrode-formed upper glass substrate 11; and a protection layer 15 formed on the upper dielectric layer 14.
The upper dielectric layer 14 serves to limit a plasma discharge current and accumulate a wall charge when plasma is discharged.
The back substrate 20 includes: a lower glass substrate 25; an address electrode 24 formed on the lower glass substrate 25; a lower dielectric layer 23 formed entirely on the address electrode-formed lower glass substrate 25; a barrier rib 22 formed on the lower dielectric layer 23; and a phosphor 21 formed entirely on the lower dielectric layer 23 and the barrier rib 22.
The operation principle of the general PDP constructed as described above will now be explained.
First, as a discharge sustain voltage is applied to the transparent electrode 12 and the bus electrode 13, charges are accumulated on the upper dielectric layer 14, and as a discharge starting voltage is applied to the address electrode 24, a discharge gas comprising He, Ne and Xe or the like injected in each discharge cell of the PDP is separated to electron and ion to turn to plasma.
Thereafter, in the PDP, when the phosphor 21 is excited by ultraviolet generated at a moment when the electron and ion are re-coupled, a visible light is generated by which a character or a graphic is displayed. Herein, in order to prevent thermal deformation of the dielectric layer or the phosphor 21 caused as the accelerated gas ions collide with each other, the PDP uses Ne gas having a relatively greater molecular weight as a principal component.
However, since Ne gas generates an orange-colored visible light (585 nm) when discharged, color purity and a contrast of the PDP deteriorate.
In order to avoid such a problem, a PDP having a color filter layer or a black strip layer additionally formed on the upper substrate has been proposed.
FIG. 2 is a sectional view showing a front substrate of the PDP in accordance with a conventional art.
As shown in FIG. 2, the front substrate of the conventional PDP includes an upper substrate 11; transparent electrode 12 and bus electrode 13 formed on the upper glass substrate 11; an upper dielectric layer 14 formed on the transparent and bus electrode-formed upper glass substrate 11; a color filter layer 14A formed on the upper dielectric layer 14; and a protection layer 15 formed on the color filter layer 14A. The color filter layer 14A can control a light transmittance and prevent a surface reflection by an external light.
Accordingly, in the conventional PDP, the color purity of the PDP can be enhanced by controlling the light transmittance of a color filter by virtue of the color filter layer, and the contrast of the PDP can be enhanced by preventing a surface reflection by an external light.
However, in the conventional PDP, formation of the color filter layer on the upper dielectric layer of the PDP complicates a fabrication process of the PDP.
In addition, in the conventional PDP, since the light transmittance of a blue (B) visible light is relatively low compared to the red (R) and green (G) visible light, the color temperature of the PDP is approximately 6000K. Thus, in order to compensate the low color temperature, input signals corresponding to R, G and B are controlled, the barrier rib structure is formed asymmetrically or the light transmittance and dye of the color filter layer are controlled, but in this case, the luminance of the PDP is reduced.
Meanwhile, the color filter layer may be replaced by a black stripe layer. However, the black strip layer has a small aperture plane, a light emitting efficiency of the PDP is degraded.
As mentioned above, the conventional PDP has the following problems.
That is, since the color filter layer is additionally included, the fabrication process of the PDP is complicated.
In addition, since the light transmittance of the B visible light is relatively low compared to the R and G visible light, the color temperature of the PDP is low.
SUMMARY OF THE INVENTION
Therefore, one object of the present invention is to provide an upper dielectric layer of a PDP formed containing a colorant capable of controlling a light transmittance to thereby enhance a color temperature of the PDP, and its fabrication method.
Another object of the present invention is to provide an upper dielectric layer of a PDP formed containing a colorant capable of controlling a light transmittance to thereby enhance a color purity of the PDP, and its fabrication method.
Still another object of the present invention is to provide an upper dielectric layer of a PDP formed containing a colorant capable of controlling a light transmittance to thereby enhance a contrast of the PDP, and its fabrication method.
Yet another object of the present invention is to provide an upper dielectric layer of a PDP formed containing a colorant as much as a prescribed rate capable of controlling a light transmittance to thereby simplify a fabrication process of the PDP, and its fabrication method.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described herein, there is provided a front substrate of a PDP including a colorant-added upper dielectric layer.
To achieve the above objects, there is also provided a method for fabricating a front substrate of a PDP including: forming a colorant-added upper dielectric layer.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.



BRIEF DESCRIPTION OF THE DRAWINGS
The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention.
In the drawings:
FIG. 1 is a view showing a structure of a general three-electrode AC surface discharge type PDP;
FIG. 2 is a sectional view showing a front substrate of a PDP in accordance with a conventional art;
FIG. 3 is a sectional view showing a front substrate of a PDP in accordance with the present invention;
FIG. 4 is a flow chart of a method for fabricating the front substrate of the PDP in accordance with the present invention;
FIG. 5 is a flow chart of a method for fabricating an upper dielectric layer of FIG. 3;
FIG. 6 is a graph showing an experimentation result of the light transmittance of a PDP in accordance with a first embodiment of the present invention; and
FIG. 7 is a graph showing an experimentation result of the light transmittance of a PDP in accordance with a second embodiment of the present invention



DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings.
A PDP having an upper dielectric layer containing a colorant that is able to control a light transmittance to thereby enhance a color temperature, color purity and a contrast, and a fabrication method of the upper dielectric layer in accordance with a preferred embodiment of the present invention will now be described with reference to the accompanying drawings.
FIG. 3 is a sectional view showing a front substrate of a PDP in accordance with the present invention.
As shown in FIG. 3, a front substrate of a PDP in accordance with the present invention includes: an upper glass substrate 11; transparent electrode 12 and a bus electrode 13 formed on the upper glass substrate 11; an upper dielectric layer 14B entirely formed on the transparent and bus electrode-formed upper glass substrate 11 and containing a colorant; and a protection layer 15 formed on the upper dielectric layer 14B.
A method for fabricating the front substrate of the PDP constructed as described above will now be explained with reference to FIG. 4.
As shown in FIG. 4, the method for fabricating the front substrate of the PDP in accordance with the present invention includes: forming the upper glass substrate 11 (step S41); forming the transparent electrode 12 and bus electrode 13 on the upper glass substrate 11 (step S42); forming the upper dielectric layer 14B containing a colorant at a prescribed rate entirely on the transparent and bus electrode-formed upper glass substrate 11 (step S43); and forming the protection layer 15 on the upper dielectric layer 14B.
The method for fabricating the front substrate of the PDP will now be described.
First, the upper glass substrate 11 is formed (step S41), on which the transparent electrode 12 and the bus electrode 13 are formed (step S42).
And then, the upper dielectric layer 14B with the colorant added as much as a prescribed rate is formed entirely on the upper glass substrate 11 on which the transparent electrode 12 and the bus electrode 13 have been formed.
A method for fabricating the upper dielectric layer of the PDP will now be described with reference to FIG. 5.
FIG. 5 is a flow chart of a method for fabricating an upper dielectric layer of FIG. 3.
As shown in FIG. 5, the method for forming an upper dielectric layer of the PDP in accordance with the present invention includes: forming glass powder containing a colorant at a prescribed rate (step S51); forming a dielectric paste by mixing the glass powder, binder and solvent (step S52); coating the dielectric paste entirely on the transparent and bus electrode-formed upper glass substrate to form a dielectric paste layer or a green sheet layer (step S53); and firing the dielectric paste layer or the green sheet layer to form an upper dielectric layer (step S54).
The method for forming the upper dielectric layer of the PDP in accordance with the present invention will now be described in detail.
First, glass is fabricated by mixing a colorant that can control a light transmittance at a prescribed rate to parent glass. Herein, preferably, a material used as the colorant includes at least one of Nd2O3 and cobalt oxide such as CoO, Co3O4 and Co2O3. The prescribed rate means a ratio of the colorant to the parent glass, and Nd2O3 is added in the range of 0 ̃40 wt % and cobalt oxide such as CoO, Co3O4 and Co2O3 is added in the range of 0 ̃10 wt %.
As shown in Table 1 ̃Table 4 shown below, the parent glass comprises one of components shown in the Table 1 and Table 2 (PbO—B2O3—SiO2—Al2O3—RO-based glass), Table 3 (P2O5—B2O3—ZnO-based glass) and Table 4 (ZnO—B2O3—RO-based glass). The unit representing each component in Table 1 to Table 3 is weight %.
The method for adding the colorant that can control the light transmittance to the parent glass at a prescribed rate will now be described with reference to first to fourth embodiments of the present invention.
First, in the method for adding a colorant to parent glass in accordance with a first embodiment, Nd2O3 is added in the range of 0 ̃40 wt % to PbO—B2O3—SiO2—Al2O3—RO-based glass as shown in Table 1. Herein, RO, a constituent of the parent glass in Table 1, is one of BaO, SrO, La2O, Bi2O3, MgO and ZnO.












TABLE 1







PbO
B2O3
SiO2 + Al2O3
RO





















50
10
25
15



55
15
20
10



60
20
10
10



65
10
20
5










A result of an experimental measurement of the light transmittance of the PDP in accordance with the first embodiment of the present invention will now be described with reference to FIG. 6.
FIG. 6 is a graph showing an experimentation result of the light transmittance of a PDP in accordance with a first embodiment of the present invention.
As shown in FIG. 6, a light transmittance of the orange-colored visible light (585 nm) is lower than that of the blue visible light (454 nm), green visible light (525 nm) and red visible light (611 nm). Accordingly, through this experimentation result, an improvement of the color temperature, color purity and contrast of the PDP in accordance with the present invention can be expected.
Second, in a method for adding a colorant to parent glass in accordance with the second embodiment of the present invention, cobalt oxide is added in the range of 0 ̃10 wt % to PbO—B2O3—SiO2—Al2O3—RO-based glass as shown in Table 2. Herein, cobalt oxide is one of CoO, Co3O4 and Co2O3 each having a lower light transmittance of the red visible light (611 nm) and green visible light (525 nm) than that of the blue visible light (454 nm).












TABLE 2







PbO
B2O3
SiO2 + Al2O3
RO





















65
10
25
0



60
12.5
22.5
5



55
15
20
10



50
20
17.5
12.5










A result of an experimental measurement of the light transmittance of the PDP in accordance with the first embodiment of the present invention will now be described with reference to FIG. 7.
FIG. 7 is a graph showing an experimentation result of the light transmittance of a PDP in accordance with a second embodiment of the present invention.
As shown in FIG. 7, a light transmittance of the blue visible light (454 nm) is higher than that of the red visible light (611 nm) and green visible light (525 nm). Accordingly, through this experimentation result, a remarkable improvement of the color temperature, color purity and contrast of the PDP can be expected.
Third, in a method for adding a colorant to parent glass in accordance with a third embodiment, both Nd2O3 in the range of 0 ̃40 wt % and cobalt oxide in the range of 0 ̃10 wt % are added to P2O5—B2O3—ZnO-based glass as shown in Table 3.







TABLE 3







wt %









B2O3
ZnO
P2O5





00.0
46.2
53.8


03.3
44.7
52.0


06.8
43.1
50.1


10.4
41.4
48.2


14.1
39.7
46.2


18.0
37.9
44.1


22.0
36.1
41.9









Fourth, in a method for adding a colorant to parent glass in accordance with a fourth embodiment of the present invention, both Nd2O3 in the range of 0 ̃40 wt % and cobalt oxide in the range of 0 ̃10 wt % are added to ZnO—B2O3—RO-based glass as shown in Table 4. Herein, RO, a constituent of parent glass of Table 4, is one of BaO, SrO, La2O, BiO3, MgO and ZnO.









TABLE 4





ZnO
B2O3
RO







19.8
42.4
37.8


24.6
37.9
37.5


29.3
33.4
37.3


34.0
29.0
37.0









The thusly fabricated glass is crushed to a prescribed particle size to from glass powder. The prescribed particle size is preferably in the range of 1 ̃5 μm.
The formed glass powder is mixed together with an ethylcellulose binder in a solvent such as α-terpineol or BCA (Butyl Cabitol Acetate) which dissolves the binder, to form a dielectric paste.
At this time, the formed dielectric paste is coated at the entire surface of the upper glass substrate on which the transparent electrode and bus electrode have been formed. This will now be described in detail.
First, the formed dielectric paste is coated at the entire surface of the transparent and bus electrode-formed upper glass substrate through a screen-printing method or a thick film coating method, to form a dielectric paste layer.
Second, the dielectric paste is shaped in a sheet by a doctor blading method and then dried to be formed as a green sheet. The green sheet is coated at the entire surface of the transparent and bus electrode-formed upper glass substrate by a laminating method, to form a green sheet layer.
The thusly formed dielectric paste layer or the green sheet layer is fired at 550° C. ̃600° C. for 10 ̃30 minutes to be formed as an upper dielectric layer containing Nd2O3 and cobalt oxide to serve as a color filter. The thickness of the upper dielectric layer is approximately 20 ̃40 μm.
As so far described, the front substrate of the PDP and its fabrication method in accordance with the present invention has the following advantages.
That is, first, since the upper dielectric layer contains the light transmittance-controllable colorant at a prescribed rate, its light transmittance can be controlled and thus a color purity of the PDP can be enhanced.
Second, since the upper dielectric layer contains the light transmittance-controllable colorant at a prescribed rate, light transmittance of the blue visible light is enhanced and thus a color temperature of the PDP can be improved.
Third, since the upper dielectric layer contains the light transmittance-controllable colorant at a prescribed rate, a surface reflection of an external light is prevented and thus a contrast of the PDP can be enhanced.
Fourth, since the upper dielectric layer contains the light transmittance-controllable colorant at a prescribed rate, a filter layer is not necessary and thus a fabrication process of the PDP can be simplified.
As the present invention may be embodied in several forms without departing from the spirit or essential characteristics thereof, it should also be understood that the above-described embodiments are not limited by any of the details of the foregoing description, unless otherwise specified, but rather should be construed broadly within its spirit and scope as defined in the appended claims, and therefore all changes and modifications that fall within the metes and bounds of the claims, or equivalence of such metes and bounds are therefore intended to be embraced by the appended claims.

## Claims

1. A method of fabricating a front substrate of a plasma display panel (PDP), comprising forming a colorant-added upper dielectric layer, wherein the colorant is Co2O3, and wherein a thickness of the upper dielectric layer is greater than 20 μm and less than 30 μm.

2. The method of claim 1, wherein the upper dielectric layer comprises a glass powder, wherein the glass powder includes at least three of PbO, B2O3, SiO2, Al2O3 or BaO.

3. The method of claim 2, wherein the glass powder comprises greater than 30 wt % and less than 40 wt % of the colorant.

4. The method of claim 1, wherein forming a colorant-added upper dielectric layer comprises:
forming a glass powder comprising a parent glass and the Co2O3;
coating the glass powder on a surface of an upper glass substrate of the PDP having a transparent electrode and a bus electrode formed thereon; and
firing the coated glass powder coated on the upper glass substrate.

5. The method of claim 4, wherein forming the glass powder comprises dding the Co2O3 to a parent glass which is one of PbO—B2O3—SiO2—Al2O3—RO group, P2O5—B2O3—ZnO group, or ZnO—B2O3—RO group.

6. The method of claim 5, wherein forming glass powder comprises adding the Co2O3 to a parent glass which comprises 65 wt % of PhO, 10 wt % of B2O3, 20 wt % of SiO2 and Al2O3 and 5 wt % of RO, wherein the RO is one of BaO, SrO, La2O, Bi2O3, MgO or ZnO.

7. The method of claim 5, wherein forming glass powder comprises adding the Co2O3 to a parent glass which comprises 41.9 wt %  ̃52.0 wt % of P2O5, 3.3 wt %  ̃22.0 wt % of B2O3 and 36.1 wt %  ̃44.7 wt % of ZnO.

8. The method of claim 5, wherein forming glass powder comprises adding the Co2O3 to a parent glass which comprises 34 wt % of ZnO, 29 wt % of B2O3 and 37 wt % of RO, wherein the RO is one of BaO, SrO, La2O, Bi2O3, MgO or ZnO.