Compositions: ceramic – Ceramic compositions – Glass compositions – compositions containing glass other than...
Reexamination Certificate
1999-08-30
2001-08-07
Sample, David R. (Department: 1755)
Compositions: ceramic
Ceramic compositions
Glass compositions, compositions containing glass other than...
C501S079000
Reexamination Certificate
active
06271161
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates, in general, to plasma display panels and, more particularly, to a composition for barrier ribs of such plasma display panels and to a method of fabricating such barrier ribs using the composition.
2. Description of the Prior Art
Flat display devices, such as a liquid crystal display (LCD), a field emission display (FED) and a plasma display panel (PDP), have been actively studied in recent, and the technique relative to such display devices has been somewhat actively developed.
FIG. 1
is a sectional view, showing the cell structure of a conventional AC-PDP of the surface discharge type, or the most widely used PDP in recent days. As shown in the drawing, each cell of the conventional AC-PDP comprises upper and lower parallel substrates
1
and
15
. The upper substrate
1
is preferably made of a transparent material, such as glass, thus effectively transmitting visible light, while the lower substrate
15
is preferably made of glass or metal. Two sustain electrodes
5
, individually consisting of a transparent electrode
3
and a bus electrode
7
, are arranged on the lower surface of the upper substrate
1
. Such a transparent electrode
3
is preferably made of indium tin oxide (ITO), while such a bus electrode
7
is preferably made of aluminum (Al) or chrome/copper/chrome (Cr/Cu/Cr). A first dielectric film
10
, made of PbO, is formed on the lower surface of the upper substrate
1
while covering the sustain electrodes
5
. A protection film
12
, made of MgO, is formed on the first dielectric film
10
through a vapor deposition process. The objective of the above protection film
12
is to protect the dielectric film
10
from an ion sputtering effect. The above protection film
12
has a high secondary electron generation coefficient when a low ion energy is applied to the surface of the film
12
during a PDP plasma discharging process. The protection film
12
thus effectively reduces the voltage for driving and sustaining the plasma.
An address electrode
17
is positioned on the upper surface of the lower substrate
15
, while a second dielectric film
19
is formed on the upper surface of the lower substrate
15
while covering the address electrode
17
. Two barrier ribs
21
, having a stripe shape, are parallely formed on the upper surface of the second dielectric film
19
, with the address electrode
17
being positioned on the lower substrate
15
at a middle position between the two barrier ribs
21
. A black matrix
23
is formed on the top end of each of the barrier ribs
21
, thus improving the contrast of the PDP. A plurality of phosphor layers
25
are formed on the upper surface of the second dielectric film
19
and are formed on the sidewalls of both the barrier ribs
21
and the black matrixes
23
. The above phosphor layers
25
emit R, G and B visible light corresponding to red, green and blue. The phosphor layers
25
are isolated from each other by both the barrier ribs
21
and the black matrixes
23
. In the above cell of the PDP, the R, G and B phosphor layers
25
form one pixel. The upper and lower substrates
1
and
15
are, thereafter, integrated into a single structure, thus forming a desired cell of the PDP with discharge spaces being defined by the barrier ribs
21
and being filled with mixed gas, such as Ne+Xe gas.
The above AC-PDP is operated as follows. That is, a constant voltage is applied to the gap between the address electrode and one of the two sustain electrodes, and so the address electrode discharges to select desired display cells. In the case of such an addressing discharge, a wall voltage is generated in each of the selected cells. After the addressing discharge, an AC voltage is applied to the two sustain electrodes at the same time, and so the selected cells perform a sustain discharge to emit visible light. Such a sustain discharge is controlled to change the brightness level in accordance with discharge time.
In the above PDP cell structure, the objective of the barrier ribs
21
is to secure a space for gas discharge between the upper substrate
1
and the lower substrate
15
. The formation of the above ribs
21
is also to isolate the phosphor layers
25
from each other, thus partitioning the discharge cells, and to determine the distance between the electrodes for performing discharge, and to prevent crosstalk due to discharge from neighboring cells, and to reflect light from the phosphor layers
25
to the upper substrate
1
. In order to accomplish the above-mentioned objective of the barrier ribs
21
, the ribs
21
necessarily have a low thermal expansion coefficient, a high thermal stability, a low baking temperature, a dense structure and a low dielectric constant.
In the prior art, such barrier ribs are typically made of PbO—B
2
O
3
—SiO
2
based glass or PbO—B
2
O
3
—SiO
2
based glass, including a large amount of 60~80 wt % of PbO. The composition of the above PbO—B
2
O
3
—SiO
2
based glass is given in Table 1.
TABLE 1
Components(wt %)
PbO
B
2
O
3
SiO
2
Contents(wt %)
60 ~ 80 wt %
5 ~ 15 wt %
15 ~ 20 wt %
Such a conventional barrier rib for PDPs is fabricated as follows. As shown in the processing diagram of
FIG. 2
, a glass-ceramic material, prepared by mixing an oxide filler with PbO—B
2
O
3
—SiO
2
based glass or PbO—B
2
O
3
—SiO
2
based glass at a predetermined ratio, for example, 4:6~7:3, for a predetermined time, is ground at step
31
, thus forming a fine mixture powder having a size not larger than 10 &mgr;m. In the above step, an Al
2
O
3
and TiO
3
mixture is used as the oxide filler and the composition of Al
2
O
3
and TiO
3
mixture is given in Table 2.
TABLE 2
Components (wt %)
Al
2
O
3
TiO
3
Contents(wt %)
95 ~ 100 wt %
0 ~ 5 wt %
Thereafter, the mixture powder from the step
31
is mixed with an organic vehicle, thus forming a paste or a slurry at step
32
. In such a case, the organic vehicle is formed by mixing BCA (butyl-carbitol-acetate), BC (butyl-carbitol) and EC (ethyl-cellulose) together at a predetermined mixing ratio. After the step
32
, the paste or the slurry is applied to the top surface of the second dielectric film
19
of the lower substrate
15
, thus forming a paste or slurry film having a thickness prior to forming the barrier ribs
21
at step
33
. In such a case, the formation of the barrier ribs
21
is performed through a screen print process, a sand blast process, an etching process, an additive process or a stamping process. The above processes for the formation of the barrier ribs
21
will be described later herein in more detail. Thereafter, the lower substrate
15
, having the barrier ribs
21
, is primarily baked at a temperature of 300~350° C. for a predetermined time, for example, 15~23 minutes, thus removing the organic vehicle from the paste or slurry. The lower substrate
15
is, thereafter, secondarily baked at a temperature of 600~650° C., thereby finally forming the barrier ribs
21
.
The processes of the formation of such barrier ribs
21
will be described in detail hereinbelow with reference to
FIGS. 3
a
to
3
d.
FIG. 3
a
shows a screen printing process of the formation of such barrier ribs
21
. As shown in the drawing, a screen (not shown) is primarily and precisely positioned on a lower substrate
40
coated with a thick dielectric film
41
on its top surface. A paste or slurry is applied on the top surface of the dielectric film
41
through the screen prior to being dried, thus forming a plurality of primary barrier rib layers
43
on the film
41
at step “a”. The above-mentioned process is repeated several times, thus forming a plurality of secondary, third and more barrier rib layers on the previously formed layers at steps “b” and “c”. A plurality of desired barrier ribs are thus formed on the lower substrate
40
.
FIG. 3
b
shows a sand blast process of the formation of such barrier ribs
21
. As shown in the drawing, a paste or slurry is applied on the top surface of a thick dielectric film
41
, formed on the top surface of a lower
Chang Myeong-Soo
Ryu Byung-Gil
Fleshner & Kim LLP
LG Electronics Inc.
Sample David R.
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