Electric lamp and discharge devices – With gas or vapor – Three or more electrode discharge device
Reexamination Certificate
2002-11-12
2004-04-27
Patel, Vip (Department: 2879)
Electric lamp and discharge devices
With gas or vapor
Three or more electrode discharge device
C313S466000, C313S473000
Reexamination Certificate
active
06727648
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a plasma display panel, and more particularly to a plasma display panel that is capable of preventing discoloration of a substrate caused by migration of a metal bus electrode or metal paste's running down.
2. Description of the Related Art
Generally, a plasma display panel (PDP) radiates a fluorescent body by an ultraviolet with a wavelength of 147 nm generated during a discharge of He+Xe or Ne+Xe gas to thereby display a picture including characters and graphics. Such a PDP is easy to be made into a thin-film and large-dimension type. Moreover, the PDP provides a very much improved picture quality owing to a recent technical development. Particularly, a three-electrode, alternating current (AC) surface-discharge type PDP has advantages of a low-voltage driving and a long life in that it can lower a voltage required for a discharge using wall charges accumulated on the surface thereof during the discharge and protect the electrodes from a sputtering caused by the discharge. Further, the PDP has advantages that its fabricating process is simple, it is easier to be made into a large screen and its response speed is fast because it does not have to form an active switching device every cell in the same way as a liquid crystal display panel LCD.
Referring to
FIG. 1
, a discharge cell of the three-electrode, AC surface-discharge PDP includes a scanning electrode
30
Y and a sustaining electrode
30
Z formed on an upper substrate
10
, and an address electrode
20
X formed on a lower substrate
18
.
The scanning electrode
30
Y and the sustaining electrode
30
Z include a transparent electrode
12
Y or
12
Z, and a metal bus electrode
13
Y or
13
Z having a smaller line width than the transparent electrode
12
Y or
12
Z and provided at one edge of the transparent electrode, respectively. The transparent electrodes
12
Y and
12
Z are formed from indium-tin-oxide ITO on the upper substrate
10
. The metal bus electrodes
13
Y and
13
Z are formed by going through an etching process after depositing chrome Cr/copper Cu/chrome Cr by a deposition method, or by going through a patterning and firing process after printing photosensitive silver Ag paste. On the upper substrate
10
provided with the scanning electrode
30
Y and the sustaining electrode
30
Z, an upper dielectric layer
14
and a protective film
16
are disposed. Wall charges generated upon plasma discharge are accumulated in the upper dielectric layer
14
. The protective film
16
protects the upper dielectric layer
14
from a sputtering generated during the plasma discharge and improves the emission efficiency of secondary electrons. This protective film
16
is usually made from magnesium oxide MgO. The address electrode
20
X is formed in a direction crossing the scanning electrode
30
Y and the sustaining electrode
30
Z. A lower dielectric layer
22
and barrier ribs
24
are formed on the lower substrate
18
provided with the address electrode
20
X. A fluorescent material layer
26
is coated on the surfaces of the lower dielectric layer
22
and the barrier ribs
24
. The barrier ribs
24
are formed in parallel to the address electrode
20
X to divide the discharge cell physically and prevent an ultraviolet ray and a visible light generated by the discharge from being leaked into the adjacent discharge cells. The fluorescent material layer
26
is excited and radiated by an ultraviolet ray generated upon plasma discharge to produce a red, green or blue color visible light ray. An inactive mixture gas, such as He+Xe or Ne+Xe, for a gas discharge is injected into a discharge space defined between the upper/lower substrate
10
and
18
and the barrier ribs
24
.
Such a three-electrode AC surface-discharge PDP drives one frame, which is divided into various sub-fields having a different emission frequency, so as to realize gray levels of a picture. Each sub-field is again divided into a reset interval for uniformly causing a discharge, an address interval for selecting the discharge cell and a sustaining interval for realizing the gray levels depending on the discharge frequency. When it is intended to display a picture of 256 gray levels, a frame interval equal to {fraction (1/60)} second (i.e. 16.67 msec) in each discharge cell is divided into 8 sub-fields SF
1
to SF
8
as shown in FIG.
2
. Each of the 8 sub-fields SF
1
to SF
8
is divided into a reset interval, an address interval and a sustaining interval. The reset interval and the address interval of each sub-field are equal every sub-field, whereas the sustaining interval and the discharge frequency are increased at a ratio of 2
n
(wherein n=0, 1, 2, 3, 4, 5, 6 and 7) at each sub-field. Since the sustaining interval becomes different at each sub-field as mentioned above, the gray levels of a picture can be realized.
By the way, the conventional PDP has a problem of discoloration of the substrate
10
caused by migration of the metal bus electrodes
13
and
13
Z or the fact that silver Ag paste runs down the substrate
10
in case that the silver Ag paste is printed to form the metal bus electrodes
13
Y and
13
Z. The migration means that cation of silver Ag+ is eluted from an anode and moves to a cathode under dissolved oxygen in case of there being a voltage difference between two adjacent electrodes, which are the cathode and anode respectively. Sometimes, the cation of silver eluted discolors the surface of the substrate
10
in such migration process. The most significant cause of such substrate discoloration lies in an upper plate structure of the PDP. That will be described in detail in conjunction with
FIG. 2 and 3
.
Referring to
FIG. 2
, metal bus electrodes
13
Y and
13
Z formed in a conventional PDP has their outer edge go in more by a certain length
5
toward the center of a cell than the outer edge of transparent electrodes
12
Y and
12
Z located at the outer area of the cell. And the inner edge of the conventional metal bus electrodes
13
Y and
13
Z goes in more by a certain length t
0
toward the outer of a cell than the inner edge of transparent electrodes
12
Y and
12
Z. There is a black layer
28
with conductivity formed between the metal bus electrodes
13
Y and
13
Z and the transparent electrodes
12
Y and
12
Z. The black layer
28
is formed by oxidizing metal or printing and patterning paste where metal powder and black pigment are mixed together. The black layer
28
act to prevent a contrast deterioration of a display screen caused by external light being reflected from the metal bus electrode
13
Y and
13
Z by absorbing the external light.
According to a structure of the metal bus electrodes
13
Y and
13
Z as in
FIG. 2
, the silver Ag paste is likely to run down to the transparent electrodes
12
Y and
12
Z or the substrates
10
so as to cause the substrate
10
to be discolored when the silver Ag paste is printed to form the metal bus electrodes
13
Y and
13
Z. This is because the outer edges of the metal bus electrodes
13
Y and
13
Z are close to the transparent electrodes
12
Y and
12
Z or the substrate
10
. Further, anion of the metal bus electrodes
13
Y and
13
Z is likely eluted to discolor the substrate
10
by such a structure.
There is a PDP where an oxidized film is formed on the substrate
10
as in
FIG. 3
as another scheme for reducing the problem of the substrate discoloration.
Referring to
FIG. 3
, another conventional PDP includes an oxidized film
30
formed of silicon oxide SiO between transparent electrodes
12
Y and
12
Z and a substrate
10
. In this PDP too, metal bus electrodes
13
Y and
13
Z has their outer edge go in more by a certain length &dgr; toward the center of a cell than the outer edge of transparent electrodes
12
Y and
12
Z located at the outer area of the cell. And the inner edge of the metal bus electrodes
13
Y and
13
Z goes in more by a certain length to toward the outer of a cell than the inner edge of transparent electrodes
12
Y and
12
Z. T
Fleshner & Kim LLP
LG Electronics Inc.
Patel Vip
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