Electric lamp and discharge devices – With gas or vapor – Three or more electrode discharge device
Reexamination Certificate
2001-01-11
2004-03-30
Beatty, Robert (Department: 2852)
Electric lamp and discharge devices
With gas or vapor
Three or more electrode discharge device
C313S576000, C313S643000
Reexamination Certificate
active
06713958
ABSTRACT:
BACKGROUND OF THE INVENTION AND RELATED ART STATEMENT
The present invention relates to an alternating current driven type plasma display device having a characteristic feature in a discharge gas sealed in a discharge space where discharge takes place.
As an image display device that can be substituted for a currently mainstream cathode ray tube (CRT), flat-screen (flat-panel) display devices are studied in various ways. Such fat-panel display devices include a liquid crystal display (LCD), an electroluminescence display (ELD) and a plasma display device (PDP). Of these, the plasma display device has advantages that it is relatively easy to produce a larger screen and attain a wider viewing angle, that it has excellent durability against environmental factors such as temperatures, magnetism, vibrations, etc., and that it has a long lifetime. The plasma display device is therefore expected to be applicable not only to a home-use wall-hung television set but also to a large-sized public information terminal.
In the plasma display device, a voltage is applied to discharge cells formed by charging discharge spaces with a discharge gas composed of a rare gas, and a fluorescence layer in each discharge cell is excited with ultraviolet ray generated by glow discharge in the discharge gas, to give light emission. That is, each discharge cell is driven according to a principle similar to that of a fluorescent lamp, and generally, the discharge cells are put together on the order of hundreds of thousands to constitute a display screen. The plasma display device is largely classified into a direct current driven type (DC type) and an alternating current driven type (AC type) according to methods of applying a voltage to the discharge cells, and each type has advantages and disadvantages. The AC type plasma display device is suitable for attaining a higher fineness, since separation walls which work to separate the discharge cells within a display screen can be formed, for example, in the form of stripes. Further, it has an advantage that electrode is less worn out and has a long lifetime, since the surface of the electrode for discharge is covered with a dielectric material.
FIG. 1
shows a schematic exploded perspective view of typical constitution of the AC type plasma display device. This AC type plasma display device comes under a so-called tri-electrode type, and discharging takes place mainly between a pair of sustain electrodes
12
. In the AC type plasma display device shown in
FIG. 1
, a first panel
10
corresponding to a front panel and a second panel
20
corresponding to a rear panel are bonded to each other in their circumferential portions. Light emission from fluorescence layers
25
on the second panel
20
is viewed, for example, through the first panel
10
.
The first panel
10
comprises a transparent first substrate
11
; pairs of sustain electrodes
12
composed of a transparent electrically conductive material and formed on the first substrate
11
in the form of stripes; bus electrodes
13
composed of a material having a lower electric resistivity than the sustain electrode
12
and formed on the sustain electrodes
12
for decreasing the impedance of the sustain electrode
12
; a dielectric material layer
14
composed of a dielectric material and formed on the sustain electrodes
12
, the bus electrodes
13
and the first substrate
11
; and a protective layer
15
composed of MgO and formed on the dielectric material layer
14
.
The second panel
20
comprises a second substrate
21
; address electrodes (also called data electrodes)
22
formed on the second substrate
21
in the form of stripes; a dielectric film
23
formed on the second substrate
21
and on the address electrodes
22
; insulating separation walls
24
which are formed in regions on the dielectric film
23
and between neighboring address electrodes
22
and which extend in parallel with the address electrodes
22
; and fluorescence layers
25
which are formed on, and extend from, upper surfaces of the dielectric film
23
and which are also formed on side walls of the separation walls
24
. When the AC type plasma display device is used for display in colors, each fluorescence layer
25
is constituted of a red fluorescence layer
25
R, a green fluorescence layer
25
G and a blue fluorescence layer
25
B, and the fluorescence layers
25
R,
25
G and
25
B of these colors are formed in a predetermined order.
FIG. 1
is an exploded perspective view, and in an actual embodiment, top portions of the separation walls
24
on the second panel side are in contact with the protective layer
15
on the first panel side. A region where a pair of the sustain electrodes
12
and the address electrode
22
positioned between two of the separation walls
25
overlap corresponds to a discharge cell. A discharge gas is sealed in each discharge space surrounded by neighboring two separation walls
24
, the fluorescence layer
25
and the protective layer
15
. The first panel
10
and the second panel
20
are bonded to each other with a frit glass in their circumferential portions.
The extending direction of a projection image of the sustain electrode
12
and the extending direction of a projection image of the address electrode
22
cross each other at right angles, and a region where a pair of the sustain electrodes
12
and one combination of the fluorescence layers
25
R,
25
G and
25
B for emitting light in three primary colors overlap corresponds to one pixel. Since glow discharge is caused between a pair of the sustain electrodes
12
, the AC type plasma display device of the above type is called “surface discharge type”. For example, a pulse voltage lower than the discharge initiating voltage of the discharge cell is applied to the address electrode
22
immediately before the application of a voltage between the pair of the sustain electrodes
12
. As a result, a wall charge is accumulated in the discharge cell (selection of a discharge cell for display), and the apparent discharge initiating voltage decreases. Then, the discharge initiated between the pair of the sustain electrodes
12
can be sustained at a voltage lower than the discharge initiating voltage. In the discharge cell, the fluorescence layer excited by irradiation with vacuum ultraviolet ray generated by glow discharge in the discharge gas emits light in a color characteristic of a fluorescence material. Vacuum ultraviolet ray having a wavelength according to a kind of the charged discharge gas is generated.
Generally, the discharge gas charged in the discharge space is composed of a mixture prepared by mixing approximately 4% by volume of a xenon gas with an inert gas such as neon (Ne) gas, helium (He) gas or argon (Ar) gas. The distance between a pair of the sustain electrodes
12
is approximately 100 &mgr;m, specifically 70 &mgr;m to 120 &mgr;m.
Currently commercialized AC type plasma display devices have a problem that the brightness thereof is low. For example, a 42-inch AC type plasma display device has a brightness of approximately 500 cd/m
2
at the highest. For practically commercializing an AC type plasma display device, further, it is required, for example, to attach a sheet or a film as a shield against electromagnetic waves or external light to the outer surface of the first panel
10
, and the AC type plasma display device comes to be dark on an actual screen.
When the discharge gas charged in the discharge space is pressure-increased for increasing the brightness, there is caused a problem that the discharge voltage increases, that the discharge comes to be unstable, or that the discharge is non-uniform. When the discharge gas charged in the discharge space is pressure-increased, the discharge gas exerts a force on the first panel
10
and the second panel
20
to separate them from each other. As a result, the reliability of the bonding of the first panel
10
and the second panel
20
with the frit glass may decrease. Further, when the discharge gas is expanded due to a temperature added to the AC type plasma
Beatty Robert
Kananen Ronald P.
Rader & Fishman & Grauer, PLLC
Sony Corporation
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