Electric lamp and discharge devices – With gas or vapor – Three or more electrode discharge device
Reexamination Certificate
1998-11-17
2001-05-15
Patel, Ashok (Department: 2879)
Electric lamp and discharge devices
With gas or vapor
Three or more electrode discharge device
C313S584000, C313S587000, C313S112000
Reexamination Certificate
active
06232717
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a color plasma display panel for use in an information display terminal or a flat panel television and, in particular, to a color plasma display panel which is high in contrast and excellent in color fidelity or color reproducibility.
A color plasma display panel (hereinafter abbreviated to a color PDP) is a display in which ultraviolet rays are produced by gas discharge to excite phosphors so that visible lights are emitted therefrom to perform a display operation. Depending upon a discharge mode, the color PDP is classified into an AC (alternating current) or a DC (direct current) type. The AC type is superior to the DC type in luminance, luminous efficiency, and lifetime.
Referring to
FIGS. 1 through 3
, a conventional reflection AC type surface discharge color PDP will be described.
As illustrated in the figures, the conventional color PDP comprises a transparent glass plate as a front substrate
1
. The front substrate
1
is provided with a plurality of transparent electrodes
2
arranged in stripes. In
FIG. 2
, the transparent electrodes
2
extend in a direction perpendicular to the drawing sheet. Between adjacent ones of the transparent electrodes
2
, an AC pulse voltage of several tens to several hundreds kilohertz (kHz) is applied to cause discharge which triggers a display operation.
In the reflection AC type surface discharge color PDP, it is required to avoid interception of the visible lights emitted from phosphor layers
9
R,
9
G, and
9
B which will later be described. To this end, the transparent electrodes
2
typically comprise a transparent conductive film of tin oxide (SnO2) or indium tin oxide (ITO) deposited by a thin film technique such as sputtering.
However, the transparent conductive film mentioned above is high in sheet resistance. In case of a large panel or a high-definition panel, an electrode resistance will become as high as several tens kiloohms (k&OHgr;) or more. This may result in insufficient pulse rise or voltage drop of the pulse voltage applied to the transparent electrodes
2
. In this event, it is difficult to drive the color PDP. Taking the above into account, it is proposed to provide each of the transparent electrodes
2
with a bus electrode
3
comprising a multilayer thin film of chromium/copper/chromium, a metal thin film such as an aluminum thin film, or a metal thick film using a silver paste. A combination of each transparent electrode
2
and each bus electrode
3
forms a surface discharge electrode set
2
H reduced in resistance by presence of the bus electrode
3
.
On the surface discharge electrode sets
2
H, color filter layers
4
R,
4
G, and
4
B comprising fine powder pigments are formed in stripes to perpendicularly intersect with the surface discharge electrode sets
2
H. Generally, the color filter layers
4
R,
4
G, and
4
B are formed from selected materials having optical characteristics such that luminescent colors of the phosphor layers
9
R,
9
G, and
9
B faced to the color filter layers
4
R,
4
G, and
4
B are exclusively allowed to pass through the color filter layers
4
R,
4
G, and
4
B, respectively. Furthermore, the color filter layers
4
R,
4
G, and
4
B are coated with a transparent dielectric layer
5
. The transparent dielectric layer
5
has a current limiting function specific to the AC type PDP. The current limiting function will hereinafter be explained. When two adjacent ones of the surface discharge electrode sets
2
H are applied with the voltage, surface discharge is caused therebetween. As a result of the discharge, electric charges are stored in the transparent dielectric layer
5
. When the sum of the voltage between the surface discharge electrode sets
2
H and the voltage owing to the electric charges stored in the transparent dielectric layer
5
becomes smaller than a discharge maintaining voltage, the discharge is stopped.
In order to assure the dielectric strength and to facilitate the production, the transparent dielectric layer
5
is typically formed by preparing a paste mainly containing a low-melting-point glass, applying the paste by thick-film printing, and baking the paste at a high temperature not lower than a softening point of the glass so that the glass is subjected to reflowing. The transparent dielectric layer
5
thus obtained is flat and does not contain air bubbles. The transparent dielectric layer
5
has a thickness on the order between 20 and 40 microns.
Next, a protection layer
6
is formed to cover an entire surface of the transparent dielectric layer
5
. The protection layer
6
comprises a MgO thin film formed by vapor deposition or sputtering or a Mgo film formed by printing or spraying. The protection layer
6
has a thickness on the order between 0.5 and 1 micron. The protection layer
6
serves to lower the discharge voltage and to prevent surface sputtering.
On the other hand, a rear substrate
10
is provided with a plurality of data electrodes
8
arranged in stripes to write display data. in
FIG. 2
, the data electrodes
8
extend in a direction parallel to the drawing sheet. The data electrodes
8
intersect with the surface discharge electrode sets
2
H formed on the front substrate
1
. As illustrated in
FIG. 1
, a plurality of barrier ribs
7
are formed typically by thick-film printing so as not to overlap the data electrodes
8
and to extend in parallel to the data electrodes
8
. The barrier ribs
7
serve to avoid discharge error and optical crosstalk between neighboring discharge cells
11
. The barrier ribs
7
are not illustrated in
FIG. 2
,
Furthermore, the phosphor layers
9
R,
9
G, and
9
B corresponding to the luminescent colors of red, green, and blue, respectively, are formed by applying three kinds of phosphors in three successive steps, one step for one color, to cover side walls of the barrier ribs
7
and the data electrodes
8
. Since the phosphor layers
9
R,
9
G, and
9
B are also formed on the side walls of the barrier ribs
7
, phosphor coated areas are increased to achieve high luminance. The formation of the phosphor layers
9
R,
9
G, and
9
B is typically carried out by screen printing.
Thereafter, the front substrate
1
and the rear substrate
10
are coupled face to face to each other with the barrier ribs
7
interposed therebetween in the manner such that the surface discharge electrode sets
2
H and the data electrodes
8
perpendicularly intersect with each other. Then, an assembly of the front and the rear substrates
1
and
10
is sealed airtight. A dischargeable gas, such as a mixed gas of He, Ne, and Xe, is confined within the discharge cells
11
at a pressure on the order of 500 Torr.
In each discharge cell
11
, a pair of the surface discharge electrode sets
2
H are arranged each of which comprises one transparent electrode
2
and one bus electrode
3
. In a gap between the surface discharge electrode sets
2
H in each pair, the surface discharge occurs to produce plasma in each discharge cell
11
. At this time, ultraviolet ray is produced to excite the phosphor layers
9
R,
9
G, and
9
B so that the visible lights of red, green, and blue are produced therefrom Through the color filter layers
4
R,
4
G, and
4
B formed on the front substrate
1
, the visible lights are observed as display lights.
As described above, the surface discharge occurs between each pair of the surface discharge electrode sets
2
H adjacent to each other. Herein, one and the other of the electrode sets
2
H in each pair serve as a scanning electrode and a maintaining electrode, respectively. While the color PDP is actually driven, maintaining pulses are applied between the scanning electrode and the maintaining electrode. In order to cause writing discharge, an electric voltage is applied between the scanning electrode and the data electrode
8
to trigger opposed discharge. By the maintaining pulses subsequently applied, maintaining discharge is generated between the surface discharge electrode sets
2
H.
Referring to
FIGS. 4 and 5
, a reflection AC type
Oida Osamu
Shinohara Takuo
McGinn & Gibb PLLC
NEC Corporation
Patel Ashok
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