Electric lamp and discharge devices – With gas or vapor – Three or more electrode discharge device
Reexamination Certificate
1999-12-17
2002-11-19
Patel, Ashok (Department: 2879)
Electric lamp and discharge devices
With gas or vapor
Three or more electrode discharge device
C313S587000
Reexamination Certificate
active
06483238
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to plasma display panels (PDPs). More particularly, the invention relates to PDPs having at least one constituent layer whose structure is porous.
BACKGROUND OF THE INVENTION
Plasma display panels are flat display screens in which the displayed image consists of a set of luminous discharge points. The luminous discharges are produced in a gas contained between two insulating plates. Each discharge point is generated by a discharge cell defined by a point of intersection in arrays of electrodes carried by at least one of the plates.
Thus, a PDP comprises a two-dimensional matrix of cells, which is organized in rows and columns copied from the geometry of the electrode arrays. Relief elements, called barriers, may be placed so as to separate the cell rows or the cell columns. In some panels, the barriers may also separate both the cell rows and the cell columns, thus forming a grid pattern of the latter.
The barriers have several functions. By partitioning the space of each cell, at least in the direction of the rows or the columns, the barriers prevent a discharge in one cell causing undesirable discharges in adjacent cells by an ionization effect. They thus prevent crosstalk phenomena.
Moreover, the barriers constitute optical screens between the adjacent cells, making it possible for the radiation emitted by each cell to be well confined in the space. This function is particularly important in colour PDPs in which the adjacent cells constitute respective elementary dots of different colours, for example in order to form triads. In this case, the barriers ensure good colour saturation.
Finally, the barriers often serve as a spacer between the two plates of the panel. What is exploited in this case is the fact that the barriers can have a height which corresponds to the required separation between the two plates and that they are uniformly distributed over the useful area outside the discharge points. In this case, the plate not provided with barriers rests on the tops of the barriers that are present on the other plate. There are also panels in which barriers are present on each of the plates, the plates being joined together with the barriers top against top.
FIGS. 1 and 2
illustrate an AC colour plasma display panel having a so-called coplanar structure, according to a known architecture.
The PDP comprises a first glass plate
2
and a second glass plate
4
a few millimetres in thickness, these being placed face to face with a separation of the order of 100 microns between the internal faces when they are joined together (FIG.
2
).
The first plate
2
has, on its internal face, an array of parallel electrodes grouped in closely spaced pairs of electrodes Y
1a
-Y
1b
, Y
2a
-Y
2b
, . . . , Y
5a
-Y
5b
, etc. Each pair of electrodes constitutes a display row of the panel. The electrodes are embedded in a thick layer of dielectric material
6
, for example glass, which cover the entire useful area of the plate
2
. This layer
6
is itself covered with a thin layer
8
(less than 1 micron in thickness) of another dielectric material, in this case magnesium oxide (MgO), the surface of which is exposed to the discharge gas.
In the example, the internal surface of the first plate
2
may, for example, be provided with a contrast-improving matrix
10
. The said matrix consists of a mosaic of elementary colour filters surrounded by generally black rings.
The second plate
4
has, on its internal face, an array of uniformly spaced parallel electrodes X
1
, X
2
, . . . , X
6
, etc., perpendicular to the row electrodes Y
1a
-Y
1b
, Y
2a
-Y
2b
, . . . , Y
5a
-Y
5b
, etc., which constitutes the address electrodes of the plasma display panel. As in the case of the first plate
2
, these electrodes X
1
, X
2
, . . . , X
6
, etc. are embedded in a thick dielectric layer
12
which is itself covered with a thin layer of magnesium oxide
14
.
A discharge cell of the PDP is thus formed by the intersection of an address electrode X
1
, X
2
, . . . , X
6
, etc. with a pair of electrodes Y
1a
-Y
1b
, Y
2a
-Y
2b
, . . . , Y
5a
-Y
5b
, etc. of a display row.
In operation, an AC voltage, called a sustain voltage, is applied between the electrodes forming the pair of electrodes of each display row. The discharges are produced on the surface between these electrodes according to a voltage signal applied to the address electrode, using well-known multiplexing techniques.
It is especially possible to modify the luminous discharge state of each cell using row-by-row scanning in order to produce a display in video mode.
Straight barriers
16
are placed on the thin layer
14
of the second plate
4
at each place between adjacent address electrodes X
1
, X
2
, . . . , X
6
, etc. and parallel with the latter. The barriers
16
have walls perpendicular to the surface of the plate
4
and a flat top serving as a bearing surface for the internal face of the first plate
2
. In some constructions, the barriers may be of trapezoidal cross section so as to improve the luminous intensity. They thus partition the discharge cells in the direction perpendicular to the address electrodes X
1
, X
2
, . . . , X
5
, etc. and serve at the same time as a carrier structure for the spacing of the two plates
2
,
4
.
Typically, the barriers
16
have a height of the order of 100 microns and a pitch of 220 microns for a 50 micron width.
Phosphors
18
R,
18
G,
18
B are placed in stripes on the exposed surface of the second plate
4
. A phosphor stripe covers one surface portion of the thin magnesium oxide layer
14
bordered between two adjacent barriers
16
. It also covers the perpendicular walls of the two barriers
16
which are turned towards this surface portion. Each phosphor stripe
18
R,
18
G,
18
B has its own elementary emission colour among red, green and blue in response to a luminous discharge (generally in the ultraviolet) received from a cell. Together, the phosphors constitute a repeat pattern of three successive stripes each having a different emission colour so that a succession of elementary colour triads are created in the direction of the address electrodes, X
1
, X
2
, . . . , X
5
, etc.
The two plates
2
and
4
are sealed together and the space that they contain is filled with the discharge gas at a low pressure, after vacuum pumping through a stem.
It should be noted that the presence of the layers of dielectric material
6
,
8
and
12
,
14
on top of the electrodes Y
1a
-Y
1b
, Y
2a
-Y
2b
, . . . , Y
5a
-Y
5b
and X
1
, X
2
, . . . , X
5
, etc. is characteristic of AC PDPs. The dielectric material forms with the electrodes a capacitor across which is applied, in the gas, the voltages necessary to generate and sustain the luminous discharges.
An advantageous feature of AC PDPs is that the AC sustain voltage automatically fixes the state of a luminous discharge point from the last command received, namely either the luminous discharge is maintained or it remains absent, depending on the command previously transmitted. This thus results in an inherent image memory effect, hence the possibility of addressing the points only when their luminous state has to change.
FIG. 3
shows another example of an AC PDP, this time with a matrix structure. This type of PDP differs from coplanar panels essentially by the fact that the discharges are produced between the respective surfaces of the two facing plates
2
and
4
.
The components that are analogous between this panel and the one described previously bear the same references.
As in the previous case, the PDP comprises a first plate
2
and a second plate
4
, each provided with an array of mutually parallel electrodes Y
1
, Y
2
, Y
3
, . . . , Y
7
, etc. and X
1
, X
2
, X
3
, . . . , X
7
, etc. which are embedded in a thick layer of dielectric
6
and
12
, this layer itself being covered with a thin layer of magnesium oxide
8
and
14
. For both plates, the pitch between the electrodes is in the order of 0.5 mm.
The array carried by the first plate
2
constitutes the row of electrodes Y
1
, Y
2
Baret Guy
Brun Jean-Yves
Jobert Pierre Paul
Moi Agide
Raverdy Yvan
Herrera Carlos M.
Irlbeck Dennis H.
Patel Ashok
Thomson Plasma
Tripoli Joseph S.
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