Electric lamp or space discharge component or device manufacturi – Process – With assembly or disassembly
Reexamination Certificate
2000-05-18
2003-03-25
Dawson, Robert (Department: 1712)
Electric lamp or space discharge component or device manufacturi
Process
With assembly or disassembly
C445S024000, C315S169400, C427S386000
Reexamination Certificate
active
06537121
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the production of components on glass substrates that have to be sealed, such as flat display screens of the plasma-panel type or field-emission display (also known by the name FED) devices.
BACKGROUND OF THE INVENTION
In such uses, a component is produced by an assembly of two glass substrates which have to be sealed one against the other. The substrates, whose size is at least equal to the working area of the display screen, may amount to more than 100 cm in diagonal. They constitute fundamental elements for the component. Glass is chosen as the substrate material for several reasons.
Firstly, when a substrate forms the visible part of a display screen it is imperative for the latter to have suitable optical and mechanical properties.
Secondly, the various steps which are involved in the manufacture of a component of the aforementioned type expose the substrate to high temperatures, of the order of 600° C. in the case of some of them. It is therefore necessary to ensure that the material of the substrate can, on the one hand, withstand these temperatures and, on the other hand, meet its precise original dimensions after the manufacturing steps.
At the present time, only mineral glass is capable of meeting these prerogatives in an inexpensive manner.
Moreover, the production of the aforementioned components on a glass substrate involves the deposition of successive superposed layers in order to form structural elements or to create laminated layers. It may especially be necessary to superpose two or more layers of different materials. In this case, the various superposed materials often do not have the same thermal expansion coefficients. It follows that superposed layers are subjected to high mechanical stresses when they are exposed to high temperatures. These stresses, which act in shear at the interface between two layers, may generate, in the layers, cracks or microcracks which are liable to reduce the performance or the lifetime of the component.
In order to allow these stresses that a substrate is subjected to during the manufacture of a component to be better understood, we will consider, with reference to
FIGS. 1
to
5
, the example of a colour plasma panel (PP) produced from two glass substrates.
The PP illustrated is of the AC type with a matrix structure. Its operation is thus based on the light discharge between two facing dielectric layers, each covered with a layer of magnesia (magnesium oxide) MgO, the said layers covering an array of electrodes on a respective glass substrate. Such a panel is described in particular in the Applicant's French Application No. 97/07181.
As shown in
FIG. 1
, each of the substrates is in the form of a glass tile
2
,
3
having an area which corresponds to the display aspect ratio of the screen, plus a peripheral portion comprising the connection elements and the means for sealing the substrates (
FIGS. 2
to
5
). These substrates
2
,
3
are placed opposite each other with a small separation between the facing faces (the internal faces) making it possible, when they are joined together, for a discharge gas to be contained.
The first substrate
2
, intended to form the front face of the PP (with respect to the observer), carries a first array of parallel electrodes Y
1
-Y
3
which constitutes the row electrodes. These electrodes are embedded in a thick layer
5
of dielectric material. This layer is itself covered with a thin dielectric layer
51
, for example of magnesia (MgO), which is intended to be exposed to the discharge gas.
The second substrate
3
carries a second array of parallel electrodes X
1
-X
5
, also embedded in a thick layer
6
of dielectric material which is itself covered with a thin dielectric layer
61
intended to be exposed to the discharge gas. These electrodes are placed so as to be perpendicular to the electrodes Y
1
-Y
3
of the first array and constitute the column electrodes.
The second substrate
3
furthermore includes a set of straight barriers
7
on the thin layer, one barrier being placed along each mid-axis between two adjacent column electrodes X
1
-X
5
.
The surface of the second substrate
3
between the barriers
7
is covered with phosphor stripes
8
,
9
,
10
deposited directly on the thin layer. Each phosphor stripe is contained between two adjacent barriers
7
. Together, the stripes form a repetitive pattern of three successive adjacent stripes
8
,
9
,
10
of different emission colours, for example red, green and blue.
The phosphor stripes
8
,
9
,
10
include areas Ep
1
-Ep
n
recessed in the phosphor material, vertically in line with each electrode Y
1
-Y
3
of the first array of electrodes of the opposed substrate
2
. These areas, called “apertures”, thus directly expose the thin dielectric layer to the discharge gas at the points of intersection between the first and second electrode arrays. They make it possible to produce discharge cells that correspond with these points.
Thus, in the example illustrated, the intersections made by the first row electrode Y
1
with the column electrodes X
1
-X
5
define a row of cells, each cell being physically formed by an aperture: the first cell C
1
is located at the first aperture Ep
1
, the second cell C
2
is located at the second aperture Ep
2
and so on, until the fifth aperture Ep
5
illustrated, which physically forms a fifth cell C
5
. The first, second and third apertures Ep
1
, Ep
2
, and Ep
3
are located in a green phosphor stripe
8
, a red phosphor stripe
9
and a blue phosphor stripe
10
respectively. They thus correspond to monochromatic cells of three different colours which, among the three, may form a trichromatic cell.
The barriers
7
have two functions. On the one hand, they serve to confine the light discharges to the cell which generates them, especially by preventing the propagation of the discharges towards the row electrodes Y
1
-Y
3
by ionization effect. They thus prevent the phenomenon of crosstalk between the cells. On the other hand, the barriers
7
constitute screens for the light radiation from one cell with respect to the neighbouring cells towards the row electrodes Y
1
-Y
3
, avoiding a crosstalk effect with is manifested by a lack of colour saturation.
The barriers
7
may also have a function of spacing the substrates
2
,
3
, as in the example illustrated. In this case, the height H
1
of the barriers fixes the separation between the tiles, the tile
2
carrying the row electrodes Y
1
-Y
3
bearing on the top of the barriers.
According to other designs, the space in between the substrates
2
,
3
is fixed not by means of barriers but by spacer elements distributed over the surface of at least one of the substrates. These spacer elements, also known as spacers, make it possible in particular to clear a space above the barriers for better distribution of the ionization around the cells.
The geometry and the sealing of the two substrates will now be described with reference to
FIGS. 2
to
5
.
FIG. 2
is a simplified plan view showing the first substrate
2
superposed on the second substrate
3
when the PP is in the assembly phase.
The column electrodes X
1
, X
2
, X
3
, etc. and the row electrodes Y
1
, Y
2
, Y
3
, etc. of the respective substrates
3
and
2
extend slightly beyond the edges of the latter so as to form connection regions Xa
1
, Xa
2
and Ya
1
, Ya
2
with outputs of an electronic drive circuit (not illustrated). The electronic drive circuit delivers to the electrodes the various voltages (of the order of 100 to 150 volts) necessary for selectively igniting, maintaining or extinguishing a light discharge at the points of intersection between the row and column electrodes.
The first substrate
2
comprises two regions Ya
1
, Ya
2
for connecting the electrodes Y
1
, Y
2
, Y
3
, etc. to opposed respective edges perpendicular to the direction of these electrodes. Each connection region Ya
1
or Ya
2
includes the extensions of one column electrode in two, alternating with those that the other connection regio
Dawson Robert
Feely Michael J
Herrera Carlos M.
Laks Joseph J.
Thomson Licensing S. A.
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