Electric lamp and discharge devices – With gas or vapor – Three or more electrode discharge device
Reexamination Certificate
1999-12-06
2002-09-10
Patel, Vip (Department: 2879)
Electric lamp and discharge devices
With gas or vapor
Three or more electrode discharge device
C313S461000, C313S584000, C313S631000
Reexamination Certificate
active
06448711
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to image display screens of the << flat screen >> type. It relates more particularly to means used to facilitate and simplify operations for the positioning of the constituent elements of these screens.
BACKGROUND OF THE INVENTION
There are different types of image display screens that come under the category of flat screens, for example plasma panels, liquid crystal displays, screens whose cells use a “point effect” phenomenon to produce an electron beam each or again light-emitting diode screens.
These different flat screens have the common feature of having a matrix structure: to each elementary dot of the displayed image there corresponds a cell (or even several cells in the case of color images) and each cell is defined substantially at the intersection of two or more arrays of electrodes. Consequently, the manufacture of these different types of flat screens entails the same difficult problem for each of them, a problem that lies in the difficulty of registering the different elements used to form a cell, namely the difficulty of positioning all these elements with respect to one another and in the same way for all the cells of the screen.
The following explanations, given with the example of plasma panels (abbreviated as PP hereinafter in the description), will provide for a clearer understanding of the importance of the above-mentioned problem of registration.
PPs work on the principle of an electrical discharge in gases. They generally comprise two insulating plates each bearing one or more arrays of electrodes and mutually demarcating a gas-filled space. The plates are assembled with respect to one another so that the arrays of electrodes are orthogonal. Each intersection of electrodes defines a cell to which there corresponds a gas space.
FIG. 1
shows the structure of an alternating color PP of the type using only two intersecting electrodes to define and control a cell as described especially in the French patent application published under No. 2 417 848.
The PP has two substrates or plates
2
,
3
. One of them is a front plate
2
, namely the one that is on an observer's side (not shown). It has a first array of electrodes called “row electrodes” of which only three electrodes Y
1
, Y
2
, Y
3
are shown. The second plate
3
forms the rear plate. It is opposite the observer and therefore it is this plate that, preferably, is provided with elements that can prevent the transmission of light to the observer. It has a second array of electrodes called “column electrodes”, of which only five electrodes X
1
to X
5
are shown. The two plates
2
,
3
are made of the same material, generally glass. These two plates
2
,
3
are designed to be joined to each other so that the arrays of row and column electrodes are orthogonal with respect to each other.
It is common practice that, in the front plate
2
, as in the example shown, the row electrodes Y
1
to Y
3
should be separated from one another by black strips
4
(forming what is called a “black array”) designed to improve the contrast between cells of different rows. The row electrodes Y
1
to Y
3
are covered with a layer
5
of dielectric material by which they are insulated from the gas.
On the rear plate
3
, the column electrodes X
1
to X
5
are also covered with a layer
6
of dielectric material. The dielectric layer
6
is itself covered with layers forming strips
7
,
8
,
9
of luminophor materials respectively corresponding in the example to the colors green, red and blue. The luminophor strips
7
,
8
,
9
are positioned in parallel to the column electrodes X
1
to X
5
, above these column electrodes from which they are separated by the dielectric layer
6
. The rear plate
3
furthermore has separation barriers
11
that are parallel to the luminophor strips
7
,
8
,
9
and separate these strips from one another.
The PP is formed by the joining of the front and rear plates
2
,
3
. This joining sets up a matrix of cells. The cells are then defined each at the intersection between a row electrode Y
1
to Y
3
and a column electrode X
1
to X
5
with a pitch P
1
parallel to the row electrodes that is given by the distance between the column electrodes and with a pitch P
2
along the column electrodes that is given by the distance between the row electrodes. Each cell has a discharge zone whose section corresponds substantially to the facing surface of the two crossed electrodes. In each cell, the discharge into the gas generates electrical charges and in the case of a “alternating” PP, these charges collect at the dielectrics
5
,
6
facing the row and column electrodes. In the example shown, this operation is obtained by means of recesses Ep
1
to Epn made in the luminophor strips
7
,
8
,
9
substantially on the useful surfaces of the column electrodes X
1
to X
5
, namely the surfaces of these electrodes that define the section of the discharge zone.
Thus, in the example shown, the intersections made by the first row electrode Y
1
with the column electrodes X
1
to X
5
define a row of cells, each cell being represented by a recess: the first cell C
1
is located at the first recess Ep
1
, the second cell C
2
is located at the second recess Ep
2
and so on and so forth until the fifth recess Ep
5
which represents a fifth cell C
5
. The first, second and third recesses Ep
1
, Ep
2
, Ep
3
are respectively located in a green luminophor strip
7
, a red strip
8
and a blue strip
9
. They thus correspond to monochromatic cells having three different colors which, in a set of three, may constitute a colored cell. Thus, for 1024 colored cells per row for example, the plate
3
must contain 1024 times per line the above-described structure. The column electrodes X
1
to X
5
have a width Lg
1
of about 50 microns and their longitudinal axes are spaced out for example by 250 microns. This gives an idea of the difficulties of manufacture, especially for obtaining an accurate position of the recesses Ep
1
to Epn.
The operating quality of the PP depends on the geometrical and dimensional characteristics of the cells, and hence on the quality of registration which is defined as the precision of the positioning, with respect to one another, of its elements such as the row electrodes and the column electrodes, the barriers
11
and the recesses Ep
1
to Epn for which, in particular, the required precision of registration may be in the range of ±20 ppm (20 parts per million), i.e. for example 10 &mgr;m.
Such precision is very difficult and hence very costly to obtain in the context of industrial-scale manufacture. Indeed, the manufacture on a plate
2
,
3
of the different elements referred to here above makes use in particular of the technique of photographic masks used on photosensitive layers and/or techniques of silk-screen printing. For the rear plate
3
for example, after the array of column electrodes X
1
to X
5
has been formed and then the dielectric layer
6
has been deposited, the lumionophor strips
7
,
8
,
9
are deposited on this dielectric layer
6
. Then, the recesses Ep
1
to Epn are made in the luminophor strips, along with the separation barriers
11
, with all the precision possible. The masks used to define the different patterns such as electrodes, recesses, etc. furthermore comprise, in a standard way, specific alignment or positioning patterns used to align elements to be made with those obtained at a previous level or stage of manufacture. It must be noted that the term “mask” is used to designate both photographic masks and silk screens.
FIGS. 2
a,
2
b
show alignment patterns Ma
1
, Ma
2
of this kind corresponding in the example respectively to a mask
20
for the definition of the recesses Ep
1
to Epn or a mask
21
for the definition of the column electrodes X
1
to X
5
. These alignment patterns consist of registration patterns along the two axes X and Y and conventionally they are located outside a useful surface S
1
, S
2
bearing the drawing (not shown) of the elements to be defined
Deschamps Jacques
Salavin Serge
Herrera Carlos M.
Irlbeck Dennis H.
Patel Vip
Thomson Licensing S.A.
Tripoli Joseph S.
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