Liquid crystal cells – elements and systems – Nominal manufacturing methods or post manufacturing...
Reexamination Certificate
1999-03-18
2001-02-20
Dudek, James A. (Department: 2871)
Liquid crystal cells, elements and systems
Nominal manufacturing methods or post manufacturing...
C349S158000
Reexamination Certificate
active
06191840
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention concerns a manufacturing method for electro-optical cells, in particular liquid crystal cells, or electrochemical photovoltaic cells, each cell including a transparent front substrate and a back substrate which may or may not be transparent onto which is formed a pattern of conductive elements forming electrodes and conductive paths connecting these electrodes to contact pads, the two substrates being bonded together by a sealing frame defining a sealed volume in which an active medium is confined. The present invention also concerns a cell obtained from this method.
“Electro-optical cell” is used to mean a display cell wherein the electro-optical features of the liquid crystals confined between the two substrates of said cell can be modified by electric control signals applied across the electrodes. Moreover, the electrochemical photovoltaic cells are cells capable of converting visible light into electricity by exploiting the photoelectric effect which appears in a semi-conductor substrate sensitised by a dye.
A batch manufacturing method for liquid crystal display cells of the type described hereinbefore will be examined with reference to
FIGS. 1
to
3
annexed to the present Application,
FIG. 1
being a partial schematic plane view of a batch of liquid crystal display cells during manufacturing, and
FIGS. 2 and 3
being respectively a plane view and a cross-section along the line III—III of
FIG. 2
of an individual display cell.
The above method consists in forming, conventionally by photolithography, on two large front and back substrates respectively
1
and
2
which are made of glass or a synthetic material and at least one of which is transparent, a pattern of conductive elements which are also transparent. These conductive elements form control electrodes
4
and
6
. These electrodes
4
and
6
are situated at the location of pictures to be displayed and conductive paths connect them to contact pads
8
situated at the periphery of each cell
10
. A network of material forming sealing frames
12
is then deposited on one of substrates
1
,
2
, said sealing frames each forming a sealed volume in which the liquid crystal will subsequently be confined. For this purpose, a filling aperture
14
is arranged in sealing frames
12
for each cell
10
, then substrates
1
,
2
are bonded to each other to form an assembly including several rows of open cells
10
. This assembly is then divided into rectilinear strips
16
by glass scribing and breaking techniques, or by sawing along dividing lines
18
which form the longitudinal edges
20
of strips
16
. These dividing lines
18
are rectilinear and parallel and are shown in dot and dash lines in FIG.
1
. As filling apertures
14
are all situated along the same longitudinal edge
20
of strip
16
, it is easy to fill cells
10
then to hermetically seal the filling apertures
14
thereof. Strips
16
are finally divided into individual rectangular cells
10
along straight lines perpendicular to the preceding lines. At this stage, if the contour of cells
10
has to have portions different from the rectangular shape, such portions are shaped by grinding. Any outer layers such as, for example, a polariser film
22
, are applied subsequently, since otherwise there is a risk of the deterioration thereof by the cutting and grinding operations. These manufacturing steps which have to be effected individually on each cell
10
make manufacturing more complex and expensive than if they could be performed on a complete batch of cells
10
.
Further, as shown in
FIGS. 2 and 3
, each cell
10
has a rectilinear edge
24
where back substrate
2
projects with respect to front substrate
1
, in order to allow contact pads
8
to appear and thus to create a connection zone
26
which can be accessed to establish the electric connection between electrodes
4
,
6
of cell
10
and an electric control circuit (not shown) capable of modifying the electro-optical features of the liquid crystal. As is clear from
FIG. 1
, connection zones
26
of cells
10
are all aligned along one of longitudinal edges
20
of strips
16
and are opposite to filling apertures
14
of cells
10
.
Rectilinear edge
24
of cells
10
is conventionally marked by scribing by means of a diamond tool, so that lines of least mechanical resistance
28
, which are rectilinear and parallel to dividing lines
18
, are generated at the surface of front substrate
1
. After cutting out a strip
16
, the glass can be broken manually along line
28
, by slight bending transversely to said line
16
, thus allowing connection pads
8
of cells
10
to appear.
The above glass scribing and breaking operation is relatively simple to implement. Cells
10
thereby obtained have, however, the significant drawback of having only one connection zone
26
, which limits the number of available connection pads
8
, and thus the number of pictures which it is possible to display by means of such a cell
10
. In order to overcome this difficulty, a known solution consists in multiplexing electrodes
4
,
6
of cells
10
, which means that a same electrode can control the display of at least two different pictures. It has however been observed that the nigher the multiplexing rate of electrodes
4
,
6
, the less satisfactory the resulting optical display quality.
There therefore existed a need in the state of the art for display cells having two connection zones
26
instead of a single such zone. One possible solution to this problem would have been to envisage arranged connection zones
26
not opposite filling apertures
14
, i.e. longitudinally to strips
16
, but transversely to said strips
16
. A major prejudice has however always opposed the implementation of this solution.
It is known that glass scribing by means of a diamond tool generates at the surface of the glass a network of superficial mechanical stress which contribute to breakage of the glass at the place where it was scribed. It was nonetheless commonly admitted to date that the glass had to be broken shortly after being scribed. It was thought that if this was not the case, the network of stress generated by scribing the glass would tend to relax so that the glass would break less cleanly and would have irregularities which are unacceptable within the field of display cell manufacture. It is for this reason that connection zones
26
of cells
10
have until now always been aligned along one of longitudinal edges
20
of strips
16
, so that the glass of front substrate
1
could be broken shortly after having been scribed, i.e. immediately after cutting a strip
16
. However, in the hypothesis in which connection zones
26
are arranged transversely to strip
16
, the bending of said strip
16
would not allow the glass between two adjacent cells
10
to be broken. This operation would thus have to be performed after application of polariser films
22
, a long and difficult step, and dividing cells
10
individually. It was thus thought that the period of time between the moment when the glass is scribed and the moment when the latter is broken was too long and make this operation impossible because of the phenomenon of stress relaxation described hereinbefore. This is why those skilled in the art has always rejected this solution to date.
SUMMARY OF THE INVENTION
An object of the present invention is to overcome the above problems and drawbacks by providing a batch manufacturing method for electro-optical cells or electrochemical photovoltaic cells allowing the connection pads of the cell electrodes to appear at any location on the perimeter of said cells.
The present invention thus concerns a manufacturing method for a plurality of electro-optical cells, in particular liquid crystal cells, or electrochemical photovoltaic cells, including the steps of:
forming on two substrates made of glass or a synthetic material at least one of which is transparent, a pattern of conductive elements, these conductive elements forming electrodes situated at the location
Dudek James A.
EM Microelectronic-Marin SA
Sughrue Mion Zinn Macpeak & Seas, PLLC
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