Patent Application
20050217720
The present invention concerns connection means for setting up an electrical connection between an electro-optical cell such as a liquid crystal cell or an electrochemical photovoltaic cell and an external electronic power or control circuit. The invention also concerns a method for manufacturing such cells.
A first known category of photovoltaic cells converts light into electricity by exploiting the photovoltaic effect that appears at the junction of semi-conductor materials. The semi-conductor material fulfils both the function of light absorption and of separation of the resulting electrical charges (electrons and holes). The material has to be of great purity, free of any defects, otherwise electrons and holes are recombined before being able to be separated. The cost price of such cells is thus quite high.
The present invention concerns a second type of photovoltaic cells called electrochemical cells, which include a semi-conductor material that is normally insensitive to visible light because of its forbidden bandwidth, and that only starts to absorb in the near ultraviolet. Such a material can nonetheless be sensitised by adsorption of a colouring agent such as a transition metal complex which allows a conversion rate between an incident photon and an electron close to one. After having been excited by the absorption of a photon, the colouring agent can transfer an electron into the conduction band of a semi-conductor material. The electric field prevailing within the semi-conductor material enables the electron to be extracted. After transferring the electron, the colouring agent returns to the fundamental oxidised state. Recombination between the electron in the conduction band of the semi-conductor material and the hole on the oxidised colouring agent is much slower than the reduction of the oxidised colouring agent by a mediator. Consequently, the charge separation is efficient.
The cells of the type described hereinbefore generally include a first transparent front substrate and a second back substrate, which generally can either be transparent or not. These two substrates each include on their faces that are opposite each other a first electrode also called the counter-electrode, and a second electrode usually called known as the photo-electrode. These electrodes are to be connected to an electrical supply circuit and are conventionally made in the form of a thin layer of a transparent conductive oxide such as a mixture of indium/tin oxide or antimony/tin oxide.
The two substrates are joined to each other by a sealing frame, which extends along the periphery of the latter. This sealing frame defines a sealed volume for retaining the semi-conductor material deposited in layers on one of the substrates and an electrolyte containing the aforementioned mediator.
The present invention also concerns so-called electro-optical cells, in particular liquid crystal cells, which, like electrochemical photovoltaic cells, include:
A constant problem in the field of electrochemical photovoltaic cells of the type described hereinbefore, is raised by the connecting means that are used to establish the electrical connection between the electrodes of the cell and an electric power circuit. This problem is also encountered with electro-optical display cells where the electrodes of the cell have to be connected to the device generating the electrical control signals that alter the optical features of the sensitive material retained between the substrates of the cell.
In fact, the most frequently used technique for making the connection pads which enable the electrodes of such cells to be connected to an electronic power or control circuit, consists in letting the connection pads emerge along at least one edge of the cell where the substrate which carries the electrodes projects with respect to the other substrate. This solution thus involves having to offset the substrates of the cell in relation to each other, in order to be able to access the electrodes and make the electrical connections. Such an arrangement makes it difficult to manufacture the cells on a large scale, particularly when the latter are circular, and it requires additional glass scribing and breaking operations which are time consuming.
In order to overcome these problems, the Applicant in his EP Patent Application No A1-0 936 496 has provided a first solution. This European Patent Application discloses an electrochemical photovoltaic cell wherein each of the two substrates of the cell carries on most of its surface a transparent electrode. Contact bumps, made of an electrically conductive material, are added to each electrode in the lateral contact zone where the latter is flush with the edge of the substrate on which it has been deposited.
Owing to the features of the invention briefly described hereinbefore, it is possible to increase the surface of the electrical contact lateral zone via which each electrode of the cell is connected to the electric power or control circuit. The electrical connection between the electrodes and the electrical power or control circuit is thus much more reliable.
However, deposition of the sealing frame is carried out by screen printing, a technique that consists, let us recall, in depositing a material of paste-like consistency through the unobstructed mesh of a screen, for example made of nylon or stainless steel, with a very fine mesh using a squeegee that is actuated by hand or mechanically. There are two major drawbacks with the techniques for depositing sealing frames by screen printing. The first of these drawbacks lies in the fact that it is difficult to control with precision the final dimensions of the frames. In fact, when the top substrate is applied onto the bottom substrate, the sealing material is compressed and tends to spread out via the effect of the pressure exerted, such that the width of the sealing frame can only be controlled with a precision typically of the order of a tenth of a millimetre. Moreover, the inner wall of the sealing frames deposited by screen printing which is in contact with the liquid crystal usually has irregularities in shape, such that these frames have to be arranged at a sufficient distance from the electrodes to prevent them from overlapping thereon. Such a situation may be acceptable if there is a large enough space between the edges of the cell from where the connections emerge and the actual active zone of the cell. However, as soon as one tries to reduce the dimensions of the dead zone reserved for the connector technology, in order to optimise the surface of the display zone of the cell or to answer problems of bulkiness, the precision offered by screen printing techniques is no longer sufficient.
The other drawback of screen printing deposition techniques lies in the fact implementing these techniques generates not insignificant mechanical stresses which are often harmful to the neighbouring structures that have already been deposited when the screen printing step takes place. In order to preserve these fragile structures, it is preferable to deposit them after deposition of the sealing frame. This is the case in European Patent Application No. A-1-0 936 496 where the contact bumps are deposited on the corresponding electrodes by means of a syringe type dispenser. But this technique is inaccurate and considerably limits the number of contact bumps that it is possible to make on the same cell, which means that use of this technique is reserved for cells having low connection density.
There is also known from European Patent No. EP-B1-0 708 931 in the name of the South Korean company Samsung Electronics Co. Ltd., a liquid crystal cell with a thin sealing frame and a method of manufacturing such a cell. In accordance with this method, a cord of sealing material is deposited on the periphery of a first substrate whose dimensions are larger than those of the desired liquid crystal cell. A second substrate of the same dimensions as the first substrate is then deposited on said first substrate so as to create a cavity defined by the first and second substrates and the sealing cord. After which, the sealing material is solidified so as to join the two substrates, then the cavity is filled with the liquid crystal via a filling aperture which is then blocked. Finally, the assembly of the two substrates is sawn through the sealing material to return it to the dimensions of the desired display cell.
In the Samsung Patent, the sealing cord is deposited using a syringe type dispenser. Thus, the contact bumps must be less high than the space separating the two substrates of the cell since, if this is not the case, there is a risk of extra thick areas being observed at the places where the sealing material covers said contact bumps, such extra thick areas being unacceptable insofar as they involve parallelism defects between the two substrates meaning that the cell is not sealed. Further, as the contact bumps are not high, they must be wide in order to offer a sufficient electrical contact surface area, which considerably limits the number of electrodes that it is possible to connect and thus the resolution of the display thereby obtained.
It is an object of the present invention to overcome the drawbacks of the aforementioned prior art in addition to others still, by providing an electro-optical cell, in particular a liquid crystal display cell, or an electrochemical photovoltaic cell including connection means for setting up a reliable and compact electrical connection between the electrodes of the cell and an electric power or control circuit.
The present invention also concerns a method of manufacturing a cell of the aforementioned type, which is easy to implement and which limits especially the risk of deterioration of the cell elements that have already been deposited.
The present invention thus concerns an electro-optical cell, in particular a liquid crystal display cell, or an electrochemical photovoltaic cell, including:
this cell being characterised in that the sealing frame includes at least one wall structured on one of the two substrates and which defines via its inner lateral face the volume for retaining the sensitive material, this wall extending in a set back position with respect to the edges of the cell, so as to free the connection contacts and thus with the electrodes passing through the wall, the substrates being joined by a sealing joint, which occupies at least partly the gap defined by said substrates and the outer lateral face of the wall, and in that the electrical connection means include contact bumps made of an electrically conductive material added onto the extension of each electrode at the place where the latter emerges from the wall.
Owing to these features, it is possible to increase the surface of the lateral electrical contact zone via which each electrode of the cell is connected to the electrical power or control circuit. The electrical connection between the electrodes and the power or control circuit is thus much more reliable. Moreover, the fact that the sealing frame is formed of two parts, namely a wall which defines a volume for retaining the sensitive material and a cord of sealing material that is deposited against the external face of the wall and which fills the gap left vacant between the two substrates because of the fact that said wall is structured slightly further back than the edges of the cell, enables the dimensions of the dead zone reserved for the connection of the cell to be substantially reduced and thus the surface of the display zone of said zone to be optimised or its space requirement to be reduced. Finally, the sealing material covers the contact bumps, which prevents any risk of the bumps deteriorating.
According to another aspect, the present invention also concerns a method of manufacturing at least one cell of the aforementioned type, this method being characterised in that it includes the steps of:
Other features and advantages of the present invention will appear more clearly from the following detailed description of an example embodiment of the cell according to the invention, this example being given solely by way of non-limiting illustration, in conjunction with the annexed drawing, in which:
The present invention proceeds from the general inventive idea, which consists in making the sealing frame for a cell, for example a liquid crystal cell, in two parts, namely, a wall that can be made very precisely in proximity to the edges of the cell and which defines, via its inner lateral face, a volume for retaining a sensitive material such as a liquid crystal, and a sealing joint which is introduced into the gap between the two substrates and which gives the resulting sealing frame its mechanical resistance and its adhesion power for said substrates. It is thus possible to reduce the space necessary for making the electrodes emerge of the cell, such that a more compact cell is obtained or one offering a larger active surface. In fact, as it has been difficult until now to deposit a sealing frame with precision, the latter had to be arranged sufficiently far from the edges of the cell to be sure that the electrodes would emerge properly from said sealing frame, which resulted in a considerable reduction in the active surface of the cell. Moreover, since the sealing material covers the conductive bumps arranged at the end of the conductive paths, this prevents any risk of said connecting means being damaged.
The present invention will be described in conjunction with a liquid crystal display cell. It goes without saying that this example is given solely by way of illustrative example, and that the present invention applies in a similar way to any type of electro-optical or electrochemical photovoltaic cell.
It can be seen in
Electrodes 14 and 16 of cell 2 extend up to close to the edge of substrates 4 and 6 on which they are deposited to form connecting means 18 in order to set up the electrical connection between said cell 2 and the control circuit. However, wall 12 extends set back from the edges of the cell, so as to release connecting means 18, and thus electrodes 14 and 16 pass through it.
Connecting means 18 are formed by contact bumps 20 (more visible in
According to one feature of the invention, contact bumps 20 are not as high as the space separating the two substrates 4 and 6 and which is determined by the height of the sealing frame which connects the two substrates to each other.
In the example shown in
It is clear, of course, that wall 10 can be omitted, only wall 12 which is in contact via its inner lateral face with the liquid crystal being kept. In such case, after structuring said wall 12 and positioning top substrate 4 on bottom substrate 6, the sealing material will be introduced into gap 28 defined by the outer lateral face of wall 12 and the two superposed substrates 4 and 6 until at least a part of the volume of said gap 28 is occupied by said sealing material as shown in
This operation could be achieved by means of a sealing material dispenser. The dispenser will be moved along at least a part of the periphery of the two substrates 4 and 6, so as to form a cord of sealing material 30, which, by abutting against the external lateral face of wall 12 and joining said two substrates 4 and 6, will form the sealing frame. It is not necessary for the sealing frame 30 to extend as far as the edges of the cell. It only needs to be sufficiently wide to play the part of a sealing frame, i.e. to isolate the sensitive material from the external environment, to prevent the latter from leaking outside the cell and to keep the two substrates 4 and 6 together.
In order to deposit the cord of sealing material 26, one can also dip one of the edges of cell 2 defined by the two superposed substrates 4 and 6 into a receptacle containing a certain quantity of the sealing material. By capillary action, the sealing material will gradually fill the vacant volume 28 located outside the perimeter of wall 12. Another possibility consists in injecting the sealing material between the two substrates 4 and 6 via a filling hole pierced in one of said substrates 4 or 6 outside the perimeter of wall 12.
According to the invention, after having deposited all of the structures necessary for the proper operation of the forthcoming cell 2 on the inner face of one of the two substrates 4 or 6, such as for example the electrodes or the contact bumps (these manufacturing steps will be described in detail hereinafter), the substrate is covered with a layer of photoresist material. This photoresist layer is then structured by conventional photo-etching techniques to give it the form of the aforementioned filling channel 22 defined by walls 10 and 12. Once filling channel 22 has been obtained, the remaining substrate, also suitably primed, is joined to the first substrate. Of course, the order of these operations is given purely by way of illustration, and could be altered.
According to a variant of the method, the photoresist layer is structured so as to form not only the filling channel, but also spacers (not shown in the drawing for the sake of clarity) for maintaining a constant distance between the two substrates 4 and 6. Owing to the present invention, it is thus possible to structure the distance structures and the filling channel in a single manufacturing step. In addition to the savings in time and money achieved by such a method, another advantage of this implementation variant of the method according to the invention lies in the fact that, since the spacers and the sealing frame are made in a concomitant manner, said spacers are not liable to be damaged during a subsequent step for manufacturing the sealing frame as was the case in the prior art. Finally, the filling channel and the spacers are made using the same material, which simplifies the present method still further.
The photolithographic techniques used within the scope of the present invention are of a conventional type and are well known to those skilled in the art. They consist, essentially, in sensitising the photoresist layer by means of a light passing through the transparent zones of a mask reproducing the shapes of the zones to be sensitised. As regards the photoresist material, this is also, in a very conventional manner, a photosensitive resin that those skilled in the art will be able to choose without any difficulty, and whose usual purpose is to protect the surface of the layer to be etched from the action of a chemical reactant at the locations where the resin subsists after sensitisation by the optical radiation and chemical removal of the zones covering the places to be etched. One can cite the photosensitive cycloten from Dow Chemical and the product marketed under the reference SU8 by MicroChem Corp. as materials well suited for making walls 10 and 12.
As was described hereinbefore, after structuring the sealed walls 10 and 12 defining filling channel 22 and, where appropriate, spacers, the two substrates 4 and 6 are joined. Said channel 22 can then start to be filled. In order to do this, a vacuum starts to be made in the working enclosed space in which cell 2 is made. Once the vacuum is established, a drop of sealing material is deposited above hole 24 which communicates with filling channel 22. By capillary action, the sealing material starts to flow into channel 22. Then the atmospheric pressure is re-established in the working enclosed space. Via the effect of the pressure difference between the filling channel in which a quite high vacuum prevails and the atmospheric pressure, the sealing material is driven to the bottom of the filling channel.
Typically, the material used for sealing cell 2 is a photosensitive resin which is introduced in the liquid state into filling channel 22 and which is then polymerised by sensitisation using an ultraviolet light through top substrate 4. The sealing material has to hermetically seal the edges of cell 2 in order to efficiently retain the liquid crystal and protect it from gas diffusion phenomena from the ambient atmosphere. The sealing material must also have an adhesive power in order to enable it to hold the two substrates 4 and 6 together. By way of variant, the sealing material can also be formed by a resin which will polymerise via the effect of a rise in temperature in the working enclosed space. A dual component adhesive whose components harden over time or via the effect of a rise in temperature when they are put in each other's presence can also be used as sealing material. The products Loctite 3492 and Norland Optical Adhesives 61 can be cited as materials well suited for making the sealing frame. Another family of adhesives well suited to the requirements of the present invention is formed by the cyanoacrylate adhesives. Finally thermoplastic resins can also be used within the scope of the invention.
Once the sealing material has been introduced into filling channel 22 then solidified, the liquid crystal can be introduced into cell 2 via filling hole 26. Advantageously, the introduction of the sealing material, its solidification, then the step of introducing the liquid crystal can be carried out one after the other or simultaneously in the same machine. Finally, liquid crystal filling hole 26 is blocked as well as space 32 in immediate proximity to filling hole 26, in order to achieve sealing continuity with the closest parts of wall 12 so that the whole of the periphery of cell 2 is perfectly sealed. Finally, additional layers such as polarisers can also be deposited on substrates 4 and 6.
Electrodes 14 and 16 are usually made by photo-etching in the form of thin layers of a transparent conductive oxide such as a mixture of indium/tin oxide or “ITO”. After the step of structuring electrodes 14, 16, comes the step of making contact bumps 20. Of course, according to a variant, it would also be possible to first of all deposit a layer of conductive material, then to make the contact bumps at the surface of that layer, and finally to structure the conductive layer in order to form the electrodes.
Contact bumps 20 are preferably, but not restrictively, made by galvanic growth using a conductive material such as gold. Thus, a layer of gold is deposited by vapour deposition over the entire surface of the two substrates 4 and 6. Prior to the disposition of the gold layer a chromium layer for example could be vapour deposited on the surface of substrates 4 and 6, which allows a better adhesion of said gold layer at the surface of substrates 4 and 6. The layer of gold is commonly called the seed layer.
After evaporation of the gold layer, there is deposited a layer of a photoresist agent in which apertures are made at the places where one wishes the galvanic growth phenomenon to occur, in other words at the end of electrodes 14 and 16. The layer of growth will be electrically contacted to form the cathode, then substrates 4 and 6 will be immersed in a galvanic growth bath opposite a platinum piece which acts as the anode. The bath is a dual gold and potassium cyanure base marketed under the commercial name of AURALL 292 by the Lea Ronal Company. Via the effect of application of an electrical voltage, the electrochemical couple present in solution in the galvanic growth bath will dissociate and the gold will be deposited on the locations of substrates 4 and 6 that are not protected by the photoresist layer. As a function of the value of the electrical voltage and the time during which the voltage is applied, the speed of growth of contact bumps 20 can be controlled. When these contact bumps 20 have reached the desired dimensions, the electrical voltage is cut. Substrates 4 and 6 then only need to be dipped in the chemical etching baths to successively remove the layers of photoresist, gold and chromium. When the gold layer is removed, contact bumps 20 will also be slightly etched and their height will decrease by a value close to that of the thickness of the gold layer initially deposited on substrates 4 and 6. It should be noted that these different chemical etches have no effect on electrodes 14, 16 which are made of ITO.
According to a variant, contact bumps 20 can be made using a selective printing deposition technique such as screen printing using an adhesive material like epoxy charged with conductive particles.
After structuring contact bumps 20, liquid crystal molecule alignment layers are deposited on substrates 14, 16. These alignment layers can be deposited for example by flexographic printing.
After the alignment layers have been deposited, holes 24 and 26 for introducing the sealing material and the liquid crystal are pierced in one of the substrates, here front substrate 4.
The wall or walls 10 and 12 are then structured in accordance with the operating mode described in detail hereinbefore. At the same time as walls 10 and 12, one can, if appropriate, simultaneously make the distance structures, for example in the form of rectilinear bars or bumps.
Once walls 10 and/or 12 have been structured, front substrate 4 can then be applied onto back substrate 6 and filling channel 22 can start to be filled. If only inner wall 12 has been made, the gap 28 defined by the external lateral face of wall 12 and the two superposed substrates 4 and 6 can be filled, for example by dipping one of the edges of cell 2 into a receptacle containing liquid sealing material. By capillary action, the sealing material will gradually fill gap 28 and cover contact bumps 20 without any risk of damaging them. If, however, both inner wall 12 and outer wall 10 have been structured at the same time, so as to form the aforementioned filling channel 22, the sealing material will be introduced into said channel 22 via filling hole 24 arranged in front substrate 4 for this purpose.
Once the sealing material has solidified and the two substrates 4 and 6 are permanently joined, cavity 8 can be filled with the liquid crystal via filling hole 26 pierced in top substrate 4 then, when filling has finished, said filling hole 26 is sealed by means of an adhesive plug, all of these operations being able to be carried out simultaneously in the same machine.
At this stage of the manufacturing method, cell 2 is cut out, for example by sawing or water jet cutting, an operation that can be followed by a grinding step to bring the dimensions of cell 2 to its definitive size. The saw line is shown in dotted lines in
It goes without saying that the invention is not limited to the embodiments that have just been described, and that various simple alterations and variants can be envisaged without departing from the scope of the present invention. In particular, the invention applies identically to a cell including more than two substrates, for example four, the substrates being joined in pairs by a sealing frame according to the invention and formed of at least one wall which defines the volume for retaining the sensitive material or fluid, as well as a cord of sealing material which fills the gap between the two substrates concerned, bumps of conductive material being added onto the extension of each electrode at the location where the latter emerges from said wall.
Likewise, it would be entirely possible to envisage the contact bumps being located outside the perimeter defined by the sealing cord.
Finally, the present invention applies in a similar manner to a large-scale manufacturing method for cells as shown in
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP03/06375 | 6/17/2003 | WO | 12/20/2004 |
