GB2067330A

GB2067330A - Method for manufacturing the substrate of an electrochromic display cell

Info

Publication number: GB2067330A
Application number: GB8038845A
Authority: GB
Original assignee: Ebauches SA
Current assignee: Ebauches SA
Priority date: 1979-12-18
Filing date: 1980-12-04
Publication date: 1981-07-22
Also published as: FR2472241B1; DE3046746A1; FR2472241A1; GB2067330B; DE3046746C2

Abstract

In manufacturing an electrochromic display cell substrate the ionic conductor (5) is kept out of contact with the transparent conductive elements (2, 2b). In a first method a transparent dielectric (3) is deposited over the whole surface of the transparent plate (1) which already carries the conductive elements (2, 2b). It is etched through a protective mask which is then used for the deposition of the electrochromic material (4). In a second method a layer of electrochromic material (4) is deposited on the whole surface of the transparent plate (1) which carries the conductive elements (2, 2b). It is etched through a protective mask which is then used for the deposition of the transparent dielectric material (3). Both methods thus result in the conductive elements (2, 2b) being covered with a continuous layer formed from areas of the dielectric material (3) and the electrochromic material (4). <IMAGE>

Description

SPECIFICATION Method for manufacturing the substrate of an electrochromic display cell and the substrate obtained thereby Background of the invention 1. Field of the invention This invention relates to a method for manufacturing the substrate of an electrochromic display cell from an insulating transparent plate provided with a network of transparent conductive elements including control electrodes situated at the places of the patterns to be displayed, terminal connection contacts of the cell, and tracks interconnecting electrodes and the terminal contacts.

Due to their low consumption, such cells are specially suitable for the display of numeric information or other forms of display in self-contained apparatus powered by accumulators or primary batteries of low capacity. Electronic watches constitute an example of such apparatus.

In these display cells, the optical properties of the electrochromic material deposited on the electrodes are modified by the action of electrical charges which are produced therein by an electric current which circulates between these electrodes and a counter-electrode through an ionic conductor. It is necessary to prevent any contact between the ionic conductor and the conductive electrodes, in order to preclude any electro-chemical reaction which could lead, for instance, to the dissolution of the electrodes and, consequently, to a much shortened duration of the working life of the cell.

Description of the prior art The method ordinarily used for manufacturing these substrates cannot ensure that such a contact will not occur. It consists in depositing a dielectric layer at the desired places through a first protective mask, then depositing a layer of electrochromic material through another mask which is complementary to the first one, that is to say which permits the deposition of the electrochromic material at the places left free by the deposition of the dielectric material. There is a considerable risk, with this method, that the zones which are covered by the dielectric material and the zones covered by the electrochromic material are not exactly contiguous and, consequently, that the ionic conductor can come into contact with the electrodes or the connecting tracks.

Swiss Patent No. 564,227 suggests, but for solving another problem, the provision of a marginal overlap between the electrochromic material and the layer of the dielectric material by which it is surrounded. This arrangement obviously also enables any contact between the ionic conductor and the electrodes or the connecting tracks to be prevented.

But, in this case, the coloration produced in the zone of the electrochromic material in contact with the ionic conductor diffuses under the marginal protecting zone and, consequently, cannot later be erased, with the consequential drawback of creating a permanent colored marginal edge at the places of the overlap.

Summary of the invention The object of the prevent invention is to provide a method for manufacturing the substrate of an electrochromic cell on which the electrochromic material is so closely surrounded by the dielectric material that any contact between the ionic conductor and the electrodes or the conductive tracks connecting the electrodes with the terminal connections of the cell is rigorously prevented, without the abovementioned drawback.

This object is achieved by providing a transparent isolating plate comprising the electrodes, the terminal connections and the conductive tracks connecting the electrodes with the terminal connections.

A first layer, which is a layer of transparent dielectric material in a first way of implementing the invention and a layer of electrochromic material in a second way of implementing the invention, is deposited on the whole surface of the plate, at the eventual exception of the zone of the terminal connections.

Photosensitive material is then deposited on this first layer, exposed to the light through a suitable exposure mask and developed.

The exposure mask is so arranged that the protective mask formed bythe photsensitive material remaining after the development has the shape which is desired for the first material in the finished substrate. The places uncovered by this protective mask have thus the shape which is desired for the second material in the finished substrate.

The first layer is etched away through this protective mask, by any suitable means. A second layer, which is a layer of electrochromic material in the first way of implementing the invention and a layer of transparent dielectric material in the second way of implementing the invention, is deposited on the whole surface of the substrate, with the possible exception of the zone of the terminal connections, that is partially on the protective mask and partially on the plate itself, at the places where the first layer has been etched away.

Finally, the remaining photosensitive material is removed by dissolution in a suitable solvent. During this dissolution, the portions ofthe second layer which had been deposited on the remaining photosensitive material are thus also removed.

Due to the fact that only one protective mask has been used to etch away the first layer and to deposit the second layer, the remaining of this second layer, which had been deposited on the plate itself, form with the remaining of the first layer a continuous protective layer comprising zones of electrochromic material very closely surrounded by dielectric material. The electrodes and the conductive tracks are thus efficiently protected against the ionic conductor when the substrate is mounted in the finished display cell.

The various features of the invention will be apparent from the following description, drawings and claims, the scope of the invention not being limited to the drawings themselves as the drawings are only for purpose of illustrating ways in which the principles of the invention can be applied. Other embodiments of the invention utilising the same or equivalent principles may be used and structural changes may be made as desired by those skilled in the art without departing from the present invention and the purview of the appendant claims.

Brief description of the drawings The accompanying drawings show, by way of example, a display cell and two modes of production in accordance with the invention. In the drawings: Figure 1 is a fragmentary sectional view of an electrochromic display cell; Figures 2 to 7 are fragmentary sectional views of the substrate of the cell illustrated at different stages of its manufacture, according to a first mode of production; and Figures 8 to 13 are fragmentary sectional views of the substrate of the cell illustrated at different stages of its manufacture, according to a second mode of production.

Description of the preferred embodiments The cell shown in Figure 1 comprises a substrate constituted by a transparent and insulating plate 1, for instance made of glass, covered with a network of conductive elements, also transparent and including control electrodes 2, situated at the places of the patterns to be displayed and having dimensions slightly greater than those of these patterns, term in al connection contacts such as 2a situated at the periphery of the substrate, and conductive tracks such as 2b interconnecting the electrodes and the terminal contacts. This network can be made, for instance, of tin oxide (SnO2) doped with antimony.

The electrodes 2 as well as the tracks 2b are coated with a transparent dielectric layer 3, for example of silicium oxide (SiOx where 1 < x S 2), interrupted at places corresponding to the patterns to be displayed as well as at the regions of the terminal connection contacts of the cell. At the places of the patterns to be displayed, the electrodes are covered with electrochromic material 4 constituted by an oxide of a metal of transition, such as tungsten oxide (WO3).

The whole is covered with an ionic conductor 5 which can be constituted by dilute sulphuric acid or by an ionic conducting polymer containing diffused pigments necessary to give the background of the display the desired appearance, for example tita- nium oxide (TiO2) for a white background. A small plate of graphite 6, used as a current collector, is in electrical contact with a counter-electrode 7 made of graphited paper, itself applied to the ionic conductor 5. A cover 8 made of metallized glass, of passivated metal or other suitable material, and secured at its periphery to the substrate 1, holds the whole assembly together and ensures the electrical connection of the counter-electrode 7 with the outside of the cell.

In a first way of implementing the invention, the substrate is manufactured as follows: A transparent dielectric layer 3 is deposited over the whole surface of the plate 1 which is provided, by known methods, with the network of electrodes 2, terminal connection contacts 2a and connecting tracks 2b (Figure 2). Depending on the method used, the terminal contacts 2a, which have not been shown in this figure, can be left uncovered with the dielectric layer 3, which is deposited by vacuum evaporation, sputtering, chemical vapour deposition or by any other suitable method.

Photosensitive material 9 (photoresist), for example the products sold under the tradenames AZ 1370 and AZ 1350 (Registered Trademarks of Shipley Corporation, in the United States), is then applied over the whole surface of the dielectric layer by pulverisation, spinning, dipping or any other suitable procedure (Figure 3).

This layer of photosensitive material 9 is then selectively exposed to light, through a suitable exposure mask, and the latent image so obtained is developed by techniques which are well known in photolithography (Figure 4). This is done in a manner such that the parts of the photosensitive layer 9 which remain after the development form a protective mask protecting the whole dielectric layer 3, except at the places of the patterns to be displayed and, possibly, at the regions of the terminal connection contacts of the cell which are situated at the periphery of the substrate and which have not been shown in Figure 4.

The insulating dielectric layer3 is then etched away through the protecting mask, for example by means of a buffered solution of hydrofluoric acid, at any place where it is not protected by this mask (Figure 5).

It is also possible, instead of using a chemical etching process, to use a technique of plasma etching, or an ionic etching technique. In any case, it is necessary to take care that the means of etching used is such that it does not substantially impairthe properties of the remaining photo-sensitive material which serves as the protective mask during the etching. It is moreover necessary that the rate of attack on the electrodes 2, which occurs at the end of the etching of the dielectric layer 3, be zero or in any case sufficiently low to guarantee the complete etching through of the insulating layer 3 without the properties of the electrodes 2 being impaired.

A layer of electrochromic material 4 constituted by an oxide of a metal of transition, for instance of tungsten oxide (WO3), is then deposited overthe whole surface of the substrate (Figure 6) with the exception of the regions of the terminal connection contacts of the cell which are protected, during this deposition, by a mechanical mask or other means, the dimensions and positioning of which are not critical. This deposition is effected by vacuum evaporation or by sputtering. The electrochromic material is deposited on the electrodes 2 through the maskformed by the photo-sensitive material 9 which has been already been used for the etching of the dielectric layer. it is naturally also deposited on this mask itself.

The photosensitive material 9 constituting the mask is then dissolved in a suitable solvent, which does not attack the electrochromic material, such as a ketone solvent in the case where this material is WO3.The portion of the layer 4 of electrochromic material deposited on the photo-sensitive material 9 is also removed, carried away by the dissolved photosensitive material, and the substrate then has its final form such as illustrated in Figure 7.

It is advantageous to agitate the solvent during this dissolution, mechanically or ultrasonically for example, for breaking up the removed electrochromic material and improving the elimination thereof.

It should be noted that the electrochromic material deposited on the electrodes 2 adheres strongly thereto, so that it is not at risk of also being removed by the agitation of the solvent. The same applies to the dielectric material 3 which adheres very strongly to the rest of the substrate.

In a second way of implementing the invention, the substrate is manufactured as follows: A layer 4 of electrochromic material constituted by an oxide of a metal of transition, for instance tungsten oxide (W03), is deposited on a zone, comprising at least the places of the patterns to be displayed, of the surface of the plate 1 which is provided, by known methods, with the network of electrodes 2, terminal connection contacts 2a and connecting tracks 2b (Figure 8). The terminal contacts 2a are not shown in this figure. The electrochro mic layer is deposited by vacuum evaporation, by sputtering, by chemical vapour deposition or by any other suitable method.

Photosensitive material 9 (photoresist) constituted for example by one of the products sold under the tradenames AZ 1370 and AZ 1350 (Registered Trademarks of Shipley Corporation, in the United States) is then deposited over the whole surface of the electrochromic layer by pulverisation, spinning, dipping or any other suitable method (Figure 9).

This layer of photosensitive material 9 is then selectively exposed to light, through a suitable mask, and the latent image obtained is developed by techniques well known in photolithography. The exposure mask is such that the portions of the photosensitive layer 9 which remain after this development form a protective mask protecting the portions of the electrochromic layer 4 situated at the places of the patterns to be displayed, the other portions of the electrochromic layer 4 being uncovered (Figure 10).

The electrochromic layer 4 is then etched away, through the protective mask, for example by an alkaline solution which may be a solution of ammonia (NH40H), until it is eliminated at any place where it is not protected by this mask (Figure 11).

If the photosensitive material 9 is a material which requires an alkaline developer, as it is the case when using the above-mentioned AZ 1370 and AZ 1350 materials, the operations of development and etching can be combined. This has the advantage of reducing the number of required steps in the manufacture of the substrate.

It is again also possible, instead of using a chemical etching process, to use a plasma or an ionic etching technique. In any case, attention must be paid to the fact that the etching means must be such that it does not substantially impair the properties of the remaining photosensitive material which serves as a protective mask for the etching. It is moreover necessary that the rate of attack on the conductive elements, which are partially exposed at the edge of the etched away area of the electrochromic layer 4, be zero or in any case sufficiently low as to guarantee the complete etching through of the electrochromic layer, without the properties of the conductive elements being impaired.

A layer of transparent dielectric material 3 which may be of silicium oxide (SiO, where 1 < x S 2), is then deposited over the whole surface of the substrate (Figure 12), except at the regions of the terminal connection contacts of the cell which are protected during this deposition by a suitable mask, of mechanical or other form, the dimensions and positioning of which are not critical. This deposition is effected, for example, by sputtering or by vacuum evaporation.

The dielectric material is thus deposited all around the remaining electrochromic material through the mask constituted by the photosensitive material 9 which has already been used for the etching through of the electrochromic material. It is also deposited, obviously, on the mask itself.

The protective mask is then eliminated by dissolu tionof the photosensitive material 9 in a suitable solvent which does not attack the electrochromic material 4, such as a ketone solvent in the case where the electrochromic material is tungsten oxide (WO3). The portion of the layer 3 ot dielectric material which has been deposited on and is thus carried by the photosensitive material 9 is simultaneously removed and eliminated with the photosensitive material and the substrate then has its final form, such as illustrated in Figure 13.

As in the first mode of production, it is advantageous to agitate the solvent during the dissolution procedure, for example ultrasonically, to assist the breaking up of the dielectric material and facilitating the elimination thereof. It should be noted that the dielectric material deposited on the rest of the substrate adheres very strongly thereto, so that it is not at risk of also being removed by the agitation of the solvent. The same applies to the electrochromic material which adheres very strongly to the electrodes.

It should be noted that, in the two modes of production described, the photosensitive material 9 could if desired be replaced by a material sensitive to another form of radiation, for instance electronic radiation (electronresist), in which case the exposure to light would naturally be replaced by exposure to the appropriate radiation, for example a beam of electrons. Similarly, the protection of the portions of the first deposited layer (dielectric layer in the first mode of production and layer of electrochromic material in the second mode of production) which must not be attacked could be realized by the deposition thereon of any other protective material such as, for example, ink deposited by a screenprinting or offset printing procedure.In any case, the use of a common protective mask for the two operations of etching of the first deposited layer and deposition of the second deposited layer (layer of electrochromic material in the first mode of production and dielectric layer in the second mode of production) constitutes an important feature of the invention. As a matter of fact, it guarantees the complete coating of the electrodes 2 and of the connecting tracks 2b either by the dielectric insulating layer 3 or by the electrochromic material 4, without any interruption between the zones covered by one or the other thereof. In contrast, the obtainable tolerances in the manufacture and positioning of the masks used in the known methods are such that it is not possible to prevent spaces of several microns being left between these zones. With the present invention, the electrodes 2 and the tracks 2b are completely protected, when the substrate is mounted in the finished display cell, against the ionic conductor 5 with which they have no contact, so that they cannot by subjected to any attack thereby. The effective working life of the cell is consequently substantially extended with respect to that of a cell with a substrate manufactured by previously known methods.

Finally, it should be noted that the present method of manufacture of a substrate which results in these advantages is simpler than the methods of manufacture previously known, and that this method is well suited to mass production.

Claims

1. Method for manufacturing the substrate of an electrochromic display cell comprising the steps of providing an insulating transparent plate with a network oftransparent conductive elements including control electrodes situated at the places of the patterns to be displayed, terminal connection contacts of the cell and tracks interconnecting said electrodes and said contacts; depositing a first layer on the surface of said plate provided with the said network of conductive elements, at least except for the regions of said terminal contacts; depositing a protective mask on said first layer; selectively etching the portions of said first layer which are not masked by the said protective mask; depositing a second layer over the whole surface of the substrate, with the exception of said regions of the terminal contacts; and selectively eliminating said mask with resultant removal of that portion of the said second layer which it carries, one of the said layers being a layer made of a transparent dielectric material and the other of the said layers being a layer made of an electrochromic material.

2. Method according to claim 1, wherein said first layer is deposited by vacuum evaporation.

3. Method according to claim 1 wherein said first layer is deposited by a method of chemical vapour deposition.

4. Method according to claim 1, wherein said first layer is deposited by sputtering.

5. Method according to claim 1,wherein said mask is produced by a photolithographic procedure.

6. Method according to claim 1, wherein said mask is deposited by an offset printing procedure.

7. Method according to claim 1, wherein said mask is deposited by a screen-printing procedure.

8. Method according to claim 1, wherein said portions of the said first layer which are not masked by said protective mask are etched by an ionic etching process.

9. Method according to claim 1, wherein said portions of the said first layer which are not masked by said protective mask are etched by plasma means.

10. Method according to claim 1,wherein said second layer is deposited by vacuum evaporation.

11. Method according to claim 1, wherein said second layer is deposited by sputtering.

12. Method according to claim 1,wherein said first layer is a layer of a transparent dielectric material and is etched by an acid solution.

13. Method according to claim 1, wherein said first layer is a layer of electrochromic material and is etched by an alkaline solution.

14. Method according to claim 13, wherein said mask is produced by a photolithographic procedure, and said alkaline solution is also used as a developer of the mask in the photolithographic procedure.

15. Substrate of an electrochromic display cell manufactured according to the method of claim 1.

16. A method of manufacturing the substrate of an electrochromic display cell, substantially as herein particularly described with reference to Figures 2 to 7, or Figures 8 to 13, of the accompanying drawings.

17. Asubstate manufactured bya method in accordance with claim 16 and substantially as herein particularly described with reference to and as illustrated in Figures 2 to 7, or Figures 8 to 13, of the accompanying drawings.

18. An electrochromic display cell with a substrate manufactured by a method in accordance with claim 1, and substantially as herein particularly described with reference to and as illustrated in Figure 1 of the accompanying drawings.