Passive Electro-Optic Display Cell and Method for Its Manufacturing

The present invention relates to a passive electro-optic display cell comprising at least a plate made of transparent material carrying, on its inner face, electrodes and conductive tracks or leads.

The invention relates also to a method of manufacturing of the above mentioned display cell.

The electro-optic passive display cells of the type hereabove mentioned have the drawback that the electrodes and the conductive tracks are visible through the plate of transparent material depending on the angle of incidence of observation, that is due to the fact that the index of refraction of the conductive coating is not the same as the index of refraction of the active constituent which occupies the interstices between the electrodes and the conductive tracks or leads. Hence interference phenomena are produced which render visible the electrodes and the conductive tracks or leads even when the display cell is at rest.

The object of the present invention is to remove these drawbacks.

To this effect, the display cell according to the invention is characterized by the fact that its electrodes and conductive tracks or leads are part of a transparent insulating coating applied on the inner face of the transparent plate, having the same index of refraction and the same thickness as the said electrodes and conductive tracks or leads.

The method of manufacturing of this cell is characterized by the fact that one applies on the plate of transparent material a transparent insulating coating, then dopes the said insulating coating by a ionic implantation in the areas intended to constitute the electrodes and the conductive tracks or leads, so as to render these areas electrically conductive.

The drawing shows, by way of example, one embodiment of the object of the invention.

FIG. 1 is a sectional side view of an electro-optic passive display cell, having a liquid crystal, of conventional type, and

FIG. 2 is a sectional side view of an electro-optic passive display cell, also with a liquid crystal, according to the invention.

The display cell represented in FIG. 1 comprises two transparent glass plates, one of which is the front one, designated by 1, and the other one, which is the rear one, is designated by 2. The front plate 1 carries, on its inner face, transparent electrodes and conductive tracks or leads generally designated by 3.

The rear plate 2 carries, innerly, counterelectrodes and conductive tracks or leads generally designated by 4. A liquid crystal 5 is interposed between the two plates 1 and 2 and is retained by a frame 6 made of sintered glass, known as GLASSFRIT.

This cell is obtained by depositing on the two plates 1 and 2 a coating of conductive material, for instance oxide of indium (In.sub.2 O.sub.3), doped with tin, which is then removed partially by photo-chemical means, so that the coating of conductive material remains only in the places where there must be electrodes and the conductive tracks or leads 3, and 4 respectively.

The index of refraction of the material of the electrodes and of the conductive tracks or leads 3 and 4 respectively, and of the liquid crystal 5 are not the same, and, if one observes the cell through one or the other of the two plates 1 and 2, the electrodes and conductive tracks or leads are visible, even when the cell is at rest, depending on the angle of incidence of the observation.

In the case of the cell of FIG. 2, which comprises also two transparent glass plates, designated by 7 and 8, one applied on these two plates a coating of metallic oxyde 9 and 10 respectively, for instance an oxide of indium (In.sub.2 O.sub.3). For realizing or forming the electrodes and conductive tracks or leads, generally designated by 11 for the plate 7 and by 12 for the plate 8, one exposes selected areas of the coatings 9 and 10 to an ion beam of, for instance, ions of tin. This operation of doping renders the coatings 9 and 10 electrically conductive, in the treated areas, without their index of refraction be modified substantially. The rest of the two coatings 9 and 10 remains insulating.

It results from this arrangement that the electrodes or counter-electrodes are not visible when the cell is at rest, whatever may be the angle of incidence of the observation.

As a modification, the coatings 9 and 10 could be realized or formed in an oxide of tin (SnO.sub.2) in which case they would be doped by means of ions of antimony.

It is to be noted that the cell could have coated only one of its two transparent plates, the electrodes and conductive tracks or leads of which are a part of the insulating coating, it being understood that this plate will then be the front plate of the cell.