1. Field of the Invention
The present invention relates to a method of manufacturing a flat display element having a pair of substrates opposed to each other.
2. Description of the Related Art
A known flat display element comprises a pair of substrates, formed individually of glass substrates or the like and opposed to each other, and an optical modulation layer such as a liquid crystal layer sealed in the gap between the substrates. Since flat display elements of this type are thin and lightweight, they can be widely used in various fields. These days, the flat display elements are expected to be thinner and lighter in weight. The flat display elements can be reduced in thickness and weight by thinning the substrates.
To attain this, a configuration may be proposed such that switching elements, pixel electrodes, opposite electrodes, etc. are formed on thin glass substrates that are thinner than conventional substrates. In this case, however, the respective heights of stages in various manufacturing apparatuses must be adjusted according to the thickness of the glass substrates, so that the manufacturing apparatuses require alteration, thus entailing increase in manufacturing cost. Besides, the thin glass substrates are hard to handle. If the glass substrates become thinner, the extent of their warp or deflection and their liability to deformation attributable to change of temperature increase, so that the productivity of flat display elements is lowered.
It is hard and costs high, moreover, to obtain thin glass substrates of desired large sizes. Further, large-sized glass substrates bend deep as they are transported between the manufacturing apparatuses in manufacturing processes, and may touch the apparatuses and be cracked, thereby considerably lowering the yield of production. Thus, the reduction of the thickness of the glass substrates and the enlargement of the mother glass size are limited.
In order to reduce the thickness and weight of the substrates without entailing higher cost and without failing to maintain high yield of production, a flat display element has been developed that has thinned glass substrates, as disclosed in Jpn. Pat. Appln. KOKAI Publication No. 2002-13489. The display element is manufactured as follows. First, a pair of electrode substrates are prepared. The electrode substrates include glass substrates having a conventional thickness and switching elements, pixel electrodes, an opposed electrode, etc. are formed on the glass substrates. These electrode substrates are opposed to each other to form a display cell. Then, the outer surfaces of the glass substrates are polished by mechanical or chemical etching, thereby obtaining a flat display element having thinned glass substrates.
In manufacturing the flat display element by a multi-manufacturing method, two mother glasses are prepared. One mother glass is formed having a plurality of electrode patterns and product seals surrounding the patterns, and the other mother glass having a plurality of electrode patterns. Further, an outer peripheral seal is formed extending along the peripheral edge of the one mother glass. A liquid crystal inlet and an air vent are formed in advance in each product seal and the outer peripheral seal, respectively. The two mother glasses are stuck together with the outer peripheral seal and the product seals between them. After the mother glasses are then pressurized so that air is discharged through the air vent, a sealing agent is sucked into the air vent to seal it with the mother glasses held parallel to each other. Thereafter, the respective outer surfaces of the mother glasses are polished.
According to the conventional manufacturing method, however, the gap between the mother glasses becomes too narrow at the region corresponding to the air vent when the mother glasses are stuck together and pressurized for the air discharge. Accordingly, there is the possibility of the sealing agent failing to be sufficiently sucked into the air vent. If the respective outer surfaces of the mother glasses are polished without completely sealing the air vent with the sealing agent, an abrasive or etchant inevitably gets into the gap between the mother glasses through the air vent. In the case of chemical polishing, in particular, the etchant between the mother glasses inevitably etches the inner surfaces of the glasses, so that those regions of the glass substrate which are touched by the etchant become extremely thin. In consequence, the glass substrates are easily cracked or chipped.
The abrasive or etchant that is forced into the gap between the mother glasses through the air vent further gets into regions for the formation of electrode patterns through the liquid crystal inlet, possibly exerting a very bad influence upon the display quality level of the flat display element.