1. Field of the Invention
This invention relates in general to liquid crystal displays (LCD) and, in particular, to an LCD cell and the corresponding method of manufacturing thereof.
2. Technical Background
A typical LCD device is made up of two primary optical subassemblies: an LCD cell and a back-light module (BLM). BLM provides basic display light illumination for the display system while manipulation of birefringence of liquid crystal molecules in the LCD cell controls the light transmittance across the cell under different intensities and colors for each of the display pixels.
An LCD cell is basically a component that provides a liquid crystal-containing space between two transparent substrates. A sealing material is used to enclose the thin rectangular liquid crystal-containing space corresponding to the display area of the LCD device and also serves to secure the substrates relative to each other. The manufacture of an LCD cell involves the application of the sealant along predefined rectangular path around the display area utilizing a small-caliber dispenser nozzle. The sealant is subsequently hardened in a curing process in which cross-linking results in the polymerization of the sealing material.
One of the popular LCD cell manufacturing processes involves the filling of liquid crystal into the containing space in a vacuum-induced injection scheme. Such a process requires leaving a small opening at a selected location of the rectangular enclosing sealant. Normally the opening is shaped to allow for guided injection of liquid crystal into the containing space. Protrusions in a shaped opening frequently result in the accumulation of liquid crystal residue around themselves after liquid crystal is filled into the containing space via the opening, which is subsequently sealed such as by a resin-based material. Liquid crystal droplets outside of their intended containing space constitute problems to the LCD cell manufacturing. They constitute substantial contaminants and should be avoided. Also, such residues outside of the liquid crystal-containing space represent the waste of expensive material.
One method capable of reducing LCD cell production costs via avoidance of liquid crystal residue wastes is related to the one-drop filling (ODF) of liquid crystal into its intended containing space. An ODF scheme involves preparing a rectangular sealant enclosure over the surface of one of the transparent substrates, placing sufficient droplets of liquid crystal over the surface of either one of the two substrates, and aligning and securing the two together in a sealed manner.
Predetermined amount of liquid crystal material to be delivered in the droplets assist to reduce the waste of liquid crystal. The filling of liquid crystal into the containing space is also much faster than achievable in the vacuum-induced injection scheme described above. The reduction in both the material amount and the processing time results in significantly reduced manufacturing costs.
However, capacity of the liquid crystal-containing space between the two transparent substrates alters due to various factors including, for example, slight twisting of either or both of the substrates. If the amount of liquid crystal delivered by the drops is insufficient, the containing space becomes correspondingly larger than it should be, air bubbles may form in the cell. On the other hand, if the containing space is relatively smaller than for the delivered liquid crystal droplets, the amount of the liquid crystal material becomes excessive, gravity mura may easily arise in the displace area of the cell. Regardless of whether it is excessive or insufficient liquid crystal in the containing space, an LCD cell is discarded as defective. Conventional ODF schemes allow no room for repair of these defective LCD cells. They are simply thrown away and wasted.