The present invention relates to a liquid crystal display device used in an optical display, and manufacturing method for same. More particularly, the present invention relates to a liquid crystal display (LCD) device, and manufacturing method for same, wherein the LCD device includes a plurality of insulation layers which partitions a liquid crystal layer, and having a column layer which supports the insulating layer in the liquid crystal layer.
An LCD consumes a small amount of electricity because of its low driving voltage. Various new kinds of LCDs have been developed as image display devices, such as plasma display panels and electro-luminescence effect devices, and their application fields have greatly multiplied because of the small lightweight features of the LCD.
Current LCD devices having an active matrix formed from a simple matrix or thin film transistors (TFT) typically use a twisted nematic (TN) type or super twisted nematic (STN) type liquid crystal. Such conventional LCDs, thus, require at least one polarizer, that is, at least one polarized plate to control light flow. Unfortunately, the polarized plate in the conventional LCD intercepts more than 50% of the emitted light while controlling the polarized light. Accordingly, light efficiency in the displayed image is severely curtailed.
Therefore, in order to obtain a picture image having acceptable brightness, conventional LCD image display devices add a particularly bright background light source. Thus, in the case of a laptop wordprocessor or computer which uses a dry cell battery or an accumulative battery as a power supply, extended use is limited due to the excessive power consumption of the background light source.
Conventional image display devices having TN and STN type LCDs are generally characterized by a liquid crystal substance sandwiched between two glass plates. The distance between the two glass plates defines a cell gap which must be strictly and uniformly maintained (or adjusted) since it determines the "light-controlled" region within the LCD device. Due to current technological limitations in the manufacturing of the glass plate, the super-enlargement of a LCD display devices is very hard to achieve.
Therefore, it is necessary to remove the polarized plate in order to increase light efficiency, and to eliminate cell gap adjustment problem. Of course, LCDs which do not use a polarized plate have previously been proposed. Examples of such include the cholesteric nematic transition (CNT) type which uses a phase transition effect, and the dynamic scattering mode (DSM) type which was devised during early LCD development. The DSM type LCD device is no longer commonly used since it exhibits a slow response time and cannot be made thin.
Another example of an LCD not using a polarized plate to increase the light efficiency is the polymer-dispersed liquid crystal display (PDLCD). The PDLCD is made of a polymer material of which more than 50% (by volume) is light-transmitting. Given this property light scattering should be brought about efficiently in order to obtain a clear contrast ratio. There is a structural limitation to attaining this requirement in that the thickness of the liquid crystal layer must be at least 20 .mu.m.
U.S. patent application Ser. No. 08/058,712 as well as a related continuation-in part filed on Aug. 24, 1993 disclose an improved LCD having an electrical field effect type liquid crystal with a structure which remedies many of the problems in the conventional LCD.
The foregoing "improved" LCD has a fast driving speed and a high utilization efficiency of light. The improved LCD is characterized by a liquid crystal layer provided between the opposing electrodes and isolated by a plurality of insulation layers to form a multi-layer structure. In this arrangement, a polarized plate is not used. Rather, a single sheet, glass substrate is employed on which a functional layer for controlling light is accumulated. That is, as shown in FIG. 1, an electrical field effect type liquid crystal layer is provided between opposing electrodes 10 and 18. Insulation layers 22 separate this layer into a plurality of liquid crystal layers 22. The distance between liquid crystal layers 20 is maintained by columns 12. The mutual location of insulation layers 22 is fixed by columns 12 which are provided locally. Injection holes 14 used to inject liquid crystal are provided in insulation layers 22. Here, the thickness of each respective liquid crystal layer 20 partitioned from the overall liquid crystal layer is less than or equal to 3 .mu.m. The thickness of each insulation layer is preferably less than or equal to 5 .mu.m. Each insulation layer 22 can be made of an epoxy resin material, or a metal oxide, particularly an aluminum oxide.
The new method for manufacturing a liquid crystal display device set forth in the above noted U.S. patent applications is generally limited to the use of a water-soluble polyvinyl alcohol (PVA) as the material forming the dissolution layer which secures an evacuated portion ultimately filled with liquid crystal. Similarly, an epoxy resin is typically used as an insulation layer material. However, a metal such as aluminum can be used instead of the water-soluble PVA and a metal oxide can be used instead of the epoxy resin.
The manufacturing method proposed in the above U.S. patent application is set forth in greater detail below with reference to FIGS. 1 through 9.
In FIG. 5, lower electrodes 18 having a predetermined pattern are formed on a black plastic substrate 16 using a conductive material.
In FIG. 6, the respective layers of epoxy resin layer 20 and PVA layer 22a are alternately laminated a number of times over electrodes 18 of FIG. 5, by a spin coating or roll coating method. Then, an upper electrode 10 of indium tim oxide (ITO) is formed in a predetermined pattern on the uppermost epoxy layer 20.
In FIG. 7, a photo mask pattern is formed on upper electrode 10 of FIG. 6 yielding a photoresist 24.
In FIG. 8, the portion of the overall structure not covered by photoresist 24 is plasma-etched to form first inlet holes for columns 12. Then, the first inlet holes are filled with epoxy resin to form columns 12. At the same time, an epoxy resin layer 26 is formed over photoresist 24 and columns 12.
In FIG. 9, second inlet holes 14 for injecting liquid crystal are formed by photo mask patterning and plasma etching. Here, water is injected via inlet holes 14 to thereby dissolve and remove all PVA layers 22a located between epoxy resin layers 20. Accordingly, the dissolution layers connected to second inlet holes 14 are removed, thereby allowing the formation of the evacuated portion to be filled up with liquid crystal. At this time, the vertical separation between respective epoxy resin layers 20 is maintained by columns 12.
In FIG. 10, after the resultant structure is dried, liquid crystal is injected into the evacuated portion under vacuum through the second inlet holes 14, to form a partitioned liquid crystal layer, actually a plurality of liquid crystal layers 22 located between the epoxy resin layers 20. After the liquid crystal is completely filled, an epoxy resin is coated on the whole surface of the uppermost insulation layer to seal liquid crystal inlet holes 14. Shielding layer 11 is formed directly above each respective column 12 and inlet hole 14 which require light shielding. Accordingly, the reflective-type LCD shown in FIGS. 1 through 4 is accomplished.
In the above manufacturing method, the dissolution layer used to create, or secure, the evacuation region ultimately filled with liquid crystal is typically formed from water-soluble PVA. The insulation layers are typically formed from epoxy resin. However, the materials actually employed need not be limited to these particular examples. A metal such as aluminum can be used instead of the water-soluble PVA, and a metal oxide can be used instead of the epoxy resin.
However, the steps in the foregoing method used to form the are very complicated. Furthermore, other elements in the LCD device structure may be damaged during the etching process. For example, if the dissolution layer is made of a metal and the insulation layer is made of an organic resin, the insulation layer may become cracked due to the large difference between thermal expansion coefficients of the dissolution layer and the insulation layer. In such a case the lowermost insulation layer may become cracked by the heat applied during the manufacturing process. As a result, the first electrode made of indium tin oxide (ITO) may be exposed through the cracks in the lowermost insulation layer. If the ITO electrode is exposed in this manner, it comes into contact with the solvent used to dissolve the dissolution layer. Severe etching of ITO electrode by the solvent may result in an electrical disconnection. Furthermore, while the foregoing liquid crystal display device does have a shielding layer which absorbs external light on the surface of the uppermost portion of the structure, it does not have a separate means for protecting against light interference between internal pixels. As a result, deterioration in overall picture quality occurs due to the light interference between pixels.