Abstract:
A structure for encapsulating a liquid crystal display device is disclosed. Openings are formed in a second material layer on a first substrate, exposing an underlying first material layer. The openings are substantially distributed over the perimeter of the first substrate. A sealant is placed in the openings, forming a sealant region for attachment of a second substrate to the first substrate. The sealant region is substantially perpendicular to a direction of length of the openings. In addition, the sealant contacts the first material layer and the second material layer through the openings.

Description:
BACKGROUND  
       [0001]     The invention relates to a thin film transistor liquid crystal display (TFT LCD) device and in particular to a sealant region for encapsulating a liquid crystal display device.  
         [0002]     A TFT LCD device is driven by voltage to emit light, and may be transmissive, reflective, or transflective.  
         [0003]     A TFT LCD device suffers from degradation issues related to ambient environmental conditions such as moisture which may lead to performance loss, operational instability, poor color/emission accuracy, and shortened operational life. Specifically, water can cause crystallization and formation of organic solids, electrochemical reactions at the electrode-organic layer interface, corrosion of metals and migration of ionic species. To minimize such degradation, a TFT LCD device must be properly encapsulated to prevent moisture migration. Typical encapsulation methods utilize a color filter substrate covering the entire organic polymer areas with an adhesive sealant.  
         [0004]      FIG. 1A  is a top view of a sealant region of a conventional TFT LCD device.  
         [0005]     As shown in  FIG. 1A , a color filter substrate  10  is disposed over a TFT array substrate  2 . Openings  4  are formed within a sealant region  6  distributed over the perimeter of the TFT array substrate  2 . A sealant  14 , as shown in  FIG. 1C , encapsulates a TFT LCD device by contacting the color filter substrate  10  and TFT array substrate  2 . Air is exhausted through trenches  12  when the sealant  14  is placed in the openings  4 , preventing bubbles from forming in the sealant  14  or liquid crystal. In addition, openings  4  and trenches  12  are interconnected.  
         [0006]      FIG. 1B  is an enlarged view of the portion  8  of the sealant region shown in  FIG. 1A . The sealant width is marked by distance g confined by the two vertical dotted lines.  
         [0007]      FIG. 1C  is a cross-section of the TFT LCD device shown in  FIG. 1B  along the plane defined by the horizontal dotted line AA′.  
         [0008]     As shown in  FIG. 1C , the openings  4  expose portions of the surface of the passivation layer  20 , and the sealant  14  is placed in the openings  4 . To place the sealant  14  between the TFT array substrate  2  and color filter substrate  10 , the organic polymer layer  16  is selectively removed to form the openings  4 . When the sealant  14  is placed in the openings  4 , certain portions of the sealant  14  will rest on the neighboring and remaining organic polymer layer  16 .  
         [0009]     As shown in  FIG. 1C , a TFT LCD device comprises the TFT array substrate  2 , passivation layer  20 , organic polymer layer  16 , spacers  22  disposed over organic polymer layer  16 , sealant  14 , liquid crystal  18 , and color filter substrate  10 . Spacers  22  are disposed between the organic polymer layer  16  and color filter substrate  10  to maintain the cell gap.  
         [0010]     The thickness of the sealant between the organic polymer layer  16  and color filter substrate  10  is difficult to apply in a precise manner. Moreover, as shown in FIG.  1 C, the sealant must be evenly distributed on the organic polymer layer  16 ; otherwise defects such as mura will occur.  
         [0011]     The large volume and thickness of the applied sealant may also lead to peeling of the sealant from the substrates. Such peeling will result in the loss of encapsulation integrity.  
         [0012]     What is desirable is an improved method of encapsulating a TFT LCD device.  
       SUMMARY  
       [0013]     An embodiment of a sealant region for encapsulating a liquid crystal display device is disclosed. Parallel openings are formed in a second material layer on a first substrate, exposing an underlying first material layer. The parallel openings are substantially distributed over the perimeter of the first substrate. A sealant is placed in the openings, forming a sealant region for attaching a second substrate to the first substrate. The sealant region is substantially perpendicular to a direction of length of the openings. In addition, the sealant contacts the first material layer and the second material layer through the openings.  
         [0014]     Another embodiment of a sealant region for encapsulating a liquid crystal display device is also disclosed. A sealant region comprising at least one opening having a tab-and-groove pattern is formed by removing portions of a second material layer from a first substrate, exposing an underlying first material layer. A sealant is placed in openings for attachment of a second substrate to the first substrate. Additionally, the sealant in openings is balanced along a central axis of the sealant region.  
         [0015]     The invention is less prone to the reliability and integrity issues encountered in the conventional devices. Irregular vertical gaps are avoided, reducing formation of voids in the sealant regions.  
         [0016]     The invention also leads to higher throughput, higher integrity, and longer operation life of the disclosed devices.  
         [0017]     Problems encountered in conventional devices are reduced by the invention for forming the sealant region. The invention features the use of narrow gap between the organic polymer areas, thereby enhancing adhesion between the color filter substrate and TFT array substrate.  
         [0018]     The invention is easily implemented into existing fabrication operations and processes with minimal impact on additional costs and required processes. With such improvements, a facility will maintain highly competitive cost and throughput advantages over other manufacturers of similar products.  
         [0019]     A detailed description is given in the following embodiments with reference to the accompanying drawings. 
     
    
     DESCRIPTION OF THE DRAWINGS  
       [0020]     The invention can be more fully understood by reading the subsequent detailed description and examples with reference made to the accompanying drawings, wherein:  
         [0021]      FIG. 1A  is a top view of a sealant region of a conventional TFT LCD device;  
         [0022]      FIG. 1B  is an enlarged view of the portion of the sealant region shown in  FIG. 1A ;  
         [0023]      FIG. 1C  is a cross-section of the TFT LCD device shown in  FIG. 1B  along the plane defined by the horizontal dotted line AA′;  
         [0024]      FIG. 2A  is a top view of a sealant region of a TFT LCD device according to an embodiment of the invention;  
         [0025]      FIG. 2B  is an enlarged view of the portion of the sealant region shown in  FIG. 2A .  
         [0026]      FIG. 2C  is a cross-section of the TFT LCD device shown in  FIG. 2B  along the plane defined by the horizontal dotted line BB′.  
         [0027]      FIG. 3A  is a top view of a sealant region of a TFT LCD device according to an embodiment of the invention.  
         [0028]      FIG. 3B  is an enlarged view of the portion of the sealant region shown in  FIG. 3A .  
         [0029]      FIGS. 4 and 5  are top views of TFT LCD devices with other types of sealant region according to other embodiments of the invention. 
     
    
     DETAILED DESCRIPTION  
       [0030]     An embodiment of a sealant region for encapsulating a liquid crystal display device is described in greater detail in the following.  
         [0031]      FIG. 2A  is a top view of a sealant region of a TFT LCD device according to an embodiment of the invention. The number or size of any component shown in  FIG. 2A  is specified for purposes of illustration, without intending to limit the disclosure.  
         [0032]     As shown in  FIG. 2A , a color filter substrate  210  is disposed over a TFT array substrate  222 . Roughly parallel openings  26  are formed within a sealant region  24  distributed over the perimeter of the TFT array substrate  222 . A sealant  224 , shown in  FIG. 2C , encapsulates a TFT LCD device by contacting the color filter substrate  210  and TFT array substrate  222 . Two openings  26   a , formed in the corner regions at an angle of about 45 degrees deviating from the perimeter of the TFT array substrate  222 , balance distribution of the sealant.  
         [0033]      FIG. 2B  is an enlarged view of the portion  28  of the sealant region shown in  FIG. 2A .  
         [0034]     As shown in  FIG. 2B , the sealant region  24 , extending in a direction y, is substantially perpendicular to a direction x of length of the openings  26 . The sealant width is marked by distance k confined by the two vertical dotted lines. The width, marked as w 1  or w 2  in  FIG. 2A , of any opening is less than the sealant width k. The openings  26  may have a roughly uniform width. In other embodiments, the openings  26  may have different widths (not shown).  
         [0035]      FIG. 2C  is a cross-section of the TFT LCD device shown in  FIG. 2B  along the plane defined by the horizontal dotted line BB′.  
         [0036]     As shown in  FIG. 2C , a TFT LCD device comprises TFT array substrate  222 , passivation layer  220 , organic polymer layer  214 , spacers  226  disposed over organic polymer layer  214 , sealant  224 , liquid crystal  216 , or color filter substrate  210 . Spacers  226  are disposed between the organic polymer layer  214  and color filter substrate  210  to maintain the cell gap.  
         [0037]     The openings  26  expose portions of the surface of the passivation layer  220 , and the sealant  224  is placed in the openings  26  to contact the passivation layer  220 . The passivation layer  220  may be a dielectric material layer. To place the sealant  224  between the TFT array substrate  222  and color filter substrate  210 , the organic polymer layer  214  is selectively removed to form the openings  26 .  
         [0038]     With the openings  26  perpendicular to the sealant region  24 , the sealant  224  sufficiently contacts the passivation layer  220 . Also, the sealant  224  has substantially flat contact surfaces with the organic polymer layer  214  or TFT array substrate  222 . Accordingly, problems such as uneven cell gap or peeling are reduced.  
         [0039]      FIG. 3A  is a top view of a sealant region of a TFT LCD device according to an embodiment of the invention.  
         [0040]     As shown in  FIG. 3A , a color filter substrate  340  is disposed over a TFT array substrate  332 . Openings  334  are formed within a sealant region  336  distributed over the perimeter of the TFT array substrate  332 . A sealant encapsulates the TFT LCD device by contacting the color filter substrate  340  and TFT array substrate  332 .  
         [0041]      FIG. 3B  is an enlarged view of the portion of the sealant region shown in  FIG. 3A .  
         [0042]     As shown in  FIG. 3B , the openings  334  may be formed of small segments with the surface feature such as tabs and grooves. The openings  334  may have a roughly uniform width. In other embodiments, the openings  334  may have different widths (not shown). To avoid uneven cell gap, the width marked as w 3  or w 4  of any opening  334  is less than the sealant width m. Moreover, with the openings  334 , the sealant can be evenly distributed on both sides of a central axis S of the sealant region. The openings  334  are continuous small segments, as shown in  FIGS. 3A and 3B . In other embodiments, openings  334  may be not continuous small segments (not shown).  
         [0043]      FIGS. 4 and 5  are top views of TFT LCD devices with other types of sealant region according to other embodiments of the invention.  
         [0044]     As shown in  FIG. 4 , a color filter substrate  440  is disposed over a TFT array substrate  432 . Openings  434  are formed within a sealant region  436  distributed over the perimeter of the TFT array substrate  432 . A sealant encapsulates the TFT LCD device by contacting the color filter substrate  440  and TFT array substrate  432 .  
         [0045]     As shown in  FIG. 5 , a color filter substrate  540  is disposed over a TFT array substrate  532 . Openings  534  are formed within a sealant region  536  distributed over the perimeter of the TFT array substrate  532 . A sealant encapsulates the TFT LCD device by contacting the color filter substrate  540  and TFT array substrate  532 .  
         [0046]     Although these described embodiments illustrate various patterns of the openings, such as the parallel openings in  FIG. 2A , the small segments with the surface feature such as tabs and grooves in  FIG. 3A , the modified small segments with the surface feature such as tabs and grooves in  FIG. 4 , and the modified curved small segments with the surface feature such as tabs and grooves in  FIG. 5 , they share a common feature of the sealant, placed in these openings, being substantially evenly distributed on both sides of the central axis of the sealant region. In addition, the width of these openings is much smaller than the total width of the sealant region.  
         [0047]     The modified curve saw tooth shape in  FIG. 5  avoids sharp angle formed by any two openings. In  FIG. 2A , the two openings  26   a  formed in the corner region also balance distribution of the sealant. As shown, some patterns may be asymmetric in a particular local area such as the saw tooth pattern in  FIG. 5 , but the sealant is balanced substantially along the central axis of either the horizontal or vertical sealant region. The balanced distribution of the sealant in the sealant region reduces problems caused by uneven cell gap, thereby avoiding around gap mura problem.  
         [0048]     While the invention has been described by way of example and in terms of preferred embodiment, it is to be understood that the invention is not limited thereto. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation to encompass all such modifications and similar arrangements.