Patent Document

CROSS-REFERENCE TO RELATED APPLICATION 
     This patent application is based on Japanese Priority Patent Application No. 2004-153923 filed on May 24, 2004, the entire contents of which are hereby incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention generally relates to a liquid crystal display device, and particularly, to a liquid crystal display device operating in a vertical (homeotropic) alignment mode. 
     2. Description of the Related Art 
     Because a liquid crystal display device has low power consumption and can be made compact, it is widely used in various portable information processing devices, such as a laptop computer, or a cellular phone. On the other hand, so far, performance of the liquid crystal display device has been improved significantly, and the latest liquid crystal display devices have such high response speed and contrast ratio that they can be used in a desktop computer or a workstation to replace conventional CRT (Cathode Ray Tube) display. 
     In the related art, usually, a TN (Twisted Nematic) type liquid crystal operating in a normally-white mode is used in practical liquid crystal display devices. In such a TN mode liquid crystal display device, the direction of alignment of the liquid crystal molecules in the plane of a liquid crystal layer changes in response to a driving voltage signal applied on the liquid crystal layer, and by controlling changes of the direction of alignment of the liquid crystal molecules, the transmission light is switched on or switched off. 
     This TN mode liquid crystal display device, however, is limited in a contrast ratio. This limitation can be attributed to the operation principle of the TN mode liquid crystal display device. In addition, it is difficult for the TN mode liquid crystal display device to provide a wide viewing angle, which is required by, for example, a desktop display. 
     Inventors of the present inventions have proposed a so-called vertical-alignment liquid crystal display device, that is, a liquid crystal display device in which the liquid crystal molecules are aligned along a direction substantially perpendicular to the liquid crystal layer when a driving voltage signal is not applied (that is, an un-driven state). 
       FIG. 1A  and  FIG. 1B  are schematic perspective views illustrating operation principle of the vertical-alignment liquid crystal display device  10  (also referred to as a MVA (multi-domain vertical alignment) liquid crystal display device), proposed by the inventors of the present invention. Specifically,  FIG. 1A  shows the liquid crystal display device  10  in the un-driven state, that is, the driving voltage is not applied to the liquid crystal display device  10 , and  FIG. 1B  shows the liquid crystal display device  10  in a driven state, that is, the driving voltage is applied to the liquid crystal display device  10 . 
     As illustrated in  FIG. 1A , a liquid crystal layer  12  is interposed between a glass substrate  11 A and a glass substrate  11 B. The glass substrates  11 A,  11 B, and the liquid crystal layer  12  constitute a liquid crystal panel. 
     Although not illustrated, molecule alignment films are arranged on the glass substrate  11 A and glass substrate  11 B, respectively. Because of the molecule alignment films, the liquid crystal molecules in the liquid crystal layer  12  are aligned along a direction substantially perpendicular to the liquid crystal layer  12  when the driving voltage signal is not applied (that is, the un-driven state). In this state, a polarization plane of a light beam incident to the liquid crystal device essentially does not rotate in the liquid crystal layer  12 . Therefore, in the un-driven state shown in  FIG. 1A , if a polarizer and an analyzer are arranged above and below the liquid crystal panel in a crossed-Nicol configuration, the light beam passing through the polarizer and incident on the liquid crystal layer  12  is blocked by the analyzer. 
     On the other hand, in the driven state shown in  FIG. 1B , the liquid crystal molecules are tilted due to the applied electrical field, and the polarization plane of the light beam incident to the liquid crystal layer  12  rotates in the liquid crystal layer  12 . Thus, the light beam passing through the polarizer and incident on the liquid crystal layer  12  is allowed to pass through the analyzer. 
     In the liquid crystal display device  10 , during a transition from the un-driven state to the driven state, in order to regulate the tilting direction of the liquid crystal molecules so as to improve the response speed of the liquid crystal panel, projecting patterns  13 A,  13 B are arranged in parallel to each other on the glass substrate  11 A and the glass substrate  11 B. By providing the projecting patterns  13 A,  13 B, the response speed of the liquid crystal device  10  is increased, at the same time, different domains involve different tilting directions of the liquid crystal molecules in the liquid crystal layer, as a result, the viewing angle of the liquid crystal device  10  is widened. 
       FIG. 2A  and  FIG. 2B  are schematic views illustrating operation principle of a vertical alignment liquid crystal display device  20  of the related art, which is proposed by the inventors of the present invention. 
     In Japanese Laid Open Patent Application No. 2002-107730, the inventors of the present invention proposed a vertical alignment liquid crystal display device  20 , as illustrated in  FIG. 2A  and  FIG. 2B , in which stripe patterns  24  are arranged in parallel to each other, and the stripe patterns  24  form a periodically varying electrical field in the liquid crystal layer  22 , and due to the electrical field, liquid crystal molecules  22 A are pre-tilted along the direction in which the stripe patterns  24  extend. 
     In addition, in Japanese Laid Open Patent Application No. 2002-107730, the inventors of the present invention also proposed a vertical alignment liquid crystal display device  40 , which corresponds to a combination of the above vertical alignment liquid crystal display device  10  and the vertical alignment liquid crystal display device  20 . 
     As illustrated in  FIG. 2A , basically, the liquid crystal display device  20  includes a glass substrate  21 A and a glass substrate  21 B with a liquid crystal layer  22  being interposed in between. Electrode layers  23 A and  23 B are provided on the glass substrates  21 A and  21 B, respectively. 
     In addition, fine structure patterns  24  are provided on the surface of the electrode layer  23 A to modify the pattern of the electrical field generated between the electrode layers  23 A and  23 B. On the glass substrate  21 A, a molecule alignment film  25 MA is formed on the surface of the electrode layer  23 A to cover the fine structure patterns  24 . On the glass substrate  21 B, a molecule alignment film  25 MB is formed to cover the electrode layer  23 B. 
     The molecule alignment films  25 MA,  25 MB are in contact with the liquid crystal layer  22 , and the liquid crystal molecules  22 A in the liquid crystal layer  22  are aligned along a direction substantially perpendicular to the liquid crystal layer  22  when the electrical field is not applied between the electrode layer  23 A and the electrode layer  23 B (that is, the un-driven state). 
     A polarization film  26 A, which has a first optical absorption axis and acts as a polarizer, is provided on a lower main surface of the glass substrate  21 A, while a polarization film  26 B, which has a second optical absorption axis perpendicular to the first optical absorption axis and acts as another polarizer, is provided on an upper main surface of the glass substrate  21 B. 
     In the example illustrated in  FIG. 2A , the fine structure patterns  24  are conductive or insulating fine projecting patterns arranged in parallel to each other on the electrode layer  23 A, but the fine structure patterns  24  may also have other configurations as long as it is able to locally modify the electrical field in the liquid crystal layer  22 . 
       FIG. 3  is a schematic view illustrating operation principle of another example of the vertical alignment liquid crystal display device  20  of the related art. 
     As illustrated in  FIG. 3 , the fine structure patterns  24  may also be fine depressed patterns such as plural cutouts in parallel to each other in the electrode layer  23 A. In  FIG. 3 , the same reference numbers are used for the same elements as in  FIG. 2A  and  FIG. 2B , and overlapping descriptions are omitted. 
     If the fine structure patterns  24  include projecting patterns on the electrode layer  23 A, as illustrated in  FIG. 2A , preferably, the fine structure patterns  24  are formed from a transparent material so that a light beam incident into the liquid crystal display device can pass through the fine structure patterns  24 . 
     Return to  FIG. 2B ,  FIG. 2B  shows the driven state of the liquid crystal display device  20 , that is, the driving voltage is applied between the electrode layers  23 A and  23 B to change the direction of alignment of the liquid crystal molecules  22 A on the glass substrate  21 A. 
     As illustrated in  FIG. 2B , in the driven state of the liquid crystal display device  20 , because of the effect of the electrical field locally modified by the fine structure patterns  24 , the liquid crystal molecules  22 A are aligned to be tilted toward the extending directions of the fine structure patterns  24 . 
     In the liquid crystal display device  20 , when the driving voltage is applied between the electrode layers  23 A and  23 B, and the driving electrical field is formed in the liquid crystal molecule layer  22 , because each liquid crystal molecule  22 A is tilted toward the extending directions of the fine structure patterns  24  in response to the electrical field modified by the fine structure patterns  24 , the response speed of the liquid crystal display device  20  is greatly improved compared with the liquid crystal display device  10  shown in  FIG. 1A  and  FIG. 1B , because in the liquid crystal display device  10  shown in  FIG. 1A  and  FIG. 1B , the tilt of the liquid crystal molecules has to propagate from regions near the projecting patterns  13 A,  13 B to other regions, but in the liquid crystal display device  20  in  FIG. 2B , this is not necessary. 
     In addition to the above advantages, from  FIG. 2B , it is found that in the liquid crystal display device  20 , the alignment directions of the liquid crystal molecules  22 A are essentially restricted to the extending directions of the fine structure patterns  24  in the driving state, therefore, the twisted angle of each liquid crystal molecule  22 A does not change even when interactions between the tilted liquid crystal molecules  22 A are present, and this results in display of high contrast ratio and high quality. 
     When the driving voltage is applied between the electrode layers  23 A and  23 B, the fine structure patterns  24  form electrical field in the liquid crystal layer  22 , which is uniform in a first direction along the extending directions of the fine structure patterns  24 , and varies periodically in a second direction perpendicular to the first direction. 
       FIG. 4  is a plan view of the substrate  21 A in  FIG. 3 , illustrating an example of a configuration of a liquid crystal display device of the related art. In  FIG. 4 , the same reference numbers are used for the same elements as those shown in  FIG. 3 . 
     As illustrated in  FIG. 4 , on the substrate  21 A, a thin film transistor (TFT)  21 T is formed at the cross point between a scanning electrode  22 S and a data electrode  22 D which are formed below the pixel electrode  23 A, and the pixel electrode  23 A is connected with the TFT  21 T. The substrate  21 A is also referred to as a TFT substrate. 
     On the pixel electrode  23 A, the fine structure patterns  24  are patterned to be in parallel at intervals  24 G. On the pixel electrode  23 A, large gaps  25 A, which corresponds to the structure  13 A in  FIG. 1A  and  FIG. 1B , are patterned in a zigzag manner. Due to this, a pixel region in  FIG. 4  is divided into an upper domain region and a lower domain region, and the tilting directions of the crystal liquid molecules in the upper domain region and the lower domain region are perpendicular to each other. 
     In  FIG. 4 , resist film structures  25 B are formed in a zigzag manner on the substrate  21 B facing the substrate  21 A. The structures  25 B are in correspondence to the projecting structure  13 B in  FIG. 1A  and  FIG. 1B . 
     In the configuration shown in  FIG. 4 , because of the fine structure patterns  24  and the gaps  24 G between the stripe patterns  24 , the tilting directions of the liquid crystal molecules are essentially regulated to be along the extending directions of the gaps  24 G. Further, the pre-tilt angles are defined by the structures  25 A and  25 B. Hence, this configuration exhibits a high response speed. 
     In the configuration shown in  FIG. 4 , between the upper domain region and the lower domain region, auxiliary capacitance Cs is produced by the electrode pattern  23 C. 
     Listed below are references which disclose techniques related to the present invention: 
     Japanese Laid-Open Patent Application No. 2002-107730, 
     Japanese Laid-Open Patent Application No. 2002-287158, 
     Japanese Laid-Open Patent Application No. 2000-305086, and 
     Japanese Patent Gazette No. 3456896. 
       FIG. 5  is a plan view of another example of the TFT substrate  21 A of a liquid crystal display device of the related art, having the configuration shown in  FIG. 4 . In  FIG. 5 , the same reference numbers are used for the same elements as those shown in  FIG. 3  and  FIG. 4 . 
     As illustrated in  FIG. 5 , plural configurations as shown in  FIG. 4  are arranged in correspondence to red (R), green (G), and blue (B) colors, respectively, and on the TFT substrate  21 B facing the TFT substrate  21 A, a color filter is arranged in correspondence to the configuration on the TFT substrate  21 A as shown in  FIG. 5 . 
     The structures  25 B, one of which is indicated by “BB” in  FIG. 5 , are arranged to pass through corners of the pixel electrodes  23 A on which the fine structure patterns  24  are formed. The structures  25 A, that is, the cutouts formed in the pixel electrodes  23 A, as indicated by “AA” in  FIG. 5 , bend at edges of the pixel electrodes  23 A. 
       FIG. 6A  and  FIG. 6B  are diagrams illustrating relation between the structures  25 A,  25 B and alignment of the liquid crystal molecules  22 A in the liquid crystal display device shown in  FIG. 5 , especially, the liquid crystal molecules  22 A at an edge of the pixel electrode  23 A. 
     The structure  25 A and  25 B have the function of inducing pre-tilt of the liquid crystal molecules  22 A, as described above. However, at the edge of the pixel electrode  23 A, because of interaction between the effect of the edge of the pixel electrode  23 A and the effect of the structure  25 A and  25 B, alignment of the liquid crystal molecules  22 A is disordered. 
     Nevertheless, when the bending point of the structure  25 A is at the edge of the pixel electrode  23 A, as shown in  FIG. 6A , or when the structure  25 B passes through the corner of the pixel electrode  23 A, as shown in  FIG. 6B , the effect of the structure  25 A or  25 B of constraining alignment of the liquid crystal molecules  22 A is substantially in agreement with the effect of the edge of the pixel electrode  23 A of constraining alignment of the liquid crystal molecules  22 A, and in such regions, that is, near the edge or corner of the pixel electrode  23 A, alignment of the liquid crystal molecules  22 A is not disordered. 
       FIG. 7A  and  FIG. 7B , continuing from  FIGS. 6A and 6B , are diagrams illustrating relation between the structure  25 A,  25 B and alignment of the liquid crystal molecules  22 A in the liquid crystal display device shown in  FIG. 5 , especially, the liquid crystal molecules  22 A at an edge of the pixel electrode  23 A. 
     When the bending point of the structure  25 A is not at the edge of the pixel electrode  23 A, as shown in  FIG. 7A , or when the structure  25 B does not pass through the corner of the pixel electrode  23 A, as shown in  FIG. 7B , the effect of the structure  25 A or  25 B of constraining alignment of the liquid crystal molecules  22 A is not in agreement with the effect of the edge of the pixel electrode  23 A of constraining alignment of the liquid crystal molecules  22 A, and as a result, alignment of the liquid crystal molecules  22 A is greatly disordered, and this results in a black spot as shown in  FIG. 7A  and  FIG. 7B . 
     In this way, it is ideal if the arrangement shown in  FIG. 6A  and  FIG. 6B  is formed. In practice, however, pitches of the structures  25 A and  25 B are defined according to the response speed and transmission of the liquid crystal display device, and it is difficult to realize the ideal arrangement of the structures  25 A and  25 B in a practical liquid crystal display device. 
     In a liquid crystal display device of the related art, spacers, such as silica beads having specified diameters are used in order to maintain the thickness of the liquid crystal layer, that is, the thickness of the liquid crystal cell, to be a preset value. 
     On the other hand, recently, a structure of a liquid crystal panel is proposed which does not involve a step of distributing such spacers can be omitted when being fabricated, and this eliminates the problem of non-uniform display caused by non-uniform distribution density of the spacers. 
     For example, Japanese Laid Open Patent Application No. 11-242211 discloses a columnar spacer extending between a first substrate and a second substrate. Such a columnar spacer may be formed by first depositing a resist film or a polyimide film on either the first substrate or the second substrate, and then patterning the resist film or the polyimide film to a predetermined thickness, thereby, obtaining the columnar spacer of a desired shape at a desired position. 
     Similar to the projecting patterns  13 A,  13 B in  FIG. 1A  and  FIG. 1B , such a spacer formed from an organic film has the function of constraining the alignment of the liquid crystal molecules in the liquid crystal layer. Because of the alignment constraining function of such a columnar spacer, a multi-domain structure is proposed in, for example, Japanese Laid Open Patent Application No. 2002-287158, in which the above columnar spacer is arranged at the center of a pixel electrode, and each pixel is divided into multiple sector-shaped domains with the columnar spacer as a center. 
     On the other hand, because the liquid crystal layer cannot be distributed in a region where the columnar spacer is arranged, such a region cannot be used for display. Hence, it is preferable that the columnar spacer be arranged not in the pixel region. For example, in the above mentioned Japanese Laid Open Patent Application No. 11-242211, plural columnar spacers are arranged symmetrically around a pixel region, and a symmetric domain structure as desired is formed in the pixel region. 
     When the columnar spacer is arranged in a liquid crystal display device having TFT substrates as illustrated in  FIG. 4  or  FIG. 5 , because the columnar spacer has the function of constraining the alignment of the liquid crystal molecules, the same problems as explained with reference to  FIG. 7A  and  FIG. 7B  may occur. 
       FIG. 8  is a plan view illustrating an example of a configuration of a liquid crystal display device  30 A of the related art, which is obtained by providing a columnar spacer P in the liquid crystal display device  30  having the TFT substrate  21 A. In  FIG. 8 , the same reference numbers are used for the same elements as those shown in  FIG. 4 . 
     As illustrated in  FIG. 8 , the columnar spacer P is formed on an electrode pattern  23 C across a center portion of the pixel electrode  21 A corresponding to the structure  25 A, in other words, the columnar spacer P is formed out of the visible region of the liquid crystal display device  30 A. However, as illustrated in  FIG. 8 , while it is desired that the direction of alignment of the liquid crystal molecules  22 A be parallel to the extending direction of the fine structure  24 , because of presence of the columnar spacer P, in practice, the alignment direction of the liquid crystal molecules  22 A near the spacer P turns out to be roughly perpendicular to the extending direction of the stripe patterns of the fine structure  24 . 
     In this situation, even though the columnar spacer P is formed out of the visible region of the liquid crystal display device  30 A, it causes a dark portion on a display region and can be recognized by viewers. Furthermore, in the structure shown in  FIG. 8 , the columnar spacer P causes an additional disorder of the alignment of the liquid crystal molecules  22 A besides the disorder of the alignment of the liquid crystal molecules  22 A as explained in  FIG. 7A  and  FIG. 7B . 
     SUMMARY OF THE INVENTION 
     It is a general object of the present invention to solve one or more of the problems of the related art. 
     It is a more specific object of the present invention to provide a liquid crystal display device capable of suppressing disorder of alignment of liquid crystal molecules caused by a spacer arranged between two substrates. 
     According to a first aspect of the present invention, there is provided a liquid crystal display device, comprising a first substrate; a second substrate facing the first substrate; a liquid crystal layer formed from liquid crystal molecules and held between the first substrate and the second substrate, said liquid crystal molecules being aligned to be substantially perpendicular to the first substrate and the second substrate in an un-driven state, and being aligned to be along a first direction in a plane substantially parallel to the first substrate and the second substrate in a driven state, said un-driven state corresponding to a state in which a driving electrical field is not applied on the liquid crystal layer, said driven state corresponding to a state in which the driving electrical field is applied on the liquid crystal layer; a plurality of pixel regions formed in the liquid crystal layer; a patterned structure that is provided on at least one of the first substrate and the second substrate, extends along a second direction perpendicular to the first direction, and is capable of aligning the liquid crystal molecules to be along the first direction in the driven state, said patterned structure including at least one of a first alignment control pattern formed on the first substrate and extending along the second direction and a second alignment control pattern formed on the second substrate and extending along the second direction; and a spacer that is arranged between the first substrate and the second substrate to maintain a gap between the first substrate and the second substrate to be a constant, said spacer being arranged to cover at least a portion of one of the pixel regions, said spacer being capable of aligning the liquid crystal molecules near the spacer to be substantially along the first direction. 
     According to the present invention, in a vertical alignment mode liquid crystal display device wherein liquid crystal molecules are aligned to be along the first direction due to the first alignment control pattern and the second alignment control pattern formed on the first substrate and the second substrate, respectively, because the spacer arranged between the first substrate and the second substrate is capable of aligning the liquid crystal molecules near the spacer to be substantially along the first direction, disorder of alignment of the liquid crystal molecules near the spacer is suppressed, further, even when the layout of the first alignment control pattern and the second alignment control pattern is not ideal, it is possible to reduce disorder of alignment of the liquid crystal molecules and improve transmittance of the liquid crystal display device. 
     According to a second aspect of the present invention, there is provided a liquid crystal display device, comprising a first substrate; a second substrate facing the first substrate; a liquid crystal layer formed from liquid crystal molecules and held between the first substrate and the second substrate, said liquid crystal molecules being aligned to be substantially perpendicular to the first substrate and the second substrate in an un-driven state, and being aligned to be along a first direction in a plane substantially parallel to the first substrate and the second substrate in a driven state, said un-driven state corresponding to a state in which a driving electrical field is not applied on the liquid crystal layer, said driven state corresponding to a state in which the driving electrical field is applied on the liquid crystal layer; a plurality of pixel regions formed in the liquid crystal layer; a patterned structure that is provided on at least one of the first substrate and the second substrate, extends along a second direction perpendicular to the first direction, and is capable of aligning the liquid crystal molecules to be along the first direction in the driven state, said patterned structure including at least one of a first alignment control pattern formed on the first substrate and extending along the second direction and a second alignment control pattern formed on the second substrate and extending along the second direction; and a spacer that is arranged between the first substrate and the second substrate to maintain a gap between the first substrate and the second substrate to be a constant, said spacer being arranged to cover at least a portion of one of the pixel regions, said spacer being enclosed on three sides by the second alignment control pattern. 
     According to the present invention, in a vertical alignment mode liquid crystal display device wherein liquid crystal molecules are aligned to be along the first direction due to the first alignment control pattern and the second alignment control pattern formed on the first substrate and the second substrate, respectively, because the spacer arranged between the first substrate and the second substrate is enclosed on three sides by the second alignment control pattern, capability of the second alignment control pattern of controlling alignment of the liquid crystal molecules is improved near the spacer, and this helps suppress disorder of alignment of the liquid crystal molecules caused by the spacer. 
     According to a third aspect of the present invention, there is provided a liquid crystal display device, comprising a first substrate; a second substrate facing the first substrate; a liquid crystal layer formed from liquid crystal molecules and held between the first substrate and the second substrate, said liquid crystal molecules being aligned to be substantially perpendicular to the first substrate and the second substrate in an un-driven state, and being aligned to be along a first direction in a plane substantially parallel to the first substrate and the second substrate in a driven state, said un-driven state corresponding to a state in which a driving electrical field is not applied on the liquid crystal layer, said driven state corresponding to a state in which the driving electrical field is applied on the liquid crystal layer; a plurality of pixel regions formed in the liquid crystal layer; a patterned structure that is provided on at least one of the first substrate and the second substrate, extends along a second direction perpendicular to the first direction, and is capable of aligning the liquid crystal molecules to be along the first direction in the driven state, said patterned structure including at least one of a first alignment control pattern formed on the first substrate and extending along the second direction and a second alignment control pattern formed on the second substrate and extending along the second direction; and a spacer that is arranged between the first substrate and the second substrate to maintain a gap between the first substrate and the second substrate to be a constant, said spacer being arranged to cover at least a portion of one of the pixel regions, said spacer being arranged out of the pixel regions and being separated by a distance such that the spacer does not change alignment of the liquid crystal molecules in the pixel regions. 
     According to the present invention, in a vertical alignment mode liquid crystal display device wherein liquid crystal molecules are aligned to be along the first direction due to the first alignment control pattern and the second alignment control pattern formed on the first substrate and the second substrate, respectively, because the spacer is arranged out of the pixel regions and separated by a distance so that the spacer does not change alignment of the liquid crystal molecules in the pixel regions, disorder of alignment of the liquid crystal molecules caused by the spacer is suppressed. 
     These and other objects, features, and advantages of the present invention will become more apparent from the following detailed description of the preferred embodiments given with reference to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  and  FIG. 1B  are schematic perspective views illustrating operation principle of an example of a vertical-alignment liquid crystal display device of the related art; 
         FIG. 2A  and  FIG. 2B  are schematic views illustrating operation principle of another example of a vertical alignment liquid crystal display device of the related art; 
         FIG. 3  is a schematic view illustrating operation principle of still another example of a vertical alignment liquid crystal display device of the related art; 
         FIG. 4  is a plan view of an example of a TFT substrate in a liquid crystal display device of the related art; 
         FIG. 5  is a plan view of another example of the TFT substrate in a liquid crystal display device of the related art; 
         FIG. 6A  and  FIG. 6B  are diagrams illustrating relation between the TFT structures and alignment of liquid crystal molecules in the liquid crystal display device; 
         FIG. 7A  and  FIG. 7B , continuing from  FIGS. 6A and 6B , are diagrams illustrating relation between the TFT structure and alignment of the liquid crystal molecules in the liquid crystal display device; 
         FIG. 8  is a plan view illustrating an example of a configuration of a liquid crystal display device of the related art, which is obtained by providing a columnar spacer P in the liquid crystal display device having the TFT substrate shown in  FIG. 4 ; 
         FIG. 9  is a schematic perspective view illustrating an example of a configuration of a liquid crystal display device  40  according to a first embodiment of the present invention; 
         FIG. 10A  is an enlarged view of a portion of the liquid crystal display device  40  in  FIG. 9 ; 
         FIG. 10B  is an enlarged cross-sectional view of a portion of the liquid crystal display device  40  in  FIG. 9 ; 
         FIG. 11  is a plan view illustrating a structure of the pixel electrode  34  of the liquid crystal display device  40  according to the first embodiment of the present invention; 
         FIG. 12  is a plan view illustrating a configuration of a liquid crystal display device  50  according to a second embodiment of the present invention; 
         FIG. 13  is a plan view illustrating a configuration of a liquid crystal display device  60  according to a third embodiment of the present invention; 
         FIG. 14  is a plan view illustrating a configuration of a liquid crystal display device  60  according to a fourth embodiment of the present invention; 
         FIG. 15  is a plan view illustrating a configuration of a liquid crystal display device  80  according to a fifth embodiment of the present invention; 
         FIG. 16  is a plan view illustrating a configuration of a liquid crystal display device  90  according to a sixth embodiment of the present invention; 
         FIG. 17  is a plan view illustrating a configuration of a liquid crystal display device  100  according to a seventh embodiment of the present invention; and 
         FIGS. 18A through 18C  are a plan view and cross-sectional views illustrating a configuration of a liquid crystal display device  110  according to an eighth embodiment of the present invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Below, preferred embodiments of the present invention are explained with reference to the accompanying drawings. 
     First Embodiment 
       FIG. 9  is a schematic perspective view illustrating an example of a configuration of a liquid crystal display device  40  according to a first embodiment of the present invention. 
       FIG. 10A  is an enlarged view of a portion of the liquid crystal display device  40  in  FIG. 9 . 
       FIG. 10B  is an enlarged cross-sectional view of a portion of the liquid crystal display device  40  in  FIG. 9 . 
     As illustrated in  FIG. 9 , the liquid crystal display device  40  is an active-matrix liquid crystal display device, including a TFT glass substrate  31 A and a TFT glass substrate  31 B facing the TFT glass substrate  31 A. The TFT glass substrate  31 A carries plural thin film transistors (TFT) and a transparent pixel electrode cooperative with the TFTs, which corresponds to the electrode layer  23 A as illustrated in  FIG. 3  and  FIG. 4 . The TFT glass substrate  31 B carries an electrode formed on the TFT glass substrate  31 A, which corresponds to the electrode layer  23 B. A liquid crystal layer  31  interposed between the substrate  31 A and the substrate  31 B is sealed by a sealing member  31 C. 
     In the liquid crystal display device  40  illustrated in  FIG. 9 ,  FIG. 10A  and  FIG. 10B , by selectively driving the transparent pixel electrode through a corresponding TFT, in a portion of the liquid crystal layer  31  corresponding to the selected pixel electrode, alignment of the liquid crystal molecules is selectively changed. A polarizer  31   a  and an analyzer  31   b  are arranged outside the glass substrate  31 A and the glass substrate  31 B in a crossed-Nicol configuration. Although not illustrated, molecule alignment films are arranged on respective inner sides of the glass substrate  31 A and the glass substrate  31 B in contact with the liquid crystal layer  31 . These molecule alignment films correspond to the molecule alignment films  25 MA and  25 MB in  FIG. 4 , and have functions of restricting the direction of alignment of the liquid crystal molecules in the liquid crystal layer  31  to be substantially perpendicular to the plane containing the liquid crystal layer  31  when an electrical field is not applied between the electrode layer  23 A and the electrode layer  23 B (that is, an un-driven state). 
     As illustrated in  FIG. 10A , in the liquid crystal display device  40 , there are arranged plural pad electrodes  33 A which supply scanning signals to the glass substrate  31 A, plural scanning electrodes  33  arranged subsequent to the pad electrodes  33 A, respectively, plural pad electrodes  32 A which receive video signals, and plural signal electrodes  32  arranged subsequent to the pad electrodes  32 A, respectively. The extending direction of the scanning electrodes  33  is substantially perpendicular to the extending direction of the signal electrodes  32 . As shown in  FIG. 10A , thin film transistors (TFT)  31 T are arranged at cross points between the scanning electrode  33  and the signal electrodes  32 . 
     On the glass substrate  31 A, transparent pixel electrodes  34 , formed from ITO or the like, are arranged in correspondence to the TFTs  31 T. One of the pixel electrodes  34  is selected by the scanning signal from one of the scanning electrodes  33  related to the TFT  31 T corresponding to the one of the pixel electrodes  34 , and the video signal from the corresponding signal electrode  32  drives the selected ITO pixel electrode  34  to operate. 
     The liquid crystal layer  31  may be made by using a liquid crystal having a negative anisotropy of the dielectric constant provided by Merck Ltd. The aforesaid molecule alignment film may be made by using a vertical alignment film provided by JSR Corp. Typically, a spacer as illustrated in  FIG. 10B  is used to assembly the glass substrate  31 A and the glass substrate  31 B so that the thickness of the liquid crystal layer  31  is maintained to be about 4 μm. 
     In the liquid crystal display device  40 , in the un-driven state, that is, when the driving voltage is not applied to the transparent pixel electrodes  34 , the liquid crystal molecules are aligned to be substantially perpendicular to the plane of the liquid crystal layer  31 , and due to the polarizer  31   a  and the analyzer  31   b , the liquid crystal display device  40  is in black display state. In the driven state, that is, when the driving voltage is applied to the transparent pixel electrodes  34 , the liquid crystal molecules are aligned to be substantially parallel to the liquid crystal layer  31 , the liquid crystal display device  40  is in white display state. 
     As illustrated in  FIG. 10B , the scanning electrodes  33 , which also act as gate electrodes of the TFTs  31 T, extend on the glass substrate  31 A, and a gate insulating film  33   a  is deposited on the glass substrate  31 A to cover the scanning electrodes  33 . Also not illustrated, an interlayer insulating film  33   b  is deposited on the gate insulating film  33   a  to cover an amorphous silicon layer or a poly-silicon layer constituting the TFTs  31 T, and the signal electrodes  32  are arranged on the interlayer insulating film  33   b . Further, another interlayer insulating film  33   c  is deposited on the interlayer insulating film  33   b  to cover the signal electrodes  32 . The transparent pixel electrodes  34  are formed on the interlayer insulating film  33   c  and are connected to the TFTs  31 T through not-illustrated via holes. Moreover, a molecule alignment film corresponding to the molecule alignment film  25 MA in  FIG. 4  is formed on the interlayer insulating film  33   c  to cover the transparent pixel electrodes  34 . 
     In the liquid crystal display device  40 , cutouts  34 A, which correspond to the structure  13 A in  FIG. 1A  and  FIG. 1B , are formed in a zigzag manner in a portion of the transparent pixel electrodes  34 . It should be noted that the structures  13 A and  13 B can be replaced by depressed patterns formed in the substrate  11 A or  11 B. 
     On the other hand, on the glass substrate  31 B, a black mask (BM) is formed in correspondence to the TFTs  31 T, and red (R), green (G), and blue (B) color filters  31 F are arranged in correspondence to the transparent pixel electrodes  34 . 
     An electrode  36 , which corresponds to the electrode layer  23 B in  FIG. 2A , are uniformly formed on the color filters  31 F, and a projecting pattern  38  and a columnar spacer  39 , which correspond to the structure  25 B in  FIG. 4 , are formed on the electrode  36  by depositing resist patterns. The projecting pattern  38  and the columnar spacer  39  are covered by molecule alignment films  37 , which correspond to the molecule alignment films  25 MA in  FIG. 2A . Both the projecting pattern  38  and the columnar spacer  39  have smooth inclined surfaces and projecting ends. 
     The columnar spacer  39  is higher than the projecting pattern  38 , for example, it is fabricated to have a height of four μm corresponding to the thickness of the liquid crystal cells. The end of the columnar spacer  39  is in contact with the transparent pixel electrodes  34  through the molecule alignment films  35  and  37 , and thereby, defining the thickness of the liquid crystal layer  31 . In order to form the projecting pattern  38  and the columnar spacer  39 , for example, a resist film may be deposited on the glass substrate  31 B to a desired thickness by, for example, spin coating, and after being patterned, the resist film may be heated and cured twice with different film thicknesses. In this way, the projecting pattern  38  and the columnar spacer  39  can be fabricated easily. For example, the projecting pattern  38  is formed by using a positive resist, and the aforementioned depressed pattern  39  is formed by using a negative resist. 
       FIG. 11  is a plan view illustrating a structure of the pixel electrode  34  of the liquid crystal display device  40  according to the first embodiment of the present invention. 
     As illustrated in  FIG. 11 , the projecting pattern  38  and the cutouts  34 A are formed to extend on the pixel electrode  34  in a zigzag manner and in parallel to each other. The pixel electrode  34  is divided into an upper domain region and a lower domain region by the electrode pattern  31 C, which extends in the horizontal direction through the center portion, and produces the auxiliary capacitance Cs. The electrode pattern  31 C corresponds to the electrode pattern  23 C in  FIG. 4 . Hence, the projecting pattern  38  and the cutouts  34 A extend in parallel to a certain direction (referred to as “first direction” where necessary) in both the first domain and the second domain, but the first direction in the upper domain perpendicularly intersects with the first direction in the lower domain. Therefore, the alignment of the liquid crystal molecules in the upper domain is perpendicular to the alignment of the liquid crystal molecules in the lower domain, and this reduces dependence of optical display on an azimuthal angle or a polar angle. 
     In the configuration shown in  FIG. 11 , each columnar spacer  39  partially overlaps with the upper end and lower end of the transparent pixel electrode  34  on the scanning electrodes (gate bus line)  33 . Due to such a configuration, near a corner of the transparent pixel electrode  34 , the liquid crystal molecules receive interactions from the edge of the transparent pixel electrode  34 , the cutouts  34 A, and the columnar spacer  39 . However, as illustrated in  FIG. 11 , the columnar spacer  39  is arranged to face the projecting pattern  38  with the cutouts  34 A in between, the columnar spacer  39  enhances interaction of the cutouts  34 A from the back side of the cutouts  34 A, the liquid crystal molecules are tilted to be substantially perpendicular to the extending direction of the cutouts  34 A. 
     Under this condition, if the transparent pixel electrode  34  is driven through the TFT  31 T, at the corner of the transparent pixel electrode  34 , the liquid crystal molecules are rapidly tilted to the direction substantially perpendicular to the extending direction of the cutouts  34 A. Thereby, it is possible to realize a liquid crystal display device capable of high speed display with high transmittance in the driven state. 
     According to experimental results by the present inventors, it was found that due to the configuration shown in  FIG. 11 , the transmittance was improved by 6% compared with the configuration shown in  FIG. 8 . Each pixel was investigated by using a microscope, and no abnormal domain is observed near the columnar spacer  39 . 
     Second Embodiment 
       FIG. 12  is a plan view illustrating a configuration of a liquid crystal display device  50  according to a second embodiment of the present invention. In  FIG. 12 , the same reference numbers are used for the same elements as those described previously, and overlapping descriptions are omitted. 
     As illustrated in  FIG. 12 , the projecting pattern  38  and the cutouts  34 A are formed to extend on the pixel electrode  34  in a zigzag manner and in parallel to each other. In the second embodiment, the cutout pattern  34 A is formed only at the center portion of the pixel electrode  34 , but not arranged outside the center portion, specifically, not arranged outside the projecting pattern  38 . Due to this arrangement, the constraint on the alignment of the liquid crystal molecules  22 A applied by the projecting pattern  38  is in effect even up to the outer edge of the pixel electrode  34 . 
     In the second embodiment, similarly, the columnar spacers  39  are also formed on the scanning electrodes  33 , but if the columnar spacers  39  were also arranged to partially overlap with the transparent pixel electrode  34 , as in shown in  FIG. 11 , because there is not any cutout  34 A between the columnar spacers  39  and the transparent pixel electrode  34 , the columnar spacers  39  would also regulate the alignment of the liquid crystal molecules  22 A, and this produces an effect in confliction with the alignment regulation effect of the projecting pattern  38 , and causes disorder of the alignment of the liquid crystal molecules  22 A. 
     In order to avoid this problem, as illustrated in  FIG. 12 , the columnar spacers  39  are separated from the transparent pixel electrode  34  by a distance Px. 
     Experimental results showed that the transmittance in the driven state was improved by about 3% compared with the configuration shown in  FIG. 8  when the distance Px was set to be about 6 μm. This implies that by separating the columnar spacers  39  from the transparent pixel electrode  34  by a distance Px, for example, setting the distance Px to be about 6 μm, the alignment regulation effect of the columnar spacers  39  essentially becomes negligible. 
     The configuration shown in  FIG. 12  is basically the same as that shown in  FIG. 11  except for the features described above. In addition, in order to illustrate the columnar spacers  39  arranged outside the pixel region, the sizes of the columnar spacers  39  are reduced more or less in  FIG. 12 , and for this reason, the arrangement outside the projecting pattern  38  in  FIG. 11  is illustrated in  FIG. 12 . 
     Third Embodiment 
       FIG. 13  is a plan view illustrating a configuration of a liquid crystal display device  60  according to a third embodiment of the present invention. In  FIG. 13 , the same reference numbers are used for the same elements as those described previously, and overlapping descriptions are omitted. 
     As illustrated in  FIG. 13 , in the present embodiment, in addition to the structure shown in  FIG. 11  or  FIG. 12 , the columnar spacer  39  is arranged such that the cutout patterns  34 A are formed between two projecting patterns  38  opposite to each other on the electrode pattern  31 C, which produces the auxiliary capacitance Cs, and the edges of the columnar spacer  39  are in parallel to the cutout patterns  34 A. 
     In the structure in  FIG. 13 , between the columnar spacer  39  and the projecting pattern  38 , the columnar spacer  39 , the projecting pattern  38 , and the cutout patterns  34 A cooperate with each other so as to regulate the alignment direction of the liquid crystal molecules to be substantially perpendicular to the extending direction of the cutouts  34 A. Hence, when the driving voltage is applied to the transparent pixel electrode  34 , the liquid crystal molecules are rapidly tilted to the extending direction of the transparent pixel electrode  34  and the cutouts  34 A to change transmittance of pixels. 
     As described above, in the present embodiment, with the cutout patterns  34 A in between, the columnar spacer  39  provides the same effect as the projecting pattern  38  to effectively regulate alignment of the liquid crystal molecules. In the present embodiment, it is preferable to set the distance between the edge of the columnar spacer  39  and the cutout patterns  34 A to be substantially the same as the distance between the projecting pattern  38  and the cutout patterns  34 A. 
     In the present embodiment, although the columnar spacer  39  is formed within the pixel region of the transparent pixel electrode  34 , a larger portion of the columnar spacer  39  is arranged on the bus electrode  31 C, and this enables a minimum reduction of the transmittance due to presence of the columnar spacer  39 , while ensuring a sufficiently large area for realizing the functions of a spacer. 
     Fourth Embodiment 
       FIG. 14  is a plan view illustrating a configuration of a liquid crystal display device  60  according to a fourth embodiment of the present invention. In  FIG. 14 , the same reference numbers are used for the same elements as those in  FIG. 13 , and overlapping descriptions are omitted. 
     As illustrated in  FIG. 14 , in the present embodiment, similar to the structure in  FIG. 11  or  FIG. 12 , a projecting pattern  38  is formed in a shape of “L” on the inner side of the L-shaped cutout patterns  34 A, in addition, the columnar spacer  39  is arranged on the inner side of the L-shaped projecting patterns  38 . 
     In the structure shown in  FIG. 14 , the alignment regulation effect of the columnar spacers  39  on the liquid crystal molecules  22 A is in confliction with the alignment regulation effect of the projecting pattern  38  on the outer side, however, as illustrated in  FIG. 14 , the columnar spacer  39  is arranged to be enclosed on three sides by the projecting pattern  38  so as to reduce influence of the columnar spacer  39  on the liquid crystal molecules  22 A. 
     With the structure shown in  FIG. 14 , an optical transmittance is obtained that is similar to that obtained by using the structure shown in  FIG. 12 . 
     Fifth Embodiment 
       FIG. 15  is a plan view illustrating a configuration of a liquid crystal display device  80  according to a fifth embodiment of the present invention. In  FIG. 15 , the same reference numbers are used for the same elements as those described previously, and overlapping descriptions are omitted. 
     In the present embodiment, as illustrated in  FIG. 15 , in the structure shown in  FIG. 13 , the projecting patterns  38  are replaced by the columnar spacer  39 . Hence, in the present embodiment, the columnar spacer  39  is not an isolated pattern, but a continuing pattern. 
     With the structure shown in  FIG. 15 , that is, by replacing the projecting patterns  38  with the columnar spacer  39 , it is possible to realize substantially ideal alignment of the liquid crystal molecules  22 A. 
     Sixth Embodiment 
       FIG. 16  is a plan view illustrating a configuration of a liquid crystal display device  90  according to a sixth embodiment of the present invention. In  FIG. 16 , the same reference numbers are used for the same elements as those described previously, and overlapping descriptions are omitted. 
     In the present embodiment, as illustrated in  FIG. 16 , the projecting patterns  38  originally arranged at corners of the pixel electrode  34  are replaced by spacer patterns  39 A having edges in parallel to the extending direction of a cutout patterns  34 A facing the otherwise existing projecting patterns  38 . In addition, on the auxiliary capacitance bus  31 C at the center portion, a spacer pattern  39 B having a circular cross section is arranged on the inner side of the L-shaped cutout pattern  34 A, in other words, the spacer pattern  39 B is arranged to face the L-shaped projecting pattern  38  with the cutout patterns  34 A in between. 
     In the present embodiment, by arranging the spacer patterns  39 A to be at the corners of the pixel electrode  34  with the edges of the spacer patterns  39 A being in parallel to the extending direction of the cutout patterns  34 A facing the spacer patterns  39 A, the alignment of the liquid crystal molecules  22 A at the corners of the pixel electrode  34  is regulated to be perpendicular to edges of the spacer patterns  39 A, and this suppress occurrence of display defects. 
     By arranging the spacer pattern  39 B on the inner side of the L-shaped cutout pattern  34 A, it is found that desired alignment of the liquid crystal molecules  22 A is attained even in this region. Concerning the spacer pattern  39 B, although it is thought that preferably the spacer pattern  39 B may be the triangular spacer pattern as illustrated in  FIG. 13 , in the present embodiment illustrated in  FIG. 16 , the spacer pattern  39 B is not limited to the triangular spacer pattern illustrated in  FIG. 13 . 
     In the present embodiment, by arranging the spacer patterns  39 A to be at the corners of the pixel electrode  34 , or by arranging the spacer pattern  39 A to have a triangular cross section, the TFT glass substrate  31 A and the TFT glass substrate  31 B can be stably supported. 
     Seventh Embodiment 
       FIG. 17  is a plan view illustrating a configuration of a liquid crystal display device  100  according to a seventh embodiment of the present invention. In  FIG. 17 , the same reference numbers are used for the same elements as those described previously, and overlapping descriptions are omitted. 
     In the present embodiment, as illustrated in  FIG. 17 , the spacer pattern  39 A correspond to a combination of the columnar spacer  39  in  FIG. 11  and a feature of the spacer pattern  39 A in  FIG. 16 , that is, the spacer pattern  39 A in  FIG. 16  has an edge in parallel to the extending direction of the cutout pattern  34 A. 
     Namely, in the present embodiment, the spacer pattern  39 A extends over a large area from outside of the pixel region and covers a portion of the pixel electrode  34 , and due to this, the TFT glass substrate  31 A and the TFT glass substrate  31 B are stably supported by the spacer pattern  39 A. In this situation, because the spacer pattern  39 A has an edge in parallel to the extending direction of the cutout pattern  34 A facing itself, the alignment of the liquid crystal molecules  22 A is regulated to be perpendicular to the extending direction of the cutout pattern  34 A, and this reduces disorder of alignment of the liquid crystal molecules  22 A in the pixel regions. Thereby, the liquid crystal display device  100  has good transmittance in the driven state. 
     Eighth Embodiment 
       FIGS. 18A through 18C  are plan view and cross-sectional views illustrating a configuration of a liquid crystal display device  110  according to an eighth embodiment of the present invention. In  FIGS. 18A through 18C , the same reference numbers are used for the same elements as those described previously, and overlapping descriptions are omitted. 
     As illustrated in  FIGS. 18A through 18C , the spacer patterns  39 A and  39 B in the present embodiment correspond to a combination of the columnar spacer  39  in  FIG. 14  and the columnar spacer  39 B in  FIG. 12 . 
     The columnar spacer  39 A as shown in  FIG. 14 , which acts as a main spacer pattern in the present embodiment, and the columnar spacer  39 B as shown in  FIG. 12 , which acts as a sub spacer pattern in the present embodiment, are obtained by patterning the same resist film deposited on the TFT glass substrate  31 B, and have the same height. 
     Nevertheless, the main spacer  39 A is arranged in the pixel region on the glass substrate  31 B to face a portion of the TFT glass substrate  31 A including a stacked structure of the pixel electrode  34 , an intermediate electrode  41 , a Cs electrode  31 C, and interlayer insulating films  42 , and as illustrated in  FIG. 18B , the end of the columnar spacer  39 A is in contact with the glass substrate  31 A. On the other hand, the sub spacer  39 B is arranged in the pixel region on the glass substrate  31 B to face a portion of the TFT glass substrate  31 A including a stacked structure of the scanning electrode  33  and interlayer insulating films  42 , as illustrated in  FIG. 18C . Thus, there is a gap G, for example, equaling to about 0.2 μm, between the sub spacer  39 B and the glass substrate  31 A, corresponding to the thicknesses of the pixel electrode  34  and the intermediate electrode  41 . 
     In  FIG. 18B  and  FIG. 18C , illustration of molecule alignment films and other elements are omitted. 
     Because there is a gap G between the sub spacer  39 B and the glass substrate  31 A, when an external force is applied to the glass substrate  31 A and the glass substrate  31 B in the liquid crystal display device  110 , the liquid crystal panel is bendable, and this can prevent permanent deformation in the columnar spacer, or other damages to the columnar spacer. 
     Even in the above configuration, the alignment regulation effect applied by the columnar spacer  39 A on the liquid crystal molecules  22 A is eliminated by forming the projecting pattern  38  to enclose the columnar spacer  39 A on three sides, thereby, the alignment of the liquid crystal molecules  22 A is regulated by the projecting pattern  38  and the cutout pattern  34 A. In addition, by separating the sub columnar spacer  39 B from the transparent pixel electrode  34  by a distance Px, the sub spacer  39 B essentially does not cause disorder of alignment of the liquid crystal molecules  22 A. 
     Further, in the above first through eighth embodiments, fine patterns corresponding to the fine structure patterns  24  illustrated in  FIG. 4  may be arranged on the transparent pixel electrode  34  while being perpendicular to the cutout  34 A. 
     While the invention is described above with reference to specific embodiments chosen for purpose of illustration, it should be apparent that the invention is not limited to these embodiments, but numerous modifications could be made thereto by those skilled in the art without departing from the basic concept and scope of the invention.

Technology Category: g