Patent Document

BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a liquid crystal display device, and more particularly to a half-transmission type liquid crystal display device having functions of a light-transmission type liquid crystal display device and a light-reflection type liquid crystal display device. 
     2. Description of the Related Art 
     A liquid crystal display device is generally comprised of two substrates and liquid crystal sandwiched between the two substrates, in which an intensity of electric field to be applied to the liquid crystal is controlled to thereby control a degree at which backlight passes through the liquid crystal. 
     A vertical-alignment type liquid crystal display device can completely shut out a light when no electric field is applied thereto. Namely, since a luminance in off-condition in a normally black mode is quite low, a vertical-alignment type liquid crystal display device can present a high contrast ratio in comparison with a conventional twisted nematic type liquid crystal display device. 
     In general, backlight consumes 50% or more among power consumed in a liquid crystal display device. Hence, a portable communication device is often designed to include a light-reflection type liquid crystal display device which includes a light-reflector in place of a backlight source for displaying images only by incident lights. 
     However, a light-reflection type liquid crystal display device is accompanied with a problem that displayed images cannot be seen when it is dark around the device. 
     As a solution to the problem, there has been suggested a half-transmission type liquid crystal display device including a light-reflection area and a light-transmission area, as a liquid crystal display device having advantages of both of a light-reflection type liquid crystal display device and a light-transmission type liquid crystal display device. For instance, Japanese Patent No. 2955277 has suggested such a half-transmission type liquid crystal display device. 
       FIG. 1  is a cross-sectional view of a first example of a conventional half-transmission type liquid crystal display device. 
     A half-transmission type liquid crystal display device  100  illustrated in  FIG. 1  is comprised of a first substrate  101 , a second substrate  102 , and a liquid crystal layer  103  sandwiched between the first and second substrates  101  and  102 . 
     The second substrate  102  is comprised of a second electrically insulating transparent substrate  104 , an opposing electrode  105  composed of ITO (indium tin oxide) formed on the second transparent substrate  104  in facing relation to the liquid crystal layer  103 , an alignment film  106  formed on the opposing electrode  105 , an optical compensator  107  formed on the second transparent substrate  104  in opposite side with respect to the liquid crystal layer  103 , and a polarizer  108  formed on the optic compensator  107 . 
     The half-transmission type liquid crystal display device  100  is designed to have a first area  120  in which a light is reflected and a second area  121  through which a light passes. A structure of the first substrate  101  in the first area  120  is different from a structure of the first substrate  101  in the second area  121 . 
     In the first area  120 , the first substrate  101  is comprised of a first electrically insulating transparent substrate  109 , a passivation film  110  formed on the first transparent film  109  in facing relation to the liquid crystal layer  103 , a pixel electrode  111  composed of ITO and formed on the passivation film  110 , a dielectric layer  112  formed on the pixel electrode  111  and having a wavy surface, a pixel electrode  113  covering the dielectric layer  112  therewith in wavy configuration and composed of aluminum, an alignment film  114  covering the pixel electrode  113  therewith, an optical compensator  115  formed on the first transparent substrate  109  in opposite side with respect to the liquid crystal layer  103 , and a polarizer  116  formed on the optic compensator  115 . 
     In the second area  121 , the first substrate  101  is comprised of a first electrically insulating transparent substrate  109 , a passivation film  110  formed on the first transparent film  109  in facing relation to the liquid crystal layer  103 , a pixel electrode  111  composed of ITO and formed on the passivation film  110 , an alignment film  114  formed on the pixel electrode  111 , an optical compensator  115  formed on the first transparent substrate  109  in opposite side with respect to the liquid crystal layer  103 , and a polarizer  116  formed on the optic compensator  115 . 
     In the half-transmission type liquid crystal display device  100 , liquid crystal molecules constituting the liquid crystal layer  103  are aligned so that major axes of them are perpendicular to the first and second substrates  101  and  102  when no electric field is applied to the liquid crystal display device  100 . The liquid crystal molecules have negative dielectric anisotropy. 
       FIG. 2  is a cross-sectional view of a second example of a conventional half-transmission type liquid crystal display device. 
     A half-transmission type liquid crystal display device  150  illustrated in  FIG. 2  is different from the half-transmission type liquid crystal display device  100  illustrated in  FIG. 1  in a structure of the first substrate  101  in the first area  120 . 
     That is, in the half-transmission type liquid crystal display device  150 , the pixel electrode  113  composed of aluminum is covered with the pixel electrode  111  composed of ITO, and the alignment film  114  is formed on the pixel electrode  111 . Except this difference, the half transmission type liquid crystal display device  150  is identical in structure to the half-transmission type liquid crystal display device  100 . 
     The half-transmission type liquid crystal display device  100  illustrated in  FIG. 1  displays images as follows. 
     In the first area  120 , an external light enters the half-transmission type liquid crystal display device  100 , and is reflected at the pixel electrode  113  acting as a reflector. Then, the reflected light passes through the liquid crystal layer  103  and the second substrate  102 , and reaches a viewer. 
     In the second area  121 , a backlight emitted from a backlight source (not illustrated) arranged below the first transparent substrate  109  passes through the first substrate  101 , the liquid crystal layer  103  and the second substrate  102 , and reaches a viewer. 
     As mentioned above, whereas an incident light reciprocates the liquid crystal layer  103  in the first area  120 , an incident light passes through the liquid crystal layer  103  only in one-way in the second area  121 , resulting in an optical path difference in the liquid crystal layer  103 . In order to avoid such an optical path difference, a cell gap Dr of liquid crystal in the first area  120  is designed to be about half of a cell gap Df of liquid crystal in the second area  121 , thereby optimizing an intensity of an output light caused by a difference in retardation between the first and second areas  120  and  121 . 
     For instance, the cell gaps Dr and Df are designed equal to 2 μm and 4 μm, respectively. 
     The half-transmission type liquid crystal display device  150  illustrated in  FIG. 2  displays images in the same way as the half-transmission type liquid crystal display device  100 . 
     In order to make use of advantages provided by the above-mentioned half-transmission type liquid crystal display device and vertical-alignment type liquid crystal display device, Japanese Patent Application Publications Nos. 2000-29010 and 2000-35570 suggest a liquid crystal display device having function of both of half-transmission type and vertical-alignment type liquid crystal display devices. 
     A half transmission type liquid crystal display device having the first and second areas unavoidably has the cell gaps Dr and Df different from each other, in order to avoid the above-mentioned optical path difference in the liquid crystal layer  103 . 
     However, the cell gaps Dr and Df different from each other cause a problem that liquid crystal molecules are inclined in non-uniform directions at a boundary between the first and second areas and in the vicinity of the boundary when electric field is applied to the liquid crystal layer, resulting in deterioration in visibility and reduction in a response speed. 
     Japanese Patent No. 2565639, based on U.S. patent application Ser. No. 879,256 filed on Apr. 30, 1992, has suggested a liquid crystal display device including a common electrode formed on a substrate. The common electrode is formed in alignment with a display area with a patterned opening for dividing the display area into a plurality of liquid crystal domains, and covers the substrate therewith in an area other than the opening. 
     Japanese Patent Application Publication No. 2000-250056 has suggested a liquid crystal display device including a pixel electrode formed with an opening in the form of a slit and in parallel with an orientation of alignment of liquid crystal molecules. 
     Japanese Patent Application Publication No. 2002-107724 has suggested a liquid crystal display device including a λ/4 double-refraction layer arranged between a light-reflection layer and a liquid crystal layer to thereby equalize a thickness of the liquid crystal layer in a light-reflection area to a thickness of the liquid crystal layer in a light-transmission area. 
     Japanese Patent Application Publication No. 2002-98951 has suggested a half-transmission type liquid crystal display device including a reflection electrode having a patterned opening having a side which is not in parallel with any sides of an effective frame of a liquid crystal display panel and any sides of a pixel pattern. 
     SUMMARY OF THE INVENTION 
     In view of the above-mentioned problems in the conventional liquid crystal display devices, it is an object of the present invention to provide a vertical-alignment type liquid crystal display device including a first area in which an incident light is reflected and a second area through which a light passes which device is capable of preventing deterioration in visibility and reduction in a response speed both of which are caused by a difference in cell gap found at a boundary between and in the vicinity of the first and second areas. 
     In one aspect of the present invention, there is provided a liquid crystal display device including (a) a first substrate including a first area in which an incident light is reflected and a second area through which a light passes, and further including a pixel electrode covering the first and second areas therewith, (b) a second substrate including at least an opposing electrode, (c) a liquid crystal layer sandwiched between the first and second substrates and including liquid crystal molecules each having a major axis aligned perpendicularly to the first and second substrates when no electric field is applied thereto, and (d) a first alignment-controller for controlling alignment of the liquid crystal molecules, the first alignment-controller being arranged at a boundary of the first and second areas or in the vicinity of the boundary. 
     The liquid crystal display device may further include a second alignment-controller for controlling alignment of the liquid crystal molecules, the second alignment-controller being formed in the second substrate in facing relation to the first and second areas. 
     For instance, the first alignment-controller is comprised of an opening area of the first substrate where the pixel electrode does not exist. 
     As an alternative, the first alignment-controller may be comprised of a projection formed on the pixel electrode on the first substrate, the projection being composed of dielectric substance. 
     It is preferable that a cell gap above the first area and a cell gap above the second area are different from each other. 
     It is preferable that the first substrate has a level-different portion between the first and second areas. 
     For instance, the opening area is located in the first area. 
     For instance, the opening area is located at a boundary between the first and second areas. 
     For instance, the opening area is located in the second area. 
     For instance, the projection is located in the first area. 
     For instance, the projection is located in the second area. 
     For instance, the second alignment-controller is comprised of a second opening area of the second substrate where the opposing electrode does not exist. 
     It is preferable that the pixel electrode is formed with at least one opening area for dividing the pixel electrode into a plurality of sections in the first and second areas, the second alignment-controller is comprised of a second opening area of the second substrate where the opposing electrode does not exist, the opposing electrode is formed with two second opening areas each in facing relation to the pixel electrode in the first area and the pixel electrode in the second area. 
     It is preferable that the pixel electrode is formed with at least one opening area for dividing at least a part of the pixel electrode into a plurality of sections in the first and second areas, the second alignment-controller is comprised of a second opening area of the second substrate where the opposing electrode does not exist, the opposing electrode is formed with a plurality of second opening areas in facing relation to each of the sections and/or a non-divided portion of the pixel electrode. 
     It is preferable that each of the second opening area and the pixel electrode is symmetrical about a longitudinal direction of the liquid crystal display device. 
     It is preferable that each of the sections in the first area is larger in area than each of the sections in the second area. 
     It is preferable that the opening area extends across a boundary between the first and second areas, and the pixel electrode in the first area is connected to the pixel electrode in the second area through at least one line-shaped pixel electrode. 
     It is preferable that the opening area is formed in one of the first and second areas, and is comprised of a first region located adjacent to the first or second area, a second region spaced away from the first region, and at least one line-shaped connection region connecting the first and second regions to each other. 
     For instance, the second opening area is comprised of a cross slit. 
     It is preferable that a center of the second opening area is in alignment with a center of the pixel electrode. 
     The advantages obtained by the aforementioned present invention will be described hereinbelow. 
     The present invention makes it possible in a liquid crystal display device including a first area in which an incident light is reflected and a second area through which a light passes to prevent deterioration in visibility and reduction in a response speed both of which are caused by a difference in cell gap found at a boundary between and in the vicinity of the first and second areas. 
     The above and other objects and advantageous features of the present invention will be made apparent from the following description made with reference to the accompanying drawings, in which like reference characters designate the same or similar parts throughout the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional view of a first example of a conventional half-transmission type liquid crystal display device. 
         FIG. 2  is a cross-sectional view of a second example of a conventional half-transmission type liquid crystal display device. 
         FIG. 3A  is a partial perspective view of a half-transmission type liquid crystal display device in accordance with the first embodiment of the present invention. 
         FIG. 3B  illustrates how liquid crystal in a liquid crystal layer is inclined when electric field is applied thereto in the liquid crystal display device illustrated in FIG.  3 A. 
         FIG. 4A  is a partial perspective view of a half-transmission type liquid crystal display device in accordance with the second embodiment of the present invention. 
         FIG. 4B  illustrates how liquid crystal in a liquid crystal layer is inclined when electric field is applied thereto in the liquid crystal display device illustrated in FIG.  4 A. 
         FIG. 5A  is a partial perspective view of a half-transmission type liquid crystal display device in accordance with a first variant of the second embodiment of the present invention. 
         FIG. 5B  illustrates how liquid crystal in a liquid crystal layer is inclined when electric field is applied thereto in the liquid crystal display device illustrated in FIG.  5 A. 
         FIG. 6A  is a partial perspective view of a half-transmission type liquid crystal display device in accordance with a second variant of the second embodiment of the present invention. 
         FIG. 6B  illustrates how liquid crystal in a liquid crystal layer is inclined when electric field is applied thereto in the liquid crystal display device illustrated in FIG.  6 A. 
         FIG. 7  is a partial perspective view of a half-transmission type liquid crystal display device in accordance with the third embodiment of the present invention. 
         FIG. 8  is a cross-sectional view taken along the line A—A in FIG.  3 A. 
         FIG. 9  is a cross-sectional view taken along the line A—A in FIG.  4 A. 
         FIG. 10  is a cross-sectional view taken along the line A—A in FIG.  7 . 
         FIG. 11  is a cross-sectional view of a half-transmission type liquid crystal display device in accordance with the fourth embodiment of the present invention. 
         FIG. 12  is a cross-sectional view of a half-transmission type liquid crystal display device in accordance with the fifth embodiment of the present invention. 
         FIG. 13  is a partial perspective view of a half-transmission type liquid crystal display device in accordance with the sixth embodiment of the present invention. 
         FIG. 14  is a partial perspective view of a half-transmission type liquid crystal display device in accordance with a variant of the sixth embodiment of the present invention. 
         FIGS. 15A  to  15 K are plan views each illustrating a pixel electrode and an associated second opening area formed at an opposing electrode. 
         FIGS. 16A  to  16 G are plan views each illustrating a square pixel electrode and an associated second opening area formed at an opposing electrode. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Preferred embodiments in accordance with the present invention will be explained hereinbelow with reference to drawings. 
     As mentioned below, a half-transmission type liquid crystal display device in accordance with the embodiments of the present invention is different in structure from the conventional half-transmission type liquid crystal display device  150  illustrated in  FIG. 2  in the pixel electrodes  111  and  113  of the first substrate  101  and the opposing electrode  105  of the second substrate  102 , and has the same structure as that of the conventional half-transmission type liquid crystal display device  150  except the pixel electrodes  111  and  113  and the opposing electrode  105 . Accordingly, unless explicitly indicated, only the pixel electrodes  113  and  111  of the first substrate  101  and the opposing electrode  105  of the second electrode  102  in each of the embodiments are illustrated in drawings. 
     Parts or elements that correspond to those of the conventional half-transmission type liquid crystal display device  150  illustrated in  FIG. 2  have been provided with the same reference numerals, and operate in the same manner as corresponding parts or elements in the conventional half-transmission type liquid crystal display device  150 , unless explicitly explained hereinbelow. 
     [First Embodiment] 
       FIG. 3A  is a partial perspective view of a half-transmission type liquid crystal display device  10  in accordance with the first embodiment. 
     As illustrated in  FIG. 3A , the half-transmission type liquid crystal display device  10  is designed to include an inclined surface or a level-different portion  122  between the first area  120  and the second area  121 . The first and second areas  120  and  121  are continuous to each other through the inclined surface  122 . 
     The pixel electrode  111  of the first substrate  101  is designed to have a first opening area  125 A in which the pixel electrode  111  does not exist. The first opening area  125 A defines a first alignment-controller. 
     The first opening area  125 A extends across the inclined surface  122  and over the first and second areas  120  and  121 . A pixel electrode  111 A in the first area  120  and a pixel electrode  111 B in the second area  122  are connected to each other through a line  126  extending in a longitudinal direction X of the half-transmission type liquid crystal display device  10 . The line  126  connects the pixel electrode  111 A at a center in a width-wise direction Y thereof and the pixel electrode  111 B at a center in a width-wise direction Y thereof to each other. 
     A distance between the pixel electrodes  111 A and  111 B, that is, a length of the line  126  is in the range of about 8 to about 16 μm both inclusive. 
     The opposing electrode  105  of the second substrate  102  is formed with second opening areas  135 A and  135 B in facing relation to the pixel electrodes  111 A and  111 B, respectively. Each of the second opening areas defines a second alignment-controller. 
     Each of the second opening areas  135 A and  135 B is in the form of a cross-shaped slit. A center of the second opening area  135 A is vertically in alignment with a center of the pixel electrode  111 A, and a center of the second opening area  135 B is vertically in alignment with a center of the pixel electrode  111 B. 
       FIG. 3B  illustrates how liquid crystal in the liquid crystal layer  103  is inclined when electric field is applied thereto. 
     As illustrated in  FIG. 3B , when electric field is applied to liquid crystal in the liquid crystal layer  103 , liquid crystal is inclined towards an area of the opposing electrode  105  located in alignment with the line  126  above the first opening area  125 A in the inclined surface  122 , whereas liquid crystal is inclined towards a center of an area of the opposing electrode  105  located in alignment with the center of the pixel electrode  111 A above the first area  120  and a center of an area of the opposing electrode  105  located in alignment with the center of the pixel electrode  111 B above the second area  121 . Since liquid crystal molecules are uniformly oriented in the above-mentioned way, it is possible to reduce deterioration in visibility and reduction in a response speed. 
     The number of the line  126  is not to be limited to one. The pixel electrodes  111 A and  111 B may be connected to each other through two or more lines  126 , in which case, it is preferable that the lines  126  are in parallel with one another. 
     [Second Embodiment] 
       FIG. 4A  is a partial perspective view of a half-transmission type liquid crystal display device  20  in accordance with the second embodiment. 
     The liquid crystal display device  20  in accordance with the second embodiment is different in structure from the liquid crystal display device  10  in accordance with the first embodiment in a first opening area. 
     A first opening area  125 B in the second embodiment is formed in the second area  121 . As a result, the second area  121  is comprised of a rectangular first section  121   a  connecting to the pixel electrode  111 A formed in the inclined surface  122  and the first area  120 , a second section  121   b  spaced away from the first section  121   a,  and a line-shaped connection section  121   c  connecting the first and second sections  121   a  and  121   b  to each other. 
     The connection section  121   c  connects the first section  121   a  at a center in a width-wise direction Y thereof and the second section  121   b  at a center in a width-wise direction Y thereof to each other. 
     For instance, the first section  121   a  has a longitudinal length (a length in a direction X) in the range of 8 to 16 μm, and the first opening area  125 B has a longitudinal length (a length in a direction X) in the range of 6 to 14 μm. 
     The opposing electrode  105  of the second substrate  102  is formed with second opening areas  135 A and  135 B in facing relation to the pixel electrodes  111 A and  111 B, respectively. Each of the second opening areas  135 A and  135 B defines a second alignment-controller. 
     Each of the second opening areas  135 A and  135 B is in the form of a cross-shaped slit. A center of the second opening area  135 A is vertically in alignment with a center of the pixel electrode  111 A, and a center of the second opening area  135 B is vertically in alignment with a center of the second section  121   b  of the pixel electrode  111 B. 
       FIG. 4B  illustrates how liquid crystal in the liquid crystal layer  103  is inclined when electric field is applied thereto. 
     As illustrated in  FIG. 4B , when electric field is applied to liquid crystal in the liquid crystal layer  103 , liquid crystal is inclined towards an area of the opposing electrode  105  located in alignment with a center of the first opening area  125 B, whereas liquid crystal is inclined towards a center of an area of the opposing electrode  105  located in alignment with the center of the pixel electrode  111 A above the first area  120  and a center of an area of the opposing electrode  105  located in alignment with the center of the second section  121   b  of the pixel electrode  111 B above the second area  121 . Since liquid crystal molecules are uniformly oriented in the above-mentioned way, it is possible to reduce deterioration in visibility and reduction in a response speed. 
     The number of the connection section  121   c  is not to be limited to one. The pixel electrodes  111 A and  111 B may be connected to each other through two or more connection lines  121   c , in which case, it is preferable that the connection lines  121   c  are in parallel with one another. 
       FIG. 5A  is a partial perspective view of a first variant of the half-transmission type liquid crystal display device  20 . 
     In the first variant, the first opening area  125 Ba is formed in the pixel electrode  111 B in the second area  121 . Thus, the first section  121   a  and the second section  121   b  are connected to each other through two connection sections  121   d  formed at opposite ends of the first and second sections  121   a  and  121   b  in a width-wise direction thereof. The first variant illustrated in  FIG. 5A  has the same structure as that of the half-transmission type liquid crystal display device  20 . 
       FIG. 5B  illustrates how liquid crystal in the liquid crystal layer  103  is inclined when electric field is applied thereto in the first variant illustrated in FIG.  5 A. 
     As illustrated in  FIG. 5B , since liquid crystal molecules are uniformly oriented in the first variant, it is possible to reduce deterioration in visibility and reduction in a response speed. 
       FIG. 6A  is a partial perspective view of a second variant of the half-transmission type liquid crystal display device  20 . 
     In the second variant, the first opening area  125 Bb is formed in the pixel electrode  111 B in the second area  121  in separated two areas. Hence, the first section  121   a  and the second section  121   b  are connected to each other through three connection sections  121   e  formed at opposite ends and center of the first and second sections  121   a  and  121   b  in a width-wise direction thereof. The second variant illustrated in  FIG. 6A  has the same structure as that of the half-transmission type liquid crystal display device  20 . 
       FIG. 6B  illustrates how liquid crystal in the liquid crystal layer  103  is inclined when electric field is applied thereto in the first variant illustrated in FIG.  6 A. 
     As illustrated in  FIG. 6B , since liquid crystal molecules are uniformly oriented in the second variant, it is possible to reduce deterioration in visibility and reduction in a response speed. 
     [Third Embodiment] 
       FIG. 7  is a partial perspective view of a half-transmission type liquid crystal display device  30  in accordance with the third embodiment. 
     The liquid crystal display device  30  in accordance with the third embodiment is different in structure from the liquid crystal display device  10  in accordance with the first embodiment in a first opening area. 
     A first opening area  125 C in the third embodiment is formed in the first area  120 . As a result, the first area  120  is comprised of a rectangular first section  120   a  connecting to the pixel electrode  111 B formed in the inclined surface  122  and the second area  121 , a second section  120   b  spaced away from the first section  120   a , and a line-shaped connection section  120   c  connecting the first and second sections  120   a  and  120   b  to each other. 
     The connection section  120   c  connects the first section  120   a  at a center in a width-wise direction Y thereof and the second section  120   b  at a center in a width-wise direction Y thereof to each other. 
     For instance, the first section  120   a  has a longitudinal length (a length in a direction X) in the range of 8 to 16 μm, and the first opening area  125 C has a longitudinal length (a length in a direction X) in the range of 6 to 14 μm. 
     The opposing electrode  105  of the second substrate  102  is formed with second opening areas  135 A and  135 B in facing relation to the second section  120   b  and the pixel electrode  111 B in the second area  121 , respectively. Each of the second opening areas  135 A and  135 B defines a second alignment-controller. 
     Each of the second opening areas  135 A and  135 B is in the form of a cross-shaped slit. A center of the second opening area  135 A is vertically in alignment with a center of the second section  120   b , and a center of the second opening area  135 B is vertically in alignment with a center of the pixel electrode  111 B. 
     Similarly to the second embodiment, as having been explained with reference to  FIG. 4B , when electric field is applied to liquid crystal in the liquid crystal layer  103 , liquid crystal is inclined towards an area of the opposing electrode  105  located in alignment with a center of the first opening area  125 C, whereas liquid crystal is inclined towards a center of an area of the opposing electrode  105  located in alignment with the center of the second section  120   b  above the first area  120  and a center of an area of the opposing electrode  105  located in alignment with the center of the pixel electrode  111 B above the second area  121 . Since liquid crystal molecules are uniformly oriented in the above-mentioned way, it is possible to reduce deterioration in visibility and reduction in a response speed. 
     The number of the connection section  120   c  is not to be limited to one. The pixel electrodes  111 A and  111 B may be connected to each other through two or more connection lines  120   c,  in which case, it is preferable that the connection lines  120   c  are in parallel with one another. 
     The above-mentioned first and second variants of the second embodiments may be applied to the third embodiment. 
     The inventors conducted the experiments to know behavior of liquid crystal when electric field is applied thereto in the liquid crystal display devices in accordance with the first to third embodiments. The results are shown in  FIGS. 8  to  10 .  FIG. 8  is a cross-sectional view taken along the line A—A in  FIG. 3A ,  FIG. 9  is a cross-sectional view taken along the line A—A in  FIG. 4A , and FIG.  10  is a cross-sectional view taken along the line A—A in FIG.  7 .  FIGS. 8 ,  9  and  10  correspond to the first, second and third embodiments, respectively. 
     When electric field is applied to liquid crystal in the liquid crystal layer  103 , liquid crystal behaves more stably in the second embodiment than in the first and third embodiments, and behaves more stably in the first embodiment than in the third embodiment. 
     In the second embodiment, as illustrated in  FIG. 9 , liquid crystal is inclined by means of the first opening area  125 B formed in the pixel electrode  111 B such that its end facing the opposing electrode  105  is directed to the inclined surface  122  in an area closer to the inclined surface  122  than the first opening area  125 B. Since liquid crystal is inclined at the same angle as an angle by which the pixel electrode  111 B in the inclined surface  122  is inclined, natural continuity is ensured in a direction of alignment of liquid crystal. 
     In the first embodiment, as illustrated in  FIG. 8 , liquid crystal is vertically aligned above the first opening area  125 A by virtue of the first opening area  125 A. Liquid crystal in the first area  120  is inclined such that its end facing the opposing electrode  105  is directed to the second opening area  135 A, and liquid crystal in the second area  121  is inclined such that its end facing the opposing electrode  105  is directed to the second opening area  135 B. Thus, liquid crystal is inclined in opposite directions at opposite sides about the inclined surface  122 , ensuring continuous alignment profile. 
     In the third embodiment, as illustrated in  FIG. 10 , liquid crystal existing between the first opening area  125 C and the inclined surface  122  is inclined such that its end facing the opposing electrode  105  is directed towards the inclined surface  122 , and liquid crystal existing beyond the first opening area  125 C with respect to the inclined surface  122  is inclined such that its end facing the opposing electrode  105  is directed away from the inclined surface  122 . 
     However, since liquid crystal existing above the inclined surface  122  is inclined at the same angle as an angle by which the inclined surface  122  is inclined, liquid crystal is inclined such that its end facing the opposing electrode  105  is directed to the first area  120  only in an area between the first opening area  125 C and the inclined surface  122 . As a result, continuity in alignment direction of liquid crystal molecules is deteriorated. 
     [Fourth Embodiment] 
       FIG. 11  is a cross-sectional view of a half-transmission type liquid crystal display device  40  in accordance with the fourth embodiment of the present invention. 
     In comparison with the half-transmission type liquid crystal display device  20  in accordance with the second embodiment, the liquid crystal display device  40  is designed to include a projection  126 A composed of dielectric substance, in place of the first opening area  125 B. The projection  126 A is formed at an area where the first opening area  125 B used to be. The liquid crystal display device  40  is identical in structure with the liquid crystal display device  20  except for the above-mentioned replacement. 
     The first opening area  125 B is identical with the projection  126 A in that the pixel electrode  111 B is not formed there. However, the first opening area  125 B forms a recess in comparison with an area where the pixel electrode  111 B is formed, whereas the projection  126 A projects beyond an area where the pixel electrode  111 B is formed. 
     For instance, the projection  126 A has a height in the range of 0.5 to 1 μm. 
     Similarly to the half-transmission type liquid crystal display device  20  in accordance with the second embodiment, illustrated in  FIG. 9 , liquid crystal molecules can be uniformly oriented also by the formation of the projection  126 A in place of the first opening area  125 B, it is possible to reduce deterioration in visibility and reduction in a response speed. 
     [Fifth Embodiment] 
       FIG. 12  is a cross-sectional view of a half-transmission type liquid crystal display device  50  in accordance with the fifth embodiment. 
     In comparison with the half-transmission type liquid crystal display device  30  in accordance with the third embodiment, the liquid crystal display device  50  is designed to include a projection  126 B composed of dielectric substance, in place of the first opening area  125 C. The projection  126 B is formed at an area where the first opening area  125 C used to be. The liquid crystal display device  50  is identical in structure with the liquid crystal display device  30  except for the above-mentioned replacement. 
     The first opening area  125 C is identical with the projection  126 B in that the pixel electrode  111 A is not formed there. However, the first opening area  125 C forms a recess in comparison with an area where the pixel electrode  111  is formed, whereas the projection  126 B projects beyond an area where the pixel electrode  111  is formed. 
     For instance, the projection  126 B has a height in the range of 0.5 to 1 μm. 
     Similarly to the half-transmission type liquid crystal display device  30  in accordance with the third embodiment, illustrated in  FIG. 10 , liquid crystal molecules can be uniformly oriented also by the formation of the projection  126 B in place of the first opening area  125 C, it is possible to reduce deterioration in visibility and reduction in a response speed. 
     [Sixth Embodiment] 
       FIG. 13  is a partial perspective view of a half-transmission type liquid crystal display device  60  in accordance with the sixth embodiment of the present invention. 
     The half-transmission type liquid crystal display device  60  in accordance with the sixth embodiment is different in structure from the half-transmission type liquid crystal display device  20  in accordance with the second embodiment in a shape of a first opening area. 
     The first opening area in the sixth embodiment is comprised of a first opening area  125 B illustrated in  FIG. 4A and a  first opening area  125 D. The first opening areas  125 B and  125 D are spaced away from each other, and are designed to have the same size as each other. 
     Thus, the second area  121  is comprised of a rectangular first section  121   a  connecting to the pixel electrode  111 A formed in the inclined surface  122  and the first area  120 , a second section  121   b  spaced away from the first section  121   a,  a line-shaped connection section  121   c  connecting the first and second sections  121   a  and  121   b  to each other, a third section  121   f  spaced away from the second section  121   b,  and a line-shaped connection section  121   g  connecting the second and third sections  121   b  and  121   f  to each other. 
     The second section  121   b  and the third section  121   f  have substantially the same size as each other. 
     The connection section  121   c  connects the first section  121   a  at a center in a width-wise direction Y thereof and the second section  121   b  at a center in a width-wise direction Y thereof to each other. Similarly, the connection section  121   g  connects the second section  121   b  at a center in a width-wise direction Y thereof and the third section  121   f  at a center in a width-wise direction Y thereof to each other. 
     The opposing electrode  105  of the second substrate  102  is formed with second opening areas  136 A,  136 B and  136 C in facing relation to the pixel electrode  111 A, the second section  121   b  and the third section  121   f,  respectively. Each of the second opening areas  136 A,  136 B and  136 C defines a second alignment-controller. 
     Each of the second opening areas  136 A,  136 B and  136 C is in the form of a cross-shaped slit. A center of the second opening area  136 A is vertically in alignment with a center of the pixel electrode  111 A, a center of the second opening area  136 B is vertically in alignment with a center of the second section  121   b , and a center of the second opening area  136 C is vertically in alignment with a center of the third section  121   f.    
     In accordance with the liquid crystal display device  60 , the pixel electrode  111 B in the second area  121  is divided into a plurality of sections having the same size as one another, ensuring enhancement in a response speed of liquid crystal when electric field is applied to the liquid crystal layer  103 . 
     Specifically, on application of electric field to the liquid crystal layer  103 , a part of liquid crystal molecules having been vertically aligned is inclined due to the first opening areas  125 B and  125 D. Subsequently, surrounding liquid crystal molecules are inclined in the same direction. As a result, alignment of liquid crystal molecules is sequentially varied in response to a voltage applied to the liquid crystal layer. Hence, the smaller an area of sections into which the pixel electrode  111 B is divided is, the higher a response speed of liquid crystal molecules is when electric field is applied to the liquid crystal layer. 
     In the sixth embodiment, the pixel electrode  111 B in the second area  121  is divided into two sections (the second and third sections  121   b  and  121   f ). However, the number of the sections into which the pixel electrode  111 B in the second area  121  is divided is not to be limited to two. Three or more may be selected. 
       FIG. 14  illustrates an example in which the pixel electrode  111 B in the second area  121  is divided into eight sections having substantially the same size as one another. 
     The sections into which the pixel electrode  111 B in the second area  121  is divided may be arranged in a line, as illustrated in  FIG. 13 , or may be arranged in a matrix, as illustrated in FIG.  14 . 
     In a liquid crystal display device including the first and second areas and having cell gaps different between the first and second areas, a response speed of liquid crystal in an area where a cell gap is higher is smaller than a response speed of liquid crystal in an area where a cell gap is smaller. Hence, by designing each of the sections to have an area smaller than an area of the pixel electrode  111 A in the first area  120 , it would be possible to reduce or cancel a difference in a response speed of liquid crystal which difference is caused by a difference in cell gaps. 
     In the sixth embodiment, the pixel electrode  111 B in the second area  121  is divided into a plurality of the sections by the first opening areas. However, it should be noted that it is not always necessary to divide the pixel electrode  111 B and/or  111 A. The pixel electrode  111 B or  111 A may be designed to have an appropriate area. 
     The projection  126 A or  126 B shown in the fourth and fifth embodiments may be formed in place of the first opening areas  125 B and  125 D in an area where the first opening areas  125 B and  125 D are formed. 
     [Seventh Embodiment] 
       FIGS. 15A  to  15 K are plan views each illustrating the pixel electrode  111 A or  111 B and an associated second opening area formed in the opposing electrode  105 . 
     For instance, the pixel electrodes  111 A and  111 B may be square, as illustrated in  FIGS. 15A ,  15 C,  15 E and  15 G, or rectangular, as illustrated in  FIGS. 15I ,  15 J and  15 K. 
     As illustrated in  FIGS. 15B ,  15 D,  15 F and  15 H, the pixel electrodes  111 A and  111 B may be chamfered at four corners. 
     The pixel electrodes  111 A and  111 B may have rectangular or trapezoidal projections on any one or more of four sides. 
     The second opening area formed in the opposing electrode  105  may be a cross in shape, as illustrated in  FIGS. 15A  to  15 H, or may be a vertically elongate cross, as illustrated in  FIGS. 15I  to  15 K. 
     By forming the cross-shaped second opening area in the opposing electrode  105  in facing relation to the square or rectangular pixel electrodes  111 A and  111 B, a liquid crystal display device could have a broad viewing angle. 
       FIGS. 16A  to  16 G are plan views each illustrating the pixel electrodes  111 A and  111 B which are formed square, and an associated second opening area formed in the opposing electrode  105 . 
     The second opening area may be a circle (FIG.  16 A), a square (FIG.  16 B), a vertical line (FIG.  16 C), a horizontal line (FIG.  16 D), a cross (FIGS.  16 E and  16 F), or a combination of a cross and a square (FIG.  16 G). 
     While the present invention has been described in connection with certain preferred embodiments, it is to be understood that the subject matter encompassed by way of the present invention is not to be limited to those specific embodiments. On the contrary, it is intended for the subject matter of the invention to include all alternatives, modifications and equivalents as can be included within the spirit and scope of the following claims. 
     The entire disclosure of Japanese Patent Application No. 2002-224997 filed on Aug. 1, 2002 including specification, claims, drawings and summary is incorporated herein by reference in its entirety.

Technology Category: 3