Patent Publication Number: US-RE44470-E

Title: Liquid crystal display device comprising a picture element region including different electric field strength regions

Description:
This application is a continuation of application Ser. No. 09/783,217, filed Feb. 15, 2001, now U.S. Pat. No. 6,850,301 the entire content of which is hereby incorporated herein by reference in this application. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to a liquid crystal display device. More specifically, the present invention relates to a liquid crystal display device having a wide viewing angle characteristic. 
     A liquid crystal display device is a flat display device with advantageous features such as a reduced thickness, a reduced weight, a reduced power consumption, etc. However, a problem of a liquid crystal display device is that the appearance of the displayed image varies depending upon the direction from which it is viewed, i.e., the “viewing angle dependency” is substantial. The substantial viewing angle dependency of a liquid crystal display device is primarily due to the fact that liquid crystal molecules having a uniaxial optical anisotropy are uniformly oriented in the display plane. 
     An effective method to improve the viewing angle characteristic of a liquid crystal display device is to produce a so-called “multi-domain orientation” by forming a plurality of regions of different orientations within a picture element region. Various methods have been proposed in the art to realize a multi-domain orientation. Typical methods, among others, for realizing a multi-domain orientation in a liquid crystal display device of a vertical alignment mode include those disclosed in Japanese Laid-Open Patent Publication No. 6-301036 and Japanese Laid-Open Patent Publication No. 11-258606. 
     Japanese Laid-Open Patent Publication No. 6-301036 discloses a method in which an opening is provided in a counter electrode which opposes a picture element electrode via a liquid crystal layer interposed therebetween so as to control the orientation direction of the liquid crystal molecules by utilizing the inclination (bending) of an electric field in the vicinity of the region where the opening is provided. An inclination of an electric field means the production of an electric field component parallel to the substrate plane (the plane of the liquid crystal layer). Therefore, the direction in which liquid crystal molecules having a negative dielectric anisotropy (which are in a vertical alignment in the absence of an applied voltage) are inclined in the presence of an applied voltage (i.e., the azimuth angle direction: the direction of the long axis of inclined liquid crystal molecules as it is projected onto the substrate surface) is defined by the electric field component parallel to the substrate plane. In other words, a component of an inclined electric field which is parallel to the substrate plane exerts an orientation-regulating force. 
     Japanese Laid-Open Patent Publication No. 11-258606 discloses that a multi-domain orientation can be obtained by forming a protrusion, a depression or a slit (an opening provided in an electrode) on one surface of each of a pair of substrates opposing each other via a liquid crystal layer interposed therebetween (e.g., a TFT substrate and a color filter substrate) which is closer to the liquid crystal layer. With either one of the methods disclosed in these publications, it is possible to realize a desirable viewing angle characteristic by using the method in combination with an appropriate optical compensation film. 
     However, a study conducted by the inventor of the present invention revealed that the techniques disclosed in the publications above have the following problems. 
     With the method of Japanese Laid-Open Patent Publication No. 6-301036, it is difficult to obtain a uniform multi-domain orientation. Moreover, when the value of the voltage applied across the liquid crystal layer is changed, it takes a relatively long time to complete the change in the orientation according to the change in the voltage value; that is, the response speed is slow. It is believed that these problems are caused by the fact that the orientation-regulating force for achieving a multi-domain orientation (a force for orienting the liquid crystal molecules in a particular direction) is relatively weak in this method. 
     The problems as described above do not occur with the method of Japanese Laid-Open Patent Publication No. 11-258606. It is believed that with this method, a sufficiently strong orientation-regulating force is obtained, thereby realizing a relatively stable multi-domain orientation. However, this method has the following problems. 
     First, if the method disclosed in this publication is employed, it is necessary to provide a protrusion, a depression or a slit on both of the pair of substrates interposing the liquid crystal layer therebetween in order to achieve a multi-domain orientation, thereby complicating the production process of the liquid crystal display device and lowering the production efficiency. 
     In a plasma-addressed liquid crystal display device (hereinafter, referred to as a “PALC”), a thin glass plate (which forms a part of a plasma cell substrate) having a thickness on the order of 10 μm and an area on the order of 1 m 2  is arranged on the side of the liquid crystal layer. Therefore, it is difficult to provide a protrusion or a depression on the surface of the plasma cell substrate which is closer to the liquid crystal layer. Moreover, although the thin glass plate itself functions as an electrode (it is sometimes called a “virtual electrode”), it is not an electrode made of a conductive layer, whereby a slit (an opening provided in an electrode) cannot be provided therein. Therefore, it is very difficult to use the method disclosed in this publication with PALCs. 
     With the method of this publication, the orientation-regulating force can be increased by miniaturizing an orientation region by narrowing the interval between adjacent protrusions, depressions or slits, which defines the orientation region. However, since the positional precision of the orientation regions depends directly upon the precision of the attachment of the substrates with each other, the orientation region cannot be miniaturized excessively. 
     SUMMARY OF THE INVENTION 
     In view of the above-mentioned conventional problems, the present invention has been devised for the purpose of realizing a liquid crystal display device with a desirable viewing angle characteristic which has a sufficiently stable orientation and a sufficiently high response speed and yet can be produced efficiently. 
     A liquid crystal display device of the present invention includes a first substrate, a second substrate and a liquid crystal layer interposed between the first substrate and the second substrate, wherein: a plurality of picture element regions are provided each of which is defined by a first electrode provided on one side of the first substrate which is closer to the liquid crystal layer and a second electrode provided on the second substrate so as to oppose the first electrode via the liquid crystal layer; the liquid crystal layer is a vertical alignment type liquid crystal layer containing a liquid crystal material having a negative dielectric anisotropy; and each of the plurality of picture element regions includes at least one orientation-regulating region, the orientation-regulating region including a first region in which an electric field applied across the liquid crystal layer by the first electrode and the second electrode has a first electric field strength, a second region in which the electric field has a second electric field strength which is smaller than the first electric field strength, and a third region in which the electric field has a third electric field strength which is smaller than the second electric field strength, wherein the first, second and third regions are arranged in this order in a predetermined direction. Thus, the object described above is achieved. 
     Alternatively, a liquid crystal display device of the present invention includes a first substrate, a second substrate and a liquid crystal layer interposed between the first substrate and the second substrate, wherein: a plurality of picture element regions are provided each of which is defined by a first electrode provided on one side of the first substrate which is closer to the liquid crystal layer and a second electrode provided on the second substrate so as to oppose the first electrode via the liquid crystal layer; the liquid crystal layer is a vertical alignment type liquid crystal layer containing a liquid crystal material having a negative dielectric anisotropy; and each of the plurality of picture element regions includes at least one orientation-regulating region, the orientation-regulating region including a first region in which the first electrode and the second electrode have a first inter-electrode distance therebetween, a second region in which the first electrode and the second electrode have a second inter-electrode distance therebetween which is greater than the first inter-electrode distance, and a third region in which the first electrode and the second electrode have a third inter-electrode distance therebetween which is greater than the second inter-electrode distance, wherein the first, second and third regions are arranged in this order in a predetermined direction. Thus, the object described above is achieved. 
     Alternatively, a liquid crystal display device of the present invention includes a first substrate, a second substrate and a liquid crystal layer interposed between the first substrate and the second substrate, wherein: a plurality of picture element regions are provided each of which is defined by a first electrode provided on one side of the first substrate which is closer to the liquid crystal layer and a second electrode provided on the second substrate so as to oppose the first electrode via the liquid crystal layer; the liquid crystal layer is a vertical alignment type liquid crystal layer containing a liquid crystal material having a negative dielectric anisotropy; the first electrode includes a lower conductive layer, a dielectric layer covering the lower conductive layer, and an upper conductive layer provided on one side of the dielectric layer which is closer to the liquid crystal layer; the upper conductive layer includes an upper layer opening for each of the plurality of picture element regions, and the lower conductive layer includes a lower layer opening for each of the plurality of picture element regions; and each of the plurality of picture element regions includes at least one orientation-regulating region, the orientation-regulating region including a first region in which the liquid crystal layer is arranged between the upper conductive layer of the first electrode and the second electrode, a second region in which the liquid crystal layer and the dielectric layer located within the upper layer opening are arranged between the lower conductive layer of the first electrode and the second electrode, and a third region in which the liquid crystal layer and the dielectric layer located within the upper layer opening are arranged between the lower layer opening of the first electrode and the second electrode, wherein the first, second and third regions are arranged in this order in a predetermined direction. Thus, the object described above is achieved. 
     Preferably, each of the upper layer opening and the lower layer opening has a side extending in a direction perpendicular to the predetermined direction, and a boundary between the first region and the second region and a boundary between the second region and the third region extend along the side. 
     Preferably, a boundary between the first region and the second region and a boundary between the second region and the third region extend in a direction perpendicular to the predetermined direction. 
     Preferably, in each of the plurality of picture element regions, one surface of the first substrate which is closer to the liquid crystal layer is substantially flat. 
     Preferably, in each of the plurality of picture element regions, the liquid crystal layer has a substantially constant thickness. 
     Each of the plurality of picture element regions may include a plurality of orientation-regulating regions, the plurality of orientation-regulating regions having the same direction of arrangement of the first, second and third regions. 
     Preferably, each of the plurality of picture element regions includes a first orientation-regulating region in which the first, second and third regions are arranged in this order in a first direction, and a second orientation-regulating region in which the first, second and third regions are arranged in this order in a second direction which is different from the first direction. 
     Each of the plurality of picture element regions may include a plurality of at least one of the first orientation-regulating region and the second orientation-regulating region. 
     The first direction and the second direction may be opposite to each other. 
     More preferably, each of the plurality of picture element regions further includes a third orientation-regulating region in which the first, second and third regions are arranged in this order in a third direction which is different from the first and second directions, and a fourth orientation-regulating region in which the first, second and third regions are arranged in this order in a fourth direction which is different from the first, second and third directions, wherein the third and fourth directions are perpendicular to the first and second directions. 
     Preferably, the first orientation-regulating region and the second orientation-regulating region share at least one of the first region and the third region. 
     Each of the upper layer opening and the lower layer opening may have a polygonal shape or a circular shape, with the lower layer opening being located within the upper layer opening. In such a case, the center of gravity of the upper layer opening and that of the lower layer opening preferably coincide with each other in the substrate plane. While the shape of the upper layer opening and that of the lower layer opening may differ from each other, they are preferably similar to each other. 
     The first electrode may be a picture element electrode which is provided for each of the plurality of picture element regions, and a voltage may be applied to the first electrode via an active element which is provided for each of the plurality of picture element regions. 
     The second electrode may be a single counter electrode which is provided commonly for the plurality of picture element regions. 
     The plurality of picture element regions may be arranged in a matrix pattern having rows and columns; the first electrode may be provided as a plurality of electrodes which are arranged in a stripe pattern corresponding to the columns; and the second substrate may include a thin dielectric plate, an insulative substrate, and a plurality of plasma channels which are arranged in a stripe pattern corresponding to the rows between the thin dielectric plate and the insulative substrate, and the second electrode may be provided as a plurality of virtual electrodes respectively formed by corresponding regions of the thin dielectric plate respectively opposing the plurality of plasma channels which are arranged in a stripe pattern. 
     The upper conductive layer and the lower conductive layer may be electrically connected to each other. 
     The functions of the present invention will now be described. 
     A liquid crystal display device of a vertical alignment mode according to the present invention includes a first electrode and a second electrode which apply a voltage across liquid crystal molecules having a negative dielectric anisotropy (which are vertically aligned in the absence of an applied voltage). The orientation direction of the liquid crystal molecules changes in each picture element region according to an electric field which is produced in a liquid crystal layer by the voltage applied between the first electrode and the second electrode, thereby displaying an image. 
     Each of the plurality of picture element regions includes at least one orientation-regulating region, the orientation-regulating region including a first region in which an electric field applied across the liquid crystal layer by the first electrode and the second electrode has a first electric field strength, a second region in which the electric field has a second electric field strength which is smaller than the first electric field strength, and a third region in which the electric field has a third electric field strength which is smaller than the second electric field strength, wherein the first, second and third regions are arranged in this order in a predetermined direction. 
     Such first, second and third regions can be provided by setting different inter-electrode distances between the first electrode and the second electrode, for example. The electric field strength distribution as described above can be realized by employing a structure where the orientation-regulating region of each of the plurality of picture element regions includes a first region in which the first electrode and the second electrode have a first inter-electrode distance therebetween, a second region in which the first electrode and the second electrode have a second inter-electrode distance therebetween which is greater than the first inter-electrode distance, and a third region in which the first electrode and the second electrode have a third inter-electrode distance therebetween which is greater than the second inter-electrode distance. The inter-electrode distance of a region refers to the distance between a pair of electrodes in the region which substantially determines the strength of the electric field produced therebetween. A picture element region having such an inter-electrode distance distribution can be realized by employing the following structure, for example. 
     The first electrode includes, for each picture element region, a lower conductive layer, a dielectric layer covering the lower conductive layer, and an upper conductive layer provided on one side of the dielectric layer which is closer to the liquid crystal layer. The upper conductive layer includes an upper layer opening, and the lower conductive layer includes a lower layer opening. The upper conductive layer and the lower conductive layer are arranged so as to provide a first region in which the liquid crystal layer in the picture element region is arranged between the upper conductive layer of the first electrode and the second electrode (this interval defines the first inter-electrode distance), a second region in which the liquid crystal layer and the dielectric layer located within the upper layer opening are arranged between the lower conductive layer of the first electrode and the second electrode (this interval defines the second inter-electrode distance), and a third region in which the liquid crystal layer and the dielectric layer located within the upper layer opening are arranged between the lower layer opening of the first electrode and the second electrode (this interval defines the third inter-electrode distance). Thus, in this structure, the distance between the upper conductive layer (a region excluding the upper layer opening) and the second electrode defines the first inter-electrode distance, and the distance between the lower conductive layer (a region excluding the lower layer opening) and the second electrode defines the second inter-electrode distance. The third inter-electrode distance is defined by the distance between the opening of the first electrode (a portion where the upper layer opening and the lower layer opening overlap with each other and where no conductive layer is formed) and the second electrode, whereby the third inter-electrode distance is infinite. 
     The inter-electrode distance as used herein is as described above, and when at least one of a pair of opposing electrodes has an opening (a region where no conductive film exists), the inter-electrode distance of the region corresponding to the opening is infinite. The “first electrode” and the “second electrode” as used herein are electrodes which define a picture element region, and are members having a function of producing an electric field in the liquid crystal layer so as to change the orientation of the liquid crystal layer, thereby producing a display. Each of the “first electrode” and the “second electrode” may include not only a single conductive layer but also a plurality of conductive layers separated from one another by a dielectric layer. Moreover, each conductive layer may include an opening. 
     The functions of a liquid crystal display device of the present invention will be described by illustrating, for example, an orientation-regulating region formed by the first electrode (having the upper conductive layer and the lower conductive layer) and the second electrode. 
     The strength of an electric field produced in the liquid crystal layer of the first region is directly influenced primarily by the potential difference between the upper conductive layer and the second electrode, and the strength of an electric field produced in the liquid crystal layer of the second region is directly influenced by the potential difference of a liquid crystal layer portion which is obtained by division (primarily capacitance division) of the potential difference between the lower conductive layer and the second electrode by the dielectric layer and the liquid crystal layer. Therefore, the strength of the electric field applied across the liquid crystal layer by the first electrode and the second electrode can be easily made smaller in the second region than in the first region. As a result, in the vicinity of the boundary between the first region and the second region, an inclination (bending) of an electric field occurs. As described above, an inclination of an electric field means the production of an electric field component parallel to the substrate plane (the plane of the liquid crystal layer), and the component parallel to the substrate plane exerts an orientation-regulating force. Thus, an orientation-regulating force occurs in the vicinity of the boundary between the first region and the second region. The above-described relationship can be realized with, for example, a simple structure where the upper conductive layer and the lower conductive layer are electrically connected to each other. 
     The liquid crystal layer of the third region is located between the lower layer opening located within the upper layer opening and the second electrode, and there are no electrodes (conductive layers) opposing each other which would produce an electric field directly across the liquid crystal layer of the third region, whereby the liquid crystal layer of the third region is influenced by an electric field from other regions of electrodes (conductive layers) existing around the third region. Therefore, the strength of the electric field to be applied across the liquid crystal layer of the third region is smaller than the strength of the electric field to be applied across the liquid crystal layer of surrounding regions. As a result, an inclination (bending) of an electric field occurs also in the vicinity of the boundary between the second region and the third region, thereby producing an orientation-regulating force also in the vicinity of the boundary between the second region and the third region. Since the first, second and third regions are arranged in a single direction, the direction of the orientation-regulating force occurring in the vicinity of the boundary between the first region and the second region and that occurring in the vicinity of the boundary between the second region and the third region are the same, whereby a substantial orientation-regulating force occurs also in the second region which exists between these boundaries. Of course, the direction of the orientation-regulating force substantially occurring in the second region is the same as that of the orientation-regulating force in the vicinity of these two boundary regions. Thus, the first, second and third regions, arranged in a single direction as a set, serve as a single orientation-regulating region, wherein the orientation direction of the liquid crystal molecules which are regulated by the orientation-regulating region is the direction of arrangement of the first, second and third regions. 
     At least one orientation-regulating region is provided for each picture element region, and in the orientation-regulating region, the first, second and third regions are arranged in this order in a predetermined direction. Therefore, the strength of an electric field produced in the liquid crystal layer gradually decreases in the predetermined direction. An inclined electric field is produced between the first region and the second region, and an inclined electric field is produced between the second region and the third region, wherein these inclined electric fields have the same inclination direction in the predetermined direction. Therefore, the liquid crystal molecules of the liquid crystal layer in the orientation-regulating region change the orientation direction thereof so that they are inclined in a single direction in the presence of an applied voltage. As a result, it is possible to obtain a sufficiently stable orientation and a sufficiently high response speed. Moreover, this function can be obtained by changing the structure of only the first electrode. Therefore, the present invention does not complicate the production process and can easily be used with various types of liquid crystal display devices. The predetermined direction in which the liquid crystal molecules in the orientation-regulating region are inclined can be suitably set according to the viewing angle characteristic which is required for the liquid crystal display device. 
     The functions of the present invention have been described in the above with respect to a structure where the orientation-regulating region includes first, second and third regions. Of course, these functions can be obtained if the orientation-regulating region includes at least the first, second and third regions, and the orientation-regulating region may further include a fourth region, a fifth region, and so on, as necessary. The fourth region is a region with a fourth electric field strength which is smaller than the third electric field strength of the third region, and the fifth region is a region with a fifth electric field strength which is even smaller than the fourth electric field strength. The fourth region and the fifth region are arranged in this order in the predetermined direction, following the third region. Thus, the first, second, third, fourth and fifth regions, arranged in a single direction as a set, serve as a single orientation-regulating region, wherein the orientation direction of the liquid crystal molecules which are regulated by the orientation-regulating region is the direction of arrangement of the first to fifth regions. 
     For example, the fourth region has a fourth inter-electrode distance which is greater than the third inter-electrode distance, and the fifth region has a fifth inter-electrode distance which is greater than the fourth inter-electrode distance. Specifically, for example, a further dielectric layer is provided under the lower conductive layer (on the substrate side) of the first electrode, and a conductive layer (referred to as the “additional conductive layer”) having an opening (referred to as the “additional opening”) is provided under the further dielectric layer. The additional conductive layer is arranged so that the opening of the additional conductive layer is located within the lower layer opening of the lower conductive layer. In such a structure, a region of the liquid crystal layer which is located between a conductive portion of the additional conductive layer (i.e., a portion thereof excluding the additional opening) and the second electrode (this interval defines the fourth inter-electrode distance) serves as the fourth region, and a region of the liquid crystal layer which is located between the additional opening of the additional conductive layer and the second electrode (this interval defines the fifth inter-electrode distance, which in this example infinite) serves as the fifth region. Alternatively, the third region can be formed by providing a dielectric layer under the lower layer opening defining the third region and further providing a conductive layer having no opening under this dielectric layer (that is, the third inter-electrode distance, which is infinite in the above example, may be finite). This structure is preferred because all regions of the liquid crystal layer are sandwiched by conductive layers, whereby the electric field produced in the liquid crystal layer is less likely affected by an external influence. 
     Preferably, the boundary between the first region and the second region and the boundary between the second region and the third region extend in a direction perpendicular to the predetermined direction. For example, if one employs a structure where each of the upper layer opening and the lower layer opening has a side extending in a direction perpendicular to the predetermined direction, and the boundary between the first region and the second region and the boundary between the second region and the third region extend in parallel to the side of the upper layer opening and the lower layer opening, the directions of the inclined electric fields produced around the respective region boundaries coincide with each other also in terms of the azimuth angle direction (the direction in the display plane), thereby increasing the orientation-regulating effect. 
     The orientation-regulating region can be formed by changing the structure of one of the pair of electrodes opposing each other via the liquid crystal layer (i.e., the first electrode). Therefore, the surface of the first substrate (the substrate on which the first electrode is formed) which is closer to the liquid crystal layer can be made substantially flat in each of the picture element regions. In other words, it is not necessary to provide a protrusion or a depression for defining the orientation direction of the liquid crystal molecules. Moreover, the thickness of the liquid crystal layer in the picture element regions can be made substantially constant. Therefore, the orientation-regulating region according to the present invention can be easily used with various types of liquid crystal display devices, and does not complicate the production process. 
     It is possible to reduce the area of each orientation-regulating region by providing in each picture element region a plurality of orientation-regulating regions which regulate the orientation direction of the liquid crystal molecules in the same direction. Thus, it is possible to improve the response speed of a mono-domain-orientation picture element region. 
     For improving the viewing angle characteristic, it is preferred to provide in each picture element region a plurality of orientation-regulating regions which regulate the orientation direction of the liquid crystal molecules in directions different from one another, thereby forming a multi-domain orientation. In such a case, it is possible to reduce the area of each orientation-regulating region by providing a plurality of orientation-regulating regions which regulate the orientation direction of the liquid crystal molecules in the same direction. Thus, it is possible to improve the response speed of the picture element region of a multi-domain orientation. 
     The plurality of orientation-regulating regions preferably include orientation-regulating regions where the directions in which the liquid crystal molecules are oriented by the orientation-regulating regions (such a direction is also referred to as the orientation direction, the inclination direction or the orientation axis of the orientation-regulating region) are opposite to each other. When a plurality of orientation-regulating regions are provided for each picture element region, it is preferred that the orientation-regulating regions have opposite inclination directions of liquid crystal molecules, so that the respective viewing angle dependencies of the orientation-regulating regions can be compensated for by each other, thereby efficiently improving the viewing angle characteristic. 
     Moreover, it is possible to obtain an even more symmetrical viewing angle characteristic by providing four or more orientation-regulating regions having different inclination directions (orientation axes). Particularly, it is possible to obtain a liquid crystal display device having a high light efficiency in addition to the highly symmetrical viewing angle characteristic, by providing four orientation-regulating regions respectively having four different inclination directions (orientation axes) so that any two inclination directions selected from among the four inclination directions have an angle which is an integral multiple of about 90° with respect to each other. 
     When a plurality of orientation-regulating regions which regulate the orientation direction of the liquid crystal molecules in different directions are provided in each picture element region (i.e., in the case of a multi-domain orientation), it is preferred to arrange the plurality of orientation-regulating regions so that at least two of the orientation-regulating regions share the first and second regions so as to obtain a display with a high light efficiency (i.e., a bright display). 
     Each of the first region and the third region is provided for the purpose of inclining the electric field along the boundary between that region and the second region, i.e., to obtain an orientation-regulating force therebetween. The second region is a region in which the liquid crystal molecules are oriented substantially uniformly due to this orientation-regulating force, thereby obtaining a substantially uniform amount of transmitted light across the region. Generally, in a liquid crystal display device, if one employs a structure with which a uniform amount of transmitted light can be obtained across the entire picture element region (e.g., a TN type liquid crystal display device), it is possible to obtain the maximum light efficiency (the highest transmittance) for the picture element region as a whole (or for the display region of the liquid crystal display device as a whole). Thus, in the case of a liquid crystal display device of the present invention, it is preferred in terms of the light efficiency that the area of the entire picture element region which is occupied by the second region (where a uniform amount of transmitted light can be obtained) is increased as much as possible, thereby increasing the light efficiency. Accordingly, in order to increase the light efficiency, it is preferred that the area of the entire picture element region which is occupied by the first and third regions is reduced as much as possible within such an extent that a desired orientation-regulating force can be obtained so as to increase as much as possible the area occupied by the second region. 
     It is possible to reduce the area of a picture element region occupied by the first region and the third region by arranging the plurality of orientation-regulating regions so that the orientation-regulating regions share at least one of the first region and the third region. Thus, it is possible to improve the light efficiency. When two types of orientation-regulating regions respectively having orientation-regulating directions opposite to each other (different from each other by 180°) are arranged in an alternating pattern, the first region and the third region can be shared around boundaries between the orientation-regulating regions. The first region and the third region can be shared because the electric field inclination directions, i.e., the orientation-regulating directions, are opposite to each other(different from each other by 180°) between the two boundaries respectively between the first region and the second region and between the third region and the second region. 
     It is possible to improve the viewing angle characteristic also by orienting the liquid crystal molecules in an axial symmetry. It is possible to obtain a stable axially symmetrical orientation for example by providing an upper layer opening and a lower layer opening each having a polygonal shape or a circular shape, with the lower layer opening being provided within the upper layer opening. When employing a polygonal shape for the openings, it is preferred to employ a regular polygon in terms of the symmetry. However, it is possible to realize a substantially axially symmetrical orientation with an irregular polygon by selecting the irregular polygon according to the shape of the picture element region, etc. 
     A sufficient response speed and viewing angle characteristic may be obtained even when a mono-domain structure is employed for each picture element region. Since the display signals of adjacent picture element regions are correlated with each other, it is possible to improve the viewing angle characteristic when the orientation directions of the orientation-regulating regions are different from each other (preferably perpendicular to each other) between adjacent picture element regions. In the case of a color display device, this can be achieved by employing different orientation directions for adjacent pixel regions, each pixel region being comprised of R, G and B picture element regions. If a picture element region is small, it is possible to achieve a sufficient response speed by providing one orientation-regulating region therein. Moreover, as described above, it is possible to improve the response speed of a mono-domain-orientation picture element region by forming a plurality of orientation-regulating regions therein which regulate the liquid crystal molecules in the same direction. 
     The electrode structure including at least two conductive layers (each having openings therein) with a dielectric layer interposed therebetween can be used for either the picture element electrodes or the counter electrode of an active matrix type liquid crystal display device. Moreover, the electrode structure can also be used for the signal electrodes in a PALC which are arranged to oppose the plasma channels via a liquid crystal layer interposed therebetween. Thus, the electrode structure can be widely used with known liquid crystal display devices. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a diagram schematically illustrating a cross-sectional structure of a liquid crystal display device  100  of one embodiment of the present invention along with electric force lines. 
         FIG. 1B  is a diagram schematically illustrating the cross-sectional structure of the liquid crystal display device  100  of one embodiment of the present invention along with an equipotential line. 
         FIG. 1C  is a diagram schematically illustrating a potential distribution produced in the vicinity of the interface between a liquid crystal layer and a first electrode of the liquid crystal display device  100  of one embodiment of the present invention. 
         FIG. 1D  is a plan view schematically illustrating the liquid crystal display device  100  of one embodiment of the present invention. 
         FIG. 2A  is a diagram schematically illustrating a cross-sectional structure of a liquid crystal display device  200  of Comparative Example along with an equipotential line. 
         FIG. 2B  is a plan view schematically illustrating the liquid crystal display device  200  of Comparative Example. 
         FIG. 3A  is a plan view schematically illustrating a liquid crystal display device  300  of Embodiment 1 of the present invention. 
         FIG. 3B  is a cross-sectional view schematically illustrating the liquid crystal display device  300  of Embodiment 1 of the present invention. 
         FIG. 4  is a diagram schematically illustrating a liquid crystal display device  400  of Embodiment 1 of the present invention. 
         FIG. 5  is a graph illustrating the applied voltage dependency of the transmittance of the liquid crystal display device  400 . 
         FIG. 6  is an iso-contrast contour curve (contrast ratio=30) of the liquid crystal display device  400 . 
         FIG. 7  is a diagram schematically illustrating a liquid crystal display device  500  of Embodiment 1 of the present invention. 
         FIG. 8  is a plan view of a counter substrate  600 b used in a liquid crystal display device of Embodiment 2 of the present invention. 
         FIG. 9  is a perspective view schematically illustrating a liquid crystal display device  700  of Embodiment 3 of the present invention. 
         FIG. 10  is a cross-sectional view schematically illustrating the liquid crystal display device  700  of Embodiment 3 of the present invention. 
         FIG. 11  is a diagram schematically illustrating the planar structure of a data electrode  714  of the liquid crystal display device  700 . 
         FIG. 12  is a diagram schematically illustrating the structure of a first electrode  814  used in a liquid crystal display device according to the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. First, the electrode structure of the liquid crystal display device of the present invention and the function thereof will be described. 
     In the present specification, a region of a liquid crystal display device corresponding to a “picture element”, which is the minimum unit of display, will be referred to as a “picture element region”. In a color liquid crystal display device, R, G and B “picture elements” correspond to one “pixel”. In an active matrix type liquid crystal display device, a picture element region is defined by a picture element electrode and a counter electrode which opposes the picture element electrode. In a PALC, a picture element region is defined as a region where one of column electrodes which are arranged in a stripe pattern crosses one of plasma channels which are also arranged in a stripe pattern perpendicular to the column electrodes. In an arrangement with a black matrix, strictly speaking, a picture element region is a portion of each region across which a voltage is applied according to the intended display state which corresponds to an opening of the black matrix. 
     A liquid crystal display device  100  of one embodiment of the present invention will be described with reference to  FIG. 1A ,  FIG. 1B ,  FIG. 1C  and  FIG. 1D .  FIG. 1A  and  FIG. 1B  are cross-sectional views of the liquid crystal display device  100 , and  FIG. 1D  is a plan view thereof.  FIG. 1A  and  FIG. 1B  are cross-sectional views both taken along line  1 A- 1 A′ of  FIG. 1D .  FIG. 1C  schematically illustrates the potential distribution produced in the liquid crystal layer of the liquid crystal display device  100 . 
     In the following description, the color filter and the black matrix are omitted for the sake of simplicity. In subsequent figures, each element having substantially the same function as that of the liquid crystal display device  100  will be denoted by the same reference numeral and will not be further described. 
     The liquid crystal display device  100  includes a first substrate (e.g., an active matrix substrate)  100 a, a second substrate (e.g., a counter substrate)  100 b, and a liquid crystal layer  30  provided between the first substrate  100 a and the second substrate  100 b. Liquid crystal molecules  30 a of the liquid crystal layer  30  have a negative dielectric anisotropy, and are oriented by a vertical alignment layer (not shown), which is provided on one surface of each of the first substrate  100 a and the second substrate  100 b which is closer to the liquid crystal layer  30 , in a vertical alignment with respect to the surface of the vertical alignment layer in the absence of an applied voltage across the liquid crystal layer  30 . Since the surface of the vertical alignment layer is substantially parallel to the surfaces of the substrates  100 a and  100 b, the liquid crystal molecules  30 a are also referred to as being “vertical to the substrate surface”. In the present specification, the liquid crystal layer  30  in the absence of an applied voltage is referred to as being in a “vertical alignment”, and the liquid crystal layer  30  is referred to as a “vertical alignment type liquid crystal layer”. However, the liquid crystal molecules  30 a of the liquid crystal layer  30  in the vertical alignment may be slightly inclined from the normal to the surface of the vertical alignment film (the substrate surface) depending upon the type of the vertical alignment film or the type of the liquid crystal material being used. Generally, the vertical alignment refers to a state where the liquid crystal molecular axis is oriented at an angle of about 85° or more with respect to the surface of the vertical alignment film. 
     The first substrate  100 a of the liquid crystal display device  100  includes a transparent substrate (e.g., a glass substrate)  10  and a first electrode (e.g., a picture element electrode)  14  which is formed on the surface thereof. The second substrate  100 b includes a transparent substrate (e.g., a glass substrate)  20  and a second electrode (e.g., a counter electrode)  22  which is formed on the surface thereof. The orientation of the liquid crystal layer  30  changes for each picture element region according to the voltage applied thereacross between the first electrode  14  and the second electrode  22  which are arranged so as to oppose each other via the liquid crystal layer  30 . A display is produced by utilizing a phenomenon that the polarization of light having passed through the liquid crystal layer  30  changes along with the change in the orientation of the liquid crystal layer  30 . 
     The first electrode  14  of the liquid crystal display device  100  includes a lower conductive layer  11 , a dielectric layer  12  covering the lower conductive layer  11 , and an upper conductive layer  13  provided on one side of the dielectric layer  12  which is closer to the liquid crystal layer  30 . The lower conductive layer  11  includes a lower layer opening  11 a, and the upper conductive layer  13  includes an upper layer opening  13 a. They are arranged so that the lower layer opening  11 a is located within the upper layer opening  13 a. The lower layer opening  11 a and the upper layer opening  13 a each refer to a portion of the respective conductive layers where a conductive film is not formed. 
     For the sake of simplicity, the second electrode  22  is herein assumed to be a single film of a conductive material (having no opening within a picture element region) which is formed across the entirety of one picture element region. However, the second electrode  22 , having such a structure as described above and opposing the first electrode  14 , is not required to have any special structure for obtaining the effects of the present invention, and may be one which has a known electrode structure. 
     The two-dimensional arrangement of the first electrode  14  and the second electrode  22  in the display plane will be described. The upper layer opening  13 a of the upper conductive layer  13  is formed so as to include therein the lower layer opening  11 a of the lower conductive layer  11 . Thus, as illustrated in  FIG. 1D , the upper layer opening  13 a has a width (length in the lateral direction of the figure) which is greater than that of the lower layer opening  11 a. Preferably, the upper layer opening  13 a and the lower layer opening  11 a have sides parallel to each other, and the lower layer opening  11 a is arranged to be located in the center of the upper layer opening  13 a in the width direction thereof. 
     The first electrode  14  and the second electrode  22  arranged as described above form regions therebetween having different structures. Specifically, the liquid crystal display device  100  includes a first region R 1  in which the liquid crystal layer  30  is arranged between the upper conductive layer  13  and the second electrode  22 , a second region R 2  in which the liquid crystal layer  30  and the dielectric layer  12  located within the upper layer opening  13 a are arranged between the lower conductive layer  11  and the second electrode  22 , and a third region R 3  in which the liquid crystal layer  30  and the dielectric layer  12  located within the upper layer opening  13 a are arranged between the lower layer opening  11 a and the second electrode  22 . 
     In the present embodiment, orientation-regulating regions T 1  and orientation-regulating regions T 2  are arranged in an alternating pattern. In the orientation-regulating region T 1 , the first region R 1 , the second region R 2  and the third region R 3  are arranged in this order in a direction L in  FIG. 1A  and  FIG. 1B . In the orientation-regulating region T 2 , the regions R 1 , R 2  and R 3  are arranged in this order in a direction −L (opposite to the direction L). The first region R 1  and the third region R 3  are arranged so that they are shared by the orientation-regulating region T 1  and the orientation-regulating region T 2  adjacent to each other. 
     The function of the electrode structure of the liquid crystal display device  100  will be described with reference to  FIG. 1A ,  FIG. 1B  and  FIG. 1C . 
       FIG. 1A  schematically illustrates an electric force line EF of an electric field produced in the liquid crystal layer  30  of the liquid crystal display device  100  in the presence of an applied voltage, along with the change in the orientation direction of the liquid crystal molecules  30 a.  FIG. 1B  schematically illustrates an equipotential line EQ (the cross section of the equipotential surface) of an electric field produced through the liquid crystal layer  30  in the presence of an applied voltage, along with the change in the orientation direction of the liquid crystal molecules  30 a. It is assumed that the absolute value of the voltage is greater than the absolute value of the threshold voltage. Generally, in the present invention, an orientation-regulating force from an electric field can be obtained if the relationship Vb≦Va&lt;Vc or Vb≧Va&gt;Vc is satisfied, wherein Va denotes the potential applied to the lower conductive layer  11  of the first electrode  14 , Vb denotes the potential applied to the upper conductive layer  13  of the first electrode  14 , and Vc denotes the potential applied to the second electrode  22 . A case where a positive voltage is applied to the first electrode  14  will be described below while assuming that the second electrode  22  is at the ground potential for the sake of simplicity. It is also assumed that an equal potential is applied to the lower conductive layer  11  and the upper conductive layer  13  of the first electrode  14 . 
     The strength of an electric field produced in the liquid crystal layer  30  of the first region R 1  is directly influenced primarily by the potential difference between the upper conductive layer  13  and the second electrode  22 , and the strength of an electric field produced in the liquid crystal layer  30  of the second region R 2  is directly influenced by the potential difference which is obtained by division (primarily capacitance division) of the potential difference between the lower conductive layer  11  and the second electrode  22  by the dielectric layer  12  and the liquid crystal layer  30 . Therefore, the potential difference applied across the liquid crystal layer  30  by the first electrode  14  and the second electrode  22  is smaller in the second region R 2  than in the first region R 1 , whereby the electric field produced in the liquid crystal layer  30  in the vicinity of the boundary between the second region R 2  and the first region R 1  is inclined. 
     There are no electrodes (conductive layers) opposing each other which would produce an electric field directly through the liquid crystal layer  30  of the third region R 3 , whereby the liquid crystal layer  30  of the third region R 3  is influenced by an electric field from other regions of electrodes (conductive layers) existing around the third region R 3 . Therefore, the strength of the electric field to be applied across the liquid crystal layer  30  of the third region R 3  is smaller than the strength of the electric field to be applied across the liquid crystal layer  30  of the regions R 2  existing around the third region R 3 , whereby the electric field produced in the liquid crystal layer  30  in the vicinity of the boundary between the second region R 2  and the first region R 1  is inclined. 
     As a result, the electric field (electric force line EF) produced in the orientation-regulating region T 1  or T 2  of the liquid crystal layer  30  of the liquid crystal display device  100  is inclined in the vicinity of the boundary between the first region R 1  and the second region R 2  and in the vicinity of the boundary between the second region R 2  and the third region R 3  as illustrated in  FIG. 1A . The inclination direction is in the direction in which the first region R 1 , the second region R 2  and the third region R 3  are arranged in this order. Specifically, the electric field is inclined leftward in the orientation-regulating region T 1  and rightward in the orientation-regulating region T 2 . The liquid crystal molecules  30 a having a negative dielectric anisotropy are subject to, in the electric field, a torque such as to orient the molecular axis vertically to the direction of the electric field (electric force line EF), whereby the liquid crystal molecules  30 a are inclined in the vicinity of the boundary between the first region R 1  and the second region R 2  and in the vicinity of the boundary between the second region R 2  and the third region R 3  according to the directions of the respective inclined electric fields (see arrows in  FIG. 1A ,  FIG. 1B  and  FIG. 1D ). The liquid crystal molecules  30 a are inclined counterclockwise in the first orientation-regulating region T 1  and clockwise in the second orientation-regulating region T 2 . 
     An electric field substantially vertical to the substrate is produced in the vicinity of the center of the second region R 2  located between the first region R 1  and the third region R 3 . Therefore, the liquid crystal molecules  30 a present in this region are not subject to a torque from an electric field which would incline the liquid crystal molecules  30 a in a particular direction. However, the second region R 2  is provided between the first region R 1  and the third region R 3 , and the direction of the produced inclined electric field is the same in the vicinity of the boundary between the first region R 1  and the second region R 2  and in the vicinity of the boundary between the second region R 2  and the third region R 3 , whereby the liquid crystal molecules  30 a therein are accordingly inclined in the same direction. Therefore, the liquid crystal molecules present in the vicinity of the center of the second region R 2  are influenced by the change in the orientation of the liquid crystal molecules  30 a in the vicinity of the boundaries so as to be inclined in the same direction. In other words, the liquid crystal molecules  30 a in the vicinity of the boundary between the second region R 2  and the first region R 1  and those in the vicinity of the boundary between the second region R 2  and the third region R 3  (which influence the orientation direction (inclination direction) of the liquid crystal molecules  30 a present in the vicinity of the center of the second region R 2  in which the inclination direction is not uniquely regulated by an electric field) are both inclined in the same direction. As a result, all of the liquid crystal molecules  30 a are stably inclined in the same direction within each orientation-regulating region. 
       FIG. 1C  is a diagram schematically illustrating the potential distribution along the boundary between the first electrode  14  and the liquid crystal layer  30 . The vertical axis denotes the potential, and the horizontal axis corresponds to the position in  FIG. 1A  or  FIG. 1D . Assuming that the potential of the second electrode  22  is zero (ground potential), the value of a voltage to be applied across the liquid crystal layer  30  in each region is equal to the value of the potential of that region as illustrated in  FIG. 1C . Thus, the voltages applied across the liquid crystal layer  30  in the respective regions, the first region R 1 , the second region R 2  and the third region R 3 , have values of V 1 , V 2  and V 3 , respectively. Therefore, as illustrated in  FIG. 1C , the voltage V 2  applied across the liquid crystal layer  30  of the second region R 2  is lower than the voltage V 1  applied across the liquid crystal layer  30  of the first region R 1 , and the voltage V 3  applied across the third region R 3  is even lower than the voltage V 2  applied across the second region R 2 . Therefore, the electric field produced in the orientation-regulating region T 1  or T 2  as represented by the equipotential line EQ is a curve which repeatedly goes up and down in a stepped manner as illustrated in  FIG. 1B . 
     The equipotential line EQ illustrated in  FIG. 1B  is inclined where adjacent regions have different potentials, i.e., in the vicinity of the boundary between the first region R 1  and the second region R 2  and in the vicinity of the boundary between the second region R 2  and the third region R 3 . The direction of the potential gradient is in the direction in which the first region R 1 , the second region R 2  and the third region R 3  are arranged in this order (see, for example, arrows in  FIG. 1D ). The liquid crystal molecules  30 a having a negative dielectric anisotropy are subject to a torque from an electric field such that the molecular axis is oriented in parallel to the equipotential line EQ. Therefore, in a region having such a potential gradient as described above, the liquid crystal molecules  30 a are inclined in the direction of the potential gradient. 
     As the area (length in a cross-sectional view) of the second region R 2  increases, there may be a region with no potential gradient in the vicinity of the center of the second region R 2 . (this is indicated by vertical electric force lines EF in  FIG. 1A ). The liquid crystal molecules  30 a in this region are not subject to a torque from an electric field which would incline the liquid crystal molecules  30 a in a particular direction. However, the second region R 2  is provided between the first region R 1  and the third region R 3 , and the liquid crystal molecules  30 a are inclined in the same direction according to the direction of the produced potential gradient in the vicinity of the boundary between the first region R 1  and the second region R 2  and in the vicinity of the boundary between the second region R 2  and the third region R 3 . Therefore, the liquid crystal molecules present in the vicinity of the center of the second region R 2  are influenced by the change in the orientation of the liquid crystal molecules  30 a in the vicinity of the boundaries so as to be inclined in the same direction. In other words, the liquid crystal molecules  30 a in the vicinity of the boundary between the second region R 2  and the first region R 1  and those in the vicinity of the boundary between the second region R 2  and the third region R 3  (which influence the orientation direction (inclination direction) of the liquid crystal molecules  30 a present in the vicinity of the center of the second region R 2  in which the inclination direction is not uniquely regulated by an electric field) are both inclined in the same direction. As a result, all of the liquid crystal molecules  30 a are stably inclined in the same direction within each orientation-regulating region T 1  or T 2 . 
     The greater is the extent of the second region R 2 , the larger the portion (a portion of the second region) where a uniform orientation is exhibited in a picture element region. The region where a uniform orientation is exhibited is a region where a uniform transmittance is obtained in a produced liquid crystal display device. The larger is this region, the higher the transmittance of the entire picture element region can be made (ideally, a uniform orientation should be exhibited across the entire picture element region as in, for example, a TN type liquid crystal display device known in the art), thereby providing an advantage in terms of the light efficiency. 
     As is apparent from the above description, the potential of the lower conductive layer  11  and the potential of the upper conductive layer  13  can be set so that the voltage applied across the liquid crystal layer  30  in the second region R 2  is lower than the voltage applied across the liquid crystal layer  30  in the first region R 1 , thereby producing a sufficient potential gradient to regulate the orientation direction (inclination direction) of the liquid crystal molecules  30 a in the vicinity of the boundary therebetween. The potential of the lower conductive layer  11  and the potential of the upper conductive layer  13  can be set in view of the voltage decrease due to the presence of the dielectric layer  12 . If the degree of voltage drop by the dielectric layer  12  is sufficiently high, the lower conductive layer  11  and the upper conductive layer  13  can have the same potential. In such a case, there is an advantage that the structure of the liquid crystal display device  100  can be simplified. If the degree of voltage drop by the dielectric layer  12  is not sufficiently high, the potential of the lower conductive layer  11  can be set to be lower than the potential of the upper conductive layer  13  so that a sufficient potential gradient can be obtained. 
     In the description above, the correlation between the potentials of the lower conductive layer  11  and the upper conductive layer  13  with respect to the potential of the second electrode  22  has been described. Generally, an orientation-regulating force from an electric field can be obtained if the relationship Vb≦Va&lt;Vc or Vb≧Va&gt;Vc is satisfied, wherein Va denotes the potential of the lower conductive layer  11 , Vb denotes the potential of the upper conductive layer  13 , and Vc denotes the potential of the second electrode  22 . The specific level of potential can be suitably set so as to obtain a desirable response speed and a desirable viewing angle characteristic in view of the structure of the liquid crystal display device  100  (the size of each picture element region, the physical property of the liquid crystal material, the width and number of openings, etc.). 
     In order to further clarify the characteristic function of the electrode structure of the liquid crystal display device  100  according to the present invention, it will be compared with the function of a conventional electrode structure having an opening (slit). Conventionally, an opening is provided in an electrode made of a single conductive film. The conventional electrode structure as Comparative Example includes a first electrode  51  having an opening  51 a therein as illustrated in  FIG. 2A  and  FIG. 2B .  FIG. 2A  and  FIG. 2B  correspond to  FIG. 1A  and  FIG. 1D , respectively. 
     A liquid crystal display device  200  of Comparative Example illustrated in  FIG. 2A  and  FIG. 2B  can be considered as the liquid crystal display device  100  from which the dielectric layer  12  and the upper conductive layer  13  (and of course the upper layer opening  13 a) are removed. It can be considered that the lower conductive layer  11  and the lower layer opening  11 a correspond to the first electrode  51  and the opening  51 a, respectively. The other elements of the liquid crystal display device  200  are denoted by the same reference numerals as those of the liquid crystal display device  100 , and will not be further described below. 
     In the presence of an applied voltage, an electric field as represented by electric force lines EF and an equipotential line EQ illustrated in  FIG. 2A  is produced in the liquid crystal layer  30  of the liquid crystal display device  200 . An inclined electric field (potential gradient) is produced in the vicinity of the opening  51 a, and the liquid crystal molecules  30 a are inclined in the direction of the inclined electric field (potential gradient) (see  FIG. 2A ). 
     However, the electric force line EF of the electric field produced in the vicinity of the center of the first electrode  51  is vertical to the substrate and has no potential gradient. Therefore, a torque which would uniquely define the inclination direction does not act upon the liquid crystal molecules  30 a present in the vicinity of the center of the first electrode  51 , as indicated by a double-headed arrow in  FIG. 2A . Moreover, the liquid crystal molecules  30 a in the vicinity of the openings  51 a on opposing sides of the liquid crystal molecules  30 a in the vicinity of the center of the first electrode  51  have opposite inclination directions, and therefore the orientation direction of the liquid crystal molecules  30 a in the vicinity of the center of the first electrode  51  is not regulated by the orientations of those liquid crystal molecules  30 a. Thus, there is no factor which uniquely regulates the inclination direction of the liquid crystal molecules  30 a in the vicinity of the center of the first electrode  51  of the liquid crystal display device  200 . Therefore, the inclination direction of these liquid crystal molecules  30 a is dominated by very subtle and uncertain factors such as by chance (probability), subtle geometric variations in the surface of the alignment layer (not shown), subtle variations in the tilt angle, and subtle variations in the resistivity of the electrode  51 . 
     Prior art also shows (e.g., Japanese Laid-Open Patent Publication No. 11-109393) a structure similar to that illustrated in  FIG. 2A  and  FIG. 2B  but with an additional electrode being provided on the lower side (away from the liquid crystal layer) of the opening  51 a via a dielectric layer so as to cover the entirety of the opening  51 a with a conductive layer for the purpose of actively controlling the shape of the potential gradient, etc. Still, the behavior of the liquid crystal molecules as described above, i.e., the uncertainty and instability of the inclination direction (rotation direction) of the liquid crystal molecules in the vicinity of the center of the electrode  51  are not improved. 
     As described above, with the conventional electrode structure of the liquid crystal display device  200 , it is not possible to obtain an orientation-regulating force on the liquid crystal molecules located in the vicinity of the center of the electrode  51 . As a result, the boundary between the regions of different inclination directions (the adjacent regions whose inclination directions are respectively defined by the openings  51 a) is not well defined, whereby it is not possible to realize a desirable viewing angle characteristic. 
     In contrast, with the electrode structure of the liquid crystal display device  100  of the present invention, the liquid crystal molecules  30 a which are present on opposing sides of the liquid crystal molecules  30 a of the second region R 2  which are not subject to a torque from an electric field which would uniquely regulate the inclination direction (strictly speaking, they may be subject to an inclined electric field), i.e., the liquid crystal molecules  30 a which are present in the vicinity of the boundary between the second region R 2  and the first region R 1  and in the vicinity of the boundary between the second region R 2  and the third region R 3 , are inclined in the same direction by an influence of the inclined electric field. Therefore, with the change in the orientation of these liquid crystal molecules  30 a being a trigger, the liquid crystal molecules  30 a of the second region R 2  are also uniquely inclined in the same direction as the liquid crystal molecules  30 a on opposing sides thereof. Therefore, the electrode structure of the liquid crystal display device  100  according to the present invention generates an orientation-regulating force which uniquely determines the inclination direction of the liquid crystal molecules  30 a across the entirety of the orientation-regulating region T 1  or T 2 . 
     Next, a preferred arrangement of the orientation-regulating region T 1  or T 2  will be described. 
     Preferably, each of the upper layer opening  13 a and the lower layer opening  11 a has a side perpendicular to the direction in which the liquid crystal molecules  30 a are inclined, and the boundary between the first region R 1  and the second region R 2  and the boundary between the second region R 2  and the third region R 3  extend along the side of the upper layer opening  13 a and the lower layer opening  11 a, as illustrated in  FIG. 1D . With such a structure, the directions of the inclined electric fields produced around the respective region boundaries (between R 1  and R 2  and between R 2  and R 3 ) coincide with each other also in terms of the azimuth angle direction, thereby increasing the orientation-regulating effect. For example, each of the upper layer opening  13 a and the lower layer opening  11 a has a rectangular shape such that a pair of opposing sides thereof are perpendicular to the inclination direction. 
     For improving the viewing angle characteristic and the response speed, it is preferred to provide in each picture element region a plurality of orientation-regulating regions which regulate the orientation direction of the liquid crystal molecules in directions different from one another, thereby forming a multi-domain orientation. A sufficient response speed and viewing angle characteristic may be obtained even when a mono-domain structure is employed for each picture element region. Since the display signals of adjacent picture element regions are correlated with each other, it is possible to improve the viewing angle characteristic when the orientation directions of the orientation-regulating regions are different from each other between adjacent picture element regions. If a picture element region is small, it is possible to achieve a sufficient response speed by providing one orientation-regulating region therein. Moreover, it is possible to improve the response speed of a mono-domain-orientation picture element region by forming a plurality of orientation-regulating regions therein which orient the liquid crystal molecules in the same direction. 
     It is possible to improve the viewing angle characteristic by the unit of picture element region by providing a plurality of orientation-regulating regions T 1  or T 2  for each picture element region. It is preferred to provide in each picture element region orientation-regulating regions T 1  (direction L) and T 2  (direction −L) which define opposite inclination directions of the liquid crystal display device  100 . The orientation-regulating regions T 1  and T 2  provided in each picture element region may take any of various arrangements. For example, as illustrated in  FIG. 1A  and  FIG. 1B , the orientation-regulating regions T 1  having the arrangement direction L and the orientation-regulating regions T 2  having the arrangement direction −L may be provided in an alternating pattern so that the first region R 1  and the third region R 3  are shared by the orientation-regulating region T 1  and the orientation-regulating region T 2  which are adjacent to each other. Alternatively, each picture element region may be provided with a region TT 3  in which the orientation-regulating regions T 1  and T 2  adjacent to each other share the first region R 1 , or each picture element region may be provided with a region TT 4  in which the orientation-regulating regions T 1  and T 2  adjacent to each other share the third region R 3 . Such arrangements can be easily realized by employing the illustrated electrode structure. 
     Moreover, in order to obtain a highly symmetrical viewing angle characteristic, it is preferred to provide four or more orientation-regulating regions having different inclination directions (orientation axes). Particularly, in order to obtain a liquid crystal display device having a high light efficiency in addition to the highly symmetrical viewing angle characteristic, it is preferred to provide four orientation-regulating regions respectively having four different inclination directions. In such a case, it is preferred that the four inclination directions (orientation axes) are such that any two inclination directions selected from among the four inclination directions have an angle which is an integral multiple of about 90° with respect to each other. Moreover, when the plurality of orientation-regulating regions provided for each picture element region include a plurality of orientation-regulating regions having the same inclination direction, it is preferred that the total area of the orientation-regulating regions of the same inclination direction is equal to that of other orientation-regulating regions of another inclination direction. It is preferred that there are four respectively different inclination directions, and it is more preferred that any two inclination directions thereof have an angle which is an integral multiple of about 90° with respect to each other. Moreover, it is preferred that the number of orientation-regulating regions having one of the four inclination directions is equal to the number of orientation-regulating regions having any other one of the four inclination directions, and it is more preferred that the area of each orientation-regulating region is equal to that of any other orientation-regulating region. 
     As described above, it is preferred to provide in each picture element region a plurality of the orientation-regulating regions of the present invention. When a plurality of orientation-regulating regions are provided, the number thereof, the positional relationship therebetween (e.g., the setting of the orientation axis direction), and the area (the respective areas of the orientation-regulating regions) can be suitably set in view of the size and shape of the picture element region, the required response speed and viewing angle characteristic. 
     A sufficient response speed and viewing angle characteristic may be obtained even when a mono-domain structure (a single inclination direction) is employed for each picture element region. Since the display signals of adjacent picture element regions are correlated with each other, it is possible to improve the viewing angle characteristic when the inclination directions of the orientation-regulating regions are different from each other (preferably perpendicular to each other) between adjacent picture element regions. In the case of a color display device, this can be achieved by employing different inclination directions for adjacent pixel regions, each pixel region being comprised of R, G and B picture element regions. If a picture element region is small, it is possible to achieve a sufficient response speed by providing one orientation-regulating region therein. Moreover, it is possible to improve the response speed of a mono-domain-orientation picture element region by forming a plurality of orientation-regulating regions therein which have the same inclination direction. 
     As described above, the second electrode  22  opposing the first electrode  14  is not required to have any special structure for obtaining the effects of the present invention, and may be one which has a known electrode structure. Therefore, the following combinations, for example, are possible as the combination of the first electrode and the second electrode. 
     
       
         
           
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                   
                 First electrode 
                 Second electrode 
               
               
                   
               
             
            
               
                 Active matrix type 
                 Picture element 
                 Counter electrode 
               
               
                   
                 electrode 
                 (common electrode) 
               
               
                   
                 Counter electrode 
                 Picture element 
               
               
                   
                 (common electrode) 
                 electrode 
               
               
                 Japanese Patent 
                 Counter striped 
                 Picture element 
               
               
                 Publication for 
                 electrode 
                 electrode 
               
               
                 Opposition No. 
                 Picture element 
                 Counter striped 
               
               
                 7-113722 (see FIG. 7) 
                 electrode 
                 electrode 
               
               
                 PALC (see FIG. 9) 
                 Striped electrode 
                 Virtual electrode 
               
               
                   
                   
                 (thin dielectric plate) 
               
               
                   
               
            
           
         
       
     
     Moreover, with an active matrix type liquid crystal display device or a liquid crystal display device disclosed in Japanese Patent Publication for Opposition No. 7-113722, the second electrode  22  may have a similar structure to that of the first electrode  14  for each of the combinations. 
     Preferred embodiments of the present invention will now be described. 
     EMBODIMENT 1 
     A liquid crystal display device of Embodiment 1 is an active matrix type liquid crystal display device using TFTs, wherein picture element electrodes arranged in a matrix having rows and columns function as the first electrode, and a counter electrode which is used commonly to the plurality of picture element electrodes functions as the second electrode. 
       FIG. 3A  and  FIG. 3B  schematically illustrate a liquid crystal display device  300  according to Embodiment 1 of the present invention.  FIG. 3A  is a plan view schematically illustrating a single picture element region (a TFT element, a storage capacitor element, etc., are omitted), and  FIG. 3B  is a cross-sectional view taken along line  3 B- 3 B′ of  FIG. 3A . 
     The liquid crystal display device  300  includes a TFT substrate  300 a, a counter substrate  300 b and a liquid crystal layer  330  provided between the TFT substrate  300 a and the counter substrate  300 b. The liquid crystal layer  330  is a vertical alignment type liquid crystal layer containing liquid crystal molecules (not shown) having a negative dielectric anisotropy. Vertical alignment films  315  and  325  are provided on one surface of the TFT substrate  300 a and the counter substrate  300 b, respectively, which is closer to the liquid crystal layer  330 . 
     The TFT substrate  300 a of the liquid crystal display device  300  includes a glass substrate  310  and a picture element electrode  314  provided on the surface thereof. The counter substrate  300 b includes a color filter substrate  320  and a counter electrode  322  provided on the surface thereof. The orientation of the liquid crystal layer  330  for each picture element region changes according to the voltage applied between the picture element electrode  314  and the counter electrode  322  which are arranged so as to oppose each other via the liquid crystal layer  330  therebetween. 
     The picture element electrode  314  of the liquid crystal display device  300  includes a lower conductive layer  311 , a dielectric layer  312  covering the lower conductive layer  311 , and an upper conductive layer  313  provided on one side of the dielectric layer  312  which is closer to the liquid crystal layer  330 . The lower conductive layer  311  includes a lower layer opening  311 a, and the upper conductive layer  313  includes an upper layer opening  313 a. The lower layer opening  311 a is arranged so as to be located within the upper layer opening  313 a. The upper conductive layer  313  and the lower conductive layer  311  are electrically connected to each other via a contact hole  312 a provided in the dielectric layer  312 , and thus are at the same potential. The lower conductive layer  311  and the upper conductive layer  313  are electrically connected to a driving circuit (not shown) via a TFT (not shown). The TFT and the driving circuit may have structures known in the art. 
     The two-dimensional structure of the picture element electrode  314  will be described with reference to  FIG. 3A . The shape of the picture element electrode  314  is an elongated rectangular shape as illustrated in  FIG. 3A . The upper conductive layer  313  and the lower conductive layer  311  are each formed of a continuous conductive film. Each of the lower layer opening  311 a and the upper layer opening  313 a has a side extending in a direction at 45° with respect to the longer side and the shorter side of the picture element electrode  314  (the column direction and the row direction of the matrix arrangement). The direction in which the side extends differs by 90° between the upper half and the lower half of the picture element electrode  314 . 
     First, the upper half of the picture element region in  FIG. 3A  will be focused upon. As illustrated in  FIG. 3B , the structure of the cross section taken along line  3 B- 3 B′ is substantially the same as that illustrated in  FIG. 1A . Therefore, as illustrated in  FIG. 3A , the upper half of the picture element region of the liquid crystal display device  300  includes two pairs of orientation-regulating regions T 1  and T 2  having opposite liquid crystal molecule inclination directions, and the liquid crystal molecules in the orientation-regulating regions T 1  and T 2  are inclined as indicated by arrows in the figure. The lower half of the picture element region in  FIG. 3A  is in axisymmetry with the upper half with respect to the shorter side direction (e.g., the row direction) of the picture element electrode  314 . The orientation-regulating regions T 3  and T 4  of the lower half have substantially the same function as that of the orientation-regulating regions T 1  and T 2  of the upper half except that the liquid crystal molecule inclination direction is different by 90°. 
     As described above, the picture element region of the liquid crystal display device  300  includes the orientation-regulating regions T 1 , T 2 , T 3  and T 4  having different liquid crystal molecule inclination directions (sometimes referred to as a “4-division multi-domain orientation”), thereby providing a desirable viewing angle characteristic. The orientation-regulating regions T 1 , T 2 , T 3  and T 4  have an equal area. Moreover, the four orientation-regulating regions T 1 , T 2 , T 3  and T 4  incline the liquid crystal molecules in respective directions (azimuth angle directions) which are shifted from one another by 90°. Thus, the uniformity of the viewing angle characteristic is high. In the illustrated example, two of each of the orientation-regulating regions T 1 , T 2 , T 3  and T 4  (a total of 8 orientation-regulating regions) are provided. However, it is not necessary to provide so many orientation-regulating regions. Generally, in view of the viewing angle characteristic, a sufficient characteristic can be obtained by dividing each picture element region into four orientation-regulating regions of different orientation directions. The number of orientation-regulating regions for each picture element region can be selected according to the required response speed. 
     The thickness d LC  of the liquid crystal layer  330  (referred to also as the “cell gap”) of the liquid crystal display device  300  is, for example, about 4 μm. As the liquid crystal material, a typical liquid crystal material having a negative dielectric anisotropy (for example, MJ95955 manufactured by Merck &amp; Co., Inc.: dielectric constants ε// =3.4, ε ⊥ =6.7, Δε=−3.3) is used. As the vertical alignment films  315  and  325 , a typical vertical alignment film (for example, JALS2004 manufactured by JSR) is used. The thickness d LC  of the liquid crystal layer  330  is not limited to the example above, but may take any other value as long as it is generally in the range of about 2 μm to about 20 μm and the product between the refractive index anisotropy Δn of the liquid crystal material and d LC  (“retardation”) is in the range of 100 nm to 500 nm. 
     The thickness d D  of the dielectric layer  312  is, for example, about 3 μm. The dielectric layer  312  is formed by using a typical organic material (for example, a photosensitive organic insulative material having a relative dielectric constant of about 3.4). The material of the dielectric layer  312  is not limited to an organic material (typically, a polymer material), but may alternatively be an inorganic material (for example, silicon oxide (SiO x ) or silicon nitride (SiN x )). 
     The thickness d D  of the dielectric layer  312  is not limited to the example above, but may take any other value as long as it is about 0.01 to about 1000 times the thickness d LC  of the liquid crystal layer  330 . The thickness d D  of the dielectric layer  312  is preferably in the range of 0.5 to 5 μm, and more preferably in the range of 1 to 3 μm. Alternatively, the thickness d D  of the dielectric layer  312  is preferably such that the value ε D /d D  is about 0.05 to about 20, and more preferably about 0.3 to 5, times the value ε// /d LC  (wherein ε D  denotes the dielectric constant of the dielectric layer  312 , d LC  the thickness of the liquid crystal layer  330 , and ε// the dielectric constant of the liquid crystal material). 
     When the thickness d D  of the dielectric layer  312  increases, the voltage applied across the liquid crystal layer  330  above the upper layer opening  313 a decreases due to the capacitance division of the dielectric layer  312  and the liquid crystal layer  330 , thereby requiring a high voltage in order to obtain a desirable transmittance. On the other hand, when the voltage decrease by the dielectric layer  312  increases, the inclination (bending) of an electric field produced in the vicinity of the boundary of the upper layer opening  313 a increases, thereby providing an advantageous effect that the orientation-regulating force increases. The thickness d D  of the dielectric layer  312  can be suitably set as necessary. 
     The width W of the upper conductive layer  313  illustrated in  FIG. 3B  (corresponding to the width of R 1  in  FIG. 1A ) and the width S of the lower layer opening  311 a (corresponding to the width of R 3  in  FIG. 1A ) are each 10 μm, for example. The width W and the width S are each a width in a direction perpendicular to the direction in which the liquid crystal molecules are inclined in the orientation-regulating region. The widths W and S are not limited to the value shown above, but may take any other value as long as it is about 0.1 to about 100 times the thickness d LC  of the liquid crystal layer  330 . The preferred range for the widths W and S depends upon the thickness d LC  of the liquid crystal layer  330  because the electric field distribution produced in the liquid crystal layer  330  is dependent upon the physical positions of the lower conductive layer  311 , the upper conductive layer  313  and the counter electrode  322  (the inter-electrode distance) and the dielectric constant of the dielectric layer  312  and the liquid crystal layer  330  being interposed therebetween. In view of the dielectric constants of typical dielectric materials and liquid crystal materials, a sufficient orientation-regulating force can be realized by setting the widths W and S generally in the above-described range. 
     The pitch P of the upper conductive layer  313  (corresponding to the width of (R 2 ×2)+R 1 +R 3  in  FIG. 1A ) is 50 μm, for example. Therefore, the width of the upper layer opening  313 a in the illustrated structure is pitch P (50 μm)−width W of the upper conductive layer (10 μm), thus 40 μm. In this way, the structure of the lower conductive layer  311 , the lower layer opening  311 a, the upper conductive layer  313  and the upper layer opening  313 a can be optimized. 
     Generally, each of the width of the first region (corresponding to the width of R 1  in  FIG. 1A , or the width W in  FIG. 3B ) and the width of the third region (corresponding to the width of R 3  in  FIG. 1A , or the width S in  FIG. 3B ) is preferably about 1 μm to about 100 μm. When the width is less than 1 μm, the inclination of an electric field in the vicinity of the boundary between the first region and the second region and the boundary between the second region and the third region is reduced so that a sufficient orientation-regulating force cannot be obtained. As a result, the response speed may be too slow or the orientation stability may be undesirably low. When the width is greater than 200 μm, a sufficient orientation-regulating force may not be obtained for the liquid crystal molecules in the vicinity of the center of the region, thereby deteriorating the display quality. A more preferred range for the width of the first and third regions is about 5 μm to about 20 μm, and the range of about 10 μm to about 20 μm is particularly preferred. When these widths are too small, a sufficient orientation-regulating force cannot be obtained, and the widths being too large are not preferred because then the region which is not used for display increases. 
     The width of the second region (corresponding to the width of R 2  in  FIG. 1A , or (P−W−S)/2 in  FIG. 3B ) is preferably about 5 μm to about 1000 μm. When the width is smaller than 5 μm, an electric field is inclined in all of the first, second and third regions, whereby the rotation angle (inclination angle) of the liquid crystal molecules, i.e., the retardation value of the liquid crystal layer, varies throughout the regions. As a result, the light efficiency decreases. When the width of the second region is greater than 1000 μm, the light efficiency increases, but the response speed decreases significantly. The reason for this is as follows. When the width of the second region is so large, the electric field in the central portion of the second region in the width direction thereof is not inclined, whereby an orientation-regulating force from the electric field is not generated. The liquid crystal molecules in the central portion are inclined in a certain direction by being influenced by the orientation of the liquid crystal molecules which are inclined in the vicinity of the boundary between the second region and the first region and in the vicinity of the boundary between the second region and the third region. Therefore, as the distance from the central portion of the second region to its boundary with the adjacent first or third region increases, the propagation of the influence from the orientation of the liquid crystal molecules in the vicinity of the boundary slows down or is lost. In order to obtain a sufficient orientation-regulating force and light efficiency, the width of the second region is more preferably in the range of about 10 μm to about 50 μm. 
     Thus, the electrode structure for producing a sufficient orientation-regulating force of the present invention can be obtained by suitably setting the number of regions into which a picture element region is divided (the variation in the number of orientation-regulating regions and the inclination direction thereof), the width W of the upper conductive layer  313 , the width S of the lower layer opening  311 a, the pitch P of the upper conductive layer  313 , etc., according to the size and shape of a picture element region of the particular liquid crystal display device to be produced. The variation in the division number and the inclination direction is set primarily in connection with the viewing angle characteristic, and the physical structure (size, shape, etc.) of the electrode is set primarily in connection with the response speed. 
     The lower conductive layer  311  and the upper conductive layer  313  of the picture element electrode  314 , and the counter electrode  322 , are formed by using a transparent conductive material (ITO), for example. The upper conductive layer  313  may be formed by using an opaque material because it has a high proportion of the upper layer opening  313 a. The upper conductive layer  313  may be formed by using a metal material (e.g., aluminum, an aluminum alloy, copper). The metal material is generally superior to a transparent conductive material in terms of the machinability, and therefore preferably used as a material of the upper conductive layer  313 , in which case a minute pattern can be formed efficiently. 
     The liquid crystal display device  300  having such a structure as described above can function as a transmission type liquid crystal display device. However, the liquid crystal display device  300  can be provided as a reflection type liquid crystal display device by, for example, forming the upper conductive layer  313  and the lower conductive layer  311  by using a metal material. 
     The liquid crystal display device  300  having such a structure as described above is provided with, for example, polarizers (including a polarizing plate, a polarizing film, and the like)  404  and  405 , phase difference compensation elements (including a phase plate, a phase film, and the like)  402  and  403 , and a backlight  406 , as illustrated in  FIG. 4 , thereby obtaining a transmission type liquid crystal display device  400  of a normally black mode having a desirable display quality. In  FIG. 4 , arrows in the polarizers  404  and  405  denote the respective transmission axes (polarization axes) thereof, and arrows in the phase difference compensation elements  402  and  403  denote the primary axis directions of index ellipsoids representing the respective refractive index anisotropies of the phase difference compensation elements. 
     The polarizers  404  and  405  are arranged in a crossed-Nicols state so as to produce a black display in the absence of an applied voltage (when the liquid crystal layer  330  is in a vertical alignment). The transmission axes of the polarizers  404  and  405  are arranged in parallel to the top-bottom direction and the left-right direction, respectively, of the display plane. The transmission axes are typically arranged so as to form an angle of 45° with respect to the inclination directions of the orientation-regulating regions T 1 , T 2 , T 3  and T 4  which are indicated by arrows in  FIG. 3A . It is possible to improve the transmittance (the light efficiency) by dividing each picture element region into four regions so that the inclination direction of each of the orientation-regulating regions T 1 , T 2 , T 3  and T 4  forms an angle of 45° with respect to the transmission axis of each of the polarizers  404  and  405  which are arranged in a crossed-Nicols state. 
     The phase difference compensation elements  402  and  403  are designed so as to compensate for changes in the retardation value of the liquid crystal layer  330  due to changes in the viewing angle in a black display state in the absence of an applied voltage. This design can be achieved by using a method known in the art. 
       FIG. 5  illustrates the applied voltage dependency of the transmittance of the liquid crystal display device  400 . As is apparent from  FIG. 5 , the liquid crystal display device  400  has a desirable voltage-transmittance characteristic of a normally black mode. The vertical axis of  FIG. 5  denotes the relative transmittance, and the horizontal axis denotes the absolute value of the voltage applied between the picture element electrode  314  and the counter electrode  322 . 
     Next,  FIG. 6  illustrates an iso-contrast contour curve (contrast ratio=30) of the liquid crystal display device  400 . The symbol ψ in the iso-contrast contour curve denotes the azimuth angle (the angle in the display plane), with ψ=0° corresponding to the 12 o&#39;clock direction of the display plane, and the value increasing as the angle moves clockwise. The symbol θ denotes the viewing angle (the angle with respect to the normal to the display plane), and the value increases as the viewing angle moves radially away from the center of the circle. As is apparent from  FIG. 6 , the contrast ratio is 30 or more in the region where the viewing angle θ is 60° or less for substantially any azimuth angle ψ, thus indicating that the liquid crystal display device  400  has a desirable viewing angle characteristic. Moreover, as illustrated in  FIG. 6 , the azimuth angle dependency of the viewing angle characteristic is uniform (i.e., the contour pattern is equivalent for any of the four directions; the contour pattern has a four-fold rotational symmetry). Thus, it is assumed that the liquid crystal display device  400  has a desirable 4-division multi-domain orientation. In the liquid crystal display device  400 , whether or not a desirable 4-division multi-domain orientation is realized for each picture element region according to the orientation-regulating forces produced respectively in the orientation-regulating regions T 1 , T 2 , T 3  and T 4  illustrated in  FIG. 3A  can be confirmed by observing with a microscope the picture element region from an inclined direction (with respect to the normal to the display plane). 
     While a typical TFT type liquid crystal display device has been shown above as an example of the liquid crystal display device  300 , the present invention can be used with a TFT type liquid crystal display device having a structure as illustrated in  FIG. 7  which is disclosed in, for example, Japanese Patent Publication for Opposition No. 7-113722. 
     A liquid crystal display device  500  illustrated in  FIG. 7  includes a first substrate  500 a, picture element electrodes  514  arranged in a matrix, TFTs  516  whose drains are connected to the picture element electrodes  514 , and scanning lines (scanning bus lines)  517  which are connected to the gates of the TFTs  516 . A second substrate  500 b which opposes the first substrate  500 a via the liquid crystal layer (not shown) therebetween includes signal lines (data bus lines)  522  arranged in a stripe pattern on the side of the liquid crystal layer. The scanning lines  517  and the signal lines  522  extend perpendicular to each other. The TFT type liquid crystal display device  500  is different from the above-described typical TFT type liquid crystal display device which has a single counter electrode used commonly to all of the picture element electrodes in that the former includes, as the electrodes on the second substrate  500 b, signal lines electrically independent of each other and arranged in a stripe pattern. Also in the liquid crystal display device  700 , the effects of the present invention can be obtained by employing the structure of the picture element electrode  314  illustrated in  FIG. 3A  and  FIG. 3B  for the picture element electrode  514 . 
     EMBODIMENT 2 
     The TFT type liquid crystal display device  300  of Embodiment 1 employs the structure of the first electrode  14  illustrated in  FIG. 1A  for the picture element electrodes of the conventional TFT type liquid crystal display device. In contrast, a TFT type liquid crystal display device of Embodiment 2 employs a structure similar to that of the first electrode  14  illustrated in  FIG. 1A  for a counter electrode of the conventional TFT type liquid crystal display device. The structure of the liquid crystal display device of Embodiment 2 may be the same as that of the conventional liquid crystal display device (having the structure of the liquid crystal display device  300  of Embodiment 1 except for the picture element electrode  314 ) except for the structure of the counter electrode. Accordingly, only the structure of the counter electrode will be described below. 
       FIG. 8  shows a plan view of a counter substrate  600 b of the liquid crystal display device of Embodiment 2. The counter substrate  600 b includes a counter electrode  614  on one side thereof which is closer to the liquid crystal layer. The counter electrode  614  includes a lower conductive layer  611 , a dielectric layer  612  covering the lower conductive layer  611 , and an upper conductive layer  613  provided on one side of the dielectric layer  612  which is closer to the liquid crystal layer. The lower conductive layer  611  includes a lower layer opening  611 a, and the upper conductive layer  613  includes an upper layer opening  613 a. The lower layer opening  611 a is arranged so as to be located within the upper layer opening  613 a. The upper conductive layer  613  and the lower conductive layer  611  are electrically connected to each other along their straight portions  611 S and  613 S extending in the column direction of the matrix, for example, and thus are at the same potential. The dielectric layer  612  along the straight portions  611 S and  613 S includes contact holes (not shown; not limited to holes, but may be grooves) for electrically connecting the upper conductive layer  613  and the lower conductive layer  611  to each other. 
     The counter electrode  614  has a structure similar to that of the first electrode  14  illustrated in  FIG. 1A , corresponding to, for example, an elongated rectangular picture element electrode (not shown; for example, 70 μm×210 μm for 18-inch type SXGA). For example, two rectangular regions in  FIG. 8  (those provided with arrows therein) correspond to a single rectangular picture element region. The respective widths L 1  and S 1  of the upper conductive layer  613  and the lower layer opening  611 a which are each arranged in a striped pattern between two adjacent upper layer openings  613 a are set similarly to the widths W and S, respectively, of the liquid crystal display device  300  of Embodiment 1. Each of the lower layer opening  611 a and the upper layer opening  613 a has a side extending in a direction at 45° with respect to the longer side and the shorter side of the picture element region (the column direction and the row direction of the matrix arrangement). The direction in which the side extends differs by 90° between the upper half and the lower half of the picture element region. This structure of the regions corresponding to a single picture element region of the counter electrode  614  is similar to that of the picture element electrode  314  illustrated in  FIG. 3A , forming the orientation-regulating regions T 1 , T 2 , T 3  and T 4 . 
     Thus, the picture element region of the liquid crystal display device of the present embodiment includes the orientation-regulating regions T 1 , T 2 , T 3  and T 4  having different liquid crystal molecule inclination directions (sometimes referred to as a “4-division multi-domain orientation”), thereby providing a desirable viewing angle characteristic as the liquid crystal display device of Embodiment 1. In the liquid crystal display device of the present embodiment, whether or not a desirable 4-division multi-domain orientation is realized for each picture element region according to the orientation-regulating forces produced respectively in the orientation-regulating regions T 1 , T 2 , T 3  and T 4  illustrated in  FIG. 8  can be confirmed by observing with a microscope the picture element region from an inclined direction (with respect to the normal to the display plane). 
     In order to prevent the orientation of the liquid crystal molecules from being disturbed by an external electric field (an electric field caused by a electrostatic charge, etc.) entering the liquid crystal layer through the lower layer opening  611 a, it is preferred that a conductive layer fixed to a certain potential is provided surrounding the lower layer opening  611 a (for example, surrounding the counter substrate, the surface of a polarizer, or under a further dielectric layer provided under (on the substrate side of) the lower layer opening  611 a). 
     Moreover, the liquid crystal display device is provided with the polarizers (including a polarizing plate, a polarizing film, and the like)  404  and  405 , the phase difference compensation elements (including a phase plate, a phase film, and the like)  402  and  403 , and the backlight  406 , as illustrated in  FIG. 4 , thereby obtaining a transmission type liquid crystal display device of a normally black mode having a desirable display quality. 
     EMBODIMENT 3 
     According to the present invention, it is possible to obtain a sufficient orientation-regulating force by, for example, employing an electrode structure similar to that of the first electrode  14  illustrated in  FIG. 1A  for the structure of one of a pair of electrodes which oppose each other via a liquid crystal layer therebetween. Therefore, even with a PALC, for which it is difficult to obtain an orientation-regulating force with the conventional structure (e.g., that disclosed in Japanese Laid-Open Patent Publication No. 11-258606), a sufficient orientation-regulating force can be obtained by employing the electrode structure of the present invention. 
     The structure and operation of a liquid crystal display device  700  of Embodiment 3, which uses the present invention with a PALC, will now be described. 
       FIG. 9  schematically illustrates the liquid crystal display device  700  of Embodiment 3. The liquid crystal display device  700  includes a liquid crystal display cell  701  and a plasma cell  702 . The liquid crystal display cell  701  and the plasma cell  702  share a thin dielectric plate  703 . 
     The liquid crystal display cell  701  includes an upper substrate (e.g., a glass substrate)  704 , a thin dielectric plate  703 , and a liquid crystal layer  707  provided therebetween. A plurality of data electrodes  714  arranged in a stripe pattern which extend in parallel to one other (in, for example, the row direction) are provided on one side of the upper substrate  704  which is closer to the liquid crystal layer  707 . The upper substrate  704  and the thin dielectric plate  703  are attached to each other while keeping a predetermined gap (cell gap) by means of a sealant  706 . The gap between the upper substrate  704  and the thin dielectric plate  703  is filled with a liquid crystal material having a negative dielectric anisotropy, and a vertical alignment film (not shown) is provided on one surface of each of the upper substrate  704  and the thin dielectric plate  703  which is closer to the liquid crystal layer  707 . The liquid crystal layer  707  is in a vertical alignment in the absence of an applied voltage. 
     The plasma cell  702  includes a plurality of plasma discharge channels  712  extending in parallel to one another (in, for example, the column direction) which are formed by a lower substrate (for example, a glass substrate)  708 , the thin dielectric plate  703 , and partition walls  710  provided therebetween. On one side of the lower substrate  708  which is closer to the plasma discharge channels  712 , a plurality of anode electrodes  709 a and a plurality of cathode electrodes  709 b extending in parallel to each other (in, for example, the column direction) are provided in an alternating pattern with a predetermined interval therebetween. The anode electrodes  709 a and the cathode electrodes  709 b are sometimes referred to collectively as a “plasma electrode  709 ”. The partition walls  710  are provided with a predetermined width so as to extend in parallel to one another and substantially along the central portion of the upper surface of each of the anode electrodes  709 a and the cathode electrodes  709 b. The lower substrate  708  along the periphery thereof is hermetically attached to the thin dielectric plate  703  by means of a frit seal  715  using a low melting point glass, or the like. The plasma discharge channels  712  are filled with an ionizable gas (for example, helium, neon, argon, or a mixed gas thereof), and a plasma discharge occurs by applying a voltage through the gas by the plasma electrode  709 . 
     The plasma discharge channels  712  and the data electrodes  714  are perpendicular to each other. Each of the data electrodes  714  is a unit of column driving operation, for example, and each of the plasma discharge channels  712  is a unit of row driving operation, for example. Each intersection between the data electrodes  714  and the plasma discharge channels  712  defines a picture element region. 
     The liquid crystal display device  700  operates as follows. 
     When a predetermined voltage is applied between the anode electrode  709 a and the cathode electrode  709 b which correspond to a predetermined plasma discharge channel  712 , the gas in the plasma discharge channel  712  is selectively ionized to generate a plasma discharge, and the inside of the plasma discharge channel  712  is kept generally at the anode potential (row addressing state; write period). In this state, if a data voltage is applied to the data electrode  714 , a voltage corresponding to the difference between the anode potential and the data potential of the data electrode  714  is applied via the thin dielectric plate  703  across the liquid crystal layer  707  of the picture element regions which are arranged in the column direction corresponding to the plasma discharge channel  712 . At this time, a region of the thin dielectric plate  703  corresponding to the plasma discharge channel  712  which is in a discharge state functions as a virtual scanning electrode. Thus, data is written to the picture element regions arranged in the column direction. 
     Upon completion of the plasma discharge, the inside of the plasma discharge channel  712  has a floating potential, whereby the data voltage which has been written to the liquid crystal layer  707  of each picture element region is maintained until the following write period which is, for example, one field or one frame later. In such a case, the plasma discharge channel  712  functions as a sampling switch while the liquid crystal layer  707  of each picture element region functions as a sampling capacitor. 
     An image is displayed by successively scanning, in the row direction, the plasma discharge channels  712  which extend in the column direction, thereby writing data voltages from the data electrodes  714  extending in the row direction to the liquid crystal layer  707  of a plurality of picture element regions arranged in the column direction. 
     In the PALC, the voltage applied across the liquid crystal layer  707  corresponds to a voltage which is obtained by dividing the potential difference between the anode potential and the data potential of the data electrode  714  by the thin dielectric plate  703  and the liquid crystal layer  707 . Therefore, it is preferred to reduce the thickness of the thin dielectric plate  703  as much as possible in order to suppress as much as possible the voltage drop by the thin dielectric plate  703 . Typically, a thin glass plate having a thickness of about 50 μm is used. Since such a thin glass plate is poor in physical strength, it is very difficult to form a special structure on the thin dielectric plate  703 . Therefore, it is not possible to use an orientation-regulating method which requires a special structure to be provided on substrates on both sides of the liquid crystal layer, as that disclosed in Japanese Laid-Open Patent Publication No. 11-258606. 
     In the liquid crystal display device  700  of Embodiment 3, the data electrode  714  has a structure similar to that of the first electrode  14  illustrated in  FIG. 1A .  FIG. 11  schematically illustrates the planar structure of the data electrode  714  of the liquid crystal display device  700 . 
     The data electrode  714  includes a lower conductive layer  711 , a dielectric layer  712  covering the lower conductive layer  711 , and an upper conductive layer  713  provided on one side of the dielectric layer  712  which is closer to the liquid crystal layer. The lower conductive layer  711  includes a lower layer opening  711 a, and the upper conductive layer  713  includes an upper layer opening  713 a. The lower layer opening  711 a is arranged so as to be located within the upper layer opening  713 a. The upper conductive layer  713  and the lower conductive layer  711  are electrically connected to each other along their straight portions  711 S and  713 S extending in the column direction of the matrix, for example, and thus are at the same potential. The dielectric layer  712  along the straight portions  711 S and  713 S includes contact holes (not shown; not limited to holes, but may be grooves) for electrically connecting the upper conductive layer  713  and the lower conductive layer  711  to each other. 
     The data electrode  714  has a structure similar to that of the first electrode  14  illustrated in  FIG. 1A , corresponding to, for example, an elongated rectangular picture element electrode (not shown; for example, 70 μm×210 μm for 18-inch type SXGA). For example, two rectangular regions in  FIG. 11  (those provided with arrows therein) correspond to a single rectangular picture element region. The respective widths L 2  and S 2  of the upper conductive layer  713  and the lower layer opening  711 a which are each arranged in a striped pattern between two adjacent upper layer openings  713 a are set similarly to the widths W and S, respectively, of the liquid crystal display device  300  of Embodiment 1. Each of the lower layer opening  711 a and the upper layer opening  713 a has a side extending in a direction at 45° with respect to the longer side and the shorter side of the picture element region (the column direction and the row direction of the matrix arrangement). The direction in which the side extends differs by 90° between the upper half and the lower half of the picture element region. This structure of the regions corresponding to a single picture element region of the data electrode  714  is similar to that of the picture element electrode  314  illustrated in  FIG. 3A , forming the orientation-regulating regions T 1 , T 2 , T 3  and T 4 . 
     Thus, the picture element region of the liquid crystal display device of the present embodiment includes the orientation-regulating regions T 1 , T 2 , T 3  and T 4  having different liquid crystal molecule inclination directions (sometimes referred to as a “4-division multi-domain orientation”), thereby providing a desirable viewing angle characteristic as the liquid crystal display device of Embodiment 1. In the liquid crystal display device of the present embodiment, whether or not a desirable 4-division multi-domain orientation is realized for each picture element region according to the orientation-regulating forces produced respectively in the orientation-regulating regions T 1 , T 2 , T 3  and T 4  illustrated in  FIG. 11  can be confirmed by observing with a microscope the picture element region from an inclined direction (with respect to the normal to the display plane). 
     Moreover, the liquid crystal display device is provided with the polarizers (including a polarizing plate, a polarizing film, and the like)  404  and  405 , the phase difference compensation elements (including a phase plate, a phase film, and the like)  402  and  403 , and the backlight  406 , as illustrated in  FIG. 4 , thereby obtaining a transmission type liquid crystal display device of a normally black mode having a desirable display quality. 
     In Embodiments 1 to 3 above, a case where a 4-division multi-domain orientation is realized by using the electrode structure of the present invention has been described, but the present invention is not limited to such an example as described above. 
     For example, an axially symmetric orientation can be realized by employing an electrode structure as illustrated in  FIG. 12 . A first electrode  814  illustrated in  FIG. 12  can be used in place of the picture element electrode  314  illustrated in  FIG. 3A , the counter electrode  614  illustrated in  FIG. 8 , or the data electrode  714  illustrated in  FIG. 11 . 
     The first electrode  814  includes a lower conductive layer  811 , a dielectric layer  812  covering the lower conductive layer  811 , and an upper conductive layer  813  provided on one side of the dielectric layer  812  which is closer to the liquid crystal layer. The upper conductive layer  813  provided corresponding to a rectangular picture element region includes three openings  813 a each having a generally square shape. The lower conductive layer  811  includes lower layer openings  811 a each of which has a shape similar to that of the upper layer opening  813 a and which are respectively located generally at the center of the upper layer openings  813 a. The upper conductive layer  813  and the lower conductive layer  811  are electrically connected to each other, for example, under the upper conductive layer  813 , and thus are at the same potential. The dielectric layer  812  under the upper conductive layer  813  includes contact holes (not shown; not limited to holes, but may be grooves) for electrically connecting the upper conductive layer  813  and the lower conductive layer  811  to each other. 
     The cross-sectional structure of the first electrode  814  along, for example, line  12 A- 12 A′ is substantially the same as that of the region TT 4  of the first electrode  14  shown in  FIG. 1A  and  FIG. 1B , and the upper layer openings  813 a and the lower layer openings  811 a all have substantially the same cross-sectional structure along a line which includes the center SA thereof. Therefore, the first electrode  814  has an orientation-regulating force which inclines the liquid crystal molecules in an axially symmetrical orientation with respect to the center SA. 
     The shape of the lower layer opening  811 a or the upper layer opening  813 a is preferably close to a square so as to stabilize the axially symmetrical orientation, though it is not limited to a square. The size and arrangement of the lower layer openings  811 a and the upper layer openings  813 a can be suitably set as in the preceding embodiments in view of the viewing angle characteristic and the response characteristic. The two-dimensional arrangement of the openings in the electrode structure of the present invention is not limited to any of those described above, but various modifications thereto can be made. 
     In order to stably obtain an axially symmetrical orientation, it is preferred to mix an appropriate amount of chiral agent into a liquid crystal material. The amount of chiral agent to be mixed in is preferably such that the pitch of twist of the liquid crystal material having the chiral agent mixed therein is about ½ to about 10 times the thickness of the liquid crystal layer. More preferably, the amount of chiral agent to be mixed in is such that the twist angle of the liquid crystal molecules is 80° to 100° when the maximum voltage to be used is applied across the liquid crystal layer. 
     Moreover, in order to stably obtain an axially symmetrical orientation, the shape of the opening illustrated in  FIG. 12  may be changed from a square to a circle or a polygon. However, in order to effectively use the picture element region, a square is most preferred. When a shape other than a square is selected, a regular hexagon is preferred because regular hexagons can be closely arranged within a rectangular picture element. Although a regular polygon is preferred in view of symmetry, it is possible to realize a substantially axially symmetrical orientation even if an irregular polygon is employed according to the shape of the picture element region, etc. 
     Also in the present embodiment, a liquid crystal display device having the structure illustrated in  FIG. 12  can be used in place of the liquid crystal display device  300  of Embodiment 1 illustrated in  FIG. 4 . In such a case, the phase difference compensation elements  403  and  402  are suitably designed by using a technique known in the art. As a result, it is possible to obtain a liquid crystal display device having a desirable viewing angle characteristic as in Embodiment 1. 
     Where an axially symmetrical orientation is employed as in the present embodiment, it is preferred to employ, in the structure illustrated in  FIG. 4 , circular polarizers in place of the linear polarizers  404  and  405 . The reason for this is as follows. a phase difference compensation element which most efficiently changes the polarization of linearly-polarized light is a phase difference compensation element which has a slow axis forming an angle of 45° with respect to the polarization axis of the linearly-polarized light. Therefore, in a liquid crystal display device where a pair of linear polarizers are arranged in a crossed-Nicols state as illustrated in  FIG. 12 , the highest light efficiency is obtained when the inclination direction of the liquid crystal molecules forms an angle which is an integral multiple of 45° with respect to the polarization axis of the polarizers. In contrast, in an axially symmetrical orientation, the orientation axis (orientation direction) of the liquid crystal molecules continuously changes, whereby it is not possible to satisfy the positional relationship between the polarization axis of the linearly-polarized light and the orientation axis for all of the orientation axes. A phase difference compensation element gives a change in the polarization in a constant amount (the absolute value of the phase difference) for circularly-polarized light irrespective of the angle of the slow axis. Therefore, in the present embodiment which employs a liquid crystal layer whose orientation axis continuously changes (which has an infinite number of slow axes), it is possible to obtain a liquid crystal display device having a high light efficiency by substituting the linear polarizers  404  and  405  with circular polarizers. In such a case, the phase difference compensation elements  402  and  403  can be suitably designed by using a technique known in the art. 
     As described above, according to the present invention, it is possible to give an orientation-regulating force from an electric field to a liquid crystal layer containing vertically-aligned liquid crystal molecules having a negative dielectric anisotropy. Therefore, according to the present invention, it is possible to obtain various types of liquid crystal display devices having a desirable viewing angle characteristic. 
     According to the present invention, it is possible to obtain a sufficient orientation-regulating force only by modifying the structure of one of a pair of electrodes for applying a voltage across a liquid crystal layer. Thus, it is possible to provide a vertical alignment type liquid crystal display device which has a sufficiently stable orientation and a sufficiently high response speed and yet can be produced efficiently. 
     By variously changing the structure of an electrode which uses two conductive layers each having openings, it is possible to realize a so-called multi-domain orientation (where there are a plurality of regions of different liquid crystal molecule inclination directions) or an axially symmetrical orientation, and thus to improve the viewing angle characteristic. Moreover, it is possible to change the magnitude of the orientation-regulating force by variously changing the electrode structure, whereby it is possible to optimize the response characteristic. 
     Moreover, the liquid crystal display device according to the present invention can be obtained only by changing the electrode structure in a conventional liquid crystal display device. Thus, the liquid crystal display device according to the present invention can be produced by using a conventional production method.