Patent Publication Number: US-9424786-B2

Title: Liquid crystal display device

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a Continuation application of PCT Application No. PCT/JP2012/053545, filed Feb. 15, 2012 and based upon and claiming the benefit of priority from Japanese Patent Application No. 2011-086561, filed Apr. 8, 2011, the entire contents of all of which are incorporated herein by reference. 
    
    
     FIELD 
     Embodiments described herein relate generally to a liquid crystal display device. 
     BACKGROUND 
     In recent years, flat-panel display devices have been vigorously developed. By virtue of such advantageous features as light weight, small thickness and low power consumption, special attention has been paid to liquid crystal display devices among others. In particular, in active matrix liquid crystal display devices in which switching elements are incorporated in respective pixels, attention is paid to the configuration which makes use of a lateral electric field (including a fringe electric field), such as an IPS (In-Plane Switching) mode or an FFS (Fringe Field Switching) mode. Such a liquid crystal display device of the lateral electric field mode includes pixel electrodes and a counter-electrode, which are formed on an array substrate, and liquid crystal molecules are switched by a lateral electric field which is substantially parallel to a major surface of the array substrate. 
     On the other hand, there has been proposed a technique wherein a lateral electric field or an oblique electric field is produced between a pixel electrode formed on an array substrate and a counter-electrode formed on a counter-substrate, thereby switching liquid crystal molecules. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a view which schematically shows the structure of a liquid crystal display device according to an embodiment. 
         FIG. 2  is a view which schematically shows a structure and an equivalent circuit of a liquid crystal display panel shown in  FIG. 1 . 
         FIG. 3  is a plan view which schematically shows a minimum unit structure in one pixel in a basic structure of the embodiment. 
         FIG. 4  is a schematic cross-sectional view showing a cross section of the liquid crystal display panel including a switching element. 
         FIG. 5  is a plan view which schematically shows the structure of one pixel on a counter-substrate of a liquid crystal display panel in a first structure example of the embodiment. 
         FIG. 6  is a plan view which schematically shows the structure of an array substrate, at a time when the pixel of the liquid crystal display panel in the first structure example of the embodiment is viewed from the counter-substrate side. 
         FIG. 7  is a plan view which schematically shows the structure of one pixel on a counter-substrate of a liquid crystal display panel in a second structure example of the embodiment. 
         FIG. 8  is a plan view which schematically shows the structure of an array substrate, at a time when the pixel of the liquid crystal display panel in the second structure example of the embodiment is viewed from the counter-substrate side. 
         FIG. 9  is a plan view which schematically shows the structure of one pixel on a counter-substrate of a liquid crystal display panel in a third structure example of the embodiment. 
         FIG. 10  is a plan view which schematically shows the structure of an array substrate, at a time when the pixel of the liquid crystal display panel in the third structure example of the embodiment is viewed from the counter-substrate side. 
         FIG. 11  is a plan view which schematically shows the structure of an array substrate, at a time when one pixel of a liquid crystal display panel in a fourth structure example of the embodiment is viewed from the counter-substrate side. 
         FIG. 12  is a view showing a summary of the combinations between the array substrates described in the first to fourth structure examples and the counter-substrates described in the first to third structure examples. 
         FIG. 13  is a plan view which schematically shows one variation of the embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     In general, according to one embodiment, a liquid crystal display device includes: a first substrate including gate lines and a storage capacitance line which extend in a first direction, a first source line and a second source line which extend in a second direction crossing the first direction, a main pixel electrode which is located between the first source line and the second source line and has a strip shape extending in the second direction, a sub-pixel electrode which is continuous with the main pixel electrode and has a strip shape extending in the first direction toward the first source line and the second source line, and a first alignment film which is formed of a material exhibiting horizontal alignment properties and covers the main pixel electrode and the sub-pixel electrode; a second substrate including second main common electrodes extending in the second direction on both sides of the main pixel electrode, second sub-common electrodes which are continuous with the second main common electrodes and extend in the first direction on both sides of the sub-pixel electrode, and a second alignment film which is formed of a material exhibiting horizontal alignment properties and covers the second main common electrodes and the second sub-common electrodes; and a liquid crystal layer including liquid crystal molecules held between the first substrate and the second substrate. 
     According to another embodiment, a liquid crystal display device includes: a first substrate including gate lines and a storage capacitance line which extend in a first direction, a first source line and a second source line which extend in a second direction crossing the first direction, a main pixel electrode which is located between the first source line and the second source line and has a strip shape extending in the second direction, a sub-pixel electrode which is continuous with the main pixel electrode and has a strip shape extending in the first direction toward the first source line and the second source line, first main common electrodes which are opposed to the first source line and the second source line, respectively, and extend in the second direction, and a first alignment film which is formed of a material exhibiting horizontal alignment properties and covers the main pixel electrode, the sub-pixel electrode, and the first main common electrodes; a second substrate including second sub-common electrodes which extend in the first direction on both sides of the sub-pixel electrode and have the same potential as the first main common electrodes, and a second alignment film which is formed of a material exhibiting horizontal alignment properties and covers the second sub-common electrode; and a liquid crystal layer including liquid crystal molecules held between the first substrate and the second substrate. 
     According to another embodiment, a liquid crystal display device includes: a first substrate including gate lines and a storage capacitance line which extend in a first direction, a first source line and a second source line which extend in a second direction crossing the first direction, a main pixel electrode which is located between the first source line and the second source line and has a strip shape extending in the second direction, a sub-pixel electrode which is continuous with the main pixel electrode and has a strip shape extending in the first direction toward the first source line and the second source line, first sub-common electrodes which are opposed to the gate lines and extend in the first direction, and a first alignment film which is formed of a material exhibiting horizontal alignment properties and covers the main pixel electrode, the sub-pixel electrode and the first sub-common electrodes; a second substrate including second main common electrodes extending in the second direction on both sides of the main pixel electrode and having the same potential as the first sub-common electrodes, and a second alignment film which is formed of a material exhibiting horizontal alignment properties and covers the second main common electrodes; and a liquid crystal layer including liquid crystal molecules held between the first substrate and the second substrate. 
     Embodiments will now be described in detail with reference to the accompanying drawings. In the drawings, structural elements having the same or similar functions are denoted by like reference numerals, and an overlapping description is omitted. 
       FIG. 1  is a view which schematically shows the structure of a liquid crystal display device  1  according to an embodiment. 
     Specifically, the liquid crystal display device  1  includes an active-matrix-type liquid crystal display panel LPN, a driving IC chip  2  and a flexible wiring board  3  which are connected to the liquid crystal display panel LPN, and a backlight  4  which illuminates the liquid crystal display panel LPN. 
     The liquid crystal display panel LPN is configured to include an array substrate AR as a first substrate, a counter-substrate CT as a second substrate which is disposed to be opposed to the array substrate AR, and a liquid crystal layer (not shown) which is disposed between the array substrate AR and the counter-substrate CT. The liquid crystal display panel LPN includes an active area ACT which displays an image. The active area ACT is composed of a plurality of pixels PX which are arrayed in a matrix of m×n (m and n are positive integers). 
     In the example illustrated, the backlight  4  is disposed on the back side of the array substrate AR. As the backlight  4 , various modes are applicable, and use may be made of either a backlight which utilizes a light-emitting diode (LED) as a light source, or a backlight which utilizes a cold cathode fluorescent lamp (CCFL) as a light source. A description of the detailed structure of the backlight  4  is omitted. 
       FIG. 2  is a view which schematically shows a structure and an equivalent circuit of the liquid crystal display panel LPN shown in  FIG. 1 . 
     The liquid crystal display panel LPN includes, in the active area ACT, an n-number of gate lines G (G 1  to Gn), an n-number of storage capacitance lines C (C 1  to Cn), and an m-number of source lines S (S 1  to Sm). The gate lines G and storage capacitance lines C extend, for example, substantially linearly in a first direction X. The gate lines G and storage capacitance lines C neighbor at intervals along a second direction Y crossing the first direction X, and are alternately arranged in parallel. In this example, the first direction X and the second direction Y are perpendicular to each other. The source lines S cross the gate lines G and storage capacitance lines C. The source lines S extend substantially linearly along the second direction Y. It is not always necessary that each of the gate lines G, storage capacitance lines C and source lines S extend linearly, and a part thereof may be bent. 
     Each of the gate lines G is led out of the active area ACT and is connected to a gate driver GD. Each of the source lines S is led out of the active area ACT and is connected to a source driver SD. At least parts of the gate driver GD and source driver SD are formed on, for example, the array substrate AR, and are connected to a driving IC chip  2  which incorporates a controller. 
     Each of the pixels PX includes a switching element SW, a pixel electrode PE and a common electrode CE. A storage capacitance CS is formed, for example, between the storage capacitance line C and the pixel electrode PE. The storage capacitance line C is electrically connected to a voltage application module VCS to which a storage capacitance voltage is applied. 
     In the present embodiment, the liquid crystal display panel LPN is configured such that the pixel electrodes PE are formed on the array substrate AR, and at least a part of the common electrode CE is formed on the counter-substrate CT, and liquid crystal molecules of the liquid crystal layer LQ are switched by mainly using an electric field which is produced between the pixel electrodes PE and the common electrode CE. The electric field, which is produced between the pixel electrodes PE and the common electrode CE, is an oblique electric field which is slightly inclined to an X-Y plane, which is defined by the first direction X and second direction Y, or to a substrate major surface of the array substrate AR or a substrate major surface of the counter-substrate CT (or a lateral electric field which is substantially parallel to the substrate major surface). 
     The switching element SW is composed of, for example, an n-channel thin-film transistor (TFT). The switching element SW is electrically connected to the gate line G and source line S. In the active area ACT, an (m×n) number of switching elements SW are formed. 
     The pixel electrodes PE are disposed in the respective pixels PX, and are electrically connected to the switching elements SW. In the active area ACT, an (m×n) number of pixel electrodes PE are formed. The common electrode CE has, for example, a common potential, and is disposed common to the pixel electrodes PE of plural pixels PX via the liquid crystal layer LQ. 
     The array substrate AR includes a power supply module VS for applying a voltage to the common electrode CE. The power supply module VS is formed, for example, on the outside of the active area ACT. Of the common electrode CE, at least a part of the common electrode CE formed on the counter-substrate CT is led out to the outside of the active area ACT, and is electrically connected to the power supply module VS formed on the array substrate AR via an electrically conductive member (not shown). Incidentally, in a case where a part of the common electrode CE is formed on the array substrate AR, a part of the common electrode CE formed on the array substrate AR is electrically connected to the power supply module VS, for example, on the outside of the active area ACT. 
     Next, a basic structure of the embodiment is described. 
       FIG. 3  is a plan view which schematically shows a minimum unit structure in one pixel PX. 
     The pixel electrode PE includes a main pixel electrode PA and a sub-pixel electrode PB. The main pixel electrode PA and sub-pixel electrode PB are electrically connected to each other. In the present embodiment, both the main pixel electrode PA and sub-pixel electrode PB are provided on the array substrate AR. The main pixel electrodes PA extends in a second direction Y. The sub-pixel electrode PB extends in a first direction X which is different from the second direction Y. 
     In the example illustrated, the pixel electrode PE is formed in a substantially cross shape. To be more specific, the main pixel electrode PA is formed in a strip shape linearly extending in the second direction Y at a substantially central part of the pixel. The sub-pixel electrode PB is formed in a strip shape linearly extending in the first direction X at a central part of the pixel. 
     The sub-pixel electrode PB is coupled to a substantially central part of the main pixel electrode PA (or the vicinity of a middle point of the length of the main pixel electrode PA in the second direction Y), and extends from the main pixel electrode PA toward both sides thereof, that is, toward the left side and right side of the pixel PX. In other words, the main pixel electrode PA is coupled to a substantially central part of the sub-pixel electrode PB (or the vicinity of a middle point of the length of the sub-pixel electrode PB in the first direction X), and extends from the sub-pixel electrode PB toward both sides thereof, that is, toward the upper side and lower side of the pixel PX. The main pixel electrode PA and sub-pixel electrode PB are substantially perpendicular to each other. The pixel electrode PE is electrically connected to the switching element (not shown), for example, at the sub-pixel electrode PB. 
     The common electrode CE includes main common electrodes CA and sub-common electrodes CB. The main common electrodes CA and sub-common electrodes CB are electrically connected to each other. The common electrode CE is electrically insulated from the pixel electrode PE. In the present embodiment, at least a part of the main common electrodes CA and sub-common electrodes CB of the common electrode CE is provided on the counter-substrate CT. 
     The main common electrodes CA extend in the second direction Y. The main common electrodes CA are disposed on both sides of the main pixel electrode PA. At this time, in the X-Y plane, neither of the main common electrodes CA overlaps the main pixel electrode PA, and substantially equal intervals are provided between the main common electrodes CA, on the one hand, and the main pixel electrode PA, on the other hand. In short, the main pixel electrode PA is located at a substantially middle point between the neighboring main common electrodes CA. 
     The sub-common electrodes CB extend in the first direction X. The sub-common electrodes CB are disposed on both sides of the sub-pixel electrode PB. At this time, in the X-Y plane, neither of the sub-common electrodes CB overlaps the sub-pixel electrode PB, and substantially equal intervals are provided between the sub-common electrodes CB, on the one hand, and the sub-pixel electrode PB, on the other hand. In short, the sub-pixel electrode PB is located at a substantially middle point between the neighboring sub-common electrodes CB. 
     In the example illustrated, each main common electrode CA is formed in a strip shape linearly extending in the second direction Y. Each sub-common electrode CB is formed in a strip shape linearly extending in the first direction X. In the meantime, two main common electrodes CA are arranged in parallel with an interval in the first direction X. In the description below, in order to distinguish these main common electrodes CA, the main common electrode located on the left side in the Figure is referred to as “CAL”, and the main common electrode located on the right side is referred to as “CAR”. In addition, two sub-common electrodes CB are arranged in parallel with an interval in the second direction Y. In the description below, in order to distinguish these sub-common electrodes CB, the sub-common electrode located on the upper side in the Figure is referred to as “CBU”, and the sub-common electrode located on the lower side is referred to as “CBB”. The main common electrode CAL and main common electrode CAR have the same potential as the sub-common electrode CBU and sub-common electrode CBB. In the example illustrated, the main common electrode CAL and main common electrode CAR are continuous with the sub-common electrode CBU and sub-common electrode CBB. 
     The main common electrode CAL and main common electrode CAR are disposed, respectively, between the present pixel PX and pixels neighboring this pixel on the left and right sides. Specifically, the main common electrode CAL is disposed to extend over a boundary between the illustrated pixel PX and a pixel (not shown) neighboring on the left side thereof, and the main common electrode CAR is disposed to extend over a boundary between the illustrated pixel PX and a pixel (not shown) neighboring on the right side thereof. 
     The sub-common electrode CBU and sub-common electrode CBB are disposed, respectively, between the present pixel PX and pixels neighboring this pixel on the upper and lower sides. Specifically, the sub-common electrode CBU is disposed to extend over a boundary between the illustrated pixel PX and a pixel (not shown) neighboring on the upper side thereof, and the sub-common electrode CBB is disposed to extend over a boundary between the illustrated pixel PX and a pixel (not shown) neighboring on the lower side thereof. 
     One main pixel electrode PA is located between the neighboring main common electrode CAL and main common electrode CAR. Thus, the main common electrode CAL, main pixel electrode PA and main common electrode CAR are arranged in the named order in the first direction X. Specifically, the main pixel electrode PA and main common electrodes CA are alternately arranged in the first direction X. The main pixel electrode PA, main common electrode CAL and main common electrode CAR are arranged substantially in parallel to each other. In addition, the distance between the main common electrode CAL and main pixel electrode PA in the first direction X is substantially equal to the distance between the main common electrode CAR and main pixel electrode PA in the first direction X. 
     One sub-pixel electrode PB is located between the neighboring sub-common electrode CBU and sub-common electrode CBB. Thus, the sub-common electrode CBB, sub-pixel electrode PB and sub-common electrode CBU are arranged in the named order in the second direction Y. Specifically, the sub-pixel electrode PB and sub-common electrodes CB are alternately arranged in the second direction Y. The sub-pixel electrode PB, sub-common electrode CBB and sub-common electrode CBU are arranged substantially in parallel to each other. In addition, the distance between the sub-common electrode CBB and sub-pixel electrode PB in the second direction Y is substantially equal to the distance between the sub-common electrode CBU and sub-pixel electrode PB in the second direction Y. 
     Specifically, in the example illustrated, in one pixel PX, four regions, which are divided by the pixel electrode PE and common electrode CE, are formed as aperture portions or transmissive parts which mainly contribute to display. 
     In the example illustrated, the initial alignment direction of liquid crystal molecules LM is, for example, a direction which is substantially parallel to the second direction Y. 
     Although not described here in detail, at least one of the main common electrodes CA may be opposed to a source line S which extends substantially parallel to the main common electrodes CA (or extending in the second direction Y). In addition, one of the sub-pixel electrode PB and sub-common electrodes CB may be opposed to a gate line G or storage capacitance line C which extends substantially parallel to these electrodes (or extending in the first direction X). 
     Besides, as will be described later, the main common electrodes CA may include at least one of a first main common electrode CA 1  which is provided on the array substrate AR, and a second main common electrode CA 2  which is provided on the counter-substrate CT. In addition, the sub-common electrodes CB may include at least one of a first sub-common electrode CB 1  which is provided on the array substrate AR, and a second sub-common electrode CB 2  which is provided on the counter-substrate CT. The first main common electrode CA 1 , second main common electrode CA 2 , first sub-common electrode CB 1  and second sub-common electrode CB 2  have the same potential. 
       FIG. 4  is a schematic cross-sectional view showing a cross section of the liquid crystal display LPN including a switching element SW. The depiction of the common electrode is omitted, and only the parts necessary for the description are illustrated. 
     A backlight  4  is disposed on the back side of the array substrate AR which constitutes the liquid crystal display panel LPN. 
     The array substrate AR is formed by using a first insulative substrate  10  having light transmissivity, such as a glass substrate or a plastic substrate. The array substrate AR includes a switching element SW, a pixel electrode PE and a first alignment film AL 1  on that side of the first insulative substrate  10 , which is opposed to the counter-substrate CT. 
     In the example illustrated, the switching element SW is a top-gate-type thin-film transistor, but it may be a bottom-gate-type thin-film transistor. In addition, although a semiconductor layer SC of the switching element SW is formed of, for example, polysilicon, it may be formed of amorphous silicon. 
     The semiconductor layer SC includes a source region SCS and a drain region SCD on both sides of a channel region SCC. Incidentally, an undercoat layer, which is an insulation film, may be provided between the first insulative substrate  10  and the semiconductor layer SC. The semiconductor layer SC is covered with a gate insulation film  11 . In addition, the gate insulation film  11  is also disposed on the first insulative substrate  10 . 
     A gate electrode WG of the switching element SW is formed on the gate insulation film  11 , and is located above the channel region SCC of the semiconductor layer SC. A gate line G and a storage capacitance line C are also formed on the gate insulation film  11 . The gate electrode WG, gate line G and storage capacitance line C can be formed of the same material in the same fabrication step. The gate electrode WG is electrically connected to the gate line G. 
     The gate electrode WG, gate line G and storage capacitance line C are covered with a first interlayer insulation film  12 . In addition, the first interlayer insulation film  12  is also disposed on the gate insulation film  11 . The gate insulation film  11  and first interlayer insulation film  12  are formed of, for example, an inorganic material such as silicon oxide and silicon nitride. 
     A source electrode WS and a drain electrode WD of the switching element SW are formed on the first interlayer insulation film  12 . A source line S is also formed on the first interlayer insulation film  12 . The source electrode WS, drain electrode WD and source line S can be formed of the same material in the same fabrication step. The source electrode WS is electrically connected to the source line S. 
     The source electrode WS is put in contact with the source region SCS of the semiconductor layer SC via a contact hole which penetrates the gate insulation film  11  and first interlayer insulation film  12 . The drain electrode WD is put in contact with the drain region SCD of the semiconductor layer SC via a contact hole which penetrates the gate insulation film  11  and first interlayer insulation film  12 . The gate electrode WG, gate line G, storage capacitance line C, source electrode WS, drain electrode WD and source line S are formed of electrically conductive materials such as molybdenum, aluminum, tungsten and titanium. 
     The switching element SW with this structure is covered with a second interlayer insulation film  13 . Specifically, the source electrode WS, drain electrode WD and source line S are covered with a second interlayer insulation film  13 . In addition, the second interlayer insulation film  13  is also disposed on the first interlayer insulation film  12 . The second interlayer insulation film  13  is formed of, for example, various organic materials such as an ultraviolet-curing resin and a thermosetting resin. 
     The pixel electrode PE is formed on the second interlayer insulation film  13 . Although not described in detail, the main pixel electrode PA and sub-pixel electrode PB, which constitute the pixel electrode PE, are formed on the second interlayer insulation film  13 . The pixel electrode PE is electrically connected to the drain electrode WD via a contact hole which penetrates the second interlayer insulation film  13 . Although the pixel electrode PE is formed of a light-transmissive, electrically conductive material such as indium tin oxide (ITO) or indium zinc oxide (IZO), it may be formed of other metallic material such as aluminum. 
     The first alignment film AL 1  is disposed on that surface of the array substrate AR, which is opposed to the counter-substrate CT, and extends over substantially the entirety of the active area ACT. The first alignment film AL 1  covers the pixel electrode PE, and is also disposed on the second interlayer insulation film  13 . The first alignment film AL 1  is formed of a material which exhibits horizontal alignment properties. 
     In the meantime, there may be a case in which the array substrate AR further includes a first main common electrode and a first sub-common electrode as a part of the common electrode. 
     On the other hand, the counter-substrate CT is formed by using a second insulative substrate  20  with light transmissivity, such as a glass substrate or a plastic substrate. The counter-substrate CT includes, on that side of the second insulative substrate  20  which is opposed to the array substrate AR, at least one of a second main common electrode and a second sub-common electrode of the common electrode, the depiction of which is omitted, and a second alignment film AL 2 . In addition, although not illustrated, a black matrix which partitions pixels PX (or is disposed to be opposed to wiring portions such as source lines S, gate lines G, storage capacitance lines C and switching elements SW), color filter layers which are disposed in association with the respective pixels PX, and an overcoat layer, which reduces the effect of asperities on the surfaces of the black matrix and color filter layers, may be disposed on the counter-substrate CT. 
     The common electrode is formed of, for example, a light-transmissive, electrically conductive material such as ITO or IZO. 
     The second alignment film AL 2  is disposed on that surface of the counter-substrate CT, which is opposed to the array substrate AR, and extends over substantially the entirety of the active area ACT. The second alignment film AL 2  covers the common electrode, etc. The second alignment film AL 2  is formed of a material which exhibits horizontal alignment properties. 
     The first alignment film AL 1  and second alignment film AL 2  are subjected to alignment treatment (e.g. rubbing treatment or optical alignment treatment) for initially aligning liquid crystal molecules LM. A first alignment treatment direction PD 1 , in which the first alignment film AL 1  initially aligns the liquid crystal molecules LM, is parallel to a second alignment treatment direction PD 2 , in which the second alignment film AL 2  initially aligns the liquid crystal molecules LM. In an example illustrated in part (A) of  FIG. 3 , the first alignment treatment direction PD 1  and second alignment treatment direction PD 2  are substantially parallel to each other, and are identical. In an example illustrated in part (B) of  FIG. 3 , the first alignment treatment direction PD 1  and second alignment treatment direction PD 2  are substantially parallel to each other, and are opposite to each other. 
     The above-described array substrate AR and counter-substrate CT are disposed such that their first alignment film AL 1  and second alignment film AL 2  are opposed to each other. In this case, columnar spacers, which are formed of, e.g. a resin material so as to be integral to one of the array substrate AR and counter-substrate CT, are disposed between the first alignment film AL 1  of the array substrate AR and the second alignment film AL 2  of the counter-substrate CT. Thereby, a predetermined cell gap, for example, a cell gap of 2 to 7 μm, is created. The array substrate AR and counter-substrate CT are attached by a sealant on the outside of the active area ACT in the state in which the predetermined cell gap is created therebetween. 
     The liquid crystal layer LQ is held in the cell gap which is created between the array substrate AR and the counter-substrate CT, and is disposed between the first alignment film AL 1  and second alignment film AL 2 . The liquid crystal layer LQ includes liquid crystal molecules LM. The liquid crystal layer LQ is composed of a liquid crystal material having a positive (positive-type) dielectric constant anisotropy. 
     A first optical element OD 1  is attached by, e.g. an adhesive, to an outer surface of the array substrate AR, that is, an outer surface of the first insulative substrate  10  which constitutes the array substrate AR. The first optical element OD 1  is located on that side of the liquid crystal display panel LPN, which is opposed to the backlight  4 , and controls the polarization state of incident light which enters the liquid crystal display panel LPN from the backlight  4 . The first optical element OD 1  includes a first polarizer PL 1  having a first polarization axis AX 1 . In the meantime, another optical element, such as a retardation plate, may be disposed between the first polarizer PL 1  and the first insulative substrate  10 . 
     A second optical element OD 2  is attached by, e.g. an adhesive, to an outer surface of the counter-substrate CT, that is, an outer surface of the second insulative substrate  20  which constitutes the counter-substrate CT. The second optical element OD 2  is located on the display surface side of the liquid crystal display panel LPN, and controls the polarization state of emission light emerging from the liquid crystal display panel LPN. The second optical element OD 2  includes a second polarizer PL 2  having a second polarization axis AX 2 . In the meantime, another optical element, such as a retardation plate, may be disposed between the second polarizer PL 2  and the second insulative substrate  20 . 
     The first polarization axis AX 1  of the first polarizer PL 1  and the second polarization axis AX 2  of the second polarizer PL 2  have a positional relationship of crossed Nicols. In this case, one of the polarizers is disposed such that the polarization axis thereof is parallel or perpendicular to the initial alignment direction of liquid crystal molecules LM, that is, the first alignment treatment direction PD 1  or second alignment treatment direction PD 2 . When the initial alignment direction is parallel to the second direction Y, the polarization axis of one of the polarizers is parallel to the second direction Y, or is parallel to the first direction X. 
     In an example shown in part (a) of  FIG. 3 , the first polarizer PL 1  is disposed such that the first polarization axis AX 1  thereof is perpendicular to the second direction Y that is the initial alignment direction of liquid crystal molecules LM, and the second polarizer PL 2  is disposed such that the second polarization axis AX 2  thereof is parallel to the initial alignment direction of liquid crystal molecules LM. In addition, in an example shown in part (b) of  FIG. 3 , the second polarizer PL 2  is disposed such that the second polarization axis AX 2  thereof is perpendicular to the second direction Y that is the initial alignment direction of liquid crystal molecules LM, and the first polarizer PL 1  is disposed such that the first polarization axis AX 1  thereof is parallel to the initial alignment direction of liquid crystal molecules LM. 
     Thereby, a normally black mode is realized. 
     Next, the operation of the liquid crystal display panel LPN having the above-described structure is described. 
     Specifically, in a state in which no voltage is applied to the liquid crystal layer LQ, that is, in a state (OFF time) in which no electric field is produced between the pixel electrode PE and common electrode CE, the liquid crystal molecules LM of the liquid crystal layer LQ are aligned such that the major axes thereof are positioned in the first alignment treatment direction PD 1  of the first alignment film AL 1  and the second alignment treatment direction PD 2  of the second alignment film AL 2 , as indicated by broken lines in  FIG. 3 . This OFF time corresponds to the initial alignment state, and the alignment direction of the liquid crystal molecules LM at the OFF time corresponds to the initial alignment direction. 
     Strictly speaking, the liquid crystal molecule LM is not always aligned in parallel to the X-Y plane, and, in many cases, the liquid crystal molecule LM is pre-tilted. Thus, the initial alignment direction of the liquid crystal molecule LM is, in the strict sense, a direction in which the alignment direction of the liquid crystal molecule LM at the OFF time is orthogonally projected onto the X-Y plane. However, in the description below, for the purpose of simplicity, it is assumed that the liquid crystal molecules LM are aligned in parallel to the X-Y plane, and the liquid crystal molecules LM rotate in a plane parallel to the X-Y plane. 
     In this example, each of the first alignment treatment direction PD 1  and the second alignment treatment direction PD 2  is substantially parallel to the second direction Y. At the OFF time, the liquid crystal molecule LM is initially aligned such that the major axis thereof is substantially parallel to the second direction Y, as indicated by a broken line in  FIG. 3 . Specifically, the initial alignment direction of the liquid crystal molecule LM is parallel to the second direction Y (or is at 0° to the second direction Y). 
     When the first alignment treatment direction PD 1  and the second alignment treatment direction PD 2  are parallel and identical to each other, as in the example illustrated, the liquid crystal molecules LM are substantially horizontally aligned (the pre-tilt angle is substantially zero) in the middle part of the liquid crystal layer LQ in the cross section of the liquid crystal layer LQ, and the liquid crystal molecules LM are aligned with such pre-tilt angles that the liquid crystal molecules LM become symmetric in the vicinity of the first alignment film AL 1  and in the vicinity of the second alignment film AL 2 , with respect to the middle part as the boundary (splay alignment). In the state in which the liquid crystal molecules LM are splay-aligned, optical compensation can be made by the liquid crystal molecules LM in the vicinity of the first alignment film AL 1  and the liquid crystal molecules LM in the vicinity of the second alignment film AL 2 , even in a direction inclined to the normal direction of the substrate. Therefore, when the first alignment treatment direction PD 1  and the second alignment treatment direction PD 2  are parallel and identical to each other, light leakage is small in the case of black display, a high contrast ratio can be realized, and the display quality can be enhanced. 
     In the meantime, when the first alignment treatment direction PD 1  and the second alignment treatment direction PD 2  are parallel and opposite to each other, the liquid crystal molecules LM are aligned with substantially equal pre-tilt angles, in the cross section of the liquid crystal layer LQ, in the vicinity of the first alignment film AL 1 , in the vicinity of the second alignment film AL 2 , and in the middle part of the liquid crystal layer LQ (homogeneous alignment). 
     Part of light from the backlight  4  passes through the first polarizer PL 1 , and enters the liquid crystal display panel LPN. The light, which enters the liquid crystal display panel LPN, is linearly polarized light which is perpendicular to the first polarization axis AX 1  of the first polarizer PL 1 . The polarization state of such linearly polarized light hardly varies when the light passes through the liquid crystal display panel LPN at the OFF time. Thus, the linearly polarized light, which has passed through the liquid crystal display panel LPN, is absorbed by the second polarizer PL 2  that is in the positional relationship of crossed Nicols in relation to the first polarizer PL 1  (black display). 
     On the other hand, in a state in which a voltage is applied to the liquid crystal layer LQ, that is, in a state (ON time) in which a potential difference is produced between the pixel electrode PE and common electrode CE, a lateral electric field (or an oblique electric field), which is substantially parallel to the substrates, is produced between the pixel electrode PE and the common electrode CE. The liquid crystal molecules LM are affected by the electric field, and the major axes thereof rotate within a plane which is substantially parallel to the X-Y plane, as indicated by solid lines in the Figure. 
     In the example shown in  FIG. 3 , in the region between the pixel electrode PE and the main common electrode CAL, the liquid crystal molecule LM in the lower half part of this region rotates clockwise relative to the second direction Y, and is aligned in a lower left direction in the Figure, and the liquid crystal molecule LM in the upper half part of this region rotates counterclockwise relative to the second direction Y, and is aligned in an upper left direction in the Figure. In the region between the pixel electrode PE and the main common electrode CAR, the liquid crystal molecule LM in the lower half part of this region rotates counterclockwise relative to the second direction Y, and is aligned in a lower right direction in the Figure, and the liquid crystal molecule LM in the upper half part of this region rotates clockwise relative to the second direction Y, and is aligned in an upper right direction in the Figure. 
     As has been described above, in the state in which the electric field is produced between the pixel electrode PE and common electrode CE in each pixel PX, the liquid crystal molecules LM are aligned in a plurality of directions, with boundaries at positions overlapping the pixel electrode PE, and domains are formed in the respective alignment directions. Specifically, a plurality of domains are formed in one pixel PX. 
     At such ON time, linearly polarized light, which is perpendicular to the first polarization AX 1  of the first polarizer PL 1 , enters the liquid crystal display panel LPN, and the polarization state of such linearly polarized light varies depending on the alignment state of the liquid crystal molecules LM when the light passes through the liquid crystal layer LQ. At this ON time, at least part of the light emerging from the liquid crystal layer LQ passes through the second polarizer PL 2  (white display). 
     According to the present embodiment, four domains can be formed in one pixel. Thus, the viewing angle can optically be compensated in four directions, and a wider viewing angle can be realized. Therefore, it is possible to provide a liquid crystal display device with good display quality, which is free from gray level inversion and can realize high-transmittance display. 
     In addition, the four regions, which are divided by the pixel electrode PE and common electrode CE in one pixel, are set to have substantially equal areas of aperture portions. Thereby, the transmittances of the respective regions become substantially equal, light components passing through the respective aperture portions optically compensate each other, and uniform display can be realized over a wide viewing-angle range. 
     Compared to a vertical alignment-type liquid crystal display device in which the initial alignment state of liquid crystal molecules is vertical to the substrate, it was confirmed that in the present embodiment the viewing angle is wide and the brightness is high even at intermediate gray levels. 
     At the ON time, a lateral electric field is hardly produced (or an electric field enough to drive liquid crystal molecules LM is not produced) near the main pixel electrode PA of pixel electrode PE and near the sub-pixel electrode PB, or near the main common electrodes CA of common electrode CE and near the sub-common electrodes CB. Thus, the liquid crystal molecules LM scarcely move from the initial alignment direction, like the case of the OFF time. Thus, even if the pixel electrode PE and common electrode CE are formed of a light-transmissive, electrically conductive material, as described above, little backlight passes through these regions, and these regions hardly contribute to display at the ON time. Thus, the pixel electrode PE and common electrode CE do not necessarily need to be formed of a transparent, electrically conductive material, and may be formed of an electrically conductive material such as aluminum or silver. 
     In addition, when misalignment has occurred between the array substrate AR and the counter-substrate CT, there is a case in which the distances between the pixel electrode PE, on the one hand, and the common electrodes CE on both sides of the pixel electrode PE, on the other hand, become different. However, since such a difference occurs commonly in all pixels PX, the electric field distribution does not differ between the pixels PX, and the influence on the display of images is very small. 
     The shape of the above-described minimum unit structure in one pixel is not limited to a square shape, and may be a rectangular shape with no restrictions on the increase/decrease in dimension in the second direction Y or in the first direction X. Specifically, a desired pixel size can be designed by the unit structure itself or by a combination of unit structures. Even if the dimensions of the unit structure are freely designed, since the liquid crystal molecules LM are aligned horizontal to the substrate by the electric field produced between the electrodes, there is little influence on the retardation in the normal direction to the substrate. Therefore, a change in pixel size hardly affects the brightness and viewing angle. 
     On the other hand, in the case of the vertical alignment-type liquid crystal display device in which the initial alignment state is vertical to the substrate and is made horizontal by an application voltage, if the intensity of the electric field which is produced between the electrodes is different among pixels, the degree of inclination of liquid crystal molecules to the substrate is also different, and thus the influence on the retardation in the normal direction to the substrate is great. Therefore, the change in pixel size greatly affects the brightness and viewing angle. From this, if the vertical alignment-type liquid crystal molecules are applied to this unit structure, it is necessary to form the unit structure in a square shape, thereby to make uniform the electric field intensity and electric field distribution in the pixel. 
     Next, structure examples of the embodiment will be described. 
     First Structure Example 
     To begin with, a first structure example of the embodiment is described. 
       FIG. 5  is a plan view which schematically shows the structure of one pixel PX on a counter-substrate CT 1  of a liquid crystal display panel LPN in the first structure example of the embodiment. 
     In the first structure example, a common electrode CE includes second main common electrodes CA 2  which are provided on a counter-substrate CT 1  as main common electrodes, and second sub-common electrodes CB 2  which are provided on the counter-substrate CT 1  as sub-common electrodes. The second main common electrodes CA 2  and second sub-common electrodes CB 2  are covered with a second alignment film AL 2 . 
     Specifically, the illustrated counter-substrate CT 1  includes second main common electrodes CA 2  each having a strip shape linearly extending in the second direction Y, and second sub-common electrodes CB 2  each having a strip shape linearly extending in the first direction X. The second main common electrodes CA 2  and the second sub-common electrodes CB 2  are electrically connected. In the example illustrated, the second main common electrodes CA 2  and second sub-common electrodes CB 2  are formed integral (or continuous) with each other. In short, in the counter-substrate CT 1 , the common electrode CE is formed in a grid shape. 
     In the meantime, the illustrated second main common electrodes CA 2  are two second main common electrodes CA 2  which are arranged in parallel with an interval in the first direction X. In the description below, in order to distinguish these second main common electrodes CA 2 , the second main common electrode located on the left side in the Figure is referred to as “CAL 2 ”, and the second main common electrode located on the right side is referred to as “CAR 2 ”. In addition, the illustrated second sub-common electrodes CB 2  are two second sub-common electrodes CB 2  which are arranged in parallel with an interval in the second direction Y. In the description below, in order to distinguish these second sub-common electrodes CB 2 , the second sub-common electrode located on the upper side in the Figure is referred to as “CBU 2 ”, and the second sub-common electrode located on the lower side is referred to as “CBB 2 ”. The second main common electrode CAL 2  and second main common electrode CAR 2  are continuous with the second sub-common electrode CBU 2  and second sub-common electrode CBB 2 . 
     Although not described in detail, the common electrode CE with this structure is led out to the outside of the active area, is electrically connected to a power supply module formed on an array substrate via an electrically conductive member, and is supplied with a common potential. 
     Next, a description is given of an array substrate AR 1  which is suitably combined with the counter-substrate CT 1  shown in  FIG. 5 . 
       FIG. 6  is a plan view which schematically shows the structure of the array substrate AR 1 , at a time when the pixel PX of the liquid crystal display panel LPN in the first structure example of the embodiment is viewed from the counter-substrate CT 1  side. The common electrode CE is illustrated by broken lines, in order to explain the positional relationship between the pixel electrode PE and common electrode CE. In addition, only the structure of the pixel PX, which is necessary for the description, is illustrated, and the depiction of a switching element, etc. is omitted. 
     The array substrate AR 1  includes a storage capacitance line C 1  which extends in the first direction X, a gate line G 1  and a gate line G 2  which extend in the first direction X, a source line S 1  and a source line S 2  which extend in the second direction Y, and a pixel electrode PE. The storage capacitance line C 1 , gate line G 1  and gate line G 2  are formed on the gate insulation film  11  and are covered with the first interlayer insulation film  12 . The source line S 1  and source line S 2  are formed on the first interlayer insulation film  12  and are covered with the second interlayer insulation film  13 . The pixel electrode PE is formed on the second interlayer insulation film  13 . 
     In the example illustrated, the pixel PX corresponds to an area indicated by a broken line, and has a rectangular shape having a greater length in the second direction Y than in the first direction X. In addition, in the illustrated example, in the pixel PX, the source line S 1  is disposed at a left side end portion, and the source line S 2  is disposed at a right side end portion. Strictly speaking, the source line S 1  is disposed to extend over a boundary between the pixel PX and a pixel neighboring on the left side, and the source line S 2  is disposed to extend over a boundary between the pixel PX and a pixel neighboring on the right side. In addition, in the pixel PX, the gate line G 1  is disposed at an upper side end portion, the gate line G 2  is disposed at a lower side end portion, and the storage capacitance line C 1  is disposed at a substantially central part of the pixel. Specifically, the distance in the second direction Y between the gate line G 1  and the storage capacitance line C 1  is substantially equal to the distance in the second direction Y between the gate line G 2  and the storage capacitance line C 1 . 
     The pixel electrode PE is disposed between the source line S 1  and source line S 2 , or between the gate line G 1  and gate line G 2 , and is electrically connected to the switching element (not shown). The pixel electrode PE includes a main pixel electrode PA having a strip shape linearly extending in the second direction Y, and a sub-pixel electrode PB having a strip shape linearly extending in the first direction X. The main pixel electrode PA and sub-pixel electrode PB are electrically connected. In the example illustrated, the main pixel electrode PA and sub-pixel electrode PB are formed integral (or continuous) with each other. In short, in the array substrate AR 1 , the pixel electrode PE is formed in a cross shape. In addition, the main pixel electrode PA and sub-pixel electrode PB are covered with the first alignment film AL 1 . 
     The main pixel electrode PA is located, within the pixel PX, at a position inside the positions immediately above the neighboring source line S 1  and source line S 2 , and is disposed at a substantially middle point between the source line S 1  and source line S 2 . The main pixel electrode PA extends from the vicinity of the upper side end portion of the pixel PX to the vicinity of the lower side end portion thereof. 
     The sub-pixel electrode PB is disposed at a substantially central part of the pixel PX and crosses the main pixel electrode PA. The sub-pixel electrode PB linearly extends from a substantially middle part of the main pixel electrode PA toward both sides thereof, that is, toward the source line S 1  on the left side of the main pixel electrode PA and the source line S 2  on the right side of the main pixel electrode PA. The sub-pixel electrode PA extends from the vicinity of the left side end portion of the pixel PX to the vicinity of the right side end portion thereof. 
     In the first structure example, the sub-pixel electrode PB is opposed to the storage capacitance line C 1 . In the example illustrated, the sub-pixel electrode PB is disposed above the storage capacitance line C 1 . The first interlayer insulation film  12  and second interlayer insulation film  13  are interposed as insulation films between the sub-pixel electrode PB and storage capacitance line C 1 . 
     As regards the length in the first direction X of the sub-pixel electrode PB, when the sub-pixel electrode PB covers the storage capacitance line C 1 , the length in the first direction X of the sub-pixel electrode PB is equal to or greater than the length in the first direction X of the storage capacitance line C 1  which is located between the source line S 1  and source line S 2 . 
     In addition, as regards the width in the second direction Y of the sub-pixel electrode PB, when the sub-pixel electrode PB is configured to be electrically connected to the switching element (not shown) on the storage capacitance line C 1 , the width in the second direction Y of the sub-pixel electrode PB is set to be relatively large. When the sub-pixel electrode PB covers the storage capacitance line C 1 , the width of the sub-pixel electrode PB is equal to or greater than the width of the storage capacitance line C 1 . 
     In the structure in which the gate line G 1  is disposed at the upper side end portion of the pixel and the storage capacitance line C 1  is disposed at a substantially central part of the pixel, as described above, the sub-pixel electrode PB can be disposed in a manner to cover the storage capacitance line C 1  which is located between the source line S 1  and source line S 2 . 
     Besides, the storage capacitance line C 1  may be disposed at the upper side end portion or lower side end portion of the pixel PX, and the gate line G 1  may be disposed at a substantially central part of the pixel. In this case, the sub-pixel electrode PB may be opposed to the gate line G 1  (or the sub-pixel electrode PB may be disposed above the gate line G 1 ). 
     On the other hand, in the common electrode CE, the second main common electrode CAL 2  and second main common electrode CAR 2  are disposed on both sides of a position immediately above the main pixel electrode PA, and the second sub-common electrode CBU 2  and second sub-common electrode CBB 2  are disposed on both sides of a position immediately above the sub-pixel electrode PB. In other words, the main pixel electrode PA is disposed between the second main common electrode CAL 2  and second main common electrode CAR 2 , and the sub-pixel electrode PB is disposed between the second sub-common electrode CBU 2  and second sub-common electrode CBB 2 . 
     In the example illustrated, the second main common electrode CAL 2  is disposed at the left side end portion of the pixel PX and is opposed to the source line S 1  (or the second main common electrode CAL 2  is disposed above the source line S 1 ). In addition, the second main common electrode CAR 2  is disposed at the right side end portion of the pixel PX and is opposed to the source line S 2  (or the second main common electrode CAR 2  is disposed above the source line S 2 ). The second sub-common electrode CBU 2  is disposed at the upper side end portion of the pixel PX and is opposed to the gate line G 1  (or the second sub-common electrode CBU 2  is disposed above the gate line G 1 ). In addition, the second sub-common electrode CBB 2  is disposed at the lower side end portion of the pixel PX and is opposed to the gate line G 2  (or the second sub-common electrode CBB 2  is disposed above the gate line G 2 ). 
     According to the first structure example, as described above, since four domains can be formed in one pixel, the viewing angle can optically be compensated in four directions, and a wider viewing angle can be realized. 
     The second main common electrode CAL 2  and second main common electrode CAR 2  are opposed to the source line S 1  and source line S 2 , respectively. In particular, when the second main common electrode CAL 2  and second main common electrode CAR 2  are disposed above the source line S 1  and source line S 2 , respectively, the aperture portions which contribute to display can be made larger, compared to the case in which the second main common electrode CAL 2  and second main common electrode CAR 2  are disposed on the main pixel electrode PA side of the source line S 1  and source line S 2 , and the transmittance of the pixel PX can be enhanced. 
     In addition, by disposing the second main common electrode CAL 2  and second main common electrode CAR 2  above the source line S 1  and source line S 2 , respectively, the distances between the main pixel electrode PA, on the one hand, and the second main common electrode CAL 2  and second main common electrode CAR 2 , on the other hand, can be increased, and a lateral electric field, which is closer to a horizontal electric field, can be produced. Therefore, a wider viewing angle, which is an advantage of, e.g. the IPS mode of the conventional configuration, can be maintained. 
     Furthermore, since the sub-pixel electrode PB of the pixel electrode PE is disposed to be opposed to the storage capacitance line or gate line, an undesired electric field from the storage capacitance line or gate line can be shielded. It is thus possible to suppress application of an undesired bias from the storage capacitance line or gate line to the liquid crystal layer LQ, and to suppress the occurrence of a display defect such as burn-in. Therefore, a liquid crystal display device with a higher display quality can be provided. 
     Second Structure Example 
     Next, a second structure example of the embodiment is described. The same structural parts as in the first structure example are denoted by like reference numerals, and a detailed description is omitted. 
       FIG. 7  is a plan view which schematically shows the structure of one pixel PX on a counter-substrate CT 2  of a liquid crystal display panel LPN in the second structure example of the embodiment. 
     In the second structure example, a common electrode CE includes first main common electrodes CA 1  which are provided as main common electrodes on an array substrate that will be described later, and second sub-common electrodes CB 2  which are provided on a counter-substrate CT 2  as sub-common electrodes. The second sub-common electrodes CB 2  are covered with a second alignment film AL 2 . 
     Specifically, the illustrated counter-substrate CT 2  includes the second sub-common electrodes CB 2  each having a strip shape linearly extending in the first direction X, but does not include a main common electrode. In other words, in the counter-substrate CT 2 , the common electrode CE is formed in a stripe shape extending in the first direction X. In the meantime, the illustrated second sub-common electrodes CB 2  are two second sub-common electrodes CB 2  which are arranged in parallel with an interval in the second direction Y. In the description below, in order to distinguish these second sub-common electrodes CB 2 , the second sub-common electrode located on the upper side in the Figure is referred to as “CBU 2 ”, and the second main common electrode located on the lower side is referred to as “CBB 2 ”. 
     Although not described in detail, the second sub-common electrodes CB 2  of the common electrode CE are led out to the outside of the active area, are electrically connected to a power supply module formed on the array substrate via an electrically conductive member, and are supplied with a common potential. 
     Next, a description is given of an array substrate AR 2  which is suitably combined with the counter-substrate CT 2  shown in  FIG. 7 . 
       FIG. 8  is a plan view which schematically shows the structure of the array substrate AR 2 , at a time when the pixel PX of the liquid crystal display panel LPN in the second structure example of the embodiment is viewed from the counter-substrate CT 2  side. The common electrode CE is illustrated by broken lines, in order to explain the positional relationship between the pixel electrode PE and common electrode CE. In addition, only the structure of the pixel PX, which is necessary for the description, is illustrated, and the depiction of a switching element, etc. is omitted. 
     The array substrate AR 2 , like the array substrate AR 1 , includes a storage capacitance line C 1  which extends in the first direction X, a gate line C 1  and a gate line G 2  which extend in the first direction X, a source line S 1  and a source line S 2  which extend in the second direction Y, and a pixel electrode PE. The pixel electrode PE is covered with the first alignment film AL 1 . In addition, the array substrate AR 2  includes, as a part of the common electrode CE, first main common electrodes CA 1  each having a strip shape linearly extending in the second direction Y. The first main common electrodes CA 1  have the same potential as the second sub-common electrodes CB 2 . 
     In the meantime, the illustrated first main common electrodes CA 1  are two first main common electrodes CA 1  which are arranged in parallel with an interval in the first direction X. In the description below, in order to distinguish these first main common electrodes CA 1 , the first main common electrode located on the left side in the Figure is referred to as “CAL 1 ”, and the first main common electrode located on the right side is referred to as “CAR 1 ”. For example, like the pixel electrode PE, the first main common electrode CAL 1  and first main common electrode CAR 1  are formed on the second interlayer insulation film  13 , and are covered with the first alignment film AL 1 . In this case, the first main common electrode CAL 1  and first main common electrode CAR 1  can be formed of the same material (e.g. ITO) as the pixel electrode PE in the same fabrication step. 
     In the example illustrated, the first main common electrode CAL 1  is disposed at the left side end portion of the pixel PX, and is opposed to the source line S 1  (or the first main common electrode CAL 1  is disposed above the source line S 1 ). In addition, the first main common electrode CAR 1  is disposed at the right side end portion of the pixel PX, and is opposed to the source line S 2  (or the first main common electrode CAR 1  is disposed above the source line S 2 ). The second interlayer insulation film  13  is interposed as an insulation film between the first main common electrode CAL 1  and first main common electrode CAR 1 , on the one hand, and the source line S 1  and source line S 2 , on the other hand. 
     The first main common electrode CAL 1  and first main common electrode CAR 1  linearly extend within the active area, are led out of the active area, are electrically connected to the power supply module formed on the array substrate AR 2 , and are supplied with a common potential. In addition, in the case where the first main common electrode CAL 1  and first main common electrode CAR 1  cover the source line S 1  and source line S 2  in the active area, the width in the first direction X of each of the first main common electrode CAL 1  and first main common electrode CAR 1  is equal to or greater than the width in the first direction X of each of the source line S 1  and source line S 2 . 
     Like the first structure example, the pixel electrode PE is disposed between the gate line G 1  and gate line G 2 . Alternatively, the pixel electrode PE is disposed between the source line S 1  and source line S 2 , that is, between the first main common electrode CAL 1  and first main common electrode CAR 1 . The pixel electrode PE includes the main pixel electrode PA and sub-pixel electrode PB. 
     The main pixel electrode PA is located at a substantially middle point between the first main common electrode CAL 1  and first main common electrode CAR 1 . The main pixel electrode PA extends toward the gate line G 1  and gate line G 2 . 
     The sub-pixel electrode PB is disposed at a substantially middle point between the gate line G 1  and gate line G 2 . The sub-pixel electrode PB extends toward the first main common electrode CAL 1  and first main common electrode CAR 1 . However, in the case where the pixel electrode PE, together with the first main common electrode CAL 1  and first main common electrode CAR 1 , is formed on the second interlayer insulation film  13 , the sub-pixel electrode PB is disposed so as not to come in contact with the first main common electrode CAL 1  and first main common electrode CAR 1  (or the sub-pixel electrode PB is disposed so as to be spaced apart from the first main common electrode CAL 1  and first main common electrode CAR 1 ). In addition, the sub-pixel electrode PB is opposed to the storage capacitance line C 1  (or the sub-pixel electrode PB is disposed above the storage capacitance line C 1 ). 
     In the meantime, the storage capacitance line C 1  may be disposed at the upper side end portion or lower side end portion of the pixel PX, and the gate line G 1  may be disposed at a substantially central part of the pixel. In this case, the sub-pixel electrode PB may be opposed to the gate line G 1  (or the sub-pixel electrode PB may be disposed above the gate line G 1 ). 
     On the other hand, in the common electrode CE, the second sub-common electrode CBU 2  and second sub-common electrode CBB 2  are disposed on both sides of a position immediately above the sub-pixel electrode PB. In other words, the main pixel electrode PA is disposed between the first main common electrode CAL 1  and first main common electrode CAR 1 , and the sub-pixel electrode PB is disposed between the second sub-common electrode CBU 2  and second sub-common electrode CBB 2 . 
     In the example illustrated, the second sub-common electrode CBU 2  is disposed at the upper side end portion of the pixel PX and is opposed to the gate line G 1  (or the second sub-common electrode CBU 2  is disposed above the gate line G 1 ). In addition, the second sub-common electrode CBB 2  is disposed at the lower side end portion of the pixel PX and is opposed to the gate line G 2  (or the second sub-common electrode CBB 2  is disposed above the gate line G 2 ). 
     According to the second structure example, as described above, since four domains can be formed in one pixel, the viewing angle can optically be compensated in four directions, and a wider viewing angle can be realized. Furthermore, in addition to the advantageous effects described in connection with the first structure example, since at least one of the first main common electrodes CA 1  of the common electrode CE is so disposed as to be opposed to the source line, an undesired electric field from the source line can be shielded. It is thus possible to suppress application of an undesired bias from the source line to the liquid crystal layer LQ, and to suppress the occurrence of a display defect such as crosstalk (e.g. a phenomenon that when a pixel potential for displaying white is supplied to the source line that is connected to the pixel PX in the state in which the pixel PX is set at a pixel potential for displaying black, light leaks from a part of the pixel PX and the brightness increases). Therefore, a liquid crystal display device with a higher display quality can be provided. 
     In the meantime, the array substrate AR 2 , which has been described in connection with the second structure example, may be combined with the counter-substrate CT 1  which was described in connection with the first structure example. In this case, the common electrode CE is configured to include, as the main common electrode, the first main common electrodes CA 1  provided on the array substrate AR 2  and the second main common electrodes CA 2  provided on the counter-substrate CT 1 . In regions where the first main common electrodes CA 1  and the second main common electrodes CA 2  are opposed to each other with the liquid crystal layer being interposed, it becomes possible to suppress the occurrence of an undesired vertical electric field (i.e. an electric field in a direction normal to the substrate major surface). 
     Third Structure Example 
     Next, a third structure example of the embodiment is described. The same structural parts as in the first structure example are denoted by like reference numerals, and a detailed description is omitted. 
       FIG. 9  is a plan view which schematically shows the structure of one pixel PX on a counter-substrate CT 3  of a liquid crystal display panel LPN in the third structure example of the embodiment. 
     In the third structure example, a common electrode CE includes second main common electrodes CA 2  which are provided as main common electrodes on a counter-substrate CT 3 , and first sub-common electrodes CB 1  which are provided as sub-common electrodes on an array substrate that will be described later. The second main common electrodes CA 2  are covered with a second alignment film AL 2 . 
     Specifically, the illustrated counter-substrate CT 3  includes the second main common electrodes CA 2  each having a strip shape linearly extending in the second direction Y, but does not include a sub-common electrode. In other words, in the counter-substrate CT 3 , the common electrode CE is formed in a stripe shape extending in the second direction Y. In the meantime, the illustrated second main common electrodes CA 2  are two second main common electrodes CA 2  which are arranged in parallel with an interval in the first direction X. In the description below, in order to distinguish these second main common electrodes CA 2 , the second main common electrode located on the left side in the Figure is referred to as “CRL 2 ”, and the second main common electrode located on the right side is referred to as “CAR 2 ”. 
     Although not described in detail, the second main common electrodes CA 2  of the common electrode CE are led out to the outside of the active area, are electrically connected to a power supply module formed on an array substrate via an electrically conductive member, and are supplied with a common potential. 
     Next, a description is given of an array substrate AR 3  which is suitably combined with the counter-substrate CT 3  shown in  FIG. 9 . 
       FIG. 10  is a plan view which schematically shows the structure of the array substrate AR 3 , at a time when the pixel PX of the liquid crystal display panel LPN in the third structure example of the embodiment is viewed from the counter-substrate CT 3  side. The common electrode CE is illustrated by broken lines, in order to explain the positional relationship between the pixel electrode PE and common electrode CE. In addition, only the structure of the pixel PX, which is necessary for the description, is illustrated, and the depiction of a switching element, etc. is omitted. 
     The array substrate AR 3 , like the array substrate AR 1 , includes a storage capacitance line C 1  which extends in the first direction X, a gate line G 1  and a gate line G 2  which extend in the first direction X, a source line S 1  and a source line S 2  which extend in the second direction Y, and a pixel electrode PE. The pixel electrode PE is covered with the first alignment film AL 1 . In addition, the array substrate AR 3  includes, as a part of the common electrode CE, first sub-common electrodes CB 1  each having a strip shape linearly extending in the first direction X. The first sub-common electrodes CB 1  have the same potential as the second main common electrodes CA 2 . 
     In the meantime, the illustrated first sub-common electrodes CB 1  are two first sub-common electrodes CB 1  which are arranged in parallel with an interval in the second direction Y. In the description below, in order to distinguish these first sub-common electrodes CB 1 , the first sub-common electrode located on the upper side in the Figure is referred to as “CBU 1 ”, and the first sub-common electrode located on the lower side is referred to as “CBB 1 ”. For example, like the pixel electrode PE, the first sub-common electrode CBU 1  and first sub-common electrode CBB 1  are formed on the second interlayer insulation film  13 , and are covered with the first alignment film AL 1 . In this case, the first sub-common electrode CBU 1  and first sub-common electrode CBB 1  can be formed of the same material (e.g. ITO) as the pixel electrode PE in the same fabrication step. 
     In the example illustrated, the first sub-common electrode CBU 1  is disposed at the upper side end portion of the pixel PX and is opposed to the gate line G 1  (or the first sub-common electrode CBU 1  is disposed above the gate line G 1 ). In addition, the first sub-common electrode CBB 1  is disposed at the lower side end portion of the pixel PX and is opposed to the gate line G 2  (or the first sub-common electrode CBB 1  is disposed above the gate line G 2 ). The first interlayer insulation film  12  and second interlayer insulation film  13  are interposed as insulation films between the first sub-common electrode CBU 1  and first sub-common electrode CBB 1 , on the one hand, and the gate line G 1  and gate line G 2 , on the other hand. 
     The first sub-common electrode CBU 1  and first sub-common electrode CBB 1  linearly extend within the active area, are led out of the active area, are electrically connected to the power supply module formed on the array substrate AR 3 , and are supplied with a common potential. In addition, in the case where the first sub-common electrode CBU 1  and first sub-common electrode CBB 1  cover the gate line G 1  and gate line G 2  in the active area, the width in the second direction Y of each of the first sub-common electrode CBU 1  and first sub-common electrode CBB 1  is equal to or greater than the width in the second direction Y of each of the gate line G 1  and gate line G 2 . 
     Like the first structure example, the pixel electrode PE is disposed between the source line S 1  and source line S 2 . Alternatively, the pixel electrode PE is disposed between the gate line G 1  and gate line G 2 , that is, between the first sub-common electrode CBU 1  and first sub-common electrode CBB 1 . The pixel electrode PE includes the main pixel electrode PA and sub-pixel electrode PB. 
     The main pixel electrode PA is located at a substantially middle point between the source line S 1  and source line S 2 . The main pixel electrode PA extends toward the first sub-common electrode CBU 1  and first sub-common electrode CBB 1 . However, in the case where the pixel electrode PE, together with the first sub-common electrodes CBU 1  and first sub-common electrodes CBB 1 , is formed on the second interlayer insulation film  13 , the main pixel electrode PA is disposed so as not to come in contact with the first sub-common electrode CBU 1  and first sub-common electrode CBB 1  (or the main pixel electrode PA is disposed so as to be spaced apart from the first sub-common electrode CBU 1  and first sub-common electrode CBB 1 ). 
     The sub-pixel electrode PB is disposed at a substantially middle point between the first sub-common electrode CBU 1  and first sub-common electrode CBB 1 . The sub-pixel electrode PB extends toward the source line S 1  and source line S 2 . In addition, the sub-pixel electrode PB is opposed to the storage capacitance line C 1  (or the sub-pixel electrode PB is disposed above the storage capacitance line C 1 ). 
     In the meantime, the storage capacitance line C 1  may be disposed at the upper side end portion or lower side end portion of the pixel PX, and the gate line G 1  may be disposed at a substantially central part of the pixel. In this case, the sub-pixel electrode PB may be opposed to the gate line G 1  (or the sub-pixel electrode PB may be disposed above the gate line G 1 ), and the first sub-common electrode CBU 1  or first sub-common electrode CBB 1  may be opposed to the storage capacitance line C 1  (or the first sub-common electrode CBU 1  or first sub-common electrode CBB 1  may be disposed above the storage capacitance line C 1 ). 
     On the other hand, in the common electrode CE, the second main common electrode CAL 2  and second main common electrode CAR 2  are disposed on both sides of a position immediately above the main pixel electrode PA. In other words, the main pixel electrode PA is disposed between the second main common electrode CAL 2  and second main common electrode CAR 2 , and the sub-pixel electrode PB is disposed between the first sub-common electrode CBU 1  and first sub-common electrode CBB 1 . 
     In the example illustrated, the second main common electrode CAL 2  is disposed at the left side end portion of the pixel PX, and is opposed to the source line S 1  (or the second main common electrode CAL 2  is disposed above the source line S 1 ). In addition, the second main common electrode CAR 2  is disposed at the right side end portion of the pixel PX, and is opposed to the source line S 2  (or the second main common electrode CAR 2  is disposed above the source line S 2 ). 
     According to the third structure example, as described above, since four domains can be formed in one pixel, the viewing angle can optically be compensated in four directions, and a wider viewing angle can be realized. Furthermore, in addition to the advantageous effects described in connection with the first structure example, since the first sub-common electrode CB 1  of the common electrode CE is so disposed as to be opposed to the gate line, an undesired electric field from the gate line can be shielded. It is thus possible to suppress application of an undesired bias from the gate line to the liquid crystal layer LQ, and to suppress the occurrence of a display defect such as burn-in. Therefore, a liquid crystal display device with a still higher display quality can be provided. 
     In the meantime, the array substrate AR 3 , which has been described in connection with the third structure example, may be combined with the counter-substrate CT 1  which was described in connection with the first structure example. In this case, the common electrode CE is configured to include, as the sub-common electrode, the first sub-common electrodes CB 1  provided on the array substrate AR 3  and the second sub-common electrodes CB 2  provided on the counter-substrate CT 1 . In the region where the first sub-common electrodes CB 1  and the second sub-common electrodes CB 2  are opposed to each other with the liquid crystal layer being interposed, it becomes possible to suppress the occurrence of an undesired vertical electric field (i.e. an electric field in a direction normal to the substrate major surface). 
     Fourth Structure Example 
     Next, a fourth structure example of the embodiment is described. The same structural parts as in the first structure example are denoted by like reference numerals, and a detailed description is omitted. 
       FIG. 11  is a plan view which schematically shows the structure of an array substrate AR 4 , at a time when the pixel PX of the liquid crystal display panel LPN in the fourth structure example of the embodiment is viewed from the counter-substrate CT side. Only the structure of the pixel PX, which is necessary for the description, is illustrated, and the depiction of a switching element, etc. is omitted. 
     In the fourth structure example, a common electrode CE includes first main common electrodes CA 1  which are provided as main common electrodes on the array substrate AR 4 , and first sub-common electrodes CB 1  which are provided as sub-common electrodes on the array substrate AR 4 . 
     The array substrate AR 4 , like the array substrate AR 1 , includes a storage capacitance line C 1  which extends in the first direction X, a gate line G 1  and a gate line G 2  which extend in the first direction X, a source line S 1  and a source line S 2  which extend in the second direction Y, and a pixel electrode PE. The pixel electrode PE is covered with the first alignment film AL 1 . In addition, the array substrate AR 4  includes a common electrode CE including first main common electrodes CA 1  (CAL 1  and CARL) each having a strip shape linearly extending in the second direction Y, and first sub-common electrodes CB 1  (CBU 1  and CBB 1 ) each having a strip shape linearly extending in the first direction X. In short, in the array substrate AR 4 , the common electrode CE is formed in a grid shape. The structure of the first main common electrodes CA 1  is as has been described in connection with the array substrate AR 2 . The structure of the first sub-common electrodes CB 1  is as has been described in connection with the array substrate AR 3 . 
     Although not described in detail, the first main common electrodes CA 1  and first sub-common electrodes CB 1  of the common electrode CE are led out to the outside of the active area, are electrically connected to a power supply module formed on the array substrate AR 4  via an electrically conductive member, and are supplied with a common potential. 
     The array substrate AR 4 , which has been described in connection with the fourth structure example, can be combined with any one of the counter-substrate CT 1  which was described in connection with the first structure example, the counter-substrate CT 2  which was described in connection with the second structure example, and the counter-substrate CT 3  which was described in connection with the third structure example. 
       FIG. 12  shows a summary of the combinations between the array substrate AR 1 , array substrate AR 2 , array substrate AR 3  and array substrate AR 4 , which have been described in the first to fourth structure examples, and the counter-substrate CT 1 , counter-substrate CT 2  and counter-substrate CT 3 , which have been described in the first to third structure examples. In  FIG. 12 , a slash mark corresponds to combinations which cannot realize the basic structure of the embodiment, a double circle (⊚) corresponds to combinations described in the respective structure examples, and a white circle (◯) corresponds to combinations which are feasible in the respective structure examples. 
     Next, a brief description will be given of structure of the pixel PX according to a further variation of the embodiment. 
       FIG. 13  is a plan view which schematically shows one variation of the embodiment. 
     The pixel electrode PE includes two main pixel electrodes PA which extend in the second direction Y and are arranged in parallel at intervals in the first direction X, and a sub-pixel electrode PB which extends in the first direction X, crosses the two main pixel electrodes PA, and is disposed at a substantially central part of the pixel. The pixel electrode PE is provided on the array substrate. 
     The common electrode CE includes main common electrodes CA which extend in the second direction Y, and sub-common electrodes CB which extend in the first direction X. The main common electrodes CA are disposed on both sides of the two main pixel electrodes PA. Specifically, three main common electrodes CA and two main pixel electrodes PA are alternately arranged. The sub-common electrodes CB are disposed on both sides of the sub-pixel electrode PB. Specifically, the sub-pixel electrode PB and two sub-common electrodes CB are alternately arranged. As regards this common electrode CE, too, at least a part of the main common electrodes CA and sub-common electrodes CB is provided on the counter-substrate. 
     In this structure, eight regions are formed in one pixel PX, and at the ON time, liquid crystal molecules are aligned in directions indicated by arrows in the Figure. With this structure, the same advantageous effects as with the above-described structure examples can be obtained. 
     The above-described embodiment is particularly suited to such a configuration that capacitance coupling driving (CC driving) is performed. Specifically, in the capacitance coupling driving (CC driving), a predetermined voltage is reached by superimposing a storage capacitance signal on the pixel electrode PE via the storage capacitance CS of each pixel. Thus, when the storage capacitance CS and the pixel capacitance are made substantially equal, the signal voltage amplitude can be substantially halved. The above-described gate driver GD, source driver SD, and driving IC chip  2 , which incorporates a controller, function as a driving mechanism for executing such CC driving, and are provided on the array substrate AR. 
     According to the structure in which the CC driving is applied, the power consumption can be reduced and the degradation in display quality can be suppressed. 
     As has been described above, according to the present embodiment, a liquid crystal display device with good display quality can be provided. 
     While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel embodiments described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.