Fringe-field switching mode liquid crystal display device and method of manufacturing the same

A liquid crystal display device includes an alignment layer having an alignment direction inclined at an angle α where 0°<α<90° with respect to an extending direction of a gate line, a pixel electrode, and a common electrode placed opposite to the pixel electrode with an insulating layer interposed therebetween. One of the pixel electrode and the common electrode has a slit for generating a fringe electric field to liquid crystals with the other of the pixel electrode and the common electrode. The slit includes a first slit lying in the alignment direction or a direction perpendicular to the alignment direction, and a plurality of second slits and a plurality of third slits respectively inclined at an angle ±θ with respect to the first slit.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a liquid crystal display device and a method of manufacturing the same and, particularly, to a fringe-field switching mode liquid crystal display device and a method of manufacturing the same.

2. Description of Related Art

A fringe-field switching (FFS) mode of a liquid crystal display device is a display technique that displays an image by applying a fringe electric field to liquid crystals filled between substrates placed opposite to each other. Because a pixel electrode and a counter electrode are formed by transparent conductive layers in the FFS mode liquid crystal display device, it is possible to obtain a higher aperture ratio and transmittance compared to an in-plane switching (IPS) mode.

In liquid crystal display devices, viewing angle characteristics are degraded due to the occurrence of a phenomenon called color shift that an image looks yellowish or bluish depending on the angle of view, tone reversal or the like. Thus, the FFS mode liquid crystal display device has the structure as shown inFIG. 8so as to suppress the color shift and the tone reversal and thereby improve the viewing angle characteristics. Referring toFIG. 8, in the FFS mode liquid crystal display device according to related art, molecules of liquid crystals20are oriented perpendicular to or in parallel with a gate line43. Further, a common electrode8placed opposite to a pixel electrode6with an insulating layer interposed therebetween has slits at an angle of ±1 to 20° with respect to the orientation axis (slow axis) of the liquid crystals20, which are symmetric about the center of a pixel. In this structure, the orientation of the liquid crystals20changes as indicated by the dotted line inFIG. 8when a voltage is applied, so that the liquid crystals20operate symmetrically in one pixel. This prevents the birefringence effect of the liquid crystals20from varying depending on the oblique angle of view, thereby improving the viewing angle characteristics.

In this structure, as shown inFIG. 9, it is necessary that the absorption axis of a polarizing plate on the array substrate side is at 0° or 90° and the absorption axis of a polarizing plate on the counter substrate side is at 90° or 0°, each with respect to the orientation axis (slow axis) of the liquid crystals20, so that they are in crossed Nichols arrangement. In this arrangement, the polarization direction (optical axis) of transmitted light that is transmitted from the FFS mode liquid crystal display device is at 0° or 90° with respect to the gate line43.

In the case of using a liquid crystal display device outdoors, a user may watch an image through polarized sunglasses. The absorption axis of the polarized sunglasses is oriented horizontally in order to prevent reflected light from entering the eyes. Accordingly, if transmitted light from the liquid crystal display device is in the horizontal direction, the polarized sunglasses absorb the light, and a user cannot view a displayed image. Therefore, when looking at an image through the polarized sunglasses, display looks all black in either horizontal (landscape) or vertical (portrait) position.

In order to address the above concern, a technique of attaching λ/4 plate on top of the polarizing plate is disclosed in Japanese Unexamined Patent Publication No. 10-10523. Further, a technique of attaching a polarization canceling plate that combines two quartz plates on top of the polarizing plate to thereby improve the visibility when looking at images through polarized sunglasses is disclosed in Japanese Unexamined Patent Publication No. 10-10522. Furthermore, a technique of specifying the polarization direction of the polarizing plate on the display surface side to thereby improve the visibility when looking at images through polarized sunglasses is disclosed in Japanese Unexamined Patent Publication No. 10-49082.

However, because the techniques disclosed in Japanese Unexamined Patent Publications Nos. 10-10523 and 10-10522 require an additional member such as the λ/4 plate or the polarization canceling plate, the costs increase. Further, if such a member is attached to a liquid crystal display device, the thickness of the liquid crystal display device increases. On the other hand, if the technique disclosed in Japanese Unexamined Patent Publication No. 10-49082 is used in an FFS mode liquid crystal display device, the contrast decreases.

In light of the foregoing, it is desirable to provide an FFS mode liquid crystal display device with high display quality that enables a display to be viewed in both landscape and portrait positions through polarized sunglasses without need of any additional member, and a method of manufacturing the same.

SUMMARY OF THE INVENTION

According to an embodiment of the present invention, there is provided a liquid crystal display device including a plurality of pixels, which includes a first substrate having a thin film transistor, a second substrate placed opposite to the first substrate, liquid crystals filled between the first substrate and the second substrate, alignment layers respectively placed on surfaces of the first substrate and the second substrate in contact with the liquid crystals and having an alignment direction inclined at an inclination angle α where 0°<α<90° with respect to an extending direction of a gate line connected to a gate electrode of the thin film transistor, a pixel electrode placed in each pixel and connected to a drain electrode of the thin film transistor, and a common electrode placed opposite to the pixel electrode with an insulating layer interposed therebetween, one of the pixel electrode and the common electrode having a slit for generating a fringe electric field to the liquid crystals with the other of the pixel electrode and the common electrode, wherein the slit includes a first slit (which is a slit C in an embodiment of the present invention) placed in each pixel and lying in the alignment direction or a perpendicular direction to the alignment direction, a plurality of second slits (which are slits A in an embodiment of the present invention) placed in a first region on one side of the first slit in each pixel and inclined at an angle θ to a given direction with respect to a longitudinal direction of the first slit, and a plurality of third slits (which are slits B in an embodiment of the present invention) placed in a second region on another side of the first slit opposite to the first region in each pixel and inclined at the angle θ to a direction opposite to the given direction with respect to the longitudinal direction of the first slit.

According to another embodiment of the present invention, there is provided a method of manufacturing a liquid crystal display device including a plurality of pixels, which includes steps of forming a thin film transistor on a first substrate, forming a pixel electrode connected to a drain electrode of the thin film transistor in each pixel, forming a common electrode placed opposite to the pixel electrode with an insulating layer interposed therebetween, the common electrode having a slit for generating a fringe electric field with the pixel electrode, forming an alignment layer on the common electrode, the alignment layer having an alignment direction inclined at an inclination angle α where 0°<α<90° with respect to an extending direction of a gate line connected to a gate electrode of the thin film transistor, and attaching a second substrate to the first substrate and filling liquid crystals between the first substrate and the second substrate, wherein the step of forming the common electrode makes a first slit placed in each pixel and lying in the alignment direction or a perpendicular direction to the alignment direction, a plurality of second slits placed in a first region on one side of the first slit in each pixel and inclined at an angle θ to a given direction with respect to a longitudinal direction of the first slit, and a plurality of third slits placed in a second region on another side of the first slit opposite to the first region in each pixel and inclined at the angle θ to a direction opposite to the given direction with respect to the longitudinal direction of the first slit.

According to the embodiments of the present invention, it is possible to provide an FFS mode liquid crystal display device with high display quality that enables a display to be viewed in both landscape and portrait positions through polarized sunglasses without need of any additional member, and a method of manufacturing the same.

DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

A liquid crystal display device according to an embodiment of the present invention is described hereinafter with reference toFIG. 1.FIG. 1is a front view showing the structure of a thin film transistor (TFT) array substrate to be used in a liquid crystal display device. The liquid crystal display device according to the embodiment is an FFS mode liquid crystal display device in which a pixel electrode and a counter electrode are placed in the TFT array substrate.

The liquid crystal display device according to the embodiment includes a substrate10. The substrate10is an array substrate such as a TFT array substrate, for example. The substrate10includes a display area41and a frame area42surrounding the display area41. In the display area41, a plurality of gate lines (scanning signal lines)43and a plurality of source lines (display signal lines)44are placed. The plurality of gate lines43are arranged in parallel with each other. Likewise, the plurality of source lines44are arranged in parallel with each other. The gate lines43and the source lines44intersect with each other. Each area surrounded by the adjacent gate lines43and the adjacent source lines44serves as a pixel47. Thus, a plurality of pixels47are arranged in matrix in the substrate10.

In the frame area42of the substrate10, a scanning signal driving circuit45and a display signal driving circuit46are placed. The gate lines43extend from the display area41to the frame area42and are connected to the scanning signal driving circuit45at the end of the substrate10. Likewise, the source lines44extend from the display area41to the frame area42and are connected to the display signal driving circuit46at the end of the substrate10. An external line48is connected in the vicinity of the scanning signal driving circuit45. Further, an external line49is connected in the vicinity of the display signal driving circuit46. The external lines48and49are wiring boards such as a flexible printed circuit (FPS), for example.

External signals are supplied to the scanning signal driving circuit45and the display signal driving circuit46through the external lines48and49. The scanning signal driving circuit45supplies a gate signal (scanning signal) to the gate lines43based on an external control signal. The gate lines43are sequentially selected by the gate signal. On the other hand, the display signal driving circuit46supplies a display signal to the source lines44based on an external control signal and display data. A display voltage according to display data is thereby supplied to each pixel47.

Each pixel includes at least one TFT50. The TFT50is placed in the vicinity of the intersection of the source line44and the gate line43. For example, the TFT50supplies a display voltage to a pixel electrode. Specifically, the TFT50, which is a switching element, is turned on by the gate signal from the gate line43. A display voltage is thereby applied from the source line44to the pixel electrode that is connected to a drain electrode of the TFT50. The pixel electrode is placed opposite to a common electrode (counter electrode) having slits with an insulating layer interposed therebetween. A fringe electric field corresponding to the display voltage is generated between the pixel electrode and the counter electrode. Further, an alignment layer (not shown) is placed on the surface of the substrate10. The detailed structure of the pixel47is described later.

Further, a counter substrate is placed opposite to the substrate10. The counter substrate is a color filter substrate, for example, and it is placed on the viewing side. The counter substrate is placed to face the array substrate with a cell gap of about 1 to 5 μm, for example. On the counter substrate, a black matrix (BM), a color filter, an alignment layer and soon are placed. Further, an overcoat layer or a columnar photospacer may be placed between the color filter and the alignment layer.

A liquid crystal layer is placed between the substrate10and the counter substrate. In other words, liquid crystals are filled between the substrate10and the counter substrate. In this embodiment, the liquid crystals are oriented at an angle α, which is larger than 0° and smaller than 90°, with respect to the gate line43when no voltage is applied. Thus, the orientation direction (slow axis) of the liquid crystals is set at the angle α, which is 0°<α<90°, with respect to the extending direction of the gate line43. Accordingly, the alignment layers that are placed on the respective surfaces of the substrate10and the counter substrate in contact with the liquid crystals have the alignment direction which is inclined at the angle α with respect to the extending direction of the gate line43.

Further, a polarizing plate, a retardation film and so on are placed on the outer sides of the substrate10and the counter substrate. Furthermore, a backlight unit or the like is placed on the non-viewing side of the liquid crystal display panel. In this embodiment, the absorption axis of the polarizing plate is set to be in the direction perpendicular to or in parallel with the orientation direction (slow axis) of the liquid crystals. This is described hereinafter with reference toFIG. 2.FIG. 2is a view to describe the arrangement direction of polarizing plates according to an embodiment of the present invention. As shown inFIG. 2, if the absorption axis of a polarizing plate15on the array substrate side is set at the angle α with respect to the extending direction of the gate line43, which is the direction in parallel with the orientation direction (slow axis) of the liquid crystals, the absorption axis of a polarizing plate25on the counter substrate side is set at the angle α+90°, so that they are in crossed Nichols arrangement. On the other hand, if the absorption axis of the polarizing plate15on the array substrate side is set at the angle α+90° with respect to the extending direction of the gate line43, which is the direction perpendicular to the orientation direction (slow axis) of the liquid crystals, the absorption axis of the polarizing plate25on the counter substrate side is set at the angle α, so that they are in crossed Nichols arrangement. In this manner, the polarizing plates15and25have the absorption axes that are set in the orientation direction of the liquid crystals or in the direction perpendicular to the orientation direction.

The liquid crystals are driven by a fringe electric field between the pixel electrode and the counter electrode. Specifically, the orientation of the liquid crystals between the substrates changes by an applied voltage. The polarization state of light passing through the liquid crystal layer thereby changes. Specifically, the polarization state of linearly polarized light having passed through the polarizing plate changes by the liquid crystal layer. To be more precise, as shown inFIG. 2, light from the backlight unit becomes linearly polarized light by the polarizing plate15on the array substrate side. Then, the linearly polarized light passes through the liquid crystal layer, so that its polarization state changes.

The amount of light passing through the polarizing plate25on the counter substrate side varies depending on the polarization state. Specifically, among the transmitted light that is transmitted through the liquid crystal display panel from the backlight unit, the amount of light passing through the polarizing plate25on the viewing side varies. The orientation of liquid crystals varies depending on a display voltage to be applied. Therefore, it is possible to change the amount of light passing through the polarizing plate25on the viewing side by controlling the display voltage. Thus, it is possible to display a desired image by varying the display voltage for each pixel.

Transmitted light30that has been transmitted through the polarizing plate25on the counter substrate side is linearly polarized light having the optical axis at the angle α or α+90° with respect to the gate line43. Specifically, as shown inFIG. 2, if the absorption axis of the polarizing plate25on the counter substrate side is set at the angle α+90° with respect to the gate line43, the transmitted light30in the polarization direction at the angle α with respect to the gate line43is transmitted from the liquid crystal display device. On the other hand, if the absorption axis of the polarizing plate25on the counter substrate side is set at the angle α with respect to the gate line43, the transmitted light30in the polarization direction at the angle α+90° with respect to the gate line43is transmitted from the liquid crystal display device. The value of the angle α is set to be 0°<α<90° with respect to the extending direction of the gate line43, as mentioned previously. Accordingly, the polarization direction of the transmitted light30that is transmitted from the liquid crystal display device does not completely coincide with the horizontal direction in which the absorption axis of polarized sunglasses35is placed. It is thereby possible to prevent a display from looking all black in either horizontal (landscape) or vertical (portrait) position when looking at an image through the polarized sunglasses35. This enables a user to view a display in both horizontal (landscape) and vertical (portrait) positions while wearing the polarized sunglasses35.

The pixel structure of the liquid crystal display device according to an embodiment of the present invention is described hereinafter with reference toFIGS. 3 and 4.FIG. 3is a plan view showing the pixel structure of a TFT array substrate according to an embodiment of the present invention.FIG. 4is a sectional view along line IV-IV inFIG. 3.FIG. 3shows one of the pixels47of the TFT array substrate. The structure having the channel-etch type TFT50is described hereinbelow by way of illustration.

Referring toFIGS. 3 and 4, the gate line43, a part of which serves as a gate electrode1, is placed on the transparent insulating substrate10such as glass. The gate line43extends linearly in one direction on the substrate10. The gate electrode1and the gate line43are made of Cr, Al, Ta, Ti, Mo, W, Ni, Cu, Au or Ag, an alloy film made mainly of those or a stacked film of those, for example.

Agate insulating layer11, which is a first insulating layer, is placed to cover the gate electrode1and the gate line43. The gate insulating layer11is made of an insulating film such as silicon nitride or silicon oxide. Further, in the formation area of the TFT50, a semiconductor layer2is placed opposite to the gate electrode1with the gate insulating layer11interposed therebetween. In this example, the semiconductor layer2is placed on the gate insulating layer11so as to overlap the gate line43, and the part of the gate line43which overlaps the semiconductor layer2serves as the gate electrode1. The semiconductor layer2is made of amorphous silicon, polycrystalline polysilicon or the like, for example.

Further, ohmic contact layers into which conductive impurity is doped are placed on both ends of the semiconductor layer2. The parts of the semiconductor layer2which correspond to the ohmic contact layers are source and drain regions, respectively. Specifically, the part of the semiconductor layer2which corresponds to the ohmic contact layer on the upper side inFIG. 3serves as the source region. The part of the semiconductor layer2which corresponds to the ohmic contact layer on the lower side inFIG. 3serves as the drain region. In this manner, the source and drain regions are formed at the both ends of the semiconductor layer2. The part of the semiconductor layer2between the source and drain regions serves as a channel region. The ohmic contact layer is not placed on the channel region of the semiconductor layer2. The ohmic contact layer is made of n-type amorphous silicon, n-type polycrystalline silicon or the like into which impurity such as phosphorus (P) is doped at high concentration, for example.

A source electrode4and a drain electrode5are respectively placed on the ohmic contact layers. Specifically, the source electrode4is placed on the ohmic contact layer on the source region side. The drain electrode5is placed on the ohmic contact layer on the drain region side. The channel-etch type TFT50is formed in this manner. The source electrode4and the drain electrode5extend to the outside of the channel region of the semiconductor layer2. Thus, like the ohmic contact layers, the source electrode4and the drain electrode5are not placed on the channel region of the semiconductor layer2.

The source electrode4extends to the outside of the channel region of the semiconductor layer2and is connected to the source line44. The source line44is placed on the gate insulating layer11and extends linearly in the direction intersecting the gate line43over the substrate10. Thus, the source line44branches off at the intersection with the gate line43and extends along the gate line43, to form the source electrode4.

On the other hand, the drain electrode5extends to the outside of the channel region of the semiconductor layer2. Thus, the drain electrode5has an extending part that extends to the outside of the TFT50. The source electrode4, the drain electrode and the source line44are made of Cr, Al, Ta, Ti, Mo, W, Ni, Cu, Au or Ag, an alloy film made mainly of those or a stacked film of those, for example.

Further, a second insulating layer12is placed to cover the source electrode4, the drain electrode5and the source line44. The second insulating layer12has a contact hole (not shown) that reaches the extending part of the drain electrode5. The second insulating layer12is made of an insulating film such as silicon nitride or silicon oxide.

On the second insulating layer12, a pixel electrode6that is electrically connected to the drain electrode5through the contact hole is placed. The pixel electrode6is connected to the extending part of the drain electrode5through the contact hole. Further, the pixel electrode6extends from the extending part of the drain electrode5to the inside of the pixel47. Specifically, as shown inFIG. 3, the pixel electrode6is placed substantially all over the area surrounded by the source line44and the gate line43except the TFT50. The pixel electrode6is made of a transparent conductive film such as ITO.

Furthermore, a third insulating layer13is placed to cover the pixel electrode6. The third insulating layer13is made of an insulating film such as silicon nitride or silicon oxide. Further, a common electrode8is placed on the third insulating layer13. The common electrode8is placed opposite to the pixel electrode6with the third insulating layer13interposed therebetween. As shown inFIG. 4, the common electrode8has slits to generate a fringe electric field with the pixel electrode6. In this example, the common electrode8is placed substantially all over the display area41except the slit parts. Thus, the common electrode8is electrically connected to the common electrodes8of all the adjacent pixels47. The common electrode8is made of a transparent conductive film such as ITO. InFIG. 3, only the outer shape of slits is illustrated as the common electrode8.

In this embodiment, the common electrode8has a plurality of slits that lie in different directions as shown inFIG. 3. Specifically, a plurality of slits A1, A2, . . . , An (which are referred to collectively as the slits A) are placed in a first region81, which is a part of the pixel47. Further, a plurality of slits B1, B2, . . . , Bm (which are referred to collectively as the slits B) are placed in a second region82, which is another part of the pixel47. Furthermore, a slit C is placed between the first region81and the second region82. The slit C is located on the boundary between the first region81and the second region82.

The slit C lies in the same direction as the orientation direction (slow axis) of the liquid crystal20when no voltage is applied or in the direction perpendicular to the orientation direction. Thus, the slit C lies in the alignment direction of the alignment layer or in the direction perpendicular to the alignment direction. Accordingly, the slit C is inclined at the angle α or α+90° with respect to the gate line43.FIG. 3shows the case where the slit C lies in the same direction as the orientation direction (slow axis) of the liquid crystal20, which is the direction that is inclined at the angle α with respect to the gate line43, by way of illustration. In each pixel47, the part above the slit C is the first region81, and the part below the slit C is the second region82. Thus, the first region81is located on one side of the slit C, and the second region82is located on the other side of the slit C, which is the side opposite to the first region81.

The slits A in the first region81and the slits B in the second region82are placed to be inclined at ±θ with respect to the slit C. Specifically, as shown inFIG. 3, the longitudinal direction of the slits B is set at the angle +θ with respect to the longitudinal direction of the slit C. Thus, the slits B are inclined to a given direction at the angle θ with respect to the longitudinal direction of the slit C. The angle θ is preferably in the range of 1° to 20°. On the other hand, the longitudinal direction of the slits A is set at the angle −θ with respect to the longitudinal direction of the slit C. Thus, the slits A are inclined to the direction opposite to the inclination direction of the slits B at the angle θ with respect to the longitudinal direction of the slit C. Accordingly, the angle of inclination of the slits A with respect to the slit C is symmetric to the angle of inclination of the slits B with respect to the slit C about the longitudinal direction of the slit C. By placing the slits A and B in such an inclined manner, the liquid crystals20can operate symmetrically about the slit C in one pixel47. This allows the birefringence effect to be symmetric in the first region81and the second region82. It is thereby possible to prevent color shift from occurring when viewing an image from different angles, thus obtaining suitable viewing angle characteristics.

The angle of inclination of the slits A and the angle of inclination of the slits B with respect to the slit C may be opposite. Specifically, the slits A may be inclined at the angle +θ and the slits B may be inclined at the angle −θ with respect to the slit C. Accordingly, one of the slits A and the slits B is inclined at the angle +θ and the other one is inclined at the angle −θ, where 1°≦θ≦20°, with respect to the slit C. A difference in the angle of inclination between the slits A and the slits B is 2θ.

The plurality of slits A1, A2, . . . , An are arranged in parallel with each other in the first region81. The plurality of slits B1, B2, . . . , Bm are also arranged in parallel with each other in the second region82. The plurality of slits A1, A2, . . . , An are arranged at a regular interval Sa. The plurality of slits B1, B2, . . . , Bm are arranged at a regular interval Sb, which is equal to the interval Sa. Generally, the intervals Sa and Sb are preferably in the range of 1 to 10 μm.

The plurality of slits A1, A2, . . . , An have a fixed slit width Wa. The slits A1, A2, . . . , An have slit lengths L(a1), L(a2), . . . , L(an), respectively. It is not necessary that all of the slit lengths L(a1), L(a2), . . . , L(an) have the same value. Likewise, the plurality of slits B1, B2, . . . , Bm have a fixed slit width Wb. The slits B1, B2, . . . , Bm have slit lengths L(b1), L(b2), . . . , L(bm), respectively. It is not necessary that all of the slit lengths L(b1), L(b2), . . . , L(bm) have the same value. In this embodiment, it is preferred that the respective slit lengths are adjusted in such a way that a total slit length L(A)=L(a1)+L(a2)+ . . . +L(an) of the slits A is the same as a total slit length L(B)=L(b1)+L(b2)+ . . . +L(bm) of the slits B.

By making the slits so as to satisfy L(A)=L(B), the operating region of the liquid crystals20is equalized between the first region81and the second region82. This is described hereinbelow.FIG. 5is a graph showing the relationship between a total slit length when a slit width is fixed and transmittance per unit area when viewed from the front. As shown inFIG. 5, the total slit length and the transmittance are in a proportional relationship. Thus, the operating region of the liquid crystals20is proportional to the total slit length. Therefore, by equalizing the total slit length L(A) of the slits A in the first region81and the total slit length L(B) of the slits B in the second region82, the operating region of the liquid crystals20is the same between the first region81and the second region82. It is thereby possible to prevent color shift from occurring when viewing an image from different angles more reliably, thus obtaining more suitable viewing angle characteristics.

A specific size of the slits A, B and C or the like is described hereinafter with reference toFIG. 6.FIG. 6is a view to describe a specific example of arrangement of the slits A, B and C according to the embodiment. InFIG. 6, in the pixel47having an opening of 150 μm×50 μm, for example, the slit C at the angle α=45°, which is the same as the angle of the orientation (slow axis) of the liquid crystals20, is made. InFIG. 6, the first region81above the slit C has nine slits A1to A9, and the second region82below the slit C has seven slits B1to B7. The slit width Wa of the slits A1to A9is 3.5 μm, and the interval Sa of the slits A1to A9is 5.0 μm. Likewise, the slit width Wb of the slits B1to B7is 3.5 μm, which is the same as Wa, and the interval Sb of the slits B1to B7is 5.0 μm, which is the same as Sa. In this manner, the slits A1to A9have the same slit width as the slits B1to B7in the example ofFIG. 6. The angle of inclination +θ of the slits B1to B7with respect to the slit C is +10°, and the angle of inclination −θ of the slits A1to A9with respect to the slit C is −10°. Accordingly, as shown in FIG.6, the slits B1to B7are inclined at an angle of 55° with respect to the extending direction of the gate line43. On the other hand, the slits A1to A9are inclined at an angle of 35° with respect to the extending direction of the gate line43.

The slit width Wa of the slits A and the slit width Wb of the slits B may not be the same value. Thus, L(A)=L(B) may be satisfied by adjusting the slit width Wa of the slits A to be a different value from the slit width Wb of the slits B. In other words, the slit width Wa may be set differently from the slit width Wb so as to satisfy L(A)=L(B).FIG. 7is a view to describe another specific example of arrangement of the slits A, B and C according to the embodiment. InFIG. 7, the respective slit lengths of the slits A1to A9and the slits B1to B7are adjusted in such a way that the total slit length L (A) of the slits A1to A9and the total slit length L(B) of the slits B1to B7satisfy L(A)=L(B)=380 μm.

The size of the opening of the pixel47is 150 μm×50 μm, and the angle of inclination of the slit C is α=45°, which is the same as the angle of the orientation (slow axis) of the liquid crystals20. The angle of inclination +θ of the slits B1to B7with respect to the slit C is +10°, and the angle of inclination −θ of the slits A1to A9with respect to the slit C is −10°. Further, the interval Sa of the slits A1to A9and the interval Sb of the slits B1to B7are both 5.0 μm. In such a case, it is preferred that the slit width Wb of the slits B1to B7is 3.5 μm, and the slit width Wa of the slits A1to A9is 3.0 μm, which is smaller than Wb.

As described above, the slits A1to A9have a different slit width from the slits B1to B7in the example ofFIG. 7. Thus, in the case where L(A)=L(B) is not satisfied because either one of the first region81or the second region82is not large enough when the slit width Wa and the slit width Wb are fixed the same value, for example, it is possible to satisfy L(A)=L(B) by decreasing the slit width in the region that is not large enough or increasing the slit width in the region that is large enough. Further, in the case L(A)=L(B) is satisfied but the slits A or B are arranged unevenly in a part of the first region81or the second region82, it is possible to arrange the slits evenly all over each region by increasing the slit width as appropriate. Generally, the slit widths Wa and Wb are preferably in the range of 2 to 10 μm.

Hereinafter, a method of manufacturing the liquid crystal display device according to an embodiment of the present invention is described. Firstly, a film made of Cr, Al, Ta, Ti, Mo, W, Ni, Cu, Au or Ag, an alloy film made mainly of those or a stacked film of those is deposited all over the transparent insulating substrate10such as glass. The film is formed all over the substrate10by sputtering or vapor deposition, for example. Next, a resist is applied thereon, and the applied resist is exposed to light through a photomask. The resist is then developed, thereby pattering the resist. This series of processes is referred to hereinafter as photolithography. After that, the film is etched using the resist pattern as a mask, thereby removing the photoresist pattern. The gate electrode1and the gate line43are thereby patterned.

Next, a first insulating layer to serve as the gate insulating layer11, a material of the semiconductor layer2and a material of the ohmic contact layer are deposited in this order so as to cover the gate electrode1and the gate line43. They are formed all over the substrate10by plasma CVD, atmospheric pressure CVD, low pressure CVD or the like, for example. Silicon nitride, silicon oxide or the like may be used as the gate insulating layer11.

The material of the semiconductor layer2may be amorphous silicon, polycrystalline polysilicon or the like, for example. The material of the ohmic contact layer may be n-type amorphous silicon, n-type polycrystalline silicon or the like into which impurity such as phosphorus (P) is doped at high concentration, for example. After that, the layer to serve as the semiconductor layer2and the layer to serve as the ohmic contact layer are patterned into an island shape above the gate electrode1by the process of photolithography, etching and resist removal.

After that, in this embodiment, a film made of Cr, Al, Ta, Ti, Mo, W, Ni, Cu, Au or Ag, an alloy film made mainly of those or a stacked film of those is deposited to cover the layers formed above. The film is formed by sputtering or vapor deposition, for example. After that, the film is patterned by the process of photolithography, etching and resist removal, thereby forming the source electrode4, the drain electrode5and the source line44. Then, the layer to serve as the ohmic contact layer is etched using the source electrode4and the drain electrode5as a mask. Specifically, the part of the ohmic contact layer having an island shape which is not covered with the source electrode4or the drain electrode5is removed by etching. The semiconductor layer2having the channel region between the source electrode4and the drain electrode5and the ohmic contact layer are thereby formed.

Although the etching is performed using the source electrode4and the drain electrode5as a mask in this example, the etching of the ohmic contact layer may be performed using the resist pattern that is used when patterning the source electrode4and the drain electrode5as a mask. In this case, the ohmic contact layer is etched before removing the resist pattern on the source electrode4and the drain electrode5.

After that, the second insulating layer12is deposited to cover the source electrode4, the drain electrode5and the source line44. For example, an inorganic insulating film such as silicon nitride or silicon oxide is deposited as the second insulating layer12all over the substrate10by CVD or the like. The channel region of the semiconductor layer2is thereby covered with the second insulating layer12. Then, after depositing the second insulating layer12, a contact hole that reaches the extending part of the drain electrode5is made in the second insulating layer12by the process of photolithography, etching and resist removal.

Then, a transparent conductive film such as ITO is deposited on the second insulating layer12all over the substrate10by sputtering or the like. The transparent conductive film is then patterned by the process of photolithography, etching and resist removal. The pixel electrode6that is connected to the drain electrode5through the contact hole is thereby formed.

Further, the third insulating layer13is deposited to cover the pixel electrode6. For example, an inorganic insulating film such as silicon nitride or silicon oxide is deposited as the third insulating layer13all over the substrate10by CVD or the like. The pixel electrode6is thereby covered with the third insulating layer13.

Furthermore, a transparent conductive film such as ITO is deposited on the third insulating layer13all over the substrate10by sputtering or the like. The transparent conductive film is then patterned by the process of photolithography, etching and resist removal. The common electrode8having a plurality of slits A, B and C lying in different directions is thereby formed opposite to the pixel electrode6with the third insulating layer13interposed therebetween. By the processes described above, the TFT array substrate according to the embodiment is completed.

On the TFT array substrate fabricated as above, an alignment layer is formed by the subsequent cell manufacturing process.

Further, an alignment layer is formed also on a counter substrate that is fabricated separately. Then, an alignment process (rubbing process) is performed on the respective alignment layers so as to make micro scratches in one direction on contact surfaces with the liquid crystals20. In this embodiment, the direction that is the same as or perpendicular to the longitudinal direction of the slit C made in the common electrode8on the TFT array substrate is the rubbing direction. The alignment layers having the alignment direction that is inclined at the angle α of inclination, where 0°<α<90°, with respect to the extending direction of the gate line43are thereby formed.

After that, a sealing material is applied to attach the TFT array substrate and the counter substrate together. After attaching the TFT array substrate and the counter substrate, the liquid crystals20are filled through a liquid crystal filling port by vacuum filling method or the like. The liquid crystal filling port is then sealed. The liquid crystals20are oriented in such a way that its orientation (slow axis) is in the same direction as the rubbing direction. Further, polarizing plates are attached to both sides of the liquid crystal cell that is formed in this manner. Finally, driving circuits are connected, and a backlight unit is mounted. At this time, the absorption axis of one of the polarizing plate15on the TFT array substrate side and the polarizing plate25on the counter substrate side is set to the direction perpendicular to the orientation direction (slow axis) of the liquid crystals20, and the absorption axis of the other polarizing plate is set to the direction in parallel with the orientation direction (slow axis) of the liquid crystals20. The liquid crystal display device according to the embodiment is thereby completed.

As described above, in this embodiment, the orientation direction (slow axis) of the liquid crystals20when no voltage is applied between the pixel electrode6and the common electrode8is at the angle α, where 0°<α<90°, with respect to the extending direction of the gate line43. Therefore, the polarizing plates are placed in such a way that their absorption axes are perpendicular to or in parallel with the orientation direction (slow axis) of the liquid crystals20. The optical axis of the transmitted light30that is transmitted from the liquid crystal display device is thereby different from the horizontal direction in which the absorption axis of the polarized sunglasses35is placed in both landscape and portrait positions. It is thereby possible to prevent a display from looking all black in either landscape or portrait position when looking at the display through the polarized sunglasses35.

Further, the slits A and the slits B of the common electrode8are inclined at +θ or −θ with respect to the slit C that lies in the direction in parallel with or perpendicular to the orientation direction (slow axis) of the liquid crystals20, so that the liquid crystals20operate symmetrically about the slit C. This prevents the birefringence effect in one pixel47area from varying depending on the angle of view. It is thereby possible to prevent color shift from occurring when viewing an image from different angles, and suitable viewing angle characteristics can be obtained. Further, there is no increase in thickness due to addition of a member unlike the techniques of Japanese Unexamined Patent Publications Nos. 10-10523 and 10-10522, thus allowing reduction in thickness of the liquid crystal display device. Furthermore, there is no decrease in contrast unlike when applying the technique of Japanese Unexamined Patent Publication No. 10-49082 to an FFS mode liquid crystal display device. Therefore, in this embodiment, it is possible to provide an FFS mode liquid crystal display device with high display quality that enables a display to be viewed in both landscape and portrait positions through polarized sunglasses without need of any additional member, and a method of manufacturing the same.

Although the liquid crystal display device including the channel-etch type TFT50is described in this embodiment, it may include another type of the TFT50, such as a top-gate type.

Further, although the common electrode8is placed substantially all over the display area41except the slit parts, the present invention is not limited thereto. The shape of the common electrode8may be altered as appropriate as long as the plurality of slits A, the plurality of slits B and the slit C satisfy the above-described conditions. Further, although the case where the common electrode8having the slits is placed above the pixel electrode6with the third insulating layer13interposed therebetween is described by way of illustration, the present invention is not limited thereto. For example, the common electrode8may be placed below the pixel electrode6having the slits with an insulating layer interposed therebetween. In this case, the plurality of slits A, the plurality of slits B and the slit C are made in the pixel electrode6. Thus, the slits A, B and C for generating a fringe electric field are made to satisfy the above-described conditions in either one of the pixel electrode6and the common electrode8that are placed opposite to each other with an insulating layer interposed therebetween.