JP2009053256A - Liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid crystal display device having a wide viewing angle and high contrast. <P>SOLUTION: The liquid crystal display device comprises: first substrate and second substrate opposite to each other; and a liquid crystal layer interposed between the first substrate and the second substrate. The liquid crystal layer contains a nematic liquid crystal having positive dielectric anisotropy. The first substrate has a first electrode to which variable potential is applied, a second electrode opposite to the first electrode in the first substrate plane and in a pixel area, and a first perpendicular alignment film formed on the surface on the liquid crystal layer side. The second substrate has a second perpendicular alignment film formed on the surface on the liquid crystal layer side, and the liquid crystal display device generates an electric field in the liquid crystal layer at least with the first electrode and the second electrode. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

The present invention relates to a liquid crystal display device. More particularly, the present invention relates to a liquid crystal display device suitable for a TV or monitor having a wide viewing angle, an X-ray monitor for ME (Medical Engineering), a display for a digital camera, and the like.

BACKGROUND ART A liquid crystal display device is a display device including a liquid crystal display panel having a pair of substrates (usually an active matrix substrate and a counter substrate) facing each other with a liquid crystal layer interposed therebetween. It is out. One important performance of a liquid crystal display device is a viewing angle, and various technologies and display modes have been developed to realize a wide viewing angle. At present, the so-called MVA (Multi-domain Vertical Alignment) mode and IPS (In Plane Switching) mode are mainly used as display modes (liquid crystal modes) having a wide viewing angle characteristic. Hereinafter, advantages and disadvantages of the MVA mode and the IPS mode will be described.

The advantage of the MVA mode is that light leakage in black display can be suppressed. That is, according to the MVA mode, high contrast can be realized. This is because in the MAV mode, black display is performed in a state where the liquid crystal molecules (liquid crystal major axis) are not birefringent with respect to the main surface of the substrate. More specifically, the MVA mode has the following features (1) to (3).
(1) Since there is no need to align liquid crystal molecules in a specific direction by an alignment treatment such as rubbing, light leakage due to a deviation between the alignment direction in the initial state of the liquid crystal molecules and the direction of the transmission axis of the polarizing plate does not occur.
(2) Fluctuations caused by thermal vibrations of liquid crystal molecules hardly affect the vibration surface of incident light.
(3) By using in combination with the negative C plate, it is possible to compensate for the phase difference caused by the liquid crystal layer between the oblique visual field and the direction perpendicular to the substrate main surface (display surface).

On the other hand, a demerit of the MVA mode is that white floating (γ shift) in an oblique visual field occurs remarkably particularly in low gradation. In the MVA mode, when gradation display is performed, the liquid crystal molecules are rotated in the direction to lie down by the electric field (vertical electric field) perpendicular to the main surface of the substrate. This is because it rotates at a tilt angle. More specifically, the MVA mode further has the following features (1) and (2).
(1) Since the liquid crystal molecules rotating in the sleeping direction are continuous in the normal direction of the liquid crystal layer, the birefringence of incident light by the rotating liquid crystal molecules is integrated in the vertical direction. Therefore, the phase difference of the liquid crystal layer in the oblique visual field is larger than the phase difference of the liquid crystal layer in the vertical direction.
(2) Since the gradation is obtained by lying down on the side of the liquid crystal molecules standing perpendicular to the main surface of the substrate, the liquid crystal molecules move dynamically as viewed from the line of sight. Therefore, the appearance of the liquid crystal molecules in the perpendicular direction and the oblique direction with respect to the main surface of the substrate are greatly different, and as a result, a phase difference due to large birefringence occurs.

The advantage of the IPS mode is that it is possible to suppress the occurrence of white floating (γ shift) in an oblique visual field, particularly with low gradation. This is because in the IPS mode, when gradation display is performed, liquid crystal molecules are rotated horizontally in a horizontal direction by an electric field (horizontal electric field) in a horizontal direction with respect to the main surface of the substrate. More specifically, the IPS mode has the following features (1) and (2).
(1) Since the liquid crystal rotating in the horizontal direction is limited to the vicinity of the lower substrate (the substrate on the back side), the liquid crystal rotating when viewed from the vertical direction is compared with the MVA mode. Relatively few. Therefore, the difference between the phase difference of the liquid crystal layer integrated in the vertical direction when viewed from the oblique direction and the phase difference of the liquid crystal layer integrated in the vertical direction when viewed from the perpendicular direction is minimized.
(2) Since the gradation is obtained by rotating the liquid crystal molecules lying with respect to the main surface of the substrate in the horizontal direction, the parallax of the liquid crystal molecules does not change greatly depending on the viewing direction. That is, the liquid crystal molecules are almost the same in the perpendicular direction and the oblique direction, so that the phase difference can be minimized.

On the other hand, a disadvantage of the IPS mode is that it is difficult to suppress the occurrence of light leakage in black display. That is, the IPS mode is disadvantageous in terms of contrast compared to the MVA mode. This is because in the IPS mode, the major axis of the liquid crystal is parallel to the main surface of the substrate, and black display is performed in a mode that does not generate birefringence. That is, when a deviation occurs between the major axis direction of the liquid crystal molecules and the transmission axis direction of the polarizing plate, birefringence occurs and light leakage occurs. The following (1)-(3) are mentioned as a factor of a shift | offset | difference.
(1) The rubbing direction for aligning the liquid crystal molecules in the horizontal direction and the direction of the transmission axis of the polarizing plate are shifted. This depends on the bonding accuracy of the polarizing plate.
(2) Since rubbing is performed mechanically, the alignment force fluctuates and the alignment direction of liquid crystal molecules fluctuates.
(3) Since the alignment is horizontal, fluctuations caused by thermal vibration of liquid crystal molecules tend to affect the vibration surface of incident light.

As described above, the MVA mode is advantageous for high contrast, and the IPS mode is advantageous for suppressing white floating (γ shift) in an oblique field of view. It was difficult to achieve both white floating (γ shift) in an oblique visual field.

Under such circumstances, as a novel liquid crystal display device that is easy to manufacture and control thereafter and prevents the influence of the electric field for driving the liquid crystal molecules from reaching the inside of the opposite substrate, it faces each other. And a liquid crystal layer composed of liquid crystal molecules sandwiched between the first and second substrates, and the director of the liquid crystal molecules changes mainly in a plane parallel to the substrate. Accordingly, in the liquid crystal display device that performs the display operation, the first common electrode that is provided on the first substrate side and that is supplied with the first predetermined potential, and the insulation that is provided on the first common electrode are provided. A liquid crystal molecule further comprising: a film; a pixel electrode provided on the insulating film; and a second common electrode provided on the second substrate side and provided with a second predetermined potential. The above pixel having negative dielectric anisotropy The pole has a plurality of openings, and the first common electrode is a specific region extending from the non-opening of the pixel electrode to the opening in a cross section in a direction perpendicular to the substrate. A liquid crystal display device having at least a specific portion formed in a specific region where a non-opening portion and a part thereof overlap is disclosed (for example, refer to Patent Document 1).
JP 2000-356786 A

However, the technique described in Patent Document 1 is intended to improve the alignment force of liquid crystal molecules in the horizontal direction for an IPS mode liquid crystal display device, and the effect of improving contrast is small.

The present invention has been made in view of the above-described situation, and an object thereof is to provide a liquid crystal display device having a wide viewing angle and high contrast.

The present inventors have studied various liquid crystal display devices with a wide viewing angle and high contrast, and have focused on a method for controlling liquid crystal molecules. The liquid crystal display device has a vertical alignment film as an alignment film, and an electric field (including a horizontal component) is generated in the liquid crystal layer by a first electrode and a second electrode which are provided on the same substrate and face each other. The present inventors have found that the occurrence of whitening at the time of gradation display can be suppressed while suppressing the occurrence of light leakage at the time of display, and have conceived that the above-mentioned problems can be solved brilliantly and have reached the present invention.

That is, the present invention is a liquid crystal display device comprising a first substrate and a second substrate facing each other, and a liquid crystal layer sandwiched between the first substrate and the second substrate, wherein the liquid crystal layer is positive The first substrate includes a nematic liquid crystal having dielectric anisotropy, and the first substrate includes a first electrode to which a variable potential is applied, and a second electrode facing the first electrode in the first substrate surface and in the pixel region. The first vertical alignment film formed on the surface on the liquid crystal layer side, the second substrate has a second vertical alignment film formed on the surface on the liquid crystal layer side, the liquid crystal display device, The liquid crystal display device generates an electric field in the liquid crystal layer by at least a first electrode and a second electrode.

Thereby, in a state where no electric field is generated in the liquid crystal layer (off state), the nematic liquid crystal having positive dielectric anisotropy is aligned in a direction substantially perpendicular to the first substrate and the second substrate main surface ( (Vertical alignment). Therefore, similar to the MVA mode, it is possible to suppress light leakage during black display. That is, high contrast can be realized. On the other hand, in a state in which a voltage is applied between the first electrode and the second electrode provided in the same substrate (first substrate) (on state), the first substrate and the second substrate main as in the IPS mode. An electric field is generated in a substantially horizontal direction with respect to the surface. That is, a horizontal electric field having a large horizontal component is generated. When a horizontal electric field is generated, nematic liquid crystal having positive dielectric anisotropy located on the first substrate side is also aligned (horizontal alignment) in a substantially horizontal direction with respect to the first substrate and the second substrate main surface. As a result, since birefringence occurs in the liquid crystal layer, gradation display is possible in the on state. On the other hand, the nematic liquid crystal having positive dielectric anisotropy located on the second substrate side remains in the vertical alignment by the alignment regulating force of the second vertical alignment film. Therefore, the liquid crystal display device of the present invention performs gradation display while suppressing the generation of liquid crystal molecules oriented obliquely with respect to the first substrate and the second substrate main surface that cause whitening in an oblique visual field. Therefore, it is possible to suppress whitening from occurring in an oblique visual field. Further, the vertically aligned liquid crystal molecules and the horizontally aligned liquid crystal molecules can complement each other's phase difference when viewed from an oblique field of view. Therefore, the liquid crystal display device of the present invention can suppress the occurrence of whitening in an oblique visual field more than the IPS mode. Thus, the liquid crystal display device of the present invention can achieve both a wide viewing angle and high contrast. In the liquid crystal display device of the present invention, the alignment of the nematic liquid crystal can be controlled by at least the electric field generated by the first electrode and the second electrode and the alignment regulating force of the first vertical alignment film and the second vertical alignment film. it can.

Note that the amount (thickness) of liquid crystal molecules on the first substrate side that is horizontally aligned in the on state varies depending on the strength of the horizontal electric field. Thus, the liquid crystal display device of the present invention changes the amount (thickness) of the liquid crystal molecules on the first substrate side that is horizontally aligned depending on the strength of the voltage applied between the first electrode and the second electrode, Perform gradation display.

The configuration of the liquid crystal display device of the present invention is not particularly limited as long as such components are formed as essential components, and may or may not include other components. Absent.
A preferred embodiment of the liquid crystal display device of the present invention will be described in detail below.

The first electrode and the second electrode are preferably opposed to each other with a substantially constant interval. It should be noted that the substantially constant interval does not need to be strictly constant, but is constant as much as can be achieved when the first electrode and the second electrode are designed and formed so that the interval is constant. It is sufficient to include an error that may occur in the manufacturing process.

From the viewpoint of further suppressing the occurrence of whitening in an oblique field of view, the second substrate has a third electrode on the liquid crystal layer side, and the liquid crystal display device includes a first electrode, a second electrode, and a third electrode. It is preferable to generate an electric field in the liquid crystal layer. Thereby, even in the ON state, the nematic liquid crystal having positive dielectric anisotropy located on the second substrate side can be kept in a more vertically aligned state. That is, it is possible to reduce the liquid crystal aligned in the oblique direction with respect to the first substrate and the second substrate main surface. In the liquid crystal display device of the present invention, the alignment of the nematic liquid crystal is controlled by the electric field generated by the first electrode, the second electrode, and the third electrode and the alignment regulating force of the first vertical alignment film and the second vertical alignment film. can do.

From the viewpoint of further suppressing the occurrence of whitening in an oblique view over the entire display area, the first substrate can be connected (electrically connected) to the switching element and the first electrode via the switching element. Preferably, the third electrode is formed in a stripe shape so that the longitudinal direction extends along a pixel column in a direction in which the source bus line extends, and a variable potential is applied. Accordingly, the potential of the third electrode can be set to a desired potential in each pixel to which the image signal is supplied from the source bus line.

From the viewpoint of particularly suppressing the occurrence of whitening in an oblique field of view, the liquid crystal display device has a voltage between the first electrode and the second electrode larger than the voltage between the second electrode and the third electrode, and the second electrode It is preferable to apply a potential to the first electrode, the second electrode, and the third electrode so that the voltage between the first electrode and the third electrode is proportional to the voltage between the first electrode and the second electrode.

In addition, from the viewpoint of further suppressing the occurrence of whitening in an oblique field of view, the first electrode and the second electrode may be provided side by side on the same plane. Thereby, the diagonal component (the component of the diagonal direction with respect to a 1st board | substrate and a 2nd board | substrate main surface) of the electric field which generate | occur | produces with a 1st electrode and a 2nd electrode can be reduced.

From the viewpoint of improving the contrast in the oblique visual field, the liquid crystal display device preferably further includes a negative C plate in front of the first substrate (on the observation surface side). Accordingly, it is possible to compensate for the phase difference caused by the vertically aligned liquid crystal in the oblique visual field during black display, and to suppress the occurrence of light leakage in the oblique visual field during black display.

From the viewpoint of further suppressing the occurrence of whitening in an oblique field of view, at least one of the first electrode and the second electrode is preferably formed using an opaque conductive material. More preferably, the electrode is formed using an opaque conductive material.

According to the liquid crystal display device of the present invention, both wide viewing angle characteristics and high contrast can be achieved.

Embodiments will be described below, and the present invention will be described in more detail with reference to the drawings. However, the present invention is not limited only to these embodiments.

(Embodiment 1)
FIG. 1 is a schematic plan view illustrating the configuration of the liquid crystal display panel of the first embodiment. 2 is a schematic cross-sectional view showing the configuration of the liquid crystal display panel of Embodiment 1, and shows a cross section taken along line XY in FIG.

The liquid crystal display panel 100 of Embodiment 1 includes an active matrix substrate 10, a counter substrate 50 facing the active matrix substrate 10, and a liquid crystal layer 30 provided therebetween. In addition, the liquid crystal display panel 100 includes a pair of polarizing plates 41a and 41b provided outside the active matrix substrate 10 and the counter substrate 50, and a negative C plate 42 provided between the active matrix substrate 10 and the polarizing plate 41a. With.

The liquid crystal layer 30 includes a nematic liquid crystal material having positive dielectric anisotropy. The transmission axis of the polarizing plate 41a and the transmission axis of the polarizing plate 41b are arranged to be orthogonal when the liquid crystal display panel 100 is viewed in plan. That is, the polarizing plate 41a and the polarizing plate 41b are arranged in crossed Nicols. Further, the transmission axis of the polarizing plate 41a and the transmission axis of the polarizing plate 41b are respectively arranged along the vertical or horizontal direction of the panel. The negative C plate 42 is a retardation compensation film having negative uniaxial anisotropy in which the optical axis is substantially perpendicular to the film surface, that is, a uniaxial anisotropic retardation compensation film of nx = ny> nz. It is.

The counter substrate 50 includes a transparent insulating substrate (for example, a glass substrate) 11b, a black matrix (BM) layer (not shown), a plurality of color layers (color filters) 52, and a counter electrode 53 that is a third electrode. And a second vertical alignment film 54 covering these structures.

On the other hand, the active matrix substrate 10 includes a transparent insulating substrate (for example, a glass substrate) 11a, a plurality of gate bus lines 12, a plurality of Cs bus lines (capacitance holding wirings) 13, an insulating film 14, and a plurality of sources. The bus line 16, the interlayer insulating film 19, the drain electrode 20 as the first electrode, the Cs electrode 21 as the second electrode (second drain electrode), and the surface on the liquid crystal layer 30 side covering these components The first vertical alignment film 25 is provided. The active matrix substrate 10 has a thin film transistor (TFT) 26 that is a switching element corresponding to each pixel. The TFT 26 includes a gate bus line 12, an insulating film 14, a semiconductor layer 15, a source electrode 17 and a drain wiring 18.

The plurality of gate bus lines 12 extend in parallel with each other in the left-right direction of the panel, and the plurality of source bus lines 16 extend in parallel with each other in a direction orthogonal to the gate bus lines 12, that is, in the vertical direction of the panel. Yes. The Cs bus line 13 extends in parallel to the gate bus line 12, that is, in the left-right direction of the panel. That is, the gate bus lines 12 and the Cs bus lines 13 are arranged alternately and in parallel. In the present embodiment, each pixel region is roughly defined as a region surrounded by the gate bus line 12 and the source bus line 16. That is, each pixel region is arranged in a matrix. The Cs bus line 13 is disposed so as to pass near the center of the pixel region. The gate bus line 12 and the source bus line 16 propagate the gate bus line signal (scanning signal) and the source bus line signal (image signal), respectively, as in the conventional mode.

In each of such pixel regions, a drain electrode 20 as a first electrode is provided. The drain electrode 20 has a comb shape when the liquid crystal display panel 100 is viewed in plan. More specifically, the drain electrode 20 is disposed in the vicinity of one source bus line (left source bus line 16 in FIG. 1) that defines the pixel region and in parallel with the one source bus line 16. And a plurality of branch portions 23a connected to the trunk portion 22a and extended toward the other source bus line (the source bus line 16 on the right side in FIG. 1) that defines the pixel region. The branch portion 23a has a V shape or an inverted V shape that is bent near the center of the pixel region in the direction of the gate bus line 12 when the liquid crystal display panel 100 is viewed in plan view. It is formed in a direction oblique to the bus line 12 by approximately 45 °.

Each pixel region is provided with a Cs electrode 21 as a second electrode. Similarly to the drain electrode 20, the Cs electrode 21 has a comb shape in plan view. More specifically, the Cs electrode 21 is the other source bus line defining the pixel region (the right source bus line in FIG. 1). 16) a trunk portion 22b that is in the vicinity and arranged in parallel with the other source bus line 16, and one source bus line that is connected to the trunk portion 22b and defines a pixel region (the source bus on the left side in FIG. 1) A plurality of branch portions 23b extending toward the line 16) and a central branch portion 24 connected to the central portion of the trunk portion 22b and positioned at the center of the pixel region. The branch portion 23b has a V shape or an inverted V shape that is bent near the center of the pixel region in the direction of the gate bus line 12 when the liquid crystal display panel 100 is viewed in plan view. It is formed in a direction oblique to the bus line 12 by approximately 45 °. The shape of the central branch portion 24 when the liquid crystal display panel 100 is viewed in plan is a substantially rhombus.

As described above, the branch portions 23a of the drain electrode 20 and the branch portions 23b of the Cs electrode 21 have a planar shape complementary to each other and are alternately arranged with a certain interval. In other words, the branch part 23a of the drain electrode 20, the branch part 23b and the central branch part 24 of the Cs electrode 21 are arranged to face each other in parallel in the same plane.

From the viewpoint of improving the light transmittance of the pixel, the drain electrode 20 and the Cs electrode 21 do not have a comb shape, that is, have only the trunk portion 22a and the trunk portion 22b, respectively, and two opposite sides of the pixel region. However, from the viewpoint of improving the response speed of the liquid crystal molecules, it is preferable that the drain electrode 20 and the Cs electrode 21 have a comb shape and are alternately arranged as described above.

Further, the branch portion 23a and the branch portion 23b do not have a V-shape or an inverted V-shape, that is, each of the branch portions 23a and 23b may be linearly formed in the left-right direction of the panel. From the viewpoint of dividing and realizing a wider viewing angle, the drain electrode 20 has a V-shaped or inverted V-shaped branch portion 23a as described above, and the Cs electrode 21 also has a V-shaped or inverted shape. The branch part 23b has a V-shaped branch part 23b, and the branch part 23a and the branch part 23b are inclined by about 45 ° with respect to the source bus line 16 and the gate bus line 12 (panel vertical and horizontal directions). Direction).

The drain electrode 20 is in contact with and connected to the drain wiring 18 through a contact hole 27 b provided in the interlayer insulating film 19 above the drain wiring 18. That is, the drain electrode 20 is connected to the TFT 26 via the drain wiring 18.

The source bus line 16 is connected to the TFT 26 through the source electrode 17. Thus, when the TFT 26 is turned on, the image signal supplied to the source bus line 16 is written to the drain electrode 20. The source bus line 16 and the source electrode 17 are integrally formed by the same process and the same material.

On the other hand, the Cs electrode 21 is brought into contact with and connected to the Cs bus line 13 through the contact hole 27a provided in the interlayer insulating film 19 and the insulating film 14 above the Cs bus line 13 in the central branch 24. Connected to the bus line 13. As a result, the potential of the Cs bus line 13 is applied to the Cs electrode 21.

Next, the cross-sectional structure of the liquid crystal display panel 100 will be described in detail.

The liquid crystal display panel 100 generally has a structure in which a liquid crystal layer 30 containing liquid crystal molecules is sandwiched between an active matrix substrate 10 and a counter substrate 50.

The active matrix substrate 10 includes a gate bus line 12 and a Cs bus line 13 on one main surface (on the liquid crystal layer 30 side) of the insulating substrate 11a as main materials.

An insulating film 14 is provided so as to cover the entire surface of the gate bus line 12 and the Cs bus line 13. Further, a semiconductor layer 15 made of amorphous silicon or the like is formed on the insulating film 14 in a region corresponding to the gate bus line 12. A drain wiring 18 and a source electrode 17 (including the source bus line 16) connected to each other through the semiconductor layer 15 are formed. The semiconductor layer 15 functions as a channel region in the TFT 26. As understood from this, the insulating film 14 functions as a gate insulating film above the gate bus line 12. The gate bus line 12 also functions as a gate electrode.

In the present embodiment, the TFT 26 is a channel etch type manufactured by a manufacturing method that slightly etches the semiconductor layer 15 when the drain wiring 18 and the source electrode 17 are separated as described later, and This is a reverse stagger type in which the gate bus line 12 that also functions as a gate electrode is provided below the drain wiring 18 and the source electrode 17.

Further, as described above, the source electrode 17 is formed integrally with the source bus line 16, and the drain wiring 18 is connected to the drain electrode 20. The TFT 26 having such a configuration is turned on when a predetermined voltage is supplied to the gate bus line 12, and an image signal (voltage) propagating through the source bus line 16 is written to the drain electrode 20.

Continuing the description of other components in the active matrix substrate 10, an interlayer insulating film 19 is formed on the drain wiring 18 and the source electrode 17, and the drain electrode 20 and the Cs electrode 21 are formed on the interlayer insulating film 19. Further, a first vertical alignment film 25 is applied and formed on these layers. The first vertical alignment film 25 aligns liquid crystal molecules in the vicinity of the first vertical alignment film 25 substantially perpendicularly to the surface of the first vertical alignment film 25.

On the other hand, the counter substrate 50 includes a BM layer (not shown) and a color layer 52 on one main surface (on the liquid crystal layer 30 side) of the insulating substrate 11b. The BM layer is formed of an opaque metal such as Cr, an opaque organic film such as acrylic containing carbon, and the like, around the pixel region, that is, in a region corresponding to the gate bus line 12, the source bus line 16, and the TFT 26. Is formed. On the other hand, the color layer 52 is used for performing color display, and is mainly formed in the pixel region.

A plurality of counter electrodes 53 are provided on the BM layer and the color layer 52. As is apparent from the drawing, the plurality of counter electrodes 53 are arranged corresponding to each pixel column so as to be shared between adjacent pixels in the vertical direction of the panel. Thus, the counter electrodes 53 are arranged in a stripe shape when the liquid crystal display panel 100 is viewed in plan.

A second vertical alignment film 54 is formed on the counter electrode 53 by coating. The second vertical alignment film 54 is also a vertical alignment film like the first vertical alignment film 25, and aligns liquid crystal molecules in the vicinity of the second vertical alignment film 54 substantially perpendicularly to the surface of the second vertical alignment film 54.

The first vertical alignment film 25 and the second vertical alignment film 54 do not need to align liquid crystal molecules strictly perpendicular to the film surface, but the pretilt angle (state in which no electric field is generated (off state)). The angle formed between the major axis of the liquid crystal molecules and the film surface is preferably 85 ° or more, and more preferably 88 ° or more.

Next, the configuration of the liquid crystal display device of this embodiment will be described. 3A and 3B are schematic views illustrating the configuration of the liquid crystal display device according to the first embodiment. FIG. 3A is a plan view and FIG. 3B is a side view. FIG. 4 is a schematic plan view illustrating the configuration of the active matrix substrate side according to the first embodiment.

As shown in FIG. 3, the liquid crystal display device 200 according to the first embodiment is provided on the extended portion of the active matrix substrate 10 of the liquid crystal display panel 100 in the same manner as the general liquid crystal display device in addition to the liquid crystal display panel 100 described above. And a plurality of Vd1 output driver chips 61 and gate driver chips 62, and an FPC (Flexible Printed Circuit) substrate 103 connected to the overhanging portion of the active matrix substrate 10.

As shown in FIG. 4, each Vd1 output driver chip 61 is connected to a plurality of source bus lines 16 arranged in parallel in the vertical direction of the panel via a plurality of connection wirings 64a. Supply image signals. Each gate driver chip 62 is connected to a plurality of gate bus lines 12 arranged in parallel in the left-right direction of the panel via a plurality of connection wirings 64 b, and supplies a scanning signal to each gate bus line 12. Each Vd1 output driver chip 61 and each gate driver chip 62 are also connected to an FPC board 63 on which control circuits such as a control circuit and a power supply circuit are formed via connection wiring (not shown). Furthermore, the Cs bus lines 13 arranged in parallel in the left-right direction of the panel are connected in parallel in the left and right frame areas (non-display areas) of the panel by a plurality of connection wirings 64d, and the FPC is connected via the connection wiring 64d. It is connected to a substrate 63 (a power supply or the like provided on the FPC substrate 63). In this way, the Cs bus line signal is directly input from the FPC board 63 to each Cs bus line 13.

The liquid crystal display device 200 includes a Vc output driver chip 65 mounted on the extended portion of the counter substrate 50 of the liquid crystal display panel 100. Each Vc output driver chip 65 is connected to the counter electrode 53 via a plurality of connection wires 64c. Thereby, an arbitrary potential can be supplied to each counter electrode 53.

The liquid crystal display device 200 further includes members included in a normal liquid crystal display device such as a backlight unit that supplies light to the liquid crystal display panel 100, a housing that holds electronic devices such as the liquid crystal display panel 100, and the backlight unit. Have.

Here, the operation of each driver chip will be described. 5A and 5B are timing charts (voltage waveforms) in the liquid crystal display device according to the first embodiment. FIG. 5A illustrates a gate bus line signal (scanning signal) Vg, and FIG. 5B illustrates a source bus line signal (image signal). ) Vd1, (c) shows the Cs bus line signal Vd2, and (d) shows the signal Vc supplied to the counter electrode. 5A to 5D are on the same time axis (horizontal axis). In each of FIGS. 5A to 5D, the vertical axis indicates the potential.

As shown in FIG. 5A, the gate bus line signals Vg are sequentially supplied from the gate driver chip 62 to the gate bus lines 12 arranged in parallel in the vertical direction of the panel (line sequential driving). 5A shows a state in which the gate bus line signal Vg is sequentially supplied to a plurality of (for example, three) gate bus lines 12 adjacent to each other. Further, as shown in FIG. 5B, the source bus line signal Vd1 having a potential whose amplitude is variable depending on the gradation is supplied from the Vd1 output driver chip 61 to each source bus line 16, that is, the drain electrode 20. . Note that the liquid crystal display device of the present embodiment is AC driven, and the polarity of the source bus line signal Vd1 is inverted every frame. Further, as shown in FIG. 5C, a Cs bus line signal Vd2 set to a predetermined potential, for example, 0 V, is supplied to each Cs bus line 13, that is, the Cs electrode. As shown in FIG. 5D, the Vc output driver chip 65 is supplied with a signal Vc whose amplitude is variable by gradation and whose polarity is inverted every frame from each counter electrode 53. The Note that the polarity of the signal Vc is set in the same polarity direction as that of the source bus line signal Vd.

FIG. 6 is a timing chart (voltage waveform) in the liquid crystal display device of the first embodiment, in which the source bus line signal (image signal) Vd1, the Cs bus line signal Vd2, and the signal Vc supplied to the counter electrode are overlapped. FIG. In FIG. 6, the rising and falling edges of Vd1, Vd2, and Vc are shown to be shifted for easy viewing. However, in actuality, the signals move up and down (change) at the same time. In FIG. 6, the horizontal axis represents the time axis, and the vertical axis represents the potential.

In the liquid crystal display device 200, since the polarity of the signal Vc is variable in the amplitude of the source bus line signal Vd and the signal Vc, as shown in FIG. 6, the voltage | Vd1-Vc | or the voltage | Vc-Vd2 | | Vd1-Vd2 | can be appropriately changed for each frame. Further, since the polarity of the signal Vc is in the same direction as the source bus line signal Vd, the relationship between the signals will be described later (| Vd1 | − | Vd2 |) / 2 = | Vc | − | Vd2 | Can be set to

Here, the result of having performed simulation about operation | movement of the liquid crystal display panel 100 of this embodiment is demonstrated. FIG. 7 is a cross-sectional view showing the liquid crystal display panel of Embodiment 1, and shows the result of obtaining the equipotential lines of the electric field generated in the liquid crystal layer and the alignment direction of the liquid crystal molecules by simulation at the time of low gradation. FIG. 8 is a cross-sectional view showing the liquid crystal display panel of Embodiment 1, and shows the results of obtaining the equipotential lines of the electric field generated in the liquid crystal layer and the alignment direction of the liquid crystal molecules by simulation at the time of high gradation.

Various conditions in this simulation are as follows. That is, the dielectric anisotropy Δε = 2.9 and the refractive index anisotropy Δn = 0.1 of the liquid crystal molecules were set, and the thickness (cell gap) d1 of the liquid crystal layer was 4.2 μm. Further, the width of each branch 23a of the drain electrode 20 (length in a direction perpendicular to the longitudinal direction (extension direction) of the branch 23a) La1 and the width of each branch 23b of the Cs electrode 21 (branch 23b). The length in a direction perpendicular to the longitudinal direction (stretching direction) Lb1 was 4.0 μm. Furthermore, the distance between each branch 23a of the drain electrode 20 and each branch 23b of the Cs electrode 21 (the branch 23a in a direction perpendicular to the longitudinal direction (extension direction) of the branch 23a and the branch 23b). And the length between the branch portions 23b) S1 was also set to 4.0 μm.

FIG. 7 (a diagram at a low gradation) shows a state in which 10 V is applied to the drain electrode 20, 0 V is applied to the Cs electrode 21, and 5 V is applied to the counter electrode 53. That is, in FIG. 7, the potential Vd1 of the drain electrode 20 is 10 V, the potential Vd2 of the Cs electrode 21 is 0 V, and the potential Vc of the counter electrode 53 is 5 V. On the other hand, FIG. 8 (a diagram at the time of high gradation) shows a state in which 20 V is applied to the drain electrode 20, 0 V is applied to the Cs electrode 21, and 10 V is applied to the counter electrode 53. That is, in FIG. 8, the potential Vd1 of the drain electrode 20 is 20 V, the potential Vd2 of the Cs electrode 21 is 0 V, and the potential Vc of the counter electrode 53 is 10 V.

As a result of the simulation, at the time of low gradation, as shown in FIG. 7, the horizontal electric field generated between the drain electrode 20 and the Cs electrode 21 causes only the liquid crystal molecules in the vicinity of the active matrix substrate 10 to sleep (horizontal direction). Rotation (orientation) (refer to the area surrounded by a one-dotted line in FIG. 7). Further, even at high gradation, as shown in FIG. 8, the horizontal electric field generated between the drain electrode 20 and the Cs electrode 21 causes the liquid crystal molecules on the active matrix substrate 10 side to rotate in the horizontal direction (in FIG. (See the area enclosed by the difference line). On the other hand, at the time of high gradation, the layer of liquid crystal molecules rotating in the horizontal direction spreads from the active matrix substrate 10 to the counter substrate 50 side, as indicated by white arrows in FIG. As described above, the liquid crystal display panel 100 includes a parabolic electric field (a combination of a horizontal electric field and a vertical electric field) formed by the counter electrode 53 provided on the counter substrate 50 and the drain electrode 20 and the Cs electrode 21 provided on the active matrix substrate 10. The liquid crystal layer can be controlled by the vector). Further, the liquid crystal display panel 100 includes liquid crystal molecules (horizontal aligned liquid crystal molecules) that are aligned (rotated) near the horizontal direction by a horizontal electric field, and liquid crystal molecules (vertical) that are aligned in the vertical direction almost without being affected by the horizontal electric field. The phase difference of each gradation can be generated by the ratio of the liquid crystal molecules (as-aligned) and the blend. In other words, the liquid crystal display panel 100 displays gradation by changing the thickness of the horizontally aligned liquid crystal molecule layer on the active matrix substrate 10 side and the thickness of the liquid crystal molecule layer that remains vertically aligned on the counter substrate 50 side. It can be performed. In the liquid crystal display panel 100, the thickness of the liquid crystal molecule layer that is horizontally aligned increases and the thickness of the liquid crystal molecule layer that remains vertically aligned decreases as the gray level increases from low to high.

In the liquid crystal molecules close to the horizontal direction and close to the horizontal alignment, as in the IPS mode, the phase difference in the oblique visual field hardly occurs in the shape. Therefore, the liquid crystal display panel 100 can suppress the occurrence of whitening in an oblique view to the same extent as in the IPS mode.

Further, in the liquid crystal display panel 100, the polarizing plates 41a and 41b are arranged in crossed Nicols, and when no potential difference is generated between the counter electrode 53, the drain electrode 20, and the Cs electrode 21 (that is, in the liquid crystal layer 30). When no electric field is generated, the liquid crystal molecules are vertically aligned by the first vertical alignment film 25 and the second vertical alignment film 54. Therefore, the liquid crystal display panel 100 can display black with little light leakage (normally black), as in the MVA mode. That is, the liquid crystal display panel 100 can achieve high contrast while suppressing the occurrence of whitening in an oblique visual field.

As described above, the liquid crystal display panel 100 generates a phase difference from the oblique visual field, and does not generate as much orientation (oblique orientation) as possible between the vertical direction and the horizontal direction. Gradation can be created by changing the composition ratio of two liquid crystal molecules, ie, vertical alignment and horizontal alignment, which are less likely to occur.

In the liquid crystal display panel 100, as shown in FIGS. 7 and 8, there is also an electric field (oblique electric field) generated in an oblique direction with respect to the main surfaces of the active matrix substrate 10 and the counter substrate 10. As a result, there are also liquid crystal molecules that are oriented obliquely (obliquely oriented). However, the proportion of the obliquely aligned liquid crystal molecules in the entire liquid crystal molecule is very small compared to the MVA mode described later with reference to FIG. 11, and is comparable to the IPS mode described later with reference to FIG. Therefore, as described above, the liquid crystal display panel 100 can suppress the occurrence of whitening in an oblique visual field at the same level as or more than in the IPS mode.

Further, when the width La1, the width Lb1, the interval S1, and the cell gap 1 are substantially equal, in order to establish the liquid crystal alignment of the liquid crystal display panel 100 described above, a vertical electric field (Y-axis direction, ie, perpendicular to the substrate). It is preferable that the horizontal electric field (the X-axis direction, that is, the electric field in the direction horizontal to the substrate) be larger than the electric field in the right direction. Then, as a result of performing simulations at some level, the relationship between the vertical electric field and the horizontal electric field is as follows. When (vertical electric field magnitude) :( horizontal electric field magnitude) = 1: 2, an oblique electric field is generated. It was found that it can be controlled relatively. That is, when the width La1, the width Lb1, the interval S1, and the cell gap d1 are substantially equal, the potential Vd1 of the drain electrode 20 and the potential Vd2 of the Cs electrode 21 and the opposite side are sufficiently suppressed in order to sufficiently suppress the occurrence of whitening in the oblique field of view. It has been found that the potential Vc of the electrode 53 is preferably controlled so that the relationship of (| Vd1 | − | Vd2 |) / 2 = | Vc | − | Vd2 | is satisfied.

Note that the liquid crystal display panel 100 is concerned that a phase difference may occur in an oblique visual field during black display (off), as in the MVA mode, but the liquid crystal display panel 100 includes the negative C plate 42. The phase difference in the oblique visual field at the time of black display can be effectively compensated.

In addition, the vertically aligned liquid crystal molecules and the horizontally aligned liquid crystal molecules have a complementary relationship in phase difference when viewed from an oblique field of view. That is, the vertically aligned liquid crystal molecules and the horizontally aligned liquid crystal molecules are in a relationship of self-compensating for a change in phase difference depending on the visual field. Therefore, the liquid crystal display panel 100 can obtain better viewing angle characteristics than the MVA mode or IPS mode provided with the conventional negative C plate.

Next, the manufacturing method of the liquid crystal display device according to the present embodiment having such a configuration will be described.

First, a method for manufacturing the active matrix substrate 10 will be described. A gate bus line 12 made of a single layer of a metal such as Cr or a multilayer film of a metal such as Cr and / or a transparent conductive film such as ITO (indium tin oxide) on a transparent insulating substrate 11a such as glass The Cs bus line 13 is formed by sputtering and a photoresist process. From the viewpoint of lowering the resistance of the gate bus line 12 and the Cs bus line 13, the material of the gate bus line 12 and the Cs bus line 13 is made of a metal such as Cr rather than a transparent conductive film such as ITO. preferable.

Next, an insulating film 14 made of a single layer film or a multilayer film of a silicon insulating film such as silicon nitride or silicon oxide is formed on the gate bus line 12 and the Cs bus line 13 by CVD (Chemical Vapor Deposition) and a photoresist process. To form. The insulating film 14 is formed on substantially the entire surface of the insulating substrate 11a.

Next, an island-shaped semiconductor layer 15 made of amorphous silicon (a-Si layer and n ⁺ a-Si layer) is formed in a region of the insulating film 14 above the gate bus line 12 by CVD and a photoresist process.

Next, the drain wiring 18, the source electrode 17 and the source bus line 16 made of a single layer of a metal such as Cr or a multilayer film of a metal such as Cr and / or a transparent conductive film such as ITO are sputtered and subjected to a photoresist process. To form. Thereby, the source electrode 17 and the source bus line 16 are integrally formed. Further, when the drain wiring 18 and the source electrode 17 are separated in this photoresist process, the channel region of the semiconductor layer 15 is slightly etched together. As a result, the channel etch type TFT 26 is formed as described above.

On the other hand, a protective layer is formed in a predetermined region of the semiconductor layer 15 before the electrode material such as the drain wiring 18 is sputtered, and a channel region is formed when the drain wiring 18 and the source electrode 17 are separated. If not etched, a channel protection type TFT can be formed.

Through the steps described so far, the gate bus line 12, the source bus line 16, and the Cs bus line 13 and the TFT 26 located near the intersection of the gate bus line 12 and the source bus line 16 are formed.

Next, an interlayer insulating film 19 made of silicon nitride is formed by CVD and a photoresist process. At this time, the interlayer insulating film 19 above the drain wiring 18 and the interlayer insulating film 19 and the insulating film 14 above the Cs bus line 13 are removed, whereby the contact hole 27a positioned above the Cs bus line 13 and the drain A contact hole 27b located above the wiring 18 is formed.

Thereafter, a drain electrode 20 and a Cs electrode 21 made of a single layer of a metal such as Cr or a multilayer film of a metal such as Cr and / or a transparent conductive film such as ITO are formed by sputtering and a photoresist process. At this time, the trunk portion 22 a of the drain electrode 20 is in contact with the drain wiring 18 through the contact hole 27 b, whereby the drain electrode 20 is connected to the drain wiring 18. Also, the Cs electrode 21 is connected to the Cs bus line 13 by the trunk portion 22b of the Cs electrode 21 coming into contact with the Cs bus line 13 through the contact hole 27a.

At this time, the drain electrode 20 and the Cs electrode 21 are formed on the same surface. In this way, by arranging the drain electrode 20 and the Cs electrode 21 in the same layer, the oblique component of the electric field generated by the drain electrode 20 and the Cs electrode 21 can be reduced, and as a result, white floating in the oblique field of view can be achieved. Generation | occurrence | production can be suppressed more. The drain electrode 20 and the Cs electrode 21 may be formed as different layers, but in this case, the oblique component of the electric field generated by the drain electrode 20 and the Cs electrode 21 increases, and the whitening suppression effect in the oblique field of view is increased. Will be reduced.

Further, as shown in FIGS. 7 and 8, the liquid crystal molecules above the drain electrode 20 and the Cs electrode 21 are hardly aligned even when an electric field is applied, that is, remain in the vertical alignment. Accordingly, since the region above the drain electrode 20 and the Cs electrode 21 does not contribute much to the light transmittance of the pixel, the drain electrode 20 and the Cs electrode 21 do not need to be formed of a transparent conductive material, and are opaque. A conductive material may be used. The alignment of the liquid crystal molecules in the vicinity of the electrode boundary is more prominent than the alignment of the liquid crystal molecules in the slit (the gap between the drain electrode 20 and the Cs electrode 21). That is, the major axis of the liquid crystal near the electrode boundary is closer to being perpendicular to the main surface of the insulating substrate 11a than the major axis of the liquid crystal in the slit portion. Therefore, by forming the drain electrode 20 or the Cs electrode 21 (more preferably, the drain electrode 20 and the Cs electrode 21) using an opaque conductive material, the alignment of the liquid crystal molecules near the electrode boundary can be shielded from light. As a result, the whitening in the oblique view can be further improved. In addition, as an opaque electroconductive material, metals, such as Cr, are mentioned, for example.

In the present embodiment, the width La1 of each branch portion 23a of the drain electrode 20 can be set as appropriate, but is preferably 2.5 μm or more. The width La1 of the branch portion 23a is preferably as narrow as possible from the viewpoint of increasing the light transmittance of the pixel. However, when the width La1 of the branch part 23a is less than 2.5 μm, the liquid crystal molecule located above one end of the branch part 23a and the liquid crystal molecule located above the other end of the branch part 23a The separation of the orientation (orientation boundary) is not stable, and orientation blurring occurs above both ends of the branch portion 23a, resulting in a slow response speed. On the other hand, the width Lb1 of each branch part 23b of the Cs electrode 21 is also preferably 2.5 μm or more like the branch part 23a.

Note that the width La1 of each branch 23a of the drain electrode 20 and the width Lb1 of each branch 23b of the Cs electrode 21 are not necessarily the same, but the drain electrode 20 and the Cs electrode 21 are formed in the same layer. Considering the case of forming, it is preferable that they are approximately the same from the viewpoint of the manufacturing process (etching uniformity).

Further, the spacing S1 between each branch 23a of the drain electrode 20 and each branch 23b of the Cs electrode 21 can be set as appropriate. However, if it is too small, the oblique electric field increases, and the whitening suppression effect is obtained. On the other hand, if it is larger, the light transmittance of the pixel increases, but the response speed becomes slower. Therefore, more specifically, the interval S1 between the branch part 23a and the branch part 23b is preferably 2.5 μm or more and 5.0 μm or less.

The width of the trunk portion 22a of the drain electrode 20 (the length in the direction perpendicular to the longitudinal direction (stretching direction) of the trunk portion 22a) can be set as appropriate, but is preferably 2.5 μm or more. On the other hand, the width of the trunk portion 22b of the Cs electrode 21 (the length in the direction perpendicular to the longitudinal direction (stretching direction) of the trunk portion 22b) is also preferably 2.5 μm or more, like the trunk portion 22a.

Subsequently, a manufacturing method of the counter substrate 50 will be described. First, an opaque metal (for example, Cr) and an organic film (for example, an acrylic resin containing carbon) are formed on a transparent insulating substrate 11b such as glass by a conventionally known method. ) And the like, and a color layer 52 made of an organic film (for example, an acrylic resin containing a pigment) or the like.

Then, a plurality of stripe-like counter electrodes 53 made of a transparent conductive film such as ITO are formed on the light shielding film and the color layer 52 by sputtering and a photoresist process.

A first vertical alignment film 25 and a second vertical alignment film 54 made of an organic film such as polyimide are formed on the opposing surfaces of the active matrix substrate 10 and the counter substrate 50 thus manufactured. In addition, as a material of the 1st vertical alignment film 25 and the 2nd vertical alignment film 54, the vertical alignment film material used for the conventional MVA mode can be used.

Next, a spacer for keeping the distance between the active matrix substrate 10 and the counter substrate 50 constant is spread on one of the active matrix substrate 10 and the counter substrate 50 and the active matrix substrate 10 and the counter substrate 50 are sealed. After applying the sealing material for this purpose, the active matrix substrate 10 and the counter substrate 50 are bonded together so that the first vertical alignment film 25 and the second vertical alignment film 54 face each other. In the present embodiment, the thickness (cell gap) d1 of the liquid crystal layer 30 in the pixel opening (the light transmitting region) is about 2 to 5 μm.

The liquid crystal layer 30 is formed by filling the gap between the active matrix substrate 10 and the counter substrate 50 from the injection port which is an opening of the sealing material with a liquid crystal material and sealing the injection port. As the liquid crystal material, nematic liquid crystal having positive dielectric anisotropy is used. As the liquid crystal material, refractive index anisotropy Δn = 0.06 to 0.2, dielectric anisotropy Δε = 2.5 to 8, nematic-isotropic phase transition temperature Tni = 70 to 120 ° C. Those exhibiting are preferred.

Next, after the negative C plate 42 is attached to the outer main surface of the active matrix substrate 10, polarizing plates 41 a and 41 b are attached to the outer main surfaces of the active matrix substrate 10 and the counter substrate 50. At this time, the polarizing plate 41 a and the polarizing plate 41 b are arranged so that their transmission axes are parallel to either the gate bus line 12 or the source bus line 16 when the liquid crystal display panel 100 is viewed in plan. .

Thus, the liquid crystal display panel 100 of this embodiment can be produced. Subsequently, the Vd1 output driver chip 61, the gate driver chip 62, and the Vc output driver chip 65 are mounted on the liquid crystal display panel 100 by a COG (Cip On Glass) method.

Lastly, the liquid crystal display device 200 can be manufactured by connecting the FPC board 63 to the liquid crystal display panel 100 and storing the liquid crystal display panel 100 and the backlight unit in a housing.

As described above, according to the liquid crystal display device 200 of the present embodiment, a wide viewing angle and a high contrast are realized by improving whitening in an oblique view while maintaining a high contrast obtained by vertical alignment. can do.

In the liquid crystal display device 200 of the present embodiment, the counter electrode 53 may be formed so as to cover the entire display area, like the counter electrode (common electrode) in the MVA mode. Thereby, the manufacturing process can be simplified. However, from the viewpoint of enabling fine potential setting corresponding to each pixel and realizing better display quality, the counter electrode 53 may be formed corresponding to each pixel column as described above. preferable.

In the liquid crystal display device 200 of the present embodiment, the counter electrode 53 may not be provided. Thereby, the manufacturing process can be further simplified.

Here, the result of having performed simulation about operation | movement of the liquid crystal display panel without a counter electrode is demonstrated. FIG. 9 is a cross-sectional view showing the liquid crystal display panel of Embodiment 1 having no counter electrode, and the result of obtaining by simulation the equipotential lines of the electric field generated in the liquid crystal layer and the orientation direction of the liquid crystal molecules at the time of low gradation Indicates. FIG. 10 is a cross-sectional view showing the liquid crystal display panel of Embodiment 1 without the counter electrode, and shows the results of obtaining the equipotential lines of the electric field generated in the liquid crystal layer and the orientation direction of the liquid crystal molecules by simulation at the time of high gradation. Show. FIG. 9 (a diagram at the time of low gradation) shows a state in which 10 V is applied to the drain electrode 20 and 0 V is applied to the Cs electrode 21. That is, in FIG. 9, the potential Vd1 of the drain electrode 20 is set to 10V, and the potential Vd2 of the Cs electrode 21 is set to 0V. On the other hand, FIG. 10 (a diagram at the time of high gradation) shows a state in which 20 V is applied to the drain electrode 20 and 0 V is applied to the Cs electrode 21. That is, in FIG. 10, the potential Vd1 of the drain electrode 20 is set to 20V, and the potential Vd2 of the Cs electrode 21 is set to 0V. This simulation was performed under the same conditions as the simulations shown in FIGS. 7 and 8 except that the counter electrode was not arranged.

As a result of the simulation, as shown in FIGS. 9 and 10, the liquid crystal display panel 100 of this embodiment can horizontally align the liquid crystal molecules in the vicinity of the active matrix substrate 10 without providing the counter electrode, and can also perform horizontal alignment. It can be seen that gradation display is possible by changing the thickness of the liquid crystal molecule layer. However, when the counter electrode 53 is not provided, the liquid crystal molecules on the counter substrate 50 side are slightly aligned in the oblique direction due to the influence of the alignment of the horizontally aligned liquid crystal molecules on the active matrix substrate 10 side (in FIGS. 9 and 10). (See the area enclosed by the single point difference line). Therefore, it was found that the form in which the counter electrode 53 is not provided on the counter substrate 50 is a slightly disadvantageous form with respect to the white floating suppression effect. On the other hand, it is found that by providing the counter electrode 53 and appropriately adjusting the potential Vc applied to the counter electrode 53, the liquid crystal display panel 100 can suppress the alignment of the liquid crystal molecules on the active matrix substrate 10 side in the oblique direction. It was.

(Comparative form 1)
The results of simulation of the operation of the MVA mode liquid crystal display panel will be described. FIG. 11 is a cross-sectional view showing a MVA mode liquid crystal display panel as a comparative form, and shows the results of obtaining the equipotential lines of the electric field generated in the liquid crystal layer and the alignment direction of the liquid crystal molecules by simulation at the time of low gradation. Show.

Various conditions in this simulation are as follows. That is, the dielectric constant anisotropy Δε = 2.9 and the refractive index anisotropy Δn = 0.1 of the liquid crystal molecules were set, and the thickness (cell gap) d2 of the liquid crystal layer 130 was 3.2 μm. The width L2 of the drain electrode 120 provided on the active matrix substrate 110 was 44.0 μm, and the interval between adjacent drain electrodes 120 (the width of the slit of the drain electrode 120) S2 was 4.0 μm. On the other hand, a counter electrode (common electrode) 153 is provided on the entire surface of the counter substrate 150. The voltage between the drain electrode 120 and the counter electrode 153 was set to 2V.

As a result, in the MVA mode liquid crystal display panel, there are liquid crystal molecules aligned in an oblique direction over the entire thickness direction of the liquid crystal layer even at a low gradation. Therefore, white floating occurs remarkably in an oblique view.

(Comparative form 2)
The results of simulation of the operation of the IPS mode liquid crystal display panel will be described. FIG. 12 is a cross-sectional view showing a comparative example of an IPS mode liquid crystal display panel, and shows the results of obtaining the equipotential lines of the electric field generated in the liquid crystal layer and the alignment direction of the liquid crystal molecules by simulation at the time of high gradation. .

Various conditions in this simulation are as follows. That is, the dielectric anisotropy Δε = 4.3 and the refractive index anisotropy Δn = 0.1 of the liquid crystal molecules were set, and the thickness (cell gap) d3 of the liquid crystal layer 230 was 4.2 μm. The width La2 of the drain electrode 220 provided on the active matrix substrate 210 and the width Lb2 of the Cs electrode (common electrode) 221 provided on the active matrix substrate 210 were set to 4.0 μm. Further, the distance S3 between the drain electrode 220 and the Cs electrode 221 is also set to 4.0 μm. The voltage between the drain electrode 220 and the Cs electrode 221 was set to 7V.

As a result, in the IPS mode liquid crystal display panel, the occurrence of whitening in an oblique field of view can be suppressed because there are few liquid crystal molecules aligned in an oblique direction even at a high gradation. However, the IPS mode liquid crystal display panel tends to cause light leakage in black display.

2 is a schematic plan view illustrating a configuration of a liquid crystal display panel of Embodiment 1. FIG. It is a cross-sectional schematic diagram which shows the structure of the liquid crystal display panel of Embodiment 1, and shows the cross section in the XY line in FIG. 3A and 3B are schematic views illustrating the configuration of the liquid crystal display device according to the first embodiment. FIG. 3A is a plan view and FIG. 3B is a side view. FIG. 2 is a schematic plan view illustrating a configuration on the active matrix substrate side of the first embodiment. 4 is a timing chart in the liquid crystal display device of Embodiment 1, where (a) shows a gate bus line signal (scanning signal) Vg, (b) shows a source bus line signal (image signal) Vd1, and (c). Indicates the Cs bus line signal Vd2, and (d) indicates the signal Vc supplied to the counter electrode. 4 is a timing chart (voltage waveform) in the liquid crystal display device of Embodiment 1, in which a source bus line signal (image signal) Vd1, a Cs bus line signal Vd2, and a signal Vc supplied to a counter electrode are superimposed. is there. FIG. 3 is a cross-sectional view showing the liquid crystal display panel of Embodiment 1 and shows the results of obtaining the equipotential lines of the electric field generated in the liquid crystal layer at the time of low gradation and the alignment direction of liquid crystal molecules by simulation. FIG. 3 is a cross-sectional view showing the liquid crystal display panel of Embodiment 1 and shows the results of obtaining the equipotential lines of the electric field generated in the liquid crystal layer at the time of high gradation and the alignment direction of liquid crystal molecules by simulation. FIG. 3 is a cross-sectional view showing the liquid crystal display panel of Embodiment 1 having no counter electrode, and shows the results of obtaining the equipotential lines of the electric field generated in the liquid crystal layer and the alignment direction of the liquid crystal molecules by simulation at the time of low gradation. FIG. 3 is a cross-sectional view showing the liquid crystal display panel of Embodiment 1 without a counter electrode, and shows the results of obtaining the equipotential lines of the electric field generated in the liquid crystal layer and the alignment direction of the liquid crystal molecules by simulation during high gradation. It is sectional drawing which shows the liquid crystal display panel of the MVA mode which is a comparison form, and shows the result of having calculated | required by the simulation the equipotential line of the electric field which generate | occur | produces in the liquid crystal layer at the time of a low gradation, and the orientation direction of a liquid crystal molecule. It is sectional drawing which shows the liquid crystal display panel of the IPS mode which is a comparative form, and shows the result of having calculated | required by the simulation the equipotential line of the electric field which generate | occur | produces in the liquid crystal layer at the time of a high gradation, and the orientation direction of a liquid crystal molecule.

Explanation of symbols

10, 110, 210: Active matrix substrate 11: Insulating substrate 12: Gate bus line 13: Cs bus line (capacitance holding wiring)
14: Insulating film 15: Semiconductor layer 16: Source bus line 17: Source electrode 18: Drain wiring 19: Interlayer insulating films 20, 120, 220: Drain electrode 21, 221: Cs electrodes 22a, 22b: Trunk parts 23a, 23b: Branches Part 24: central branch part 25: first vertical alignment film 26: thin film transistor (TFT)
27a, 27b: contact holes 30, 130, 230: liquid crystal layers 41a, 41b: polarizing plate 42: negative C plates 50, 150, 250: counter substrate 51: insulating substrate 52: color layer (color filter)
53: counter electrode 54: second vertical alignment film 61: driver chip for Vd1 output 62: gate driver chip 63: FPC boards 64a, 64b, 64c, 64d: connection wiring 65: driver chip for Vc output 100: liquid crystal display panel 121 : Cs electrode (common electrode)
153: Counter electrode (common electrode)
200: Liquid crystal display devices La1, Lb1: Branch width L2: Drain electrode width La3: Drain electrode width Lb3: Cs electrode (common electrode) width S1: Drain electrode branches and Cs electrode branches S2 between adjacent portions S2: spacing between adjacent drain electrodes S3: spacing between drain electrode and Cs electrode d1, d2, d3: thickness of liquid crystal layer (cell gap)

Claims (7)

A liquid crystal display device comprising a first substrate and a second substrate facing each other, and a liquid crystal layer sandwiched between the first substrate and the second substrate,
The liquid crystal layer contains a nematic liquid crystal having a positive dielectric anisotropy,
The first substrate includes a first electrode to which a variable potential is applied, a second electrode facing the first electrode in the first substrate surface and in the pixel region, and a first vertical formed on the surface on the liquid crystal layer side. An alignment film,
The second substrate has a second vertical alignment film formed on the surface on the liquid crystal layer side,
The liquid crystal display device generates an electric field in a liquid crystal layer by at least a first electrode and a second electrode. The second substrate has a third electrode on the liquid crystal layer side,
The liquid crystal display device according to claim 1, wherein the liquid crystal display device generates an electric field in the liquid crystal layer by the first electrode, the second electrode, and the third electrode. The first substrate includes a switching element and a source bus line that can be connected to the first electrode through the switching element.
3. The liquid crystal display device according to claim 2, wherein the third electrode is formed in a stripe shape so that a longitudinal direction thereof extends along a pixel column in a direction in which the source bus line extends, and a variable potential is applied. . In the liquid crystal display device, the voltage between the first electrode and the second electrode is larger than the voltage between the second electrode and the third electrode, and the voltage between the second electrode and the third electrode is the first electrode and the second electrode. 4. The liquid crystal display device according to claim 3, wherein a potential is applied to the first electrode, the second electrode, and the third electrode so as to be proportional to the voltage therebetween. The liquid crystal display device according to claim 1, wherein the first electrode and the second electrode are arranged side by side on the same plane. The liquid crystal display device according to claim 1, further comprising a negative C plate in front of the first substrate. The liquid crystal display device according to claim 1, wherein at least one of the first electrode and the second electrode is formed using an opaque conductive material.

Images