JP2021110790A - Liquid crystal display device - Google Patents

Abstract

To improve display performance.SOLUTION: A liquid crystal display device includes: substrates 10, 11; a liquid crystal layer 12 sandwiched between the substrates 10, 11; an insulating film 14 provided on the substrate 10; a lower electrode 18 provided on the insulating film 14; an insulating film 20 provided on the lower electrode 18; an upper electrode 21 provided on the insulating film 20, arranged above the lower electrode 18, and extending in a direction oblique to a first direction; an alignment layer 23 provided on the insulating film 20 and the upper electrode 21, and subjected to rubbing processing in the first direction; a color filter 25 provided on the substrate 11; and an alignment layer 26 provided on the color filter 25. The thickness of the alignment layer 23 is at least 1.8 times and less than 3.3 times the thickness of the upper electrode 21.SELECTED DRAWING: Figure 3

Description

The present invention relates to a liquid crystal display device.

High-definition, miniaturized, and wide viewing angles are required for liquid crystal display devices. An FFS (fringe field switching) type liquid crystal display device is known as one of means for widening the viewing angle. In this liquid crystal display device, an electric field in a direction parallel to the substrate, that is, a transverse electric field is generated, and the transverse electric field causes the liquid crystal molecules to rotate in a plane parallel to the substrate to change the transmittance. It is useful to use the transverse electric field method because it is possible to realize a wide viewing angle and the like in the liquid crystal display device.

The pair of substrates of the liquid crystal display device are provided with an alignment film for regulating the orientation direction of the liquid crystal by rubbing. The alignment film is rubbed with, for example, a roller wrapped with a cloth, and the liquid crystal molecules are oriented in the rubbing direction. The liquid crystal display device using the transverse electric field method is, for example, a normally black method in which a liquid crystal layer is sandwiched between a pair of opposing substrates and a black display is performed without applying an electric field to the liquid crystal layer. One of the pair of substrates has an upper electrode and a lower electrode arranged via an insulating layer. Due to the influence of the upper electrode, the surface of the alignment film has an uneven structure.

Rubbing is performed by rubbing the organic film in one direction with a roller or the like around which a cloth is wrapped. Due to the unevenness on the surface of the alignment film, a non-uniform portion of rubbing may occur along the rotation direction of the roller. The non-uniform portion of the rubbing is visually recognized as a fine streak-like scratch when no voltage is applied to the liquid crystal layer.

Fine streak-like scratches due to non-uniform rubbing are conspicuous in the normally black method, which displays black when no electric field is applied between the electrodes, and have a large effect on display performance.

Japanese Patent No. 5162969

The present invention provides a liquid crystal display device capable of improving display performance.

The liquid crystal display device according to one aspect of the present invention includes a first and second substrates, a liquid crystal layer sandwiched between the first and second substrates, and a first insulating film provided on the first substrate. The lower electrode provided on the first insulating film, the second insulating film provided on the lower electrode, and the second insulating film provided on the second insulating film and arranged above the lower electrode in the first direction. An upper electrode extending obliquely with respect to the above, a first alignment film provided on the second insulating film and the upper electrode and subjected to rubbing treatment in the first direction, and a collar provided on the second substrate. It includes a filter and a second alignment film provided on the color filter. The thickness of the first alignment film is 1.8 times or more and less than 3.3 times the thickness of the upper electrode.

According to the present invention, it is possible to provide a liquid crystal display device capable of improving display performance.

FIG. 1 is a plan view of the liquid crystal display device according to the embodiment. FIG. 2 is a plan view from which common electrodes are extracted. FIG. 3 is a cross-sectional view of the liquid crystal display device along the AA'line of FIG. FIG. 4 is a cross-sectional view of the liquid crystal display device along the line BB'of FIG. FIG. 5 is a schematic diagram illustrating a rubbing process. FIG. 6 is a schematic view illustrating the rubbing direction. FIG. 7 is a schematic diagram illustrating a rubbing process. FIG. 8 is a cross-sectional view illustrating the configuration of the alignment film according to the first embodiment. FIG. 9 is a cross-sectional view illustrating the configuration of the alignment film according to the second embodiment. FIG. 10 is a graph illustrating a change in black transmittance. FIG. 11 is a cross-sectional view illustrating the configuration of the alignment film according to the third embodiment. FIG. 12 is a cross-sectional view illustrating the configuration of the alignment film according to the fourth embodiment. FIG. 13 is a graph illustrating the relationship between the peak voltage change and the thickness of the alignment film.

Hereinafter, embodiments will be described with reference to the drawings. However, the drawings are schematic or conceptual, and the dimensions and ratios of each drawing are not necessarily the same as the actual ones. Further, even when the same part is represented between the drawings, the relationship and ratio of the dimensions of each other may be represented differently. In particular, some embodiments shown below exemplify devices and methods for embodying the technical idea of the present invention, and depending on the shape, structure, arrangement, etc. of the components, the technical idea of the present invention. Is not specified. In the following description, elements having the same function and configuration are designated by the same reference numerals, and duplicate explanations will be given only when necessary.

[1] Configuration of Liquid Crystal Display Device The liquid crystal display device according to the present embodiment is an FFS (fringe field switching) type liquid crystal display device. The FFS method is a method in which a homogeneously oriented liquid crystal is switched by a fringe electric field.

FIG. 1 is a plan view of the liquid crystal display device 1 according to the embodiment. FIG. 2 is a plan view of the common electrode 21 extracted. FIG. 3 is a cross-sectional view of the liquid crystal display device 1 along the AA'line of FIG. FIG. 4 is a cross-sectional view of the liquid crystal display device 1 along the line BB'of FIG. In FIG. 1, a portion corresponding to one pixel is extracted and shown, and in reality, a plurality of pixels in FIG. 1 are arranged in a matrix.

The liquid crystal display device 1 includes a TFT substrate 10 on which a switching element, pixel electrodes, and the like are formed, and a color filter substrate (CF substrate) 11 on which a color filter and the like are formed and arranged to face the TFT substrate 10. Each of the TFT substrate 10 and the CF substrate 11 is composed of a transparent substrate (for example, a glass substrate or a plastic substrate).

The liquid crystal layer 12 is filled (or sandwiched) between the TFT substrate 10 and the CF substrate 11. Specifically, the liquid crystal layer 12 is enclosed in a display area surrounded by the TFT substrate 10 and the CF substrate 11 and a sealing material (not shown). The sealing material is made of, for example, an ultraviolet curable resin, a thermosetting resin, an ultraviolet / heat combined type curable resin, etc., is applied to the TFT substrate 10 or the CF substrate 11 in the manufacturing process, and then cured by ultraviolet irradiation, heating, or the like. Be made to.

The liquid crystal material constituting the liquid crystal layer 12 changes its optical characteristics by manipulating the orientation of the liquid crystal molecules according to the applied electric field. In the present embodiment, as the liquid crystal layer 12, a positive type (P type) nematic liquid crystal having a positive dielectric anisotropy is used. The liquid crystal layer 12 is horizontally oriented (homogeneously oriented) in the initial state. The liquid crystal molecules are oriented almost horizontally with respect to the main surface of the substrate when there is no voltage (no electric field). When a voltage is applied (electric field is applied), the director of the liquid crystal molecule tilts toward the electric field.

Next, the configuration on the TFT substrate 10 side will be described. A switching element 13 is provided for each pixel on the liquid crystal layer 12 side of the TFT substrate 10. As the switching element 13, for example, a TFT (Thin Film Transistor) is used, and an n-channel TFT is used. As will be described later, the TFT 13 is provided on the semiconductor layer with a gate electrode functioning as a scanning line, a gate insulating film provided on the gate electrode, and a semiconductor layer provided on the gate insulating film. The source electrode and the drain electrode are provided.

A gate electrode GL extending in the X direction is provided on the TFT substrate 10. The gate electrode GL functions as a scanning line. A plurality of pixels for one line arranged in the X direction are commonly connected to one scanning line. A gate insulating film 14 is provided on the TFT substrate 10 and the gate electrode GL.

A semiconductor layer 15 is provided on the gate insulating film 14 for each pixel. As the semiconductor layer 15, for example, amorphous silicon is used.

A source electrode 16 and a drain electrode 17 are provided on the semiconductor layer 15 and the gate insulating film 14 so as to be separated from each other in the Y direction (direction orthogonal to the X direction). The source electrode 16 and the drain electrode 17 partially overlap the semiconductor layer 15. ^{An n +} type semiconductor layer into which a high concentration of n-type impurities is introduced may be provided between the source electrode 16 and the semiconductor layer 15 in order to improve the electrical connection between the source electrode 16 and the semiconductor layer 15. ^{Similarly, an n +} type semiconductor layer may be provided between the drain electrode 17 and the semiconductor layer 15.

A pixel electrode 18 extending in the Y direction is provided on the gate insulating film 14. The pixel electrode 18 is also called a lower electrode. The planar shape of the pixel electrode 18 is, for example, a rectangle. The pixel electrode 18 is electrically connected to the drain electrode 17.

A signal line SL extending in the Y direction is provided on the gate insulating film 14. The signal line SL is arranged at the boundary portion between two pixels adjacent to each other in the X direction. A plurality of pixels for one row arranged in the Y direction are commonly connected to one signal line SL. The source electrode 16 is electrically connected to the signal line SL via the connection electrode 19 extending in the X direction.

An insulating film 20 is provided on the source electrode 16, the drain electrode 17, the pixel electrode 18, the connection electrode 19, the signal line SL, and the gate insulating film 14.

A common electrode 21 is provided on the insulating film 20. The common electrode 21 is also called an upper electrode. The common electrode 21 is commonly provided for a plurality of pixels. The common electrode 21 has a plurality of slits 22 for each pixel. In the present embodiment, as an example, a configuration in which three slits 22 are formed for each pixel is shown.

As shown in FIG. 2, the common electrode 21 includes a first common electrode 21-1 and a second common electrode 21-2. The first common electrode 21-1 and the second common electrode 21-2 are separated by a slit 22 in the X direction. The first common electrode 21-1 and the second common electrode 21-2 are electrically connected at the end in the Y direction by an electrode portion included in the common electrode 21.

The first common electrode 21-1 extends in an oblique direction with respect to the Y direction. In the present embodiment, the first common electrode 21-1 has a dogleg shape so as to be refracted at the central portion thereof. That is, the first common electrode 21-1 extends obliquely to the left with respect to the Y direction, and extends obliquely to the right with respect to the Y direction from the central portion thereof. Similarly, the slit 22 has a dogleg shape. For example, the width of the first common electrode 21-1 and the width of the slit 22 are substantially the same. The configuration of the second common electrode 21-2 is also the same as that of the first common electrode 21-1.

In this embodiment, the domain of liquid crystal orientation can be divided at the center of the pixel. As a result, the liquid crystal layer can be made into a multi-domain.

The first common electrode 21-1 and the second common electrode 21-2 may extend linearly in an oblique direction without being refracted at the central portion.

An alignment film 23 that controls the orientation of the liquid crystal layer 12 is provided on the common electrode 21 and the insulating film 20. The alignment film 23 orients the liquid crystal molecules horizontally in the initial state of the liquid crystal layer 12. Further, the alignment film 23 is subjected to a rubbing treatment so that the long axis of the liquid crystal molecules faces the Y direction.

Next, the configuration on the CF substrate 11 side will be described. A black matrix (also called a black mask or a light-shielding film) 24 for shading is provided on the liquid crystal layer 12 side of the CF substrate 11. The black matrix 24 is arranged at the boundary between pixels and is formed in a mesh pattern. The black matrix 24 has a function of shielding the TFT 13 and a function of improving the contrast by shielding unnecessary light between color filters having different colors.

A plurality of color filters 25 are provided on the CF substrate 11 and the black matrix 24. The plurality of color filters (color members) 25 include a plurality of red filters, a plurality of green filters, and a plurality of blue filters. A general color filter is composed of the three primary colors of light, red (R), green (G), and blue (B). An adjacent set of three colors of R, G, and B is a display unit (pixel), and the monochromatic part of any one of R, G, and B in one pixel is the minimum called a sub-pixel (sub-pixel). It is a drive unit. The TFT 13 and the pixel electrode 18 are provided for each sub-pixel. In the description of the present specification, a sub-pixel is referred to as a pixel unless it is particularly necessary to distinguish between a pixel and a sub-pixel. As the color filter array, any array including a stripe array, a mosaic array, and a delta array can be applied. In this embodiment, the pixels of the red filter are illustrated.

An alignment film 26 for controlling the orientation of the liquid crystal layer 12 is provided on the color filter 25 and the black matrix 24. The alignment film 26 orients the liquid crystal molecules horizontally in the initial state of the liquid crystal layer 12. Further, the alignment film 26 is subjected to a rubbing treatment so that the long axis of the liquid crystal molecules faces the Y direction.

Although not shown, the first polarizing plate is laminated on the side of the TFT substrate 10 opposite to the liquid crystal layer 12, and the second polarizing plate is laminated on the side of the CF substrate 11 opposite to the liquid crystal layer 12. The first polarizing plate and the second polarizing plate are arranged so that their transmission axes are orthogonal to each other, that is, in an orthogonal Nicol state.

(Example of material)
The gate electrode GL, the source electrode 16, the drain electrode 17, and the signal line SL include, for example, any one of aluminum (Al), molybdenum (Mo), chromium (Cr), and tungsten (W), or one or more of them. An alloy containing the above is used. The pixel electrode 18 and the common electrode 21 are composed of transparent electrodes, and for example, ITO (indium tin oxide) is used. The gate insulating film 14 and the insulating film 20 are made of a transparent insulating material, and for example, silicon nitride (SiN) is used. As the alignment films 23 and 26, for example, polyimide resin is used.

[2] Operation The liquid crystal display device 1 of the present embodiment is a normally black system that displays black when no electric field is applied to the liquid crystal.

A common voltage Vcom is applied to the common electrode 21. The common voltage Vcom is, for example, 0V. The off state is a state in which an electric field is not applied to the liquid crystal layer 12, and the same common voltage Vcom as that of the common electrode 21 is applied to the pixel electrode 18. The on state is a state in which an electric field is applied to the liquid crystal layer 12, and a positive voltage is applied to the pixel electrodes 18. Actually, inversion drive (alternating current drive) is performed in which the polarity of the electric field between the pixel electrode 18 and the common electrode 21 is inverted at a predetermined cycle. By performing the inverting drive, deterioration of the liquid crystal can be prevented. The reverse drive cycle can be set arbitrarily.

In the off state, the liquid crystal molecules are set to the initial state, that is, the liquid crystal molecules are horizontally oriented and the long axis of the liquid crystal molecules is oriented in the Y direction. The Y direction is the same as the rubbing direction of the alignment films 23 and 26.

In the on state, an electric field from the common electrode 21 to the pixel electrode 18 is applied to the liquid crystal layer 12. The liquid crystal molecules to which the electric field is applied swirl in the horizontal plane in an oblique direction with respect to the Y direction. As a result, the liquid crystal display device 1 can control the amount of incident light transmitted. That is, the transmittance of the liquid crystal display device 1 can be changed.

[3] Rubbing process FIG. 5 is a schematic diagram illustrating a rubbing process.

The substrate provided with the alignment film is placed on the stage. The rubbing roller has a structure in which a rubbing cloth is wound around the roller. For example, as shown in FIG. 5, the rubbing roller rotates in the direction of rotation shown, and the stage moves in the direction of movement of the stage shown.

The alignment film is rubbed by a rubbing roller. As a result, the liquid crystal molecules are oriented in the rubbing direction. The rubbing direction corresponds to the orientation direction of the liquid crystal. The orientation direction of the liquid crystal is the direction in which the long axis of the liquid crystal molecules faces in the initial state (state in which no electric field is applied). The alignment film orients the liquid layer molecules in the rubbing direction.

FIG. 6 is a schematic view illustrating the rubbing direction. FIG. 6 shows a part of the first common electrode 21-1 and the second common electrode 21-2. The X and Y directions in FIG. 6 are the same as the X and Y directions in FIG.

The rubbing direction is the same as the Y direction. That is, the alignment film 23 is subjected to a rubbing treatment in a direction intersecting the extending direction of the first common electrode 21-1. The rubbing direction of the alignment film 26 is also the same as that of the alignment film 23.

FIG. 7 is a schematic diagram illustrating a rubbing process. A common electrode 21 is provided on the insulating film 20. An alignment film 23 is provided on the common electrode 21. Concavities and convexities (steps) are formed on the surface of the alignment film 23 due to the common electrode 21.

When the bristles 30 of the cloth wound around the roller hit the stepped portion of the alignment film 23, a non-uniform rubbing portion is generated at the stepped portion. The arrow shown in FIG. 7 represents the force applied to the alignment film 23. This non-uniform portion of rubbing disturbs the orientation of the liquid crystal molecules and prevents the liquid crystal molecules from being uniformly arranged in the Y direction. Therefore, the non-uniform portion of the rubbing is visually recognized as a fine streak-like scratch (for example, a white scratch) when an electric field is not applied to the liquid crystal.

Fine streaks caused by uneven rubbing are conspicuous in the normally black method, which displays black when no electric field is applied to the liquid crystal, and have a large effect on display performance.

[4] Configuration of Alignment Film 23 Next, the configuration of the alignment film 23 will be described. Hereinafter, the first to fourth embodiments will be described in order.

FIG. 8 is a cross-sectional view illustrating the configuration of the alignment film 23 according to the first embodiment. FIG. 8 is a cross-sectional view of the alignment film 23 cut in the X direction. FIG. 8 shows three common electrodes 21 provided on the insulating film 20. The alignment film on the insulating film 20 is 23a, the alignment film on the common electrode 21 is 23b, the thickness of the alignment film 23a is t1, the thickness of the alignment film 23b is t2, and the alignment film 23a on the insulating film 20 and the common electrode 21. The step with the alignment film 23b above is referred to as D. The thickness of the common electrode 21 is, for example, 60 nm.

In the first embodiment, the thickness t1 = 43 nm of the alignment film 23a on the insulating film 20 and the thickness t2 = 18 nm of the alignment film 23b on the common electrode 21. In this case, the step D = 35 nm. In the first embodiment, since the alignment film 23 is thin, the driving voltage for driving the pixels can be reduced. However, since the step D becomes large, there is a high possibility that a non-uniform portion of rubbing occurs in the alignment film 23.

FIG. 9 is a cross-sectional view illustrating the configuration of the alignment film 23 according to the second embodiment. In the second embodiment, the thickness t1 of the alignment film 23a on the insulating film 20 is 113 nm, and the thickness of the alignment film 23b on the common electrode 21 is t2 = 63 nm. In this case, the step D = 10 nm. That is, in the second embodiment, the step D can be reduced to 1/3 or less as compared with the first embodiment. In the second embodiment, the thickness t1 (= 113 nm) of the alignment film 23 is about 1.8 times the thickness (= 60 nm) of the common electrode 21.

In the second embodiment, since the step D becomes small, the bristles of the rubbing cloth can easily hit the alignment film 23 uniformly, and the non-uniform portion of the liquid crystal alignment is reduced. As a result, the light leakage due to the small scratches seen when the black display of the normally black method is performed is improved.

FIG. 10 is a graph illustrating a change in black transmittance. The black transmittance is the transmittance in the black display, that is, in the off state. FIG. 10 shows the black transmittance of the first embodiment and the second embodiment. As shown in FIG. 10, in the second embodiment, the black transmittance can be reduced by about 10% as compared with the first embodiment.

As described above, from the viewpoint of reducing the step D between the alignment film 23a on the insulating film 20 and the alignment film 23b on the common electrode 21, the thickness t1 (= 113 nm) of the alignment film 23 is the thickness of the common electrode 21. It is desirable that it is 1.8 times or more of the (= 60 nm). Further, it is desirable that the thickness t1 of the alignment film 23a is 100 nm or more. Further, it is desirable that the step D between the alignment film 23a on the insulating film 20 and the alignment film 23b on the common electrode 21 is 10 nm or less.

FIG. 11 is a cross-sectional view illustrating the configuration of the alignment film 23 according to the third embodiment. In the third embodiment, the thickness t1 of the alignment film 23a on the insulating film 20 is t1 = 150 nm, and the thickness of the alignment film 23b on the common electrode 21 is t2 = 92 nm. In this case, the step D is almost eliminated. In the third embodiment, the thickness t1 (= 150 nm) of the alignment film 23 is about 2.5 times the thickness (= 60 nm) of the common electrode 21.

In the third embodiment, since the step is smaller, the bristles of the rubbing cloth uniformly hit the alignment film 23, and the non-uniform portion of the liquid crystal alignment is further reduced. As a result, the light leakage due to the small scratches seen during the black display of the normally black method is further improved. In the third embodiment, the black transmittance can be further reduced by about 10% as compared with the second embodiment.

FIG. 12 is a cross-sectional view illustrating the configuration of the alignment film 23 according to the fourth embodiment. In the fourth embodiment, the thickness t1 of the alignment film 23a on the insulating film 20 is t1 = 200 nm, and the thickness of the alignment film 23b on the common electrode 21 is t2 = 140 nm. In this case, the step D disappears. In the fourth embodiment, the thickness t1 (= 200 nm) of the alignment film 23 is about 3.3 times the thickness (= 60 nm) of the common electrode 21.

In the fourth embodiment, since the step is eliminated, the bristles of the rubbing cloth uniformly hit the alignment film 23, and the non-uniform portion of the liquid crystal alignment is further reduced. As a result, the light leakage due to the small scratches seen during the black display of the normally black method is further improved. In the fourth embodiment, the black transmittance can be further reduced by about 10% as compared with the third embodiment.

Next, the peak voltage change of the liquid crystal display device 1 will be described. A drive voltage is applied to the pixels by a drive circuit. The peak voltage is the peak of the drive voltage, and is the voltage when displaying at the maximum gradation (for example, white display in black-and-white display). The peak voltage change is a change from the peak voltage of the first embodiment with reference to the peak voltage of the first embodiment (thickness t1 = 43 nm of the alignment film 23a). The peak voltage of the first embodiment is, for example, 6V.

FIG. 13 is a graph illustrating the relationship between the peak voltage change and the thickness of the alignment film. The vertical axis of FIG. 13 represents the peak voltage change (V), and the horizontal axis of FIG. 13 represents the thickness (nm) of the alignment film. The thickness of the alignment film corresponds to the thickness t1 of 23a of the alignment film on the insulating film 20 described above.

The thicker the alignment film, the larger the peak voltage change. When the thickness of the alignment film is 200 nm (corresponding to the fourth embodiment), the peak voltage change is 0.8 V. If the peak voltage change exceeds 0.8 V, it is not preferable due to the specifications of the peripheral circuits of the pixel array. Specifically, as the peak voltage (or change in peak voltage) increases, it is necessary to increase the drive capacity and size of the drive circuit that drives the pixels, and the power consumption also increases. Therefore, in order to make the peak voltage change less than 0.8 V (for example, the peak voltage less than 6.8 V), the thickness t1 (= 200 nm) of the alignment film 23 is the thickness (= 60 nm) of the common electrode 21. It is desirable that it is less than 3.3 times. Further, the thickness of the alignment film 23 is preferably less than 200 nm.

The thickness of the alignment film 26 on the CF substrate 11 side is not particularly limited, and is set to be the same as that of the alignment film 23 of the first embodiment, for example.

[5] Effect of the Embodiment In the present embodiment, the liquid crystal display device 1 is an FFS system and a normally black system. The liquid crystal display device 1 is provided on the pixel electrode (lower electrode) 18 provided on the gate insulating film 14, the insulating film 20 provided on the pixel electrode 18, and above the pixel electrode 18 provided on the insulating film 20. The common electrode (upper electrode) 21-1 arranged in the Y direction and extending obliquely with respect to the Y direction, and the alignment film 23 provided on the insulating film 20 and the common electrode 21-1 and subjected to the rubbing treatment in the Y direction. Be prepared. The thickness of the alignment film 23 is set to be 1.8 times or more and less than 3.3 times the thickness of the common electrode 21-1.

Therefore, according to the present embodiment, the step between the alignment film 23 on the insulating film 20 and the alignment film 23 on the common electrode 21 can be reduced. Therefore, the alignment film can be rubbed more uniformly, and the non-uniform portion of the rubbing in the alignment film can be reduced. As a result, the non-uniform portion of the liquid crystal orientation can be reduced. As a result, it is possible to prevent the appearance of fine streak-like scratches due to the non-uniform portion of the rubbing when the black is displayed in the normally black method. As a result, it is possible to improve the display performance. Moreover, it is possible to improve the contrast.

In addition, it is possible to suppress a large peak of the drive voltage while improving the display performance. As a result, it is possible to suppress an increase in power consumption.

[6] Modification Example In the above embodiment, the pixel electrode 18 is arranged on the lower side as the lower electrode, and the common electrode 21 (including the first common electrode 21-1 and the second common electrode 21-2) is used as the upper electrode. It is placed on the upper side. The configuration is not limited to this, and the common electrode 21 may be arranged on the lower side as the lower electrode, and the pixel electrode 18 may be arranged on the upper side as the upper electrode. In the case of this configuration, the lower common electrode 21 is composed of a flat electrode having no slit (opening). The common electrode 21 is arranged between the signal line SL and the pixel electrode 18 via an insulating film, respectively. Further, the upper pixel electrode 18 is configured to have one or more slits and an electrode on the line. The pixel electrode 18 is configured to be separated for each pixel.

Further, although the FFS type liquid crystal display device has been described as an example, the present invention is not limited to this, and it can be applied to a horizontal electric field type liquid crystal display device including an IPS (In-Plane Switching) type.

Further, although the active matrix type liquid crystal display device has been described as an example, the description is not limited to this, and it is also possible to apply to other methods, for example, a passive matrix type liquid crystal display device.

Further, as the switching element, the TFT has been described as an example, but the present invention is not limited to this, and other switching elements such as a diode element may be used.

Further, although the driving electric field has been described as being formed between the common electrode and the pixel electrode, the present invention is not limited to this. Any liquid crystal display device in which a driving electric field is formed between the two electrodes may be used, and the present embodiment can be applied regardless of the type of electrodes.

The present invention is not limited to the above-described embodiment, and can be variously modified at the implementation stage without departing from the gist thereof. In addition, each embodiment may be carried out in combination as appropriate, in which case the combined effect can be obtained. Further, the above-described embodiment includes various inventions, and various inventions can be extracted by a combination selected from a plurality of disclosed constituent requirements. For example, even if some constituent requirements are deleted from all the constituent requirements shown in the embodiment, if the problem can be solved and the effect is obtained, the configuration in which the constituent requirements are deleted can be extracted as an invention.

1 ... liquid crystal display device, 10 ... TFT substrate, 11 ... CF substrate, 12 ... liquid crystal layer, 13 ... switching element, 14 ... gate insulating film, 15 ... semiconductor layer, 16 ... source electrode, 17 ... drain electrode, 18 ... pixel Electrodes, 19 ... Connection electrodes, 20 ... Insulating film, 21 ... Common electrodes, 22 ... Slits, 23 ... Alignment film, 24 ... Black matrix, 25 ... Color filter, 26 ... Alignment film.

Claims (6)

1st and 2nd boards,
The liquid crystal layer sandwiched between the first and second substrates,
The first insulating film provided on the first substrate and
The lower electrode provided on the first insulating film and
A second insulating film provided on the lower electrode and
An upper electrode provided on the second insulating film, arranged above the lower electrode, and extending obliquely with respect to the first direction,
A first alignment film provided on the second insulating film and the upper electrode and subjected to rubbing treatment in the first direction, and a first alignment film.
The color filter provided on the second substrate and
A second alignment film provided on the color filter and
Equipped with
A liquid crystal display device in which the thickness of the first alignment film is 1.8 times or more and less than 3.3 times the thickness of the upper electrode. The liquid crystal display device according to claim 1, wherein the thickness of the first alignment film is 100 nm or more. The liquid crystal display device according to claim 1 or 2, wherein the thickness of the first alignment film is less than 200 nm. The liquid crystal display device according to any one of claims 1 to 3, wherein the step between the alignment film on the second insulating film and the alignment film on the upper electrode is 10 nm or less. The liquid crystal display device according to any one of claims 1 to 4, wherein the first alignment film is made of a polyimide resin. The liquid crystal display device according to any one of claims 1 to 5, wherein the liquid crystal layer is horizontally oriented in an initial state in which an electric field is not applied and has positive dielectric anisotropy.

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