JP2004077699A - Liquid crystal display - Google Patents

Abstract

A liquid crystal display device having excellent in-plane uniformity of transmittance is provided.
A liquid crystal display device according to the present invention includes first and second substrates facing each other, a pixel electrode provided on a surface of the first substrate facing the second substrate, and a second substrate. A common electrode provided on a surface facing the first substrate, and a liquid crystal layer interposed between the pixel electrode 10 and the common electrode. The pixel electrodes 10 are separated from each other and electrically connected to each other. A plurality of sub-pixel electrodes 10A to 10C that are electrically connected to each other, and each of the plurality of sub-pixel electrodes 10A to 10C has a plurality of comb-shaped conductive layers that are different from each other in the longitudinal direction of the comb teeth and are electrically connected to each other. 10A to 10D, the shapes of the patterns formed by the different longitudinal directions are equal to each other between the plurality of sub-pixel electrodes 10A to 10C, and the orientation of the pattern is the plurality of sub-pixel electrodes 10A to 10C. In, characterized in that different from each other.
[Selection] Figure 2

Description

【００７６】
上記表に示すように、実施例に係る液晶表示装置１は、比較例１及び２に係る液晶表示装置１に比べ、透過率の面内均一性に優れていた。なお、実施例並びに比較例１及び２に係る液晶表示装置１の何れにおいても、ドメイン間の境界位置を設計通りに生じさせることができ、良好な配向分割均一性を実現することができた。
【００７７】
【発明の効果】
以上説明したように、本発明では、１つの画素領域を複数のサブ画素領域で構成するとともに、それらサブ画素領域間で液晶分子のチルト方向を僅かに異ならしめることにより、セルギャップの変動に応じた個々の画素領域の透過率の変動量を小さくすることができる。そのため、本発明によると、透過率の面内均一性を高めることが可能となる。
すなわち、本発明によると、透過率の面内均一性に優れた液晶表示装置が提供される。
【図面の簡単な説明】
【図１】本発明の一実施形態に係る液晶表示装置を概略的に示す断面図。
【図２】（ａ）は、図１に示す液晶表示装置で利用可能な画素電極構造の一例を概略的に示す平面図、（ｂ）は（ａ）に示す画素電極の一部を拡大して示す平面図。
【図３】（ａ）〜（ｄ）は、図１に示す液晶表示装置に図２（ａ），（ｂ）に示す構造を採用した場合に生じる液晶分子の配向変化を概略的に示す図。
【図４】図１に示す液晶表示装置に図２（ａ），（ｂ）に示す構造を採用した場合に得られるセルギャップと透過率との関係の一例を示すグラフ。
【図５】図１に示す液晶表示装置に図２（ａ），（ｂ）に示す構造を採用した場合に観察される透過率分布の一例を示す画像。
【図６】図１に示す液晶表示装置で利用可能な画素電極構造の他の例を概略的に示す平面図。
【図７】図１に示す液晶表示装置に図６に示す構造を採用した場合に生じる液晶分子の配向変化を概略的に示す図。
【図８】比較例１に係る液晶表示装置で採用した構造を概略的に示す平面図。
【図９】比較例２に係る液晶表示装置で採用した構造を概略的に示す平面図。
【符号の説明】
１…液晶表示装置
２…アクティブマトリクス基板
３…対向基板
４…液晶層
７…透明基板
８…スイッチング素子
９…カラーフィルタ層
９ａ〜９ｃ…着色層
１０…画素電極
１０Ａ〜１０Ｃ…サブ画素電極
１０ａ〜１０ｄ…櫛形導電層
１０−１…櫛歯部
１０−２…スリット部
１１…配向膜
１５…透明基板
１６…共通電極
１７…配向膜
２５…液晶分子
３１，３２…矢印[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a liquid crystal display device.
[0002]
[Prior art]
Liquid crystal display devices have various features such as thinness and low power consumption, and are widely used as displays for word processors, notebook computers, mobile phones, car navigation systems, and the like. In such a liquid crystal display device, at present, an active element such as a thin film transistor (hereinafter, referred to as a TFT) is used as a switching element, and a TFT-TN mode using a nematic liquid crystal is mainly used. In a liquid crystal display device using this display mode, a screen size of about 10 inches and full color display are realized, and such a liquid crystal display device is used as a display for an information terminal.
[0003]
However, when a configuration capable of full-color display is employed in a TN mode liquid crystal display device, there is a problem that the viewing angle becomes extremely narrow. Further, there is a problem that a trailing phenomenon occurs when a moving image is displayed, and the moving image display quality is low. For these reasons, the use of the liquid crystal display device using the nematic liquid crystal is limited.
[0004]
In recent years, liquid crystal display devices have begun to be applied to televisions in addition to monitors of desktop computers and workstations. In the TN mode described above, the viewing angle characteristics and the response speed required for such applications cannot be realized, and therefore, the OCB mode using a nematic liquid crystal, the VAN (Vertical Aligned Nematic) mode, and the IPS mode In addition, adoption of a surface stabilized ferroelectric liquid crystal (SMC) mode using a smectic liquid crystal and an antiferroelectric liquid crystal mode are being studied.
[0005]
Among these display modes, the VAN mode can provide a faster response speed than the conventional TN (Twisted Nematic) mode, and does not require a rubbing process for generating defects such as electrostatic breakdown due to vertical alignment. Above all, the multi-domain VAN mode in which each pixel region is divided into a plurality of domains in which tilt directions of liquid crystal molecules are different from each other has attracted particular attention because compensation design of a viewing angle is relatively easy.
[0006]
Meanwhile, in the liquid crystal display device, when the in-plane uniformity of the cell gap is low, the in-plane uniformity of the transmittance is reduced. Conventionally, granular spacers, columnar spacers, and the like have been used to achieve high in-plane transmittance uniformity, but there is a limit to improving the in-plane uniformity of transmittance using only spacers.
[0007]
[Problems to be solved by the invention]
The present invention has been made in view of the above problems, and has as its object to provide a liquid crystal display device having excellent in-plane uniformity of transmittance.
[0008]
[Means for Solving the Problems]
According to a first aspect of the present invention, a first and a second substrate facing each other, a pixel electrode provided on a surface of the first substrate facing the second substrate, and a first electrode of the second substrate are provided. A common electrode provided on the surface facing the substrate, and a liquid crystal layer interposed between the pixel electrode and the common electrode, wherein a voltage is applied between the pixel electrode and the common electrode. Dividing the pixel region of the liquid crystal layer between the pixel electrode and the common electrode into a plurality of sub-pixel regions adjacent to each other in the in-plane direction; A plurality of striped regions adjacent to each other, wherein each of the plurality of striped regions alternately extends in the in-plane direction with first and second strip-shaped regions having different electric field intensities. Repeatedly arranged, each of the plurality of sub-pixel regions Wherein the longitudinal direction of the first band-shaped region is different from at least two of the plurality of striped regions, and the shape of a pattern formed by the different longitudinal directions is equal to each other between the plurality of sub-pixel regions, A liquid crystal display device is provided, wherein the orientation of the pattern is different between the plurality of sub-pixel regions.
[0009]
According to a second aspect of the present invention, a first and a second substrate facing each other, a pixel electrode provided on a surface of the first substrate facing the second substrate, and a first electrode of the second substrate are provided. A common electrode provided on a surface facing the substrate; and a liquid crystal layer interposed between the pixel electrode and the common electrode, wherein the pixel electrodes are separated from each other and electrically connected to each other. A plurality of sub-pixel electrodes, each of the plurality of sub-pixel electrodes includes a plurality of comb-shaped conductive layers having different comb teeth longitudinal directions and electrically connected to each other, and a pattern formed by the mutually different longitudinal directions. Is provided among the plurality of sub-pixel electrodes, and the orientation of the pattern is different between the plurality of sub-pixel electrodes.
[0010]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In each of the drawings, the same or similar components are denoted by the same reference numerals, and redundant description will be omitted.
[0011]
FIG. 1 is a sectional view schematically showing a liquid crystal display device according to an embodiment of the present invention. The liquid crystal display device 1 shown in FIG. 1 is a VAN type liquid crystal display device having a structure in which a liquid crystal layer 4 is sandwiched between an active matrix substrate (or an array substrate) 2 and a counter substrate 3. I have. The distance between the active matrix substrate 2 and the counter substrate 3 is kept constant by a spacer (not shown). Further, polarizing films 5 are attached to both surfaces of the liquid crystal display device 1.
[0012]
The active matrix substrate 2 has a transparent substrate 7 such as a glass substrate. On one main surface of the transparent substrate 7, wirings and switching elements 8 are formed. A color filter layer 9, a pixel electrode 10, and an alignment film 11 are sequentially formed thereon.
[0013]
The wirings formed on the transparent substrate 7 are scanning lines, signal lines, auxiliary capacitance lines, and the like made of aluminum, molybdenum, copper, or the like. The switching element 8 is, for example, a TFT having a semiconductor layer of amorphous silicon or polysilicon and a metal layer of aluminum, molybdenum, chromium, copper, tantalum, or the like. Wirings such as scanning lines and signal lines, and pixel electrodes 10 is connected. With such a configuration, the active matrix substrate 2 can selectively apply a voltage to a desired pixel electrode 10.
[0014]
The color filter layer 9 includes blue, green, and red coloring layers 9a to 9c. The color filter layer 9 is provided with a contact hole, and the pixel electrode 10 is connected to the switching element 8 via the contact hole. The coloring layers 9a to 9c can be formed using a photosensitive resin containing a coloring dye or a coloring pigment.
[0015]
The pixel electrode 10 can be made of a transparent conductive material such as ITO. The pixel electrode 10 can be formed by forming a thin film by, for example, a sputtering method, and then patterning the thin film using a photolithography technique and an etching technique.
[0016]
The alignment film 11 formed on the pixel electrode 10 is formed of a thin film made of a transparent resin such as polyimide. In this embodiment, the alignment film 11 is provided with a vertical alignment without performing a rubbing process.
[0017]
The counter substrate 3 has a structure in which a common electrode 16 and an alignment film 17 are sequentially formed on a transparent substrate 15 such as a glass substrate. The common electrode 16 and the alignment film 17 can be formed of the same material as the pixel electrode 10 and the alignment film 11 provided on the active matrix substrate 2. In the present embodiment, the common electrode 16 is formed as a flat continuous film.
[0018]
FIG. 2A is a plan view schematically showing an example of a pixel electrode structure that can be used in the liquid crystal display device 1 shown in FIG. FIG. 2B is an enlarged plan view showing a part of the pixel electrode 10 shown in FIG.
[0019]
The pixel electrode 10 illustrated in FIG. 2A includes three sub-pixel electrodes 10A to 10C. Further, as shown in FIG. 2B, each of the sub-pixel electrodes 10A to 10C is composed of four comb-shaped conductive layers 10a to 10d whose comb teeth have different longitudinal directions and are electrically connected to each other. I have. Each of the comb-shaped conductive layers 10a to 10d constituting the pixel electrode 10 has a structure in which comb-tooth portions 10-1 and slit portions 10-2 are alternately and repeatedly arranged.
[0020]
In the liquid crystal display device 1 shown in FIG. 1, by adopting such a configuration, the pixel region is divided into three sub-pixel regions corresponding to the sub-pixel electrodes 10A to 10C constituting the pixel electrode 10, and Each sub-pixel region can be divided into four domains in which the tilt directions of the liquid crystal molecules 25 are different from each other, corresponding to the comb-shaped conductive layers 10a to 10d. This will be described with reference to FIGS.
[0021]
FIGS. 3A to 3D are diagrams schematically showing changes in the alignment of liquid crystal molecules that occur when the structure shown in FIGS. 2A and 2B is employed in the liquid crystal display device 1 shown in FIG. is there. 3 (a) and 3 (c) are plan views, and FIGS. 3 (b) and 3 (d) are side views of the structure shown in FIGS. 3 (a) and 3 (c) as viewed from below. is there. 3A to 3D, some components are omitted for simplification.
[0022]
When no voltage is applied between the pixel electrode 10 and the common electrode 16, the alignment films 11 and 17 form liquid crystal molecules 25 constituting the liquid crystal layer 4, specifically, liquid crystal molecules having a negative dielectric anisotropy. , Act to orient them vertically. Therefore, the liquid crystal molecules 25 are aligned such that their major axes are substantially perpendicular to the film surface of the alignment film 11.
[0023]
When a relatively low first voltage is applied between the pixel electrode 10 and the common electrode 16, a leakage electric field is generated above the slit 10-2 provided in the pixel electrode 10. Therefore, the electric lines of force are inclined there as shown in FIG.
[0024]
An electric field generated by applying a voltage between the pixel electrode 10 and the common electrode 16 acts to orient the liquid crystal molecules 25 in a direction perpendicular to the lines of electric force. Therefore, the liquid crystal molecules 25 try to align as shown in FIG. 3A by the action from the alignment films 11 and 17 and the electric field.
[0025]
However, in the state shown in FIG. 3A, the alignment state of the right liquid crystal molecules 25 and the alignment state of the left liquid crystal molecules 25 interfere with each other. Therefore, the liquid crystal molecules 25 try to change the tilt direction upward or downward in the drawing to take a more stable alignment state.
[0026]
Here, as shown in FIG. 3A, it is assumed that the comb-tooth portion 10-1 and its vicinity have a symmetric (or isotropic) shape in the vertical direction in the figure. In this case, the probability of the liquid crystal molecules 25 changing the tilt direction upward as indicated by the arrow 31 is equal to the probability of changing the tilt direction downward as indicated by the arrow 32.
[0027]
On the other hand, as shown in FIG. 3C, when the comb tooth 10-1 and its vicinity have an asymmetric (or anisotropic) shape in the vertical direction in the figure, the pixel The lines of electric force are asymmetric between both ends of the electrode 10, and similarly, the lines of electric force are also asymmetric between both ends of the slit 10-2. Therefore, the alignment state in which the liquid crystal molecules 25 are aligned in the direction indicated by the arrow 32 is more stable than the alignment state in which the liquid crystal molecules 25 are aligned in the direction indicated by the arrow 31. As a result, the average tilt direction (director) of the liquid crystal molecules 25 becomes downward as indicated by the arrow 32 in FIG.
[0028]
When the voltage applied between the pixel electrode 10 and the common electrode 16 is increased to a second voltage higher than the first voltage, the alignment films 11 and 17 cause the liquid crystal molecules 25 to vertically align. The action of the electric field to orient the liquid crystal molecules 25 in a direction perpendicular to the line of electric force is increased. Therefore, the liquid crystal molecules 25 change the tilt angle in a direction approaching the horizontal alignment.
[0029]
Here, even when the voltage applied between the electrodes 10 and 16 is the second voltage, similarly to the case where the voltage applied between the electrodes 10 and 16 is the first voltage, the liquid crystal molecules 25 move in the direction indicated by the arrow 32. Is more stable than the liquid crystal molecules 25 are aligned in the direction indicated by the arrow 31. Therefore, when the voltage applied between the electrodes 10 and 16 is changed between the first and second voltages, the director of the liquid crystal molecules 25 is placed on a surface perpendicular to the arrangement direction of the comb teeth 10-1 and the slits 10-2. Within. That is, when the voltage applied between the electrodes 10 and 16 is changed between the first and second voltages, the liquid crystal molecules 25 change the average tilt direction of the comb teeth 10-1 and the slits 10-2. The tilt angle is changed while being maintained in a plane perpendicular to the arrangement direction.
[0030]
Therefore, the tilt direction of the liquid crystal molecules 25 is shown in FIG. 2 by making the longitudinal directions of the comb teeth 10-1 and the slits 10-2 different among the four comb-shaped conductive layers 10a to 10d constituting the pixel electrode 10. The tilt angle can be changed while maintaining the above. That is, only the structure provided on the active matrix substrate 2 can form four domains in which the tilt directions of the liquid crystal molecules 25 are different from each other in one pixel region. In the present embodiment, the tilt angle can be changed while maintaining the average tilt direction of the liquid crystal molecules 25 in a plane perpendicular to the direction in which the comb teeth 10-1 and the slits 10-2 are arranged. In addition to achieving a higher response speed, poor alignment is less likely to occur and good alignment division is possible.
[0031]
In the present embodiment, as shown in FIG. 2, the shape of the pattern formed by the longitudinal direction of the comb teeth 10-1 and the slits 10-2 is the same between the sub-pixel electrodes 10A to 10C. In FIG. 2, the pattern formed by the longitudinal directions is indicated by a pair of double-headed arrows crossing in a cross shape. In the present embodiment, the orientation of the pattern formed by the longitudinal directions of the comb teeth 10-1 and the slits 10-2 is different among the sub-pixel electrodes 10A to 10C.
[0032]
That is, in the structure of FIG. 2, the comb teeth 10-1 and the slits 10-1 of the comb-shaped conductive layers 10b and 10c are arranged in the longitudinal direction of the comb teeth 10-1 and the slit 10-2 of the comb-shaped conductive layers 10a and 10d. The angle formed by the longitudinal direction of 10-2 is equal among the sub-pixel electrodes 10A to 10C. Further, in the structure of FIG. 2, the longitudinal direction of the comb teeth 10-1 and the slit 10-2 of the sub-pixel electrode 10A is the same as the longitudinal direction of the comb teeth 10-1 and the slit 10-2 of the sub-pixel electrode 10B. Is slightly rotated clockwise with respect to the vertical axis of the comb-tooth portion 10-1 and the slit portion 10-2 of the sub-pixel electrode 10C. The relationship is such that it is slightly rotated counterclockwise with respect to the longitudinal direction of the portion 10-2.
[0033]
As described above, in the liquid crystal display device 1 according to the present embodiment, when the voltage applied between the electrodes 10 and 16 is changed between the first and second voltages, the liquid crystal molecules 25 have the average tilt direction. Is maintained in a plane perpendicular to the arrangement direction of the comb teeth 10-1 and the slits 10-2, and the tilt angle is changed. That is, in the liquid crystal display device 1 according to the present embodiment, the slow axis at the time of applying the second voltage is also different between domains in which the longitudinal directions of the comb teeth 10-1 and the slits 10-2 are different from each other. Therefore, for example, the slow axis of the domain corresponding to the comb-shaped conductive layer 10a of the sub-pixel electrode 10A and the slow axis of the domain corresponding to the comb-shaped conductive layer 10a of the sub-pixel electrode 10C are determined by the comb-shaped conductive layer 10a of the sub-pixel electrode 10C. Are slightly rotated clockwise and counterclockwise with respect to the slow axis of the domain corresponding to.
[0034]
The transmittance of each domain of the liquid crystal display device 1 changes according to the phase difference that the domain gives between the incident light and the outgoing light when the second voltage is applied, and this phase difference changes when the domain is applied with the second voltage. Is proportional to the product Δn · d of the difference Δn = (n ₁ −n ₂ ) between the refractive index n _{1 in} the slow axis direction and the refractive index n _{2 in the} direction perpendicular to the slow axis direction and the cell gap d. Also, assuming that linearly polarized light is incident on a certain domain, the transmittance of that domain changes according to the angle between the slow axis and the vibration direction of the incident linearly polarized light. Therefore, when the structure as shown in FIG. 2 is employed, even if the cell gap d varies, the sub-pixel regions corresponding to the sub-pixel electrodes 10A to 10C compensate each other, so that the transmittance between the pixel regions is large. There is no variation. This will be described in more detail with reference to FIG.
[0035]
FIG. 4 is a graph showing an example of the relationship between the cell gap and the transmittance obtained when the structure shown in FIGS. 2A and 2B is employed in the liquid crystal display device 1 shown in FIG. In the figure, the horizontal axis shows the cell gap d, and the vertical axis shows the transmittance T. Curves 51A to 51C indicate data relating to domains corresponding to the sub-pixel electrodes 10A to 10C, respectively, and a curve 52 indicates data relating to a pixel region corresponding to the pixel electrode 10, that is, an average value of data indicated by the curves 51A to 51C. Is shown.
[0036]
When the shapes and orientations of the sub-pixel electrodes 10A and 10C are equal to those of the sub-pixel electrode 10B, in each pixel region, the transmittance T changes with respect to the cell gap d as shown by a curve 51B. Therefore, the variation of the transmittance T with respect to the variation of the cell gap d is large. For example, as shown in FIG. 4, when the deviation from the design value of the cell gap d is [Delta] d, the deviation from the design value of the transmittance T becomes [Delta] T _2.
[0037]
As shown by the curves 51A to 51C in FIG. 4, the transmittance T is maximized in the domain corresponding to the sub-pixel electrode 10A, the domain corresponding to the sub-pixel electrode 10B, and the domain corresponding to the sub-pixel electrode 10C. The cell gaps d are different from each other. Therefore, as shown by the curve 52, in the pixel region including those domains, the change in the transmittance T with respect to the change in the cell gap d is small. For example, as shown in FIG. 4, when the deviation of the cell gap d from the design value is Δd, the deviation of the transmittance T from the design value is only ΔT ₁ (<< ΔT ₂ ).
[0038]
As described above, according to the present embodiment, the amount of change in the transmittance T of each pixel region according to the change in the cell gap d can be reduced. Therefore, according to the present embodiment, the in-plane uniformity of the transmittance T can be improved.
[0039]
As described above, in the present embodiment, in each of the sub-pixel electrodes 10A to 10C, the orientation of the pattern formed by the longitudinal direction of the comb tooth portion 10-1 and the slit portion 10-2 is different from each other. It is preferable that the azimuth of the pattern on the sub-pixel electrode 10A is rotated clockwise by 5 ° or more with respect to the azimuth of the pattern on the sub-pixel electrode 10B. It is preferable that the azimuth of the pattern on the sub-pixel electrode 10C is in a relationship rotated counterclockwise by 5 ° or more with respect to the azimuth of the pattern on the sub-pixel electrode 10B. When these angles are small, the effect of changing the azimuth of the pattern among the sub-pixel electrodes 10A to 10C usually does not significantly appear.
[0040]
It is preferable that the azimuth of the pattern on the sub-pixel electrode 10A is in a relationship rotated clockwise by 40 ° or less with respect to the azimuth of the pattern on the sub-pixel electrode 10B. Further, it is preferable that the azimuth of the pattern on the sub-pixel electrode 10C is in a relationship rotated by 40 ° or less counterclockwise with respect to the azimuth of the pattern on the sub-pixel electrode 10B. When these angles are large, it is usually difficult to control the relationship between the cell gap d and the transmittance T in the pixel region corresponding to the pixel electrode 10 as shown by the curve 52 in FIG.
[0041]
In the present embodiment, the angle formed by the orientation of the pattern in the sub-pixel electrodes 10A and 10C with respect to the orientation of the pattern in the sub-pixel electrode 10B is determined by the pixel electrode 10 corresponding to the blue coloring layer 9a and the green coloring layer 9a. The pixel electrode 10 corresponding to 9b and the pixel electrode 10 corresponding to the red coloring layer 9c may be different from each other. Since blue, green, and red have different luminosity factors, the angle can be set in consideration of the difference.
[0042]
In the present embodiment, as described above, display is performed by forming the distribution of the intensity of the plane-wave electric field in the pixel region and controlling the optical characteristics of the liquid crystal layer 4 by changing the intensity. When such control is performed, a stronger electric field is formed in the portion on the comb portion 10-1 in the liquid crystal layer 4 than in the portion on the slit portion 10-2. Therefore, the liquid crystal molecules 25 are more greatly inclined in the portion on the comb portion 10-1 than in the portion on the slit portion 10-2. That is, the average tilt angle of the liquid crystal molecules 25 is different between the portion on the comb tooth portion 10-1 and the portion on the slit portion 10-2 of the liquid crystal layer 4. Such a difference in tilt angle can be observed as an optical difference.
[0043]
FIG. 5 is a diagram showing an example of the transmittance distribution observed when the structure shown in FIGS. 2A and 2B is adopted in the liquid crystal display device 1 shown in FIG. FIG. 5 shows a plane wave transmission observed in the sub-pixel region corresponding to the sub-pixel electrode 10B when a third voltage in the range of the first voltage or the second voltage is applied between the electrodes 10 and 16. The rate distribution is shown. As described above, according to the present embodiment, the features described with reference to FIGS. 1 to 3 can be observed as optical features.
[0044]
In the structure described with reference to FIGS. 2 and 3, the width of the comb teeth 10-1 and the slit 10-2 is fixed, but the width of the comb teeth 10-1 and the slit 10-2 is May be changed along the longitudinal direction.
[0045]
FIG. 6 is a plan view schematically showing another example of the pixel electrode structure that can be used in the liquid crystal display device 1 shown in FIG. FIG. 7 is a diagram schematically showing a change in alignment of liquid crystal molecules that occurs when the structure shown in FIG. 6 is employed in the liquid crystal display device 1 shown in FIG. In FIG. 6, only the conductive layer 10a among the four comb-shaped conductive layers 10a to 10d constituting the sub-pixel electrode 10b is illustrated. In FIG. 7, only a part of the conductive layer 10a illustrated in FIG. 6 is illustrated. Have been.
[0046]
In the structure shown in FIGS. 6 and 7, the width of the comb-tooth portion 10-1 continuously decreases from the center of the sub-pixel electrode 10 B toward the peripheral edge, and the width of the slit portion 10-2 is reduced to the width of the sub-pixel electrode 10 B. Continuously increases from the center to the periphery. According to such a structure, as shown in FIG. 7, in addition to the liquid crystal alignment at the upper end of the comb part 10-1 and the liquid crystal alignment at the lower end of the slit part 10-2, the comb part 10-1 and the slit part 10-1 The liquid crystal alignment on both side edges of 2 also acts so that the direction of the director is the direction shown by arrow 32. Therefore, according to the structures shown in FIGS. 6 and 7, the transmittance and the response speed can be further improved.
[0047]
In the above description, by configuring the pixel electrode 10 with the comb-shaped conductive layers 10a to 10d having the comb teeth 10-1 and the slits 10-2, the region where the electric field strength is weak is formed in each domain. An electric field distribution was generated in which regions having a strong electric field were alternately and periodically arranged. When the comb-shaped conductive layers 10a to 10d are used as described above, the design can be performed with a relatively high degree of freedom. However, such an electric field distribution can be created in other ways.
[0048]
For example, a dielectric layer may be provided in a pattern similar to that of the slit 10-2 on the pixel electrode 10 having a general shape in which the slit 10-2 is not provided. In this case, if the dielectric layer is made of a material having a lower dielectric constant than the liquid crystal material, such as an acrylic resin, an epoxy resin, or a novolak resin, the electric field strength is weaker above the dielectric layer. Regions can be formed. Therefore, the same effect as in the case where the slit portion 10-2 is provided can be obtained.
[0049]
Further, a wiring may be provided via a transparent insulator layer on the pixel electrode 10 having a general shape in which the slit portion 10-2 is not provided. This wiring is, for example, a signal line, a gate line, an auxiliary capacitance wiring, or the like, and is arranged in the same pattern as the slit section 10-2. According to such a structure, a region where the electric field strength is higher can be formed above the wiring. Therefore, also in this case, the same effect as when the slit portion 10-2 is formed can be obtained.
[0050]
When the liquid crystal display device 1 is of a transmission type, it is preferable that the above-mentioned materials of the dielectric layer and the wiring are transparent materials from the viewpoint of transmittance. In the case where the liquid crystal display device 1 is of a reflection type, an opaque material such as a metal material may be used as a material of the dielectric layer and the wiring in addition to a transparent material.
[0051]
In the embodiment described above, it is preferable sum W ₁₂ of the width W ₂ of the strength of the weaker region width W ₁ and the electric field strength of the electric field in the liquid crystal layer 4 is stronger regions are 20μm or less . Usually, if the sum W ₁₂ is 20μm or less, it is possible to control the orientation of liquid crystal molecules as described above, it is possible to achieve sufficient permeability. Also, the sum _{W 12} is preferably at 6μm or more. In general, if the sum W ₁₂ is 6 μm or more, a structure for generating a region where the electric field strength is stronger and a region where the electric field strength is weaker in the liquid crystal layer 4 can be formed with sufficiently high precision. In addition, the liquid crystal alignment described above can be stably generated.
[0052]
Incidentally, the sum W _12, the width and the sum of the width of the slit portion 10-2, the width and the dielectric layer in a region sandwiched between the dielectric layer on the pixel electrodes 10 of the comb-teeth portion 10-1 of the pixel electrode 10 , The sum of the width of the wiring provided on the pixel electrode 10 and the width of the region sandwiched between the wirings, and the width of the region with a larger tilt angle and the width of the smaller region when the third voltage is applied. The sum is almost equal to the sum of the width of a region having a higher transmittance and the width of a region having a lower transmittance when the third voltage is applied. Therefore, it is preferable that these widths are also 20 μm or less and 6 μm or more.
[0053]
In the present embodiment, the width _{W 1} and the width _{W 2,} respectively, is preferably 8μm or less. Further, it is preferable that each of the width W ₁ and the width W ₂ is 4 μm or more. In this range, practically sufficient performance can be expected in response speed and transmittance.
[0054]
Incidentally, the width W ₁ and the width W ₂ is the width of the width and the slit portion 10-2 of the comb-teeth portion 10-1 of the pixel electrode 10, the width of the region sandwiched between the dielectric layer on the pixel electrode 10 and the dielectric The width of the body layer, the width of the wiring provided on the pixel electrode 10 and the width of the region sandwiched between the wirings, the width of the region where the tilt angle is larger and the width of the region where the tilt angle is smaller when the third voltage is applied, and the width of the region where the tilt angle is smaller when the third voltage is applied It corresponds to the width of a region having a higher transmittance and the width of a region having a lower transmittance. Therefore, it is preferable that these widths are also 8 μm or less and 4 μm or more.
[0055]
In the present embodiment, the length of the weaker region length and intensity of the electric field stronger region the intensity of the electric field in the liquid crystal layer 4, respectively, may be longer than the width W ₁ and the width W ₂ it is preferred for the width W ₁₂ is the sum of them is more than twice. In this case, more liquid crystal molecules can be aligned in the length direction of those regions.
[0056]
In the above embodiment, both the region where the electric field strength is stronger and the region where the electric field strength is weaker in the liquid crystal layer 4 are asymmetric with respect to the vertical direction as shown in FIG. 3 (c), but are shown in FIG. 3 (a). Thus, it may be symmetrical with respect to the vertical direction. However, the former case is advantageous in terms of response speed and the like.
[0057]
In the present embodiment, the VAN mode in which nematic liquid crystal having a negative dielectric anisotropy is vertically aligned is employed. However, a nematic liquid crystal having a positive dielectric anisotropy may be used. In particular, when a high contrast is desired, adopting the VAN mode and using normally black enables a high contrast of, for example, 500: 1 or more and a bright screen design by a high transmittance design.
[0058]
In the present embodiment, in order to apparently speed up the optical response of the liquid crystal, the angle between the light transmission easy axis or light absorption axis of the polarizing film 5 and the arrangement direction of the strong and weak electric fields is set to a predetermined angle from 45 °. May be shifted by the angle θ. Can be set according to the viewing angle or the like, but it is most effective to set it to 22.5 ° in order to shorten the response time.
[0059]
In the present embodiment, the shapes of the comb-shaped conductive layers 10a to 10d constituting the pixel electrode 10 are not particularly limited, and may be, for example, rectangular or fan-shaped. Further, in the present embodiment, each of the pixel electrode 10 or the sub-pixel electrodes 10A to 10C is constituted by the four comb-shaped conductive layers 10a to 10d. However, the comb-shaped conductive layers constituting each of the pixel electrode or the sub-pixel electrodes 10A to 10C. Is not particularly limited as long as it is two or more.
[0060]
In the present embodiment, linearly polarized light is incident on the liquid crystal layer 4, but elliptically polarized light may be incident on the liquid crystal layer 4. Also in this case, the effect described with reference to FIG. 4 can be obtained.
[0061]
In the present embodiment, the structure for generating a region where the electric field strength is stronger and a region where the electric field strength is weaker in the liquid crystal layer when the third voltage is applied is provided only in the active matrix substrate 2. 3 may be provided. However, in the former case, when the active matrix substrate 2 and the counter substrate 3 are bonded to each other to form a cell, it is not necessary to perform high-precision alignment using an alignment mark or the like.
[0062]
Further, in the present embodiment, a structure in which the color filter layer 9 is provided on the active matrix substrate 2 (COA: color filter on array) is employed, but the color filter layer 9 may be provided on the counter substrate 3. However, in the former case, when the active matrix substrate 2 and the counter substrate 3 are bonded to each other to form a cell, it is not necessary to perform high-precision alignment using an alignment mark or the like.
[0063]
【Example】
Hereinafter, examples of the present invention will be described.
(Example)
The liquid crystal display device 1 shown in FIG. 1 was manufactured by the method described below. In this example, the structure shown in FIG. The angle formed by the longitudinal direction of the comb teeth 10-1 and the slit 10-2 of the sub-pixel electrode 10A with respect to the longitudinal direction of the comb teeth 10-1 and the slit 10-2 of the sub-pixel electrode 10B is +5. And the angle formed by the longitudinal direction of the comb teeth 10-1 and the slit 10-2 of the sub-pixel electrode 10C with respect to the longitudinal direction of the comb teeth 10-1 and the slit 10-2 of the sub-pixel electrode 10B is as follows. −5 °.
[0064]
First, film formation and patterning were repeated in the same manner as in a normal TFT forming process, and wirings such as scanning lines and signal lines and TFTs 8 were formed on the glass substrate 7. Next, a color filter layer 9 was formed on the surface of the glass substrate 7 on which the TFT 8 and the like were formed by a conventional method.
[0065]
Next, ITO was sputtered on the surface of the glass substrate 7 on which the transparent insulating film 9 was formed, through a mask having a predetermined pattern. Thereafter, a resist pattern was formed on the ITO film, and the exposed portion of the ITO film was etched using the resist pattern as a mask. As described above, the pixel electrode 10 was formed as shown in FIG. Here, the width of each of the comb teeth 10-1 and the width of each of the slits 10-2 was 5 μm.
[0066]
Thereafter, a thermosetting resin was applied to the entire surface of the glass substrate 7 on which the pixel electrodes 10 were formed, and the coating was baked to form a 70-nm-thick alignment film 11 having vertical alignment. As described above, the active matrix substrate 2 was manufactured.
[0067]
Next, an ITO film was formed as a common electrode 16 on one main surface of a separately prepared glass substrate 15 by a sputtering method. Subsequently, an alignment film 17 was formed on the entire surface of the common electrode 16 by the same method as described for the active matrix substrate 2. As described above, the opposing substrate 3 was manufactured.
[0068]
Next, the active matrix substrate 2 and the peripheral edge of the opposing surface of the opposing substrate 3 are set so that the surfaces on which the alignment films 11 and 17 are formed face each other, and an injection port for injecting a liquid crystal material is left. A liquid crystal cell was formed by bonding via an adhesive. The cell gap of the liquid crystal cell was kept constant by interposing a resin having a height of 4 μm as a spacer between the active matrix substrate 2 and the counter substrate 3. Further, when the substrates 2 and 3 were bonded, the substrates 2 and 3 were aligned by aligning their end faces, and high-accuracy alignment using alignment marks and the like was not performed.
[0069]
Next, a liquid crystal material having a negative dielectric anisotropy was injected into the empty liquid crystal cell by an ordinary method to form a liquid crystal layer 4. Thereafter, the liquid crystal injection port was sealed with an ultraviolet curable resin, and the polarizing films 5 were attached to both sides of the liquid crystal cell to obtain the liquid crystal display device 1 shown in FIG.
[0070]
Next, the liquid crystal display device 1 manufactured as described above was observed while a predetermined voltage was applied between the pixel electrode 10 and the common electrode 16. As a result, a transmittance distribution corresponding to the comb teeth 10-1 and the slits 10-2 of the pixel electrode 10 was observed.
[0071]
(Comparative Example 1)
FIG. 8 is a plan view schematically showing the structure employed in the liquid crystal display device according to Comparative Example 1. In this comparative example, the liquid crystal display device 1 shown in FIG. 1 was manufactured by the same method as that described in the above embodiment, except that the structure shown in FIG. That is, in the present comparative example, the directions of the sub-pixel electrodes 10A to 10C are the same.
[0072]
When the liquid crystal display device 1 was observed in a state where a predetermined voltage was applied between the pixel electrode 10 and the common electrode 16, the liquid crystal display device 1 corresponded to the comb portions 10-1 and the slit portions 10-2 of the pixel electrode 10. A transmittance distribution was observed.
[0073]
(Comparative Example 2)
FIG. 9 is a plan view schematically showing a structure employed in the liquid crystal display device according to Comparative Example 2. In this comparative example, the liquid crystal display device 1 shown in FIG. 1 was manufactured by the same method as that described in the above embodiment, except that the structure shown in FIG. 9 was employed for the pixel electrode 10. That is, in the present comparative example, the pixel electrode 10 was not constituted by the sub-pixel electrodes 10A to 10C, but was constituted by four comb-shaped conductive layers 10a to 10d.
[0074]
When the liquid crystal display device 1 was observed in a state where a predetermined voltage was applied between the pixel electrode 10 and the common electrode 16, the liquid crystal display device 1 corresponded to the comb portions 10-1 and the slit portions 10-2 of the pixel electrode 10. A transmittance distribution was observed.
Next, the transmittance and the response speed of the liquid crystal display devices 1 according to the example and the comparative examples 1 and 2 were measured. The results are shown in the table below.
[0075]
[Table 1]

[0076]
As shown in the above table, the liquid crystal display device 1 according to the example was superior to the liquid crystal display devices 1 according to comparative examples 1 and 2 in in-plane uniformity of transmittance. In each of the liquid crystal display devices 1 according to the example and the comparative examples 1 and 2, the boundary position between the domains could be generated as designed, and good alignment division uniformity could be realized.
[0077]
【The invention's effect】
As described above, according to the present invention, one pixel region is composed of a plurality of sub-pixel regions, and the tilt direction of liquid crystal molecules is slightly different between the sub-pixel regions, thereby responding to a change in the cell gap. In addition, the amount of change in the transmittance of each pixel region can be reduced. Therefore, according to the present invention, it is possible to improve the in-plane uniformity of the transmittance.
That is, according to the present invention, a liquid crystal display device having excellent in-plane uniformity of transmittance is provided.
[Brief description of the drawings]
FIG. 1 is a sectional view schematically showing a liquid crystal display device according to an embodiment of the present invention.
2A is a plan view schematically showing an example of a pixel electrode structure usable in the liquid crystal display device shown in FIG. 1, and FIG. 2B is an enlarged view of a part of the pixel electrode shown in FIG. FIG.
FIGS. 3A to 3D are diagrams schematically showing a change in alignment of liquid crystal molecules caused when the structure shown in FIGS. 2A and 2B is adopted in the liquid crystal display device shown in FIG. .
4 is a graph showing an example of a relationship between a cell gap and transmittance obtained when the structure shown in FIGS. 2A and 2B is adopted in the liquid crystal display device shown in FIG.
FIG. 5 is an image showing an example of a transmittance distribution observed when the structure shown in FIGS. 2A and 2B is adopted in the liquid crystal display device shown in FIG.
FIG. 6 is a plan view schematically showing another example of the pixel electrode structure that can be used in the liquid crystal display device shown in FIG.
FIG. 7 is a diagram schematically showing a change in alignment of liquid crystal molecules that occurs when the structure shown in FIG. 6 is employed in the liquid crystal display device shown in FIG.
FIG. 8 is a plan view schematically showing a structure employed in the liquid crystal display device according to Comparative Example 1.
FIG. 9 is a plan view schematically showing a structure employed in a liquid crystal display device according to Comparative Example 2.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Liquid crystal display device 2 ... Active matrix substrate 3 ... Opposite substrate 4 ... Liquid crystal layer 7 ... Transparent substrate 8 ... Switching element 9 ... Color filter layers 9a-9c ... Coloring layer 10 ... Pixel electrodes 10A-10C ... Sub-pixel electrodes 10a- 10d Comb-shaped conductive layer 10-1 Comb portion 10-2 Slit portion 11 Alignment film 15 Transparent substrate 16 Common electrode 17 Alignment film 25 Liquid crystal molecules 31, 32 Arrows

Claims (5)

First and second substrates facing each other, a pixel electrode provided on a surface of the first substrate facing the second substrate, and a common electrode provided on a surface of the second substrate facing the first substrate. An electrode, comprising a liquid crystal layer interposed between the pixel electrode and the common electrode,
When a voltage is applied between the pixel electrode and the common electrode, a plurality of sub-pixels adjacent in the in-plane direction to a pixel region of the liquid crystal layer that is a region sandwiched between the pixel electrode and the common electrode A liquid crystal display device that divides into a plurality of regions and forms a plurality of stripe-shaped regions adjacent in an in-plane direction in each sub-pixel region,
Each of the plurality of striped regions is configured by alternately and repeatedly arranging first and second band-shaped regions having different electric field strengths in an in-plane direction,
In each of the plurality of sub-pixel regions, a longitudinal direction of the first band-shaped region is different from at least two of the plurality of striped regions,
The shapes of the patterns formed by the different longitudinal directions are equal to each other among the plurality of sub-pixel regions,
The liquid crystal display device according to claim 1, wherein the orientation of the pattern is different between the plurality of sub-pixel regions. First and second substrates facing each other, a pixel electrode provided on a surface of the first substrate facing the second substrate, and a common electrode provided on a surface of the second substrate facing the first substrate. An electrode, comprising a liquid crystal layer interposed between the pixel electrode and the common electrode,
The pixel electrode includes a plurality of sub-pixel electrodes separated from each other and electrically connected to each other,
Each of the plurality of sub-pixel electrodes includes a plurality of comb-shaped conductive layers in which longitudinal directions of comb teeth are different from each other and are electrically connected to each other,
The shapes of the patterns formed by the different longitudinal directions are equal to each other between the plurality of sub-pixel electrodes,
The liquid crystal display device according to claim 1, wherein the orientation of the pattern is different between the plurality of sub-pixel electrodes. The liquid crystal layer further comprises a polarizing plate disposed to face at least one outer surface of the first and second substrates, and configured to make linearly polarized light or elliptically polarized light incident on the liquid crystal layer. The liquid crystal display device according to claim 1. 4. The liquid crystal display device according to claim 3, wherein the liquid crystal layer contains a liquid crystal material having a negative dielectric anisotropy. The liquid crystal display of claim 4, further comprising an alignment layer having a vertical alignment property on each of the pixel electrode and the common electrode.

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