JP2009025638A - Liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid crystal display device capable of displaying an image of excellent display quality by improving transmissivity. <P>SOLUTION: The liquid crystal display device has a liquid crystal display panel having a liquid crystal layer held between a first substrate and a second substrate, where the first substrate has, on an insulating substrate, scan lines Y extending in a row direction of respective pixels, signal lines Y extending in a column direction of respective pixels, switching elements W disposed by the pixels, pixel electrodes EP connected to the switching elements, and a counter electrode ET opposed to the pixel electrodes with an inter-layer insulating film interposed therebetween, and the pixel electrodes EP are formed in a comb-line shape. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a liquid crystal display device, and more particularly to a liquid crystal display device having a structure in which a pixel electrode and a counter electrode are provided on one substrate side constituting a liquid crystal display panel.

2. Description of the Related Art In recent years, flat display devices that replace CRT displays have been actively developed. Among them, liquid crystal display devices have attracted particular attention because of their advantages such as light weight, thinness, and low power consumption. In particular, in an active matrix liquid crystal display device in which a switching element is incorporated in each pixel, a structure using a lateral electric field (including a fringe electric field) such as an IPS (In-Plane Switching) mode or an FFS (Fringe field Switching) mode is used. Attention has been paid. (For example, see Patent Document 1 and Patent Document 2.)
This IPS mode or FFS mode liquid crystal display device includes a pixel electrode and a counter electrode formed on an array substrate, and switches liquid crystal molecules with a lateral electric field substantially parallel to the main surface of the array substrate. Further, polarizing plates are arranged on the outer surfaces of the array substrate and the counter substrate so that the deflection axis directions are orthogonal to each other. With such a polarizing plate arrangement, for example, a black screen is displayed when no voltage is applied, and a white screen is displayed by gradually increasing the transmittance (modulation factor) by applying a voltage corresponding to the video signal to the pixel electrode. To do. In such a liquid crystal display device, since the liquid crystal molecules rotate in a plane substantially parallel to the main surface of the substrate, the polarization state does not greatly affect the incident direction of transmitted light, so the viewing angle dependency is small and a wide field of view. There is a feature of having angular characteristics.
JP 2005-107535 A JP 2006-139295 A

  In particular, in an FFS mode liquid crystal display device, the pixel electrode is disposed so as to face the counter electrode with an interlayer insulating film interposed therebetween. Further, the pixel electrode is provided with a slit facing the counter electrode. With such a configuration, liquid crystal molecules are driven by an electric field formed between the pixel electrode and the counter electrode via the slit.

  In the pixel electrode having such a shape, the ratio L / S between the width L of the electrode portion and the width S of the slit between the electrode portions is 4.5 / 5, and the design based on this is made. However, in the vicinity of both ends of the slit, the direction of the electric field may not be uniform, and the alignment direction of the liquid crystal molecules driven by such an electric field is also not uniform. That is, when a voltage is applied (when a white screen is displayed), alignment defects (disclination) of liquid crystal molecules occur near both ends of the slit, and the transmittance at this portion is low, resulting in dark lines. Therefore, there is a problem that a sufficiently high luminance cannot be obtained when a white screen is displayed.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a liquid crystal display device capable of improving the transmittance and displaying an image with good display quality.

A liquid crystal display device according to an aspect of the present invention includes:
A liquid crystal display panel having a configuration in which a liquid crystal layer is held between a first substrate and a second substrate;
The first substrate is on an insulating substrate,
A scanning line extending in the row direction of each pixel;
A signal line extending in the column direction of each pixel;
Switching elements arranged for each pixel;
A pixel electrode connected to the switching element;
A counter electrode facing the pixel electrode through an interlayer insulating film,
The pixel electrode is formed in a comb shape.

  According to the present invention, it is possible to provide a liquid crystal display device capable of improving the transmittance and displaying an image with good display quality.

  A liquid crystal display device according to an embodiment of the present invention will be described below with reference to the drawings. Here, an FFS mode liquid crystal display device will be described as an example of a liquid crystal mode in which a pixel electrode and a counter electrode are provided on one substrate and liquid crystal molecules are switched using a lateral electric field formed therebetween.

  As shown in FIGS. 1 to 3, the liquid crystal display device is an active matrix type liquid crystal display device and includes a liquid crystal display panel LPN. The liquid crystal display panel LPN includes an array substrate (first substrate) AR, a counter substrate (second substrate) CT arranged opposite to the array substrate AR, and between the array substrate AR and the counter substrate CT. And a held liquid crystal layer LQ. Such a liquid crystal display device includes a display area DSP for displaying an image. The display area DSP is composed of a plurality of pixels PX arranged in an mxn matrix.

  The array substrate AR is formed using a light-transmissive insulating substrate such as a glass plate or a quartz plate. In other words, the array substrate AR includes m × n pixel electrodes EP arranged for each pixel and n scanning lines Y (Y1 to Yn) extending in the row direction H of each pixel PX in the display area DSP. ) M signal lines X (X1 to Xm) each extending in the column direction V of each pixel PX, and m × arranged in a region including the intersection of the scanning line Y and the signal line X in each pixel PX. There are provided n switching elements W, a counter electrode ET disposed opposite to the pixel electrode EP via the interlayer insulating film IL, and the like.

  The array substrate AR is further connected to at least a part of the scanning line driver YD connected to the n scanning lines Y and to the m signal lines X in the driving circuit area DCT around the display area DSP. And at least a part of the signal line driver XD. The scanning line driver YD sequentially supplies scanning signals (driving signals) to the n scanning lines Y based on control by the controller CNT. Further, the signal line driver XD supplies video signals (drive signals) to the m signal lines X at the timing when the switching elements W in each row are turned on by the scanning signal based on the control by the controller CNT. Thereby, the pixel electrode EP of each row is set to a pixel potential corresponding to the video signal supplied via the corresponding switching element W.

  Each switching element W is configured by, for example, a thin film transistor. The semiconductor layer SC of the switching element W can be formed of, for example, polysilicon or amorphous silicon. The gate electrode WG of the switching element W is connected to the scanning line Y (or formed integrally with the scanning line Y). The source electrode WS of the switching element W is connected to the signal line X (or formed integrally with the signal line X) and is in contact with the source region of the semiconductor layer SC. The drain electrode WD of the switching element W is connected to the pixel electrode EP (or formed integrally with the pixel electrode EP) and is in contact with the drain region of the semiconductor layer SC.

  For example, the counter electrode ET is arranged in an island shape in each pixel PX, and is electrically connected to a common wiring COM to which a common potential is supplied. The pixel electrode EP is disposed to face the counter electrode ET through the interlayer insulating film IL. The pixel electrode EP is provided with a plurality of slits SL facing the counter electrode ET. The pixel electrode EP and the counter electrode ET are formed of a light-transmitting conductive material such as indium tin oxide (ITO) or indium zinc oxide (IZO). The pixel electrodes EP corresponding to all the pixels PX are covered with the alignment film 20.

  On the other hand, the counter substrate CT is formed using an insulating substrate 30 having optical transparency such as a glass plate or a quartz plate. In particular, in a color display type liquid crystal display device, as shown in FIG. 3, the counter substrate CT has a black matrix 32 that partitions each pixel PX on the inner surface of the insulating substrate 30, that is, the surface facing the liquid crystal layer LQ. A color filter layer 34 disposed in each pixel surrounded by the black matrix 32 is provided. Further, the counter substrate CT further includes a shield electrode for reducing the influence of the external electric field, an overcoat layer disposed with a relatively thick film thickness so as to flatten the unevenness of the surface of the color filter layer 34, and the like. It may be provided.

  The black matrix 32 is arranged on the insulating substrate 30 so as to face wiring portions such as scanning lines Y and signal lines X provided on the array substrate AR. The color filter layer 34 is disposed on the insulating substrate 30 and is formed of colored resins that are respectively colored in a plurality of different colors, for example, three primary colors such as red, blue, and green. The red colored resin, the blue colored resin, and the green colored resin are disposed corresponding to the red pixel, the blue pixel, and the green pixel, respectively. The color filter layer 34 is covered with an alignment film 36.

  When the counter substrate CT and the array substrate AR as described above are arranged so that the alignment film 20 and the alignment film 36 face each other, a predetermined gap is formed by a spacer (not shown) arranged between the two. It is formed. The liquid crystal layer LQ is composed of a liquid crystal composition including liquid crystal molecules sealed in a gap formed between the alignment film 20 of the array substrate AR and the alignment film 36 of the counter substrate CT.

  The liquid crystal display device also includes a polarizing plate PL1 provided on one outer surface of the liquid crystal display panel LPN (that is, the outer surface opposite to the surface facing the liquid crystal layer LQ of the array substrate AR), and the liquid crystal display panel A polarizing plate PL2 is provided on the other outer surface of the LPN (that is, the outer surface opposite to the surface facing the liquid crystal layer LQ of the counter substrate CT).

  With such a configuration, the backlight light from the backlight unit arranged on the array substrate AR side with respect to the liquid crystal display panel LPN is selectively transmitted through the liquid crystal display panel LPN to display an image.

  In particular, in this embodiment, the pixel electrode EP is formed in a comb-teeth shape as shown in FIG. 2 and includes a plurality of comb-teeth electrodes CE. The comb-tooth electrode CE shown in FIG. 2 extends toward the signal line XA that supplies a video signal to the pixel electrode ET of the own pixel PX via the switching element W. In the pixel electrode EP having such a shape, a slit SL is formed between the comb electrodes CE.

  The effects of the configuration of the present embodiment will be described in comparison with a comparative example.

  FIG. 4 is a plan view schematically showing the structure of the pixel electrode and the counter electrode for one pixel in the comparative example. FIG. 5 is a plan view schematically showing the structure of the pixel electrode and the counter electrode for one pixel in the present embodiment.

  In any example, it is assumed that the liquid crystal molecules LM included in the liquid crystal layer LQ are aligned in parallel with the row direction H, for example, by the regulating force of the alignment film 20 and the alignment film 36. At this time, when a voltage is applied between the pixel electrode EP and the counter electrode ET, an electric field E is formed in a direction orthogonal to the edge SLE of the slit SL via the slit SL. The liquid crystal molecules LM are switched by such an electric field (that is, the liquid crystal molecules LM are driven so as to be aligned in a direction parallel to the electric field E).

  In the comparative example shown in FIG. 4, the pixel electrode EP is provided with a slit SL extending linearly. The slit SL is formed in an arc shape at both ends. For this reason, when a voltage is applied, the electric field E along the edge SLE at both ends of the slit SL is formed radially, and the alignment of the liquid crystal molecules LM switched by such an electric field is disturbed. For this reason, alignment failure occurs at both ends of the slit, and the transmittance is lowered.

  On the other hand, in the present embodiment shown in FIG. 5, the pixel electrode EP is formed in a comb shape. That is, in contrast to the comparative example, in the pixel electrode EP of the present embodiment, one of the connection portions of the pixel electrodes EP that do not contribute to transmission, that is, the peripheral portions at both ends of the slit SL, is on the extension line of the slit SL. It is open. Thereby, the area of the slit SL that contributes to the transmission can be increased while the area of the portion that becomes a dark line due to the alignment failure (that is, the transmittance is reduced) can be reduced. Therefore, it is possible to improve the transmittance of the liquid crystal display panel LPN when a voltage is applied, and an image with good display quality can be displayed.

  In addition, the pixel electrode EP includes a comb electrode CE that extends in an orientation that intersects the row direction H at an acute angle. That is, the edge SLE of the slit SL between the comb-tooth electrodes CE also intersects the row direction H at an acute angle. With such a configuration, it becomes possible to switch the liquid crystal molecules LM aligned substantially parallel to the row direction H in accordance with the electric field E orthogonal to the edge SLE.

  The pixel electrode EP is different from the first comb-tooth electrode CE1 extending in the first direction intersecting with the row direction H at an acute angle and the second direction intersecting with the row direction H at an acute angle. It is desirable to include the second comb electrode CE2 extending in the direction. That is, as shown in FIG. 5, it is desirable that the pixel electrode EP is configured to include a comb electrode extending in at least two directions intersecting at an acute angle with respect to the row direction H.

  As a result, the in-plane rotation direction (clockwise) of the liquid crystal molecules LM corresponding to the shape of the first comb electrode CE1 and the rotation direction (left rotation) of the liquid crystal molecules LM according to the shape of the second comb electrode CE2. Is a conflict. Therefore, it is possible to compensate for coloring depending on the viewing direction of the liquid crystal display panel LPN, and it is possible to obtain a good display quality in a wide viewing angle range.

  The pixel electrode EP preferably includes a plurality of substantially parallelogram-shaped comb electrodes CE, and slits SL having a substantially parallelogram shape are formed between the comb electrodes CE. That is, at least some of the comb-tooth electrodes CE are formed to have a substantially constant width, and the tip end portion CEP thereof has an edge that extends substantially parallel to the column direction V without being rounded. On the other hand, the slit SL is formed to have a substantially constant width, and the one end SLP has an edge extending substantially parallel to the column direction V without being rounded.

  Thereby, it is possible to suppress the occurrence of alignment failure due to the uneven electric field direction, and it is possible to suppress a decrease in transmittance.

  Further, as shown in FIG. 2, the pixel electrode EP is arranged closer to the signal line XA corresponding to the own pixel than the signal line XB corresponding to the adjacent pixel, and the tip of the comb-tooth electrode CE. The portion CEP may be configured to include a comb electrode CE that faces the signal line XA. That is, a part of the pixel electrode EP (the tip side of the comb electrode CE) may overlap with the signal line XA corresponding to the own pixel PX, but is arranged so as not to overlap with the adjacent signal line XB. ing. Such a gap between the pixel electrode EP and the adjacent signal line XB is shielded by the black matrix 32 on the counter substrate CT side.

  The pixel electrode EP and the signal line X are arranged in different layers. In the process of forming the pixel electrode EP, a positional shift may occur relative to the signal line X. At this time, if the design is such that the pixel electrode EP is arranged closer to the signal line XA, even if the signal line XA and the pixel electrode EP overlap with each other through the insulating layer due to the positional deviation, a part of the comb electrode CE ( Only the tip portion CEP) overlaps the signal line XA. For this reason, a sufficiently small capacitance is originally formed with respect to the pixel capacitance formed by the pixel electrode EP and the counter electrode ET, and the influence on the display can be minimized.

  As described above, according to the liquid crystal display device of this embodiment, it is possible to improve the transmittance and display an image with high display quality, particularly a high luminance image when displaying a white screen. Is possible.

  In addition, this invention is not limited to each said embodiment itself, In the stage of the implementation, a component can be deform | transformed and embodied in the range which does not deviate from the summary. Further, various inventions can be formed by appropriately combining a plurality of constituent elements disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, you may combine the component covering different embodiment suitably.

FIG. 1 is a diagram schematically showing a configuration of a liquid crystal mode liquid crystal display device using a lateral electric field according to an embodiment of the present invention. FIG. 2 is a plan view schematically showing the structure of the array substrate applied to the liquid crystal display device shown in FIG. FIG. 3 schematically shows a cross-sectional structure of the liquid crystal display panel when the array substrate shown in FIG. 2 is cut along the line III-III. FIG. 4 is a plan view schematically showing the structure of the pixel electrode and the counter electrode for one pixel in the comparative example. FIG. 5 is a plan view schematically showing the structure of the pixel electrode and the counter electrode for one pixel in the present embodiment.

Explanation of symbols

LPN ... Liquid crystal display panel AR ... Array substrate CT ... Counter substrate LQ ... Liquid crystal layer DSP ... Display area PX ... Pixel EP ... Pixel electrode ET ... Counter electrode COM ... Common wiring IL ... Interlayer insulating film SL ... Slit CE ... Comb electrode 30 ... Insulating substrate 32 ... Black matrix 34 ... Color filter layer

Claims (5)

A liquid crystal display panel having a configuration in which a liquid crystal layer is held between a first substrate and a second substrate;
The first substrate is on an insulating substrate,
A scanning line extending in the row direction of each pixel;
A signal line extending in the column direction of each pixel;
Switching elements arranged for each pixel;
A pixel electrode connected to the switching element;
A counter electrode facing the pixel electrode through an interlayer insulating film,
The liquid crystal display device, wherein the pixel electrode is formed in a comb shape.   2. The liquid crystal display device according to claim 1, wherein the pixel electrode includes a comb-like electrode extending in a direction intersecting at an acute angle with respect to a row direction.   3. The liquid crystal according to claim 2, wherein the pixel electrode includes a first comb electrode extending in a first direction and a second comb electrode extending in a second direction different from the first direction. Display device. The pixel electrode includes a plurality of comb electrodes having a substantially parallelogram shape,
2. The liquid crystal display device according to claim 1, wherein slits having a substantially parallelogram shape are formed between the comb electrodes.   The pixel electrode includes a comb-shaped electrode that is disposed closer to the signal line corresponding to the own pixel than the signal line corresponding to the adjacent pixel, and whose tip portion faces the signal line corresponding to the own pixel. The liquid crystal display device according to claim 1.

Images