JP4095872B2 - Liquid crystal display - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an active matrix type liquid crystal display device used as a small and medium-sized high-definition monitor such as a mobile phone and a car navigation, and more particularly, generation of a reverse tilt domain due to a horizontal electric field generated between adjacent pixel electrodes in line inversion driving. It relates to measures to suppress the problem.
[0002]
[Prior art]
In recent years, along with the daily development of information infrastructure, devices such as mobile phones, PDAs, digital cameras, video cameras, car navigation systems, etc. have been deeply penetrating into people's lives. It is well known that liquid crystal display devices are adopted in most of these devices. With this liquid crystal display device, as the amount of information handled by the device body increases, it is desired to be able to display more information with high quality, with higher brightness, higher contrast, more colors, Market demand for high definition is increasing day by day.
[0003]
One technique that meets these requirements is to increase the aperture ratio of a pixel. As an example, a technique described in Patent Document 1 is known. This is an active matrix type liquid crystal display device using TFT as a switching element. An insulating layer is used to connect a gate line (scanning wiring) and a source line (data wiring) connected to the gate electrode and the source electrode of the TFT, respectively. The pixel electrode overlaps each part of the gate line and the source line through this insulating layer, thereby reducing the interval between adjacent pixel electrodes and improving the aperture ratio.
[0004]
On the other hand, in the active matrix liquid crystal display device as described above, in general, when DC driving is performed, impurity ions are unevenly distributed in the alignment film on the liquid crystal layer or the electrode substrate to cause polarization of liquid crystal molecules, and voltage-transmittance characteristics. In order to prevent the so-called image sticking phenomenon of changing, the potential of the liquid crystal is always refreshed by AC driving. Further, when all fields are driven at the same potential, a minute change in light transmittance due to polarity inversion tends to appear as flicker. Therefore, line inversion driving in which the polarity is inverted for each line or every plurality of lines so as to cancel the flicker is generally used.
[0005]
14 is a horizontal view of pixel electrodes 11, 11,... Arranged on the TFT substrate 10 so as to be arranged in a matrix in the horizontal direction and the vertical direction of the display screen in a conventional liquid crystal display device using TFTs. An example of the state of the polarity at the time of line drive is shown typically. Here, the pixel electrodes 11, 11,... Arranged in the horizontal direction (generally the gate line direction) have the same polarity, and the pixel electrodes 11, 11,... Arranged in the vertical direction (generally the source line direction) The polarity is alternately inverted for each gate line. The liquid crystal layer is made of a homogeneous liquid crystal material (horizontal alignment liquid crystal material). In addition, an alignment film is formed on the surface of each TFT layer 10 and CF substrate 20 (color film substrate) on the liquid crystal layer side, and each alignment film is parallel to the source line as indicated by an arrow in the figure. In addition, rubbing treatment is performed in a direction that makes an angle of 180 ° with each other. As the line inversion drive, there is also a vertical line inversion drive in which the polarity is alternately inverted in the horizontal direction and the pixel electrodes having the same polarity are arranged in the vertical direction, contrary to the case shown in FIG.
[0006]
[Patent Document 1]
Japanese Patent Laid-Open No. 58-172585 (first page, FIG. 6-9)
[Patent Document 2]
JP 11-194342 A (page 5, FIG. 2, FIG. 4, FIG. 5)
[Patent Document 3]
Japanese Unexamined Patent Publication No. 6-11715 (first page, FIG. 1)
[0007]
[Problems to be solved by the invention]
By the way, when the line inversion driving as described above is performed, a potential difference of about twice the potential difference with respect to the counter electrode is generated between the adjacent pixel electrodes 11 and 11 having different polarities. A strong lateral electric field is generated between the pixel electrodes 11 and 11. At this time, the conventional liquid crystal display device has a problem that a domain arranged in a direction different from the original alignment of liquid crystal molecules is generated under the influence of the lateral electric field.
[0008]
Hereinafter, the generation mechanism of such a domain will be described in detail with reference to FIG. FIG. 2 is an enlarged cross-sectional view showing a portion between adjacent pixel electrodes 11 and 11 that are adjacent to each other in the source line direction of a liquid crystal panel and have different polarities in a conventional liquid crystal display device. In the following description, “left”, “right”, “upper”, and “lower” in the figure are simply “left”, “right”, “upper”, and “lower”, respectively. Here, the polarity of the right pixel electrode 11, the polarity (potential) of the counter electrode 21, and the polarity of the left pixel electrode 11 are “+”, “0”, and “−”, respectively.
[0009]
When no voltage is applied, the liquid crystal molecules 31 extend in the left-right direction and are arranged in an inclined state with the right end side being slightly displaced upward. When a driving voltage is applied thereto, a potential line as indicated by an arrow is generated between the three electrodes 11, 11, and 21, and accordingly, each liquid crystal molecule 31 has a molecular long axis as a potential line. Try to align. At that time, the liquid crystal molecules 31 in the region not affected by the potential line of the horizontal electric field on each pixel electrode 11 and the liquid crystal molecules 31 on the right end of the left pixel electrode 11 are in a state regulated by the pretilt. Stand up as it is. On the other hand, the liquid crystal molecules 31 on the left end in the right pixel electrode 11 stand up in a state where the left end is displaced upward, contrary to the pretilt restriction. This is the reverse tilt domain.
[0010]
At the boundary between the reverse tilt domain and the normal alignment portion, the alignment of the liquid crystal molecules 31, 31,... Becomes discontinuous. Further, in the reverse tilt domain, the viewing angle characteristics are different from the original orientation, so that the image quality when the screen is viewed obliquely is impaired.
[0011]
In particular, in a high-definition liquid crystal display device, since the distance between adjacent pixels is short, the lateral electric field is strong and a large number of domains are generated, and since the pixels are fine, the ratio of the domain area to the pixel area is high. As a result, display quality is greatly impaired.
[0012]
As a countermeasure against such a domain, for example, as described in Patent Document 2, a rubbing process for each alignment film of a TFT substrate and a CF substrate is performed approximately parallel to a potential line of a lateral electric field and approximately 180 mutually. Adopting a technology that reduces the amount of domains by adopting an ECB mode (birefringence control mode) using a vertically aligned liquid crystal material as the liquid crystal material of the liquid crystal layer when applied in the direction of an angle of °. However, in this case, since the vertically aligned liquid crystal material has a high viscosity, productivity is impaired, the response speed is slow, and the selection range of the material is narrow. There is another problem that blends of properties are difficult to formulate and it is difficult to achieve high color reproducibility.
[0013]
Further, in the liquid crystal display device in which the gate line or the source line is arranged in the same layer as the pixel electrode, the fourth line is provided between the adjacent pixel electrodes separately from the main lines of the gate line, the source line, and the auxiliary capacitance line. There is also one (Patent Document 3) in which the wiring portion is arranged to induce a potential.
[0014]
The present invention has been made in view of such various points, and its main object is to provide an active matrix type liquid crystal display device in which gate lines or source lines are arranged under a pixel electrode and driven to invert lines. In order to prevent the occurrence of reverse tilt domains due to a strong lateral electric field generated between adjacent pixel electrodes, a homogeneous liquid crystal material is employed by modifying the alignment process.
[0015]
[Means for Solving the Problems]
In order to achieve the above object, in the present invention, the horizontal line inversion drive in the horizontal alignment ECB mode is in the horizontal direction (gate line direction), and the vertical line inversion drive is in the vertical direction (source line direction). Each was subjected to an orientation treatment.
[0016]
Specifically, in the invention of claim 1, a pair of electrode substrates and a liquid crystal layer disposed between the pair of electrode substrates and made of a homogeneous liquid crystal material are provided. A plurality of scanning wirings and a plurality of data wirings provided so as to cross each other, at least an insulating layer provided on the plurality of scanning wirings, and each intersection between the plurality of scanning wirings and the plurality of data wirings Each switching element is provided so as to overlap with at least a part of the scanning wiring located in the vicinity of the intersection via the insulating layer, and performs switching operation based on the signal of the scanning wiring passing through the intersection And the pixel electrodes connected to the data lines passing through the intersection, and the pixels on the same scanning line have the same polarity and the pixels on the same data line. It assumes a liquid crystal display apparatus that perform line inversion driving which inverts alternately the polarity of the poles in every predetermined number of scanning lines.
[0017]
In addition, at each interface between the pair of electrode substrates and the liquid crystal layer, the alignment direction of the liquid crystal molecules in the liquid crystal layer in the vicinity of the interface is restricted to a direction that is substantially parallel to the scanning wiring and forms an angle of approximately 180 ° with each other. It is assumed that the orientation treatment is performed.
[0018]
In the above configuration, the liquid crystal molecules in the liquid crystal layer are aligned in a state where they are parallel to the scanning wiring and rise from one end side in the major axis direction (front end side in the alignment direction) by the alignment treatment when no voltage is applied.
[0019]
When a driving voltage is applied to this, a potential line is generated between the counter electrode and the pixel electrode, and a strong lateral electric field is generated between adjacent pixel electrodes on the same data wiring (in the case of 1-line inversion driving). appear.
[0020]
At this time, since the liquid crystal molecules on each pixel electrode are oriented in the scanning wiring direction, which is substantially perpendicular to the direction of the potential line of the horizontal electric field (data wiring direction), the potential line between the pixel electrode and the counter electrode Thus, the orientation is continuously changed in the horizontal direction (direction parallel to the substrate) by the potential line of the horizontal electric field while standing up in a state regulated by the pretilt. Therefore, the situation in which the liquid crystal molecules rise from the end side (alignment direction rear end side) opposite to the pretilt regulation is avoided, so that the reverse tilt domain on the end of the pixel electrode on the adjacent pixel electrode side is avoided. Occurrence will be suppressed.
[0021]
The above-described operation is also performed in the case of multiple line inversion in which the polarity of the pixel electrode on the same data wiring is inverted every predetermined number of scanning wirings, such as 2-line inversion and 3-line inversion. In other words, in a plurality of pixel electrodes arranged on the same data wiring, the polarity inversion of adjacent pixel electrodes occurs every two lines or three lines, and the alignment is disturbed by the horizontal electric field between the pixel electrodes having different polarities. Is greatly improved by adopting an ECB mode in which the alignment of the liquid crystal is parallel to the line (in the case of the present invention, the scanning wiring).
[0022]
In a second aspect of the present invention, the apparatus includes a pair of electrode substrates and a liquid crystal layer disposed between the pair of electrode substrates and made of a homogeneous liquid crystal material, and the one electrode substrate intersects with each other. A plurality of scanning wirings and a plurality of data wirings provided, an insulating layer provided on at least the plurality of data wirings, and each intersection between the plurality of scanning wirings and the plurality of data wirings, The intersection is provided via a switching element that is provided so as to overlap with at least a part of the data wiring located in the vicinity of the intersection via the insulating layer and performs switching operation based on a signal of a scanning wiring passing through the intersection. Each pixel electrode on the same data line is equal to each other, and each pixel electrode on the same scan line has the same polarity. There has been the premise of the liquid crystal display device to perform the line inversion driving which inverts alternately every predetermined number of data lines.
[0023]
Then, at each interface between the pair of electrode substrates and the liquid crystal layer, the alignment direction of the liquid crystal molecules in the liquid crystal layer in the vicinity of the interface is regulated to be substantially parallel to the data wiring and at an angle of approximately 180 ° to each other. It is assumed that the orientation treatment is performed.
[0024]
That is, according to the present invention, “scanning wiring” and “data wiring” in claim 1 are replaced with “data wiring” and “scanning wiring”, respectively.
[0025]
In a third aspect of the invention, in the first and second aspects of the invention, the liquid crystal layer has a plurality of domains provided in the same pixel so as to extend between adjacent pixels across the scanning wiring and the data wiring. In addition, the alignment process for each electrode substrate is performed so that the regulation direction of the alignment process forms an angle of approximately 180 ° between adjacent domains.
[0026]
That is, according to the first and second aspects of the invention, as in the present invention, the liquid crystal cell is a multi-domain cell obtained by dividing the liquid crystal cell into a plurality of alignment regions, and the alignment division lines are the scanning wiring and the data wiring. Even if it doesn't overlap, it is run in the same way. Also in this case, it is assumed that the orientation of each region is an ECB mode parallel to the wiring (scanning wiring when claim 1 is cited, and data wiring when claim 2 is cited).
[0027]
According to a fourth aspect of the present invention, in the first to third aspects of the present invention, the pixel corresponding portions of both electrode substrates are provided transparently. In other words, in this case, the liquid crystal display device arranges a surface light source on one side of the liquid crystal panel and directly views it from the opposite side, and projects the transmitted light of the liquid crystal panel on a screen or the like to view the projected image. It is used as a system, a system in which a reflection plate is arranged on one side of a liquid crystal panel, and reflection of external light is viewed from the opposite side.
[0028]
According to a fifth aspect of the present invention, in the first to third aspects of the invention, the pixel corresponding portion of one electrode substrate is transparent, and at least a part of the pixel corresponding portion of the electrode on the other electrode substrate is made of a light reflector. Shall be. That is, in this case, the liquid crystal display device is a reflection type that does not require a reflection plate outside the liquid crystal panel, or a transflective type that includes a transmission region and a reflection region in a pixel.
[0029]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0030]
(Embodiment 1)
2 and 3 schematically show the longitudinal sectional configuration of the main part of the liquid crystal panel of the transmissive liquid crystal display device according to Embodiment 1 of the present invention. The liquid crystal display device is arranged on one side of the liquid crystal panel. A surface light source is arranged and the liquid crystal panel is viewed directly from the opposite side of the surface light source, or the light transmitted through the liquid crystal panel is projected onto a screen and the projected image is viewed. In other words, a reflection plate is disposed on one side of the liquid crystal panel, and reflection of external light is viewed from the side opposite to the reflection plate. In the following description, “left”, “right”, “upper”, and “lower” in the figures are simply “left”, “right”, “upper”, and “lower”, respectively.
[0031]
The liquid crystal panel includes a TFT substrate 100 as an electrode substrate having a transparent pixel electrode 101 and a TFT 102 provided for each pixel, and a transparent counter electrode 201, and has a predetermined gap (with respect to the TFT substrate 100 ( For example, a CF substrate 200 (color filter substrate) as an electrode substrate bonded in parallel so as to form 3.7 μm) and a homogeneous liquid crystal material (for example, birefringence Δn is Δn = 0.094, Merck) And a liquid crystal layer 300 arranged in a gap between the TFT substrate 100 and the CF substrate 200.
[0032]
The TFT substrate 100 has a transparent glass substrate 103 (substrate size is, for example, 9.398 cm [= 3.7 inch]), and the CF substrate 200 side of this glass substrate 103 (upper side in FIGS. 2 and 3). 4, as shown in FIG. 4, gate lines 104, 104,... As scanning lines extending in the horizontal direction of the display screen (left-right direction in FIG. 4), respectively, and vertical to the display screen, respectively. A plurality of source lines 105, 105,... As data wirings extending in the direction (vertical direction in the figure) are arranged. The TFTs 102, 102,... Are arranged in the vicinity of the intersections of the gate lines 104, 104,... And the source lines 105, 105,. A source electrode 107 connected to the corresponding source line 105 and a drain electrode 108 connected to the corresponding pixel electrode 101 are provided. At that time, between the gate electrode 106 and the source electrode 107 and the drain electrode 108, a transparent gate insulating film 109 insulates the gate lines 104, 104,... And the source lines 105, 105,. Is provided. Further, a transparent insulating layer 110 is provided on the gate lines 104, 104,..., The source lines 105, 105,.
[0033]
The pixel electrodes 101, 101,... Are arranged on the insulating layer 110 and are connected to the drain electrode 108 of the TFT 102 by a contact hole plug provided so as to penetrate the insulating layer 110 in the substrate normal direction. ing. Further, since the gate lines 104, 104,... And the source lines 105, 105,... Are covered with the insulating layer 110, each pixel electrode 101 includes the gate lines 104, 104 and the sources positioned around the pixel electrode 101. It is provided so as to overlap a part of each of the lines 105 and 105 (see FIG. 2). With this, the distance between the pixel electrodes 101 and 101 adjacent to each other in the gate line direction and the source line direction is set to the gate. It is made smaller than each wiring width of the line 104 and the source line 105. 2 and 3, only two pixel electrodes 101 are shown for simplicity, but in an actual display, several tens to thousands of pixel electrodes 101, 101,... Are arranged in a matrix. Yes. An alignment film that is rubbed in a predetermined direction on the pixel electrodes 101, 101,... And the insulating layer 110 in order to regulate the alignment direction of liquid crystal molecules in the vicinity of the interface with the liquid crystal layer 300 of the TFT substrate 100. 111 (for example, polyimide) is provided.
[0034]
On the other hand, the CF substrate 200 also has a transparent glass substrate 202 similar to the case of the TFT substrate 100, and the counter electrode 201 is on the TFT substrate 100 side of the glass substrate 202 (lower side of FIGS. 2 and 3). Is arranged. A color filter layer (not shown) is provided on the counter electrode 201, and the alignment direction of liquid crystal molecules in the vicinity of the interface with the liquid crystal layer 300 of the CF substrate 200 is regulated on the color filter layer. An alignment film 203 (for example, polyimide-based) that is rubbed in a predetermined direction is provided.
[0035]
Further, although not shown, on the side of the glass substrate 202 of the CF substrate 200 opposite to the TFT substrate 100 (the upper side of the glass substrate 202), the rubbing process is performed in the alignment film 203 on the CF substrate 200 side. On the other hand, a uniaxial retardation film having a slow axis of 70 nm is disposed in the orthogonal direction, and on this uniaxial retardation film, the polarizing plate has an angle of 45 ° between the absorption axis and the rubbing treatment direction. It is arranged to make. A polarizing plate is disposed on the side of the glass substrate 103 of the TFT substrate 100 opposite to the CF substrate 200 (below the glass substrate 103) so that the absorption axis thereof is orthogonal to the absorption axis of the polarizing plate. Yes.
[0036]
Further, as shown in the plan view of FIG. 4, the present liquid crystal display device is connected to the gate lines 104, 104,... And the source lines 105, 105,. A driver circuit (not shown) that performs line inversion driving so as to invert the polarities of the pixel electrodes 101 on the same source line 105 for each line of the gate line is provided.
[0037]
In the present embodiment, as indicated by arrows in the perspective view of FIG. 1, the rubbing process for the alignment film 111 on the TFT substrate 100 side and the rubbing process for the alignment film 203 on the CF substrate 200 side are the gate line 104, Are parallel to each other and at an angle of 180 ° to each other, whereby the alignment direction of the liquid crystal molecules in the liquid crystal layer in the vicinity of the interface with the liquid crystal layer 300 of the TFT substrate 100 and the CF substrate 200 are arranged. The orientation direction of the liquid crystal molecules in the liquid crystal layer in the vicinity of the interface with the liquid crystal layer 300 is regulated to a direction parallel to the gate lines 104, 104,.
[0038]
Next, a manufacturing method of the liquid crystal display device configured as described above will be described. First, TFTs 102, 102, ..., gate lines 104, 104, ..., source lines 105, 105, ... are formed on the glass substrate 103 by known means. After forming an insulating layer 110 of acrylic resin on them, the insulating layer 110 on the drain electrode 108 of each TFT 102 is partially removed, and each pixel electrode 101 is formed so as to be in contact with the corresponding drain electrode 108. To do. Thereafter, a polyimide material is applied to form an alignment film 111, and the alignment film 111 is rubbed with a rayon cloth in a direction parallel to the source lines 105, 105,.
[0039]
On the other hand, for the CF substrate 200, the counter electrode 201 is formed on the glass substrate 202, and a polyimide material is applied thereon to form the alignment film 203. Then, the rubbing process is performed in the same manner as in the case of the TFT substrate 100 so that the rubbing directions after bonding are antiparallel to the TFT substrate 100.
[0040]
Next, the alignment film 111 of the TFT substrate 100 and the alignment film 203 of the CF substrate 200 are opposed to each other, the TFT substrate 100 and the CF substrate 200 are bonded together, and a liquid crystal material is injected therein. Thereafter, on the surface of the CF substrate 200 opposite to the TFT substrate 100, a uniaxial retardation film is disposed in a state where the slow axis is perpendicular to the rubbing direction, and a polarizing plate is disposed on the uniaxial retardation film. It arrange | positions in the state which makes an angle of 45 degrees with a rubbing direction. Further, another polarizing plate is disposed on the surface of the TFT substrate 100 opposite to the CF substrate 200 so that the absorption axis thereof is orthogonal to the absorption axis of the polarizing plate on the CF substrate 100 side.
[0041]
In the liquid crystal display panel thus completed, the gate lines 104, 104,... And the source lines 105, 105, so that the polarities of the pixel electrodes 101, 101,. Install the driver circuit that drives. As described above, the liquid crystal display device according to the present embodiment is obtained.
[0042]
Here, the operation of the liquid crystal display device configured as described above will be described. The liquid crystal molecules of the liquid crystal layer 300 have a positive dielectric anisotropy in the molecular major axis direction. Therefore, when no voltage is applied, the liquid crystal layer 300 is parallel to the gate lines 104, 140,. Arrange the rubbing direction side) slightly up.
[0043]
When a driving voltage is applied thereto, a potential line is generated between the counter electrode 201 and each pixel electrode 101, and the liquid crystal molecules of the liquid crystal layer 300 are basically opposed to the pixel electrode 101. The arrangement direction is continuously changed in the direction perpendicular to the substrates 100 and 200 in accordance with the potential difference with the electrode 201, thereby changing the phase of the light transmitted through the liquid crystal layer 300 and using it together with the polarizing plate. As a result, the amount of transmitted light is modulated, and as a result, an image is displayed. At that time, since the polarities are different between the pixel electrodes 101 adjacent to each other in the source line direction, a strong lateral electric field is generated.
[0044]
At this time, the liquid crystal molecules on each pixel electrode 101 are aligned in the gate line direction, which is a direction substantially orthogonal to the direction of the potential line of the horizontal electric field. , 200 in a direction parallel to 200), and the vertical direction (direction perpendicular to the substrates 100, 200) of rising in the direction opposite to the direction regulated by the pretilt does not occur. Therefore, the occurrence of a reverse tilt domain on the end portion on the pixel electrode 101 side adjacent to each pixel electrode 101 in the gate line direction is suppressed.
[0045]
Therefore, according to the present embodiment, in an active matrix transmissive liquid crystal display device that is driven by 1H line inversion, a horizontal alignment liquid crystal material is used instead of a vertical alignment ECB mode that uses a vertical alignment liquid crystal material. The alignment ECB mode is adopted, and the rubbing process for the alignment film 111 of the TFT substrate 100 and the alignment film 203 of the CF substrate 200 is performed in a direction parallel to the gate lines 104, 104,. As a result, the generation of a domain due to a horizontal electric field between the pixel electrodes 101 and 101 adjacent to each other in the source line direction is suppressed without causing a reduction in transfer productivity as in the case of using a vertically aligned liquid crystal material. The contrast of the screen can be improved and information such as images can be displayed with high quality.
[0046]
In the above embodiment, the alignment films 111 and 203 are provided, and the alignment films 111 and 203 are rubbed to perform the alignment process on the liquid crystal layer side surfaces of the TFT substrate 100 and the CF substrate 200. However, as the alignment treatment of the present invention, known techniques can be appropriately employed.
[0047]
In the above embodiment, the case where the liquid crystal layer 300 has a single domain has been described. However, as shown in the cross-sectional view of FIG. 5, each liquid crystal cell includes alignment dividing lines 400, 400,. Thus, even in the case of a multi-domain cell divided into a plurality of alignment regions, the alignment division lines 400, 400,... Are patterns that do not overlap the gate lines 104, 104,. As long as the effect is the same.
[0048]
Here, as an example of the case of the multi-domain cell, three modified examples 1 to 3 are shown in plan views of FIGS. 6A to 6C, respectively. In each of the figures, the domains are shown divided by a two-dot chain line, and the rubbing direction in each modified example is the upward direction in the dotted domain, and the lower direction in the white domain. is there. In Modification 1 of FIG. 6A, each liquid crystal cell has two domains that are divided into two in the vertical direction at the center in the vertical direction of the display screen. In Modification 2 of FIG. 6B, each liquid crystal cell has two domains that are divided in the horizontal direction at the center in the horizontal direction. In Modification 3 of FIG. 6C, each liquid crystal cell has two domains that are divided into two in the direction of a straight line that passes through the other diagonal in a straight line portion that passes through the diagonal of the pixel.
[0049]
In the above embodiment, the case of one horizontal line inversion drive is described. However, the present invention can also be applied to the case of multiple line inversion drive such as two lines or three lines. The present invention can also be applied to vertical line inversion driving. However, in the case of vertical line inversion driving, a potential line with a strong lateral electric field is generated not in the source line direction but in the gate line direction, so the rubbing direction is not the gate lines 104, 104,. 105,...
[0050]
In the above embodiment, the case where the gate lines 104, 104,... And the source lines 105, 105,... Are all disposed below the pixel electrodes 101, 101,. However, in the present invention, only the gate lines 104, 104,... Are arranged below the pixel electrodes 101, 101,..., Or only the source lines 105, 105,. The present invention can also be applied to a case where it is arranged in a lower layer of 101, 101,.
[0051]
In the above embodiment, the case of a transmissive liquid crystal display device has been described. However, one of the pixel electrodes 101, 101,... It is also possible to use it as a reflection type liquid crystal display device that allows viewing light traveling back and forth. In this case, it goes without saying that an electrode that is not a light reflector and its electrode substrate are made transparent and the display device is viewed from the transparent electrode substrate side.
[0052]
-Orientation simulation test-
An alignment simulation test performed using the liquid crystal alignment simulation software “DIMOS” (manufactured by autronic-Melchers) on the liquid crystal cell model having the above configuration will be described.
[0053]
Here, the thickness of the liquid crystal layer was set to 3.5 μm, and the interval between the pixel electrodes was set to 5 μm. As for the parameters related to the liquid crystal layer, the data of “ZLI-4792 (without chiral material)” (manufactured by Merck), which is a liquid crystal material, is used, the pretilt angle is 2 °, and the anchoring of the interface between the liquid crystal and the electrode is performed. Is a strong anchoring, and this is an invention example.
[0054]
As a first test, when the drive voltage is changed in the range of 1.5 V (white display) to 4.5 V (black display), the potential of the counter electrode is set to 0 V, while each of the two adjacent pixel electrodes is When the potentials were -4.5 V and 4.5 V, respectively, that is, the change in orientation when the strongest transverse electric field was generated was simulated. The result is shown in FIG. 7A which is a cross-sectional view in a plane orthogonal to the gate line direction.
[0055]
In addition, a polarizing plate is disposed on the TFT substrate side so that its absorption axis forms an angle of 45 ° with the liquid crystal alignment direction, and another polarizing plate is disposed on the CF substrate side, the absorption axis of which is absorbed by the polarizing plate. It was arranged so as to be orthogonal to the axis, and the light transmittance [unit:%] on the front surface at each position in the source line direction was calculated. The result is shown in the characteristic diagram of FIG.
[0056]
The horizontal axis of FIG. 7B corresponds to each position in the source line direction of FIG. 7A, one scale is 1 μm, and the maximum light transmittance is 50%. In addition, since the liquid crystal layer has residual retardation even after voltage application, the light transmittance at the time of black display is not 0% in the above polarizing plate configuration (in the actual cell configuration, it remains using a retardation compensation plate). Here, the retardation is canceled out), but since the calculation is performed with the polarizing plate configuration as it is, the value of the light transmittance is only a reference level.
[0057]
On the other hand, for comparison, in the inventive example, the rubbing direction is changed to a direction parallel to the source line, and the liquid crystal cell model, which is the same as the inventive example in other points, is used as a comparative example. The orientation change was simulated under the same conditions as in the inventive example. The state of the liquid crystal molecules after the orientation change and the front light transmittance at each position in the source line direction are shown in FIG. 8A corresponding to FIG. 7A and FIG. ) And FIG.
[0058]
In the case of the inventive example, as can be seen from FIG. 7B, no portion causing light leakage occurred on the pixel electrode. This is because liquid crystal molecules continuously change their orientation in the transverse direction by a transverse electric field, and therefore light leakage due to orientation discontinuity at the domain boundary does not occur. Note that light leakage between the pixels is shielded by the source line, so that there is actually almost no light leakage.
[0059]
On the other hand, in the case of the comparative example, as can be seen from FIG. 8A, in the portion 401 on the left end of the right pixel electrode, liquid crystal molecules rise to the upper left due to the influence of the lateral electric field. A light leakage state in which the orientation was discontinuous occurred at the boundary with the portion 402 rising to the upper right on the central portion of. In FIG. 5B, there is light leakage in the circled area from the left end of the right pixel electrode to the center side of 3 to 5 μm, resulting in an increase in black luminance and a decrease in contrast. Yes.
[0060]
In order to block the above light leakage, it is necessary to make the wiring width of the gate line located between the two pixels lower than necessary or to dispose a black matrix (BM) for light blocking on the CF substrate side. In any case, since the aperture ratio is greatly reduced, the brightness and contrast of the entire liquid crystal display device are reduced.
[0061]
As a second test, an alignment simulation performed for testing an alignment change between two pixel electrodes of the same polarity adjacent in the source line direction in the example of the invention will be described.
[0062]
First, a simulation of the orientation change when the potential of the pixel electrode on the rubbing direction side is 4.5 V (black display) and the potential of the pixel electrode on the anti-rubbing direction side is 1.5 V (white display). went. This is a test for the case where the lateral electric field becomes the largest between the pixel electrodes adjacent in the source line direction. The result is shown in FIG. 9A, which is a cross-sectional view in a plane orthogonal to the gate line direction. Also, the light transmittance of the front at each position in the gate line direction is shown in FIG.
[0063]
In this case, as can be seen from FIG. 9 (b), on the right side (rubbing direction side) of the pixel electrode, a light omission part is observed in the range from the left end to the pixel electrode central side 1 to 4 μm. It was done. However, since this portion corresponds to a black-and-white boundary portion, the light omission is visually absorbed by the white display, and thus it is considered that the display is hardly affected.
[0064]
Next, an orientation change simulation was performed when the potentials of the two pixel electrodes were both 4.5 V (black display). This is to test the case where a black display where light leakage is most noticeable is performed. The results are shown in FIG. 10 (a) and FIG. 10 (b) corresponding to FIG. 9 (a) and FIG. 9 (b), respectively.
[0065]
There was no reverse tilt in the alignment of the liquid crystal, the alignment state was continuous, and no light leakage occurred due to the domain boundary. Further, in the characteristic diagram of FIG. 10B, although some waviness of the light transmittance is observed in the portion between the two pixel electrodes, the generated portion is compared with the comparative example of FIG. 8B. Both change width and brightness are much smaller. Furthermore, since this portion is shielded by the gate line under the pixel boundary, it is assumed that the actual light leakage is very small. .
[0066]
From the above alignment simulation test, it can be seen that the invention example can expect a decrease in black luminance and an increase in contrast due to the decrease in black luminance, as compared with the conventional example.
[0067]
(Embodiment 2)
FIG. 11 schematically shows a vertical cross-sectional configuration of the main part of the liquid crystal panel of the transflective liquid crystal display device according to the second embodiment of the present invention. The same reference numerals are given to the same components as those in the first embodiment. It is attached.
[0068]
In this embodiment, each pixel is divided into a transmissive region and a reflective region, and accordingly, each pixel electrode 101 is composed of a rectangular transparent electrode 101a made of a transparent material and a light reflecting material. The reflective electrode 101b is formed so as to surround the transparent electrode 101a.
[0069]
The portion of each transmissive region in the insulating layer 110 on the gate insulating film 109 is omitted, and each transparent electrode 101 a is directly disposed on the gate insulating film 109. On the other hand, the reflective electrode 101b is disposed on the insulating layer 110, and is connected to the drain electrode 108 of the TFT 102 through a contact hole plug that penetrates the insulating layer 110 in the normal direction of the substrate. That is, a step is formed at the boundary portion between the transmissive electrode 101a and the reflective electrode 101b.
[0070]
By the way, in order to match the optical path lengths of the reflection mode and the transmission mode with each other, it is effective to make the thickness of the liquid crystal layer 300 in the transmission region larger than the thickness of the liquid crystal layer 300 in the reflection region. Most preferably, the thickness of the layer 300 is twice the thickness of the liquid crystal layer 300 in the reflective region. Therefore, for example, when the gap between the TFT substrate 100 and the CF substrate 200 in the reflection region is 2.5 μm, the thickness of the insulating layer 110 is also set to 2.5 μm, and the gap in the transmission region is set to 2 of the gap in the reflection region. Double (5.0 μm).
[0071]
The liquid crystal layer 300 is made of a liquid crystal material having a dielectric anisotropy Δn of Δn = 0.065 nm (without a chiral agent), for example. When aligning the liquid crystal on a surface having a step as described above, if the liquid crystal is twisted, disclination is likely to occur at the stepped portion that becomes the boundary between the two regions. Accordingly, horizontal alignment with a twist angle of 0 ° is most preferable.
[0072]
Further, although not shown, a uniaxial retardation film having a slow axis of 103 nm is disposed on the surface of the CF substrate 200 opposite to the TFT substrate 100 with the slow axis parallel to the rubbing direction. Further, a polarizing plate is disposed thereon so that the absorption axis forms an angle of 45 ° with the rubbing direction. On the other hand, a polarizing plate is disposed on the surface of the TFT substrate 100 opposite to the CF substrate 200 so that the absorption axis is orthogonal to the absorption axis on the CF substrate 200 side.
[0073]
In the above-mentioned liquid crystal panel, as schematically shown in the plan view of FIG. 12, the polarities of the pixel electrodes 101, 101,... A data signal that changes the polarity of the pixel electrodes 101, 101,... On the source line 104 for each source line is input, and 1V line inversion drive is performed so as to invert the polarity of the input signal to each source line 105 in the next frame. A driver circuit (not shown) is attached. Note that the transmissive region is surrounded by the reflective region and is not affected by the lateral electric field between adjacent pixels, so that the characteristics do not change by driving. Other configurations are the same as those in the first embodiment, and thus description thereof is omitted.
[0074]
In this embodiment, as indicated by arrows in the perspective view of FIG. 13, the rubbing process for the alignment film 111 on the TFT substrate 100 side and the rubbing process for the alignment film 203 on the CF substrate 200 side are the same as those in the first embodiment. Unlike the case, the liquid crystal molecules are aligned in the direction parallel to the source lines 105, 105,... And at an angle of 180.degree. , And the alignment direction of the liquid crystal molecules in the vicinity of the interface with the liquid crystal layer 300 of the CF substrate 200 are regulated to a direction parallel to the source lines 105, 105,. .
[0075]
Next, a manufacturing method of the liquid crystal display device having the above configuration will be described. On the glass substrate 103, TFTs 102, 102, ..., gate lines 104, 104, ..., source lines 105, 105, ..., transparent electrodes 101a, 101a, ... are formed by known means. Next, after forming the insulating layer 110 of acrylic resin, the insulating layer 110 portion on the drain electrode 108 of each TFT 102 and the insulating layer 110 portion on the transparent electrode 101a are removed, and the drain electrode 108 and the transparent electrode are removed. A reflective electrode 101b is formed so as to be in contact with 101a. After that, a polyimide material is applied to form an alignment film 111, and unlike the case of the first embodiment, a rayon cloth is applied to the alignment film 111 in a direction parallel to the gate lines 104, 104,. Apply rubbing rubbing treatment.
[0076]
On the other hand, for the CF substrate 200, the counter electrode 201 is formed on the glass substrate 202, and a polyimide material is applied thereon to form the alignment film 203. Then, the rubbing process is performed in the same manner as the TFT substrate 100 so that the rubbing directions after the CF substrate 200 and the TFT substrate 100 are bonded to each other are antiparallel to each other.
[0077]
Next, the alignment film 111 of the TFT substrate 100 and the alignment film 203 of the CF substrate 200 are opposed to each other, and the TFT substrate 100 and the CF substrate 200 are bonded together. A liquid crystal material is injected into this. Thereafter, a uniaxial retardation film is disposed on the surface of the CF substrate 200 opposite to the TFT substrate 100, and a polarizing plate is disposed thereon. A polarizing plate is also disposed on the surface of the TFT substrate 100 opposite to the CF substrate 200.
[0078]
A liquid crystal display device according to this embodiment is obtained by attaching a driver circuit for 1V line inversion driving to the liquid crystal display panel thus completed.
[0079]
Therefore, according to the present embodiment, each pixel electrode 101 of the TFT substrate 100 includes the transparent electrode 101a and the reflective electrode 101b formed so as to surround the transparent electrode 101a, and is driven to invert the vertical line. In the active matrix type transflective liquid crystal display device, a horizontal alignment liquid crystal material is used, and the alignment film 111 of the TFT substrate 100 and the alignment film 203 of the CF substrate 200 are parallel to the source lines 105, 105,. The liquid crystal molecules in the vicinity of the interfaces between the TFT substrate 100 and the CF substrate 200 with each liquid crystal layer 300 are aligned in a direction substantially perpendicular to the potential lines of the lateral electric field by rubbing treatment performed in directions that form an angle of 180 ° with each other. Therefore, not only in the transmission mode that is not affected by the transverse electric field, but also in the reflection mode that is affected by the transverse electric field. It can have, it is possible to improve the contrast of the display screen by suppressing the generation of a domain due to the lateral electric field to display information such as an image with high quality.
[0080]
In the above embodiment, the case of 1 vertical line inversion drive is described, but the present invention can also be applied to the case of multiple line inversion drive such as 2 lines or 3 lines. The present invention can also be applied to horizontal line inversion driving. However, in the case of horizontal line inversion driving, the potential line of strong lateral electric field is generated not in the gate line direction but in the source line direction, so that the rubbing direction is not the source lines 105, 105,. 104 and so on.
[0081]
In the above embodiment, the case where the gate lines 104, 104,... And the source lines 105, 105,... Are all disposed below the pixel electrodes 101, 101,. However, according to the present invention, only the source lines 105, 105,... Are arranged under the pixel electrodes 101, 101,..., Or only the gate lines 104, 104,. The present invention can also be applied to a case where it is arranged in a lower layer of 101, 101,.
[0082]
-Contrast ratio test-
A test conducted by measuring the reflection contrast ratio by applying a black voltage (4.5 V) and a white voltage (1.5 V) to the liquid crystal display device configured as described above as an invention example. Will be described.
[0083]
Here, for comparison, in the above liquid crystal panel, instead of the driver circuit of the invention example, the polarities of the pixel electrodes 101, 101,... On the same gate line 104 are equal to each other and on the same source line 105. A driver circuit adapted to perform 1H line inversion driving for alternately inverting the polarities of the pixel electrodes 101, 101,... For each line of the gate line is used as a comparative example, and this comparative example is also the case of the invention example. A similar test was performed.
[0084]
As a result, a contrast of 320 was obtained in the comparative example, whereas it was 130 in the comparative example.
[0085]
【The invention's effect】
As described above, according to the first aspect of the present invention, the pixel electrode overlaps at least a part of the scanning wiring through the insulating layer, and the polarity of the pixel electrode on the same data wiring is set to the predetermined number of scanning wirings. In an active matrix liquid crystal display device that performs line inversion driving that alternately inverts every time, a homogeneous liquid crystal material is used for the liquid crystal layer, and the liquid crystal molecules in the vicinity of the interface with the liquid crystal layer of each electrode substrate are scanned with wiring. Are aligned in a direction substantially parallel to each other and at an angle of approximately 180 ° to each other, so that it is possible to suppress the occurrence of domains due to a lateral electric field between pixel electrodes of different polarities adjacent to each other in the data wiring direction. The contrast can be improved by reducing the luminance of black display without causing a decrease in productivity as in the case of using a vertical liquid crystal material for the liquid crystal layer.
[0086]
According to the invention of claim 2, the pixel electrode overlaps at least a part of the data wiring via the insulating layer, and the polarity of the pixel electrode on the same scanning wiring is alternately inverted every predetermined number of data wirings. In an active matrix liquid crystal display device in which line inversion driving is performed, a homogeneous liquid crystal material is used for the liquid crystal layer, and liquid crystal molecules in the vicinity of the interface with the liquid crystal layer of each electrode substrate are arranged substantially parallel to each other and to the data wiring. Since the alignment is performed in a direction that forms an angle of about 180 °, it is possible to suppress the occurrence of a domain due to a lateral electric field between pixel electrodes of different polarities adjacent to each other in the scanning wiring direction. The contrast can be improved by reducing the luminance of black display without causing a decrease in productivity as in the case of using a liquid crystal material.
[Brief description of the drawings]
FIG. 1 is a perspective view schematically showing a rubbing direction with respect to each electrode substrate of a liquid crystal panel in a transmissive liquid crystal display device according to Embodiment 1 of the present invention.
FIG. 2 is a longitudinal sectional view schematically showing a configuration of a main part of a liquid crystal panel.
FIG. 3 is a longitudinal sectional view schematically showing a configuration around a TFT of a liquid crystal panel.
FIG. 4 is a plan view schematically showing the polarity of a pixel electrode by 1H line inversion driving.
FIG. 5 is a longitudinal sectional view schematically showing alignment division lines of a multi-domain cell.
FIG. 6 is a plan view schematically showing Modification 1 to Modification 3 in the case of a multi-domain cell.
FIG. 7 is a cross-sectional view (a) in the plane orthogonal to the gate line of the orientation simulation result when the potentials of two pixel electrodes adjacent in the source line direction are −4.5 V and 4.5 V, respectively, in the example of the invention in the same direction; It is a figure shown together with the characteristic (b) of the light transmittance in each position.
FIG. 8 is a cross-sectional view (a) in the plane orthogonal to the gate line of the orientation simulation result when the potentials of two pixel electrodes adjacent in the source line direction are −4.5 V and 4.5 V, respectively, in the comparative example in the same direction; FIG. 8 is a view corresponding to FIG. 7 shown together with a light transmittance characteristic (b) at each position of FIG.
FIG. 9 is a cross-sectional view (a) in the plane orthogonal to the source line of the orientation simulation result when the potentials of two pixel electrodes adjacent in the gate line direction are 1.5 V and 4.5 V, respectively, in the example of the invention in the same direction; It is a figure shown together with the characteristic (b) of the light transmittance in each position.
FIG. 10 is a cross-sectional view (a) in the plane orthogonal to the source line of the orientation simulation result when the potentials of two pixel electrodes adjacent in the gate line direction are both 4.5 V in the example of the invention. FIG. 10 is a view corresponding to FIG. 9 shown together with the transmittance characteristic (b).
FIG. 11 is a view corresponding to FIG. 3 schematically showing a configuration of a main part of a liquid crystal panel in a transflective liquid crystal display device according to Embodiment 2 of the present invention.
12 is a view corresponding to FIG. 4 schematically showing the polarity of a pixel electrode by 1V line inversion driving.
FIG. 13 is a view corresponding to FIG. 1 schematically showing a rubbing direction with respect to each electrode substrate of the liquid crystal panel.
FIG. 14 is a view corresponding to FIG. 1 schematically showing a rubbing direction with respect to each electrode substrate of a liquid crystal panel in a conventional liquid crystal display device.
FIG. 15 is a longitudinal sectional view schematically showing a state in which a reverse tilt is generated by a horizontal electric field between two pixel electrodes having different magnetism.
[Explanation of symbols]
100 TFT substrate (one electrode substrate)
101 Pixel electrode
102 TFT (switching element)
104 Gate line (scanning wiring)
105 Source line (data wiring)
110 Insulating layer
111 Alignment film
200 CF substrate (the other electrode substrate)
201 Counter electrode
203 Alignment film
300 Liquid crystal layer

Claims (5)

A pair of electrode substrates, and a liquid crystal layer disposed between the pair of electrode substrates and made of a homogeneous liquid crystal material,
One electrode substrate includes a plurality of scanning wirings and a plurality of data wirings provided so as to cross each other, an insulating layer provided on at least the plurality of scanning wirings, the plurality of scanning wirings and the plurality of data Each intersection between wirings is provided so as to overlap at least a part of the scanning wiring located in the vicinity of the intersection via the insulating layer, and switching is performed based on a signal of the scanning wiring passing through the intersection. A pixel electrode connected to a data line passing through the intersection through an operating switching element;
The other electrode substrate has a counter electrode,
A liquid crystal display device that performs line inversion driving in which the polarities of the pixel electrodes on the same scanning line are equal to each other and the polarities of the pixel electrodes on the same data line are alternately reversed every predetermined number of scanning lines. ,
Alignment treatment for restricting the alignment direction of the liquid crystal molecules of the liquid crystal layer in the vicinity of the interface to a direction that is substantially parallel to the scanning wiring and at an angle of approximately 180 ° to each interface with the liquid crystal layer of the pair of electrode substrates. A liquid crystal display device characterized by that. A pair of electrode substrates, and a liquid crystal layer disposed between the pair of electrode substrates and made of a homogeneous liquid crystal material,
One electrode substrate includes a plurality of scanning wirings and a plurality of data wirings provided so as to cross each other, an insulating layer provided on at least the plurality of data wirings, the plurality of scanning wirings and the plurality of data At each intersection between wirings, switching is performed based on a signal of a scanning wiring that is provided so as to overlap at least part of the data wiring located in the vicinity of the intersection via the insulating layer. A pixel electrode connected to a data line passing through the intersection through an operating switching element;
The other electrode substrate has a counter electrode,
A liquid crystal display device that performs line inversion driving in which the polarities of the pixel electrodes on the same data line are equal to each other and the polarities of the pixel electrodes on the same scanning line are alternately reversed every predetermined number of data lines. ,
Alignment treatment for restricting the alignment direction of the liquid crystal molecules in the liquid crystal layer in the vicinity of the interface to the direction of forming an angle of approximately 180 ° with each other at each interface with the liquid crystal layer of the pair of electrode substrates. A liquid crystal display device characterized by that. 3. The liquid crystal display device according to claim 1, wherein the liquid crystal layer has a plurality of domains provided in the same pixel so as to extend between the adjacent pixels across the scanning wiring and the data wiring, and each electrode substrate. The liquid crystal display device is characterized in that the alignment treatment is performed so that the restriction directions of the alignment treatment form an angle of approximately 180 ° between adjacent domains. 4. The liquid crystal display device according to claim 1, wherein the pixel corresponding portions of both electrode substrates are provided transparently. 4. The liquid crystal display device according to claim 1, wherein a pixel corresponding portion of one electrode substrate is provided transparent, and at least a part of the pixel corresponding portion of the electrode on the other electrode substrate is made of a light reflector. Liquid crystal display device

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