Patent Application
20110304797
The present invention relates to a liquid crystal display device. More particularly, the present invention relates to a liquid crystal display device with a display mode for imparting vertical alignment as the initial alignment to liquid crystal molecules, and controlling the liquid crystal molecules by an electric field (for example, a transverse electric field) generated.
Liquid crystal display devices have been widely used in various fields because of its characteristics such as thinness, light weight, and low power consumption. Liquid crystal display devices are generally provided with backlight units for display. Sunlight may be used as light sources for display by reflecting the sunlight. However, liquid crystal display devices which are mainly used indoors such as word processors, laptop personal computers, and on-vehicle display devices, and liquid crystal display devices which are used outdoors and constantly needing a certain brightness require backlight units including light sources.
Edge light backlight units and direct backlight units are generally known as backlight units. Liquid crystal display devices including small screens can perform display with low power consumption because of their small number of light sources. Therefore, edge light backlight units suitable for realizing thin-profile devices are commonly used in such liquid crystal display devices.
Examples of members of backlight units include, in addition to light sources, reflective sheets, diffusion sheets, prism sheets, and light guide plates. In the edge light backlight units, light emitted from the light sources enters the light guide plates from the side faces of the light guide plates, and is reflected and diffused. The resulting light is then emitted as planar light from main faces of the light guide plates. The light further passes through prism sheets, and goes out as display light from the backlight units.
However, in the case where a large number of pixel portions forming a display pixel of a liquid crystal display panel are arranged in a matrix pattern, and the alignment pitch of the pixel portions and the alignment pitch of a prism sheet of a backlight unit are close to each other, light interference may cause fringes (moiré). In order to solve this problem, Patent Document 1, for example, examines improved techniques of suppressing moiré by tilting the extending direction of a prism array of the prism sheet at a predetermined angle to the direction of a pixel portion array, and adjusting the angle formed by the direction of the optical axis of the prism sheet and the length direction of the incidence face of a light guide structure and the angle formed by the direction of the transmission axis of a polarizing plate of a liquid crystal display element and the length direction of the incidence face of the light guide structure so as to satisfy a predetermined relationship between these two angles.
Patent Document 2, for example, discloses improved techniques of suppressing moiré by a diffraction grating. Specifically, in order to obscure a matrix-like pixel pattern and the same color dot cycle in a liquid crystal display element with multiple pixels arranged therein, the diffraction grating and a birefringent plate are disposed on an observation face side of a liquid crystal display element to perform a pixel diffusion with a large shift amount by the diffraction grating.
However, the means disclosed in Patent Document 1 still has room for improvement in that the direction of the polarization axis of the polarizing plate of the liquid crystal display panel is strictly limited, and luminance tends to fall in the liquid crystal display panel in which the polarization axis is tilted at an angle of from 0° to 180° or from 90° to 270° to the length direction of the backlight. Further, the means disclosed in Patent Documents 2 has room for improvement in that character blurring or character bleeding may occur because display is likely to be affected by ambient light.
Display modes of liquid crystal display devices are classified according to methods for aligning liquid crystal. Examples of conventionally known display modes of liquid crystal display devices include a TN (Twisted Nematic) mode, a VA (Vertical Alignment) mode, an IPS (In-Plane Switching) mode, and an OCB (Optically self-Compensated Birefringence) mode.
Alternately, a display mode has been recently proposed in which nematic liquid crystal with positive dielectric anisotropy is used as a liquid crystal material, the nematic liquid crystal is vertically aligned to provide and maintain high contrast, and in addition, a transverse electric field is generated using a pair of comb-shaped electrodes to control alignment of liquid crystal molecules. How the present invention is completed will be described with reference to the above-mentioned mode. The present invention is not limited to such a mode.
In the mode, directors (liquid crystal molecules) are aligned along a transverse electric field generated in an arch shape between a pair of comb-shaped electrodes arranged on one and the same substrate. According to this, directors forms an arch-shaped distribution having symmetry along a transverse electric field, and the directors form alignment similar to bend alignment in a transverse direction. As a result, even if a display face is observed in an oblique direction, the same display quality as that observed in a front direction can be visually recognized. Therefore, as in a VA mode, for example, the problem will be solved in that rod-shaped liquid crystal molecules cause different states of optical birefringence between the front direction and the oblique direction and change voltage-transmission characteristics (V-T characteristics) depending on the viewing angle.
However, in the mode, when a voltage is applied to a liquid crystal layer, that is, during white display, interference fringes (moiré) may occur on a display screen.
The present invention has been made in view of the above-mentioned state of the art. It is an object of the present invention to provide a liquid crystal display device that suppress moiré generated when a voltage is applied in a liquid crystal mode that drives a vertical alignment liquid crystal by using at least a pair of comb-shaped electrodes.
The present inventors made various investigations on the reason why interference fringes occur in the mode. They noted that although almost all directors shift from perpendicular alignment (black display) to bend alignment (white display) when a voltage is applied, in principle, directors just above an electrode remain aligned perpendicularly, and display by the electrode remains black. They further noted the configuration of a backlight unit, and fount that in the case where the surface of a lens sheet of the backlight unit has a periodic recessed and projecting pattern, light interference occurs because of a periodic shape of the lines of the recessed and projecting pattern and a periodic shape of lines of comb teeth of a comb-shaped electrode, which causes generation of interference fringes on a display screen.
As a means for suppressing generation of interference fringes, for example, the lens sheet can be rotated so that the lines of the recessed and projecting pattern have an angle to the lines of the comb teeth. However, in this case, light from a light source is not sufficiently used effectively, and luminance may be deteriorated.
As a result of further earnest investigations made by the present inventors, they found that the period of the lines of the recessed and projecting pattern of the lens sheet and the period of the lines of the comb teeth are shifted, whereby generation of moiré can be avoided without rotation of the lens sheet. Specifically, they found that the pitch width of the lines of the comb teeth is adjusted to be different from an integral multiple of the pitch width of the recessed and projecting lines of the lens sheet, whereby generation of moiré can be sufficiently suppressed. As a result, the above-mentioned problems have been admirably solved, leading to completion of the present invention.
That is, the present invention is a liquid crystal display device, comprising:
a liquid crystal display panel including a liquid crystal layer and a pair of substrates sandwiching the liquid crystal layer; and
a backlight unit disposed on a back side of the liquid crystal display panel,
one of the pair of substrates including a pair of comb-shaped electrodes each having comb teeth, the comb teeth of one of the pair of comb-shaped electrodes and the comb teeth of the other of the pair of comb-shaped electrodes being disposed alternately and spaced apart from each other,
the liquid crystal layer containing liquid crystal molecules with positive dielectric anisotropy,
the liquid crystal molecules being aligned in a direction perpendicular to a surface of the one of the pair of substrates when no voltage is applied,
the backlight unit having an optical sheet with multiple folds parallel to one another on a surface,
the pitch width of the pair of comb-shaped electrodes being different from an integral multiple of the pitch width of the folds of the optical sheet.
The liquid crystal display device of the present invention includes a liquid crystal display panel including a liquid crystal layer and a pair of substrates sandwiching the liquid crystal layer, and a backlight unit disposed on a back side of the liquid crystal display panel. The liquid crystal layer is filled with liquid crystal molecules whose alignment is controlled by applying a certain voltage. The pair of substrates is provided with lines, electrodes, semiconductor devices, and the like. With such substrates, a voltage is applied to the liquid crystal layer, which controls alignment of the liquid crystal molecules. The backlight unit includes a light source, and is provided with optical members such as a lens sheet, a diffusion sheet, a reflective sheet, and a light guide plate. The backlight unit is disposed on a back face side of the liquid crystal display panel and emits light to the observation face side.
The one of the pair of substrates includes a pair of comb-shaped electrodes each having comb teeth. The comb teeth of one of the pair of comb-shaped electrodes and the comb teeth of the other of the pair of comb-shaped electrodes are disposed alternately and spaced apart from each other. The term “comb-shaped” as used herein refers to a shape basically composed of a handle portion as a trunk and a comb-teeth portion protruded from the handle portion. An electric field is, for example, an arch-shaped transverse electric field when a potential difference is given between the pair of comb-shaped electrodes. The liquid crystal molecules are aligned according to the direction of such an electric field, and therefore display in a front direction and display in an oblique direction, relative to a substrate surface, are the same as each other.
The liquid crystal layer includes liquid crystal molecules with positive dielectric anisotropy. Such liquid crystal molecules are aligned in the same direction as that of the electric field by applying a voltage to the liquid crystal layer. As a result, for example, the liquid crystal molecules show alignment similar to transverse bend alignment.
The liquid crystal molecules are aligned in a direction perpendicular to a surface of the one of the pair of substrates in a state where no voltage is applied (hereinafter referred to simply as “vertical alignment”). Thus, the initial alignment of the liquid crystal molecules is adjusted, which efficiently blocks light for performing black display. In order to vertically align the liquid crystal molecules in a state where no voltage is applied, a vertical alignment film is disposed on a surface, which is in contact with the liquid crystal layer, of one or both of the pair of substrates. Here, if one line is perpendicular to another line, they form an angle of 90±4°. If the angle is less than 86° or exceeds 94°, contrast decreases.
Accordingly, according to the liquid crystal display device of the present invention, the liquid crystal molecules are vertically aligned in a state where no voltage is applied, which achieves high contrast. Further, the liquid crystal molecules are transversely aligned to form alignment similar to bend alignment in a state where a voltage is applied, which achieves a wider viewing angle.
The backlight unit has an optical sheet which has multiple folds parallel to one another on a surface. Examples of the optical sheet that can have such a structure include a lens sheet that condenses light, and a light guide plate that guides light in a direction of the display surface. The optical sheet having the folds have such a pattern on at least a surface, and the entire optical sheet may have such a pattern along the folds.
The pitch width of the comb teeth of the pair of comb-shaped electrodes is different from an integral multiple of the pitch width of the folds of the optical sheet. The “pitch width” used herein is a concept to specify a periodic width in a periodic structure having multiple lines, and is defined by the distance between center lines of each line. Further, this pitch width is also defined in the same way even in the total length of one line width and one space width in a periodic structure having lines with a constant width and spaces (distance) with a constant width.
For example, the pitch width between two members, such as the pitch width of the comb teeth of a pair of comb-shaped electrodes, means the length between lines of each of the two members, that is, the length between the center line of the comb tooth line of one comb-shaped electrode and the center line of the comb tooth line of the other comb-shaped electrode. In the case where the pitch width of the pair of comb-shaped electrodes is specified with one line width and one space width, the one line width means the size of the comb tooth in the width direction that is orthogonal to the length direction of the comb teeth of one comb-shaped electrode or the comb teeth of the other comb-shaped electrode. In addition, the one space width means the size of the comb tooth in the width direction that is orthogonal to the length direction of the comb teeth in the space between the comb teeth of one comb-shaped electrode and the comb teeth of the other comb-shaped electrode. The total width of the one line width and the one space width corresponds to the pitch width of a pair of comb-shaped electrodes.
Meanwhile, the pitch width in one member, such as the pitch width of folds of an optical sheet, refers to the length between the center lines of the line of the member, that is, the length between the center lines of the fold.
In the present invention, the pitch width of the comb teeth of a pair of comb-shaped electrodes is different from an integral multiple of the pitch width of the folds of the optical sheet. Therefore, canceling due to interference occurs in light that consecutively transmits through both the pair of comb-shaped electrodes and the optical sheet, and interference fringes in which a black display portion and a white display portion appear periodically can be prevented. Specifically, the expression “different from an integral multiple” used herein means that a ratio of a larger pitch width to a smaller pitch width out of the pitch width of the comb teeth of the pair of comb-shaped electrodes and the pitch width of the folds of the optical sheet, that is, a value represented by “a larger pitch width/a smaller pitch width” is not an integer. The term “integral multiple” used herein includes an error range of less than 0.1 times. For example, the integral multiple does not include 1.2 times, but includes 1.02 times or 0.98 times.
The configuration of the liquid crystal display device according to the present invention is not especially limited as long as the above-mentioned components are essentially comprised. The liquid crystal display device may or may not comprise other components.
Preferable embodiments of the liquid crystal display device of the present invention will be described in detail.
It is preferable that comb tooth lines of the comb-shaped electrodes are each parallel to the folds of the optical sheet. The higher the angle formed by comb tooth lines of the comb-shaped electrodes and a fold of the optical sheet is, the worse the light use efficiency is, and the worse the luminance of the entire display is. Therefore, according to the present embodiment, moiré interference can be prevented while high luminance is maintained. The term “parallel” used herein refers to the range of from 0° to 3.0°.
It is preferable that the pitch width of the comb teeth of the pair of comb-shaped electrodes is 9.5 μm or less. If the pitch width of the pair of comb-shaped electrodes exceeds 9.5 μm, the larger the pitch width is, the more likely generation of moiré is to be visually observed. The pitch width of the pair of comb-shaped electrodes in the above range of this embodiment can give better effects of suppressing moiré.
It is preferable that the pitch width of the comb teeth of the pair of comb-shaped electrodes is 9.5 to 12.5 μm, and the angle formed by a comb tooth line of the comb-shaped electrodes and a fold of the optical sheet is lower than 3°. The larger the angle formed by the comb tooth line of the comb-shaped electrodes and the fold of the optical sheet is, the less likely moiré is to be generated. An angle of lower than 3° is an allowable range because the luminance does not significantly decrease. Meanwhile, if the angle formed by the comb tooth line of the comb-shaped electrodes and the fold of the optical sheet is 3° or higher, the luminance significantly decreases. Accordingly, the above allowable range with a good balance between the reduction in luminance and generation of moiré enables good display.
It is preferable that the pitch width of the comb teeth of the pair of comb-shaped electrodes is 7.5 μm or higher. The pitch width of the pair of comb-shaped electrodes of less than 7.5 μm is not problematic in terms of suppression of moiré, but a pitch width of 7.5 μm or higher is preferable in terms of the transmittance.
The present invention provides a liquid crystal display device that suppress moiré interference generated by comb-shaped electrodes of a liquid crystal display panel and an optical sheet of a backlight unit when a voltage is applied in a vertical alignment type liquid crystal mode.
[
[
[
[
[
[
[
[
[
[
[
[
[
[
[
[
[
[
[
[
[
[
The present invention will be mentioned in more detail referring to the drawings in the following embodiments, but is not limited to these embodiments.
As shown in
The pixel electrode 21 is connected with a thin film transistor (TFT) including a semiconductor layer, and further connected with a source line via the TFT. The TFT is connected with a gate line, and a gate voltage is applied to the semiconductor layer via the gate line. At the same time, the source line and the pixel electrode 21 are electrically connected with each other, and the signal voltage is applied to the pixel electrode 21.
The counter electrode 22 is connected with the common line that is located at an area overlapping with the gate line and source line. An insulating film is disposed between the common line, and the gate line and source line. The gate line and the source line are arranged perpendicular to each other. A region surrounded with two gate lines and two source lines, that is, a region surrounded with the common lines forms one sub pixel. One color filter is arranged to correspond one sub pixel, and a plurality of sub pixels form one pixel.
The TFT substrate 11 has a glass substrate 31, and the pixel electrode 21 and the counter electrode 22 disposed on the liquid-crystal-layer-13-side surface of the glass substrate 31. The pixel electrode 21 and the counter electrode 22 are alternately arranged in a transverse direction when viewed in a cross section.
The counter substrate 12 includes a glass substrate 32 and a color filter 41. The color filter 41 is arranged on the liquid-crystal-layer-13-side surface of the glass substrate 32. The color filter 41 is composed of at least one of a red color filter 41R, a green color filter 41G, and a blue color filter 41B. One color filter corresponds to one sub pixel. Combination of red, green, and blue sub pixels forms one pixel. The color filter 41 may include colors other than these colors. A black-colored black matrix (BM) 42 is arranged between the adjacent two color filters having colors different from each other to prevent color mixing and light leakage.
Vertical alignment films 51 and 52 are arranged on surfaces of the TFT substrate 11 and the counter substrate 12, respectively. The surfaces are in contact with the liquid crystal layer 13. As shown in
As shown in
The TFT substrate 11 and the counter substrate 12 have polarizers 71 and 72, respectively. The polarizer 71 is arranged in the outermost portion of the back face side of the TFT substrate 11. The polarizer 72 is arranged in the outermost portion of the observation face side of the counter substrate 12. The polarizers 71 and 72 are allowed to convert natural light emitted from a light source into polarized light vibrating in a certain direction (a polarization axis direction). The arrows in the polarizers 71 and 72 shown in
According to Embodiment 1, the liquid crystal molecules 61 are aligned in a direction perpendicular to the substrates 11 and 12 when no voltage is applied. Therefore, the transmission axis of the polarizer 71 of the TFT substrate 11 intersects with the transmission axis of the polarizer 72 of the counter substrate 12 (they are in a cross-Nicol state). Accordingly, light transmitting through the liquid crystal layer 13 when no voltage is applied is blocked with the polarizers 71 and 72. As mentioned above, the liquid crystal molecules 61 have a vertical alignment as the initial alignment, and the polarizers 71 and 72 are in a cross-Nicol state, which provide a normally black display mode with a high contrast ratio.
Meanwhile, in the case where a voltage is applied, the liquid crystal molecules 61 are aligned along a transverse electric field, and at this time a vibrating direction (polarized light axis) of light transmitted through the liquid crystal layer 12 is changed. So, the light transmitted through the liquid crystal layer 12 can pass through the polarizer 72 on the counter substrate 12 side. As a result, the light passes through the liquid crystal display panel 1 and is used as display light.
The configuration of the backlight unit 2 in Embodiment 1 is described in detail below. The backlight unit 2 includes a reflective sheet 81, a light source 82, a light guide plate 83, a lens sheet 84, and a diffusion sheet 85. Among such members, the reflective sheet 81 is arranged in the outermost portion of the back face side, and the light guide plate 83 is arranged on the reflective sheet 81 (observation face side of the reflective sheet). The light source 82 is arranged beside the light guide plate 83, and the lens sheet 84 is arranged on the light guide plate 83. The light source 82 emits light to the light guide plate 83. Further, the diffusion sheet 85 is disposed on the lens sheet 84.
The reflective sheet 81 is a member arranged for improvement of utilization efficiency of light emitted from the light source 82, and covers the entire bottom face of the backlight unit 2. Examples of a material of the reflective sheet 81 include polyethylene terephthalate (PET), a multilayer structure of a polyester resin, and a mixture of a polyester resin and an urethane resin.
The light source 82 is a member which emits light used for display in the liquid crystal display device. Examples of the light source 82 include a cold cathode fluorescent tube (CCFT), a light-emitting diode (LED), and an organic electro-luminescence (OEL). When used as the light source 82, the multiple LEDs are arranged along a side face of the light guide plate.
The light guide plate 83 is a transparent and colorless plate which guides light entering the light guide plate 83 to a display face. In Embodiment 1, light emitted from the light source 82 once enters the light guide plate 83 from the side face thereof, and the incident light is reflected, refracted, and diffused with a structure pattern formed in the light guide plate 83, and emitted as planar light from a main face side of the light guide plate 83 toward the liquid crystal display panel 1.
The lens sheet (prism sheet) 84 is an optical sheet that condenses diffused light emitted from the light guide plate 83 in a front direction and increases the luminance.
Examples of the lens sheet 84 include BEF lenses (produced by Sumitomo 3M Limited.). Among the BEF lenses, BEFII has a height (including recessed and projecting portions and a base portion) of 155 μm and a height of the base portion of 125 μm. The distance between the tips of adjacent projections is 50 μm, that is, the pitch width of the lens sheets upon use of the BEFII is 50 μm. The angle formed between the slanted surfaces of adjacent projections is 90°.
The diffusion sheet 85 is an optical sheet that diffuses the outgoing light emitted from the lens sheet 84 to widen a viewing angle of display. Examples of the diffusion sheet 85 include a sheet diffusing light using surface roughness thereof due to a sheet material, and a sheet on which beads are dispersed in a binder. Examples of a material of the diffusion sheet 85 include PET, PC (polycarbonate), and PMMA (polymethyl methacryl acid).
The optical sheet used herein includes the reflective sheet 81, the lens sheet 84, and the diffusion sheet 85. In Embodiment 1, multiple folds parallel to one another are configured on the surface of the lens sheet 84, and therefore at least the lens sheet 84 corresponds to the optical sheet of the present invention.
As shown in
As shown in
Hereinafter, the cases where moiré caused by light interference occurs and does not occur will be described specifically by way of examples and comparative examples.
Then, an alignment film coating material JALS-204 (5 wt %, γ-butyrolactone solution) produced by JSR was coated on the comb-shaped electrode and the glass substrate by spin coating, and baked at 200° C. for 2 hours.
Next, a BM having a width of 10 μm, a length of 100 μm in a transverse direction, and a length of 300 μm in a longitudinal direction was formed on another glass substrate, an OC (overcoat) layer was formed by spin coating on the BM and the glass substrate, and then baking was performed at 200° C. for one hour.
Subsequently, a liquid material of a columnar spacer was applied to an OC layer by spin coating, and thereafter a columnar spacer having a height of 3.4 μm was produced by photolithography. Further, the same alignment film coating material JALS-204 was applied to the OC layer by spin coating (5 wt %, γ-butyrolactone solution), and then baked at 200° C. for two hours. The thickness of each of the alignment films thus formed on both glass substrates was about 1000 Å.
Next, a seal resin produced by Mitsui Chemicals, Inc. (STRUCTBOND XN-21S) was printed on a pair of substrates thus produced, and these was bonded to each other, and baked at 135° C. for one hour to produce a liquid crystal cell.
Thereafter, a positive type liquid crystal material produced by Merck (Δε=18, Δn=0.1) was sealed between a pair of the substrates by vacuum injection, and a polarizing plate was attached to the opposite sides of the liquid crystal layer sides of the pair of the substrates, and thereby the liquid crystal display element was completed.
Then, the thus-produced liquid crystal display element was put on a backlight unit that equips an LED as a light source, the various angles of a line of each projection of a BEF lens of the backlight unit produced by Sumitomo 3M Limited was selected in an incident light direction of LED light (extension of LED) in the range of θ=from 0 to ±15°, and the state of moiré when a voltage is applied was observed. The smaller the value of θ is, the closer to each other the line direction of the lens sheet and the line direction of the BM and the comb teeth of the comb-shaped electrodes are, and the more likely moiré is to occur. The larger the value of θ is, the less likely moiré is to occur, and the worse the light use efficiency is. Thus, the luminance tends to be deteriorated.
As shown in
In contrast, thin slight moiré stripes were observed until the angle of rotation of the BEF lens reached ±0.5° in the liquid crystal display device of Example 1, good display without any moiré visually observed on any conditions of Examples 2 and 3 was obtained.
In the liquid crystal display devices of Examples 1 to 3 and Comparative Examples 1 and 2, Table 1 summarizes the evaluation results of the level of moiré in the display screen.
1.5
9.5
±14°
Regarding the evaluation of OFF-time and ON-time operation for the driving voltage in Table 1, “◯” shows good display with no moiré, “Δ” shows not good display with slight moiré, and “×” shows poor display with remarkable moiré.
Regarding the comprehensive evaluation in Table 1, “◯” shows a liquid crystal display device which may be used as a product, and “×” shows a liquid crystal display device which may not be used as a product.
The ratio of the pitch width (line width+space width) of the comb teeth of a pair of comb-shaped electrodes to the pitch width of the folds of the BEF lens was 100/50 (twice) in Comparative Example 1, and was 50/12.5 (four times) in Comparative Example 2. Therefore, the ratio was confirmed to be an integral multiple in Comparative Examples 1 and 2.
Meanwhile, the ratio of the pitch width (line width+space width) of the comb teeth of a pair of comb-shaped electrodes to the pitch width of the folds of a BEF lens is 50/10.5 (4.7619 . . . times) in Example 1, 50/7.5 (6.6666 . . . times) in Example 2, and 50/9.5 (5.2631 . . . times) in Example 3. Therefore, in each of these examples, the ratio was confirmed to be different from an integral multiple.
Next, the relationship between the pitch width of the comb teeth of a pair of comb-shaped electrodes and the transmittance was studied. First, as samples for comparing the pitch widths of comb teeth, five samples whose pitch widths were 5.0 μm, 7.5 μm, 9.5 μm, 10.5 μm, and 12.5 μm and which had the same configurations as those of Examples 1 to 3 were used. Table 2 shows the results of aperture ratios and transmittances of these five samples.
Table 2 shows the aperture ratios and transmittances calculated by the comb teeth pitch. In fact, members such as BMs, lines, and TFTs block light to an aperture ratio portion, the aperture ratios and transmittances fall to substantially 80% relative to the actual aperture ratios and transmittances. In consideration of this respect, a good transmittance is obtained in the case of using a pair of comb-shaped electrodes having an aperture ratio of substantially 54.0% or higher, a transmittance of 4.5% or higher, and a pitch width of 7.5 μm or higher. The aperture ratios were calculated by removing a line portion from an aperture portion was used in each case of disposing these five samples having the pitch widths shown in Table 2 under assumption that light does not transmit the line and that the size of each pixel is 100×300 μm.
Subsequently, color change of the moiré portion was examined by a general formula of transmission diffraction efficiency. Specifically, transmission efficiency of multiple diffraction pitches in each wavelength when a substrate surface was viewed from a front direction was calculated by the general formula of the diffraction efficiency upon transmission. Here, the examination is made such that red is 700 nm, green is 550 nm, and blue is 450 nm. The general formula of the transmission diffraction efficiency upon transmission is expressed by the following formula.
η=sin2(πΔnd/λ cos θ)
The parameters of the formula are as follows.
The Δn was obtained by calculating the average refractive index of the incident polarization upon voltage application and the average refractive index of the incident polarization upon no voltage application and thereafter calculating the difference of these average refractive indices. Before and after voltage application, no change of the inclination of the liquid crystal molecules was observed above the comb tooth line, and therefore the average refractive index was 0 and did not change. Meanwhile, the inclination of liquid crystal molecules above a space changes. Therefore, polarized light enters a liquid-crystal-layer surface also from a direction at an angle of 45°, and the average refractive index changes from 0 and comes close to λ/2. The extraordinary index ne of the liquid crystal molecules used in examples and comparative examples was 1.578, and the ordinary index no was 1.477. Therefore, the average refractive index of the liquid crystal molecules was 1.5275, obtained by (ne+no)/2, when a voltage was applied. The average refractive index of the liquid crystal molecules was 1.477 obtained by no when no voltage was applied. Therefore, the Δn was 0.0505 obtained by subtracting the average refractive index upon no voltage application from the average refractive index upon voltage application.
Table 3 and
As shown in
A closer examination was performed with a simulator based on the experimental results. The examination showed that green coloring occurred at a diffraction pitch of 6 μm, yellowish green coloring occurred at a diffraction pitch of 7 μm, yellowish red coloring occurred at a diffraction pitch of 8 μm, red coloring occurred at a diffraction pitch of 9 μm, reddish purple coloring occurred at a diffraction pitch of 10 μm, purple coloring occurred at a diffraction pitch of 11 μm, and bluish purple coloring occurred at a diffraction pitch of 12 μm.
A liquid crystal display panel was produced such that the pitch of a pair of comb-shaped electrodes have the above diffraction pitch, and the color change was visually examined. As a result, slightly yellow coloring was visually observed at a pitch of the pair of comb-shaped electrodes of 7.5 μm, slightly yellow coloring was visually observed at a pitch of the pair of comb-shaped electrodes of 9.5 μm, slightly purple coloring was visually observed at a pitch of the pair of comb-shaped electrodes of 10.5 μm, and blue purple coloring was visually observed at a pitch of the pair of comb-shaped electrodes of 12.5 μm. The results were in agreement with the tendency of the color change with a simulator and supported the spectrum in simulation. The visual observation proved that the reduction in the level of moiré involved less color change of moiré.
The liquid crystal display device of Embodiment 2 differs from that of Embodiment 1 in the following points. The present liquid crystal display device has a counter electrode 62 disposed on a counter-substrate-12 side. The counter electrode 62, a dielectric layer (insulating layer) 63, and a vertical alignment film 52 are stacked in this order on the liquid-crystal-layer-13-side main surface of a glass substrate included in the counter substrate 12. A color filter and/or a black matrix (BM) may be disposed between the counter electrode 62 and the glass substrate 32.
The counter electrode 62 is formed of a transparent conductive film such as an ITO film and an IZO film. The seamless counter electrode 62 and the seamless dielectric layer 63 are each formed at least over the entire display region. Predetermined electric potential is applied to the counter electrode 62. The electric potential is common between each pixel and each sub pixel.
The dielectric layer 63 is formed of a transparent insulating material. Specific examples of the insulating material include inorganic insulating films such as a silicon nitride film, and organic insulating films such as an acrylic resin film.
Meanwhile, similarly to Embodiment 1, a pair of comb-shaped electrodes including a pixel electrode 21 and a counter electrode 22, and a vertical alignment film 51 are disposed on the liquid-crystal-layer-13-side main surface of the glass substrate 31 included in the TFT substrate 11. Polarizers 71 and 72 are arranged on the outer main surfaces of the two glass substrates 31 and 32, respectively.
Different voltages are applied between the pixel electrode 21 and the counter electrode 22, and between the pixel electrode 21 and the counter electrode 62, during non-black display. The counter electrode 22 and the counter electrode 62 may be grounded. The same level of a voltage with the same polarity may be applied to the counter electrode 22 and the counter electrode 62. Different levels of voltages with different polarities may be applied to the counter electrode 22 and the counter electrode 62.
According to the liquid crystal display device of Embodiment 2, similarly to Embodiment 1, generation of moiré when a voltage is applied can be suppressed. Further, response speed can be increased by forming the counter electrode 62.
On the liquid-crystal-layer-13-side main surface of the glass substrate 31, signal lines 23, scanning lines 25, a common line 34, a thin film transistor (TFT) 27 that is a switching element (active element) and is formed in each sub pixel, a pixel electrode 21 separately formed in each sub pixel, and a counter electrode 22 connected with the common line 34 formed to be commonly used among a plurality of pixels (for example, all sub pixels) are disposed.
The scanning lines 25, and the common line 34, and the counter electrode 22 are formed on the glass substrate 31. A gate insulating film (not shown) is formed on the scanning lines 25, the common line 34, and the counter electrode 22. The signal lines 23 and the pixel electrode 21 are formed on the gate insulating film, and a vertical alignment film 51 is formed on the signal lines 23 and the pixel electrode 21.
The common line 34, the counter electrode 22, and the pixel electrode 21 are patterned by photolithography using the same film in the same step, and may be arranged on the same layer (the same insulating film).
The signal lines 23 are linearly arranged in parallel with each other, and extend in an up-down direction between the adjacent two sub pixels. The scanning lines 25 are linearly arranged in parallel with each other, and extend in a horizontal direction between the adjacent two sub pixels. The signal lines 23 are perpendicular to the scanning lines 25. The region partitioned by the signal lines 23 and the scanning lines 25 is approximately one sub pixel. The scanning lines 25 function as a gate of the TFT 27 in a display region.
The TFT 27 is formed near the intersection portion of each of the signal lines 23 and each of the scanning lines 25, and includes a semiconductor layer 28 formed in an island shape on the scanning line 25. The TFT 27 has a source electrode 24 which functions as a source, and a drain electrode 26 which functions as a drain. The source electrode 24 connects the TFT 27 and the signal line 23, and the drain electrode 26 connects the TFT 27 and a pixel electrode 21. The source electrode 24 and the signal lines 23 are patterned in the same film, and are connected with each other. The drain electrode 26 and the pixel electrode 21 are patterned in the same film, and are connected with each other.
A signal voltage (picture signal) is applied to the pixel electrode 21 from the signal lines 23 at predetermined timing during on-state of the TFT 27. Meanwhile, a predetermined electric potential (common voltage) is applied to the common line 34 and the counter electrode 22. The electric potential is common between each pixel.
The pixel electrode 21 has a comb-teeth shape in plan view. The pixel electrode 21 has a linear trunk portion (pixel trunk portion 45) and a plurality of linear comb-tooth portions (pixel comb-tooth portions 46). The pixel trunk portion 45 is formed along a short side (lower side) of a pixel. The pixel comb-tooth portions 46 are connected with the pixel trunk portion 45. Each of the pixel comb-tooth portions 46 extends from the pixel trunk portion 45 toward a short side (upper side) facing the pixel trunk portion 45, that is, in the about 90° direction.
The counter electrode 22 has a comb-teeth shape in plan view, and has a plurality of linear comb-tooth portions (counter comb-tooth portions 35). The counter comb-tooth portions 35 and the common line 34 are patterned in the same film, and are connected with each other. That is, the common line 34 is also a trunk portion (counter trunk portion) of the counter electrode 22 that connects the plurality of counter comb-tooth portions 35 with each other. The common line 34 is formed in a linear shape and parallel with the scanning lines 25, and extends in a horizontal direction between the adjacent two sub pixels. The counter comb-tooth portions 35 extend from the common line 34 toward a lower side facing the common line 34, that is, in the about 270° direction.
Thus, the pixel electrode 21 and the counter electrode 22 are arranged to face each other so that the comb teeth of the pixel electrode 21 and the counter electrode 22 (pixel comb-tooth portions 46, counter comb-tooth portions 35) are disposed alternately and spaced apart from each other. That is, the pixel comb-tooth portions 46 and the counter comb-tooth portions 35 are arranged parallel to each other, and are spaced apart from each other and alternately arranged.
According to one example shown in
According to one example shown in
The present application claims priority to Patent Application No. 2009-130187 filed in Japan on May 29, 2009, and Patent Application No. 2010-005108 filed in Japan on Jan. 13, 2010 under the Paris Convention and provisions of national law in a designated State, the entire contents of which are hereby incorporated by reference.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2009-130187 | May 2009 | JP | national |
| 2010-005108 | Jan 2010 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2010/053807 | 3/8/2010 | WO | 00 | 8/22/2011 |
