JP2002139736A - Liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid crystal display device wherein an electric field in a direction as near to the lateral direction as possible between a pixel electrode and a counter electrode is generated without increasing a special manufacturing process, in the liquid crystal display device of a lateral electric field system. SOLUTION: In the liquid crystal display device wherein a first and a second substrates 1 and 7 are disposed opposite to each other and a liquid crystal is encapsulated between both the substrates 1 and 7, the comb-teeth shaped pixel electrodes 4 and comb-teeth shaped common electrodes 6 are disposed on the first substrate 1 so that comb-shape parts of both the electrodes are parallel to each other and the flat electrode shaped counter electrode 8 is disposed on the second substrate 7. A color filter 9 is laminated so as to cover the counter electrode 8 and the color filter 9 is set so as to have the film thickness which functions so that the direction of the electric field generated between the pixel electrode 9 and the counter electrode 8 when voltage is applied to the pixel electrodes 4 draws near to the parallel direction of the substrates 1 and 7.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device which generates an electric field in an oblique direction with respect to a substrate when an electric field is applied, and controls an alignment state of liquid crystal molecules.

[0002]

2. Description of the Related Art The TN system is widely used in current liquid crystal display devices, and maintains high performance and quality. But TN
The IPS (In-Plane Swivel) method applies an electric field applied to the liquid crystal layer in a direction parallel to the substrate as a method that can obtain a wider viewing angle than the TN method because the method has a problem that the viewing angle becomes narrower.
(Tching) type liquid crystal display devices have been proposed. However, in the IPS method, since a comb-shaped pixel electrode and a common electrode are provided on one substrate, the behavior of liquid crystal molecules located on the substrate side where no electrode is present when an electric field is applied is not stable, or the liquid crystal molecules between the substrates are not stable. However, there is a problem that the alignment state is not uniform and disclination occurs. Therefore, in order to stabilize the alignment state of the liquid crystal molecules between the two substrates, a configuration in which a pixel electrode and a common electrode are arranged on one substrate and a common electrode is arranged on the other substrate has been proposed. This is described, for example, in JP-A-2000-81641. In addition, a liquid crystal display device in which the electric field generated between the substrates is made as parallel to the substrate as possible by covering the common electrode of the other substrate with an insulating film is called "Fast-Switching L."
CD with Multi-domain Vertical Alignment Driven by
an Oblique Electric Field ”(SID 00 DIG
ESTs p334-337).

A conventional in-plane switching type liquid crystal display device will be described with reference to the drawings. FIG. 5 is a schematic cross-sectional view of a conventional liquid crystal display device, showing an arrangement state of liquid crystal molecules when an electric field is applied. A plurality of scanning lines and a plurality of signal lines 101 are arranged in a matrix on the first substrate 100.
At the intersection of 01, a TFT as a switching element is formed. One pixel is composed of a region surrounded by the scanning line and the signal line 101, and a comb-shaped pixel electrode 102 is arranged in each pixel. The TFT has a gate electrode connected to the scanning line, a source electrode connected to the signal line 101, and a drain electrode connected to the pixel electrode 102. When the TFT is turned on, the signal line 101 is turned on.
Is applied to the pixel electrode 102. A comb-shaped common electrode 103 is provided in a pixel of the first substrate 100, and the comb-shaped portion of the common electrode 103 is arranged in parallel with the comb-shaped portion of the pixel electrode 102. An RGB color filter 105 is provided on the second substrate 104 corresponding to each pixel, and a common electrode 106 is formed on the entire surface of the color filter 105.
Are laminated.

A liquid crystal layer having a positive dielectric anisotropy is interposed between the substrates 100 and 104, and liquid crystal molecules 107 are vertically aligned when no voltage is applied to the pixel electrode 102. When a voltage is applied to the pixel electrode 102, an electric field in a direction parallel to the substrate 100 is generated between the pixel electrode 102 and the common electrode 103 on the first substrate 100, and the pixel electrode 102 and the second substrate An electric field is generated between the common electrode 106 and the common electrode 106 in a direction slightly oblique from the direction perpendicular to the substrate 100, and the arrangement of the liquid crystal molecules changes along the electric field. The dotted line in FIG. 5 schematically shows the state of the electric field. Here, the liquid crystal molecules 107 on the pixel electrode 102 and on the second substrate 104 side are slightly tilted mainly due to the effect of the electric field in the oblique direction, and the liquid crystal molecules 107 located between the pixel electrode 102 and the common electrode 103 are mainly tilted. It is greatly inclined under the influence of the electric field in the parallel direction.

[0005]

However, in the case of the liquid crystal display device as shown in FIG.
When the liquid crystal molecules 107 are formed on the entire surface on the side, the direction of the electric field generated between the pixel electrode 102 and the common electrode 106 is close to the vertical direction, so that the liquid crystal molecules 107 are not so inclined. Therefore, a dielectric film 108 is laminated on the common electrode 106, and the pixel electrode 1
There is a liquid crystal display measure in which the electric field generated between the liquid crystal 02 and the common electrode 103 is made closer to the parallel direction. FIG. 6 is a schematic cross-sectional view of the liquid crystal display device, showing an arrangement state of liquid crystal molecules when an electric field is applied. The configuration other than the dielectric film 108 is the same as that of the liquid crystal display device of FIG. Dielectric film 108
When there is no equipotential line, the equipotential lines exist only in the liquid crystal layer. However, by providing the dielectric film 108, the equipotential lines also More. Therefore, when an electric field is applied, the liquid crystal molecules tilt more greatly than in the liquid crystal display device of FIG.

However, in the case of the liquid crystal display device shown in FIG. 6, a step of forming a dielectric film on the common electrode is required.
Therefore, there has been a problem that the number of steps increases and the cost increases.

Accordingly, an object of the present invention is to provide a liquid crystal display device in which liquid crystal molecules are greatly inclined when an electric field is applied, without increasing the number of steps.

[0008]

According to the present invention, there is provided a liquid crystal display in which a first substrate and a second substrate are opposed to each other and a liquid crystal is sealed between the two substrates. A pixel electrode formed for each, a common electrode formed on the first substrate and arranged substantially parallel to the pixel electrode in each pixel, and a solid electrode-like counter electrode formed on the second substrate, A color filter laminated on the counter electrode,
The color filter is characterized in that it has a film thickness that acts so that an electric field generated between the pixel electrode and the counter electrode when a voltage is applied to the pixel electrode is as parallel to the substrate as possible.

As described above, by providing a color filter acting as a dielectric film on the counter electrode to make the electric field generated between the pixel electrode and the counter electrode as horizontal as possible,
This eliminates the need for a special step of forming a dielectric film as in the related art, thereby increasing the efficiency of the manufacturing process.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic sectional view of the liquid crystal display device when an electric field is applied, and FIG. 2 is a plan view showing the structure of an electrode in one pixel.

Reference numeral 1 denotes a first substrate such as a glass substrate, on which scanning lines 2 and signal lines 3 are arranged in a matrix. A region surrounded by the scanning line 2 and the signal line 3 corresponds to one pixel, and a comb-shaped pixel electrode 4 is arranged in this region. A thin film transistor 5 (hereinafter referred to as a TFT) is provided at an intersection of the scanning line 2 and the signal line 3. Is formed. TFT5
Is formed by stacking a source electrode 5b, a drain electrode 5c, and the like extending from the signal line 3 on a gate electrode 5a extending from the scanning line 2, and the drain electrode 5c is connected to the pixel electrode 4. Reference numeral 6 denotes a common electrode provided on the first substrate side, and I
It is formed of TO or the like. The common electrode 6 has a comb-like shape, and is arranged such that the comb-tooth portion of the common electrode 6 and the comb-tooth portion of the pixel electrode 4 are parallel in each pixel. The common electrode 6 in each pixel is connected to the common electrode 6 in an adjacent pixel and is kept at the same potential. Note that FIG. 2 illustrates a pixel electrode 4 having three toothed electrodes and a common electrode 6 having four toothed electrodes in one pixel, but FIG. 1 illustrates a toothed shape of the pixel electrode 4 and the common electrode 6. One and two electrodes respectively
One is simplified.

Reference numeral 7 denotes a second substrate formed of a glass substrate or the like, and a counter electrode 8 such as ITO is laminated on the second substrate 7. The opposing electrode 8 is formed on the entire surface opposing the pixel and is kept at the same potential as the common electrode 6. 9
Is a color filter 9 covering the counter electrode 8, and one of R, G, and B color filters 9 is formed corresponding to each pixel. The color filters 9 are formed without gaps so as to cover at least the entire surface of the counter electrode 8 in the display area. Color filter 9
Has a uniform film thickness irrespective of the colors of RGB, but this color filter 9 acts as a dielectric film for generating an electric field in a direction as parallel as possible between the substrates 1 and 7, and the film thickness also reduces the distribution of the electric field. It is decided in consideration of.

A liquid crystal having a positive dielectric anisotropy is sealed between the substrates 1 and 7, and a vertical alignment film (not shown) formed on the substrates 1 and 7 allows a liquid crystal to be applied when no electric field is applied. The molecules 10 are arranged vertically. When a voltage is applied to the pixel electrode 4, an electric field is applied to the liquid crystal layer, and the dotted line in FIG. 1 indicates the electric field when the electric field is applied. At this time, an electric field in a direction parallel to the first substrate 1 is generated between the pixel electrode 4 and the common electrode 6, and an electric field in a direction oblique to the first substrate 1 is generated between the pixel electrode 4 and the counter electrode 8. Occurs. Here, when the common electrode 6 and the counter electrode 8 are maintained at 0 V and a voltage of 5 V is applied to the pixel electrode 4, for example, the potential of the surface of the color filter 9 is V _A1 = 3V at point A and V _B1 = 1 at point B. 0.5V, C point is V _C1 = 0V
become. If the color filter 9 as a dielectric film does not exist on the opposing electrode 8, the potential at the position opposing the pixel electrode 4 becomes 0 V, so that a strong electric field is generated in the vertical direction of the substrates 1 and 7. In the case of the embodiment, since a larger potential difference is generated between the pixel electrode 4 and the points B and C than between the pixel electrode 4 and the point A, a strong electric field is generated at this location and the electric field is parallel to the substrates 1 and 7. Approach the direction.

When the thickness of the color filter 9 is further increased, for example, the potential of the surface of the color filter 9 becomes V _A2 = 4 V at point A, V _B2 = 2 V at point B, and V _C2 = 0 V at point C. the relationship of _{V A1 <V A2, V B1} <V B2 is satisfied. That is, as the film thickness of the color filter 9 is increased, the potential difference between the pixel electrode 4 and the point A is reduced, and
The positions at which the potential difference becomes the same as when the upper film thickness is small move toward the side away from the pixel electrode 4, so that the electric field in the vertical direction on the pixel electrode 9 becomes weaker and the electric field in the parallel direction of the substrates 1 and 7. Becomes relatively strong. Therefore, an oblique electric field closer to the parallel direction of the substrates 1 and 7 is generated in the liquid crystal layer, and the liquid crystal molecules 10 are largely inclined. When the color filter 9 is thickened in this way, an oblique electric field near the parallel direction of the substrates 1 and 7 is generated in the liquid crystal layer, but the loss of light transmitted by the color filter 9 increases. When the permittivity of the color filter 9 is smaller than the permittivity of the liquid crystal, the electric field between the pixel electrode 4 and the counter electrode 8 is higher than that of the case where the permittivity of the color filter 9 is large. It becomes closer to the parallel direction. In consideration of these factors, the thickness and the dielectric constant of the color filter 9 are determined so that the loss of transmitted light is small and an electric field is generated in an oblique direction as much as possible.

The two substrates 1 and 7 are sandwiched between a pair of polarizing plates set in orthogonal Nicols, and the polarization direction is set such that the transmission axis of one of the polarizing plates and the tilt direction of the liquid crystal molecules 10 when an electric field is applied are about 45 °. If a plate is arranged, the liquid crystal molecules 10 are vertically aligned when no electric field is applied, so that incident light passing through one polarizing plate is blocked by the other polarizing plate, and the liquid crystal display device displays black. When an electric field is applied, the liquid crystal molecules 10 tilt in the direction parallel to the substrate along the electric field.
The incident light that has passed through one of the polarizing plates becomes elliptically polarized light due to the birefringence effect of the liquid crystal molecules 10, and passes through the other polarizing plate to display white. At this time, the liquid crystal molecules 10 are largely tilted by the action of the oblique electric field, so that a high-brightness liquid crystal display device is obtained.

As described above, in the present invention, by providing the color filter 9 acting as a dielectric film on the counter electrode 8, an electric field as close as possible in the horizontal direction can be generated between the pixel electrode 4 and the counter electrode 8. As a result, a high-brightness liquid crystal display device can be obtained. In addition, there is no need to provide a special step of manufacturing a dielectric film for generating a horizontal electric field between the pixel electrode 4 and the counter electrode 8 as much as possible, and the manufacturing process can be made more efficient.

Next, a second embodiment will be described with reference to FIG. The second embodiment is different from the first embodiment in that the film thickness of the color filter 11 is different for each color, but the other configuration is the same as the first embodiment. Therefore, the same portions as those in the first embodiment are denoted by the same reference numerals, and description thereof is omitted. FIG. 3 is a schematic sectional view of the liquid crystal display device when an electric field is applied, and corresponds to FIG. 1 of the first embodiment. FIG. 4 shows a conventional liquid crystal display device in which the thickness of the color filter 109 is different. The difference between the present invention and the conventional liquid crystal display device will be described with reference to FIGS.

Since the color filter 11 has different spectral characteristics depending on each color, when the color filter 11 has the same thickness regardless of the color, when a constant voltage is applied to each pixel electrode, an intermediate color which is a mixed color of RGB is applied. Is displayed with a yellow tint. Therefore, by changing the film thickness of the color filter 11 of each color, the balance of the light passing through the color filter 11 of each color is adjusted so that the mixed color of the three primary colors is displayed in an accurate color. In the second embodiment and the conventional example, the color filters 11 and 109 are made thicker in the order of red, green and blue.

In the second embodiment shown in FIG.
The color filter 11 is laminated on the counter electrode 8. In the conventional example shown in FIG. 4, a color filter 109 is formed on a second substrate 104, and a counter electrode 106 and a dielectric film 108 are laminated on the color filter 109 in this order. When an electric field is applied to the pixel electrodes 4 and 102, an electric field in the direction parallel to the substrates 1 and 100 is generated between the pixel electrodes 4 and 102 and the common electrodes 6 and 103, and the pixel electrodes 4 and 102 and the opposing electrode 8. Between the substrates 1 and 10
A zero oblique electric field is generated, and the liquid crystal molecules 10 and 107 are inclined along the electric field. At this time, the transmitted light passing through the liquid crystal layer changes from linearly polarized light to elliptically polarized light due to the birefringence of the liquid crystal, so that white light is displayed by passing through the polarizing plate. However, the retardation R is set so that the transmittance is optimized. You. The retardation R is represented by R = dΔn · sin ² φ, d is the cell thickness, Δn is the difference between the refractive indices of the liquid crystal molecules 10 and 107 in the major axis direction and the minor axis direction, and φ is the liquid crystal molecules 10 and 107 Is the inclination angle. The tilt angle φ of the liquid crystal molecules 10 and 107
Are the normal directions of the substrates 1 and 100 and the liquid crystal molecules 10 and 10
7 shows the angle formed by the long axis direction. If the thickness of the color filter 11 for each color is set to be different, the thickness d of the cell differs for each color, but it is preferable that the retardation R is constant irrespective of the color of the color filter 11. In the case of the second embodiment, since the distance between the counter electrode 8 and the pixel electrode 4 is constant and the thickness of the color filter 11 also serving as a dielectric film is different, when 5 V is applied to the pixel electrode, , The point A _{R of the} R layer is 2V, and the point A _{G of the} G layer is 3V.
V, points A _B of the B layer becomes 4V, the inclination angle of the liquid crystal molecules 10 differs according to each color. That is, in the R layer having a large cell thickness d _R , an electric field close to the vertical direction is generated, so that the liquid crystal molecules 10 do not fall so much, and Δn · sin ² φ _R becomes small.
On the other hand, in the B layer having a small cell thickness d _B , an electric field close to the horizontal direction is generated, so that the liquid crystal molecules 10 largely fall, and Δn · si
n ² φ _B increases. Therefore, the difference of the retardation R corresponding to each color of the color filter 11 becomes small, and the display unevenness caused by the retardation R can be suppressed.

On the other hand, in the case of the conventional example, since the counter electrode 106 is formed on the color filters 109 having different film thicknesses, a weak electric field is generated in the R layer having a large cell thickness d _R , and the cell thickness d _{R A} strong electric field is generated in the B layer where _B is large. Therefore, in the R layer, the electric field approaches the horizontal direction and the liquid crystal molecules 1
07 falls significantly, the electric field approaches the vertical direction in the B layer, and the liquid crystal molecules 107 do not fall much. Therefore, the difference of the retardation R corresponding to each color of the color filter 109 becomes large, and the display unevenness caused by the retardation R easily appears.

As described above, according to the present invention, by providing the color filter 11 acting as a dielectric film on the counter electrode 8, the dielectric film for generating a horizontal electric field between the pixel electrode 4 and the counter electrode 8 as much as possible. In addition to reducing the number of manufacturing steps, display unevenness due to a difference in retardation between the color filters 11 having different film thicknesses can be suppressed.

[0022]

According to the present invention, a horizontal electric field of the substrate is generated between the pixel electrode and the common electrode formed on the same substrate, and the oblique electric field of the substrate is generated between the pixel electrode and the counter electrode on the counter substrate. In a liquid crystal display device that generates an image, a color filter that acts as a dielectric film for making the oblique electric field as horizontal as possible is provided on the counter electrode. Can be made more efficient.
Further, even when the film thickness of the color filter is different for each color, the difference in retardation due to the color filter can be reduced, and display unevenness due to the difference in retardation for each pixel can be reduced.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of a liquid crystal display device according to a first embodiment of the present invention when an electric field is applied.

FIG. 2 is a plan view showing an arrangement of each electrode in one pixel.

FIG. 3 is a schematic sectional view of a liquid crystal display device according to a second embodiment of the present invention when an electric field is applied.

FIG. 4 is a schematic sectional view of a conventional example corresponding to the second embodiment when an electric field is applied.

FIG. 5 is a schematic cross-sectional view of a conventional example in which no dielectric film is present on a common electrode when an electric field is applied.

FIG. 6 is a schematic cross-sectional view of a conventional example having a dielectric film on a common electrode when an electric field is applied.

[Explanation of symbols]

 Reference Signs List 1 first substrate 4 pixel electrode 6 common electrode 7 second substrate 8 counter electrode 9 color filter 10 liquid crystal molecule 11 color filter

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Hiroyuki Kase 3-201 Minamiyoshikata, Tottori-shi, Tottori Sanyo Electric Co., Ltd. (72) Inventor Yoshitaka Mori 3-201 Minamiyoshikata, Tottori-shi, Tottori Sanyo Tottori Inside Electric Co., Ltd. (72) Inventor Shinichiro Tanaka 3-201, Minamiyoshikata, Tottori City, Tottori Prefecture GA14 GA23 HA04 JA24 NA01 NA27 NA29 PA08

Claims (7)

[Claims] 1. A liquid crystal display device in which a first substrate and a second substrate are disposed to face each other, and a liquid crystal is sealed between the two substrates. A pixel electrode formed for each pixel of the first substrate; A common electrode formed on the second substrate and substantially parallel to the pixel electrode in each pixel; a solid electrode-shaped counter electrode formed on the second substrate; and a color filter stacked on the counter electrode. Wherein the color filter has a thickness such that an electric field generated between the pixel electrode and the counter electrode when a voltage is applied to the pixel electrode acts so as to approach a parallel direction of the substrate. Liquid crystal display device. 2. A liquid crystal having a positive dielectric anisotropy is sealed between the two substrates, and liquid crystal molecules are vertically arranged when no voltage is applied, and are inclined in a horizontal direction of the substrate along an electric field when a voltage is applied. The liquid crystal display device according to claim 1, wherein: 3. The liquid crystal display device according to claim 1, wherein the color filter has a dielectric constant smaller than a dielectric constant of liquid crystal. 4. The liquid crystal display device according to claim 1, wherein said common electrode and said counter electrode are set at substantially the same potential. 5. The color filter according to claim 1, wherein the color filter of any one of R, G, and B is arranged according to the pixel, and a film thickness of the color filter is different according to each color. 5. The liquid crystal display device according to 4. 6. A plurality of scanning lines and signal lines are arranged in a matrix on the first substrate, a switching element is provided at an intersection of the scanning line and the signal line, and a comb-shaped pixel is provided in the switching element. An electrode is connected, and a comb-shaped common electrode is arranged so that the comb-teeth portion is substantially parallel to the comb-teeth portion of the pixel electrode.
The liquid crystal display device according to the above. 7. In a liquid crystal display device in which both substrates are sandwiched between a pair of polarizing plates, the transmission axes of the polarizing plates are orthogonal to each other, and the transmission axis of one of the polarizing plates is tilted when liquid crystal molecules are applied with an electric field. 7. The liquid crystal display device according to claim 1, wherein both polarizing plates are arranged so as not to be orthogonal to the direction.