JP2000010105A - Liquid crystal display element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to obtain a response speed equivalent to that of a TN mode by providing the display element with two polarizing plates arranged across a liquid crystal cell in such a manner that the axes of polarization forming an angle of approximately 45 deg. in a substrate intra-surface direction intersect orthogonally with a liquid crystal molecule array. SOLUTION: A liquid crystal layer 15 which is negative in dielectric constant anisotropy is filled at a pretilt angle 10 deg. in the inter-substrate spacing between an array substrate 12 and a counter substrate 13. The polarizing plates 10, 11 forming the angle of approximately 45 deg. with the direction of the liquid crystal molecule array which is an electric field direction are orthogonally arranged. A uniaxial negative optical compensation plate 14 for compensating the optical anisotropy of the liquid crystal molecules in the thickness direction of the liquid crystal layer at the time of voltage impression is disposed between the counter substrate 13 and the liquid crystal layer 15. As a result, the liquid crystal molecules do not move and a bright state transparent to light is established when a transverse electric field is not applied. The liquid crystal molecules rise and a dark state to shut off the light is established when the transverse electric field is applied. Since the liquid crystal molecules rise to the direction of the surface perpendicular to alignment regulation force, the way that the liquid crystal molecules receive the influence of the alignment regulation force is weak and the response speed improves.

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, and more particularly to an active matrix type liquid crystal display device using a lateral electric field.

[0002]

2. Description of the Related Art As a display mode of a general liquid crystal display element, a TN (Twisted Nematic) mode is known.
The TN mode is a liquid crystal cell in which nematic liquid crystal is arranged by twisting 90 ° between two glass substrates, and is a mode in which a polarizing plate is used and light is modulated by using light-emitting properties of the liquid crystal by applying an electric field. .

[0003] The features of this TN mode are that the driving voltage is lower than those of other modes, and the power consumption is low due to the extremely high resistance. Further, since the contrast ratio is as high as 100 or more and high image quality can be achieved, it is used for an active matrix. However, a polarizing plate with low transmittance is used.In particular, the liquid crystal molecules are moved by a vertical electric field perpendicular to the glass substrate. No,
Viewing angle dependence occurred.

As one method for solving these problems, an IPS (In-Plane) method in which a horizontal electric field is applied to liquid crystal molecules and the liquid crystal molecules are rotated in the horizontal direction to obtain excellent visual field characteristics.
(Switing) mode is attracting attention. The 1PS mode is advantageous in terms of cost since the number of PEPs is reduced as compared with the conventional TN mode, and an ITO electrode on the opposing substrate is not required.

[0005]

However, the 1PS mode has a serious problem that the response speed is slow. This response speed is usually defined as the operation speed of the liquid crystal molecules, and is defined as the “rise time” from when a voltage for generating an electric field is applied to when the liquid crystal molecules operate and the amount of transmitted light changes. , From the stop of voltage application to the return to the original state. Ideally, it is sufficient to respond within one field period (30 ms).

However, when the response speed is slow, it is impossible to follow a fast movement such as a moving image display screen. Therefore, an object of the present invention is to provide a liquid crystal display element that can obtain a response speed comparable to that of the TN mode at the same cost as the IPS mode.

[0007]

In order to achieve the above object, the present invention provides a liquid crystal display element driven by a lateral electric field generated by applying a voltage, comprising a liquid crystal cell in which two substrates sandwich a liquid crystal. Two polarizing plates sandwiching the liquid crystal cell and arranged so that respective polarization axes forming an angle of approximately 45 degrees in the in-plane direction of the substrate with respect to the liquid crystal molecule arrangement are orthogonal to each other. Has a negative dielectric anisotropy, the long axis of the liquid crystal molecules is substantially parallel to the transparent substrate when no voltage is applied to the liquid crystal molecules, and the long axis of the liquid crystal molecules is in the thickness direction of the liquid crystal cell when the voltage is applied to the liquid crystal molecules. And a liquid crystal display element that rises almost in parallel.

In the liquid crystal display device having the above-described structure, the liquid crystal molecules rise in the direction perpendicular to the alignment regulating force, so that the influence of the alignment regulating force is weak.
Response speed is faster than mode. The liquid crystal molecules are I
It is necessary to provide a relatively high pretilt angle so that rotation parallel to the substrate does not occur as in the PS mode.
The angle is set to 5 ° or more, preferably 10 ° or more, and the viewing angle is widened by an optical compensator having a uniaxial negative characteristic.

[0009]

Embodiments of the present invention will be described below in detail with reference to the drawings. First, the concept of an active matrix type liquid crystal display device using a lateral electric field according to the present invention will be described with reference to FIG.

FIGS. 1A and 1B show a sectional structure of a liquid crystal cell. This liquid crystal cell has two glass substrates 1 and 2
A liquid crystal 3 having a negative dielectric anisotropy is injected therebetween, and a metal electrode 4 for generating a lateral electric field is formed on one substrate 1. FIG. 1A shows a state of the liquid crystal molecules 5 when no voltage for generating an electric field is applied. At this time, one end of the liquid crystal molecules 5 is lifted at a pretilt angle of, for example, 10 °, and the liquid crystal molecules 5 are vertically aligned with the alignment film surface being a horizontal plane (θ = 0 °). It is in a bright state in which light is transmitted while being stacked and arranged in a line.

Then, as shown in FIG. 1B, when a voltage is applied to the metal electrode 4 to generate a horizontal electric field 6, the liquid crystal molecules 5 rise and are arranged in the vertical direction to block the light. State.

FIGS. 1C and 1D are schematic views of a liquid crystal cell viewed from a vertical direction (from above). FIG.
(C) shows a state as viewed from above in FIG. (A). When no lateral electric field is applied, the liquid crystal molecules 5 are arranged such that the major axis direction is between the metal electrodes 4. . FIG.
(D) shows a state viewed from above in FIG. (B), and when a horizontal electric field is applied, the liquid crystal molecules 5 rise.

Next, FIG. 2 shows a schematic configuration example of the liquid crystal display device according to the first embodiment of the present invention, and will be described. FIG. 2A is a plan view of the liquid crystal display element as viewed from above,
FIG. 1B is a sectional view showing a schematic sectional structure.

The liquid crystal display device comprises a liquid crystal cell 16 formed by holding a liquid crystal layer 15 between an array substrate 12 made of glass or the like and a counter substrate 13 which are arranged to face each other.
And a driving circuit unit 17 for driving the liquid crystal cell 16
It is composed of Polarizing plates 10 and 11 are arranged on the outer surfaces of the array substrate 12 and the counter substrate 13, respectively. An optical compensator 14 is arranged between the counter electrode 13 and the polarizing plate 11.

This liquid crystal display device has a 15-inch diagonal effective display area 18 capable of color display. For example, (1024 × 3) × 786 display pixels are arranged in a matrix.

Next, the structure of the liquid crystal display device will be described in detail with reference to FIG. FIG. 3A is a plan view of the liquid crystal display element as viewed from above, and FIG. 3B is a cross-sectional view showing a cross-sectional structure.

The array substrate 12 is placed on a transparent glass substrate 19 having a thickness of about 0.7 mm with its surface polished (102).
4 × 3) molybdenum / aluminum / molybdenum laminated signal lines 20 and 786 molybdenum-tungsten alloy (MoW alloy) scanning lines 21
The thin film transistors (TFTs) 22 are arranged orthogonal to each other, and near each intersection.

More specifically, the TFT 22 is connected to the scanning line 21.
Using itself as a gate electrode, a hydrogenated amorphous silicon semiconductor layer (a-Si: H) 24 is formed via a gate insulating film 23 made of a silicon nitride film (SiNx).

A channel protection film 25 made of a silicon nitride film is formed on this upper layer, and a litho-doped low-resistance hydrogenated amorphous silicon semiconductor layer (n + a-Si: H) 2
A source 28 and a drain electrode 29 that are electrically connected to a-Si: H24 via the layers 6 and 27 are arranged.

The drain electrode 29 is formed integrally with the signal line 20, and the source electrode 28 has a laminated structure of molybdenum / aluminum / molybdenum similarly to the signal line 20, and has a stripe shape so as to form the pixel electrode 30. And extends along the signal line 20.

An end of the pixel electrode 30 is connected to a storage capacitor Cs
Is formed. A counter electrode 32 formed of a MoW alloy like the scanning line 21 and substantially parallel to the scanning line 21 is provided.

The counter electrode 32 includes first and second electrode portions 33 and 34 that are wired substantially in parallel with the pixel electrode 30,
A second auxiliary capacitance electrode portion 35 overlaps with the auxiliary capacitance electrode portion 31 with the gate insulating film 23 interposed therebetween.

As described above, the array substrate 12 includes the pixel electrodes 3
The liquid crystal molecules are controlled in accordance with the horizontal electric field generated between 0 and the first electrode unit 33 and the horizontal electric field generated between the pixel electrode 30 and the second electrode unit 34, respectively. Further, an alignment film 36 is formed as an upper layer.

On the other hand, the opposing substrate 13 is provided on a transparent glass substrate 37 having a thickness of about 0.7 mm, the surface of which is polished, between the signal lines 20 and the opposing electrodes 32 of the array substrate 12 and the scanning lines 21. Light leaking from between the counter electrode 32 and the TFT 22
In order to block undesired light irradiated thereon, a resin light-shielding film 38 is arranged in a matrix.

Between the light-shielding films 38, red (R), blue (B), and green (G) color filters 39 are arranged to realize color display. Further, an alignment film 41 is disposed on this upper layer via a surface smoothing layer 40 made of a transparent resin.

Further, fine polymer (not shown) is dispersed between the array substrate 12 and the opposing substrate 13, and the substrate gap is maintained at 3.5 μm. A liquid crystal layer 15 having a negative dielectric anisotropy at a pull tilt angle of 10 ° shown in FIG. 1 is injected into the gap between the substrates.

The rubbing angle between the direction of the electric field and the rubbing direction is 0 °, and as shown in FIG. 4, the polarizers 10 and 11 make an angle of approximately 45 ° with the direction of the liquid crystal molecule arrangement as the direction of the electric field. Are arranged orthogonally. These polarizing plates 10,
As 11, for example, G1220DU (manufactured by Nitto Denko Corporation)
Is used. Then, a uniaxial negative optical compensator 14 for compensating the optical anisotropy of the liquid crystal molecules in the thickness direction of the liquid crystal layer when a voltage is applied is provided between the counter substrate 13 and the polarizing plate 11.

In the liquid crystal display element of the present embodiment, when no horizontal electric field is applied (when no voltage is applied), the liquid crystal molecules do not move, and a light state is transmitted, and when the horizontal electric field is applied (when a voltage is applied). In (), the liquid crystal molecules rise and enter a dark state in which light is blocked.

For comparison with the present embodiment, a pixel structure similar to that described above, a liquid crystal having the same negative dielectric anisotropy, a pretilt angle of 1 °, and a rubbing angle of 20 ° were used. In comparison with the liquid crystal display device formed in the IPS mode, the response speed of the liquid crystal display device of the present embodiment is 50 ms, and the response speed of the conventional IPS mode liquid crystal display device is 80 ms. However, the contrast is
In the present embodiment, a value of "100" is obtained in the conventional IPS mode, and a value of "200" is obtained in the conventional IPS mode, and a higher contrast value is obtained in the conventional IPS mode.

As described above, the liquid crystal display device of this embodiment is
The response speed is improved over the conventional IPS mode. In the IPS mode, the liquid crystal molecules are rotated in the liquid crystal alignment plane (rotated in parallel to the substrate) by the lateral electric field in the IPS mode, which is greatly affected by the alignment control force. It is considered that, in the display element, the liquid crystal molecules rise in the direction of the plane perpendicular to the alignment regulating force, so that the influence of the liquid crystal molecules is weak.

The liquid crystal molecules of the present embodiment need to have a relatively high pretilt angle so as not to generate a rotation parallel to the substrate as in the IPS mode.
5 ° or more, preferably 10 ° or more.

The optical compensator provided in the liquid crystal display device of the present embodiment is used because the viewing angle is narrower than that in the IPS mode, and is used for a uniaxial negative type such as used in a vertical alignment type LCD. Apply

Next, FIG. 5 shows an example of the configuration of a liquid crystal display element according to the second embodiment, which will be described. In the present embodiment, parts that are the same as in the first embodiment are given the same reference numerals, and descriptions thereof are omitted.

In the liquid crystal layer of the first embodiment described above, the liquid crystal molecules near the interface cannot be fully raised due to the alignment regulating force, so that retardation remains in the liquid crystal molecule alignment direction, which may cause a decrease in contrast. . Therefore, in the second embodiment, in order to improve this, for example, a retardation plate of 150 nm or less is inserted in a direction orthogonal to the liquid crystal molecule alignment direction.

As shown in FIG. 5, on the outer surfaces of the array substrate 12 and the counter substrate 13, for example, optical retardation plates 42 and 43 made of triacetyl cellulose having a retardation value of 25 nm are arranged.

By arranging the optical phase difference plates 42 and 43, the contrast which was "100" in the first embodiment can be improved to "180".
The optical phase difference plates 42 and 43 may be provided in place of the optical compensator 14 in addition to the one added to the first embodiment.

[0037]

As described in detail above, according to the present invention, I
It is possible to provide a liquid crystal display element that can obtain a response speed comparable to that of the TN mode at the same cost as the PS mode.

[Brief description of the drawings]

FIG. 1 is a view showing the concept of an active matrix type liquid crystal display device using a lateral electric field according to the present invention.

FIG. 2 is a diagram illustrating a schematic configuration example of a liquid crystal display element according to the first embodiment.

FIG. 3 is a diagram illustrating in detail a cross-sectional structure of the liquid crystal display element according to the first embodiment.

FIG. 4 is a view for explaining a direction of an electric field (a direction of a liquid crystal molecule arrangement) and deflection of a polarizing plate in the first embodiment.

FIG. 5 is a diagram showing in detail a cross-sectional structure of a liquid crystal display device according to a second embodiment.

[Explanation of symbols]

 1, 2, glass substrate 3, liquid crystal 4, metal electrode 5, liquid crystal molecule 6, lateral electric field 10, 11, polarizing plate 12, array substrate 13, counter substrate 14, optical compensator 15, liquid crystal layer 16, liquid crystal cell

Claims (6)

[Claims] 1. A liquid crystal display element driven by a lateral electric field generated by applying a voltage, comprising: a liquid crystal cell in which two substrates sandwich liquid crystal; and a liquid crystal cell sandwiching the liquid crystal cell; Two polarizers arranged so that respective polarization axes forming an angle of approximately 45 degrees in the in-plane direction of the substrate are orthogonal to each other, wherein the liquid crystal has a negative dielectric anisotropy, Wherein the major axis of the liquid crystal molecules is substantially parallel to the transparent substrate when no voltage is applied, and the major axis of the liquid crystal molecules rises substantially parallel to the thickness direction of the liquid crystal cell when a voltage is applied. . 2. In the liquid crystal display element, a uniaxial negative optical compensator for compensating optical anisotropy of liquid crystal molecules in a thickness direction of the liquid crystal cell when a voltage is applied is provided between the transparent substrate and the liquid crystal. 2. The liquid crystal display device according to claim 1, wherein the liquid crystal display device is disposed at a position other than that of the liquid crystal display. 3. The liquid crystal display device according to claim 1, wherein a retardation plate for compensating for a retardation of liquid crystal molecules near an interface of the substrate when a voltage is applied is arranged between the polarizing plate and the liquid crystal cell. The liquid crystal display device according to claim 1. 4. The liquid crystal display device according to claim 3, wherein the retardation of the retardation plate is 150 nm or less. 5. The liquid crystal display device according to claim 1, wherein a pretilt angle of the liquid crystal molecules when no voltage is applied is 5 degrees or more. 6. A liquid crystal display element using a horizontal electric field, comprising: a first substrate formed of a transparent substrate and having a drive circuit including a thin film transistor; and a transparent substrate disposed to face the first substrate;
A second substrate on which a color filter is formed, and liquid crystal molecules having a negative dielectric anisotropy with a pull tilt angle of 10 ° arranged in substantially the same direction as the direction of the horizontal electric field generated by the driving circuit, and when no voltage is applied. A bright state, a liquid crystal layer that takes a dark state by rising liquid crystal molecules when voltage is applied, and a liquid crystal layer provided between the liquid crystal layer and the second substrate;
An optical compensator having a uniaxial negative characteristic for compensating for optical anisotropy of liquid crystal molecules that rises when a voltage is applied; and an arrangement direction of the liquid crystal molecules on outer surfaces of the first substrate and the second substrate. And a polarizing plate that is orthogonally arranged at an angle of approximately 45 degrees in opposite directions to each other.