JP2950288B2 - Active matrix liquid crystal display - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an active matrix liquid crystal display panel having a structure in which a liquid crystal is sandwiched between transparent insulating substrates.

[0002]

2. Description of the Related Art Thin-film field-effect transistors (hereinafter TF)
An active matrix liquid crystal display panel (hereinafter abbreviated as AMLCD) using T) as a pixel switching element has high quality image quality and is widely used as a display device of a portable computer or a monitor of a space-saving desktop computer recently. Have been.

A liquid crystal display is generally realized by changing the amount of transmitted light or the like by electrically controlling the orientation of the liquid crystal. Therefore, the gradation is determined by the relationship between the orientation of the liquid crystal and the viewing angle. There is a disadvantage that the characteristics and color are changed. Various methods have been proposed so as to compensate for this and to obtain a substantially constant gradation characteristic and hue even when viewed from any direction.

In recent years, in order to improve the image quality of a liquid crystal display,
In order to improve the viewing angle characteristics, a display method using a lateral electric field has been proposed. This is, for example, Proceeding
s of15th international display research conferenc
e, page 707. This is achieved by forming a linear pixel electrode and a counter electrode in parallel with each other as shown in FIG. 13 and applying a voltage between them to form a parallel horizontal electric field in the liquid crystal layer plane, thereby forming a liquid crystal layer. The direction of the director is rotated in the plane of the substrate, thereby controlling the amount of transmitted light.

In this liquid crystal display system, since the director moves only in a direction substantially parallel to the plane of the liquid crystal layer, as in the case of the TN mode, the director rises out of the plane of the liquid crystal layer and rises from the direction of the director. However, when viewed from the normal direction of the liquid crystal layer, the problem that the relationship between the amount of transmitted light and the applied voltage does not greatly differ does not occur,
It has a feature that almost the same image can be obtained when viewed from a very wide viewing angle.

[0006]

As described above, in the active matrix liquid crystal display device constructed using the lateral electric field, good display characteristics can be obtained in a wider viewing angle as compared with the conventional TN mode.

[0007] However, on the other hand, there is a lot of highly confidential information in the information handled by the computer, and in such a case, except for the person operating the computer,
It is necessary to make the displayed contents difficult to see.

[0008] There are two conflicting requirements in a computer display, and it is desirable to be able to realize these two requirements with a single switch.

An object of the present invention is to provide a good wide viewing angle characteristic of a horizontal electric field display and a good view angle other than from the front of the display.
It is an object of the present invention to provide an active matrix liquid crystal display device that can switch between narrow visibility angle characteristics and low visibility with a single switch.

[0010]

In order to achieve the above object, an active matrix liquid crystal display device according to the present invention comprises a plurality of scanning lines and a plurality of signal lines which are arranged in a grid and intersect with each other; A switch element provided in the vicinity of each intersection of the signal lines, a pixel electrode connected to the switch element, and a counter electrode capable of applying a voltage between the pixel electrode and the pixel electrode are arranged on an insulating substrate. A first liquid crystal layer, which is homogeneously oriented substantially parallel to the substrate, is sandwiched between another transparent insulating substrate and a pair of polarizing plates whose polarization directions are orthogonal to each other outside the transparent insulating substrates. However, the liquid crystal is operated using an electric field that is substantially parallel to the liquid crystal layer generated by applying a voltage between the pixel electrode and the counter electrode, with one polarization axis aligned with the orientation direction of the liquid crystal. Acte with structure In a matrix liquid crystal display device, between at least one of the transparent insulating substrates and the polarizing plate, the liquid crystal layer is homogeneously aligned in a direction parallel to the polarization axis of the polarizing plate, and is different from the first liquid crystal layer. A compensation liquid crystal cell having a transparent electrode for applying an electric field perpendicular to the substrate is disposed on the liquid crystal layer, and a predetermined potential that is changed between both transparent electrodes in the compensation liquid crystal cell can be applied. It has a mechanism.

Here, as a preferred embodiment of the active matrix liquid crystal display panel of the present invention, two or more compensation liquid crystal cells disposed between a transparent insulating substrate and a polarizing plate are disposed. Thereby, the visible range in the narrow visual field state can be efficiently narrowed.

Further, it is desirable that, among the compensating liquid crystal cells arranged in two or more layers between the transparent insulating substrate and the polarizing plate, at least two liquid crystal cells have liquid crystal orientations orthogonal to each other.

Further, four or more compensating liquid crystal cells are disposed between the transparent insulating substrate and the polarizing plate. At least two liquid crystal cells are arranged so that the alignment direction is parallel to the incident side polarization axis, and the pretilt is mutually shifted. It is also possible to make the directions opposite to each other, make the alignment direction parallel to the exit-side polarization axis in at least two layers of liquid crystal cells, and make the directions of the pretilts mutually opposite. This makes it possible to select some narrow viewing angle regions.

Further, it is desirable that the transparent insulating substrate constituting the liquid crystal cell disposed between the transparent insulating substrate and the polarizing plate is a plastic film. Thereby, the liquid crystal display panel can be made lightweight and thin.

Hereinafter, the principle of the present invention will be described.

First, the reason why a wide viewing angle characteristic can be obtained with a liquid crystal display device having a conventional structure will be described.

As shown in FIG. 13, the first liquid crystal layer 8 which is homogeneously aligned is sandwiched between two-phase polarizing plates forming crossed Nicols, and the direction of the liquid crystal director is made to coincide with the polarization axis of the exit-side polarizing plate. , A black display is obtained.

Even when viewed obliquely, since the absorption axis of the incident side polarizing plate and the anisotropic axis of the refractive index of the liquid crystal layer are parallel,
The polarization direction after transmission through the incident-side polarizing plate matches the direction of ordinary light in the liquid crystal layer, and hardly undergoes retardation in the liquid crystal. Therefore, the black level is almost equal to a good black level obtained by crossed Nicols without interposing the liquid crystal layer in all directions.

On the other hand, when the liquid crystal is rotated using a lateral electric field, the liquid crystal layer generates retardation according to the rotation angle, and a white display is obtained. At this time, since the amount of transmitted light increases as the rotation angle of the liquid crystal increases in almost any direction, the gradation characteristics when viewed from the front and the gradation characteristics when viewed obliquely are in good correspondence. Have a relationship.
This is the principle that a wide viewing angle characteristic can be obtained in a normal lateral electric field driving type liquid crystal display.

In the active matrix liquid crystal display device of the present invention, the compensating liquid crystal cell which is homogeneously oriented in parallel to the absorption axis of the incident side polarizing plate is sandwiched between the first liquid crystal layer and the incident side polarizing plate. Form. In the compensation liquid crystal cell,
A transparent conductive film is formed at the interface between the two substrates so that an electric field perpendicular to the substrates can be applied to the liquid crystal.

When no vertical electric field is applied to the compensating liquid crystal layer, the anisotropic axis of the refractive index of the compensating liquid crystal layer is parallel to the absorption axis of the incident side polarizing plate. It matches the direction of ordinary light in the compensating liquid crystal layer, and hardly receives retardation in the compensating liquid crystal layer. Therefore,
The viewing angle characteristics are equal to those of the conventional liquid crystal display device (FIG. 3) having no compensation liquid crystal cell, and a wide viewing angle characteristic can be obtained. This is referred to as a first state.

On the other hand, when a vertical electric field is applied to the compensating liquid crystal layer, the liquid crystal rises due to the electric field, and the direction of the anisotropic axis of the refractive index of the compensating liquid crystal layer coincides with the absorption axis of the incident side polarizing plate. Disappears.

When viewed from the front, the polarization direction after transmission through the incident-side polarizing plate matches the direction of ordinary light in the compensating liquid crystal layer, so that the compensating liquid crystal cell does not affect the display, and the first liquid crystal cell is By controlling, good front display characteristics can be obtained. On the other hand, when viewed obliquely, as a result of the mismatch between the direction of the refractive index anisotropic axis of the liquid crystal layer and the absorption axis of the incident side polarizing plate, the polarization direction after transmission through the incident side polarizing plate and the direction of ordinary light in the compensating liquid crystal layer , The compensation liquid crystal cell generates a sufficiently large retardation. For this reason, a monotonous relationship between the rotation angle of the liquid crystal and the amount of transmitted light controlled by the first liquid crystal cell cannot be maintained.

The amount of retardation that can be generated can be controlled by the refractive index anisotropy of the liquid crystal, the thickness of the liquid crystal cell, and the state of rising of the liquid crystal. By optimizing the amount of retardation, the amount of retardation depends on the viewing angle direction. By inclining the viewing angle a little from the front, gradation inversion is caused, and a display with a considerably narrow viewing angle can be obtained. This is the second state.

If the voltage applied to the compensating liquid crystal cell can be switched between 0 V and a fixed level by an external switch in advance, the first switch having a very wide viewing angle can be obtained by switching the switch. It is possible to easily switch between the state and the second state having a considerably narrow viewing angle.

Further, by using a plurality of cells as the compensating liquid crystal cells and making them orthogonal to each other to apply a voltage to both of them, the viewing angle can be narrowed more efficiently.

[0027]

Next, embodiments of the present invention will be described in detail with reference to the drawings.

Referring to FIG. 1, FIG. 2 and FIG. 3 showing the first embodiment of the present invention, a pixel electrode constituting a pixel is connected to a source electrode of a thin film transistor having a scanning line 17 as a gate electrode. I have. The drain electrode of the thin film transistor is connected to the signal line 16. The pixel electrode 5
It is formed in parallel with the counter electrode 4 connected by the signal line 16 and the counter electrode bus line 18.

The first liquid crystal layer 8 is sandwiched between two glass substrates 2. An alignment film 3 is provided on both interfaces of the first liquid crystal layer 8.
Are arranged, and are homogeneously oriented in the direction of 13 in FIG. 1B by a rubbing treatment. An electric field substantially parallel to the liquid crystal layer is applied to the first liquid crystal layer 8 by a potential difference between the written and held potential of the pixel electrode 5 and the potential of the counter electrode 4 via a switching element formed of a thin film transistor. The liquid crystal layer rotates in the plane of the liquid crystal layer.

Outside the two glass substrates 2, two compensating liquid crystal cells constituted by an insulating transparent plastic substrate 6 are arranged. A transparent conductive film 7 is formed inside the transparent plastic substrate 6, and a voltage is supplied from the outside to form the second and third liquid crystal layers 9 and 10.
Then, an electric field in a direction perpendicular to the substrate can be applied.

Second liquid crystal layer 9 and third liquid crystal layer 10
Is homogeneously aligned substantially parallel to the substrate by the alignment film 3. The alignment direction of the second liquid crystal layer 9 is
The orientation is the same as the orientation direction shown in FIG. 1B. The orientation direction 14 of the third liquid crystal layer 10 is
The direction is perpendicular to the alignment direction 13 of the first and second liquid crystal layers 8 and 9.

Outside the two liquid crystal cells formed by the transparent plastic substrate 6, two polarizing plates 1 are arranged. The polarization axis 1a of the incident side polarizing plate is the first and the second.
Are set in parallel with the alignment direction 13 of the liquid crystal layers 8 and 9. The polarization axis 1b of the exit-side polarizing plate is set parallel to the orientation direction 14 of the third liquid crystal layer.

As shown in FIG. 3, a liquid crystal cell 20 composed of the second and third liquid crystal cells 9 and 10 has an AC rectangular shape having a constant voltage by a switch 22 and a resistor 23 which is sufficiently smaller than the resistance of the liquid crystal cell 20. It is connected so that the wave 24 and 0V can be switched.

When the voltage applied to the second and third liquid crystal cells 9 and 10 is 0 V, the second liquid crystal layer and the third liquid crystal layer 9 and 10 respectively have the absorption axes of the polarizing plate 1 on the emission side. Since the liquid crystal layers 9 and 10 are parallel to the absorption axis of the polarizing plate 1 on the incident side, retardation does not occur. Therefore, a state equivalent to a case where there is no liquid crystal cell including the second and third liquid crystal layers 9 and 10 is provided. By controlling the voltage between the pixel electrode 5 and the counter electrode 4, the first liquid crystal layer 8 is controlled. , It is possible to directly obtain good display characteristics in a wide viewing angle that can be obtained by changing the direction.

On the other hand, when the switch 22 is switched and an AC rectangular wave 24 is applied to the second and third liquid crystal cells 20 and 21, the directors of the second and third liquid crystal layers 9 and 10 rise from within the substrate plane. Second and third liquid crystal layers 9,
When the rising of 10 is viewed from the front, no retardation is caused by these, so that good display characteristics can be obtained as in the case of applying 0V. On the contrary,
When viewed obliquely, the second and third liquid crystal layers 9,
10 generates the appropriate retardation. At this time, by controlling the rising amount of the director to an appropriate state, while maintaining the display characteristics when viewed from the front, the display characteristics when the substrate is viewed from an oblique direction are significantly deteriorated, That is, a display having narrow viewing angle characteristics can be obtained.

Here, the rising direction 26 of the second liquid crystal layer 9 and the third liquid crystal layer 10 is, as shown in FIG.
It is determined by setting the pretilt direction of each liquid crystal layer to the pretilt angle 25. If the pretilt directions of the second and third liquid crystal layers 9 and 10 are determined as 27 and 28 as shown in FIG. 4B, when the switch 22 is switched to the narrow viewing angle mode, When the substrate is viewed obliquely from the hatched azimuthal direction 29, the contrast can be sharply reduced.

When the present technology is applied to the display of a portable computer, the direction of the pretilt is set to 2 in FIG.
7, 28. In this way, the direction 30 in which the viewing angle is not narrowed can be limited to only the direction in which the computer keyboard 31 exists. Since it is virtually impossible for a person to expect from this direction, it is possible to make it difficult for a person other than the person using the display to recognize the displayed contents.

In the above-described embodiment, the second liquid crystal cell 9 and the third liquid crystal cell 1 are used to control the viewing angle.
0, the orientation direction of the second liquid crystal layer 9 was set parallel to the incident side polarization axis 1a, and the orientation direction of the third liquid crystal layer 10 was set parallel to the emission side polarization axis 1b. While the orientation directions of the second and third liquid crystal layers 9 and 10 are orthogonal to each other, the orientation direction of the second liquid crystal layer 9 is changed to the exit side polarization axis 1b.
Even if the orientation of the third liquid crystal layer 10 is parallel to the incident side polarization axis 1a, substantially the same characteristics can be obtained.

In the above-described embodiment, the polarization axis 1a on the incident side is made to coincide with the orientation direction of the first liquid crystal layer 8, and the polarization axis 1b on the emission side is perpendicular to this. Even if the polarization axis 1b on the side is parallel to the alignment direction of the first liquid crystal layer 8 and the polarization axis 1a on the incidence side is perpendicular to this, almost the same characteristics can be obtained.

In the above-described embodiment, the order of the second and third liquid crystal cells 9 and 10 is changed between the two polarizing plates and the first liquid crystal cell, or they are arranged at different positions. It is also possible.

Furthermore, it is possible to use only one of the second liquid crystal cell 9 and the third liquid crystal cell 10 and omit one of them. In this case, the azimuth at which the viewing angle is narrowed is limited, but there is an advantage that the structure is simplified and the manufacturing cost is reduced.

Next, a second embodiment of the present invention will be described in detail with reference to the drawings.

Referring to FIG. 6, FIG. 2 and FIG. 3 showing a second embodiment of the present invention, a pixel electrode forming a pixel is connected to a source electrode of a thin film transistor having a scanning line 17 as a gate electrode. I have. The drain electrode of the thin film transistor is connected to the signal line 16. The pixel electrode 5
It is formed in parallel with the counter electrode 4 connected by the signal line 16 and the counter electrode bus line 18.

The first liquid crystal layer 8 is sandwiched between two glass substrates 2. The alignment films 3 are disposed on both sides of the liquid crystal layer 8, and are homogeneously aligned in the direction of 13 in FIG. 6B by rubbing. An electric field substantially parallel to the liquid crystal layer is applied to the first liquid crystal layer 8 by a potential difference between the written and held potential of the pixel electrode 5 and the potential of the counter electrode 4 via a switching element formed of a thin film transistor. The liquid crystal layer rotates in the plane of the liquid crystal layer.

Outside the two glass substrates 2, four compensating liquid crystal cells each composed of an insulating transparent plastic substrate 6 are arranged. A transparent conductive film 7 is formed inside the plastic substrate 6, and a voltage is supplied from the outside, and the second liquid crystal layer 9, the third liquid crystal layer 10, the fourth liquid crystal layer 20, and the fifth liquid crystal layer At 21, an electric field in a direction perpendicular to the substrate can be applied.

The second liquid crystal layer 9, the third liquid crystal layer 10, the fourth liquid crystal layer 20, and the fifth liquid crystal layer 21 are homogeneously aligned by the alignment film 3 almost in parallel with the substrate. The alignment direction of the second liquid crystal layer 9 and the fourth liquid crystal layer 20 is equal to the alignment direction of the first liquid crystal layer 8, and is taken in the direction 22 shown in FIG. The orientation direction 23 of the third and fifth liquid crystal layers 10 and 21 is set to be a direction perpendicular to the orientation direction 22 of the first, second, and fourth liquid crystal layers 8, 9, and 20. Further, the second and fourth liquid crystal layers 9 and 2
The directions of the pretilt of 0 are set so as to be opposite to each other. Similarly, the third and fifth liquid crystal layers 1
The directions of the pretilts 0 and 21 are also set to be opposite to each other.

Two polarizing plates 1 are arranged outside the four liquid crystal cells constituted by the transparent plastic substrate 6. The polarization axis 1a of the incident side polarizing plate is set parallel to the alignment direction 22 of the first, second, and fourth liquid crystal layers 8, 9, 20. Further, the polarization axis 1b of the output side polarizing plate is
The third and fifth liquid crystal layers 10 and 21 are set in parallel to the alignment direction 28.

A liquid crystal cell composed of the second, third, fourth and fifth liquid crystal layers 9, 10, 20, 21 is:
As shown in FIG. 7, a switch 22 and a resistor 23 that is sufficiently smaller than the resistance of the liquid crystal cell are connected so as to be able to switch between an AC rectangular wave 24 having a constant voltage and 0 V. In this case, each of the second to fifth liquid crystal cells 9, 10, 20, 21 can be independently switched as shown in FIG. 7A,
As shown in FIG. 7B, the second and fourth liquid crystal cells 9, 20
, One of the third and fifth liquid crystal cells 10 and 21 is turned on or all of them are set to the 0V state. Can also. In the former case, basically 2 ⁴ =
Although 16 viewing angle characteristics can be selected, it is difficult to select a desired viewing angle state in a short time. In the latter case, basically only five types can be selected. However, as described in the first embodiment, when the liquid crystal rises in two directions orthogonal to each other, the viewing direction is approximately in the direction shown in FIG. The corner can be narrowed. Therefore, it becomes possible to efficiently select five types of viewing angle modes and switch them according to the situation.

Also, in the above-described embodiment, the second to fifth four liquid crystal cells 9, 10,
20 and 21, the orientation directions of the second and fourth liquid crystal layers 9 and 20 are set in parallel with the incident side polarization axis 1a, and the third and fifth liquid crystal layers 9 and 20 are aligned.
The liquid crystal layers 10 and 21 of the second liquid crystal layer are set to be parallel to the emission-side polarization axis 1b, but the alignment directions of the second and third liquid crystal layers 9 and 10 are kept perpendicular to each other, and The orientation direction of the layers 9 and 20 is set in parallel with the exit side polarization axis 12,
Even if the orientation directions of the third and fifth liquid crystal layers 10 and 21 are parallel to the incident side polarization axis 1a, substantially the same characteristics can be obtained.

In the above-described embodiment, the order of the second to fifth liquid crystal cells 9, 10, 20, 21 is changed between the two polarizers and the first liquid crystal cell, or the order is changed. It is also possible to arrange in a position.

In the above-described embodiment, the polarization axis 1a on the incident side is made to coincide with the orientation direction of the first liquid crystal layer 8, and the polarization axis 1b on the emission side is perpendicular to this. Even if the polarization axis 1b on the side is parallel to the orientation direction of the first liquid crystal layer 8 and the polarization axis 1a on the incidence side is perpendicular to this, almost the same characteristics can be obtained.

In the above-described embodiment, it is also possible to omit either the fourth liquid crystal cell 20 or the fifth liquid crystal cell 21. In this case, the range of selection of the viewing angle state is limited, but the structure is simplified,
There is an advantage that the manufacturing cost is reduced.

[0053]

EXAMPLE An example of the first embodiment of the present invention will be described in detail below using specific numerical values based on a manufacturing method thereof.

First, a method for manufacturing an active matrix substrate will be described.

On a transparent glass substrate, a Cr film is deposited in a thickness of 150 nm as a metal layer to be the scanning lines 17, the counter electrodes 4 and the counter electrode bus lines 18, and is patterned. Further, a silicon nitride film is 400 nm as the gate insulating film 12, a non-doped amorphous silicon film is formed thereon at 350 nm, and an n-type amorphous silicon film is formed at 30 nm.
Deposit continuously. Thereafter, an n-type amorphous silicon layer and a non-doped amorphous silicon layer are formed on the island-shaped amorphous silicon 19 pattern. After a while, the signal line 16
And a 150 nm Cr film as a metal layer to be the pixel electrode 5
m, and this is patterned. Further, a protective insulating film 11 is formed, and the protective insulating film 11 is removed from the peripheral terminal portion, thereby completing the TFT array.

The active mat produced as described above
Rix substrate and counter substrate with color filter
To the active matrix substrate side.
Rubbing in the direction of 15 of 2
Rubbing is performed in a direction opposite to the rubbing direction 15 in FIG.
After fixing the surroundings with a sealing material,
Then, liquid crystal is injected and sealed. Thereby, the first liquid
The crystal layer 8 is homogenized in the direction of the orientation direction 13 in FIG.
As aligned. Longitudinal direction of pixel electrode and alignment direction of liquid crystal
Was 15 degrees. For the ordinary light of the injected liquid crystal
The refractive index doctor is n ₀ = 1.476, the refractive index anisotropy is Δn =
0.067, and the cell gap was 4.5 μm.

Next, a liquid crystal cell comprising the second liquid crystal layer 9 of FIG. 1 is formed. First, the alignment film 3 is applied to the surfaces of the two transparent plastic substrates 6 on which the transparent conductive film 7 is formed, rubbed in the direction of the polarization axis 11 on the incident side, bonded together, and injected with liquid crystal. And homogeneous alignment. At this time, the direction of the pretilt was set as shown at 27 and 28 in FIG. The pretilt angle was 3 degrees. Similarly, a liquid crystal cell including the third liquid crystal layer 10 of FIG. 1 is formed. The orientation direction of the third liquid crystal layer 10 is shown in FIG.
In the direction of 14, the light was made parallel to the exit-side polarization axis. The direction of the pretilt was as shown in FIG. The second liquid crystal layer and the third liquid crystal layer have a thickness of 9 μm, and the first liquid crystal layer 8 has a thickness of 9 μm.
The same liquid crystal material was used.

The liquid crystal cell composed of the first liquid crystal layer 8, the liquid crystal cell composed of the second liquid crystal layer 9, and the liquid crystal cell composed of the third liquid crystal layer 10 formed in this way are shown in FIG.
As shown in (a), the polarizing plates 1 were attached on both sides such that the polarization axis was in the direction of FIG. 1 (b).

In the periphery, in addition to a driving circuit for driving the first liquid crystal layer 8 in an active matrix, as shown in FIG. 3, an AC rectangular wave is applied to the second liquid crystal cell 20 and the third liquid crystal cell 21. A circuit is configured so that the switch 22 can switch between applying 24 and 0V. The amplitude of the AC rectangular wave 24 was set to 2V.

FIG. 9 shows that the switch 22 is turned off and the second
When the voltage is not applied to the third liquid crystal cells 9 and 10 and the voltage applied to the pixel electrode 5 of the first liquid crystal cell 8 is used as a parameter, the line of sight is tilted in the direction A of FIG. The angle (tilt angle) between the substrate normal and the line of sight
Is a graph in which the horizontal axis represents the transmittance and the vertical axis represents the transmittance. Even if the inclination angle is considerably large, the contrast and gradation are very good, and the second liquid crystal layer 9 and the third liquid crystal layer 1
Very good viewing angle characteristics were obtained, almost equivalent to the case without 0.

FIG. 10 plots the transmittance in each of the white and black states when the azimuth angle is changed with the inclination angle kept constant at 50 degrees in this state. The black and white contrast is kept high in all directions.

On the other hand, when the switch 22 is turned on and a voltage is applied to the second and third liquid crystal cells 9 and 10, the relationship between the tilt angle and the transmittance in the direction A of FIG. ,
As shown in FIG. It was confirmed that black-and-white grayscale inversion occurred between 30 degrees and 40 degrees, and when the line of sight was slightly tilted, the state became very poor in visibility.

FIG. 12 plots the transmittance in each of the white and black states when the azimuth angle is changed while the inclination angle is kept constant at 50 degrees in this state. The black-and-white contrast is extremely low except for the range from 70 degrees to 170 degrees, and gradation inversion occurs in a wide range.

As described above, the active matrix liquid crystal display device of the present embodiment can be switched between the state where the viewing angle is very wide and the state where the viewing angle is very narrow when viewed from the designated direction, by simply switching the switch 22. Was able to switch.

Next, an example of the second embodiment of the present invention will be described in detail using specific numerical values based on the manufacturing method.

First, a method for manufacturing an active matrix substrate will be described.

On a transparent glass substrate, a Cr film is deposited to a thickness of 150 nm as a metal layer to be the scanning lines 17, the counter electrode 4 and the counter electrode bus line 18, and is patterned. Further, a silicon nitride film is 400 nm as the gate insulating film 12, a non-doped amorphous silicon film is formed thereon at 350 nm, and an n-type amorphous silicon film is formed at 30 nm.
Deposit continuously. Thereafter, an n-type amorphous silicon layer and a non-doped amorphous silicon layer are formed on the island-shaped amorphous silicon 19 pattern. After a while, the signal line 16
And a Cr film as a metal layer to be the pixel electrode 5
nm, and this is patterned. Further, a protective insulating film 11 is formed, and the protective insulating film 11 is removed from the peripheral terminal portion, thereby completing the TFT array.

The active mat produced as described above
Rix substrate and counter substrate with color filter
To the active matrix substrate side.
Rubbing in the direction of 15 of 2
Rubbing is performed in a direction opposite to the rubbing direction 15 in FIG.
After fixing the surroundings with a sealing material,
Then, liquid crystal is injected and sealed. Thereby, the first liquid
The crystal layer 8 is homogenized in the direction of the orientation direction 13 in FIG.
As aligned. Longitudinal direction of pixel electrode and alignment direction of liquid crystal
Was 15 degrees. For the ordinary light of the injected liquid crystal
The refractive index doctor is n ₀ = 1.476, the refractive index anisotropy is Δn =
0.067, and the cell gap was 4.5 μm.

Next, a liquid crystal cell comprising the second liquid crystal layer 9 of FIG. 6 is formed. First, the alignment film 3 is applied to the surfaces of the two transparent plastic substrates 6 on which the transparent conductive film 7 is formed, rubbed in the direction of the polarization axis 11 on the incident side, bonded together, and injected with liquid crystal. And homogeneous alignment. At this time, 27, 28, 37, 38 in FIG.
The direction of the pretilt was set as follows. The pretilt angle was 3 degrees. Similarly, a liquid crystal cell including the third, fourth, and fifth liquid crystal layers 10, 33, and 34 in FIG. 6 is formed.
The orientation direction of the third and fifth liquid crystal layers is the orientation direction 14 in FIG.
The orientation direction of was 13 and was parallel to the incident side polarization axis 11. The direction of the pretilt was as shown in FIG.
The thickness of the second to fifth liquid crystal layers was 9 μm, and the same liquid crystal material as that of the first liquid crystal layer was used.

The liquid crystal cells comprising the first to fifth liquid crystal layers 8 thus formed are stacked as shown in FIG.
Polarizing plates 1 were attached to both sides such that the polarization axis was in the direction shown in FIG.

In the periphery, in addition to a driving circuit for driving the first liquid crystal layer 8 in an active matrix, as shown in FIG. 7A or FIG. A circuit is configured so that the switch 22 can switch between applying the AC rectangular wave 24 and setting the voltage to 0 V. The amplitude of the AC rectangular wave 24 was set to 2V.

With such a circuit, when the second to fifth liquid crystal layers are turned off, good viewing angle characteristics can be obtained as in the first embodiment. Also, for example, when only the second and third liquid crystal layers are turned on, narrow viewing angle characteristics can be obtained in the same direction as in the first embodiment. When the second and fifth liquid crystal layers are turned on, the viewing angle can be reduced in the direction having the relationship shown in FIG. In addition, it is possible to narrow the viewing angle range in other directions by selecting the switch 22.

As described above, in the active matrix liquid crystal display device of the present embodiment, it is possible to switch between a state in which the viewing angle is very wide and a state in which several kinds of viewing angles are narrow by switching the switch. is there.

[0074]

As described above, according to the present invention, one or more layers of another liquid crystal cell homogeneously aligned in the direction of the polarization axis are laminated, and a wide viewing angle state in which no voltage is applied to this liquid crystal layer, a vertical electric field, Can be switched with a single switch between a narrow viewing angle state in which the liquid crystal is raised by applying a voltage, and there is an effect that it is possible to realize a display that can easily keep information confidential depending on the situation.

[Brief description of the drawings]

FIG. 1 is a sectional view of a first embodiment of the present invention (FIG.
(A)) and a plan view ((b) of the same figure).

FIG. 2 is a plan view of one pixel of an active matrix array according to the first and second embodiments of the present invention.

FIG. 3 is an equivalent circuit diagram of a portion for applying a voltage to second and third liquid crystal layers in the first embodiment of the present invention.

FIG. 4 shows the relationship between the direction of the pretilt and the rising direction of the liquid crystal when a voltage is applied in the first and second embodiments of the present invention (FIG. 4A), and the relationship between the direction of the pretilt and the direction in which the viewing angle decreases. (B) of FIG.

FIG. 5 is a diagram showing an arrangement when the liquid crystal display device according to the embodiment of the present invention is applied to a portable computer.

FIG. 6 is a cross-sectional view (FIG. 6A) and a plan view (FIG. 6B) of a second embodiment of the present invention.

FIG. 7 shows the second to fifth embodiments in the second embodiment of the present invention.
FIG. 4 is an equivalent circuit diagram of a portion for applying a voltage to the liquid crystal layer of FIG.

FIG. 8 shows pretilt directions of second and third liquid crystal layers according to the first embodiment of the present invention (FIG. 8A), and second to fifth liquid crystal layers according to the second embodiment of the present invention. FIG. 3 is a diagram showing the direction of a pretilt of a liquid crystal layer (FIG. 2B).

FIG. 9 is a diagram illustrating a voltage applied to the pixel electrode 5 of the first liquid crystal cell as a parameter when the switch 22 is turned off and no voltage is applied to the second and third liquid crystal cells in the first embodiment. 8A is a graph in which the horizontal axis represents the angle (tilt angle) between the substrate normal and the line of sight when the line of sight is inclined in the direction of A in FIG. 8A, and the vertical axis represents the transmittance.

FIG. 10 is a diagram plotting transmittance in each of a white state and a black state when the azimuth is changed while the switch 22 is turned off and the inclination angle is fixed at 50 degrees in the first embodiment.

FIG. 11 shows the tilt angle and transmission in the direction A of FIG. 8A when the switch 22 is turned on and a voltage is applied to the second and third liquid crystal cells in the first embodiment. It is a figure which shows the relationship of a rate.

FIG. 12 is a graph plotting transmittance in each of a white state and a black state when the azimuth is changed while the tilt angle is constant at 50 degrees with the switch 22 turned on in the first embodiment. FIG.

FIG. 13 is a cross-sectional view (FIG. 13A) and a plan view (FIG. 13B) of a conventional wide viewing angle liquid crystal display device.

[Explanation of symbols]

Reference Signs List 1 polarizing plate 2 glass substrate 3 alignment film 4 counter electrode 5 pixel electrode 6 transparent plastic substrate 7 transparent conductive film 8 first liquid crystal layer 9 second liquid crystal layer 10 third liquid crystal layer 1a incident side polarization axis 1b exit side polarization Axis 11 Protective insulating film 12 Gate insulating film 13 Alignment direction of first and second liquid crystal layers 14 Alignment direction of third liquid crystal layer 15 Rubbing direction 16 Signal line 17 Scan line 18 Counter electrode bus line 19 Island-shaped amorphous Silicon 20 Second liquid crystal cell 21 Third liquid crystal cell 22 Switch 23 Resistance 24 AC rectangular wave 25 Pretilt angle 26 Rising direction 27 Rising direction of pretilt of second liquid crystal layer 28 Rising direction of pretilt of third liquid crystal layer 29 The direction in which the contrast decreases when viewed from an oblique direction 30 The direction in which the viewing angle does not narrow 31 Keyboard 32 Liquid crystal display 33 Fourth liquid crystal layer 34 Fifth liquid crystal layer 35 Fourth liquid crystal cell 36 Fifth liquid crystal cell 37 Pretilt rising direction of fourth liquid crystal layer 38 Pretilt rising direction of fifth liquid crystal layer

Continuation of the front page (56) References JP-A-7-333640 (JP, A) JP-A-10-268251 (JP, A) JP-A-9-325346 (JP, A) JP-A-11-30783 (JP) , A) Hira 2-73617 (JP, U) (58) Fields investigated (Int. Cl. ⁶ , DB name) G02F 1/136 G02F 1/1343 G02F 1/1347 G09F 9/30

Claims (5)

(57) [Claims] 1. A plurality of scanning lines and a plurality of signal lines arranged in a grid and intersecting, a switch element provided near each intersection of the scanning line and the signal line, and a pixel connected to the switch element. An electrode and a counter electrode to which a voltage can be applied between the pixel electrode and the counter electrode are disposed on the insulating substrate, and the other transparent insulating substrate is homogeneously oriented substantially parallel to the substrate. A pair of polarizing plates whose polarization directions are orthogonal to each other are arranged outside the transparent insulating substrates so that one polarization axis matches the alignment direction of the liquid crystal. In an active matrix liquid crystal display device having a structure in which a liquid crystal is operated using an electric field substantially parallel to a liquid crystal layer generated by applying a voltage between the common electrode and at least one of the transparent insulating substrates, a polarizing plate, Between A compensating liquid crystal cell having a liquid crystal layer which is homogeneously oriented in a direction parallel to a polarization axis of a polarizing plate and which is different from the first liquid crystal layer and a transparent electrode for applying an electric field perpendicular to the substrate to the liquid crystal layer. And a mechanism capable of applying a predetermined potential that is changed between both transparent electrodes in the compensation liquid crystal cell. 2. The active matrix liquid crystal display device according to claim 1, wherein two or more compensation liquid crystal cells are arranged between the transparent insulating substrate and the polarizing plate. 3. Between the transparent insulating substrate and the polarizing plate,
3. The active matrix liquid crystal display device according to claim 2, wherein at least two of the compensating liquid crystal cells having at least two layers have liquid crystal orientation directions orthogonal to each other. 4. A liquid crystal cell for compensating is provided in four or more layers between the transparent insulating substrate and the polarizing plate. In at least two liquid crystal cells, the orientation direction is parallel to the incident side polarization axis and the pretilt direction is 2. The active matrix liquid crystal display device according to claim 1, wherein in at least two layers of liquid crystal cells, the alignment directions are parallel to the emission-side polarization axis and the pretilt directions are opposite to each other. 5. The active matrix according to claim 1, wherein the transparent insulating substrate forming the compensating liquid crystal cell disposed between the transparent insulating substrate and the polarizing plate is a plastic film. Liquid crystal display.