JP3000871B2 - Liquid crystal display - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a thin film transistor (T
FT) In a liquid crystal display device driven by an array substrate, the present invention relates to a configuration of a TFT liquid crystal display device using liquid crystal molecules driven by an electric field in a direction horizontal to a substrate surface.

[0002]

2. Description of the Related Art First, a liquid crystal display device using liquid crystal molecules driven by an electric field in a horizontal direction with respect to a substrate surface will be described. 8 and 9 are examples of schematic diagrams of the present liquid crystal display device. Liquid crystal molecules 6 are injected into two transparent glass substrates 1a and 1b arranged with a certain gap. Conductor patterns 7a and 7b extend in parallel on a surface of one of the substrates 1a in contact with the liquid crystal molecules at a predetermined interval. Also, on the surface of each of the two substrates that is in contact with the liquid crystal,
An alignment film is applied, and each substrate is subjected to an alignment process along a direction in which the conductor pattern extends. And
Polarizing plates 8a and 8b are provided outside each of the two substrates. 23a and 23b show the polarization axis of each polarizing plate. The polarization axis 23a on the light incident side is set in a direction parallel to the direction in which the liquid crystal molecules are arranged. On the other hand, the polarization axis 23b on the light emission side is set in a direction perpendicular to the direction in which the liquid crystal molecules are arranged. Here, the light incident side is the upper side of the figure, and the light emitting side, that is, the observer's viewpoint is the lower side of the figure.

First, a state where no voltage is applied between the two conductor patterns 7a and 7b, that is, a state where the conductor pattern is off, will be described. All rod-like liquid crystal molecules 6 in the liquid crystal display device
Are arranged substantially in parallel with the substrate and along the direction in which the conductor patterns 7a and 7b extend. At this time, first, light 21a having a random polarization direction 22a is emitted from the light source. Then, when the light 21a passes through the polarizing plate 8b, only the linearly polarized light 22b parallel to the polarizing axis 23a of the polarizing plate passes. In the liquid crystal layer, light passes through without changing the polarization direction. Then, in the polarizing plate on the emission side, the light does not pass through the polarizing plate because the polarization axis 23b is perpendicular to the polarization direction 22c of the light. Therefore, from an observer's viewpoint, it appears as a dark state.

Next, 7a and 7b are formed on the two conductor patterns.
In the meantime, a state in which a voltage is applied, that is, a state in an ON state will be described. Although the major axis of the liquid crystal molecules 6 is kept parallel to the substrate, the liquid crystal molecules 6 located in the vicinity of the substrate 1a are subjected to a horizontal voltage applied to the substrate between the two conductor patterns 7a and 7b. They are arranged perpendicular to the direction in which the conductor patterns extend. On the other hand, the liquid crystal molecules located in the vicinity of the substrate 1b are arranged in the direction in which the conductor pattern extends as in the off state. Therefore, the liquid crystal molecules are arranged in a spiral from the substrate 1b to the substrate 1a. As a result,
First, a light 21 having a random polarization direction 22a is emitted from a light source.
After a is emitted, it passes through the polarizing plate 8b,
Light 22b of linearly polarized light parallel to the polarization axis of the polarizing plate passes. In the liquid crystal layer, the polarization direction of light also changes by 90 degrees along the helical rotation of the liquid crystal molecules. As a result, in the polarizing plate on the emission side, the polarization axis 23b is parallel to the polarization direction 22c of the light, so that the light passes through the polarizing plate. Therefore, from an observer's viewpoint, it appears as a bright state.

When a low voltage is applied, these two states are in an intermediate state, and display of an intermediate brightness is possible.

This configuration is a configuration of a normally black mode liquid crystal display device. The above configuration is an example of a liquid crystal display device driven by an electric field in the horizontal direction. By changing the direction of the polarization axis and the alignment direction of the polarizing plate, a bright state when no voltage is applied and a dark state when a voltage is applied. A configuration of a normally white mode is also possible.

Conventionally, in many liquid crystal display devices which have been commercialized so far, electrodes are arranged on each of two substrates sandwiching a liquid crystal, and the electrodes arranged on each of the substrates are interposed. , And the display state is changed by changing the arrangement state of the liquid crystal molecules by an electric field perpendicular to the substrate surface. However, in this configuration, the display performance when viewed from the front is excellent, but there is a problem that the display performance such as contrast and gradation display when the viewpoint is inclined is rapidly deteriorated.

On the other hand, the liquid crystal display device driven by the electric field in the horizontal direction has a feature that the difference in display performance when the front and the viewpoint are tilted is small and the viewing angle characteristics are excellent.

[0009]

FIGS. 5, 6, and 7 are schematic plan views of one pixel of a conventional liquid crystal display device driven by a horizontal electric field. This configuration is a JAPAN DISP
At a conference of LAY '92, R. Published by Kiefer et al. As shown in FIG. 5, two electrodes 7a,
7b are each processed into a comb shape with the same conductor in the same step. The two electrodes are uniformly separated by a distance of about 10 μm. By applying a constant voltage between the two electrodes, an electric field is generated in the horizontal direction with respect to the substrate surface between the two electrodes, and the arrangement state of the liquid crystal molecules between the electrodes changes.

In this configuration, the alignment of the liquid crystal molecules is controlled by the electric field between the electrodes 7a and 7b. In this case, it is necessary to determine the alignment state of the liquid crystal in the state where no voltage is applied. . Therefore, it is necessary to apply an alignment film on the substrate and perform a rubbing process. In FIG. 5, the liquid crystal molecules in the state where no voltage is applied need to be aligned in the direction along the drain electrode and the common electrode, so that the rubbing direction is the direction of the arrow in this case. FIG. 10 shows a voltage-transmittance characteristic of a liquid crystal display panel by a lateral electric field control in a conventional structure. The liquid crystal molecules whose alignment is controlled in a fixed direction in which no voltage is applied in this way are supplied with the liquid crystal molecules 7a and 7
The control is performed by an electric field applied to a gap of about 10 μm between b. However, a driving voltage of a conventional liquid crystal panel driven by an electric field in a horizontal direction required generally more than ten volts. In order to move the liquid crystal molecules, the electric energy for overcoming the anchoring energy between the liquid crystal molecules and the substrate surface generated by the rubbing process or the like is generated by the electric energy 7a, 7
This is because it is necessary between b. On the other hand, from the viewpoint of a driver for driving a liquid crystal, it is desirable that the driving voltage be as low as possible due to the limitation of the driver manufacturing cost or the demand for downsizing the chip. As described above, if a drive voltage of several tens of volts or more is required, the driver chip size will be increased, which will increase the cost of the entire liquid crystal panel.
Generally, it is desired that a driver for an image signal of a liquid crystal panel can be controlled with a driving voltage of 5 V or less.

[0011]

According to the present invention, there is provided a thin film transistor liquid crystal display device in which a liquid crystal is sandwiched between two substrates.
The first substrate has a thin film transistor on its surface in contact with the liquid crystal.
And a drain electrode drawn from the thin film transistor
And a plurality of common electrodes are formed, between the plurality of common electrodes.
By constantly applying a constant electric field, the first substrate surface
Determining the orientation of the liquid crystal molecules of, the drain electrode and the front
By a voltage applied to the serial plurality of common electrodes, and configured to vary the arrangement of the liquid crystal molecules is intended to achieve a reduction in the driving voltage. Further, it is another object of the present invention to provide a liquid crystal display panel which does not require the application of an alignment film and a rubbing treatment, thereby simplifying the steps.

[0012]

By providing a plurality of common electrodes and applying a constant electric field between the common electrodes, the alignment state of the liquid crystal molecules on the substrate surface is always determined, and therefore any voltage is applied to the drain electrode. In this case, the alignment state is not unstable. Therefore, strong anchoring energy for determining the alignment state in the state where no voltage is applied is not required, and the driving voltage of a liquid crystal display device controlled by a flat electric field can be reduced.

Although the application of the alignment film on the substrate and the rubbing treatment are basically unnecessary by adopting the structure of the present invention,
Of course, this step can be added to obtain a more stable alignment state. However, even in this case, it is not necessary to obtain a strong alignment state as in the conventional example, and it is possible to reduce the pressing of the rubbing cloth, which is effective for the purpose of reducing the driving voltage. Although any number of the common electrodes can be provided in principle, a sufficient effect can be obtained with two electrodes in order to achieve the object of the present embodiment.

[0014]

This embodiment will be described with reference to FIGS. FIG. 1 is a plan view of a TFT array substrate in the TFT liquid crystal device of the present embodiment. FIG. 2 is a cross-sectional view of the TFT array substrate taken along line aa ′ in FIG. First, a method for manufacturing the present TFT liquid crystal display device will be described with reference to FIGS. First, a gate electrode 2a and two common electrodes 2b are formed on a transparent glass substrate 1a by using a metal such as chromium.
1 and 2b-2 are simultaneously formed. At this time, the common electrode buses 2b-1 and 2b-2 are drawn out in a configuration extending in the horizontal direction in parallel with the gate electrode, and in a pixel unit, are drawn out from the bus in a comb shape in the vertical direction. Next, TF
A silicon nitride film as the T gate insulating film 3 and TF
Amorphous silicon as a semiconductor layer 4 serving as a T channel layer, and a-Si on a TFT channel
In order to protect the semiconductor device, a protective insulating layer is continuously deposited using a plasma CVD apparatus. After that, only the protective insulating layer 4 is patterned using a mixed solution of hydrofluoric acid and nitric acid. Finally, using a metal such as titanium, a source electrode 5a serving as an image signal wiring and a drain electrode 5b serving as a pixel electrode are simultaneously formed. The drain electrode is the common electrode 2b formed earlier.
-1 and 2b-2 are drawn in a comb-like manner in the horizontal direction from the drain electrode drawn in the vertical direction in a direction orthogonal to -1 and 2b-2. Through the above steps, the TFT array substrate is completed. After applying an alignment film to another transparent glass substrate 1b, an alignment process is performed on each substrate along a direction in which the source wiring extends. Thereafter, the two gaps are separated by a constant gap of about 5 μm.
After laminating the two substrates, the liquid crystal 6 is injected into the gap, and a polarizing plate is arranged outside each of the two substrates, whereby a liquid crystal display device is completed.

Next, a method of driving the present liquid crystal display device will be described. A constant voltage Vc1 is externally applied to the common electrode 2b-1. The common electrode 2b-2 has a constant voltage V
Apply c2. A scanning signal Vg having a pulse waveform of one fixed period is externally input to the gate line 2a. When this pulse signal is input, the TFT on this gate line
Is turned on. On the other hand, an AC video signal Vs centered on Vsc is input to the source wiring. Then, a video signal is input from the source wiring to the drain electrode 5b through the TFT in the ON state. The pixel signal Vd at the drain electrode keeps the same voltage until a pulse signal is input from the next gate line. As described above, the pixel signal Vd applied to the drain electrode 5b and the constant voltage Vc applied to the common electrodes 2b-1 and 2b-2 are used.
The degree of twist of liquid crystal molecules interposed between the electrodes is determined by the direction of the total electric field of 1 and Vc2.

The direction of polarization of light passing through the liquid crystal layer changes due to the twisted state of the liquid crystal molecules, and the amount of light passing through the pixel changes in the liquid crystal display device.

It is assumed that the same voltage as Vc1 is applied to this drain electrode.

In this case, the electric field distribution in the pixel is as shown in FIG. The liquid crystal molecules in the pixel are oriented according to the electric field, and the incident light is deflected by the orientation of the liquid crystal molecules and can modulate the transmitted light intensity.

Next, it is assumed that the same voltage as Vc2 is applied to the drain electrode. In this case, the electric field distribution in the pixel is as shown in FIG. The liquid crystal molecules in the pixel are aligned according to the electric field, and the incident light is deflected by the liquid crystal alignment to determine the transmitted light intensity. Basically, these modulations use the birefringence effect of the electric field control of the liquid crystal molecules.

FIG. 11 shows a voltage-transmittance characteristic in this embodiment. The required application voltage of the image from the lowest transmittance to the highest transmittance was 5 V or less, and the driving voltage could be greatly reduced.

[0021]

According to the present invention, it is possible to drive a lateral electric field driven liquid crystal display panel having a good viewing angle characteristic at a low voltage of 5 V or less, which is very technically significant.

[Brief description of the drawings]

FIG. 1 shows a TFT in a TFT liquid crystal display device of the present embodiment.
Plan view of array substrate

FIG. 2 is a cross-sectional configuration view taken along a line aa ′ in FIG. 1 and viewed from a lateral direction.

FIG. 3 is a view for explaining an alignment state of liquid crystal molecules when the same voltage as Vc1 is applied to a drain electrode in the TFT liquid crystal display device of the present embodiment.

FIG. 4 is a diagram for explaining an alignment state of liquid crystal molecules when the same voltage as Vc2 is applied to a drain electrode in the TFT liquid crystal display device of the present embodiment.

FIG. 5 is a schematic plan view of a liquid crystal display device in a conventional liquid crystal display device driven by a horizontal electric field.

FIG. 6 is a schematic cross-sectional view of a conventional liquid crystal display device driven by a horizontal electric field when no voltage is applied to the liquid crystal display device.

FIG. 7 is a schematic sectional view of a conventional liquid crystal display device driven by a horizontal electric field when a voltage is applied to the liquid crystal display device.

FIG. 8 is a schematic view showing a light passage path of the conventional liquid crystal display device driven by a horizontal electric field when no voltage is applied to the liquid crystal display device.

FIG. 9 is a schematic diagram showing a light passage path when a voltage is applied to the liquid crystal display device in a conventional liquid crystal display device driven by a horizontal electric field.

FIG. 10 is a diagram showing a voltage-transmittance characteristic in a conventional liquid crystal display device driven by a horizontal electric field.

FIG. 11 is a diagram showing a voltage-transmittance characteristic in a liquid crystal display device driven by a horizontal electric field according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1a, 1b Substrate 2a Gate electrode and gate wiring 2b Common electrode and common wiring 3 Gate insulating film 4 Semiconductor layer 5a Source electrode and source wiring 5b Drain electrode 6 Liquid crystal molecule 7a Electrode 1 7b Electrode 2 8 AC signal source 9a, 9b Polarizing plate 10 Thin film transistor (TFT) 11 Additional capacitance 21a Incident light 21b Outgoing light 22a, 22b, 22c Polarizing direction of each light 23a, 23b Polarizing axis of polarizing plate

Continuation of the front page (56) References JP-A-6-273803 (JP, A) JP-A-8-5990 (JP, A) JP-B-53-23212 (JP, B2) JP-B-55-26447 (JP, A) , B2) (58) Fields investigated (Int. Cl. ⁷ , DB name) G02F 1/1343 G02F 1/136 G02F 1/133 G09F 9/00

Claims (5)

(57) [Claims] A liquid crystal is sandwiched between two substrates.
Sheets of the first surface in contact with the liquid crystal substrate of the substrate, a common electrode is formed led out a drain electrode and a plurality of the thin film transistor and the thin film transistor, the plurality of common
By providing a constant electric field between the electrodes, the first
A liquid crystal display device, wherein an alignment state of liquid crystal molecules on a substrate surface is determined , and an arrangement of the liquid crystal molecules is changed by a voltage applied to the drain electrode and the plurality of common electrodes. 2. The method according to claim 1, wherein the plurality of common electrodes are two kinds of common electrode mothers.
The common electrode buses are different from each other,
2. The liquid crystal display device according to claim 1, wherein a constant voltage is applied . 3. The method according to claim 2, wherein the plurality of common electrodes and the drain electrode are
2. The device according to claim 1, wherein the second member is formed in a substantially orthogonal shape.
Or the liquid crystal display device according to 2. 4. The method according to claim 1, wherein the plurality of common electrodes and the drain electrode are
Claims each formed in a comb shape
Item 4. The liquid crystal display device according to any one of Items 1, 2, and 3. 5. The semiconductor device according to claim 5, wherein the thin film transistor is formed.
Claim 1 wherein no alignment film is present on the substrate.
Item 5. The liquid crystal display device according to any one of Items 1, 2, 3, and 4.
Place.