JPH06289367A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To provide the liquid crystal display device which can make gradation display, has high-speed respoonsiveness and is relatively easy in driving. CONSTITUTION:A ferroelectric liquid crystals having a tilting effect is used. Namely, this liquid crystal display device has a first substrate 12 which is formed with driving elements 14, pixel electrodes 15 connected to these driving elements 14 and control electrode regions including the electrode lines connected to the driving elements 14, a second substrate 13 which is disposed opposite to this first substrate 12 apart a prescribed spacing and is formed with a common electrode 17 on the surface and a layer 11 of the ferroelectric liquid crystal having the tilting effect which is arranged between the first and second substrates 12 and 13 and changes the tilting angle of the liquid crystal molecules 10 dependent on the voltage between the pixel electrodes 15 and the common electrode 17.

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 a liquid crystal display device capable of gradation display.

[0002]

2. Description of the Related Art FIG. 4 shows a sectional structure of a thin film transistor (TFT) liquid crystal display device manufactured by a conventional method.

In the structure shown in FIG. 4, the TN is arranged so that the major axis of the liquid crystal molecules 30 is aligned parallel to the electrode surface in the electric field off state, and is rotated from one substrate to the other substrate. It is composed of a (twisted nematic) type liquid crystal cell. In FIG. 4, the liquid crystal layer 31 is held between two transparent glass substrates 32 and 33, which are opposed to each other with a predetermined interval by a spacer (not shown).

On the lower glass substrate 32 in FIG. 4, a TFT 34, which is a driving element for applying an electric field to a pixel portion in accordance with a gate signal, and source, drain and gate electrodes of the TFT 34 (not shown). No.) and a matrix line (not shown) including a gate (scanning) line and a signal line connected to the electrodes, and a pixel electrode 35 connected to the TFT 34. Furthermore, an alignment film 36 is formed on top of it.
Is formed.

A common electrode 37 is formed on the upper glass substrate 33 in FIG. On the surface of the common electrode 37 in contact with the liquid crystal layer 31, an alignment film 38 subjected to alignment treatment is formed. In addition, a color filter layer (not shown) and a light-shielding film called a black mask for preventing light transmission in areas other than the pixel display portion and improving contrast may be formed.

The liquid crystal layer 31 shown in FIG. 4 is a twisted nematic liquid crystal. The alignment films 36 and 38 are rubbed so that their alignment directions differ by 90 ° and are orthogonal to each other. As shown by A in FIG. 4, in a state where no electric field is applied between the electrodes,
The liquid crystal molecules 30 are aligned such that their major axis directions are substantially perpendicular to the optical axis, and the liquid crystal molecules 30 gradually rotate along their optical axes so that the pixel electrode 35 side and the common electrode 37 side are aligned. The alignment direction of the liquid crystal molecules 30 is rotated by 90 °.

In the state of FIG. 4A, for example, the glass substrate 32
When the linearly polarized light that is aligned with the alignment direction along the optical axis is incident from below, the liquid crystal layer 31 is incident, and the incident linearly polarized light is rotated by 90 ° by the liquid crystal layer 31, and the glass substrate 33 is rotated.
Exit from. Then, the light is transmitted through a polarizing plate (not shown) having a polarization axis orthogonal to the polarization axis on the incident side to bring the display into a bright state.

When an electric field is applied between the pixel electrode 35 and the common electrode 37 which sandwich the liquid crystal layer 31, all the liquid crystal molecules 30 are aligned in the optical axis direction as shown in FIG. The display goes dark without being rotated and is blocked by the orthogonal polarizing plates.

The conventional manufacturing method of the above twisted nematic liquid crystal display device is, for example, as follows.
First, a TFT 34, a matrix line (not shown) including signal lines and scanning lines, and a pixel electrode 35 are formed on the glass substrate 32, and these are interconnected to form a TFT substrate. Next, the common electrode 37 is formed on the other glass substrate 33 to make a common electrode substrate. Alignment films 36 and 38 are formed on both the TFT substrate and the common electrode substrate, and a rubbing process is performed.

After aligning the alignment films 36 and 38 so that the alignment direction is 90 °, a gap control material (not shown) is sandwiched between both substrates, and a nematic liquid crystal is injected between both substrates. After that, the injection port is sealed and completed.

As a control element of the active matrix, a MIM (Metal Insu) is used instead of the TFT.
This is basically the same even when a later metal diode is used. In addition to the TN type, a ferroelectric liquid crystal or a polymer dispersed type liquid crystal may be used as the liquid crystal.

[0012]

In the above-mentioned conventional liquid crystal display device, although the TN type liquid crystal, the ferroelectric liquid crystal and the polymer dispersion type liquid crystal have their respective features and advantages,
The following problems have been encountered in terms of application to display devices.

The TN type liquid crystal display device has a slow optical response speed, a narrow viewing angle, and burns in the pattern after a fixed pattern is displayed for a long time. Since the liquid crystal has a memory effect, the ferroelectric liquid crystal display device has to perform an operation of canceling the previous state when changing the state, and the driving method is difficult.

The polymer dispersion type liquid crystal display device is not suitable for direct view display. An object of the present invention is to provide a liquid crystal display device capable of gradation display, having high-speed response, and being relatively easy to drive.

[0015]

A liquid crystal display device according to the present invention uses a ferroelectric liquid crystal having an electroclinic effect. That is, a first substrate having a control electrode region including a driving element, a pixel electrode connected to the driving element, and an electrode line connected to the driving element on the surface is opposed to the first substrate at a predetermined interval. The second substrate, which is disposed and has a common electrode formed on its surface, is disposed between the first and second substrates, and the tilt angle of the liquid crystal molecules changes depending on the voltage value between the pixel electrode and the common electrode. And a layer of ferroelectric liquid crystal having an electroclinic effect.

[0016]

[Function] Ferroelectric liquid crystal having an electroclinic effect has voltage dependence. That is, the inclination angles of the positive electric field and the negative electric field are opposite to each other, and the inclination angle changes according to the change of the voltage value.
It does not have a memory property, the light transmittance can be changed according to the voltage, and gradation display can be performed. Further, a high-speed response operation as a ferroelectric liquid crystal can be performed.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a liquid crystal display device according to the present invention will be described with reference to FIG. In FIG. 1, the transparent glass substrate 12
Above the TFT, a TFT 14 for applying an electric field to the pixel portion according to a gate signal, a source and a drain of the TFT 14,
A pixel electrode 15 connected to each electrode line (not shown) of the gate and the TFT 14, and an alignment film 16 are further formed.

A common electrode 17 is formed on the other transparent glass substrate 13 shown in FIG. Also, the liquid crystal layer 1 of the common electrode 17
An alignment film 18 is formed on the surface in contact with 1, and the rubbing process is performed to give the alignment direction.

In addition, a color filter layer (not shown) for coloring transmitted light and a light-shielding film called a black mask for preventing light transmission other than the pixel display portion and improving contrast may be formed. .

Both of the above substrates can be manufactured by conventional substrate manufacturing techniques. Next, the two substrates 12 and 13 are arranged so as to face each other with a gap control material (not shown) interposed therebetween, an injection port (not shown) is provided, and the both are bonded at the end portions.

The liquid crystal of the liquid crystal layer 11 is a ferroelectric liquid crystal having an electroclinic effect. As a liquid crystal material having an electroclinic effect,
For example, there are 764E and 860E manufactured by Merck.
The cone angle of a ferroelectric liquid crystal (FLC) having an electroclinic effect is relatively small. Even 764E, which is known as a material exhibiting a large electroclinic effect, has a value of 7 to 7 for an electric field of 10 MV / m.
Only a cone angle of about 8 °. In order to obtain a large electric field strength at a low voltage, it is necessary to reduce the cell thickness. For example, the cell thickness is selected to be 2 μm or less. Furthermore, since a high voltage is applied, it is preferable to use an IC for driving a high voltage.

Further, in order to apply a high voltage, in the case of an active matrix LCD, it is necessary to design the channel of the driving thin film transistor (TFT) so as to withstand the high voltage.

For example, the substrates 12 and 13 are arranged so as to face each other with a gap control material sandwiched so that the cell thickness is about 2 μm or less, and 764E liquid crystal manufactured by Merck is injected by a known means to form a liquid crystal display cell. . Further, a polarizing plate whose polarization axis is aligned with the direction of stable liquid crystal molecules is arranged on one substrate of the liquid crystal display cell, and a polarizing plate whose polarization axes are orthogonal to each other is arranged on the other substrate.

Further, in order to make the cone angle look as wide as possible, the orientation of the polarizing plate may be adjusted not to the stable point but to the orientation of liquid crystal molecules when an electric field is applied. In this case, one of the polarizing plates is aligned with the direction of the liquid crystal molecules when an electric field is applied, and the other polarizing plate is arranged orthogonally. With this arrangement, the contrast is improved.

Next, the electroclinic effect will be described with reference to FIGS. 2 and 3. As shown in FIG. 2, the electroclinic effect means that the liquid crystal molecule has a cone angle (2) depending on the direction (positive or negative) of the voltage and its value.
This is a phenomenon in which the tilt (tilt angle) of the major axis changes in an angle range called θ). FIG. 2 shows the case of the SmA phase. That is, in case of a certain positive electric field,
With a tilt angle of θ and a negative electric field of the same strength, −θ
It has a tilt angle of, and settles to an intermediate stable point when the electric field is removed.

A graph of the relationship between the voltage and the tilt angle is shown in FIG. Therefore, since the tilt angle can be changed in proportion to the voltage value by changing the voltage, it is possible to continuously display the intermediate gradation between the dark state and the bright state.

The liquid crystal display device as described above can be applied to both a simple matrix liquid crystal display device and an active matrix liquid crystal display device. Further, the present invention can be applied to a liquid crystal display device using either a TFT or a MIM diode as a driving element.

It will be apparent to those skilled in the art that the structures, materials, numerical values, etc. of the embodiments described above are merely examples, and the present invention is not limited to these, and various changes, improvements, combinations and the like can be made. .

[0029]

As described above, in the liquid crystal display device according to the present invention, since the ferroelectric liquid crystal having the electroclinic effect is used, gradation display is possible and the optical response is fast, The display device has a wide viewing angle. Further, since the liquid crystal has no dielectric anisotropy, no seizure occurs even in a fixed pattern for a long time. Further, since the stable point is returned to immediately after removing the voltage, the same driving method as that of the TN type liquid crystal can be adopted.

[Brief description of drawings]

FIG. 1 is a diagram illustrating a liquid crystal display device according to an embodiment of the present invention.

FIG. 2 is a diagram illustrating an electroclinic effect of liquid crystal of a liquid crystal display device.

FIG. 3 is a graph showing characteristics of an electric field and a tilt angle due to an electroclinic effect.

FIG. 4 is a sectional view of a conventional liquid crystal display device.

[Explanation of symbols]

 10 liquid crystal molecules 11 liquid crystal layer 12 and 13 glass substrate 14 TFT 15 pixel electrode 16 and 18 alignment film 17 common electrode

Claims (2)

[Claims] 1. A first substrate on a surface of which a control electrode region including a drive element, a pixel electrode connected to the drive element, and an electrode line connected to the drive element is formed, and a predetermined distance from the first substrate. A second substrate, which is disposed so as to face each other and has a common electrode formed on its surface, and a tilt of liquid crystal molecules, which is disposed between the first and second substrates and is dependent on a voltage value between the pixel electrode and the common electrode. A liquid crystal display device having a layer of a ferroelectric liquid crystal having an electroclinic effect with changing angles. 2. The liquid crystal display device has polarizing plates outside the first and second substrates respectively, and a polarizing axis of the polarizing plate provided on one substrate applies an electric field to the ferroelectric liquid crystal. 2. The liquid crystal display device according to claim 1, wherein the liquid crystal molecules are arranged in the same direction as the liquid crystal molecules.