JPH095708A - Liquid crystal display device and its driving method - Google Patents

Abstract

PURPOSE: To provide an antiferroelectric liquid crystal display device having high quality free from flickering. CONSTITUTION: This liquid crystal display device has a display panel which has matrix pixels formed by intersection of scanning signal electrodes 111 to 116 and information signal electrodes 121 to 126 orthogonal with each other, ferroelectric liquid crystals which exist in the spacing between the two electrodes and attain a first stable state consisting of an antiferroelectric phase at the time of non-electric field and a second or third stable state consisting of a ferroelectric phase according to the polarities of electric fields at the time of impression of the electric fields and a polarizing device which puts the first stable state into a dark state and the second and third states into a bright state. The display device is so constituted that the scanning of the scanning signal electrodes is executed by interlaced scanning of every other piece and that the polarities of the selection voltage to be impressed on the liquid crystals are inverted at every one horizontal period of the scanning.

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 using a ferroelectric liquid crystal having an antiferroelectric phase and a ferroelectric phase, and a driving method thereof.

[0002]

2. Description of the Related Art Liquid crystal display devices that take three optical states by an electric field are disclosed in Japanese Patent Laid-Open Nos. 2-153322 and 2-17.
No. 3724 and the like. It was subsequently revealed by Chandani et al. (Japanese Journal of Applied Physics 28 (1989) L1265 page) that this is due to the antiferroelectricity of liquid crystals.

According to this, a ferroelectric liquid crystal exhibiting antiferroelectricity (hereinafter referred to as an antiferroelectric liquid crystal) unwinds a spiral in a thin substrate gap as in a normal ferroelectric liquid crystal, and FIG.
As shown in (a), when there is no electric field (E = 0), liquid crystal molecules are tilted in opposite directions for each smectic layer. Therefore, when there is no electric field, the optical axis is oriented in the layer normal direction.

The transition to the ferroelectric phase occurs due to the application of an electric field (E> 0, E <0), and the liquid crystal molecules have a structure in which all layers are tilted in the same direction determined by the direction of the electric field. It is one of two directions that are symmetric from the normal to the tilted layer normal. This is shown in FIGS. 4 (b) and 4 (c).

When this antiferroelectric liquid crystal is applied to a display device, it is usually sandwiched between two polarizing plates, and the absorption axis of the polarizing plate is parallel to the layer normal as indicated by the double-headed arrow line in FIG. The two polarizing plates are arranged vertically so as to form a crossed Nicols. In this arrangement, the antiferroelectric state when there is no electric field is the dark state,
The ferroelectric state when the electric field is applied becomes the bright state.

The feature of this arrangement is that there are two bright states, and a method of switching the polarity of the applied voltage in the bright state at regular intervals using this is disclosed in Japanese Patent Laid-Open No. 2-173724. The present invention is an invention of an antiferroelectric liquid crystal device having a simple matrix structure, and FIG. 5 shows an example of its drive waveform.

FIG. 5 shows how the voltage applied to the liquid crystal changes with time, and the polarities of the voltages applied to the pixels are exchanged for each frame. As is clear from FIG. 5, the voltage applied to the liquid crystal is averaged over time and becomes zero. This has the advantage of preventing deterioration of the liquid crystal due to the DC voltage component.

[0008]

However, the polarity inversion driving method for each frame has a drawback in that the screen flickers when the display panel is viewed obliquely. The reason is shown below.

FIG. 6 shows liquid crystal molecules and the transmission axes of the upper and lower polarizing plates when the display panel is viewed from diagonally lower right. 4A shows a dark state, and FIGS. 4B and 4C show two bright states.
It corresponds to (b) and (c).

Comparing (b) and (c), in (b), the liquid crystal molecules are viewed almost from the side, so the effective refractive index anisotropy is not much different from that when viewed from the front.
In (c), the liquid crystal molecules are viewed from the vicinity of their major axes, and the refractive index anisotropy is significantly smaller than when viewed from the front. Therefore, there is a difference in transmittance between (b) and (c), and this is switched for each frame, so that it appears as a flicker.

Further, since the optical path length becomes long when viewed obliquely, in the case of (b), the retardation deviates from the optimum value, which is one of the causes of the flicker that the yellow color appears.

Consider a display device in which such elements are arranged in a matrix. Generally, when displaying a television image or the like, so-called interlaced scanning is performed in which scanning lines are skipped one by one and selected. FIGS. 7A to 7D show the states of the pixels in each frame at this time.

In FIG. 7, 511, 512, 513,
Is a scanning electrode, 521, 522, 623, ... Is a signal electrode, and 53 is a pixel. The short line segment in a pixel represents the direction of the optical axis of the liquid crystal in that pixel. Those parallel to the information signal line are in the antiferroelectric state (dark), and those that are inclined are in the ferroelectric state (bright). Indicates. Note that, here, for convenience, the signal line is set as the normal direction, but this is not necessarily required and may be an arbitrary direction. It is assumed that the state of leaning to the right is written by a positive voltage and the state of leaning to the left is written by a negative voltage. This depends on the liquid crystal because it is determined by the sign of spontaneous polarization. 54 and 55 are the axial directions of the upper and lower polarizing plates.

It is assumed that all the pixels are in a bright state and a certain frame has a state as shown in FIG. This is the state written by the positive voltage. Here, if the odd-numbered scan electrodes are subjected to negative voltage selective interlace scanning, the result is shown in FIG. 7B. Next, a negative voltage interlaced scan of the even scan electrodes is performed, resulting in FIG. 7C, and a positive voltage interlaced scan of the odd scan electrodes results in FIG. 7D. The next even interlaced scan returns to FIG. 7A, and the same cycle is repeated thereafter. That is, since the molecular arrangement state changes with 4 frames as one cycle, the frequency of transmittance fluctuation is low and flicker is significant.

It is an object of the present invention to provide a high quality anti-ferroelectric liquid crystal display device without flicker.

[0016]

According to the present invention, there is provided a display panel having a matrix pixel formed by intersections of scanning signal electrodes and information signal electrodes which are orthogonal to each other, and in a gap between the two electrodes, there is no electric field. First composed of antiferroelectric phase
And a ferroelectric liquid crystal that takes a second or third stable state consisting of a ferroelectric phase according to the polarity of the electric field when an electric field is applied, and the first stable state is the dark state, the second and the third stable state. In a liquid crystal display device including a polarizing device for turning the state 3 into a bright state, scanning of the scanning signal electrodes is performed by interlaced scanning one by one, and the selection voltage applied to the liquid crystal is applied every horizontal period of the scanning. It is characterized in that the polarity is reversed.

Further, according to the present invention, there is provided a display panel having a matrix pixel formed by intersections of scanning signal electrodes and information signal electrodes which are orthogonal to each other, and an antiferroelectric phase in a gap between the two electrodes when no electric field is applied. A ferroelectric liquid crystal that takes a first stable state consisting of a ferroelectric liquid crystal that takes a second or third stable state consisting of a ferroelectric phase according to the polarity of the electric field when an electric field is applied, and the first stable state is a dark state, In a method of driving a liquid crystal display device, comprising: a polarizing device for turning a second and a third stable state into a bright state, scanning of the scanning signal electrodes is performed by interlaced scanning one by one, and every one horizontal period of the scanning. In addition, the polarity of the selection voltage applied to the liquid crystal is reversed.

[0018]

Since the present invention is constructed as described above,
For example, when the display surface is in the bright state, the scanning lines are set to the second stable state or the third stable state for every two lines, and the molecular arrangement becomes 2
Since the columns are alternately arranged, the transmittance and coloring are averaged, and they are not distinguished from each other, and the flicker is significantly reduced.

[0019]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic view of a display panel surface displayed according to an embodiment of the present invention.
Reference numerals 13, 114, 115 and 116 denote scan electrodes, 121 and
122, 123, 124, 125, 126 are signal electrodes, and the short line 13 is the optical axis direction of liquid crystal molecules.
(A) has shown the initial state. However, the display surface is in a bright state.

Here, as interlaced scanning of odd-numbered scanning lines, the first, fifth, ninth, thirteenth, ... (Generally, 4k + 1,
(k is an integer) The third scanning line is the positive writing, the third,
1, 11, 15, ... (Generally 4k + 3) The scanning lines on the main surface are selectively scanned so that the writing is of negative polarity, and the result is as shown in FIG.

Next, as an interlaced scan of even scan lines, the second, sixth, tenth, 14, ... (Generally 4k +
(2, k is an integer) When the selective scanning is performed such that the scanning line of the fourth scanning line is for positive polarity writing and the scanning lines of the fourth, eighth, 12, 16, ... (Generally 4k) scanning lines are for negative polarity writing, The result is as shown in FIG.

Next, odd-numbered interlaced scanning is performed in the opposite polarity to that of the previous case, and the first, fifth, ninth, thirteenth, ... Scanning lines are written in the negative polarity, third, seventh, 11, 15 ,. ...
When selective scanning is performed so that the scanning line on the main surface has positive polarity writing, the result is as shown in FIG.

Next, even-numbered interlaced scanning is performed in the opposite polarity to the previous one, and the second, sixth, tenth, fourteenth, ... Scanning lines are written in the negative polarity, the fourth, eighth, 12, 16, ... .. If the scanning line on the main surface is selectively scanned so that the writing is of negative polarity, the result returns to FIG.

This scanning is repeated thereafter.

Also in this case, the display cycle is 4 frames as shown in FIG.
1 is the same as that of FIG.
Since the molecular arrangement is alternately arranged for each scanning line, the transmittance and the coloring are averaged and the eyes cannot distinguish each other.

The molecular arrangement periods of (a) (c) and (b) (d) are shifted by one line, but this is also not discerned by the eye due to averaging, and in the case of FIG. It was felt as a frame cycle, and the degree of flicker was remarkably reduced as compared with FIG. 7.

FIG. 2 shows specific drive waveforms for setting the display screen state shown in FIG. Reference numerals 611 to 618 are voltages applied to the scanning electrodes, and 62 is a voltage applied to the signal electrodes.

Immediately before the scanning line selection period T, there is a reset period R of 0 volt, and all the pixels on the line are reset to the dark state. During the ratio selection period N after selection, a DC voltage for maintaining the written state is applied. This is similar to the conventional type (FIG. 5).

Only odd scan lines are selected in the first and third frames, and only even scan lines are selected in the second and fourth frames. The polarity of the selection voltage is inverted for each line in each frame. As a result, the display shown in FIG. 1 is obtained.

In the image signal 62, the period indicated by H is 1 unit. When the combined voltage with the scanning line selection voltage exceeds the threshold value, the pixel becomes bright. In 62, all pixels are in a bright state. The dark state gives the opposite polarity.

As the antiferroelectric liquid crystal material used in this embodiment, those shown in Chemical formula 1 can be cited.

[0033]

Embedded image Next, a specific cell configuration will be described.

A display panel was manufactured by bankruptcy of the liquid crystal shown in Chemical formula 1 in a gap (gap 2.5 μm) between two transparent substrates having electrodes formed on opposite surfaces. FIG. 3 shows a cross section of the display panel.

A scanning electrode 72 is formed on one of the substrates 71, and a layer formed by rubbing a nylon thin film 73 (thickness: 5 nm) covers the scanning electrode 72. Polyimide can be used instead of nylon.

The other substrate 74 has a signal electrode 75 and a mixed film 76 of titanium oxide and zirconium oxide formed thereon for preventing a short circuit between the substrates, and further has a siloxane as a main component thereon. Surface treatment film 77 has a thickness of 10 nm
Covered below.

This surface-treated film has a smaller surface energy than the rubbing film on the opposite side, and therefore has a weak force for homogeneously aligning the liquid crystal. Therefore, when the liquid crystal comes to the smectic layer by cooling from the isotropic layer, the directional order and the smectic layer order occur preferentially from the rubbing film surface side, and there is no alignment defect caused by the disorder occurring from both surfaces. As a result, uniform alignment can be obtained.

[0038]

As described above, according to the present invention,
Since the scanning of the scanning signal electrodes is performed by interlaced scanning one by one and the polarity of the selection voltage applied to the liquid crystal is inverted every horizontal period of the scanning, the flicker of the image is reduced and the diagonal The difference between the transmittance and the hue when viewed from above is eliminated, and the viewing angle characteristics are improved as a whole.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of the present invention.

FIG. 2 is a drive waveform diagram for performing the display of FIG.

FIG. 3 is a sectional view of a ferroelectric liquid crystal device according to an example.

FIG. 4 is a diagram showing an arrangement of liquid crystal molecules in an antiferroelectric phase and a ferroelectric phase.

FIG. 5 is a diagram showing a conventional liquid crystal drive waveform.

FIG. 6 is a view of the state of FIG. 4 seen obliquely.

FIG. 7 is an explanatory diagram of a display surface in which flicker occurs.

[Explanation of symbols]

 13 Optical axis direction of liquid crystal molecule 111 Scan electrode 112 Scan electrode 113 Scan electrode 114 Scan electrode 115 Scan electrode 116 Scan electrode 121 Signal electrode 122 Signal electrode 123 Signal electrode 124 Signal electrode 125 Signal electrode 126 Signal electrode

Claims (2)

[Claims] 1. A display panel having a matrix pixel formed by intersections of scanning signal electrodes and information signal electrodes which are orthogonal to each other, and a first panel formed of an antiferroelectric phase in a gap between the two electrodes when no electric field is applied. And a ferroelectric liquid crystal that takes a second or third stable state consisting of a ferroelectric phase according to the polarity of the electric field when an electric field is applied, and the first stable state is the dark state, the second and the third stable state. In a liquid crystal display device including a polarizing device for turning the stable state of No. 3 into a bright state, the scanning signal electrodes are scanned by interlaced scanning one by one, and a selection voltage applied to the liquid crystal in each horizontal period of the scanning. A liquid crystal display device characterized in that the polarity of the liquid crystal display is reversed. 2. A display panel having a matrix pixel formed by intersections of scanning signal electrodes and information signal electrodes orthogonal to each other, and a first antiferroelectric phase in a gap between the two electrodes and having no electric field. And a ferroelectric liquid crystal that takes a second or third stable state consisting of a ferroelectric phase according to the polarity of the electric field when an electric field is applied, and the first stable state is the dark state, the second and the third stable state. In a method of driving a liquid crystal display device including a polarization device for making a stable state into a bright state, the scanning signal electrodes are scanned by interlaced scanning one by one, and the liquid crystal is applied to the liquid crystal every horizontal period of the scanning. A method for driving a liquid crystal display device, characterized in that the polarity of the selection voltage is reversed.