JPH095709A - Liquid crystal display device and its driving method - Google Patents

Abstract

PURPOSE: To provide a liquid crystal display device which decreases flickering in spite of viewing of a display panel from the side and is formed by using antiferroelectric liquid crystals. CONSTITUTION: This liquid crystal display device has the display panel which has matrix pixels formed by intersection of scanning signal electrodes and information signal electrodes 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. Each pixel is composed of at least >=2 sub-pixels 14, 15 and the corresponding scanning electrodes 11, 12 are arranged therein so that the other sub-pixel attains the third stable state if the one sub-pixel of the pixel attains the second stable sate at the time the pixel attains the bright state by a driving device.

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 antiferroelectric liquid crystal) unwinds a helix in a thin substrate gap as in a normal ferroelectric liquid crystal.
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. 6 (b) and 6 (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 invention is an invention of an anti-ferroelectric liquid crystal device having a simple matrix structure, and FIG. 7 shows an example of its drive waveform.

FIG. 7 shows how the voltage applied to the liquid crystal changes with time, and the polarities of the voltages applied to the pixels are changed every frame. As is clear from FIG. 7, 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 above-mentioned frame-by-frame polarity inversion drive method has a drawback that the screen flickers when the display panel is viewed from an oblique direction. The reason will be described below.

FIG. 8 shows liquid crystal molecules and the transmission axes of the upper and lower polarizing plates when the display panel is viewed from the lower right. (A) is a dark state, (b) and (c) are two bright states, each of which is viewed from the front is shown in FIG.
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.

It is an object of the present invention to provide a liquid crystal display device using an antiferroelectric liquid crystal, which has little flicker even when the display panel is viewed from the side, and a driving method thereof.

[0013]

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 that brings the state 3 into a bright state, each pixel is configured by at least two or more sub-pixels, and corresponding scanning electrodes are arranged, and a driving device is provided. It is characterized in that, when one sub-pixel of the pixel takes the second stable state when the pixel takes the bright state, the other sub-pixel becomes the third stable state.

The present invention is also the method for driving a liquid crystal display device as described above, wherein the image signal is an AC signal including at least one positive voltage pulse and one negative voltage pulse, and the image signal is synchronized with one voltage pulse. Of the sub-pixels by selecting one of the scanning signal electrodes with the second selection voltage having a polarity opposite to that of the first selection voltage synchronized with the voltage pulse of the other and selecting the other scanning signal electrode. The feature is that the state is decided.

[0015]

Since the present invention is configured as described above, when a pixel is in a bright state, two states coexist in one pixel and are switched for each frame. Therefore, the difference in transmittance and the difference in coloring are averaged. High quality display without flicker.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows a part of the display panel taken out and shown, in which 11 and 12 are scanning signal electrodes (hereinafter simply referred to as scanning lines) and 13 are information signal electrodes (hereinafter simply referred to as signal lines). , 14 and 15 are pixel electrodes. The scanning line and the pixel electrode are formed on one substrate, and the signal line is formed on the other substrate. The short line segment in the pixel electrode shows the optical axis direction of the liquid crystal in the pixel, the one parallel to the signal line shows the antiferroelectric (dark) state, and the inclined one shows the ferroelectric (bright) state. Shows. Reference numerals 16 and 17 are the axial directions of the upper and lower polarizing plates. Note that, here, for convenience, the signal line is set to the layer normal direction, but this is not always necessary and may be an arbitrary direction.

As shown in the figure, one pixel is composed of two pixel electrodes 14 and 15, each of which constitutes a sub-pixel. When the pixel is in the dark state, both of the two subpixels are in the antiferroelectric state, and the optical axis is in the axial direction of the polarizing plate. In the bright state, the two sub-pixels are in a ferroelectric state with tilts opposite to each other. Since each sub-pixel is driven by reversing the polarity for each frame as in the conventional case, if the first sub-pixel is right tilted and the second sub-pixel is left tilted in one frame, the next sub-frame is The first subpixel has a left tilt, and the second subpixel has a right tilt.

Since the two sub-pixels have light states opposite to each other, the bright-state region is a two-state mixture in which the transmittance and the coloring are different, and the eyes see the average transmittance and the coloring. Therefore, there is no difference between frames and no flicker occurs.

FIG. 2 shows the timing of the voltage driving each electrode of FIG. 51a, 51b, 52
a is a scanning line applied voltage, 53 and 54 are signal line applied voltages, 55 is a composite voltage applied to the sub-pixel at the intersection of 51a and 53, and 56 is a sub-pixel at the intersection of 51b and 53. The composite voltage applied, 57 is the composite voltage applied to the subpixel at the intersection of 51a and 54, and 58 is the composite voltage applied to the subpixel at the intersection of 51b and 54.

There are two scanning lines for each line of the matrix pixel array, which are distinguished by a and b. Immediately before the 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. In the non-selected period N after selection, a DC voltage (bias voltage) for maintaining the written state is applied.

The two types of scanning lines a and b are connected to the first subpixel and the second subpixel, respectively, and are sequentially selected within H within one unit period of the image signal.

In the odd-numbered frame, a positive selection voltage is applied to the scanning line a and a negative selection voltage is applied to the scanning line b in each selection period, and in synchronization therewith, positive / negative or negative / negative signals are applied to the signal line in accordance with the image signal.
A positive AC signal voltage is applied. When the signal line voltage is positive or negative, the voltage applied to both sub-pixels by being combined with the scanning line voltage becomes less than or equal to the threshold value as indicated by 55 and 56, and the immediately preceding reset (dark) state is maintained. On the other hand, the signal line voltage is negative
When it is positive, the voltage combined with the scanning line voltage and applied to the pixel becomes higher than the threshold value for both sub-pixels, as indicated by 57 and 58.
One bright state is written to the first subpixel, and the other bright state is written to the second subpixel. Hereinafter, this operation is repeated for each line to complete one frame.

In the even-numbered frame, the polarities of the scanning line voltage are reversed for both a and b as shown in FIG. 2, and the polarities of the signal line voltages are also reversed. Therefore, the bright pixel is written with a composite voltage having a polarity opposite to that of the odd frame, and the tilt state is inverted.

Next, a second embodiment of the present invention will be described.

FIG. 3 shows the embodiment. 6
1-64 are scan electrodes, 65R, 66R, 65G, 66
G, 65B and 66B are signal lines, and 67 and 68 are pixel electrodes. The scanning electrodes are formed on one substrate, and the signal lines and the pixel electrodes are formed on the other substrate. One pixel is a region 69 surrounded by a dotted line in the drawing and extends over two scan electrodes. One pixel is subdivided into three regions of red R, green G, and blue B by a color filter (not shown), and is divided into two by a scanning electrode, and is composed of a total of six subpixels.
However, there are three signal lines of RGB for one pixel and another signal line for pixels that are vertically aligned.

FIG. 4 shows the timing of the voltage applied to each signal line and each scanning line in FIG. 71-74 are voltages applied to the scan electrodes 61-64 of FIG. 3, respectively,
75R and 76R are voltages applied to the signal lines 65R and 66R. Reference numeral 77 is a composite voltage of 71 and 75R, which is a in FIG.
3 is a combined voltage of 72 and 75R, which is applied to the sub-pixel of b in FIG. Further, 79 is a composite voltage of 71 and 76R, and shows the voltage applied to the sub-pixel (c in FIG. 3) belonging to the pixel one above.

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. A DC voltage for maintaining the written state is applied in the non-selected period N after the selection. These are similar to the first.

The scanning lines are selected by alternately inverting the polarities one by one. A positive selection voltage is supplied during the selection period 71, and then a negative selection voltage is supplied during the selection period 72. 75R on the signal line 65R within the period H synchronized with this
When a negative / positive AC voltage as shown in Fig.
Voltages above the positive and negative thresholds are applied to the sub-pixels, and a bright state having a tilt in the opposite direction is written. When writing the dark state, it is sufficient to apply a reverse phase (positive / negative) AC voltage to 65R.

Incidentally, the signal line 66 is synchronized with the selection period of 71 and the selection period immediately preceding by one scanning line (not shown).
Another AC signal 76R shown at H'in FIG. 4 is applied to R to determine the state of the pixel including the sub-pixel in FIG. 3c. Further, in synchronization with the selection period of 72 and the selection period of the scanning line 63 immediately below that immediately after that, the next AC signal is further applied to the signal line 66R, and the state of the pixel including the sub-pixel of FIG. It is determined. In this way, the alternating-current image signals whose phases are shifted by the anti-cycle are supplied to the signal lines 65R and 66R.

Other signal lines 65G, 66G, 65B, 66
Similarly, a voltage signal corresponding to the color is supplied to B as well.

As described above, the scanning lines are sequentially selected, one screen is written, and one frame is completed. Then, a voltage signal with all polarities reversed is applied in the same manner to write the next frame.

This embodiment is the same as the first embodiment in that the pixel is divided into two and each is driven by different scanning electrodes.
Since the sub-pixels of the pixels adjacent in the signal line direction share the scanning electrode, the number of scanning lines is half that of the first embodiment, and the scanning time is half. Instead, the number of signal lines is doubled.

The antiferroelectric liquid crystal material used in this embodiment is shown in Chemical formula 1.

[0035]

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

A display panel was prepared by sandwiching the above-mentioned liquid crystal in a gap (gap 2.5 μm) between two transparent substrates having electrodes formed on opposite surfaces.

FIG. 5 shows a cross section of the panel used in the second embodiment.

A scanning line electrode 82 is formed on one substrate 81, and a layer formed by rubbing a nylon thin film 83 (thickness: 5 nm) is covered on the scanning line electrode 82. Polyimide may be used instead of nylon.

The other substrate 84 has a color filter 85.
R, 85G, 85B, the signal line 86 and the pixel electrode 87, and a mixed film 88 of titanium oxide and zirconium oxide is formed on the signal line 86 and the pixel electrode 87 to prevent a short circuit between the substrates, and a surface mainly containing siloxane is formed on the mixed film 88. The treatment film 89 covers the film with a thickness of 10 nm or less.

This surface-treated film has a smaller surface energy than the rubbing film on the opposite side, and therefore has a weaker force for homogeneously aligning the liquid crystal. Therefore, when liquid crystal is cooled from the isotropic layer, smectic phase ordering occurs preferentially from the rubbing film surface side, and there is no alignment defect caused by random ordering from both surfaces, and as a result, uniform alignment is obtained.

[0041]

As described above, according to the present invention,
Each pixel consists of at least two sub-pixels, so that when the pixel is in the bright state, one sub-pixel of the pixel is in the second stable state and another one is in the third stable state. Therefore, the flicker of the image can be reduced, the difference between the transmittance and the hue when viewed from an angle is eliminated, and the viewing angle characteristics are improved as a whole.

[Brief description of drawings]

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

FIG. 2 is a diagram showing a voltage applied to each electrode and a combined voltage applied to a pixel in the first embodiment.

FIG. 3 is a diagram showing a second embodiment of the present invention.

FIG. 4 is a diagram showing each electrode applied voltage and a composite voltage applied to a pixel in the second embodiment.

FIG. 5 is a sectional view of a liquid crystal display device according to a second embodiment.

FIG. 6 is a diagram showing alignment of liquid crystal molecules in an antiferroelectric phase and a ferroelectric phase.

FIG. 7 is a diagram showing a conventional example of a driving method of a liquid crystal display element.

FIG. 8 is a diagram showing the state of FIG. 6 as viewed obliquely.

[Explanation of symbols]

 11 scanning signal electrode 12 scanning signal electrode 13 information signal electrode 14 sub-pixel electrode 15 sub-pixel 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 that brings the state 3 into a bright state, each pixel is configured by at least two or more sub-pixels, and corresponding scanning electrodes are arranged, and a driving device is provided.
A liquid crystal display device, characterized in that, when one sub-pixel of the pixel is in a second stable state when the pixel is in a bright state, the other sub-pixel is in a third stable state. 2. The image signal is composed of an alternating current signal including at least one positive voltage pulse and one negative voltage pulse, and one scanning signal electrode is selected by a first selection voltage synchronized with one voltage pulse, and the other scanning signal electrode is selected. 2. The state of the sub-pixel is determined by selecting the other scanning signal electrode by a second selection voltage having a polarity opposite to that of the first selection voltage synchronized with the voltage pulse. A driving method for driving the liquid crystal display device described.