JPH0895090A - Reflection type ferroelectric liquid crystal display element - Google Patents

Abstract

PURPOSE: To provide a reflection ferroelectric liquid crystal display element of which display is bright and coloring of display image can be prevented. CONSTITUTION: A ferroelectric liquid crystal display element is constituted of a pair of substrates 11, 12 formed with electrodes 13, 17, ferroelectric liquid crystal 21 which is arranged between the substrates 11, 12, and oriented according to impressed voltage in oriented states nearly arranging the molecules in first and second directions, and in an intermediate oriented state arranging the mean direction of the molecules in an optional direction between the first and the second directions, dichroic dyestuff 26 added to the ferroelectric liquid crystal 21, a polarising plate 23 of which the transmission axis is set in parallel with the first or the second direction, and a reflecting plate 27 arranged outside the polarising plate 23. When voltage is impressed between the electrodes 13, 17 to change the oriented state of liquid crystal, the oriented state of the dichroic dyestuff 26 is also changed, absorbing rate of linearly polarized light reflected by the reflecting plate 27 and transmitted through the polarising plate 23 by dichroic dyestuff 26 is changed, and hence the transmission factor is changed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reflective liquid crystal display device using a ferroelectric liquid crystal (including an antiferroelectric liquid crystal) having ferroelectricity, and particularly to a ferroelectric liquid crystal display device containing a dichroic dye. The present invention relates to a reflective ferroelectric liquid crystal display device including a dielectric liquid crystal and one polarizing plate.

[0002]

2. Description of the Related Art A conventional reflective ferroelectric liquid crystal display device is
As shown in FIG. 7, a ferroelectric liquid crystal 75 is sealed between a pair of transparent substrates 71 and 72 having electrodes 73 and 74 formed on the opposite surfaces, and both substrates 71 and 72 are formed by a pair of polarizing plates 76 and 77. It is composed by sandwiching. Alignment films 78 and 79 are provided on the electrode formation surfaces of the transparent substrates 71 and 72, respectively. Further, a reflection plate 80 is arranged outside the polarizing plate 77.

[0003]

Since the conventional reflective ferroelectric liquid crystal display element uses the two polarizing plates 76 and 77, the amount of light absorbed by the polarizing plates 76 and 77 is large. There is a problem that the display is dark. That is, since the incident light of the liquid crystal display element passes through the polarizing plate a total of four times in the forward path and the backward path, the display becomes very dark. Further, the light passing through the layer of the liquid crystal 75 is subjected to the birefringence effect which is different for each wavelength to become the elliptically polarized light which is different for each wavelength, and the component of each elliptically polarized light which is parallel to the transmission axis of the exit side polarization plate is transmitted by this. Emit from the axis. Therefore, there is a problem that the intensity of the emitted light differs for each wavelength and the display is colored. Further, since the optical characteristics of the liquid crystal display element depend on the optical anisotropy Δn of the liquid crystal 75 and the product Δnd of the optical anisotropy Δn and the layer thickness d of the liquid crystal 75, the selection of the liquid crystal 75 and its layer thickness is limited. Will end up.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a reflective ferroelectric liquid crystal display device having a bright display. Another object of the present invention is to provide a reflective ferroelectric liquid crystal display device capable of preventing coloring of a display image. Still another object of the present invention is to provide a reflective ferroelectric liquid crystal display device having a high degree of freedom in design.

[0005]

In order to achieve the above object, in a reflective ferroelectric liquid crystal display element according to the present invention, pixel electrodes and active elements connected to the pixel electrodes are arranged in a matrix. A first substrate; a second substrate on which a counter electrode facing the pixel electrode is formed;
A first alignment state in which the liquid crystal molecules are substantially aligned in the first alignment direction according to a voltage applied between the pixel electrode and the counter electrode, the liquid crystal molecules are arranged between the first alignment state and the second substrate. ,
A second alignment state in which the liquid crystal molecules are substantially aligned in the second alignment direction, and an intermediate alignment state in which the average alignment direction of the liquid crystal molecules is an arbitrary direction between the first and second alignment directions. A ferroelectric liquid crystal having a ferroelectricity oriented in the direction of, a dichroic dye added to the ferroelectric liquid crystal, and one of the first and second substrates, and the first dichroic dye. A polarizing plate whose optical axis is set in a direction substantially parallel to one of the orientation direction of the second orientation direction and the second orientation direction, and a reflection plate arranged outside the polarizing plate. Characterize.

[0006]

Function The average alignment direction of the liquid crystal molecules and the average direction of the long axis of the dichroic dye coincide with each other. When the optical axis of the polarizing plate is the light transmission axis, the light absorption axis of the dichroic dye substantially coincides with the major axis direction thereof, so that the average alignment direction of the liquid crystal molecules is the first and second When one of the alignment directions is almost parallel to the optical axis of the polarizing plate, the light having a component parallel to the absorption axis of the polarizing plate of the incident light is absorbed by the dichroic dye and polarized. Of the components, only the polarized component that is not absorbed by the dichroic dye passes through the polarizing plate and enters the reflecting plate. The linearly polarized light reflected by the reflection plate and transmitted through the polarizing plate proceeds in the layer of the ferroelectric liquid crystal as it is, and the linearly polarized light and the light absorption axis of the dichroic dye are parallel to each other. Is further absorbed by the dichroic dye. Therefore, the transmittance becomes the lowest.

Further, as the angle between the average alignment direction of the liquid crystal molecules and the one alignment direction increases, the direction of the polarization component absorbed by the dichroic dye of the incident light and the transmission axis of the polarizing plate The angle formed between the linearly polarized light reflected by the reflection plate and transmitted through the polarizing plate and the light absorption axis of the dichroic dye is large, and the linearly polarized light transmitted through the polarizing plate is the birefringence of the ferroelectric liquid crystal. Due to the effect, it becomes elliptically polarized light. Therefore, of the incident light, the intensity of the light that passes through the polarizing plate becomes strong, and the ratio of the light reflected by the reflecting plate and transmitted through the polarizing plate being absorbed by the dichroic dye decreases, and the transmittance Becomes higher. Then, when the average alignment direction of the liquid crystal molecules is the other alignment direction of the first and second alignment directions, the transmittance becomes maximum. Therefore, by controlling the voltage applied between the opposing electrodes to control the alignment direction of the liquid crystal molecules, the transmittance can be controlled and a gradation image can be displayed.

In the reflection type ferroelectric liquid crystal display device having the above-mentioned structure, the light that has passed through the polarizing plate among the light that has entered the device is directly reflected by the reflecting plate and passes through the polarizing plate. Therefore, in the reflection type liquid crystal display device having the above-mentioned configuration, the loss of light in the polarizing plate is substantially only the loss when transmitting through the polarizing plate once. Therefore, the amount of light absorbed by the polarizing plate is small and the display becomes bright. Further, since the transmission of light is controlled by the dichroic dye, the influence of birefringence of the liquid crystal is small and the display is not colored. In addition, the degree of freedom in selecting the liquid crystal and its layer thickness is improved.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view of a ferroelectric liquid crystal display element of this embodiment, and FIG. 2 is a plan view of a transparent substrate on which pixel electrodes and active elements of the ferroelectric liquid crystal display element are formed. This ferroelectric liquid crystal display element is of an active matrix type, and as shown in FIG. 1, a liquid crystal cell 25 formed by enclosing a liquid crystal 21 between a pair of transparent substrates (for example, glass substrates) 11 and 12. And a single polarizing plate 23 arranged outside the liquid crystal cell 25, and a reflecting plate 27 arranged outside the polarizing plate 23.

In FIG. 1, a lower transparent substrate (hereinafter, lower substrate) 11 has a pixel electrode 13 made of a transparent conductive material such as ITO, and a thin film transistor (hereinafter, TFT) having a source connected to the pixel electrode 13. And 14 are formed in a matrix.

As shown in FIG. 2, the gate lines 15 are arranged between the rows of the pixel electrodes 13 and the data lines (gradation signal lines) 16 are arranged between the columns of the pixel electrodes 13.
The gate electrode of each TFT 14 corresponds to the corresponding gate line 15
And the drain electrode is connected to the corresponding data line 16
It is connected to the. The gate line 15 is the row driver 3
1 and the data line 16 is connected to the column driver 32. The row driver 31 scans the gate line 15 by applying a gate voltage described later. On the other hand, the column driver 32 receives the image data (gradation signal) and applies the data signal corresponding to the image data to the data line 16.

In FIG. 1, an upper transparent substrate (hereinafter, upper substrate) 12 is formed with a counter electrode 17 facing each pixel electrode 13 of the lower substrate 11 and applied with a reference voltage V0. The counter electrode 17 is a transparent electrode made of, for example, ITO. Alignment films 18 and 19 are provided on the electrode formation surfaces of the lower substrate 11 and the upper substrate 12, respectively. The alignment films 18 and 19 are horizontal alignment films made of an organic polymer compound such as polyimide, and the facing surfaces thereof are subjected to an alignment treatment by rubbing.

The lower substrate 11 and the upper substrate 12 are adhered to each other at their outer peripheral edges with a frame-shaped sealing material 20 interposed therebetween.
The gap between the alignment films 18 and 19 is, for example, 2 μm (1.7 μm to 2.4 μm) depending on the sealing material 20 and the gap material 22.
The liquid crystal 21 is enclosed in a region surrounded by the substrates 11 and 12 and the sealing material 20. The liquid crystal 21 is a ferroelectric liquid crystal (hereinafter, referred to as DHF) in which the spiral pitch of the chiral smectic C phase is smaller than the distance between the substrates 11 and 12, and the alignment state has no memory property.
(Deformed Helix Ferroelectric) liquid crystal). DHF
The liquid crystal 21 has a spiral pitch that is a wavelength in the visible light band.
00nm-400nm or less (for example, 400nm-300nm)
The ferroelectric liquid crystal composition has a large spontaneous polarization and a cone angle of about 27 ° to 45 ° (desirably 27 ° to 30 °).

The DHF liquid crystal 21 forms a uniform layer structure by directing the normal of the layer structure of the chiral smectic C phase toward the alignment treatment direction of the alignment films 18 and 19. Further, since the spiral pitch is smaller than the distance between the substrates, the spiral pitch is enclosed between the substrates 11 and 12.
When a voltage having a sufficiently large absolute value is applied between the pixel electrode 13 and the counter electrode 17, the DHF liquid crystal 21 has almost the first alignment direction (long axis direction, director) of liquid crystal molecules depending on the polarity of the applied voltage. The first alignment state (first
(Ferroelectric phase) and a second alignment state (second ferroelectric phase) in which the alignment direction of the liquid crystal molecules is substantially the second alignment direction. Further, when a voltage whose absolute value is lower than the voltage for aligning the liquid crystal molecules in the first or second alignment state is applied between the pixel electrode 13 and the counter electrode 17, the spiral of the molecular alignment of the DHF liquid crystal 21 is distorted, and the DHF liquid crystal The average alignment direction of 21 is an intermediate alignment state in which the average alignment direction is between the first alignment direction and the second alignment direction.

A dichroic dye (dichroic pigment) 26 is added to the DHF liquid crystal 21. The dichroic dye 26 is, for example, an azo or anthraquinone black color, and is composed of a pigment having a dichroic ratio of 5 to 12. The amount added is DH
It is appropriately selected according to the layer thickness of the F liquid crystal 21 and the dichroic ratio of the dichroic dye.
It is set to 7% by weight. It should be noted that if the addition amount of the dichroic dye 26 is small, it is difficult to display low gradation, and if the addition amount of the dichroic dye 26 is too large, the display becomes dark and the dichroic dye 26 becomes a DHF liquid crystal. It becomes difficult to dissolve in 21 and DH
This hinders the proper alignment of the F liquid crystal 21. Therefore, the addition amount is preferably about 0.7 to 4% by weight, particularly 1 to 3% by weight. The added amount may be decreased as the layer thickness of the DHF liquid crystal 21 increases. The dichroic dye 26 is spirally aligned according to the alignment of the liquid crystal molecules, and the average direction of the long axis thereof coincides with the average alignment direction of the liquid crystal molecules of the DHF liquid crystal 21. In this embodiment, the anisotropy of absorptivity of the dichroic dye 26 is positive, and the absorption axis of the dichroic dye 26 coincides with its long axis.

As the reflection plate 27, for example, a reflection layer made of aluminum or the like is deposited on the back surface of the polarizing plate 23 by vacuum vapor deposition, sputtering or the like, or an aluminum foil or the like is attached to the back surface of the polarizing plate 23. it can.

The direction of the alignment treatment applied to the alignment films 18 and 19, the relationship between the optical axis of the polarizing plate 23 and the alignment direction of the liquid crystal molecules of the DHF liquid crystal 21 will be described with reference to FIG.

In FIG. 3, reference numeral 21C indicates an alignment film 18,
19 shows the direction of the alignment treatment applied to the DHF liquid crystal 21.
Are oriented with the normal of the layer having the layer structure of the chiral smectic C phase oriented in the orientation direction 21C. When a voltage having one polarity and a sufficiently large absolute value is applied to the DHF liquid crystal 21, the DHF liquid crystal 21 is in the first alignment state, and the alignment direction of the liquid crystal molecules is the first alignment direction 21A substantially indicated by a chain line. . When a voltage having a sufficiently large absolute value with the other polarity is applied to the DHF liquid crystal 21,
Is in the second alignment state, and the alignment direction of the liquid crystal molecules is almost 2
It becomes the second orientation direction 21B shown by the dotted line. On the other hand, when the applied voltage is 0, the average alignment direction of the liquid crystal molecules is the normal direction of the layer of the liquid crystal smectic phase, that is, the intermediate direction between the first and second alignment directions 21A and 21B (direction of the alignment treatment). )
21C.

The first alignment direction 21A and the second alignment direction 2
The deviation angle from 1B varies depending on the type of the DHF liquid crystal 21, but is selected to be 25 ° to 45 °, preferably 27 ° to
It is 45 °. The dichroic dye 26 is aligned along the alignment of the liquid crystal molecules, and the direction of its long axis changes between the first alignment direction 21A and the second alignment direction 21B. The optical axis (transmission axis in this embodiment) 23A of the polarizing plate 23 is set substantially parallel to the second alignment direction 21B.

Next, the operation of the ferroelectric liquid crystal display device having the structure shown in FIGS. 1 to 3 will be described. Incident from the upper side of FIG.
Light that has passed through the substrate 12 and the DHF liquid crystal 21 is DHF liquid crystal 2
The dichroic dye 26 in 1 absorbs the polarized component in the direction of the light absorption axis, and passes through the substrate 11 and the polarizing plate 23 to become linearly polarized light. This linearly polarized light is reflected by the reflection plate 27, passes through the polarizing plate 23 again as it is, and enters the layer of the DHF liquid crystal 21.

In the second alignment state in which the liquid crystal molecules of the DHF liquid crystal 21 are aligned in the second alignment direction 21B, the upper substrate 1
Of the components of the dichroic dye 26 in the absorption axis direction, only the light that is not absorbed by the dichroic dye 26 passes through the polarizing plate 23 to become linearly polarized light, and then enters the reflecting plate 27. To do. The linearly polarized light reflected by the reflecting plate 27 and transmitted through the polarizing plate 23 passes through the layer of the DHF liquid crystal 21 as it is, and this linearly polarized light is also absorbed by the absorption axis (long axis) of the dichroic dye 26 and the polarizing plate 23. Since the transmission axes 23A of are parallel,
The light is absorbed by the dichroic dye, and the light transmittance of the liquid crystal display element is minimized.

On the other hand, the average orientation direction of the liquid crystal molecules is the second
When the orientation direction 21B of the polarizing plate 23 gradually changes from the orientation direction 21B to the first orientation direction 21A, the angle between the direction of the polarization component absorbed by the dichroic dye of the incident light and the transmission axis 23A of the polarizing plate 23 and the reflection plate 27. The crossing angle of the absorption axis of the dichroic dye 26 and the linearly polarized light which is reflected by the polarizer 23 and is transmitted through the polarizing plate 23 gradually increases, and due to the birefringence effect of the DHF liquid crystal 21, the DHF liquid crystal 2
The linearly polarized light entering 1 becomes elliptically polarized light. Therefore, of the light incident from the upper substrate 12, the intensity of the light passing through the polarizing plate 23 becomes strong, and the light reflected by the reflecting plate 27 and transmitted through the polarizing plate 23 is absorbed by the dichroic dye 26. The amount gradually decreases, the amount of light emitted from the DHF liquid crystal 21 increases, and the display gradually becomes brighter. Then, when the average alignment direction of the liquid crystal molecules of the DHF liquid crystal 21 becomes the first alignment direction 21A, the transmittance and the display gradation become the highest.

The average orientation direction of the DHF liquid crystal 21 depends on the polarity and voltage value (absolute value) of the voltage applied between the pixel electrode 13 and the counter electrode 17, and the first orientation direction 21A and the second orientation direction 21A. It continuously changes between the alignment directions 21B, and accordingly, the amount of absorption of light in the layer of the DHF liquid crystal 21 changes as described above.

Therefore, when a low-frequency triangular wave voltage of about 0.1 Hz is applied between the pixel electrode 13 and the counter electrode 17 of this ferroelectric liquid crystal display element, the transmittance is applied as shown by the solid line in FIG. The gradation image can be displayed by continuously changing with respect to the voltage. Since this ferroelectric liquid crystal display element is of the active matrix type, it is possible to hold a voltage for maintaining the DHF liquid crystal 21 in an arbitrary alignment state even during the non-selection period. Therefore, the ferroelectric liquid crystal display element having the above-described structure can change the transmittance and display with gradation.

In the ferroelectric liquid crystal display device having the above-mentioned structure, since one polarizing plate is used, the amount of light absorbed by the polarizing plate is smaller and the display is brighter than when two polarizing plates are used. Become. Further, coloring of the displayed image can be prevented. Further, unlike the conventional ferroelectric liquid crystal display element, the transmittance is DHF.
Optical anisotropy Δn of liquid crystal 21 and optical anisotropy Δn and DHF
Since it does not depend on the product Δnd of the layer thickness d of the liquid crystal 21, DHF
The degree of freedom in selecting the liquid crystal 21 and its layer thickness is improved.

In the above embodiment, the transmission axis 23 of the polarizing plate 23
Although A is aligned with the second alignment direction 21B, it may be aligned with the first alignment direction 21A. In this case, as shown by the broken line in FIG. 4, the transmittance is the lowest in the first alignment state and the transmittance is the highest in the second alignment state. Further, the absorption axis of the polarizing plate 23 may be aligned with the first or second alignment direction.

In the above embodiment, as the dichroic dye 26,
Although one having a positive absorptivity anisotropy is used, a dichroic dye 26 having a negative absorptivity anisotropy having an absorption axis in a direction orthogonal to the major axis may be used. Further, the driving method of this embodiment is not limited to the one using the TFT as the active element, but can be applied to the driving of the ferroelectric liquid crystal display element using the MIM as the active element. Further, although an example of using the DHF liquid crystal as the liquid crystal 21 has been shown, the SBF liquid crystal,
Alternatively, an antiferroelectric liquid crystal having a ferroelectric phase and an antiferroelectric phase can be used.

Next, referring to FIGS. 5A to 5C, a practical driving method of the ferroelectric liquid crystal display element having the above structure will be described with reference to a DHF liquid crystal and a positive absorptivity anisotropy. A reflective ferroelectric liquid crystal display element in which the transmission axis 23A of the polarizing plate 23 is arranged as shown in FIG. 3 using a color dye will be described as an example.

Since the ferroelectric liquid crystal has a large hysteresis of its optical characteristics and the applied voltage of the liquid crystal display element is turned on / off at high speed, it is shown between the counter electrode 17 and the pixel electrode 13 by a solid line or a broken line in FIG. The desired display gradation cannot be obtained by simply applying the voltage corresponding to the display gradation. Therefore, in this embodiment, in order to obtain the desired transmittance, DH
The F liquid crystal 21 is once aligned in the first alignment state or the second alignment state, and then a voltage (hereinafter referred to as a writing voltage) according to the display gradation is applied to the DHF liquid crystal 21 to obtain the voltage before applying the writing voltage. It is assumed that the alignment state of the DHF liquid crystal 21 is constant and a gradation corresponding to the writing voltage is obtained.

5A to 5C, paying attention to an arbitrary pixel, the gate signal applied to the gate line 15 by the row driver 31 and the data signal applied to the data line 16 by the column driver 32, and The transmittance of each pixel is shown.

Further, in FIGS. 5A to 5C, T
F is one frame period, TS is the pixel selection period, TO
Indicates a non-selection period. Each selection period TS is equally divided into four slots t1, t2, t3, and t4. The period Δt of each one slot is about 45 μsec. First slot t
1 is the application period of the compensation pulse P11, slot t2 is the application period of the reset compensation pulse P12, slot t3 is the application period of the reset pulse P13, and last slot t4 is the application period of the write pulse P14.

The write pulse P14 is a pulse having a voltage VD corresponding to image data. Compensation pulse P11
Is applied to the DHF liquid crystal 21 by applying the write pulse P14.
The pulse is a pulse for compensating that the DC voltage component is biased to and is a pulse having a polarity opposite to that of the write pulse P14. The absolute value of the voltage of the compensation pulse P11 (compensation voltage) -VD is the voltage of the writing pulse P14 (writing voltage).
Same as VD. The voltage VD of the write pulse P14 is controlled to various values according to the image data, and the voltage -VD of the compensation pulse P11 is also controlled correspondingly.

The reset pulse P13 is a pulse for eliminating the influence of hysteresis in the optical characteristics, and the voltage -VR of the reset pulse P13 is such that most of the liquid crystal molecules of the DHF liquid crystal 21 are aligned in the second alignment direction 21B. Has a sufficient value for. In addition, the reset compensation pulse P1
2 is the DHF liquid crystal 2 by the application of the reset pulse P13.
This is a pulse of opposite polarity for compensating that the DC voltage component is biased to 1. The absolute value of the voltage VR of the reset compensation pulse P12 and the absolute value of the voltage −VR of the reset pulse P13 are the same.

Each pulse P11, P12, P13, P14
The polarity and voltage value of are the polarity and voltage of the data signal with respect to the reference voltage V0. The reference voltage V0 is the same as the voltage of the counter electrode 17.

In this driving method, the minimum value of the write voltage VD is V0, and the maximum value Vmax is the reset pulse P13.
The write voltage VD is controlled in the range of V0 to Vmax as a value slightly lower than the absolute value of the voltage -VR of the above.

When the ferroelectric liquid crystal display device is driven by using the gate signal and the data signal having the above waveforms,
During the selection period TS of each row, the voltage (compensation voltage) −VD of the compensation pulse P11 and the voltage VR of the reset compensation pulse P12.
Then, the voltage −VR of the reset pulse P13 and the voltage (write voltage) VD of the write pulse P14 are sequentially applied to the TFT.
It is applied to the pixel electrode 13 via 14.

Immediately before applying the write pulse P14, the reset pulse P13 is applied to align the liquid crystal molecules in the second alignment direction. Therefore, the liquid crystal molecules and the dichroic dye 26 are aligned.
The average orientation direction of the long axis of the
When D is V0, the state of being substantially parallel to the second alignment direction 21B is maintained, and the state of the transmittance is almost minimum. Further, when the write voltage VD is Vmax, the write voltage VD is almost parallel to the first alignment direction 21A, and the transmittance is almost maximum. For example, when the write voltage VD is 1/2 of the reset voltage VR, the average alignment direction of the liquid crystal molecules and the dichroic dye 26 substantially coincides with the alignment process direction 21C, and the transmittances thereof are the highest and the lowest. The transmittance is almost intermediate. When the write voltage VD is ¼ of the reset voltage VR, the average alignment direction of the liquid crystal molecules and the dichroic dye 26 is an intermediate direction between the alignment processing direction 21C and the second alignment direction 21B. .
Therefore, the transmittance of the liquid crystal display element is a value approximately halfway between the intermediate transmittance and the lowest transmittance.

In the non-selection period TO, the TFT 14 is turned off, and a voltage corresponding to the write voltage VD applied to the final slot t4 of the selection period TS is formed by the pixel electrode 13, the counter electrode 17 and the DHF liquid crystal 21 between them. The alignment state of the liquid crystal molecules of the pixel is maintained, and the transmittance of each pixel is maintained at a value corresponding to the write voltage VD until the selection period TS of the next frame.

Therefore, in this driving method, the write voltage VD is varied in the range of V0 to Vmax, whereby the direction of the absorption axis of the dichroic dye 26 is set to the first alignment direction 21A and the second alignment direction 21B. It is possible to control the display gradation by changing the display gray scale by changing the transmittance and the transmittance as shown in FIG.

Further, in the above driving method, since the pair of voltages VR and -VR and the pair of write voltage VD and write compensation voltage -VD are applied between the electrodes 13 and 17 for each selection period TS, DHF is applied. The direct-current voltage components applied to the liquid crystal 21 are canceled out, and a display burn-in phenomenon and deterioration of the liquid crystal do not occur.

In the above embodiment, the reset compensation pulse P1
2 and the reset pulse P13 are applied to the liquid crystal display element in this order, but the order of application may be reversed. Voltage VR, -V
In R, most of the liquid crystal molecules have the first and second alignment directions 2
It is sufficient that the voltage is oriented to 1A and 21B, and the voltage is not necessarily oriented to the first and second orientation directions 21A and 21B. Further, a voltage (V which is obtained by adding the voltage −VD of the compensation pulse P11 and the voltage VR of the reset compensation pulse P12 (V
R-VD) with one compensation pulse P1
DHF liquid crystal 2 instead of 1 and reset compensation pulse P12
1 may be applied.

The driving method described above is one example of the driving method of the reflection type ferroelectric liquid crystal display element described with reference to FIGS. 1 to 4, and the reflection type ferroelectric liquid crystal display element according to the present invention. The driving method is not limited to the above driving method, and any driving method can be adopted.

[0043]

The reflective ferroelectric liquid crystal display device having the above-mentioned structure requires only one polarizing plate, and the amount of light absorbed by the polarizing plate is small, so that the display is bright. Further, coloring of the displayed image can be prevented. Further, unlike the conventional reflection type ferroelectric liquid crystal display element, the transmittance does not depend on the optical anisotropy Δn of the liquid crystal and the product Δnd of the optical anisotropy Δn and the layer thickness d of the liquid crystal, and therefore, the ferroelectric liquid crystal The degree of freedom in selecting the layer thickness is improved.

[Brief description of drawings]

FIG. 1 is a sectional view showing a structure of a reflective ferroelectric liquid crystal display element according to an embodiment of the present invention.

FIG. 2 is a plan view showing a configuration of a lower substrate of the reflective ferroelectric liquid crystal display element shown in FIG.

FIG. 3 is a diagram showing the relationship between the orientation direction, the orientation direction of liquid crystal molecules, and the direction of the transmission axis of the polarizing plate.

FIG. 4 is a graph showing the relationship between applied voltage and transmittance.

FIG. 5 is a waveform diagram for explaining a practical driving method of the reflective ferroelectric liquid crystal display element according to the embodiment of the present invention, in which (A) shows the waveform of the gate signal supplied to the gate line. FIG. (B) is a diagram showing an example of a waveform of a data signal supplied to the data line. (C) is a graph showing changes in transmittance.

FIG. 6 is a graph showing the relationship between the write voltage and the transmittance when the driving method shown in FIGS. 5A to 5C is used.

FIG. 7 is a sectional view showing a structure of a conventional reflective ferroelectric liquid crystal display device.

[Explanation of symbols]

11 ... Transparent substrate, 12 ... Transparent substrate, 13 ... Pixel electrode, 14 ... TFT, 15 ... Gate line, 16 ... Data line, 17 ... Counter electrode, 18. ..Alignment films, 19 ...
・ Alignment film, 20 ... Sealing material, 21 ... Liquid crystal, 22 ... Gap material, 23 ... Polarizing plate, 25 ... Liquid crystal cell, 26 ... Dichroic dye, 27 ... .Reflector, 31 ... Row driver, 32 ...
・ Column driver

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location G02F 1/1337 510 510 G09G 3/36

Claims (4)

[Claims] 1. A first substrate in which pixel electrodes and active elements connected to the pixel electrodes are arranged in a matrix, a second substrate in which a counter electrode facing the pixel electrodes is formed, Is disposed between the first and second substrates and has a layered structure,
A first alignment state in which liquid crystal molecules are substantially aligned in a first alignment direction and a second alignment state in which liquid crystal molecules are substantially aligned in a second alignment direction according to a voltage applied between the pixel electrode and the counter electrode.
And the average alignment direction of liquid crystal molecules is the first
A ferroelectric liquid crystal having a ferroelectric property that is aligned in an intermediate alignment state that is an arbitrary direction between the first alignment direction and a second alignment direction; and a dichroic dye added to the ferroelectric liquid crystal, A sheet of polarizing plate disposed close to one of the first and second substrates and having an optical axis set in a direction substantially parallel to one of the first alignment direction and the second alignment direction; A reflective ferroelectric liquid crystal display device, comprising: a reflective plate disposed outside the polarizing plate; 2. A pair of substrates, each having electrodes formed on opposite surfaces thereof, and a layer structure, which is disposed between the pair of substrates and has a layered structure. The first alignment state in which the liquid crystal molecules are aligned in the first alignment direction, the second alignment state in which the liquid crystal molecules are aligned in the second alignment direction, and the average alignment direction in which the liquid crystal molecules are aligned in the first and second alignment directions. A ferroelectric liquid crystal having a ferroelectricity that is oriented in an intermediate orientation state in an arbitrary direction between the orientation directions, a dichroic dye added to the ferroelectric liquid crystal, and the pair of One polarizing plate arranged on one side of the substrate and having an optical axis set in a direction substantially parallel to one of the first alignment direction and the second alignment direction; A reflection type ferroelectric liquid crystal display device comprising: a reflection plate arranged. 3. The optical axis of the polarizing plate is a light transmission axis, and the light absorption axis of the dichroic dye is substantially parallel to the average alignment direction of the liquid crystal molecules. The reflective ferroelectric liquid crystal display element according to claim 1 or 2. 4. A first voltage having an absolute value corresponding to a signal corresponding to a display image, and the liquid crystal molecules are set to either the first alignment state or the second alignment state. The second voltage and the third voltage for canceling the first voltage and the second voltage are opposed to each other in the order of the third voltage, the third voltage, and the first voltage. The reflection-type ferroelectric liquid crystal display element according to claim 1, 2 or 3, further comprising a driving unit that applies a voltage between the electrodes.