JP3535769B2 - Liquid crystal display device and method of driving the liquid crystal display device - Google Patents

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 element used for a light valve used in a flat panel display, a projection display, a printer and the like, and a driving method of the liquid crystal display element .

[0002]

2. Description of the Related Art Conventionally, in a nematic liquid crystal display element, a liquid crystal element called an active matrix in which an active element such as a transistor (for example, thin film transistor / TFT) is arranged in each pixel has been developed. The nematic liquid crystal modes currently used in this active matrix type liquid crystal display device include, for example, M. Schatt and W.
Applie by W. Helfrich
d Physics Letters Vol. 18, No. 4, Issued February 15, 1971, pages 127-128, Twisted Nematic (Twist)
The ed Nematic) mode is widely used.
Further, recently, an in-plane switching (In-Plane Switching) mode using a lateral voltage has been announced, and the viewing angle characteristic, which is a drawback of the twisted nematic mode liquid crystal display, has been improved.

In addition, as a typical example of a nematic liquid crystal display element which does not use an active element such as the above-mentioned TFT, a super twisted nematic (Super Twi) is used.
There is a "steady Nematic" mode. As described above, although there are various modes in the liquid crystal display device using such nematic liquid crystal, there is a problem that the response speed of the liquid crystal takes several tens of milliseconds or more in any of the modes. did.

In order to improve the drawbacks of such a conventional nematic liquid crystal device, a device in which the liquid crystal exhibits bistability (SSFLC / Surface Stabilize).
dFLC) has been proposed by Clark and Lagerwall (JP 56-107216, U.S. Pat. No. 4,367,924).
Specification). As the liquid crystal exhibiting this bistability, a ferroelectric liquid crystal exhibiting a chiral smectic C phase is generally used. In this ferroelectric liquid crystal, when a voltage is applied, the voltage acts on the spontaneous polarization of the liquid crystal molecules to cause the inversion switching of the molecules, so that a very fast response speed is obtained and a bistable state with a memory property is exhibited. Can be made. Further, since it has excellent viewing angle characteristics, it is considered to be suitable as a high-speed, high-definition, large-area display element or light valve.

On the other hand, recently, attention has been paid to an antiferroelectric liquid crystal in which the liquid crystal exhibits a tri-stable state. Like the ferroelectric liquid crystal, the antiferroelectric liquid crystal has a very fast response speed because the molecules undergo inversion switching due to the action on the spontaneous polarization of the liquid crystal molecules. This liquid crystal material has a molecular alignment structure in which liquid crystal molecules cancel each other's spontaneous polarization when no voltage is applied, and thus is characterized by the absence of spontaneous polarization when no voltage is applied.

Both the ferroelectric liquid crystal and the antiferroelectric liquid crystal that perform inversion switching by spontaneous polarization are liquid crystals exhibiting a chiral smectic liquid crystal phase. That is,
In the sense that the problems related to the response speed that the nematic liquid crystal has had in the past can be solved, realization of a liquid crystal display device using a smectic liquid crystal is expected.

[0007]

As described above, smectic liquid crystals having spontaneous polarization have been expected for next-generation displays such as high-speed response performance. In particular, modes using the above-mentioned bistable state and tristable state are expected. Then, it was difficult in principle to realize gradation display within one pixel.

Therefore, in recent years, "short pitch type ferroelectric liquid crystal", "polymer stable ferroelectric liquid crystal" and "thresholdless anti-reflective liquid crystal" have been used as modes for gradation control using liquid crystals exhibiting a chiral smectic phase. "Ferroelectric liquid crystals" have been proposed, but none of them have reached a level sufficient for practical use.

On the other hand, in a liquid crystal display device, recently, it is not possible to obtain a moving image high-speed response characteristic perceived by humans simply by increasing the response speed of a liquid crystal portion of a conventional device (mode using a nematic phase). Research (Science Technical Report EID
96-4p. 19)).
In these research results, as a method for humans to feel that moving images are displayed at high speed, the time aperture ratio is set to 5 by using a shutter.
It has been concluded that it is effective to improve the moving image quality by using the method of 0% or less or the double speed display method.

However, since the response speed of the liquid crystal is insufficient in the conventional mode using the nematic phase,
In addition to being unable to use the above-mentioned moving image display method, a chiral smectic liquid crystal device with a fast response that has been proposed so far, and the above-mentioned "short pitch type ferroelectric liquid crystal" and "polymer stable type strong liquid crystal device" have been proposed. Dielectric liquid crystal ",
In order to realize good moving image display at high speed using "thresholdless anti-ferroelectric liquid crystal", etc., there is a drawback that the driving method and peripheral circuits become complicated regardless of which smectic mode is used. This was a factor in increasing costs. Further, when the time aperture ratio is completely set to 50% or less, the brightness itself of the entire display element becomes 50% or less, and it is obvious that the display brightness is lowered.

In recent years, full-color display using a liquid crystal element has been desired, and one method of performing full-color display is to irradiate each color light sequentially and to switch the color light by the liquid crystal element. is there. Also in such a liquid crystal element, when the time aperture ratio is set to 50% or less as described above, there is a similar problem of reduction in brightness. Hereinafter, description will be made with reference to FIGS. 19 and 20.

FIG. 19 is a block diagram showing an example of the structure of a conventional liquid crystal device. The liquid crystal device includes a liquid crystal element 80.
A color light source 101 capable of emitting light of each color (red light, green light, blue light), and a color light source 10 based on a synchronization signal.
1 and a color light source driving unit 102 for driving the driving unit 1.

When driving the liquid crystal device, as shown in FIG. 20, one frame period F ₀ is divided into _three field periods F ₁ , F ₂ and F ₃ (for example, the frame frequency is 60 Hz). In this case, one frame period F ₀ becomes 16.7 ms and one field period F
₁ , F ₂ , F ₃ is about 5.5 ms), and each color light (red light, green light, blue light) is emitted from the color light source 101 to the liquid crystal element 80 for each field period F ₁ , F ₂ , F _3. Sequential irradiation (see (a) (b) (c) in the same figure), each field period F
A black and white image for R in the liquid crystal element 80 for each of ₁ , F ₂ , and F ₃ ,
A black-and-white image for G and a black-and-white image for B are sequentially displayed (see the same figure).
(See (d)), and these images are visually mixed to be recognized as a full-color image.

In the case of such a liquid crystal device, since it is not necessary to provide a color filter on the liquid crystal element 80, the production yield is lowered due to the formation of the color filter,
Attenuation of illumination light in color filter (decrease in brightness)
In addition, there is no problem that the light quantity of the backlight has to be increased to prevent the decrease in the brightness, but the image display period is half of the field periods F ₁ , F ₂ , and F ₃ , so that the color light source 101 The use efficiency is reduced to about 1/2, and the brightness is reduced even though the illumination light is not attenuated by the color filter. To prevent the brightness reduction, the color light source 101 must be made to have high brightness. There was a problem.

Further, when a ferroelectric liquid crystal (for example, a liquid crystal exhibiting a chiral smectic C phase) is used for such a liquid crystal element 80, it is necessary to apply a reset pulse, but the reset pulse has a negative polarity and a write pulse. Even in the case of positive polarity, the writing pulse becomes small depending on the display gradation, and a direct current component is applied to the liquid crystal, so that so-called burn-in occurs.

The present invention has been made in view of the above problems, and an object of the present invention is a liquid crystal display device capable of high-speed response and gradation control while ensuring practical brightness. And an inexpensive liquid crystal display element with improved moving image quality without using a complicated circuit , and driving of the liquid crystal display element
Is to provide a method .

[0017]

According to the present invention, in order to solve the problems], Kaila
Rusmectic liquid crystal and a pair of liquid crystal
At least one of the electrodes faces the electrode while sandwiching the liquid crystal.
Uniaxial alignment treatment for aligning the liquid crystal on the opposite surface
A pair of substrates, a polarizing plate, and a pair of electrodes
A drive circuit for applying a voltage to drive the liquid crystal
A liquid crystal display that displays images in multiple frames per second
An element, wherein the liquid crystal is an electric current between the pair of substrates.
The average molecular axis of the liquid crystal was mono-stabilized when no pressure was applied.
Shows the state, and when the voltage of the first polarity is applied, the liquid crystal is flat.
The mono-stabilization is performed at an angle where the homogenous molecular axis corresponds to the magnitude of the applied voltage.
Tilted from one side to one side,
When a voltage of the second polarity opposite to the one polarity is applied,
From the position where the average molecular axis of liquid crystal is mono-stabilized, the first pole
Biased to the opposite side of the applied voltage
Then, the tilt angle when the voltage of the first polarity is applied
Is the maximum value of when the voltage of the second polarity is applied.
If the tilt angle is larger than the maximum value, the drive circuit
The frame is divided into at least two fields and displayed.
In the first field of the frame, the voltage of the first polarity
Is applied to obtain the gradation display state of the first brightness, and the second
In the field, the voltage of the second polarity is applied and the first brightness is applied.
The same image as the one displayed in degrees, but only the brightness is different.
To obtain the gradation display state of the brightness of and display the image.
A characteristic liquid crystal display device is provided.

[0018]

[0019]

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION (First Embodiment) In the display element of the present invention, an image is formed from a frame of high brightness (first brightness) and a frame of low brightness (second brightness), By displaying images with substantially the same content in each of these two frames, although the brightness is different, it is possible to obtain a moving image that is perceived by humans as high-speed, and display by setting a low-luminance frame other than 0. It is possible to realize a moving image display without significantly impairing the brightness of the element.

The display element is used in the form of an element of a type that displays an image by optically modulating external light or a self-luminous element such as an EL element or a plasma display device.

In particular, as a preferred mode of the above display element, a liquid crystal, a pair of electrodes for applying a voltage to the liquid crystal, and a pair of electrodes for sandwiching and facing the liquid crystal, and for orienting the liquid crystal on at least one of the facing surfaces are provided. Provided is a liquid crystal element that includes a pair of substrates that have been subjected to uniaxial alignment treatment and a polarizing plate on at least one of the substrates, and that displays an image in a plurality of frames per second.

In the display element and the liquid crystal element, it is preferable that the second luminance is set to 1/5 or less of the first luminance. In particular, in a liquid crystal element, optical modulation is performed so that the transmittance of light passing through the element becomes the first transmittance in a field where display is performed at the first brightness so as to correspond to the first brightness and the second brightness. It is preferable to perform the optical modulation so that the second transmittance is smaller than ⅕ of the first transmittance and larger than 0 in the field where the display is performed at the second luminance.

Further, in the liquid crystal element, a liquid crystal device is provided in which an external light source (backlight) is provided on one substrate side of the liquid crystal element, and the light source is turned on at a first illuminance in at least one field in one frame. In the remaining field in one frame, the light source is set to be turned on with a second illuminance smaller than the first illuminance and larger than 0, and the frame of the first luminance and the second illuminance of It is possible to display by a frame.

Another driving method of the display device 100 by controlling the illuminance of the color light source 101 will be described below with reference to FIGS.
Will be described with reference to.

For example, when each color light emitted from the color light source 101 is of three colors of RGB (red, green, blue), the number of field periods included in one frame period F ₀ is three (F ₁ , F ₂ , F ₃ ).

Explaining with reference to FIG. 21, one frame period F ₀ is divided into a plurality of field periods F ₁ , F ₂ , F ₃ as shown in FIG. 21, and each field period F ₁ ,
F ₂ and F ₃ are further divided into a plurality of subfield periods 1F and 2
It is divided into F and 3F, and from the color light source 101 to the display element 80.
, The BRG color light is sequentially emitted while changing the color for each of the field periods F ₁ , F ₂ , and F ₃ , and the color light source 101 is further provided in the subfield period 1F in the field period F ₁ , F _2, or F ₃ . Is turned off, and the color light source 10 is illuminated with the first illuminance in the subfield period 2F.
1 is turned on (R1 light emission), and in the subfield period 3F, the color light source 101 is turned on (R2 light emission) with a second illuminance smaller than the first illuminance and larger than 0. A high-brightness image is displayed in the sub-field period 2F, and a low-brightness image is displayed in the third sub-field period 3F. Each of the field periods F ₁ , F ₂ , F ₃ is displayed. The displayed color image is visually mixed to be recognized as a full-color image.

The number of field periods included in one frame period F ₀ may be determined according to the number of color lights emitted from the color light source 101. For example, when each color light emitted from the color light source 101 has four colors of RGBW (red, green, blue, white), the number of field periods included in one frame period F ₀ is four (F
₁ , F ₂ , F ₃ , F ₄ ).

In the above example, the field period is set in the order of BRG color and the light of BRG color is sequentially emitted within one frame period. Of course, the field period is set in the order of RGB and the light of RGB color is set. May be sequentially emitted. RGB
The order of emitting light of colors may be any order within one frame period.

This will be described in more detail with reference to FIGS. 21, 11 and 12.

In the subfield period 1F in the second field period F ₂ , any one gate line G _i
Is applied with the gate voltage Vg for a certain period (selection period Ton), and the gate voltage Vg is applied to any one source line S _j.
During the selection period Ton synchronized with the application of g, the common electrode 42
Source voltage Vs (= Vx) with the potential Vc of the reference voltage as the reference potential
Is applied. Then, the TFT 94 of the electrode is turned on by the application of the gate voltage Vg, and the source voltage Vx becomes T.
The liquid crystal capacitance Clc and the storage capacitance Cs are charged by being applied via the FT 94 and the pixel electrode 95.

By the way, in the non-selection period Toff other than the selection period Ton, the gate voltage Vg is set to the other gate lines G ₁ ,
Since it is applied to G ₂ , ... And not to the gate line G _i , the TFT 94 of the pixel is turned off. Therefore,
The liquid crystal capacitance Clc and the storage capacitance Cs will hold the electric charges charged during this period. Thus will be throughout the field period F ₂ to the liquid crystal 49 voltage Vpix (= Vx) is continuously applied, so that the liquid crystal molecules is continuously maintained at substantially the same position throughout one field period F _2.

Similarly, scanning is performed up to the last gate line G _n ,
The color light source 101 is not lit during the first sub-field period 1F until all the liquid crystal molecules are held in a predetermined state, and as a result, the amount of transmitted light during this period is zero.

In the subsequent second subfield period 2F, the color light source 101 is turned on with the first illuminance, and in the third subfield period 3F, the color intensity is smaller than the first illuminance and more than 0. The color light source 101 is turned on with a large second illuminance, and transmitted light amounts Tx and Ty are obtained, respectively. As a result, the transmitted light amount obtained by averaging Tx, Ty, and 0 is obtained in the entire one field period F ₂ .

At this time, in the second field period F ₂ , the color light source 101 irradiates the liquid crystal element with red light so that the monochrome image displayed on the liquid crystal element is recognized as a red image, and the previous field is displayed. In the period F ₁ , blue light is emitted to be recognized as a blue image, and in the next field period F ₃ , green light is emitted to be recognized as a green image, and these color images are visually mixed. Then, it is recognized as a full-color image.

Further, by applying a source voltage −Vx having a polarity opposite to that of the source voltage Vx of the previous frame to the source line S _j for each frame, the liquid crystal 49 has a positive voltage Vx and a negative voltage. Voltage -Vx is applied alternately, which prevents deterioration of the liquid crystal 49, which is preferable.

When the frame inversion drive is performed by controlling the illuminance of the color light source as shown in FIG. 21, the liquid crystal 49 is not limited to the liquid crystal shown in FIG. 7 and may have the voltage-transmittance characteristic shown in FIG. It can be used and the degree of freedom in selecting a liquid crystal mode is increased.

In such a liquid crystal device, it is preferable that the second illuminance is smaller than ⅕ of the first illuminance.

Further, in the present invention, as an element that most preferably realizes the display with the first luminance and the second luminance as described above, the liquid crystal exhibits a monostable state when no voltage is applied as described above. A liquid crystal element using a chiral smectic liquid crystal, particularly an element proposed in Japanese Patent Application No. 10-17145 is provided.

Hereinafter, the alignment state of the chiral smectic phase and the switching process in the liquid crystal device using the liquid crystal exhibiting the chiral smectic phase of the present invention will be modeled with reference to the drawings in comparison with the conventional SSFLC type described above. Described above.

In the model described below, the explanation is based on the relationship between the liquid crystal molecules and the virtual cone that can be the position range of the liquid crystal molecules, the smectic layer normal, and the average uniaxial alignment treatment axis. Are present in the liquid crystal element, for example, twisted to some extent in the substrate normal direction,
It is observed optically (for example, by a polarization microscope) as the behavior of the average molecular axis. That is, the average molecular axis defined in the present invention described above substantially corresponds to the behavior of a single liquid crystal molecule.

In SSFLC, liquid crystal molecules are stabilized in two states in the SmC * phase, thereby exhibiting bistability, that is, memory property. This memory state will be described using the model shown in FIGS.

FIG. 1 illustrates the layer structure of liquid crystal molecules and liquid crystal (structure of smectic layer) in the SSFLC type device. In the element, as shown in FIGS. 11A and 11B, in the portion of the liquid crystal 13 sandwiched between the substrates 11 and 12, the liquid crystal molecules 14 are uniaxial in each substrate near the interface between the substrates 11 and 12. Rise at a predetermined pretilt angle α from the substrates along the alignment processing direction A (in this example, the uniaxial alignment processing directions A of both substrates are parallel and are set to the same direction, that is, to make the liquid crystal molecules rise in the same direction with respect to the substrates. (The above setting is made), the smectic layer 16 having a chevron structure is formed between the substrates 11 and 12 with an inclination angle δ with respect to the substrate normal.

On the other hand, the liquid crystal molecule 14 becomes 2
Θ (Θ: Cone angle that is a physical property of liquid crystal material) Stable in the vicinity of the two positions while switching between two positions on the wall surface of the virtual cone 15 having an apex angle and no voltage applied. To do. The alignment state in which the smectic layer 16 shown in FIGS. 6A and 6B has a chevron structure depends on the relationship between the pretilt direction of the liquid crystal molecules 14 between the substrates and the bending direction of the chevron structure of the smectic layer 16. The orientation state of (a) is called C1 orientation, and the orientation state of (b) is called C2 orientation.

In the orientation state of SSFLC shown in FIG. 1, both C1 orientation state and C2 orientation state are generally Θ>
By satisfying the relationship of δ, the liquid crystal molecules 14 are imaginary cones in almost the entire thickness direction including the kink position of the chevron-structured smectic layer 16 (the bent portion at the center between the substrates) between the substrates 11 and 12 when no voltage is applied. Two positions can be stably taken within 15, and a bistable state is developed. Figure 2
1A and 1B show projections of liquid crystal molecules onto the bottom surface 17 of the virtual cone 15 in the C1 orientation state and the C2 orientation state shown in FIGS. 1A and 1B, respectively. , Bistable states of liquid crystal molecules 14a and 14b (projection 1
8a, 18b).

In the element in which the liquid crystal exhibits the bistable alignment state as described above, one average molecular axis (position of the liquid crystal molecule) in the bistable state of the pair of polarizing plates under crossed Nicols.
The polarization axis is aligned with, switching between bistable states is performed, and black (dark state) and white (bright state) are displayed. This switching is performed, for example, by the creation of a domain from one state to the other, that is, with the creation and disappearance of a domain wall.

However, when the display is performed by using such a switching mechanism, basically only binary display of black and white can be performed, and it is difficult to display the gradation (halftone) between black and white.

On the other hand, the liquid crystal device of the present invention has a memory property (bistability) as shown in FIGS. 1 and 2 in order to realize gradation display in a device using a liquid crystal exhibiting a chiral smectic phase. It is made to disappear so that the position of liquid crystal molecules can be continuously changed by the applied voltage. Because of this setting, in the present invention, preferably I-
A liquid crystal material exhibiting a Ch-SmC * or I-SmC * phase transition is used.

FIG. 3 (a) shows a process of forming a layer (smectic layer) structure of a liquid crystal material showing a Ch-SmA-SmC * phase series at least in a lowered temperature in the liquid crystal element.
(B) shows a process for forming a layered structure of a liquid crystal material exhibiting the Ch-SmC * phase series at least at a temperature decrease. In the figure, arrow R indicates the direction of the average uniaxial orientation treatment axis in the device. The liquid crystal molecules 14 can be switched along the wall surface of the virtual cone 15 area when a voltage is applied.

Here, the "average uniaxial orientation treatment axis" means that uniaxial orientation treatment is performed on the surfaces of both substrates constituting the element in contact with the liquid crystal, and the directions (for example, rubbing directions) are parallel and in the same direction. If they are in opposite directions (antiparallel),
In the case where only one substrate is subjected to the uniaxial orientation treatment, the axis itself of the uniaxial orientation treatment is equivalent, and the directions in which the uniaxial orientation treatment is applied to both substrates (for example, rubbing directions) cross each other. In this case, it corresponds to the central axis of both uniaxial orientation treatment axes, that is, the direction of 1/2 of the cross angle. The “direction” of the average uniaxial alignment treatment axis is, for example, the direction in which liquid crystal molecules in the vicinity of the substrate subjected to the alignment treatment are raised with respect to the substrate, that is, the direction in which pretilt is generated, and only one substrate is provided. When the uniaxial alignment treatment is performed or when the uniaxial alignment treatment is performed on both substrates and the directions (for example, rubbing directions) are parallel and in the same direction, it is the treatment direction itself and parallel to both substrates. When the processing is performed in the opposite direction (antiparallel), the processing direction is on one of the substrates, and the directions where the uniaxial orientation processing is performed on both substrates (for example, the rubbing direction) are crossing each other. Then, it is the direction of the central axis.

As shown in FIG. 3A, Sm is included in the phase series.
In the case of the liquid crystal material having the A phase, the liquid crystal molecules 14 are arranged in the SmA phase so that the direction of the normal line of the smectic layer (lateral arrow LN in the plane of the drawing) coincides with the uniaxial alignment treatment direction to form a smectic layer structure. In the SmC * phase, the liquid crystal molecules 14 tilt from the smectic layer normal direction LN,
Stabilization is performed near the edge of the virtual cone 15 or slightly inside thereof.

On the other hand, FIG. 3 preferably used in the present invention.
As shown in (b), in the phase series not including the SmA phase, for example, in the process of phase transition from the Ch phase to the SmC * phase, the liquid crystal molecules 14 are tilted with respect to the smectic layer normal direction LN, and the average uniaxial The smectic layer structure is formed by arranging so as to be slightly inclined from the alignment treatment direction R.

In the present invention, the liquid crystal molecule 14 is Sm.
It is adjusted so as to be stabilized at a position inside the edge of the virtual cone 15 in the operating temperature range within the C * phase. Here, as a case of "stabilizing at a position inside the edge of the virtual cone 15", a structure in which the smectic layer has an inclination angle such as a chevron structure or an oblique bookshelf structure is conceivable, but it is a complete bookshelf structure. Even in such a case, if the pretilt angle is high, or if the polar interaction at the substrate interface is strong and the bulk molecule is twisted, it may be stabilized inside the cone edge. Further, in a material having a remarkable electroclinic effect, the molecules are tilted further to the outside of the virtual cone edge by the electric field, but the liquid crystal element of the present invention has a molecular orientation direction and a layer normal direction when an electric field is applied. Deviation angle is larger than the deviation angle between the molecular orientation direction when no electric field is applied and the layer normal direction, that is, the direction of liquid crystal molecules when no electric field is applied and one of the polarization axes of crossed Nicols are made to coincide with each other. In the dark state, the optical axis of the liquid crystal is shifted and birefringence is exhibited when a voltage of either positive or negative polarity is applied. The present invention can also be applied to a material in which molecules are inclined to the outside.

Here, as a mode of the present invention, a case of having a layer inclination angle such as a chevron structure or an oblique bookshelf will be described in detail with reference to FIG. 4 using a model.
Similar to FIG. 3B, FIG. 4A shows a change in the transposition of liquid crystal molecules in a phase series that does not include the SmA phase. For example, in the process of phase transition from the Ch phase to the SmC * phase (especially Sm
Immediately below the transition temperature to the C * phase), the liquid crystal molecules 14 are arranged so as to be inclined with respect to the smectic layer normal direction LN, and a smectic layer structure is formed.

However, in FIG. 4A, there is a difference in the cone angle Θ (1/2 of the apex angle of the virtual cone 15) on the high temperature side (T1) and the low temperature side (T2) in the SmC * phase, for example. .

Here, the cone angle on the high temperature side T1 is Θ
1, the cone angle on the low temperature side T2 is Θ2, and Θ1 <Θ
When a material satisfying the relationship of 2 is used, usually, the layer spacing d1 of the smectic layer at each of these temperatures is
And d2, the relationship of d1> d2 is established. Therefore, if the layer structure has a bookshelf structure at the temperature T1, the layer inclination angle δ that satisfies at least the relational expression δ = cos ⁻¹ (d2 / d1) is obtained at the temperature T2.

Therefore, at the temperature T2, a chevron structure or an oblique bookshelf structure is formed. Of these, the layer structure and the state of the c-director and the projection on the virtual cone bottom surface when the chevron structure is taken are shown in FIGS. 4B and 4C (reference numerals are the same as those in FIG. 2). As shown in the figure, C1 and C2 can be defined from the relationship between the rubbing direction and the layer inclination angle, as in the case of a normal bistable SSFLC. According to the principle described above, the liquid crystal molecules 14 are adjusted so as to be stabilized at a position inside the edge of the virtual cone 15.

3 (a) and 3 (b) and FIG. 4 (a), the liquid crystal molecules 14 as shown in FIGS. 1 and 2, for example, are in a bistable orientation state of chevron structure, that is, substantially the substrate. Should be stable in two parallel states, but Fig. 3
In the case of (b) and FIG. 4 (a), the binding force of the uniaxial orientation treatment becomes strong, only one of these two states becomes stable, and the memory property disappears. Also, FIG.
(B), at the time of the Ch-SmC * phase transition shown in FIG. 4 (a) (immediately below the transition temperature to the SmC * phase), as shown in FIG.
It is conceivable that a smectic layer structure showing different layer normal directions (LN1 and LN2) is formed. At this time, the state of uniaxial orientation treatment of the pair of upper and lower substrates of the cell sandwiching the chiral smectic liquid crystal (conditions such as treatment direction,
If the (orientation material, etc.) is completely symmetrical, two smectic layer structures as shown in FIG. 5 are formed in equal proportions.

Further, in the liquid crystal element of the present invention, FIG.
Only one of the two layer structures shown in Fig. 4 is aligned, that is, the average uniaxial orientation axis and the direction of deviation of the smectic layer normal direction are constant, and as shown in Fig. 4 (b) or (c). The liquid crystal molecules 14 are stabilized inside one edge of the virtual cone 15 with no voltage applied, and the alignment state of the SmC * phase in which the memory property is lost is obtained.

Next, in the cell having the alignment state of the liquid crystal element of the present invention, that is, the alignment state in which one of the layer structures in the SmC * phase is preferentially formed as shown in FIG. A model of behavior (projection on the top surface, side surface, and cone bottom surface of the device) will be described with reference to FIG. In addition, in FIG. 6, the inversion behavior with respect to the electric field will be described by using the C2 orientation state in the parallel rubbing cell (cells subjected to rubbing treatment in parallel and in the same direction on both substrates). C1 orientation, oblique bookshelf orientation, antiparallel The orientation in the cell can be discussed in the same way.

In FIG. 6, the behavior (I) when viewed from above the cell in the state of voltage application, the behavior (II) in the cell cross-sectional direction, and the projection (I) on the virtual cone bottom surface in the SmC * phase (I
II) are shown respectively. In the case of I, it means an average molecular axis of liquid crystal molecules in the cell cross section direction.

First, as shown in FIG. 6B, when no voltage is applied, the liquid crystal molecules 14 (projection (18) on the bottom surface of the virtual cone 17 is slightly deviated from the average uniaxial alignment treatment direction (arrow R). Oriented The spontaneous polarization (18 ') of the liquid crystal is oriented in substantially the same direction between the substrates.

Here, a cell is arranged under the crossed Nicols (d) in which one of the polarization axes (P) is aligned with the position of the liquid crystal molecules when no voltage is applied, and the amount of light transmitted through the liquid crystal is set to the minimum state. A dark state (black state, first amount of emitted light) is obtained.

When a voltage is applied to this alignment state, the liquid crystal molecules 14 are aligned with the polarity of the voltage E with respect to the position when no voltage is applied, as shown in FIGS. 6 (a) and 6 (c). The spontaneous polarizations 18 'are aligned in the opposite direction and tilted (switched). The tilt angle (see II) based on the position of the liquid crystal molecules when no voltage is applied depends on the magnitude of the applied voltage (absolute value of voltage), as shown in FIGS. 6 (a) and 6 (c). As shown, the tilt angle when a voltage of one polarity is applied (when a positive voltage is applied) and the tilt angle when a voltage of the other polarity is applied (when a negative voltage is applied) are , If the polarities of the voltages are opposite, even if they have the same voltage absolute value, they are greatly different.

In the case of FIG. 6, when no voltage is applied, the molecules are already monostabilized in a direction inclined from the direction of the smectic layer normal, and a sufficiently large electric field is applied to each of the positive and negative sides. As a result of attempting to arrange the molecules so that the direction of spontaneous polarization of the molecules near the substrate interface also faces the direction of the electric field as in the bulk part from the state of FIG. Since it exists on the edge, the maximum tilt state can be obtained with reference to the position when no voltage is applied. As a result, a uniform orientation state in which there is almost no twist at the molecular position with the layer normal axis as the axis of symmetry is formed. The maximum tilt state of the liquid crystal molecules is the tilt angle in the maximum tilt state based on the position when no voltage is applied by applying a voltage of one polarity and the tilt angle in the maximum tilt state by applying a voltage of the other polarity. 6, the angle in the maximum tilt state when the positive voltage is applied is adjusted to be larger than the angle in the maximum tilt state when the negative voltage is applied in FIG.

Here, for example, when the refractive index anisotropy Δn of the liquid crystal is d, the cell thickness is d, and Δnd is set in the vicinity of a half wavelength of visible light, a positive polarity as shown in FIG. 6C is obtained. At the applied voltage of, as the voltage (absolute value) increases,
The amount of light emitted from the liquid crystal element, that is, a predetermined tilt state can be obtained. Then, it is possible to obtain the second emitted light amount that is the most different from the emitted light amount when the voltage is not applied (the most different in the positive voltage application range), that is, the maximum transmitted light amount.

On the other hand, as shown in FIG. 6 (a), when a negative voltage is applied, the amount of light transmitted through the liquid crystal element rises, but the amount of optical response thereof is very small, and a predetermined voltage (positive polarity) is obtained. The third emitted light amount that is the most different from the emitted light amount when no voltage is applied (most different in the negative voltage application range) when the liquid crystal molecules are in a predetermined tilt state with the same absolute value voltage as the voltage side. That is, the maximum transmitted light amount is obtained. However, the difference between the maximum amount of transmitted light when the negative voltage is applied and the amount of transmitted light when no voltage is applied as shown in FIG. 6B is equal to the maximum amount of transmitted light when the positive voltage is applied in the case of FIG. 6C. It is smaller than the difference with the amount of transmitted light when no voltage is applied, that is, the maximum amount of transmitted light in the liquid crystal element can be obtained when a positive voltage is applied.

Here, for example, when a pair of polarizing plates as shown in FIG. 6D is used, the position of the liquid crystal molecule 14 when no voltage is applied in the maximum tilt state of the liquid crystal molecule 14 when a positive voltage is applied. The tilt angle is 45
When it is less than °, the liquid crystal molecule 14 is a virtual cone 15
When the positive voltage is applied, the maximum amount of transmitted light (second amount of emitted light) can be obtained at the edge of, that is, in the state of maximum tilt. On the other hand, when the tilt angle is larger than 45 °, when the liquid crystal molecules 14 are inside the edge of the virtual cone 15, the maximum transmitted light amount (second emitted light amount) when the positive voltage is applied is obtained. To be In any of the above cases, when the negative voltage is applied, the maximum amount of transmitted light (third emitted light amount) when the negative voltage is applied can be obtained in the maximum tilt state.

An example of the voltage (V) -light transmittance (T) characteristic of the element exhibiting the switching behavior of the liquid crystal molecules as described above, particularly the maximum when the liquid crystal molecules are in the maximum tilt state when a positive voltage is applied. FIG. 7 shows an example of an element when the transmittance can be obtained. When a positive voltage is applied, the transmittance increases due to the tilt of the liquid crystal molecules along the voltage value, and the maximum transmittance T1 is shown at a voltage V1 or higher. On the other hand, when a negative voltage is applied, the liquid crystal molecules are tilted along with the voltage value and the transmissivity is slightly increased, but the transmissivity is saturated at the maximum transmissivity T2 which is much smaller than T1 at the voltage -V1 or less.

The liquid crystal device of the present invention has the switching operation shown in FIG. 6 and the characteristics shown in FIG.
It is applied to an active matrix type liquid crystal panel equipped with an FT, an AC drive waveform is applied, the device functions as an optical shutter, and a unipolar voltage application period (for example, voltage application on the positive polarity side shown in FIG. 7 is applied. The time aperture ratio is set to 50% or less by combining the period (using the optical response due to V.) with the voltage application period with the opposite polarity (for example, the period during which the optical response is applied due to the voltage application on the negative polarity side shown in FIG. 7). The same effect as the method can be obtained. In this way, it is possible to demonstrate a liquid crystal element with improved moving image quality without using a complicated peripheral circuit or the like.

In particular, the maximum tilt state angle of the liquid crystal molecules (average molecular pongee) when a voltage of the first polarity (positive polarity in FIG. 6) is applied and the second polarity (negative polarity in FIG. 6) The ratio of the angle of the liquid crystal molecule (average molecular axis) to the maximum tilt state when a voltage is applied is preferably 5 or more,
Then, when the voltage of the first polarity (positive polarity) is applied, the maximum amount of light emitted from the liquid crystal element in a predetermined tilt state of the liquid crystal molecules (average molecular axis) (for example, T1 in the characteristic of FIG. 7), It is preferable to adjust the ratio of the maximum amount of light emitted from the liquid crystal element (for example, T2 in the characteristic of FIG. 7) in the maximum tilt state of the liquid crystal molecules (average molecular axis) at the time of applying a polarity (negative polarity) voltage to 5 or more. As a result, the effect of improving the moving image quality can be obtained most remarkably.

Next, the inversion mechanism of liquid crystal molecules in the alignment state of the liquid crystal element of the present invention will be described.

In the alignment state in SSFLC shown in FIGS. 1 and 2, in order for the liquid crystal molecules 14 to switch between the bistable states, it is necessary to exceed an energy barrier of a predetermined height. Existence is the origin of bistability. On the other hand, in the liquid crystal element of the present invention, in the alignment state as shown in FIG.
1 is extremely stabilized at a position near one side of the bistable potential in SSFLC. As a result, there is only one stable state, the stable state corresponding to the magnitude of the applied voltage exists in an analog manner, and the applied voltage and the stable molecular position have a one-to-one correspondence. Inversion without generation can be realized.

A model of the state of this energy barrier (potential) is shown in FIGS. 8 and 9.

FIGS. 8A and 8B show potential states in the bistable orientation state in SSFLC for the C1 orientation state and the C2 orientation state, respectively. A
1 and A2 represent the potentials of the respective states of the bistable state. As is clear from these figures, the state of the potential is slightly different depending on the C1 orientation and the C2 orientation. In SSFLC, the C1 orientation has a larger opening angle of liquid crystal molecules at the liquid crystal-substrate interface than in the C2 orientation (see the projection near the substrate interface in FIGS. 2A and 2B). The height of the barrier also increases.

On the other hand, FIGS. 9 (a) and 9 (b) show the potential state in the aligned state in the liquid crystal element of the present invention for the C1 aligned state and the C2 aligned state, respectively. B1 is the potential of the liquid crystal molecule when no voltage is applied (in the case of FIG. 6B), and B2 is the potential of the liquid crystal molecule at the maximum tilt due to the application of the voltage of one polarity (in the case of FIG. 6C). , B3 are the potentials of the liquid crystal molecules at the maximum tilt due to the application of the voltage of the other polarity (see FIG.
(In the case of (a)) is shown.

C as shown in the above SSFLC case
When one of the bistable states is stabilized, the driving characteristics are different from those of the 1-oriented and C2 oriented orientation states in which the height of the energy barrier between the bistable states is different. Will end up. In particular, in the C1 orientation state having a high energy barrier, as shown in FIG. 9A, even when one of the bistable potentials (B1) is extremely stabilized, two stable states remain. A state occurs in which one is left as it is, or one is in a metastable state (B2 has a high potential level but is stable as compared with the surroundings). As a result, when a voltage is applied, a stable state corresponding to the magnitude of the applied voltage exists in an analog manner until a certain potential is reached, and the applied voltage and the stable molecular position correspond one-to-one. Although continuous inversion without domain formation can be realized, discontinuous orientation state is formed when a certain potential is exceeded, that is, discontinuous inversion behavior with domain wall formation. is there.

On the other hand, in the C2 oriented state, the energy barrier in the case of the bistable SSFLC is low, so that one (B1) is extremely stabilized, as shown in FIG. 9 (b). Even in the case, the inversion can be realized continuously up to the state of B2 and without domain generation. Further, it can be understood from these figures that the driving voltage tends to be higher in the C1 orientation.

From the above points, the alignment state of the liquid crystal element of the present invention is C in the parallel-rubbed cell from the viewpoint of analog gray scale performance and low driving voltage.
It is desirable to use two orientations. Alternatively, in the case of an alignment state in which C1 alignment and C2 alignment are mixed, it is desirable that the pretilt angle be low in order to minimize the characteristic variations. Alternatively, antiparallel rubbing is desirable.

6A to 6C and 9 as described above.
The liquid crystal molecules 14 are stabilized to the inside of one edge of the virtual cone 15 in the state where no voltage is applied, and the alignment state in the SmC * phase in which the memory property is lost and the switching behavior when a voltage is applied are shown in FIG. And a liquid crystal element exhibiting optical response characteristics as shown in FIG.
It is realized by adjusting the design of the cell and further performing a treatment for imparting a bias to the internal potential in the cell in the process of the Ch—SmC * phase transition of the liquid crystal material.

Examples of the liquid crystal material exhibiting the chiral smectic phase include, for example, hydrocarbon-based liquid crystal materials having a phenylpyrimidine skeleton, a biphenyl skeleton, and a phenylcyclohexane ester skeleton, in the temperature range of the chiral smectic phase. Of the chiral smectic phase has a maximum value (d <dtc, d: the distance in the temperature range of the chiral smectic phase) at the maximum temperature of the chiral smectic phase, and the chevron structure is formed in the cell. 3 ° <δ <Θ for materials with
(Δ: inclination angle of the smectic layer with respect to the substrate normal in the cell of the liquid crystal material, Θ: cone angle peculiar to the liquid crystal material, that is, 1/2 of the apex angle of the virtual cone). It is also possible to use the liquid crystal composition thus blended.

Further, the layer spacing d is almost constant in the temperature range of the chiral smectic phase like a hydrocarbon liquid crystal material having a naphthalene skeleton or a polyfluorine liquid crystal material, and δ ≦ 3 ° in the cell. Which is a material to be used, and Θ at the temperature just below the phase transition temperature from the high temperature side to the chiral smectic phase.
On the other hand, a liquid crystal composition is used in which components are blended so that Θ increases with a temperature drop in the temperature range of the chiral smectic phase.

Θ in the chiral smectic phase of the liquid crystal material
Is ideally 22.5 degrees or more in order to further increase the contrast between the state of maximum light amount and the state of minimum light amount due to switching, for example, the maximum transmittance T1 under the characteristics shown in FIG. is there. Further, when Θ is very large, the tilt from the monostable state due to the application of the electric field to the reverse polarity, that is, the tilt to the side of FIG. 6A also becomes a large angle, and for example, the reverse polarity voltage application of FIG. 7 is applied. Maximum transmittance T2
May increase, and the real-time aperture ratio may reach 100%. Therefore, Θ is preferably less than 30 degrees. If the change of Θ with temperature is large, the darkest state set between the polarizing plates under crossed Nicols may not be kept constant. For this reason, it is preferable to set the maximum change width of Θ depending on the temperature in the driving temperature range of the liquid crystal element to 3 degrees or less.

As in the case of a general SmC * phase material, the molecules are tilted from the normal of the smectic layer so that the layer spacing decreases, that is, the cone angle Θ increases toward the lower temperature side. As the layer spacing decreases, the factor of decreasing becomes larger, but in the case of a liquid crystal material that spontaneously adopts a bookshelf layer structure such as the case of a polyfluorinated liquid crystal material, the layer measured in bulk at the lower temperature side. It is considered that the reason why the chevron structure is difficult to obtain is that the change in the layer spacing d is extremely small due to the characteristic of the material that the spacing is long. in this case,
The interface molecules may be oriented in the rubbing direction by the uniaxial orientation control force, and the bulk may be oriented in a direction deviated from the rubbing direction depending on the temperature characteristics of the tilt angle. At this time, the molecules near the interface are also oriented in a direction deviated from the rubbing direction by applying an electric field.

On the other hand, of the two layered structures developed as shown in FIG. 5, only one layered structure is aligned, that is, the average uniaxial orientation process axis and the direction of deviation of the smectic layer normal direction are constant. As a method of giving a bias of the internal potential in the device, 1) applying a positive or negative DC voltage between the pair of substrates at the time of Ch-SmC * phase transition or at the time of I-phase-SmC * phase transition To do. 2) Alignment films made of different materials are used for the pair of upper and lower substrates. 3) Method of treating the alignment films of the pair of upper and lower substrates (film forming conditions,
Change processing conditions such as rubbing intensity and UV irradiation. 4) The film type or film thickness of the layer provided as the base of the alignment film of the pair of upper and lower substrates is changed. There are various methods such as
Either means may be used.

In particular, the DC application condition according to 1) is D
In order to avoid a short circuit between a pair of substrates forming the device by applying C for a long time, DC is Ch-SmC.
* In the vicinity of the phase transition, it is preferable to keep the minimum application time necessary to align the layer directions in one direction. Specifically, D in the range of 100 mV or more and 10 V or less
It is preferable to apply a C voltage.

The liquid crystal material as described above and the above 2) to
Ions in the alignment film and liquid crystal material set in 4) are TF
It is desirable to reduce as much as possible so as not to adversely affect the T drive.

In the liquid crystal device of the present invention, a large uniaxial orientation regulating force is required for monostabilization of liquid crystal molecules (average molecular axis) when no voltage is applied. Regarding this alignment regulating force, a method of evaluating the alignment regulating force using a cholesteric liquid crystal is Uchida et al. (Liquid Crystals,
5, p. 1127 (1989)). That is, the orientation regulating force can be evaluated by evaluating the "effective twist angle" determined by the torque balance between the helical pitch in the cholesteric phase and the orientation regulating force.
Also in the present invention, using this idea, the uniaxial orientation regulating force is defined as follows. When a Ch phase is present in the element of the present invention, the cholesteric pitch in the Ch phase is p,
And the cell thickness dg, if there is no orientation regulating force, and the twist angle φ in the cell is dg / p = φ / 2
The relationship is π. In addition, φ is zero when the uniaxial orientation is regulated in parallel on the upper and lower substrates and the orientation regulating force is infinite. The value of φ can be easily evaluated by measuring the optical rotatory power under a polarizing microscope as in the case of Uchiyoshi et al. That is, in the cell, the virtual pitch p * (=
2π · dg / φ), and it can be rephrased that the alignment regulating force is zero when P * = P and the alignment regulating force is infinite when P * = infinity.

In the present invention, at least p * ≧ 2 × p is preferable for monostabilization. More preferably, p * ≧ 10 × p. It is preferable to appropriately adjust the uniaxial alignment treatment conditions (rubbing conditions, etc.), alignment film thickness, alignment film type, firing conditions, etc. under the conditions 2) to 4) in consideration of the fact that these values are obtained. .

In the liquid crystal element of the present invention, hysteresis may be present when the voltage-transmittance curve when a triangular wave is applied is obtained. However, in the case of driving with an AC waveform as in the case of an element equipped with an actual TFT, there is no continuous optical modulation from the white state to the halftone state as in the case of applying a triangular wave. It doesn't matter. That is, since optical modulation is always performed while inverting black and white in accordance with the applied polarity, for example, when optical modulation is performed from white to halftone, after the white state is passed through the black alignment state, halftone is performed. Since it is modulated to the orientation state of, the drive of writing after always being reset to the black side with one polarity when applying an alternating current is realized, so the influence of the history of the previous state is suppressed to a large extent. can do.

A specific embodiment of the liquid crystal element of the present invention will be described below with reference to FIG.

In the liquid crystal element 80 shown in the figure, a pair of substrates 81 made of a highly transparent material such as glass and plastic.
A cell in which a liquid crystal 85, preferably a liquid crystal exhibiting a chiral smectic phase, is sandwiched between a and 81b is sandwiched between a pair of polarizing plates 87a and 87b whose polarization axes are orthogonal to each other.

On the substrates 81a and 81b, electrodes 82a and 82b made of a material such as In ₂ O ₃ and ITO for applying a voltage to the liquid crystal 85 are provided in stripes, for example, and these electrodes intersect each other. Form a matrix electrode structure (simple matrix). As will be described later, dot-shaped transparent electrodes are arranged in a matrix on one substrate, and TFTs or MIM (Meta) are arranged on each transparent electrode.
It is preferable to connect a switching element such as l-Insulator-Metal) and to provide an active matrix structure by providing a counter electrode on one surface of the other substrate or in a predetermined pattern.

[0094] electrodes 82a, On 82b, SiO ₂ having a function such as to prevent these short as necessary,
An insulating film 83a made of a material such as TiO ₂ or Ta ₂ O ₅ ,
83b are provided respectively.

Further, on the insulating films 83a and 83b, alignment control films 84a and 84b which are in contact with the liquid crystal 85 and function to control the alignment state thereof are provided. Uniaxial alignment treatment is applied to at least one of the alignment control films 84a and 84b. As such a film, for example, an organic material such as polyimide, polyimide amide, polyamide, or polyvinyl alcohol, which is solution-coated, is rubbed on the surface of the film, or an oxide or a nitride such as SiO is obliquely applied to the substrate. An oblique vapor deposition film of an inorganic material vapor-deposited at a predetermined angle from the direction can be used.

Regarding the orientation control films 84a and 84b, the pretilt angle of the molecules of the liquid crystal 85 (the film surface near the interface of the orientation control film of the liquid crystal molecules) depends on the selection of the material, the condition of the treatment (uniaxial orientation treatment, etc.) and the like. The angle with respect to) is adjusted.

When the alignment control films 84a and 84b are both uniaxially oriented, the uniaxial orientations of the respective films (particularly the rubbing direction) are parallel or antiparallel depending on the liquid crystal material used. Alternatively, it can be set to cross in the range of 45 ° or less.

The substrates 81a and 81b are the spacer 86.
Are facing through. The spacer 86 determines the distance (cell gap) between the substrates 81a and 81b, and silica beads or the like are used. Regarding the cell gap determined here, the optimum range and the upper limit differ depending on the liquid crystal material, but uniform uniaxial orientation,
Further, in order to develop an alignment state in which the average molecular axis of liquid crystal molecules is substantially the same as the average direction axis of the alignment treatment axis when no voltage is applied, it is preferable to set it in the range of 0.3 to 10 μm.

In addition to the spacer 86, in order to improve the adhesiveness between the substrates 11a and 11b and to improve the impact resistance of the liquid crystal exhibiting a chiral smectic phase, adhesive particles made of a resin material such as an epoxy resin are dispersedly arranged. It is also possible (not shown).

In the liquid crystal element 80 having the above structure, when a liquid crystal exhibiting a chiral smectic phase is used as the liquid crystal 85, the composition of the material is adjusted, and further the treatment of the liquid crystal material and the element constitution, for example, the alignment control films 84a and 84b. By appropriately setting the materials, processing conditions, and the like of FIG.
As shown in, when no voltage is applied, the average molecular axis (liquid crystal molecule) of the liquid crystal shows an alignment state in which the voltage is applied, and when driving, one polarity (first polarity) is applied when a voltage is applied. The tilt angle with respect to the mono-stabilized position of the average molecular axis continuously changes according to the magnitude of the voltage, and when the voltage of the other polarity (second polarity) is applied, the average molecular axis of the liquid crystal becomes
The tilt is made at an angle corresponding to the magnitude of the applied voltage, and the maximum tilt angle by the voltage application of the first polarity is larger than the maximum tilt angle by the voltage application of the second polarity. Preferably, as a liquid crystal material exhibiting a chiral smectic phase, I phase-Ch phase-SmC * is set at a lowered temperature.
The phase transition series of the phase or the phase transition series of the I-SmC * phase is used, and the SmC is treated by the above-mentioned treatments 1) to 4).
* Form a state in which the memory property is lost in the phase.

Further, it is preferable to set the helical pitch in the bulk state of the liquid crystal exhibiting the chiral smectic phase to be twice the cell gap or more.

The liquid crystal material 85 exhibiting a chiral smectic phase has the above-described characteristics (characteristic value cone angle Θ peculiar to the liquid crystal material, layer spacing d of the smectic layer, and inclination angle δ). A composition prepared by appropriately selecting a hydrocarbon liquid crystal material having a biphenyl skeleton, a phenylcyclohexane ester skeleton, a phenylpyrimidine skeleton, a naphthalene liquid crystal material, or a polyfluorine liquid crystal material is used.

Under such characteristics, a polarizing plate is provided on at least one side of the substrates 81a and 81b, and the cells are arranged so as to be in the darkest state when no voltage is applied. With the continuous change of the corner,
For example, the amount of light transmitted through the element (the amount of light emitted from the element) can be controlled in an analog manner according to the voltage change with the characteristics shown in FIG.

In the liquid crystal element, the substrates 81a and 81b are
It is also possible to provide a color liquid crystal element by providing at least R, G, B color filters on one side.

The liquid crystal element is composed of the substrates 81a and 81a.
A transparent liquid crystal element in which a pair of polarizing plates are provided on both substrates of b, that is, both substrates 81a and 81b are transparent substrates, and incident light from one substrate side (for example, light from an external light source) Of the type which modulates light and outputs it to the other side, or a reflective liquid crystal element in which a polarizing plate is provided on at least one substrate, that is, a reflector is provided on either one of the substrates 81a and 81b, or one substrate. The present invention can be applied to any type of element that modulates incident light and reflected light by using a reflective material as itself or as a member provided on the substrate and emits light to the same side as the incident side.

In the present invention, a drive circuit for supplying a gradation signal to the above-mentioned liquid crystal element is provided, and a continuous tilt angle from the monostable position of the average molecular axis of the liquid crystal is applied by applying the voltage as described above. It is possible to configure a liquid crystal display element that performs gradation display by utilizing the characteristics of the change and the amount of light emitted from the element that continuously changes. For example, it is possible to perform analog gray scale display by using an active matrix substrate having the above-described TFT or the like as one substrate of the liquid crystal element and performing active matrix driving by amplitude modulation in the drive circuit.

An example using such an active matrix substrate in the liquid crystal element of the present invention will be described with reference to FIGS.

FIG. 11 is a diagram schematically showing the element with a driving means, focusing on the structure of one substrate (active matrix substrate).

In the structure shown in FIG. 11, in the panel portion 90 corresponding to a liquid crystal element, the gate lines G1, G2, ... In the drawing, which correspond to the scanning lines connected to the scanning signal driver 91 which is the driving means, and the driving. , Which correspond to the information signal line connected to the information signal driver 92 as a means, are provided so as to be orthogonal to each other while being insulated from each other in the vertical direction in the drawing, and correspond to pixels at respective intersections. Then, a thin film transistor (TF
T) 94 and a pixel electrode 95 (only 5 × 5 pixel region is shown in the figure for simplification). As the switching element, a MIM element can be used instead of the TFT. The gate lines G1, G2, ... Are connected to the gate electrode (not shown) of the TFT 94, and the source lines S1, S2.
Is connected to the source electrode (not shown) of the TFT 94,
The pixel electrode 95 is a drain electrode (not shown) of the TFT 94.
It is connected to the. In such a configuration, the gate lines G1, G2, ... Are scan-selected, for example, in a line-sequential manner by the scan signal driver 91 to be supplied with a gate voltage, and the information signal driver 92 writes data to each pixel in synchronization with the scan selection of the gate lines. The information signal voltage corresponding to the information is the source line S1,
It is supplied to S2 ... And is applied to each pixel electrode through the TFT 94.

FIG. 12 shows an example of a sectional structure of each pixel portion (for one bit) in the panel structure as shown in FIG. In the structure shown in the figure, the TFT 94 and the pixel electrode 9 are
A liquid crystal layer 49 having spontaneous polarization is sandwiched between an active matrix substrate 20 including 5 and a counter substrate 40 including a common electrode 32 to form a liquid crystal capacitor (Clc) 31.

Regarding the active matrix substrate 20, an example using an amorphous SiTFT as the TFT 94 is shown. The TFT 94 is formed on the substrate 21 made of glass or the like, and silicon nitride (SiNx) is formed on the gate electrode 22 connected to the gate lines G1, G2 ... Shown in FIG.
An a-Si layer 24 is provided via an insulating film (gate insulating film) 23 made of a material such as the above, and a source electrode 27 is provided on the a-Si layer 24 via n + a-Si layers 25 and 26, respectively. The drain electrodes 28 are provided separately from each other. The source electrodes 27 are the source lines S1, S2 ... Shown in FIG.
The drain electrode 28 is connected to the pixel electrode 95 made of a transparent conductive film such as an ITO film. In addition, TFT9
The channel protective film 29 covers the a-Si layer 24 in FIG. The TFT 94 is turned on by applying a gate pulse to the gate electrode 22 during a period in which the corresponding gate line is scanned and selected.

Furthermore, in the active matrix substrate 20, the insulating film 23 (continuously provided with the insulating film on the gate electrode 22) is formed by the pixel electrode 95 and the storage capacitor electrode 30 provided on the glass substrate side of the pixel electrode 95. The storage capacitor (CS) 32 is provided in parallel with the liquid crystal capacitor Clc due to the structure in which the film is sandwiched. When the area of the storage capacitor electrode is large, the aperture ratio is lowered, so that the storage capacitor electrode is formed of a transparent conductive film such as an ITO film.

TFT of active matrix substrate 20
An alignment film 43a that has been subjected to a uniaxial alignment process such as a rubbing process for controlling the alignment state of the liquid crystal is provided on the pixel electrodes 95 and the pixel electrodes 95.

On the other hand, in the counter substrate 40, the glass substrate 41
A common electrode 42 and an alignment film 43b for controlling the alignment state of the liquid crystal are laminated on the upper surface of the same thickness as the entire surface.

The cell structure is sandwiched between a pair of polarizing plates whose polarizing axes are orthogonal to each other (not shown).

In the pixel portion of the panel having the above structure, a liquid crystal having spontaneous polarization, for example, a liquid crystal exhibiting a chiral smectic phase is used as the liquid crystal layer 49. The liquid crystal layer 49 is set so as to exhibit the switching operation shown in FIG. 6 and the optical characteristics shown in FIG.

In the panel structure shown in FIGS. 11 and 12, a substrate provided with a polycrystalline Si (p-Si) TFT can be used as the active matrix substrate. FIG. 13 shows an equivalent circuit of the pixel portion of the panel shown in FIG.

Active matrix driving utilizing the characteristics of the liquid crystal element having the above structure will be described with reference to FIGS. 13 and 14. In active matrix driving in the liquid crystal element of the present invention, for example, a period (one frame) for displaying certain information in one pixel is divided into a plurality of fields (for example, 1F and 2F shown in FIG. 13),
In these two fields, the amount of emitted light corresponding to predetermined information is obtained on average. Hereinafter, an example in which the liquid crystal layer 49 is divided into two fields in the case where the liquid crystal layer 49 exhibits the optical characteristics as shown in FIG. 7 will be described.

FIG. 14A shows that when one pixel is focused,
The voltage applied to one gate line which is a scan line connected to the pixel is shown. In the liquid crystal element having the above structure, the gate lines G1, G2, ... Are selected line by line for each field,
A predetermined gate voltage Vg is applied to one gate line in the selection period Ton, the voltage Vg is applied to the gate electrode 22, and the TFT 94 is turned on. During the non-selection period Toff corresponding to the period in which another gate line is selected, the TFT 12 is in a high resistance state (off state) without applying a voltage to the gate electrode 22, and a predetermined same gate line is selected for each Toff. The gate voltage Vg is applied to the gate electrode 22.

FIG. 14B shows the voltage Vs applied to the information signal line (source line) of the pixel. 14
As shown in (a), when the gate voltage is applied to the gate electrode 22 in the selection period Ton in each field, the source lines S1 and S that become the information lines connected to the pixel in synchronization with this are applied.
A predetermined source voltage (information signal voltage) Vs (the reference potential is the potential Vc of the common electrode 42) is applied from 2 to the source electrode 27.

Here, in the first field (1F) which constitutes one frame, the pixel is based on the information written in the pixel, for example, the voltage-transmittance characteristic as shown in FIG. 7 according to the liquid crystal used. The positive source voltage (information signal voltage) of level Vx corresponding to the optical state or display information (transmittance) to be obtained in (the reference potential is the potential Vc of the common electrode 42).
Is applied). At this time, since the TFT 14 is in the ON state, the voltage Vx applied to the source electrode 27 is
Is applied to the pixel electrode (95) through the drain electrode 28, and the liquid crystal capacitance (Clc) 31 and the storage capacitance 32 (Cs).
Then, the electric potential of the pixel electrode becomes the information signal voltage Vx. Subsequently, since the TFT 14 has a high resistance (OFF state) in the non-selection period Toff of the gate line to which the pixel belongs, the liquid crystal cell (the liquid crystal capacitance Cl
In c) 31 and the storage capacitor (Cs) 32, the selection period Ton
The state in which the charge charged in
Is retained. Then, the voltage Vx is applied to the liquid crystal layer 49 in the pixel through the period of the first field 1F, and the liquid crystal portion of the pixel obtains an optical state (amount of transmitted light) corresponding to the voltage value.

Next, in the selection period Ton of the second field (2F), the source voltage (-Vx) having the voltage value Vx which is opposite in polarity to the first field 1F and has substantially the same voltage value Vx.
Is applied to the source electrode 27. At this time, the TFT 14 is in the ON state, the voltage −Vx is applied to the pixel electrode 95, and the liquid crystal capacitance (Clc) 31 and the storage capacitance 32 (Cs).
Is charged, and the potential of the pixel electrode is changed to the information signal voltage -Vx.
become. Subsequently, in the non-selection period Toff, the TFT1
Since 4 has a high resistance (off state), a liquid crystal cell (liquid crystal capacitance Clc) 31 and a storage capacitor (C
In s) 32, the state in which the charge charged in the selection period Ton is accumulated is maintained and the voltage −Vx is held. And
The voltage −Vx is applied to the liquid crystal layer 49 of the pixel in the second field 2F period, and the pixel obtains an optical state (amount of emitted light) corresponding to the voltage value.

FIG. 14C shows the voltage value Vpix which is actually held in the liquid crystal capacity and the holding capacity of the pixel as described above and is applied to the liquid crystal layer 49. FIG. 14D shows the liquid crystal in the pixel. The optical response (optical response in the case of using a transmissive liquid crystal element) is schematically shown.

As shown in (c), the applied voltage is at the same level (absolute value) Vx whose polarities are mutually inverted through the two fields 1F and 2F. On the other hand, as shown in (d), in the first field 1F, a gradation display state (amount of emitted light) corresponding to Vx is obtained based on the characteristics shown in FIG. 7, for example, and in the second field 2F, according to -Vx. However, according to the characteristics shown in FIG. 7, for example, only a slight change in the amount of transmitted light is actually obtained, and the amount of transmitted light is smaller than Tx (= T ₁ ) and close to 0 level. Ty
(= T ₂ ).

In the active matrix driving as described above, when a liquid crystal exhibiting a chiral smectic phase is used, gradation display based on excellent high-speed response is possible, and at the same time gradation display of a level of one pixel is performed. Since the first field that obtains a high transmitted light amount and the second field that obtains a low transmitted light amount are divided and continuously performed, the time aperture ratio is 50
% Or less, the moving image high-speed response characteristics that human eyes perceive will be good. Further, in the second field, the amount of transmitted light does not completely become zero due to a slight switching operation of the liquid crystal molecules, so that the brightness perceived by human eyes during the entire frame period is secured. Note that, in FIG. 14, the first transmitted light amount Tx is displayed in the first field 1F and the low transmitted light amount Ty is displayed in the second field 2F. A low-brightness display with a low transmitted light amount Ty may be performed in the field 1F, and a high-brightness display with a high transmitted light amount Tx may be performed in the second field 2F. When such a display is performed, the voltage V is increased during the selection period Ton of the first field 1F.
It is sufficient to apply the voltage −Vx to the source lines S1, ... Instead of x, and the voltage Vx instead of the voltage −Vx may be applied to the source lines S1, ... In the selection period Ton of the second field 2F. By applying such a voltage, a transmitted light amount Ty (= T ₂ ) close to 0 level can be obtained in the first field 1F based on the characteristics shown in FIG. 7, and the second field 2F can be obtained.
Then, a high transmitted light amount Tx (= T ₁ ) can be obtained.

Further, the voltages of the same level in the first and second fields are inverted in polarity and applied to the liquid crystal layer 49, so that the voltage actually applied to the liquid crystal layer 49 is made alternating and the deterioration of the liquid crystal is prevented. To do.

In the above active matrix drive,
In one frame consisting of 2 fields, Tx and Ty
The average amount of transmitted light is obtained. Therefore, as for the information signal voltage Vs, according to the characteristics shown in FIG. 7, a large amount of transmitted light is increased by a predetermined level in accordance with the image information (gradation information) to be actually obtained in the pixel in the frame. It is also preferable to select and apply a voltage value that can be obtained to display a gradation state with a level transmitted light amount higher than a desired gradation state in the first field 1F.

(Second Embodiment) Hereinafter, a second embodiment of the present invention will be described with reference to the drawings.

As shown in FIG. 15, the display device 100 according to this embodiment includes a color light source 101 for sequentially emitting light of a plurality of colors and a display element 80 for switching the light in synchronization with the emission of the light. And are equipped with.

As the display element 80, a liquid crystal element can be cited. The liquid crystal element, as shown by reference numeral 80 in FIG. 10, is a pair of substrates 81a and 81b arranged with a predetermined gap therebetween, The liquid crystal 85 arranged between the pair of substrates 81a and 81b, and the pair of electrodes 8 that are arranged so as to sandwich the liquid crystal 85 while forming a plurality of pixels.
2a, 82b. In such a case, the liquid crystal element 80 may be a simple matrix type or an active matrix type (see FIGS. 11 and 1).
2), and may be a transmissive type or a reflective type. As a specific structure of the liquid crystal element 80,
Depending on whether it is the active matrix system, the simple matrix system, the transmissive system or the reflective system, the first
Various types as described in the above embodiment can be considered.

Further, the substrates 81a and 81b and the electrodes 82a,
With respect to the material, shape, manufacturing method, etc. of 82b, various ones as described in the first embodiment can be cited.

Further, in the liquid crystal element 80, as in the first embodiment, the insulative films 83a and 83b, the orientation control films 84a and 84b, spacers, adhesive particles, active elements (switching elements) 94, etc. May be disposed, and the materials, shapes, and manufacturing methods (particularly, the uniaxial orientation processing method and the uniaxial orientation processing direction of the orientation control films 84a and 84b) are the same as those described in the first embodiment. Various things can be mentioned.

On the other hand, as the liquid crystal 85, a liquid crystal having spontaneous polarization, for example, a liquid crystal exhibiting a chiral smectic phase may be used, and preferably a liquid crystal having the optical characteristic shown in FIG. 7 while performing the switching operation shown in FIG. You can use it. That is, in the state where no voltage is applied, the average molecular axis of the liquid crystal molecules shows a mono-stabilized alignment state, and in the state where a voltage of one polarity is applied,
The average molecular axis of the liquid crystal molecules is tilted from the mono-stabilized position to one side, and a voltage of another polarity (reverse polarity to the one polarity; the same applies hereinafter) is applied. In the state, the average molecular axis of the liquid crystal molecules tilts from the mono-stabilized position to the other side (that is, the side opposite to the side that tilts when a voltage of the one polarity is applied). Should be used.

When the voltage of the one polarity or the other polarity is applied, the tilt angle (hereinafter referred to as “tilt angle”) with reference to the position where the average molecular axis is mono-stabilized is used. Is continuously changed according to the magnitude of the voltage. As a result, the amount of light emitted from the liquid crystal element P continuously changes according to the magnitude of the voltage applied to the chiral smectic liquid crystal 85, which enables gradation control. In order to perform such gradation control, it is advisable to connect a drive circuit that supplies a gradation signal to the liquid crystal element P.

In this case, it is preferable that the maximum value of the tilt angle when the voltage of the one polarity is applied is different from the maximum value of the tilt angle when the voltage of the other polarity is applied. In such a case, the maximum value of the amount of light emitted from the liquid crystal element P in the state where the voltage of the one polarity is applied (hereinafter referred to as “first amount of light”) and the voltage of the other polarity are applied. In this state, the maximum value of the amount of light emitted from the liquid crystal element P (hereinafter referred to as "second amount of light") is different.

Further, it is preferable that the maximum value of the tilt angle when the voltage of the one polarity is applied is larger than the maximum value of the tilt angle when the voltage of the other polarity is applied.
In such a case, the first light amount becomes larger than the second light amount.

Specifically, if the maximum value of the tilt angle when the voltage of the one polarity is applied is 5 times or more the maximum value of the tilt angle when the voltage of the other polarity is applied. good. In such a case, the first light amount is 5 times or more the second light amount.

Further, it is preferable that the tilt angle when the voltage of the other polarity is applied is approximately 0 °.

Furthermore, by appropriately disposing the polarizing plate, the light quantity (third light quantity) emitted from the liquid crystal element may be substantially zero in the state where no voltage is applied.

To obtain the chiral smectic liquid crystal 85 having the above-mentioned characteristics, the liquid crystal 85 is required.
In addition, the phase transition series of isotropic liquid phase (Iso) -cholesteric phase (Ch) -chiral smectic C phase (SmC ^* ), and isotropic liquid phase (Iso) -chiral smectic phase (SmC ^* ) under reduced temperature ^. , Showing the phase transition series of
The smectic layer of the liquid crystal 85 having a substantially normal line direction may be used, and a state in which the memory property is lost in the SmC ^* phase may be formed by any of the following methods. Ch-SmC ^* phase transition, or Iso-SmC
^* Method of applying either positive or negative DC voltage to liquid crystal 85 between a pair of substrates at the time of phase transition Method of arranging alignment control films made of different materials so that liquid crystal 85 is sandwiched Pair of liquid crystal 85 sandwiched For the orientation control film of, the processing method (film forming conditions, rubbing strength, U
Different treatment conditions such as V light irradiation) A pair of alignment control films are arranged so as to sandwich the liquid crystal 85, and a base layer is arranged on the back side (substrate side) of each alignment control film. Method of varying species and film thickness As the liquid crystal exhibiting the chiral smectic phase, the liquid crystal described in the first embodiment can be used.
A polarizing plate may be used as appropriate as shown in the above embodiment.

Next, the display device 100 according to the present embodiment.
The driving method of will be described with reference to FIGS. 16 and 17.

[0142] In this embodiment, one frame period F _0, is divided into a plurality of field periods F _1, F _2, F ₃ as shown in FIG. 16, each field period F _1, F
₂ , F ₃ is further divided into a plurality of subfield periods 1F, 2F
The color light source 101 to the display element 80.
In contrast, a plurality of colors of light are sequentially emitted while changing the colors for each of the field periods F ₁ , F ₂ , and F ₃ (see (a) in the figure).
By switching the light in synchronization with the emission of the light by the display element 80, a high-brightness image is displayed in at least one subfield period 1F in one field period F ₁ , F ₂ or F ₃ . , A low-brightness image is displayed in at least one other sub-field period 2F (see (d) in the same figure), and the color displayed in each field period F ₁ , F ₂ , F ₃ is displayed. The images are visually mixed to be recognized as a full-color image.

In this case, each field period F ₁ , F ₂ ,
As shown in FIG. 17, F ₃ is divided into three subfield periods 1F, 2F, 3F, a high-luminance image is displayed in one subfield period 1F, and a low-luminance image is displayed in one subfield period 2F. Is displayed and the remaining one
In one subfield period 3F, the luminance may be set to almost 0.

The number of field periods included in one frame period F ₀ may be determined according to the number of color lights emitted from the color light source 101. For example, when each color light emitted from the color light source 101 is of three colors of RGB (red, green, blue), the number of field periods included in one frame period F ₀ is three (F ₁ ,
F ₂ , F ₃ ).

Further, the high-luminance image and the low-luminance image in the same field period F ₁ , F ₂ or F ₃ may be the same image having only different luminances.
The image at ₁ , F ₂ or F ₃ may be an image corresponding to the color of the irradiated light (that is, an image that provides good color reproducibility of a full-color image).

On the other hand, it is preferable that the luminance of the low-luminance image is ⅕ or less of the luminance of the high-luminance image and greater than 0. When a liquid crystal element is used as the display element 80, the brightness adjustment is performed by the pair of electrodes 82a,
This may be achieved by applying a voltage to 82b to drive the liquid crystal 85 to adjust the light transmittance, and when the liquid crystal 85 having the characteristics shown in FIG. 7 is used, + V in the case of a high-luminance image. _{When the} voltage of ₁ is applied and the low brightness image is -V
_A voltage of ₁ may be applied.

Image display on the display element 80 may be performed by line-sequential scanning.

FIG. 14 is a diagram showing a driving method of the active matrix type liquid crystal element shown in FIGS. 11 and 12, as an example of the driving method of the display device. FIG. 14A shows a certain gate. A state where the gate voltage Vg is applied to the line G _i is shown, (b) of the same figure shows a state where the source voltage Vs is applied to one source line S _j, and (c) of the same figure is shown. A state in which the voltage Vpix is applied to the pixel (that is, the liquid crystal 49) at the intersection of the gate line G _i and the source line S _j is shown, and FIG. 7D shows the change in the amount of transmitted light in the pixel.

In the present driving method, one frame period F ₀ is divided into _three field periods F ₁ , F ₂ , F ₃ , and each field period F ₁ , F ₂ , F ₃ is further divided into two subfield periods. It is divided into 1F and 2F. Therefore, when the frame frequency is 60 Hz, one frame period F ₀ is 16.7 msec, and one field period F ₁ , F ₂ , F ₃ is 16.7 msec / 3≈.
It becomes 5.5 msec, and one subfield period 1
F and 2F are 5.5 msec / 2≈2.8 msec. The liquid crystal 49 has the voltage-transmitted light amount characteristic shown in FIG.

Now, in a certain subfield period 1F, a certain gate line G _i has a certain period (selection period T
on), the gate voltage Vg is applied (see (a) in the figure), and the potential Vc of the common electrode 42 is applied to one source line S _j in the selection period Ton synchronized with the application of the gate voltage Vg. A source voltage Vs (= Vx) that is a potential is applied. Then, the TFT 94 of the pixel concerned has a gate voltage V
The source voltage Vx is turned on by the application of g
4 and the liquid crystal capacitance Clc applied via the pixel electrode 95.
And the storage capacitor Cs is charged.

By the way, during the non-selection period Toff other than the selection period Ton, the gate voltage Vg changes to the other gate lines G ₁ ,
The gate line G _i shown in FIG. 7 (a) is applied to G ₂ ,.
Is not applied to the TFT 94, and the TFT 94 of the pixel is turned off.
Therefore, the liquid crystal capacitance Clc and the storage capacitance Cs hold the charged electric charges during this period (see FIG. 7C). As a result, the voltage Vpix (= Vx) is continuously applied to the liquid crystal 49 during one sub-field period 1F, and the same amount of transmitted light is maintained throughout one sub-field period 1F (see FIG. 3D). ).

In the next subfield period 2F,
The gate voltage Vg is again applied to the above-mentioned gate line G _i (see (a) in the same figure), and in synchronization with this, the source voltage −Vx having the opposite polarity to the previous one is applied to the source line S _j. (See Figure (b)). Therefore, the source voltage −Vx
Is charged in the liquid crystal capacitance Clc and the storage capacitance Cs, and its charge is held in the non-selection period Toff (see FIG. 7C).

By the way, since the liquid crystal 49 having the voltage-transmitted light amount characteristic shown in FIG. 7 is used, the sub-field period 1 in which the positive source voltage Vx is applied.
The transmitted light amount T _{1 of} F increases, and the negative source voltage −V
The transmitted light amount T _{2 in the} subfield period 2F in which x is applied becomes almost 0 level. Then, although the transmitted light amount obtained by averaging Tx (= T ₁ ) and Ty (= T ₂ ) is obtained in the entire one field period F ₁ , bright and dark display is alternately performed in the subfield period unit. . Therefore, when displaying a moving image, the image quality is good. Further, since the positive voltage Vx and the negative voltage −Vx are alternately applied to the liquid crystal 49, deterioration of the liquid crystal 49 is prevented.

Here, the voltage value of the positive source voltage Vx is the voltage-transmitted light amount characteristic of the liquid crystal 49, the information to be written in the pixel (that is, the optical state or display information to be obtained in the pixel). It may be decided based on. However, since the amount of transmitted light in the entire one field period F ₁ is the average of Tx (= T ₁ ) and Ty (= T ₂ ) as described above, T ₂ is significantly increased as shown in FIG. 7, for example. When the liquid crystal 49 having a small characteristic is used, the value of T ₁ (that is, the voltage value of Vx that defines the value of T ₁ ) should be set to a large value in consideration of that amount.

By the way, during the driving as described above (that is, in the field period F ₁ shown in FIG. 16), the liquid crystal element is irradiated with red light from the color light source 101, and the black and white image displayed on the liquid crystal element is displayed. The image is recognized as a red image, green light is irradiated in the next field period F _{2 to} be recognized as a green image, and blue light is irradiated in the next field period F _{3 to} be recognized as a blue image. At the very least, these color images are visually mixed to be recognized as a full-color image.

On the other hand, FIG. 17 is similar to FIG. 11 and FIG.
Is a diagram illustrating a driving method of an active matrix type liquid crystal element shown in each field period F _1, F _2, F ₃ and instead of two three subfield 1F, 2F, 3
Divided into F. It should be noted that FIG.
1B shows the light radiated from No. 1, and FIG. 1B shows a state in which the gate voltage Vg is applied to _one certain gate line G ₁ .
In the same figure (c), the source voltage Vs is applied to one source line S _i.
FIG. 6D shows a state in which the voltage Vpix is applied to the pixel (that is, the liquid crystal 49) at the intersection of the gate line G ₁ and the source line S _i .
(e) shows a change in the amount of transmitted light in the pixel. Further, FIG. 6F shows a state where the gate voltage Vg is applied to a certain one gate line G _n, and FIG. 6G shows that the source voltage Vs is applied to a certain one source line S _j. FIG. 6H shows the gate line G _n and the source line S _j.
The voltage Vpix is applied to the pixel (that is, the liquid crystal 49) at the intersection of
Is applied, and FIG. 6 (i) shows a change in the amount of transmitted light in the pixel.

In the present driving method, the driving is performed by the same method as in FIG. 14 in the first two subfield periods 1F and 2F, but the source line S _i of the third subfield period 3F is driven. The gate voltage Vg is applied to the gate line G ₁ again with the potential kept at 0 V (see (b) and (c) of the same figure). Accordingly, the liquid crystal capacitance Clc
The storage capacitor Cs is discharged, and the liquid crystal 49 is not applied with a voltage, and the transmitted light amount T ₃ becomes 0% (see (d) and (e) in the same figure). In this way, the last gate line G
_The liquid crystal 49 is switched by scanning up to _n (see (f) to (i) of the same figure), and T is displayed in the entire one field period F _1.
The amount of transmitted light obtained by averaging x (= T ₁ ), Ty (= T ₂ ) and Tz (= 0 V) can be obtained.

Here, in the G emission in the next field period F ₂ , the third gate voltage Vg is applied to the last gate line G _n.
(I.e., not immediately after applying the gate voltage Vg applied in the subfield period 3F), but after the liquid crystal 49 of the pixel along the last gate line G _n is completely reset to the black state. It is more preferable from the viewpoint of perfect color reproducibility.

Next, the effect of this embodiment will be described.

According to the present embodiment, both the high-luminance image and the low-luminance image are displayed, so that one field period F
It is equivalent to displaying an image of the average brightness of ₁ , F ₂ and F _{3 as a} whole, and the brightness of the image can be increased as compared to the case where a period in which no image is displayed is provided as in the past. . Further, it is not necessary to increase the brightness of the color light source 101, and the power consumption can be reduced.

On the other hand, when the image display is performed by line-sequential scanning, it is impossible to synchronize the emission timing of the color light source 101 with the scanning timing for all the scanning lines, and it is impossible to synchronize them. When a timing shift occurs and the driving method shown in FIG. 16 is used, a black-and-white image for blue is displayed on the liquid crystal element when red light is emitted, for example, as shown in FIG. Will be done. In such a case, if the brightness of the black-and-white image for blue is high, the color reproducibility will be reduced. When it is increased, it is possible to suppress the deterioration of color reproducibility.

When the driving method shown in FIG. 17 is used, as shown in FIG. 17 (i), for example, a blue monochrome image (previous frame The black and white image for blue) will be displayed. However, since the brightness of the black-and-white image is almost 0, it is possible to further suppress the deterioration of color reproducibility as compared with the case of the driving method of FIG.

[0163]

EXAMPLES (Example 1) (Preparation of liquid crystal cell) A pair of glass substrates having a thickness of 1.1 mm and having a 700-liter ITO film formed as transparent electrodes were prepared. On the transparent electrode of the substrate, the following repeating unit PI-
The polyimide precursor having a is applied by spin coating, and then pre-dried at 80 ° C. for 5 minutes, and then 2
It was heated and baked at 00 ° C. for 1 hour to obtain a polyimide film having a film thickness of 200 Å.

[0164]

[Outer 1] Subsequently, the polyimide film on the substrate was subjected to rubbing treatment with a nylon cloth as uniaxial orientation treatment. The condition of the rubbing treatment is nylon (N
F-77 / made by Teijin) using a rubbing roll laminated, push amount 0.3 mm, feed speed 10 cm / se
c, the number of revolutions was 1000 rpm, and the number of feeds was 4 times.

Subsequently, silica beads having an average particle size of 2.0 μm are dispersed as spacers on one of the substrates, and the substrates are made to face each other so that the rubbing directions of the substrates are antiparallel (antiparallel), and uniform. A cell with a cell gap (empty cell with a single pixel) was obtained.

(Production of Active Matrix Cell) Using the same materials and conditions as above, a transparent electrode and a polyimide alignment film were used, and one substrate was used as an active matrix substrate having an a-Si TFT having a silicon nitride film as a gate insulating film. An active matrix cell (panel) having a pixel structure shown in FIG. 10 was manufactured by having R, G, B color filters on one substrate. Screen size is 10.
The size was 4 inches and the number of pixels was 800 × 600 × RGB.

(Preparation of Liquid Crystal Composition) The following liquid crystal compounds were mixed to prepare a liquid crystal composition LC-1. It is also shown in the structural formula. The numerical values given in the structural formulas are weight ratios upon mixing.

[0168]

[Outside 2] The physical property parameters of the liquid crystal composition LC-1 are shown below.

[0169]

[Outside 3] The liquid crystal composition LC-1 was injected at a temperature of an isotropic phase into the single pixel cell and the active matrix cell produced by the above process, and the liquid crystal was cooled to a temperature showing a chiral smectic liquid crystal phase. Before and after the -SmC * phase transition, the liquid crystal element sample A was subjected to a treatment of applying an offset voltage (direct current) voltage of -5 V to perform cooling.
B was produced. With respect to such a sample, the following items were evaluated.

1. Alignment state The alignment state of the liquid crystal of element sample A was observed with a polarizing microscope.

As a result, at room temperature (30 ° C.), the darkest axis was slightly deviated from the rubbing direction when no voltage was applied, and the layer normal direction was only one direction in the entire cell, resulting in a substantially uniform orientation state. Was observed.

2. In order to measure the electro-optical response of the optically responsive liquid crystal device, the cell of the device sample A was placed under a crossed nicols in a polarization microscope with a photomultiplier so that the polarization axis was in the dark field in the absence of voltage application.

At 30 ° C., ± 5 V, 0.2 Hz
Observing the optical response when the triangular wave was applied, the amount of transmitted light (transmittance) gradually increased according to the magnitude of the applied voltage when a positive voltage was applied. On the other hand, regarding the state of optical response when a negative voltage is applied, although the transmitted light amount changes with respect to the voltage level, the maximum light amount is 1 when compared with the maximum transmittance when a positive voltage is applied. / 10
It was about.

3. Using a device similar to the triangular wave response for the rectangular wave response sample A,
The optical level was measured while changing the voltage by marking a rectangular wave voltage of 60 Hz (± 5 V).

As a result, it was confirmed that a sufficient positive optical response was made to the positive voltage, and a stable halftone state was obtained without depending on the previous state of the optical response. In addition, even with respect to the negative voltage, the optical response of about 1/10 of the case of applying the positive voltage of the same voltage absolute value can be confirmed, and the average value of the optical response with respect to the positive and negative voltages does not depend on the previous state. It was confirmed that a stable halftone could be obtained.

Further, the rising time by applying the positive polarity rectangular wave voltage (the transmissivity to be obtained by applying a predetermined voltage or the transmissivity of 90% from the darkest state)
And the response time at the fall time (the time when the transmittance becomes 10% of the transmittance from the saturated transmittance state at the voltage for obtaining a predetermined halftone) is when a high voltage (about 5 V) is applied. Are 0.7 ms and 0.3 ms, respectively, and low voltage (1
(Approx. V), it was 2.0 ms and 0.2 ms, respectively, and high-speed response was confirmed even when compared with switching in a general nematic liquid crystal.

4. The image quality was evaluated by driving the sample B, which is an active matrix panel using a moving image quality evaluation TFT, based on the driving method shown in FIG. This moving image quality evaluation was a subjective evaluation by about 10 non-experts, and was evaluated according to the following 5 scales (categories). The images used for evaluation were selected from three types (skin color chart, tourist information board, yacht harbor) from the BTA high-definition standard image (still image), and 432 × 168 pixels in the central portion were cut out and used.

Further, these images were moved at a constant speed of 6.8 (deg / sec) which is a general moving speed of television programs to create moving images, and the blurring of the images was evaluated. -Scale 5: Good image quality with good sharpness without any peripheral blurring of the screen being observed.・ Measurement 4 ... Bokeh around the screen is of little concern. -Scale 3 ... Blurring around the screen is observed, making it difficult to distinguish small characters. -Scale 2 ... Blurring around the screen becomes noticeable, making it difficult to distinguish large characters. -Scale 1 ... Blurring becomes noticeable on the entire screen, and the original image is almost indistinguishable.

The output of the image source from the computer side at this time was set to a picture rate such that 60 screens were sequentially scanned (progressive) per second.

First, for display on the TFT panel side (sample), 60 frames were displayed per second, and frame inversion driving was performed without dividing one frame into a plurality of fields.

As a result, the peripheral blur of the moving image was slightly observed. Subjective evaluation of the degree of peripheral blur was about 3 to 4 in the above-mentioned five-level evaluation.

Further, one frame was divided into two fields, a positive voltage was applied in the first field, and a negative voltage (the voltage level in both fields was the same) was applied in the subsequent fields, and the system was operated substantially at a frequency of 120 Hz. In this case, a moving image having practically sufficient brightness, no flicker was observed, and no peripheral blur was observed was observed, and an ideal moving image was obtained. The level was 5 in the above 5-point evaluation.

If this evaluation is carried out using a general CRT, all of them are 5 in a 5-step evaluation, and if a commercially available TFT type liquid crystal display that requires a response of several tens of ms is used, it is about 2-3 in a 5-step evaluation. It was an evaluation result.

Example 2 (Preparation of Liquid Crystal Cell) A pair of glass substrates having a thickness of 1.1 mm and having a 700 Å ITO film formed thereon as transparent electrodes were prepared. On the transparent electrode of the substrate, the following repeating unit PI-
The polyimide precursor having b is applied by spin coating, and then pre-dried at 80 ° C. for 5 minutes, and then 2
It was heated and baked at 00 ° C. for 1 hour to obtain a polyimide film having a film thickness of 50 Å.

[0185]

[Outside 4] Subsequently, the polyimide film on the substrate was subjected to rubbing treatment with a nylon cloth as uniaxial orientation treatment. The condition of the rubbing treatment is nylon (N
F-77 / made by Teijin) using a rubbing roll laminated, push amount 0.3 mm, feed speed 10 cm / se
c, the number of revolutions was 1000 rpm, and the number of feeds was 4 times.

Subsequently, silica beads having an average particle size of 1.4 μm were dispersed as spacers on one of the substrates, and the substrates were made to face each other so that the rubbing treatment directions of the substrates were antiparallel to each other, and uniform. A cell with a cell gap (empty cell with a single pixel) was obtained.

(Production of Active Matrix Cell) Using the same materials and conditions as above, a transparent electrode and a polyimide alignment film were used, and one substrate was used as an active matrix substrate having an a-Si TFT having a silicon nitride film as a gate insulating film. An active matrix cell (panel) having a pixel structure shown in FIG. 10 was manufactured by having R, G, B color filters on one substrate. Screen size is 10.
The size was 4 inches and the number of pixels was 800 × 600 × RGB.

The liquid crystal composition LC-1 was injected into these single pixel cells and active matrix cells at an isotropic phase temperature, and the liquid crystal was cooled to a temperature showing a chiral smectic liquid crystal phase. Samples C (single pixel cell) and D (active matrix cell) to which a DC offset (−5 V) was applied during the SmC * phase transition were prepared.

Regarding Samples C and D,
When the same evaluation as in Example 4 was performed, the same behavior and characteristics as those of Samples A and B of Example 1 were obtained.
It was confirmed that the same state was reproduced even if the orientation film thickness and the cell thickness were changed.

By applying the positive rectangular wave voltage,
Rise time (time from the darkest state to a transmittance of 90% of the transmittance to be obtained by applying a predetermined voltage),
The response speed at the fall time (the time when the transmittance becomes 10% of the transmittance from the saturated transmittance state at the voltage for obtaining a predetermined halftone) is as follows when a high voltage (about 4 V) is applied. , 0.6 ms and 0.2 ms, respectively, and low voltage (1 V
(Approx.), It was 1.7 ms and 0.2 ms, respectively, and high-speed response was confirmed even when compared with switching in a general nematic liquid crystal.

Example 3 (Production of Liquid Crystal Cell) An empty cell and an active matrix cell were produced in the same manner as in Example 1 except that rubbing was performed in parallel, and an offset voltage application cooling treatment was performed at the time of liquid crystal injection. Liquid crystal element samples E and F were obtained.

These samples E and F were evaluated in the same manner as in Example 1 (aligned pair, optical response, rectangular wave response, moving image quality response).

1. Regarding the orientation state sample E, at room temperature (30 ° C.), the darkest axis was slightly displaced from the rubbing direction, and a substantially normal orientation state in which the layer normal direction was only one direction in the entire cell was observed. In addition, the C1 orientation region and the C2 orientation region were in a mixed state at a ratio of half.

2. For optical response sample E, ± 5 V, 0.2 Hz as in Example 1.
When the optical response of the entire cell when the triangular wave of 1 was applied was observed, the same results as in Example 1 were obtained.

Next, when the C1 region and the C2 region in the cell are individually observed, the C1 region is domainless-switched up to an optical level of about 50%, but when the voltage intensity is further increased, domain inversion occurs. It was observed that it was doing. On the other hand, in the C2 region, domainless switching was performed until the saturation voltage was reached. Further, the voltage value required to obtain the same amount of transmitted light was lower in the C2 oriented portion.

3. For the rectangular wave response sample E, the optical response characteristics were measured while applying a rectangular wave of 60 Hz and changing the voltage in the same manner as in Example 1.

As a result, when the optical response of the entire cell was observed, the same result as in Example 1 was obtained. Therefore, the TFT
Analog gradation display is possible by amplitude modulation by active matrix driving. On the other hand, when C1 and C2 were observed individually, the voltage required to obtain the same amount of transmitted light was lower in the C2 oriented portion, as in the triangular wave response experiment.

Further, the rising time by applying this positive polarity rectangular wave voltage (the time when the transmittance becomes 90% of the transmittance which is to be obtained by applying a predetermined voltage from the most recent state).
And the response speed at the fall time (the time when the transmittance becomes 10% of the transmittance from the saturated transmittance state at a predetermined voltage) is 0. 6m
s, 0.3 ms, and 1.8 ms and 0.2 ms, respectively, when a low voltage (about 1 V) is applied, and high-speed response is confirmed even when compared with general nematic liquid crystal switching. It was

4. With respect to the moving image quality evaluation sample F, the moving image quality in the active matrix driving was evaluated in the same manner as in Example 1 (60 Hz driving and 120 Hz driving by frame division driving). Similar to the results of Example 1, a moving image having a brightness considered to be practically sufficient and no peripheral blur was observed was observed. Subjective evaluation of the degree of blurring around this area gives 5 out of 5 categories.
Met.

Example 4 (Fabrication of Liquid Crystal Cell) A pair of glass substrates having a thickness of 1.1 mm and having a 700-liter ITO film formed as transparent electrodes were prepared. A commercially available alignment film SE for TFT is formed on the transparent electrode of the substrate.
-7992 (manufactured by Nissan Kagaku Co., Ltd.) was applied by spin coating, and then pre-dried at 80 ° C. for 5 minutes, and then 2
It was heated and baked at 00 ° C. for 1 hour to obtain a polyimide film having a film thickness of 50 Å.

Subsequently, the polyimide film on the substrate was subjected to rubbing treatment with a nylon cloth as uniaxial orientation treatment. The condition of the rubbing treatment is a rubbing roll in which nylon (NF-77 / manufactured by Teijin) is bonded to a roll having a diameter of 10 cm, and the pushing amount is 0.3 mm and the feeding speed is 10
cm / sec, the number of revolutions was 1000 rpm, and the number of feeds was 4 times.

Subsequently, silica beads having an average particle size of 1.4 μm were dispersed as spacers on one of the substrates and faced so that the rubbing treatment directions of the respective substrates were parallel to each other, and a uniform cell gap was formed. Cells (single pixel empty cell) were obtained.

(Production of Active Matrix Cell) Using the same materials and conditions as above, a transparent electrode and a polyimide alignment film were used, and one substrate was used as an active matrix substrate having an a-Si TFT having a silicon nitride film as a gate insulating film. An active matrix cell (panel) having a pixel structure shown in FIG. 10 was manufactured by having R, G, B color filters on one substrate. Screen size is 10.
The size was 4 inches and the number of pixels was 800 × 600 × RGB.

The liquid crystal composition LC-1 was injected into each of the single pixel cell and the active matrix panel at an isotropic phase temperature, and the liquid crystal was cooled to a temperature showing a chiral smectic liquid crystal phase. Before and after the SmC * phase transition, an offset (direct current) voltage of −5 V was applied to perform cooling, and element samples G and H were obtained.

These samples G and R were evaluated in the same manner as in Example 1 (alignment state, optical response, rectangular wave response, moving image quality response).

1. Regarding the alignment state sample G, at room temperature (30 ° C.), the darkest axis was slightly displaced from the rubbing direction, and a substantially normal alignment state in which the layer normal direction was only one direction in the entire cell was observed. It was also observed that the entire cell had a C2 orientation.

2. For optical response sample G, ± 5 V, 0.2 Hz as in Example 1.
When the optical response of the entire cell when the triangular wave of 1 was applied was observed, the same results as in Example 1 were obtained.

In this cell, domainless switching was performed until the saturation voltage was reached.

[0209] 3. For the rectangular wave response sample G, the optical response characteristics were measured while applying a rectangular wave of 60 Hz and changing the voltage in the same manner as in Example 1.

As a result, when the optical response of the entire cell was observed, the same result as in Example 1 was obtained.

Therefore, analog gradation display is possible by amplitude modulation by driving the TFT active matrix.

Further, the rising time by applying the positive rectangular wave voltage (the time when the transmittance becomes 90% of the transmittance to be obtained by applying a predetermined voltage from the darkest state).
And the response speed at the fall time (time when the transmittance becomes 10% of the transmittance from the saturated transmittance state at a predetermined voltage) is 0. 5m
s, 0.2 ms, and 1.6 ms and 0.2 ms, respectively, when a low voltage (about 0.6 V) is applied, and high-speed responsiveness is obtained even when compared with general nematic liquid crystal switching. confirmed.

4. With respect to the moving image quality evaluation sample H, the moving image quality in active matrix driving was evaluated in the same manner as in Example 1 (60 Hz driving and 120 Hz driving by frame division driving). Similar to the results of Example 1, a moving image having a brightness considered to be practically sufficient and no peripheral blur was observed was observed. Subjective evaluation of the degree of blurring around this area gives 5 out of 5 categories.
Met.

Example 5 This example relates to the second embodiment described above, and the same active matrix type liquid crystal panel as in Example 1 was used as the display element.

As the color light source, the backlight light source 101 shown in FIG. 18 was used. That is, the backlight light source 101 is configured by three power supplies 110, three transistors 111, 7 × 3 sets of LEDs 112 that emit light of each color of RGB, and one waveform generator 113. And transistor 111 and 7 L
ED112 is connected in series to create one closed circuit,
The transistor 111 is turned on / off by the waveform generator 113.
It can be turned off so that the RGB lights are sequentially emitted.

As an RGB light source material, R is GaA
GaN was used for lAs, G, and B. Further, the voltage of the power source 110 was such that R was about 14 V, G and B were about 25 V, and the maximum current value was 20 mA.

The liquid crystal device as described above was driven by the driving method shown in FIG. 16 and the color luminosity of each of the maximum brightness R, G, and B at the time of white display was evaluated.

As a result, the panel brightness at ± 5 V drive is 1
It was 10 [cd / m ² ]. In addition, when the color purity was observed by driving ± 5 V, a slight change in tint was gradually observed according to the order of the scanning lines, but the change was not so large and practically no problem.

A single pixel cell was prepared in the same manner as in Example 1, and the alignment state, optical response and rectangular wave response (however, the frequency of the rectangular wave was 180 Hz instead of 60 Hz) were examined. The same evaluation as 1 was obtained.

Comparative Example In this comparative example, the liquid crystal composition shown below was mixed in the weight ratio shown on the right side thereof to prepare a liquid crystal 49.

[0221]

[Chemical 1] The physical property parameters of the liquid crystal prepared were as follows.

[0222]

[Table 1] An offset voltage (DC voltage) of + 3V was applied during cooling after the liquid crystal injection. The other configurations and manufacturing conditions were the same as in Example 5.

Further, when a cell of a single pixel was prepared by the same method as in Example 1 and the alignment state, triangular wave response and rectangular wave response were examined, the results were as follows. 1. Alignment state The alignment state of the liquid crystal was observed with a polarizing microscope. As a result, an alignment state was observed in which the darkest axis was almost parallel to the rubbing direction, and the layer normal direction was only one direction throughout the cell, and a substantially uniform alignment state was observed. 2. In order to measure the electro-optical response of the triangular wave response liquid crystal device, a polarization microscope with a photomultiplier under crossed Nicols was used.
The polarization axis was aligned with the rubbing direction so as to form a dark field.

In addition, at Tc-T = 10 ° C., ± 5 V,
Observing the optical response when a 0.2 Hz triangular wave is applied, the response to the positive polarity gradually increases as the voltage intensity increases, whereas the response to the negative polarity shows It was found that the amount of transmitted light did not substantially change from the black state when no electric field was applied.

When the voltage is turned off from the state where the positive voltage is applied (white display), the state is relaxed to the black state (switching).
It was confirmed to do. 3. Rectangular Wave Response Using an apparatus similar to the triangular wave response, a 180 Hz rectangular wave was applied and the optical level was measured while changing the voltage in the range of 0 to 5V.

As a result, all the elements responded only to the positive voltage, and it was possible to change the luminance level by changing the voltage level.

Further, the rising time (90% of the transmittance to be obtained by applying a predetermined voltage from the darkest state) by applying the rectangular wave voltage of positive polarity (saturation voltage is all about 5 V).
%), And the fall time (the time when the transmittance becomes 10% of the transmittance from the saturated transmittance state at a predetermined voltage) at the fall time, a high voltage (about 5 V) is applied. In case of, 0.6-0.9ms, 0.2-0.3m respectively
It was confirmed that a high-speed response of 1 ms or less was realized and RGB serial driving was possible.

Further, using the active matrix type liquid crystal panel prepared in this comparative example, the same R as in Example 5 was used.
When GB serial drive was evaluated, color purity was observed at ± 5 V drive. A uniform color was expressed on the entire panel surface, but panel brightness at ± 5 V drive was 100 [c
d / m ² ], which was darker than that of Example 5.

Example 6 This example relates to the second embodiment described above, and an active matrix type liquid crystal panel and a backlight source 101 similar to those in Example 5 were prepared.

When driven by the driving method shown in FIG. 17 to perform RGB serial drive evaluation (evaluation of color purity of each color of R, G, B when ± 5 V drive), good color reproducibility was obtained. .

A single pixel cell was prepared in the same manner as in Example 1, and the alignment state, optical response and rectangular wave response (however, the frequency of the rectangular wave was 270 Hz instead of 60 Hz) were examined. The same evaluation as 1 was obtained.

[0232]

As described in detail above, according to the present invention,
A liquid crystal display element using a liquid crystal exhibiting a chiral smectic phase, capable of high-speed response and gradation control, and providing a liquid crystal display element of the highest brightness with excellent moving image quality.

If a high-brightness image is displayed in at least one subfield period in one field period and a low-brightness image is displayed in another at least one subfield period, 1 In the entire field period, it is equivalent to displaying an image with an averaged luminance, and the luminance of the image can be increased as compared with the case where a period in which no image is displayed is provided as in the conventional case. Further, it is not necessary to increase the brightness of the color light source, and the power consumption can be reduced.

Furthermore, when the image display is performed by line-sequential scanning, it is possible to suppress the deterioration of color reproducibility.

[Brief description of drawings]

1A and 1B are schematic views showing a layer structure of liquid crystal molecules and liquid crystals in a liquid crystal alignment state in an SSFLC type device.

2A and 2B are schematic diagrams showing directors in a liquid crystal alignment state shown in FIGS. 1A and 1B.

FIG. 3A is a schematic diagram showing an alignment state in each liquid crystal phase in SSFLC. (B): A schematic view showing an alignment state in each liquid crystal phase in one embodiment of the liquid crystal element of the present invention.

FIG. 4 is a schematic diagram showing an alignment state in a chiral smectic liquid crystal phase in one embodiment of the liquid crystal element of the present invention.

FIG. 5 is a schematic diagram showing an alignment state in a chiral smectic C phase.

6A to 6D are schematic diagrams showing inversion behavior of liquid crystal molecules by voltage application in a chiral smectic liquid crystal phase in one embodiment of the liquid crystal element of the present invention.

FIG. 7 is a diagram showing an example of voltage-transmittance characteristics in the liquid crystal element of the present invention.

8 (a) and (b): C1 orientation state and C2 potential state in bistable orientation state in SSFLC.
The schematic diagram shown about each of an orientation state.

9 (a) and (b): C1 alignment state and C2 potential state in the alignment state in the liquid crystal device of the present invention.
The schematic diagram shown about each of an orientation state.

FIG. 10 is a sectional view showing an embodiment of a liquid crystal element of the present invention.

FIG. 11 is a plan view showing a configuration example when the liquid crystal element of the present invention is applied to an active matrix type element.

FIG. 12 is a cross-sectional view showing a configuration example of one pixel when the liquid crystal element of the present invention is applied to an active matrix type element.

13 is a diagram showing an equivalent circuit of the element structure shown in FIG.

FIG. 14 is a diagram showing an example of drive waveforms and optical characteristics when an active matrix drive of the liquid crystal element of the present invention is performed.

FIG. 15 is a block diagram showing an example of the configuration of a display device driven by the present invention.

FIG. 16 is a timing chart showing an example of a driving method according to the present invention.

FIG. 17 is a timing chart showing another example of the driving method according to the present invention.

FIG. 18 is a circuit diagram showing an example of a configuration of a backlight light source.

FIG. 19 is a block diagram showing an example of a configuration of a conventional liquid crystal device.

FIG. 20 is a timing chart showing an example of a driving method of a conventional liquid crystal device.

FIG. 21 is a timing chart showing another example of the driving method according to the present invention.

FIG. 22 is a diagram showing an example of voltage-transmittance characteristics in another liquid crystal element of the present invention.

[Explanation of symbols]

11, 12 substrate 13 LCD 14,14a, 14b, 14C Liquid crystal molecules 15 cones 16 smectic layers 17 Cone bottom 18a, 18b C director 81a, 81b substrate 82a, 82b electrodes 83a, 83b insulating film 84a, 84b Orientation control film 85 chiral smectic liquid crystal 86 spacer

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Makoto Mori 3-30-2 Shimomaruko, Ota-ku, Tokyo Ki Canon Inc. (72) Takashi Moriyama 3-30-2 Shimomaruko, Ota-ku, Tokyo Ki Canon Inc. (72) Inventor Ryuichiro Isobe 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (56) Reference JP-A-6-33059 (JP, A) JP-A-7-140933 ( JP, A) JP-A-7-318939 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) G02F 1/133 560 G09G 3/36

Claims (12)

(57) [Claims] 1. A chiral smectic liquid crystal, a pair of electrodes for applying a voltage to the liquid crystal, and a pair of electrodes sandwiching and facing the liquid crystal, and at least one opposing surface is subjected to a uniaxial alignment treatment for aligning the liquid crystal. Paired substrates, A voltage is applied to the polarizing plate and the pair of electrodes to drive the liquid crystal.
With a drive circuit for multiple frames per second
A liquid crystal display device for displaying an image , wherein the liquid crystal exhibits a state in which the average molecular axis of the liquid crystal is mono-stabilized between the pair of substrates when no voltage is applied,
When a voltage is applied to the first polarity, shows a state where the average molecular axis of the liquid crystal is tilted to one side from the unit stabilized the position at an angle corresponding to the magnitude of the applied voltage, said first polarity and is at the time of applying a voltage of a second polarity opposite polarity, shows a state in which the tilt in the opposite side to the when the average molecular axis of the liquid crystal is applied a first polarity of the voltage from the single stabilized position , The maximum tilt angle when the voltage of the first polarity is applied.
The large value is the chill when the voltage of the second polarity is applied.
The drive circuit is larger than the maximum value of the frame angle ,
It is divided and displayed, and in the first field in one frame,
Gray scale display of the first brightness by applying the voltage of the first polarity
Get the state, in the second field, the voltage of the second polarity
And the same image as the image displayed at the first brightness.
The gradation display state of the second brightness, which differs only in brightness, is obtained, and the
The liquid crystal display device for displaying an image, characterized in that. 2. The second brightness is 1 of the first brightness.
The liquid crystal display according to claim 1 , wherein the liquid crystal display is smaller than / 5.
Display element . 3. A field for displaying an image at a predetermined first brightness is optically modulated so as to have a first transmittance, and a field for displaying an image at the second brightness has a first transmittance of the first transmittance. the liquid crystal display of claim 1, wherein the made smaller than the optical modulator such that 0 is greater than the second transmittance is 1/5
Element . 4. The average molecular axis at the time of applying the voltage of the second polarity at an angle based on the mono-stabilized position of the maximum tilt state of the average molecular axis at the time of applying the voltage of the first polarity. the ratio to the maximum the angle relative to the monostable position of the tilt state of at least 5 according to claim 1
The liquid crystal display element described. 5. The amount of light emitted from the device is such that no voltage is applied.
When the voltage of the first polarity is applied, the second light amount becomes the second light amount most different from the first light amount in a predetermined tilt state of the average molecular axis of the liquid crystal. When a voltage is applied, the third light amount is the most different from the first light amount in a predetermined tilt state of the average molecular axis of the liquid crystal, and the light amount emitted from the element is the magnitude of the voltage of the first polarity. By changing the tilt angle of the average molecular axis of the liquid crystal from the mono-stabilized position, it becomes continuously variable between the first and second light amounts, and the third light amount and the difference of the first light quantity, the liquid crystal display device according to claim 1, wherein a smaller than the difference between said second quantity and said first quantity. 6. The liquid crystal display according to claim 5, wherein the first amount of light is the lowest value of the amount of light emitted from the device, and the second amount of light is the maximum value of the amount of light emitted from the device. Element . 7. The liquid crystal display device according to claim 6 , wherein the ratio of the second light amount to the third light amount is 5 or more. 8. The phase transition series of the chiral smectic liquid crystal is an isotropic liquid phase (ISO.)-Cholesteric phase (Ch) -chiral smectic C phase or an isotropic liquid phase (ISO.)-From the high temperature side. a chiral smectic C phase, and a liquid of claim 1 wherein the normal direction of the smectic layers of the liquid crystal is characterized by a substantially unidirectional
Crystal display element . Wherein said chiral smectic helical pitch of the liquid crystal bulk state is longer claim than twice the cell thickness 1
The liquid crystal display element described. 10. A substrate having a plurality of pixels, one of the pair of substrates having an active element connected to an electrode corresponding to each pixel, comprising a drive circuit for performing active matrix drive, and an analog floor. The liquid crystal display device according to claim 1 , wherein the liquid crystal display device performs gray scale display. 11. A method of driving a liquid crystal display element according to any one of claims 1 to 10, wherein one frame period is divided into a plurality of field periods,
Each field period is further divided into a plurality of subfield periods, the color of light applied to the liquid crystal display element is changed for each field period, and a high-luminance image is obtained in at least one subfield period in one field period. Is displayed,
Show low luminance image in at least one other sub-field period, the driving method of the liquid crystal display element characterized by. 12. Each field period is divided into three subfield periods, and a high luminance image is displayed in one subfield period, a low luminance image is displayed in one subfield period, and one subfield period is displayed. The method for driving a liquid crystal display element according to claim 11 , wherein the luminance is set to substantially 0 in the subfield period.