JPH05203959A - Ferroelectric liquid crystal element - Google Patents

Abstract

PURPOSE:To lessen the increase in cell thickness at the end of a liquid crystal for which a ferroelectric liquid crystal is used by setting the pretilt angle of the ferroelectric liquid crystal at a specific value or above and setting the inter-layer spacing in the structure of the smectic layer substantially constant. CONSTITUTION:Insulating films 33a, 33b and orientation control films 34a, 34b formed of high-pretilt polyimide are laminated on substrates 31a, 31b coated with transparent electrodes 32a, 32b. The oriented films 34a, 34b are subjected to rubbing treatments at the same directions and the directions intersected with each other within angles of a prescribed range. The ferroelectric smectic liquid crystal 35 having >=10 deg. pretilt angle is disposed between the substrates 31a and 31b. The distance between the substrates 31a and 31b is set at the distance sufficiently small to suppress the formation of the spiral arranging structure of the ferroelectric smectic liquid crystal. The ferroelectric smectic liquid crystal 35 generates a bistable direction. This distance is held by spacers 36 disposed between the substrates 31a and 31b.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal element using a ferroelectric liquid crystal capable of discriminating contrast according to the direction of an electric field.

[0002]

2. Description of the Related Art The use of liquid crystal devices having bistability is described by Clark and Lager Wall.
Both of them have been proposed in JP-A-56-107216, US Pat. No. 4,367,924, and the like. As the bistable liquid crystal, a ferroelectric liquid crystal having a chiral smectic C phase (SmC ^* ) or H phase (SmH ^* ) is generally used, and in these states, the first optical response is made in response to an applied electric field. A stable state or a second optically stable state, and has the property of maintaining that state when an electric field is not applied, that is, bistability, and has a quick response to a change in the electric field, It is expected to be widely used in the field of high speed and memory type display devices.

[0003]

However, when the above-mentioned ferroelectric liquid crystal cell is continuously driven for a long time, the cell thickness at the cell edge gradually increases, and it becomes visible that it is colored yellow. Admitted. Therefore, it is an object of the present invention to reduce an increase in cell thickness at the end of a liquid crystal cell using a ferroelectric liquid crystal.

[0004]

SUMMARY OF THE INVENTION The present invention is to solve the above-mentioned problems. The first one is a pair of substrates each having a scanning electrode group and an information electrode group, each of which is provided with a uniaxial alignment treatment. In a liquid crystal cell in which a ferroelectric liquid crystal is sandwiched between a pair of substrates whose uniaxial alignment treatment axes are parallel or substantially parallel to each other, the pretilt angle of the ferroelectric liquid crystal is 1
A ferroelectric liquid crystal device, characterized in that it is 0 ° or more and the layer spacing in the smectic layer structure is substantially constant, and the second is provided with a scanning electrode group and an information electrode group,
A first substrate and a second substrate each provided with a uniaxial alignment treatment.
A liquid crystal element in which a ferroelectric liquid crystal is sandwiched between the pair of substrates consisting of the substrate and the liquid crystal molecules of the liquid crystal molecules near the interface of the substrate in accordance with the direction of the applied electric field. The directions of the dipole moments are inward and outward, and in the vicinity of the respective substrate interfaces, the pretilt angle is substantially in a state in which the dipole moments are inward and in a state in which they are outward. A ferroelectric liquid crystal element having equal alignment states in which the pretilt angles are substantially equal in the vicinity of the first substrate interface and in the vicinity of the second substrate interface, regardless of the direction of the dipole moment. Is.

According to the research conducted by the present inventors, the increase in the cell thickness at the cell edges as described above causes the liquid crystal itself to move in a specific direction between the liquid crystal cells due to the driving, so that the pressure at the cell edges is increased. It was observed that the cell thickness increased as a result. The cause of the force that the liquid crystal molecules move in the liquid crystal cell is unknown, but it is presumed that it is probably an electrodynamic effect caused by the fluctuation of the dipole moment of the liquid crystal molecules in the alternating electric field due to the driving pulse. ..

Further, as shown in FIG. 12A, according to an experiment by the present inventors, the moving direction 62 is the rubbing direction 60.
And the average molecular axis directions 61 and 61 'of the liquid crystal molecules. Since the moving direction of the liquid crystal molecules depends on the rubbing direction as described above, it is presumed that the phenomenon depends on the pretilt state at the substrate interface. The average molecular axis directions 61 and 61 'indicate average molecular positions in the bistable state of the ferroelectric liquid crystal molecules. Here, for example, when an appropriate AC electric field that does not cause switching of the liquid crystal is applied in the state where the average molecular axis direction is 61, the liquid crystal molecules move in the direction of arrow 62.

However, the moving direction of the liquid crystal molecules may differ depending on the conditions of the liquid crystal material or the liquid crystal cell. In an actual liquid crystal cell, as shown in FIG. 12, if the liquid crystal molecule position is in the state shown by arrow 61 in the entire cell, the liquid crystal moves inside the cell from the right side to the left side of the drawing. As a result, as shown in FIG. 12B, the cell thickness in the region 63 becomes thicker with time, and coloring occurs. When the liquid crystal molecules are in the state shown by the arrow 61 ′, the movement direction under the AC electric field is opposite, but in any case, the movement of the liquid crystal in the direction perpendicular to the rubbing direction 60, that is, in the smectic layer. Occurs. Therefore, it is estimated that the state of the smectic layer structure is one factor.

Further, this liquid crystal movement phenomenon depends on the orientation state of the cell. That is, this phenomenon is extremely unlikely to occur in the C2 orientation described later, and is significantly observed in the C1 orientation and the uniform orientation.

Two kinds of orientation states of C1 and C2 are shown in FIG.
It is explained by the difference in the chevron structure of the smectic layer as shown in FIG. In FIG. 9, 41 is a smectic layer and 42
Represents a C1-oriented region, and 43 represents a C2-oriented region.

Smectic liquid crystals generally have a layered structure, but when the S _A phase transitions to the S _C phase or the S _C ^* phase, the layer spacing shrinks, so that the layers are bent at the centers of the upper and lower substrates 46a and 46b as shown in FIG. Has a different structure (chevron structure). There can be two bending directions, C1 and C2, as shown in the figure.
As is well known, the rubbing causes the liquid crystal molecules at the substrate interface to form an angle with the substrate (pretilt), and the liquid crystal molecules lift their heads in the rubbing direction A (the tip becomes floating). It is facing. Due to this pretilt, the C1 orientation and the C2 orientation are not elastically energy-equivalent, and a transition occurs at a certain temperature as described above. Further, mechanical strain may cause dislocation.

When the layered structure of FIG. 9 is viewed in plan view, the boundary 44 at the time of shifting from the C1 orientation to the C2 orientation in the rubbing direction A is zigzag lightning and is called a lightning defect.
The boundary 45 at the time of moving from C2 to C1 has a wide and gentle curved shape and is called a hairpin defect.

A pair of substrates, which are substantially parallel to each other and are uniaxially oriented in the same direction for orienting the ferroelectric liquid crystal, are provided. The pretilt angle of the ferroelectric liquid crystal is α _C and the tilt angle (cone angle is ½) and the tilt angle of the S _C ^* layer is δ so that the ferroelectric liquid crystal has an alignment state represented by the following mathematical formula (1), it further has a chevron structure in the C1 alignment state. There are four states.

Θ <α _C + δ (1) These four C1 orientation states are different from the conventional C1 orientation states. Among them, two of the four C1 orientation states are bistable states (uniform states). ) Is formed. Here, assuming that the apparent tilt angle in the absence of an electric field is θ _a , of the four states in the C1 orientation state, the state showing the relationship of the following mathematical expression (2) is called the uniform state.

Θ> θ _a > Θ / 2 (2) In the uniform state, it is considered that the director is not twisted between the upper and lower substrates in view of its optical properties. FIG. 10 is a schematic view showing the arrangement of directors at respective positions between substrates in each state of C1 orientation. 51-in the figure
Reference numeral 54 shows a state in which the director is projected on the bottom surface of the cone in each state (hereinafter referred to as “C director”) and seen from the bottom surface direction. 51 and 52 are in a spray state, 53 and 54 are in a uniform state. This is a possible director layout.

As can be seen from the figure, the uniform 2
In the states 53 and 54, the positions of the liquid crystal molecules on either the upper or lower substrate interface are replaced with the positions in the spray state. FIG. 11 shows the C2 orientation, and there are two states 55 and 56 due to internal switching without interface switching. This uniform state of C1 orientation has a larger tilt angle θ than the bistable state of C2 orientation used conventionally.
_a and the contrast is high.

The arrow 57 indicates the dipole moment μs, and the direction indicated by A indicates the rubbing direction.

The present inventors have investigated in detail the relationship between the above-mentioned phenomenon of liquid crystal movement and the smectic layer structure in the S _C ^* phase. As a result, the detailed mechanism is unknown but the uniformity of the layer structure is disturbed. We found that liquid crystal movement is likely to occur. That is, it has been found that the torque for moving the liquid crystal is large in the alignment state in which the uniformity of the layer spacing is not maintained within or between the layers. Hereinafter, this point will be described.

FIG. 1 shows that the pretilt angle is small, for example α _C
FIG. 3 is a diagram schematically showing a smectic layer structure in a liquid crystal cell of about 2 ° for a parallel rubbing cell and an antiparallel rubbing cell, respectively. It is estimated that the layer structure is uniformly formed in the cell having the low pretilt angle as shown in FIG. That is, it is considered that the layer spacing is substantially uniform within and between layers.

Regarding the uniformity of the layer structure, for example, "Ph
ysisal Review Letters Vol
ume 59, Number 23, 2658 (198)
7) ”, etc., and can be evaluated by the X-ray diffraction method. FIG. 3 is a block diagram of a measurement system showing its optical arrangement. 30 is a measurement cell, and ki and ks are incident X-rays, respectively. , Represents the wave vector of the scattered X-rays.
2θ _B represents the Bragg angle, and θ represents the rotation angle of the measuring cell.

The Bragg angle 2θ _B can be obtained by scanning the angle with respect to the scattering center of the detector for detecting scattered X-rays, with the liquid crystal not contained in the cell.

FIG. 2E is an example of the measurement result and is a chart showing the diffraction intensity with respect to the rotation angle of the detector. Since the liquid crystal is not constrained from the cell interface when it is not put in the cell, a layer structure as a bulk state peculiar to the liquid crystal is formed in random directions. Therefore, a sharp peak is detected at an angle satisfying the Bragg condition, that is, an angle of Bragg angle 2θ _B. The full width at half maximum Γ _o of this peak is almost constant unless the measurement accuracy of the measurement system, for example, the width of the slit is changed, and it can be used as a reference value for the full width at half maximum of the diffraction peak. Therefore, the uniformity of the layer structure in the state where the liquid crystal is injected into the cell can be evaluated by the ratio of the half width of the diffraction peak to the reference value Γ _o .

FIG. 2A shows the measurement results of the low pretilt angle cell described above and shows the diffraction intensity (arbitrary scale) with respect to the rotation angle θ of the cell. Measurement conditions to fix the position of the detector in 2 [Theta] _B, except that rotating the cell is the same as FIG. 2 (E). The low pretilt angle cell (hereinafter referred to as “cell A”) will be described below with reference to specific examples.

A thin film of tantalum oxide is formed on a glass substrate having a transparent electrode by a sputtering method, and a thin film of Toray Co., Ltd. is formed on the thin film.
A 1% NMP solution of polyamic acid LP64 manufactured by Co., Ltd. was applied with a spinner and baked at 270 ° C. for 1 hour. Next, this substrate was rubbed, and another substrate that had been subjected to the same treatment was 1.5 μm.
A cell was prepared by laminating with a gap of m. The pretilt angle of this cell was 2.5 ° as measured by the crystal rotation method. This cell is a mixed liquid crystal containing phenylpyrimidine as a main component and has a tilt angle of 15 ° at room temperature and a layer tilt angle of 10 at room temperature.
Injected ferroelectric liquid crystal of °. The phase transition temperature was as follows.

[0024]

[Chemical 1] This liquid crystal cell does not satisfy the above-mentioned formula (1), and the orientation becomes the above-mentioned C2 orientation. Further, the full width at half maximum of the X-ray diffraction peak is about 1.4 ° from FIG. 2 (A). This value is about 28 times the reference value Γ _o , and it can be seen that there is a considerable difference in the degree of order between the liquid crystal layer structures in the bulk state and in the aligned state in the cell.

However, the cell A gives at least the sharpest diffraction peak among many cells measured by the present inventors, and the reproducibility is extremely good. In addition, alignment defects that show disorder of the layer structure are hardly found.

Therefore, it can be considered that the uniform layer structure is realized, as shown in FIG. 1A, in which the layer spacing is kept substantially constant, and the X detected in the cell A is realized. The full width at half maximum of the line diffraction peak can be used as another reference value Γ _l .

According to experiments conducted by the present inventors, the full width at half maximum of the X-ray diffraction peak is almost the same in a cell in which the pretilt angle is 5 ° or less and uniform alignment is realized. I am getting the result.

On the other hand, FIGS. 2B to 2D show the X of the same cell in which an alignment film having a high pretilt angle, for example, 10 ° or more is arranged.
The line diffraction peaks are shown (the half width of these diffraction peaks is Γ _h ). The relationship between the full width at half maximum of the X-ray diffraction peak and the moving speed of the liquid crystal described above will be described along with Examples and Comparative Examples described later.

Next, with respect to the direction of the dipole moment μs attached to the liquid crystal molecules near the substrate interface, S _C1 ^{* in} FIG.
Orientation will be described as an example. In the splay alignment shown by 51 and 52 in FIG. 10, μs of liquid crystal molecules near the substrate interface is directed from the substrate to the liquid crystal layer in both the upper substrate and the lower substrate, and this direction is called an inward direction. In FIG. 10, 53 has the same orientation as 51 and 52 on the lower substrate side, but μs of liquid crystal molecules near the upper substrate is oriented from the liquid crystal layer to the substrate, and this orientation is outward (outward outward). Call.

In the conventional device, as shown in FIG.
It was general that the pretilt angle was different depending on the orientation of the. That is, the interaction between the substrate interface and the liquid crystal molecules near the interface varies depending on the direction of μs.
Alignment states with different pretilt angles were common.

The inventors of the present invention have investigated in detail the relationship between the above-mentioned phenomenon of liquid crystal movement and the pretilt angle α _C in the S _C ^* phase. We also found that it is caused by the difference in angle. That is, it was found that a torque for moving liquid crystal molecules is generated when an AC drive pulse is applied in an alignment state in which the pretilt angle is asymmetric.

This point will be described below by taking the above-mentioned C1 uniform orientation as an example. Here, the symbol for the pretilt angle is defined as follows. In the S _C ^* phase, the pretilt angles when μs of liquid crystal molecules near the upper substrate are inward and outward are α ¹ _Ci and α, respectively.
¹ _Co , similarly for liquid crystal molecules near the lower substrate, α ² _Ci ,
α ² _Co.

The pretilt angles of the liquid crystal molecules near the upper substrate and near the lower substrate in the S _A phase are
Let α ¹ _A and α ² _A.

7A to 7C show the C director and dipole moment μs of liquid crystal molecules near the upper and lower substrates and in the bent portion of the chevron structure in the conventional device, respectively.
It is the figure which represented spontaneous polarization Ps typically about each orientation state of UP and DOWN. In this figure, each pretilt angle α _C corresponds to the length of a perpendicular line drawn on each of the upper and lower substrates from the point where the C director intersects with the circle that is the projection of the cone.

FIG. 7A shows the case where the upper substrate 11 and the lower substrate 12 are subjected to the same alignment treatment. In this case, α ¹ _A = α ² _A in the S _A phase, but the pretilt angle generally differs in the S _C ^* phase due to the difference in the direction of μs. For example, if μs has a high pretilt when outward, the pretilt expressed by the relationship of α ¹ _Co > α ² _Ci when Ps is DOWN, α ² _Co > α ¹ _Ci and Ps is UP. It is considered that angular asymmetry occurs and a liquid crystal moving torque corresponding to this difference occurs under an AC electric field. Also, α ¹ _A = α
^Since this is ² _A , this difference is equal to | α ¹ _Ci −α ² _Co
Since | = | α ¹ _Co −α ² _Ci |, the liquid crystal movement torque is the same in the UP and DOWN states of Ps, and it has been experimentally confirmed that the liquid crystal movement is almost the same under the application of alternating current. There is.

FIG. 7B shows a case where, for example, the upper and lower substrates are subjected to orientation treatment under different rubbing conditions, and α ¹ _A <α ² _A. Since the pre-tilt angle at S _A is asymmetrical between the upper and lower substrates, not only the pre-tilt is different for μs inward and outward in the S _C ^* phase, but also for Ps UP and DOW.
Even for N, the symmetry as shown in FIG. As a result, if | α ¹ _A −α ² _A | is properly controlled, the following orientation state can be realized.

[0037]

[Equation 1] In this case, liquid crystal movement is remarkable in the Ps DOWN state,
It hardly occurs in the Ps UP state, and it has been confirmed experimentally.

In contrast to FIG. 7B, FIG. 7C shows α ¹ _A <α ² _A
That is the case. By the same discussion as in FIG. 7B,

[0039]

[Equation 2] And the liquid crystal movement is remarkable in the Ps UP state,
It hardly happens in the s DOWN state.

As described above, since the model and the experimental result correspond well with each other, the detailed mechanism is unknown, but the static alignment state of the asymmetry of the pretilt angles of the upper and lower substrates is a cause of the liquid crystal movement under the electric field. It was confirmed that it became. Therefore, in order to prevent the moving torque of the liquid crystal from being generated, it is necessary to make the pretilt angles symmetrical between the upper and lower substrates.

FIG. 6A shows an example of an alignment state in which the pretilt angles are symmetrical on the upper and lower substrates. Such an alignment state is
For example, it can be realized by forming different alignment films on the upper and lower substrates. That is, the upper substrate 11 has a proper pretilt angle when μs is inward, and the lower substrate 12 has a proper pretilt angle when μs is outward, and α ¹ _Ci = α ² _Co and α ¹ _Co = α ² _Ci can be set.

As can be seen from the discussion so far, the liquid crystal does not actually move in the alignment state satisfying this condition, but considering the twist of the liquid crystal molecules from the upper substrate to the lower substrate, DOWN and UP of Ps are considered. The states of are not elastically equivalent. That is, bistability does not hold, and
In the case of (A), the Ps UP state becomes a stable monostable state, which is not preferable in terms of drive characteristics as a display element.

From the above, in order to prevent both liquid crystal movement and bistability, the alignment state shown in FIG. 6B is preferable. The alignment state of FIG. 6B is an alignment state in which the pretilt angle is the same for μs inward and outward, and the pretilt angles are also the same for the upper and lower substrates. That is, α ¹ _Ci = α ¹ _Co = α ² _Ci = α ² _{Co In} order to realize such an orientation, the pretilt angle in the S _C ^* phase is influenced by the dipole moment of the molecule near the substrate interface. Since it is considered that it is hardly received and that it is necessary to have a symmetric pretilt angle between the upper and lower substrates, α ¹ _A = α ² _A = α ¹ _Ci = α ¹ _Co = α ² _Ci = α ² _Co ( 3) It is considered that the alignment state is such that the following condition is substantially satisfied. At present, the following is considered to be experimentally effective as a specific means for realizing the orientation state that satisfies the mathematical expression (3). A liquid crystal material having a small spontaneous polarization Ps, for example, 10 nC / cm ² or less is used. _A reorientation treatment for changing the phase in the order of S _C ^* → S _A → S _C ^* is performed. An appropriate AC electric field is applied during the slow cooling process from the isotropic phase or the reorientation process described above.

[0044]

【Example】

Example 1 A thin film of acid value tantalum on a glass substrate having a transparent electrode was formed by a sputtering method, and a 1% NMP solution of polyamic acid LQ1802 manufactured by Hitachi Chemical Co., Ltd. was applied on the thin film by a spinner, and at 270 ° C. It was baked for 1 hour. Next, this substrate is rubbed, and the rubbing direction of another substrate subjected to the same treatment intersects the right-hand screw direction by about 10 ° in the upper substrate and the lower substrate, and the direction is the same 1.5 μm. A bonded cell was created with the gap maintained. The pretilt angle of the cell is 17 ° by the crystal rotation method.
The same mixed liquid crystal as in the cell A was injected into this cell, and Iso
It was gradually cooled from the tropic state. Thereafter, as a reorientation treatment, a process of raising the temperature to the S _A phase and then lowering it to the S _C ^* phase again while applying an alternating rectangular wave of 100 Hz and ± 10 V was repeated several times to obtain a desired orientation (cell B). The apparent tilt angle θ _a of this cell is about 11 °, which satisfies the above-mentioned formulas (1) and (2), and therefore uniform C1 uniform orientation can be obtained.

FIG. 2B shows an X-ray diffraction peak of cell B, showing a sharp diffraction peak comparable to that of cell A, and Γ _h was about 1.9 °. In addition, the alignment defect due to the disorder of the layer structure was hardly detected by the observation of the orientation with a polarization microscope, and like the cell A, the layer spacing was substantially constant as shown in FIG. It was confirmed that the structure was formed.

FIG. 8 schematically shows an example in which the ferroelectric liquid crystal element of the present invention is applied to a liquid crystal display device.

Reference numerals 31a and 31b denote substrates (glass plates) covered with transparent electrodes 32a and 32b such as In ₂ O ₃ and ITO (Indium Tin Oxide), respectively, on which an insulating film 33a having a thickness of 200 to 3000 Å is formed. And 3
3b (SiO ₂ film, TiO ₂ film, Ta ₂ O ₅ film, etc.)
And 50 made of the above-mentioned high pretilt polyimide
Alignment control films 34a and 34b each having a thickness of up to 1000 Å are laminated.

The orientation control films 34a and 34b are oriented in the same direction,
Further, the rubbing treatment is performed such that the directions intersect with each other in the right-hand screw direction at an angle of 3 ° to 20 °.

A ferroelectric smectic liquid crystal 35 is disposed between the substrates 31a and 31b, and the substrates 31a and 31b are provided.
The distance between the ferroelectric smectic liquid crystal 35 and the ferroelectric smectic liquid crystal 35 is set to be sufficiently small (for example, 0.1 to 3 μm) to suppress the formation of the helical alignment structure of the ferroelectric smectic liquid crystal 35. Is causing a condition. The bead spacer 36 (silica bead, alumina bead) disposed between the substrates 31a and 31b has a sufficiently small distance.
Held by 37a and 37b are polarizing plates.
The display area of this panel is 114 × 228 mm.

In the display device having such a structure, after the above-mentioned redistribution processing is performed, the orientation of the entire cell is shown in FIG.
Aligned in the average molecular axis direction 21 shown in (A), the pulse width is 2
The cell thickness (gap) in the region 23 of FIG. 12B was measured after applying a rectangular wave of 5 μs, a voltage amplitude of 40 V, and a 1/2 duty for about 7 hours. Did not increase.

Example 2 The same cell as the cell B was gradually cooled from the Isotropic state, and as a reorientation treatment, the process of raising the temperature to the S _A phase and then lowering it to the S _C ^* phase again was repeated several times (cell C And).

FIG. 2C shows the X-ray diffraction peak of cell C, which is slightly broader than that of cell A (Γ _h ≈
Although it is 2.4 °), it is considered that an approximately uniform layer structure is formed as a result of detecting some alignment defects in the alignment observation. Furthermore, the same liquid crystal display device as in Example 1 was subjected to the same re-orientation treatment as in Cell C, and then the same evaluation as in Example 1 was carried out. As a result, the cell thickness increased by only about 10% compared to the initial stage. It was

Comparative Example The same cell as the cell B was gradually cooled from the Isotropic state, and then no reorientation treatment was performed (cell D).

FIG. 2D shows the X-ray diffraction peak of cell D, which is considerably broader than that of cell A (Γ _h ≈
3.6 °). A broad diffraction peak means that the order of the smectic layer is lowered in some way. The cause is, for example, FIG.
As shown in (B), it is considered that in the state of slow cooling from the isotropic phase, the influence of the substrate interface is strongly exerted, so that the smectic layer bends are generated, and the layer structure in which the layer spacing is not constant is realized. Yes, but the detailed mechanism is currently unknown.

In the alignment observation, many alignment defects, which are considered to be caused by the disorder of the layer structure, were detected. As shown in FIG. 5, for example, such an alignment defect causes an alignment defect indicated by 50 due to a layer misalignment in order to locally maintain a constant layer interval by the bend of the layer. I am thinking, but the details are unknown.

When the same liquid crystal display device as in Example 1 was subjected to the same evaluation as in Example 1 without subjecting it to re-orientation treatment, the cell thickness was increased by about 30% as compared with the initial stage.

Table 1 shows the characteristics of the cells A to D and the evaluation results of the cell thickness change amount due to the liquid crystal movement corresponding thereto.

[0058]

[Table 1] Example 3 FIG. 8 is a sectional view schematically showing a liquid crystal cell according to a second example of the present invention. As shown in FIG. 8, this liquid crystal cell has a pair of upper substrate 31a and lower substrate 31 arranged in parallel.
b and the wiring on each substrate, for example, the thickness is about 400
It is equipped with transparent electrodes 32a and 32b of up to 2000 Å.
Ferroelectric liquid crystal is provided between the upper substrate 31a and the lower substrate 31b,
Preferably, a non-helical ferroelectric smectic liquid crystal 35 having at least two stable states is arranged.
On the transparent electrodes 32a and 32b, for example, a thickness of 10
A 1000Å polymer organic film, for example, alignment control films 34a and 34b formed of a polyimide resin are arranged.
The alignment control films 34a and 34b are rubbed so that the alignment directions are parallel and in the same direction (the direction of arrow A in FIG. 8). The rubbing directions may intersect at an angle of 5 ° to 20 °. In addition, the orientation control films 34a, 34
b and the transparent electrodes 32a and 32b, for example, insulating films 33a and 33b (SiO ₂₎ having a thickness of 200 to 3000 Å, for example.
Film, TiO ₂ film, Ta ₂ O ₅ film, etc.) may be arranged. The space between the substrates is held by silica beads 36 having an average particle diameter of about 1.5 μm (generally 0.1 to 3.5 μm) dispersed in the liquid crystal layer 35. 37a and 37b are polarizing plates. Here, the upper substrate 31a and the lower substrate 31b are subjected to equivalent alignment treatment so as to effectively generate equal pretilt angles.

[0059] As the ferroelectric liquid crystal 35, it is possible to use a chiral smectic phase state, specifically, a chiral smectic C phase (S _C ^*), H phase (S _H ^*), I phase (S _I ^* ) liquid crystals can be used.

As a particularly preferable ferroelectric liquid crystal, one exhibiting a cholesteric phase on the higher temperature side can be used, and for example, a pyrimidine-based mixed liquid crystal having a phase transition temperature and a physical property value represented by the following formula is used. it can.

[0061]

[Chemical 2] Tilt angle Θ = 14 ° Spontaneous polarization Ps = 4 nC / cm ² Layer tilt angle δ = 10 ° Apparent tilt angle θ _a = 11 ° After slowly cooling the above liquid crystal cell from the isotropic phase, 100 Hz,
While applying an alternating rectangular wave of about ± 10 V, the temperature was raised to the S _A phase and then dropped again to the S _C ^* phase to obtain the desired orientation.

The pretilt angle is Appl. Phys. L
ett. , Vol. 53, no. 24, 2397 (19
88) and the like according to the total internal reflection method (TIR method).

However, the measuring cell is the upper substrate 31 shown in FIG.
Instead of a, a hemispherical prism with a high refractive index is used, and S for liquid crystal molecules near the liquid crystal interface in contact with the hemispherical prism is used.
Pretilt angle α _{A in} phase _A and dipole moment μs
The pretilt angles α _Ci and α _Co in each of the inward and outward states were measured. Pretilt angle is small relatively temperature vary, at least in the temperature range within 3 ° C. before and after S _A → S _C ^* phase transition temperature T _AC, were _{α A ≒ α Ci ≒ α Co} ≒ 19 °.

This orientation state satisfies the equations (1) and (2), and thus the above-mentioned C1 uniform orientation is obtained.

In the cell having such a structure, the orientation of the entire cell is aligned in the average molecular axis direction 21 shown in FIG. 12A, and a rectangular wave having a pulse width of 25 μs, a voltage amplitude of 40 V, and a 1/2 duty is formed. After applying for about 7 hours, FIG.
When the cell thickness (gap) in the region 23 of (B) was measured, it increased by only about 5% compared to the initial stage. The bistability was also very good.

Comparative Example 2 The same cell as in Example 3 was prepared, and after gradually cooling from the isotropic phase, the subsequent reorientation treatment was not performed.

When the pretilt angle was measured in the same manner as in the example under these orientation conditions, α _Co > α _Ci , and the difference was about 3 °. In addition, α _A was a value around the center of α _Co and α _Ci .

When a voltage was applied to this cell under the same conditions as in Example 1, the cell thickness increased by about 30% compared to the initial stage.

[0069]

As described above, according to the first aspect of the present invention, even in the case of a high pretilt angle cell having a pretilt angle of 10 ° or more, the layer of the smectic layer can be formed by performing the above-mentioned realignment treatment. The order can be enhanced, and as a result, it has become possible to significantly reduce the change in cell thickness over time due to the movement of liquid crystals.

As a specific means for increasing the layer order of the smectic layer, it is effective to use, for example, a ferroelectric liquid crystal having a phase sequence of Iso → S _ch → S _C ^* in addition to the re-orientation treatment described above. It was

In a cell (antiparallel rubbing cell) in which the directions of the rubbing axes are opposite between the upper substrate and the lower substrate, the phenomenon of liquid crystal movement described above does not occur, but means for eliminating defects in the smectic layer structure. The reorientation treatment described above was effective.

That is, as in the parallel rubbing cell, the antiparallel rubbing cell is strongly influenced by the substrate interface as shown in FIG. 4C, and the state where the smectic layer is bent is shown in FIG. It is presumed that a uniform layer structure such as the above is formed, but the details are not clear.

Further, according to the second aspect of the invention, since the pretilt angle is optimized, a ferroelectric liquid crystal element excellent in bistability and realizing high contrast alignment is provided, and a local cell by driving is provided. The thickness variation can be significantly reduced.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a smectic layer structure in the present invention.

FIG. 2 is a chart showing diffraction peaks obtained by an X-ray diffraction method.

FIG. 3 is a block diagram showing an optical arrangement in an X-ray diffraction method.

FIG. 4 is a schematic diagram showing a smectic layer structure in a conventional example.

FIG. 5 is a schematic diagram showing a smectic layer structure for explaining alignment defects.

FIG. 6 is a schematic view showing the arrangement of C directors at respective positions between substrates in a uniform orientation state according to the present invention.

FIG. 7 is a schematic view showing the arrangement of C directors at respective positions between substrates in a conventional uniform orientation state.

FIG. 8 is a schematic view showing an example of a liquid crystal display device of the present invention.

FIG. 9 is a schematic view showing a layer structure of C1 orientation and C2 orientation.

FIG. 10 is a schematic diagram showing the arrangement of directors at respective positions between substrates in each state of C1 orientation.

FIG. 11 is a schematic view showing the arrangement of directors at respective positions between substrates in each state of C2 orientation.

FIG. 12 is an explanatory diagram for explaining a moving direction of liquid crystal.

[Explanation of symbols]

 11 Upper Substrate 12 Lower Substrate 30 Measurement Cell 31a, 31b Substrate 32a, 32b Transparent Electrode 33a, 33b Insulating Film 34a, 34b Alignment Control Film 35 Ferroelectric Smectic Liquid Crystal 36 Spacer 37a, 37b Polarizing Plate 41 Smectic Layer 42 C1 Alignment Region 43 C2 alignment region 44 Lightning defect 45 Hairpin defect 50 Alignment defect 51,52 Spray alignment 53,54 Uniform alignment 57 Dipole moment 60 Rubbing direction 61,61 'Average molecular axis direction

Claims (9)

[Claims] 1. A pair of substrates, each of which includes a scanning electrode group and an information electrode group and which has been subjected to a uniaxial orientation treatment, wherein the uniaxial orientation treatment axes are parallel or substantially parallel to each other. A liquid crystal cell sandwiching a volatile liquid crystal, the pretilt angle of the ferroelectric liquid crystal is 10 ° or more, and
A ferroelectric liquid crystal device characterized in that the layer spacing in the smectic layer structure is substantially constant. 2. A pair of substrates each comprising a scanning electrode group and an information electrode group, each of which is provided with a uniaxial alignment treatment and which comprises a first substrate and a second substrate, and a ferroelectric liquid crystal between the substrates. In the sandwiched liquid crystal element, the liquid crystal has a dipole moment of liquid crystal molecules in the vicinity of the interface of the substrate depending on the direction of the applied electric field.
In addition, in the vicinity of each of the substrate interfaces, the pretilt angle is substantially equal between the state in which the dipole moment faces the inner direction and the state in which the dipole moment faces the outer direction, and the pretilt angle is close to the first substrate interface and the second substrate dipole moment. A ferroelectric liquid crystal device having an alignment state in which pretilt angles are substantially equal to each other regardless of the direction of the dipole moment in the vicinity of a substrate interface. 3. A bulk state in which the ferroelectric liquid crystal is not injected into a liquid crystal cell at an X-ray diffraction peak, which is obtained as a diffraction by a smectic layer structure of the ferroelectric liquid crystal and is expressed by a diffraction intensity with respect to a tilt angle of the layer. The half width at Γ _o ,
2. The ferroelectric liquid crystal according to claim 1, wherein the ferroelectric liquid crystal has an alignment state represented by a relationship of 20 <Γ _h / Γ _o <50 when a half width after injection into the liquid crystal cell is Γ _h. element. 4. When the full width at half maximum of the X-ray diffraction peak in a liquid crystal element in which the pretilt angle of the ferroelectric liquid crystal is 5 ° or less is Γ _l , the full width at half maximum Γ _{h of the} liquid crystal element is 1 <Γ _h The ferroelectric liquid crystal device according to claim 1, having an alignment state represented by a relationship of / Γ _l <2. 5. When the pretilt angle of the ferroelectric liquid crystal is α _C , the tilt angle is Θ, and the tilt angle of the S _C ^* layer is δ, the ferroelectric liquid crystal has an alignment state represented by Θ <α _C + δ. And the ferroelectric liquid crystal in the alignment state exhibits at least two stable states, and θ _a , which is ½ of the angle formed by the optical axes thereof, and the tilt angle Θ of the ferroelectric liquid crystal are θ> The ferroelectric liquid crystal device according to claim 1 or 2, which has an alignment state represented by θ _a > θ / 2. 6. The uniaxial alignment treatment axis has the same direction, and the upper substrate and the lower substrate intersect at an angle θ _c (where θ _c <90 °). The ferroelectric liquid crystal device described. 7. The method according to claim 1, wherein the directions of the uniaxial alignment treatment axes are opposite and the upper substrate and the lower substrate intersect at an angle θ _c (where θ _c <90 °). Ferroelectric liquid crystal element. 8. The ferroelectric liquid crystal device according to claim 1, wherein the uniaxial alignment treatment is a rubbing treatment. 9. The ferroelectric liquid crystal has a smectic A phase (S _A phase) on the high temperature side of the chiral smectic phase,
The pretilt angles (α _A ) of liquid crystal molecules near the first substrate and the second substrate in the S _A phase are substantially equal, and α _A is substantially equal to the pretilt angle α _C in the chiral smectic phase. The ferroelectric liquid crystal device according to claim 2, having an alignment state.