JP3180171B2 - Ferroelectric liquid crystal 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 device and a liquid crystal display.
The present invention relates to a liquid crystal element used for an optical shutter or the like, and further relates to a conductive alignment film for a liquid crystal element having improved alignment characteristics of liquid crystal molecules and a liquid crystal element using the same.

[0002]

2. Description of the Related Art A TV image is a moving image having a fine and halftone. When displaying this TV image, high resolution,
High-speed response, multi-step display, high contrast, high reliability,
The most advanced technology such as colorization is required. In this regard,
The quality of the TV image displayed on the CRT is very good. However, liquid crystal display devices that can be reduced in light of the trend toward larger display images have attracted attention, and recently, an active matrix type device in which a switching element is provided for each pixel to directly drive a nematic liquid crystal is provided. Research has been actively conducted mainly on a TV image display method using a liquid crystal element. However, the switching element to be incorporated is TFT
Although the method is considered to be the best, it is a major obstacle to increasing the area, such as the complexity of the device manufacturing process and the number of steps.

On the other hand, a display device in which transmitted light is controlled in combination with a polarizing element using the refractive index anisotropy of ferroelectric liquid crystal molecules has been proposed by Clark and Lagerwall. (JP-A-56-107216, U.S. Pat.
No. 7924). The ferroelectric liquid crystal generally has a non-helical chiral smectic C phase (SmC ^* ) or H phase (SmH ^* ) in a specific temperature range, and in this state, responds to an applied electric field. 1
Has the property of taking one of the optically stable state and the second optically stable state, and maintaining the state when no electric field is applied, that is, it has bistability, and also has a response corresponding to a change in the electric field. It is expected to be used promptly, at high speed, and widely used as a storage type display element. In particular, its function is expected to be applied to a large-screen, high-definition display element using a simple matrix drive system.

[0004] A ferroelectric liquid crystal element is a bistable 2
Because it is essentially a binary representation based on state control,
It is believed that it would not be suitable for displaying halftones. However, it is expected that the development of the gradation display technology of the ferroelectric liquid crystal will enable a wider range of applications utilizing the excellent characteristics of the liquid crystal. As a gray scale display method using a simple matrix driving method, an area gray scale method based on micro-domain formation in which transition between two bistable alignment states of the liquid crystal in a pixel is controlled in a micro region has been proposed. (Japanese Patent Laid-Open No. 59
193427). However, with the conventional orientation control technology, sufficient control is performed on the contrast ratio between the binary states, the hysteresis in the switching process, and the generated microdomain stability and controllability, thereby realizing practical gradation. It is hard to say that.

In order for the optical modulation element using the bistable liquid crystal to exhibit predetermined driving characteristics, the liquid crystal disposed between the pair of parallel substrates needs to be driven by the liquid crystal element irrespective of the electric field application state. It is necessary to be in a molecular alignment so that conversion between the two stable states can occur effectively.

Further, in a liquid crystal device utilizing birefringence of a liquid crystal, the transmittance under crossed Nicols ^{_{is, I / I O = sin 2}} 4θsin 2 (Δndπ / λ) formula: I _O is the intensity of incident light, I is the transmitted light intensity, θ is the tilt angle, Δn is the refractive index anisotropy, d is the thickness of the liquid crystal layer, and λ is the wavelength of the incident light. It is represented by The tilt angle θ in the above-described non-helical structure appears as an angle in the average molecular axis direction of the twisted liquid crystal molecules in the first and second alignment states. According to the above equation, it is necessary that the tilt angle θ be as close as possible to 22.5 °.

As a method of aligning a ferroelectric liquid crystal, it is necessary to uniaxially align a liquid crystal molecular layer formed of a plurality of molecules forming a smectic liquid crystal over a large area along a normal line thereof. For this reason, a polyimide film that has been usually subjected to a rubbing treatment has been widely used. In particular, as an alignment method for a chiral smectic liquid crystal having a non-helical structure, for example, US Pat.
No. 26 is known. The tilt angle θ (the angle shown in FIG. 3 described later) of a non-helical structure ferroelectric liquid crystal obtained by orientation using a conventional rubbed polyimide film is the tilt angle of a ferroelectric liquid crystal having a helical structure. Θ
Generally, the angle is smaller than (an angle which is の of the apex angle of the triangular pyramid shown in FIG. 2 described later). In particular, the tilt angle θ of a ferroelectric liquid crystal having a non-helical structure obtained by orientation by a rubbed polyimide film is generally about 3 ° to 8 °, and the transmittance at that time is at most 3 to 5%.
It was about.

As described above, according to Clark and Ragawall, the tilt angle of a ferroelectric liquid crystal having a non-helical structure for realizing bistability is the same as the tilt angle of a ferroelectric liquid crystal having a helical structure. Although it should have, the tilt angle θ in the non-helical structure is actually greater than the tilt angle Θ in the helical structure.
It is smaller. Moreover, it has been revealed that the cause of the tilt angle θ in the non-helical structure being smaller than the tilt angle Θ in the helical structure is due to the twisted arrangement of the liquid crystal molecules in the non-helical structure. In other words, in the ferroelectric liquid crystal having a non-helical structure, the liquid crystal molecules continuously move in the axis 43 of the liquid crystal molecules adjacent to the upper substrate (the direction of twist alignment 44) with respect to the normal line of the substrate as shown in FIG. The twisted arrangement at the twist angle δ causes the tilt angle θ in the non-helical structure to be smaller than the tilt angle Θ in the helical structure.

In FIG. 1, reference numeral 41 denotes a uniaxial orientation axis formed on the upper and lower substrates by rubbing or oblique deposition.

In addition, the alignment state of the chiral smectic liquid crystal generated by the conventional rubbed polyimide alignment film is determined by the presence of the polyimide alignment film as an insulator layer between the electrode and the liquid crystal layer, and the first optically stable state ( For example, if one polarity voltage for switching from a white display state to a second optically stable state (for example, a black display state) is applied, after the application of the one polarity voltage is canceled,
A reverse electric field Vref of the other polarity is generated in the ferroelectric liquid crystal layer,
There is a problem that such a reverse electric field Vref causes an afterimage phenomenon at the time of display (Akio Yoshida, 1st 1987)
"LCD Symposium Reruns", p. 142-143, "SSF"
Switching Characteristics of LC "), and problems such as hysteresis in switching due to charge dyeing due to ionic species and the like.

[0011]

SUMMARY OF THE INVENTION The main object of the present invention is to solve the above-mentioned problems in the technique of aligning ferroelectric liquid crystals, to improve the contrast ratio between bistable binary states,
In order to eliminate the afterimage phenomenon and hysteresis in the switching process, and to realize practical gradation,
An object of the present invention is to provide a ferroelectric liquid crystal element having sufficient control over stability and controllability of micro domains generated in each pixel. Furthermore, the present invention provides a ferroelectric liquid crystal element which generates a large tilt angle in a non-helical structure of a chiral smectic liquid crystal, displays a high-contrast image, and can perform a display without an afterimage phenomenon or a hysteresis in a switching process. The purpose is to do so.

[0012]

SUMMARY OF THE INVENTION The present invention is a liquid crystal element is formed by sandwiching a ferroelectric liquid crystal between a pair of substrates having electrodes and Oriented films respectively, said Oriented films, on a substrate Set in
Formed on a conductive protective film that covers the
The linear π-conjugated conductive polymer has a structure one-dimensionally oriented in a direction substantially parallel to the substrate surface, and the optical dichroic ratio in the one-dimensional orientation axis direction is 2 or more. Is a ferroelectric liquid crystal device characterized by the following.

[0013] In the present invention, as the linear π-conjugated conductive polymer, preferably with a rigid π-conjugated conductive polymer, also preferably has a conductive protrusions on said Oriented film. In this case, it is preferable that the conductive protrusions are also made of a rigid π-conjugated conductive polymer. Furthermore, in the present invention, the magnitude of the spontaneous polarization of the ferroelectric liquid crystal is 10 nC
/ Cm ² or more. In the liquid crystal device of the present invention, the initial alignment state of the liquid crystal is desirably obtained by applying an AC electric field.

Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 1 is a schematic diagram showing an example of a ferroelectric liquid crystal device using an alignment film for a liquid crystal device of the present invention (hereinafter, referred to as an alignment film). Hereinafter, the characteristics of the alignment film of the present invention will be described based on the evaluation of the characteristics of the liquid crystal cell having the alignment film of the present invention with reference to FIG. In FIG. 1, 11a and 11b
Are transparent electrodes 12a and 12b of In ₂ O ₃ or ITO, respectively.
Is a glass substrate coated with
Protective films 13a and 13b slightly imparted with conductivity for preventing electrification of 00 ° and an alignment film 1 of a film made of the polymer.
4a and 14b are respectively laminated. The protective film having antistatic properties has a conductivity of 10 ⁻¹⁰ S / cm or more, more preferably a conductivity of 10 ⁻⁸ to 10 ⁻⁵ S / cm, and transmits light in the visible region. A medium having excellent properties is preferable. In the present invention, the condition is satisfied protective film mainly using WO ₃ thin films prepared by the EB sputtering as, but preparation of the WO ₃ film is not limited thereto. Further, not limited to the WO _3, can be used as a protective film conductivity imparting long as the material has the above characteristics.
For example, SnO ₂ , TiO ₂ , ZnO, ZnS, Cd
Many metal oxides and sulfides such as O and CdS can be used, and these oxides and sulfides also have an advantage that their conductivity can be controlled over a wide range by adding a small amount of dopant. Further, the mixture of the metal oxide and the sulfide is also effective because a film having higher flatness can be obtained by making the protective film amorphous.

A ferroelectric smectic liquid crystal 15 is disposed between the alignment films 14a and 14b, and the distance between the ferroelectric smectic liquid crystals 15 is small enough to suppress the formation of a helical array structure of the ferroelectric smectic liquid crystal 15. (For example, 0.
1 to 3 μm), and the ferroelectric smectic liquid crystal 15 has a bistable alignment state. The sufficiently small distance between the liquid crystals in which the ferroelectric smectic liquid crystal 15 is disposed is held by a bead spacer 16 (for example, silica beads, alumina beads, or the like) disposed between the alignment films 14a and 14b. . Also, 17a, 1
7b shows a polarizing plate.

As the rigid π-conjugated conductive polymer used in the present invention, for example, poly (p-phenylene) [P
PP], poly (thiophene-2,5-diyl) [PT
h], poly (pyridine-2,5-diyl) [PPy],
Poly (2,2'-bipyridine-2,5-diyl) [PB
Py], poly (pyridine-5,2-diyl-thiophene-2,5-diyl) [PTPy], poly (pyrrole-
2,5-diyl) [PPr] or the like may be used alone or in combination of two or more.

In order to impart high conductivity to the rigid π-conjugated conductive polymer, a dopant is required. However, a film having a conductivity of 10 ⁻¹⁰ S / cm or more can be obtained without special use of a dopant. More preferably, 10 ^-8 to 10 ^-4
What is necessary is just to give the electrical conductivity of the range of S / cm. Further, a medium having excellent transparency to light in the visible region is preferable, and the thickness of the alignment film is usually 1000 ° or less, preferably 500 ° or less, more preferably 200 ° or less.

The rigid π-conjugated conductive polymer described above has a rigid structure even in a solution from the measurement of the degree of depolarization by the light scattering method, and has a significantly larger polarizability in the main chain direction than in the other two directions. The measured value of the degree of depolarization is 0.33, which is close to the theoretical limit (1/3), and is known to have an ideal rigid structure which has not been known for other molecules. .

Therefore, if the molecular chains can be arranged in a certain direction, it becomes possible to produce an alignment film having high alignment anisotropy. As a method for giving orientation anisotropy, a stretching method, a flow orientation method, and the like are known. We have found that an alignment film having a structure in which a linear π-conjugated conductive polymer is one-dimensionally aligned in a direction substantially parallel (1 ° or less) to the substrate surface on the substrate can be produced by the flow alignment method. Was. When linearly polarized light was applied to this alignment film, strong dichroism was observed. When a solution of the linear π-conjugated conductive polymer was flowed through a capillary having an inner diameter of 1φ or less at a flow rate of 1 cc / min or more, ultraviolet-visible absorption when polarized light parallel and perpendicular to the flow axis was applied. at the maximum absorption wavelength in the spectrum, there is a large difference between the absorbance a _b to the absorbance a _a perpendicular polarization for polarized light parallel to the alignment axis, the dichroic ratio, R _d = a _a
As for / _Ab , two or more films were obtained. The larger the dichroic ratio is, the higher the uniaxial orientation is.
A liquid crystal having a chromaticity ratio is preferable, but an alignment film having a dichroic ratio of 2 or more can uniformly align the liquid crystal.

However, in the rubbing method or the LB method, which has been conventionally used as a liquid crystal alignment technique, macroscopic and statistical uniaxial alignment of a polymer chain also occurs due to the stretching effect.
In these methods, the orientation of the polymer chain axis cannot be controlled even in a micro region. The misalignment of the alignment axes of the ferroelectric liquid crystal molecules near the interface due to the microscopic alignment axis distribution of the alignment film itself causes hysteresis at the time of driving, an afterimage phenomenon, and drive deterioration of the liquid crystal alignment state. It is pointed out that it may be caused.

On the other hand, the rigid π-conjugated conductive polymer is
By heating under high vacuum below ^-6 Torr,
Evaporates without thermal decomposition relatively easily. For example, a PPP deposited film formed on a carbon substrate by a vacuum deposition method has good orientation and crystallinity, and the axis of the PPP crystal, that is, the molecular chain is oriented almost perpendicular to the carbon substrate surface. It has been known.

The rigid π-conjugated conductive polymer is an ideal rigid polymer having high crystallinity as described above, and the orientation film characteristics resulting from the crystallinity include a micro-alignment axis (crystal axis).
The distribution controllability and the fact that the formed micro-orientation axis (crystal axis) itself is unlikely to shift. Based on these alignment film characteristics, more stable liquid crystal alignment can be realized, and more specifically, an alignment film in which the alignment axis of the ferroelectric liquid crystal molecules near the interface does not easily shift can be provided. In the present invention, the uniaxial alignment characteristic (reflecting the crystallization ratio) of the rigid π-conjugated conductive polymer alignment film is evaluated by the dichroic ratio. Any alignment film having a dichroic ratio may be used. Preferably, an alignment film having a dichroic ratio of 10 or more, and more preferably 20 or more for microscopic alignment axis (crystal axis) distribution control.

In order to impart more effective orientation to the orientation film thus formed, the surface of the orientation film can be further rubbed. At this time, the rubbing direction is
Rubbing may be performed in only one direction, but it is preferable to perform rubbing (parallel, antiparallel) along the orientation direction of the polymer chain. When the alignment films are used for the upper and lower substrates, the alignment axes of the upper and lower substrates are parallel,
The directions may be antiparallel or intersect with a slight angle of 1 ° or less, and may be performed by various methods according to the orientation characteristics of the ferroelectric liquid crystal material used.

In the present invention, in order to control the alignment state of the liquid crystal molecules, the uniaxial alignment of the polymer chain axis of the linear π-conjugated conductive polymer in the substrate plane is controlled, and the linear π-conjugated conductive polymer is controlled.
Utilizing the conductive properties of conjugated conductive polymers, bistability 2
In order to improve the contrast ratio between the value states, eliminate after-image phenomena and hysteresis in the switching process, and achieve practical gradation, the micro-domain stability and controllability generated in each pixel are improved. On the other hand, a ferroelectric liquid crystal element having sufficient control can be provided. Further, as a method of forming an in-plane uniaxial orientation of the polymer chain axis,
Although the flow alignment method has been described, the method of forming an alignment film of the present invention is not limited thereto, and any other method may be used as long as the method can realize the uniaxial alignment. For example, a desired alignment film can be formed by heating and vapor-depositing a linear π-conjugated conductive polymer under a high vacuum of 10 ⁻⁶ Torr or less on a substrate that has been subjected to a rubbing alignment treatment in advance.

The liquid crystal substance used in the liquid crystal device using the alignment film of the present invention is not particularly limited. However, when evaluated from the ease of initial uniform alignment during liquid crystal injection,
Liquid crystals that generate a chiral smectic C phase through an isotropic phase, a cholesteric phase, and a smectic A phase are preferred. In particular, those having a pitch of 0.8 μm or more in the cholesteric phase are preferable (however, those measured at the central point in the temperature range of the cholesteric phase). However, the application of the liquid crystal alignment film of the present invention is not limited only to the liquid crystal having the above characteristics, and in particular, from the viewpoint of stability and reproducibility of the switching process, the spatial divergence of spontaneous polarization of ferroelectric liquid crystal molecules, That is, a ferroelectric liquid crystal having a large spontaneous polarization such that a polarization field generated by space charge can affect the molecular orientation of liquid crystal molecules, for example, a ferroelectric liquid crystal having a spontaneous polarization Ps of 10 nC / cm ² or more. It is preferably used. Also,
Even if a ferroelectric liquid crystal having no cholesteric phase during the temperature-falling process and a helical pitch of 0.5 μm or less in the SmC ^* phase can be used satisfactorily, it is difficult to achieve the initial uniform alignment at the time of liquid crystal injection.

FIG. 2 schematically shows an example of a cell for explaining the operation of the ferroelectric liquid crystal. 21a and 2
1b is a substrate (glass plate) covered with a transparent electrode made of a thin film such as In ₂ O ₃ , SnO ₂ or ITO,
In the meantime, SmC ^* (chiral smectic C) phase or SmH ^* (chiral smectic H) phase liquid crystal in which the liquid crystal molecular layer 22 is oriented so as to be perpendicular to the glass substrate surface is sealed. A bold line 23 represents a liquid crystal molecule, and the liquid crystal molecule 23 has a dipole moment 24 in a direction orthogonal to the molecule. The angle forming the apex angle of the triangular pyramid at this time represents the tilt angle Θ in the chiral smectic phase of the helical structure. Substrates 21a and 21b
When a voltage equal to or higher than a certain threshold is applied between the upper electrodes, the helical structure of the liquid crystal molecules 23 is unwound, and the dipole moment 24
Are oriented in the direction of the electric field, the liquid crystal molecules 23 can change the alignment direction. The liquid crystal molecules 23 have an elongated shape and exhibit refractive index anisotropy in the major axis direction and the minor axis direction. Therefore, for example, if crossed Nicol polarizers are placed above and below the glass substrate surface, voltage It is easily understood that the liquid crystal optical modulation element whose optical characteristics change depending on the polarity.

The surface stable ferroelectric liquid crystal cell in the bistable alignment state used in the liquid crystal device having the conductive alignment film of the present invention has a sufficiently small thickness (for example, 0.1 to 3 μm).
can do. As shown in FIG. 3, as the liquid crystal layer becomes thinner, the helical structure of the liquid crystal molecules is unwound and becomes a non-helical structure even when no electric field is applied, and the dipole moment Pa or Pb is directed upward (34a). ) Or downward (34b). When an electric field Ea or Eb having a different polarity or more than a certain threshold is applied to such a cell by the voltage applying means 31a and 31b as shown in FIG. 3, the dipole moment is changed to the electric field Ea or Eb.
34a or downward 34 corresponding to the electric field vector of
Then, the liquid crystal molecules are oriented in either the first stable state 33a or the second stable state 33b. The angle between the first and second stable states at this time is 1 /
2 corresponds to the tilt angle θ.

The effects obtained by the ferroelectric liquid crystal cell are firstly that the response speed is extremely fast, and secondly that the orientation of liquid crystal molecules has bistability. The second point will be further described with reference to, for example, FIG.
When the electric field Ea is applied, the liquid crystal molecules are in the first stable state 33a.
This state is stable even when the electric field is turned off.
When an electric field Eb in the opposite direction is applied, the liquid crystal molecules are oriented to the second stable state 33b and change the direction of the molecules.
Again, this state remains even when the electric field is turned off. Also,
As long as the applied electric field Ea does not exceed a certain threshold value, each orientation state is also maintained.

Next, FIG. 5A is a cross-sectional view schematically showing an alignment state of liquid crystal molecules aligned by the alignment method using the alignment film of the present invention, and FIG. 5B shows a C-director thereof. FIG. 5A and 51B shown in FIG. 5A represent an upper substrate and a lower substrate, respectively. 50 is a liquid crystal molecule 5
In the liquid crystal molecular layer organized in 2, the liquid crystal molecules 52 have a cone 53
Are arranged at different positions along the bottom surface 54 (circular). FIG. 5B is a diagram showing a C-director,
In the drawing, U ₁ is the C-director 81 in one stable orientation state, and U ₂ is the C-director 81 in the other stable orientation state. The C-director 81 is a projection of the molecular long axis onto a virtual plane perpendicular to the normal of the liquid crystal molecular layer 50 shown in FIG.

On the other hand, the alignment state produced by the conventional rubbed polyimide film is shown by the C-director diagram in FIG. The orientation state shown in FIG.
Since the torsion of the molecular axis is large from the upper substrate 51a toward the lower substrate 51b, the tilt angle θ is small.

Next, FIG. 6A shows a C-director 81.
Is an explanatory view showing the tilt angle θ in the state of FIG. 5B (referred to as a uniform alignment state), and FIG. 6B is a state in which the C-director 81 is in the state of FIG. 5C (referred to as a splay alignment state). FIG. 4 is an explanatory diagram showing a tilt angle θ of FIG. In the figure, reference numeral 60 denotes a pulling direction of the substrate when the alignment film is formed by the Langmuir-Blodgett method, or a rubbing treatment axis when the alignment film is formed by the coating method or the vapor deposition method,
61a shows an average molecular axis in the orientation state U _1, 61b denotes an average molecular axis in the orientation state U _2, 62a denotes an average molecular axis in the orientation state S _1, 62b is an average molecular axis in the orientation state S _2.
The average molecular axes 61a and 61b can be converted by applying opposite polarity voltages exceeding the threshold voltage to each other. The same occurs between the average molecular axes 62a and 62b.

Next, the usefulness of the uniform alignment state with respect to the delay (afterimage) of the optical response due to the reverse electric field Vrev will be described. Capacitance Ci of the alignment control layer of the liquid crystal cell and the capacitance of the liquid crystal layer to the C _LC and _the spontaneous polarization of the liquid crystal and Ps, Vrev causing after-image is expressed by the following equation.

Vrev = 2 · Ps / (Ci + C _LC ) FIG. 7 is a sectional view schematically showing the charge distribution in the liquid crystal cell, the direction of the spontaneous polarization Ps, and the direction of the reverse electric field Vrev.
FIG. 7A shows the distribution state of + and-charges under the memory state before the application of the pulse electric field, and the spontaneous polarization Ps at this time is shown.
Is the direction from the positive charge to the negative charge. FIG. 7B shows the direction of the spontaneous polarization Ps immediately after the release of the pulse electric field. The spontaneous polarization Ps is opposite to the direction of FIG. 7A (therefore, the liquid crystal molecules move from one stable alignment state to the other). (Reversal occurs in the stable alignment state), but since the distribution state of + and-charges is the same as that in FIG. 7A, a reverse electric field Vrev is generated in the liquid crystal in the direction of arrow B. This reverse electric field Vr
After a while, ev disappears as shown in FIG. 7C, and the distribution of the + and-charges changes.

FIG. 8 is an explanatory diagram showing a change in the optical response in the splay alignment state caused by the conventional polyimide alignment film instead of a change in the tilt angle θ. As shown in FIG.
Slightly increased the average molecular axis tilt angle θ to U ₂ under uniform alignment state in the vicinity of the maximum tilt angle Θ from the average molecular axis S under splay alignment state along the direction of the arrow X ₁ (A) at the time of pulse electric field is applied A stable alignment state is obtained.
FIG. 9 is a graph showing the state of the optical response at this time.

According to the present invention, by using the above-mentioned alignment film of the present invention, the average molecular axes S (A), S (B) and S in the spray state shown in FIG.
(C) does not occur, and therefore, it can be arranged on the average molecular axis that generates a tilt angle θ close to the maximum tilt angle Θ.

FIG. 10 is a graph showing the state of the optical response when the alignment film of the present invention is used. According to FIG. 10, it is recognized that the optical response is not delayed due to the afterimage and that high contrast is caused under the memory condition. FIG. 12 is a graph (VT characteristic) showing the relationship between the transmittance when the alignment film of the present invention is used and the peak value of an applied pulse of 50 μsec. As shown by the solid line and the dotted line in FIG.
It was recognized that an alignment state having no difference in -T characteristics was achieved.

The present invention provides a large optical contrast between the bright state and the dark state by using a highly-aligned conductive alignment film, as will be apparent from the examples described below. No. 4,655,561, a large contrast is generated with respect to non-selected pixels at the time of multiplexing driving, and a delay in optical response at the time of switching (at the time of multiplexing driving) which causes an afterimage at the time of display is reduced. An alignment state that does not occur can be achieved, and a change in the alignment state due to switching was not observed, confirming that a stable alignment state was achieved.

[0039]

The present invention will be described in more detail with reference to the following examples.

(Example 1) As a substrate, two glass substrates of 1.1 mm thickness provided with an ITO film of 1500 mm thickness were prepared, and WO ₃ was formed on each of the substrates by sputtering using WO _3. A thick film was formed as a protective film. The sheet resistance of this film was 0.1 × 10 ⁻⁷ S / cm.

PPy was dissolved in formic acid to a concentration of 0.3% by weight, and the solution was passed through a stainless steel tube having an inner diameter of 1φ (length: 5 mm), and then applied onto the substrate with a constant flow velocity axis. FIG. 14 shows a schematic diagram of the application. The thickness of the alignment film is 10
nm and the dichroic ratio was 48. Also, almost no absorption component perpendicular to the alignment film surface was observed, indicating that the polymer chain axis was oriented almost parallel to the substrate surface. When the conductivity of the alignment film produced in the same manner was measured, it was 10
^-6 S / cm.

Next, the penetration length of the tip of the pressed hair into this film is set at 0.
A rubbing treatment was performed substantially in parallel with the polymer chain axis direction under the conditions of 4 mm, a rotation speed of 1000 rpm, and a substrate feeding speed of 12 mm / sec to form an alignment film.

Thereafter, alumina beads having an average particle size of about 1.5 μm were sprayed on one of the substrates, and the two substrates were overlapped so that the rubbing axes of the substrates were parallel to each other and in the same direction. A cell was prepared. In this cell, "CS-101" which is a ferroelectric liquid crystal manufactured by Chisso Corporation
4 "(trade name) was vacuum-injected under the isotropic phase, and the orientation was achieved by gradually cooling the isotropic phase to 30 ° C at 0.5 ° C / h. This ferroelectric liquid crystal "CS-10"
The phase change in the cell of this example using "14" was as follows.

[0044]

(Equation 1) The above-mentioned liquid crystal cell was sandwiched between a pair of 90 ° crossed Nicol polarizers, and the VT specification was measured by changing the peak value of the write pulse voltage of 50 μs. The result is shown in FIG.
The pulse voltage waveform at this time is shown in FIG. FIG. 12 shows that there is no difference in VT characteristics regardless of whether the initial state is a dark state or a bright state, and that there is no hysteresis at the time of driving.

After applying a 30 V pulse of 50 μsec, the 90 ° crossed Nicols is set to the extinction position (darkest state), the transmittance at this time is measured by a photomultiplier, and then a -30 V pulse of 50 μsec is applied. Is applied, and the transmittance (bright state) at this time is measured by the same method.
The ratio between the tilt angle θ and the transmittance between the darkest state and the brightest state, that is, the contrast ratio was determined. The transmittance in the darkest state was 0.8%, while the transmittance in the brightest state was 45% and the contrast ratio was 55: 1. In addition, the delay of the optical response that caused the afterimage was 0.1 second or less, and all were good results.

Further, even after the switching operation was performed 10 ⁷ times or more, no change occurred in the orientation state of the ferroelectric liquid crystal.

When this liquid crystal cell was displayed by multiplexing driving using the driving waveforms shown in FIG. 11, a high-contrast high-quality display was obtained. When the image was erased to a white state, the occurrence of an afterimage was not legible. Note that S _N , S _{N + 1} , and S _{N + 2} in FIG. 11 represent voltage waveforms applied to the scanning lines, and I represents a voltage waveform applied to a typical information line. (I−S _N ) indicates the information line I and the scanning line S
₉ is a composite waveform applied to an intersection with _N. In this embodiment, the operation was performed at V _O = 5 to 8 V and ΔT = 20 to 70 μsec.

(Example 2) A film in which PPy produced in Example 1 was flow-oriented (film thickness: 10 mm, dichroic ratio: 48)
On top, the deposition angle was 15 ° or less, and PPP was vacuum deposited by resistance heating to form an alignment film. The total thickness of the alignment film is 19
nm and the dichroic ratio was 40. Also, almost no absorption component perpendicular to the alignment film surface was observed, indicating that the polymer chain axis was oriented substantially parallel to the substrate surface. After subjecting the alignment film to rubbing treatment in the same manner as in Example 1,
When a liquid crystal cell was fabricated and evaluated in the same manner as in Example 1, good results similar to those in Example 1 were obtained. Also in the display by the multiplexing drive, the same good results as in Example 1 were obtained with respect to the contrast and the afterimage.

(Example 3) Instead of the ferroelectric liquid crystal "CS-1014" used in Example 1, another ferroelectric liquid crystal which is also a biphenyl ester compound and has the following phase transition state is used. The following experiment was performed.

[0050]

(Equation 2) When the liquid crystal layer was sufficiently thick (〜100 μm), SmC ^* had a helical structure and the pitch was about 4 μm. From the state of spontaneous polarization by the triangular wave method, spontaneous polarization is about 10 nC
/ Cm ² and the tilt angle Θ at a cell thickness of 1.5 μm is 2
It has a value near the optimal value at 3.5 °.

The liquid crystal was injected into the liquid crystal cell prepared in Example 2 (without rubbing treatment). The apparent tilt angle θ at that time was 16 °, which was less than the optimum value.

A voltage of ± 45 V to 55 V is applied to these liquid crystal cells.
When an AC voltage having a frequency of 40 Hz was applied for 15 minutes, a domain having a tilt angle θ of 20.1 ° began to appear, and at a voltage of 55 to 70 V, this domain spread over the entire area and a very good contrast was obtained. On the other hand, when the voltage was 70 V or more, many defects occurred, and the monodomain collapsed. The reversal between the bistable states after the appearance of the stable monodomain was performed with the following pulses.

[0053]

[Table 1] It is considered that the change in the orientation state after the application of the AC voltage is the effect of releasing the twist of the layer shown in FIG. The reversal voltage is higher than the reversal voltage before application, but the cause is not clear. However, in order for the tilt angle θ to approach Θ, the energy for reversing the liquid crystal molecules near the interface of the alignment film is also required. Therefore, it is necessary that the driving voltage required for inversion be high. Due to the tilt angle θ after the application of the AC voltage, the amount of transmitted light greatly increased the contrast ratio as compared with that before the application of the voltage. Also, stable switching was possible with a delay of optical response of 0.1 sec or less due to the anti-electric field effect.

The ferroelectric liquid crystal phase having a bistable state is usually obtained by lowering the temperature from a high temperature state. At this time, when the temperature is lowered while applying an AC electric field of 50 Hz and 140 V, a uniform monodomain over a wide range is obtained. The alignment state was realized.

(Example 4) A liquid crystal cell was manufactured using the PPy flowing alignment film (thickness: 10 nm, dichroic ratio: 48) prepared in Example 1 as an alignment film without rubbing treatment.
The same ferroelectric liquid crystal as in Example 3 was injected, and an AC voltage (40
Hz, 60 V) for 15 minutes, the tilt angle θ
A uniform monodomain orientation state of 21.7 ° appeared. When the same evaluation as in Example 1 was performed on the liquid crystal cell, good switching drive characteristics without hysteresis were exhibited. Further, it was found that a good liquid crystal cell having a significantly improved contrast ratio was obtained as compared with Example 1. When display was performed by multiplexing drive in the same manner as in Example 1, similar good results were obtained for contrast and afterimages. Even after the switching operation was performed 10 ⁷ times or more, no change occurred in the orientation state of the ferroelectric liquid crystal.

Example 5 A liquid crystal was obtained in the same manner as in Example 3 except that a PTPy alignment film (thickness: 10 nm, dichroic ratio: 45) was used instead of the PPy alignment film used in Example 4. When a cell was fabricated and evaluated, the tilt angle θ was 21.
A uniform 9 ° monodomain orientation appeared. When the same evaluation as in Example 1 was performed on the liquid crystal cell, good switching drive characteristics without hysteresis were exhibited. Further, it was found that a good liquid crystal cell having a significantly improved contrast ratio was obtained as compared with Example 1. When display was performed by multiplexing drive in the same manner as in Example 1, similar good results were obtained for contrast and afterimages. Even after the switching operation was performed 10 ⁷ times or more, no change occurred in the orientation state of the ferroelectric liquid crystal.

(Embodiment 6) In the production of the liquid crystal cell of Embodiment 1,
A liquid crystal cell was prepared in exactly the same manner as described above except that fine protrusions (size: 5 μm, height: 9 nm, interval: 10 μm) of regular square pillars of PPP were formed by vapor deposition using a mask pattern on the entire surface of the PPy alignment film. When the ferroelectric liquid crystal used in Example 3 was injected and the relationship between the transmittance and the peak value of the applied pulse of 50 μsec was measured, the characteristics shown by the solid line in FIG. 15 were obtained. As is clear from FIG. 15, the distribution of the regions having different threshold voltages over the entire pixel results in a transmittance / voltage characteristic having a wide transmission range (a transmission characteristic that changes gradually), and the halftone can be adjusted. I understood.

Although the PPP microprojections used in this example are square prisms, the shape is not limited to the examples, and the size, height, and spacing of the projections are not limited. The present invention is not limited to the embodiment, and differs depending on, for example, the material of the protrusion. The liquid crystal cell of this embodiment exhibits the same display characteristics as those of the other embodiments, and further has a transmittance having a wide transmission region (a transmission characteristic that changes gradually) by distributing regions having different threshold voltages over the entire pixel. / Voltage characteristic, and it was found that the display characteristics of halftone were also improved by mixing the conductive polymer compound with the polyimide alignment material.

[0059]

As described above, by using the alignment film of the present invention, a large tilt angle is generated particularly in the non-helical structure of the chiral smectic liquid crystal, and the contrast between the bright state and the dark state is high. The display contrast at the time of cusing driving is very large, and a high-quality display can be obtained, and further, an effect of not causing a noticeable afterimage phenomenon can be obtained.

It has been pointed out that when the spontaneous polarization Ps of the ferroelectric liquid crystal increases, the driving characteristics deteriorate due to the reverse electric field effect. However, the liquid crystal device of the present invention can provide good driving characteristics without the reverse electric field effect. It became so.

A liquid crystal alignment state was obtained in which there was no hysteresis at the time of driving, and the alignment was hardly disturbed by driving.

By using the liquid crystal element of the present invention, regions having different threshold voltages are distributed over the entire pixel,
Since the transmittance / voltage characteristic has a wide transmission range (a transmission characteristic that gradually changes), the halftone can be adjusted.

[Brief description of the drawings]

FIG. 1 is a schematic view showing one example of a ferroelectric liquid crystal device of the present invention.

FIG. 2 is a perspective view showing an alignment state of a chiral smectic liquid crystal having a helical structure.

FIG. 3 is a perspective view showing an alignment state of a non-helical chiral smectic liquid crystal.

FIG. 4 is an explanatory diagram showing a relationship between a uniaxial orientation axis of a substrate and an axis of a ferroelectric liquid crystal molecule having a non-helical structure.

FIG. 5 is a diagram illustrating an alignment state of liquid crystal molecules in the present invention.

FIG. 6 is an explanatory diagram of a tilt angle θ of a ferroelectric liquid crystal.

FIG. 7 is an explanatory diagram of a reverse electric field Vrev in a ferroelectric liquid crystal element.

FIG. 8 is an explanatory diagram showing a change in tilt angle θ due to application of an electric field.

FIG. 9 is a diagram showing optical response characteristics of a conventional liquid crystal element.

FIG. 10 is a diagram showing optical response characteristics of the liquid crystal element of the present invention.

FIG. 11 is a waveform diagram of a driving voltage according to the embodiment of the present invention.

FIG. 12 is a diagram showing a voltage-transmittance characteristic in the liquid crystal element of the present invention.

FIG. 13 is an applied voltage waveform diagram in the measurement of voltage-transmittance characteristics.

FIG. 14 is an explanatory diagram of an alignment film coating method using flow alignment.

FIG. 15 is a diagram showing a voltage-transmittance characteristic in a liquid crystal element using an alignment film having minute projections.

Claims (10)

(57) [Claims] 1. A liquid crystal element formed by sandwiching a ferroelectric liquid crystal between a pair of substrates having electrodes and Oriented films respectively, said Oriented films, conductive covering the electrode provided on the substrate
A linear π-conjugated conductive polymer is formed on a protective film imparted with a property, and has a structure in which a linear π-conjugated conductive polymer is one-dimensionally oriented in a direction substantially parallel to a substrate surface, and has an optical axis A ferroelectric liquid crystal device having a chromaticity ratio of 2 or more. 2. The ferroelectric liquid crystal device according to claim 1, wherein the linear π-conjugated conductive polymer is a rigid π-conjugated conductive polymer. 3. A ferroelectric liquid crystal device according to claim 1 or 2, characterized in that a conductive protrusions on Oriented film. 4. The ferroelectric liquid crystal device according to claim 3, wherein the conductive projection is a rigid π-conjugated conductive polymer. 5. The spontaneous polarization of a ferroelectric liquid crystal is 10
5. The composition according to claim 1, wherein the concentration is at least nC / cm ^2.
The ferroelectric liquid crystal device according to any one of the above. 6. The ferroelectric liquid crystal device according to claim 1, wherein an initial alignment state of the ferroelectric liquid crystal is obtained by applying an AC electric field. 7. The protective film having a conductivity of 10 ^-Ten S / cm or more
The ferroelectric liquid crystal element according to claim 1, wherein
Child. 8. The protective film having a conductivity of 10 ^-8 -10 ^-Five S / c
7. The ferroelectric liquid crystal element according to claim 1, wherein
Child. 9. The protective film is made of a metal oxide or a metal sulfide.
9. The ferroelectric liquid crystal element according to claim 1, comprising:
Child. 10. The protective film is made of a metal oxide and a metal sulfide.
Amorphous, comprising a mixture of
8. The ferroelectric liquid crystal device according to any one of 8.