JP2002031821A - Liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a liquid crystal display device exhibiting an excellent half tone. SOLUTION: As regards a ferroelectric liquid crystal display device A, in a lower substrate 20 pixel electrodes 12 and active elements 10 are formed on a transparent substrate 14 and an alignment layer 8 is laminated thereon, and in an upper substrate 19 a common electrode 4 and an alignment layer 6 are successively laminated on a transparent substrate 2. Furthermore, a liquid crystal layer 7 is constructed by applying an AC electric field to a ferroelectric liquid crystal composition containing a liquid crystalline (meth)acrylate monomer in the state exhibiting a chiral smectic C phase and making ultraviolet rays or electron rays irradiate the composition so as to make the liquid crystalline (meth)acrylate monomer photoset and polymerize.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a liquid crystal display, and more particularly, to a ferroelectric liquid crystal display.

[0002]

2. Description of the Related Art At present, a TN mode or a STN mode using a nematic liquid crystal is mainly used as a liquid crystal display element. In addition, a ferroelectric liquid crystal material has a high response speed and a wide viewing angle. It is noted for its excellent properties. It is described that the ferroelectric liquid crystal material proposed by Clark and Ragawall has spontaneous polarization such that the molecule has a permanent dipole moment perpendicular to the long axis of the molecule, and can be switched by an electric field ( JP-A-56-107216).

A liquid crystal display (display) using the ferroelectric liquid crystal material has the following advantages. First, the switching speed of the TN mode liquid crystal display device is on the order of milliseconds, but it achieves a high-speed response of about 1000 times as much as this. Second, there is basically no twisted structure in the molecular arrangement, and there is an operation (in-plane switching) by switching in the molecular direction in a plane horizontal to the substrate, and therefore, there is little viewing angle dependence.

However, in such a ferroelectric liquid crystal material, two orientation states are developed with respect to the threshold value of the applied voltage, and the states are stored as bistable, so that the light transmittance can be arbitrarily controlled. Can't do this,
There is a problem that it is difficult to control the halftone display, and it is not possible to realize the grayscale display. In order to solve this problem, there has been proposed a ferroelectric liquid crystal composition in which a hardened liquid crystalline (meth) acrylate is added to a ferroelectric liquid crystal material (Japanese Patent Application Laid-Open Nos. 11-21554 and 11-554). 3
26909).

Hereinafter, this technique will be described in detail. After injecting a ferroelectric liquid crystal composition containing a ferroelectric liquid crystal material and a liquid crystalline (meth) acrylate monomer into a liquid crystal cell, ultraviolet rays are applied while applying a DC voltage at a temperature at which the liquid crystal composition exhibits ferroelectricity. This is a ferroelectric liquid crystal display device obtained by irradiating and polymerizing a liquid crystalline (meth) acrylate monomer, whereby the bistability of the ferroelectric liquid crystal material is lost and halftone display is possible. It becomes.

In such a polymer-stabilized ferroelectric liquid crystal display device, when no voltage is applied, the alignment direction of the liquid crystal molecules is in the direction of the easy axis of the alignment film (the axis in which the liquid crystal molecules are easily aligned). From a certain angle in a direction determined by the polarity of the DC voltage applied at the time of ultraviolet irradiation. When this angle is defined as a memory angle, the memory angle is usually slightly smaller than the tilt angle of the ferroelectric liquid crystal itself.

Therefore, when driving such a ferroelectric liquid crystal display device, if a DC voltage having the same polarity as the DC voltage applied at the time of irradiating the ultraviolet rays is applied, the ferroelectric liquid crystal material can be driven above a certain voltage. Makes an angle larger than the memory angle with respect to the easy axis of the alignment film. Then, when the applied voltage is removed, the ferroelectric liquid crystal is again arranged at a position having a memory angle with respect to the easy axis of the alignment direction because the bistability is lost.

On the other hand, when a DC voltage of a different polarity is applied to the polymer-stabilized liquid crystal liquid crystal element with respect to the DC voltage applied at the time of irradiating the ultraviolet light, the voltage is proportional to the absolute value of the DC voltage.
The orientation direction of the ferroelectric liquid crystal material is inclined in a direction opposite to the direction of the memory angle with respect to the easy axis of the orientation film. Even in this case, since the bistability has disappeared, if the applied voltage is removed, the ferroelectric liquid crystal material is again arranged at a position having a memory angle with respect to the easy axis of the alignment film. As described above, the halftone display can be performed by utilizing the change in the orientation direction when a voltage having a different polarity is applied to the applied DC voltage at the time of ultraviolet irradiation.

As another technique for performing halftone display, a liquid crystal display device using an antiferroelectric liquid crystal material has been proposed (JP-A-8-328046, JP-A-9-500).
No. 47 and JP-A-10-307304). According to this proposal, an antiferroelectric liquid crystal material having two ferroelectric phases and one antiferroelectric phase in a stable state is sealed between a pair of substrates. A liquid crystal material having a characteristic of forming a ferri phase in which liquid crystal molecules exhibiting one ferroelectric phase) and liquid crystal molecules exhibiting the other ferroelectric phase (second ferroelectric phase) are used. According to such a liquid crystal display device using an antiferroelectric liquid crystal, when a sufficiently high voltage is applied at the positive polarity, the liquid crystal molecules are oriented to exhibit the first ferroelectric phase, and the negative polarity is sufficient. When a high voltage is applied, the liquid crystal molecules are oriented to exhibit the second ferroelectric phase.

When an intermediate voltage is applied, the alignment direction of a part of the liquid crystal molecules is reversed in accordance with the polarity, and the liquid crystal in the alignment state showing the first ferroelectric phase or the second ferroelectric phase. The number of molecules decreases, and on the other hand, the number of aligned liquid crystal molecules exhibiting the second ferroelectric phase or the first ferroelectric phase increases. ,
The ratio of the liquid crystal molecules in the alignment state exhibiting the second ferroelectric phase changes continuously according to the polarity and value of the applied voltage.

Therefore, in the optical characteristics of a liquid crystal display device using this antiferroelectric liquid crystal material, the applied voltage is 0 V
In the vicinity, there is no flat portion, and as the value of the applied voltage increases, the optical characteristics also increase continuously and smoothly, and the transmittance curve becomes symmetrical with respect to the polarity of the applied voltage. Can be displayed.

[0012]

As described above, halftone display can be performed by using either a ferroelectric liquid crystal material or an antiferroelectric liquid crystal material. There are issues. First, a problem of a ferroelectric liquid crystal display device using a ferroelectric liquid crystal material will be described. (A) In a polymer-stabilized ferroelectric liquid crystal display device, the absolute value of the deflection angle of the ferroelectric liquid crystal molecules does not become equal even if a DC voltage having the same absolute value is applied from the above operation principle, The same light transmittance was not obtained even when DC voltages of different polarities having the same absolute value were applied.

(B) By using only a voltage having a polarity that provides a continuous voltage-transmittance characteristic, an undesired static charge is accumulated in the liquid crystal display device, thereby causing a problem such as display burn-in. Was. (C) It is conceivable to use a voltage of both positive and negative polarities in order to cancel the DC component which causes the accumulation of the electrostatic charge. However, when such a voltage is applied, the change in the light transmittance is very small. During the application of the voltage, the display is invalidated, and the period of time in which a predetermined selection state is taken is shortened. Further, there is a problem that the display flickers due to an invalid state.

(D) If the signal application period is further limited, a part of the period must be assigned to an invalid pulse for canceling the DC component, and the pulse width of the write signal becomes narrower, and the usable ferroelectricity is reduced. The liquid crystal material is limited to a material having a response speed that can follow it. On the other hand, in a liquid crystal display device using an antiferroelectric liquid crystal material, as described above, the voltage-transmittance characteristic is symmetric with respect to the polarity of the applied voltage, and therefore, in a polymer stabilized ferroelectric liquid crystal display device, Although the problems arising have been solved, on the other hand, the antiferroelectric liquid crystal material itself has unique physical properties, and the degree of freedom in selecting a material having both temperature characteristics and a spontaneous polarization value suitable for active driving is extremely high. It was getting smaller.

[0015]

Accordingly, the present inventor has conducted intensive studies in view of the above circumstances, and as a result, has found that the liquid crystal (meta)
An AC electric field is applied to the ferroelectric liquid crystal composition containing an acrylate monomer in a state showing a chiral smectic C phase, and the polymer is polymerized by irradiating an ultraviolet ray or an electron beam. In contrast, the inventors have found that a voltage-transmittance characteristic is symmetrical, and a liquid crystal display device capable of halftone display can be obtained.

The present invention has been completed based on the above findings, and has as its object the use of a ferroelectric liquid crystal composition containing a liquid crystalline (meth) acrylate monomer to provide high quality and high quality halftone display. An object of the present invention is to provide a high-performance ferroelectric liquid crystal display device. The liquid crystal display device of the present invention is such that a ferroelectric liquid crystal layer is interposed between a pair of substrates, and an electrode portion for applying a voltage to the ferroelectric liquid crystal layer is provided on the inner surfaces of both substrates, and The ferroelectric liquid crystal layer applies an AC electric field to a ferroelectric liquid crystal composition containing a liquid crystalline (meth) acrylate monomer in a state showing a chiral smectic C phase and irradiates an ultraviolet ray or an electron beam. , Characterized in that the liquid crystal (meth) acrylate monomer is cured and polymerized.

Further, another liquid crystal display device of the present invention is characterized in that the liquid crystalline (meth) acrylate is represented by the following chemical formula 2.

[0018]

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[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS (Embodiment 1) Hereinafter, the present invention will be described in detail with reference to FIGS. FIG. 1 is a schematic sectional view of a ferroelectric liquid crystal display device A of the present invention, and FIG. 2 is a schematic plan view showing a lower substrate of the ferroelectric liquid crystal display device A of the present invention.

The ferroelectric liquid crystal display device A has a structure in which a pair of upper and lower substrates 19 and 20 are joined to each other with a predetermined gap therebetween. In the lower substrate 20, a transparent substrate 14 made of glass or the like is provided. A protective film 13 made of SiO ₂ or the like is covered, and a transparent pixel electrode 12 made of ITO or the like and the active elements 10 connected to the pixel electrode 12 are formed in a matrix on the protective film 13. I have.
Then, S on the pixel electrode 12 and the active element 10
sequentially laminating an alignment film 8 made iO ₂ or SiN or the like made of an insulating film 9 and the polyimide resin.

The active element 10 is composed of, for example, a thin film transistor (TFT 10a).
Oa includes a gate electrode, a gate insulating film covering the gate electrode, a semiconductor layer formed on the gate insulating film, and a source electrode and a drain electrode formed on the semiconductor layer. Further, as for the lower substrate 20, as shown in FIG. 2, the scanning electrodes (scanning lines) 11 are wired between the rows of the pixel electrodes 12 on the transparent substrate 14, and the signal electrodes 16 are wired between the columns of the pixel electrodes 12. I have. The gate electrode of each TFT 10a is connected to the scanning line 11, and the drain electrode is the signal line 1.
6 is connected. The scanning line 11 is connected to a gate driver 18, and the signal line 16 is connected to a source driver 17.

On the other hand, in the upper substrate 19, the transparent substrate 2
Is covered with a protective film 3 made of SiO ₂ or the like, and a transparent common electrode 4 made of ITO or the like is formed on the protective film 3 so as to face the pixel electrodes 12 and a reference voltage is applied.
Further, an insulating film 5 made of SiO ₂ or SiN and an alignment film 6 made of polyimide resin or the like are sequentially laminated on the common electrode 4. As the alignment films 6 and 8, a conventionally known polyimide alignment film subjected to a rubbing process may be used. In addition, a UV alignment is performed by irradiating a polyvinyl thin film or a polyimide thin film with ultraviolet light so that the rubbing process is not required. A membrane may be used.

In the liquid crystal cell having such a configuration, the polarizing plates 1 and 15 are provided outside the pair of upper and lower substrates 19 and 20.
Then, by applying a voltage between the pixel electrode 12 and the common electrode 4, the orientation direction of the liquid crystal molecules in the liquid crystal layer 7 is controlled, and the director (the average direction of the long axis of the liquid crystal molecules) is controlled.
Is continuously changed, whereby the optical axis of the liquid crystal layer 7 is continuously controlled, whereby a display gradation can be obtained.

Next, the alignment state of liquid crystal molecules in the liquid crystal layer 7 will be described. According to the present invention, the liquid crystal layer 7 applies an AC electric field to the ferroelectric liquid crystal composition containing a liquid crystalline (meth) acrylate monomer while exhibiting a chiral smectic C phase, and irradiates ultraviolet rays or electron beams. In this way, the liquid crystal (meth) acrylate monomer is photo-cured and polymerized, and thereby the average orientation direction of the liquid crystal skeleton of the polymerized liquid crystal (meth) acrylate is enhanced. It is almost coincident with the normal direction of the smectic layer of the dielectric liquid crystal.

Referring to FIG. 3, P indicates the transmission axis direction in the polarizing plate 1, A indicates the transmission axis direction in the polarizing plate 15, and 21a indicates the average of the liquid crystal skeleton of liquid crystal (meth) acrylate. 21b is the normal direction (rubbing direction) of the smectic layer of the ferroelectric liquid crystal, and the average alignment direction 21a of the liquid crystalline skeleton of the polymerized liquid crystalline (meth) acrylate is the ferroelectric liquid crystal. It is almost coincident with the normal direction 21b of the smectic layer of the liquid crystal. That is, according to the ferroelectric liquid crystal display device A, the average orientation direction of the ferroelectric liquid crystal layer 7 when no drive voltage is applied is obtained when the polarizing plates 1 and 15 are arranged in a crossed Nicols state. From the positional relationship of the maximum dark state to be obtained, it substantially matches the normal direction 21b of the smectic layer.

Although the present inventors have not been able to get out of the range of inference, the present inventors have found that a liquid crystal (meta-state) is obtained by irradiating an ultraviolet ray or an electron beam and applying an AC electric field in particular while exhibiting a chiral smectic C phase. ) The liquid crystal skeleton (liquid crystalline skeleton 21a) of the acrylate photo-cured product almost coincides with the normal direction 21b of the smectic layer, and cannot be caused by the application of a direct current electric field in the direction of emission of the smectic layer of the liquid crystalline skeleton 21a. This is considered to have contributed favorably to the orientation of.

Thus, the ferroelectric liquid crystal display device A of the present invention
According to the method, when a voltage (positive or negative) having a different polarity is applied, the orientation direction of the ferroelectric liquid crystal material is continuously in a form proportional to the absolute value of the applied voltage, and furthermore, in two bistable states. Approaching the position of each bistable state corresponding to the respective polarities, and the optical characteristics of such a liquid crystal display device show a maximum dark state without a flat portion near an applied voltage of 0 V. With an increase in the absolute value of, the optical characteristics also increase continuously and smoothly, and the transmittance curve also becomes symmetrical with respect to the polarity of the applied voltage, whereby an excellent halftone display can be realized.

According to the present invention, a conventionally well-known ferroelectric liquid crystal material can be used. Preferably, a material exhibiting a smectic A phase in a temperature range above a chiral smectic C phase is preferably used. . In order to obtain an optimum good orientation state, it is preferable to use a material exhibiting a smectic A phase and a nematic phase in a temperature range higher than the smectic C phase. As the liquid crystalline (meth) acrylate monomer, a polymer obtained by photocuring exerts an alignment stabilizing effect on the ferroelectric liquid crystal material, and furthermore, does not cause an increase in the driving voltage of the ferroelectric liquid crystal material. Those having a small effect on the phase transition temperature are preferred.

The liquid crystalline (meth) acrylate is a monofunctional (meth) acrylate which is an acrylic acid or methacrylic acid ester of a cyclic alcohol, phenol or aromatic hydroxy compound having a liquid crystal skeleton having at least two 6-membered rings as a partial structure. A) Acrylate is preferred. According to such a monofunctional (meth) acrylate, (meth)
There is no flexible linking group such as an alkylene group or an oxyalkylene group between the acryloyloxy group and the liquid crystal skeleton (referred to as a spacer in the liquid crystal technical field), and therefore, it is obtained by polymerizing a monofunctional (meth) acrylate. A rigid liquid crystal skeleton is directly bonded to the main chain of the polymer without using a spacer, so that the thermal motion of the liquid crystal skeleton is restricted from that of the polymer main chain, and as a result, the ferroelectric liquid crystal material is aligned. A stabilizing effect is provided. In addition, since the polymer is a monofunctional (meth) acrylate, the polymer does not form a three-dimensional cross-linked structure even when photocured, and therefore, the driving voltage caused by surrounding the ferroelectric liquid crystal with the polymer cage. Rise is avoided.

An example of the above liquid crystalline (meth) acrylate is shown in Chemical formula 3.

[0031]

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With respect to the liquid crystalline (meth) acrylate having such a molecular structure, in particular, X is a hydrogen atom, n is zero (0), and the six-membered rings A and C are each independently 1,4. A phenylene group or a 1,4-transcyclohexyl group. Further, Y1 is a single bond or -C≡
C- and Y ₂ are a single bond, Z is a halogen atom, a cyano group or an alkyl group or an alkoxy group having 1 to 20 carbon atoms, and if such a compound is used, it is easy to develop a liquid crystal phase near room temperature. Moreover, it is preferable in that it is easy to handle.

A compound having a pyrimidine ring introduced into any of rings A, B, and C is preferable because it easily exhibits a smectic liquid crystal phase and has excellent compatibility with a ferroelectric liquid crystal material. Examples of such liquid crystalline (meth) acrylate compounds are shown in Chemical formulas 4 to 24. The monofunctional (meth) acrylate in the liquid crystal composition of the present invention is not limited to these.

[0034]

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[0035]

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[0036]

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[0037]

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[0038]

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[0039]

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[0040]

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[0041]

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[0042]

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[0043]

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[0044]

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[0045]

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[0046]

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[0047]

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[0048]

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[0049]

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[0050]

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[0051]

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[0052]

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[0053]

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[0054]

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In the chemical formulas 4 to 24, the cyclohexane ring is a transcyclohexane ring, C is a crystal phase, N is a nematic phase, S is a smectic phase, I is an isotropic liquid phase, and the numbers are phase transitions. Represents temperature. Among these compounds, the use of compounds of formulas 19 and 20 having an optically active group is preferred in that the helical pitch can be finely adjusted and the driving voltage is reduced.

The concentration of the liquid crystal (meth) acrylate in the liquid crystal composition containing the liquid crystal (meth) acrylate and the ferroelectric liquid crystal material is preferably adjusted to 3 to 10% by weight, more preferably 4 to 10% by weight. ~ 9 wt%, optimally 6-8
It is good to be the weight%. If the concentration of the liquid crystalline (meth) acrylate is less than 3% by weight, the effect of stabilizing the alignment may not be obtained depending on the type of the liquid crystal material, and the desired operating characteristics may not be obtained. The driving voltage of the ferroelectric liquid crystal material tends to increase.

The thickness of the liquid crystal layer 7 depends on the refractive index anisotropy of the ferroelectric liquid crystal material, but may be 1 to 20 μm.
Preferably it is 1.3 to 10 μm, most preferably 1.5 to 6 μm. If the thickness of the liquid crystal layer 7 is less than 1 μm, sufficient optical switching may not be obtained, and the contrast tends to decrease. On the other hand, if the thickness of the liquid crystal layer 7 exceeds 10 μm, a spiral structure of a ferroelectric liquid crystal material may be formed, and bistability may not be obtained.

To a liquid crystal composition containing a liquid crystal acrylate monomer and a ferroelectric liquid crystal material, a photopolymerization initiator is added in order to rapidly perform photocuring of the photocurable composition in the chiral smectic C phase. Is also good. The photopolymerization initiator may be selected from, for example, known benzoin ethers, benzophenones, acetophenones, and benzyl ketals. The addition amount is 10 to the liquid crystal acrylate monomer contained in the liquid crystal composition.
It is preferable that the content is not more than% by weight.

Further, a stabilizer may be added to the liquid crystal composition containing the liquid crystal acrylate monomer and the ferroelectric liquid crystal material, whereby the storage stability is improved. The stabilizer may be selected from, for example, known hydroquinones, hydroquinone monoalkyl ethers, tertiary butyl catechols and the like. The amount of the stabilizer added may be 0.05% by weight or less based on the photocurable composition contained in the liquid crystal composition.

The irradiation amount of ultraviolet rays or electron beams in the step of polymerizing the photocurable composition depends on the concentration of the liquid crystal composition and the photopolymerization initiator.
The range is preferably 000 mJ / cm ² . The dose of ultraviolet rays or electron beams, the less than 50 mJ / cm ^2, may photocurable composition is not sufficiently cured, which change over time after production by increases, the liquid crystal composition exceeds 10000 mJ / cm ² The thing itself tends to deteriorate.

The frequency of the AC electric field applied in the step of irradiating the ultraviolet ray or the electron beam depends on the response speed of the ferroelectric liquid crystal material, but is preferably in the range of 50 Hz to 6 kHz, more preferably 1 kHz to 5 kHz. Well, especially 2kHz-4
kHz is preferred. When the frequency is less than 50 Hz, the orientation uniformity can be obtained, but on the other hand, the luminance in the dark state increases and the chromaticity of black tends to deteriorate. On the other hand, when the frequency exceeds 6 kHz, uniform orientation cannot be obtained.

Further, the amplitude of the applied AC electric field is
It is preferable that the size is set to be higher than the voltage at which the ferroelectric liquid crystal responds. Below the voltage at which the ferroelectric liquid crystal responds, the change in the orientation of the ferroelectric liquid crystal molecules does not occur due to the alternating electric field, and the smectic layer of the liquid crystal skeleton in the liquid crystal (meth) acrylate is considered to be caused by the response of the ferroelectric liquid crystal molecules. Good orientation in the normal direction cannot be obtained. Further, the ferroelectric liquid crystal layer is preferably in a state where the liquid crystal composition of the chiral smectic C phase has lost the helical structure. By making the spiral structure disappear,
It becomes easier to obtain good alignment of the smectic layer of the liquid crystal skeleton in the liquid crystal (meth) acrylate in the normal direction. (Embodiment 2) In the ferroelectric liquid crystal display device A shown in (Embodiment 1), the active element 10 is constituted by a TFT, but in the ferroelectric liquid crystal display device B of this embodiment, the active element A metal insulator metal element (MIM) 10b was used instead of the element 10.

FIG. 9 and FIG. 10 show such a ferroelectric liquid crystal display device B. FIG. 9 is a schematic sectional view of the ferroelectric liquid crystal display device B, and FIG. 10 is a schematic plan view showing a wiring pattern of the ferroelectric liquid crystal display device B. The same reference numerals as those of the ferroelectric liquid crystal display device A shown in FIGS. 1 and 2 indicate the same members. The MIM 10 b includes a scan electrode, an insulating film formed by, for example, anodic oxidation so as to cover the scan electrode, and a conductive film formed on the insulating film. The conductive film is connected to the pixel electrode 12. Have been. Also, 22
Denotes a liquid crystal layer 7 between the pixel electrode 12 and the signal electrode 4a and between the two.
Is a liquid crystal display pixel portion constituted by.

Further, as shown in FIG. 10, the scanning electrodes 11 are wired between the rows of the pixel electrodes 12 on the transparent substrate 14, and are connected to the scanning driver 18a. Upper substrate 19
, A transparent signal electrode 4a facing each pixel electrode 12 of the lower substrate 20 is formed. The signal electrode 4a is made of ITO or the like, is formed in a stripe shape on the pixel electrode 12, and is connected to the data driver 17a as shown in FIG.

Also in the ferroelectric liquid crystal display device B having the above-described structure, by applying a voltage to the liquid crystal display pixel section 22, the orientation direction of the liquid crystal molecules in the liquid crystal layer 7 is controlled, and the magnitude of the voltage and And / or by changing the period during which the voltage is applied, the director (the average direction of the long axis of the liquid crystal molecules) is continuously changed, thereby changing the liquid crystal layer 7.
Are controlled continuously, and the display gradation is favorably controlled. (Embodiment 3) In the ferroelectric liquid crystal display device A shown in (Embodiment 1), the active element 10 is constituted by a TFT, but in the ferroelectric liquid crystal display device C of this embodiment, the active element is As another mode related to the driving using the TFT, a method using a field-effect transistor formed on a single crystal silicon substrate instead of the TFT was used.

FIG. 11 shows a ferroelectric liquid crystal display device having the same structure as an active element formed of a TFT except that a field effect transistor formed on a single crystal silicon substrate is used and a pixel electrode is formed as a reflector. It is a schematic sectional drawing of C. This ferroelectric liquid crystal display device C also has a configuration in which a transparent substrate 23 and a single-crystal silicon substrate 29 are joined to each other with a predetermined gap therebetween, and a transparent common electrode 4 made of ITO or the like is formed on the transparent substrate 23. And a reference voltage is applied. Further, an insulating film 5 made of SiO ₂ or SiN and an alignment film 6 made of polyimide resin or the like are sequentially laminated on the common electrode 4.

The field effect transistors P are arranged in a matrix on the single crystal silicon substrate 29 by using the DRAM technique. The field effect transistor P has a scan electrode (scan line) 1
1, signal line 16, drain electrode 30, and source electrode 3
1 Then, SiO ₂ or S
iN consisting like insulation film 28, made of aluminum and chromium, the light shielding layer 27 made of silver, a planarization film 26 made of resin or SiO _2, SiN, the reflective pixel electrode 25 made of aluminum or the like, resin or SiO _2, SiN The dielectric layer 24 and the alignment film 8 made of polyimide resin or the like are sequentially laminated. Each reflection pixel electrode 25 is connected to the field effect transistor 22 via the source electrode 31.

Also in the ferroelectric liquid crystal display device C having the above configuration, by applying a voltage to the reflective pixel electrode 25 and the common electrode 4, the orientation direction of the liquid crystal molecules is controlled, and the director (liquid crystal molecules) is controlled. (The average direction of the long axis) is continuously changed, whereby the optical axis of the liquid crystal layer 7 is continuously controlled, and the display gradation is controlled.

[0069]

Embodiments of the present invention will be described below. (Example 1)
The ferroelectric liquid crystal display devices A, B and C of the present invention are
(Example 2) shows a comparative example. (Example 1) The active matrix driving type ferroelectric liquid crystal display devices A, B, and C shown in FIGS. 1 and 2 and FIGS. 9, 10 and 11 were produced. For the alignment films 6 and 8, a polyimide film RN-1199 (manufactured by Nissan Chemical Industries, Ltd.) was used.
を was formed and rubbed. The rubbing direction between the two substrates was set to be parallel. Further, the thickness of the liquid crystal layer 7 is set to 1.5 μm.
m, for which a spherical spacer was provided.

In order to adjust the liquid crystal composition, 49.5% by weight of the compound represented by Chemical Formula 25 and 4% by weight of the compound represented by Chemical Formula 26 were used.
A liquid crystalline acrylate composition (a) containing 9.5% by weight and 1% by weight of Irgacure 651 (manufactured by Ciba Geigy) as a photopolymerization initiator was prepared. This liquid crystalline acrylate (a) exhibits a nematic liquid crystal phase at room temperature, and has a clearing point of 41 ° C.

[0071]

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[0072]

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Next, the liquid crystal cell was maintained at a temperature of 100 ° C., and 6% by weight of the liquid crystalline acrylate composition (a) prepared as described above was mixed with a ferroelectric liquid crystal material FELIX.
A liquid crystal composition containing 4851/100 (manufactured by Clariant) at 94% by weight was injected, then the temperature of the liquid crystal cell was lowered to room temperature, and the liquid crystal composition injected into the liquid crystal cell was transferred to a chiral smectic C phase. Was. Thereafter, while applying a triangular wave signal having a frequency of 2 kHz and an amplitude of ± 10 V between the pixel electrode 12 and the common electrode 4, 250 mJ / cm 2
Irradiation of ultraviolet light of ² .

After the irradiation of the ultraviolet rays, the alignment of the liquid crystal molecules was examined by a polarizing microscope in a state where no voltage was applied.
It was confirmed that the liquid crystal molecules were averagely oriented substantially perpendicular to the smectic layer and substantially parallel to the rubbing direction. Then
Two polarizing plates 1 and 15 were arranged on both sides of the liquid crystal cell. One of the polarizing plates was set so that the polarization axis was parallel to the orientation direction of the liquid crystal molecules, and the polarization axis of the other polarizing plate was perpendicular to the orientation direction of the liquid crystal molecules.

A voltage was applied to the ferroelectric liquid crystal display device A thus manufactured, and a voltage-transmittance characteristic was measured. The result is shown in FIG. The horizontal axis is the applied voltage, the unit is volt (V), and the vertical axis is the light transmission intensity, which is shown as a relative value. As is apparent from this result, the maximum dark state is obtained when the applied voltage is near 0 V, and the optical characteristics continuously and smoothly increase as the absolute value of the applied voltage increases. Furthermore, the light transmittance curve is also symmetric with respect to the polarity of the applied voltage.

When the present inventors operate using the same signal as that of the TFT drive as shown in FIG. 5, almost the same light transmission intensity can be obtained for applied voltages of different polarities, and thereby, there is no flicker. Halftone display was completed. (Example 2) Ferroelectric liquid crystal display device A manufactured in (Example 1)
In the above, while maintaining the liquid crystal cell at 100 ° C., 2% by weight of the liquid crystalline acrylate composition (a) adjusted as described above
And a liquid crystal composition composed of 98% by weight of a ferroelectric liquid crystal material FELIX4851 / 100 (manufactured by Clariant), and thereafter, the temperature of the liquid crystal cell is lowered to room temperature, and the liquid crystal composition injected into the liquid crystal cell is subjected to chiral smectic C. The phase was transferred to.

Next, while applying a DC voltage of 4 V between the pixel electrode 12 and the common electrode 4, ultraviolet rays of 120 mJ / cm ² were irradiated. After such ultraviolet irradiation, the alignment of the liquid crystal molecules was examined with a polarizing microscope under no voltage application. As shown in FIG. 6, the liquid crystal molecules were tilted to the right by 17 degrees from the rubbing direction, as shown in FIG. all right. Next, two polarizing plates 1 and 15 were arranged on both sides of the liquid crystal cell. At that time, the polarization axis of one polarizing plate is parallel to the direction inclined to the right by 17 degrees from the rubbing direction, and the polarization axis of the other polarizing plate is perpendicular to the direction inclined to the right from the rubbing direction. Was set as follows.

When a voltage was applied to the ferroelectric liquid crystal display device thus manufactured and the voltage-transmittance characteristics were measured in the same manner, the results shown in FIG. 7 were obtained. As is apparent from this result, in this ferroelectric liquid crystal display device, halftone display is possible, but the same transmittance cannot be obtained when voltages of different polarities are applied even if the absolute value is the same. You can see that. Therefore, when the ferroelectric liquid crystal display device having such a configuration is operated by TFT driving, as shown in FIG. 8, in order to cancel the DC component that causes display deterioration such as burn-in, it is necessary to apply both positive and negative voltages. Must be used. At this time, a period during which a voltage having a small change in transmittance is applied is an erasing period in which display is invalid. If this period exists,
The drive takes a short period of time for a predetermined selection state effective for display, and the display state flickers under the influence of this period. In addition, if the transmittance during the erasing period is increased, it causes light leakage in a dark state, and the contrast is reduced.

The present invention is not limited to the above embodiment, and various changes and improvements can be made without departing from the scope of the present invention. For example, in the above embodiment, the case where a thin film transistor (TFT) element is used as an active element as a liquid crystal display device has been described. However, instead of this, an active element such as a thin film diode (TFD) element is used. By controlling the voltage value or the voltage application period applied to the ferroelectric liquid crystal layer, the average direction of the director of the ferroelectric liquid crystal layer is continuously changed according to the applied signal, whereby the gradation display is performed. May be performed.

[0080]

As described above, according to the liquid crystal display device of the present invention, a ferroelectric liquid crystal layer is interposed between a pair of substrates, and a voltage is applied to the inner surfaces of both substrates to the ferroelectric liquid crystal layers. An electrode portion is provided, and a ferroelectric liquid crystal layer applies an AC electric field to the ferroelectric liquid crystal composition containing a liquid crystalline (meth) acrylate monomer in a state showing a chiral smectic C phase, and emits ultraviolet light. Alternatively, the liquid crystal (meth) acrylate monomer is cured and polymerized by irradiating an electron beam, thereby controlling the orientation direction of the liquid crystal molecules and continuously changing the director. As a result, the optical axis of the liquid crystal layer was continuously controlled, and as a result, a high-quality and high-performance liquid crystal display device with excellent halftone display was obtained.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of a liquid crystal display device of the present invention.

FIG. 2 is a plan view showing a schematic configuration of a lower substrate of the liquid crystal display device of the present invention.

FIG. 3 is a schematic diagram illustrating an alignment state of a liquid crystal layer in the present invention.

FIG. 4 is a diagram showing an applied voltage-transmittance characteristic in the liquid crystal display device of the present invention.

FIG. 5 is a diagram showing a timing chart when a TFT drive signal is used in the present invention.

FIG. 6 is a schematic diagram illustrating an alignment state of a liquid crystal layer in a conventional liquid crystal display device.

FIG. 7 is a diagram illustrating an applied voltage-transmittance characteristic in a conventional liquid crystal display device. Graph.

FIG. 8 is a diagram illustrating a timing chart when a TFT drive signal is used in the related art.

FIG. 9 is a schematic sectional view of another liquid crystal display device of the present invention.

FIG. 10 is a plan view showing a wiring pattern of another liquid crystal display device of the present invention.

FIG. 11 is a schematic sectional view of still another liquid crystal display device of the present invention.

[Explanation of symbols]

 A, B, C Ferroelectric liquid crystal display device 1, 15 Polarizer 2, 14, 23 Transparent substrate 3, 13 Protective film 4 Common electrode 5, 9 Interlayer insulating film 6, 8 Alignment film 7 Liquid crystal layer 10 Active element 10a TFT Element 10b MIM element 11 Scan electrode 12 Pixel electrode 4a, 16 Signal electrode 17 Source driver 18 Gate driver 17a Data driver 18a Scan driver 19 Upper substrate 20 Lower substrate 22 Liquid crystal display pixel part P Field effect transistor 24 Dielectric layer 25 Reflection pixel Electrode 26 Flattening film 27 Light-shielding layer 28 Interlayer insulating film 29 Single crystal silicon substrate 30 Drain electrode 31 Source electrode 32 Retardation plate 21a Liquid crystal skeleton of liquid crystalline acrylate 21b Normal direction (rubbing direction) of smectic layer

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Yoshio Miyazaki 999-3, Hayato-cho, Aira-gun, Kagoshima Prefecture KYOCERA Inside Hayato Kagoshima Co., Ltd. F Term (in reference) 2H088 EA02 GA04 GA06 HA08 JA17 LA09 MA13 2H090 HB08Y KA14 MA05 MB12 MB14 4H027 BA06 BA13 BB03 BD08 BD21

Claims (2)

[Claims] A ferroelectric liquid crystal layer interposed between a pair of substrates;
A liquid crystal display device comprising an electrode portion for applying a voltage to a ferroelectric liquid crystal layer on each of inner surfaces of both substrates,
The ferroelectric liquid crystal layer, while applying an AC electric field to the ferroelectric liquid crystal composition containing a liquid crystalline acrylate monomer in a state showing a chiral smectic C phase, by irradiating ultraviolet rays or electron beams, A liquid crystal display device having a configuration made to polymerize with a liquid crystal acrylate monomer. 2. The liquid crystal display device according to claim 1, wherein said liquid crystalline acrylate is represented by the following chemical formula 1. Embedded image