JP2003195311A - Method for manufacturing liquid crystal element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To stabilize picture quality. <P>SOLUTION: A chiral smectic liquid crystal 2 is disposed in a gap between a pair of substrates as shown in figure 1. For the chiral smectic liquid crystal 2, a liquid crystal exhibiting a phase transition sequence of an isotropic liquid phase (ISO.) - a cholesteric phase (Ch) - a chiral smectic C phase (SmC*), or an isotropic liquid phase (ISO.) - a chiral smectic C phase (SmC*) recited from the higher temperature side is used, and a rectangular wave alternating voltage is applied to the liquid crystal via electrodes 3a, 3b. Owing to the voltage application, moving ions in the liquid crystal are adsorbed on alignment layers 5a, 5b and are decreased. As a result, the picture quality is stabilized even when driving voltage application to the electrodes 3a, 3b is continued to display a picture. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a liquid crystal device having a chiral smectic liquid crystal.

[0002]

2. Description of the Related Art (1) Conventionally, a nematic liquid crystal has been used for a liquid crystal element, but this nematic liquid crystal has a problem that the response speed is slow. Hereinafter, that point will be described in detail.

Conventionally, as a liquid crystal element using a nematic liquid crystal, an active matrix type (that is, a type in which an active element such as a transistor is arranged in each pixel) has been developed.

A twisted nematic mode is widely known as a mode of the nematic liquid crystal used in the active matrix type liquid crystal element. The details of the mode are described in “For example, M. Schadt and Double.
Applie by W. Helfrich
d Physics Letters Volume 18, Issue 4 (Published February 15, 1971), pages 127-128.
Page ”.

However, in the twisted nematic mode [TN mode], since the response speed of the liquid crystal is as slow as several tens of ms, it cannot cope with the video rate and is not suitable for displaying moving images.

(2) Unlike such a nematic liquid crystal,
Smectic liquid crystals such as ferroelectric liquid crystals and anti-ferroelectric liquid crystals are expected to be applied to the next-generation displays and the like because they can increase the response speed because they perform inversion switching due to spontaneous polarization. The liquid crystal will be described below.

A device in which liquid crystal exhibits bistability (SSFLC /
Surface Stabilized FLC by Clark and Lagerwell
all) (JP-A-56-1072).
16 and U.S. Pat. No. 4,367,924). As the liquid crystal exhibiting this bistability, a ferroelectric liquid crystal exhibiting a chiral smectic C phase is generally used. In this ferroelectric liquid crystal, when a voltage is applied, the voltage acts on the spontaneous polarization of the liquid crystal molecules to cause the inversion switching of the molecules, so that a very fast response speed is obtained and a bistable state with a memory property is exhibited. Can be made. Further, since it has excellent viewing angle characteristics, it is considered to be suitable as a high-speed, high-definition, large-area display element or light valve.

A liquid crystal element (SSFLC) using a bistable ferroelectric liquid crystal will be briefly described with reference to FIG. Reference numerals 124 and 125 in the figure indicate polarizers, and reference numerals 124a and 125a indicate the directions of the respective polarization axes. Reference numeral 122 indicates a liquid crystal element, the liquid crystal average molecular axis of which is 122 a or 122 depending on the polarity of the applied voltage.
The position shown in b is selectively taken. Here, strictly speaking, the liquid crystal average molecular axis indicates either the high refractive index axis or the low refractive index axis in the liquid crystal layer plane of the refractive index ellipsoid formed by the liquid crystal layer.

Now, when the liquid crystal average molecular axis is 122a, the light rays passing through the polarizer 124 pass through the liquid crystal element 122 while maintaining the polarization state and reach the polarizer 125. Since the polarization direction 125a and the polarization direction 122a of the light beam are orthogonal to each other, the light beam cannot pass through the polarizer 125, and the light beam exhibits a black state. On the other hand, when the average molecular axis of the liquid crystal is 122b, the light ray passing through the polarizer 124 is polarized and rotated by the birefringence characteristic of the liquid crystal panel 122 to take the azimuth indicated by reference numeral 125a, and the polarizer is left as it is. It passes through 125 and exhibits a white state.
The transmittance at this time is represented by sin ² (2θ) · sin ² (π · Δnd / λ) (see “Liquid Crystal Device Handbook (edited by the 142nd Committee, Japan Society for the Promotion of Science)”). Here, θ is the cone angle of the chiral smectic liquid crystal, Δn is the birefringence of the liquid crystal, d is the distance between the substrates, and is the wavelength of the light beam. In designing a display element, a wavelength around 550 nm, which is the peak wavelength of the human spectral luminous efficiency curve, is often used.
This is because this wavelength range has the greatest influence on the light intensity and the contrast perceived by humans. At this time, the retardation amount Δn · d of the liquid crystal panel is set according to the maximum transmittance condition
Is preferably set to half of 550 nm.

Recently, in addition to the ferroelectric liquid crystal exhibiting the above-mentioned bistability, attention has been paid to the anti-ferroelectric liquid crystal exhibiting the tri-stable state. Similar to the ferroelectric liquid crystal, the antiferroelectric liquid crystal has a very fast response speed because the molecules undergo inversion switching due to the action on the spontaneous polarization of the liquid crystal molecules. This liquid crystal material has a molecular alignment structure in which liquid crystal molecules cancel each other's spontaneous polarization when no voltage is applied, and thus is characterized by the absence of spontaneous polarization when no voltage is applied.

On the other hand, there is a chiral smectic liquid crystal that does not exhibit a plurality of stable states as described above but only one stable state (Japanese Patent Application No. 10-117145).
issue). The liquid crystal has the following properties: -When no voltage is applied, the average molecular axis of the liquid crystal is in a monostable position.-When a voltage of one polarity is applied, the average molecular axis depends on the magnitude of the applied voltage. It tilts to one side from the monostable position at different angles, and when a voltage of the other polarity is applied, the average molecular axis tilts to the opposite side. The liquid crystal is used for gradation display by utilizing the characteristic that the tilt angle (angle at which the average molecular axis tilts) changes according to the applied voltage.

[0012]

However, the above-mentioned chiral smectic liquid crystal (Japanese Patent Application No. 10-117145).
No.), there is a problem that the relationship between the applied voltage and the tilt angle is not stable and changes with time, and the quality of the displayed image deteriorates. For example, even if a predetermined voltage is applied in an attempt to display a predetermined gradation, the displayed gradation may deviate due to the change in the relationship between the applied voltage and the tilt angle as described above. Therefore, there was a problem that the image quality deteriorates.

In order to confirm the cause of the above phenomenon (a phenomenon in which the relationship between the applied voltage and the tilt angle changes with time), the present inventor manufactured a single pixel liquid crystal panel having no active element. , When the drive voltage is continuously applied, the ions in the liquid crystal layer (hereinafter referred to as “movable ions”)
It was confirmed that the particles migrated to the vicinity of the alignment film interface and were adsorbed by the alignment film, and the voltage holding ratio during driving changed. From this, it can be easily inferred that in a liquid crystal panel having active elements, the transmittance may change with time due to a change in voltage holding ratio.

Therefore, it is an object of the present invention to provide a method of manufacturing a liquid crystal element which prevents a shift in display gradation.

[0015]

SUMMARY OF THE INVENTION The present invention has been made in consideration of the above circumstances, and a step of arranging a pair of substrates with a predetermined gap left therebetween and a chiral smectic liquid crystal in the gap between the pair of substrates. A step of arranging, a step of arranging a pair of electrodes so as to form a plurality of pixels while sandwiching the chiral smectic liquid crystal, a step of arranging an active element in a state of being connected to one electrode for each pixel, In the method for producing a liquid crystal device, the chiral smectic liquid crystal is added to the isotropic liquid phase (I
SO. ) -Cholesteric phase (Ch) -Chiraral smectic C phase (SmC *) or isotropic liquid phase (IS
O. ) -Chiral smectic C phase (SmC *), a liquid crystal exhibiting a phase transition sequence of a cholesteric phase (Ch)
-Chiral smectic C phase (SmC *) or isotropic liquid phase (ISO.)-Chiral smectic C phase (SmC *)
An alternating voltage is applied to the liquid crystal through the pair of electrodes at a temperature higher than the phase transition temperature of 1.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, referring to FIG. 1 and FIG.
An embodiment of the present invention will be described.

(1) First, the overall structure of the liquid crystal element manufactured and driven in this embodiment will be described with reference to FIG.

As shown in FIG. 1, the liquid crystal element according to the present embodiment is arranged in a pair of substrates 1a and 1b which are arranged with a predetermined gap therebetween, and in the gap between the pair of substrates 1a and 1b. The chiral smectic liquid crystal 2, a pair of electrodes 3a and 3b arranged so as to sandwich the chiral smectic liquid crystal 2 while constituting a plurality of pixels, and either one of the pair of electrodes (electrode 3b in FIG. 1). A plurality of active elements 4 arranged for each pixel in a state of being connected to each other, and driven by applying a voltage to the chiral smectic liquid crystal 2 through the pair of electrodes 3a and 3b. Is configured.

As the chiral smectic liquid crystal 2, from the high temperature side, an isotropic liquid phase (ISO.)-Cholesteric phase (Ch) -chiral smectic C phase (SmC).
*) Or an isotropic liquid phase (ISO.)-Chiral smectic C phase (SmC *), which exhibits a phase transition series. The liquid crystal 2 is preferably used in a state where liquid crystal molecules are stabilized at the edge of the virtual cone or at the position inside the virtual cone in the state where no voltage is applied.

(2) Next, a method of manufacturing the liquid crystal element according to the present embodiment will be described.

In manufacturing the above-mentioned liquid crystal element, a step of arranging the pair of substrates 1a and 1b with a predetermined gap left between them, and a chiral smectic liquid crystal 2 in the gap between the pair of substrates 1a and 1b. And a step of arranging a pair of electrodes 3a and 3b so as to form a plurality of pixels while sandwiching the chiral smectic liquid crystal 2, and a state in which an active element 4 is connected to one electrode 3b for each pixel. And the step of arranging in step 1.

Then, at a temperature higher than the phase transition temperature of the cholesteric phase (Ch) -chiral smectic C phase (SmC *) or the isotropic liquid phase (ISO.)-Chiral smectic C phase (SmC *), A pair of electrodes 3a,
An alternating voltage is applied to the liquid crystal 2 via 3b (hereinafter,
Such voltage application processing is referred to as “movable ion reduction processing”). As a result, the amount of mobile ions in the liquid crystal can be reduced.

The application of the alternating voltage may be performed while the active element 4 is periodically turned on. The alternating voltage may be a rectangular wave alternating voltage, and the amplitude may be ± 1 V or more.

(3) Next, the detailed structure of the liquid crystal element will be described.

(3-1) The chiral smectic liquid crystal 2 will be described.

As the chiral smectic liquid crystal 2 used in the present embodiment, those of the above phase transition series,
That is, from the high temperature side, isotropic liquid phase (ISO.)-Cholesteric phase (Ch) -chiral smectic C phase (SmC *) or isotropic liquid phase (ISO.)-Chiral smectic C phase (SmC *) ), And those showing the phase transition series of the above, specifically, the compounds shown in the following (1) to (4) can be mentioned.

(1)

[Chemical 1] _{R 1,} R 2: an alkyl group _X 1 having 1 to 20 carbon atoms and is optionally substituted linear or _{branched, X} 2: single _{bond, O, COO, OOC Y 1} , Y ₂ , Y ₃ , Y ₄ : H or F n: 0 or 1

(2)

[Chemical 2] _{R 1,} R 2: an alkyl group _X 1 having 1 to 20 carbon atoms and is optionally substituted linear or _{branched, X} 2: single _{bond, O, COO, OOC Y 1} , Y ₂ , Y ₃ , Y ₄ : H or F

(3)

[Chemical 3] _{R 1,} R 2: an alkyl group _X 1 having 1 to 20 carbon atoms and is optionally substituted linear or _{branched, X} 2: single _{bond, O, COO, OOC Y 1} , Y ₂ , Y ₃ , Y ₄ : H or F

(4)

[Chemical 4] _{R 1,} R 2: an alkyl group _X 1 having 1 to 20 carbon atoms and is optionally substituted linear or _{branched, X} 2: single _{bond, O, COO, OOC Y 1} , Y ₂ , Y ₃ , Y ₄ : H or F

By the way, in the present embodiment, with respect to the chiral smectic liquid crystal 2, the composition of the liquid crystal material is adjusted, and further the treatment of the liquid crystal material and the element configuration, for example, the materials of the orientation control films 5a and 5b, the treatment conditions and the like are set. By setting appropriately, when the drive voltage is not applied, the average molecular axis (liquid crystal molecule) of the liquid crystal shows an alignment state in which the liquid crystal molecules are mono-stabilized, and the drive voltage of one polarity is applied to drive. In this case, the average molecular axis of the liquid crystal molecules tilts from the mono-stabilized position to one side at an angle according to the magnitude of the driving voltage, and the other polarity (reverse polarity to the one polarity is set). Hereinafter, when the same voltage is applied, the average molecular axis of the liquid crystal molecules is at an angle corresponding to the magnitude of the driving voltage from the mono-stabilized position on the other side (that is, the one side). Mark the polarity voltage May the side to tilt when tilt in the opposite side), as shown in the characteristic way. That is, the liquid crystal 2 used in the present embodiment is one in which the original memory property (bistability) of the chiral smectic liquid crystal is lost, and the magnitude of the tilt angle can be continuously controlled by the applied voltage. Accordingly, the light quantity of the liquid crystal element can be continuously changed, and gradation display is possible. In this case, the tilt angle in the maximum tilt state by applying the drive voltage of the one polarity may be different from the tilt angle in the maximum tilt state by applying the voltage of the other polarity. good. For example, when a voltage of the other polarity is applied, the property may be such that the average molecular axis of the liquid crystal hardly tilts regardless of the magnitude of the voltage.

(3-2) Next, the chiral smectic liquid crystal 2
Each component other than the above will be described.

For the substrates 1a and 1b described above, a highly transparent material such as glass or plastic may be used.

The electrodes 3a and 3b may be made of a material such as In ₂ O ₃ or ITO (indium tin oxide), and these electrodes 3a and 3b may be formed on the respective substrates 1a and 1b. . The electrodes 3b for connecting the active elements 4 may be arranged in a dot-like matrix, and the other electrode 3a may be formed on almost the entire surface (or a specific region) of the substrate 1a. Further, as the active element 4, a TFT or MIM (Metal-In) is used.
It is sufficient to use such as a "slutor-Metal". In FIG. 1, a TFT element is shown as an example.

In addition, at the position in contact with the chiral smectic liquid crystal 2, alignment control films 5a and 5b subjected to uniaxial alignment treatment in order to control the alignment state may be arranged. As the orientation control films 5a and 5b, * those obtained by applying a solution made of an organic material such as polyimide, polyimideamide, polyamide, polyvinyl alcohol or the like to form a film, and subjecting the surface of the film to a rubbing treatment, * An oblique vapor deposition film formed by vapor-depositing an inorganic material such as an oxide such as SiO or a nitride on the substrates 1a and 1b at a predetermined angle from an oblique direction, * Optical alignment capable of generating a uniaxial alignment regulating force by ultraviolet irradiation or the like The thing using a membrane can be mentioned. In addition,
Depending on the material of the alignment control films 5a and 5b, the condition of the uniaxial alignment treatment, etc., the pretilt angle of the liquid crystal molecules (that is, the angle formed by the liquid crystal molecules with respect to the alignment control films 5a and 5b near the interface between the alignment control films 5a and 5b). ) Is adjusted.

Such alignment control films 5a and 5b may be arranged on both sides of the chiral smectic liquid crystal 2 and both of them may be subjected to uniaxial alignment treatment. In that case, the relationship of the uniaxial alignment treatment direction (particularly the rubbing direction). Takes into account the liquid crystal material used, * anti-parallel (both uniaxial alignment treatment directions are parallel and opposite directions), * parallel (both uniaxial alignment treatment directions are parallel and same directions), * crosses within 45 ° It can be set so that it is either relationship or. 45 °
The relationship of crossing in the following range is a case where two vectors (vectors indicating the uniaxial orientation processing directions) cross in a range of 45 ° or less, and the respective vector directions are in the same direction (to be exact, 45 There is an angle deviation of less than °.)
And the case where the respective vector directions are opposite directions. When the value of the crossing angle (narrower crossing angle) between the vectors is 45 ° or less and close to 0 °, the relation between the respective vectors is regarded as a substantially antiparallel or parallel relation. Good. Further, the above-mentioned anti-parallel or parallel relationship may be regarded as a substantially anti-parallel or parallel relationship, in addition to the fact that the vectors are always parallel to each other, for example, even when they are deviated by several degrees. In the present specification, the orientation control film refers to a film which has some influence on the alignment of the liquid crystal by being in direct contact with the liquid crystal, in addition to the film subjected to the uniaxial alignment treatment. In addition,
The alignment control films on both sides may not be subjected to the uniaxial alignment treatment, but the alignment control films on one side may be subjected to the uniaxial alignment treatment.

Further, a spacer (not shown) made of silica beads or the like is arranged in the gap between the substrates 1a and 1b,
The gap size may be defined by such a spacer. It should be noted that the gap size may be adjusted so as to be in an optimum range in consideration of the liquid crystal material, but it is possible to achieve uniform uniaxial orientation and to determine the average molecular axis of liquid crystal molecules in the state where no voltage is applied. It is preferable to set it in the range of 0.3 to 10 μm in order to substantially coincide with the axis of the average orientation direction axis.

Furthermore, by disposing adhesive particles (not shown) made of epoxy resin or the like in the gap between the substrates 1a and 1b to improve the adhesion between the substrates 1a and 1b and the impact resistance of the liquid crystal element. good.

Further, the liquid crystal element may be of a transmissive type or a reflective type. In the case of the transmissive type, both substrates 1a and 1b need to be transparent, and in the case of the reflective type, one of the substrates 1a and 1b needs to have a function of reflecting light. Here, as a method of imparting a function of reflecting light, * a method of providing a reflection plate or a reflection film separately from the substrate 1a or 1b, or a method of forming the substrate 1a or 1b itself with a reflection member, or , And the like. Here, in the case of a transmissive liquid crystal element, polarizing plates may be arranged on both substrates 1a and 1b (so that their polarization axes are orthogonal to each other), and in the case of a reflective liquid crystal element, at least one of them may be arranged. Substrate 1a or 1
A polarizing plate may be provided on b.

(3-3) Next, a detailed structure when the TFT element is used as an active element will be described.

[0041] the side of the substrate 1b of FIG. 1, as shown in FIG. 2, the gate lines _G 1, _{G 2,} ... are arranged in large numbers in the illustrated transverse direction, the gate lines _G 1, _{G 2,} ... and the insulating A large number of source lines S ₁ , S ₂ , ... In the opened state are arranged in the vertical direction in the drawing. Then, these gate lines _G 1, _{G 2,} ... and the source lines _S 1, _{S 2,} ... to the pixels of each intersection of a thin film transistor (amorphous SiTF as an active element
T) 4 or the pixel electrode 3 made of a transparent conductive film such as an ITO film
b, the storage capacitor electrode 6 and the like are arranged.

Of these, the amorphous SiTFT 4 is
As shown in FIG. 1, a gate electrode 42, an insulating film (gate insulating film) 43 made of silicon nitride (SiNx),
A-Si layer 44 and n + a-Si layers 45 and 4 which are semiconductor layers
6, a source electrode 47, a drain electrode 48, and a channel protective film 49 that protects the channel. That is, the gate electrode 42 is formed for each pixel on the glass substrate 1b, the surface of the gate electrode 42 is covered with the insulating film 43, and at the position of the surface of the insulating film 43 where the gate electrode 42 is formed. An a-Si layer 44 is formed. Further, n + a-Si layers 45 and 46 are formed on the surface of the a-Si layer 44 so as to be separated from each other, and a source electrode 47 and a drain electrode 48 are provided on each of the n + a-Si layers 45 and 46. It is formed in a separated state. Furthermore, these a-Si layer 44 and electrodes 47, 48
A channel protective film 49 is formed so as to cover the.

The gate electrode 42 of the TFT 4 is connected to the scanning signal driver 7 via the above-mentioned gate lines G ₁ , G ₂ , ... And the source electrode 47 of the TFT 4 is connected to the source line S.
Is connected to the information signal driver 8 via ₁ , S ₂ ,.
The drain electrode 48 of the TFT 4 is connected to the pixel electrode 3b.

By the way, the above-mentioned storage capacitor electrode 6 is formed on the surface of the glass substrate 1b, and the above-mentioned insulating film 4 is formed.
3 is formed up to the position covering the storage capacitor electrode 6 and the glass substrate 1b, and the source electrode 47 and the pixel electrode 3 described above are formed.
b is formed on the surface of the insulating film 43. As a result, the storage capacitor electrode 6 and the pixel electrode 3b are arranged with the insulating film 43 sandwiched between them.
The storage capacitor Cs provided in parallel with the liquid crystal 2 is configured. The storage capacitor electrode 6 is preferably made of transparent ITO in order to prevent the aperture ratio from decreasing when the area is increased.

Further, as shown in FIG. 1, the above-mentioned TFT
An alignment control film 5b is formed on the surfaces of the pixel electrodes 4 and the pixel electrodes 3b, and the surface is subjected to uniaxial alignment treatment (rubbing treatment).

Furthermore, a chiral smectic liquid crystal 2 having spontaneous polarization is arranged between the pixel electrodes 3b and the common electrode 3a in the gap between the glass substrates 1a and 1b, and constitutes a liquid crystal capacitance Clc. Will be done.

A pair of polarizing plates (not shown) having polarization axes orthogonal to each other are arranged on both sides of such a liquid crystal element.

Although the liquid crystal element shown in FIG. 1 uses an amorphous SiTFT, it is of course not limited to this, and a polycrystalline Si (P-Si) TFT or a single crystal Si is used.
(C-Si) TFT may be used.

(3-4) Next, an example of the driving method of the above-mentioned liquid crystal element P (driving method for normal image display) will be described.

In the above-mentioned liquid crystal element, the gate voltage is line-sequentially applied from the scanning signal driver 7 to each gate line G ₁ , G ₂ , ... And the TFT 4 is turned on by applying the gate voltage. .

On the other hand, in synchronization with the application of the gate voltage, the source voltage (the information signal voltage corresponding to the information to be written in each pixel) is applied from the information signal driver 8 to the source lines S ₁ , S ₂ ,. Therefore, in the pixel in which the TFT 4 is in the ON state, the source voltage is applied to the liquid crystal 2 via the TFT 4 and the pixel electrode 3b, and the liquid crystal 2 is switched in a pixel unit.

Then, such driving is repeated every fixed period (frame period) to rewrite the image.

By the way, when a detailed phase transition process of a phase transition from a cholesteric phase to a chiral smectic C phase is observed with a polarization microscope, an alignment state very similar to that of the smectic A phase may be observed. However, the essence of the device used in the present invention is that the normal direction of the smectic layer and the uniaxial orientation treatment direction are greatly different, and the stable molecular position is close to the rubbing direction when no voltage is applied. That is, when the layer forming direction having such a relationship is realized, the above-mentioned smectic A-phase liquid crystal phase does not contribute to the alignment. Therefore, in the present application, such a material is also referred to as a material not containing the smectic A phase. Define.

When the movable ion reduction process is performed in the liquid crystal device shown in FIG. 2, a gate voltage is applied from the scanning signal driver 7 to each gate line G ₁ , G ₂ , ... And synchronized with this voltage application. As described above, it is preferable to apply the movable ion reducing voltage from the information signal driver 8 to the source lines S ₁ , S ₂ , ... Alternatively, the voltage applied to each gate line and the source line may be set to 0 V, and the movable ion reducing voltage may be applied to the common electrode 3a.

(4) Next, the effect of this embodiment will be described.

According to the present embodiment, by applying the alternating voltage as described above in the manufacturing process of the liquid crystal element, the movable ions in the liquid crystal 2 are adsorbed to the alignment films 5a and 5b, and the liquid crystal in the liquid crystal is absorbed. The amount of mobile ions can be reduced (the ions once adsorbed on the alignment films 5a and 5b are fixed on the alignment films 5a and 5b by the dispersion force and do not re-migrate to the liquid crystal 2). Therefore, even if a drive voltage is applied thereafter for image display, the change in the amount of movable ions in the liquid crystal is suppressed, the relationship between the applied voltage and the tilt angle is stabilized, and the deterioration of the image quality of the displayed image is prevented. It That is, since the relationship between the applied voltage and the tilt angle is stable,
When a predetermined voltage is applied, a predetermined gradation is always displayed, and the image quality is stable.

The migration of mobile ions becomes more remarkable as the temperature of the liquid crystal 2 increases. In this embodiment, the alternating voltage is applied from the phase transition temperature of the cholesteric phase (Ch) -chiral smectic C phase (SmC *) or the isotropic liquid phase (ISO.)-Chiral smectic C phase (SmC *). Also at a high temperature, it is possible to promote adsorption of mobile ions to the alignment film.

[0058]

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

(1) Preparation of Liquid Crystal Composition First, the following liquid crystal compounds were mixed in the weight ratios shown on the right side of each to prepare a liquid crystal composition LC-1.

[0060]

[Chemical 5]

Cone angle (30 ° C.): Θ = 24.1 ° The physical property parameters of the liquid crystal composition LC are shown below. Spontaneous polarization (30 ° C.): Ps = 2.9 nC / cm^Two Cone angle (30 ° C): Θ = 23.3 ° (100Hz, ±
12.5V, substrate gap 1.4μm) Helical pitch in SmC * phase (30 ° C): 20 μm or less
Up

(2) Preparation of Single Pixel Liquid Crystal Cell In this example, a single pixel liquid crystal cell was prepared for confirming the effect of the present invention. This single pixel liquid crystal cell is provided with a pair of glass substrates arranged with a predetermined gap therebetween, and a transparent electrode is formed on the surface of each glass substrate so as to cover each transparent electrode. An alignment film is formed on the substrate, and a chiral smectic liquid crystal is arranged between the substrates, and one pixel is formed without forming the transparent electrode into a matrix.

In producing this single-pixel liquid crystal cell, two glass substrates (thickness: 1.1 mm) were provided with 70
An ITO film (transparent electrode) having a thickness of 0Å was formed. Then, a commercially available alignment film for TFT (SE7992 manufactured by Nissan Kagaku Co., Ltd.) was applied by a spin coating method so as to cover each transparent electrode, and then pre-dried at a temperature of 80 ° C. for 5 minutes,
Further, it was heated and baked at 200 ° C. for 1 hour to obtain a polyimide film (alignment film) having a film thickness of 150 Å.

Subsequently, each polyimide film was subjected to rubbing treatment with a nylon cloth as uniaxial orientation treatment. For this rubbing treatment, nylon (NF
-77 / made by Teijin) with a rubbing roll with a diameter of 10 cm and a pushing amount of 0.7 mm and a feed rate of 1
The rotation frequency was 0 cm / sec, the rotation speed was 1000 rpm, and the feeding frequency was 4 times.

After that, silica beads (average particle size: 1.5 μm) as spacers are scattered on one of the substrates, and the two substrates are bonded so that the rubbing treatment directions are antiparallel to each other. It was Then, the liquid crystal composition LC-1 was injected into the gap between the substrates at a temperature of the Ch phase to manufacture a single pixel liquid crystal cell.

Two such single pixel liquid crystal cells were prepared,
For one liquid crystal cell, the liquid crystal is in the Ch phase state 6
Cool down to around 3 ℃, at that temperature ± 5V, 60H
A rectangular wave voltage of z is applied for 24 hours to reduce the ions in the liquid crystal layer, and then cooled to "the temperature at which the liquid crystal exhibits a chiral smectic liquid crystal phase", and the liquid crystal undergoes a phase transition from the Ch phase to the SmC * phase. In doing so, an offset voltage (DC voltage) of -2 V was applied.

The rectangular wave voltage as described above is not applied to the other liquid crystal cell, but the liquid crystal is cooled to "the temperature at which the liquid crystal exhibits a chiral smectic liquid crystal phase", and the liquid crystal changes from the Ch phase to the SmC * phase. Only an offset voltage of −2 V (DC voltage) was applied during the phase transition.

The movable ion amount of the two single-pixel liquid crystal cells thus produced was measured by using a liquid crystal ion amount measuring device MTR-1 manufactured by Toyo Technica. The liquid crystal cell to which a rectangular wave voltage was applied was measured. Mobile ion amount is 1 nC / cm
^{It was} about ² , and the movable ion amount of the liquid crystal cell to which the rectangular wave voltage was not applied was about 4 nC / cm ² .

When the voltage holding ratio was measured using a voltage holding ratio measuring system manufactured by Toyo Technica, the voltage holding ratio of the liquid crystal cell to which the rectangular wave voltage was applied was about 55%. The voltage holding ratio of the liquid crystal cell to which no voltage was applied was about 48%.

Next, a driving durability test was conducted on both liquid crystal cells. That is, for each liquid crystal cell (to be precise, for one transparent electrode on each liquid crystal cell) T
An FT was connected, a gate voltage was applied to the gate electrode at a frequency of 60 Hz, and a source voltage of ± 5 V was alternately applied to the source electrode, and the drive durability test was continuously performed for 50 hours. After that, when the movable ion amount and the voltage holding ratio of each liquid crystal cell were measured again, the movable ion amount of the liquid crystal cell to which the rectangular wave voltage was applied was 1 nC / c.
The voltage holding ratio was 56% at about m ² , and the movable ion amount of the liquid crystal cell to which the rectangular wave voltage was not applied was 1 nC / c.
The voltage holding ratio was about 55% at about m ² , and it was confirmed that in the liquid crystal cell to which the rectangular wave voltage was applied, changes in the amount of movable ions and the voltage holding ratio during driving at room temperature were reduced.

In this embodiment, the liquid crystal element using the chiral nematic liquid crystal as the liquid crystal is subjected to the ion reduction treatment, but it is also useful for the nematic liquid crystal element.

(3) Preparation of Active Matrix Liquid Crystal Panel Next, an active matrix liquid crystal panel (liquid crystal element) shown in FIGS. 1 and 2 was prepared.

The thickness of the substrates 1a and 1b is 1.1 mm.
The transparent electrodes 3a and 3b were formed on these glass substrates. An RGB color filter (not shown) was formed on one glass substrate 1a. The screen size was 10.4 inches and the number of pixels was 800 × 600.

Further, the active element 4 is made of a-SiT.
FT was used, and a silicon nitride film was used as the gate insulating film 43 of the TFT 4.

The orientation control films 5a and 5b are formed of polyimide film. Specifically, a commercially available alignment film for TFT (SE7992 manufactured by Nissan Chemical Co., Ltd.) is applied by a spin coating method so as to cover the electrodes 3a and 3b, and then at 80 ° C.
Was pre-dried at a temperature of 5 minutes and further heated and baked at a temperature of 200 ° C. for 1 hour to form a film having a thickness of 150 Å. In addition, these alignment control films 5
Rubbing treatment (uniaxial orientation treatment) with a nylon cloth was applied to a and 5b. For this rubbing treatment, a rubbing roll having a diameter of 10 cm with a cotton cloth bonded to the outer peripheral surface was used, the pushing amount was 0.7 mm, and the feeding speed was 10 cm /
sec, the number of rotations was 1000 rpm, and the number of feeds was 4 times.

Subsequently, the average grain size of 1.
5 μm silica beads (spacers) were scattered and bonded so that the rubbing directions of the substrates 1a and 1b were anti-parallel to each other to obtain cells having uniform substrate gaps.

A liquid crystal panel was prepared by injecting the liquid crystal composition LC-1 into the cell prepared by the above process at the temperature of Ch phase.

Next, the produced liquid crystal panel P was subjected to ion reduction treatment at a temperature of 63 ° C. Specifically, the frame rate is 60 Hz, and one frame period (= 1/6)
0 sec) is two field periods (= 1 / 120se)
c), and the selection period Ton = 13.9 for 600 gate lines G ₁ , G ₂ , ... In each field period.
A gate voltage Vg = + 12 V of μs was applied and line by line scanning was performed one by one. The potential of the gate lines G ₁ , G ₂ , ... In the non-selection period Toff is -12 V, and the source voltage Vs is an alternating voltage of ± 5 V at a frequency of 60 Hz.

Then, the liquid crystal is cooled to a temperature at which it exhibits a chiral smectic liquid crystal phase, and when the liquid crystal undergoes a phase transition from the Ch phase to the SmC * phase, an offset voltage (DC voltage) of -2V is applied.
Was applied.

A specific image (black and white checkered pattern, etc.) was displayed for about 4 hours on the liquid crystal cell P which had been subjected to the ion reduction treatment by the above method. After that, full screen black image, full screen halftone image,
A full-screen white image was displayed, but no burn-in pattern corresponding to the specific image was confirmed. This is considered to be due to the reduction in the amount of change in the voltage holding ratio confirmed in the above-mentioned single pixel liquid crystal cell.

[0081]

As described above, according to the present invention,
By applying an alternating voltage, the mobile ions in the liquid crystal can be adsorbed to the alignment film or the like, and the amount of mobile ions in the liquid crystal can be reduced. Therefore, even if a drive voltage is applied thereafter for image display, the change in the amount of movable ions in the liquid crystal is suppressed, the relationship between the applied voltage and the tilt angle is stabilized, and the deterioration of the image quality of the displayed image is prevented. It That is, since the relationship between the applied voltage and the tilt angle is stable, a predetermined gradation is always displayed when a predetermined voltage is applied, and the image quality is stable.

The migration of mobile ions becomes more remarkable as the temperature of the liquid crystal is higher. In the present invention, the application of the alternating voltage is higher than the phase transition temperature of the cholesteric phase (Ch) -chiral smectic C phase (SmC *) or the isotropic liquid phase (ISO.)-Chiral smectic C phase (SmC *). Since it is performed at a temperature, adsorption of mobile ions to the alignment film can be promoted.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing the structure of a liquid crystal panel manufactured according to the present invention.

FIG. 2 is a plan view showing the shape of electrodes.

FIG. 3 is an exploded perspective view for explaining a driving principle of a liquid crystal element using a ferroelectric liquid crystal.

[Explanation of symbols]

1a, 1b substrate 2 Chiral smectic liquid crystal 3a Common electrode 3b Pixel electrode

Continued front page    (72) Inventor Yasushi Asao             3-30-2 Shimomaruko, Ota-ku, Tokyo             Non non corporation F-term (reference) 2H088 GA03 GA04 GA17 HA08 JA17                       JA20 MA10 MA13                 2H090 KA14 KA15 LA02 LA04 MA02                       MA10 MA17 MB01 MB14

Claims (3)

[Claims] 1. A step of disposing a pair of substrates in a state where a predetermined gap is formed, a step of disposing a chiral smectic liquid crystal in the gap between the pair of substrates, and sandwiching the chiral smectic liquid crystal to form a plurality of pixels. As such, a step of disposing a pair of electrodes, a step of disposing an active element in a state of being connected to one electrode for each pixel, in a method of manufacturing a liquid crystal element, wherein the chiral smectic liquid crystal is from a high temperature side, Isotropic liquid phase (ISO.)-Cholesteric phase (Ch) -chiral smectic C phase (SmC *), or isotropic liquid phase (ISO.)-Chiral smectic C phase (SmC *),
Which is a liquid crystal exhibiting a phase transition sequence of cholesteric phase (Ch) -chiral smectic C phase (SmC *) or isotropic liquid phase (ISO.)-Chiral smectic C phase (SmC *). A method for manufacturing a liquid crystal element, comprising applying an alternating voltage to the liquid crystal through the pair of electrodes at a high temperature. 2. The alternating voltage is a rectangular wave alternating voltage,
The method for manufacturing a liquid crystal element according to claim 1, wherein 3. The method for manufacturing a liquid crystal element according to claim 1, wherein the alternating voltage has an amplitude of ± 1 V or more.