JPH0547086B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a liquid crystal element applied to a liquid crystal display element, a liquid crystal-optical shutter array, etc., and more specifically, a liquid crystal element with improved display and driving characteristics by improving the initial alignment state of liquid crystal molecules. Regarding. [Prior Art] As a conventional liquid crystal element, for example, M. Schadt (M.Schadt) and Double You. “Applied Physics” by W. Helfrich.
“Applied Physics Letters” No. 18
Volume, No. 4 (published February 15, 1971), pp. 127~
“Voltage dependent optical activity of a twisted nematic liquid crystal” on page 128
(“Voltage Dependent Optical Activity of a
Twisted Nematic Liquid Crystal”
(nematic) liquid crystal display is known. This TN liquid crystal has a problem in that crosstalk occurs during time-division driving using a matrix electrode structure with high pixel density, so the number of pixels is limited. Furthermore, a display element is known in which a switching element using a thin film transistor is connected to each pixel and switching is performed for each pixel, but the process of forming the thin film transistor on the substrate is extremely complicated, and
There is a problem in that it is difficult to create a display element with a large area. To improve the drawbacks of conventional liquid crystal devices, the use of bistable liquid crystal devices was proposed by Clafk and Lagerwall (Japanese Patent Application Laid-Open No. 1983-1993).
-107216, US Pat. No. 4,367,924, etc.). In general, liquid crystals with bistability include:
A ferroelectric liquid crystal having a chiral smectic C phase (SmC ^* ) or H phase (SmH ^* ) is used.
The film thickness of this liquid crystal is kept small enough to release the helical structure of the ferroelectric liquid crystal, thus creating a bistable state consisting of a first optically stable state and a second optically stable state in response to an electric field. It will last. Therefore, unlike the optical modulation element used in the above-mentioned TN type liquid crystal, for example, the liquid crystal is oriented in the first optically stable state with respect to one electric field vector, and the first optically stable state with respect to the other electric field vector. The liquid crystal is aligned in the optically stable state of 2. [Problems to be Solved by the Invention] In order for the optical modulation element using the above-mentioned bistable liquid crystal to exhibit predetermined drive characteristics, the liquid crystal disposed between a pair of parallel substrates must be It is necessary that the molecules be arranged in such a state that conversion between stable orientation states can occur effectively. However, the above-mentioned chiral smectic liquid crystal device, in which the helical structure is released and bistability is imparted, has extremely difficult problems in producing the device. That is, based on the research conducted by the present inventors, in order to solidify the bistability of the chiral smectic liquid crystal described above, the film thickness of the liquid crystal (corresponding to the distance between a pair of substrates) can be reduced. However, it has been found that the thinner the film thickness is, the more likely the occurrence of orientation defects will be. Moreover, it was discovered that the occurrence of the alignment defects mentioned above was caused by the presence of a spacer, which was placed to maintain a uniform liquid crystal film thickness over the entire surface of the device. . Therefore, in view of the above-mentioned circumstances, an object of the present invention is to provide a liquid crystal such as a ferroelectric liquid crystal, as a display element having high-speed response, high-density pixels, and a large area, or as an optical shutter having a high shutter speed.
In particular, in optical modulation elements using ferroelectric liquid crystals with bistability, we provide liquid crystal elements that can fully demonstrate their characteristics by improving monodomain formation or initial orientation, which has been a problem in the past. It's about doing. [Means and effects for solving the problems] The present invention has fine protrusions that serve as spacers formed by using a photolithography process,
The first substrate is uniaxially aligned in one direction, and the second substrate is opposed to the first substrate. A liquid crystal element in which a chiral smectic liquid crystal formed by phase transition in the order of a cholesteric phase, a smectic A phase, and a chiral smectic C phase is arranged, wherein the protrusions first have the uniaxial orientation. It has a cylindrical shape with a diameter of 50 μm or less in the direction perpendicular to the processing direction, or a square prism shape has a width of 20 μm or less in the direction perpendicular to the uniaxial alignment treatment direction, or The present invention is characterized by a liquid crystal element having a hexagonal column shape having a width of 50 μm or less in the direction perpendicular to the direction of the uniaxial alignment process. [Example] The present invention will be described in further detail below with reference to the drawings as necessary. Figure 1 is for explaining the operation of ferroelectric liquid crystal.
This is a schematic drawing of an example of a cell. 21a
and 21b are substrates (glass plates) covered with transparent electrodes made of thin films such as In ₂ O ₃ , SnO ₂ or ITO (indium-tein oxide),
In between, liquid crystal of SmC ^* phase or SmH ^* phase, which is oriented so that the liquid crystal molecular layer 22 is perpendicular to the glass surface, is sealed. A thick line 23 represents a liquid crystal molecule, and this liquid crystal molecule 23 has a dipole moment (P⊥) 24 in a direction perpendicular to the molecule. When a voltage higher than a certain threshold is applied between the electrodes on the substrates 21a and 21b, the helical structure of the liquid crystal molecules 23 is unraveled, and the dipole moment (P⊥)2
The alignment direction of the liquid crystal molecules 23 can be changed so that all of the liquid crystal molecules 4 are oriented in the direction of the electric field. liquid crystal molecule 23
has an elongated shape and exhibits refractive index anisotropy in its long and short axis directions. Therefore, for example, if crossed Nicol polarizers are placed above and below the glass surface, the polarity of the applied voltage will change. It is easily understood that this results in a liquid crystal optical modulation element whose optical properties change. The thickness of the liquid crystal cell used in the liquid crystal element of the present invention can be made sufficiently thin (for example, 10 μm or less). As the liquid crystal layer becomes thinner, the helical structure of the liquid crystal molecules unravels due to the wall effect between the substrates, which are spaced sufficiently apart, even when no electric field is applied, as shown in Figure 2. structure can be adopted. Its dipole moment Pa or Pb is upward 34a or downward 34
Take either state b. In a cell like this,
As shown in FIG. 2, when an electric field Ea or Eb of different polarity above a certain threshold value is applied by the voltage applying means 31a and 31b, the dipole moment is directed upward 34a or downward depending on the electric field vector of the electric field Ea or Eb. 34b, and accordingly, the liquid crystal molecules are oriented to either the first stable state 33a or the second stable state 33b. As mentioned earlier, there are two advantages to using such ferroelectricity as an optical modulation element. The first is that the response speed is extremely fast, and the second is that the response speed is extremely fast.
is that the orientation of liquid crystal molecules has bistability. To further explain the second point using, for example, FIG. 2, when an electric field Ea is applied, the liquid crystal molecules
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 a second stable state 33b and change their orientation, but they remain in this state even after the electric field is turned off. Further, as long as the applied electric field Ea does not exceed a certain threshold value, each orientation state is maintained. In order to effectively realize such fast response speed and bistability, it is preferable that the cell be as thin as possible. FIG. 3 specifically shows the liquid crystal element of the present invention, with FIG. 3A being a cross-sectional view thereof, and FIG. 3B being a plan view thereof. The liquid crystal element 300 shown in FIG.
(preferably flexible glass or flexible plastic) and a substrate 302 (preferably a glass plate), and the substrate 301 has a striped transparent electrode 303 and an insulating material is formed on the substrate 301. The formed orientation control film 304 is applied. or,
The substrate 302 includes a striped transparent electrode 305 perpendicular to the transparent electrode 303, a spacer 307 formed of an insulating material thereon, and an alignment control film 306 subjected to uniaxial alignment treatment (rubbing treatment, etc.) in the 312 direction. It is painted. The spacer 307 used in the present invention is made of polyvinyl alcohol, polyimide, polyamideimide, polyesterimide, polyparaxylerin, polyester, polycarbonate, polyvinyl acetal, polyvinyl chloride, polyvinyl acetate on the substrate 302 on which the alignment control film 306 is formed. , polyamide, polystyrene, cellulose resin, melamine resin, urea resin, acrylic resin, and other resins, or SiO, SiO ₂ or
It is obtained by forming an inorganic insulating film such as TiO ₂ and then etching it into a predetermined shape using a normal photolithography process. At this time, the dry film thickness of the insulating film that becomes the spacer 307 corresponds to the height of the spacer. In the present invention, the above-mentioned uniaxial orientation treatment direction 312
It is particularly preferable that the length of the side a of the spacer 307 along the vertical direction is 0 μm to 20 μm.
When the length b of the component in the direction parallel to the uniaxial orientation treatment direction 312 in 07 is set to 300 μm or less, no orientation defects can occur. This point will be explained in more detail below. In a preferred embodiment of the invention, spacer 307
If these are provided at a rate of 0.1 to 100 per mm ² of the flat surface of the liquid crystal element 300, the occurrence of alignment defects can be effectively prevented. In particular, the liquid crystal element 30
If the spacers 307 are provided at a rate of 0.5 to 50 per 1 mm ² of the plane 0, the substrates 301 and 302
When the spacing is made sufficiently small (0.5 μm to 5 μm), the bistable monodomains provided by the liquid crystal film thickness can be completely free from alignment defects. Further, as the shape of the spacer 307 used in the present invention, in addition to the above-mentioned quadrangular prism, a cylinder, an inert cylinder, and a hexagonal prism shown in FIGS. 4 to 6 can be used. a and b and 31 in Figures 4 to 6
2 means the same as a and b and 312 in FIG. Particularly, a in FIGS. 4 and 5 means the contact points of the cylindrical body and the inert cylindrical body with respect to the uniaxial orientation processing direction 312, respectively. Further, c in FIG. 5 represents the short axis of the cylindrical body, which is perpendicular to the uniaxial orientation processing direction 312. The hexagonal prism shown in FIG. 6 is formed with a width d and a length b, and the direction of the width d is perpendicular to the uniaxial alignment direction 312. The above-mentioned spacer 307 has a pitch of 5 to 50 times the length b, preferably in the case of the cylindrical body shown in FIG.
It is preferable that they are provided at a pitch 10 to 20 times larger and that the length b corresponding to the diameter in the plane of the substrate is 50 μm or less. In the case of the inertia cylindrical body shown in Fig. 5, the pitch is 5 to 50 times the length c, preferably 10 to 20 times the length c, and the long axis b corresponding to the component parallel to the rubbing direction is 300 μm or less. It is preferable to do so. In the case of the hexagonal prism shown in Fig. 6, the pitch is 5 to 50 times the length d, preferably 10 to 20 times, and the length b corresponds to the component parallel to the rubbing direction.
is preferably 300 μm or less. Further, the liquid crystal shown in FIG. 3, particularly the ferroelectric chiral smectic liquid crystal 308,
It is sealed with a sealing material 309 (for example, epoxy adhesive) provided around the . In the liquid crystal element 300 of the present invention, crossed Nicol polarizers 310 and 311 are arranged on substrates 301 and 311, respectively.
It is placed on both sides of 2. Further, the alignment control films 304 and 306 used in the liquid crystal element 300 of the present invention include, for example, silicon monoxide, silicon dioxide, aluminum oxide, zirconia, magnesium fluoride, cerium oxide, cerium fluoride, silicon nitride, silicon carbide, and boron nitride. It can be obtained by forming a film by, for example, vapor deposition using a compound such as . Besides that,
For example, resins such as polyvinyl alcohol, polyimide, polyamideimide, polyesterimide, polyparaxylerin, polyester, polycarbonate, polyvinyl acetal, polyvinyl chloride, polyvinyl acetate, polyamide, polystyrene, cellulose resin, melamine resin, urea resin, and acrylic resin. It can also be formed as a similar coating. The thickness of the alignment control films 304 and 306 depends on the charge injection prevention ability of the material and the thickness of the liquid crystal layer, but is usually 50 Å to 5 μ, preferably 500 Å to 5000 Å.
It is set within the range of Å. The alignment control films 304 and 306 have the effect of aligning the molecular direction of the uniaxial liquid crystal (smectic A phase, nematic phase, etc. that appears at a higher temperature than the ferroelectric chiral smectic liquid crystal phase) in one direction. I can do it. As a specific uniaxial alignment treatment method, a method of rubbing the plane of the substrate in one direction or an oblique vapor deposition method can be used (see 3 in the figure).
12 is the rubbing direction). The ferroelectric chiral smectic liquid crystal 308 used in the liquid crystal element 300 of the present invention has an isotropic phase (Iso) → cholesteric phase (Ch) → under cooling (slow cooling; 0.5°C/hour to 5°C/hour). Those that cause a phase transition from smectic A phase (SmA) to chiral smectic phase or those that cause a phase transition from isotropic phase to SmA to chiral smectic phase are preferred. Hereinafter, the present invention will be explained according to examples. Examples 1 to 23 A polyimide forming solution (polyamic acid obtained by dehydration condensation of pyromellitic dianhydride and 4,4'-diaminodiphenyl ether) was placed on a glass substrate provided with ITO striped pattern electrodes. The film thickness after heating and curing N-methylpyrrolidone solution is 1500.
After coating to give a coating thickness of 100 Å, the polyimide acid was cured by heating to form a polyimide acid. Two glass substrates provided with this polyimide film were prepared. Of these two glass substrates, one glass plate was coated with another polyimide forming liquid (“PIQ” by Hitachi Chemical Co., Ltd.) so that the film thickness after curing was
It was applied to a thickness of 1 μm. Next, a positive resist solution ("AZ1350" manufactured by Shipey) was applied using a spinner and prebaked.
This resist layer was exposed using a 3 mm mask. The shape of the mask used at this time was square or rectangular, and a and b in Figure 3 were used.
The length corresponding to the length was taken as the value shown in Table 1.
Next, by developing with a developer containing tetramethylammonium hydroxide "MF312", the resist film in the exposed area and the underlying polyimide film are etched to form through holes, and after washing and drying, The resist film in unexposed areas was removed using methyl ethyl ketone. Thereafter, it was cured by heating at 200° C. for 60 minutes and at 350° C. for 30 minutes to form a spacer of polyimide isoindoquinazolinedione. Next, a rubbing treatment was performed with a cloth along the direction perpendicular to the side b of the square prism (spacer), followed by washing with water and acetone sequentially, and drying. Next, the other glass substrate on which the polyimide film described above was provided (after rubbing in advance, epoxy adhesive was applied around it by screen printing except for the injection port) and the spacer. A cell was created by laminating the glass substrate with a glass substrate provided with a rectangular prism, and curing the epoxy adhesive. At this time, the cells were assembled so that the rubbing directions applied to the two glass substrates were parallel to each other and the striped pattern electrodes were perpendicular to each other. Next, the cell was placed in a vacuum chamber, the inside of the cell was sufficiently evacuated, and the liquid crystal material described below was brought into contact with the injection port of the cell to isolate the inside of the cell from the outside. When the vacuum chamber was returned to atmospheric pressure, liquid crystal material was injected inside the cell. This injection step was carried out under the isotropic phase (75° C.) of the liquid crystal material. After injecting the liquid crystal material into the cell, the injection port is sealed, and the liquid crystal material in the isotropic phase is gradually cooled at a rate of approximately 0.5°C/hour to sequentially transform from the isotropic phase to the cholesteric phase, smectic A phase, and so on. A ferroelectric chiral smectic liquid crystal device (memory device) was produced at 28° C. by causing a phase transition in the chiral smectic C phase. The alignment state of this liquid crystal element was observed using a polarizing microscope under crossed Nicols. Furthermore, bistability was evaluated by applying voltages of 30 volts and -30 volts to this liquid crystal element. The results of these experiments are shown in Table 1. In the table, ○ indicates a good alignment state with no alignment defects and good bistability, while △ indicates a sample with some alignment defects but exhibits bistability within a practical range. In the samples shown, x indicates a sample in which a large number of orientation defects 71 shown in FIG. 7 occur, making it impossible to put it into practical use. Note that among the numbers in FIG. 7, the same numbers as in FIG. 3 indicate the same members.

【table】

[Table] According to these experiments, by setting the length of side a to 20 μm or less, a liquid crystal element with no alignment defects can be obtained, and in this case, the length b of the quadrangular prism spacer is It can be seen that this is not a major factor in the occurrence of orientation defects. Examples 24 to 32 Instead of the rectangular prism spacer used in Examples 1 to 23, a cylindrical spacer (length b
(shown in Table 2), liquid crystal devices were prepared in exactly the same manner and evaluated. The results are shown in Table 2.

[Table] According to these experiments, the length of side a is 0 μm (side a
is the contact point with respect to the rubbing direction)
In this device, a practical orientation state and bistability can be obtained when the diameter (b) is 100 μm or less, and especially when the diameter (b)
It can be seen that an element in an oriented state with no orientation defects was obtained when the thickness was set to 50 μm or less. Examples 33 to 40 The square columnar spacers used in Examples 1 to 23 were replaced with cylindrical spacers shown in FIG. 5 (lengths b and c are shown in Table 3). , liquid crystal devices were fabricated using the same method and evaluated. The results are shown in Table 3.

[Table] According to these experiments, a practically usable liquid crystal element can be obtained when the length b of the cylinder is set to 300 μm or less in a liquid crystal device using a cylinder spacer.
In particular, it can be seen that when the length b is set to 100 μm or less, a liquid crystal element with no alignment defects can be obtained. Examples 41 to 67 In place of the square prism spacers used in Examples 1 to 23, hexagonal prism spacers shown in FIG. 6 (lengths a, b, and d are shown in Table 4) were used. created a liquid crystal device using exactly the same method and evaluated it. The results are shown in Table 4.

【table】

〔effect〕

This phenomenon has never been observed in nematic liquid crystals or cholesteric liquid crystals, and
This phenomenon also occurs characteristically in chiral smectic liquid crystals when the cell is thin enough to release its helical structure. In the above-mentioned experiment, it was found that if the length of side b was 20 μm or less, the incidence of defects could be reduced.

[Brief explanation of the drawing]

FIG. 1 is a perspective view schematically showing a ferroelectric liquid crystal element used in the present invention. FIG. 2 is a perspective view schematically showing another ferroelectric liquid crystal element used in the present invention. FIG. 3A is a sectional view of the liquid crystal element of the present invention, and FIG. 3B is a plan view thereof. Fourth
5 and 6 are plan views showing the shape of the spacer used in the present invention, respectively. Figure 7 shows
FIG. 3 is an explanatory diagram showing a sketch of the state of alignment defects occurring in a comparative element.

Claims (1)

[Claims] 1. A first substrate having minute protrusions forming spacers formed by using a photolithography process and subjected to uniaxial alignment treatment in one direction, and the first substrate and a second substrate facing the first substrate.
A liquid crystal element in which a chiral smectic liquid crystal formed by phase transition in the order of a cholesteric phase, a smectic A phase, and a chiral smectic C phase is arranged between a substrate and a second substrate at a lower temperature. A liquid crystal element characterized in that the protrusion has a cylindrical shape with a diameter of 50 μm or less in a direction perpendicular to the uniaxial alignment treatment direction. 2. A first substrate having fine protrusions forming spacers formed by using a photolithography process and subjected to uniaxial alignment treatment in one direction, and a second substrate facing the first substrate. a substrate, the first
A liquid crystal element in which a chiral smectic liquid crystal formed by phase transition in the order of a cholesteric phase, a smectic A phase, and a chiral smectic C phase is arranged between a substrate and a second substrate at a lower temperature. A liquid crystal device characterized in that the protrusion has a square prism shape having a width of 20 μm or less in a direction perpendicular to the uniaxial alignment treatment direction. 3. A first substrate having fine protrusions forming spacers formed by using a photolithography process and subjected to uniaxial alignment treatment in one direction, and a second substrate facing the first substrate. a substrate, the first
A liquid crystal element in which a chiral smectic liquid crystal formed by phase transition in the order of a cholesteric phase, a smectic A phase, and a chiral smectic C phase is arranged between a substrate and a second substrate at a lower temperature. A liquid crystal element characterized in that the protrusion has a hexagonal column shape having a width of 50 μm or less in a direction perpendicular to the uniaxial alignment treatment direction.