JP2006030584A - Liquid crystal element and liquid crystal device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid crystal element capable of obtaining a strong contrast and a liquid crystal device provided with the same.
A first substrate 31 and a second substrate 32 sandwich a liquid crystal holding member 33 which is filled with liquid crystal 35 and has a single or a plurality of pores 34 penetrating in the substrate direction. Then, electrodes 36 and 37 are respectively formed on the surfaces of the first substrate 31 and the second substrate 32 on the liquid crystal holding member side, and disclination is generated in at least two places in the pores by the change of the voltage between the electrodes. To.
[Selection] Figure 1

Description

  The present invention relates to a liquid crystal element and a liquid crystal device, and more particularly to a liquid crystal in which pores are filled with liquid crystal.

  2. Description of the Related Art Conventionally, in a liquid crystal element used for a liquid crystal device such as a liquid crystal display device or a liquid crystal optical switching device, for example, a cavity (pore) is formed in a substrate and the cavity is formed so as to increase the contrast and increase the switching speed. There is known a method of filling a liquid crystal and applying a voltage to the liquid crystal to change the alignment state to obtain a change in transmittance (see Patent Document 1).

  According to such a method, the orientation distribution of the liquid crystal in the cavity section is point-symmetric with respect to the center of the section, so that the viewing angle of the display configured with such a substrate is wide and has no relation to the viewing direction. There is.

  FIG. 18 shows an alignment state of liquid crystal filled in a cylindrical cavity as an example of such a liquid crystal element. In this example, the vertical alignment treatment is performed on the inner surface of the cavity 34A.

  Then, as shown in FIG. 18A, the liquid crystal molecules filled in such a cavity are oriented in the radial direction as it approaches the inner surface of the cavity 34A, and the center thereof as it approaches the central axis of the cavity 34A. Orient along the axis. In this state, when an electric field is applied in the cavity central axis direction, as shown in FIG. 18B, more liquid crystal molecules are aligned along the central axis of the cavity 34A, and the transmittance changes. .

Japanese Patent No. 3251519

  However, in such a conventional liquid crystal element and a liquid crystal device including the same, the liquid crystal molecules in the vicinity of the cavity central axis are always aligned in the central axis direction regardless of the presence or absence of an electric field. The change in the alignment state is smaller than the change in the alignment state as obtained with a normal Twisted Nematic liquid crystal, and there is a drawback that a strong contrast cannot be obtained.

  According to the present invention, in a liquid crystal element in which liquid crystal is filled between a first substrate and a second substrate, the liquid crystal element is sandwiched between the first substrate and the second substrate and filled with the liquid crystal and penetrates in the substrate direction. Or a liquid crystal holding member having a plurality of pores, and electrodes respectively formed on surfaces of the first substrate and the second substrate on the liquid crystal holding member side, and the inside of the pores is changed by the change of the voltage between the electrodes. Disclinations are generated in at least two places.

  As in the present invention, a liquid crystal holding member having a single or a plurality of pores is sandwiched between the first substrate and the second substrate, and the voltage between the electrodes is changed to discriminate at least two locations in the pores. A strong contrast can be obtained by generating a nation.

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

  FIG. 1 is a diagram for explaining a configuration of a liquid crystal element according to an embodiment of the present invention, in which 31 is a first substrate, 32 is a second substrate, and 33 is first and second substrates 31 and 32. It is the 3rd board | substrate which is a liquid-crystal holding member distribute | arranged between. Reference numeral 34 denotes a single or a plurality of, in this embodiment, a plurality of pores penetrating the third substrate 33 in the first and second substrate directions, and the inside of the pores 34 is filled with liquid crystal 35. ing. At least one of the first substrate 31 and the second substrate 32 is a light transmissive glass, or a transparent plastic substrate such as polycarbonate or PMMA, and the third substrate 33 is an Al substrate.

  Reference numerals 36 and 37 denote electrodes for applying a voltage in the direction of the central axis of the pore 34 filled with the liquid crystal 35. The electrodes 36 and 37 are formed by vacuum deposition, sputtering, or the like on an indium tin oxide thin film or the like on the surfaces of the first substrate 31 and the second substrate 32 on the third substrate side.

  Here, in the present embodiment, the cross-sectional shape of the pores 34 may be a circle and an ellipse, or a triangle having three corners, a square having four or more corners, that is, a square or hexagon having diagonal lines. It has a shape.

  Next, a method for manufacturing a liquid crystal element having such a configuration will be described.

  First, the pores 34 as described above are formed in the third substrate 33. In addition, this pore is produced as follows based on the technique currently disclosed by literature (Advanced Materials, 200113, No. 3, February 5, p189-p192).

  First, a SiC mold in which protrusions are arranged is created using an electron beam lithography technique. Here, the way in which the protrusions are arranged depends on the shape of the pores to be created. That is, for example, when creating a hexagonal pore, as shown in FIG. 2A, the projections 41 are arranged to create a hexagonal lattice, and when creating a square pore, As shown in FIG. 2 (b), when the projections 41 are arranged so as to form a square lattice to create triangular pores, the projections 41 are formed in a triangular lattice as shown in FIG. 2 (c). Arrange to do.

  Note that the shape of the finally created pores substantially coincides with the Voronoi diagram indicated by reference numeral 42 with the protrusion 41 as a base point in FIG. Here, the Voronoi diagram is a diagram showing a region in which when there are a plurality of generating points, the generating point closest to an arbitrary point included in a certain region is a generating point included in the region. Furthermore, in FIG. 2, the code | symbol 41 which shows a protrusion has also shown the starting point of the production | generation of a pore.

Next, the SiC mold in which such protrusions 41 are arranged is pressed against the surface of the Al substrate (third substrate) at 1600 kgcm ⁻² using hydraulic pressure. By this operation, a minute dent is formed at a point on the surface of the Al substrate in contact with the protrusion 41 on the SiC mold. Thereafter, the Al substrate is anodized using 5% by weight of oxalic acid or phosphoric acid under a constant voltage condition. When such an anodic oxidation treatment is performed, initially, the anodic oxidation rate is the highest in the dent, that is, the elution rate of Al is high, so that the pores grow around the dent. For this reason, at the stage immediately after the start of the anodizing treatment, the cross section of the pores is circular.

  Further, when the anodic oxidation proceeds thereafter, the pores approach each other, and when the distance between the pores is short, the elution rate of the Al ions is small, so that the growth of the pores is suppressed. The cross section gradually approaches the Voronoi diagram, creating pores.

  FIG. 3 is a diagram showing how the pores are gradually enlarged when forming the square pores. In FIG. 3, 51 is first formed on the Al substrate by pressing the SiC mold. A dent, 52 is a Voronoi diagram with the dent 51 as a generating point, and 53 is a pore. Then, the pore 53 gradually grows according to the arrow from the dent 51 created first. As a result, as shown in FIG. 1, a single or a plurality of penetrating pores 34 are formed in the third substrate 33.

  Next, the pores 34 of the third substrate 33 formed in this way are filled with a vertical alignment treatment agent such as organosilane or a horizontal alignment treatment agent such as PVA, and the inner wall surfaces of the pores 34 are each vertically aligned. Treatment or horizontal alignment treatment is performed. Thereafter, the liquid crystal 35 is filled in the pores, and the third substrate 33 is sandwiched between the first substrate 31 and the second substrate 32 on which the electrodes 36 and 37 are formed, respectively, thereby forming a liquid crystal element.

  By the way, FIG. 4 shows the existence of a stable alignment state different from that in FIG. 18 of the liquid crystal with positive dielectric anisotropy filled in the pores 34 in which the inner side surfaces of the pores are vertically aligned. This is confirmed by numerical calculation based on theory. FIG. 4A shows the alignment state of the liquid crystal when the electric field is cut when viewed from above the cylindrical pores and when viewed from the cross section along AA ′. . FIG. 4B shows a state when an electric field is applied.

  In this orientation state, as shown in FIG. 4A, disclinations 41 and 42 are generated at two locations in the pore, so that almost all liquid crystal molecules in the pore are 90 ° to the pore central axis. It has an orientation angle close to.

  Disclination is a peculiar point of liquid crystal alignment, and when a virtual circuit of one circumference is taken around it, the direction (director) of the liquid crystal along the circuit is π (= 180 °). It changes by an integer multiple. In FIG. 4A, two disclinations 41 and 42 are generated vertically in a plane perpendicular to the axis of the cylinder. In this case, the disclinations 41 and 42 are on the wall surface of the pore 34. At this time, if one part takes the virtual peripheral circuits 43 and 44 along the wall surface, the direction of the liquid crystal changes by π. Yes. In the present invention, both the singular point inside the liquid crystal and the singular point on the wall surface are called disclination.

  When an electric field is applied in the central axis direction of the pores 34 in this state, the disclination disappears as shown in FIG. 4B, and the orientation angle of the liquid crystal molecules with respect to the central axis of the pores approaches 0 °. 4A and 4B, most of the liquid crystal molecules are changed from horizontal alignment to vertical alignment. This means that optical properties such as refractive index and retardation between these two states are greatly different, and as a result, a higher contrast than the orientation change of FIG. 18 can be obtained.

  FIG. 5 shows an alignment state of a liquid crystal in which a liquid crystal having a negative dielectric anisotropy is filled in a pore 34 whose horizontal inner surface is subjected to a horizontal alignment treatment. In this case, when there is no electric field, as shown in FIG. 5 (a), all liquid crystal molecules are parallel to the cylindrical axis and energy is minimized, and an electric field in the cylindrical axis direction is applied. As a result, the liquid crystal becomes perpendicular to the electric field direction, and disclinations 51 and 52 are generated on the wall surface as shown in FIG. Also in this case, it is possible to obtain switching with high contrast accompanying the generation and disappearance of disclination as in FIGS. 4 (a) and 4 (b). In FIG. 5, reference numerals 53 and 54 denote peripheral lines.

  As described above, the first substrate 31 and the second substrate 32 sandwich the third substrate 33 having a single or a plurality of pores 34 and change the voltage between the electrodes to at least two locations in the pores. By causing disclination, the switching speed can be increased and a strong contrast can be obtained. Furthermore, by providing such a liquid crystal element, a liquid crystal device (not shown) can have both a switching speed and contrast strength that are not conventionally provided.

  Next, as an example of this embodiment, the result of examination by numerical calculation simulation of liquid crystal alignment based on the continuum theory performed on the switching characteristics of the liquid crystal element will be described. In this study, the cross-sectional shape of the pores was circular.

  First, a case will be described in which a vertical alignment treatment is performed on the inner side surface of the pore and 7CB nematic liquid crystal having positive dielectric anisotropy is filled.

  FIG. 6 shows the relationship between the applied electric field and the average cosine (cos) of the orientation angle θ between the liquid crystal molecules and the pore central axis at different pore diameters, for example, 200 nm and 500 nm. According to the liquid crystal element of the embodiment, it can be understood that a very strong contrast can be obtained because almost all liquid crystal molecules can be rotated by nearly 90 ° at maximum by applying an electric field (see FIGS. 4 and 5). .

  FIG. 7A shows the relationship between the rise time until the orientation reaches a steady state by applying an electric field and the average value of the cosine (cos) of the orientation angle θ, and FIG. , And shows the relationship between the fall time from returning the electric field to zero and returning to the steady state, and the average value of the cosine (cos) of the orientation angle θ. From this graph (graph), While it takes several to several tens of ms for switching, it can be seen that the liquid crystal element of this embodiment can perform very fast switching of several tens of μs.

  Note that in the liquid crystal element of this embodiment, the alignment state shown in FIG. 18 (hereinafter referred to as “tilt alignment”) is also stable. Next, FIG. 8 shows the results of calculating the difference ΔU (= Upplaner−Utilt) of free energy between the orientation state shown in FIG. 18 and the orientation state of FIG. 4 (hereinafter referred to as planar orientation) in various pore diameters. .

  Here, both orientation states were stable in all the calculated pore diameters, but as shown in FIG. 8, the planar orientation becomes more stable when the pore diameter is less than 300 nm. The switching of the present invention is not necessarily achieved unless the pore diameter is less than or equal to this, but in terms of stability, the pore diameter is preferably 300 nm or less.

  Next, the case where a horizontal alignment process is performed on the inner surface of the pores and MBBA nematic liquid crystal having negative dielectric anisotropy is filled will be described in the same manner.

  FIG. 9 shows the relationship between the applied electric field and the average value of the sine of the orientation angle θ formed between the liquid crystal molecules and the pore central axis at different pore diameters, for example, 200 nm and 500 nm. (A) shows the relationship between the rise time until the orientation reaches a steady state when an electric field is applied and the average value of the sine of the orientation angle θ, and (b) in FIG. 10 then returns the electric field to zero. 3 shows the relationship between the fall time from the time point until the steady state returns to the steady state and the average value of the sine of the orientation angle θ.

  9 and 10, the inner surface of the pore is subjected to a horizontal alignment treatment, and even when MBBA nematic liquid crystal having a negative dielectric anisotropy is filled, the inner surface of the pore is subjected to the vertical alignment treatment. It can be seen that a high contrast and a fast switching speed can be obtained as in the case of filling 7CB nematic liquid crystal having positive dielectric anisotropy.

  By the way, as shown in FIG. 8, the planar orientation is more stable than the tilt orientation as the pore diameter is smaller, but both are in a bistable relationship. Therefore, when an electric field is applied to the planar alignment state, it may be trapped by the tilt alignment in some cases, and even if the electric field is zero, there is a possibility that the planar alignment is not restored.

  Specifically, as shown in FIG. 11A, when an electric field is applied to the planar alignment liquid crystal molecules (electric field ON), when the liquid crystal rises symmetrically with respect to the central axis of the pore 34, it is trapped in the tilt alignment. After that, even if the electric field is zero (OFF), it does not return to the planar alignment, but if all the liquid crystals rotate in the same direction as shown in FIG. 11B, it will not fall into the tilt alignment. .

  FIG. 18 shows the case where the pore wall surface is subjected to the vertical alignment treatment. However, when the pore wall surface is subjected to the horizontal alignment treatment, when an electric field is applied, the pore wall surface of FIG. ), And there is a risk of falling into a tilt orientation as shown in FIG. Also at this time, if the rotation direction of the liquid crystal starting from FIG. 5A is determined in one direction, the orientation of FIG. 5B can be realized without falling into FIG.

  Therefore, in order to reliably realize such a rise, the following processing is performed.

  First, in the structure shown in FIG. 1, an oxide such as SiO or TiO 2 is obliquely deposited on at least one surface of the first substrate 31 and the second substrate 32 on which the electrodes 36 and 37 are formed. Further, if necessary, a vertical alignment treatment agent is further applied to perform an inclined alignment treatment having an arbitrary alignment angle. As a result, as shown in FIG. 12, a rise similar to that shown in FIG. 11B is realized with the liquid crystal in the vicinity of the inclined alignment treatment surface as the starting point.

  The other is that a plurality of minute electrode elements 36a and 37a are formed on the first substrate 31 and the second substrate 32 as shown in FIG. 13, and the direction of the electric field induced by both the electrodes 36a and 37a is narrow. In this method, the first and second substrates 31 and 32 are arranged so as to be inclined in one direction with respect to the central axis of the hole 34.

  FIG. 13 (a) shows the arrangement viewed from the axial direction of the pores, and FIG. 13 (b) shows the arrangement taken from the lateral direction by taking the cross section BB ′. Here, the electrode 36a is on the first substrate and the electrode 36b is on the second substrate, and they are arranged 180 ° symmetrically with respect to the central axis of the pore.

  As a result, as shown in FIG. 14, an orientation tilted from the central axis of the pore is realized when an electric field is applied, and when the electric field is turned off, all liquid crystal molecules rotate in the same direction within the inclined plane. 11B is realized.

  Also in the case of the horizontal alignment process, the planar alignment of FIG. 5B is realized without falling into the tilt alignment of FIG.

  By the way, in the description so far, the circular shape is described as an example of the cross-sectional shape of the pore 34. However, the present invention is not limited to this, and the cross-sectional shape of the pore 34 is shown in FIGS. ) May be oval. In this case, disclination occurs at both ends of the long axis of the ellipse.

  (A) of FIG. 15 shows the change in the alignment state when the vertical alignment treatment is performed on the inner surface of the pore, and (b) shows the change of the alignment state when the horizontal alignment processing is performed on the inner surface of the pore. Then, as shown in FIG. 15A, in the cell in which the surface is vertically aligned and filled with liquid crystal having positive dielectric anisotropy, the long axis end 2 of the ellipse is obtained when no electric field is applied. Disclinations 41 and 42 are generated at locations, and disappear by application of an electric field.

  Further, as shown in FIG. 15B, in a cell that has been subjected to a horizontal alignment process and filled with liquid crystal having a negative dielectric anisotropy, when the electric field is not applied, the cell is aligned in the direction of the cylinder axis that has the minimum energy. By aligning and applying an electric field, the liquid crystal becomes perpendicular to the direction of the electric field, and disclinations 51 and 52 are generated at two positions on the major axis end of the ellipse.

  Further, the cross-sectional shape of the pore 34 may be a triangular pore having three corners. In this case, the disclination occurs at two of the three triangular corners. FIG. 16A shows a case where the cross-sectional shape is a regular triangle and the inner surface of the pore is subjected to a vertical alignment treatment, and FIG. 16B shows a case where the cross-sectional shape is a regular triangle and is aligned horizontally on the inner surface of the pore. The change of the orientation state by the electric field in the case where the process is performed is shown.

  Furthermore, even if the cross-sectional shape of the pores 34 is a polygon whose cross-sectional shape has at least two diagonal lines, disclination occurs at two diagonal portions. 17A shows a case where the cross-sectional shape is square and the inner surface of the pore is subjected to the vertical alignment treatment, and FIG. 17B shows a case where the cross-sectional shape is square and the inner surface of the pore is subjected to the horizontal alignment treatment. The change of the alignment state by the electric field in the case where it is given is shown.

4A and 4B illustrate a structure of a liquid crystal element according to an embodiment of the present invention. The figure which shows the example of the protrusion arrangement | sequence of a SiC mold for forming a pore in the 3rd board | substrate of the said liquid crystal element. The figure which shows the growth process of the said pore. (A) is a figure which shows the orientation of a liquid crystal when the inner surface of the said pore is given the vertical alignment process, (b) is a figure which shows the orientation of the liquid crystal when an electric field is given. (A) is a figure which shows the orientation of a liquid crystal when the inner surface of the said pore is given the horizontal orientation process, (b) is a figure which shows the orientation of the liquid crystal when an electric field is given. The figure which shows the relationship between the applied electric field and the orientation angle | corner of a liquid crystal molecule in case the said inner surface of a pore is performed the vertical alignment process. The figure which shows the relationship between the orientation angle | corner of a liquid crystal molecule | numerator, and the switching speed in case the said inner surface of a pore is performed the vertical alignment process. The figure which shows the relationship between the pore diameter in case the said inner surface of a pore is performing the vertical alignment process, and the energy difference between tilt alignment and planar alignment state. The figure which shows the relationship between the applied electric field and the orientation angle | corner of a liquid crystal molecule in case the horizontal inner surface is given to the said pore inner surface. The figure which shows the relationship between the orientation angle of a liquid crystal molecule | numerator, and switching speed in case the horizontal inner surface is given to the said pore inner surface. The figure which shows the mode of switching in the case where the said pore inner surface is given the vertical alignment process. The figure which shows the mode of switching when the inclination alignment process is performed to the 1st board | substrate and the 2nd board | substrate, when the said pore inner surface is subjected to the vertical alignment process. 4A and 4B illustrate a configuration in which an oblique electric field is applied to a pore center axis in the liquid crystal element. The figure which shows the mode of switching when the direction of an electric field makes a finite angle with the central axis of a pore, when the said pore inner surface is subjected to the vertical alignment process. The figure which shows the mode of switching in case the cross-sectional shape of the said pore is an ellipse. The figure which shows the mode of switching when the cross-sectional shape of the said pore is an equilateral triangle. The figure which shows the mode of switching when the cross-sectional shape of the said pore is a square. The figure which shows the orientation state of the liquid crystal in the conventional cylindrical cavity. The figure which shows the tilt orientation which arises when an electric field is applied when the said pore wall surface is subjected to horizontal orientation processing.

Explanation of symbols

31 First substrate 32 Second substrate 33 Third substrate 34 Pore 35 Liquid crystal 36 Electrode on first substrate 36a Electrode on first substrate 37 Electrode on second substrate 37a Electrode on second substrate

Claims (7)

In the liquid crystal element in which the liquid crystal is filled between the first substrate and the second substrate,
A liquid crystal holding member sandwiched between the first substrate and the second substrate, filled with the liquid crystal and having a single or a plurality of pores penetrating in the substrate direction;
Electrodes respectively formed on surfaces of the first substrate and the second substrate on the liquid crystal holding member side;
With
A liquid crystal element, wherein disclination is generated in at least two places in the pores by a change in the voltage between the electrodes.   By applying vertical alignment treatment to the inner side surface of the pore and filling the pore with a liquid crystal having positive dielectric anisotropy, at least two locations in the pore are discriminated when no voltage is applied by the electrode. The liquid crystal element according to claim 1, wherein a nation is generated.   By applying a horizontal alignment treatment to the inner side surface of the pore and filling the pore with a liquid crystal having a negative dielectric anisotropy, at least two locations in the pore are disclinated when a voltage is applied by the electrode. The liquid crystal element according to claim 1, wherein:   4. The tilt alignment process is performed on at least one of the first substrate and the second substrate that faces the pores of the liquid crystal holding member. 5. Liquid crystal element.   4. The electrode according to claim 1, wherein the electrodes of the first substrate and the second substrate are arranged so as to give an electric field having an inclination with respect to a central axis of the pore. 5. Liquid crystal element.   6. The liquid crystal device according to claim 1, wherein a cross-sectional shape of the pores is a circle, an ellipse, or a polygon. A liquid crystal device comprising the liquid crystal element according to claim 1.

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