JP2007114623A - Liquid crystal device, liquid crystal display medium, and manufacturing method for liquid crystal device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid crystal device with display memory functionality that can hold an alignment state of liquid crystal molecules and maintain a displayed gray scale without applying a voltage signal between a pair of electrodes between which the liquid crystal space is sandwiched thereafter once the gray scale is displayed by coordinating liquid crystal molecules in a liquid crystal space. <P>SOLUTION: An intermediate layer 3 having many pores 6 formed is sandwiched between a rear substrate 1 and a front substrate 2 and the pores 6 are filled with liquid crystals 8. A control part applies an AC voltage of tens of Hz between a common electrode 9 and a display electrode 12 to change a planar alignment state to a tilt alignment state and applies an AC voltage of ≥6 kHz to change the tilt alignment state to the planar alignment state. Even when the potential difference between the common electrode 9 and display electrode 12 is eliminated after a desired gray scale is displayed, the gray-scale display of a pixel 11 is maintained until next writing. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a liquid crystal device in which a large number of liquid crystal spaces partitioned by partition walls are arranged between a pair of opposed electrodes, and more specifically, an alternating voltage signal is applied between a pair of electrodes to display a binary gradation. The present invention relates to a liquid crystal device.

  Liquid crystal devices that perform gradation display by changing the alignment state of liquid crystal molecules in a liquid crystal space in response to an applied voltage signal have been put into practical use. A general liquid crystal device is formed by facing a pair of glass substrates having transparent electrodes formed on the inner surface thereof at intervals of about 5 μm and filling the liquid crystal in the facing interval. A general liquid crystal device can display binary gradations in an application state in which a voltage is applied between a pair of electrodes and a non-application state in which the potentials of the pair of electrodes are equal.

  Patent Document 1 discloses a liquid crystal device in which an intermediate layer in which a large number of pores (cavities) are formed between a pair of opposed electrodes is sandwiched, and the pores are filled with liquid crystal. Here, an alignment treatment is performed on the inner wall surface of the pore so that the liquid crystal molecules stand upright radially from the inner wall of the tapered pore. Then, a DC voltage is applied between the pair of electrodes so that the liquid crystal molecules in the pores are coordinated in the thickness direction of the intermediate layer, and the potentials of the pair of electrodes are made equal, so that the liquid crystal molecules in the pores Binary gradations can be displayed in a state in which the dots are radially arranged.

  According to the structure of the liquid crystal space and the driving method, since the coordination distribution of the liquid crystal in the cross section of the pore is point-symmetric with respect to the center of the cross section, the viewing angle of the display configured with such a liquid crystal device Has the advantage of being wide and unrelated to the viewing orientation. Non-Patent Document 1 discloses a technique for forming pores of such a size with high accuracy.

Japanese Patent Laid-Open No. 10-232398 Advanced Materials, 200113, no. 3, February 5, p189-p192

  Most of the conventional practical liquid crystal devices including the liquid crystal device disclosed in Patent Document 1 constrain the liquid crystal molecules at the interface to one direction by the alignment treatment applied to the interface of the liquid crystal space, and the liquid crystal at the interface. Gradation is displayed by deflecting the alignment state of the liquid crystal molecules that are elastically connected to the molecules with a DC voltage. Then, when the DC voltage is released, the liquid crystal molecules in the liquid crystal space return to the original alignment state so that the stretched spring returns. Therefore, in order to maintain the gradation state displayed in the liquid crystal space, it is necessary to continue to apply the same DC voltage so as to hold the extended spring in an extended state.

  In the present invention, once a gradation is displayed by arranging liquid crystal molecules in a liquid crystal space, the alignment state of the liquid crystal molecules is maintained without applying a voltage signal between a pair of electrodes sandwiching the liquid crystal space. It is an object of the present invention to provide a liquid crystal device having a display memory property that can maintain the displayed gradation.

  The liquid crystal device of the present invention includes an intermediate layer having a large number of pores, a pair of sealing substrates disposed with the intermediate layer interposed therebetween, and a space in the pores facing the thickness direction of the intermediate layer. In a liquid crystal device including a pair of electrodes that form an electric field and a liquid crystal filled in the pores, the inner wall surface of the pores is in the major axis direction of the molecules of the liquid crystal along the inner wall surface of the pores A surface property that restrains the liquid crystal molecules to the inner wall surface while allowing the liquid crystal molecules to be rotated, and applying an AC voltage signal to the pair of electrodes, an AC electric field in the thickness direction of the intermediate layer in the space in the pores It is provided with the control means which forms.

  In the liquid crystal device of the present invention, the liquid crystal molecules at the interface are adsorbed on the inner wall surface of the pores, the side portions are along the inner wall surface, and the voltage between the pair of electrodes remains while the liquid crystal molecules are lying on the inner wall surface. The major axis can be rotated 360 degrees in response to the polarity. In the liquid crystal space in the pores, the liquid crystal molecules connected to the liquid crystal molecules on the interface lying on the inner wall surface drag and rotate the liquid crystal molecules on the interface to control the major axis direction.

  Therefore, when a DC voltage or a low-frequency AC voltage is applied to a pair of electrodes, the liquid crystal space in the pores has an alignment state of liquid crystal molecules aligned in the thickness direction of the intermediate layer in response to the voltage polarity. It is formed. This alignment state is formed without generating stress between the liquid crystal molecules in the liquid crystal space including the interface. In addition, the free movement is anchored to the non-free liquid crystal molecules due to the constraint of the inner wall surface, and a stable state is maintained in which the alignment state is maintained by resisting temperature rise and disturbance voltage. Therefore, even if the voltage between the pair of electrodes is released, the alignment state is maintained as it is, and the gradation displayed by the liquid crystal space does not change.

  On the other hand, when an AC voltage with a high frequency that cannot be followed by liquid crystal molecules in the liquid crystal space is applied, the liquid crystal molecules vibrate while being aligned in a direction perpendicular to the thickness direction, and the stress state of the liquid crystal space including the interface is minimized. It shifts to such an orientation state. That is, the inner wall surface liquid crystal molecules are aligned following the liquid crystal molecules in the liquid crystal space with the major axis direction aligned with the maximum width direction of the pores (see FIG. 3). As a result, the liquid crystal molecules are connected in the transverse direction of the pores, and an alignment state anchored by the liquid crystal molecules aligned in the thickness direction of the inner wall surface is formed.

  This alignment state is also formed between the liquid crystal molecules in the liquid crystal space including the interface without generating a stress toward another coordination, so that the alignment is achieved even if the voltage between the pair of electrodes is released. The state is maintained as it is. Therefore, the gradation displayed by the liquid crystal space does not change, resisting temperature rise and disturbance voltage.

  Hereinafter, a liquid crystal display device 100 according to an embodiment of the present invention will be described in detail with reference to the drawings. The liquid crystal device of the present invention is not limited to the constituent members and the arrangement of the embodiments described below, but as various embodiments in which some or all of the constituent members are replaced with other constituent members having equivalent functions. It can be implemented. For example, a liquid crystal display device having a different electrode arrangement and drive circuit from the liquid crystal display device 100, an electric bulletin board, a sign board, a segment display device that does not perform pixel display, an electronic paper that performs one-way scanning writing through a writing head, an alternating current An electronic blackboard or the like for writing with an electric field pen.

  The liquid crystal display device 100 is a transmissive device that performs transmissive illumination with a backlight, but the present invention may be implemented as a reflective or transflective device in which a reflective electrode is provided.

  In addition, the liquid crystal display device 100 performs gradation display according to the change of the birefringence of the liquid crystal layer by combining the polarizing plates, but without using the polarizing plate, the liquid crystal space due to the difference in the alignment state of the liquid crystal molecules. The display may be performed using the apparent light and shade difference.

  Note that the general structure and the general manufacturing method of the liquid crystal device disclosed in Patent Document 1 are different from the gist of the present invention, and therefore some illustrations are omitted and detailed description is also omitted.

<Liquid crystal display device>
FIG. 1 is an explanatory diagram of a cross-sectional configuration of the liquid crystal display device of the present embodiment, FIG. 2 is an explanatory diagram of AC voltage driving, FIG. It is explanatory drawing of the orientation state at the time of applying an alternating voltage. The liquid crystal display device 100 according to the present embodiment is an electronic bulletin board that performs black and white two-tone image display using a dot matrix.

  As shown in FIG. 1, the liquid crystal display device 100 of this embodiment is configured by sandwiching an intermediate layer 3 in which a large number of pores 9 are formed between a transparent rear substrate 1 and a transparent front substrate 2. The A transparent common electrode 9 is formed on the inner surface of the front substrate 2 disposed on the observation side.

  On the other hand, display electrodes 12 and 15 for each of the pixels 11 and 14 are formed on the inner surface of the rear substrate 1 on the illumination side, and switching elements 13 and 16 are formed on the interlayer insulating layer 7 below the display electrodes 12 and 15. ing. The common electrode 9 and the display electrodes 12 and 15 are electrodes for applying a voltage in the liquid crystal 8 in the direction of the central axis of the pore 6, and are on the surface facing the intermediate layer 3 of the rear substrate 1 and the front substrate 2. Indium tin oxide (ITO) thin film is formed by vacuum deposition, sputtering or the like.

  The size of the display electrode 12 is determined in units of pixels, and the diameter of the pore 6 may be several tens of nanometers or more. One display electrode 12 is arranged on the plurality of pores 6 group, and one pixel Configure.

  The display electrodes 12 and 15 and the switching elements 13 and 16 are all transparent and do not hinder illumination by a backlight (not shown) arranged outside the rear substrate 1. At least one of the rear substrate 1 and the front substrate 2 is a light transmissive glass or a transparent plastic substrate such as polycarbonate or acrylic (PMMA).

  The intermediate layer 3 is formed of an aluminum vapor-deposited thin film, and has pores 6 that are partitioned by partition walls resembling a honeycomb structure and penetrate the intermediate layer 3. A plurality of pores 6 are assigned to the pixels 11 and 14, respectively, and the space inside the pores 6 is filled with liquid crystal 8. The control unit 20 controls the switching elements 13 and 16 to apply a predetermined AC voltage signal between the common electrode 9 and the display electrodes 12 and 15, thereby arranging the liquid crystal 8 in the pores 6. Are changed between a tilt (TILT) alignment state and a planar (PLANAR) alignment state in two ways.

  A polarizing plate 4 is overlaid on the outer surface of the rear substrate 1, and a polarizing plate 5 is overlaid on the outer surface of the front substrate 2. The polarizing plates 4 and 5 set the inclinations of the polarization planes of each other so as to form the maximum contrast between the alignment state of the liquid crystal 8 in the pores 6 and the planar alignment state. It is.

  Referring to FIG. 1, as shown in FIG. 2, the control unit 20 applies a low-frequency AC voltage signal between the common electrode 9 and the display electrodes 12 and 15, thereby liquid crystal in the pores 6. 8 is a tilt alignment state. Further, by applying an alternating voltage signal having a high frequency, the liquid crystal 8 in the pore 6 is brought into a planar alignment state.

  As shown in FIG. 3, in the planar alignment state, a part of the liquid crystal molecules near the inner wall surface of the pore 6 is aligned in the major axis direction of the pore 6 and the other liquid crystal molecules are approximately the length of the pore 6. In this state, it is oriented perpendicular to the axial direction. Then, when an electric field such that the major axis of the liquid crystal molecules extends along the central axis direction of the pore 6 with respect to the planar alignment state is given with an intensity greater than a certain threshold value, the state shifts to the tilt alignment state shown in FIG. Even if the application is stopped, the tilt alignment state is maintained.

  As shown in FIG. 4, the tilt alignment state is a state in which all the liquid crystal molecules in the pores 6 are aligned in the major axis direction of the pores 6. Then, when an alternating voltage signal having a high frequency that cannot be followed by rotation of the liquid crystal molecules is applied to the tilt alignment state, an electric field that causes the major axis direction of the liquid crystal molecules to be perpendicular to the central axis direction of the pores 6 is applied. As in the case where the intensity is given at a certain threshold value or more, the planar alignment state of FIG. 3 is entered, and the planar alignment state is maintained even when the application of the electric field is stopped.

  In the present embodiment, the cross-sectional shape of the pores 6 is circular and elliptical, or a triangle having three corners, a square having four or more corners, that is, a square or hexagon having a diagonal line. ing.

  The plurality of pores 6 (may be single) penetrate the intermediate layer 3 sandwiched between the gaps between the rear substrate 1 and the front substrate 2 in the direction perpendicular to the substrate surface. The horizontal alignment process is performed. The horizontal alignment treatment is a condition that the liquid crystal molecules are always perpendicular to the normal vector of the inner wall surface, that is, the liquid crystal molecules only lie along the inner wall surface, and the long axis direction is not limited to 360 degrees. Represents. For example, the interface condition is such that a rubbing process for constraining the major axis direction of liquid crystal molecules is omitted from an alignment layer applied to a substrate surface of a normal liquid crystal display device. If such an alignment treatment is performed, the bistable state shown in FIGS. 3 and 4 can be obtained without any particular limitation on the type of nematic liquid crystal.

  In these two alignment states, since the alignment state of the liquid crystal molecules changes greatly, the liquid crystal 8 itself has a difference in transmittance and reflectance, but the polarizing plate 4 in which the crossing angle of the polarization planes is set appropriately. By superimposing 5, it is possible to display a higher contrast using the birefringence difference between the two alignment states. Which of the two alignment states is assigned to the light shielding / transmission can be arbitrarily set according to the crossing angle of the polarization planes of the polarizing plates 4 and 5.

  In the liquid crystal display device 100 of the present embodiment, as described above, it is possible to go back and forth between two stable states having different orientation angles and different light transmittances by applying a temporary electric field. Therefore, a desired transmittance can be maintained in the pixels 11 and 14 without continuously applying an electric field, and the liquid crystal display device can be used with low power consumption. In other words, it is not necessary to apply a voltage except during switching, and is used as a liquid crystal display device with low power consumption.

<Method for producing intermediate layer>
FIG. 5 is an explanatory diagram of a method for producing an intermediate layer having pores having a square cross section, and FIG. 6 is an explanatory diagram of a method for producing pores having another cross sectional shape. In FIG. 5, (a) shows the arrangement of protrusions, and (b) shows the growth process of pores by anodic oxidation. In the liquid crystal display device 100 of this embodiment, the pores 6 are produced by processing the aluminum thin film laminated on the rear substrate 1 based on the technique disclosed in Non-Patent Document 1.

  As shown in FIG. 5A, first, a silicon carbide SiC mold 40 in which the protrusions 41 are arranged is formed using an electron beam lithography technique. The arrangement of the protrusions 41 is determined by the cross-sectional shape of the pores 6 to be created. When it is desired to create a square pore, the protrusions 41 are arranged so as to form a square lattice.

  The shape of the pore 6 finally created substantially coincides with the Voronoi figure 42 having the protrusion 41 as a generating point. The Voronoi graphic 42 is a graphic indicating an area in which when there are a plurality of generating points, the generating point closest to an arbitrary point included in a certain area is a generating point included in the area. The protrusion 41 also indicates the starting point of the generation of the pore 6.

  In addition, as shown to (a) of FIG. 6, when producing the hexagonal pore 6, the protrusion 41 is arranged so that a hexagonal lattice may be created. Further, as shown in FIG. 6B, when the triangular pores 6 are formed, the protrusions 41 are arranged so as to form a triangular lattice.

Next, the SiC mold 40 in which the protrusions 41 are arranged is pressed against the surface of the rear substrate 1 on which the aluminum thin film is formed with a pressure of 1600 kg / cm ² using hydraulic pressure. By this operation, as shown in FIG. 5B, an array of minute recesses 51 by the protrusions 41 on the SiC mold 40 is formed on the surface of the aluminum thin film.

  Next, the aluminum thin film of the rear substrate 1 is anodized using 5% by weight of oxalic acid or phosphoric acid under constant voltage conditions. When such an anodic oxidation treatment is performed, initially, the anodic oxidation rate is the highest in the dent 51, that is, the elution rate of aluminum is high, so that the pores 6 gradually grow outward from the dent 51.

  Therefore, the cross-sectional shape of the pore 6 is circular immediately after the start of the anodizing treatment. 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 aluminum ions is small, so that the growth of the pores 6 is suppressed. The cross-sectional shape of 6 gradually approaches the Voronoi figure 52, and the pore 6 is created.

  FIG. 5B is a diagram illustrating a state in which the pores 6 are gradually enlarged when the pores 6 having a square cross-sectional shape are formed. In the figure, the recess 51 is transferred to the surface of the aluminum thin film by pressing the SiC mold 40 (a). The pore 6 gradually grows according to the arrow toward the Voronoi figure 52 with the first created recess 51 as a generating point. And the pore 6 makes the intermediate | middle layer 3 penetrate the single or some pore 6 from the dent 51 by the said method.

  Since the aluminum thin film is processed by the anodic oxidation method, the intermediate layer 3 is changed to aluminum oxide (alumina) (at least the inner wall surface and the substrate surface are sure). Since alumina has an insulating property, an insulating layer for insulating the common electrode 9 and the display electrodes 12 and 15 is unnecessary.

  Since the pores 6 are electrically insulated from each other by the aluminum remaining in the center of the partition wall, bleeding due to electric field leakage does not occur at the boundary portion between the adjacent display electrodes 12 and 15.

  If an aluminum alloy substrate whose composition ratio is modulated in a direction perpendicular to the rear substrate 1 is used instead of a single composition aluminum thin film, the electrical resistance value and resistance to acid change in proportion to the change in the alloy composition ratio. For this reason, the degree of expansion of the diameter of the pores 6 caused by the anodic oxidation process is changed, and the tapered pores (conical shape) in which the diameter linearly increases or decreases in the central axis direction can be created. Then, as will be described later, the planar alignment state in the pores 6 can be stabilized by forming the pores 6 in a tapered shape.

  An alloy thin film whose composition ratio changes in the film thickness direction can be formed by changing the bias voltage balance between the two sputtering targets in the film forming process using a sputtering deposition apparatus in which two sputtering targets are arranged. The metal species of the sputtering target used for the alloy may be any of Ti, Zr, Hf, Nb, Ta, Mo, and W. Moreover, a desired taper angle can be obtained by adjusting the degree of change in the composition ratio.

  Next, the horizontal alignment treatment agent is filled into the pores 6, and the horizontal alignment treatment is performed on the inner wall surfaces of the pores 6. In addition, as a horizontal alignment processing agent, it is in the solution which mixed NMP (N methylpyrrolidone) and nBC (n butyl cellosolve) of polyamic acid LP64 (made by Toray Industries, Inc.) which is a polyimide precursor in a ratio of 2: 1. LP64 adjusted to 1.0% by weight is used. Thereafter, the liquid crystal 8 is filled in the pores 6, the front substrate 2 on which the common electrode 9 (FIG. 1) is formed is arranged on the surface, and the intermediate layer 3 on the rear substrate 1 is sandwiched, whereby the liquid crystal display device 100 is formed.

  The liquid crystal 8 is filled with a two-frequency nematic liquid crystal material. A dual frequency nematic liquid crystal material is a material that has positive dielectric anisotropy under a low frequency electric field and negative under a high frequency electric field.

  For example, TX2A liquid crystal, which is a two-frequency nematic liquid crystal material, has a crossover frequency of 6 KHz, and the common electrode 9 and display electrodes 12 and 15 in FIG. When the voltage is applied, the liquid crystal 8 tends to be aligned along the central axis of the pores 6 due to the positive dielectric anisotropy. Therefore, if it is in the planar alignment state, it shifts to the tilt alignment state.

  In addition, when an AC voltage having a frequency higher than 6 KHz is applied at a voltage higher than a certain threshold, the liquid crystal 8 tends to be aligned so as to be orthogonal to the central axis of the pore 6 due to negative dielectric anisotropy. If it is in the alignment state, it transitions to the planar alignment state.

  That is, an AC electric field is required for both switching operations. In the planar alignment state → tilt alignment state, the liquid crystal molecules must be along the electric field direction (= positive dielectric anisotropy), and in the tilt alignment state → planar alignment state, the liquid crystal molecules are orthogonal to the electric field direction ( = Has negative dielectric anisotropy).

  Therefore, in the planar alignment state → tilt alignment state, an AC electric field of 6 kHz or less having a positive dielectric anisotropy is applied to the two-frequency driving liquid crystal, and in the tilt alignment state → planar alignment state, it has a negative dielectric anisotropy. An AC electric field of 6 kHz or more is applied.

<Stability of alignment state>
FIG. 7 is a diagram of voltage drive from the planar alignment state, FIG. 8 is an explanatory diagram of changes in alignment state due to 3.0e6 [V / m] drive, and FIG. 9 is an alignment state due to 4.0e6 [V / m] drive. FIG. 10 is a diagram of voltage drive from the tilt alignment state, FIG. 11 is an explanatory diagram of the change in alignment state by 1.0e7 [V / m] drive, and FIG. 12 is 1.1e7 [V / m] An explanatory diagram of changes in the orientation state due to driving, FIG. 13 is a diagram of the relationship between the aperture diameter of the pores and the orientation state, and FIG. 14 is a voltage drive line from the planar orientation state where the aperture diameters of the pores are different. 15 is an explanatory diagram of a planar orientation state in a pore having a square cross-sectional shape, FIG. 16 is an explanatory diagram of a planar orientation state in a pore having a circular cross-sectional shape, and FIG. 17 is a pore having a rectangular and rhombus cross-sectional shape. FIG. 18 is an explanatory view of the planar alignment state in FIG. FIG. 19 is an explanatory diagram of a planar orientation state in a triangular pore, FIG. 19 is an explanatory diagram of a planar orientation state in a triangular pore whose cross-sectional shape is different from the base / height ratio, and FIG. 20 is an explanatory diagram of an unstable planar orientation state. FIG.

  Regarding the alignment characteristics and switching characteristics of the liquid crystal display device 100 manufactured as described above, the results of examination by numerical simulation of liquid crystal alignment based on the continuum theory will be described. The continuum theory is a theory based on the relational expression between the alignment state of liquid crystal molecule aggregates (= director) such as Landau-de Gennes free energy and Frank free energy, and the energy of the liquid crystal layer. The dynamic behavior of the liquid crystal phase can be calculated using these equations and the macroscopic properties of the liquid crystal obtained by experiments such as elastic constants and Landau parameters.

  In this numerical simulation simulation, the pore 6 having a taper shape with an apex angle of 30 ° is assumed in which the cross-sectional shape of the pore 6 is circular, the pretilt angle in the horizontal alignment characteristics of the inner wall surface of the pore 6 is 15 °. Modeled. In order to model the driving of the two-frequency nematic liquid crystal according to the embodiment, the transition from the planar alignment state to the tilt alignment state was calculated for 7CB nematic liquid crystal having positive dielectric anisotropy. The transition from the tilt alignment state to the planar alignment state was calculated for MBBA nematic liquid crystal having negative dielectric anisotropy. In other words, 7CB liquid crystal with positive dielectric anisotropy is used for simulation calculation from planar alignment state to tilt alignment state, and MBBA liquid crystal with negative electric anisotropy is targeted for simulation calculation from tilt alignment state to planar alignment state. Switching is confirmed. Both applied electric fields have the same polarity and opposite dielectric anisotropy.

  First, switching from planar alignment to tilt alignment will be described. 7 to 9 show the alignment of liquid crystal molecules when an electric field is applied in the thickness direction of the intermediate layer 3 using the common electrode 9 and the display electrode 12 with respect to the liquid crystal 8 in the planar alignment state in the pores 6. It is a figure which shows an angular change. Here, the orientation angle refers to the average value of the angles formed by the major axis of the liquid crystal molecules and the major axis of the pores.

  As shown in FIG. 7, when an electric field having an electric field strength of 3.0e6 [V / m] is applied, the orientation angle decreases from 65 ° to around 20 °, but the application of the electric field is canceled after reaching a steady state ( X), it rises to the original 65 ° and returns to the planar alignment state.

  FIG. 8 shows a simulation result of the orientation distribution of liquid crystal molecules in the cross section of the pore 6 to which an electric field of 3.0e6 [V / m] is applied. 8A shows a planar alignment state before application of an electric field, FIG. 8B shows a steady state during application of the electric field, and FIG. 8C shows a steady state after cancellation of the electric field.

  On the other hand, when the electric field strength is 4.0e6 [V / m], as shown in FIG. 7, the orientation angle greatly decreases to around 5 °, and even if the application of the electric field is canceled (x), it does not return to the original state. It becomes steady at around 10 ° and transitions to a tilt alignment state.

  FIG. 9 shows a simulation result of the orientation distribution of the liquid crystal molecules in the cross section of the pore 6 to which an electric field of 4.0e6 [V / m] is applied. 9A shows a planar alignment state before application of an electric field, FIG. 9B shows a steady state during application of the electric field, and FIG. 9C shows a steady state after cancellation of the electric field.

  Next, switching from tilt alignment to planar alignment will be described. 10 to 12 show liquid crystal molecules when an AC electric field is applied in the thickness direction of the intermediate layer 3 using the common electrode 9 and the display electrode 12 with respect to the liquid crystal 8 in the tilt alignment state in the pores 6. It is the result of having simulated the orientation angle change of.

  As shown in FIG. 10, when an electric field having an electric field strength of 1.0e7 [V / m] is applied, the orientation angle increases from 10 ° to near 75 °, but the application of the electric field is canceled after reaching a steady state. Then, (x), the tilt is lowered to the original 10 ° to return to the tilt alignment state.

  FIG. 11 shows a simulation result of the orientation distribution of liquid crystal molecules in the cross section of the pore 6 to which an electric field of 1.0e7 [V / m] is applied. 11A shows a planar alignment state before application of an electric field, FIG. 11B shows a steady state during application of the electric field, and FIG. 11C shows a steady state after cancellation of the electric field.

  On the other hand, when the electric field strength is 1.1e7 [V / m], as shown in FIG. 12, the orientation angle greatly increases to near 90 °, and it does not return even when the application of the electric field is canceled (x). It becomes steady around 65 °. That is, the tilt alignment state is shifted to the planar alignment state.

  As described above, the common electrode 9 and the display electrode 12 of the present embodiment that apply a voltage in the thickness direction of the intermediate layer 3 using the two-frequency nematic liquid crystal whose sign of dielectric anisotropy changes depending on the frequency of the electric field, It was confirmed that the liquid crystal 8 in the pore 6 can be switched between the planar alignment state and the tilt alignment state.

  In the simulation calculation, the case where the diameter of the pore 6 is 1000 nm is shown. However, switching between the planar alignment state and the tilt alignment state is not limited to this diameter. FIG. 13 shows the relationship between the pore diameter and the switching orientation angle, and FIG. 14 shows the switching characteristics from the planar orientation state to the tilt orientation state when the pore diameter is 500 nm.

  As shown in FIG. 13, even when the diameter of the pores 6 is changed in the range of 100 nm to 10 μm, the alignment angles in the planar alignment state and the tilt alignment state are substantially constant.

  On the other hand, in the case of the diameter of 500 nm shown in FIG. 14 as compared with the case of the diameter of 1000 nm shown in FIG. 7, the electric field intensity required for switching increases and the time required for switching is greatly shortened. This is because, as the diameter of the pore 6 becomes smaller, the binding force of the liquid crystal molecules by the inner wall surface becomes larger, so that a larger electric field is required to change the alignment state. The reason why the response speed is increased is that the electric field has become stronger, and another reason is that the response from the release of the electric field to the steady state becomes faster as the diameter of the pore 6 becomes smaller.

  As described above, a desired threshold electric field and switching speed can be obtained by selecting the diameter of the pore 6 without changing the transmittance (the thickness of the intermediate layer 3).

  Further, the above simulation calculation shows a case where the cross-sectional shape of the pore 6 is a perfect circle. However, switching between the planar alignment state and the tilt alignment state is not limited to the perfect circular cross-sectional shape. 15 shows a case where the cross-sectional shape of the pore is a square, FIG. 16 shows a case where the cross-sectional shape of the pore is an ellipse, and FIG. 17 shows a case where the cross-sectional shape of the pore is a rectangle and a rhombus. Shows the respective simulation results when the cross-sectional shape of the pores is triangular.

  As shown in FIG. 8, when the cross-sectional shape of the pore 6 is a perfect circle, the in-plane direction of the planar alignment state is not determined, but when the cross-sectional shape of the pore 6 is square, as shown in FIG. The planar in-plane direction of the planar alignment state is limited to two directions perpendicular to the opposite sides.

  Also, in the case of an elliptical, rectangular, or rhombus cross-sectional shape in which the aspect ratio (major axis / minor axis ratio) is not 1 with respect to a circle or square having a plurality of in-plane directions in the planar alignment state, FIG. As shown in FIG. 17, the in-plane direction in the planar alignment state can be limited to one direction. As shown in FIG. 16, when the cross-sectional shape of the pore 6 is elliptical, the in-plane direction of the cross-sectional plane in the planar alignment state is the major axis direction. As shown in FIG. 17A, when the cross-sectional shape of the pore 6 is rectangular, the in-plane direction of the cross-sectional plane in the planar alignment state is the long side direction. As shown in FIG. 17B, when the cross-sectional shape of the pore 6 is a rhombus, the planar in-plane direction in the planar alignment state is a long diagonal direction.

  The aspect ratio represents the ratio of the long side to the short side of the rectangle and the ratio of the long axis to the short axis of the ellipse. In the formation of the pores 6 by the anodic oxidation method, the vertical interval and the horizontal If the direction interval is shifted, the pores 6 having an aspect ratio other than 1 are formed.

  On the other hand, in the case of an equilateral triangle, as shown in FIG. 18, the disclination is generated at the center, so that a state in which three orientation directions for each corner coexist can be obtained. Further, by changing the aspect ratio of the triangle, the balance of coexistence of the three orientation directions can be changed as shown in FIG.

  As described above, in order to obtain various in-plane alignment states of the planar alignment, the cross-sectional shape of the pores 6 can be arbitrarily selected from circular, elliptical, polygonal, and the like.

  Further, in the above simulation calculation, the tapered shape of the pores 6 is a cone shape with an apex angle of 30 °, but switching between the planar alignment state and the tilt alignment state is a cone-shaped taper shape with an apex angle of 30 °. It is not limited to.

  However, in the case of a complete columnar shape with an apex angle of 0 °, when switching from tilt alignment to planar alignment, as shown in FIG. 20, all liquid crystal molecules were biased in the direction of rotation in the same direction. The possibility of taking a state increases a little. In this case, when the application of the electric field is released, all the liquid crystal molecules rotate in the same direction and return to the original tilt alignment. Therefore, it is desirable to give the pore 6 a finite apex angle.

<Pore of Comparative Example>
FIG. 21 is an explanatory diagram of the pseudo planar alignment state of the liquid crystal in the pore of the comparative example, and FIG. 22 is an explanatory diagram of the pseudo tilt alignment state of the liquid crystal in the pore of the comparative example.

  As shown in FIG. 21, the cavity (pore) 6D of the intermediate layer disclosed in Patent Document 1 is subjected to an alignment process on the inner wall surface 6E so that liquid crystal molecules stand upright from the inner wall surface 6E. Accordingly, the liquid crystal molecules in the cylindrical cavity 6D are oriented in the radial direction of the cross section of the cavity 6D as it approaches the inner wall surface 6E of the cavity 6D, and along the central axis of the cavity 6D as it approaches the central axis of the cavity 6D. Orient. When an electric field in the central axis direction of the cavity 6D is applied to such a quasi-planar alignment state, when the liquid crystal molecules have positive dielectric anisotropy, as shown in FIG. Aligned along the central axis of the pixel, a pseudo tilt alignment state is obtained, and the transmittance of the pixel changes.

  However, the pseudo-tilt alignment state shown in FIG. 22 releases the electric field because the liquid crystal molecules trying to return to the pseudo-planar alignment state shown in FIG. Then, the pseudo planar alignment state is quickly restored. That is, in order to maintain the desired transmittance in the pseudo tilt alignment state, an axial electric field must be continuously applied to the cavity 6D, which causes a problem of high power consumption.

<Correspondence with Invention>
The liquid crystal display device 100 according to the present embodiment has an intermediate layer 3 having a large number of pores 6, a pair of rear substrate 1 and front substrate 2 disposed with the intermediate layer 3 interposed therebetween, and is opposed to the thickness direction of the intermediate layer 3. The common electrode 9 and the display electrode 12 that form an electric field in the space inside the pore 6 and the liquid crystal filled in the pore 6 are provided. The inner wall surface of the pore 6 has a surface property that restrains the liquid crystal molecules to the inner wall surface while allowing the major axis direction of the liquid crystal molecules to rotate along the inner wall surface of the pore 6. 12 is provided with a control unit 20 that applies an AC voltage signal to 12 and forms an AC electric field in the thickness direction of the intermediate layer 3 in the space in the pore 6.

  Therefore, in the space in the pore 6, the liquid crystal molecules at the interface are adsorbed on the inner wall surface of the pore 6 and the side portions are along the inner wall surface, and the liquid crystal molecules are lying on the inner wall surface and remain in the common electrode. 9. The major axis direction can be rotated 360 degrees in response to the voltage polarity between the display electrodes 12. In the liquid crystal space in the pore 6, the liquid crystal molecules connected to the liquid crystal molecules on the interface lying on the inner wall surface drag and rotate the liquid crystal molecules on the interface to control the major axis direction.

  Therefore, when a DC voltage or a low-frequency AC voltage is applied to the common electrode 9 and the display electrode 12, the liquid crystal space in the pore 6 is aligned in the thickness direction of the intermediate layer 3 in response to the voltage polarity. An alignment state of liquid crystal molecules is formed. Since this alignment state is formed without generating stress between the liquid crystal molecules in the liquid crystal space including the interface, the alignment state is maintained as it is even if the voltage between the common electrode 9 and the display electrode 12 is released. The gradation displayed by the liquid crystal space does not change.

  On the other hand, when an AC voltage having a high frequency that the liquid crystal molecules in the pores 6 cannot follow is applied, the liquid crystal molecules vibrate while being coordinated in a direction perpendicular to the penetration direction of the pores 6 to include the interface. The mutual positional relationship and posture are changed in such a direction that the stress state of the liquid crystal space is minimized. As a result, the liquid crystal molecules are connected in the transverse direction of the pores 6, and an alignment state brazed by the liquid crystal molecules on the inner wall surface coordinated in the penetration direction of the pores 6 is formed. Since this alignment state is also formed between the liquid crystal molecules in the liquid crystal space including the interface without causing stress to move to another coordination, the voltage between the common electrode 9 and the display electrode 12 is released. However, the alignment state is maintained as it is, and the gradation displayed by the liquid crystal space does not change.

  In the liquid crystal display device 100 of the present embodiment, the control unit 20 equalizes the potential difference between the common electrode 9 and the display electrode 12 after applying the AC voltage signal. Therefore, the display gradation of the pixel can be maintained without power consumption and voltage holding until the next writing.

  In the liquid crystal display device 100 of the present embodiment, the control unit 20 applies an alternating voltage signal having a frequency exceeding 6 kHz and an alternating voltage signal having a frequency less than 6 kHz to the common electrode 9 and the display electrode 12. Accordingly, the gradation in the planar alignment state by the AC voltage signal having a frequency exceeding 6 kHz and the gradation in the tilt alignment state by the AC voltage signal having a frequency less than 6 kHz can be displayed on the pixel 11.

  In addition, when a DC voltage is used, in switching between the planar alignment state and the tilt alignment state, it is necessary to always generate an electric field in the transverse direction of the pore 6 for switching in one direction. Since switching between the planar alignment state and the tilt alignment state is performed only by the frequency of the voltage signal, a pair of electrodes opposed to each other in the transverse direction for generating an electric field in the transverse direction of the pore 6, its wiring, its driver, its A signal circuit or the like is unnecessary.

  In addition, since an AC voltage signal is applied to the liquid crystal 8 in the pore 6, the liquid crystal 8 is agitated by the rotation and vibration of the liquid crystal molecules due to the AC electric field as compared with the case of the DC voltage, and the local liquid crystal in the liquid crystal 8 is A highly stable orientation state in which molecular inversion, inclination, density difference, stress state, etc. are highly removed can be obtained.

  The liquid crystal display device 100 of the present embodiment is filled in the pores 6, the intermediate layer 3 in which a large number of pores 6 are formed, a pair of rear substrate 1 and front substrate 2 arranged with the intermediate layer 3 interposed therebetween. Liquid crystal 8. The inner wall surface of the pore 6 has a surface property that restrains the liquid crystal molecule to the inner wall surface while allowing the major axis direction of the liquid crystal molecule to rotate along the inner wall surface of the pore 6.

  Therefore, the liquid crystal 8 in the pore 6 is stable in the planar alignment state and the tilt alignment state, and the gradation display of the pixel 11 is maintained even if the electric field is released. Accordingly, various embodiments utilizing the memory property of pixel display, for example, instead of the common electrode 9 and the display electrode 12, the electrode that applies the electric field in the thickness direction of the intermediate layer 3 to the liquid crystal 8 of the pore 6 is polarized. An embodiment is also possible in which gradation writing is performed while moving relative to the pixels 11 and 14 by being arranged outside the plates 4 and 5.

  In the liquid crystal display device 100 of this embodiment, the pore 6 has a circular, elliptical, or polygonal opening, and penetrates the intermediate layer 3 in the thickness direction. Therefore, the pores 6 are formed by dividing the liquid crystal space for each pixel by a material other than the metal described in the present embodiment, various methods other than the anodizing method, for example, pattern exposure by ultraviolet rays using a photosensitive acrylic resin. It can also be produced by a forming method or the like.

  The pores 6 in the liquid crystal display device 100 of the present embodiment may be formed so that the longitudinal direction is aligned with one direction of the plane of the rear substrate 1 with different aspect ratios of the openings. As a result, the liquid crystals in all the pores 6 have the same alignment direction according to writing, and the gradations for each of the pores 6 through the polarizing plates 4 and 5 are equalized. The gradation of

  The pores 6 in the liquid crystal display device 100 of the present embodiment desirably have a taper shape in the thickness direction of the intermediate layer 3 by making the opening area on the observation side larger than the opening area on the opposite side. This is because the tapered shape can avoid the occurrence of an unstable planar arrangement state as shown in FIG.

The liquid crystal display device 100 of the present embodiment fills the liquid crystal 8 in the pores 6 having the inner wall surface that adsorbs the liquid crystal molecules while allowing the long axis direction of the liquid crystal molecules to rotate along the inner wall surface. An alternating electric field is applied in the penetration direction of the pores 6. Then, by switching the liquid crystal molecules in the pores 6 between the tilt alignment state and the planar alignment state according to the frequency of the alternating electric field, a black and white two-tone display using the liquid crystal 8 is performed.
Therefore, two stable alignment states can be formed using the same pair of electrodes, and gradation can be stably maintained even after the electric field is released.

  The liquid crystal display device 100 of this embodiment includes an intermediate layer 3 forming step of forming a metal thin film layer on a transparent substrate on which a transparent electrode is formed, and anodization treatment by forming a number of depressions on the surface of the metal thin film layer. The intermediate layer 3 formation process which forms the through-hole for every said hollow by performing, and the intermediate | middle layer 3 process process which apply | coats a horizontal alignment processing agent to the inner wall face of the said through-hole are provided. Accordingly, the pore 6 having a much smaller (submicron) aperture than that of pattern exposure or the like is formed, and the write response to the pixel 11 and the gradation display stability (endurance voltage) can be improved. it can.

It is explanatory drawing of the cross-sectional structure in the liquid crystal display device of this embodiment. It is explanatory drawing of an alternating voltage drive. It is explanatory drawing of the orientation state at the time of high frequency alternating voltage signal application. It is explanatory drawing of the orientation state at the time of the low frequency alternating voltage application. It is explanatory drawing of the manufacturing method of the intermediate | middle layer which has the pore of a square cross section. It is explanatory drawing of the preparation methods of the pore of another cross-sectional shape. It is a diagram of voltage drive from the planar alignment state. It is explanatory drawing of the change of the orientation state by 3.0e6 [V / m] drive. It is explanatory drawing of the change of the orientation state by 4.0e6 [V / m] drive. It is a diagram of voltage drive from the tilt alignment state. It is explanatory drawing of the change of the orientation state by 1.0e7 [V / m] drive. It is explanatory drawing of the change of the orientation state by 1.1e7 [V / m] drive. It is a diagram of the relationship between the opening diameter of a pore and an orientation state. It is a diagram of voltage drive from the planar alignment state in which the aperture diameters of the pores are made different. It is explanatory drawing of the planar orientation state in a cross-sectional square pore. It is explanatory drawing of the planar orientation state in a fine hole with a cross-sectional shape of an ellipse. It is explanatory drawing of the planar orientation state in the cross-sectional shape of a rectangular and rhombus-shaped pore. It is explanatory drawing of the planar orientation state in a cross-sectional fine pore. It is explanatory drawing of the planar orientation state in the triangular pore from which cross-sectional shape varied base / height ratio. It is explanatory drawing of the unstable planar alignment state. It is explanatory drawing of the pseudo planar alignment state of the liquid crystal in the pore of a comparative example. It is explanatory drawing of the pseudo tilt alignment state of the liquid crystal in the pore of a comparative example.

Explanation of symbols

1, 2 Sealing substrate (rear substrate, front substrate)
3 Intermediate layer 4, 5 Polarizing plate 6 Pore 8 Liquid crystal 9, 12, 15 A pair of electrodes (common electrode, display electrode, display electrode)
13, 16 Switching element 20 Control unit 100 Liquid crystal display device

Claims (9)

An intermediate layer having a large number of pores;
A pair of sealing substrates disposed across the intermediate layer;
A pair of electrodes that form an electric field in the space in the pores facing the thickness direction of the intermediate layer;
In a liquid crystal device comprising a liquid crystal filled in the pores,
The inner wall surface of the pore has a surface property that restrains the liquid crystal molecule to the inner wall surface while allowing the major axis direction of the liquid crystal molecule to rotate along the inner wall surface of the pore.
A liquid crystal device comprising: a control unit that applies an AC voltage signal to the pair of electrodes to form an AC electric field in the thickness direction of the intermediate layer in the space in the pore.   The liquid crystal device according to claim 1, wherein the control unit equalizes the potential difference between the pair of electrodes after applying the AC voltage signal.   3. The control means applies the AC voltage signal having a frequency exceeding a predetermined frequency and the AC voltage signal having a frequency less than the predetermined frequency to the pair of electrodes. The liquid crystal device described. An intermediate layer in which a large number of pores are formed;
A pair of sealing substrates disposed across the intermediate layer;
In a liquid crystal display medium comprising a liquid crystal filled in the pores,
The inner wall surface of the pore has a surface property that restrains the liquid crystal molecule to the inner wall surface while allowing the major axis direction of the liquid crystal molecule to rotate along the inner wall surface of the pore. Display medium.   The liquid crystal display medium according to claim 4, wherein the pore has a circular, elliptical, or polygonal opening and penetrates the intermediate layer in the thickness direction.   The liquid crystal display medium according to claim 5, wherein the fine pores are formed so that the aspect ratio of the opening is different and the major axis direction is aligned with one direction of a plane of the sealing substrate.   The liquid crystal display medium according to claim 5, wherein the pore has an opening area on the observation side larger than an opening area on the opposite side and has a tapered shape in the thickness direction.   Liquid crystal is filled in a through-hole having the inner wall surface that adsorbs the liquid crystal molecule while allowing the major axis direction of the liquid crystal molecule to rotate along the inner wall surface, and an alternating electric field is applied to the liquid crystal in the through-hole direction. Applied to switch the liquid crystal molecules in the through hole between the alignment state in the through direction and the alignment state in a direction substantially perpendicular to the through direction according to the frequency of the alternating electric field. Driving method. An intermediate layer forming step of forming a metal thin film layer on a transparent substrate on which a transparent electrode is formed;
An intermediate layer forming step of forming through holes for each of the depressions by forming a number of depressions on the surface of the metal thin film layer and performing anodization treatment;
And an intermediate layer treatment step of applying a horizontal alignment treatment agent to the inner wall surface of the through-hole.

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