JP2012194402A - Liquid crystal element and liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the viewing angle characteristic of a novel liquid crystal element that utilizes transition between two alignment states.SOLUTION: A liquid crystal element includes: a first substrate and a second substrate disposed to face each other; a prism array provided for the first substrate or the second substrate; a first alignment film provided for the first substrate; a second alignment film provided for the second substrate; a liquid crystal layer provided between the first substrate and the second substrate; a first polarization plate disposed outside the first substrate; a second polarization plate disposed outside the second substrate; and voltage application means provided for each of the first substrate and the second substrate. Alignment processing is performed on each alignment film on the first substrate and the second substrate so that a liquid crystal molecule of the liquid crystal layer is twisted in a first direction. The liquid crystal layer includes a chiral material for twisting the liquid crystal molecule in a second direction that is opposite to the first direction. The voltage application means includes a first electrode provided for the first substrate and a second electrode provided for the second substrate.

Description

  The present invention relates to a technique for improving electro-optical characteristics in a liquid crystal element and a liquid crystal display device.

  In Japanese Patent No. 2510150 (Patent Document 1), liquid crystal molecules are twisted and aligned in a direction opposite to the direction of rotation controlled by the combination of the directions of alignment treatments applied to each of a pair of opposed substrates. Thus, a liquid crystal display device with improved electro-optical characteristics is disclosed (Prior Art 1). In addition, JP 2007-293278 A (Patent Document 2) describes a turning direction (first turning direction) regulated by a combination of directions of orientation processing applied to each of a pair of substrates arranged opposite to each other. While adding a chiral agent that twists in the reverse swirl direction (second swirl direction), the strain in the liquid crystal layer is increased by twisting the liquid crystal molecules in the first swirl direction, thereby increasing the threshold value. A liquid crystal element that can be driven at a low voltage by lowering the voltage is disclosed (Prior Art 2).

  By the way, the above-described liquid crystal display device of the first example has an unstable reverse twist alignment state, and it is possible to obtain a reverse twist alignment state by applying a relatively high voltage to the liquid crystal layer. However, there is an inconvenience that the state transitions to a forward twisted orientation state over time. In addition, the liquid crystal element of the prior example 2 has the merit of lowering the threshold voltage as described above. However, as soon as the voltage is turned off (for example, about several seconds), the liquid crystal element transitions to a forward twisted alignment state, and conversely. There is a disadvantage that the threshold voltage is increased. Moreover, in any of the preceding examples 1 and 2, it has not been assumed that the two orientation states of the forward twist and the reverse twist are positively used for applications such as display. That is, there has been no disclosure or suggestion of technical ideas such as a configuration and a driving method necessary for actively using bistability.

  On the other hand, Japanese Patent Application Laid-Open No. 2010-186045 (Patent Document 3) describes a reverse TN (Reverse Twisted Nematic) type that is splay twist alignment in the initial state but is stable in reverse twist alignment when a vertical electric field is applied once. A technique related to the liquid crystal element is disclosed (Prior Art 3). However, the liquid crystal element of Prior Example 3 still has room for improvement in that the range in which good contrast can be obtained is narrow.

Japanese Patent No. 2510150 JP 2007-293278 A JP 2010-186045 A

A specific aspect of the present invention is to provide a technique capable of improving the viewing angle characteristics of a novel liquid crystal element that utilizes a transition between two alignment states.
Another aspect of the present invention is to provide a liquid crystal display device that can be driven with low power consumption using a novel liquid crystal element.

  A liquid crystal element according to an aspect of the present invention includes (a) a first substrate and a second substrate which are arranged to face each other, (b) a prism array provided on at least one of the first substrate and the second substrate, (C) a first alignment film provided on the first substrate and subjected to alignment treatment; (d) a second alignment film provided on the second substrate and subjected to alignment treatment; A liquid crystal layer provided between the first substrate and the second substrate; (f) a first polarizing plate disposed outside the first substrate; and (g) disposed outside the second substrate. A second polarizing plate; and (h) voltage applying means provided on the first substrate and the second substrate, and (i) the first substrate and the second substrate are configured to convert liquid crystal molecules of the liquid crystal layer into A direction of the alignment treatment is arranged so as to be twisted in one direction; (j) the liquid crystal layer has the liquid crystal molecules in the first direction; Contains a chiral material that twists in the opposite second direction, and (k) the voltage applying means includes at least a first electrode provided on the first substrate and a second electrode provided on the second substrate. A liquid crystal element having an electrode.

  According to the above configuration, the alignment state of the liquid crystal molecules is stably maintained at a relatively high desired pretilt angle due to the shape effect of the prism array, so that a bistable display with high contrast can be easily realized. Further, the range in which the maximum contrast can be obtained can be widened by the refraction action at the interface between the liquid crystal layer and the prism array, and the direction can be set to the optimum direction according to the application. Therefore, it is possible to improve the viewing angle characteristics in a novel liquid crystal element that utilizes a transition between two alignment states.

  In the liquid crystal element, the voltage application unit includes, for example, a comb-like third electrode and a fourth electrode provided above the second electrode of the second substrate via an insulating layer.

  Thereby, it is possible to efficiently perform transition between two orientation states (a spray twist state and a reverse twist state).

  In the liquid crystal element, it is also preferable that the voltage application unit includes a comb-shaped third electrode and a fourth electrode provided above the prism array of the first substrate.

  Even with such a configuration, the transition between the two alignment states can be performed efficiently. In addition, since the prism array can also be used for the function of ensuring the insulation state between the first electrode, the third electrode, and the fourth electrode on the first substrate, the configuration can be simplified and the manufacturing process can be shortened.

  In the liquid crystal element, it is preferable that a twist angle of liquid crystal molecules in the liquid crystal layer determined by the direction of the alignment treatment is approximately 90 °. In this case, it is preferable that the first polarizing plate and the second polarizing plate are arranged so that their transmission axes are substantially orthogonal or substantially parallel.

  Thereby, a favorable normally white state or a normally black state can be realized.

  A liquid crystal display device according to one embodiment of the present invention is a liquid crystal display device including a plurality of pixel portions, and each of the plurality of pixel portions is configured using the liquid crystal element according to the present invention described above.

  According to said structure, the liquid crystal display device excellent in the viewing angle characteristic is obtained. Further, by utilizing the bistability (memory property) of the liquid crystal element, basically no power is required except during display rewriting, so that a liquid crystal display device with low power consumption can be obtained.

It is a schematic diagram which shows roughly the operation | movement of a reverse TN type | mold liquid crystal element. It is sectional drawing which shows the structural example of the reverse TN type | mold liquid crystal element of 1st Embodiment. It is a typical perspective view of the prism array incorporated in a liquid crystal element. It is a figure which shows the viewing angle dependence of the contrast ratio in the liquid crystal element of an Example. It is a figure which shows the viewing angle dependence of the contrast ratio in the liquid crystal element of a comparative example. It is sectional drawing which shows the other structural example of a reverse TN type | mold liquid crystal element. It is sectional drawing which shows the structural example of the reverse TN type | mold liquid crystal element of 2nd Embodiment. It is a schematic diagram explaining the electric field which can be given to each liquid crystal layer using each electrode. It is sectional drawing which shows the other structural example of a reverse TN type | mold liquid crystal element. It is a figure which shows typically the structural example of a liquid crystal display device.

  Embodiments of the present invention will be described below with reference to the drawings.

(Basic structure of reverse TN liquid crystal element)
FIG. 1 is a schematic diagram schematically showing the operation of the reverse TN liquid crystal element. The reverse TN type liquid crystal element includes, as a basic configuration, an upper substrate 1 and a lower substrate 2 which are disposed to face each other, and a liquid crystal layer 3 provided therebetween. Each surface of the upper substrate 1 and the lower substrate 2 is subjected to an alignment process such as a rubbing process. The upper substrate 1 and the lower substrate 2 are relatively arranged so that the directions of these alignment treatments (indicated by arrows in the drawing) intersect each other at an angle of about 90 °. The liquid crystal layer 3 is formed by injecting a nematic liquid crystal material between the upper substrate 1 and the lower substrate 2. The liquid crystal layer 3 is made of a liquid crystal material to which a chiral material that causes the liquid crystal molecules to twist in a specific direction (right-turning direction in the example of FIG. 1) in the azimuth direction is added. When the mutual distance (cell thickness) between the upper substrate 1 and the lower substrate 2 is d and the chiral pitch of the chiral material is p, the value of the ratio d / p is set to about 0.4, for example. Such a reverse TN liquid crystal element is in a splay twist state in which the liquid crystal layer 3 is twisted while being splay aligned in the initial state due to the action of the chiral material. When a voltage exceeding the saturation voltage is applied to the liquid crystal layer 3 in the splay twist state, the liquid crystal molecules transition to a reverse twist state (uniform twist state) in which the liquid crystal molecules are twisted in the counterclockwise direction. In the liquid crystal layer 3 in such a reverse twist state, since the liquid crystal molecules in the bulk are inclined, an effect of reducing the driving voltage of the liquid crystal element appears.

(First embodiment)
FIG. 2 is a cross-sectional view illustrating a configuration example of the reverse TN liquid crystal element according to the first embodiment. In FIG. 2, for the sake of convenience, hatching is omitted except for some components (the same applies to the drawings described later). The reverse TN type liquid crystal element 5 of this embodiment shown in FIG. 2 includes a first substrate 51, a first electrode 52, a prism array 53, a first alignment film 54, a second substrate 55, a second electrode 56, and a second alignment film. 57, a liquid crystal layer 60, a first polarizing plate 61, and a second polarizing plate 62.

  The first substrate 51 and the second substrate 55 are arranged to face each other, and are transparent substrates such as a glass substrate and a plastic substrate, respectively. Between the first substrate 51 and the second substrate 55, for example, a large number of spacers (granular bodies) are distributed (not shown), and the first substrate 51 and the second substrate are arranged by these spacers. The mutual space | interval with 55 is maintained. Although not particularly shown, a switching element such as a thin film transistor may be formed on any substrate.

  The first electrode 52 is provided on one surface side of the first substrate 51. Similarly, the second electrode 56 is provided on one surface side of the second substrate 55. The first electrode 52 and the second electrode 56 are each configured using a transparent conductive film such as indium tin oxide (ITO). For example, in the present embodiment, both the first electrode 52 and the second electrode 56 are formed on the entire surface of the substrate. The first electrode 52 and the second electrode 56 may be appropriately patterned.

  The prism array 53 is configured by arranging a plurality of minute inclined projection shapes (prisms) in one direction. A schematic perspective view of the prism array 53 is shown in FIG. As shown in the drawing, the cross-sectional shape of each prism is a right triangle (for example, a vertical angle of 75 ° and a base angle of 15 ° and 90 °). Further, the arrangement pitch P of each prism is, for example, about 8 μm, and the height t is, for example, about 2 μm. As shown in FIG. 3, the prism array 53 is formed in a slit shape when viewed from above. The prism array 53 can be obtained by molding a resin material having excellent heat resistance and adhesion, for example. Details of the method of forming the prism array 53 will be described later.

  The first alignment film 54 is provided on one surface side of the first substrate 51 so as to cover the first electrode 52 and the prism array 53. The second alignment film 57 is provided on one surface side of the second substrate 55 so as to cover the second electrode 56. In the present embodiment, the first alignment film 54 and the second alignment film 57 regulate the alignment state of the liquid crystal molecules 60 in the initial state (when no voltage is applied) to the horizontal alignment state (horizontal alignment film). Is used. The first alignment film 54 and the second alignment film 57 are subjected to predetermined surface treatment (rubbing treatment, photo-alignment treatment, etc.). In the first alignment film 54 and the second alignment film 57, an angle formed by each alignment processing direction is set to, for example, around 90 °.

  The liquid crystal layer 60 is provided between one surface of the first substrate 51 and one surface of the second substrate 55. In the present embodiment, the liquid crystal layer 60 is configured using a nematic liquid crystal material having a positive dielectric anisotropy Δε (Δε> 0). The ellipse illustrated in the liquid crystal layer 60 schematically shows the liquid crystal molecules in the liquid crystal layer 60. The liquid crystal molecules when no voltage is applied are aligned substantially horizontally with a predetermined pretilt angle with respect to the substrate surfaces of the first substrate 51 and the second substrate 55.

  The first polarizing plate 61 is disposed outside the first substrate 51. The second polarizing plate 62 is disposed outside the second substrate 55. In this embodiment, it is visually recognized by the user from the second polarizing plate 62 side. The first polarizing plate 61 and the second polarizing plate 62 are arranged, for example, with their transmission axes substantially orthogonal to each other (crossed Nicols arrangement).

  Next, an example of a manufacturing method of the reverse TN type liquid crystal element 5 will be described in detail.

  First, glass substrates for use as the first substrate 51 and the second substrate 55 are prepared. As these glass substrates, those having a conductive film made of a transparent conductive material such as ITO (indium tin oxide) in advance are more preferable. For example, a pair of glass substrates having an ITO film with a thickness of 1500 mm, a plate thickness of 0.7 mm, and a glass material made of non-alkali glass are prepared. About each of the 1st board | substrate 51 and the 2nd board | substrate 55, the 1st electrode 52 and the 2nd electrode 56 are formed by patterning an ITO film | membrane suitably.

  Next, the prism array 53 is formed on the first electrode 52 of the first substrate 51. Here, the cross section is triangular, the pitch P is 8 μm, the height t is about 2 μm, the apex angle is 75 °, the base angles are 15 ° and 90 °, and a mold having a slit shape is seen from above. The prism array 53 is formed by using this.

  Specifically, a photocurable resin material is dropped onto the first substrate 51, a mold is placed thereon, and pressing is performed in a state where the back side of the first substrate 51 is reinforced with a thick quartz substrate or the like. . After being pressed for a certain period of time (for example, 1 minute or longer), the photocurable resin material is sufficiently spread, and then the photocurable resin material is cured by irradiating light from the first substrate 51 side. The amount of light irradiation is appropriately set to a value sufficient to cure the photocurable resin material. Here, in general, the prism material has low heat resistance, and the characteristics are often deteriorated by heat treatment (for example, 180 ° C. or more) when the first alignment film 54 is formed on the prism array 53. On the other hand, in this embodiment, a photo-curing (for example, UV-curing) acrylic resin material that hardly causes a decrease in transmittance characteristics before and after the heat treatment is used. The refractive index of the photocurable resin material used in this embodiment is, for example, about 1.51.

  When the prism array 53 made of a transparent resin film is formed on the first substrate 51, the first substrate 51 on which the prism array 53 is formed is then cleaned by a cleaning machine. The cleaning can be performed, for example, in the order of brush cleaning using an alkaline detergent, pure water cleaning, air blow, ultraviolet (UV) irradiation, and infrared (IR) drying, but is not limited thereto. High pressure spray cleaning or plasma cleaning may be performed.

  Next, a first alignment film 54 is formed on the first substrate 51 on which the prism array 53 is formed. Similarly, a second alignment film 57 is formed on the second substrate 55. Here, for example, the alignment film is formed using an alignment material (polyimide) that generates a pretilt angle of 1 to 2 ° with respect to the liquid crystal molecules on the surface of the alignment film. Appropriate film thicknesses on the first substrate 51 and the second substrate 55 by an appropriate method such as a flexographic printing method, an inkjet method, a spin coating method, a slit coating method, or a combination of a slit method and a spin coating method. (For example, about 500 to 800 mm) and heat treatment (for example, baking at 180 ° C. for 1.5 hours) is performed.

  Next, an alignment process is performed on each of the first alignment film 54 and the second alignment film 57 obtained by the heat treatment. Here, for example, a rubbing process is performed, and the pressing amount as a condition thereof is set to 0.8 mm (strong rubbing condition). This alignment process is performed so that the alignment direction of the liquid crystal molecules on each substrate is twisted by approximately 90 ° when the first substrate 51 and the second substrate 55 are overlapped. The alignment process is performed so that the direction of the alignment process on the first alignment film 54 is 45 ° with respect to the extending direction of each prism of the prism array 53.

  Next, a main sealant containing an appropriate amount (for example, 2 to 5 wt%) of a gap control agent is formed on one substrate (for example, the first substrate 51). The main sealant is formed by screen printing or a dispenser, for example. The diameter of the gap control agent can be selected so that the thickness of the liquid crystal layer 60 is about 4 to 6 μm including the base layer of the prism array 53 and the height of the prism. In this embodiment, a plastic ball having a diameter of 8 μm is used as the gap control agent. A gap control agent is sprayed on the other substrate (for example, the second substrate 55). For example, in this embodiment, 6-8 μm plastic balls are sprayed by a dry gap spreader.

  Next, the first substrate 51 and the second substrate 55 are overlaid, and the main sealant is cured by heat treatment in a state where pressure is constantly applied by a press machine or the like. Here, for example, heat treatment is performed at 150 ° C. for 3 hours. Thereafter, a liquid crystal layer 60 is formed by filling a gap between the first substrate 51 and the second substrate 55 with a liquid crystal material. The liquid crystal material is filled by, for example, a vacuum injection method. In the present embodiment, a liquid crystal material having a positive dielectric anisotropy Δε and a refractive index anisotropy Δn of 0.15 and a chiral pitch of 40 μm by adding an appropriate amount of chiral material is used. After the liquid crystal material is injected, an end sealant is applied to the injection port and sealed. Then, the alignment state of the liquid crystal molecules of the liquid crystal layer 60 is adjusted by appropriately performing a heat treatment (for example, at 120 ° C. for 1 hour) after sealing.

  Next, the first polarizing plate 61 is bonded to the outside of the first substrate 51, and the second polarizing plate 62 is bonded to the outside of the second substrate 55. The first polarizing plate 61 and the second polarizing plate 62 are arranged so that their transmission axes are substantially orthogonal (crossed Nicol arrangement). As described above, the reverse TN liquid crystal element 5 of the present embodiment is obtained. By applying a voltage (for example, AC 5 to 15 V) to the reverse TN liquid crystal element 5 using the first electrode 52 and the second electrode 56, the liquid crystal layer 60 can be transitioned to the reverse twist state. . The reverse TN liquid crystal element 5 in the reverse twist state is in a relatively black state (a state with a low transmittance).

  FIG. 4 is a diagram showing the viewing angle dependence of the contrast ratio in the reverse TN liquid crystal element of the example manufactured according to the above-described conditions. FIG. 5 is a diagram showing the viewing angle dependence of the contrast ratio in the reverse TN liquid crystal element of the comparative example. The reverse TN type liquid crystal element of the comparative example has a configuration in which the prism array is omitted from the liquid crystal element of the above example. In order to realize a high pretilt angle without using a prism array, a polyimide alignment film material having a lower side chain density than an alignment film material normally used as a vertical alignment film was used. In combination with the following alignment treatment conditions, a pretilt angle of 23 ° to 35 ° was obtained in this comparative example. The polyimide alignment film of the comparative example was formed by applying an alignment film material by flexographic printing, inkjet printing, spin coating, and the like, and baking at 160 ° C. for 1 hour in a clean oven. The film thickness of the alignment film after film formation was 500 to 800 mm. The alignment film after firing was uniaxially aligned by rubbing. The pushing amount of the rubbing cloth during rubbing was 0.8 mm. Except for the prism array and the alignment film, the conditions were the same as those of the liquid crystal element of the example. 4 and 5, numerical values of 0 ° to 330 ° written along the outer edge represent directions in the substrate surface, and directions of 270 ° to 90 ° correspond to the horizontal direction of the liquid crystal element. The direction of −180 ° corresponds to the vertical direction of the liquid crystal element. Moreover, the numerical value of 0 degree-70 degree described along the vertical axis | shaft represents the inclination angle (polar angle) from a board | substrate normal line direction. Further, “CR” in each figure indicates a contrast ratio. For example, an area labeled “CR: 25” is an area showing a contrast ratio of 25 or more. Regarding the contrast ratio, each of the reverse TN type liquid crystal elements of the example and the comparative example was measured in the viewing twist transmittance state, and then the voltage was applied to the liquid crystal layer to transit to the reverse twist state. The visual angle transmittance characteristics were measured by the above, and the ratio of the transmittance obtained by each was calculated.

  As shown in FIG. 4, it can be seen that the reverse TN type liquid crystal element of the example has the maximum contrast position in the front direction as compared with the reverse TN type liquid crystal element of the comparative example shown in FIG. It can also be seen that the region "CR: 5" having a high contrast ratio overall (contrast ratio 25 or more) and a contrast ratio of 5 or more is wider. These results indicate that the prism array 53 stably holds the alignment state of the liquid crystal molecules at the interface on the first substrate 51 side at a relatively high desired pretilt angle, and the refractive index at the interface between the prism array 53 and the liquid crystal layer 60. This is considered to be because the direction in which the maximum contrast ratio is obtained is controlled by bending the light path due to the difference.

FIG. 6 is a cross-sectional view illustrating another configuration example of the reverse TN liquid crystal element according to the first embodiment. The reverse TN liquid crystal element 5a shown in FIG. 6 includes a first substrate 51, a first electrode 52a, a prism array 53a, a first alignment film 54a, a second substrate 55, a second electrode 56, a second alignment film 57, and a liquid crystal layer. 60, the 1st polarizing plate 61, and the 2nd polarizing plate 62 are comprised. In the reverse TN type liquid crystal element 5 shown in FIG. 2 described above, the prism array 53 is disposed above the first electrode 52. However, the reverse TN type liquid crystal element 5a in the example shown in FIG. 6 is arranged on the prism array 53a. The difference in structure is that one electrode 52a is arranged. If it is on the prism array 53a formed using a resin material having high heat resistance as described above, the first electrode 52a made of a transparent conductive material such as ITO is provided on the prism array 53a as in this example. You can also. Although not shown, it is also preferable that a silicon oxide (SiO ₂ ) film is provided between the prism array 53a and the first electrode 52a in order to further improve the adhesion between them. In the reverse TN type liquid crystal element 5a illustrated in FIG. 6, the liquid crystal layer 60 does not have the prism array 53a between the first electrode 52a on the first substrate 51 and the liquid crystal layer 60, and the liquid crystal is directly supplied from the first electrode 52a. Since a voltage can be applied to the layer 60, the driving voltage can be further reduced. Note that in either of the reverse TN type liquid crystal element 5 shown in FIG. 2 and the reverse TN type liquid crystal element 5a shown in FIG. 6, one or both of the first electrode and the second electrode have a stripe shape (strip shape). It may be patterned into a shape.

(Second Embodiment)
FIG. 7 is a cross-sectional view illustrating a configuration example of the reverse TN liquid crystal element according to the second embodiment. The reverse TN type liquid crystal element 5b of this embodiment shown in FIG. 7 includes a first substrate 51, a first electrode 52, a prism array 53, a first alignment film 54, a second substrate 55, a second electrode 56, and a second alignment film. 57, a third electrode 58, a fourth electrode 59, a liquid crystal layer 60, a first polarizing plate 61, a second polarizing plate 62, and an insulating film 63. In addition, the same code | symbol is attached | subjected about the member which is common in the reverse TN type liquid crystal element 5 of 1st Embodiment, and detailed description is abbreviate | omitted about them.

  The insulating film (insulating layer) 63 is provided on the second substrate 55 so as to cover the second electrode 56. The insulating film 63 is, for example, an inorganic insulating film such as a silicon oxide film, a silicon nitride film, a silicon oxynitride film, or a laminated film thereof, or an organic insulating film (for example, an acrylic organic insulating film).

  The third electrode 58 and the fourth electrode 59 are respectively provided on the upper side of the insulating film 63 of the second substrate 55. The third electrode 58 and the fourth electrode 59 in this embodiment are comb-like electrodes each having a plurality of electrode branches, and are arranged so that the electrode branches are alternately arranged (see FIG. 8 described later). ). The third electrode 58 and the fourth electrode 59 are each configured by appropriately patterning a transparent conductive film such as indium tin oxide (ITO). Each electrode branch of the third electrode 58 and the fourth electrode 59 has a width of 30 μm, for example, and is arranged with an electrode interval set to 20 μm.

  The second alignment film 57 b is provided so as to cover the third electrode 58 and the fourth electrode 59. As the second alignment film 57b, a film (horizontal alignment film) that restricts the alignment state of the liquid crystal molecules in the liquid crystal layer 60 in the initial state (when no voltage is applied) to the horizontal alignment state is used. The second alignment film 57b is subjected to predetermined surface treatment (rubbing treatment, photo-alignment treatment, etc.).

  FIG. 8 is a schematic diagram for explaining an electric field that can be applied to the liquid crystal layer using each electrode. FIG. 8A is a plan view schematically showing the arrangement of the first electrode to the fourth electrode. FIG. 8B to FIG. 8D are cross-sectional views schematically showing the arrangement of the first electrode to the fourth electrode. As shown in FIG. 8B, the first electrode 52 and the second electrode 56 are arranged to face each other, and in the region where the first electrode 52 and the second electrode 56 overlap as shown in FIG. The third electrode 58 and the fourth electrode 59 are arranged on the front. Further, as shown in FIG. 8A, the plurality of electrode branches of the third electrode 58 and the plurality of electrode branches of the fourth electrode 59 are alternately arranged one by one.

  As shown in FIG. 8B, an electric field can be generated between both electrodes by applying a voltage between the first electrode 52 and the second electrode 56. The electric field in this case is an electric field along the thickness direction (cell thickness direction) of the first substrate 51 and the second substrate 55 as shown. This electric field may hereinafter be referred to as a “longitudinal electric field”.

  Further, as shown in FIG. 8C, an electric field can be generated between the third electrode 58 and the fourth electrode 59 by applying a voltage between them. The electric field in this case is an electric field in a direction substantially parallel to each surface of the first substrate 51 and the second substrate 55 as shown in the figure. Hereinafter, this electric field may be referred to as a “lateral electric field”. Hereinafter, a mode using such an electric field may be referred to as an “IPS mode”.

  Further, as shown in FIG. 8D, by applying a voltage between the second electrode 56 and the third electrode 58 and the fourth electrode 59 that are arranged to face each other with the insulating film 63 interposed therebetween, a voltage is applied between both electrodes. An electric field can be generated. The electric field in this case is an electric field along a direction substantially parallel to each surface of the first substrate 51 and the second substrate 55 as shown in the figure. Hereinafter, this electric field may be referred to as a “lateral electric field”. Hereinafter, a mode using such an electric field may be referred to as an “FFS mode”.

  In the liquid crystal element, in the initial state, the liquid crystal molecules of the liquid crystal layer 60 are aligned in a spray twist state. In contrast, when a vertical electric field is generated using the first electrode 52 and the second electrode 56 as described above, the alignment state of the liquid crystal layer 60 transitions to the reverse twist state. Thereafter, when a lateral electric field is generated using the third electrode 58 and the fourth electrode 59 (IPS mode), the alignment state of the liquid crystal layer 60 transitions to the spray twist state. Similarly, when a lateral electric field is generated using the second electrode 56, the third electrode 58, and the fourth electrode 59 (FFS mode), the alignment state of the liquid crystal layer 60 transitions from the reverse twist state to the spray twist state. To do. In comparison with the IPS mode, the alignment state of the liquid crystal layer 60 can be changed more uniformly in the FFS mode. This is because a lateral electric field is also applied to each of the third electrode 58 and the fourth electrode 59. Therefore, it can be said that the FFS mode is more suitable in terms of the aperture ratio (transmittance, contrast ratio).

  The reason why the alignment state can be switched is considered as follows. In the spray twist state, the liquid crystal molecules at the approximate center in the layer thickness direction of the liquid crystal layer 60 lie sideways, but the liquid crystal molecules at the approximate center incline in the vertical direction due to the reverse twist state due to the vertical electric field. Thereafter, a lateral electric field is applied to the liquid crystal molecules at the approximate center in the thickness direction of the liquid crystal layer 60 in the reverse twist state by a lateral electric field in the IPS mode or the FFS mode, and the liquid crystal molecules at the approximate center of the liquid crystal layer 60 in the spray twist state. Since it is in the direction of the director, there is a transition to the spray twist state which is the initial state again. As described above, it is considered that the spray twist state and the reverse twist state can be switched by utilizing the vertical electric field and the horizontal electric field.

  Next, an example of a method for manufacturing a liquid crystal element will be described in detail.

  As in the first embodiment, the first substrate 51 having the first electrode 52 and the second substrate 55 having the second electrode 56 are formed, and then the prism array 53 is formed on the first substrate 52. .

Next, an insulating film 63 is formed on the second electrode 56 of the second substrate 55. At that time, it is necessary to devise so that the insulating film 63 is not formed on the extraction electrode portion. As the method, a resist is formed in advance on the extraction electrode portion and lifted off after the insulating film 63 is formed, or the insulating film 63 is formed by sputtering or the like with the extraction electrode portion hidden by a metal mask or the like. The method etc. are mentioned. Examples of the insulating film 63 include an organic insulating film, an inorganic insulating film such as a silicon oxide film or a silicon nitride film, and a combination thereof. Here, a laminated film of an acrylic organic insulating film and a silicon oxide film (SiO ₂ film) is used as the insulating film 63.

A heat-resistant film (polyimide tape) is attached to the extraction electrode portion (terminal portion), and the material liquid of the organic insulating film is spin-coated in that state. For example, a film thickness of 1 μm is obtained under the condition of spinning at 2000 rpm for 30 seconds. This is baked in a clean oven (eg, 220 ° C., 1 hour). A SiO ₂ film is formed by sputtering (alternating current discharge) while a heat resistant film is stuck. For example, the substrate is heated to 80 ° C. to form 1000 Å. Here, when the heat-resistant film is peeled off, both the organic insulating film and the SiO ₂ film can be peeled off cleanly. Thereafter, baking is performed in a clean oven (for example, 220 ° C., 1 hour). This is to increase the insulation and transparency of the SiO ₂ film. It is not always necessary to form the SiO ₂ film, but it is preferable to form the SiO ₂ film because the adhesion and patterning of the ITO film formed thereon are improved. Also, the insulation is improved. On the other hand, there can be considered a method of taking insulation only with a SiO ₂ film without forming an organic insulating film, but in that case, the SiO ₂ film is likely to be porous, so that a film thickness of about 4000 to 8000 mm can be secured. desirable. Also, a laminated film with SiNx may be used. Although the sputtering method has been described as a method for forming the inorganic insulating film, a forming method such as a vacuum evaporation method, an ion beam method, or a CVD method (chemical vapor deposition method) may be used.

  Next, the third electrode 58 and the fourth electrode 59 are formed on the insulating film 63. Specifically, first, an ITO film is formed on the insulating film 63 by a sputtering method (AC discharge). This is heated to, for example, 100 ° C., and an ITO film of about 1200 mm is formed on the entire surface. The ITO film is patterned by a general photolithography technique. As the photomask at this time, a photomask having a light shielding portion corresponding to the comb-like electrode as shown in FIG. 8 is used. Here, the width of the comb-like electrode branch is 30 μm and the electrode interval is 20 μm. If there is no pattern in the extraction electrode portion, the lower ITO film is also removed by etching. Therefore, a photomask having a pattern formed on the extraction electrode portion is used.

  The first substrate 51 and the second substrate 55 manufactured as described above are cleaned. Specifically, first, washing with water (brush washing or spray washing, pure water washing) is performed, followed by UV washing after draining, and finally IR drying.

  Next, as in the first embodiment described above, the first alignment film 53 and the second alignment film 57 are formed on the first substrate 51 and the second substrate 55, respectively, and an alignment process is performed on each alignment film.

  Next, the first substrate 51 and the second substrate 55 are bonded together. A spacer material is sprayed on the first substrate 51 in advance, and a seal material is further printed. Thereafter, the first polarizing plate 61 and the second polarizing plate 62 are attached.

  Thus, the liquid crystal element 5b according to this embodiment is completed. The liquid crystal element 5b of the present embodiment has excellent viewing angle characteristics like the liquid crystal element of the first embodiment. Further, by providing the third electrode and the fourth electrode in addition to the first electrode and the second electrode, the transition between the spray twist state and the reverse twist state can be performed more favorably.

  FIG. 9 is a cross-sectional view illustrating another configuration example of the reverse TN liquid crystal element according to the second embodiment. 9 includes a first substrate 51, a first electrode 52, a prism array 53c, a first alignment film 54, a second substrate 55, a second electrode 56, a second alignment film 57, and a third alignment film. The electrode 58c, the fourth electrode 59c, the liquid crystal layer 60, the first polarizing plate 61, and the second polarizing plate 62 are included. In the reverse TN type liquid crystal element 5b shown in FIG. 7 described above, the third electrode 58 and the fourth electrode 59 are arranged on the second substrate 55 side. However, the reverse TN type liquid crystal element 5c in the example shown in FIG. The difference in structure is that the third electrode 58c and the fourth electrode 59c are arranged on the array 53c. If it is on the prism array 53c formed using the resin material having high heat resistance as described above, the third electrode 58c made of a transparent conductive material such as ITO and the like are formed on the prism array 53c as in this example. Four electrodes 59c can also be provided. In this structure, the function of the insulating film 63 in the reverse TN type liquid crystal element 5b shown in FIG. 7 can be replaced by the prism array 53c. As a result, the insulating film 63 becomes unnecessary, and the manufacturing process can be shortened.

(Third embodiment)
Next, a configuration example of a liquid crystal display device capable of low power consumption driving using the memory property of the liquid crystal element of the second embodiment will be described.

  FIG. 10 is a diagram schematically illustrating a configuration example of a liquid crystal display device. The liquid crystal display device illustrated in FIG. 10 is a simple matrix type liquid crystal display device configured by arranging a plurality of pixel portions 74 in a matrix, and the liquid crystal element 5b or the liquid crystal element 5c described above is used as each pixel portion 74. It has been. Specifically, the liquid crystal display device includes m control lines B1 to Bm extending in the X direction, a driver 71 that gives control signals to the control lines B1 to Bm, and control lines B1 to Bm, respectively. The n control lines A1 to An that cross and extend in the Y direction, the driver 72 that gives control signals to the control lines A1 to An, and the control lines B1 to Bm that cross each other and extend in the Y direction. Each of n control lines C1 to Cn and D1 to Dn, a driver 73 for giving a control signal to these control lines C1 to Cn and D1 to Dn, each of the control lines B1 to Bm and the control lines A1 to An And a pixel portion 74 provided at the intersection.

  Each control line B1-Bm, A1-An, C1-Cn, and D1-Dn consists of transparent conductive films, such as ITO formed in stripe form, for example. The portions where the control lines B1 to Bm and A1 to An intersect function as the first electrode 52 and the second electrode 56 described above. The control lines C1 to Cn are connected to a comb-like electrode branch (not shown in FIG. 5) provided in a region corresponding to each pixel portion 74 and serving as the third electrode 58 (or 58c). . Similarly, the control lines D1 to Dn are connected to a comb-like electrode branch provided in a region corresponding to each pixel portion 74 and serving as the fourth electrode 59 (or 59c).

  Various methods are conceivable as driving methods of the liquid crystal display device having the configuration shown in FIG. For example, a control line B1, B2, B3... And a method of rewriting display for each line (line sequential driving method) will be described. In this case, a vertical electric field may be applied to the pixel portion 74 that is desired to have a relatively bright display, and a horizontal electric field may be applied to the pixel portion 74 that is desired to have a relatively dark display.

  For example, a rectangular wave voltage (for example, about 5 V and 150 Hz) is applied to the control line B1, and the control lines A1 to An, C1 to Cn, and D1 to Dn are synchronized therewith, or A rectangular wave voltage (for example, about 5 V and 150 Hz) having a threshold voltage shifted by a half cycle is applied.

  Specifically, among the control lines A1 to An, a rectangular wave voltage that is shifted from the rectangular wave voltage applied to the control line B1 by a half cycle is applied to the control line corresponding to the pixel portion 74 that is desired to be brightly displayed. At this time, no voltage is applied to the control lines C1 to Cn and D1 to Dn. Thereby, a voltage (vertical electric field) of about 10 V is effectively applied to the liquid crystal element of the pixel portion 74. If this voltage is equal to or higher than the saturation voltage, the light transmittance of the pixel portion 74 can be changed by causing a transition of the alignment state in the liquid crystal layer 60. On the other hand, of the control lines A1 to An, a rectangular wave voltage synchronized with the rectangular wave voltage applied to the control line B1 is applied to the control line corresponding to the pixel portion 74 that does not need to change the display. Also at this time, no voltage is applied to the control lines C1 to Cn and D1 to Dn. As a result, no voltage is effectively applied to the pixel portion 74. Accordingly, the alignment state does not change in the liquid crystal layer 60, and the light transmittance does not change.

  Further, among the control lines C1 to Cn and D1 to Dn, a rectangular wave voltage that is shifted from the rectangular wave voltage applied to the control line B1 by a half cycle is applied to the control line corresponding to the pixel portion 74 that is desired to be brightly displayed. At this time, no voltage is applied to the control lines A1 to An. As a result, a voltage (lateral electric field) of about 10 V is effectively applied to the liquid crystal element of the pixel portion 74. If this voltage is equal to or higher than the saturation voltage, the light transmittance of the pixel portion 74 can be changed by causing a transition of the alignment state in the liquid crystal layer 60. On the other hand, among the control lines C1 to Cn and D1 to Dn, a rectangular wave voltage synchronized with the rectangular wave voltage applied to the control line B1 is applied to the control line corresponding to the pixel unit 74 that does not need to change the display. To do. Also at this time, no voltage is applied to the control lines A1 to An. As a result, no voltage is effectively applied to the pixel portion 74. Accordingly, the alignment state does not change in the liquid crystal layer 60, and the light transmittance does not change.

  The dot matrix display can be performed by sequentially executing the above driving with the control lines B2, B3. The display state rewritten by such driving can be held semipermanently. In order to rewrite this display, the above control may be executed again from the control line B1. Note that although an example in which the present invention is applied to a so-called simple matrix liquid crystal display device is described here, the present invention can also be applied to an active matrix liquid crystal display device using a thin film transistor or the like. In the case of an active matrix liquid crystal display device, it is not necessary to rewrite each line such as the control line B1, so that the rewriting time can be shortened. Further, since it is possible to apply a voltage more than twice the threshold, rewriting can be performed at a higher speed. However, since there are electrodes for a horizontal electric field and a vertical electric field on one substrate, two thin film transistors or the like are required per pixel.

  As described above, according to each embodiment and example, the alignment effect of the liquid crystal molecules is stably maintained at a relatively high desired pretilt angle due to the shape effect of the prism array, so that a bistable display with high contrast can be easily performed. realizable. Further, the range in which the maximum contrast can be obtained can be widened by the refraction action at the interface between the liquid crystal layer and the prism array, and the direction can be set to the optimum direction according to the application. Therefore, it is possible to improve the viewing angle characteristics in a novel liquid crystal element that utilizes a transition between two alignment states.

  Further, since a general alignment film can be used, long-term stability of the alignment state can be expected, and the reliability of the liquid crystal element can be improved.

  In addition, since a driving method (line sequential rewriting method or the like) using a memory property can be applied, a large-capacity dot matrix display can be performed by a simple matrix display without using a switching element such as a TFT. Therefore, large-capacity display is possible at low cost.

  In addition, the manufacturing process of such a bistable reverse TN type liquid crystal element is basically the same as the manufacturing process of a general TN type liquid crystal element. Like the TN liquid crystal element, it can be manufactured at low cost.

  In addition, this invention is not limited to the content mentioned above, In the range of the summary of this invention, it can change and implement variously. For example, in each of the embodiments described above, the twist angle of the liquid crystal layer is set to about 90 °, but the twist angle is not limited to this. In this case, the retardation value in the liquid crystal layer may be adjusted in order to further secure the brightness in white display. Further, although the liquid crystal element in the normally white state in which the angle formed by the transmission axes of the first polarizing plate and the second polarizing plate is about 90 ° has been illustrated, it may be a liquid crystal element in a normally black state. However, the normally white state is more preferable in that good black display can be obtained and higher contrast can be obtained. In each of the above embodiments, the prism array is provided on only one of the substrates, but the prism array may be provided on both substrates.

1: upper substrate 2: lower substrate 3: liquid crystal layers 5, 5a, 5b, 5c: liquid crystal element 51: first substrate 52, 52a: first electrodes 53, 53a, 53c: prism arrays 54, 54a: first alignment Film 55: second substrate 56: second electrode 57: second alignment film 58, 58c: third electrode 59, 59c: fourth electrode 60: liquid crystal layer 61: first polarizing plate 62: second polarizing plate 63: insulation Films 71, 72, 73: Driver 74: Pixel portions A1 to An, B1 to Bm, C1 to Cn, D1 to Dn: Control lines

Claims (5)

A first substrate and a second substrate disposed opposite to each other;
A prism array provided on at least one of the first substrate and the second substrate;
A first alignment film provided on the first substrate and subjected to alignment treatment;
A second alignment film provided on the second substrate and subjected to alignment treatment;
A liquid crystal layer provided between the first substrate and the second substrate;
A first polarizing plate disposed outside the first substrate;
A second polarizing plate disposed outside the second substrate;
Voltage applying means provided on the first substrate and the second substrate;
Including
The first substrate and the second substrate are arranged in a direction of the alignment treatment so as to twist liquid crystal molecules of the liquid crystal layer in a first direction;
The liquid crystal layer contains a chiral material having a property of twisting the liquid crystal molecules in a second direction opposite to the first direction,
The voltage application means includes at least a first electrode provided on the first substrate and a second electrode provided on the second substrate.
Liquid crystal element.   2. The liquid crystal element according to claim 1, wherein the voltage application unit includes a comb-like third electrode and a fourth electrode provided on an upper side of the second electrode of the second substrate via an insulating layer.   2. The liquid crystal element according to claim 1, wherein the voltage applying unit includes a comb-shaped third electrode and a fourth electrode provided on an upper side of the prism array of the first substrate.   The liquid crystal element according to claim 1, wherein a twist angle of liquid crystal molecules in the liquid crystal layer determined by the direction of the alignment treatment is approximately 90 °.   A liquid crystal display device comprising a plurality of pixel portions, wherein each of the plurality of pixel portions is configured using the liquid crystal element according to claim 1.