JP5290225B2 - Liquid crystal display - Google Patents

Description

  The present invention relates to a liquid crystal display device.

  In a display device using a medium whose optical anisotropy is changed by applying an electric field as shown in Patent Document 1, a reduction in transmittance of the display element and uneven brightness are prevented, and high-speed response performance is achieved. A liquid crystal display device to be realized has been proposed. In addition, as a method of using a liquid crystal material exhibiting a blue phase exhibiting optical isotropy described in Patent Document 1 for a liquid crystal display device, a method of stabilizing a polymer as described in Non-Patent Document 1 can be given. It is done. As other prior art documents related to the present invention, there are the following patent documents 2 to 3 and non-patent documents 2 to 8.

JP 2005-234541 A JP 2006-89622 A JP 2008-303381 A

Y. Hisakado and three others, Advanced Materials, 2005, 17, pp. 96-98 M.M. Goh et al., Journal of Chemical Society, 2007, 129, 8159-8527 Color Science Handbook (2nd edition, Color Society of Japan) p. 1025-1026 Y. Fujimura et. al. SID'91 Digest pp. 739-742 M.M. Born, E.M. Wolf, Volume 3 of the Principle of Optics T.A. Ishinab, T .; Miyashita, T .; Uchida, SID'00 Technical Paper (2000). pp. 1094-1097 J. et al. MACLOMOL. SCI. -CHEM. , A25 (5-7), pp. 519-535 (1988) Crystal optics of the Japan Society of Applied Physics

  An object of the present invention is to improve a contrast ratio in a liquid crystal display device having a liquid crystal layer in which blue phase liquid crystal is sealed.

  In order to solve the above problems, the features of the present invention are as follows.

  (1) a first polarizing plate and a second polarizing plate, a first substrate and a second substrate disposed between the first polarizing plate and the second polarizing plate, the first substrate and the second polarizing plate A liquid crystal layer in which a blue phase liquid crystal is sealed, and a first electrode and a second electrode for applying a voltage to the liquid crystal layer. A liquid crystal display device which exhibits optical rotation when heated, and an optical rotation angle α of the liquid crystal layer when no voltage is applied satisfies 0 ° <| α | ≦ 15 °.

  (2) The liquid crystal display device according to (1), wherein the optical rotation angle α satisfies 0 ° <| α | ≦ 8 °.

  (3) The liquid crystal display device according to (1), wherein the optical rotation angle α satisfies 0 ° <| α | ≦ 5 °.

  (4) In the liquid crystal display device according to any one of (1) to (3), the first polarizing plate includes a first polarizing layer having an absorption axis, and the second polarizing plate includes A second polarizing layer having an absorption axis in a direction different from the first polarizing layer; and the liquid crystal display device further includes an optical rotation reducing member between the first polarizing layer and the second polarizing layer. A liquid crystal display device, wherein the liquid crystal layer exhibits optical rotation in a direction opposite to the optical rotation exhibited when no voltage is applied.

  (5) The liquid crystal display according to any one of (1) to (4), wherein the blue phase liquid crystal contains a chiral agent, and the chiral pitch of the chiral agent is 400 nm or less. apparatus.

  (6) In the liquid crystal display device of any one of (1) to (4), the blue phase liquid crystal contains a chiral agent, and the chiral pitch of the chiral agent is 380 nm or less. apparatus.

  (7) In the liquid crystal display device according to any one of the above (1) to (6), the first polarizing plate and the second polarizing plate include an absorption axis of the first polarizing plate and the second polarized light. A liquid crystal display device satisfying −5.5 ° ≦ P− (90 ° −α) ≦ 5.5 °, where P is an angle formed by the absorption axis of the plate.

  (8) In the liquid crystal display device according to any one of the above (1) to (6), the first polarizing plate and the second polarizing plate include an absorption axis of the first polarizing plate and the second polarized light. A liquid crystal display device satisfying −0.5 ° ≦ P− (90 ° −α) ≦ 0.5 °, where P is an angle formed by the absorption axis of the plate.

  (9) In the liquid crystal display device according to any one of (1) to (8), the side of the first substrate on which the liquid crystal layer is disposed, and the liquid crystal layer of the second substrate are disposed. An alignment film is formed on at least one side of the liquid crystal display device.

  (10) In the liquid crystal display device of (9), the first alignment film is formed on the side of the first substrate where the liquid crystal layer is disposed, and the liquid crystal layer of the second substrate is disposed. A liquid crystal display device, wherein a second alignment film is formed on the side.

  (11) In the liquid crystal display device according to any one of (1) to (8), a plurality of signal wirings and a plurality of scanning wirings are arranged on one of the first substrate and the second substrate. Each of the regions surrounded by the signal wiring and the scanning wiring is a pixel, and the liquid crystal display device is characterized in that it is a pixel.

  (12) In the liquid crystal display device according to any one of (1) to (8), the liquid crystal display device includes a thin film transistor in which one of a source electrode and a drain electrode is connected to the first electrode, the source electrode, A liquid crystal display device comprising: a signal wiring connected to the other drain electrode; and a scanning wiring connected to the gate electrode of the thin film transistor.

  (13) In the liquid crystal display device according to any one of (1) to (8), the first substrate or the second substrate has a color material layer showing three or more colors. Liquid crystal display device.

  (14) The liquid crystal display device according to (13), wherein at least two of the areas of the respective colors constituting the color material layer are different.

  (15) The liquid crystal display device according to (13), wherein the liquid crystal layer has a different thickness for each color constituting the color material layer.

  (16) The liquid crystal display device according to (13), wherein a planarizing layer is disposed on a side of the colorant layer on which the liquid crystal layer is disposed.

  (17) The liquid crystal display device according to (13), wherein the colorant layer is added or coated with a material that reduces the optical rotation exhibited by the liquid crystal layer when no voltage is applied. Display device.

  (18) In the liquid crystal display device of (4), a material for reducing the optical rotation exhibited by the liquid crystal layer when no voltage is applied is added or applied to one of the first substrate and the second substrate. A liquid crystal display device characterized by that.

  (19) In the liquid crystal display device of the above (4), a material for reducing the optical rotation exhibited by the liquid crystal layer when no voltage is applied is added or applied to both the first substrate and the second substrate. A liquid crystal display device.

  (20) In the liquid crystal display device of (4), the liquid crystal display device has an insulating film, and a material for reducing the optical rotation exhibited by the liquid crystal layer when no voltage is applied to the insulating film is added or applied. A liquid crystal display device.

  (21) In the liquid crystal display device according to (4), the first polarizing plate includes the first polarizing layer, a first protective film, and a second protective film, and the second polarizing film. The polarizing plate includes the second polarizing layer, a third protective film, and a fourth protective film, and the first protective film is disposed on the liquid crystal layer side of the first polarizing layer. The third protective film is disposed on the liquid crystal layer side of the second polarizing layer, and a first adhesive layer is disposed between the first substrate and the first protective film. A second adhesive layer is disposed between the second substrate and the second protective film, and the first protective film, the third protective film, the first adhesive layer, the first In order to reduce the optical rotation exhibited by the liquid crystal layer when no voltage is applied to at least one of the two adhesive layers A liquid crystal display device comprising the material is added or applied, it.

  (22) In the liquid crystal display device of (16), the planarizing layer is added or coated with a material for reducing the optical rotation exhibited by the liquid crystal layer when no voltage is applied. Liquid crystal display device.

  (23) In the liquid crystal display device according to any one of (9) to (10), the liquid crystal layer side of the first substrate and the liquid crystal layer of the second substrate are disposed. A liquid crystal display device, wherein an alignment film formed on at least one side is added or coated with a material for reducing the optical rotation exhibited by the liquid crystal layer when no voltage is applied.

  (24) In the liquid crystal display device according to any one of (1) to (8), at least one of the first electrode and the second electrode is formed in a comb shape. Display device.

  (25) The liquid crystal display device according to (24), wherein the first electrode is formed in a comb shape, and the second electrode is formed in a flat plate shape.

  (26) In the liquid crystal display device according to (24) or (25), the first electrode and the second electrode are disposed on one of the first substrate and the second substrate. A characteristic liquid crystal display device.

  (27) In the liquid crystal display device according to any one of the above (1) to (8), the first electrode or the second electrode is connected to the first substrate or the second electrode via a protruding electrode member. A liquid crystal display device arranged on a substrate.

  (28) In the liquid crystal display device according to any one of (1) to (8), the first electrode and the second electrode are connected to the first substrate or the second electrode via a protruding electrode member. A liquid crystal display device arranged on a substrate.

  (29) The liquid crystal display device according to any one of (1) to (8), wherein the first electrode or the second electrode has a wall shape.

  (30) The liquid crystal display device according to any one of (1) to (8), wherein the first electrode and the second electrode are wall-shaped.

  (31) In the liquid crystal display device of the above (29) or (30), when the thickness of the liquid crystal layer is dLC, the wall-like electrode thickness is greater than 0 and less than or equal to dLC. .

  (32) In the liquid crystal display device according to any one of (1) to (8), an electric field application direction by the first electrode and the second electrode is parallel to a first in-plane direction of the substrate, 2. A liquid crystal display device, wherein the electric field application direction has two or more directions in a pixel.

  (33) The liquid crystal display device according to (32), wherein an angle formed by any two directions of the electric field application directions is 75 degrees or more and 105 degrees or less.

  (34) In the liquid crystal display device according to any one of (1) to (8), the first electrode and the second electrode are formed on one of the first substrate and the second substrate. A liquid crystal display device, wherein an insulating layer is formed between the first electrode and the second electrode.

  (35) In the liquid crystal display device according to any one of (1) to (8), a plurality of signal wirings and a plurality of scanning wirings are disposed on any one of the first substrate and the second substrate. Each of the regions surrounded by the signal wiring and the scanning wiring serves as a pixel, and a storage capacitor is formed in a part or a periphery of the pixel adjacent to the pixel.

  (36) In the liquid crystal display device according to any one of the above (1) to (8), at least one between the first polarizing plate and the liquid crystal layer, and between the second polarizing plate and the liquid crystal layer. Includes a viewing angle compensation phase difference plate.

  (37) In the liquid crystal display device of (36), the slow axis azimuth angle of the viewing angle compensating retardation plate is orthogonal or parallel to the absorption axis of the first polarizing plate or the absorption axis of the second polarizing plate. A liquid crystal display device characterized by the above.

  (38) The liquid crystal display device according to (36), wherein the retardation of the viewing angle compensation phase difference plate is a half wavelength.

  (39) The liquid crystal display device according to (36), wherein the viewing angle compensation phase difference plate has an Nz coefficient of 0.4 or more and 0.6 or less.

  (40) In the liquid crystal display device according to any one of (1) to (8), the first substrate is disposed farther than the second substrate with reference to a display surface for displaying an image. The liquid crystal display device, wherein the first substrate has a reflective layer that reflects light on the display surface side.

  (41) The liquid crystal display device according to (40), wherein the surface of the reflective layer on the display surface side is uneven.

  (42) In the liquid crystal display device of (41), one of the first electrode and the second electrode has a flat plate shape, and the electrode having the flat plate shape reflects light toward the display surface. A liquid crystal display device comprising the reflective layer.

  (43) The liquid crystal display device according to (41), wherein a quarter-wave plate is disposed between the second polarizing plate and the liquid crystal layer.

  (44) In the liquid crystal display device of (43), the angle formed by the slow axis of the quarter-wave plate and the absorption axis of the second polarizing plate is 43 degrees or greater and 47 degrees or less. A liquid crystal display device.

  (45) The liquid crystal display device according to (43), wherein the quarter-wave plate is a broadband quarter-wave plate.

  (46) In the liquid crystal display device of (43), a material for reducing the optical rotation exhibited by the liquid crystal layer when no voltage is applied is added between the quarter-wave plate and the liquid crystal layer. Alternatively, a liquid crystal display device in which a coated optical rotation reducing member is disposed.

  (47) The liquid crystal display device according to any one of (1) to (8), wherein the pixel includes a transmissive display portion and a reflective display portion.

  (48) In the liquid crystal display device of (47), a quarter-wave plate is disposed between the liquid crystal layer and the second polarizing plate in the reflective display section. Liquid crystal display device.

  (49) In the liquid crystal display device of (47), the electric field strength applied to the liquid crystal layer of the transmissive display portion is stronger than the electric field strength applied to the liquid crystal layer of the reflective display portion. A liquid crystal display device.

  (50) In the liquid crystal display device according to (49), the electric field strength applied to the liquid crystal layer of the transmissive display unit is approximately twice the electric field strength applied to the liquid crystal layer of the reflective display unit. A liquid crystal display device characterized by the above.

  (51) In the liquid crystal display device according to (49), a reflective transparent dielectric layer is disposed between the first electrode, the second electrode, and the liquid crystal layer in the reflective display unit. A liquid crystal display device characterized by the above.

  (52) In the liquid crystal display device according to (49), the first electrode and the second electrode are formed in a comb-tooth shape, and a repetition pitch of the comb-tooth structure in the reflective display unit is determined by the transmission display unit. A liquid crystal display device, wherein the pitch is larger than the repetitive pitch of the comb structure.

  (53) In the liquid crystal display device of (52), the repetition pitch of the comb structure in the reflective display unit is 1.8 times or more and 2.2 times or less of the repetition pitch of the comb structure in the transmissive display unit. A liquid crystal display device characterized by that.

  (54) The liquid crystal display device according to (52), wherein the comb-tooth structure is branched at a boundary portion between the reflective display portion and the transmissive display portion.

  (55) In the liquid crystal display device of (47), a first quarter-wave plate is disposed between the first polarizing plate and the liquid crystal layer, and the second polarizing plate and the liquid crystal layer A liquid crystal display device, wherein a second quarter-wave plate is disposed therebetween.

  (56) In the liquid crystal display device of (55), the slow axis of the first quarter-wave plate and the slow axis of the second quarter-wave plate are orthogonal to each other, and An angle formed by an absorption axis of a polarizing plate and a slow axis of the first quarter-wave plate is 45 degrees.

  (57) In the liquid crystal display device of (56), an Nz coefficient of the first quarter-wave plate is not less than 0.4 and not more than 0.6, and Nz of the second quarter-wave plate A liquid crystal display device having a coefficient of 0.4 to 0.6.

  (58) In the liquid crystal display device of (56), one of the Nz coefficient of the first quarter-wave plate and the Nz coefficient of the second quarter-wave plate is −0.1 or more and 0 .. 1 or less, and the other is 0.9 or more and 1.1 or less.

  (59) The liquid crystal display device according to (47), wherein, in the reflective display portion, the color material layer has a hole portion.

  (60) The liquid crystal display device according to (47), wherein a thickness of the color material layer in the reflective display portion is smaller than a thickness of the color material layer in the transmissive display portion.

  (61) In the liquid crystal display device of (12), the thin film transistor is disposed along the signal line in the long side direction of the pixel, and a storage capacitor is disposed along the scan line in the short side direction of the pixel. A liquid crystal display device characterized by being arranged.

  (62) In the liquid crystal display device of (12), one of a source electrode and a drain electrode is connected to the first electrode, and one of the source electrode and the drain electrode is connected to the second electrode. A second signal connected to the other of the source and drain electrodes of the second thin film transistor, and a second signal connected to the other of the source and drain electrodes of the second thin film transistor. And a scanning wiring connected to gate electrodes of the first thin film transistor and the second thin film transistor, and a voltage having a reverse polarity is applied to the first signal wiring and the second signal wiring. A liquid crystal display device, wherein a liquid crystal is driven by a voltage difference between the first electrode and the second electrode.

  (63) In the liquid crystal display device according to (62), a first storage capacitor is connected to the first electrode, a second storage capacitor is connected to the second electrode, and the first electrode is connected to the first electrode. The capacity of the storage capacitor and the capacity of the second storage capacitor are the same.

  (64) The first polarizing plate and the second polarizing plate, the first substrate disposed between the first polarizing plate and the second polarizing plate, the first polarizing plate and the second polarizing plate. A second substrate disposed between the polarizing plates and disposed closer to the second polarizing plate than the first substrate; a liquid crystal layer disposed between the first substrate and the second substrate; A first electrode and a second electrode for applying a voltage to the liquid crystal layer, the liquid crystal layer exhibits a blue phase, and the liquid crystal layer exhibits optical rotation when no voltage is applied. A liquid crystal display device characterized by the above.

  (65) In the liquid crystal display device according to any one of (1) to (6), the absorption axis of the second polarizing plate is based on a direction that forms 90 ° with the absorption axis of the first polarizing plate. A liquid crystal display device, wherein light transmitted through the first polarizing plate is shifted to a side rotated by the liquid crystal layer to which no voltage is applied.

  (66) In the liquid crystal display device of (65), the absorption axis of the second polarizing plate is the same as that of the first polarizing plate with reference to a direction that forms 90 degrees with the absorption axis of the first polarizing plate. A liquid crystal display device characterized in that the transmitted light has a direction rotated by an angle of 0.5 to 1.25 times the angle of rotation of the liquid crystal layer to which no voltage is applied.

  (67) In the liquid crystal display device of (65), the absorption axis of the second polarizing plate rotates by 4 ° or more and 10 ° or less with reference to a direction that forms 90 ° with the absorption axis of the first polarizing plate. A liquid crystal display device characterized in that the liquid crystal display device is oriented in the direction.

  According to the present invention, the contrast ratio can be improved. Problems, configurations, and effects other than those described above will be clarified by the following description of embodiments.

1 is a schematic cross-sectional view of a liquid crystal display device of Example 1. FIG. 2 is a schematic cross-sectional view of a polarizing plate used in the liquid crystal display device of Example 1. FIG. 3 is a schematic cross-sectional view of a liquid crystal cell used in the liquid crystal display device of Example 1. FIG. It is the figure which showed the material name for making the liquid-crystal material used in Example 1, and its mixing ratio. It is a figure which shows an example of the cross-sectional schematic of the comb-tooth electrode structure of the liquid crystal display device of Example 1. FIG. It is a figure which shows an example of the cross-sectional schematic of the comb-tooth electrode structure of the liquid crystal display device of Example 1. FIG. It is a figure which shows an example of the cross-sectional schematic of the comb-tooth electrode structure of the liquid crystal display device of Example 1. FIG. FIG. 3 is a diagram illustrating an example of a schematic cross-sectional view of a protruding electrode structure of the liquid crystal display device of Example 1. FIG. 3 is a diagram illustrating an example of a schematic cross-sectional view of a protruding electrode structure of the liquid crystal display device of Example 1. FIG. 3 is a diagram illustrating an example of a schematic cross-sectional view of a protruding electrode structure of the liquid crystal display device of Example 1. FIG. 3 is a diagram illustrating an example of a schematic cross-sectional view of a wall electrode structure of a liquid crystal display device of Example 1. FIG. 3 is a diagram illustrating an example of a schematic cross-sectional view of a wall electrode structure of a liquid crystal display device of Example 1. FIG. 3 is a diagram illustrating an example of a schematic cross-sectional view of a wall electrode structure of a liquid crystal display device of Example 1. It is the schematic which showed a mode that the electric force line | wire generated when a comb-tooth electrode was used. It is the schematic which showed a mode that the electric force line | wire generated when the electrode for protrusions was used. It is the figure which showed the measurement result of the angle and transmittance | permeability intensity | strength which a pair of polarizing plate makes when the liquid crystal cell produced in Example 1 was used. It is a figure which shows the definition of the coordinate axis of the angle P which the absorption axis of a pair of polarizing plate comprises. It is the figure which defined the sign of optical rotation. It is the figure which defined the sign of optical rotation. It is the figure which showed the result of having calculated the relationship between the optical rotation angle (alpha) and the contrast ratio of the liquid crystal cell which has a liquid crystal layer with which the blue phase liquid crystal was enclosed. It is the figure which showed the result of having calculated the relationship between the optical rotation angle (alpha) and the transmittance | permeability. It is the figure which showed the result of having calculated the relationship between the optical rotation angle (alpha), the angle P which a polarizing plate comprises, and contrast ratio. It is a figure which shows the measurement result of the spectral transmittance of the liquid crystal cell used in Example 1. FIG. 6 is a schematic cross-sectional view of a liquid crystal cell used in the liquid crystal display device of Example 4. FIG. 10 is a schematic plan view of one pixel of a liquid crystal cell in Example 5. FIG. FIG. 16 is a schematic cross-sectional view of the liquid crystal cell between A-B-A ′ in FIG. 15. FIG. 10 is a schematic diagram illustrating waveform examples of scanning wiring, signal wiring, and liquid crystal applied voltage in Example 5. 10 is a schematic diagram illustrating an example of the size of each film of a color material layer in Example 5. FIG. FIG. 10 is a schematic plan view of one pixel of a liquid crystal display device in Example 6. FIG. 10 is a schematic cross-sectional view taken along S1-S2 of the liquid crystal display device in Example 6. 10 is a schematic plan view of one pixel of a liquid crystal display device in Example 7. FIG. FIG. 10 is a schematic cross-sectional view between S3 and S4 of a liquid crystal display device in Example 7. FIG. 10 is a schematic plan view of one pixel of a liquid crystal display device in Example 8. 10 is a schematic cross-sectional view taken along S5-S6 of the liquid crystal display device in Example 8. FIG. 10 is a schematic cross-sectional view taken along S7-S8 of the liquid crystal display device in Example 8. FIG. 10 is a schematic plan view of one pixel of a liquid crystal display device in Example 9. FIG. 10 is a schematic cross-sectional view taken along the line S9-S10 of the liquid crystal display device in Example 9. FIG. 10 is a schematic cross-sectional view taken along the line S11-S12 of the liquid crystal display device in Example 9. FIG. 24 is a schematic cross-sectional view taken along the line S5-S6 in FIG. 23 of the liquid crystal display device according to Example 10. FIG. FIG. 24 is a schematic cross-sectional view taken along S7-S8 in FIG. 23 of the liquid crystal display device according to Example 10. It is the schematic which showed the coordinate axis of the slow axis azimuth at the time of observing from a polar angle direction. It is the figure which showed the result of having calculated the slow axis azimuth at the time of observing from a polar angle direction when Nz coefficient is 1.0. It is the figure which showed the result of having calculated the slow axis azimuth at the time of observing from a polar angle direction when Nz coefficient is 0.5. It is the figure which showed the result of having computed the slow axis azimuth at the time of observing from a polar angle direction when Nz coefficient is 0.0. It is the figure which showed the result of having calculated the black display viewing angle characteristic when Nz coefficient of a quarter wave plate is set to 0.5. It is the figure which showed the result of having calculated the black display viewing angle characteristic when Nz coefficient of a quarter wave plate was set to 1.0. It is the figure which showed the result calculated as a thing with the slow axis of both orthogonally crossing in the normal line direction in the combination of the quarter wavelength plate whose Nz coefficient is 1.0 and 0.0. It is the schematic which shows the refractive index ellipsoid of a negative C plate and a positive C plate. It is the schematic showing the cross section in the arbitrary viewing angle directions of a refractive index ellipsoid. It is the schematic showing the refractive index ellipsoid of the combination of the quarter wavelength plate whose Nz coefficient is 1.0 and 0.0. It is a figure which shows the result of having calculated the black display viewing angle characteristic when Nz coefficient shall be 1.0 and 0.0. It is the schematic when the absorption axis of a polarizing plate is observed from an azimuth | direction direction and an oblique direction. It is the schematic when the absorption axis of a polarizing plate is observed from an azimuth | direction direction and an oblique direction. It is the schematic when a polarizing plate is observed with the Poincare sphere projected on S1 and S3 plane. It is the schematic when a polarizing plate is observed with the Poincare sphere projected on S1 and S3 plane. It is a figure which shows the result of having calculated the black display viewing angle characteristic in order to confirm the effect of a viewing angle compensation phase difference plate. It is a figure which shows the result of having calculated the black display viewing angle characteristic in order to confirm the effect of a viewing angle compensation phase difference plate. 22 is a schematic plan view of one pixel of a liquid crystal cell in Example 14. FIG. FIG. 40 is a schematic cross-sectional view taken along the line A-A ′ of FIG. 39 in Example 14. It is the schematic showing the example of the equivalent circuit of 1 pixel. FIG. 17 is a schematic diagram illustrating an equivalent circuit of one pixel in Example 15. 22 is a schematic plan view of one pixel of a liquid crystal cell in Example 15. FIG. FIG. 44 is a schematic cross-sectional view taken along the line A-A ′ of FIG. 43 in Example 15. FIG. 44 is a schematic cross-sectional view taken along B-B ′ of FIG. 43 in Example 15. FIG. 17 is a schematic diagram illustrating waveform examples of scanning wiring, signal wiring, and liquid crystal applied voltage in Example 15. It is a figure which shows an example of the optically active substance which has positive optical rotation. In Example 16, it is a schematic diagram which shows a mode that the optical rotation reducing member is arrange | positioned. In Example 16, it is a schematic diagram which shows a mode that the 1st board | substrate and the 2nd board | substrate with which the member for reducing optical rotation was added were arrange | positioned. In Example 16, it is a schematic diagram which shows a mode that the member for reducing optical rotation was added to the color material layer. It is a figure which shows an example of the product which can apply the liquid crystal display device of this invention.

  Each embodiment of the present invention will be described below with reference to the drawings. Note that components having the same function are denoted by the same reference symbols throughout the drawings for describing the embodiments, and the repetitive description thereof is omitted. Further, the following examples show specific examples of the contents of the present invention, and the present invention is not limited to these examples, and within the scope of the technical idea disclosed in this specification. Various changes and modifications by the vendor are possible. Note that the present invention can be used for, for example, a display unit of a mobile phone or a display unit of a television as shown in FIG.

  FIG. 1 to FIG. 11 are schematic diagrams for explaining the schematic configuration and operation of the liquid crystal display device of Example 1 according to the present invention.

  FIG. 1 is a schematic cross-sectional view of the liquid crystal display device of this embodiment. FIG. 2 is a schematic cross-sectional view of a polarizing plate used in the liquid crystal display device of this example. FIG. 3 is a schematic sectional view of a liquid crystal cell used in the liquid crystal display device of this embodiment.

  As shown in FIG. 1, the liquid crystal display device of this embodiment includes a liquid crystal cell 11, a first polarizing plate 14, a second polarizing plate 15, and a backlight unit 28. The liquid crystal cell 11 includes a first substrate 12 disposed on the first polarizing plate 14 side, a second substrate 13 disposed on the second polarizing plate 15 side, and the first substrate 12 and the first substrate 12. The liquid crystal layer 29 is disposed between the two substrates 13.

  The 1st polarizing plate 14 and the 2nd polarizing plate 15 are arrange | positioned in order to control the intensity | strength of the light of the liquid crystal display device of a present Example. As shown in FIG. 2, the first polarizing plate 14 adsorbs iodine to Poly Vinyl Alcohol (hereinafter referred to as PVA) and stretches the polarizing layer 32 and a first protective film 30 for protecting the polarizing layer 32. And the second protective film 31. The second polarizing plate 15 has the same configuration. The polarizing layer 32 has a transmission axis and an absorption axis, and light transmitted through the polarizing layer 32 becomes linearly polarized light. Here, the first protective film 30 is disposed on the side where the liquid crystal cell 11 is disposed, and the second protective film 31 is disposed on the opposite side where the liquid crystal cell 11 is disposed. The first protective film 30 and the second protective film 31 may be triacetyl cellulose (TAC) having a phase difference or a phaseless protective film having almost no phase difference. For the retardation-less protective film, for example, a norbornene-based material or a methacrylic resin can be used. By using the retardation-less protective film, the contrast ratio is further improved because the phase difference is smaller than that of TAC, and a thin display device can be manufactured because it is thinner than TAC. The retardation-less protective film may be used only on the liquid crystal layer 29 side (first protective film 30). An adhesive layer 103 is disposed on the side of the first polarizing plate 14 and the second polarizing plate 15 where the liquid crystal cell 11 is disposed. The first polarizing plate 14 and the second polarizing plate 15 are attached to the liquid crystal cell 11 by the adhesive layer 103. Examples of the adhesive layer 103 include an acrylic adhesive material. The absorption axis of the first polarizing plate 14 and the absorption axis of the second polarizing plate 15 are arranged so as to be orthogonal to each other. The backlight unit 28 includes a light source, a light guide plate, a diffusion plate, a prism sheet, and the like. The backlight unit 28 only needs to be able to irradiate the liquid crystal cell 11 from the back surface, and the light source and structure are not limited thereto. For example, CCFL (Cold Cathode Fluorescent Lamp), LED (Light Emitting Diode), organic EL (Electro Luminescence), etc. can be used as a light source. However, although the backlight unit 28 is necessary when the liquid crystal display device is a transmissive type or a transflective type, the backlight unit 28 is not necessary when the liquid crystal display device is a reflective type. In the case of field sequential driving, light sources of a plurality of colors (for example, red, blue, and green LEDs) can be used.

  As shown in FIG. 3, the liquid crystal cell 11 includes a first substrate 12, a second substrate 13, and a liquid crystal layer 29. A liquid crystal layer 29 is sandwiched between the first substrate 12 and the second substrate 13, and blue phase liquid crystal is sealed in the liquid crystal layer 29. Various members such as wiring are added to the first substrate 12 and the second substrate 13, but only the substrate is shown and omitted here for details.

  The first substrate 12 and the second substrate 13 are transparent to transmit light, and for example, glass or a polymer film can be used. The first substrate 12 is disposed on the backlight unit 28 side, and the second substrate 13 is disposed on the opposite side of the backlight unit 28 and on the side close to the display surface. In the case of a polymer film, plastic or polyether sulfone is particularly desirable. However, since plastic and polyethersulfone allow air to pass therethrough, it is desirable to form a gas barrier layer on the substrate surface. The gas barrier layer can be formed of a silicon nitride film or the like.

  In the liquid crystal layer 29 of this embodiment, blue phase liquid crystal stabilized with a polymer is sealed. Here, the blue phase liquid crystal in this specification has a crystal structure exhibiting Bragg diffraction in the visible or ultraviolet region, and appears between a chiral nematic phase having a relatively short helical pitch and an isotropic phase. It is a liquid crystal. The blue phase liquid crystal is generally known to exhibit optical isotropy. For example, when the blue phase liquid crystal is sealed in the liquid crystal cell 11, the optical rotation is performed despite no application of an electric field. May develop.

  When an electric field is applied to the liquid crystal layer 29 enclosing the blue phase liquid crystal, a phase difference corresponding to the magnitude and direction of the electric field is generated. In this example, the liquid crystal composition of the blue phase liquid crystal was prepared with reference to the liquid crystal material and monomer material described in Non-Patent Document 1 and the chiral agent described in Patent Document 2. The names of the materials used and the mixing ratios are shown in FIG. Some of the compounds used were synthesized for this study. In addition, the synthesis | combining method of the compound 1, the compound 2, and the compound 3 which are the materials synthesize | combined for this examination is mentioned later. Of these, the liquid crystal material may be any material that exhibits a blue phase at an arbitrary temperature range by adding an arbitrary chiral agent. JC1041XX (manufactured by Chisso Petrochemical Co., Ltd.), 5CB (Aldrich) listed in the table. It is not limited to those manufactured by the company.

  As for the chiral agent, in this example, compounds 1 to 3 mixed at the ratio described in FIG. 4 were used, but those described in Non-Patent Document 1, Non-Patent Document 2, Patent Document 2, and the like were used. A material may be used, and a plurality of types of chiral agents may be used to adjust the chiral pitch.

  Similarly, as for the monomer material, in Non-Patent Document 1, ethylhexyl acrylate (manufactured by Aldrich) and ST3021 (manufactured by DKSH) were used as acrylic monomers, and these were also used in this example. It is not limited, and either a photopolymerizable monomer or a thermopolymerizable monomer can be selected according to the process conditions. In this case, a polymerization initiator may be selected in accordance with the monomer and its production process. In the present specification, detailed description is omitted, but as a representative monomer to be used, for example, one or more of an acrylic group, a methacrylate group, an epoxy group, and a vinyl group are bonded to an arbitrary molecular group. Such a monomer can be considered.

  In the liquid crystal composition prepared by selecting materials as described above, 10% by weight of dimethoxyphenylacetophenone (manufactured by Aldrich) as a polymerization initiator is added by a dropping encapsulation method. The solution was dropped on the first substrate 12. Thereafter, the liquid crystal composition was sandwiched between the second substrates 13, and the sealing agent at the outer peripheral portion was cured to prepare the liquid crystal cell 11. In this encapsulation process, a general vacuum encapsulation method may be used. Thereafter, the surface temperature of the panel was set to 21.5 ° C., which is the temperature at which the blue phase appears. Next, while maintaining the set temperature, ultraviolet light was applied using a high-pressure mercury lamp so that the light with a wavelength of 365 nm would be 1800 mJ. Thereby, the liquid crystal cell 11 in which the liquid crystal layer 29 was filled with the blue phase liquid crystal could be obtained.

  Here, Compound 1, Compound 2, and Compound 3 used in this example were synthesized as follows.

[Synthesis Method of Compound 1]
1.64 g of 4-n-propylbenzoic acid (manufactured by Tokyo Chemical Industry) was dissolved in 50 ml of benzene, and 2.38 g of thionyl chloride was added dropwise. Thereafter, the mixture was stirred for 2 hours under reflux and then concentrated with an evaporator. The concentrate was dissolved by adding 25 ml of benzene, and further concentrated under reduced pressure to obtain 4-n-propylbenzoic acid chloride.

  Next, 1.55-g of 2,6-difluoro-4-hydroxybenzonitrile was dissolved in 30 ml of methylene chloride, 1.50 g of triethylamine was added, and the resulting 4-n-propylbenzoic acid hydrochloride was obtained under ice cooling. A solution of the product in 30 ml of methylene chloride was added dropwise. The mixture was stirred overnight at room temperature, washed with 50 ml of water, dried over magnesium sulfate, and the solvent was removed. The residue was dissolved in a small amount of methylene chloride and purified by silica chromatography with a developing solvent of hexane: ethyl acetate (10: 1) to obtain Compound 1 of the formula (1).

[Synthesis Method of Compound 2]
In place of 4-n-propylbenzoic acid used in compound 1, 4-n-pentylbenzoic acid (manufactured by Tokyo Chemical Industry Co., Ltd.) was used except that 1.80 g was used. As a result, a compound 2 of the chemical formula (2) was obtained.

[Synthesis Method of Compound 3]
15.6 g of 4-n-propylbenzoic acid (manufactured by Tokyo Chemical Industry Co., Ltd.) was dissolved in 100 ml of benzene, and 16.6 g of thionyl chloride was added dropwise under ice cooling. After dropwise addition, the mixture was stirred for 3 hours under reflux and then concentrated under reduced pressure. To this, 50 ml of benzene was added, stirred well, and then concentrated under reduced pressure to obtain 4-n-propylbenzoic acid chloride.

  Next, 10.0 g of (R)-(+)-1,1′-bi-2-naphthol (manufactured by Tokyo Chemical Industry Co., Ltd.) was added to 100 ml of methylene chloride, and then 10.1 g of triethylamine was added. A solution prepared by dissolving 4-n-propylbenzoic acid chloride synthesized previously in 50 ml of methylene chloride was added dropwise and stirred overnight at room temperature. The reaction solution was washed with water, dried over magnesium sulfate, and the solvent was concentrated under reduced pressure. The residue was dissolved in a small amount of methylene chloride and purified by silica chromatography with a developing solvent of hexane: ethyl acetate (10: 1) to obtain a compound (3) of the chemical formula 3. The raw material (R)-(+)-1,1'-bi-2-naphthol exhibits positive optical rotation, and the obtained compound 3 exhibits negative optical rotation.

  Further, a first substrate for applying a voltage to the liquid crystal layer 29 is applied to one of the first substrate 12 and the second substrate 13, or both the first substrate 12 and the second substrate 13. An electrode and a second electrode are disposed. The first electrode and the second electrode may be transparent or opaque as long as they are low resistance conductive materials. For example, indium tin oxide (ITO), zinc oxide (ZnO), chromium, tantalum-molybdenum, tantalum, aluminum, copper, or the like is used.

  In driving the liquid crystal display device having the liquid crystal layer 29 encapsulating the blue phase liquid crystal and exhibiting optical rotation when no electric field is applied, in this embodiment, an electric field component in the in-plane direction of the substrate is generated. This is because the blue phase liquid crystal generates a phase difference corresponding to the magnitude of the applied voltage in the direction of the applied electric field. Since the generated phase difference is preferably in the direction of 45 degrees with respect to the absorption axis of the first polarizing plate 14, the electric field direction in the substrate plane is also 45 degrees with respect to the absorption axis of the first polarizing plate 14. It is desirable to make it. Here, the electric field direction in the substrate plane means the direction of the electric field parallel to the substrate. The electric field applied to the liquid crystal layer 29 may be an electric field having a substrate in-plane direction component. Moreover, you may employ | adopt the electrode structure demonstrated below as a 1st electrode and a 2nd electrode of a present Example. Examples of electrode structures are shown in FIGS. FIG. 5 is an example of a schematic cross-sectional view of a comb electrode structure. FIG. 6 is an example of a schematic cross-sectional view of a protruding electrode structure. FIG. 7 is an example of a schematic cross-sectional view of a wall electrode structure.

  An alternating voltage is applied to the first electrode and the second electrode. In the description of this embodiment, the first electrode is the pixel electrode 18 and the second electrode is the common electrode 19. In FIG. 5A, the pixel electrode 18 and the common electrode 19 are disposed only on the first substrate 12, and both the pixel electrode 18 and the common electrode 19 are formed in a comb shape, and the pixel electrode 18 and the common electrode 19 are formed. Are arranged so that the comb teeth portions are alternately arranged. In FIG. 5A, both the pixel electrode 18 and the common electrode 19 are arranged on the first substrate 12, but the pixel electrode 18 and the common electrode 19 may be arranged only on the second substrate 13. . In order to apply an in-plane electric field, the following electrode structure is preferable. Although the pixel electrode 18 and the common electrode 19 may be in the same layer as shown in FIG. 5A, they may be arranged in different layers through an insulating film. Further, as shown in FIG. 5B, either one of the pixel electrode 18 and the common electrode 19 may have a comb shape, and the other may have a flat plate shape (solid shape). At this time, the common electrode 19 is disposed on the pixel electrode 18 via the interlayer insulating film 34. 5B shows a structure in which the pixel electrode 18 has a comb-tooth shape and the common electrode 19 has a flat plate shape. However, the flat pixel electrode 18 exists at the position of the common electrode 19, and the pixel electrode 18 The same effect can be obtained even when the comb-like common electrode 19 exists at the position. Further, the comb-like pixel electrode 18 and the comb-like common electrode 19 may be provided on both the first substrate 12 and the second substrate 13 as shown in FIG. 5C. Although not shown, the same effect can be obtained by combining the electrode structures shown in FIGS. 5A, 5B, and 5C, or having a plurality of structures in each pixel.

  The interlayer insulating film 34 in FIG. 5B is disposed between the pixel electrode 18 and the common electrode 19 in order to electrically insulate them, and is formed on a part or the entire area of the common electrode 19. Further, in the normal direction of the substrate surface, the pixel electrode 18 and the common electrode 19 overlap with each other via the interlayer insulating film 34. The material of the interlayer insulating film 34 is not particularly limited as long as it can be electrically insulated. As the interlayer insulating film 34, for example, a silicon oxide film, a silicon nitride film, or the like is used.

  Further, as shown in FIGS. 6A and 6B, the protruding electrode member 102 is disposed on the first substrate 12, and the pixel electrode 18 and the common electrode 19 are disposed at the protruding end of the protruding electrode member 102. Also good. By adopting an electrode structure as shown in FIGS. 6A and 6B, more electric fields in the in-plane direction can be obtained, and light utilization efficiency can be improved. Different materials may be used for the protruding electrode member 102 formed under the pixel electrode 18 and the common electrode 19. Further, as shown in FIG. 6B, the protruding electrode member 102 may be disposed on the first substrate 12, and the pixel electrode 18 or the common electrode 19 may be disposed at the protruding tip of the protruding electrode member 102. Many electric fields in the in-plane direction can be obtained, and light utilization efficiency can be improved. This will be described with reference to FIG.

  FIG. 8A shows a schematic diagram of lines of electric force when an electric field is applied when both the pixel electrode 18 and the common electrode 19 are formed in a comb shape. FIG. 8B shows a schematic diagram of lines of electric force when an electric field is applied to the protruding electrode as shown in FIG. 6A. As can be seen from a comparison between FIG. 8A and FIG. 8B, the projection electrode can obtain more electric fields in the in-plane direction. As can be seen from FIG. 8B, it is desirable that the electrode is disposed near the center in the thickness direction of the liquid crystal cell, but a sufficient effect can be obtained with only one side as shown in FIG. 6B. Moreover, since the electric field is easily generated in the oblique direction by forming the convex electrode shape as shown in FIG. 6C, more electric fields in the in-plane direction can be obtained, and the efficiency can be further improved. Although FIG. 6C shows the protruding electrode member 102 with a triangle, a similar effect can be obtained with a semicircle or a quadrangle.

  The protruding electrode member 102 is arranged to adjust the position and shape of the electrode. The protruding electrode member 102 is an insulating material and can be adjusted in position and shape. The protruding electrode member 102 is formed according to the shape of the pixel electrode 18 or the common electrode 19. In the case of FIGS. 6A to 6C, the protruding electrode member 102 is formed in a comb shape on the first substrate 12. The cross-sectional shape of the protruding electrode member 102 may be a rectangle or a triangle. As the protruding electrode member 102, for example, an acrylic resin, a silicon oxide film, a silicon nitride film, or the like is used.

  For the pixel electrode 18 and the common electrode 19, for example, the cross section as shown in FIG. Both or one of the pixel electrode 18 and the common electrode 19 has a wall shape, and is disposed between the first substrate 12 and the second substrate 13. At this time, the height of the wall-like electrode may be equal to the thickness of the liquid crystal layer as shown in FIG. 7A, or may be lower than the thickness of the liquid crystal layer as shown in FIG. 7B. Specifically, it is desirable that the height of the wall-shaped electrode be higher than a quarter thickness of the liquid crystal layer 29. The height of the wall electrode is most preferably equal to the thickness of the liquid crystal layer 29. The wall electrode structure can reduce the driving voltage because the fluctuation of the electric field strength distribution in the liquid crystal thickness direction is small, the liquid crystal layer thickness can be reduced, and the light utilization efficiency of the liquid crystal display device can be increased. Further, as shown in FIG. 7C, when the wall electrode is formed, the wall electrode insulating film 101 is first disposed, and then the electrode member is provided in the vicinity thereof, thereby facilitating the production. Examples of the wall electrode insulating film 101 include a silicon oxide film, a silicon nitride film, a resist material, and an organic film.

  Although not shown here, each electrode structure may have a multi-domain structure within one pixel, thereby reducing a color shift depending on the viewing direction and achieving a wide viewing angle. The multi-domain structure means that there are a plurality of electric field directions applied in the in-plane direction of the substrate, and there are a plurality of directions in which a phase difference is generated, and a relationship of optical compensation is obtained. In order to improve the light utilization efficiency, the electric field directions are defined so that any two of the electric field directions applied in the in-plane direction of the substrate are different by approximately 90 degrees within one pixel, and each electric field direction is the first polarized light. It is desirable to form 45 degrees with respect to the absorption axis of the plate 14. The electric field may be defined so that an angle of 75 degrees or more and 105 degrees or less is different within one pixel with respect to any two of the electric field directions applied in the substrate in-plane direction. In forming the multi-domain structure, the structure of the electrode is not limited. For example, an electrode structure in another embodiment described later may be employed.

  The optical characteristics of the liquid crystal cell 11 having the liquid crystal layer 29 encapsulating the blue phase liquid crystal produced by the method as described above were measured. The optical characteristic is that the liquid crystal cell 11 before the first polarizing plate 14 and the second polarizing plate 15 are attached is disposed between a pair of polarizing plates, and the transmitted light of the liquid crystal cell 11 is rotated while rotating one of the polarizing plates. It was measured by measuring the strength.

  FIG. 9A is a graph showing the transmitted light intensity when the produced liquid crystal cell 11 is disposed between a pair of polarizing plates and one polarizing plate is rotated. FIG. 9B is a diagram illustrating the definition of the coordinate axis of the angle P formed by the absorption axes of the pair of polarizing plates, and the angle P is arranged on the transmitted light intensity observation side with respect to the absorption axis of the first polarizing plate. The absorption axis of the second polarizing plate is defined as an angle that is counterclockwise when viewed from the transmitted light intensity observation side. When rotating the polarizing plate, only the second polarizing plate was rotated as shown in FIG. 9B. FIG. 9A also shows the result of rotating only the polarizing plate without placing anything between the polarizing plates. Referring to FIG. 9A, in the case of only the polarizing plate, the transmitted light intensity is lowest when the angle formed by the absorption axis of the polarizing plate is 90 degrees. On the other hand, when the liquid crystal cell 11 having the liquid crystal layer 29 enclosing the blue phase liquid crystal was sandwiched between a pair of polarizing plates, the transmitted light intensity was lowest when the angle formed by the absorption axis of the polarizing plate was 98 degrees. This result shows that the liquid crystal layer 29 encapsulating the blue phase liquid crystal exhibits optical rotation.

  Uniaxial phase difference is a phase difference caused by refractive index anisotropy with respect to orthogonal linearly polarized light. On the other hand, optical rotation is a phase difference caused by refractive index anisotropy with respect to left and right circularly polarized light. This amount can be measured using, for example, a phase difference measuring apparatus (for example, AxoScan manufactured by Axometrics). It was found that the liquid crystal layer 29 encapsulating the blue phase liquid crystal has optical rotatory power although the uniaxial phase difference is substantially zero when no electric field is applied. In general, a medium having optical rotation is called an optically active substance.

  The optical rotatory power can be expressed as the optical rotatory power. In general, the optical rotation power ORP (Optical Rotation Power) is expressed by the following equation (1).

Here, α is called an optical rotation angle, and is a difference in angle between the linearly polarized light that is incident and the linearly polarized light that is emitted when linearly polarized light is incident on the optically active substance. D is the thickness of the optically active substance. In this embodiment, in the following description, when the optical rotation ability of the liquid crystal layer 29 in which the blue phase liquid crystal is encapsulated is expressed, the optical rotation angle α independent of the thickness is used as the optical rotation ability of the liquid crystal layer 29 itself. The optical rotation angle α is measured by sandwiching an optically active substance between a pair of polarizing plates as shown in FIG. 9A and measuring an angle θ _min that minimizes the transmitted light intensity with respect to the angle formed by the absorption axis of the pair of polarizing plates. can do. The optical rotation angle α is a parameter that depends on the measurement wavelength and the measurement temperature. In this example, luminance (transmitted light intensity) was used for measurement. The measurement was performed at room temperature (22 degrees). The optical rotation angle α is expressed by the following equation (2).

  The sign of the optical rotation angle α represents the direction of rotation of the outgoing polarization with respect to the incoming polarization. In the present specification, as shown in FIG. 10, when the outgoing polarized light rotates clockwise as viewed from the outgoing side with respect to the incident polarized light, the optical rotation is defined as positive, and the optical rotation angle α is defined as positive. To do. On the contrary, when the outgoing polarized light rotates counterclockwise as viewed from the outgoing side with respect to the incident polarized light, the optical rotation is called negative, and the optical rotation angle α is defined as negative. In this specification, the measurement wavelength of the optical rotation angle is 550 nm.

The liquid crystal cell 11 having the liquid crystal layer 29 encapsulating the blue phase liquid crystal produced under the above conditions was θ _min when the angle defined in FIG. 9B was 98 degrees. Therefore, it is seen that the optical rotation angle α is negative and −8 degrees since it is rotated counterclockwise when observed from the emission side. The sign of the optical rotation angle of the liquid crystal cell 11 is determined by the material contained in the blue phase liquid crystal, and may be positive.

  In general, the blue phase liquid crystal exhibits optical isotropy, but in this embodiment, the liquid crystal layer 29 exhibits a blue phase and optical rotation. In principle, it is considered difficult to completely eliminate the optical rotation of the liquid crystal layer 29 in which the blue phase liquid crystal is sealed.

  Since the liquid crystal layer 29 enclosing the blue phase liquid crystal has optical rotation, light leakage occurs when no voltage is applied, that is, when black is displayed, depending on the magnitude of the optical rotation angle α, and the contrast ratio is lowered. In the following, the relationship between the optical rotation angle α and the contrast ratio was examined by simulation. As the simulator, a commercially available LCD-Master (manufactured by Shintech) was used. In the simulation, the liquid crystal is assumed to be ZLI-4792 (manufactured by Merck), and the thickness of the liquid crystal layer is set to 50 μm. The optical rotation was assumed by giving a twist deformation to the liquid crystal layer. Since ΔLI of ZLI-4792 is 0.0974 (wavelength 550 nm), Δnd is approximately 4870 nm, and Δnd is sufficiently larger than the wavelength (550 nm), so that the Morgan condition is satisfied and the twist deformation angle and the optical rotation angle α of the liquid crystal are satisfied. Are substantially equal.

  The liquid crystal layer in which the blue phase liquid crystal is sealed assumes a state in which no voltage is applied, and assumes a state in which uniaxial phase difference does not appear and optical rotation occurs. In order to virtually calculate the contrast ratio in such a state, the simulation assumes that ZLI-4792 (manufactured by Merck) has a twisted orientation as described above. In order to ignore the uniaxial retardation of the liquid crystal, the orientation direction of the center of the liquid crystal layer in the thickness direction is made parallel to one of the axes of the polarizing plate in the simulation. As a result, the conversion of the polarization due to the uniaxial phase difference can be ignored, and only the optical rotation can be considered.

  The contrast ratio of the pair of polarizing plates (the transmittance ratio between the parallel arrangement and the orthogonal arrangement) was 30000. When calculating the contrast ratio, two polarizing plates are arranged so as to form an angle of 90 °, and a layer assuming a liquid crystal layer in which a blue phase liquid crystal is enclosed and showing optical activity is arranged between them. The transmittance was obtained while changing the angle α. Assuming that the cause of light leakage of the liquid crystal cell 11 is only the optical rotation shown by the liquid crystal layer 29 filled with the blue phase liquid crystal, if the optical rotation is zero, the contrast ratio becomes equal to the contrast ratio of the polarizing plate 30000. It became. In addition, the contrast ratio is determined by the ratio of the brightness for white display and the brightness for black display. Assuming that the brightness for white display is constant, the contrast ratio is affected only by the brightness for black display. did. Simulation was performed under the above conditions, and FIG. 11 shows the relationship between the optical rotation angle α and the contrast ratio of a liquid crystal cell having a liquid crystal layer in which blue phase liquid crystal is sealed.

  FIG. 11 shows that the contrast ratio decreases as the absolute value of the optical rotation angle α increases. This indicates that light leakage occurs due to the optical rotation exhibited by the liquid crystal layer filled with the blue phase liquid crystal.

  Further, as described in Non-Patent Document 3, considering the light responsiveness of human retinal cells, a contrast ratio of 100 or more is sufficient to enhance visibility in a bright environment. Below 1000 is required. At present, since the environment in which the liquid crystal display device is used is various, the contrast ratio is desirably 1000 or more. Therefore, it is desirable to make the optical rotation angle α closer to zero from −15 degrees.

  Further, the blue phase liquid crystal cell 11 produced in this example had an optical rotation angle of −8 degrees as described above. Also, from FIG. 11, it can be confirmed that the optical rotation angle α has an inflection point in the vicinity of −5 degrees, and the contrast ratio increases rapidly as it approaches zero from −5 degrees. Therefore, it is more desirable to make the optical rotation angle α approach -5 degrees to zero. The optical rotation angle α is influenced by an absolute value. That is, 0 degree <| α | ≦ 15 degrees is desirable, 0 degree <| α | ≦ 8 degrees is further desirable, and 0 degree <| α | ≦ 5 degrees is desirable.

  With the above configuration, the contrast ratio can be improved in the liquid crystal display device using the blue phase liquid crystal having optical rotation.

  Next, Example 2 of the liquid crystal display device according to the present invention will be described. In this example, in the same liquid crystal display device as in Example 1, the optical rotation angle α expressed in the liquid crystal layer 29 and the angle P formed by the absorption axes of the first polarizing plate 14 and the second polarizing plate 15 are A case of changing will be described. The optical rotation angle α is considered to change depending on the liquid crystal composition used for the liquid crystal layer 29. In the liquid crystal display device according to the present embodiment, description of portions having the same configurations as those of the first embodiment will be omitted as appropriate.

  In the liquid crystal cell 11 having the liquid crystal layer 29 in which the blue phase liquid crystal is sealed, the incident polarization plane rotates by the magnitude of the optical rotation angle α due to the optical rotation exhibited by the liquid crystal layer 29. Since the liquid crystal cell 11 having the liquid crystal layer 29 filled with the blue phase liquid crystal has optical rotation, light leakage occurs when the two absorption axes of the two polarizing plates are arranged at 90 degrees. .

FIG. 12A shows the relationship between the optical rotation angle α and the transmittance at that time when the angle P formed by the absorption axes of the first polarizing plate 14 and the second polarizing plate 15 is the following four conditions. Here, the angle P is defined by FIG. 9B as in the case of the first embodiment, and in FIG. 12A, the second polarizing plate 15 corresponds to the second polarizing plate in FIG. 9B. .
(A): P = 90 ° + α
(B): P = 90 °
(C): P = 90 ° -α
(D): P = 90 ° -2α

  Legends (a) to (d) in FIG. 12A represent the angle P formed by the absorption axes of the two polarizing plates. As can be seen from FIG. 12A, when P = 90 ° −α, the transmittance is the smallest regardless of the optical rotation angle α. This is because the polarization plane rotates by α due to optical rotation, and the angle formed by the absorption axes of the two polarizing plates is set to 90 ° −α to compensate for the rotation of the polarization plane, thereby obtaining the minimum transmittance. It means that you can.

  FIG. 12B shows the contrast ratio with respect to the difference between the angle P formed by the absorption axes of the two polarizing plates and (90 ° −α). The contrast ratio of the polarizing plate (the ratio of the transmittance in the parallel arrangement and the orthogonal arrangement) was 30000. In FIG. 12B, the contrast ratio was determined on the assumption that light leakage that occurs when the liquid crystal cell is sandwiched between two polarizing plates occurs only due to the effect of optical rotation.

  Referring to FIG. 12B, no light leakage occurs when P− (90 ° −α) is zero regardless of the optical rotation angle α, and thus the contrast ratio takes a maximum value. The region where the contrast ratio was 1000 or more was a region where P- (90 ° -α) was 5.5 ° or less, or −5.5 ° or more. That is, when a liquid crystal cell using a blue phase liquid crystal having optical rotation is sandwiched between two polarizing plates, P− (90 ° −α) is −5.5 ° ≦ P− (90 ° −α) ≦ 5. It is desirable to be 5 °. Further, as shown in FIG. 12B, there is an inflection point at ± 2.5, and P− (90 ° −α) is a region smaller than 2.5 ° and larger than −2.5 °, that is, −2. .5 ° ≦ P− (90 ° −α) ≦ 2.5 ° is desirable because the contrast ratio is further improved. Furthermore, −0.5 ° ≦ P− (90 ° −α) ≦ 0.5 ° is desirable.

  With the configuration described above, the contrast ratio can be improved in the liquid crystal display device having the liquid crystal layer 29 exhibiting optical rotation.

  That is, the direction of the absorption axis of the second polarizing plate 15 is the direction rotated according to the optical rotation that the liquid crystal layer 29 develops, with reference to the direction that forms 90 degrees with the absorption axis of the first polarizing plate 14. To do. Specifically, when the liquid crystal layer 29 exhibits optical rotation that rotates light transmitted through the first polarizing plate 14 on the counterclockwise (clockwise) side when viewed from the observer side when no voltage is applied. The direction of the absorption axis of the second polarizing plate 15 is shifted counterclockwise (clockwise) as viewed from the observer side. Thereby, the contrast ratio is improved.

  The liquid crystal layer 29 rotates the light transmitted through the first polarizing plate 14 with respect to the direction of the absorption axis of the second polarizing plate 15 that is 90 degrees with the absorption axis of the first polarizing plate 14. It is desirable that an angle of 0.5 times or more and 1.25 times or less of the angle to be rotated is in the rotated direction. Further, it is more preferable to set the angle of 0.75 times or more and 1.1 times or less to the rotated direction.

  In the case of Example 1, the optical rotation angle is -8 degrees. In this case, as shown in FIG. 12A, the transmittance is smallest when the angle P is 98 degrees, and the transmittance decreases in the order of 90 degrees, 82 degrees, and 106 degrees. That is, if the liquid crystal layer 29 is further shifted beyond the angle of rotation of the polarization plane, the transmittance is likely to increase. Therefore, when the optical rotation angle expressed in the liquid crystal layer 29 is −8 degrees as in the first embodiment, the direction of the absorption axis of the second polarizing plate 15 is 90 with respect to the absorption axis of the first polarizing plate 14. It is preferable that the liquid crystal layer 29 is shifted by 4 degrees or more and 10 degrees or less, more preferably 6 degrees or more and 9 degrees or less, in the direction in which the liquid crystal layer 29 rotates the polarization plane with reference to the direction of the angle.

  Next, a third embodiment of the liquid crystal display device of the present invention will be described. In the present embodiment, in a liquid crystal display device having a liquid crystal layer in which blue phase liquid crystal is sealed to express optical rotation, the chiral pitch induced by the chiral agent added to the blue phase liquid crystal is set to a visible light wavelength or less. The chiral pitch can be measured by the Grand Jean Canoe method (wedge method). The contrast ratio can be increased by setting the chiral pitch to be equal to or less than the visible light wavelength. The configuration of the present embodiment is basically the same as that of the first embodiment, and the description of the same points will be omitted as appropriate. Changes from the first embodiment will be described with reference to FIG.

  When a liquid crystal cell having a liquid crystal layer sealed with a blue phase liquid crystal is arranged between two polarizing plates arranged so that the absorption axes are perpendicular to each other at 90 degrees, and the spectral transmittance is measured, it corresponds to the chiral pitch. A peak is detected at the wavelength. This is due to the diffraction of the blue phase liquid crystal. This is also observed in the liquid crystal layer in which the blue phase liquid crystal is encapsulated and expresses optical rotation. When the spectral transmittance of the liquid crystal cell 11 in Example 1 is measured, a peak is observed at a wavelength of about 570 nm. FIG. 13 is a diagram illustrating this measurement example. The full width at half maximum of the peak changes due to variations in the lattice size of the blue phase liquid crystal.

  As can be seen from FIG. 13, the spectral transmittance of the liquid crystal cell 11 is diffracted by the chiral pitch and causes light leakage. Further, the optical rotation angle α appearing in the liquid crystal layer 29 depends on the chiral pitch, and the optical rotation angle α can be reduced by shortening the chiral pitch. That is, in the liquid crystal cell 11 having the liquid crystal layer 29 in which the blue phase liquid crystal is sealed, when the chiral pitch of the blue phase liquid crystal is shortened, the black luminance is reduced and the contrast ratio is improved.

  Visible light is said to be from 380 (-400 nm) to 700 (-780) nm, so that black luminance reduction due to diffraction can be prevented by making the peak of spectral transmittance out of visible light. Since the peak of spectral transmittance has a correlation with the chiral pitch, the spectral transmittance peak can be shifted to the short wavelength side by reducing the chiral pitch.

Further, since the optical rotation angle α is lowered by shortening the chiral pitch, it is desirable to shift the peak of the spectral transmittance to a short wavelength. The blue phase liquid crystal has a lattice with a size corresponding to the chiral pitch. This is because one lattice has a double twist cylinder structure. When the chiral pitch is shortened, the lattice size is also reduced. If the length of one side of the grating is d _L and a slight refractive index anisotropy Δn is generated in the blue phase liquid crystal, a smaller grating corresponds to a lower Δnd _L per grating. In general, it is known that when the retardation Δnd is lowered, the optical rotation is also lowered. Therefore, when the chiral pitch is shortened, the optical rotation angle α decreases. That is, in the liquid crystal display device having the liquid crystal layer 29 in which the blue phase liquid crystal is sealed, by reducing the chiral pitch of the blue phase liquid crystal sealed in the liquid crystal layer to 400 nm or less, light leakage due to diffraction is reduced, and the optical rotation is further improved. The angle α is also reduced. Further, by setting the chiral pitch of the blue phase liquid crystal to 380 nm or less, light leakage due to diffraction is further reduced, and the optical rotation angle α is further reduced.

  With the above structure, the contrast ratio can be increased in the liquid crystal display device in which the blue phase liquid crystal is sealed and the liquid crystal layer having the optical rotation is provided.

  Next, a fourth embodiment of the liquid crystal display device of the present invention will be described. In this embodiment, an alignment film is used in a liquid crystal display device having a liquid crystal layer enclosing blue phase liquid crystal and exhibiting optical rotation. Thereby, optical rotation can be reduced and contrast ratio can be improved. The configuration of the present embodiment is basically the same as that of the first embodiment, and description of points that are the same as those of the first embodiment will be omitted as appropriate. Differences from the first embodiment will be described with reference to FIG.

  FIG. 14 is a schematic cross-sectional view of a liquid crystal cell used in the liquid crystal display device of this example. As shown in FIG. 14, the liquid crystal layer 29 is sandwiched between the first substrate 12 and the second substrate 13. A first alignment film 401 is disposed between the liquid crystal layer 29 and the first substrate 12, and a second alignment film 402 is disposed between the liquid crystal layer 29 and the second substrate 13. That is, the first alignment film 401 is disposed on the side of the first substrate 12 where the liquid crystal layer 29 is disposed, and the second alignment film 402 is disposed on the side of the second substrate 13 where the liquid crystal layer 29 is disposed. Has been. In FIG. 14, only one of the first alignment film 401 or the second alignment film 402 may exist.

  The first alignment film 401 and the second alignment film 402 have a function of aligning liquid crystals. The orientation direction is not limited and may be any of horizontal, diagonal, and vertical. The first alignment film 401 and the second alignment film 402 are preferably polyimide organic films, but may be SiO vertical vapor deposition films, surfactants, chromium complexes, or the like.

  The role of the alignment film is used to regularly align the liquid crystal in the nematic phase or the like. However, when the liquid crystal layer 29 encapsulating the blue phase liquid crystal exhibits optical rotation, an alignment film is used to reduce the optical rotation. Since the alignment direction of the blue phase liquid crystal is various, the same effect can be obtained with either the horizontal alignment film or the vertical alignment film. The first alignment film 401 and the second alignment film 402 may be different alignment films. Further, by performing an alignment process by rubbing on the first alignment film 401 or the second alignment film 402, an effect of reducing optical rotation can be further obtained. Although the rubbing direction is arbitrary, it is more desirable that the rubbing direction is 45 degrees or more and less than 90 degrees from the direction in which the electric field is applied so that a phase difference is more easily generated when the electric field is applied.

  For example, in the case where the electrode is provided only on the first substrate 12 as shown in FIG. 5A, the first alignment film 401 is an insulator, so that a voltage drop occurs and the potential applied to the liquid crystal layer 29 Decreases. In order to prevent this, the alignment film may be only the second alignment film 402.

  With the above configuration, in the liquid crystal display device in which the liquid crystal layer in which the blue phase liquid crystal is sealed exhibits optical activity, the optical activity can be reduced and the contrast ratio can be improved.

  Next, a fifth embodiment of the liquid crystal display device of the present invention will be described. In this embodiment, a liquid crystal display device having a liquid crystal layer 29 in which blue phase liquid crystal is sealed is driven using a TFT (Thin Film Transistor). Thereby, the number of pixels can be increased to achieve high image quality, the contrast ratio can be increased, and writing deficiency can be reduced. The configuration of the present embodiment is basically the same as that of the first embodiment, and description of points that are the same as those of the first embodiment will be omitted as appropriate. Differences from the first embodiment will be described with reference to FIGS. 15 to 18.

  FIG. 15 is a schematic plan view of one pixel of the liquid crystal cell in this example. FIG. 16 is a schematic cross-sectional view of the liquid crystal cell between A-B-A ′ in FIG. 15. FIG. 17 is a schematic diagram illustrating waveform examples of scanning wiring, signal wiring, and liquid crystal applied voltage in the present embodiment.

  An example in which a pixel is specifically configured in the liquid crystal display device having the liquid crystal layer 29 in which the blue phase liquid crystal is encapsulated and exhibiting optical rotation is shown below. In this embodiment, an inverted staggered TFT structure is used, and the TFT 20 includes a scanning wiring 16 made of an aluminum alloy, an interlayer insulating film 34 made of a silicon nitride film (not shown in FIG. 15), and an island-like silicon 501 made of amorphous silicon. The signal wiring 17 made of aluminum alloy, the pixel electrode 18 made of ITO, and the common electrode 19 were formed by repeating patterning in this order. Further, the scanning wiring 16 and the common electrode 19 are connected through the interlayer insulating film 34 through the contact hole 23. In the lower part of FIG. 15, the scanning wiring 16 is arranged, and on the left side of the figure, the signal wiring 17 is arranged, and the island-like silicon 501 is arranged at the intersection of the signal wiring 17 and the scanning wiring 16 to form the TFT 20. Is done. A region that is partitioned by the signal wiring 17 and the scanning wiring 16 and surrounded by the signal wiring 17 and the scanning wiring 16 is a pixel. It can be said that the gate wiring of the TFT 20 also serves as a part of the scanning wiring 16, and the entire island-shaped silicon 501 overlaps with the scanning wiring 16, and the gate electrode of the TFT 20 is connected to the scanning wiring 16. The drain electrode of the TFT 20 is connected to the signal wiring 17, and the source electrode of the TFT 20 is connected to the comb-like pixel electrode 18. It can be said that the drain electrode of the TFT 20 is drawn out from the intersection of the signal wiring 17 and the scanning wiring 16, and the source electrode of the TFT 20 is disposed on the scanning wiring 16. A similar comb-shaped common electrode 19 is formed so as to face the pixel electrode 18 in a nested manner. Further, the storage capacitor 21 is formed between the island-like pattern of the layer common to the signal wiring 17 disposed on the upper side of the one scanning electrode, the scanning wiring 16, and the island-like pattern and the scanning wiring 16. The interlayer insulating film 34 forms a plate capacitance.

  A signal for controlling the TFT 20 is applied to the scanning wiring 16, and a voltage signal for controlling the liquid crystal layer 29 is applied to the signal wiring 17. The material of the scanning wiring 16 and the signal wiring 17 is preferably a low-resistance conductive material, for example, chromium, tantalum-molybdenum, tantalum, aluminum, aluminum alloy, copper, or the like.

  FIG. 16 shows a cross-sectional structure of the pixel along the line AB-A ′ in FIG. 15. The pixel is configured by sandwiching a liquid crystal layer 29 between two glass substrates, a first substrate 12 and a second substrate 13.

  On the first substrate 12, the TFT undercoat film 22, the scanning wiring 16, the interlayer insulating film 34, the island-shaped silicon 501, the signal wiring 17, the pixel electrode 18, and the common electrode 19 (not shown in FIG. 16). Are sequentially stacked. Although the pixel electrode 18 and the common electrode 19 are shown in different hatching patterns in FIG. 16, they are formed by patterning the same ITO layer and are arranged in the same layer in direct contact with the signal wiring 17. A black BM (Black Matrix) layer 26 in which only the display portion is opened is disposed inside the second substrate 13 which is disposed to be opposite, and a color which selectively transmits a single color which is slightly larger than the opening portion of the BM layer 26 for each pixel. A material layer 24 and a flattening layer 25 covering the entire pixel surface are stacked in order to obtain surface flatness. Since the BM layer 26 and the color material layer 24 are made of a material having low conductivity such as a resin, the electric field distribution of the pixel electrode 18 can be prevented from being affected, and a luminance difference between the peripheral portion and the central portion of the pixel region can be achieved. And a uniform transmission state can be obtained, and the contrast ratio can be increased. The TFT undercoat film 22 needs to have insulating properties, and silicon nitride or the like is desirable. The planarizing layer 25 is preferably an organic film such as an acrylic resin. Further, although not shown, a back electrode 27 may be disposed on the side of the second substrate 13 where the liquid crystal layer 29 is not disposed in order to prevent display defects due to static electricity. The back electrode 27 may be any transparent film having conductivity, and is preferably ITO or ZnO.

  The color material layer 24 is configured by arranging a plurality of kinds of films that selectively transmit a predetermined color, and is configured by arranging three kinds of films that selectively transmit each color of blue, green, and red. Is desirable. For example, such an arrangement includes a stripe arrangement and a delta arrangement. Although only three colors of blue, green, and red are described here, no white or other colors may be mixed, or three or more colors may exist. The presence of three or more colors widens the color reproduction range and improves the light utilization efficiency. Furthermore, since the wavelength of light can be selected, the optical rotation having wavelength dependency can be reduced. Further, by changing the area of each film of the color material layer 24 and making the areas of the respective colors constituting the color material layer 24 different, the light use efficiency can be further improved and the optical rotation can be reduced. For example, in the case of having three colors of blue, green, and red, the light use efficiency is improved by making the blue pixel area the largest as shown in FIG. FIG. 18 is a conceptual diagram showing the size of the pixel area. Also, the light utilization efficiency can be improved by changing the thicknesses of the liquid crystal layers in the blue, green, and red regions and changing the thicknesses of the liquid crystal layers of the respective colors. For example, the light use efficiency is improved by making only the thickness of the liquid crystal layer in the blue pixel region smaller than the thickness of the liquid crystal layer in the green or red pixel region. At this time, the thickness of the liquid crystal layer is controlled by the thickness of the color material layer 24. In addition, by making the planarizing layer 25 thin, liquid crystal layers having different thicknesses in blue, green, and red regions can be manufactured. The flattening layer 25 is disposed on the color material layer 24 on the side where the liquid crystal layer 29 is disposed. In this embodiment, the case where only one place is changed with respect to the size of the pixel and the thickness of the liquid crystal layer is shown, but the light use efficiency is further improved by controlling a plurality of places.

  The common electrode 19 and the pixel electrode 18 have a comb shape, and are formed in a nested manner. Further, since the common electrode 19 and the pixel electrode 18 are alternately arranged, by applying a voltage between the common electrode 19 and the pixel electrode 18, electric lines of force enter and exit between adjacent electrodes. In the vicinity of the electrode between the common electrode 19 and the pixel electrode 18, a horizontal electric field mainly in the in-plane direction of the substrate is applied to the liquid crystal layer 29. The blue phase liquid crystal sealed in the liquid crystal layer 29 generates a uniaxial phase difference when a voltage is applied, and is transmitted by two polarizing plates arranged outside the first substrate 12 and the second substrate 13. The non-transmission state is arbitrarily controlled. Accordingly, light incident on the pixel from the backlight unit 28 arranged further below the first substrate 12 in FIG. 16 is transmitted upward in FIG. 16 through the color material layer 24, and the pixel is arbitrarily selected. Can blink at a brightness of.

  By arranging the pixels described above in a matrix and driving the matrix as described below, a display device that displays each pixel at an arbitrary brightness can be formed. As described above, each of the pixels arranged in a matrix is surrounded by the scanning wiring 16 and the signal wiring 17. A plurality of scanning wirings 16 and a plurality of signal wirings 17 are laid on the first substrate 12, and the pixels correspond to the areas partitioned by these, and the respective pixels are arranged in a matrix. The Rukoto.

  In the liquid crystal display device according to the present embodiment, as in the case of the first embodiment, the periphery of the blue phase liquid crystal is surrounded by the polymer network, and the alignment regulating force such as the interface regulating force between the polymer and the liquid crystal is strong. The displacement of the alignment due to the same electric field is smaller than that in the IPS mode using nematic liquid crystal having no light, and as a result, the driving electric field for maximizing the transmittance is increased. Further, the relative dielectric constant of the liquid crystal composition sealed in the liquid crystal layer 29 is small in the relative dielectric constant difference during driving because there is little change in the liquid crystal alignment between application and non-application of voltage. However, in order to lower the drive voltage, the value of the dielectric constant needs to be larger than that of a general IPS (In Plane Switching) type liquid crystal display device in which nematic liquid crystal is sealed, and the pixel between the pixel electrode and the common electrode The liquid crystal capacity is greatly increased. The dielectric anisotropy of the liquid crystal layer 29 is desirably 30 or more, and more desirably 50 or more.

  As described above, in order to drive the blue phase liquid crystal, it is necessary to increase the capacity and the voltage as compared with the IPS liquid crystal display device. In particular, in order to reduce the luminance of black and increase the contrast ratio, it is necessary to make the voltage applied to the non-lighted pixels sufficiently lower than the threshold value. Therefore, it is preferable to use a large storage capacity (holding capacity) in order to reduce the leakage current at the time of holding. The storage capacitor is formed in a part of the pixel (that is, inside the pixel region) or the periphery (that is, a portion that overlaps with the signal wiring or the scanning wiring that divides the pixel region). Specifically, the storage capacitor is formed on the scanning wiring 16 of the adjacent pixel, but may be formed across the pixel region and the scanning wiring 16. The holding capacitor is useful for reducing voltage fluctuation during holding or reducing voltage fluctuation applied to the liquid crystal during the holding period. These voltage fluctuations are proportional to the TFT leakage current or liquid crystal capacitance, and inversely proportional to the gate capacitance. The value of the storage capacitor is preferably equal to or more than about 5 times the value of the liquid crystal capacitance that can reduce the leakage current. In other embodiments to be described later, a configuration is proposed in which two TFTs are arranged to reduce leakage by voltage sharing. Even when two TFTs are arranged, the storage capacitor may have the above value. As for the writing characteristics, since the pixel capacity is larger than that of the conventional TFT-LCD, driving can be performed by making the channel width W larger than the channel length L as the W / L value of the TFT.

  A drive waveform for obtaining drive characteristics will be described with reference to FIG. The driving is composed of a positive scan pulse applied to the scanning wiring 16 and a signal waveform applied to the signal wiring 17. The TFT is turned on at the timing of the pulse applied to the scanning wiring 16, and a voltage is applied to the liquid crystal layer 29. The voltage applied to the liquid crystal layer 29 is shown as the liquid crystal applied voltage in FIG. Further, in order to charge and discharge the pixel with a large capacity and a high voltage, a part of the scan pulse width may be overdrive driven so that the signal voltage is higher than the display voltage. The overdrive drive is indicated by a positive overdrive pulse and a negative overdrive pulse in FIG. By doing so, high speed writing of 2 to 5 times is possible. FIG. 17 shows two types of liquid crystal applied voltages in the case of the present embodiment and the case of overdrive driving. When the positive polarity is narrowed in the width of the overdrive pulse, the positive polarity writing is insufficient and a necessary drive voltage cannot be obtained. Therefore, by widening the positive polarity in the width of the overdrive pulse, higher positive polarity write compensation can be performed and a high drive voltage can be obtained.

  When driving by TFT, it may be difficult to make the voltage applied to the liquid crystal layer 29 completely zero. In the case of a liquid crystal display device having a liquid crystal layer 29 exhibiting optical rotation, particularly when the voltage is completely zero (when no voltage is applied), the optical ratio is exhibited in the liquid crystal layer 29, so the contrast ratio is reduced. By inducing a uniaxial phase difference in the liquid crystal layer 29, the optical rotation that is exhibited can be reduced. Therefore, by performing the driving using the TFT, it is possible to reduce the decrease in the contrast ratio due to the optical rotation angle α indicated by the liquid crystal layer 29.

  As described above, in the liquid crystal display device having the liquid crystal layer 29 exhibiting optical rotation, the number of pixels can be increased to achieve high image quality, the contrast ratio can be increased, and insufficient writing can be reduced.

  Next, Example 6 of the liquid crystal display device of the present invention will be described. In the present embodiment, in the liquid crystal display device having the liquid crystal layer 29 in which the blue phase liquid crystal is sealed and exhibiting optical rotation, the reflective display is performed, and the backlight unit is unnecessary. The configuration of the present embodiment is basically the same as that of the first embodiment, and description of points that are the same as the first embodiment will be omitted as appropriate. Differences from the first embodiment will be described with reference to FIGS. 19 to 20.

  FIG. 19 is a schematic plan view of one pixel of the liquid crystal display device in this example. FIG. 20 is a schematic cross-sectional view taken along the line S1-S2 of the liquid crystal display device according to this embodiment.

  A planarizing layer 25 and a color material layer 24 are laminated on the second substrate 13 from the side close to the liquid crystal layer 29. Considering that light passes through the color material layer 24 twice by being reflected by the reflective layer 601, the reflective display is designed to have higher transmittance than the color material layer 24 for transmissive display. ing. As a result, a reflective color display with sufficient reflectivity becomes possible. Further, since the liquid crystal layer 29 also reciprocates and transmits, the optical rotation angle simply increases twice as compared with the case where the liquid crystal layer 29 is transmitted once.

  In FIG. 20, a reflective layer 601, an insulating film 33, a pixel electrode 18, and a common electrode 19 are disposed on the first substrate 12 farther from the display surface than the second substrate 13 on the side close to the liquid crystal layer 29. ing. Among these, the pixel electrode 18 and the common electrode 19 are closest to the liquid crystal layer 29, and then the insulating film 33 and the reflective layer 601 are stacked in this order. The reflective layer 601 reflects light incident from the display surface side to the display surface side. Each of the pixel electrode 18 and the common electrode 19 is a transparent electrode having a comb-like planar shape, and is made of ITO. The insulating film 33 is a transparent organic film made of acrylic resin. In order to ensure insulation between the pixel electrode 18 and the common electrode 19 and the reflective layer 601, the thickness of the insulating film 33 is about 2 μm. The reflective layer 601 is an aluminum film, and a smooth recess is provided on the surface of the reflective layer 601 (specifically, the surface on the display surface side). This reduces specular reflection and exhibits diffuse reflection like paper. Note that the planar distribution of the reflective layer 601 is a flat plate shape, and in the plan view as shown in FIG. 19, the reflective layer 601 is distributed over the entire surface excluding the periphery of the contact hole. In FIG. 19, in order to achieve a multi-domain structure, the pixel electrode 18 and the common electrode 19 are bent 90 degrees. Specifically, the pixel electrode 18 and the common electrode 19 are formed such that the comb-tooth portion is bent and extends in a plurality of directions (specifically, two directions), and are arranged in a nested manner. As a result, the electric field direction can be rotated by approximately 90 degrees in the upper half and the lower half of FIG.

  The unevenness of the reflective layer 601 is provided by the unevenness forming layer 602 in the lower layer, and this is formed as follows. First, an organic resist is applied on one surface, and then patterned into a columnar shape. Next, the columnar structure is heated and melted and solidified. When the columnar structure is melted, it becomes a convex structure having a parabolic cross-sectional shape due to its surface tension, and solidifies while maintaining this shape. If an organic film such as an acrylic resin is further laminated thereon, an unevenness forming layer 602 having smooth unevenness can be obtained. Here, the distribution of the columnar structure is based on a honeycomb shape, and is randomly distributed from this position. That is, if the honeycomb distribution is used, the slopes can be formed densely, but the regular arrangement causes interference in the reflected light. When interference occurs, the intensity of reflected light of a specific wavelength is increased at a specific angle, so that a rainbow color is observed in the reflected light. Note that the rainbow color distribution changes rapidly due to subtle changes in the observation position or the like, which is not preferable. In this embodiment, the regularity of the distribution is reduced by randomly shifting the position of the columnar structure from the honeycomb-like distribution, thereby reducing the occurrence of interference. Further, by providing irregularities at random, it is possible to compensate for the optical rotation generated in the liquid crystal layer 29 and to reduce the optical rotation as a whole.

  A quarter-wave plate 603 is disposed between the liquid crystal layer 29 and the second polarizing plate 15. Examples of the quarter-wave plate 603 include cycloolefin and polycarbonate. The quarter-wave plate 603 is arranged so that its slow axis forms 45 degrees with respect to the absorption axis of the second polarizing plate 15. In addition, it is not necessary to satisfy 45 degrees strictly, and the angle formed by the slow axis of the quarter-wave plate 603 and the absorption axis of the second polarizing plate 15 may be 43 degrees or more and 47 degrees or less. Thereby, the light that has passed through the second polarizing plate 15 and the quarter-wave plate 603 is converted into circularly polarized light. When no voltage is applied to the liquid crystal layer 29, the light reaching the reflective layer 601 becomes substantially circularly polarized light, is reflected by the reflective layer 601, and when it reaches the second polarizing plate 15 again, its absorption axis. It becomes linearly polarized light whose vibration direction is substantially parallel to. Here, the light is absorbed by the second polarizing plate 15 and a black display is realized.

  In the case where the optical rotation reducing member described in detail in another embodiment described later is disposed, for example, the optical rotation reducing member is disposed between the quarter-wave plate 603 and the liquid crystal layer 29. The characteristics of members exhibiting optical anisotropy, such as the liquid crystal layer 29, the quarter-wave plate 603, and the optical rotation reducing member, are generally represented by a determinant. Therefore, the action of the optical rotation reducing member is affected by the order in which the members exhibiting the optical anisotropy are laminated. When the liquid crystal layer 29 and the optical rotation reducing member are laminated without interposing a member exhibiting optical anisotropy between the liquid crystal layer 29 and the optical rotation reducing member, the optical rotation reducing member is opposite to the liquid crystal layer 29 in optical rotation. The optical rotation can be easily reduced.

  In order to realize the above-described polarization state conversion in a wider visible wavelength range, the quarter-wave plate 603 may be a broadband quarter-wave plate. The broadband quarter-wave plate is a laminate of a half-wave plate and a quarter-wave plate, and a half-wave plate and a quarter-wave plate from the side adjacent to the second polarizing plate 15. Are stacked in this order. The slow axes of the half-wave plate and the quarter-wave plate may be arranged to be 150 degrees and 210 degrees, for example, counterclockwise with respect to the absorption axis of the second polarizing plate 15.

  An example of an electric field EF formed between the pixel electrode 18 and the reflective layer 601 is shown with a broken line in FIG. A so-called lateral electric field is formed between the pixel electrode 18 and the common electrode 19, and this causes a phase difference in the liquid crystal layer 29. Since a phase difference occurs in the liquid crystal layer 29 when a voltage is applied, the polarization state of the light reaching the reflection layer 601 is not circularly polarized light. At this time, the polarization state when re-entering the second polarizing plate 15 is not linearly polarized light whose vibration direction is parallel to the absorption axis. Thereby, the light passes through the second polarizing plate 15 and a bright display is obtained.

  With the above configuration, in a liquid crystal display device having a liquid crystal layer in which blue phase liquid crystal is sealed, reflection display is performed, a backlight unit is unnecessary, and optical rotation can be reduced.

  Next, Example 7 of the liquid crystal display device of the present invention will be described. In the present embodiment, in the liquid crystal display device having the liquid crystal layer 29 in which the blue phase liquid crystal is sealed and exhibiting optical rotation, the reflective display is performed by using both the reflective layer and the reflective electrode, and the backlight unit is unnecessary. Thereby, optical rotation can be reduced.

  The configuration of the present embodiment is basically the same as that of the first embodiment, and the description of the same points will be omitted as appropriate. Differences from the first embodiment will be described with reference to FIGS. FIG. 21 is a schematic plan view of one pixel of the liquid crystal display device according to the present embodiment. FIG. 22 is a schematic cross-sectional view taken along S3-S4 in FIG.

  The reflective layer 601 is a highly reflective metal layer and is conductive. Therefore, in addition to the pixel structure shown in FIG. 20 in Example 6, for example, one of the pixel electrode 18 and the common electrode 19 may be overlapped with the reflective layer 601 and the reflective layer 601 may be used as the reflective electrode. 21 and 22 are examples of such a pixel structure. On the surface close to the liquid crystal layer 29 of the first substrate 12, the comb-like pixel electrode 18, the insulating film 33, the reflective layer 601, and the flat common electrode 19 are stacked from the side close to the liquid crystal layer 29. . The reflective layer 601 is connected to the common electrode 19 and has the same potential as the common electrode 19. As described above, the common electrode 19 and the reflective layer 601 are continuously laminated so that the common electrode 19 and the reflective layer 601 have the same potential, but the common electrode 19 (or the pixel electrode 18) is formed in a flat plate shape, The reflectance on the display surface side may be improved to serve as the reflective layer 601.

  In this case, the electric field EF formed between the pixel electrode 18 and the reflective layer 601 via the insulating film 33 is partially shown in FIG. A so-called fringe electric field is formed between the pixel electrode 18 and the reflective layer 601, and this is also distributed in the liquid crystal layer to cause a phase difference in the liquid crystal layer 29.

  With the above configuration, in the liquid crystal display device using the liquid crystal layer 29 exhibiting optical rotation, the reflective layer 601 also serves as the common electrode 19 (or the pixel electrode 18) to perform reflective display, eliminating the need for a backlight unit. , Optical rotation can be reduced.

  Next, an eighth embodiment of the liquid crystal display device of the present invention will be described. In the present embodiment, in the liquid crystal display device having the liquid crystal layer 29 in which the blue phase liquid crystal is sealed and having optical rotation, by having the reflective display portion and the transmissive display portion in one pixel, In a bright environment, reflection display using external light is performed, and in a dark environment, transmission display using light from the backlight unit 28 is performed. The configuration of the present embodiment is basically the same as that of the first embodiment, and the description of the same points will be omitted as appropriate. Differences from the first embodiment will be described with reference to FIGS.

  FIG. 23 is a schematic plan view of one pixel of the liquid crystal display device in this example. FIG. 24A is a schematic cross-sectional view taken along the line S5-S6 of the liquid crystal display device according to this embodiment. FIG. 24B is a schematic cross-sectional view taken along S7-S8 of the liquid crystal display device according to this embodiment.

  As shown in FIG. 23, a reflective display part (RD) and a transmissive display part (TD) are formed in one pixel, the central part including the bent part is a transmissive display part, and the upper and lower parts are reflective displays. Part. Both the reflective display portion and the transmissive display portion include portions where the electric field directions differ from each other by approximately 90 degrees, and a wide viewing angle is obtained for both the reflective display portion and the transmissive display portion. Further, the base portion of the comb-tooth portion of the pixel electrode 18 or the common electrode 19 formed in a comb-tooth shape is formed in the reflective display portion RD.

  The first substrate 12 has the common electrode 19 and the pixel electrode 18 from the side close to the liquid crystal layer 29, and the common electrode 19 and the pixel electrode 18 are in the same layer. The portion corresponding to the reflective display portion (RD) has a reflective layer 601, and the common electrode 19 and the pixel electrode 18 are stacked on the liquid crystal layer 29 side of the reflective layer 601 with an insulating film 33 interposed therebetween. . The reflective layer 601 is an aluminum film, and has smooth unevenness on the surface. That is, in each pixel region, there are a region where the reflective layer 601 is disposed and a region where the reflective layer 601 is not disposed, and light from the backlight unit 28 is transmitted to the display surface side in a region where the reflective layer 601 is not disposed.

  A planarizing layer 25 and a color material layer 24 are laminated on the second substrate 13 from the side close to the liquid crystal layer 29. In consideration of the fact that light passes through the color material layer 24 once in the transmissive display but passes twice in the reflective display, a hole is formed in a part of the color material layer 24 in the reflective display portion. ing. Additive color mixing occurs in the portion where the hole portion and the color material layer 24 exist, and color display is possible in the reflective display portion, and color display with sufficient reflectance becomes possible. Further, the thickness of the color material layer 24 in the reflective display portion and the transmissive display portion may be changed so that the thickness of the color material layer 24 in the reflective display portion is smaller than the thickness of the color material layer 24 in the transmissive display portion. Good. Specifically, the layer thickness of the color material layer 24 in the reflective display portion may be about half of the layer thickness of the color material layer 24 in the transmissive display portion.

  Considering that light passes through the liquid crystal layer 29 once in the transmissive display but passes twice in the reflective display, the reflective transparent dielectric layer 801 is disposed in the reflective display portion. The reflective transparent dielectric layer 801 is disposed between the liquid crystal layer 29, the pixel electrode 19, and the common electrode 19. As shown in FIG. 24B, the reflective transparent dielectric layer 801 is laminated so as to cover the pixel electrode 18 and the common electrode 19 from the liquid crystal layer 29 side, and the pixel electrode 18 and the common electrode 19 are formed of the reflective transparent dielectric layer. It is embedded in the body layer 801. The reflective transparent dielectric layer 801 is a silicon nitride film, and the electric field strength applied to the liquid crystal layer 29 of the reflective display portion is made weaker than the electric field strength applied to the liquid crystal layer 29 of the transmissive display portion. Specifically, it is desirable that the electric field strength applied to the liquid crystal layer 29 of the reflective display portion is approximately half of the electric field strength applied to the liquid crystal layer 29 of the transmissive display portion. If the thickness of the silicon nitride film is optimized and the retardation generated in the liquid crystal layer 29 of the transmissive display unit is double that of the reflective display unit, the luminance-voltage characteristics of the reflective display unit and the transmissive display unit are the same. At the applied voltage, the reflectance of the reflective display portion and the transmittance of the transmissive display portion take the maximum values. Reflective display and transmissive display are observed simultaneously in many use environments. If the luminance-voltage characteristics are the same in the reflective display portion and the transmissive display portion, a constant display can be obtained even if the use environment changes.

  Although not shown in FIG. 23, the planar distribution of the reflective layer 601 and the reflective transparent dielectric layer 801 is the same, and these are distributed only in the reflective display unit. Accordingly, although not shown in FIG. 23, in FIG. 23, the reflective layer 601 and the reflective transparent dielectric layer 801 are distributed above and below two broken lines indicating the boundary between the reflective display portion and the transmissive display portion. It will be.

  In addition, a first quarter-wave plate 802 and a first polarizing plate 14 are stacked on the outside of the first substrate 12 in order from the side close to the first substrate 12. On the outer side of the second substrate 13, a second quarter-wave plate 803 and a second polarizing plate 14 are laminated in order from the side close to the second substrate 13. That is, the first quarter-wave plate 802 is disposed between the first polarizing plate 14 and the liquid crystal layer 29, and the second quarter wave plate is disposed between the second polarizing plate 15 and the liquid crystal layer 29. A wave plate 803 is disposed. The slow axis of the first quarter-wave plate 802 is 45 degrees with respect to the absorption axis of the first polarizer 14, and the slow axis of the second quarter-wave plate 803 is the second It forms 45 degrees with respect to the absorption axis of the polarizing plate 15. Since the absorption axis of the first polarizing plate 14 and the absorption axis of the second polarizing plate 15 are orthogonal to each other, the slow axis of the first quarter-wave plate 802 and the second quarter The slow axis of the first wave plate 803 is also orthogonal. As described above, since the slow axis of the first quarter-wave plate 802 and the slow axis of the second quarter-wave plate 803 are orthogonal to each other, at least in the substrate normal direction. Optical anisotropy is compensated. Thereby, in the liquid crystal display device having the liquid crystal layer 29 in which the blue phase liquid crystal is encapsulated and exhibiting optical rotation, good black display can be achieved.

  With the above-described configuration, reflection display using outside light is performed in a bright environment, and transmission display using light from the backlight unit 28 is performed in a dark environment to provide good visibility in a wide environment. Can be reduced.

  Next, a ninth embodiment of the liquid crystal display device of the present invention will be described. In this embodiment, in a transflective liquid crystal display device using a liquid crystal layer 29 enclosing a blue phase liquid crystal image and exhibiting optical rotation, a reflective display portion (RD) and a transmissive display portion (TD) are included in one pixel. The electric field strength of the reflective display portion and the electric field strength of the transmissive display portion are made smaller. Thereby, favorable visibility can be given in a wide environment and optical rotation can be reduced. Since the configuration of the present embodiment is basically the same as that of the first embodiment, the description of the same points will be omitted as appropriate. Differences from the first embodiment will be described with reference to FIGS.

  FIG. 25 is a schematic plan view of one pixel of the liquid crystal display device according to this embodiment. 26A is a schematic cross-sectional view taken along the line S9-S10 in FIG. 25 of the liquid crystal display device according to this embodiment. 26B is a schematic cross-sectional view taken along the line S11-S12 in FIG. 25 of the liquid crystal display device according to this embodiment.

  A cross section of one pixel of the liquid crystal display device of this example is shown in FIGS. 26A and 26B. In this embodiment, in order to reduce the electric field strength applied to the liquid crystal layer of the reflective display unit as compared with the transmissive display unit, the electric field strength applied to the liquid crystal layer 29 is the length of the gap between the common electrode 19 and the pixel electrode 18. The width of the gap between the common electrode 19 and the pixel electrode 18 is set wider in the reflective display portion by utilizing the fact that it is inversely proportional to the thickness. That is, the repetitive pitch of the comb structure in the reflective display portion is made larger than the repetitive pitch of the comb structure in the transmissive display portion. 26A and 26B are sectional views of the reflective display portion and the transmissive display portion, respectively. In FIG. 26B, which is a cross-sectional view of the reflective display portion, two common electrodes 19 and pixel electrodes 18 are arranged, whereas in FIG. 26A, which is a cross-sectional view of the transmissive display portion, the same pixel width is obtained. Four common electrodes 19 and pixel electrodes 18 are arranged.

  As the planar structure of the common electrode 19 and the pixel electrode 18, a branching structure as shown in FIG. 25 is formed, so that the electrode repetition period (pitch) in the reflective display unit is changed to the electrode repetition period (pitch) in the transmissive display unit. The number of electrodes arranged in the transmissive display portion is twice that of the reflective display portion. As shown in FIG. 25, the branch structure is formed at the boundary between the reflective display portion and the transmissive display portion (branches across the boundary position). Thereby, the electric field strength applied to the liquid crystal layer 29 of the reflective display portion can be reduced more than that of the transmissive display portion while simplifying the manufacturing process except for the reflective portion transparent dielectric layer 801. By setting the repetition period of the electrodes in the transmissive display unit to be twice the repetition period of the electrodes in the reflective display unit, the electric field strength applied to the liquid crystal layer 29 of the reflective display unit can be reduced more than in the transmissive display unit.

  With the above configuration, good visibility can be given in a wide environment and optical rotation can be reduced.

  Next, Example 10 of the liquid crystal display device of the present invention will be described. In the present embodiment, in a transflective liquid crystal display device having a liquid crystal layer 29 enclosing blue phase liquid crystal and exhibiting optical rotation, a reflective display portion and a transmissive display portion are provided in one pixel, Only have a built-in retardation plate. Thereby, favorable visibility can be given in a wide environment and optical rotation can be reduced while maintaining transmission image quality. Since the configuration of the present embodiment is basically the same as that of the first embodiment, the description of the same portions will be omitted as appropriate. Changes from the first embodiment will be described with reference to FIG.

  A schematic plan view of one pixel of the liquid crystal display device in the present embodiment is the same as FIG. 23 in the eighth embodiment. FIG. 27A is a schematic cross-sectional view of the liquid crystal display device in this example, and shows a schematic cross-section between S5 and S6 in FIG. FIG. 27B is a schematic cross-sectional view of the liquid crystal display device in the present embodiment, and shows a schematic cross-section between S7 and S8 in FIG.

  FIG. 27A shows a transmissive display portion (TD), which is the same as that shown in FIG. 24A in the eighth embodiment. On the other hand, FIG. 27B shows a reflective display portion (RD). In this embodiment, the built-in quarter-wave plate 804 is formed on the second substrate 13 on the side close to the liquid crystal layer 29, and the built-in quarter-wave plate 804 is formed only on the portion corresponding to the reflective display unit. Formed. A first polarizing plate 14 is disposed outside the first substrate 12, and a second polarizing plate 15 is disposed outside the second substrate 13.

  The built-in quarter wave plate 804 was produced as follows. First, an alignment film is applied on the planarizing layer 25, and a photopolymerizable low-molecular liquid crystal is applied thereon. If this is subjected to pattern exposure and ultraviolet rays are irradiated only on the portion corresponding to the reflective display portion, a photopolymerization reaction occurs only in the portion corresponding to the reflective display portion. Thereafter, by washing with an organic solvent or the like, the unreacted low-molecular liquid crystal remaining on the transmissive display portion is removed. In this way, the built-in quarter-wave plate 804 is formed only in the reflective display portion.

  If attention is paid to the transmissive display portion of the liquid crystal display device of this embodiment, the quarter-wave plate is not laminated. Originally, the quarter-wave plate is necessary only for the reflective display portion, and not for the transmissive display portion. By arranging the quarter-wave plate as the built-in quarter-wave plate 804 only in the portion corresponding to the reflective display portion, the transflective liquid crystal display device of this embodiment is equivalent to the transmissive liquid crystal display device. A transparent display with the image quality can be obtained.

  With the configuration as described above, in a liquid crystal display device having a liquid crystal layer 29 in which blue phase liquid crystal is enclosed and exhibiting optical rotation, good visibility is provided in a wide environment and optical rotation is reduced while maintaining transmission image quality. Can do.

  Next, Example 11 of the liquid crystal display device of the present invention will be described. In this embodiment, a transflective liquid crystal display device having a liquid crystal layer 29 in which blue phase liquid crystal is sealed to show optical rotation has a reflective display portion and a transmissive display portion in one pixel. Since the configuration of this embodiment is basically the same as that of the first embodiment, the description of points that are the same as those of the first embodiment will be omitted as appropriate. Differences from the first embodiment will be described with reference to FIGS.

  In the transflective liquid crystal display device of this embodiment, the first quarter-wave plate 802 is provided between the first substrate 12 and the first polarizing plate 14, and the second substrate 13 and the second polarizing plate are provided. Since the second quarter-wave plate 803 is disposed between 15 and the slow axes of both are orthogonal to each other in the normal direction, these optical anisotropies are offset. However, when observed from an oblique direction, the slow axis of the first quarter-wave plate 802 and the slow axis of the second quarter-wave plate 803 are not orthogonal. Moreover, these retardations also deviate from the quarter wavelength. Therefore, the optical anisotropy of the first quarter-wave plate 802 and the optical anisotropy of the second quarter-wave plate 803 are not offset in the oblique direction, and the transmittance of black display increases. The contrast ratio decreases.

  Therefore, in this embodiment, the optical characteristics of the first quarter-wave plate 802 and the optical characteristics of the second quarter-wave plate 803 are improved, and the reduction in contrast ratio is suppressed. Specifically, the first quarter-wave plate 802 and the second quarter-wave plate 803 are biaxial rather than uniaxially realized relatively easily by uniaxial stretching.

  In order to suppress the shift between the slow axis of the first quarter-wave plate 802 and the slow axis of the second quarter-wave plate 803 in the oblique direction, for example, the first quarter The Nz coefficient of the wave plate 802 and the Nz coefficient of the second quarter wave plate 803 may be 0.4 or more and 0.6 or less. If the Nz coefficient of the first quarter-wave plate 802 and the Nz coefficient of the second quarter-wave plate 803 are 0.5, the shift of the slow axis in the oblique direction is further suppressed. Hereinafter, with respect to the optical system in which the Nz coefficient is described as 0.5, the case where the Nz coefficient is 0.4 or more and 0.6 or less is allowed. Here, the Nz coefficient is defined by the following expression (3) based on Non-Patent Document 4.

Here, n _z , n _s , and n _f are a refractive index in the layer thickness direction, a refractive index in the slow axis direction in the layer, and a refractive index in the fast axis direction in the layer, respectively. In the case of a phase plate that can be realized relatively easily by uniaxial stretching, the Nz coefficient is 1.0. Also, when the Nz coefficient is 0.0, it is optically uniaxial. The case where the Nz coefficient is a value other than this is biaxial.

The angle dependence of the slow axis angle and retardation of the optically anisotropic medium can be obtained by Lagrange's undetermined multiplier method, and is described in Non-Patent Document 5, for example. Referring to Non-Patent Document 5, if the refractive indexes in the x-axis, y-axis, and z-axis directions of the optically anisotropic medium are n _x , n _y , and _nz , the slow phase at the azimuth angle θ and polar angle ψ The refractive index n _{s of} the axis and the refractive index n _f of the fast axis are expressed by the following equation (4).

また、遅相軸の向き（ｋ_ｓｘ、ｋ_ｓｙ、ｋ_ｓｚ）は次式（５）で表される。

The direction of the slow axis (k _sx , k _sy , k _sz ) is expressed by the following equation (5).

Considering a refractive index ellipsoid whose refractive indexes in the x-axis, y-axis, and z-axis directions are n _x , n _y , and _nz , (k _sx , k _sy , k _sz ) is as shown in FIG. The cross section includes the center of the refractive index ellipsoid and is perpendicular to the azimuth angle θ and the polar angle ψ. At this time, the cross section is always elliptical, and (k _sx , k _sy , k _sz ) corresponds to the length of the major axis of the ellipse.

  By using the above, it is possible to calculate the slow axis azimuth when observed from the polar angle direction. Thereafter, the slow axis azimuth angle when observed from the polar angle direction is represented in the counterclockwise direction with the horizontal direction as 0 degrees as shown in FIG. FIG. 29 shows an example of calculating the slow axis azimuth when observed from the polar angle direction when the Nz coefficient is 1.0, 0.5, and 0.0. The number on the vertical axis in FIG. 29 is the slow axis azimuth when observed from the normal direction. As is clear from FIG. 29B, when the Nz coefficient is 0.5, the slow axis azimuth when observed from the polar angle direction is substantially constant without depending on the polar angle. Thus, if the Nz coefficient of the first quarter-wave plate 802 and the Nz coefficient of the second quarter-wave plate 803 are 0.5, the angle formed by both slow axis azimuths is the viewing angle. Regardless of this, 90 degrees is derived. Therefore, it is preferable that the Nz coefficient of the first quarter-wave plate 802 and the Nz coefficient of the second quarter-wave plate 803 be 0.4 or more and 0.6 or less.

  FIG. 30 shows an example in which the black display viewing angle characteristics are calculated when the Nz coefficient of the first quarter-wave plate 802 and the Nz coefficient of the second quarter-wave plate 803 are 0.5. Here, the absorption axis azimuth of the first polarizing plate 14 and the absorption axis azimuth of the second polarizing plate 15 are 45 degrees and 135 degrees, respectively. Further, the slow axis azimuth of the first quarter-wave plate 802 and the slow axis azimuth of the second quarter-wave plate 803 are set to 0 degree and 90 degrees, respectively. Further, in such a configuration, since the azimuth angle is 90 degrees, the black display viewing angle characteristics in the range of the azimuth angle from 0 degree to 90 degrees are shown every 15 degrees. As a comparison, FIG. 30B shows an example of calculating the black display viewing angle characteristics when the Nz coefficient of the first quarter-wave plate 802 and the Nz coefficient of the second quarter-wave plate 803 are 1.0. Show. As is clear by comparing FIG. 30A and FIG. 30B, the Nz coefficient of the first quarter-wave plate 802 and the Nz coefficient of the second quarter-wave plate 803 are 0.5. However, the increase in the transmittance when the polar angle is increased is suppressed. This is because when the Nz coefficient of the first quarter-wave plate 802 and the Nz coefficient of the second quarter-wave plate 803 are 1.0, the slow axes of both are not orthogonal in the viewing angle direction. On the other hand, when the Nz coefficient is set to 0.5, it is orthogonal to the viewing angle direction. As described above, an increase in transmittance in the viewing angle direction in black display can be suppressed, and a decrease in contrast ratio in the viewing angle direction can be suppressed.

  With the above configuration, in the liquid crystal display device having the liquid crystal layer 29 in which the blue phase liquid crystal is sealed and exhibiting optical rotation, the viewing angle can be improved and the optical rotation can be reduced.

  Next, a liquid crystal display device according to a twelfth embodiment of the present invention will be described. In this embodiment, a transflective liquid crystal display device using blue phase liquid crystal has a reflective display portion and a transmissive display portion in one pixel. Thereby, a viewing angle can be improved and optical rotation can be reduced. The configuration of the present embodiment is basically the same as that of the first embodiment, and the description of the same portions as those of the first embodiment will be omitted as appropriate. Differences from the first embodiment will be described with reference to FIG.

  In this embodiment, another method for suppressing a decrease in contrast ratio in the viewing angle direction was implemented. Regarding the Nz coefficient of the first quarter-wave plate 802 and the Nz coefficient of the second quarter-wave plate, one is 1.0 and the other is 0.0. When a quarter-wave plate with Nz coefficients of 1.0 and 0.0 is combined, the slow axes of both are orthogonal in any viewing angle direction. In FIGS. 29A and 29C, the slow axis azimuth is calculated with the slow axis seen from the normal direction being the same, but in the combination of quarter wave plates with Nz coefficients of 1.0 and 0.0. FIG. 31 shows an example in which both slow axes are calculated as orthogonal to each other in the normal direction. In FIG. 31, the slow axis azimuth of a quarter wave plate with an Nz coefficient of 1.0 approaches 180 degrees, that is, 0 degrees as the polar angle increases, and a quarter wave plate with an Nz coefficient of 0.0. The slow-axis azimuth angle approaches 90 degrees as the polar angle increases. In FIG. 31, the two always change in parallel.

  This can be understood from analogy with the combination of negative C plate and positive C plate. The negative C plate and the positive C plate are uniaxial, and the optical axis is in the layer thickness direction. These refractive index ellipsoids are shown in FIG. As defined, the negative C plate has a refractive index in the optical axis direction smaller than its vertical direction, and the positive C plate has a refractive index in the optical axis direction larger than its vertical direction. Moreover, the cross section by the layer plane shown with the broken line is a circle. A cross section of these refractive index ellipsoids in an arbitrary viewing angle direction is shown in FIG. In FIG. 33, VS is a cut surface of the refractive index ellipsoid in an arbitrary viewing angle direction, and is a surface passing through the center of the refractive index ellipsoid that is perpendicular to the viewing angle direction. Moreover, the cross section of the refractive index ellipsoid by this cut surface is marked with a broken line. In the negative C plate and the positive C plate, the directions of the major axis ns ′ of the ellipsoid as a cross section are always the horizontal direction and the vertical direction, respectively. From the above, in the combination of the negative C plate and the positive C plate, the slow axis is orthogonal in any viewing angle direction.

  A refractive index ellipsoid of a combination of quarter wave plates with Nz coefficients of 1.0 and 0.0 is shown in FIG. The shape of the refractive index ellipsoid of the quarter-wave plate whose Nz coefficient is 0.0 is equal to the shape of the negative C plate shown in FIG. 32, and the only difference is that the optical axis is in the in-plane direction. . Further, the shape of the refractive index ellipsoid of the quarter-wave plate whose Nz coefficient is 1.0 is equal to the shape of the positive C plate shown in FIG. 32, and the only difference is that the optical axis is in the in-plane direction. is there. Even in a combination of quarter wave plates with Nz coefficients of 1.0 and 0.0, if the optical axes are orthogonal to each other when viewed from the layer thickness direction, the optical axes are mutually aligned as shown in FIG. Become parallel. The first quarter-wave plate 802 and the second quarter-wave plate 803 of the liquid crystal display device of this embodiment satisfy this condition. Therefore, like the first quarter-wave plate 802 and the second quarter-wave plate 803 of the liquid crystal display device of this embodiment, one Nz coefficient is set to 1.0 and the other Nz coefficient is set to If it is set to 0.0, both slow axes can be made orthogonal in any viewing angle direction. Even if one Nz coefficient is 0.9 or more and 1.1 or less and the other Nz coefficient is -0.1 or more and 0.1 or less, both slow axes have the same effect in any viewing angle direction. can get.

  Example of calculating the black display viewing angle characteristic when the Nz coefficient of the first quarter-wave plate 802 and the Nz coefficient of the second quarter-wave plate are 1.0 and 0.0, respectively. Is shown in FIG. As is apparent from comparison between FIG. 35 and FIG. 30B, the Nz coefficient of the first quarter-wave plate 802 is 1.0, and the other is the Nz coefficient of the second quarter-wave plate 803. When the value is 0.0, an increase in transmittance when the polar angle is increased is suppressed. As described above, an increase in transmittance in the viewing angle direction in black display can be suppressed, and a decrease in contrast ratio in the viewing angle direction can be suppressed.

  With the above configuration, in the liquid crystal display device having the liquid crystal layer 29 in which the blue phase liquid crystal is sealed and exhibiting optical rotation, the viewing angle can be improved and the optical rotation can be reduced.

  Next, a liquid crystal display device according to a thirteenth embodiment of the present invention will be described. In this embodiment, the liquid crystal display device having the liquid crystal layer 29 in which the blue phase liquid crystal is sealed and exhibiting optical rotation, further includes a viewing angle compensation phase difference plate. Thereby, the increase in transmittance in the viewing angle direction during black display can be reduced. The configuration of the present embodiment is basically the same as that of the first embodiment, and description of portions that are the same as those of the first embodiment will be omitted as appropriate. Differences from the first embodiment will be described with reference to FIGS.

  In the present embodiment, a phase plate is newly added to reduce the increase in transmittance in the viewing angle direction in black display. A phase plate newly added for such a purpose is hereinafter referred to as a viewing angle compensation phase plate. Examples of the viewing angle compensating phase plate include cycloolefin and polycarbonate. The viewing angle compensation phase plate is disposed between the first polarizing plate 14 and the liquid crystal layer 29 or between the second polarizing plate 15 and the liquid crystal layer 29. The viewing angle compensation phase plate may be disposed between the first polarizing plate 14 and the liquid crystal layer 29 and between the second polarizing plate 15 and the liquid crystal layer 29. When two viewing angle compensation phase plates are used, the Nz coefficient of one viewing angle compensation phase plate may be set to 0.25, and the Nz coefficient of the other viewing angle compensation phase plate may be set to 0.75. As described in Non-Patent Document 6, the transmittance increase in the viewing angle direction in black display is such that the absorption axis of the first polarizing plate 14 and the absorption axis of the second polarizing plate 15 are orthogonal to each other in the viewing angle direction. By disappearing. FIG. 36 is a diagram showing this, and shows only the first polarizing plate 14 and the second polarizing plate 15 extracted from the liquid crystal display device of the present invention. Even if the absorption axis (a1) of the first polarizing plate 14 and the absorption axis (a2) of the second polarizing plate 15 are arranged so as to be orthogonal to each other in the normal direction as shown in FIG. 36A, they are shown in FIG. 36B. As shown, it is apparently not orthogonal in the viewing angle direction.

  In order to reduce this, as shown in Non-Patent Document 6, the viewing angle compensation phase plate is arranged so that the slow axis is parallel or orthogonal to the transmission axis of the adjacent polarizing plate, and Δnd and Nz of the viewing angle compensation phase plate are arranged. The coefficients may be set to 1/2 wavelength and 0.5, respectively. The Nz coefficient of the viewing angle compensation phase plate may be 0.4 or more and 0.6 or less. The action of the viewing angle compensating phase plate can be expressed using a Poincare sphere display. FIG. 37 is a Poincare sphere obtained by projecting FIG. 36 onto the S1 and S3 planes. 37A and 37B correspond to FIGS. 36A and 36B, respectively. In FIG. 37, pt1 and pa2 represent the polarization states of linearly polarized light corresponding to the transmission component of the first polarizing plate 14 and the absorption component of the second polarizing plate 15, respectively. FIG. 37A shows the polarization state in the normal direction, and the positions of the two coincide on the Poincare sphere. FIG. 37B shows the polarization state in the viewing angle direction, and pt1 and pa2 do not coincide on the Poincare sphere. The arrows in FIG. 37B indicate the operation of the viewing angle compensation phase plate. The viewing angle compensation phase plate matches the absorption component of the second polarizing plate 15 before the light from the backlight unit 28 that has traveled from the first polarizing plate 14 side enters the second polarizing plate 15. Convert. For the Poincare sphere display, refer to books such as Non-Patent Document 8.

  The content described in Non-Patent Document 6 assumes a case where the liquid crystal layer is a nematic liquid crystal. When the nematic liquid crystal is in homogeneous alignment, the first polarizing plate 14 and the second polarizing plate 15 are arranged so that the absorption axis is parallel or orthogonal to the alignment direction. Thereby, the optical anisotropy of the nematic liquid crystal can be eliminated in the normal direction, but the optical anisotropy appears in the viewing angle direction. Since the effect is superimposed on the effect of the polarizing plate shown in FIG. 36B and FIG. 37B, more complicated optical compensation is required. In this embodiment, since the liquid crystal display device has the liquid crystal layer 29 in which the blue phase liquid crystal is sealed and exhibits optical rotation, it is not necessary to consider the orientation direction of the liquid crystal. Further, by optimizing the Δnd and Nz coefficients of the viewing angle compensation phase difference plate, the optical rotation in the normal direction of the substrate can be reduced and the contrast ratio can be further increased.

  FIG. 38A shows an example in which the black display viewing angle characteristic is calculated when a viewing angle compensating phase plate is disposed between the first polarizing plate 14 and the liquid crystal layer 29. For comparison, an example calculated for the case where the viewing angle compensation phase plate is not used is shown in FIG. 38B, but the scale of the vertical axis in FIG. 38A is one tenth of FIG. 38B. In FIG. 38A, the azimuth angle corresponding to each plot is not shown, but it is clear that the transmittance is lower than that in FIG. 38B at any azimuth angle. Thus, by using the viewing angle compensation phase plate, an increase in transmittance when the polar angle is increased is suppressed. As described above, an increase in transmittance in the viewing angle direction in black display can be suppressed, and a decrease in contrast ratio in the viewing angle direction can be suppressed.

  With the configuration as described above, in the liquid crystal display device having the liquid crystal layer 29 having the optical rotation and enclosing the blue phase liquid crystal, the increase in transmittance in the viewing angle direction during black display can be reduced.

  Next, Example 14 of the liquid crystal display device of the present invention will be described. In this embodiment, in a liquid crystal display device having a liquid crystal layer 29 in which blue phase liquid crystal is sealed and having optical rotation, the TFT channel width W is more than 10 times the channel length L, and a TFT with high driving capability is mounted on the pixel. It is arranged along the signal wiring 17 in the vertical direction (long side direction of the pixel). Thereby, reduction of an aperture ratio can be suppressed. The configuration of the present embodiment is basically the same as that of the first embodiment, and description of the same parts will be omitted as appropriate. Differences from the first embodiment will be described with reference to FIGS.

  FIG. 39 is a schematic plan view of one pixel of the liquid crystal cell in this example. FIG. 40 is a schematic cross-sectional view of a portion where the TFT and the common electrode in this embodiment are arranged so as to overlap the scanning wiring, and is a schematic cross-sectional view taken along line A-A ′ in FIG. 39. FIG. 41 is a schematic diagram showing an equivalent circuit of one pixel in the present embodiment.

  A pixel configuration illustrated in FIG. 39 will be described. In this pixel, a TFT 806 having a high driving capability with a channel width W of 10 times or more the channel length L is arranged in the vertical direction along the signal wiring 17 (drain electrode in FIG. 40) of the pixel. In this way, TFTs with high driving ability can be arranged while suppressing a decrease in aperture ratio, and high-voltage and large-capacity pixels can be charged and discharged at high speed. A reduction in driving voltage and a reduction in leakage current are both important for driving a blue phase liquid crystal with a TFT. In this embodiment, it is desirable that either the width or the gap of the pixel electrode 18 is 3 μm or less. The channel width W may be 20 μm or more. More specifically, it is preferably 50% or more of the short side of the pixel (the length in the scanning wiring 16 direction), and more than the length of the short side of the pixel. More preferable. More preferably, the channel width W is 50% or more of the long side of the pixel. Further, an overdrive may be combined. Note that a storage capacitor 806 having a large capacity can be further suppressed by further reducing the aperture ratio by using a horizontal storage capacitor 807 arranged in the horizontal direction (the short side direction of the pixel) in combination with the vertically arranged TFT 806 as shown in FIG. And retention characteristics can be improved. As shown in FIG. 39, the storage capacitor 807 is disposed along the scanning wiring 16 so as to overlap the scanning wiring 16.

  In this embodiment, the TFT 806 and the common electrode 19 are formed on the scanning wiring 16 so as to overlap each other. FIG. 40 is a diagram schematically showing the cross-sectional structure of this portion. In order from the left in FIG. 40, a drain electrode (signal wiring 17), a source electrode (pixel electrode 18), and a part of the common electrode 19 of the vertically arranged TFT 806 are arranged on the scanning wiring 16, and the common electrode 19 is arranged on the right. Has been. By doing so, the influence of the potential around the pixel electrode 18 due to capacitive coupling or electric lines of force from the signal wiring 17 and the scanning wiring 16 can be reduced. For example, even if a high scanning voltage or signal voltage exceeding 40 V is applied, The variation in the electric field applied to the liquid crystal is suppressed, and uniform display in the pixel region can be achieved. As shown in FIG. 39, the source electrode formed so as to run on the island-like silicon 501 is formed in parallel with the other comb-tooth portion of the pixel electrode 18. The source electrode is formed adjacent to and in parallel with the comb-tooth portion of the common electrode 19.

  With the configuration as described above, in a liquid crystal display device having a liquid crystal layer 29 in which blue phase liquid crystal is encapsulated and exhibiting optical rotation, a TFT having a high driving capability can be disposed while suppressing a decrease in aperture ratio.

  FIG. 41 shows a configuration example of the TFT circuit in the pixel, and shows a circuit configuration different from that of the fourteenth embodiment. As shown in FIG. 41, two TFTs in a pixel are connected in series, and the voltage applied to the signal wiring 17 (signal voltage) and the differential voltage between the pixel electrodes 18 are shared by the two TFTs and driven. The source / drain voltage is half the difference voltage per TFT. As a result, leakage current can be reduced, and fluctuations in the storage period when the storage capacitor and the potential of the pixel electrode 18 are not applied with a scan pulse can be greatly reduced. Furthermore, even when the signal voltage and the voltage difference between the pixel electrodes 18 exceed 40 V, for example, a high transmittance at the time of lighting pixels and a low black luminance state at the time of non-lighting can be obtained, and the contrast ratio can be increased.

  Next, an embodiment 15 of the liquid crystal display device of the present invention will be explained. In this embodiment, two or more TFTs are arranged in a pixel in a liquid crystal display device having a liquid crystal layer 29 in which blue phase liquid crystal is encapsulated and exhibiting optical rotation. Thereby, the leakage current can be reduced and the contrast ratio can be increased. Since the configuration of the present embodiment is basically the same as that of the first embodiment, description of portions that are the same as those of the first embodiment will be omitted as appropriate. Differences from the first embodiment will be described with reference to FIGS. 42 to 45.

  FIG. 42 is a schematic diagram showing an equivalent circuit of one pixel in the present embodiment. FIG. 43 is a schematic plan view of one pixel of the liquid crystal cell in this example. 44 is a schematic cross-sectional view taken along lines A-A ′ and B-B ′ of FIG. 43. FIG. 45 is a schematic diagram showing waveform examples of scanning wiring, signal wiring, and liquid crystal applied voltage in the present embodiment.

  In FIG. 42, one pixel includes one scanning wiring 16, two signal wirings of a first signal wiring 17a and a second signal wiring 17b, and two sets of comb-shaped first pixel electrodes. 18a and the second pixel electrode 18b, two TFTs, a first TFT 20a and a second TFT 20b, and two capacitors, a first storage capacitor 21a and a second storage capacitor 21b. . In FIG. 42, the scanning wiring belonging to the previous stage pixel is added for the sake of explanation. In the present embodiment, the first pixel electrode 18a corresponds to the first electrode, and the second pixel electrode 18b corresponds to the second electrode.

  A pixel connection configuration will be described. The drain and source terminals of the n-ch type first TFT 20a are connected to the first signal wiring 17a and the first pixel electrode 18a, respectively, and the gate terminal of the first TFT 20a is connected to the scanning wiring 16. ing. One terminal of the first storage capacitor 21 a is connected to the first pixel electrode 18 a and the other terminal is connected to the scanning wiring 16. As illustrated, the second signal wiring 17b, the second pixel electrode 18b, the second TFT 20b, and the second storage capacitor 21b are connected in the same manner. The first pixel electrode 18 a and the second pixel electrode 18 b are arranged in a nested manner, and drive the liquid crystal sealed in the liquid crystal layer 29.

  Next, the planar arrangement of the pixels will be described with reference to FIG. Note that the pixel formation process of this example is substantially the same as that of Example 5, but the contact hole formation process is unnecessary in this configuration, and the interlayer between the common electrode 19 and the scanning wiring 16 that was necessary in Example 5 was used. No connection is required and the process is easy. The layer structure of the pixel is such that the TFT undercoat layer 22, the scanning wiring 16, the interlayer insulating film 34, the island-like silicon 501, the first signal wiring 17a, the second signal wiring 17b, and the first pixel electrode 18a from the substrate. The second pixel electrodes 18b are stacked in this order. The two pixel electrodes are made of ITO and are formed in the same layer as the first signal wiring 17a and the second signal wiring 17b, and are mutually connected to the first signal wiring 17a and the second signal wiring 17b in the stacked portion. ing. In the drawing, the scanning wirings 16 arranged in the horizontal direction and the two first signal wirings 17a and the second signal wirings 17b are arranged so as to be orthogonal to each other to constitute one pixel region. The first TFT 20a and the second TFT 20b are arranged in a vertical arrangement inside the pixel of each signal wiring. The source terminal of the first TFT 20a is formed by the first pixel electrode 18a, and is further connected to each comb tooth of the first pixel electrode 18a. The upper end of the square comb tooth portion of the first pixel electrode 18a overlaps with the scanning wiring 16, and the overlapping portion forms the first storage capacitor 21a. As shown in FIG. 44A, at the right end of the first TFT 20a, one of the left ends of the first pixel electrodes 18a overlaps with the gate electrode portion of the TFT extending from the scanning wiring 16 in the upward direction in the drawing. Yes. This portion serves as an electric field shielding portion of the scanning wiring 16, reduces the influence of the potential and pulse applied to the scanning wiring 16 on the electric field distribution around the first pixel electrode 18a, and changes in luminance near the right end of the first TFT 20a. Can be suppressed, and the luminance uniformity within the pixel can be improved. Similarly, the source terminal of the second TFT 20b is formed by the second pixel electrode 18b, and the wiring is extended in the upward direction in the drawing, and further, the scanning wiring 16 is extended in the left direction in the drawing. The root of the comb portion of the second pixel electrode 18b is overlapped with the scan wiring 16 portion, and the overlap portion forms the second storage capacitor 21b. In addition, the left end portion of the source electrode of the second TFT 20b overlaps one of the right ends of the second pixel electrodes 18b and the gate electrode portion of the TFT extending in the upward direction from the scanning wiring 16. This portion serves as an electric field shielding portion of the scanning wiring 16, reduces the influence of the potential and pulse applied to the scanning wiring 16 on the electric field distribution around the second pixel electrode 18b, and changes in luminance near the left end of the second TFT 20b. Can be suppressed, and the luminance uniformity within the pixel can be improved.

  In FIG. 43, a part of the upper, lower, left and right adjacent pixels is shown. In such a configuration, a capacitance of the pixel electrode 18 using a liquid crystal or a glass substrate as a dielectric is formed between the first pixel electrode 18a and the second pixel electrode 18b.

  Next, the driving waveform of the pixel of this embodiment will be described with reference to FIG. The driving of this embodiment uses matrix driving by line sequential driving, and a positive operation pulse is applied to the scanning wiring 16 as a selection pulse. As shown in the drawing, the first signal wiring 17a and the second signal wiring 17b are applied with signal voltages having substantially the same amplitude around the reference voltage Vc and having opposite polarities as the center voltage of the amplitude. When one is positive (+ polarity), the other is negative (-polar). This signal voltage is applied to the gate terminal of the first TFT 20a and the gate terminal of the second TFT 20b from the scanning wiring 16 to simultaneously turn on the two TFTs. Thereby, the voltage of the first signal wiring 17a and the voltage of the second signal wiring 17b are energized to the first pixel electrode 18a and the second pixel electrode 18b at the same timing, and the capacitance of the pixel electrode 18 and the first The storage capacitor 21a and the second storage capacitor 21b are charged. This storage capacitor can reduce voltage fluctuation due to leakage current during holding. In addition, by using an independent storage capacitor for each pixel electrode 18, an equal amount can be maintained for each of the positive and negative polarities, there is no fluctuation at the center of the amplitude of the drive voltage, and image quality failure due to flicker can be prevented. At this time, a voltage difference between the first pixel electrode 18a and the second pixel electrode 18b is applied to the liquid crystal. At this time, the first signal wiring 17a and the second signal wiring 17b are applied with voltages having opposite polarities and substantially the same amplitude, so that the liquid crystal driving voltage is the first signal wiring 17a and the second signal wiring 17b. The voltage is about twice the voltage applied to. Therefore, since the voltage applied to the signal wiring is only ½ of the required liquid crystal driving voltage, the interlayer dielectric strength of the wiring can be lower than that of the above-described embodiment. Similarly, the amplitude of the output voltage of the external drive circuit that drives the signal wiring is also halved, so that the withstand voltage and power supply voltage of the drive circuit can be reduced. Further, with respect to the maximum voltage amplitude between the source and drain of the first TFT 20a and the second TFT 20b, the same voltage as the liquid crystal driving voltage amplitude is applied in the above-described embodiment, whereas in the configuration of this embodiment, The voltage range is ½ of the amplitude of the liquid crystal drive voltage. For this reason, since the source-drain voltage of the TFT can be reduced, the breakdown voltage of the TFT can be lowered. Further, since the maximum voltage of the leakage current between the source and drain of the TFT only needs to be ½, the fluctuation of the liquid crystal applied voltage during the holding period can be greatly reduced to about 1/10. Therefore, the fluctuation of the liquid crystal applied voltage due to the leakage current during the period when the scanning line voltage is low and the TFT is off can be remarkably reduced. In addition, the difference between the voltage applied to the signal wiring and the voltage of the pixel electrode 18 is reduced, and the applied voltage is accurately held in the pixel, so that the accuracy gradation display can be increased and the image quality defect can be reduced. it can.

  In this embodiment, an inversely staggered TFT using amorphous silicon is described. However, the same effect as in this embodiment can be obtained with a polysilicon TFT and a coplanar TFT. In addition, a pch TFT may be used, and in this case, the polarity of the scanning pulse of the scanning wiring may be negative. Further, the pixel structure does not depend on the material of the pixel electrode 18. In addition, the shape of the pixel electrode 18 is not limited as long as a liquid crystal capacitor is formed between the electrodes. One of the first pixel electrode 18a or the second pixel electrode 18b is a comb tooth and the other is a planar electrode. It may be a mesh electrode.

  Next, Example 16 of the liquid crystal display device of the present invention will be described. In the present embodiment, in a liquid crystal display device having a liquid crystal layer 29 in which blue phase liquid crystal is enclosed and exhibiting optical rotation, a member having optical activity opposite to that of the liquid crystal layer 29 is disposed. Thereby, it is possible to reduce the influence of the optical rotation that occurs when no voltage is applied in the liquid crystal layer 29 and to improve the contrast ratio. Since the configuration of the present embodiment is basically the same as that of the first embodiment, description of portions that are the same as those of the first embodiment will be omitted. Changes from the first embodiment will be described below.

  It has been described with reference to FIG. 9A that the liquid crystal layer 29 encapsulating the blue phase liquid crystal exhibits optical rotation. This optical rotation has a direction, and the material used in Example 1 had a negative optical rotation. The sign of this optical rotation angle depends on the material used, and in particular depends on the direction of optical rotation possessed by the chiral agent.

  In this embodiment, the optical rotation of the liquid crystal layer 29 in which the blue phase liquid crystal is sealed and the optical rotation of the liquid crystal layer 29 are compensated by the optical rotation reducing member having the optical rotation in the reverse direction, and the contrast ratio can be improved. The optical rotation reducing member only needs to have the optical rotation of the liquid crystal layer 29 in which the blue phase liquid crystal is sealed and the optical rotation in the opposite direction. The optical rotation reducing member is an organic molecule having an asymmetric carbon or an asymmetric axis in its molecular structure, such as amino acids, sugars, amino acid or sugar derivatives, chiral agents used in TN liquid crystals, or metal complexes. Such an inorganic compound may be included. Since the liquid crystal layer 29 in Example 1 has negative optical rotation, the contrast ratio can be improved by configuring the optical rotation reduction member with the material shown in FIG. 46 having positive optical rotation, for example. Other than the compounds shown here, for example, even with the structure of the chiral agent described in Patent Document 2, Patent Document 3, or Non-Patent Document 2, the optical rotation opposite to that of the liquid crystal layer 29 is achieved. The contrast ratio can be improved if the material is expressed. Further, for example, an optical rotation compensation layer may be formed by dispersing an organic polymer having an asymmetric center in a repeating unit and the repeating unit itself having optical activity in a transparent substrate. Alternatively, the optical rotation compensation layer may be formed using such an organic polymer as a base material. As described in Non-Patent Document 7, an organic polymer in which the repeating unit itself exhibits optical activity is obtained, for example, by asymmetric polymerization of a methacrylic ester. The optical rotation reducing member may be disposed anywhere between the first polarizing plate 14 and the second polarizing plate 15. Strictly speaking, the optical rotation reducing member may be disposed anywhere as long as it is between the polarizing layer in the first polarizing plate 14 and the polarizing layer in the second polarizing plate 15.

  Although the optical rotation reducing member can improve the contrast ratio even if it exists as a single member, the optical rotation is added to the member having other functions existing between the first polarizing plate 14 and the second polarizing plate 15. The same effect can be obtained even if the material to be reduced is added or applied. Specifically, the first protective film 30, the first substrate 12, the second substrate 13, the color material layer 24, the planarization layer 25, the first alignment film 401, the second alignment film 402, the interlayer insulation Film 34, TFT undercoat film 22, back electrode 27, liquid crystal layer 29, insulating film 33, reflective layer 601, quarter-wave plate 603, reflective transparent dielectric layer 801, built-in quarter-wave plate 804, You may make it comprise an optical rotation reducing member by adding or apply | coating the material for reducing optical rotation to the viewing angle compensation phase difference plate 805, the adhesion layer 103, etc. FIG. In addition, the contrast ratio can be improved by applying or adding a material for reducing the optical rotation to each of the above members, but a material for reducing the optical rotation is added to a plurality of the above members. Even if it is applied or added, the contrast ratio can be improved. In this embodiment, the insulating film 33 or the interlayer insulating film 34 is illustrated as the insulating film. However, any insulating film disposed in the liquid crystal display device can be used regardless of the insulating film disposed. The contrast ratio can be improved by applying or adding a material for reducing the above (a material exhibiting optical rotation in the opposite direction to the optical rotation exhibited in the liquid crystal layer 29). That is, the optical rotatory reduction member is a member that exhibits optical rotatory power in the opposite direction to the optical rotatory power developed in the liquid crystal layer 29.

  FIG. 47 is a diagram showing a state in which optical rotation reducing members 201 a and 201 b are arranged between the first polarizing plate 14 and the second polarizing plate 15 and the liquid crystal cell 11. As described above, the optical rotation reducing member may be disposed independently between the first polarizing plate 14 or the second polarizing plate 15. Further, for example, the optical rotation reducing member may be constituted by the adhesive layer 103 to which a material for reducing optical rotation is added.

  FIG. 48 is a diagram showing a state in which a material for reducing optical rotation is added to the first substrate 12 and the second substrate 13. As described above, the first substrate 121 or the second substrate 131 to which the material for reducing optical rotation is added is disposed between the first polarizing plate 14 or the second polarizing plate 15. Also good.

  FIG. 49 is a diagram showing a state in which a material for reducing optical rotation is added to the color material layer 24. The film 241 and the film 242 constituting the color material layer 24 reduce optical rotation. The materials for are added in different addition amounts. By using a material for reducing the optical rotation developed in the liquid crystal layer 29 for the color material layer 24, an optimal correction amount can be obtained for each color, and the contrast ratio can be further increased. At this time, the amount and type of the material for reducing the optical rotation may be different for each of a plurality of types of films in the color material layer 24. Further, the thicknesses of a plurality of types of films (red, green, and blue films) in the color material layer 24 are changed for each color so that the compensation amount is in the order of blue <green <red, that is, the color material layer 24. The film thickness may be increased in the order of blue <green <red. The film thickness can be controlled by the coating amount or the ink supply amount in the process of forming the color material layer 24. Also, when the compensation is performed by the planarization layer 25, the contrast ratio can be increased by increasing the compensation amount in the order of blue <green <red. In this case, since the surface of the flattening layer 25 is flat, the thickness of the color material is formed so that blue> green> red, and the flattening layer 25 is formed so that the film thickness of the flattening layer 25 is blue. <Green <Red can be formed, and can be formed in the desired film thickness order without increasing the number of processing steps.

  With the configuration as described above, in the liquid crystal display device using the liquid crystal layer 29 that exhibits blue rotation by enclosing the blue phase liquid crystal, the contrast ratio can be improved by forming the optical rotation reduction member 201a and the like. As described in Example 2, the angle formed by the absorption axes of the first polarizing plate 14 and the second polarizing plate 15 is shifted from 90 degrees, and the above-described optical rotation reducing member is combined. Thus, the contrast ratio may be improved.

  DESCRIPTION OF SYMBOLS 10 Liquid crystal display device, 11 Liquid crystal cell, 12 1st board | substrate, 13 2nd board | substrate, 14 1st polarizing plate, 15 2nd polarizing plate, 16 Scanning wiring, 17 Signal wiring, 18 Pixel electrode, 19 Common electrode , 20 TFT, 21 storage capacity, 22 TFT undercoat film, 23 contact hole, 24 color material layer, 25 planarization layer, 26 BM layer, 27 back electrode, 28 backlight unit, 29 liquid crystal layer, 30 first protection Film, 31 second protective film, 32 polarizing layer, 33 insulating film, 34 interlayer insulating film, 101 wall electrode insulating film, 102 protruding electrode member, 103 adhesive layer, 201 optical rotation reducing member, 401 first orientation Film, 402 second alignment film, 501 island-like silicon, 601 reflecting layer, 602 unevenness forming layer, 603 quarter-wave plate, 801 reflecting portion transparent Dielectric layer, 802 First quarter wave plate, 803 Second quarter wave plate, 804 Built-in quarter wave plate, 805 Viewing angle compensation phase difference plate, 806 Vertically arranged TFT, 807 Horizontal The storage capacity of the arrangement.

Claims (18)

A first polarizing plate and a second polarizing plate;
A first substrate disposed between the first polarizing plate and the second polarizing plate;
A second substrate disposed between the first polarizing plate and the second polarizing plate and disposed closer to the second polarizing plate than the first substrate;
A liquid crystal layer disposed between the first substrate and the second substrate and encapsulating a blue phase liquid crystal;
A first electrode and a second electrode for applying a voltage to the liquid crystal layer,
The liquid crystal layer exhibits optical rotation when no voltage is applied,
Optical rotation angle alpha when no voltage is applied the liquid crystal layer, 0 ° <| meets ≦ 15 °, | α
The absorption axis of the second polarizing plate is rotated in the liquid crystal layer with no voltage applied to the light passing through the first polarizing plate with reference to a direction that forms 90 ° with the absorption axis of the first polarizing plate. It becomes the direction rotated 4 degrees or more and 10 degrees or less on the side to be done,
A liquid crystal display device characterized by the above. A first polarizing plate and a second polarizing plate;
A first substrate disposed between the first polarizing plate and the second polarizing plate;
A second substrate disposed between the first polarizing plate and the second polarizing plate and disposed closer to the second polarizing plate than the first substrate;
A liquid crystal layer disposed between the first substrate and the second substrate and encapsulating a blue phase liquid crystal;
A first electrode and a second electrode for applying a voltage to the liquid crystal layer,
The liquid crystal layer exhibits optical rotation when no voltage is applied,
The optical rotation angle α when no voltage is applied to the liquid crystal layer satisfies 5 ° ≦ | α | ≦ 15 °,
The first polarizing plate has a first polarizing layer having an absorption axis,
The second polarizing plate has a second polarizing layer having an absorption axis in a direction different from that of the first polarizing layer,
Further comprising an optical rotation reducing member between the first polarizing layer and the second polarizing layer,
The optical rotatory reduction member exhibits optical rotatory power in a direction opposite to the optical rotatory power exhibited by the liquid crystal layer when no voltage is applied,
A liquid crystal display device characterized by the above. The liquid crystal display device according to claim 1 .
The first polarizing plate has a first polarizing layer having an absorption axis,
The second polarizing plate has a second polarizing layer having an absorption axis in a direction different from that of the first polarizing layer,
The liquid crystal display device
Further comprising an optical rotation reducing member between the first polarizing layer and the second polarizing layer,
The optical rotatory reduction member exhibits optical rotatory power in a direction opposite to the optical rotatory power exhibited by the liquid crystal layer when no voltage is applied,
A liquid crystal display device characterized by the above. The liquid crystal display device according to any one of claims 1 to 3 ,
The blue phase liquid crystal contains a chiral agent,
The chiral pitch of the chiral agent is 400 nm or less,
A liquid crystal display device characterized by the above. The liquid crystal display device according to any one of claims 1 to 3 ,
The blue phase liquid crystal contains a chiral agent,
The chiral pitch of the chiral agent is 380 nm or less,
A liquid crystal display device characterized by the above. The liquid crystal display device according to claim 2 ,
The absorption axis of the second polarizing plate is rotated in the liquid crystal layer with no voltage applied to the light passing through the first polarizing plate with reference to a direction that forms 90 ° with the absorption axis of the first polarizing plate. On the side that will be shifted,
A liquid crystal display device characterized by the above. The liquid crystal display device according to claim 1 or 6 ,
The absorption axis of the second polarizing plate is rotated in the liquid crystal layer with no voltage applied to the light passing through the first polarizing plate with reference to a direction that forms 90 degrees with the absorption axis of the first polarizing plate. It becomes the direction rotated the angle of 0.5 times or more and 1.25 times or less of the angle to be
A liquid crystal display device characterized by the above. The liquid crystal display device according to claim 6 .
The absorption axis of the second polarizing plate is a direction rotated by 4 ° or more and 10 ° or less with reference to a direction that forms 90 ° with the absorption axis of the first polarizing plate.
A liquid crystal display device characterized by the above. The liquid crystal display device according to any one of claims 1 to 8 ,
The first polarizing plate and the second polarizing plate are
When the angle formed by the absorption axis of the first polarizing plate and the absorption axis of the second polarizing plate is P, −5.5 ° ≦ P− (90 ° −α) ≦ 5.5 ° is satisfied. ,
A liquid crystal display device characterized by the above. The liquid crystal display device according to any one of claims 1 to 8 ,
The first polarizing plate and the second polarizing plate are
When the angle formed by the absorption axis of the first polarizing plate and the absorption axis of the second polarizing plate is P, −0.5 ° ≦ P− (90 ° −α) ≦ 0.5 ° is satisfied. ,
A liquid crystal display device characterized by the above. The liquid crystal display device according to any one of claims 1 to 10 ,
An alignment film is formed on at least one of the side of the first substrate on which the liquid crystal layer is disposed and the side of the second substrate on which the liquid crystal layer is disposed.
A liquid crystal display device characterized by the above. The liquid crystal display device according to any one of claims 1 to 10 ,
The liquid crystal display device
A thin film transistor in which one of a source electrode and a drain electrode is connected to the first electrode;
A signal wiring connected to the other of the source electrode and the drain electrode;
A scanning wiring connected to the gate electrode of the thin film transistor,
A liquid crystal display device. The liquid crystal display device according to any one of claims 1 to 10 ,
The first substrate or the second substrate is:
Having a color material layer showing three or more colors,
A liquid crystal display device characterized by the above. The liquid crystal display device according to any one of claims 1 to 10 ,
At least one of the first electrode and the second electrode is formed in a comb shape.
A liquid crystal display device characterized by the above. The liquid crystal display device according to any one of claims 1 to 10 ,
An electric field application direction by the first electrode and the second electrode is parallel to the first in-plane direction of the substrate,
2. The liquid crystal display device according to claim 1, wherein the electric field application direction has two or more directions in the pixel. The liquid crystal display device according to any one of claims 1 to 10 ,
The first electrode and the second electrode are formed on one of the first substrate and the second substrate,
An insulating layer is formed between the first electrode and the second electrode.
A liquid crystal display device characterized by the above. The liquid crystal display device according to any one of claims 1 to 10 ,
A viewing angle compensation phase difference plate is disposed between at least one of the first polarizing plate and the liquid crystal layer and between the second polarizing plate and the liquid crystal layer.
A liquid crystal display device characterized by the above. The liquid crystal display device according to any one of claims 1 to 10 ,
A pixel having a transmissive display portion and a reflective display portion;
A liquid crystal display device characterized by the above.

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