US20080049178A1 - Liquid crystal display device - Google Patents

Liquid crystal display device Download PDF

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Publication number
US20080049178A1
US20080049178A1 US11/828,583 US82858307A US2008049178A1 US 20080049178 A1 US20080049178 A1 US 20080049178A1 US 82858307 A US82858307 A US 82858307A US 2008049178 A1 US2008049178 A1 US 2008049178A1
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United States
Prior art keywords
retardation plate
liquid crystal
plate
crystal display
display device
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Abandoned
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US11/828,583
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English (en)
Inventor
Emi Kisara
Kazuhiro Nishiyama
Mitsutaka Okita
Shigesumi Araki
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Japan Display Central Inc
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Toshiba Matsushita Display Technology Co Ltd
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Assigned to TOSHIBA MATSUSHITA DISPLAY TECHNOLOGY CO. , LTD. reassignment TOSHIBA MATSUSHITA DISPLAY TECHNOLOGY CO. , LTD. ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: ARAKI, SHIGESUMI, KISARA, EMI, NISHIYAMA, KAZUHIRO, OKITA, MITSUTAKA
Publication of US20080049178A1 publication Critical patent/US20080049178A1/en
Priority to US13/282,651 priority Critical patent/US8237901B2/en
Abandoned legal-status Critical Current

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    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells
    • G02F1/137—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells characterised by the electro-optical or magneto-optical effect, e.g. field-induced phase transition, orientation effect, guest-host interaction or dynamic scattering
    • G02F1/139—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells characterised by the electro-optical or magneto-optical effect, e.g. field-induced phase transition, orientation effect, guest-host interaction or dynamic scattering based on orientation effects in which the liquid crystal remains transparent
    • G02F1/1393—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells characterised by the electro-optical or magneto-optical effect, e.g. field-induced phase transition, orientation effect, guest-host interaction or dynamic scattering based on orientation effects in which the liquid crystal remains transparent the birefringence of the liquid crystal being electrically controlled, e.g. ECB-, DAP-, HAN-, PI-LC cells
    • G02F1/1395—Optically compensated birefringence [OCB]- cells or PI- cells
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells
    • G02F1/133—Constructional arrangements; Operation of liquid crystal cells; Circuit arrangements
    • G02F1/1333—Constructional arrangements; Manufacturing methods
    • G02F1/1335—Structural association of cells with optical devices, e.g. polarisers or reflectors
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells
    • G02F1/133—Constructional arrangements; Operation of liquid crystal cells; Circuit arrangements
    • G02F1/1333—Constructional arrangements; Manufacturing methods
    • G02F1/1335—Structural association of cells with optical devices, e.g. polarisers or reflectors
    • G02F1/13363—Birefringent elements, e.g. for optical compensation
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells
    • G02F1/133—Constructional arrangements; Operation of liquid crystal cells; Circuit arrangements
    • G02F1/1333—Constructional arrangements; Manufacturing methods
    • G02F1/1335—Structural association of cells with optical devices, e.g. polarisers or reflectors
    • G02F1/13363—Birefringent elements, e.g. for optical compensation
    • G02F1/133631—Birefringent elements, e.g. for optical compensation with a spatial distribution of the retardation value
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells
    • G02F1/133—Constructional arrangements; Operation of liquid crystal cells; Circuit arrangements
    • G02F1/1333—Constructional arrangements; Manufacturing methods
    • G02F1/1335—Structural association of cells with optical devices, e.g. polarisers or reflectors
    • G02F1/13363—Birefringent elements, e.g. for optical compensation
    • G02F1/133634—Birefringent elements, e.g. for optical compensation the refractive index Nz perpendicular to the element surface being different from in-plane refractive indices Nx and Ny, e.g. biaxial or with normal optical axis

Definitions

  • the present invention relates generally to a liquid crystal display device, and more particularly to a liquid crystal display device which uses an optically compensated bend (OCB) alignment technique that is capable of realizing a wide viewing angle and a high speed response.
  • OBC optically compensated bend
  • Liquid crystal display devices have been applied to various technical fields by virtue of their features of light weight, small thickness and low power consumption.
  • the OCB mode liquid crystal display device is configured such that a liquid crystal layer including bend-aligned liquid crystal molecules is held between a pair of substrates in the state in which a predetermined voltage is applied between the pair of substrates.
  • a twisted nematic (TN) mode the OCB mode can realize a higher response speed and can optically self-compensate the influence of birefringence of light that passes through the liquid crystal layer by the alignment state of liquid crystal molecules.
  • the viewing angle can advantageously be increased.
  • This circular polarization plate includes a liquid crystal film in which a nematic hybrid alignment structure is fixed.
  • the object of the present invention is to provide a liquid crystal display device to which an OCB mode is applicable, and which is capable of increasing a viewing angle.
  • a liquid crystal display device comprising: an OCB mode liquid crystal display panel which is configured such that a liquid crystal layer is held between a first substrate and a second substrate; and an optical compensation element which is disposed outside of the liquid crystal layer and optically compensates a retardation of the liquid crystal layer in a predetermined display state in which a voltage is applied to the liquid crystal layer, wherein the optical compensation element includes; a polarizer plate; a first retardation plate which is disposed between the polarizer plate and the liquid crystal layer and imparts a phase difference of a 1 ⁇ 4 wavelength; and a second retardation plate which is disposed between the polarizer plate and the first retardation plate and has a biaxial refractive index anisotropy, and the second retardation plate has a refractive index anisotropy which is set in such a manner as to compensate (a) a difference of a polarization state due to an influence of optical rotatory power that differs between azimuth directions of light passing
  • a liquid crystal display device comprising: a liquid crystal display panel which is configured such that a liquid crystal layer is held between a first substrate and a second substrate, and to which an OCB mode is applied; and a first optical compensation element and a second optical compensation element which are disposed, respectively, on outer surfaces of the first substrate and the second substrate, and optically compensate a retardation of the liquid crystal layer in a predetermined display state in which a voltage is applied to the liquid crystal layer
  • the first optical compensation element includes: a first polarizer plate; a first retardation plate which is disposed between the first polarizer plate and the liquid crystal display panel and imparts a phase difference of a 1 ⁇ 4 wavelength between light components of a predetermined wavelength, which pass through a fast axis and a slow axis thereof; and a second retardation plate which is disposed between the first polarizer plate and the first retardation plate and has a biaxial refractive index anisotropy, and the second optical compensation
  • a liquid crystal display device comprising: a liquid crystal display panel which is configured such that a liquid crystal layer is held between a first substrate and a second substrate, and to which an OCB mode is applied; and a first optical compensation element and a second optical compensation element which are disposed, respectively, on outer surfaces of the first substrate and the second substrate, and optically compensate a retardation of the liquid crystal layer in a predetermined display state in which a voltage is applied to the liquid crystal layer
  • the first optical compensation element includes: a first polarizer plate; a first retardation plate which is disposed between the first polarizer plate and the liquid crystal display panel and imparts a phase difference of a 1 ⁇ 4 wavelength between light components of a predetermined wavelength, which pass through a fast axis and a slow axis thereof; and a second retardation plate which is disposed between the first polarizer plate and the first retardation plate and has a biaxial refractive index anisotropy, and the second optical
  • a liquid crystal display device comprising: a liquid crystal display panel which is configured such that a liquid crystal layer is held between a first substrate and a second substrate, and to which an OCB mode is applied; and a first optical compensation element and a second optical compensation element which are disposed, respectively, on outer surfaces of the first substrate and the second substrate, and optically compensate a retardation of the liquid crystal layer in a predetermined display state in which a voltage is applied to the liquid crystal layer
  • the first optical compensation element includes: a first polarizer plate; a first retardation plate which is disposed between the first polarizer plate and the liquid crystal display panel and imparts a phase difference of a 1 ⁇ 4 wavelength between light components of a predetermined wavelength, which pass through a fast axis and a slow axis thereof; and a second retardation plate which is disposed between the first polarizer plate and the first retardation plate and has a biaxial refractive index anisotropy, and the second optical
  • a liquid crystal display device comprising: a liquid crystal display panel which is configured such that a liquid crystal layer is held between a first substrate and a second substrate, and to which an OCB mode is applied; and a first optical compensation element and a second optical compensation element which are disposed, respectively, on outer surfaces of the first substrate and the second substrate, and optically compensate a retardation of the liquid crystal layer in a predetermined display state in which a voltage is applied to the liquid crystal layer
  • the first optical compensation element includes: a first polarizer plate; a first retardation plate which is disposed between the first polarizer plate and the liquid crystal display panel and imparts a phase difference of a 1 ⁇ 4 wavelength between light components of a predetermined wavelength, which pass through a fast axis and a slow axis thereof; and a second retardation plate which is disposed between the first polarizer plate and the first retardation plate and has a biaxial refractive index anisotropy, and the second optical
  • the present invention can provide a liquid crystal display device to which an OCB mode is applicable, and which is capable of increasing a viewing angle.
  • FIG. 1 schematically shows the structure of a transmissive liquid crystal display device or a transreflective liquid crystal display device according to an embodiment of the present invention
  • FIG. 2 schematically shows the structure of a liquid crystal display panel which is applicable to the liquid crystal display device shown in FIG. 1 ;
  • FIG. 3 schematically shows the structure of an OCB mode transmissive liquid crystal display panel which is applicable to the liquid crystal display device shown in FIG. 1 ;
  • FIG. 4A schematically shows an example of the structure of an optical compensation element which is applicable to the liquid crystal display device shown in FIG. 1 ;
  • FIG. 4B schematically shows another example of the structure of the optical compensation element which is applicable to the liquid crystal display device shown in FIG. 1 ;
  • FIG. 4C schematically shows still another example of the structure of the optical compensation element which is applicable to the liquid crystal display device shown in FIG. 1 ;
  • FIG. 4D schematically shows still another example of the structure of the optical compensation element which is applicable to the liquid crystal display device shown in FIG. 1 ;
  • FIG. 5 is a view for explaining a relationship of compensation with liquid crystal molecules in a case where the optical compensation element shown in FIG. 4C is applied;
  • FIG. 6 is a view for explaining the definitions of axial angles relative to a rubbing direction of an alignment film in the liquid crystal display device shown in FIG. 1 ;
  • FIG. 7 is a view for explaining the structure of a transmissive liquid crystal display device or a transreflective liquid crystal display device to which a first optical compensation element and a second optical compensation element according to a first example of structure are applied;
  • FIG. 8A shows a result of simulation of a viewing angle dependency of a contrast ratio in a transmissive liquid crystal display device according to a comparative example
  • FIG. 8B shows a result of simulation of a viewing angle dependency of a contrast ratio in the transmissive liquid crystal display device according to the present embodiment
  • FIG. 9A schematically shows another structure of a transmissive liquid crystal display device or a transreflective liquid crystal display device according to an embodiment of the present invention.
  • FIG. 9B schematically shows still another structure of the transmissive liquid crystal display device or a transreflective liquid crystal display device according to the embodiment of the present invention.
  • FIG. 10A is a view for explaining the structure of a transmissive liquid crystal display device or a transreflective liquid crystal display device to which a first optical compensation element and a second optical compensation element according to a second example of structure are applied;
  • FIG. 10B shows a result of simulation of a viewing angle dependency of a contrast ratio in the transmissive liquid crystal display device according to the present embodiment
  • FIG. 10C shows a result of simulation of a viewing angle dependency of a contrast ratio in another transmissive liquid crystal display device according to the present embodiment
  • FIG. 11 schematically shows the structure of an OCB mode transreflective liquid crystal display panel which is applicable to the liquid crystal display device shown in FIG. 1 ;
  • FIG. 12A shows a result of simulation of a viewing angle dependency of a contrast ratio in a transmissive part of a transreflective liquid crystal display device according to a comparative example
  • FIG. 12B shows a result of simulation of a viewing angle dependency of a contrast ratio in a transmissive part of the transreflective liquid crystal display device according to the present embodiment
  • FIG. 13A shows a result of simulation of a viewing angle dependency of a contrast ratio in a reflective part of the transreflective liquid crystal display device according to the comparative example
  • FIG. 13B shows a result of simulation of a viewing angle dependency of a contrast ratio in a reflective part of the transreflective liquid crystal display device according to the present embodiment
  • FIG. 14 schematically shows the structure of an OCB mode reflective liquid crystal display device according to an embodiment of the invention.
  • FIG. 15 is a view for explaining an example of structure and an example of modification of a reflective liquid crystal display device
  • FIG. 16A shows a result of simulation of a viewing angle dependency of a contrast ratio in a reflective liquid crystal display device according to a comparative example.
  • FIG. 16B shows a result of simulation of a viewing angle dependency of a contrast ratio in the reflective liquid crystal display device according to the present embodiment.
  • Liquid crystal display devices according to an embodiment of the present invention will now be described with reference to the accompanying drawings.
  • OCB mode liquid crystal display devices include a transmissive liquid crystal display device in which each pixel is composed of only a transmissive part that displays an image by selectively passing backlight; a reflective liquid crystal display device in which each pixel is composed of only a reflective part that displays an image by selectively reflecting ambient light; and a transreflective liquid crystal display device in which each pixel is composed of both the reflective part and the transmissive part.
  • a transmissive liquid crystal display device includes a liquid crystal display panel 1 to which an OCB mode is applied, a backlight 60 which illuminates the liquid crystal display panel 1 , a first optical compensation element 40 which is disposed between the liquid crystal display panel 1 and the backlight 60 , and a second optical compensation element 50 which is disposed on an observation surface side of the liquid crystal display panel 1 .
  • the liquid crystal display panel 1 is configured such that a liquid crystal layer 30 is held between a pair of substrates, namely, an array substrate (first substrate) 10 and a counter-substrate (second substrate) 20 .
  • the liquid crystal display panel 1 includes an active area ACT which displays an image.
  • This active area ACT is composed of a plurality of pixels PX which are arrayed in a matrix.
  • the array substrate 10 is formed by using a light-transmissive insulating substrate 11 such as a glass substrate.
  • the array substrate 10 includes, on one major surface of the insulating substrate 11 , a plurality of scanning lines Sc which are disposed along rows of pixels PX; a plurality of signal lines Sg which are disposed along columns of pixels PX; switch elements 12 which are disposed near intersections between the scanning lines Sc and signal lines Sg in association with the individual pixels PX; pixel electrodes 13 which are disposed in association with the individual pixels PX and are connected to the associated switch elements 12 ; and an alignment film 16 which is disposed so as to cover the entire major surface of the insulating substrate 13 .
  • Each of the switch elements 12 is composed of, e.g. a thin-film transistor (TFT).
  • the switch element 12 has a gate connected to the associated scanning line Sc.
  • the switch element 12 has a source connected to the associated signal line Sg.
  • the pixel electrode 13 is disposed on an insulation film 14 , and is electrically connected to the drain of the switch element 12 .
  • the pixel electrode 13 functions as a transmissive electrode and is formed of a light-transmissive electrically conductive material such as indium tin oxide (ITO).
  • ITO indium tin oxide
  • each pixel PX corresponds to a transmissive part.
  • the counter-substrate 20 is formed by using a light-transmissive insulating substrate 21 such as a glass substrate.
  • the counter-substrate 20 includes, on one major surface of the insulating substrate 21 , a counter-electrode 22 which is disposed commonly for the plural pixels PX, and an alignment film 23 which is disposed so as to cover the entire major surface of the insulating substrate 21 .
  • the counter-electrode 22 is formed of a light-transmissive electrically conductive material such as ITO.
  • the array substrate 10 and counter-substrate 20 having the above-described structures are disposed with a predetermined gap provided therebetween by spacers (not shown), and are attached to each other by a seal material.
  • the liquid crystal layer 30 is sealed in the gap between the array substrate 10 and counter-substrate 20 .
  • the OCB mode is applied to the liquid crystal display panel 1 not only in the example of the transmissive liquid crystal display device, but also in examples of the transreflective liquid crystal display device and reflective liquid crystal display device, which will be described later.
  • the liquid crystal layer 30 is formed of a material including liquid crystal molecules 31 which have positive dielectric constant anisotropy and optically positive uniaxiality. In this liquid crystal layer 30 , as shown in FIG. 3 , the liquid crystal molecules 31 are bend-aligned between the array substrate 10 and counter-substrate 20 in a predetermined display state in which a voltage is applied to the liquid crystal layer 30 .
  • the first optical compensation element 40 and second optical compensation element 50 have functions of optically compensating retardation of the liquid crystal layer 30 in a predetermined display state in which a voltage is applied to the liquid crystal layer 30 in the above-described liquid crystal display panel 1 .
  • the first optical compensation element 40 is disposed on the outside surface of the array substrate 10
  • the second optical compensation element 50 is disposed on the outside surface of the counter-substrate 20 .
  • the first optical compensation element 40 and second optical compensation element 50 have substantially the same structure and are configured to be symmetric with respect to the liquid crystal display panel 1 .
  • the first optical compensation element 40 includes a first polarizer plate PL 1 , a first retardation plate R 1 and a second retardation plate R 2 .
  • the second optical compensation element 50 includes a second polarizer plate PL 1 , a third retardation plate R 3 and a fourth retardation plate R 4 .
  • Each of the first polarizer plate PL 1 and second polarizer plate PL 2 is configured such that a polarization layer of, e.g. polyvinyl alcohol (PVA) is held between a pair of support layers of, e.g. triacetate cellulose (TAC).
  • PVA polyvinyl alcohol
  • TAC triacetate cellulose
  • Each of the first polarizer plate PL 1 and second polarizer plate PL 2 has a transmission axis and an absorption axis which are substantially perpendicular to each other.
  • the first retardation plate R 1 is disposed between the first polarizer plate PL 1 and the liquid crystal display panel 1 .
  • the third retardation plate R 3 is disposed between the second polarizer plate PL 2 and the liquid crystal display panel 1 .
  • Each of the first retardation plate R 1 and the third retardation plate R 3 has, in a plane thereof, a fast axis and a slow axis which are substantially perpendicular to each other.
  • Each of the first retardation plate R 1 and the third retardation plate R 3 is a so-called “1 ⁇ 4 wavelength plate”, which imparts a phase difference of a 1 ⁇ 4 wavelength between light components of a predetermined wavelength, which pass through the fast axis and the slow axis.
  • Each of the combination of the first polarizer plate PL 1 and first retardation plate (1 ⁇ 4 wavelength plate) R 1 and the combination of the second polarizer plate PL 2 and third retardation plate (1 ⁇ 4 wavelength plate) R 3 ideally functions as a circular polarization element that converts linearly polarized light of a predetermined wavelength, which has passed through the transmission axis of the polarizer plate, to circularly polarized light.
  • the second retardation plate R 2 is disposed between the first polarizer plate PL 1 and the first retardation plate R 1 .
  • the fourth retardation plate R 4 is disposed between the second polarizer plate PL 2 and the third retardation plate R 3 .
  • Each of the second retardation plate R 2 and the fourth retardation plate R 4 is a retardation plate having biaxial refractive index anisotropy, and has, in a plane thereof, a fast axis and a slow axis which are substantially perpendicular to each other.
  • Each of the second retardation plate R 2 and the fourth retardation plate R 4 is a so-called “1 ⁇ 2 wavelength plate”, which imparts a phase difference of a 1 ⁇ 2 wavelength between light components of a predetermined wavelength, which pass through the fast axis and the slow axis.
  • the details of the second retardation plate R 2 and the fourth retardation plate R 4 will be described later.
  • Each of the first optical compensation element 40 and second optical compensation element 50 includes a compensation layer CL.
  • the first optical compensation element 40 includes a first compensation layer CL 1 which is disposed between the liquid crystal display panel 1 and first retardation plate R 1 .
  • the second optical compensation element 50 includes a second compensation layer CL 2 which is disposed between the liquid crystal display panel 1 and third retardation plate R 3 .
  • first optical compensation element 40 and second optical compensation element 50 which include the first compensation layer CL 1 and second compensation layer CL 2 , will now be described specifically. Examples of the structure of the first optical compensation element 40 are described with reference to FIG. 4A to FIG. 4D . The same examples of the structure are also applicable to the second optical compensation element 50 .
  • the first compensation layer CL 1 and second compensation layer CL 2 may not necessarily have the same structure.
  • the first compensation layer CL 1 includes a retardation plate RA which is disposed between the liquid crystal display panel 1 and the first retardation plate R 1 and has a refractive index anisotropy which substantially corresponds to an A-plate, and a retardation plate RC which is disposed between the first retardation plate R 1 and the retardation plate RA and has a refractive index anisotropy which substantially corresponds to a C-plate.
  • the retardation plate RA has such an in-plane phase difference as to cancel a residual retardation in the plane thereof in a specified voltage application state (e.g. a state in which black is displayed by applying a high voltage).
  • the retardation plate RA has a refractive index anisotropy of nx>ny ⁇ nz or nz ⁇ nx>ny, where nx and ny are refractive indices in mutually perpendicular directions in the plane of the retardation plate RA, and nz is a refractive index in a normal direction to the retardation plate RA.
  • the retardation plate RA By the function of the retardation plate RA, the in-plane phase difference of the liquid crystal layer 30 can be canceled, and a display quality at a time of observation in a frontal direction of the screen (a normal direction to the screen) can be improved (in particular, contrast can be improved).
  • the retardation plate RC has such a normal-directional phase difference as to cancel a residual retardation in the normal direction thereof in a specified voltage application state (e.g. a state in which black is displayed by applying a high voltage).
  • the retardation plate RC has a refractive index anisotropy of nx ⁇ ny ⁇ nz.
  • the first compensation layer CL 1 includes a retardation plate RB which has a biaxial refractive index anisotropy and is disposed between the liquid crystal display panel 1 and the first retardation plate R 1 .
  • This retardation plate RB has both a refractive index anisotropy which substantially corresponds to an A-plate and a refractive index anisotropy which substantially corresponds to a C-plate.
  • the retardation plate RB has a refractive index anisotropy of nx>ny>nz.
  • the same advantageous effects as in the example of structure shown in FIG. 4A can be obtained.
  • the number of retardation plates is less than in the example of structure shown in FIG. 4A , the reduction in thickness can be achieved.
  • the first compensation layer CL 1 includes a retardation plate Rwv which is disposed between the liquid crystal display panel 1 and the first retardation plate R 1 .
  • This retardation plate Rwv is an anisotropic film which compensates retardation of the liquid crystal layer 30 .
  • the retardation plate Rwv is an anisotropic film having such a refractive index anisotropy that a substantial major axis is inclined to the normal line, when consideration is given to the total refractive index anisotropy of the retardation plate Rwv itself.
  • a WV (Wide View) film manufactured by FUJIFILM Corporation
  • the WV film is a liquid crystal film in which discotic liquid crystal molecules having an optically negative uniaxial refractive index anisotropy are fixed in the state in which an optical axis is hybrid-aligned along the normal direction in a liquid crystal state (i.e. in the state in which the major axis is hybrid-aligned).
  • both the first compensation layer CL 1 and second compensation layer CL 2 are composed of retardation plates Rwv in relation to the OCB mode liquid crystal display panel 1
  • the discotic liquid crystal molecules which constitute the retardation plates Rwv as shown in FIG. 5 , optically compensate the bend-aligned liquid crystal molecules 31 , respectively. Therefore, the combination of the OCB mode liquid crystal display panel 1 and the retardation plates Rwv is effective in terms of optical compensation.
  • the first compensation layer CL 1 includes a retardation plate RA which is disposed between the liquid crystal display panel 1 and the first retardation plate R 1 and has a refractive index anisotropy which substantially corresponds to an A-plate.
  • a retardation plate having biaxial refractive index anisotropy is applied to the first retardation plate R 1 .
  • the refractive index anisotropy of the first retardation plate R 1 is set to have a refractive index anisotropy substantially corresponding to a C-plate, in addition to its own function as a 1 ⁇ 4 wavelength plate.
  • the first retardation plate R 1 has a refractive index anisotropy of nx>ny>nz.
  • the same advantageous effects as in the example of structure shown in FIG. 4A can be obtained.
  • the number of retardation plates is less than in the example of structure shown in FIG. 4A , the reduction in thickness can be achieved.
  • the respective structural elements are arranged with axial angles described below, in relation to a reference direction that is the rubbing direction of the alignment film 16 on the array substrate 10 side and the alignment film 23 on the counter-substrate 20 side.
  • the axial angle in this context, refers to a counterclockwise angle, relative to the reference azimuth direction (X axis), of the absorption axis of the polarizer plate and the slow axis (or optical axis) of the retardation plate, as defined in FIG. 6 .
  • an X axis and a Y axis which are perpendicular to each other, are defined, for the purpose of convenience, in a plane that is parallel to the major surface of the array substrate 10 (or counter-substrate 20 ), and a normal direction to this plane is defined as a Z axis.
  • the term “in-plane” means “within a plane” that is defined by the X axis and Y axis.
  • first compensation layer CL 1 and second compensation layer CL 2 in the first optical compensation element 40 and second optical compensation element 50 according to the first example of structure are composed of the retardation plate RA and retardation plate RC as shown in FIG. 4A .
  • the rubbing direction is set at 0° azimuth.
  • the absorption axis of the first polarizer plate PL 1 is set at 45° azimuth.
  • the slow axis of the first retardation plate R 1 is set at 0° azimuth (i.e. crossing the absorption axis of the first polarizer plate PL 1 at about 45°).
  • the optical axis of the second retardation plate R 2 in the X-Y plane is set at 45° azimuth (i.e. substantially parallel to the absorption axis of the first polarizer plate PL 1 ).
  • the slow axis of the retardation plate RA is set at 90° azimuth.
  • the absorption axis of the second polarizer plate PL 2 is set at 135° azimuth.
  • the slow axis of the third retardation plate R 3 is set at 90° azimuth (i.e. crossing the absorption axis of the second polarizer plate PL 2 at about 45°).
  • the optical axis of the fourth retardation plate R 4 in the X-Y plane is set at 45° azimuth (i.e. substantially perpendicular to the absorption axis of the polarizer plate PL).
  • the slow axis of the retardation plate RA is set at 90° azimuth.
  • the liquid crystal molecules 31 are bend-aligned, as shown in FIG. 6 , in a predetermined voltage application state (e.g. black display state) in an X-Z plane.
  • a predetermined voltage application state e.g. black display state
  • the liquid crystal molecules 31 are aligned counterclockwise from the lower side (array substrate side) to the upper side (counter-substrate side).
  • the liquid crystal molecules 31 are aligned clockwise from the lower side to the upper side.
  • the optical rotatory power of the light that passes through the liquid crystal layer 30 is affected by the alignment of liquid crystal molecules 31 in opposite rotational directions at 90° azimuth and 270° azimuth.
  • the polarization states of light, which passes through the liquid crystal layer 30 toward the respective azimuth directions are different.
  • a difference occurs in the display quality of the screen due to the difference in polarization state of light passing through the liquid crystal layer 30 , between the case where the viewing angle is increased from the normal direction (i.e.
  • the viewing angle at which a high contrast is obtained is limited.
  • the difference of the polarization state which varies depending on the influence of optical rotatory power that differs between azimuth directions of light passing through the liquid crystal layer 30 , is optically compensated.
  • the polarization state (ideally a linear polarization state) of light which emerges from the third retardation plate R 3 of the second optical compensation element 50 , shifts from the azimuth direction of the absorption axis of the second polarizer plate PL 2 , due to the influence of retardation of not only the liquid crystal layer 30 but also other structural elements. Consequently, the transmittance of the screen at the time of black display cannot sufficiently be lowered, and the contrast may deteriorate.
  • the optical compensation elements having the function of optically compensating the shift of the polarization state of light, which passes through the third retardation plate R 3 , from the azimuth direction of the absorption axis of the second polarizer plate PL 2 .
  • the contrast can be improved, and the viewing angle at which a high contrast is obtained, can be increased.
  • the first optical compensation element 40 includes, as shown in FIG. 1 , the second retardation plate R 2 with the biaxial refractive index anisotropy between the first retardation plate R 1 and the first polarizer plate PL 1 .
  • the second optical compensation element 50 includes the fourth retardation plate R 4 with the biaxial refractive index anisotropy between the third retardation plate R 3 and the second polarizer plate PL 2 .
  • the second retardation plate R 2 of the first optical compensation element 40 mainly compensates the difference of the polarization state which varies mainly due to the influence of optical rotatory power, depending on the azimuth direction of light passing through the liquid crystal layer 30 .
  • the fourth retardation plate R 4 of the second optical compensation element 50 mainly compensates the shift of the polarization state of the light, which has passed through the third retardation plate R 3 , from the azimuth direction of the absorption axis of the second polarizer plate PL 2 .
  • the Nz coefficient that is necessary for each compensation differs, and the Nz coefficient of the second retardation plate R 2 of the first optical compensation element 40 differs from the Nz coefficient of the fourth retardation plate R 4 of the second optical compensation element 50 .
  • the second retardation plate R 2 having the Nz coefficient that is set in the range of between 0.7 and 0.9. If the Nz coefficient is less than 0.7 or greater than 0.9, it is difficult to secure a viewing angle contrast at, e.g. 90° azimuth.
  • the fourth retardation plate R 4 having the Nz coefficient that is set in the range of between 0.15 and 0.3. If the Nz coefficient is less than 0.15 or greater than 0.3, the compensation of the polarization state would become deficient and it is difficult to secure the viewing angle contrast.
  • the structure of the transmissive liquid crystal display device according to the present embodiment is as shown in FIG. 1 .
  • a first optical compensation element 40 including no second retardation plate and a second optical compensation element 50 including no fourth retardation plate were applied to a liquid crystal display device, with the other structural aspects being the same as in the present embodiment.
  • FIG. 8A shows a result of simulation of the viewing angle dependency of a contrast ratio in the liquid crystal display device according to the comparative example.
  • the center corresponds to the normal direction (Z axis) of the liquid crystal display panel.
  • Concentric circles defined about the normal direction indicate tilt angles (viewing angles) to the normal direction, and correspond to 20°, 40°, 60° and 80°, respectively.
  • the characteristic diagram of FIG. 8A was obtained by connecting regions corresponding to contrast ratios (CR) of 100:1 to 10:1 in all azimuth directions.
  • the contrast ratio becomes 10:1 or less in the range of viewing angles of 60° or more, in particular, at 0° azimuth and 180° azimuth.
  • the azimuth direction parallel to the rubbing direction (0°-180° azimuth) is the vertical direction of the screen
  • the 90° azimuth direction is the right direction of the screen
  • the 270° azimuth direction is the left direction of the screen.
  • the contrast ratio considerably lowers as the viewing angle increases from the normal direction toward the upward and downward directions of the screen.
  • FIG. 8B shows a result of simulation of the viewing angle dependency of a contrast ratio in the liquid crystal display device according to the present embodiment. As is clear from FIG. 8B , it was confirmed that the contrast ratio of 10:1 or more was obtained in the range of viewing angles of 80° or more in all azimuth directions, and sufficient viewing angles were obtained.
  • the absorption axis of the first polarizer plate PL 1 and the optical axis of the second retardation plate R 2 substantially agree in the first optical compensation element 40 .
  • the absorption axis of the second polarizer plate PL 2 is substantially perpendicular to the optical axis of the fourth retardation plate R 4 .
  • the invention is not limited to this example. Specifically, since the first optical compensation element 40 and second optical compensation element 50 are symmetric in the liquid crystal display panel 1 , the first optical compensation element 40 and second optical compensation element 50 may substantially be transposed in an alternative structure.
  • the optical axis of the second retardation plate R 2 in its X-Y plane is set at 135° in the first optical compensation element 40 .
  • the absorption axis of the first polarizer plate PL 1 is substantially perpendicular to the optical axis of the second retardation plate R 2 .
  • the optical axis of the fourth retardation plate R 4 in its X-Y plane is set at 135°.
  • the absorption axis of the second polarizer plate PL 2 substantially agrees with the optical axis of the fourth retardation plate R 4 .
  • the absorption axis of the first polarizer plate PL 1 substantially agrees with the optical axis of the second retardation plate R 2 in the first optical compensation element 40 and the absorption axis of the second polarizer plate PL 2 substantially agrees with the optical axis of the fourth retardation plate R 4 in the second optical compensation element 50 , it should suffice to use the second retardation plate R 2 and fourth retardation plate R 4 , in each of which the Nz coefficient is set in the range of between 0.7 and 0.9.
  • the absorption axis of the first polarizer plate PL 1 is substantially perpendicular to the optical axis of the second retardation plate R 2 in the first optical compensation element 40 and the absorption axis of the second polarizer plate PL 2 is substantially perpendicular to the optical axis of the fourth retardation plate R 4 in the second optical compensation element 50 .
  • the second retardation plate R 2 and fourth retardation plate R 4 in each of which the NZ coefficient is set in the range of between 0.15 and 0.3. In each of these cases, the same advantageous effects as in the above-described first example of structure can be obtained, and the common structural elements are usable and the reduction in cost is realized.
  • the first optical compensation element 40 and second optical compensation element 50 have functions of optically compensating retardation of the liquid crystal layer 30 in a predetermined display state in which a voltage is applied to the liquid crystal layer 30 of the liquid crystal display panel 1 .
  • the first optical compensation element 40 which is disposed on the outer surface of the array substrate 10 , is configured to include a first polarizer plate PL 1 , a first retardation plate R 1 and a second retardation plate R 2 .
  • the second optical compensation element 50 which is disposed on the outer surface of the counter-substrate 20 , is configured to include a second polarizer plate PL 2 and a third retardation plate R 3 .
  • the first optical compensation element 40 and the second optical compensation element 50 are configured to be asymmetric with respect to the liquid crystal display panel 1 .
  • the number of retardation plates is less than in the liquid crystal display device to which the optical compensation elements according to the first example of structure are applied. Therefore, the reduction in cost and thickness can be achieved.
  • the first polarizer plate PL 1 , second polarizer plate PL 2 , the first retardation plate R 1 and the third retardation plate R 3 are the same as those in the first example of structure. Specifically, each of the combination of the first polarizer plate PL 1 and the first retardation plate (1 ⁇ 4 wavelength plate) R 1 and the combination of the second polarizer plate PL 2 and the third retardation plate (1 ⁇ 4 wavelength plate) R 3 functions ideally as a circular polarization element that converts linearly polarized light of a predetermined wavelength, which has passed through the transmission axis of the polarizer plate, to circularly polarized light.
  • the second retardation plate R 2 is disposed between the first polarizer plate PL 1 and the first retardation plate R 1 .
  • the second retardation plate R 2 is a retardation plate with a biaxial refractive index anisotropy.
  • the first optical compensation element 40 includes a first compensation layer CL 1 which is disposed between the liquid crystal display panel 1 and the first retardation plate R 1 .
  • the second optical compensation element 50 includes a second compensation layer CL 2 which is disposed between the liquid crystal display panel 1 and the third retardation plate R 3 .
  • the structures as shown in FIG. 4A to FIG. 4D are applicable to the first optical compensation element 40 and the second optical compensation element 50 , which include the first compensation layer CL 1 and the second compensation layer CL 2 , respectively.
  • first compensation layer CL 1 and second compensation layer CL 2 in the first optical compensation element 40 and second optical compensation element 50 according to the second example of structure are composed of the retardation plate RA and retardation plate RC as shown in FIG. 4A .
  • the rubbing direction is set at 0° azimuth.
  • the absorption axis of the first polarizer plate PL 1 is set at 45° azimuth.
  • the slow axis of the first retardation plate R 1 is set at 0° azimuth (i.e. crossing the absorption axis of the first polarizer plate PL 1 at about 45°).
  • the optical axis of the second retardation plate R 2 in the X-Y plane is set at 45° azimuth (i.e. substantially parallel to the absorption axis of the first polarizer plate PL 1 ).
  • the slow axis of the retardation plate RA is set at 90° azimuth.
  • the absorption axis of the second polarizer plate PL 2 is set at 135° azimuth.
  • the slow axis of the third retardation plate R 3 is set at 90° azimuth (i.e. crossing the absorption axis of the second polarizer plate PL 2 at about 45°)
  • the slow axis of the retardation plate RA is set at 90° azimuth.
  • the optical compensation elements having the function of optically compensating the difference of the polarization state, which varies depending on the influence of optical rotatory power that differs between azimuth directions of light passing through the liquid crystal layer 30 , and also optically compensating the shift of the polarization state of light, which passes through the third retardation plate R 3 , from the azimuth direction of the absorption axis of the second polarizer plate PL 2 .
  • the contrast can be improved, and the viewing angle at which a high contrast is obtained can be increased.
  • the first optical compensation element 40 includes, as shown in FIG. 9A , the second retardation plate R 2 with the biaxial refractive index anisotropy between the first retardation plate R 1 and the first polarizer plate PL 1 .
  • the structure shown in FIG. 9A the second retardation plate R 2 with the biaxial refractive index anisotropy between the first retardation plate R 1 and the first polarizer plate PL 1 .
  • the second retardation plate R 2 of the first optical compensation element 40 has the function of compensating the difference of the polarization state which varies due to the influence of optical rotatory power, depending on the azimuth direction of light passing through the liquid crystal layer 30 , and compensating the shift of the polarization state of the light, which has passed through the third retardation plate R 3 , from the azimuth direction of the absorption axis of the second polarizer plate PL 2 .
  • the second retardation plate R 2 having the Nz coefficient that is set in the range of between 0.4 and 0.6. If the Nz coefficient is less than 0.4 or greater than 0.6, the optical compensation becomes deficient and it is difficult to secure the viewing angle contrast.
  • the structure of the transmissive liquid crystal display device according to the present embodiment is as shown in FIG. 9A .
  • the viewing angle dependency of the contrast ratio in the liquid crystal display device according to the present embodiment was simulated, and it was confirmed, as shown in FIG.
  • the second retardation plate R 2 is disposed between the first polarizer plate PL 1 and the first retardation plate R 1 in the first optical compensation element 40 , and the absorption axis of the first polarizer plate PL 1 and the optical axis of the second retardation plate R 2 substantially agree with each other.
  • the invention is not limited to this example. Specifically, in the liquid crystal display panel 1 , the first optical compensation element 40 and second optical compensation element 50 may substantially be transposed.
  • the second retardation plate R 2 is not disposed in the first optical compensation element 40 , and the second retardation plate R 2 is disposed between the second polarizer plate PL 2 and the third retardation plate R 3 in the second optical compensation element 50 .
  • the optical axis of the second retardation plate R 2 in its X-Y plane is set at 135°.
  • the absorption axis of the second polarizer plate PL 2 substantially agrees with the optical axis of the second retardation plate R 2 .
  • the same advantageous effects as in the above-described second example of structure can be obtained by making use of the second retardation plate R 2 in which the Nz coefficient is set in the range of between 0.4 and 0.6.
  • the second retardation plate R 2 in the case where the second retardation plate R 2 is disposed in the first optical compensation element 40 and the absorption axis of the first polarizer plate PL 1 is substantially perpendicular to the optical axis of the second retardation plate R 2 (e.g. the absorption axis of the first polarizer plate PL 1 is set at 45° azimuth and the optical axis of the second retardation plate R 2 in the X-Y plane is set at 135° azimuth) and in the case where the second retardation plate R 2 is disposed in the second optical compensation element 50 and the absorption axis of the second polarizer plate PL 2 is substantially perpendicular to the optical axis of the second retardation plate R 2 (e.g.
  • the absorption axis of the second polarizer plate PL 2 is set at 135° azimuth and the optical axis of the second retardation plate R 2 in the X-Y plane is set at 45° azimuth), it should suffice to use the second retardation plate R 2 in which the Nz coefficient is set in the range of between 0.4 and 0.6. In each of these cases, the same advantageous effects as in the above-described second example of structure can be obtained.
  • the Nz coefficient of each retardation plate RB was set at 4.8
  • the retardation Re of each retardation plate RB was set at 90 nm
  • the Nz coefficient of the second retardation plate R 2 of the first optical compensation element 40 was set at 0.2
  • the Nz coefficient of the fourth retardation plate R 4 of the second optical compensation element 50 was set at 0.8
  • the first compensation layer CL 1 and second compensation layer CL 2 were composed of the retardation plates RB and the Nz coefficient of the second retardation plate R 2 of the second optical compensation element 50 was set at 0.5, it was confirmed that sufficient viewing angles were obtained.
  • the same advantageous effects can be obtained by setting the optical axis of the first retardation plate R 1 in its X-Y plane at 0° azimuth and by setting the optical axis of the retardation plate RA in its X-Y plane at 90° azimuth.
  • transreflective liquid crystal display device The structure of the transreflective liquid crystal display device is as shown in FIG. 11 .
  • the basic structure of this transreflective liquid crystal display device is the same as that of the transmissive liquid crystal display device shown in FIG. 3 .
  • the structure of transreflective liquid crystal display device differs from that of the transmissive liquid crystal display device in that each of a plurality of display pixels PX, which are arrayed in a matrix, includes a reflective part PR that displays an image by selectively reflecting ambient light, and a transmissive part PT that displays an image by selectively transmitting light from a backlight 60 .
  • each pixel electrode 13 includes a reflective electrode 13 R which is provided in association with the reflective part PR, and a transmissive electrode 13 T which is provided in association with the transmissive part PT. These electrodes 13 R and 13 T are electrically connected to each other, and are controlled by one switching element W.
  • the reflective electrode 13 R is formed of a light-reflective electrically conductive material such as aluminum.
  • the transmissive electrode 13 T is formed of a light-transmissive electrically conductive material such as indium tin oxide (ITO).
  • ITO indium tin oxide
  • liquid crystal molecules 31 are bend-aligned between the array substrate 10 and counter-substrate 20 in a predetermined display state in which a voltage is applied to the liquid crystal layer 30 .
  • first optical compensation element 40 and second optical compensation element 50 according to any one of the first example of structure shown in FIG. 1 , its Modification 1 , the second example of structure shown in FIG. 9A and its Modification 2 shown in FIG. 9B .
  • any one of the structures shown in FIG. 4A to FIG. 40 is applicable to the first optical compensation element 40 and second optical compensation element 50 .
  • the structure of the transreflective liquid crystal display device according to the present embodiment is as shown in FIG. 1 .
  • a first optical compensation element 40 including no second retardation plate and a second optical compensation element 50 including no fourth retardation plate were applied to a transreflective liquid crystal display device, with the other structural aspects being the same as in the present embodiment.
  • the transreflective liquid crystal display device according to the comparative example it is understood that in the transmissive part a contrast ratio of 10:1 or less is obtained in the range of viewing angles of 60° or more, in particular, at 0° azimuth and 180° azimuth.
  • FIG. 12B as regards the transreflective liquid crystal display device according to the present embodiment, it is understood that in the transmissive part a contrast ratio of 10:1 or more is obtained in the range of viewing angles of 80° or more at all azimuth directions of the screen, and sufficient viewing angles are obtained, compared to the comparative example.
  • the transreflective liquid crystal display device according to the comparative example it is understood that in the reflective part a contrast ratio of 10:1 or less is obtained in the range of viewing angles of 40° or more, in particular, at 0° azimuth and 180° azimuth.
  • FIG. 13B as regards the transreflective liquid crystal display device according to the present embodiment, it is understood that in the reflective part a contrast ratio of 10:1 or more is obtained in the range of viewing angles of 80° or more at 90°-720° azimuth and a contrast ratio of 10:1 or more is obtained in the range of viewing angles of 50° or mote at 0°-180° azimuth. It was confirmed that the viewing angle was increased, compared to the comparative example.
  • the structure of the transreflective liquid crystal display device according to the present embodiment is as shown in FIG. 9A .
  • the viewing angle dependency of the contrast ratio in the transreflective liquid crystal display device according to the present embodiment was simulated, and it was confirmed that a contrast ratio of 10:1 or more was obtained in both the transmissive part and reflective part in the range of viewing angles of 60° or more in all azimuth directions of the screen, and a contrast ratio of 10:1 or more was obtained in the transmissive part in the range of viewing angles of 80° or more at azimuth directions except 90° azimuth, and thus the sufficient viewing angles were obtained.
  • each pixel electrode 13 is formed of a light-reflective electrically conductive material such as aluminum.
  • each pixel PX corresponds to a reflective part.
  • an optical compensation element 70 is disposed on only the outer surface of the counter-substrate 20 .
  • the optical compensation element 70 is configured to include a polarizer plate PL, a first retardation plate (1 ⁇ 4 wavelength plate) R 1 which is disposed between the polarizer plate PL and the liquid crystal display panel 1 , a second biaxial retardation plate (1 ⁇ 4 wavelength plate) R 2 which is disposed between the polarizer plate PL and the liquid crystal display panel 1 , and a compensation layer CL which is disposed between the first retardation plate R 1 and the liquid crystal display panel 1 .
  • Any one of the examples of structure shown in FIG. 4A to FIG. 4D is applicable to the optical compensation element 70 .
  • the compensation layer CL in the optical compensation element 70 is composed of the retardation plate RA and retardation plate RC as shown in FIG. 4A .
  • the rubbing direction is set at 0° azimuth.
  • the absorption axis of the polarizer plate PL is set at 135° azimuth.
  • the optical axis of the second retardation plate R 2 in the X-Y plane is set at 45° azimuth (i.e. substantially perpendicular to the absorption axis of the polarizer plate PL).
  • the optical axis of the first retardation plate R 1 in the X-Y plane is set at 90° azimuth, and the optical axis of the retardation plate RA in the X-Y plane is set at 90° azimuth.
  • the optical compensation element having the function of optically compensating the difference of the polarization state, which varies depending on the influence of optical rotatory power that differs between azimuth directions of light passing through the liquid crystal layer 30 , and also optically compensating the shift of the polarization state of light, which passes through the first retardation plate R 1 , from the azimuth direction of the absorption axis of the polarizer plate PL.
  • the contrast can be improved, and the viewing angle at which a high contrast is obtained can be increased.
  • the second retardation plate R 2 with biaxial refractive index anisotropy which is disposed between the first retardation plate R 1 and the polarizer plate PL, compensates the difference of the polarization state which varies due to the influence of optical rotatory power, depending on the azimuth direction of the light that is incident from the observation side and passes through the liquid crystal layer 30 .
  • the second retardation plate R 2 compensates the shift of the polarization state of the light, which is reflected by each pixel electrode 13 and passes through the first retardation plate R 1 , from the azimuth direction of the absorption axis of the polarizer plate PL.
  • the second retardation plate R 2 in the X-Y plane is substantially perpendicular to the absorption axis of the polarizer plate PL
  • the Nz coefficient is set in the range of between 0.15 and 0.3. If the Nz coefficient is less than 0.15 or greater than 0.3, the optical compensation becomes deficient and it is difficult to secure the viewing angle contrast.
  • the structure of the reflective liquid crystal display device according to the present embodiment is as shown in FIG. 14 .
  • an optical compensation element 70 including no second retardation plate was applied to a reflective liquid crystal display device, with the other structural aspects being the same as in the present embodiment.
  • FIG. 16A As regards the reflective liquid crystal display device according to the comparative example, it is understood that a contrast ratio of 10:1 or less is obtained in the range of viewing angles of 50° or more, in particular, at 0° azimuth and 180° azimuth.
  • FIG. 16B as regards the reflective liquid crystal display device according to the present embodiment, it is understood that a contrast ratio of 10:1 or more is obtained in the range of viewing angles of 80° or more at all azimuth directions of the screen, and sufficient viewing angles are obtained, compared to the comparative example.
  • the absorption axis of the polarizer plate PL and the optical axis of the second retardation plate R 2 substantially agree in the optical compensation element 70 .
  • the invention is not limited to this example.
  • the optical axis of the second retardation plate R 2 in the X-Y plane is set at 135°.
  • the absorption axis of the polarizer plate PL and the optical axis of the second retardation plate R 2 substantially agree with each other.
  • the same advantageous effects as in the above-described structure can be obtained by using the second retardation plate R 2 in which the Nz coefficient is set in the range of between 0.7 and 0.9.
  • the present invention is not limited directly to the above-described embodiments.
  • the structural elements can be modified without departing from the spirit of the invention.
  • Various inventions can be made by properly combining the structural elements disclosed in the embodiments. For example, some structural elements may be omitted from all the structural elements disclosed in the embodiments. Furthermore, structural elements in different embodiments may properly be combined.

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KR100886287B1 (ko) 2009-03-04
TW200821691A (en) 2008-05-16

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