JP2011180303A - Liquid crystal display device - Google Patents

Abstract

A liquid crystal display device capable of improving light transmittance is provided.
A liquid crystal display device according to the present invention includes a first circularly polarizing plate 48a, a liquid crystal cell 33 disposed on the light emitting side, and a second circularly polarizing plate 48b disposed on the light emitting side. . The first circularly polarizing plate 48a converts incident light into circularly polarized light. The medium included in the liquid crystal cell 33 exhibits optical isotropy when no voltage is applied, and exhibits optical anisotropy when a voltage is applied. The second circularly polarizing plate 48b converts the circularly polarized light transmitted through the liquid crystal cell 33 into linearly polarized light.
[Selection] Figure 1

Description

  The present invention relates to a liquid crystal display device, and more particularly to a liquid crystal display device using an optically isotropic liquid crystal such as a blue phase liquid crystal.

  In recent years, a liquid crystal display device using an optically isotropic liquid crystal such as a blue phase liquid crystal has been proposed (see Patent Document 1). An optically isotropic liquid crystal is a medium that exhibits optical isotropy when no voltage is applied and exhibits optical anisotropy when a voltage is applied.

JP 2005-202383 A

  Incidentally, an IPS (In-Plane Switching) type electrode structure is adopted in a liquid crystal display device using optical isotropic liquid crystal, but only a region where an electric field is applied in a specific direction within the plane contributes to light transmission. For this reason, the light transmission may not be sufficient.

  The present invention has been made in view of the above circumstances, and a main object of the present invention is to provide a liquid crystal display device capable of improving the light transmittance.

  The above and other objects and novel features of the present invention will be apparent from the description of this specification and the accompanying drawings.

  In order to solve the above problems, a liquid crystal display device according to the present invention includes a first circularly polarizing plate, a first transparent substrate disposed on a light emitting side of the first circularly polarizing plate, and the first transparent plate. A second transparent substrate disposed on the light emitting side of the substrate; a medium held between the first transparent substrate and the second transparent substrate; and disposed on the light emitting side of the second transparent substrate. A second circularly polarizing plate. The first circularly polarizing plate converts incident light into circularly polarized light. The medium exhibits optical isotropy when no voltage is applied, and exhibits optical anisotropy when a voltage is applied. The second circularly polarizing plate converts the circularly polarized light transmitted through the first transparent substrate, the second transparent substrate, and the medium into linearly polarized light.

  1 aspect of this invention, It is provided with the 1st electrode and 2nd electrode which are arrange | positioned at the said medium side of the said 1st transparent substrate or the said 2nd transparent substrate, The said 1st electrode and the said 2nd electrode At least one of the electrodes has a linear portion extending toward the other.

  In addition, the first electrode and the second electrode may be formed in a comb shape, and the linear portions of the first electrode and the linear portions of the second electrode may be alternately arranged.

  In one embodiment of the present invention, the first transparent substrate or the second transparent substrate includes a first electrode, a second electrode, and an insulating film that are disposed on the medium side, and the first electrode includes: An exposed portion is disposed under the insulating film and exposed to the medium side through a through hole formed in the insulating film, and the second electrode is disposed on the insulating film so as to surround the exposed portion. Is done.

  The exposed portion may be formed under the through hole.

  The exposed portion may be filled in the through hole.

  Further, the edge of the second electrode may be formed in a circular shape centering on the exposed portion.

  The second electrode may have a plurality of frame-like portions arranged on the insulating film, and the exposed portion may be located inside each of the frame-like portions.

  Moreover, the said exposed part located inside each said frame-shaped part may extend | stretch linearly.

  Further, a part of the first electrode and a part of the second electrode may overlap with each other through the insulating film.

  In one embodiment of the present invention, the first and second electrodes are provided on the medium side of the first transparent substrate and the second transparent substrate, respectively, and the first electrode and the second electrode are provided. Are separated in the in-plane direction.

  The first electrode is disposed under the insulating film, and has an exposed portion exposed to the medium side through a through hole formed in the insulating film. The second electrode is formed on the insulating film. You may arrange | position so that the said exposed part may be enclosed.

  In addition, the first electrode and the second electrode may be formed in a comb shape, and the linear portions of the first electrode and the linear portions of the second electrode may be alternately arranged.

  The liquid crystal display device of the present invention includes a first polarizing plate, a first retardation plate disposed on the light exit side of the first polarizing plate, and a light exit side of the first retardation plate. First transparent substrate, a second transparent substrate disposed on the light emitting side of the first transparent substrate, and a medium held between the first transparent substrate and the second transparent substrate And a second retardation plate disposed on the light exit side of the second transparent substrate, and a second polarizing plate disposed on the light exit side of the second retardation plate. In the first retardation plate, the angle formed by the absorption axis of the first polarizing plate and the slow axis of the first retardation plate is 45 degrees, and the retardation of birefringent light is ¼. Wavelength. The medium exhibits optical isotropy when no voltage is applied, and exhibits optical anisotropy when a voltage is applied. In the second retardation plate, the phase difference of the birefringent light is ¼ wavelength. In the second polarizing plate, the angle formed by the slow axis of the second retardation plate and the absorption axis of the second polarizing plate is 45 degrees.

  The angle formed by the slow axis of the first retardation plate and the slow axis of the second retardation plate is 90 degrees, and the absorption axis of the first polarizing plate and the second polarization The angle formed by the absorption axis of the plate may be 90 degrees.

  The liquid crystal display device of the present invention includes a circularly polarizing plate that converts incident light into circularly polarized light, a transparent first substrate that transmits the circularly polarized light, and a second substrate that is disposed to face the first substrate. A substrate, and a medium held between the first substrate and the second substrate. The second substrate has a reflection surface that reflects light toward the first substrate. The medium exhibits optical isotropy when no voltage is applied, and exhibits optical anisotropy when a voltage is applied.

  According to the present invention, by providing the circularly polarizing plate, the intensity of transmitted light does not depend on the direction of the electric field, so that the light transmittance can be improved.

1 is a side view schematically illustrating an example of a layer structure of a liquid crystal display device according to a first embodiment of the present invention. It is explanatory drawing showing the example of a relationship between the absorption axis of the polarizing plate in the liquid crystal display device which concerns on 1st Embodiment of this invention, and the slow axis of a phase difference plate. It is a side view which represents schematically the example of a layer structure of the polarizing plate of the liquid crystal display device which concerns on 1st Embodiment of this invention. It is a side view which represents roughly the example of a layer structure of the liquid crystal cell of the liquid crystal display device which concerns on 1st Embodiment of this invention. FIG. 3 is a circuit diagram illustrating an equivalent circuit example of each pixel of the liquid crystal display device according to the first embodiment of the present invention. It is a top view which represents schematically the structural example of one transparent substrate of the liquid crystal display device which concerns on 1st Embodiment of this invention. 1 is a cross-sectional view schematically illustrating a configuration example of a liquid crystal display device according to a first embodiment of the present invention. It is a side view which represents schematically the example of a layer structure of the liquid crystal display device which concerns on a prior art example. It is operation | movement explanatory drawing of a prior art example. It is operation | movement explanatory drawing of this invention. It is a side view which represents schematically the example of a layer structure of the polarizing plate of the liquid crystal display device which concerns on 2nd Embodiment of this invention. It is a side view which represents schematically the example of a layer structure of the polarizing plate of the liquid crystal display device which concerns on 2nd Embodiment of this invention. It is a top view which represents schematically the structural example of one transparent substrate of the liquid crystal display device which concerns on 3rd Embodiment of this invention. It is sectional drawing which represents roughly the structural example of the liquid crystal display device which concerns on 3rd Embodiment of this invention. It is sectional drawing which represents roughly the structural example of the liquid crystal display device which concerns on 3rd Embodiment of this invention. It is a top view which represents roughly the example of terminal arrangement | positioning of the liquid crystal display device which concerns on 4th Embodiment of this invention. It is a top view which represents roughly the example of terminal arrangement | positioning of the liquid crystal display device which concerns on 4th Embodiment of this invention. It is a top view which represents roughly the example of terminal arrangement | positioning of the liquid crystal display device which concerns on 4th Embodiment of this invention. It is a top view which represents roughly the example of terminal arrangement | positioning of the liquid crystal display device which concerns on 4th Embodiment of this invention. It is a top view which represents schematically the structural example of one transparent substrate of the liquid crystal display device which concerns on 4th Embodiment of this invention. It is sectional drawing which represents roughly the structural example of the liquid crystal display device which concerns on 4th Embodiment of this invention. It is a top view which represents roughly the example of terminal arrangement | positioning of the liquid crystal display device which concerns on 5th Embodiment of this invention. It is a top view which represents roughly the example of terminal arrangement | positioning of the liquid crystal display device which concerns on 5th Embodiment of this invention. It is a top view which represents roughly the example of terminal arrangement | positioning of the liquid crystal display device which concerns on 5th Embodiment of this invention. It is a top view which represents roughly the example of terminal arrangement | positioning of the liquid crystal display device which concerns on 5th Embodiment of this invention. It is a top view which represents roughly the example of terminal arrangement | positioning of the liquid crystal display device which concerns on 5th Embodiment of this invention. It is a top view which represents schematically the structural example of one transparent substrate of the liquid crystal display device which concerns on 6th Embodiment of this invention. It is a top view which represents schematically the structural example of the other transparent substrate of the liquid crystal display device which concerns on 6th Embodiment of this invention. It is sectional drawing which represents roughly the structural example of the liquid crystal display device which concerns on 6th Embodiment of this invention. It is a top view which represents schematically the structural example of one transparent substrate of the liquid crystal display device which concerns on 7th Embodiment of this invention. It is a top view which represents schematically the structural example of the other transparent substrate of the liquid crystal display device which concerns on 7th Embodiment of this invention. It is a figure showing the example of application of the liquid crystal display device concerning the embodiment of the present invention. It is a figure showing the example of application of the liquid crystal display device concerning the embodiment of the present invention. It is sectional drawing which represents roughly the structural example of the liquid crystal display device which concerns on the modification of this invention.

  An embodiment of a liquid crystal display device of the present invention will be described with reference to the drawings.

[First Embodiment]
FIG. 1 is a side view schematically showing an example of the layer structure of the liquid crystal display device according to the first embodiment of the present invention. FIG. 2 is an explanatory diagram illustrating an example of the relationship between the absorption axis of the polarizing plate and the slow axis of the retardation plate in the liquid crystal display device. FIG. 3 is a side view schematically showing a layer structure example of a polarizing plate of the liquid crystal display device. FIG. 4 is a side view schematically showing an example of a layer structure of a liquid crystal cell of the liquid crystal display device. FIG. 5 is a circuit diagram illustrating an example of an equivalent circuit of each pixel of the liquid crystal display device. FIG. 6 is a plan view schematically illustrating a configuration example of one transparent substrate of the liquid crystal display device. FIG. 7 is a cross-sectional view schematically showing a configuration example of the liquid crystal display device.

  As shown in FIG. 1, the liquid crystal display device according to the first embodiment of the present invention includes a backlight 34, a first circularly polarizing plate 48a disposed on the light emitting side, and a light emitting side. Liquid crystal cell 33 and a second circularly polarizing plate 48b disposed on the light emitting side thereof. The first circularly polarizing plate 48a includes a first polarizing plate 32a and a first retardation plate 16a disposed on the light emitting side thereof. The second circularly polarizing plate 48b includes a second retardation plate 16b and a second polarizing plate 32b disposed on the light emitting side thereof.

  The backlight 34 includes a light source, a light guide plate, a diffusion plate, a prism sheet, and the like. The backlight 34 may be, for example, a CCFL (cold cathode fluorescent lamp), an LED (light emitting diode), an organic EL, or the like. Note that the backlight 34 is not an essential component of the present invention, and is required only when the liquid crystal cell 33 is used in the transmissive mode, and is not required when used in the reflective mode.

  The arrows in FIG. 2 indicate the absorption axis of the first polarizing plate 32a, the slow axis of the first retardation plate 16a, the slow axis of the second retardation plate 16b, and the absorption axis of the second polarizing plate 32b. Respectively. The angle formed by the absorption axis of the first polarizing plate 32a and the absorption axis of the second polarizing plate 32b is about 90 degrees. The angle formed by the slow axis of the first retardation plate 16a and the slow axis of the second retardation plate 16b is also about 90 degrees. The angle formed by the absorption axis of the first polarizing plate 32a and the slow axis of the first retardation plate 16a is about 45 degrees. The angle formed by the slow axis of the second retardation plate 16b and the absorption axis of the second polarizing plate 32b is also about 45 degrees.

  As shown in FIG. 3, the first polarizing plate 32 a and the second polarizing plate 32 b have a polarizing layer 28 that polarizes light, and a TAC film 29 for protection provided on both surfaces thereof. Yes. The polarizing layer 28 is obtained by stretching polyvinyl alcohol (hereinafter referred to as PVA) on which iodine is adsorbed. The TAC film 29 is made of triacetyl cellulose. In order to achieve normally closed, the first polarizing plate 32a and the second polarizing plate 32b sandwiching the liquid crystal cell 33 are arranged so that their absorption axes are substantially orthogonal to each other.

  The first retardation plate 16a and the second retardation plate 16b shown in FIGS. 1 and 2 are so-called λ / 4 plates in which the phase difference of birefringent light becomes a quarter wavelength. However, since it is difficult to satisfy this condition in the entire wavelength range of incident light, in this case, it is desirable to satisfy this condition, for example, at about 555 nm where the human eye has the highest visibility. That is, it is most desirable that the phase difference between the first retardation plate 16a and the second retardation plate 16b is about 139 nm. A material such as polycarbonate or norbornene resin is used for the first retardation plate 16a and the second retardation plate 16b.

  The first retardation plate 16a is arranged so that its slow axis forms an angle of about 45 degrees with the absorption axis of the first polarizing plate 32a. The set of the first polarizing plate 32 a and the first retardation plate 16 a functions as the first circular polarizing plate 48 a, converts incident light from the backlight 34 into circularly polarized light, and emits it to the liquid crystal cell 33. . On the other hand, the second retardation plate 16b is arranged so that its slow axis forms an angle of about 45 degrees with the absorption axis of the second polarizing plate 32b. The set of the second retardation plate 16b and the second polarizing plate 32b functions as the second circular polarizing plate 48b, converts the circularly polarized light transmitted through the liquid crystal cell 33 into linearly polarized light, and emits it to the outside.

  Note that the first circularly polarizing plate 48a and the second circularly polarizing plate 48b are not limited to the above-described embodiments, and in order to reduce wavelength dependency, a broadband circularly polarizing plate in which a λ / 2 plate and a λ / 4 plate are combined. It may be. An example of a broadband circularly polarizing plate is disclosed in JP-A-10-68816.

  As shown in FIG. 4, the liquid crystal cell 33 is sandwiched between the first transparent substrate 13 disposed on the light incident side, the second transparent substrate 23 disposed on the light emitting side, and these. And a liquid crystal layer 25. In the drawing, for the sake of simplicity, illustration of wirings and the like provided on the first transparent substrate 13 and the second transparent substrate 23 is omitted. In the liquid crystal layer 25, the optically isotropic liquid crystal exhibits optical isotropy when no voltage is applied, and exhibits optical anisotropy when a voltage is applied. Optical anisotropy is anisotropy of refractive index. Examples of the optically isotropic liquid crystal include a blue phase liquid crystal and a medium exhibiting cubic symmetry. A blue phase liquid crystal is a liquid crystal material obtained by polymerizing monomers contained in a nematic liquid crystal composition in a temperature range of a blue phase. As the nematic liquid crystal, an organic compound having a ring structure substituted with a polar group and a long chain structure as used in a general liquid crystal display device is used. As the chiral agent, an organic compound having an asymmetric carbon in the molecule is used. An acrylic monomer or the like is used as the polymerizable monomer, and in the case of photopolymerization, a polymerization initiator such as an acetophenone derivative is used in combination.

  The first transparent substrate 13 and the second transparent substrate 23 are made of a transparent material such as glass or a polymer film. As the polymer film, for example, plastic or polyethersulfone (hereinafter referred to as PES) is desirable. Since plastic and PES transmit air, it is desirable to form a gas barrier on the surface. For example, a silicon nitride film can be applied as the gas barrier.

  As shown in FIG. 5, the liquid crystal display device has a plurality of scanning wirings 10a to 10d and a plurality of signal wirings 11a to 11c, and each region partitioned by these is a pixel. The scanning wirings 10a to 10d and the signal wirings 11a to 11c are orthogonal to each other, and at least one TFT 19 (thin film transistor) is provided at the intersecting portion. The TFT 19 is connected to the pixel electrode 12 through the contact hole 18 as shown in FIG. Further, in order to prevent the image signal held in the pixel from leaking, a storage capacitor 15 may be arranged.

  In this embodiment, active matrix driving in which the TFT 19 is arranged in each pixel is taken as an example, but passive matrix driving may be used. Further, the TFT 19 has an inverted stagger structure, and a semiconductor layer is provided as a channel portion. Further, since light does not pass through the place where the TFT 19 is disposed, a light shielding layer may be provided at that place.

  Further, a signal for controlling the TFT 19 is applied to the scanning wirings 10a to 10d, and a signal for controlling the liquid crystal layer 25 is applied to the signal wirings 11a to 11c. As materials for the scanning wirings 10a to 10d and the signal wirings 11a to 11c, low resistance conductive materials such as chromium, tantalum-molybdenum, tantalum, aluminum, and copper are desirable.

  As shown in FIGS. 6 and 7, the pixel electrode 12, the common electrode 22, the TFT 19, the contact hole 18, the scanning wiring 10, and the signal wiring 11 are arranged in the range of one pixel of the first transparent substrate 13. Yes. On the liquid crystal layer 25 side of the first transparent substrate 13, a first insulating film 14 a and a second insulating film 14 b are laminated, and the signal wiring 11 is disposed therebetween. On the other hand, a light shielding layer 21, a color filter 24, a planarization layer 27, and the like are disposed in the range of one pixel of the second transparent substrate 23. A liquid crystal layer 25 is provided between the first transparent substrate 13 and the second transparent substrate 23.

  The pixel electrode 12 and the common electrode 22 are disposed to apply an electric field to the liquid crystal layer 25. The pixel electrode 12 and the common electrode 22 are formed in a comb shape. The linear portions of the pixel electrode 12 and the linear portions of the common electrode 22 are arranged alternately and in parallel at a predetermined interval. Specifically, the linear portion of the pixel electrode 12 extends from the base portion provided at one end in the longitudinal direction of the pixel toward the other end. On the other hand, the linear portion of the common electrode 22 extends from a base portion provided at the other end in the longitudinal direction of the pixel toward one end.

  The pixel electrode 12 and the common electrode 22 may be transparent or opaque as long as they are low resistance conductive materials. As the pixel electrode 12 and the common electrode 22, for example, indium tin oxide (ITO), zinc oxide (ZnO), chromium, tantalum-molybdenum, tantalum, aluminum, copper, or the like is used. Note that in order to improve the viewing angle, the linear portion of the pixel electrode 12 and the linear portion of the common electrode 22 may be bent within a range of one pixel to achieve multi-domain.

  The first insulating film 14 a and the second insulating film 14 b are arranged to prevent the scanning wiring 10 and the signal wiring 11 from contacting each other. The first insulating film 14a and the second insulating film 14b are not particularly limited as long as they are materials that can be electrically insulated. For example, a silicon oxide film, a silicon nitride film, or the like is used as the first insulating film 14a and the second insulating film 14b.

  The light shielding layer 21 is disposed in order to block light leakage from adjacent pixels. The material used for the light shielding layer 21 can be an opaque material such as metal or resin, and is preferably chromium, tantalum-molybdenum, tantalum, aluminum, copper, or the like.

  The color filter 24 is formed so that any one of red, green, and blue light is transmitted for each pixel, and a red region, a green region, and a blue region are arranged. Examples of such an arrangement include a stripe arrangement and a delta arrangement.

  The flattening layer 27 is provided to flatten the unevenness generated when the color filter 24 is manufactured. As the planarizing layer 27, for example, an acrylic resin is used.

  For comparison with the present embodiment, a liquid crystal display device according to a conventional example will be described with reference to FIGS. 8 and 9A. FIG. 8 is a side view schematically showing an example of a layer structure of a liquid crystal display device according to a conventional example. FIG. 9A is an explanatory diagram of the operation of the conventional example. 9A, the region corresponding to the region B shown in FIG. 6 is enlarged, and the direction of the slow axis of the phase difference generated when an electric field is applied is shown.

  As shown in FIG. 8, in the liquid crystal display device according to the conventional example, the liquid crystal cell 33 is sandwiched between the first polarizing plate 32a and the second polarizing plate 32b. The first polarizing plate 32a and the second polarizing plate 32b are arranged so that their absorption axes are orthogonal to each other. The in-plane electric field applied to the liquid crystal layer of the liquid crystal cell 33 mainly forms an angle of about 45 degrees with respect to the absorption axes of the first polarizing plate 32a and the second polarizing plate 32b. ing.

  Specifically, as shown in FIG. 9A, there is a parallel direction between the linear portions of the pixel electrodes 12 and the linear portions of the common electrode 22 that are parallel to each other (that is, the extending direction of the linear portions). An electric field is generated along the direction orthogonal to each other, and the direction of the electric field forms an angle of about 45 degrees with respect to the respective absorption axes of the first polarizing plate 32a and the second polarizing plate 32b. The direction of the slow axis of the phase difference appears along the direction of this electric field. For this reason, a region between the linear portion of the pixel electrode 12 and the linear portion of the common electrode 22 is a transmission region T in which the transmission of light can be controlled.

  On the other hand, in the vicinity of the tips of the linear portions of the pixel electrode 12 and the common electrode 22, the direction of the electric field is directed in various directions, so that the slow axis direction of the phase difference is the first polarizing plate 32a and the first polarizing plate 32a. It deviates from 45 degrees with respect to each absorption axis of the second polarizing plate 32b. For this reason, the area | region near the front-end | tip of the linear part of the pixel electrode 12 or the common electrode 22 turns into the non-transmissive area | region N in which light transmission is not enough.

  According to the present embodiment shown in FIG. 9B, the region that was the non-transparent region N in the conventional example shown in FIG. 9A can be changed to the transmissive region T. The reason will be described below.

First, when light passes through a uniaxial medium having uniaxial optical anisotropy sandwiched between orthogonal polarizing plates as in the conventional example, the intensity I of the transmitted light is expressed by the following Equation 1. It is well known.

Here, I ₀ is the intensity of incident light, θ is the angle formed by the absorption axis of the polarizing plate and the slow axis of the uniaxial medium, Δn is the refractive index difference between the slow axis and the fast axis of the uniaxial medium, d represents the thickness of the uniaxial medium, and λ represents the wavelength of incident light.

  As can be seen from Equation 1, the transmittance is highest when the angle formed by the absorption axis of the polarizing plate and the slow axis of the uniaxial medium is 45 degrees, and the transmittance is highest when the angle is 0 degrees or 90 degrees. Lower. Here, the uniaxial medium can be assumed to be the liquid crystal layer 25.

Next, when light is transmitted through a uniaxial medium sandwiched between orthogonal circularly polarizing plates as in the present embodiment, the intensity of the transmitted light is expressed by Equation 2 below.

  As can be seen from Equation 2, there is no term in the slow axis direction of the uniaxial medium, and only the phase difference has an effect. That is, when the liquid crystal layer 25 as in the present embodiment is used, the transmitted light intensity is almost zero because the phase difference when no electric field is applied is zero (Δnd = 0). On the other hand, when an electric field is applied, a phase difference is generated in the in-plane direction. At this time, phase differences occur in various directions in the entire pixel, but in this embodiment, light can be transmitted regardless of which direction the phase difference occurs. As can be seen from Equation 2, the transmitted light intensity is low when Δnd = mλ (m is an integer).

  That is, in the conventional example, as shown in FIG. 9A, the direction of the slow axis of the phase difference is in various directions near the tips of the linear portions of the pixel electrode 12 and the common electrode 22. In this case, the direction of the slow axis of the phase difference deviates from 45 degrees with respect to the absorption axis of the polarizing plate. It becomes the transmissive region N.

  On the other hand, in this embodiment, as can be seen from Equation 2, light is transmitted regardless of the direction in which the slow axis of the phase difference occurs. Therefore, in the present embodiment, the region that was the non-transmissive region N in the conventional example can be used as the transmissive region T, and the light transmittance can be improved.

  In this embodiment, both the pixel electrode 12 and the common electrode 22 are comb-teeth. However, the present invention is not limited to this, and K. Ono, I. Mori, R. Oke and K. Endo, Proc. IDW07 67 (2007). One may be a solid electrode and the other may be a comb-like electrode.

[Second Embodiment]
10A and 10B are side views schematically showing a layer structure example of a polarizing plate of a liquid crystal display device according to the second embodiment of the present invention. About the structure which overlaps with the said embodiment, detailed description is abbreviate | omitted by attaching | subjecting the same number.

  Incidentally, improving the transmittance with a circularly polarizing plate in a vertical alignment type liquid crystal display device is described in JP-A-2002-40428. In such a vertical alignment type liquid crystal display device, a negative C plate is generally used to improve the viewing angle. The negative C plate is used to compensate the initial alignment of the vertical alignment method, that is, the vertical alignment state. Here, the TAC film normally included in the polarizing plate behaves as a negative C plate, and thus is an indispensable member for the polarizing plate in the vertical alignment type liquid crystal display device.

  On the other hand, since the liquid crystal display device according to the present embodiment uses an optical isotropic liquid crystal, the initial alignment exhibits optical isotropic properties. That is, since the negative C plate is unnecessary, the TAC film 29 of the first polarizing plate 32a and the second polarizing plate 32b shown in FIG. 3 is not particularly necessary. Therefore, in the liquid crystal display device according to the present embodiment, as shown in FIG. 10A, among the first polarizing plate 32 a and the second polarizing plate 32 b, the first transparent substrate 13 and the second transparent substrate 23 side. The TAC film 29 is omitted. That is, the first polarizing plate 32a and the second polarizing plate 32b include the polarizing layer 28 and the TAC film 29 provided on one surface of the polarizing layer 28, and the other surface of the polarizing layer 28 is the first surface. The transparent substrate 13 or the second transparent substrate 23 is attached. For example, an adhesive is used for attachment. With such a configuration, it is possible to reduce the thickness of the liquid crystal display device. Note that the TAC film 29 may be omitted with only one of the first polarizing plate 32a and the second polarizing plate 32b.

The TAC film 29 is known to have an Rth of about 30 to 80 nm. Rth is retardation in the layer thickness direction, and is defined by the following mathematical formula 3. Here, nx, ny, and nz are the refractive indexes in the principal axis direction of the refractive index ellipsoid, nx and ny are the refractive indexes in the in-plane direction, and nz is the refractive index in the thickness direction. D is the thickness of the retardation plate (here, the TAC film 29). Since the TAC film 29 has a different thickness depending on the application, Rth is also different.

  Further, as shown in FIG. 10B, a retardation-less protective film 17 having a smaller phase difference than the TAC film 29 may be used. In this case, since an unnecessary phase difference is reduced, the contrast is improved and the viewing angle is also improved. As the retardation-less protective film 17, for example, a norbornene-based material or a methacrylic resin can be used. The retardation-less protective film 17 may be disposed as an alternative to the TAC film 29 disposed on the first transparent substrate 13 or the second transparent substrate 23 side. The retardation-less protective film 17 has Rth in the in-plane direction of substantially zero, but actually has a Rth of ± 5 nm or less due to a phase difference caused by a production process or the like. However, the Rth in the in-plane direction of the retardation-less protective film 17 is overwhelmingly smaller than the TAC film 29 and can be made thinner than the TAC film 29. With such a configuration, it is possible to reduce the thickness of the liquid crystal display device.

[Third Embodiment]
11 and 12 are a plan view and a cross-sectional view schematically showing a configuration example of one transparent substrate of the liquid crystal display device according to the third embodiment of the present invention. About the structure which overlaps with the said embodiment, detailed description is abbreviate | omitted by attaching | subjecting the same number.

  Since the blue phase liquid crystal generates a phase difference corresponding to the electric field direction, it is general to use a comb-like electrode capable of applying an electric field in the plane. An electric field is generated in a uniform direction between the linear part of one electrode and the linear part of the other electrode, and the polarizing plate is formed so that the absorption axis forms an angle of about 45 degrees with respect to that direction Is placed. However, the direction of the electric field and the direction of the absorption axis of the polarizing plate may not make 45 degrees near the tip of the linear portion of the comb-like electrode. This is as described above.

  As shown in FIG. 11, in the present embodiment, the pixel electrode 12 has an exposed portion exposed in a dot shape, and the common electrode 22 is disposed so as to surround the exposed portion. The exposed part of the pixel electrode 12 may be circular or polygonal. The size of the exposed portion of the pixel electrode 12 is preferably as small as possible in order to increase the aperture ratio, and is preferably 15 μm or less, for example. For example, in a liquid crystal display device equivalent to a VGA having a size of about 3 inches diagonally mounted on a mobile phone, the size of one pixel in the short side direction is about 30 μm. In order to arrange a plurality of exposed portions of the pixel electrode 12 in the pixel in order to increase the transmittance, the size of the exposed portion of the pixel electrode 12 is desirably 15 μm or less, for example. The distance from the exposed portion of the pixel electrode 12 to the edge of the common electrode 22 is desirably equal at any position in order to make the in-plane luminance distribution uniform. Therefore, the edge of the common electrode 22 is preferably circular with the exposed portion of the pixel electrode 12 as the center. With this configuration, the electric field is generated radially from the exposed portion of the pixel electrode 12, and the slow axis of the phase difference is also generated radially. In the present embodiment, since the first circularly polarizing plate 48a and the second circularly polarizing plate 48b are used, light is transmitted even if the slow axis of the phase difference is generated radially. By arranging the pixel electrode 12 and the common electrode 22 in this way, it is possible to improve the aperture ratio and improve the transmittance as compared with the case of a comb-like electrode.

  As shown in FIG. 12, a second insulating film 14 b is disposed between the pixel electrode 12 and the common electrode 22. The pixel electrode 12 is formed under the second insulating film 14b, and the common electrode 22 is formed over the second insulating film 14b. A through hole penetrating in the film thickness direction is formed in the second insulating film 14b, and an exposed portion of the pixel electrode 12 is exposed under the through hole. That is, the surface of the film-like pixel electrode 12 formed under the second insulating film 14b is an exposed portion. The common electrode 22 is disposed on the second insulating film 14 b so as to surround the exposed portion of the pixel electrode 12. In such an arrangement, a part of the pixel electrode 12 and a part of the common electrode 22 are overlapped via the second insulating film 14b. Note that the common electrode 22 may not be completely closed around the exposed portion of the pixel electrode 12, and may be disposed at least at a part of the periphery of the exposed portion of the pixel electrode 12. With such a configuration, an electric field is generated radially from the exposed portion of the pixel electrode 12 below the second insulating film 14b to the common electrode 22 on the second insulating film 14b.

  Alternatively, as shown in FIG. 13, the through-hole formed in the second insulating film 14 b is filled with a conductive material, and the exposed portion of the pixel electrode 12 is provided at the same height as the common electrode 22. Also good.

  With the configuration as described above, it is possible to improve the transmittance and reduce the driving voltage as compared with the related art. In this embodiment, the pixel electrode 12 is disposed below the second insulating film 14b and the common electrode 22 is disposed on the second insulating film 14b. However, the pixel electrode 12, the common electrode 22, It is possible to obtain the same effect even if they are replaced.

[Fourth Embodiment]
14A to 14D are plan views schematically showing an example of terminal arrangement of the liquid crystal display device according to the fourth embodiment of the present invention. 15 and 16 are a plan view and a cross-sectional view schematically showing a configuration example of one transparent substrate of the liquid crystal display device. About the structure which overlaps with the said embodiment, detailed description is abbreviate | omitted by attaching | subjecting the same number.

  The relationship between the first electrode 30 and the second electrode 31 in FIGS. 14A to 14D corresponds to the relationship between the pixel electrode 12 and the common electrode 22 in the third embodiment. That is, if the first electrode 30 is the pixel electrode 12, the second electrode 31 is the common electrode 22, and if the first electrode 30 is the common electrode 22, the second electrode 31 is the pixel electrode 12. The exposed portion of the first electrode 30 is formed in a dot shape. The exposed portion of the first electrode 30 may be circular or polygonal as long as it is sufficiently smaller than the second electrode 31. On the other hand, each of the second electrodes 31 has a polygonal or circular frame shape. In the polygon, the larger the number of corners, the more preferable the distance between the first electrode 30 and the second electrode 31 approaches. In order to arrange the second electrode 31 on the second insulating film 14b, it is desirable that the second electrode 31 is a triangle, a rectangle, or a hexagon as shown in FIGS. 14A to 14C. In particular, considering the maximum packing density, the second electrode 31 is preferably hexagonal as shown in FIG. 14C.

  The first electrode 30 and the second electrode 31 are arranged to apply an electric field to the liquid crystal layer 25. The first electrode 30 and the second electrode 31 may be transparent or opaque as long as they are low-resistance conductive materials. As the first electrode 30 and the second electrode 31, for example, indium tin oxide (ITO), zinc oxide (ZnO), chromium, tantalum-molybdenum, tantalum, aluminum, copper, or the like is used.

  15 and 16, the pixel electrode 12 corresponds to the first electrode 30, the common electrode 22 corresponds to the second electrode 31, and the common electrode 22 has a hexagonal frame shape. As shown in FIG. 15, the pixel electrode 12 is arranged in a range indicated by a broken line below the second insulating film 14b, and a plurality of exposures are made by through holes formed in the second insulating film 14b. The part is exposed to the liquid crystal layer 25 side. The common electrode 22 is connected to the common electrode 22 of the adjacent pixel. With such a configuration, an electric field in the in-plane direction can be generated in most regions in the pixel. Although the slow axis of the phase difference generated in the liquid crystal layer 25 is radial, since the first circularly polarizing plate 48a and the second circularly polarizing plate 48b are used, light is emitted even if the phase difference is generated radially. Is transparent. In addition, since the phase difference occurs radially, the viewing angle characteristics are the same from any direction, and the image quality is improved. With the configuration as described above, it is possible to improve the transmittance, improve the viewing angle, and reduce the driving voltage as compared with the conventional case.

[Fifth Embodiment]
17A to 17E are plan views schematically showing an example of terminal arrangement of the liquid crystal display device according to the fifth embodiment of the present invention. About the structure which overlaps with the said embodiment, detailed description is abbreviate | omitted by attaching | subjecting the same number.

  As shown in FIGS. 17A to 17E, in the present embodiment, the exposed portion of the first electrode 30 extends linearly. The second electrode 31 has a polygonal or circular frame shape as in the fourth embodiment. Also in this embodiment, one of the first electrode 30 and the second electrode 31 corresponds to the pixel electrode 12, and the other corresponds to the common electrode 22. Specifically, the exposed portions of the first electrodes 30 located inside the adjacent second electrodes 31 are arranged so as to be aligned on the same line. In addition, between the 1st electrodes 30 arranged in this way, the 1st electrode 30 and the 2nd electrode 31 have overlapped via the 2nd insulating film 14b. Such an electrode structure can be easily produced, and the cost can be reduced. Further, since the number of types of electrode structures increases, various selections can be made so that the effective aperture ratio is maximized depending on the size of the pixel. With the configuration as described above, it is possible to improve the transmittance, improve the viewing angle, and reduce the driving voltage as compared with the conventional case.

[Sixth Embodiment]
FIG. 18A is a plan view schematically illustrating a configuration example of one transparent substrate of the liquid crystal display device according to the sixth embodiment of the present invention. FIG. 18B is a plan view schematically illustrating a configuration example of the other transparent substrate of the liquid crystal display device. FIG. 19 is a cross-sectional view schematically showing a configuration example of the liquid crystal display device. About the structure which overlaps with the said embodiment, detailed description is abbreviate | omitted by attaching | subjecting the same number.

  In the present embodiment, the pixel electrode 12 is provided on the first transparent substrate 13 side, and the common electrode 22 is provided on the second transparent substrate 23 side. Similar to the third embodiment, the pixel electrode 12 is formed under the second insulating film 14b and has an exposed portion exposed through a through hole formed in the second insulating film 14b. The common electrode 22 is formed in a hexagonal frame shape as in the fourth embodiment except that the common electrode 22 is provided on the second transparent substrate 23 side. Each exposed portion of the pixel electrode 12 is provided so as to be located inside each frame portion of the common electrode 22 in plan view. That is, the common electrode 22 is separated from the exposed portion of the pixel electrode 12 by a predetermined distance in the in-plane direction, and is disposed so as to surround the exposed portion. Each common electrode 22 is connected to a common electrode 22 of an adjacent pixel, and the common electrode 22 has the same potential throughout the panel. In this case, manufacturing is facilitated by providing the common electrode 22 on the second transparent substrate 23 side. With the configuration as described above, it is possible to improve the transmittance, improve the viewing angle, reduce the driving voltage, and simplify the manufacturing as compared with the related art.

[Seventh Embodiment]
FIG. 20A is a plan view schematically illustrating a configuration example of one transparent substrate of the liquid crystal display device according to the seventh embodiment of the present invention. FIG. 20B is a plan view schematically illustrating a configuration example of the other transparent substrate of the liquid crystal display device. About the structure which overlaps with the said embodiment, detailed description is abbreviate | omitted by attaching | subjecting the same number.

  Also in this embodiment, the pixel electrode 12 is provided on the first transparent substrate 13 side, and the common electrode 22 is provided on the second transparent substrate 23 side. The pixel electrode 12 and the common electrode 22 are formed in a comb-like shape as in the first embodiment. Each of the pixel electrode 12 and the common electrode 22 has a linear portion extending in the longitudinal direction of the pixel, and in a plan view, the linear portion of the pixel electrode 12 and the linear portion of the common electrode 22 are in the width direction of the pixel. Are arranged alternately. The pixel electrode 12 and the common electrode 22 arranged in this manner generate an oblique electric field in the liquid crystal layer 25, and a phase difference is generated in that direction, so that light is transmitted. With the configuration as described above, it is possible to improve the transmittance, improve the viewing angle, reduce the driving voltage, and simplify the manufacturing as compared with the related art.

  The liquid crystal display devices according to the first to seventh embodiments described above can be applied to, for example, the display unit of the mobile phone shown in FIG. 21A or the display unit of the television shown in FIG. 21B. .

  Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications can be made by those skilled in the art.

  For example, although the transmissive mode liquid crystal cell 33 has been described as an example in the above embodiment, the present invention is not limited to this, and a reflective mode liquid crystal cell can also be applied. That is, as shown in FIG. 22, instead of the first transparent substrate 13 (see FIG. 12), a first substrate 53 having a reflective surface on the liquid crystal layer 25 side may be arranged so that the reflection mode is set. Good.

  In the above embodiment, the first polarizing plate 32a and the second polarizing plate 32b are arranged so that the absorption axes are orthogonal to each other, and light is transmitted when a voltage is applied to the liquid crystal layer 25. However, it is not necessarily limited to this mode. For example, the first polarizing plate 32a and the second polarizing plate 32b may be arranged so that the absorption axes thereof are parallel, or the light is shielded when a voltage is applied to the liquid crystal layer 25. May be.

  DESCRIPTION OF SYMBOLS 10 Scan wiring, 11 Signal wiring, 12 Pixel electrode, 13 1st transparent substrate, 14 Insulating film, 15 Storage capacity, 16a 1st phase difference plate, 16b 2nd phase difference plate, 17 Phase difference less protective film, 18 contact hole, 19 TFT, 20 semiconductor layer, 21 light shielding layer, 22 common electrode, 23 second transparent substrate, 24 color filter, 25 liquid crystal layer, 27 flattening layer, 28 polarizing layer, 29 TAC film, 30 first Electrode, 31 second electrode, 32a first polarizing plate, 32b second polarizing plate, 33 liquid crystal cell, 34 backlight, 48a first circular polarizing plate, 48b second circular polarizing plate, 53 first Board.

Claims (16)

A first circularly polarizing plate that converts incident light into circularly polarized light;
A first transparent substrate disposed on the light exit side of the first circularly polarizing plate;
A second transparent substrate disposed on the light exit side of the first transparent substrate;
A medium that is held between the first transparent substrate and the second transparent substrate, exhibits optical isotropy when no voltage is applied, and exhibits optical anisotropy when a voltage is applied;
A second circularly polarizing plate disposed on the light emitting side of the second transparent substrate and converting the circularly polarized light transmitted through the first transparent substrate, the second transparent substrate and the medium into linearly polarized light;
A liquid crystal display device comprising: A first electrode and a second electrode disposed on the medium side of the first transparent substrate or the second transparent substrate;
At least one of the first electrode and the second electrode has a linear portion extending toward the other,
The liquid crystal display device according to claim 1. The first electrode and the second electrode are formed in a comb-teeth shape, and the linear portions of the first electrode and the linear portions of the second electrode are alternately arranged.
The liquid crystal display device according to claim 2. A first electrode disposed on the medium side of the first transparent substrate or the second transparent substrate, a second electrode, and an insulating film;
The first electrode is disposed under the insulating film, and has an exposed portion exposed to the medium side by a through hole formed in the insulating film.
The second electrode is disposed on the insulating film so as to surround the exposed portion.
The liquid crystal display device according to claim 1. The exposed portion is formed under the through hole,
The liquid crystal display device according to claim 4. The exposed portion is filled in the through hole,
The liquid crystal display device according to claim 4. An edge of the second electrode is formed in a circular shape centering on the exposed portion;
The liquid crystal display device according to claim 4. The second electrode has a plurality of frame-like portions arranged on the insulating film, and the exposed portion is located inside each frame-like portion.
The liquid crystal display device according to claim 4. The exposed portion located inside each of the frame-shaped portions extends linearly;
The liquid crystal display device according to claim 8. A part of the first electrode and a part of the second electrode overlap with each other through the insulating film;
The liquid crystal display device according to claim 4. A first electrode and a second electrode respectively disposed on the medium side of the first transparent substrate and the second transparent substrate;
The first electrode and the second electrode are separated in an in-plane direction;
The liquid crystal display device according to claim 1. The first electrode is disposed under the insulating film, and has an exposed portion exposed to the medium side by a through hole formed in the insulating film.
The second electrode is disposed on the insulating film so as to surround the exposed portion.
The liquid crystal display device according to claim 11. The first electrode and the second electrode are formed in a comb-teeth shape, and the linear portions of the first electrode and the linear portions of the second electrode are alternately arranged.
The liquid crystal display device according to claim 11. A first polarizing plate;
An angle formed between an absorption axis of the first polarizing plate and a slow axis of the first retardation plate, which is a first retardation plate disposed on the light exit side of the first polarizing plate. A first retardation plate that is 45 degrees and the phase difference of the birefringent light is ¼ wavelength;
A first transparent substrate disposed on the light exit side of the first retardation plate;
A second transparent substrate disposed on the light exit side of the first transparent substrate;
A medium that is held between the first transparent substrate and the second transparent substrate, exhibits optical isotropy when no voltage is applied, and exhibits optical anisotropy when a voltage is applied;
A second retardation plate disposed on the light exit side of the second transparent substrate, wherein the phase difference of the birefringent light is a quarter wavelength;
An angle formed between the slow axis of the second retardation plate and the absorption axis of the second polarizing plate is a second polarizing plate disposed on the light exit side of the second retardation plate. A second polarizing plate at 45 degrees;
A liquid crystal display device comprising: The angle formed by the slow axis of the first retardation plate and the slow axis of the second retardation plate is 90 degrees,
An angle formed by an absorption axis of the first polarizing plate and an absorption axis of the second polarizing plate is 90 degrees. A circularly polarizing plate that converts incident light into circularly polarized light;
A transparent first substrate through which the circularly polarized light is transmitted;
A second substrate disposed opposite to the first substrate and having a reflective surface that reflects light toward the first substrate;
A medium held between the first substrate and the second substrate, exhibiting optical isotropy when no voltage is applied, and exhibiting optical anisotropy when a voltage is applied;
A liquid crystal display device comprising:

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