JP2005128505A - Liquid crystal display apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid crystal display apparatus which can sufficiently stabilize alignment of a liquid crystal and has display quality equal to or superior to a conventional one by a relatively simple configuration having an alignment controlling structure of radially inclined alignment disposed only on one substrate, in a liquid crystal display apparatus having a plurality of radially inclined alignment domains in pixels. <P>SOLUTION: The display apparatus is equipped with: a first substrate; a second substrate disposed opposing to the first substrate; a vertical alignment liquid crystal layer disposed between the first substrate and the second substrate; a plurality of pixels each having a first electrode formed on the first substrate, a second electrode formed on the second substrate and the liquid crystal layer between the first and second electrodes; and a wall structure regularly arranged in the liquid crystal layer side of the first electrode. When at least a prescribed voltage is applied, at least one liquid crystal domain showing a radially inclined alignment state in an area substantially surrounded by the wall structure is formed in the liquid crystal layer. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a liquid crystal display device, and more particularly, to a liquid crystal display device suitably used for a personal digital assistant (for example, PDA), a mobile phone, an in-vehicle liquid crystal display, a digital camera, a personal computer, an amusement device, a television, and the like.

  In recent years, liquid crystal display devices have been widely used for information devices such as notebook personal computers, mobile phones, electronic notebooks, or camera-integrated VTRs equipped with a liquid crystal monitor, taking advantage of their thinness and low power consumption. ing.

  As a display mode capable of realizing a high contrast and a wide viewing angle, a vertical alignment mode using a vertical alignment type liquid crystal layer has attracted attention. The vertical alignment type liquid crystal layer is generally formed using a vertical alignment film and a liquid crystal material having negative dielectric anisotropy.

  For example, Patent Document 1 discloses that an oblique electric field is generated around an opening provided in a counter electrode facing a pixel electrode via a liquid crystal layer, and liquid crystal around the liquid crystal molecules in a vertically aligned state in the opening. A liquid crystal display device in which viewing angle characteristics are improved by tilting molecules is disclosed.

  However, in the configuration described in Patent Document 1, it is difficult to form an oblique electric field in the entire region in the pixel. As a result, a region in which the response of the liquid crystal molecules to the voltage is delayed occurs in the pixel, and an afterimage phenomenon occurs. The problem of appearing arises.

  In order to solve this problem, Patent Document 2 discloses a liquid crystal display device having a plurality of liquid crystal domains exhibiting a radially inclined alignment in a pixel by providing openings regularly arranged in the pixel electrode or the counter electrode. doing.

  Furthermore, Patent Document 3 discloses a technique for stabilizing the alignment state of a liquid crystal domain having a radially inclined alignment that appears around a convex portion by providing a plurality of convex portions regularly in a pixel. Further, this document discloses that the display characteristics can be improved by regulating the alignment of liquid crystal molecules using an oblique electric field by an opening provided in the electrode, together with the alignment regulating force by the convex part.

  On the other hand, in recent years, liquid crystal display devices capable of high-quality display both outdoors and indoors have been proposed (for example, Patent Document 4 and Patent Document 5). This liquid crystal display device is referred to as a transflective liquid crystal display device, and has a reflective region in a pixel for displaying in a reflective mode and a transmissive region for displaying in a transmissive mode.

  The transflective liquid crystal display devices currently on the market use the ECB mode, the TN mode, and the like. However, in Patent Document 3, the vertical alignment mode is not limited to the transmissive liquid crystal display device but also the transflective liquid crystal. A configuration applied to a display device is also disclosed. Further, in Patent Document 6, in a semi-transmissive liquid crystal display device having a vertical alignment type liquid crystal layer, an insulating layer provided to make the thickness of the liquid crystal layer in the transmissive region twice the thickness of the liquid crystal layer in the reflective region. A technique for controlling the alignment (multiaxial alignment) of liquid crystals by the formed recesses is disclosed. A configuration is disclosed in which the recess is formed in, for example, a regular octagon, and a projection (projection) or a slit (electrode opening) is formed at a position facing the recess via the liquid crystal layer (for example, FIG. 4 and FIG. 16).

Patent Documents 3 and 7 describe a technique for realizing radial alignment of liquid crystal molecules in a liquid crystal domain by forming convex portions on a substrate. It is described that the radial tilt alignment is stabilized by the effect of the alignment regulating structure provided on one substrate and the convex portion on the liquid crystal layer side provided on the other substrate in the voltage application state. .
JP-A-6-301036 JP 2000-47217 A JP 2003-167253 A Japanese Patent No. 2955277 US Pat. No. 6,195,140 JP 2002-350853 A JP 2003-315803 A

  In the technique disclosed in Patent Document 2 or Patent Document 3, a plurality of liquid crystal domains are formed by providing convex portions or openings in a pixel (that is, divided into pixels), and the alignment regulation force on liquid crystal molecules is strengthened. However, according to the study of the present inventors, in order to obtain a sufficient alignment regulating force, alignment control structures such as protrusions and openings are formed on both sides of the liquid crystal layer (the liquid crystal layer side of a pair of substrates facing each other). There is a problem that the manufacturing process becomes complicated. In addition, when the alignment regulating structure is provided in the pixel, the effective aperture ratio of the pixel may be decreased, or the contrast ratio may be decreased due to light leakage from the periphery of the convex portion in the pixel. In the case where the alignment regulating structure is provided on both the substrates, since it is affected by the alignment margin of the substrates, the effective aperture ratio and / or the contrast ratio are further reduced.

  Further, in the technique disclosed in Patent Document 6, it is necessary to arrange a convex part or an electrode opening on the side opposite to the concave part provided in order to control the multiaxial orientation. Occur.

  Furthermore, in the techniques described in Patent Documents 2, 3, 6, and 7, even if the alignment control structures are provided on both substrates, the response speed in halftone display is slow and / or the panel surface is pressed. There is a problem that it takes time until an afterimage generated at the time of disappearance, and it is particularly difficult to use as a liquid crystal display device for mobile use.

  The present invention has been made in view of the above points, and an object of the present invention is to provide an alignment control structure for a radial tilt alignment only on one substrate in a liquid crystal display device having a plurality of radial tilt alignment domains in a pixel. An object of the present invention is to provide a liquid crystal display device that can sufficiently stabilize the alignment of the liquid crystal with a relatively simple structure provided and can obtain a display quality equal to or higher than that of the conventional one.

  Another object of the present invention is to further stabilize the orientation of the liquid crystal and shorten the response time in halftone display compared to a conventional liquid crystal display device, or until the afterimage generated when the panel surface is pressed disappears. It is to provide a liquid crystal display device with a short time.

The liquid crystal display device of the present invention includes a first substrate, a second substrate provided so as to face the first substrate, and a vertical alignment type provided between the first substrate and the second substrate. A liquid crystal layer,
Each of the first electrode formed on the first substrate, the second electrode formed on the second substrate, the liquid crystal layer provided between the first electrode and the second electrode, A wall structure regularly arranged on the liquid crystal layer side of the first electrode, and the liquid crystal layer is formed by the wall structure when at least a predetermined voltage is applied. It is characterized in that at least one liquid crystal domain having a radially inclined alignment state is formed in a substantially enclosed region.

  In one embodiment, the first electrode has a plurality of openings or notches formed at predetermined positions, and the wall structure is a first formed in the plurality of openings or notches. Including wall part.

  In one embodiment, each of the plurality of openings or notches includes a rectangular portion, and the wall structure includes the first wall portion provided in parallel to the rectangular portion.

  In one embodiment, each of the plurality of openings or notches includes a rectangular portion, and the wall structure includes a second wall portion extending from the first wall portion.

  In one embodiment, the width WW of the first wall portion has a relationship of 0.4 EW <WW <0.8 EW with respect to the width EW of the opening or notch in which the first wall portion is provided. Satisfied.

  In one embodiment, the first electrode includes a transparent electrode defining a transmissive region, and a width EW of the plurality of openings or notches is 1 with respect to a thickness dt of the liquid crystal layer in the transmissive region. The relationship of .8dt <EW <2.5dt is satisfied.

  In one embodiment, the wall structure includes a third wall portion provided in a region surrounding the first electrode.

  In one embodiment, a dielectric structure is further provided on the liquid crystal layer side of the second substrate.

  In one embodiment, the dielectric structure is disposed approximately at the center of the at least one liquid crystal domain.

  In one embodiment, the dielectric structure is disposed substantially at the center in a region substantially surrounded by the wall structure.

  In one embodiment, the area of the region substantially surrounded by the wall structure is Sd, the area of the bottom surface of the dielectric structure disposed substantially at the center of the region is Sb, and Sa = ( When Sb / Sd) × 100, the relationship 2 ≦ Sa ≦ 25 is satisfied.

  In one embodiment, at least a part of the wall structure and the dielectric structure is disposed in a light shielding region.

  In one embodiment, the liquid crystal layer has a plurality of regions having different thicknesses.

  In one embodiment, the first electrode includes a transparent electrode defining a transmissive region and a reflective electrode defining a reflective region, and the thickness dt of the liquid crystal layer in the transmissive region is the liquid crystal in the reflective region. Greater than layer thickness dr.

  In one embodiment, the opening or notch includes an opening or notch provided between the transmission region and the reflection region.

  In one embodiment, the height WH of the wall structure satisfies a relationship of 0.25 dt <WH <0.4 dt with respect to the thickness dt of the liquid crystal layer in the transmissive region.

  In one embodiment, at least one of the first substrate and the second substrate has a support that defines a thickness of the liquid crystal layer.

  In one embodiment, the first substrate further includes an active element provided corresponding to each of the plurality of pixels, and the first electrode is provided for each of the plurality of pixels. It is a connected pixel electrode.

  In one embodiment, the first substrate and / or the second substrate and the pair of polarizing plates have a pair of polarizing plates disposed so as to face each other with the first substrate and the second substrate interposed therebetween. And at least one biaxial optically anisotropic medium layer.

  In one embodiment, the liquid crystal display device further includes a pair of polarizing plates disposed so as to face each other with the first substrate and the second substrate interposed therebetween, and the first substrate and / or the second substrate and the pair of polarizations It further has at least one uniaxial optically anisotropic medium layer between the plates.

  In the liquid crystal display device of the present invention, a wall structure is provided on the liquid crystal layer side of the first substrate on which the first electrode (for example, a pixel electrode) is formed. (Alignment regulating force) defines the direction in which the liquid crystal molecules of the vertical alignment type liquid crystal layer are inclined by the electric field. As a result, when at least a predetermined voltage (a voltage equal to or higher than a threshold value) is applied, a liquid crystal domain having a radially inclined alignment is stably formed in a region substantially surrounded by the wall structure. Accordingly, the liquid crystal layer side of the second substrate facing the first substrate is not provided with an alignment restricting structure such as an electrode opening, a notch or a projection, and the liquid crystal is sufficiently aligned with a simpler structure than before. It can be stabilized and display quality equivalent to or better than conventional ones can be obtained.

  Furthermore, when an opening or a notch is provided in the first electrode and a wall structure is formed in the opening, the alignment regulating force due to the oblique electric field formed around the opening or the notch when a voltage is applied is reduced. Since the direction in which the liquid crystal molecules are tilted is defined together with the alignment regulating force by the structure, the radial tilt alignment can be further stabilized. In addition, the alignment regulation force due to the oblique electric field becomes weak when the voltage is low, whereas the alignment regulation force due to the wall structure does not depend on the voltage. Define the direction stably. As a result, display quality in halftone display can be improved.

  Furthermore, by providing a dielectric structure (convex portion) at a predetermined position on the liquid crystal layer side of the second substrate on which the second electrode (for example, the counter electrode) is formed, the radial tilt alignment is further stabilized and the halftone The improvement effect becomes large also for the improvement of the response characteristic in display and the afterimage generated when the panel surface is pressed.

  The configuration of a liquid crystal display device according to an embodiment of the present invention will be described below with reference to the drawings.

  First, referring to FIGS. 1 and 2, a mechanism for forming a radial tilt alignment in the liquid crystal display device according to the embodiment of the present invention will be described.

  FIGS. 1A and 1B are diagrams for explaining the action of the alignment regulating force by the opening 14 and the wall structure 15 provided in the pixel electrode 6. FIG. 1A shows a state when no voltage is applied, and FIG. The alignment state of a liquid crystal molecule is shown typically. The state shown in FIG. 1B is a state where a halftone is displayed. FIG. 2 is a diagram (plan view) of the alignment state of the liquid crystal molecules in the halftone display state viewed from the normal direction of the substrate.

  The liquid crystal display device shown in FIG. 1 has a pixel electrode 6 having an opening 14 and an alignment film 12 in this order on a transparent substrate 1. On the other transparent substrate 17, the counter electrode 19 and the alignment film 32 are formed in this order. The liquid crystal layer 20 provided between the two substrates includes liquid crystal molecules 21 having negative dielectric anisotropy.

  As shown in FIG. 1A, when no voltage is applied, the liquid crystal molecules 21 are aligned substantially perpendicular to the substrate surface by the alignment regulating force of the vertical alignment films 12 and 32. Typically, the vertical alignment film 12 is formed so as to cover the wall-shaped structure 15, and the liquid crystal molecules 21 are aligned substantially perpendicular to the side surface in the vicinity of the inclined side surface of the wall-shaped structure 15. Therefore, it is omitted in the figure. Here, as shown in FIG. 2, four openings 14 in which rectangular portions are arranged to form a cross are provided, and the wall structure 15 is provided in the openings 14 in parallel to the rectangular portions, The orientation regulating force direction (direction in which the liquid crystal molecules are inclined) by the wall structure is arranged so as to be aligned with the orientation regulating force direction by the oblique electric field generated by the opening 14.

  When a voltage is applied, as shown in FIG. 1B, the liquid crystal molecules 21 having negative dielectric anisotropy are formed around the opening 14 because the molecular long axis tends to be perpendicular to the lines of electric force. The direction in which the liquid crystal molecules 21 are tilted is defined by the oblique electric field. As shown in FIG. 2, when the cross opening 14 and the wall structure 15 are provided, a liquid crystal domain having a radially inclined alignment is formed in a region substantially surrounded by the opening 14 and the wall structure 15. Since the liquid crystal directors are aligned in all directions (directions in the substrate surface) in the radial tilt alignment domain, the viewing angle characteristics are excellent. Here, the radial tilt alignment is synonymous with the axially symmetric alignment, and the liquid crystal molecules are continuously aligned without forming a disclination line around the center of the radial tilt alignment (the central axis of the axially symmetric alignment). In other words, the major axis of the liquid crystal molecules is aligned radially, concentrically, or spirally. In either case, the major axis of the liquid crystal molecules has a component (component parallel to the oblique electric field) inclined radially from the center of alignment.

  Here, an example in which the opening 14 is provided together with the wall structure 15 has been described. However, even if the opening 14 is omitted, the vertical alignment type is applied to the inclined side surface of the wall structure 15 by an anchoring action (orientation regulating force). The direction in which the liquid crystal molecules in the liquid crystal layer are tilted by the electric field is defined, and as a result, when a voltage higher than the threshold is applied, the liquid crystal domain having the radial tilt alignment in the region substantially surrounded by the wall structure 15 is stabilized. It is formed. As illustrated, when the opening 14 is provided together with the wall structure 15, the alignment regulating force due to the oblique electric field formed around the opening or the notch when a voltage is applied, together with the alignment regulating force due to the wall structure, is liquid crystal. Since the direction in which the molecules tilt is defined, the radial tilt alignment can be further stabilized. In addition, the alignment regulating force due to the oblique electric field becomes weaker when the voltage is low, whereas the alignment regulating force due to the wall structure does not depend on the voltage, so the alignment regulating force is exerted even in the halftone display state, and the liquid crystal molecules tilt. Define the direction stably. As a result, display quality in halftone display can be improved.

  The “substantially surrounding region” of the wall structure 15 or the opening 14 means that a single liquid crystal domain may be formed by acting an alignment regulating force continuously on the liquid crystal molecules in the region. There is no need to siege. That is, as shown in FIG. 2, it is only necessary that the adjacent wall structure 15 or the opening 14 is divided and one liquid crystal domain is formed therein.

  Here, the action of the oblique electric field formed around the opening 14 has been described, but in the vicinity of a notch formed at the edge of the pixel electrode 6 (see, for example, the notch 13 in FIG. 3). Similarly, an oblique electric field is formed, and the direction in which the liquid crystal molecules 21 are inclined by the electric field is defined.

  Next, the arrangement of the notch 13 (or the opening 14) and the wall structure 15 will be described with reference to FIGS. FIGS. 3A and 3B are plan views showing an arrangement example of the wall structure 15 in the case where a pair of rectangular cutout portions 13 are provided near the center of the pixel electrode 6. The same is true even if the notch 13 shown here is the opening 14 formed in the pixel electrode 6.

  As described above, the region in which a liquid crystal domain having a radially inclined orientation when a voltage is applied is formed (the region in which one liquid crystal domain is formed is sometimes referred to as a “sub-pixel”). 15, the wall structure 15 may be formed only in the notch 13 (or in the opening 14) as shown on the right side of FIG. As shown on the left side, the wall structure 15 may be extended so as to connect the wall structure 15 formed in the notch 13. That is, when viewed from the normal direction of the substrate, the wall structure 15 may be provided so as to appear as a dotted line, or may be provided so as to appear as a solid line.

  Next, with reference to FIGS. 3B and 3C, a preferable configuration in the case where the wall structure 15 is provided in the rectangular cutout portion 13 (or the opening portion 14) in parallel therewith will be described.

  When the width of the rectangular notch 13 is EW (FIG. 3B) and the width of the wall structure 15 is WW, the configuration is such that the relationship of 0.6EW <WW <0.9EW is satisfied. Is preferred. In the case of 0.6EW> WW, the influence of the alignment regulating force by the wall structure 15 on the liquid crystal domain in the electrode region is reduced, and it may be difficult to stabilize the liquid crystal domain in the pixel electrode region. Conversely, when WW> 0.9EW, a situation (misalignment) may occur in which the wall structure 15 is not disposed in the notch 13 due to an alignment error in the manufacturing process. Since the liquid crystal molecules near the side surface of the wall structure 15 are inclined from the vertical alignment, light leakage occurs in a black display state, which is not preferable.

  The notch width EW is preferably set to 1.8 dt <EW <2.5 dt with respect to the thickness dt of the liquid crystal layer in the transmissive region. In order to achieve stable alignment for each pixel by the oblique electric field generated by the applied voltage, the notch width EW is increased with respect to the thickness dt of the liquid crystal layer, and equipotential lines in regions where no electrode layer is present are formed. It can be sufficiently distorted so that the alignment state does not continue for each pixel.

  However, if the width EW of the notch 13 (or the opening 14) is too large, the display portion in the pixel becomes small, and the region where the display state changes even when a voltage is applied is not preferable. Further, when the thickness dt of the liquid crystal layer is reduced, the electric field, that is, the unit V / μm is increased, the change amount of the electric field per unit thickness is increased, and is substantially the same as when the notch width EW is increased. An effect is obtained. That is, in a certain cell thickness (the thickness of the liquid crystal layer), a favorable radial tilt alignment domain can be formed for each pixel, and the effective aperture ratio is as much as possible (the ratio of the area contributing to display substantially to the pixel area). In order to increase the width, it is preferable that the notch width EW and the thickness dt of the liquid crystal layer in the transmissive region satisfy 1.8 dt <EW <2.5 dt. In the case of 1.8 dt> EW, the electric field per unit thickness is weak, the radial tilt alignment of the liquid crystal in the pixel is not stabilized, and the center position of the radial tilt alignment may vary among a plurality of pixels. On the contrary, when EW> 2.5 dt, the notch 13 (or the opening 14) is too large with respect to the appropriate thickness of the liquid crystal layer.

  The height WH of the wall structure 15 is preferably 0.25 dt <WH <0.4 dt with respect to the thickness dt of the transmission region of the liquid crystal layer. In the case of WH <0.25 dt, the alignment regulating force by the wall structure 15 becomes weak, and a stable alignment state may not be obtained. Conversely, when WH> 0.4 dt, when the liquid crystal material is injected between the substrate (active matrix substrate) 1 and the substrate (counter substrate) 17, the wall structure 15 regularly arranged on the pixel electrode 15. This hinders liquid crystal injection, and it takes a long time for the injection or there is a high possibility that a region where the injection is incomplete occurs. In particular, in the case of a transflective liquid crystal display device, the thickness dr (see, for example, FIG. 4) of the liquid crystal layer in the reflective region is set to approximately half the thickness dt of the transmissive region for optimal optical design. There is even a possibility that almost no liquid crystal material can be contained. Therefore, it is preferable that 0.25 dt <WH <0.4 dt.

  In the above example, the configuration in which the wall structure 15 is provided so as to correspond to the notch 13 and / or the opening 14 is illustrated, but the present invention is not limited to this, and as illustrated in FIG. A wall structure 15 may be provided in a region surrounding 6. The peripheral region of the pixel electrode 6 is a light shielding region that does not contribute to display because, for example, a TFT, a gate signal wiring, a source signal wiring, or the like is formed, or a black matrix is formed on the counter substrate. Therefore, the wall structure 15 formed in this region does not adversely affect the display.

  Further, the wall structure 15 may be formed so as to substantially surround regions (sub-pixels) that form individual liquid crystal domains. If the wall structure 15 is not formed for each sub-pixel, the alignment regulating force by the notch 13 or the opening 14 is not sufficient when the voltage is low, and the center position of the radial tilt alignment of the liquid crystal domain is stably maintained. Cannot be achieved, and may vary between a plurality of pixels. In particular, in the transflective liquid crystal display device, it is preferable to provide an opening or a notch at least between the transmissive region and the reflective region, and the wall structure 15 is formed instead of or together with this. It is preferable to do. When the wall structure 15 is not formed between the transmission region and the reflection region, when the applied voltage is low, the orientation regulating force on the region side where the wall structure 15 is formed is stronger than the other, and the radial gradient orientation The center position of the sub-region in the transmission region or the reflection region may deviate from the center of the elementary region.

  Next, a more specific configuration example of the liquid crystal display device according to the embodiment of the present invention will be described with reference to FIG.

  The liquid crystal display device shown in FIG. 4 includes a backlight, a transflective liquid crystal panel 50, a pair of polarizing plates 40 and 43 provided so as to face each other through the transflective liquid crystal panel 50, and a polarizing plate 40. Quarter wave plates 41 and 44 provided between the liquid crystal panel 50 and the liquid crystal panel 50, and the optical anisotropy provided between the quarter wave plates 41 and 44 and the liquid crystal panel 50 is negative. The phase difference plates 42 and 45 are included. The liquid crystal panel 50 includes a vertical alignment type liquid crystal layer 20 between a transparent substrate (active matrix substrate) 1 and a transparent substrate (counter substrate) 17. As the liquid crystal panel 50, for example, a liquid crystal panel having the same configuration as the liquid crystal display device 200 described later with reference to FIG. 6 is used.

  The display operation of the liquid crystal display device shown in FIG. 4 will be briefly described below.

  For the reflection mode display, incident light from above passes through the polarizing plate 43 and becomes linearly polarized light. This linearly polarized light becomes circularly polarized light when it enters the quarter wavelength plate 44 so that the transmission axis of the polarizing plate 43 and the slow axis of the quarter wavelength plate 44 are 45 °, and is formed on the substrate 17. It passes through a color filter layer (not shown). Here, a phase difference plate 45 that does not give a phase difference to light incident from the normal direction is used.

  When no voltage is applied, since the liquid crystal molecules in the liquid crystal layer 20 are aligned substantially perpendicular to the substrate surface, the incident light is transmitted with a phase difference of approximately 0 and is reflected by the reflective electrode formed on the lower substrate 1. The The reflected circularly polarized light passes through the liquid crystal layer 20 again, passes through the color filter layer, passes again through the retardation plate 45 having negative optical anisotropy as circularly polarized light, passes through the quarter-wave plate 44, and then first. The light is converted into linearly polarized light having a polarization direction orthogonal to the polarization direction when passing through the polarizing plate 43 and reaches the polarizing plate 43, so that light cannot pass through the polarizing plate 43 and is displayed in black.

  On the other hand, when a voltage is applied, the liquid crystal molecules in the liquid crystal layer 20 are inclined in the horizontal direction from the direction perpendicular to the substrate surface, so that the incident circularly polarized light becomes elliptically polarized light due to the birefringence of the liquid crystal layer 20 and is formed on the lower substrate 1. Reflected by the reflected electrode. The reflected light is further broken in the polarization state by the liquid crystal layer 20, passes through the liquid crystal layer 20 again, passes through the color filter layer, passes through the retardation plate 45 having negative optical anisotropy again, and becomes 1/4. Since the light is incident on the wave plate 44 as elliptically polarized light, all the light does not become linearly polarized light orthogonal to the polarization direction at the time of incidence when reaching the polarizing plate 43, and part of the light is transmitted through the polarizing plate 43. In particular, by adjusting the applied voltage, the direction in which the liquid crystal molecules are tilted can be controlled, and the amount of light that can be reflected by the polarizing plate 43 is modulated, thereby enabling gradation display.

  Regarding the display of the transmission mode, the two upper and lower polarizing plates 43 and 40 are arranged so that their transmission axes are orthogonal to each other, and the light emitted from the light source becomes linearly polarized light by the polarizing plate 40, This linearly polarized light becomes circularly polarized light and has a negative optical anisotropy when incident on the ¼ wavelength plate 41 so that the slow axis between the transmission axis of the polarizing plate 40 and the ¼ wavelength plate 41 is 45 °. The light enters the transmission region A of the lower substrate 1 through the phase difference plate 42. Here, a phase difference plate 42 that does not give a phase difference to light incident from the normal direction is used.

  When no voltage is applied, the liquid crystal molecules in the liquid crystal layer 20 are aligned substantially perpendicular to the substrate surface, so that incident light is transmitted with a phase difference of approximately 0 and is incident on the lower substrate 1 in a circularly polarized state. In the state of circular polarization, the light passes through the liquid crystal layer 20 and the upper substrate 17 and passes through the retardation plate 45 having the negative optical anisotropy to reach the quarter-wave plate 44. Here, the slow axis of the lower ¼ wavelength plate 41 and the upper ¼ wavelength plate 44 intersect each other by 90 °, so that the upper ¼ wavelength plate 44 is separated by the polarizing plate 40. The linearly polarized light is orthogonal to the linearly polarized light, and is absorbed by the polarizing plate 43 to display black.

  On the other hand, when a voltage is applied, since the liquid crystal molecules 21 in the liquid crystal layer 20 are inclined in the horizontal direction from the direction perpendicular to the substrate surface, the circularly polarized light incident on the liquid crystal display device becomes elliptically polarized light due to the birefringence of the liquid crystal layer 20, and the upper side. Since the CF substrate 17 and the retardation plate 45 and the quarter wavelength plate 44 having a negative optical anisotropy on the upper side reach the polarizing plate 43 as elliptically polarized light, the linearly polarized light orthogonal to the polarization component at the time of incidence is not obtained. Instead, light passes through the polarizing plate 43. In particular, by adjusting the applied voltage, the direction in which the liquid crystal molecules are tilted can be controlled, and the amount of light that can be reflected by the polarizing plate 43 is modulated, thereby enabling gradation display.

  A retardation plate having a negative optical anisotropy minimizes the amount of change in retardation when the viewing angle is changed in a vertically aligned state of liquid crystal molecules, and suppresses black floating on the wide viewing angle side. Further, a biaxial retardation plate in which a retardation plate having negative optical anisotropy and a quarter wavelength plate are integrated may be used.

  When a normally black mode in which a black display is performed when no voltage is applied and a white display is performed when a voltage is applied is performed in the radial tilt alignment domain as in the present invention, a pair of 1/4 is formed above and below the liquid crystal display device (liquid crystal panel). By providing the wave plate, it is possible to improve the brightness by eliminating the extinction pattern caused by the polarizing plate. In addition, when the normally black mode is performed in the radially inclined alignment domain with the transmission axes of the upper and lower polarizing plates arranged orthogonal to each other, in principle, the same degree as a pair of polarizing plates arranged in crossed Nicols. Since a black display can be realized, an extremely high contrast ratio can be realized, and a wide viewing angle characteristic led to an omnidirectional orientation can be achieved.

(Transmission type liquid crystal display)
First, the configuration of a transmissive liquid crystal display device 100 according to an embodiment of the present invention will be described with reference to FIG. FIG. 5 is a diagram schematically showing the configuration of one pixel of the transmissive liquid crystal display device 100, (a) is a plan view, and (b) is 5B-5B ′ in FIG. 5 (a). It is sectional drawing along a line.

  The liquid crystal display device 100 includes a transparent substrate (for example, a glass substrate) 110a, a transparent substrate 110b provided to face the transparent substrate 110a, and a vertical alignment type liquid crystal layer provided between the transparent substrates 110a and 110b. 120. A vertical alignment film (not shown) is provided on the surfaces of the substrates 110a and 110b in contact with the liquid crystal layer 120. When no voltage is applied, the liquid crystal molecules of the liquid crystal layer 120 are substantially perpendicular to the surface of the vertical alignment film. Oriented. The liquid crystal layer 120 includes a nematic liquid crystal material having negative dielectric anisotropy, and further includes a chiral agent as necessary.

  The liquid crystal display device 100 includes a pixel electrode 111 formed on the transparent substrate 110a and a counter electrode 131 formed on the transparent substrate 110b, and a liquid crystal provided between the pixel electrode 111 and the counter electrode 131. Layer 120 defines the pixel. Here, both the pixel electrode 111 and the counter electrode 131 are formed of a transparent conductive layer (for example, an ITO layer). Typically, on the liquid crystal layer 120 side of the transparent substrate 110b, a color filter 130 provided corresponding to the pixel (a plurality of color filters may be collectively referred to as the color filter layer 130), and A black matrix (light-shielding layer) 132 provided between adjacent color filters 130, that is, between adjacent pixels is formed, and a counter electrode 131 is formed thereon, but on the counter electrode 131 (liquid crystal layer) The color filter layer 130 and the black matrix 132 may be formed on the (120 side).

  Here, the pixel electrode 111 has two notches 113 formed at predetermined positions. Further, a wall structure 115 is provided on the liquid crystal layer 120 side of the transparent substrate 110a. The wall structure 115 includes a wall portion provided so as to surround the pixel electrode 111 and a rectangular cutout portion. 113 includes a wall portion provided in parallel therewith and a wall portion extending so as to connect them.

  When a predetermined voltage is applied to the liquid crystal layer, two liquid crystal domains each having a radially inclined alignment are formed in a region surrounded by the wall structure 115. The wall structure 115 illustrated here is provided as a continuous wall, but is not limited thereto, and may be divided into a plurality of walls. Since the wall structure 115 acts to define the boundary of the liquid crystal domain, it preferably has a certain length. For example, when the wall structure is composed of a plurality of walls, the length of each wall is preferably longer than the length between adjacent walls.

  It is preferable that the support 133 for defining the thickness of the liquid crystal layer 120 (also referred to as a cell gap) be formed in the light shielding region because the display quality is not deteriorated. The support 133 can be formed by a photolithography process using a photosensitive resin, for example. The support 133 may be formed on either of the transparent substrates 110a and 110b, and is not limited to being provided on the wall structure 115 provided in the light shielding region as illustrated. When the support 133 is formed on the wall structure 115, the sum of the height of the wall structure 115 and the height of the support 133 is set to be the thickness of the liquid crystal layer 120. When the support body 133 is provided in a region where the wall structure 115 is not formed, the height of the support body 133 is set to be the thickness of the liquid crystal layer 120.

  Note that, on the liquid crystal layer 120 side of the transparent substrate 110a, for example, an active element such as a TFT and circuit elements (not shown) such as a gate wiring and a source wiring connected to the TFT are provided. Further, the transparent substrate 110a, the circuit elements formed on the transparent substrate 110a, the pixel electrode 111, the wall structure 115, the support 133, the alignment film, and the like described above may be collectively referred to as an active matrix substrate. On the other hand, the transparent substrate 110b and the color filter layer 130, the black matrix 132, the counter electrode 131, the alignment film, and the like formed on the transparent substrate 110b may be collectively referred to as a counter substrate or a color filter substrate.

  Further, although omitted in the above description, the liquid crystal display device 100 further includes a pair of polarizing plates arranged so as to face each other through the transparent substrates 110a and 110b. The pair of polarizing plates are typically arranged so that the transmission axes are orthogonal to each other. Furthermore, as described above, a biaxial optically anisotropic medium layer or a uniaxial optically anisotropic medium layer may be provided.

(Transflective liquid crystal display device)
Next, the configuration of the transflective liquid crystal display device 200 according to the embodiment of the present invention will be described with reference to FIG.

  It is a figure which shows typically the structure of one pixel of the transmissive liquid crystal display device 200 of embodiment by this invention, (a) is a top view, (b) is 6B- in FIG. 6 (a). It is sectional drawing along a 6B 'line.

  The liquid crystal display device 200 includes a transparent substrate (for example, a glass substrate) 210a, a transparent substrate 210b provided to face the transparent substrate 210a, and a vertical alignment type liquid crystal layer provided between the transparent substrates 210a and 210b. 220. A vertical alignment film (not shown) is provided on the surfaces of both the substrates 210a and 210b in contact with the liquid crystal layer 220. When no voltage is applied, the liquid crystal molecules of the liquid crystal layer 220 are in contact with the surface of the vertical alignment film. Oriented substantially vertically. The liquid crystal layer 220 includes a nematic liquid crystal material having a negative dielectric anisotropy, and further includes a chiral agent as necessary.

  The liquid crystal display device 200 includes a pixel electrode 211 formed on the transparent substrate 210a and a counter electrode 231 formed on the transparent substrate 210b, and a liquid crystal provided between the pixel electrode 211 and the counter electrode 231. Layer 220 defines the pixel. Circuit elements such as TFTs are formed on the transparent substrate 210a as will be described later. The transparent substrate 210a and the components formed thereon may be collectively referred to as an active matrix substrate 210a.

  Further, typically, a color filter 230 (corresponding to a plurality of color filters may be collectively referred to as the color filter layer 230) provided corresponding to the pixel on the liquid crystal layer 220 side of the transparent substrate 210b. A black matrix (light-shielding layer) 232 provided between adjacent color filters 230, that is, between adjacent pixels is formed, and a counter electrode 231 is formed thereon, but on the counter electrode 231 (liquid crystal layer) 220), the color filter layer 230 and the black matrix 232 may be formed. The transparent substrate 210b and the components formed thereon may be collectively referred to as a counter substrate (color filter substrate) substrate 210b.

  The pixel electrode 211 is formed of a transparent electrode 211a formed from a transparent conductive layer (for example, an ITO layer) and a metal layer (for example, an Al layer, an alloy layer including Al, and a laminated film including any of these). A reflective electrode 211b. As a result, the pixel includes a transparent area A defined by the transparent electrode 211a and a reflective area B defined by the reflective electrode 211b. The transparent area A displays in the transmissive mode, and the reflective area B displays in the reflective mode.

  Here, the pixel electrode 211 has a notch 213 formed at a predetermined position. Further, a wall structure 215 is provided on the liquid crystal layer 220 side of the transparent substrate 210a. The wall structure 215 includes a wall portion provided so as to surround the pixel electrode 211 and a rectangular notch. 213 includes a wall portion provided in parallel with 213 and a wall portion extending so as to connect them.

  When a predetermined voltage is applied to the liquid crystal layer, three liquid crystal domains each having a radially inclined alignment are formed in a region surrounded by the wall structure 215. The wall structure 215 exemplified here is provided as a continuous wall, but is not limited thereto, and may be divided into a plurality of walls. Since the wall structure 215 acts so as to define the boundary of the liquid crystal domain, it preferably has a certain length. For example, when the wall structure is composed of a plurality of walls, the length of each wall is preferably longer than the length between adjacent walls.

  Although FIG. 6 shows an example in which two liquid crystal domains are formed in the transmissive region A and one liquid crystal domain is formed in the reflective region B, the present invention is not limited to this. In addition, it is preferable that each liquid crystal domain has a substantially square shape from the viewpoint of viewing angle characteristics and alignment stability.

  The liquid crystal display device 200 has a wall structure 215 on a transparent substrate 210a in a light shielding region provided between adjacent pixels. The wall structure 215 exemplified here is provided as a continuous wall so as to surround the pixel, but is not limited thereto, and may be divided into a plurality of walls. Since the wall structure 215 acts to define a boundary formed in the vicinity of the extension of the pixels in the liquid crystal domain, it preferably has a certain length. For example, when the wall structure 215 is composed of a plurality of walls, the length of each wall is preferably longer than the length between adjacent walls.

  It is preferable to form the support 233 for defining the thickness (also referred to as a cell gap) of the liquid crystal layer 220 in the light shielding region because the display quality is not deteriorated. The support 233 can be formed by a photolithography process using a photosensitive resin, for example. The support 233 may be formed on either of the transparent substrates 210a and 210b, and is not limited to the case of being provided on the wall structure 215 provided in the light shielding region as illustrated. When the support 233 is formed on the wall structure 215, the sum of the height of the wall structure 215 and the height of the support 233 is set to be the thickness of the liquid crystal layer 220. In the case where the support 233 is provided in a region where the wall structure 215 is not formed, the height of the support 233 is set to be the thickness of the liquid crystal layer 220.

  Next, a preferable configuration unique to the transflective liquid crystal display device 200 capable of performing both transmission mode display and reflection mode display will be described.

  In the transmission mode display, the light used for display passes through the liquid crystal layer 220 only once, whereas in the reflection mode display, the light used for display passes through the liquid crystal layer 220 twice. Therefore, as schematically shown in FIG. 6B, the thickness dt of the liquid crystal layer 220 in the transmissive region A is preferably set to about twice the thickness dr of the liquid crystal layer 220 in the reflective region B. By setting in this way, the retardation that the liquid crystal layer 220 gives to the light in both display modes can be made substantially equal. Although dt = 0.5dr is most preferable, good display can be realized in both display modes as long as it is within the range of 0.3dt <dr <0.7dt. Of course, dt = dr may be used depending on the application.

  In the liquid crystal display device 200, in order to make the thickness of the liquid crystal layer 220 in the reflective region B smaller than the thickness of the liquid crystal layer in the transmissive region A, the transparent dielectric layer 234 is provided only in the reflective region B of the glass substrate 210b. Yes. The counter electrode 231 is preferably provided so as to cover the transparent dielectric layer 234 (that is, on the liquid crystal layer 220 side) as shown in the figure. By adopting such a configuration in which the transparent dielectric layer 234 is provided on the counter substrate 210b side, there is no need to provide a step using an insulating film or the like under the reflective electrode 211b, so that the manufacturing of the active matrix substrate 210a can be simplified. The advantage is obtained. Further, when the reflective electrode 211b is provided over the insulating film for providing a step for adjusting the thickness of the liquid crystal layer 220, light used for transmissive display is blocked by the reflective electrode that covers the inclined surface (tapered portion) of the insulating film. However, since the light reflected by the reflective electrode formed on the slope of the insulating film repeats internal reflection, there is a problem that it is not effectively used for reflective display. Occurrence of problems can be suppressed and light utilization efficiency can be improved.

  Furthermore, if the transparent dielectric layer 234 having a function of scattering light (diffuse reflection function) is used, a good white display close to paper white can be realized without providing the reflection electrode 211b with a diffuse reflection function. it can. Even if the transparent dielectric layer 234 is not provided with a light scattering function, a white display close to paper white can be realized by providing an uneven shape on the surface of the reflective electrode 211b. The center position of the tilted orientation may not be stable. On the other hand, if the transparent dielectric layer 234 having a light scattering function and the reflective electrode 211b having a flat surface are used, the center position can be more reliably stabilized by the opening 214 formed in the reflective electrode 211b. Is obtained. In addition, in order to provide a diffuse reflection function to the reflective electrode 211b, when forming unevenness on the surface, the uneven shape is preferably a continuous wave shape so that no interference color is generated, and the center of the radial gradient orientation is stable. It is preferable to set so that it can be realized.

  In the transmissive mode, light used for display passes through the color filter layer 230 only once, whereas in reflective mode display, light used for display passes through the color filter layer 230 twice. Therefore, when a color filter layer having the same optical density is used for the transmission region A and the reflection region B as the color filter layer 230, color purity and / or luminance in the reflection mode may be lowered. In order to suppress the occurrence of this problem, it is preferable to make the optical density of the color filter layer in the reflective region smaller than that in the transmissive region. The optical density here is a characteristic value characterizing the color filter layer, and the optical density can be reduced by reducing the thickness of the color filter layer. Alternatively, the optical density can be reduced by reducing the concentration of the added dye, for example, while maintaining the thickness of the color filter layer.

  Hereinafter, the display characteristics of the prototyped liquid crystal display device will be specifically described.

(Prototype example 1)
A pixel electrode (ITO layer: transparent electrode) 6 and a wall structure 15 as shown in FIG. 7A were formed on an active matrix substrate on which signal lines and TFTs (thin film transistors) were formed. At this time, the width of the notch 13 was 8 μm, and the width of the wall structure 15 was 6 μm. A support for defining the cell thickness was formed at a location different from the wall structure 15. The height of this support was 4.0 μm.

  A vertical alignment layer was formed on the substrate by applying a vertical alignment agent to the active matrix substrate manufactured as described above, the color filter layer, and the counter substrate (color filter substrate) on which the electrode layer was formed, and baking it. An active matrix substrate and a counter substrate were bonded to each other, and a liquid crystal material having negative dielectric anisotropy (Δn = 0.101, Δε = −5.0) was injected and sealed to manufacture a liquid crystal display device. Then, the optical film was arrange | positioned on both surfaces of the structural substrate of this liquid crystal display device, and the liquid crystal display device was obtained.

  The configuration of the liquid crystal display device of this prototype is, in order from the top, a polarizing plate (observation side), a quarter-wave plate (retardation plate 1), and a retardation plate with negative optical anisotropy (retardation plate 2 (NR). Plate)), liquid crystal layer (upper side: color filter substrate, lower side: active matrix substrate), retardation plate with negative optical anisotropy (retardation plate 3 (NR plate)), 1/4 wavelength plate (retardation) A laminated structure of a plate 4) and a polarizing plate (backlight side) was adopted. In addition, in the upper and lower quarter-wave plates (the phase difference plate 1 and the phase difference plate 4) of the liquid crystal layer, their slow axes are orthogonal to each other, and each phase difference is 140 nm (visible light (1/4 of 560 nm)). It was.

  The retardation plate (retardation plate 2 and retardation plate 3) having negative optical anisotropy has a retardation of 135 nm in a direction parallel to the optical axis (perpendicular to the film surface) and the film surface. Further, the two polarizing plates (observation side and backlight side) were arranged with their transmission axes orthogonal to each other.

  A display signal was evaluated by applying a drive signal to the liquid crystal display device (applying 4V to the liquid crystal layer). Prototype Example 1 had good voltage-transmittance characteristics shown in FIG. Further, FIG. 9 shows the viewing angle-contrast characteristic result in the transmissive display. Viewing angle characteristics in transmissive display are almost omnidirectional and symmetrical, CR> 10 (bold line area) is good at ± 80 °, and transmission contrast is high at 300: 1 or more in front. It was a thing. Also, with respect to the response speed in the halftone, the response time in the response of 6 to 7 gradations (low voltage close to black) at 8 gradation levels is 20 msec, which is a high-speed response characteristic as compared with the case without the wall structure. .

(Prototype example 2)
A pixel electrode 6 having a notch 13 having the same shape as that of Prototype Example 1 was formed on an active matrix substrate. Thereafter, a wall structure was formed on the ITO electrode as shown. At this time, the width of the notch 13 was 6 μm, and the width of the wall structure was 3 μm. The height of the support that defines the cell gap was 3.0 μm. Subsequent steps were performed in the same manner as in Prototype Example 1 to produce a liquid crystal display device. The liquid crystal display device of this prototype also had good viewing angle characteristics and high contrast characteristics in all directions.

(Prototype example 3)
On the active matrix substrate on which the pixel electrode 6 and the wall structure 15 similar to those of the prototype example 1 were formed, a support for defining the cell thickness was formed at a location (light-shielding region) different from the wall structure 15. The height of this support was 4.5 μm. Subsequent steps were performed in the same manner as in Prototype Example 1 to produce a liquid crystal display device.

  When the panel of this prototype was observed from the wide viewing angle side, some pixels were observed to be rough. When the pixel where the roughness was observed was observed with a polarizing microscope in crossed Nicols, the center of the radial tilt alignment was shifted from the center of the pixel in each pixel. From this, it can be seen that it is not preferable that the width of the notch is too large with respect to the thickness of the liquid crystal layer.

(Prototype example 4)
The pixel electrode 6 and the wall structure 15 similar to the prototype 1 were formed. At this time, the width of the notch 13 was 6 μm, and the width of the wall structure 15 was 1 μm. The height of the support that defines the cell gap was defined to be 3.0 μm. Subsequent steps were performed in the same manner as in Prototype Example 1 to produce a liquid crystal display device.

  When the panel of this prototype example is observed from the wide viewing angle side, there is a pixel in which roughness is observed. When the pixel where the roughness was observed was observed with a polarizing microscope in crossed Nicols, the center of the radial tilt alignment was shifted from the center of the pixel in each pixel. From this, it is understood that it is not preferable that the width of the wall structure is extremely smaller than the width of the notch.

(Prototype example 5)
A wall structure 15 having a width of 8 μm was formed on an active matrix substrate on which the same pixel electrode 6 as in Prototype Example 1 was formed. Thereafter, a liquid crystal display device was manufactured through the same process as in Prototype Example 1.

  When the liquid crystal display device of this prototype was observed, there was a thing in which black was felt as floating in black display. When the pixel was observed with a polarizing microscope, a wall structure was present around the transmission region, and light leakage occurred. This shows that it is not preferable that the width of the wall structure is larger than the width of the notch.

(Prototype example 6)
A wall structure was formed on an active matrix substrate on which the same pixel electrode 6 as in Prototype Example 1 was formed. At this time, the notch 13 had a width of 8 μm and a wall structure width of 5 μm. A support for defining a cell gap was formed on the active matrix substrate at a location different from the wall structure. The height of this support was 2.5 μm. Thereafter, a liquid crystal display device was manufactured through the same process as in Prototype Example 1.

  In the liquid crystal display device of this prototype, the retardation change based on the voltage signal change was small and the transmittance of the liquid crystal layer was low, so the display was relatively dark. From this, it can be seen that it is not preferable that the thickness of the liquid crystal layer in the transmissive region is smaller than the width of the notch 13.

(Prototype example 7)
A pixel electrode 6 having a notch 13 having the same shape as that of Prototype Example 1 was formed on an active matrix substrate. Without forming the wall structure, a support for defining a cell gap was formed on the active matrix substrate at a location different from the wall structure. The height of this support was 3.6 μm. Thereafter, a liquid crystal display device was manufactured through the same process as in Prototype Example 1.

  When the response time in the halftone (6 to 7 gradations) at the 8 gradation level of this liquid crystal display device was evaluated, it showed a very slow response characteristic of about 120 msec. This is because it takes time for the alignment of the liquid crystal molecules to be stable in the case where there is little restriction in black display by the notch.

(Prototype example 8)
A transparent electrode (ITO pattern) and a reflective electrode (Al pattern) as shown in FIG. 7B were formed on the active matrix substrate, which were used as a transmission region and a reflection region, respectively. A wall structure was formed on the electrode. At this time, the width of the notch 13 was 8 μm, and the width of the wall structure 15 was 6 μm. In addition, a support for setting the cell gap thickness was formed in the non-display area. The height of this support was 3.6 μm.

  After forming a color filter layer as a counter substrate of this active matrix substrate, a step having a thickness of about 1.8 μm is formed in the reflective region, an ITO electrode layer is formed on this substrate, and the counter substrate (color filter substrate) is formed. Produced.

  A vertical alignment agent was applied on the obtained active matrix substrate and the counter substrate, and then fired at 180 ° C. for 1.5 h to form a vertical alignment layer on the substrate. These substrates were bonded to each other, and a liquid crystal material having negative dielectric anisotropy was injected and sealed to produce a liquid crystal display device. At this time, due to the step of 1.8 μm formed on the color filter substrate and the support for adjusting the cell gap of 3.6 μm, the thickness of the liquid crystal layer in the transmission region is 3.6 μm, and the thickness of the liquid crystal layer in the reflection region is 1. .8 μm. Thereafter, as in Prototype Example 1, a film was attached to the liquid crystal display device based on the optical film setting, and a liquid crystal display device was produced. Good display characteristics similar to those of Prototype Example 1 were obtained for the transmissive display characteristics. Further, as the characteristics of the reflective display, the standard diffuser plate was used as a reference, and the contrast ratio was about 8.5% (aperture ratio 100% conversion). Good voltage-reflectance characteristics as shown in FIG. 10 were exhibited.

  Table 1 collectively shows the quality of the display when the numerical values of the width of the notch 13, the width of the wall structure, and the thickness of the liquid crystal layer in the transmissive region in all the prototypes described above are changed.

  As described above, according to the embodiment of the present invention, by forming a wall structure having an electrode notch and an inclined side surface for alignment control on one side substrate (in the example, an active matrix substrate), in all directions A liquid crystal display device having excellent viewing angle characteristics and high contrast characteristics could be manufactured.

  Next, a liquid crystal display device according to another embodiment of the present invention will be described.

  In a liquid crystal display device according to an embodiment described below, a dielectric is further provided on a substrate (second substrate, for example, a counter (CF) substrate) opposite to a substrate (first substrate, for example, active matrix substrate) provided with a wall structure. It differs from the liquid crystal display device of the previous embodiment in that it has a structure (convex portion). In the following description, components common to the liquid crystal display device of the previous embodiment are denoted by common reference numerals, and description thereof is omitted here.

  The liquid crystal display device of the previous embodiment has a simple configuration in which an alignment control structure (wall structure, electrode opening and / or electrode notch) is provided on a substrate on one side, and stable radial tilt alignment of the liquid crystal layer. However, in the liquid crystal display device of this embodiment, the dielectric structure is disposed on the other substrate in the region substantially surrounded by the wall structure provided on one substrate, and the liquid crystal layer is formed. By restricting the alignment of the liquid crystal molecules from the upper and lower substrates facing each other through, the radial tilt alignment is further stabilized. As a result, for example, the restoring force when the panel surface is pressed increases, and the alignment disorder is less likely to occur, or even if the alignment disorder occurs, the recovery is performed in a short time. In addition, the response time in the halftone display state is shortened.

  The alignment state of the liquid crystal molecules in the liquid crystal display device of the present embodiment will be described with reference to FIGS.

  FIGS. 11A and 11B correspond to FIGS. 1A and 1B for the liquid crystal display device of the previous embodiment, and FIG. Schematically shows the alignment state of liquid crystal molecules when a voltage is applied.

  As described with reference to FIGS. 1A and 1B, the oblique electric field generated by the opening 14 provided in the pixel electrode 6 and the inclined side surface of the wall structure 15 provided in the opening 14. Due to the alignment regulating force (anchoring effect) caused by the above, a liquid crystal domain having a radially inclined alignment is formed in a region (subpixel) substantially surrounded by the opening 14 and the wall structure 15. The liquid crystal display device of the present embodiment further includes a dielectric structure 25 in the approximate center of the sub-pixel on the liquid crystal layer 20 side of the upper substrate 17, and the alignment regulating force ( Due to the anchoring effect), the radial tilt alignment of the liquid crystal molecules 21 is further stabilized. Although simplified in FIG. 11, the vertical alignment film 32 is formed so as to cover the dielectric structure 25.

  As can be seen from FIG. 11B, the alignment regulating force due to the inclined side surface of the dielectric structure 25 provided on the liquid crystal layer 20 of the second substrate (counter substrate) 17 is provided on the first substrate (active matrix substrate). Since the liquid crystal molecules 21 are aligned in the same direction as the alignment control force by the alignment control structure (wall structure, electrode opening, etc.), the radial tilt alignment of the liquid crystal molecules in the sub-pixel is further stabilized. . Further, since the radial tilt alignment is formed around the dielectric structure 25 provided at the approximate center of the sub-pixel, the center of the radial tilt alignment is fixed in the vicinity of the dielectric structure 25.

  At this time, when the electric field is applied, the liquid crystal molecules having negative dielectric anisotropy are tilted so as to be orthogonal to the direction of the electric field (so that the major axis of the liquid crystal molecules is parallel to the substrate surface). As indicated by arrows in b), the dielectric structure 25 is preferably disposed so as to fall outward with respect to the inclined side surface. If it falls in the opposite direction, a disclination line may occur.

  As described above, the alignment regulating structure (wall structure, electrode opening, etc.) provided on the first substrate mainly regulates the alignment direction of the liquid crystal molecules around the sub-pixel, and the alignment regulating structure provided on the second substrate ( By controlling the orientation of the liquid crystal molecules in the substantially central part of the sub-pixel by the dielectric structure), the response time in halftone display is shortened, or the afterimage generated when the panel surface is pressed is lost. Time can be shortened. The reason will be described with reference to FIGS.

  FIGS. 12A to 12C are diagrams schematically showing the orientation of liquid crystal molecules in the sub-pixel of the liquid crystal display device of the present embodiment, where FIG. Immediately after the application, (c) shows a state where a sufficient time has elapsed after the voltage application. Note that FIG. 12 does not show an alignment regulating structure (a wall structure surrounding the subpixel, an electrode opening, etc.) provided around the subpixel.

  As shown in FIG. 12A, in the state where no voltage is applied, the liquid crystal molecules 21 are aligned substantially perpendicular to the substrate surface. However, the liquid crystal molecules in the vicinity of the inclined side surface of the dielectric structure 25 are inclined (pretilt) because they are oriented perpendicularly to the inclined side surface, but are ignored in the figure.

  When a voltage is applied, as shown in FIG. 12B, the liquid crystal molecules around the sub-pixel receiving the alignment regulating force of the alignment regulating structure provided around the sub-pixel, and the alignment regulating force of the dielectric structure 25 It begins to tilt from the liquid crystal molecules near the center.

  Thereafter, with the passage of time, the liquid crystal molecules existing between the alignment control structure provided around the sub-pixel and the dielectric structure 25 are continuously aligned.

  In this way, by providing the dielectric structure 25 in the approximate center of the subpixel, the alignment regulation of liquid crystal molecules proceeds from both the vicinity of the dielectric structure 25 and the alignment regulation structure around the subpixel. The effect of shortening the response time in the halftone display state and the effect of increasing the restoring force against pressing of the panel can be obtained.

[Dielectric structure]
The dielectric structure is preferably formed on the liquid crystal layer side of the opposing substrate at a predetermined position in each region substantially surrounded by the wall structure, that is, a position corresponding to a substantially central portion of each region. Here, substantially surrounded by the wall structure means that the wall structure (continuous step structure or discontinuous step structure) formed by patterning the display areas of the pixels regularly arranged as necessary. In the present invention, in each of the subdivided regions, the liquid crystal region takes a radially inclined alignment by the action of the alignment regulating structure such as the wall structure and the dielectric structure.

  Note that the dielectric structure is preferably disposed at substantially the center of the sub-pixel substantially surrounded by the wall structure or the like. Further, when the percentage of the ratio of the bottom area Sb of the dielectric structure to the area Sd of the sub-pixel (liquid crystal domain) is Sa (%), it is preferable that the value of Sa satisfies the relationship of 2 ≦ Sa ≦ 25. When the value of Sa is smaller than the above range, there may be a case where the function of stabilizing the alignment state of the liquid crystal molecules cannot be sufficiently obtained. On the other hand, when the Sa value is larger than the above range, the area ratio occupied by the dielectric structure disposed in the pixel becomes too large, and the reduction of the effective aperture ratio becomes remarkable and the display luminance is lowered. It will be. Furthermore, in the vicinity of the inclined portion (side surface) of the dielectric structure, a phase difference is given to the polarized light that passes through the liquid crystal molecules aligned in the direction inclined with respect to the polarization axis of the polarizing plate. As a result, light leakage occurs. The contrast ratio may be reduced. For this reason, the size of the dielectric structure is preferably within the above range.

  Further, in order to prevent light leakage in the vicinity of the dielectric structure, a light shielding layer may be provided on the substrate 210b as necessary. The light shielding layer may be formed by patterning a light shielding metal film or an insulating film having a light shielding function (for example, a black resin film) by a known method. By providing the light shielding layer, it is possible to suppress a decrease in contrast ratio. The light shielding layer may be provided on the active matrix substrate at a position facing the dielectric structure.

  The cross-sectional shape of the dielectric structure (the cross-sectional shape in a plane parallel to the substrate surface) is preferably matched to the shape of the pixel or sub-pixel. For example, a rectangular pixel (or sub-pixel) is rectangular Or a square, a shape having a curved surface at these corners, a circle or an ellipse is preferable. In particular, when the cross-sectional shape includes a curved surface, the liquid crystal molecules around the dielectric structure can easily take a radially inclined orientation, so that the occurrence of disclination can be suppressed.

  Next, an example of a transflective liquid crystal display device provided with a dielectric structure is shown in FIG. FIG. 13A is a plan view, and FIG. 13B is a cross-sectional view taken along line 13B-13 'in FIG.

  The transflective liquid crystal display device 200 ′ shown in FIG. 13 is the same as the transflective liquid crystal display device 200 of the previous embodiment shown in FIG. Part) 225 is provided. However, a point where a gap is provided between the pixel electrode 211 and the wall structure 215, and the wall structure 215 is provided only on the periphery of the pixel electrode 211 and in the notch 213, and provided on the pixel electrode 211. Not. By omitting the wall structure 215 on the pixel electrode 211, a decrease in aperture ratio and / or light leakage can be suppressed.

  The liquid crystal display device 200 ′ of this embodiment has higher stability of the radial tilt alignment than the liquid crystal display device 200 of the previous embodiment, and is required to eliminate the alignment disorder formed when the panel surface is pressed. The time is short and the response characteristics in halftone display are also excellent.

  The evaluation result about Prototype Examples 9-13 is illustrated below. Prototype examples 9 to 13 were basically produced by the same method as trial example 1 described above.

Here, the size of the sub pixel is 55 μm × 60 μm (Sd = 3300 μm ² ), and the dielectric structure 225 is formed at a position on the second substrate 210b corresponding to the approximate center of each sub pixel. The dielectric structure 225 was formed by a photolithography process using a transparent photosensitive resin.

The bottom surface area Sb of the dielectric structure 225 is 78 μm ² (Frustum with a bottom diameter of 10 μm) in Prototype 9 and 845 μm ² (Frustum with a bottom diameter of 32.8 μm) in Prototype 9 and Prototype 11 Is 480 μm ² (pyramidal frustum having a rectangular bottom with a curved surface of 20 μm × 24 μm), prototype 12 is 64 μm ² (conical trapezoid with a bottom diameter of 9 μm), prototype 13 is 908 μm ² (cone with a bottom diameter of 34 μm) Trapezoid). Moreover, these liquid crystal display devices obtained the liquid crystal display device by arrange | positioning an optical film on both surfaces of the structure board | substrate of this liquid crystal display device similarly to the prototype example 1. The configuration of the optical film was also the same as in Prototype Example 1.

A display signal was evaluated by applying a drive signal to each liquid crystal display device (applying 4V to the liquid crystal layer). For the display characteristics, the front contrast (CR) value when a voltage of 4 V was applied and the pressure resistance (time until the afterimage disappeared) when the panel was pressed with a pressure of 1 kgf / cm ² were evaluated.

  Further, as the response time in the halftone display state, the time required for response from the number of gradations 6 to 7 (low voltage level close to black display) at 8 gradation levels was evaluated. For the front contrast value, the design value was 300, and the lower limit allowable value was 270. Moreover, in the pressure resistance evaluation, the orientation restoring force after pressurization is evaluated, and when the defective orientation is resolved within 1 minute (which means that it cannot be visually recognized), the defective orientation is observed within 1 minute to 5 minutes. The case where it was eliminated Δ (allowable lower limit), and the case where the alignment disorder remained even after 10 minutes or more passed was marked with ×.

  These evaluation results are shown in Table 2.

  As can be seen from the results shown in Table 2, by providing the dielectric structure, the halftone response time is shortened and the pressure resistance is improved. Further, as can be seen from the result of Prototype Example 12, when Sa is less than 2%, the effect of providing the dielectric structure is not sufficiently exhibited. On the other hand, from the results of Prototype Example 13, if Sa exceeds 25%, the halftone response time is shortened, and although the pressure resistance is improved, the front contrast ratio is lowered, which is not preferable. In summary, it can be said that the dielectric structure is preferably provided so as to satisfy the relationship of 2 ≦ Sa ≦ 25. Of course, the range of Sa may be changed according to the characteristics to be given priority according to the application.

  Further, in the panel having the same configuration as that of Prototype Example 11, it was confirmed that the front contrast ratio increased to 380 when the light shielding layer was disposed in order to prevent light leakage from the vicinity of the dielectric structure. Here, in the step of forming the black matrix (light shielding layer) 232 before forming the dielectric structure 225 at the position on the second substrate 210b, the dielectric structure at the position where the dielectric structure 225 is formed. A light shielding layer having an area larger than the bottom surface of 225 was formed.

  As described above, by arranging the dielectric structure 25, the stabilization of the radial tilt alignment is greatly improved by the above-described action, and the halftone response time is shortened and the resilience improvement against the surface pressing impact of the panel is achieved. It was.

  As described above, the liquid crystal display device according to the present invention can realize a liquid crystal display device with excellent display quality with a relatively simple configuration. The present invention is suitably applied to a transmissive liquid crystal display device and a transflective (transmission / reflection) liquid crystal display device. In particular, the transflective liquid crystal display device is suitably used as a display device for mobile devices such as mobile phones.

It is the schematic explaining the operation | movement principle of the liquid crystal display device of embodiment by this invention, (a) shows the time at the time of no voltage application, and (b) at the time of voltage application, respectively. It is the schematic explaining the operation | movement principle of the liquid crystal display device of embodiment by this invention, and is a top view which shows the orientation state of the liquid crystal molecule at the time of a voltage application. (A)-(c) is a figure for demonstrating the preferable structure of the notch part 13 (or opening part 14) and the wall structure 15 in the liquid crystal display device of embodiment by this invention. It is a schematic diagram which shows an example of a structure of the liquid crystal display device of embodiment by this invention. It is a figure which shows typically the structure of one pixel of the transmissive liquid crystal display device 100 of embodiment by this invention, (a) is a top view, (b) is 5B- in FIG. 5 (a). It is sectional drawing along a 5B 'line. It is a figure which shows typically the structure of one pixel of the transflective liquid crystal display device 200 of embodiment by this invention, (a) is a top view, (b) is 6B in Fig.6 (a). It is sectional drawing along a -6B 'line. (A) is a top view which shows arrangement | positioning of the notch part and wall structure in the pixel electrode in Prototype examples 1-7, (b) is arrangement | positioning of the notch part and wall structure in the pixel electrode in Prototype example 8. FIG. FIG. FIG. 6 is a voltage-transmittance characteristic diagram in Prototype Example 1. 6 is an iso-contrast characteristic diagram in Prototype Example 1. FIG. FIG. 10 is a voltage-reflection / transmittance characteristic diagram in Prototype Example 8. It is a figure for demonstrating the orientation state of the liquid crystal molecule in the liquid crystal display device of other embodiment by this invention, (a) shows the time of voltage application, (b) shows the time of voltage application. It is a figure which shows typically the orientation of the liquid crystal molecule in the sub pixel of the liquid crystal display device of other embodiment by this invention, (a) at the time of no voltage application, (b) immediately after voltage application, (c) is A state in which a sufficient time has elapsed after the voltage application is shown. It is a figure which shows typically the structure of one pixel of transflective liquid crystal display device 200 'of other embodiment by this invention, (a) is a top view, (b) is in (a). It is sectional drawing which followed 13B-13B 'line.

Explanation of symbols

1 Transparent substrate (TFT substrate)
6 Pixel electrode 12, 32 Alignment film 13 Notch 14 Opening 15 Wall structure 17 Transparent substrate (counter (CF) substrate)
19 Counter electrode 20 Liquid crystal layer 21 Liquid crystal molecule 25 Dielectric structure (convex part)
50 Liquid crystal panel 40, 43 Polarizing plate 41, 44 1/4 wavelength plate 42, 45 Phase difference plate with negative optical anisotropy (NR plate)
100 transmissive liquid crystal display device 110a active matrix substrate 110b counter substrate (color filter substrate)
DESCRIPTION OF SYMBOLS 111 Pixel electrode 113 Notch part 115 Wall structure 130 Color filter layer 131 Counter electrode 133 Support body 200, 200 'Transflective liquid crystal display device 210a Active matrix substrate 210b Counter substrate (color filter substrate)
211 Pixel electrode 213 Notch 215 Wall structure 225 Dielectric structure (convex part)
230 Color filter layer 231 Counter electrode 232 Light shielding layer (black matrix)
233 Support 234 Transparent dielectric layer (reflection step)

Claims (20)

A first substrate, a second substrate provided to face the first substrate, and a vertical alignment type liquid crystal layer provided between the first substrate and the second substrate,
Each of the first electrode formed on the first substrate, the second electrode formed on the second substrate, the liquid crystal layer provided between the first electrode and the second electrode, A plurality of pixels including
A wall structure regularly arranged on the liquid crystal layer side of the first electrode;
The liquid crystal display device, wherein the liquid crystal layer forms at least one liquid crystal domain having a radially inclined alignment state in a region substantially surrounded by the wall structure when at least a predetermined voltage is applied.   The first electrode has a plurality of openings or notches formed at predetermined positions, and the wall structure includes a first wall portion formed in the plurality of openings or notches. The liquid crystal display device according to claim 1.   3. The liquid crystal display device according to claim 2, wherein each of the plurality of openings or notches includes a rectangular portion, and the wall structure includes the first wall portion provided in parallel to the rectangular portion.   4. The liquid crystal display according to claim 2, wherein each of the plurality of openings or notches includes a rectangular portion, and the wall structure includes a second wall portion extending from the first wall portion. apparatus.   The width WW of the first wall portion satisfies a relationship of 0.4 EW <WW <0.8 EW with respect to a width EW of an opening or notch in which the first wall portion is provided. 5. A liquid crystal display device according to any one of 2 to 4.   The first electrode includes a transparent electrode defining a transmissive region, and a width EW of the plurality of openings or notches is 1.8 dt <EW <with respect to a thickness dt of the liquid crystal layer in the transmissive region. The liquid crystal display device according to claim 2, wherein the liquid crystal display device satisfies a 2.5 dt relationship.   The liquid crystal display device according to claim 2, wherein the wall structure includes a third wall portion provided in a region surrounding the first electrode.   The liquid crystal display device according to claim 1, further comprising a dielectric structure provided on the liquid crystal layer side of the second substrate.   The liquid crystal display device according to claim 8, wherein the dielectric structure is disposed at a substantially center of the at least one liquid crystal domain.   10. The liquid crystal display device according to claim 8, wherein the dielectric structure is disposed substantially at a center in a region substantially surrounded by the wall structure.   The area of the region substantially surrounded by the wall structure is defined as Sd, the area of the bottom surface of the dielectric structure disposed substantially at the center of the region is defined as Sb, and Sa = (Sb / Sd) × 11. The liquid crystal display device according to claim 8, wherein a relationship of 2 ≦ Sa ≦ 25 is satisfied when 100 is satisfied.   The liquid crystal display device according to claim 8, wherein at least part of the wall structure and the dielectric structure is disposed in a light shielding region.   The liquid crystal display device according to claim 2, wherein the liquid crystal layer has a plurality of regions having different thicknesses.   The first electrode includes a transparent electrode defining a transmissive region and a reflective electrode defining a reflective region, and the thickness dt of the liquid crystal layer in the transmissive region is the thickness dr of the liquid crystal layer in the reflective region. The liquid crystal display device according to claim 2, wherein the liquid crystal display device is larger than the liquid crystal display device.   The liquid crystal display device according to claim 14, wherein the opening or notch includes an opening or notch provided between the transmission region and the reflection region.   16. The liquid crystal according to claim 14, wherein the height WH of the wall structure satisfies a relationship of 0.25 dt <WH <0.4 dt with respect to the thickness dt of the liquid crystal layer in the transmissive region. Display device.   17. The liquid crystal display device according to claim 1, wherein at least one of the first substrate and the second substrate has a support that defines a thickness of the liquid crystal layer.   The first substrate further includes an active element provided corresponding to each of the plurality of pixels, and the first electrode is provided for each of the plurality of pixels and is connected to the active element. The liquid crystal display device according to claim 1, wherein   A pair of polarizing plates arranged to face each other with the first substrate and the second substrate interposed therebetween, and at least between the first substrate and / or the second substrate and the pair of polarizing plates The liquid crystal display device according to claim 1, further comprising one biaxial optically anisotropic medium layer.   It further has a pair of polarizing plates arranged so as to face each other with the first substrate and the second substrate interposed therebetween, and between the first substrate and / or the second substrate and the pair of polarizing plates. The liquid crystal display device according to claim 1, further comprising at least one uniaxial optically anisotropic medium layer.