JP2008304544A - Liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a vertical alignment mode liquid crystal display device which is high in response speed and reduced in occurrence of afterimage. <P>SOLUTION: The liquid crystal display device 100 is equipped with a first substrate 60 having pixel electrodes 66 and a second substrate 70 having a counter electrode 72, wherein the pixel electrode 66 has a first unit electrode 66a and a second unit electrode 66b, and a linearly extending linear protrusion 75 is formed on the liquid crystal layer 80 side surface of the second substrate 70 opposing the second unit electrode 66b. When a predetermined voltage is applied between the electrodes, liquid crystal molecules 81 in a liquid crystal domain facing the first unit electrode 66a are approximately radially tilted relative to the nearly central section of the first unit electrode 66a, and liquid crystal molecules 81 in a liquid crystal domain facing the second unit electrode 66b are tilted in a surface vertical to the extending direction of the linear protrusion 75. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a liquid crystal display device, and more particularly to a liquid crystal display device having a wide viewing angle characteristic and performing high-quality display.

  In recent years, liquid crystal display devices having wide viewing angle characteristics have been developed, and are widely used as monitors for personal computers, display devices for portable information terminal devices, or television receivers.

  One liquid crystal display device having a wide viewing angle characteristic is one using a vertically aligned liquid crystal layer (referred to as “VA mode”). The present applicant discloses a VA mode liquid crystal display device in which a viewing angle characteristic is improved by forming a radial tilt alignment domain when a voltage is applied, in Patent Document 1. In this liquid crystal display device, when a voltage is applied, a plurality of radially inclined alignment domains are formed in each pixel, and the alignment of liquid crystal molecules in adjacent radial inclined alignment domains is continuous. The present applicant refers to a liquid crystal display mode using a characteristic alignment state disclosed in Patent Document 1 as a Continuous Pinwheel Alignment (CPA) mode (Non-Patent Document 1). The entire disclosure of Patent Literature 1 and Non-Patent Literature 1 is incorporated herein by reference.

In Patent Document 1, a non-solid portion (a portion without a conductive layer, an opening) is provided in a pixel electrode, and a radial electric field is generated using an oblique electric field generated at an edge portion of the non-solid portion of the pixel electrode when a voltage is applied. A configuration for forming a tilted orientation is disclosed. Furthermore, in order to stabilize the radial tilt alignment, a configuration is disclosed in which an alignment regulating structure is provided on the liquid crystal layer side of the substrate facing the pixel electrode through the liquid crystal layer (see, for example, FIG. 27 of Patent Document 1). . An example of such an alignment regulating structure is a protrusion protruding toward the liquid crystal layer (see, for example, FIG. 24B of Patent Document 1).
JP 2002-202511 A Kubo et al., Sharp Technical Journal, No. 80, pp. 11-14 (August 2001)

  However, as disclosed in FIG. 24B of Patent Document 1, sufficient response characteristics cannot be obtained even if a configuration in which a convex portion (protrusion) is provided on the liquid crystal layer side of the counter electrode is employed. There is. For example, as described below, when the unit electrode portion (unit solid portion in Patent Document 1) corresponding to each radially inclined alignment domain becomes large, the alignment regulating force does not sufficiently reach the liquid crystal molecules in each liquid crystal domain, There is a problem that the response speed decreases. When the response speed is slow, there arises a problem that an afterimage occurs during display.

  The problems of the conventional CPA mode liquid crystal display device will be described with reference to FIGS.

  FIG. 7 is a plan view schematically showing the structure of a region 20A ′ corresponding to one pixel of a conventional CPA mode liquid crystal display device 20 ′ described in Patent Document 1. FIG. It is typical sectional drawing along a BB 'line in the inside. The liquid crystal molecules 32a shown in FIG. 8 are liquid crystal molecules in a state where no voltage is applied to the liquid crystal layer (a state where a voltage lower than the threshold voltage is applied). Here, for simplification, the wiring structure (TFT, source bus line, gate bus line) for supplying a predetermined voltage (display signal voltage) to the pixel electrode and the voltage applied to the liquid crystal layer are held. The description of the auxiliary capacity (CS) and the like is omitted.

  As shown in FIGS. 7 and 8, a conventional liquid crystal display device 20 ′ includes a first substrate (for example, a TFT substrate) 11, a second substrate (for example, a color filter substrate) 21, a first substrate 11, and a second substrate. And a vertically aligned liquid crystal layer 32 provided between the first and second liquid crystal layers. The CPA mode liquid crystal display device includes a pair of polarizing plates arranged in crossed Nicols on both sides of the first substrate 11 and the second substrate 21 and, if necessary, a quarter wavelength plate between the substrate and the polarizing plate. It will be omitted here. The use efficiency of light can be improved by providing a quarter wavelength plate.

  The conventional liquid crystal display device 20 ′ includes a plurality of pixel electrodes 12 ′ provided on the liquid crystal layer 32 side of the first substrate 11 and a counter electrode 22 provided on the liquid crystal layer 32 side of the second substrate 21. The counter electrode 22 is typically formed as one transparent conductive film that faces all the pixel electrodes 12 '. In the CPA mode liquid crystal display device, each pixel electrode 12 ′ has a plurality of unit electrode portions 12a ′, and a predetermined voltage (threshold voltage of the liquid crystal layer) is provided between the pixel electrode 12 ′ and the counter electrode 22. Liquid crystal domains corresponding to the respective unit electrode portions 12a 'are formed, and the liquid crystal molecules 32a in the liquid crystal domains are radially inclined. State (sometimes simply referred to as “radial tilt orientation”).

  The unit electrode portions 12a 'are connected to each other by the connection portion 12b and have the same potential. For each unit electrode portion 12a ′, one radial inclined alignment domain corresponding to the unit electrode portion 12a ′ is formed at the edge portion of the unit electrode portion 12a ′ having an outer edge close to an independent island. It is a result of the effect | action of the alignment control force by the diagonal electric field.

  The pixel electrode 12 ′ illustrated here has a structure in which three island-shaped unit electrode portions 12 a ′ each having a substantially square shape with four rounded corners are connected to each other through a connection portion 12 b. Accordingly, the electric field generated at the edge portion of the unit electrode portion 12a ′ other than the portion connected by the connection portion 12b is inclined toward the center of the unit electrode portion 12a ′, and the liquid crystal molecules 32a are radially inclined and oriented. Acts as follows.

  Here, an example is shown in which the unit electrode portion 12a ′ and the connection portion 12b are formed of the same conductive film (for example, an ITO film), but the plurality of unit electrode portions 12a ′ may have the same potential. Each unit electrode portion 12a ′ is a completely independent island-shaped unit electrode portion, a contact hole is formed in an interlayer insulating film provided under each unit electrode portion 12a ′, and a drain electrode of the TFT is formed in each contact hole. You may electrically connect to. In this case, since the oblique electric field generated at the edge portion of the entire outer periphery of each unit electrode portion 12a 'acts to cause the liquid crystal molecules 32a to be radially inclined and aligned, the alignment can be stabilized.

  Further, the structure of the CPA mode pixel electrode is characterized in that a conductive film does not exist between the radially inclined alignment domains formed corresponding to each unit electrode portion 12a ′ (here, a portion without the connection portion 12b, In Patent Document 1, it is also called “non-solid part”). The portion of the liquid crystal molecules 32a where the conductive film is not present is aligned corresponding to the alignment of the liquid crystal molecules 32a of the adjacent radially inclined alignment domains so as to be aligned with each other, and thus is formed corresponding to the unit electrode portion 12a ′. It acts to stabilize the orientation of the radially inclined orientation domain.

  At a position corresponding to the substantially central portion of each unit electrode portion 12a ′ on the liquid crystal layer 32 side of the counter electrode 22, a protrusion made of a dielectric (sometimes referred to as “convex portion” or “rivet”). 23 is provided. As shown in FIG. 8, the liquid crystal molecules 32a are aligned perpendicular to the surface of the protrusion 23 (more precisely, the surface of a vertical alignment film (not shown) covering the protrusion 23). Therefore, the liquid crystal molecules 32a are radially inclined with the vertex of the protrusion 23 as the center, and the central axis SA of the radial inclination orientation is formed near the vertex of the protrusion 23.

  Thus, the protrusion 23 acts to fix the position where the central axis SA is formed. In addition, since the alignment regulating force due to the surface shape of the protrusions 23 exists regardless of the presence or absence of an electric field, it also has an effect of stabilizing the radial gradient alignment when no electric field is applied or when the electric field is weak.

  Next, the alignment of liquid crystal molecules in the conventional CPA mode liquid crystal display device 20 'will be described with reference to FIG. 9A to 9D each apply a voltage for white display (voltage for displaying the maximum gradation) to the liquid crystal layer 32 (see FIG. 8) in the state in which no voltage is applied in the liquid crystal display device 20 ′. FIG. 9A schematically shows the alignment state of the liquid crystal molecules 32a after a certain time has elapsed, FIG. 9A shows 5 msec, FIG. 9B shows 10 msec, and FIG. 9C shows 15 msec. Thereafter, FIG. 9D shows the state after 20 msec. The thickness of the liquid crystal layer 32 is 3.5 μm, and the dielectric anisotropy Δε of the nematic liquid crystal material is −2.8 (20 ° C.). The white voltage is 7V.

  As shown in FIG. 9A, an electric field is formed in the liquid crystal layer 32 by applying a white voltage. The equipotential line EQ of the electric field generated at this time falls (inclines) at the edge portion (portion where the conductive film does not exist) of the unit electrode portion 12 a ′, and between the unit electrode portion 12 a ′ and the counter electrode 22. It is almost parallel. The dielectric constant of the dielectric forming the projection 23 is preferably smaller than the average dielectric constant of the liquid crystal layer 32. In such a case, the equipotential line EQ near the projection 23 is inclined as shown in the figure. Then, the alignment regulating force due to the surface shape of the protrusion 23 and the alignment regulating force due to the electric field work together to align the liquid crystal molecules 32a in a predetermined direction.

  Since the alignment regulating force acting on the liquid crystal molecules 32a is strong at the protrusions 23 and the edge portions of the unit electrode portions 12a ′, the alignment changes from the liquid crystal molecules 32a in the vicinity so as to be parallel to the equipotential line EQ. . As shown in FIGS. 9B to 9C, the change in orientation is transmitted to the liquid crystal molecules 32a located between the protrusions 23 and the edge portions of the unit electrode portions 12a ′ as time elapses. As shown in FIG. 9D, the alignment state (steady state) corresponding to the voltage applied to the liquid crystal layer 32 is reached.

  Accordingly, when the distance between the protrusion 23 and the edge portion of the unit electrode portion 12a ′ is increased, it takes a long time for the alignment of the liquid crystal molecules 32a positioned between them to change and reach a steady state. The steady state may not be reached during one frame (one vertical scanning period: for example, 16.6 msec) and may be visually recognized by the observer as an afterimage.

  The present invention has been made to solve the above problems, and an object of the present invention is to provide a liquid crystal display device that has a high response speed and is capable of suppressing the occurrence of afterimages.

  A liquid crystal display device according to the present invention includes a first substrate, a second substrate facing the first substrate, and a vertical alignment type liquid crystal layer provided between the first substrate and the second substrate. In the liquid crystal display device, the first substrate has a plurality of pixel electrodes provided on the liquid crystal layer side, and the second substrate has a counter electrode provided on the liquid crystal layer side, Each of the plurality of pixel electrodes has a first unit electrode and a second unit electrode, and a linear protrusion extending linearly is formed on the surface of the second substrate facing the second unit electrode on the liquid crystal layer side. When a voltage is applied between the pixel electrode and the counter electrode, the liquid crystal molecules in the liquid crystal domain corresponding to the first unit electrode are substantially omitted with reference to the substantially central portion of the first unit electrode. The liquid crystal molecules of the liquid crystal domain that are radially inclined and correspond to the second unit electrode are: Tilted at a plane perpendicular to the direction of extension of the serial linear projections.

  In one embodiment, the second substrate has a dielectric layer, and the linear protrusion is formed based on the dielectric layer.

  In one embodiment, the dielectric layer is formed on a surface of the counter electrode on the liquid crystal layer side.

  In one embodiment, the dielectric layer is made of a light shielding film having a light shielding property.

  In one embodiment, a dot-like protrusion made of a dielectric is formed on the surface of the second substrate facing the substantially central portion of the first unit electrode on the liquid crystal layer side.

  In one embodiment, the first substrate includes a signal line, a scanning line, and an auxiliary capacitance line, and the linear protrusion is located at a position facing the signal line, the scanning line, or the auxiliary capacitance line. Is formed.

  In one embodiment, each of the plurality of pixel electrodes has two first unit electrodes, and the second unit electrode is disposed between the two first unit electrodes.

  In one embodiment, the first substrate includes a storage capacitor line, the second unit electrode is formed on the storage capacitor line, a direction in which the storage capacitor line extends is a first direction, and When the direction perpendicular to the first direction is the second direction, the width of the second unit electrode in the second direction is wider than the width of the storage capacitor line in the second direction.

  In one embodiment, the width in the second direction of the first unit electrode in the opening surrounded by the storage capacitor line, the signal line, and the scanning line is equal to the second direction of the second electrode in the opening. Greater than the width of

  In one embodiment, the width of the first unit electrode in the first direction is wider than the width of the second direction.

  In one embodiment, the ratio of the width of the first unit electrode in the second direction to the width of the opening in the second direction is 65% or more and 85% or less.

  In one embodiment, the ratio of the width in the second direction of the second unit electrode in the opening to the width in the second direction of the opening is not less than 10% and not more than 25%.

  According to the present invention, in one pixel area, in addition to the CPA mode alignment restriction, the alignment restriction by the linear protrusion is performed, so the CPA mode alignment restriction area (area of the first unit electrode) is reduced. can do. Therefore, the response speed of the liquid crystal molecules according to the CPA mode is improved. Further, since each alignment regulating region (or liquid crystal domain) is formed to be relatively small, the response speed of the liquid crystal molecules is improved over the entire pixel region. Therefore, according to the present invention, it is possible to provide a liquid crystal display device that has a high response speed and generates little afterimage.

  Hereinafter, embodiments of a liquid crystal display device according to the present invention will be described with reference to the drawings. However, the present invention is not limited to the embodiments exemplified in this specification.

  In this specification, “pixel” refers to a minimum unit for expressing a specific gradation in display, and in color display, for example, each floor of R (red), G (green), and B (blue). Corresponds to the unit that expresses the key, also called a dot. A combination of the R pixel, the G pixel, and the B pixel constitutes one color display pixel. The “pixel region” refers to a region of the liquid crystal display device corresponding to the “pixel” of display.

  In this specification, the “vertical alignment type liquid crystal layer” refers to a liquid crystal layer in which the liquid crystal molecular axes (also referred to as “axis orientation”) are aligned at an angle of about 85 ° or more with respect to the surface of the vertical alignment film. Say. Liquid crystal molecules have negative dielectric anisotropy, and display in a normally black mode in combination with polarizing plates arranged in a crossed Nicol arrangement. The alignment film may be provided on at least one side, but is preferably provided on both sides from the viewpoint of alignment stability. Hereinafter, an example in which vertical alignment films are provided on both sides will be described.

(Embodiment 1)
The liquid crystal display device 100 according to the first embodiment will be described with reference to FIGS. 1 and 2. FIG. 1 is a plan view schematically showing the configuration of one pixel region 50 in the liquid crystal display device 100, and FIG. 2 schematically shows a cross-sectional structure of the pixel region 50 along the line AA ′ in FIG. FIG. The liquid crystal molecules 81 in FIG. 2 represent liquid crystal molecules in a state where no voltage is applied to the liquid crystal layer 80 (a state where a voltage lower than the threshold voltage is applied).

  As shown in FIG. 2, the liquid crystal display device 100 includes a TFT substrate (first substrate) 60, a counter substrate (second substrate) 70 facing the TFT substrate, and a vertical alignment type provided between these substrates. A liquid crystal layer (also simply referred to as a liquid crystal layer) 80 is provided. The vertical alignment type liquid crystal layer 80 includes nematic liquid crystal having negative (Δε <0) dielectric anisotropy.

  As shown in FIG. 1, the TFT substrate 60 is provided with a signal line (source bus line) 61 and a scanning line (gate bus line) 62 that intersects the signal line 61 substantially perpendicularly. An auxiliary capacitance line (Cs line) 63 extending substantially in parallel with the scanning line 62 is formed in the approximate center of the line. A TFT 64 is provided in the vicinity of the intersection of the signal line 61 and the scanning line 62, and the source electrode is connected to the signal line 61 and the gate electrode is connected to the scanning line 62. Further, the drain electrode of the TFT 64 is electrically connected to a pixel electrode having a configuration described below.

  A region in the pixel region 50 where the above-described wirings and TFTs 64 are not formed is a light transmission region. Here, this region is referred to as an opening (transmission region) 68. The opening 68 in one pixel region 50 includes a first opening 68a (upper opening in FIG. 1) and a second opening 68b (lower opening in FIG. 1).

  A gate insulating layer (GI layer) is formed on the scanning line 62, and an interlayer insulating layer (PAS layer, JAS layer, etc.) is formed on the signal line 61 and the TFT 64. These insulating layers are collectively represented as an insulating layer 65. A pixel electrode 66 made of a transparent electrode material such as ITO is provided on the upper surface (surface on the liquid crystal layer side) of the insulating layer 65. The pixel electrode 66 includes two first unit electrodes 66a, one second unit electrode 66b sandwiched between the two first unit electrodes 66a, and a connection unit that connects the first unit electrode 66a and the second unit electrode 66b. 66c.

  The second unit electrode 66b is disposed so as to cover the storage capacitor line 63, and the first unit electrode 66a is located in the opening 68 surrounded by the second unit electrode 66b, the scanning line 62, and the two signal lines 61. Is formed. The peripheral part of the first unit electrode 66 a may slightly overlap the signal line 61 or the scanning line 62, and the peripheral part of the second unit electrode 66 b may also slightly overlap the signal line 61.

  When the extending direction of the auxiliary capacitance line 63 and the extending direction of the signal line 61 are the first direction and the second direction, respectively, the width in the first direction of each of the first opening 68a and the second opening 68b is about 70 μm. The width in the second direction is about 90 μm. The width of the first unit electrode 66a in the first direction is about 75 μm, the width of the second direction is about 66.5 μm, the width of the second unit electrode 66b in the first direction is about 75 μm, and the width in the second direction. Is about 45 μm. The auxiliary capacitance line 63 has a width (width in the second direction) of about 10 μm, and the width in the second direction of the second unit electrode 66b inside each of the first opening 68a and the second opening 68b (FIG. 1). Both w1 and w2) are about 15 μm. The length of the connection portion 66c (the distance between the first unit electrode 66a and the second unit electrode 66b along the second direction) is about 8.5 μm. These widths and lengths are shown as an example, and the size of each element is not limited to that of the present embodiment.

  The ratio of the width in the second direction of the first unit electrode 66a to the width in the second direction of the first opening 68a and the second opening 68b is preferably 65% or more and 85% or less. Moreover, it is preferable that the ratio of w1 to the width in the second direction of the first opening 68a and the ratio of w2 to the width in the second direction of the second opening 68b are both 10% or more and 25% or less.

  Note that the liquid crystal display device of the present embodiment is a transmissive liquid crystal display device, which is not illustrated here, but is made of a conductive metal material between the scanning line 62 and the second unit electrode 66b. A layer is formed. This layer is electrically connected to the drain electrode of the TFT 64 via the drain wiring 67 and also electrically connected to the second unit electrode 66 b via a contact hole formed in the insulating layer 65. The first unit electrode 66a and the second unit electrode 66b are electrically connected via a connection portion 66c.

  In the present embodiment, the potential of the drain electrode of the TFT 64 is supplied to the first unit electrode 66a and the second unit electrode 66b with the above-described configuration, but the first unit electrode 66a is directly drained via the contact hole. The wiring 67 may be connected. In this case, the contact hole is preferably provided under a protrusion 74 described later in order to increase the transmission region.

  As shown in FIG. 2, the counter substrate 70 includes a CF layer (color filter layer) 71 corresponding to one of the three primary colors RGB, a counter electrode 72 provided on the liquid crystal layer 80 side of the CF layer, 72, a dielectric layer 73 partially provided on the surface on the liquid crystal layer 80 side, and dot-like or island-like protrusions (dot-like protrusions) 74 made of a dielectric. The counter electrode 72 is continuously formed over almost the entire surface of the counter substrate 70. The protrusion 74 is formed on the surface on the liquid crystal layer 80 side of the counter electrode 72 facing substantially the center of each of the two first unit electrodes 66a. Note that the protrusion 74 may not be formed.

  The dielectric layer 73 is formed on the surface of the counter electrode 72 on the liquid crystal layer 80 side above the auxiliary capacitance line 63 (upward in FIG. 2). The dielectric layer 73 can be formed by the same member as the protrusion 74 and in the same manufacturing process as the protrusion 74.

  The dielectric layer 73 may be provided between the CF layer 71 and the counter electrode 72. A black matrix (BM), which is a light shielding film, is formed between the CF layer 71 and the counter electrode 72 in order to prevent light leakage from the boundary portion at the boundary portion of the pixel region 50. It can be formed in the same manufacturing process by the same material as this black matrix. The dielectric layer 73 may be formed of the same material as that of one color filter layer of RGB three colors, or may be formed by stacking a plurality of color filter layers. In this case, the dielectric layer 73 is formed in the same manufacturing process as the color filter layer. As described above, the dielectric layer 73 is formed of the same material as that of the other components and is manufactured in the same manufacturing process as the other components. Therefore, a special process is added to form the dielectric layer 73. do not have to.

  Since such a dielectric layer 73 is formed, a linear protrusion (rib) is formed on the surface of the counter substrate 70 facing the second unit electrode 66b on the liquid crystal layer 80 side along the direction in which the auxiliary capacitance line 63 extends. 75 is formed, and a step structure along the same direction is formed. A side surface 76 of the linear protrusion 75 is an inclined surface having an inclination with respect to the substrate surface. When the dielectric layer 73 is formed on the surface of the counter electrode 72 on the liquid crystal layer 80 side, the dielectric layer 73 itself becomes a linear protrusion 75, and the dielectric layer 73 is formed of the CF layer 71, the counter electrode 72, and the like. In the case of forming between the two, the counter electrode 72 on the dielectric layer 73 becomes the linear protrusion 75.

  Next, a liquid crystal domain formed according to the first unit electrode 66a and the second unit electrode 66b will be described.

  When the TFT 64 is in the OFF state, no voltage is applied between the pixel electrode 66 and the counter electrode 72 (black display state), and the liquid crystal molecules are aligned substantially perpendicular to the electrode surface by an alignment film (not shown). When the TFT 64 is turned on and a predetermined voltage is applied between the pixel electrode 66 and the counter electrode 72, a liquid crystal domain is formed in units of the first unit electrode 66a and the second unit electrode 66b. At this time, the liquid crystal molecules on the first unit electrode 66a are inclined substantially radially with respect to the protrusion 74, and the liquid crystal molecules on the second unit electrode 66b are in a plane perpendicular to the extending direction of the linear protrusion 75. Incline at.

  The alignment principle of the liquid crystal domain corresponding to the first unit electrode 66a is the alignment principle based on the CPA mode, which is the same as that described above with reference to FIGS. (The unit electrode portion 12a ′ shown in FIG. 9 corresponds to the first unit electrode 66a). In the unit electrode shown in FIG. 9, the distance between the protrusion and the edge of the unit electrode is large, and there is a problem in the response speed of liquid crystal molecules. In this embodiment, the second direction of the first pixel electrode 66a is problematic. Since the width along the line is short, the response speed is improved.

  Next, the alignment of liquid crystal molecules on the second pixel electrode 66b will be described.

  As shown in FIG. 2, when no voltage is applied, the liquid crystal molecules 81 are aligned substantially perpendicular to the substrate surface by the action of the alignment film. At this time, the liquid crystal molecules 81 in the vicinity of the side surface 76 of the linear protrusion 75 are aligned substantially perpendicular to the side surface 76, that is, in an oblique direction with respect to the substrate surface in a plane perpendicular to the extending direction of the linear protrusion 75. Yes.

  FIG. 3 schematically shows the alignment state of the liquid crystal molecules 81 after a certain period of time has elapsed after applying a voltage for white display to the liquid crystal layer 80 in a state in which no voltage is applied (see FIG. 2). Here, FIGS. 3A to 3C show the alignment state at the same time as FIGS. 9A to 9C with reference to the time point when the white voltage is applied. The thickness of the liquid crystal layer 80 is 3.5 μm, the dielectric anisotropy Δε of liquid crystal molecules is −2.8 (20 ° C.), and the voltage for white display (white voltage) is 7V.

  As shown in FIG. 3A, an electric field is formed in the liquid crystal layer 80 by starting the application of the white voltage. The equipotential line EQ of the electric field generated at this time falls (inclines) at the edge portion (portion where the conductive film does not exist) of the second unit electrode 66b, and between the second unit electrode 66b and the counter electrode 72. It is almost parallel. However, in the vicinity of the side surface 76 of the linear protrusion 75, an equipotential line EQ inclined from a direction perpendicular to the side surface 76 is formed. Here, the alignment regulating force due to the surface shape of the linear protrusion 75 and the alignment regulating force due to the electric field act on the liquid crystal molecules 81 in cooperation, whereby the liquid crystal molecules 81 are aligned in a predetermined direction.

  Since the alignment regulating force acting on the liquid crystal molecules 81 is strong in the vicinity of the side surface 76 of the linear protrusion 75 and the end of the second unit electrode 66b, the liquid crystal molecules 81 in the vicinity try to be parallel to the equipotential line EQ. The orientation change begins. The alignment direction of the liquid crystal molecules 81 is affected by the pre-tilted side surface 76 and the liquid crystal molecules 81 in the vicinity of the electrode ends, and the liquid crystal molecules are arranged on both sides (both left and right in the figure) with the center of the linear protrusion 75 as a boundary. Two liquid crystal domains having the alignment directions of 81 begin to be formed.

  Next, as shown in FIGS. 3B and 3C, the change in orientation is transmitted to the liquid crystal molecules 81 other than the side surface 76 and the vicinity of the end of the second unit electrode 66b as time passes, and finally, The alignment state (steady state) corresponding to the voltage applied to the liquid crystal layer 80 is reached, and two stable liquid crystal domains with the center of the linear protrusion 75 as a boundary are completed. Since the liquid crystal layer 80 contains a chiral agent together with the liquid crystal molecules 81, the liquid crystal molecules 81 tend to be twisted and tilted in the same direction after voltage application. Therefore, a plurality of domains (switching domains) in which the alignment direction of the liquid crystal molecules 81 is unstable are rarely generated immediately after voltage application.

  Next, effects obtained by the liquid crystal display device 100 according to the present invention will be described using a liquid crystal display device 100 ′ as a reference example.

  FIG. 4 is a plan view schematically showing the configuration of one pixel region 50 in the liquid crystal display device 100 ′ of the reference example. The same constituent elements as those in the first embodiment are given the same reference numerals, and the description thereof is omitted.

  The pixel electrode 66 ′ in the liquid crystal display device 100 ′ of the reference example includes two first unit electrodes 66a ′, one auxiliary unit electrode 66d ′, and a connection for connecting the first unit electrode 66a ′ and the auxiliary unit electrode 66d ′. Part 66c. In the conventional CPA mode liquid crystal display device, in order to increase the effective display area, the unit electrode is required to cover a wider range of the opening, but the two first unit electrodes 66a of the liquid crystal display device 100 ′ are required. 'Is provided so as to cover almost the entire surface of the first opening 68a and the second opening 68b, respectively, according to this conventional requirement. Therefore, unlike the second unit electrode 66b of the first embodiment, the auxiliary unit electrode 66d ′ sandwiched between the two first unit electrodes 66a ′ does not protrude into the first opening 68a or the second opening 68b. Instead, it is formed so as to cover only the auxiliary capacitance line 63. The counter substrate above the storage capacitor line 63 is not provided with the dielectric layer 73 as in the first embodiment, and therefore the linear protrusion 75 is not formed.

  Therefore, in this liquid crystal display device 100 ′, the distance between the protrusion 74 and the edge of the first unit electrode 66a is large as in the conventional liquid crystal display device described in FIG. It takes a relatively long time to reach a steady state. Further, with respect to the liquid crystal domain on the auxiliary unit electrode 66d ′, since no protrusion is formed on the auxiliary unit electrode 66d ′, the orientation direction of the liquid crystal molecules on the auxiliary unit electrode 66d ′ is difficult to be determined when a voltage is applied, and the liquid crystal domain is stationary. It will take a long time to reach the state.

  In the liquid crystal display device 100 of the first embodiment, since the alignment regulating force works due to the presence of the linear protrusion 75, the alignment direction of the liquid crystal molecules 81 on the second unit electrode 66b at the time of voltage application is determined, and the alignment is performed in a relatively short time. Can be stabilized in a steady state. Further, the alignment regulating force by the linear protrusion 75 can act not only on the liquid crystal molecules 81 on the auxiliary capacitance line 63 but also on the liquid crystal molecules 81 in the opening 68 near the auxiliary capacitance line 63. Therefore, even if the width of the second unit electrode 66b is wider than the width of the auxiliary capacitance line 63 as in the first embodiment, all the liquid crystal molecules 81 in the liquid crystal domain can be placed in a steady state in a short time. .

  Furthermore, since the second unit electrode 66b can partially cover the opening 68, the area of the first unit electrode 66a can be made smaller than that of the reference example. Accordingly, the distance from the edge of the first unit electrode 66a to the center position (or the protrusion 74) is shortened, and the liquid crystal molecules 81 in the liquid crystal domain can be placed in a steady state in a short time. As described above, the linear protrusion 75 has an advantage that it can be formed without adding a special process.

  As described above, the liquid crystal display device 100 according to the first embodiment employs the alignment regulation using the linear protrusions 75 in addition to the CPA mode alignment regulation, and therefore, compared with the liquid crystal display device 100 ′ of the reference example. The response speed is fast, and the occurrence of afterimages can be further reduced. In addition, the improvement effect when the response speed was compared with the reference example was about 10%.

(Embodiment 2)
Next, a second embodiment of the liquid crystal display device 100 according to the present invention will be described.

  FIG. 5 is a plan view schematically showing the configuration of one pixel region 50 in the liquid crystal display device 100 of the second embodiment. As described below, the second embodiment is different from the first embodiment only in the configuration of the pixel electrode 66 and the position of the linear protrusion 75, and the other configurations are the same as those in the first embodiment. Therefore, the same reference numerals are assigned to the same components as those in the first embodiment, and the description thereof is omitted.

  As shown in FIG. 5, the pixel electrode 66 according to the second embodiment includes two first unit electrodes 66a, four second unit electrodes 66b ′, an auxiliary unit electrode 66d, and first and second unit electrodes 66a and 66b. 'And a connecting portion 66c for connecting the'. The first unit electrode 66a is formed in the first opening 68a and the second opening 68b, and both are sandwiched between the two second unit electrodes 66b '.

  Each of the second unit electrodes 66 b ′ extends in parallel with the signal line 61, and has a portion that overlaps with the signal line 61 and a portion that overlaps with the opening 68. The peripheral portions of the first unit electrode 66 a and the second unit electrode 66 b ′ may slightly overlap the scanning line 62 or the auxiliary capacitance line 63. On the counter substrate 70 above the signal line 61, the same dielectric layer 73 and linear protrusion 75 as those described in the first embodiment are formed so as to extend in the same direction as the signal line 61.

  The auxiliary unit electrode 66d does not protrude into the first opening 68a or the second opening 68b, and is formed so as to cover only the auxiliary capacitance line 63. On the counter substrate above the auxiliary capacitance line 63, the dielectric layer 73 is not provided as in the first embodiment. In addition, it is also possible to form the same second unit electrode 66b as that of the first embodiment instead of the auxiliary unit electrode 66d.

  In the liquid crystal display device 100 of the second embodiment, the alignment control force similar to that of the first embodiment acts on the liquid crystal molecules 81 on the second unit electrode 66 b ′ by the linear protrusions 75 on the signal line 61. Thereby, the orientation direction of the liquid crystal molecules 81 on the second unit electrode 66b 'at the time of voltage application is determined, and the orientation can be stabilized in a steady state in a relatively short time. Further, since the second unit electrode 66b 'can partially cover the opening 68, the area of the first unit electrode 66a can be reduced. Accordingly, the distance from the edge of the first unit electrode 66a to the center position (or the protrusion 74) is shortened, and the liquid crystal molecules 81 in the liquid crystal domain can be placed in a steady state in a short time.

(Embodiment 3)
Next, a third embodiment of the liquid crystal display device 100 according to the present invention will be described.

  FIG. 6 is a plan view schematically showing the configuration of one pixel region 50 in the liquid crystal display device 100 according to the third embodiment. As described below, the third embodiment differs from the first embodiment only in the configuration of the pixel electrode 66 and the position of the linear protrusion 75, and the other configurations are the same as those in the first embodiment. Therefore, the same reference numerals are assigned to the same components as those in the first embodiment, and the description thereof is omitted.

  As shown in FIG. 6, the pixel electrode 66 according to the third embodiment includes two first unit electrodes 66a, one second unit electrode 66b, two second unit electrodes 66b '', and the first unit electrode 66a and the first unit electrode 66a. The connection unit 66c connects the two unit electrodes 66b and the second unit electrode 66b ''. The first unit electrode 66a is formed in the first opening 68a and the second opening 68b, and both are sandwiched between the second unit electrode 66b and the second unit electrode 66b ''. Therefore, the width in the direction along the signal line 61 of the first unit electrode 66a of the third embodiment is narrower than the width of the first unit electrode 66a of the first embodiment.

  Similar to the first embodiment, the second unit electrode 66b covers the auxiliary capacitance electrode 63 and protrudes to the opening 68 side. On the auxiliary capacitance line 63, the same linear protrusion 75 as in the first embodiment is formed. Is formed. The second unit electrode 66 b ″ extends in parallel with the scanning line 62, and has a portion overlapping the scanning line 62 and a portion overlapping the opening 68. On the counter substrate 70 above the scanning line 62, the same dielectric layer 73 and linear protrusion 75 as those described in the first embodiment are formed so as to extend in the same direction as the scanning line 62.

  In the liquid crystal display device 100 according to the third embodiment, a liquid crystal domain having the same mode as that described in the first embodiment is formed on the first unit electrode 66a and the second unit electrode 66b, and the second unit electrode 66b ′. The alignment regulating force due to the linear protrusions 75 on the scanning line 62 also acts on the liquid crystal molecules 81 above “. Accordingly, not only the liquid crystal molecules 81 on the first unit electrode 66a and the second unit electrode 66b but also the liquid crystal molecules 81 on the second unit electrode 66b '' can stabilize the alignment in a steady state in a short time. . Further, since the area of the first unit electrode 66a can be made smaller than that of the first embodiment, the liquid crystal molecules 81 on the first unit electrode 66a can be placed in a steady state in a shorter time. Note that the second unit electrode 66b of the third embodiment may be replaced with the auxiliary unit electrode 66d of the second embodiment. In this case, the linear protrusion 75 does not have to be formed on the auxiliary capacitance line 63.

  As described above, the liquid crystal display device 100 according to the present invention improves the responsiveness of the liquid crystal molecules 81 on the first unit electrode 66a because the liquid crystal display device 100 according to the present invention has a small area. Can do. At the same time, by arranging the linear protrusion 75 on the signal line 61, the scanning line 62, or the auxiliary capacitance line 63, the responsiveness of the liquid crystal molecules 81 other than on the first unit electrode 66a can be improved. Can do.

  Since the linear protrusion 75 is disposed on the light-shielding wiring portion, the transmittance is not lowered by providing the linear protrusion 75. Moreover, the linear protrusion 75 can be formed without adding a special process. Therefore, according to the present invention, it is possible to provide a liquid crystal display device capable of display with high transmittance and high response speed with high manufacturing efficiency.

  In the above-described embodiment, two first unit electrodes 66a are arranged in each pixel region. However, the liquid crystal display device according to the present invention is not limited to this, and three or more in each pixel region. The first unit electrode 66a is also included in the liquid crystal display device of the present invention.

  Further, the material, shape, size, position, and the like of the pixel electrode and the linear protrusion are not limited to those described above, and any liquid crystal display device that can obtain the effects of the present invention by disposing these components. For example, it is included in the scope of the liquid crystal display device of the present invention.

  According to the present invention, it is possible to provide a high-quality liquid crystal display device with high transmittance and reduced occurrence of afterimages at a relatively low cost. The liquid crystal display device according to the present invention is suitable for various liquid crystal display devices, for example, in-vehicle display devices such as mobile phones and car navigation systems, display devices such as ATMs and vending machines, portable display devices, and notebook PCs. Used for.

3 is a plan view schematically showing the configuration of one pixel region in the liquid crystal display device of Embodiment 1. FIG. It is the figure which represented typically the cross-section of the pixel area | region 50 along the A-A 'line of FIG. 2 is a cross-sectional view showing a state of liquid crystal molecules after voltage application is started in the liquid crystal display device of Embodiment 1, wherein (a) shows a state after 5 msec, (b) after 10 msec, and (c) shows a state after 15 msec. ing. It is the top view which represented typically the structure of one pixel area | region in the liquid crystal display device of a reference example. FIG. 6 is a plan view schematically showing the configuration of one pixel region in the liquid crystal display device of Embodiment 2. FIG. 10 is a plan view schematically showing the configuration of one pixel region in the liquid crystal display device of Embodiment 3. FIG. 10 is a diagram illustrating a configuration of a pixel electrode in a conventional CPA mode liquid crystal display device. It is sectional drawing showing the state of the liquid crystal molecule at the time of no voltage application in the conventional liquid crystal display device of CPA mode. It is sectional drawing showing the state of the liquid crystal molecule after the voltage application start in the conventional CPA mode liquid crystal display device, (a) after 5 msec, (b) after 10 msec, (c) after 15 msec, (d) Indicates the state after 20 msec.

Explanation of symbols

11 First substrate (TFT side glass substrate)
12 'pixel electrode 12a' unit electrode portion 12b connection portion 20 'liquid crystal display device 20A' region corresponding to pixel 21 second substrate (color filter side glass substrate)
22 Counter electrode 23 Protrusion (convex or rivet)
32 Vertical alignment type liquid crystal layer 32a Liquid crystal molecule 50 Pixel region 60 TFT substrate (first substrate)
61 Signal line (source bus line)
62 Scanning line (gate bus line)
63 Auxiliary capacitance line (Cs line)
64 TFT
65 Insulating layer 66, 66 ′ Pixel electrode 66a, 66a ′ First unit electrode 66b, 66b ′, 66b ″ Second unit electrode 66c Connection portion 66d, 66d ′ Auxiliary unit electrode 67 Drain wiring 68 Opening (transmission region)
68a First opening 68b Second opening 70 Counter substrate (second substrate)
71 CF layer (color filter layer)
72 Counter electrode 73 Dielectric layer (linear protrusion)
74 Protrusion (dotted protrusion)
75 Linear protrusion 76 Side surface 80 Vertical alignment type liquid crystal layer (liquid crystal layer)
81 Liquid crystal molecules 100, 100 'Liquid crystal display device

Claims (12)

A liquid crystal display device comprising: a first substrate; a second substrate facing the first substrate; and a vertical alignment type liquid crystal layer provided between the first substrate and the second substrate,
The first substrate has a plurality of pixel electrodes provided on the liquid crystal layer side,
The second substrate has a counter electrode provided on the liquid crystal layer side,
Each of the plurality of pixel electrodes has a first unit electrode and a second unit electrode,
A linear protrusion extending in a linear shape is formed on the surface of the second substrate facing the second unit electrode on the liquid crystal layer side,
When a voltage is applied between the pixel electrode and the counter electrode, the liquid crystal molecules in the liquid crystal domain corresponding to the first unit electrode are inclined substantially radially with respect to the approximate center of the first unit electrode. The liquid crystal molecules of the liquid crystal domain corresponding to the second unit electrode are inclined in a plane perpendicular to the extending direction of the linear protrusions.   The liquid crystal display device according to claim 1, wherein the second substrate has a dielectric layer, and the linear protrusions are formed based on the dielectric layer.   The liquid crystal display device according to claim 2, wherein the dielectric layer is formed on a surface of the counter electrode on the liquid crystal layer side.   The liquid crystal display device according to claim 2, wherein the dielectric layer is made of a light shielding film having a light shielding property.   5. The dot-shaped protrusion made of a dielectric material is formed on a surface of the second substrate facing the substantially central portion of the first unit electrode on the liquid crystal layer side, according to claim 1. The liquid crystal display device described.   The first substrate includes a signal line, a scanning line, and an auxiliary capacitance line, and the linear protrusion is formed at a position facing the signal line, the scanning line, or the auxiliary capacitance line. The liquid crystal display device according to claim 1.   7. The device according to claim 1, wherein each of the plurality of pixel electrodes has two of the first unit electrodes, and the second unit electrode is disposed between the two first unit electrodes. 2. A liquid crystal display device according to item 1. The first substrate includes a storage capacitor line;
The second unit electrode is formed on the storage capacitor line;
When the direction in which the storage capacitor line extends is the first direction and the direction perpendicular to the first direction is the second direction, the width of the second unit electrode in the second direction is the first direction of the storage capacitor line. The liquid crystal display device according to claim 1, wherein the liquid crystal display device is wider than a width in two directions.   The width in the second direction of the first unit electrode in the opening surrounded by the storage capacitor line, the signal line, and the scanning line is larger than the width in the second direction of the second electrode in the opening. The liquid crystal display device according to claim 8.   The liquid crystal display device according to claim 9, wherein a width of the first unit electrode in the first direction is wider than a width in the second direction.   11. The liquid crystal display device according to claim 9, wherein a ratio of a width of the first unit electrode in the second direction to a width of the opening in the second direction is 65% or more and 85% or less.   The ratio of the width in the second direction of the second unit electrode in the opening to the width in the second direction of the opening is 10% or more and 25% or less. The liquid crystal display device according to item.

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