JP2006201594A - Liquid crystal display - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid crystal display in which a problem that a contour of an image gets blurred double even when an operating system is driven hardly occurs and which is equipped with pixel division structure. <P>SOLUTION: The liquid crystal display is equipped with a plurality of pixels each of which has a liquid crystal layer and a plurality of electrodes for applying voltage to the liquid crystal layer. Each pixel has a 1st subpixel and a 2nd subpixel which are capable of applying different voltage to respective liquid crystal layers and in which at a certain gradation, voltage of higher effective value than that of the liquid crystal layer of the 2nd subpixel is applied to the liquid crystal layer of the 1st subpixel. Starting response speed of luminance of the 1st subpixel when prescribed voltage is applied to the 1st subpixel is slow than starting response speed of luminance of the 2nd subpixel when prescribed voltage is applied to the 2nd subpixel. <P>COPYRIGHT: (C)2006,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 displaying moving images.

  In recent years, liquid crystal display devices (hereinafter referred to as “LCD”) have been widely used. The mainstream so far has been TN type LCDs in which nematic liquid crystal with positive dielectric anisotropy is twisted. This TN type LCD has a problem that the viewing angle dependency due to the orientation of liquid crystal molecules is large.

  Therefore, in order to improve the viewing angle dependency, an alignment division vertical alignment type LCD has been developed and its use is spreading. For example, Patent Document 1 discloses an MVA type liquid crystal display device which is one of alignment division vertical alignment type liquid crystal display devices. This MVA type liquid crystal display device is an LCD which performs display in a normally black (NB) mode using a vertical alignment type liquid crystal layer provided between a pair of electrodes, and is provided with domain regulating means (for example, slits or protrusions). In each pixel, the liquid crystal molecules are configured to fall (tilt) in a plurality of different directions when a voltage is applied.

  Recently, there is a rapidly increasing need for displaying moving image information not only on a liquid crystal television but also on a PC monitor and a mobile terminal device (such as a mobile phone and a PDA). In order to display a moving image with high quality on the LCD, it is necessary to shorten the response time of the liquid crystal layer (to increase the response speed), and to achieve a predetermined gradation within one vertical scanning period (typically one frame). It is required to reach. The “vertical scanning period” is defined as a period from when a certain scanning line is selected until the next scanning line is selected. One vertical scanning period in the liquid crystal display device is one frame period in the case of a signal for non-interlace driving, and corresponds to one field period in the case of a signal for interlace driving.

  For an MVA type LCD, for example, Patent Document 1 discloses that the response time between black and white can be 10 msec or less. In addition, it is described that by providing regions with different distances between protrusions in a pixel, regions having different response speeds can be provided, and the apparent response speed can be improved without lowering the aperture ratio (for example, Patent Document 1). 107-110).

On the other hand, as a driving method for improving the response characteristics of the LCD, a method of applying a voltage (referred to as “overshoot voltage”) higher than a voltage (predetermined gradation voltage) corresponding to the gradation to be displayed (“ "Overshoot drive") is known. By applying an overshoot voltage (hereinafter referred to as “OS voltage”), response characteristics in halftone display can be improved. For example, Patent Document 2 discloses an MVA type LCD that is overshoot driven (hereinafter referred to as “OS drive”). In Patent Document 2, it is described that the OS voltage should not be applied when switching from the black display state to the high luminance halftone display state (see, for example, FIG. 8 of Patent Document 2). This is because when switching from the black display state to the high luminance halftone, as in the case of switching from the black display state to the low luminance halftone display or white display state, the OS voltage (1. It is described that the transmittance overshoots when a voltage (25 times higher) is applied.
Japanese Patent No. 2947350 JP 2000-231091 A JP 2004-062146 A

  However, according to the study of the present inventor, it has been found that when OS driving is applied to the alignment-divided vertical alignment type LCD such as the above-mentioned MVA type LCD, a new problem occurs. This problem will be described with reference to FIGS. 20 (a) and 20 (b).

FIGS. 20A and 20B are schematic views of a display when a halftone (for example, 32/255 gradation) square 92 is moved in a black (for example, 0 gradation) background 90, respectively. FIG. FIG. 20A shows a case where a conventional MVA type LCD is driven by a normal driving method, and FIG. 20B shows a case where a conventional MVA type LCD is driven by OS. Note that “32/255 gradation” means that, when the gradation display is set to γ ^2.2 , the luminance during black display (when V0 is applied) is 0, and the luminance during white display (when V255 is applied). The gradation is such that the luminance is (32/255) ^2.2 when set to 1, and the gradation voltage at that time is expressed as V32.

  When OS driving is not performed, the response speed of the alignment-divided vertical alignment type LCD is slow. Therefore, as schematically shown in FIG. 20A, the edge 92a on the moving direction side of the quadrangle 92 is clear. May not be observed. On the other hand, when the OS driving method is performed, as schematically shown in FIG. 20B, the response speed is improved and the edge 92a in the moving direction is clearly observed, but the dark band 92b is slightly behind the edge 92a. There was a phenomenon that was observed.

  As a result of various investigations of the cause by the present inventors, this phenomenon is a new problem that cannot be seen when the OS driving method is applied to a conventional TN type LCD. It was found that this was caused by the alignment division being performed by the alignment regulating means (domain regulating means) arranged in a shape (band shape).

  Also, a structure (pixel division structure) including a first sub-pixel having a first luminance and a second sub-pixel having a second luminance different from the first luminance with respect to a certain display signal voltage supplied with a pixel. If the OS drive is performed when the first subpixel and the second subpixel are provided, the effect of the OS voltage on the first subpixel and the second subpixel may be different, and as a result, a problem may occur that the contour of the image is blurred twice.

  The present invention has been made in view of the above points, and one of its purposes is to provide an alignment-divided vertical alignment type LCD capable of displaying high-quality moving images.

  Another object of the present invention is to provide a liquid crystal display device having a pixel division structure that hardly causes the problem that the outline of an image is blurred twice even when the OS is driven.

  The liquid crystal display device of the present invention includes a plurality of pixels each having a liquid crystal layer and a plurality of electrodes for applying a voltage to the liquid crystal layer, and each of the plurality of pixels has a different voltage across the liquid crystal layer. The first sub-pixel and the second sub-pixel can be applied with a voltage having an effective value higher than that of the liquid crystal layer of the second sub-pixel in the liquid crystal layer of the first sub-pixel at a certain gradation. The first sub-pixel has a first sub-pixel and a second sub-pixel to be applied, and the rising response speed of the luminance of the first sub-pixel when a predetermined voltage is applied to the first sub-pixel The second subpixel is slower than the rising response speed of the luminance when applied to two subpixels, and this causes a problem that the outline of the image is double blurred even when the OS is driven. It is hard to do.

  In one embodiment, the liquid crystal layer is a vertical alignment type liquid crystal layer, and each of the first subpixel and the second subpixel is connected to the first electrode via the liquid crystal layer. A second alignment electrode, a first alignment regulating means provided on the first electrode side of the liquid crystal layer and having a first width, and a second width provided on the second electrode side of the liquid crystal layer. And a liquid crystal region having a third width defined between the first alignment restricting means and the second alignment restricting means, and the first sub-pixel of the first sub-pixel. The width of 3 is larger than the third width of the second subpixel.

  In one embodiment, the area of the first subpixel is smaller than the area of the second subpixel.

  In one embodiment, the third width of the second subpixel is not less than 2 μm and not more than 14 μm. The third width of the second subpixel is preferably 2 μm or more and 14 μm or less.

  In one embodiment, the first orientation regulating means has a strip shape having the first width, the second orientation regulating means has a strip shape having the second width, and the liquid crystal region. Has a strip-like shape having the third width.

  In one embodiment, the first orientation regulating means is a rib, and the second orientation regulating means is a slit provided in the second electrode.

  In one embodiment, the first width is 4 μm or more and 20 μm or less, and the second width is 4 μm or more and 20 μm or less.

  In one embodiment, the first electrode is a counter electrode, and the second electrode is a pixel electrode.

  In one embodiment, the apparatus further includes a drive circuit capable of applying an overshoot voltage higher than a predetermined gradation voltage corresponding to a predetermined intermediate gradation when displaying a halftone.

  An electronic apparatus according to the present invention includes any one of the liquid crystal display devices described above and a circuit that receives a television broadcast.

  In another liquid crystal display device of the present invention, each includes a first electrode, a second electrode facing the first electrode, and a vertical alignment type liquid crystal layer provided between the first electrode and the second electrode. A first alignment regulating means having a first width, provided on the second electrode side of the liquid crystal layer, and provided on the second electrode side of the liquid crystal layer. And a liquid crystal region having a third width defined between the first alignment regulating means and the second alignment regulating means, wherein the third width is It is 2 μm or more and 14 μm or less.

  In one embodiment, the first orientation regulating means has a strip shape having the first width, the second orientation regulating means has a strip shape having the second width, and the liquid crystal region. Has a strip-like shape having the third width.

  In one embodiment, the third width is preferably 12 μm or less. More preferably, the third width is 8 μm or less.

  Still another liquid crystal display device according to the present invention includes a first electrode, a second electrode facing the first electrode, and a vertical alignment type liquid crystal provided between the first electrode and the second electrode. A plurality of pixels having a layer, provided on the first electrode side of the liquid crystal layer, provided on the second electrode side of the liquid crystal layer, and provided on the second electrode side of the liquid crystal layer, A second alignment regulating unit having a width of 2, a liquid crystal region having a third width defined between the first alignment regulating unit and the second alignment regulating unit, wherein the liquid crystal region is A first liquid crystal region having a first response speed adjacent to the first alignment control means; a second liquid crystal region having a second response speed adjacent to the second alignment control means; and the first liquid crystal region; A third response defined between the second liquid crystal region and slower than the first and second response speeds. A third liquid crystal region having a speed, and within the third liquid crystal region, after applying a voltage reaching a transmittance of 32/255 gradations in one vertical scanning period from the black display state, in one vertical scanning period The width of the region where the transmittance when the corresponding time has elapsed is not more than twice the transmittance in the black display state is 2 μm or less.

  In one embodiment, the first orientation regulating means has a strip shape having the first width, the second orientation regulating means has a strip shape having the second width, and the liquid crystal region. Has a strip-like shape having the third width.

  In one embodiment, one vertical scan period is 16.7 msec.

  In one embodiment, the third width is not less than 2 μm and not more than 14 μm. The third width is preferably 12 μm or less, and more preferably 8 μm or less.

  In one embodiment, the first orientation regulating means is a rib, and the second orientation regulating means is a slit provided in the second electrode.

  In one embodiment, the first width is 4 μm or more and 20 μm or less, and the second width is 4 μm or more and 20 μm or less.

  In one embodiment, the first electrode is a counter electrode, and the second electrode is a pixel electrode.

  In one embodiment, the thickness of the liquid crystal layer is less than 3 μm.

  In one embodiment, the second width / the thickness of the liquid crystal layer is 3 or more.

  In one embodiment, the third width / the second width is 1.5 or less.

  In one embodiment, the liquid crystal layer has a pair of polarizing plates arranged to face each other, the transmission axes of the pair of polarizing plates are substantially orthogonal to each other, and one transmission axis is horizontal to the display surface The first orientation regulating means and the second orientation regulating means are arranged such that each extending direction forms approximately 45 ° with the one transmission axis.

  In one embodiment, the apparatus further includes a drive circuit capable of applying an overshoot voltage higher than a predetermined gradation voltage corresponding to a predetermined intermediate gradation when displaying a halftone.

  Still another liquid crystal display device according to the present invention includes a first electrode, a second electrode facing the first electrode, and a vertical alignment type liquid crystal provided between the first electrode and the second electrode. A plurality of pixels having a layer, provided on the first electrode side of the liquid crystal layer, and provided on a side of the second electrode of the liquid crystal layer and a first strip-shaped alignment means having a first width. , A strip-shaped second alignment regulating means having a second width, and a strip-shaped liquid crystal region having a third width defined between the first alignment regulating means and the second alignment regulating means. The third width is not less than 2 μm and not more than 14 μm, and the thickness of the liquid crystal layer is less than 3 μm.

  The driving method of the liquid crystal display device according to the present invention is any one of the above-described driving methods of the liquid crystal display device, and when displaying an intermediate gray level higher than the display gray level of the previous vertical scanning period, Including a step of applying an overshoot voltage higher than a predetermined gradation voltage corresponding to the tone.

  In one embodiment, the overshoot voltage is set so that the luminance of the display reaches a predetermined luminance corresponding to the intermediate gradation within a time corresponding to one vertical scanning period.

  An electronic apparatus according to the present invention includes any one of the liquid crystal display devices described above.

  In an embodiment, the electronic device further includes a circuit that receives a television broadcast.

  According to the present invention, there is provided an LCD having a pixel division structure that hardly causes the problem that the outline of an image is double blurred even when the OS is driven.

  In addition, according to the present invention, there is provided an alignment division vertical alignment type LCD capable of displaying a high-quality moving image when the OS driving method is applied.

  The LCD of the present invention is suitably used as, for example, a liquid crystal television provided with a circuit for receiving television broadcasting. Moreover, it is used suitably for the electronic device used for the use which displays a moving image, such as a personal computer and PDA.

  Hereinafter, an LCD according to an embodiment of the present invention and a driving method thereof will be described with reference to the drawings.

  First, a basic configuration of an alignment division vertical alignment type LCD according to an embodiment of the present invention will be described with reference to FIGS.

  The LCD according to the embodiment of the present invention includes a first electrode 11, a second electrode 12 facing the first electrode 11, a vertical alignment type liquid crystal layer 13 provided between the first electrode 11 and the second electrode 12, and A plurality of pixels. The vertical alignment type liquid crystal layer 13 aligns liquid crystal molecules having negative dielectric anisotropy substantially perpendicular to the surfaces of the first electrode 11 and the second electrode 12 (for example, 87 ° or more and 90 ° or less) when no voltage is applied. Is. Typically, it is obtained by providing a vertical alignment film (not shown) on the surface of each of the first electrode 11 and the second electrode 12 on the liquid crystal layer 13 side. When ribs (projections) are provided as alignment regulating means, the liquid crystal molecules are aligned substantially perpendicular to the surface of the liquid crystal layer side such as ribs.

  First alignment regulating means (21, 31, 41) is provided on the first electrode 11 side of the liquid crystal layer 13, and second alignment regulating means (22, 32, 41) is provided on the second electrode 12 side of the liquid crystal layer 11. 42). In the liquid crystal region defined between the first alignment regulating means and the second alignment regulating means, the liquid crystal molecules 13a receive the alignment regulating force from the first alignment regulating means and the second alignment regulating means, and receive the first electrode. When a voltage is applied between the second electrode 12 and the second electrode 12, it falls (inclined) in the direction indicated by the arrow in the figure. That is, since the liquid crystal molecules are tilted in a uniform direction in each liquid crystal region, each liquid crystal region can be regarded as a domain. In this specification, the orientation regulating means corresponds to the domain regulating means described in Patent Documents 1 and 2 above.

  The first alignment regulating means and the second alignment regulating means (these may be collectively referred to as “orientation regulating means”) are provided in a strip shape within each pixel, and FIG. c) is a cross-sectional view in a direction orthogonal to the extending direction of the strip-shaped orientation regulating means. Liquid crystal regions (domains) in which the directions in which the liquid crystal molecules 13a fall are different from each other by 180 ° are formed on both sides of each alignment regulating means.

  The LCD 10A shown in FIG. 1A has ribs 21 as first alignment regulating means, and has a slit (opening) 22 provided in the second electrode 12 as second alignment regulating means. Each of the ribs 21 and the slits 22 extends in a strip shape. The rib 21 orients the liquid crystal molecules 13a substantially perpendicular to the side surface 21a, thereby acting to orient the liquid crystal molecules 13a in a direction perpendicular to the extending direction of the ribs 21. The slit 22 generates an oblique electric field in the liquid crystal layer 13 near the edge of the slit 22 when a potential difference is formed between the first electrode 11 and the second electrode 12, and is orthogonal to the extending direction of the slit 22. It acts to align the liquid crystal molecules 13a in the direction in which the liquid crystal molecules are aligned. The ribs 21 and the slits 22 are arranged in parallel to each other with a certain distance therebetween, and a liquid crystal region (domain) is formed between the ribs 21 and the slits 22 adjacent to each other.

  The LCD 10B shown in FIG. 1 (b) is different from the LCD 10A of FIG. 1 (a) in that it has ribs 31 and ribs 32 as first orientation regulating means and second orientation regulating means, respectively. The ribs 31 and the ribs 32 are arranged in parallel with each other at a predetermined interval, and act so as to align the liquid crystal molecules 13a substantially vertically on the side surfaces 31a of the ribs 31 and the side surfaces 32a of the ribs 32. A liquid crystal region (domain) is formed between them.

  The LCD 10C shown in FIG. 1C is different from the LCD 10A shown in FIG. 1A in that each of the LCD 10C includes a slit 41 and a slit 42 as a first alignment regulating means and a second alignment regulating means. The slit 41 and the slit 42 generate an oblique electric field in the liquid crystal layer 13 in the vicinity of the end sides of the slits 41 and 42 when a potential difference is formed between the first electrode 11 and the second electrode 12. The liquid crystal molecules 13a are aligned in a direction perpendicular to the extending direction of the liquid crystal molecules 42 and 42. The slit 41 and the slit 42 are arranged in parallel to each other with a predetermined interval, and a liquid crystal region (domain) is formed between them.

  As described above, ribs or slits can be used in any combination as the first orientation regulating means and the second orientation regulating means. The first electrode 11 and the second electrode 12 may be electrodes that face each other with the liquid crystal layer 13 interposed therebetween. Typically, one is a counter electrode and the other is a pixel electrode. Hereinafter, in the case where the first electrode 11 is a counter electrode and the second electrode 12 is a pixel electrode, a rib 21 is provided as the first alignment regulating means, and the slit provided in the pixel electrode as the second alignment regulating means The embodiment of the present invention will be described by taking an LCD having 22 (corresponding to the LCD 10A in FIG. 1A) as an example. When the configuration of the LCD 10A shown in FIG. 1A is adopted, an advantage that an increase in the manufacturing process can be minimized can be obtained. Even if the pixel electrode is provided with a slit, no additional process is required. On the other hand, for the counter electrode, the number of processes is less increased when the rib is provided than when the slit is provided. Of course, the present invention can be applied to a configuration using only ribs as an orientation regulating means, or a configuration using only slits.

  As a result of various studies, the present inventor has solved the above problem described with reference to FIG. 20B by performing alignment division by the first alignment regulating means and the second alignment regulating means arranged in a strip shape in the pixel. And the occurrence of the above problem can be suppressed by setting the width of the liquid crystal region defined between the first alignment regulating means and the second alignment regulating means to 14 μm or less. It was. The cause of this problem and the effect of the LCD of the present invention will be described in detail below.

  First, the basic configuration of the LCD according to the embodiment of the present invention will be described with reference to FIGS. FIG. 2 is a partial cross-sectional view schematically showing a cross-sectional structure of the LCD 100 according to the present invention, and FIG. 3 is a plan view of the pixel portion 100a of the LCD 100. Since the LCD 100 has the same basic configuration as the LCD 10A of FIG. 1A, common constituent elements are denoted by common reference numerals.

  The LCD 100 includes a vertical alignment type liquid crystal layer 13 between a first substrate (for example, a glass substrate) 10a and a second substrate (for example, a glass substrate) 10b. A counter electrode 11 is formed on the surface of the first substrate 10a on the liquid crystal layer 13 side, and a rib 21 is further formed thereon. A vertical alignment film (not shown) is provided on almost the entire surface of the counter electrode 11 including the rib 21 on the liquid crystal layer 13 side. As shown in FIG. 3, the ribs 21 are extended in a strip shape, the adjacent ribs 21 are arranged in parallel to each other, the interval (pitch) P is constant, and the width of the ribs 21 (extension) The width W1 in the direction orthogonal to the direction is also constant.

  On the surface of the second substrate (for example, glass substrate) 10b on the liquid crystal layer 13 side, gate bus lines (scanning lines), source bus lines (signal lines) 51, and TFTs (not shown) are provided to cover these. An interlayer insulating film 52 is formed. A pixel electrode 12 is formed on the interlayer insulating film 52. Here, an interlayer insulating film 52 having a flat surface is provided using a transparent resin film having a thickness of 1.5 μm or more and 3.5 μm or less, whereby the pixel electrode 12 is connected to a gate bus line and / or a source. It becomes possible to partially overlap the bus line, and the advantage that the aperture ratio can be improved is obtained.

  A strip-shaped slit 22 is formed in the pixel electrode 12, and a vertical alignment film (not shown) is formed on almost the entire surface of the pixel electrode 12 including the slit 22. As shown in FIG. 3, the slits 22 are extended in a strip shape, the adjacent slits 22 are arranged in parallel to each other, and the intervals between the adjacent ribs 21 are arranged so as to be approximately bisected. Has been. The width (width in the direction orthogonal to the extending direction) W2 of the slit 22 is constant. The shape of the slits and ribs and their arrangement may deviate from the design values due to variations in manufacturing processes and alignment errors when bonding substrates, and the above explanation excludes them. is not.

  A strip-shaped liquid crystal region 13A having a width W3 is defined between the strip-shaped rib 21 and the slit 22 extending in parallel with each other. Each liquid crystal region 13A has its orientation direction regulated by ribs 21 and slits 22 on both sides thereof, and the liquid crystal regions (domains) in which the liquid crystal molecules 13a are tilted 180 ° different from each other on both sides of the ribs 21 and slits 22 respectively. Is formed. In the LCD 100, as shown in FIG. 3, the ribs 21 and the slits 22 extend along two directions different from each other by 90 °, and the pixel portion 100a has four types of liquid crystals whose alignment directions of the liquid crystal molecules 13a are different by 90 °. It has the area 13A. The arrangement of the ribs 21 and the slits 22 is not limited to this example, but by arranging in this way, good viewing angle characteristics can be obtained.

  A pair of polarizing plates (not shown) arranged on both sides of the first substrate 10a and the second substrate 10b are arranged so that the transmission axes are substantially orthogonal to each other (crossed Nicols state). If all of the four types of liquid crystal regions 13A having different alignment directions by 90 ° are arranged so that the respective alignment directions and the transmission axis of the polarizing plate form 45 °, the change in retardation due to the liquid crystal region 13A is the most. It can be used efficiently. That is, it is preferable to arrange the polarizing plate so that the transmission axis forms approximately 45 ° with the extending direction of the rib 21 and the slit 22. Further, in a display device that often moves the observation direction horizontally with respect to the display surface, such as a television, it is possible to arrange one transmission axis of the pair of polarizing plates in the horizontal direction with respect to the display surface, This is preferable in order to suppress the viewing angle dependency of display quality.

  The MVA LCD 100 having the above-described configuration can perform display with excellent viewing angle characteristics. However, when the OS is driven, the phenomenon shown in FIG. 20B may occur. This phenomenon will be described in detail with reference to FIGS.

  FIG. 4 is a diagram illustrating a result of measuring a change in luminance distribution in the pixels of the LCD 100 when the OS is driven using a high-speed camera. The results measured at 5 ° C. are shown for ease of understanding. The horizontal axis is a direction orthogonal to the extending direction of the ribs 21 and the slits 22, and shows the position with the center in one width direction of the adjacent slits 22 as the origin. The luminance distribution shows the measurement results after 0 msec (V0 applied state: OSV32 applied at this time), 16 msec after applying OSV32, 18 msec, and 500 msec. Note that after the vertical scanning period after the vertical scanning period (here, 1 frame = 16.7 msec) in which OSV32 was applied, V32 was continuously applied until 500 msec had elapsed after the OSV32 was applied. The vertical axis represents relative luminance, where the luminance of the light shielding region is 0 and the luminance reached after 500 msec of a third liquid crystal region R3 described later is 0.1.

  The specific cell parameters of the LCD 100 used here are the thickness d of the liquid crystal layer d = 3.9 μm, the rib pitch P = 53 μm, the width W1 of the rib 21 is 16 μm (including the width of the side portion 4 μm × 2), and the slit. The width W2 of 22 is 10 μm, the width W3 of the liquid crystal region 13A is 13.5 μm, black voltage (V0) = 1.2V, white voltage (V255) = 7.1V, and γ value is 2.2. The voltage (V32) of 32 gradations (transmittance 1.04%) = 2.44V and the OS voltage (OSV32) = 2.67V. The OS voltage (OSV32) was set so that the luminance (transmittance) of the entire pixel became a luminance of 32 gradations after 16 msec from the black state (state where V0 was applied).

  As can be seen from FIG. 4, the luminance of the region near the side surface 21a of the rib 21 (referred to as “first liquid crystal region R1”) in the liquid crystal region 13A is high, and after reaching the maximum luminance in 18 msec, the luminance is descend. On the other hand, in a region other than the first liquid crystal region R1, the luminance increases monotonously with the passage of time, and the luminance once increased does not decrease. In the liquid crystal region 13A shown in FIG. 4, the region near the slit 22 (referred to as “second liquid crystal region R2”) is affected by an oblique electric field generated in the vicinity of the slit 22, and thus the region of the liquid crystal region 13A. The response speed is faster than the region near the center (the region near the center between the rib 21 and the slit 22, referred to as “third liquid crystal region R3”). Thus, in the strip-shaped liquid crystal region 13A defined between the strip-shaped rib 21 and the slit 22, three liquid crystal regions (R1, R2, and R3) characterized by three different response speeds are formed. .

  Note that in the LCD 100 exemplified here, the first alignment regulating means (rib 21) and the second alignment regulating means (slit 22) have different effects on the response speed, so the response speeds are different from each other. Three liquid crystal regions are formed. When the influences of the first alignment regulating means and the second alignment regulating means are the same, the two liquid crystal regions (R1 and R2) having the same response speed and the response higher than these. One liquid crystal region (R3) having a low speed is formed.

  Next, with reference to FIGS. 5A and 5B, the temporal change in the overall transmittance of the pixel portion 100a will be described. The vertical axis represents 0% transmittance at 0 gradation and 100% transmittance at 32 gradations. FIG. 5A shows the results when the measurement temperature is 25 ° C., and FIG. 5B shows the results when the measurement temperature is 5 ° C.

Curve 5A-1 and curve 5A-2 in FIG. 5A are for the case where the thickness d of the liquid crystal layer is 3.9 μm, curve 5A-1 is without OS drive, and curve 5A-2 is with OS drive. Results are shown. On the other hand, a curve 5A-3 and a curve 5A-4 are obtained when the cell gap is 2.8 μm, a curve 5A-3 shows a result without OS driving, and a curve 5A-4 shows a result with OS driving. Similarly, FIG. 5B shows curves 5B-1 and 5B-2 when the thickness d of the liquid crystal layer is 3.9 μm, curve 5B-1 is without OS drive, and curve 5B-2 is with OS drive. Shows the results. Curves 5B-3 and 5B-4 are obtained when the cell gap is 2.8 μm, curve 5B-3 shows the result without OS drive, and curve 5B-4 shows the result with OS drive. In any liquid crystal layer, the liquid crystal material has a rotational viscosity γ1 of about 140 mPa · s, a flow viscosity ν of about 20 mm ² / s, and the retardation (thickness d × birefringence index) of each liquid crystal layer. The liquid crystal material was selected so that Δn) was about 300 nm.

  As is apparent from FIGS. 5A and 5B, when OS driving is performed at both temperatures of 25 ° C. and 5 ° C., a predetermined transmittance (100%) is obtained within the vertical scanning period in which the OS voltage is applied. After reaching the value, the transmittance once decreases, the transmittance gradually increases again, and the phenomenon that the predetermined transmittance is reached again is observed. In this way, the phenomenon in which the minimum value appears in the temporal change in transmittance may be referred to as “corner response”.

  Further, from the comparison between FIG. 5A and FIG. 5B, this phenomenon is more remarkable at 5 ° C. where the response speed of the liquid crystal molecules is slower, and the minimum value in the temporal change in transmittance is small. In addition, it takes a long time to reach the predetermined transmittance. Further, in FIGS. 5A and 5B, when the difference in the thickness d of the liquid crystal layer is compared, the response speed is slower and the transmittance is higher when the thickness of the liquid crystal layer is larger at any temperature. It can be seen that the time of decline is long. These tendencies corresponded to the visual observation results of the phenomenon shown in FIG.

  Thus, it has been found that the dark band 92b shown in FIG. 20B is observed because the minimum value appears in the temporal change in transmittance. Further, the reason why the minimum value appears in the temporal change in transmittance is that the difference in response speed is large among the first liquid crystal region R1, the second liquid crystal region R2, and the third liquid crystal region R3 described with reference to FIG. I also found out. This phenomenon will be described with reference to FIG. 4 again.

  The liquid crystal molecules in the first liquid crystal region R1 located in the vicinity of the rib 21 are inclined before the voltage is applied under the influence of the side surface 21a of the rib 21, and therefore the response speed is fast. When an OS voltage (OSV32) set so that the transmittance of the entire pixel is from 0 gradation to 32 gradations within one frame period is applied, the response speed of the liquid crystal molecules in the first liquid crystal region R1 is fast. The transmittance of the liquid crystal region R1 exceeds the transmittance when at least V32 is constantly applied (transmittance indicated by the curve of t = 500 sec in FIG. 4), and in some cases corresponds to the OS voltage (OSV32). To reach or close to that. On the other hand, the response speed of regions other than the first liquid crystal region R1 (second liquid crystal region R2 and third liquid crystal region R3) is slow, and even when OSV32 is applied, the transmittance corresponding to V32 is reached within one frame period. Can not.

  After the next frame period in which V32 is applied (t> 16.7 msec), the transmittance of the first liquid crystal region R1 monotonously decreases to the transmittance corresponding to V32. On the other hand, the transmittance of the second liquid crystal region R2 and the third liquid crystal region R3 monotonously increases to the transmittance corresponding to V32.

  Even if the transmittance of the entire pixel reaches the transmittance corresponding to V32 within the frame period in which the OSV 32 is applied, a component whose response speed is too fast for the transmittance at that time (the transmission exceeding the transmittance corresponding to V32) Therefore, when the application of the OSV 32 is stopped and the predetermined gradation voltage V 32 is applied, a component with a response speed that is too fast is a component with a slow response speed (transmission of the second liquid crystal region and the third liquid crystal region R 3). Since the rate component) decreases to a predetermined transmittance at a rate faster than the rate at which it increases, the transmittance of the entire pixel temporarily decreases. Thereafter, the transmittance of the entire pixel increases with an increase in a component having a slow response speed. This is the detail of the temporal change in the transmittance of the pixel portion shown in FIGS. 5 (a) and 5 (b).

  Although the OS driving method is also applied to the TN type LCD, the above-mentioned angular response is not seen in the TN type LCD. The alignment division in the TN type LCD is achieved by regulating the alignment direction of the liquid crystal molecules in each liquid crystal region (domain) by the alignment film rubbed in different directions. The orientation regulating force is given to the shape (two-dimensionally). Accordingly, no response speed distribution occurs in each liquid crystal region. On the other hand, in the alignment division vertical alignment type LCD, since the alignment division is performed by the alignment regulating means provided linearly (one-dimensionally), not only the difference in the alignment regulating force of the alignment regulating means, Regions with different response speeds are formed depending on the distance from the orientation regulating means.

  Next, cell parameters (liquid crystal layer thickness d, rib pitch P, rib width W1, slit width W2, liquid crystal) are controlled in order to suppress the occurrence of this angular response characteristic, that is, the phenomenon that the transmittance takes a minimum value after the OS voltage is applied. The MVA type LCD having the basic configuration shown in FIGS. 2 and 3 was manufactured by changing the region width W3 and the rib height, and the response characteristics were evaluated.

  As a result, it was confirmed that by reducing the liquid crystal layer thickness d, the response speed was increased as described above with reference to FIGS. 5 (a) and 5 (b). Further, it was recognized that the response speed tends to be slightly increased by increasing the rib width W1 and the slit width W2. The response speed also increased slightly by increasing the ribs. However, the effect of improving the response speed obtained by adjusting the rib width W1, the slit width W2, and the rib height was small. On the other hand, it was found that the response characteristics can be greatly improved by narrowing the liquid crystal region width W3. A part of the results is shown in FIG.

  FIG. 6 is a result of measuring the change in transmittance over time shown in FIG. 5 for an LCD in which the liquid crystal region width W3 is changed for six types of cell configurations having different liquid crystal layer thickness d and rib height. The minimum value of the transmittance after applying the OS voltage is shown. The transmittance of 32 gradations is 100%. Further, the minimum value of transmittance (sometimes referred to as “minimum transmittance”) was a substantially constant value regardless of the liquid crystal layer thickness d. The rib width W1 and the slit width W2 in the LCD used here are both in the range of about 5 μm to about 20 μm, and the rib pitch P is in the range of about 25 μm to about 58 μm. The result shown in FIG. 6 is a measurement result when the panel surface temperature is 25 ° C.

  First, it can be seen from FIG. 6 that there is no difference between the liquid crystal region width W3 and the minimum transmittance regardless of the cell configuration of six types (which includes more types including the difference between the rib width W1 and the slit width W2). There is a strong correlation. Next, it can be seen that by reducing the liquid crystal region width W3, the minimum transmittance increases almost monotonously, that is, the response characteristic is improved.

  From the results of FIG. 6, it can be seen that the minimum transmittance is 85% or more by setting the liquid crystal region width W3 to about 14 μm or less, and the minimum transmittance can be 90% or more by setting it to about 12 μm or less. When the minimum transmittance is 85% or more, the dark band 92b shown in FIG. Of course, when the minimum transmittance is 90% or more, the dark band 92b is further hardly observed.

  FIGS. 7A and 7B show the results of subjective evaluation of the response characteristics improvement effect by 25 people who actually made a prototype of a 13-inch VGA LCD. The 13-inch VGA type LCD (the present invention and the conventional LCD) used here is the same as the LCD from which the result shown in FIG. 14 described later is obtained, and the OS drive conditions are the same as those described later. . Here, the effect obtained by setting the minimum transmittance to 85% or more or 90% or more will be described.

  The horizontal axis of the graphs shown in FIGS. 7A and 7B is the temperature of the display surface of the LCD (referred to as “operating temperature”), and the vertical axis is the minimum transmittance when OS driving is performed. is there. When the operating temperature of the LCD changes, the response characteristics of the LCD change as a result of changes in physical properties such as the viscosity of the liquid crystal material. The response characteristic is lowered as the operating temperature is lower, and the response characteristic is improved as the operating temperature is higher. Here, the operating temperatures were 5 ° C, 15 ° C, 25 ° C and 40 ° C. In addition, the smaller the change in display gradation, the more likely an angular response due to OS driving occurs. FIG. 7A shows the result when the display gradation is switched from 0 gradation to 32 gradation (when the square of 0 gradation is moved in the background of 32 gradations). FIG. 7B shows the result when the gradation is switched (when the square of 0 gradation is moved in the background of 64 gradations). Symbols (◯, Δ, ×) superimposed on each point in FIGS. 7A and 7B indicate the result of subjective evaluation. Also in this case, a dark band is observed similarly to the dark band 92b shown in FIG. 20B due to the influence of the angular response. ○ indicates that the dark band is hardly visible to almost all people, △ indicates that some observers can see the dark band, but it is hardly noticeable, and × indicates almost all people Indicates that a dark band is visible.

  As can be seen from FIGS. 7A and 7B, when the minimum transmittance is 85% or more, the result of subjective evaluation is Δ or ○, and when the minimum transmittance is 90% or more, the result of subjective evaluation is ○ It becomes. In the case of a conventional LCD, when switching from 0 gradation to 32 gradation (FIG. 7A), the minimum transmittance becomes 85% or more only when the operating temperature is 40 ° C., and the general use temperature (room temperature) At 25 ° C., the minimum transmittance is only about 80%, and the subjective evaluation is x. In contrast, when the LCD according to the present invention is switched from 0 gradation to 32 gradation (FIG. 7A), the minimum transmittance is 85% or more even at an operating temperature of 5 ° C., and 25 ° C. or more. A minimum transmittance of 90% or more can be obtained at the operating temperature. Further, when the gradation is switched from 0 gradation to 64 gradation (FIG. 7B), a minimum transmittance of 90% or more can be obtained even at an operating temperature of 5 ° C.

  Thus, if the minimum transmittance is 85% or more by setting the liquid crystal region width W3 to about 14 μm or less, or the minimum transmittance is 90% or more by setting the liquid crystal region width W3 to about 12 μm or less, the OS It is possible to obtain an MVA type LCD having excellent moving image display characteristics in which a dark band is hardly visible or hardly visible even when driven.

  The liquid crystal area width W3 of 12 types (3 companies, panel size: 15 to 37 inches) of MVA type LCDs (including the PVA type LCD shown in FIG. 1C) currently on the market is about 15 μm or more. It is in the range of 27 μm or less (the width W1 of the first orientation regulating means is about 7 μm or more and about 15 μm or less, and the width W2 of the second orientation regulating means is about 7 μm or more and about 10 μm or less), and based on the above results (for example, FIG. 6) Then, when OS driving similar to that of the present embodiment is performed, a dark band is observed.

  Next, the reason why the response characteristic is improved by reducing the liquid crystal region width W3 will be described with reference to FIGS.

  FIG. 8 is a graph showing the relationship between the liquid crystal region width W3 and the width of the third liquid crystal region R3. As described above with reference to FIG. 4, the third liquid crystal region R3 is located at a position away from the inner rib 21 and the slit 22 of the liquid crystal region 13A, and is the region with the slowest response speed.

  Here, in order to quantitatively represent the width of the third liquid crystal region R3, the following definition is made. An area in which the transmittance after one frame after applying the OS voltage (OSV32) for reaching 32 gradations from the state displaying the 0 gradation (black display state) is less than twice the transmittance in the black display state Is a third liquid crystal region R3. FIG. 8 is a graph plotting the results of measuring the time variation of the transmittance distribution similar to FIG. 4 and determining the width of the third liquid crystal region R3 obtained according to the above definition for LCDs having different liquid crystal region widths W3. ing. FIG. 8 shows the measurement results at 25 ° C. and 5 ° C.

  The graphs shown in FIG. 8 are all straight lines having an inclination of 1, which indicates that the widths of the first liquid crystal region R1 and the second liquid crystal region R2 are constant without depending on the liquid crystal region width W3. . Therefore, the relationship of R3 width = liquid crystal region width W3−width of first liquid crystal region R1−width of second liquid crystal region R2 is established. When the response characteristic of the liquid crystal region 13A is improved, the third liquid crystal region R3 does not substantially exist, but the width of the third liquid crystal region R3 having a negative value is obtained from the graph (straight line) of FIG. be able to. The width of the third liquid crystal region R3 can be a parameter representing the response characteristics of the liquid crystal region 13A.

  As can be seen from FIG. 8, at 25 ° C., when the liquid crystal region width W3 is about 12 μm or less, the third liquid crystal region R3 width becomes zero. That is, the third liquid crystal region R3 having a slow response speed represented by the above definition is substantially eliminated. This corresponds to the liquid crystal region width W3 having a minimum transmittance of 90% or more in FIG. 6, and a good correlation is recognized.

  On the other hand, looking at the result of 5 ° C. shown in FIG. 8, when the liquid crystal region width W3 is about 8 μm or less, the third liquid crystal region R3 width becomes zero. Therefore, it can be seen that the liquid crystal region width W3 is preferably about 8 μm or less in order to obtain better response characteristics (moving picture display characteristics).

  FIG. 9 shows a re-plot of the graph shown in FIG. 6 with respect to the width of the third liquid crystal region R3. As is clear from FIG. 9, the minimum transmittance can be increased to 85% or more by setting the width of the third liquid crystal region R3 to about 2 μm or less, and the minimum transmittance can be set to 90% or more by setting it to about 0 μm or less. can do.

  As described above, the response characteristic is improved by narrowing the liquid crystal region width W3, and the minimum transmittance in the angular response (see FIG. 5) generated when the OS is driven is set to 85% or more of the predetermined transmittance. can do. Accordingly, an LCD capable of displaying a good moving image is provided with almost no defects caused by the angular response.

  Note that if the liquid crystal region width W3 is less than 2 μm, it becomes difficult to manufacture an LCD. Therefore, the liquid crystal region width W3 is preferably 2 μm or more. For the same reason, the rib width W1 and the slit width W2 are 4 μm or more. It is preferable.

  The OS driving method applied to the LCD of the present invention is not particularly limited, and a known OS driving method can be appropriately employed. Further, for example, as described above, when the display gradation is switched every 32 gradations (for example, from V0 to V32), the OS voltage is set so that a predetermined transmittance is obtained in one vertical scanning period, and less than 32 gradations. The magnitude of the OS voltage applied at the time of change can be obtained by interpolating the magnitude of the OS voltage determined corresponding to the change in 32 gradations. Furthermore, the magnitude of the OS voltage may be changed according to the gradation before and after the change, and as described in Patent Document 2, the OS voltage is not applied to a change between some gradations. You may do it.

  Here, the magnitude of the OS voltage that gives a predetermined transmittance after one frame period is obtained every 32 gradations, and the magnitude of the OS voltage corresponding to each gradation change is determined by interpolation. When the MVA type LCD of the present embodiment in which the liquid crystal region width W3 was set to 14 μm or less was driven using the OS voltage determined in this way, good moving image display could be realized.

  Next, the aperture ratio and transmittance of the MVA type LCD according to this embodiment will be described. As can be seen from FIGS. 2 and 3, in the MVA type LCD, reducing the liquid crystal region width W3 decreases the aperture ratio: {(pixel area−rib area−slit area) / pixel area}. As a result, the display brightness is lowered. Accordingly, if the interval between the alignment regulating means (that is, the width W3 of the liquid crystal region referred to here) is uniformly narrowed in order to improve the response characteristics, the aperture ratio is lowered. In some areas in the pixel, the interval between the adjacent alignment regulating means is narrowed, and in other areas in the pixel, the interval between the orientation regulating means is widened, without reducing the aperture ratio. It is described that the response characteristics can be improved. However, for the reasons described above, as described in Patent Document 1, when a region having a narrow interval between the orientation regulating means and a wide region are formed, regions having greatly different response speeds are formed (particularly, response time). Since the area of the low speed region becomes large, the problem of angular response becomes significant.

  On the other hand, in the basic configuration of the LCD according to the embodiment shown in FIGS. 2 and 3, the distance between the first alignment regulating means 21 and the second alignment regulating means 22 (width W3 of the strip-like liquid crystal region 13A). Is set in the above range, it is possible to suppress the occurrence of the problem of angular response. In the above-described example, the case where the width of the liquid crystal region 13A is constant in the pixel has been described. However, the liquid crystal region 13A having a different width W3 due to a factor in the manufacturing process (for example, an alignment error in the substrate bonding step). Are formed in one pixel, the occurrence of the angular response problem can be suppressed if the width W3 of each liquid crystal region 13A satisfies the above condition.

  Further, as has been clarified by a series of examinations this time, the display luminance of the MVA type LCD of the present embodiment did not decrease even though the liquid crystal region width W3 was made narrower than before. This is due to an unexpected effect that the transmittance per unit area of the pixel (hereinafter referred to as “transmission efficiency”) is improved by making the liquid crystal region width W3 narrower than before. The transmission efficiency is obtained by actually measuring the transmittance of the pixel and dividing this value by the aperture ratio. Here, the transmission efficiency is represented by a numerical value from 0 to 1.

  FIGS. 10A and 10B show the results of transmission efficiency obtained for the LCD of this embodiment having various cell parameters described in relation to FIG. FIG. 10A is a graph with (liquid crystal region width W3 / slit width W2) on the horizontal axis, and FIG. 10B is a graph with (slit width W2 / liquid crystal layer thickness d) on the horizontal axis. It is. FIG. 10C shows the aperture ratio of each LCD.

  As can be seen from FIG. 10A, by setting (liquid crystal region width W3 / slit width W2) to 1.5 or less, the transmission efficiency is improved rather than the conventional (about 0.7). Further, as can be seen from FIG. 10B, when (slit width W2 / liquid crystal layer thickness d) is about 3 or more, the transmission efficiency is stabilized at a high value of about 0.7 or more.

  The reason why the transmission efficiency is improved when the liquid crystal region width W3 is narrowed as shown in FIG. 10A will be described with reference to FIG. FIG. 11 schematically shows the orientation of the liquid crystal molecules 13 a in the liquid crystal region 13 </ b> A near the slit 22. Among the liquid crystal molecules 13a in the liquid crystal region 13A, the liquid crystal molecules 13a in the vicinity of the end side (long side) 13X of the liquid crystal region 13A extending in a band shape are affected by the oblique electric field and are in a plane perpendicular to the long side 13X. Tilt. On the other hand, the liquid crystal molecules 13a affected by the oblique electric field in the vicinity of the end (short side) 13Y intersecting the long side 13X of the liquid crystal region 13A are inclined in a direction different from the liquid crystal molecules 13a in the vicinity of the long side 13X. . That is, the liquid crystal molecules 13a in the vicinity of the short side 13Y of the liquid crystal region 13A are inclined in a direction different from the predetermined alignment direction defined by the alignment regulating force by the slit 22, and disturb the alignment of the liquid crystal molecules 13a in the liquid crystal region 13A. Will work. When the width W3 of the liquid crystal region 13A is reduced (that is, the length of the short side / the length of the long side is reduced), the liquid crystal region 13A is affected by the alignment regulating force of the slit 22 in the liquid crystal molecules 13a. The ratio of the liquid crystal molecules 13a inclined in a predetermined direction will increase, and the transmission efficiency will increase. Therefore, by narrowing the liquid crystal region width W3, an effect of stabilizing the alignment of the liquid crystal molecules 13a in the liquid crystal region 13A is obtained, and as a result, the transmission efficiency is improved.

  As a result of various studies, it has been found that the alignment stabilization effect (transmission efficiency improvement effect) by narrowing the liquid crystal region width W3 becomes significant when the liquid crystal layer thickness d is small, for example, less than 3 μm. When the liquid crystal layer thickness d decreases, the action of the oblique electric field by the slit 22 becomes stronger, while the influence of the electric field from the gate bus line and the source bus line provided around the pixel electrode 12 or from the adjacent pixel electrode. It becomes affected by the electric field. These electric fields act so as to disturb the alignment of the liquid crystal molecules 13a in the liquid crystal region 13A. Therefore, it is considered that the effect of stabilizing the alignment becomes significant when the alignment of the liquid crystal molecules 13a in the liquid crystal region 13A is easily disturbed and the liquid crystal layer thickness d is small.

  In the LCD exemplified in this embodiment, the pixel electrode 12 is formed on a relatively thick interlayer insulating film 52 covering the gate bus line and the source bus line 51 as shown in FIG. With reference to FIGS. 12A and 12B, the influence of the interlayer insulating film 52 on the alignment of the liquid crystal molecules 13a will be described.

  As shown in FIG. 12A, the interlayer insulating film 52 included in the LCD of this embodiment is formed relatively thick (for example, about 1.5 μm or more and about 3.5 μm or less). Therefore, even if the pixel electrode 12 and the gate bus line or source bus line 51 partially overlap with each other via the interlayer insulating film 52, the capacitance formed between them is small and does not affect the display quality. In addition, an electric field that affects the orientation of the liquid crystal molecules 13a existing between adjacent pixel electrodes 12 is generated between the counter electrode 11 and the pixel electrode 12, as schematically shown by the lines of electric force in the figure. The oblique electric field is almost not affected by the source bus line 51.

On the other hand, when a relatively thin interlayer insulating film (for example, a SiO ₂ film having a thickness of several hundreds nm) 52 ′ is formed as schematically shown in FIG. 12B, for example, the source bus line 51 When the pixel electrode 12 partially overlaps with the interlayer insulating film 52 ′, a relatively large capacitance is formed and the display quality is deteriorated. To prevent this, the pixel electrode 12 and the source bus line 51 are connected to each other. Provide so as not to overlap. In this case, the liquid crystal molecules 13a existing between the adjacent pixel electrodes 12 are greatly affected by the electric field generated between the pixel electrode 12 and the source bus line 51, as indicated by the lines of electric force in the drawing. The orientation of the liquid crystal molecules 13a at the end of the pixel electrode 12 is disturbed.

  As is clear from the comparison between FIGS. 12A and 12B, when the relatively thick interlayer insulating film 52 is provided as in the LCD of the illustrated embodiment, the electric field generated by the liquid crystal molecules 13a is generated by the gate bus line and the source bus line. There is an advantage that the liquid crystal molecules 13a can be well aligned in a desired direction by the alignment regulating means. In addition, by providing the relatively thick interlayer insulating film 52 in this manner, the influence of the electric field from the bus line is reduced, so that the effect of stabilizing the alignment by reducing the thickness of the liquid crystal layer is remarkably exhibited.

  In the above embodiment, the combination of the rib 21 and the slit 22 is exemplified as the combination of the first and second orientation regulating means. However, the same effect can be obtained in the combination of the rib and the rib and the combination of the slit and the slit. Can be obtained. Further, for the purpose of increasing the alignment regulating force of the slit 22, an electrode having a potential different from that of the electrode is provided below the slit 22 (on the side opposite to the liquid crystal layer 13). May be arranged.

  From the viewpoint of response characteristics, it is preferable that the thickness d of the liquid crystal layer 13 is small (see, for example, FIG. 5). By making the thickness d of the liquid crystal layer 13 of the LCD having the above configuration less than 3 μm, higher quality is achieved. An MVA type LCD capable of displaying a moving image is obtained.

  With reference to FIGS. 13A and 13B, it will be described that the response characteristic is improved by reducing the thickness d of the liquid crystal layer 13. FIG.

  The horizontal axis of the graph shown in FIG. 13A is the product of the width W3 of the liquid crystal region 13A and the thickness d of the liquid crystal layer 13, and the vertical axis is the transmittance return time. Here, the definition of “transmission return time” will be described with reference to FIG. As described above, when OS driving is performed, the transmittance changes with time as schematically shown in FIG. That is, after the transmittance reaches a predetermined value after one frame (at 16.7 msec) by applying the OS voltage (at time 0 ms), the transmittance decreases and takes a minimum value. Thereafter, the transmittance gradually approaches the transmittance corresponding to a predetermined gradation voltage. In this transmittance change, the time from the time when the predetermined transmittance is first reached (16.7 ms) to the time when the transmittance reaches 99% of the predetermined transmittance through the minimum value is referred to as “return time”. . Here, the result when the display gradation is switched from 0 gradation to 32 gradations is shown.

  As can be seen from FIG. 13 (a), the smaller the d × W3, the shorter the transmittance return time, and the better the response characteristics. As described above, the liquid crystal region width W3 is preferably set to 14 μm or less, and when the thickness d of the liquid crystal layer is less than 3 μm, the transmittance return time is about 100 ms or less.

  Thus, by setting the width W3 of the liquid crystal region to 14 μm or less and the thickness d of the liquid crystal layer to less than 3 μm, it is possible to suppress the occurrence of defects caused by angular response and further improve the response characteristics. can do.

  A description will be given of the result of actually producing a 13-inch VGA LCD and evaluating the moving image display performance. The cell parameters are almost the same as the values exemplified for the LCD 100 shown in FIG. 4 except that the liquid crystal layer thickness d is 2.5 μm and the liquid crystal region width W3 is 10.7 μm. For comparison, the characteristics of a conventional product having a liquid crystal layer thickness d of 3.4 μm and a liquid crystal region width W3 of 15.4 μm were also evaluated.

  14A to 14C show the results of evaluating the temporal change (angular response characteristics) of the overall transmittance of the pixel portion for the LCD according to the embodiment of the present invention and the conventional LCD. 14A shows the case where the display is switched from 0 gradation to 32 gradations, FIG. 14B shows the case where the display is changed from 0 gradations to 64 gradations, and FIG. 14C shows the case where the display is changed from 0 gradations to 96 gradations. The angular response characteristic is shown. Both the LCD of the present invention and the conventional LCD show the results when overshoot driving is performed. Here, the result for the case where the operating temperature is 5 ° C. is shown.

  As is apparent from FIGS. 14A to 14C, the LCD of the embodiment according to the present invention has improved response characteristics. Therefore, all of the values of the minimum transmittance are higher than those of the conventional LCD, and the predetermined level. The transmittance corresponding to the tone is 80% or more. Further, as a result of the subjective evaluation as described above, a dark band was observed when the conventional LCD was driven by the OS, whereas a dark band was hardly confirmed even when the LCD of the embodiment according to the present invention was driven by the OS. It was.

  Hereinafter, specific conditions for OS driving and response characteristics of the LCD of the present invention and the conventional LCD will be described with reference to Tables 1 to 6. Tables 1 to 6 show the results at 5 ° C.

  In Tables 1 to 6, the numerical value described at the left end (start) indicates the display gradation in the initial state, and the numerical value described in the upper stage (end) indicates the display gradation after rewriting. . Here, the case where the display gradation in the initial state is 0 gradation is illustrated.

  The OS voltage value (indicated here by the corresponding display gradation) was set as shown in Table 1 for the LCD of the present invention, and as shown in Table 4 for the conventional LCD. For example, as shown in Table 1, when switching the display from 0 gradation to 32 gradations, a voltage having a voltage value corresponding to 94 gradations was applied as the OS voltage. For gradations not shown in Tables 1 and 4, the graph shown in FIG. 15 was created based on the relationships set as shown in Tables 1 and 4, and the corresponding OS gradation was obtained by complementation.

  Tables 2 and 3 show the response time of the LCD of the present invention. Table 2 shows the results when the OS is not driven, and Table 3 shows the results when the OS is driven. Similarly, Tables 5 and 6 show response times of conventional LCDs. Table 5 shows the results when the OS is not driven, and Table 6 shows the results when the OS is driven. The response time represents the time (unit: msec) required for the transmittance to change from 10% to 90%, assuming that the change in the predetermined transmittance in each gradation change is 0% to 100%.

  As shown in Tables 1 and 4, the OS voltage value was set such that every 32 gradations, each gradation reached a predetermined gradation within one frame period. For example, in the LCD of the present invention, as shown in Table 1, the OS voltage (OSV32) when switching from 0 gradation to 32 gradations was set to V94 (voltage corresponding to 94 gradations). That is, in OS driving, V94 is applied when V32 is applied in normal driving. On the other hand, for the conventional LCD, as shown in Table 4, the OS voltage (OSV32) when switching from the 0th gradation to the 32nd gradation was set to V156 (voltage corresponding to the 156 gradation). The reason why the OS voltage value of the conventional LCD is higher is that the LCD of the present invention has better response characteristics (response time is shorter), as is clear when Table 2 and Table 5 are compared. . This also shows that the response characteristics are improved by the above-described configuration.

  As can be seen from the response time shown in Table 2, the LCD of the present invention may exceed one frame period (16.7 msec) when the OS is not driven to display a low gradation. On the other hand, when OS driving is performed, as shown in Table 3, the response time can be made shorter than one frame period in all gradations. In addition to this, the problem of angular response does not occur as described above. When the conventional LCD is driven by the OS, the response time is greatly improved as shown in Table 6, but it may still exceed one frame period, and the problem of angular response also occurs as described above.

  The liquid crystal display device according to the embodiment of the present invention exhibits excellent moving image display characteristics by OS driving as described above. Therefore, for example, by further providing a circuit for receiving television broadcasting, it can be suitably used as a liquid crystal television capable of displaying high-quality moving images. In order to realize the OS driving, a known method can be widely applied, and an OS voltage (a gradation voltage is used that is higher than a predetermined gradation voltage corresponding to a predetermined intermediate gradation). In addition, a driving circuit capable of applying a voltage to the OS may be provided, or OS driving may be executed in software.

  In the above embodiment, the present invention has been described with respect to the case where the OS driving is applied. However, even when the OS driving is not used, when the same voltage is applied (for example, the display signal voltage in the order of V0 → V94 → V32). In such a case, the effect of the present invention can be obtained.

  Further, the present invention is not limited to the above-mentioned MVA type LCD, but the liquid crystal layer is not divided into a planar (two-dimensional) alignment film but to a linear (one-dimensional) alignment regulating means (slits or ribs). That is, the present invention can be applied to other alignment-divided vertical alignment LCDs in which the alignment state and response speed of liquid crystal molecules differ depending on the distance from the alignment regulating means. For example, the present invention can also be applied to a CPA (Continuous Pinwheel Alignment) LCD shown in FIG.

  A CPA type LCD having the pixel 200 a shown in FIG. 16 includes a pixel electrode (solid portion: a portion where a conductive layer actually exists) 32, an opening 42 provided in the pixel electrode 32, and a vertical to the pixel electrode 32. The liquid crystal layer is aligned and divided by ribs (protrusions) 41 provided on a counter electrode (not shown) facing each other through the alignment type liquid crystal layer. In the CPA type LCD, the vertical alignment type liquid crystal layer is divided into different alignment directions continuously around the rib 41. The rib 41 corresponds to the first orientation regulating means, and the opening 42 corresponds to the second orientation regulating means. The outer edge of the pixel electrode 32 is formed in a shape that generates an oblique electric field, like the opening 42.

  In such a CPA type LCD, as shown in FIG. 16, the width of the rib 41 corresponds to the width W1 of the first orientation regulating means, and the width of the opening 42 corresponds to the width W2 of the second orientation regulating means. A liquid crystal region having a width W3 is defined on the pixel electrode 32 between them. Also for the CPA type LCD, the same effect as that of the MVA type LCD can be obtained by setting these widths so as to satisfy the conditions described in the above embodiment. In the CPA type LCD, as shown in FIG. 16, the shape and width of the alignment regulating means (ribs and openings) differ depending on the direction, so that the above condition is satisfied in the direction in which the width W3 of the liquid crystal region is maximum. It is preferable to set so as to.

  In the above example, in both cases of the MVA type and the CPA type, the first alignment regulating means (for example, ribs) and the second alignment regulating means (for example, slits) are arranged such that the liquid crystal region side defined between them is straight or Although it has a planar shape defined by a curve (referred to as a shape when viewed from the normal direction of the display surface), it is not limited thereto.

  For example, like the MVA type LCD shown in FIG. 17, an orientation regulating means having a comb-like planar shape can be used. An MVA LCD having the pixel 300a shown in FIG. 17 includes a pixel electrode 72, an opening 62 provided in the pixel electrode 72, and a counter electrode (not shown) that faces the pixel electrode 72 via a vertical alignment type liquid crystal layer. The liquid crystal layer is divided into alignment by ribs (protrusions) 61 provided on (). The rib 61 has a belt-like shape having a constant width W1 as in the MVA LCD of the previous embodiment, but the opening 62 is a direction perpendicular to the extending direction of the belt-like trunk portion 62a and the trunk portion 62. And a branch portion 62b extending in the direction. The strip-shaped rib 61 and the strip-shaped trunk portion 62a are arranged in parallel to each other, and a liquid crystal region having a width W3 is defined therebetween. The branch 62b of the opening 62 extends in the width direction of the liquid crystal region, and the opening 62 has a comb-like planar shape as a whole. As described in Japanese Patent Application Laid-Open No. 2002-107730, by making the openings 62 comb-shaped, the ratio of liquid crystal molecules that receive an oblique electric field increases, so that the response characteristics can be improved. However, since the distribution of the response speed of the liquid crystal molecules is influenced primarily by the distance between the rib 61 and the trunk 62a of the opening 62, the above-described response speed is obtained even if the branch 62b is provided in the opening 62. A slow third liquid crystal region is formed between the rib 61 and the trunk portion 62 a of the opening 62.

  Therefore, even in the MVA type LCD having the pixel 300a, the same effect can be obtained by setting the widths W1, W2, and W3 as in the LCD of the above-described embodiment. The same applies to the CPA type LCD shown in FIG.

  In the above description, in order to explain the configuration of an alignment-divided vertical alignment LCD (particularly the width of the liquid crystal region width W3) having excellent moving image display performance when the OS driving method is applied, the influence of the black voltage is described. Did not explain. For example, the graph showing the dependence of the minimum transmittance on the liquid crystal region width W3 in FIG. 6 shows the result when the black voltage is 1.2 V as a typical example.

Here, the influence of the black voltage on the dependence of the minimum transmittance on the liquid crystal region width W3 will be described with reference to FIGS. The cell parameters of the LCD used here are as shown in Table 7 and show the measurement results when the panel surface temperature is 25 ° C. The white voltages were all 7.6V. FIG. 18 shows the minimum transmittance that appears after application of the OS voltage when switching the display from the 0 gradation to the 32 gradation, assuming that the transmittance at the 32 gradation is 100%, and FIG. The minimum transmittance that appears after the application of the OS voltage when switching the display to gradation is represented with the transmittance of 64 gradations being 100%. In any liquid crystal layer, the liquid crystal material has a rotational viscosity γ1 of about 133 mPa · s, a flow viscosity ν of about 19 mm ² / s, and the retardation (thickness d × birefringence index) of each liquid crystal layer. The liquid crystal material was selected so that Δn) was about 300 nm.

  As can be seen from FIGS. 18 and 19, for all liquid crystal region widths W3, the minimum transmittance increases as the black voltage increases. That is, it is preferable to set the black voltage high in order to improve the moving image display performance. This is because the higher the black voltage, the stronger the alignment regulating force by the oblique electric field and the larger the tilt angle of the liquid crystal molecules. As can be easily understood from this, the transmittance increases as the black voltage is increased. Therefore, in order to obtain a high contrast ratio, a lower black voltage is preferable. The contrast ratios when the liquid crystal region width W3 was 11 μm and the black voltages were 0V, 0.5V, 1.0V, and 1.6V were 657, 613, 573, and 539, respectively.

  As shown in FIG. 18, when the liquid crystal region width W3 is 14 μm or less, a minimum transmittance of 80% or more can be obtained even when the black voltage is set to 0 V. In FIG. 19, a minimum transmittance exceeding 85% is obtained. Obtainable. Further, if the liquid crystal region width W3 is set to 12 μm or less, a minimum transmittance of about 85% or more can be obtained in FIG. 18, and a minimum transmittance of 90% or more can be obtained in FIG.

  As described above, according to the embodiment of the present invention, a configuration excellent in moving image display performance can be obtained. Therefore, even when the black voltage is set lower than that in the past, a moving image display performance equal to or higher than that in the past can be obtained. That is, the contrast ratio can be improved without sacrificing the moving image display performance. It should be noted that the moving image display performance and the contrast ratio have different levels depending on the application of the LCD, and may be optimized as appropriate.

(Pixel division structure)
The illustrated vertical alignment (VA mode) liquid crystal display device has a problem that the viewing angle dependency of the γ characteristic is larger than that of the IPS mode liquid crystal display device. The γ characteristic is the gradation dependency of the display brightness. The fact that the γ characteristic is different between the front direction and the diagonal direction means that the gradation display state differs depending on the observation direction. Also, it is particularly problematic when displaying TV broadcasts. In order to solve this problem, various pixel division structures have been proposed.

  Here, the pixel division structure refers to a first subpixel having a first luminance and a second subpixel having a second luminance different from the first luminance with respect to a certain display signal voltage supplied with the pixels. A structure comprising The number of subpixels provided in one pixel may be three or more. When a plurality of subpixels having different luminances are provided in one pixel, the viewing angle dependency between the plurality of subpixels is averaged, so that the viewing angle dependency of the entire pixel can be reduced. Since the viewing angle dependency averaging depends on the area ratio of the sub-pixels, the display using the pixel division structure can also be called a kind of area gradation display. In addition, the pixel division structure may be referred to as a multi-pixel structure.

  As such a pixel division structure, the configuration described in Patent Document 3 by the present applicant can be suitably used. In particular, an auxiliary capacitor is provided for each sub-pixel, and an auxiliary capacitor counter electrode that is one of a pair of electrodes constituting the auxiliary capacitor is used as an electrically independent electrode to supply a voltage to the auxiliary capacitor counter electrode. It is possible to suitably use a configuration in which the effective voltage applied to the liquid crystal layer (liquid crystal capacitance) of the sub-pixel is made different by making it different for each sub-pixel. Note that the same display signal voltage as that of the pixel electrode (that is, each subpixel electrode) is supplied to the auxiliary capacitance electrode which is the other electrode constituting the auxiliary capacitance. When this configuration is adopted, the difference between the effective voltages applied to the sub-pixels becomes smaller as the luminance is higher (the display signal voltage is higher) (in other words, the luminance is lower (the closer to the black display) ) Since the difference in effective voltage applied to the sub-pixel becomes large, the viewing angle dependence of the γ characteristic of the normally black liquid crystal display device of normally black mode using a nematic liquid crystal material with negative dielectric anisotropy is effective. In addition, when the pixel division structure using the auxiliary capacitance is adopted, the magnitude of the auxiliary capacitance counter voltage (so-called CS voltage, which is supplied from the CS bus line) of the auxiliary capacitance of each sub-pixel. By changing the voltage, the voltage difference (luminance difference) between sub-pixels can be changed. For example, driving utilizing the advantage of the pixel division structure (pixel division driving, multi-pixel driving, area gradation driving) Also referred.) And normal drive (drive supplies the same voltage to the sub-pixel) and can be electrically switched things.

  FIG. 21 schematically shows an electrical configuration of the liquid crystal display device 400 disclosed in Patent Document 3.

  The pixel 410 is divided into sub-pixels 410a and 410b. The sub-pixels 410a and 410b are connected to TFTs 416a and 416b and auxiliary capacitors (CS) 422a and 422b, respectively. The gate electrodes of the TFTs 416a and 416b are connected to the scanning line 412, and the source electrodes are connected to a common (identical) signal line 414. The auxiliary capacitors 422a and 422b are connected to the auxiliary capacitor line (CS bus line) 424a and the auxiliary capacitor line 424b, respectively. The auxiliary capacitances 422a and 422b are provided between the auxiliary capacitance electrode electrically connected to the subpixel electrodes 418a and 418b, the auxiliary capacitance counter electrode electrically connected to the auxiliary capacitance wirings 424a and 424b, respectively. The insulating layer (not shown) is formed. The auxiliary capacitor counter electrodes of the auxiliary capacitors 422a and 422b are independent from each other and have a structure in which different auxiliary capacitor counter voltages can be supplied from the auxiliary capacitor wirings 424a and 424b, respectively.

  Next, the principle by which different effective voltages can be applied to the liquid crystal layers of the two subpixels 410a and 410b of the liquid crystal display device 400 will be described with reference to the drawings.

  FIG. 22 schematically shows an equivalent circuit for one pixel of the liquid crystal display device 400. In the electrical equivalent circuit, the liquid crystal layers of the respective sub-pixels 410a and 410b are represented as liquid crystal layers 413a and 413b. In addition, liquid crystal capacitors formed by the subpixel electrodes 418a and 418b, the liquid crystal layers 413a and 413b, and the counter electrode 417 (common to the subpixels 410a and 410b) are Clca and Clcb.

  The capacitance values of the liquid crystal capacitors Clca and Clcb are the same value CLC (V). The value of CLC (V) depends on the effective voltage (V) applied to the liquid crystal layers of the subpixels 410a and 410b. The auxiliary capacitors 422a and 422b that are independently connected to the liquid crystal capacitors of the sub-pixels 410a and 410b are Ccsa and Ccsb, respectively, and their capacitance values are the same value CCS.

  One electrode of the liquid crystal capacitor Clca and the auxiliary capacitor Ccsa of the subpixel 410a is connected to the drain electrode of the TFT 416a provided for driving the subpixel 410a, and the other electrode of the liquid crystal capacitor Clca is connected to the counter electrode. The other electrode of the auxiliary capacitance Ccsa is connected to the auxiliary capacitance wiring 424a. One electrode of the liquid crystal capacitor Clcb and the auxiliary capacitor Ccsb of the subpixel 410b is connected to the drain electrode of the TFT 416b provided to drive the subpixel 410b, and the other electrode of the liquid crystal capacitor Clcb is connected to the counter electrode. The other electrode of the auxiliary capacitance Ccsb is connected to the auxiliary capacitance wiring 424b. The gate electrodes of the TFTs 416 a and 416 b are both connected to the scanning line 412, and the source electrodes are both connected to the signal line 414.

  23A to 23F schematically show the timing of each voltage when the liquid crystal display device 400 is driven.

  23A shows the voltage waveform Vs of the signal line 414, FIG. 23B shows the voltage waveform Vcsa of the auxiliary capacitance wiring 424a, FIG. 23C shows the voltage waveform Vcsb of the auxiliary capacitance wiring 424b, and FIG. FIG. 23E shows the voltage waveform Vlca of the pixel electrode 418a of the sub-pixel 410a, and FIG. 23F shows the voltage waveform Vlcb of the pixel electrode 418b of the sub-pixel 410b. . In addition, the broken line in the figure shows the voltage waveform COMMON (Vcom) of the counter electrode 417.

  Hereinafter, the operation of the equivalent circuit of FIG. 22 will be described with reference to FIGS.

  When the voltage Vg changes from VgL to VgH at time T1, the TFT 416a and the TFT 416b are turned on at the same time (on state), and the voltage Vs of the signal line 414 is applied to the subpixel electrodes 418a and 418b of the subpixels 410a and 410b. Then, the sub-pixels 410a and 410b are charged. Similarly, the auxiliary capacitors Ccsa and Ccsb of each sub-pixel are charged from the signal line.

Next, when the voltage Vg of the scanning line 412 changes from VgH to VgL at time T2, the TFTs 416a and 416b are turned off at the same time (OFF state), and the subpixels 410a and 410b and the auxiliary capacitors Ccsa and Ccsb are all turned on. It is electrically insulated from the signal line 414. Immediately after this, due to the pull-in phenomenon due to the influence of the parasitic capacitances and the like of the TFTs 416a and 416b, the voltages Vlca and Vlcb of the respective sub-pixel electrodes decrease by substantially the same voltage Vd,
Vlca = Vs−Vd
Vlcb = Vs−Vd
It becomes. At this time, the voltages Vcsa and Vcsb of the respective auxiliary capacitance lines are Vcsa = Vcom−Vad.
Vcsb = Vcom + Vad
It is.

At time T3, the voltage Vcsa of the auxiliary capacitance line 424a connected to the auxiliary capacitance Ccsa changes from Vcom−Vad to Vcom + Vad, and the voltage Vcsb of the auxiliary capacitance line 424b connected to the auxiliary capacitance Ccsb changes from Vcom + Vad to Vcom−Vad. It changes by twice Vad. Along with this voltage change of the auxiliary capacitance lines 424a and 424b, the voltages Vlca and Vlcb of the respective subpixel electrodes are Vlca = Vs−Vd + 2 × K × Vad.
Vlcb = Vs−Vd−2 × K × Vad
To change. However, K = CCS / (CLC (V) + CCS).

At time T4, Vcsa changes from Vcom + Vad to Vcom−Vad, Vcsb changes from Vcom−Vad to Vcom + Vad by a factor of two, Vlca and Vlcb also
Vlca = Vs−Vd + 2 × K × Vad
Vlcb = Vs−Vd−2 × K × Vad
From
Vlca = Vs−Vd
Vlcb = Vs−Vd
To change.

At time T5, Vcsa changes from Vcom−Vad to Vcom + Vad, Vcsb changes from Vcom + Vad to Vcom−Vad by a factor of two, Vlca and Vlcb also
Vlca = Vs−Vd
Vlcb = Vs−Vd
From
Vlca = Vs−Vd + 2 × K × Vad
Vlcb = Vs−Vd−2 × K × Vad
To change.

Vcsa, Vcsb, Vlca, and Vlcb alternately repeat the changes in T4 and T5 at intervals of an integral multiple of the horizontal writing time 1H. Whether the repetition interval of T4 and T5 is set to 1 time, 1 time, 2 times, 3 times, or more than 1H depends on the driving method (polarity inversion method, etc.) of the liquid crystal display device and the display state ( It may be set as appropriate in consideration of flickering, display roughness, and the like. This repetition is continued until the pixel (410a and 410b) is rewritten next time, that is, until a time equivalent to T1 is reached. Therefore, the effective values of the voltages Vlca and Vlcb of the respective subpixel electrodes are
Vlca = Vs−Vd + K × Vad
Vlcb = Vs−Vd−K × Vad
It becomes.

Therefore, effective voltages V1 and V2 applied to the liquid crystal layers 413a and 413b of the subpixels 410a and 410b are
V1 = Vlca-Vcom
V2 = Vlcb-Vcom
That is,
V1 = Vs−Vd + K × Vad−Vcom
V2 = Vs−Vd−K × Vad−Vcom
It becomes.

  Therefore, the difference ΔV12 (= V1−V2) in effective voltage applied to the liquid crystal layers 413a and 413b of the sub-pixels 410a and 410b is ΔV12 = 2 × K × Vad (where K = CCS / (CLC (V) + CCS)), and different voltages can be applied.

  The relationship between V1 and V2 in the liquid crystal display device 400 is schematically shown in FIG.

  As can be seen from FIG. 24, in the liquid crystal display device 400, the smaller the value of V1, the larger the value of ΔV12. In this way, the smaller the value of V1, the larger the value of ΔV12. be able to.

  When the OS drive is applied to the liquid crystal display device having such a pixel division structure, it has been found that there is a problem that the contour of the image looks double. A phenomenon in which the outline appears to be blurred twice will be described with reference to FIGS. 25 and 26. FIG.

  FIG. 25A schematically shows two pixels adjacent in the row direction of an MVA mode liquid crystal display device 500 ′ having a pixel division structure. Each pixel has two subpixels (510a ′ and 510b ′), and a subpixel (bright sub) to which an effective voltage higher than that of the other subpixel is applied when a voltage for displaying a halftone is applied. The area ratio (also referred to as a division ratio) between the pixel) 510a ′ and the subpixel (dark subpixel) 510b ′ having a low effective voltage is 1: 3. Further, the sub-pixels are arranged so that the bright sub-pixels are in a checkered pattern so that flicker is not easily recognized when performing dot inversion driving. That is, the bright subpixels are arranged not to be adjacent to each other in the row direction and the column direction.

  Each sub-pixel has a slit 22 provided in the sub-pixel electrode 12 and a rib 21 provided in the counter electrode (not shown) as alignment regulating means. By these, the first liquid crystal region, the second liquid crystal region, A liquid crystal region and a third liquid crystal region are defined. The widths W1a ′, W2a ′, and W3a ′ of the first, second, and third liquid crystal regions of the bright subpixel 510a ′ of the liquid crystal display device 500 ′ illustrated in FIG. 25A are the same as those of the dark subpixel 510b ′. , Equal to the widths W1b ′, W2b ′ and W3b ′ of the second and third liquid crystal regions, respectively. Each sub-pixel preferably has a pixel configuration (orientation-regulating structure) as described with reference to FIGS. 1 to 19 in order to suppress angular response. Independently, it is specific to the pixel division structure. The following problems occur.

  26 (a) to 26 (c) for the reason why the liquid crystal display device having the pixel division structure shown in FIG. 25 (a) causes the problem that the outline of the image looks double blurred when the OS is driven. While explaining.

  FIG. 26A shows a normal driving method (driving method for displaying the same luminance on the entire pixel), and the vicinity of the boundary between the halftone display area and the black display area when a certain halftone display and black display are displayed. Is schematically shown. FIG. 26B shows the halftone display area and black in the (n + 1) th frame in which the halftone display area spreads to the right after the nth frame in which the display shown in FIG. The vicinity of the boundary with the display area is schematically shown. If the OS voltage value is set appropriately, a predetermined luminance is reached within one frame, so that the boundary (outline) between the halftone display area and the black display area simply moves to the right side and the boundary becomes blurred. There is no.

  On the other hand, when pixel division driving is performed, as shown in FIG. 26 (c), the display state of the halftone display area expanded in the (n + 1) th frame is the display of the halftone display area in the nth frame. Because it is different from the state, the outline looks blurry twice.

  As shown in FIG. 26C, the halftone display area in the nth frame is displayed as an average of subpixels brighter and darker than the gray level specified by the display signal voltage. If this is expanded to the right in the (n + 1) th frame, the OS voltage applied to the bright subpixel becomes too large and the OS voltage applied to the dark subpixel becomes too small. The brightness of the halftone display area that has been set is different from the brightness of the halftone display area spread in the (n + 1) th frame. The OS voltage applied to the bright subpixel becomes excessive and the OS voltage applied to the dark subpixel becomes excessively low because the OS voltage is supplied from the signal line and is electrically the same as the display signal voltage. Yes, an OS voltage applied to a bright subpixel having a high effective voltage value for the same reason that a bright subpixel having a high effective voltage value and a dark subpixel having a low effective voltage value can be formed for one display voltage signal The OS voltage value applied to the dark subpixel having a large value and a low effective voltage value is small.

  By applying the pixel structure of the embodiment according to the present invention described above, even if the response characteristics of each subpixel are set so as to satisfy the above-described conditions, the OS voltage value between the subpixels is applied when the pixel division structure is applied. As a result, the response speed (time until reaching the predetermined luminance) is different, and as a result, the luminance (time integral value) is transiently deviated from the predetermined value in the frame to which the OS voltage is applied. For this reason, the contour of the image (the boundary between regions having different luminances) appears to be blurred twice.

  In order to solve this problem, if the sub-pixel to which a higher effective voltage is applied among the sub-pixels of the pixel, the response speed is slower than the sub-pixel to which a lower effective voltage is applied. Good. In general, the response speed of the pixel varies depending on the applied voltage and the physical properties of the liquid crystal material, but also depends on the structure of the pixel. The structure having a slow response speed here refers to a structure having a slow response speed of rising brightness when a predetermined voltage is applied. For example, when each subpixel is changed from V0 to V32, the evaluation can be performed by the response time until the 32 gradations corresponding to V32 are reached. Of course, the voltage supplied from the signal line to apply V32 to the bright subpixel is smaller than V32, and the voltage supplied from the signal line to apply V32 to the dark subpixel is larger than V32. Is appropriately set according to the pixel structure.

  When the pixel has a first subpixel and a second subpixel to which a higher effective voltage is applied, the response speed of the rise of the luminance of the first subpixel when a predetermined voltage is applied to the first subpixel, Even if a higher OS voltage is applied to the liquid crystal layer of the first subpixel, if the predetermined voltage is applied to the second subpixel, the response speed of the rise of the luminance of the second subpixel is slower. As a result of the difference in the rising speed of the luminance between the first sub-pixel and the second sub-pixel being reduced, it is possible to suppress the appearance of the image from appearing double.

  For example, the width W3a of the third liquid crystal region of the bright subpixel 510a of the liquid crystal display device 500 shown in FIG. 25B is set larger than the width W3b of the third liquid crystal region of the dark subpixel 510b. The response speed of the bright subpixel 510a when the same voltage is applied is slower than the response speed of the dark subpixel 510b. That is, the response characteristic of the bright subpixel is inferior to that of the dark subpixel. Since the response time of the liquid crystal layer has the most direct effect on the width of the third liquid crystal region as described above, the widths W1 and W2 of the first liquid crystal region and the second liquid crystal region are determined by the bright and sub widths. The pixel and the dark sub-pixel may be the same or different.

  The phenomenon that the outline of the image looks double is remarkable when the area of the bright subpixel is smaller than the area of the dark subpixel as illustrated in FIG. 25, but the liquid crystal display shown in FIG. Even when the bright subpixel 610a and the dark subpixel 610b have the same area as in the device 600 ′, the widths W1a ′, W2a ′, and W3a of the first, second, and third liquid crystal regions of the bright subpixel 610a ′. When 'is equal to the widths W1b', W2b ', and W3b' of the first, second, and third liquid crystal regions of the dark sub-pixel 610b ', there occurs a phenomenon that the contour of the image looks double.

  In order to suppress the occurrence of this problem, the width W3a of the third liquid crystal region of the bright subpixel 610a is set to the width of the third liquid crystal region of the dark subpixel 610b as in the liquid crystal display device 600 shown in FIG. What is necessary is just to set larger than W3b. The widths W1 and W2 of the first liquid crystal region and the second liquid crystal region may be the same or different between the bright subpixel 610a and the dark subpixel 610b.

  In order to eliminate the angular response and suppress the occurrence of the problem that the contour of the image looks double, the third liquid crystal region width W3b of the dark sub-pixel is set to 2 μm or more and 14 μm or less, and the OS voltage is It is preferable to set the OS voltage so that the luminance of the dark sub-pixel reaches a predetermined gradation within one vertical scanning period when supplied to the line.

  Here, the configuration described in Patent Document 3 is exemplified as the pixel division structure, but the present invention is not limited to this. For example, even when the configuration described in Japanese Patent Application Laid-Open No. 2004-213011 is adopted, The effects described in the embodiment can be obtained.

  According to the present invention, the response characteristics of an alignment division vertical alignment type LCD having a wide viewing angle characteristic such as an MVA type or a CPA type are improved, and an LCD capable of displaying a high-quality moving image is provided. In particular, even when OS driving is applied to an alignment-divided vertical alignment LCD, an LCD capable of displaying a high-quality moving image without causing a deterioration in display quality due to angular response is provided.

  In addition, according to the present invention, there is provided an LCD having a pixel division structure that hardly causes the problem that the outline of an image is blurred twice even when the OS is driven.

  The LCD according to the present invention is applied to various uses including television.

(A) to (c) are cross-sectional views schematically showing a basic configuration example of an MVA type LCD according to an embodiment of the present invention. It is a fragmentary sectional view which shows typically the cross-section of LCD100 of embodiment by this invention. 3 is a schematic plan view of a pixel unit 100a of the LCD 100. FIG. It is a graph which shows the result of having measured the change of the luminance distribution in the pixel of LCD100 when OS drive | operated using the high-speed camera. (A) And (b) is a graph which shows the time change of the transmittance | permeability at the time of OS drive of the conventional MVA type | mold liquid crystal display device, (a) was measured at 25 degreeC, (b) was each measured at 5 degreeC. It is a result. 6 is a graph showing the minimum value of transmittance after application of an OS voltage, obtained as a result of measuring the temporal change in transmittance shown in FIG. 5 for various LCDs having different liquid crystal region widths W3. (A) And (b) is a graph which shows the result of having subjectively evaluated the malfunction resulting from an angular response. It is a graph which shows the relationship between the liquid crystal region width W3 and the width | variety of 3rd liquid crystal region R3 in LCD of embodiment. 7 is a graph obtained by re-plotting the graph shown in FIG. 6 with respect to the width of the third liquid crystal region R3. (A) And (b) is a graph which shows the result of the transmission efficiency calculated | required about LCD of embodiment which has various cell parameters, (c) is a graph which shows the aperture ratio of each LCD. FIG. 6 is a diagram schematically showing the state of alignment of liquid crystal molecules 13a in a liquid crystal region 13A in the vicinity of a slit 22. (A) And (b) is a schematic diagram for demonstrating the influence with respect to the orientation of the liquid crystal molecule by the interlayer insulation film which LCD has. (A) is a graph which shows the relationship between the product of liquid crystal region width W3 and liquid crystal layer thickness d, and the return time of a transmittance | permeability, (b) is a figure for demonstrating the definition of the return time of a transmittance | permeability. It is. (A)-(c) is a graph which shows the time change of the transmittance | permeability at the time of carrying out OS drive of LCD of embodiment by this invention, and conventional LCD. It is a graph for demonstrating the setting value of OS voltage used in order to obtain the change shown in the transmittance | permeability shown in FIG. It is a top view which shows typically the pixel structure in LCD of other embodiment by this invention. It is a top view which shows typically the pixel structure in LCD of other embodiment by this invention. It is a graph which shows the minimum value of the transmittance | permeability after OS voltage (V32) application about various LCD which changed liquid crystal area width W3, and has shown the difference by a black voltage. It is a graph which shows the minimum value of the transmittance | permeability after OS voltage (V64) application about various LCD which changed liquid crystal area width W3, and has shown the difference by a black voltage. (A) And (b) is a schematic diagram for demonstrating the problem in the moving image display of MVA type | mold LCD. It is a figure which shows typically the pixel division structure of the liquid crystal display device 400 described in patent document 3. FIG. 4 is a diagram showing an electrical equivalent circuit corresponding to the pixel structure of the liquid crystal display device 400. FIG. (A)-(f) is a figure which shows the various voltage waveforms used for the drive of the liquid crystal display device 400. FIG. 6 is a diagram illustrating a relationship of applied voltages to a liquid crystal layer between sub-pixels in the liquid crystal display device 400. FIG. It is a figure which shows typically the pixel of the MVA type | mold liquid crystal display device which has a pixel division structure, (a) is an example in which a bright subpixel and a dark subpixel have the same response characteristic, (b) is It is a figure which shows the structural example in which a response characteristic is inferior to a bright subpixel than a dark subpixel. (A)-(c) is a schematic diagram for demonstrating the phenomenon in which the outline of an image looks double in the liquid crystal display device shown to Fig.25 (a). It is a figure which shows typically the pixel of the other MVA type | mold liquid crystal display device which has a pixel division structure, (a) is an example in which the bright subpixel and the dark subpixel have the same response characteristic, (b ) Is a diagram illustrating a configuration example in which a bright subpixel is inferior in response characteristics to a dark subpixel.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 1st electrode 12 2nd electrode 13 Liquid crystal layer 13A Liquid crystal area 13a Liquid crystal molecule 21 1st orientation control means (rib)
22 Second orientation regulating means (slit)

Claims (10)

Each comprising a plurality of pixels having a liquid crystal layer and a plurality of electrodes for applying a voltage to the liquid crystal layer;
Each of the plurality of pixels is a first sub-pixel and a second sub-pixel capable of applying different voltages to the liquid crystal layer, and the liquid crystal layer of the first sub-pixel is applied to the liquid crystal layer of the first sub-pixel in a certain gradation. A first subpixel and a second subpixel to which a voltage having an effective value higher than that of the liquid crystal layer of the second subpixel is applied;
The rising response speed of the luminance of the first subpixel when a predetermined voltage is applied to the first subpixel is the luminance response speed of the second subpixel when the predetermined voltage is applied to the second subpixel. A liquid crystal display device that is slower than the rising response speed. The liquid crystal layer is a vertical alignment type liquid crystal layer,
Each of the first subpixel and the second subpixel is
A first electrode, a second electrode facing the first electrode through the liquid crystal layer,
A first alignment regulating means provided on the first electrode side of the liquid crystal layer and having a first width;
A second alignment regulating means provided on the second electrode side of the liquid crystal layer and having a second width;
A liquid crystal region defined between the first alignment regulating means and the second alignment regulating means and having a third width;
2. The liquid crystal display device according to claim 1, wherein the third width of the first sub-pixel is larger than the third width of the second sub-pixel.   The liquid crystal display device according to claim 1, wherein an area of the first subpixel is smaller than an area of the second subpixel.   4. The liquid crystal display device according to claim 1, wherein the third width of the second subpixel is 2 μm or more and 14 μm or less. 5.   The first alignment regulating means has a band shape having the first width, the second alignment regulating means has a band shape having the second width, and the liquid crystal region has the third shape. The liquid crystal display device according to claim 1, wherein the liquid crystal display device has a strip shape having a width.   6. The liquid crystal display device according to claim 1, wherein the first alignment regulating means is a rib, and the second alignment regulating means is a slit provided in the second electrode.   The liquid crystal display device according to claim 6, wherein the first width is 4 μm or more and 20 μm or less, and the second width is 4 μm or more and 20 μm or less.   The liquid crystal display device according to claim 1, wherein the first electrode is a counter electrode and the second electrode is a pixel electrode.   9. The display device according to claim 1, further comprising a drive circuit capable of applying an overshoot voltage higher than a predetermined gradation voltage corresponding to a predetermined intermediate gradation when displaying a halftone. The liquid crystal display device described.   An electronic apparatus comprising the liquid crystal display device according to claim 1 and a circuit that receives a television broadcast.