JP2005055645A - Liquid crystal display element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce light leakage and to make the aperture ratio as large as possible. <P>SOLUTION: The translucent liquid crystal element has a transmission opening part B for transmitting a part of light incident from a light source arranged in a rear face to be displayed, and a reflection opening part A for reflecting outside light to be displayed in a pixel. The thickness of a liquid crystal layer, corresponding to the transmission opening part B, is different from a thickness of a liquid crystal layer corresponding to the reflection opening part A. The reflection opening part is formed so that it is overlapped on at least a part of a signal line S for supplying an electrical signal to the pixel or a gate line G for driving a switching element arranged in each pixel and includes a pixel array such that in-pixel arrangements, in between adjacent pixels, the opening part B and the opening part A are different. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a so-called transflective liquid crystal display element having a transmissive opening and a reflective opening, and relates to a technique for suppressing a decrease in contrast due to light leakage.

  In recent years, liquid crystal display elements have been applied to various fields such as notebook computers, monitors, car navigation systems, scientific calculators, and small and medium-sized TVs. In particular, since the reflective liquid crystal display element does not require a backlight, application to a portable device display such as a mobile PC is being studied in order to take advantage of low power consumption, thinness, and light weight.

  By the way, the conventional reflective liquid crystal display element is basically a display using outside light like paper. Therefore, when the usage environment itself is dark, the display screen becomes dark and the display can be visually recognized. It becomes difficult. In particular, the display is completely invisible in the dark and cannot be used as a display device.

  Therefore, when the surroundings are dark, a liquid crystal display element that performs display by emitting light from a built-in light source is in the spotlight. Examples of such a liquid crystal display element include a backlight type transflective type in which a light source is disposed behind the liquid crystal display element, and a front light type reflective type in which the light source is disposed in front of the liquid crystal display element. Proposed.

  In particular, since the transflective liquid crystal display element can be manufactured with almost the same material as the transmissive liquid crystal display element conventionally used, there are many merits such as sharing of equipment, suppression of member cost, reduction of development cost, It has already been put into practical use as a display device for mobile phones, PDAs (Personal Digital Assistants) and the like.

However, it is generally difficult for a transflective liquid crystal display element to achieve sufficient light utilization efficiency for both transmissive display characteristics and reflective display characteristics. Accordingly, various liquid crystal display modes have been proposed as means for solving such problems (see, for example, Patent Document 1).
Japanese Patent Laid-Open No. 11-242226

  When considering a transflective liquid crystal display element with high light utilization efficiency, for example, it is possible to use a homogeneous mode in which a pixel is divided into a transmissive opening and a reflective opening, and the liquid crystal layer thickness is different in each region. It is advantageous. In the homogeneous mode, since the liquid crystal molecules are arranged in the same direction, the structure is simple, and optical compensation using a retardation plate or the like is easy, so that a display with a wide viewing angle can be realized.

  However, in the transflective liquid crystal display element, the thickness of the liquid crystal layer is intermediate between the optimum thickness for transmissive display and the optimum thickness for reflective display, particularly at the boundary between the transmissive opening and the reflective opening. There is a region. In such a region, sufficient display cannot be performed as transmissive display or reflective display, and light leakage occurs particularly when black display is performed, which causes a reduction in contrast of the entire display. . For example, in each pixel, as widely used in conventional transflective liquid crystal display elements, when a transmissive opening is formed at the center of the reflective opening, all four sides of the transmissive opening have an intermediate thickness. In this region, the reduction in contrast becomes remarkable.

  As one method for solving such an inconvenience, it is conceivable to divide the pixel into two and to use one as a reflection opening and the other as a transmission opening. In this case, for example, in the horizontal pixel line, the transmissive openings are adjacent to each other, so that there is no intermediate thickness region in this portion, and a reduction in contrast is suppressed. However, when such an arrangement is adopted, the signal line formed between adjacent transmission openings obstructs light transmission, and the area on the signal line cannot be used for display, resulting in loss of aperture ratio. It leads to. In addition, since the reflective openings are adjacent to each other, if the reflective openings are enlarged to, for example, the signal line to increase the aperture ratio as much as possible, a short circuit between the reflective electrodes is likely to occur.

  The present invention has been proposed for the purpose of eliminating these disadvantages. That is, according to the present invention, in a liquid crystal display element having a structure in which the thickness of the liquid crystal layer is different between the transmission opening and the reflection opening, it is possible to display with sufficient contrast by reducing light leakage, and to increase the aperture ratio. An object of the present invention is to provide a liquid crystal display element that can be made as large as possible.

  In order to achieve the above object, the liquid crystal display element of the present invention has the following configuration. First, the liquid crystal display element of the present invention includes a transmissive aperture for transmitting a part of light incident from a light source arranged on the back surface and displaying a reflective aperture for reflecting an external light in a pixel. The liquid crystal display element has different thicknesses of the liquid layer corresponding to the transmission opening and the liquid crystal layer corresponding to the reflection opening. In such a liquid crystal display element, the liquid crystal display element includes a pixel arrangement in which the arrangement of the transmission opening and the reflection opening in the pixel is different between adjacent pixels. Further, the reflection opening is formed so as to overlap at least part of a signal line for supplying an electric signal to the pixel or a gate line for driving a switching element arranged in each pixel. And

  In the liquid crystal display element of the present invention having the above-described configuration, since the arrangement of the transmissive opening and the reflective opening in the pixel includes a pixel arrangement that differs between the adjacent pixels, the transmissive opening and the reflective are reflected in the adjacent pixels. The openings are arranged close to each other. Therefore, the slope of the boundary between the transmissive opening and the reflective opening (the region where the thickness of the liquid crystal layer is intermediate between the optimal thickness for transmissive display and the optimal thickness for reflective display) That is, it overlaps with the signal line or the gate line, and the light leakage in this region is blocked by the signal line or the gate line, and the decrease in contrast is suppressed. Further, in the liquid crystal display element of the present invention, the reflection opening portion overlaps at least a part of a signal line for supplying an electric signal to the pixel or a gate line for driving a switching element in which each pixel is arranged. Since the reflection electrode (for example, the reflection electrode) is enlarged, the loss of the aperture ratio due to the signal line and the gate line is compensated, and the light use efficiency is ensured.

  According to the present invention, in a liquid crystal display element having a structure in which the thickness of the liquid crystal layer is different between the transmission opening and the reflection opening, it is possible to reduce the light leakage and realize display with sufficient contrast. At the same time, loss of the aperture ratio due to the signal line and the gate line can be compensated, so that display with high light utilization efficiency and good contrast can be realized.

  Hereinafter, a transflective liquid crystal display element to which the present invention is applied will be described in detail with reference to the drawings.

  First, the cross-sectional structure of the transflective liquid crystal display element of this embodiment is shown in FIG. The transflective liquid crystal display element 1 also has basically the same structure as a normal liquid crystal display element, and a liquid crystal cell is formed by a pair of glass substrates, and a liquid crystal material is sealed in the gap to form a liquid crystal layer. Has been. The transflective liquid crystal display element 1 of this embodiment is no exception, and a liquid crystal layer 4 is sealed between an upper glass substrate 2 and a lower glass substrate 3.

  The upper glass substrate 2 corresponds to a counter substrate, and a color filter layer 5 corresponding to each pixel is formed on the surface on the liquid crystal layer 4 side, and the surface is covered with a transparent conductive material such as ITO. A transparent electrode 6 made of a material is formed on the entire surface. The color filter layer 5 is a resin layer colored in colors by pigments or dyes, and is configured by combining filter layers of R, G, B colors, for example. A so-called black matrix layer 7 is formed at the boundary between the color filter layers 5 for the purpose of improving the contrast.

  The lower glass substrate 3 corresponds to a so-called array substrate, and pixel electrodes and thin film transistors (TFTs) as switching elements are formed in a matrix corresponding to each pixel, and the pixel electrodes are electrically connected. A signal line for sending a signal and a gate line for supplying a signal to a thin film transistor which is a switching element are wired orthogonally to each other.

  In the transflective liquid crystal display element of the present embodiment, the area is divided into a reflective opening A in which a reflective electrode 8 is formed as each pixel electrode and a transparent opening B in which a transparent electrode 9 is formed. In such a transflective liquid crystal display element, external light is used in the reflective aperture A, and image display is performed in the transmissive aperture B using the backlight 10 disposed on the back side as a light source.

  Hereinafter, the lower glass substrate 3 which is an array substrate will be described in detail. In the surface of the lower glass substrate 3 facing the upper glass substrate 2, in the region corresponding to the reflective opening, fine irregularities are formed on the surface. The insulating layer 11 is formed, and the reflective electrode 8 made of a metal material having a high light reflection efficiency such as aluminum is formed thereon, and a liquid crystal driving switching element is formed at a position hidden by the reflective electrode 8. A TFT 12 is formed. By forming the reflective electrode 8 on the insulating layer 11 on which the fine irregularities are formed, the fine irregularities are reflected also on the reflective electrode 8, and the reflected light is made uniform by scattering when reflecting external light. The insulating layer 11 also serves to adjust the thickness (cell gap) of the liquid crystal layer 4 in the reflective opening. Since the TFT 12 serving as a switching element is positioned on the back side of the reflective electrode 8, there is no hindrance during image display.

  On the other hand, in the transmissive opening, the insulating layer 11 is not formed, and only the transparent electrode 9 made of a transparent conductive material such as ITO is formed. Therefore, in this transmissive opening, light from the backlight 10 passes through the lower glass substrate 3 and the transparent electrode 9 and enters the liquid crystal layer 4, and is observed as image display light from the upper glass substrate 2 side. .

  The transflective liquid crystal display element of this embodiment is a so-called multi-gap type transflective liquid crystal display element in which the cell gap of the transmissive opening is thicker than the cell gap of the reflective opening. Therefore, the lower glass substrate 3 has a step corresponding to the thickness of the insulating layer 11 at the boundary between the region with a small cell gap (reflection opening) and the region with a large cell gap (transmission opening). However, in this portion, a steep step is eliminated by providing a gradient in the thickness of the insulating layer 11 and forming the inclined portion 11a.

  An alignment film that aligns liquid crystal molecules constituting the liquid crystal layer 4 in a predetermined direction is formed on the surfaces of the upper glass substrate 2 and the lower glass substrate 3 that are in contact with the liquid crystal layer 4. A normal alignment film used for this type of liquid crystal display element can be used, and the description thereof is omitted here.

  A first polarizing plate 13, a first λ / 2 plate 14, and a first retardation plate 15 are disposed on the surface of the upper glass substrate 2 opposite to the surface in contact with the liquid crystal layer 4. ing. Similarly, the second polarizing plate 16, the second λ / 2 plate 17, and the second retardation plate 18 are disposed on the surface of the lower glass substrate 3 opposite to the surface in contact with the liquid crystal layer 4. Has been. The λ / 2 plates 14 and 17 are retardation plates having a retardation value of about 270 nm. However, the λ / 2 plates 14 and 17 are referred to as λ / 2 plates in order to be distinguished from the retardation plates 15 and 18. It is not intended to limit. In addition, for the sake of simplification, illustration and description of a protective insulating layer, a capacitor electrode, and the like that are not necessary for describing the liquid crystal display element of the present invention are omitted.

  For the liquid crystal layer 4, any liquid crystal material used for a normal liquid crystal display element can be used. Moreover, although the thickness of the liquid crystal layer 4 differs between the reflective opening A and the transmissive opening B, the thickness of the liquid crystal layer 4 may be set as appropriate depending on the type of liquid crystal material used. In the present embodiment, for example, a nematic liquid crystal having a refractive index anisotropy Δn = 0.06 is used as the liquid crystal material, the thickness d1 of the liquid crystal layer 4 in the transmission opening B is 5.0 μm, and the liquid crystal layer 4 in the reflection opening A. The thickness d2 was set to 3.0 μm.

  FIG. 2 shows a planar arrangement of pixels in the liquid crystal display element of this embodiment. In the liquid crystal display element of the present embodiment, a rectangular (rectangular) pixel divided by the signal line S and the gate line G is divided into two in the longitudinal direction, one of which is a reflection opening A and the other is a transmission opening B. Has been. In FIG. 2, the shape of the reflective electrode 8 is displayed as the shape of the reflective opening A, and the shape of the transparent electrode 9 is displayed as the shape of the transmissive opening B.

  The liquid crystal display element of this embodiment is characterized in that it includes a pixel arrangement in which the arrangement of the transmissive opening B and the reflective opening A in the pixel is different between adjacent pixels. Specifically, in the horizontal pixel line, pixels whose transmission openings B and reflection openings A are arranged differently are alternately arranged. As shown in FIG. 2A, transmission is performed between adjacent pixels. The arrangement of the opening B and the reflection opening A is upside down. In the vertical pixel line, pixels having the same arrangement of the transmissive aperture B and the reflective aperture A are arranged so as to be lined up and down.

  By adopting the arrangement as described above, the transmission aperture B of a certain pixel is in contact with the reflection aperture A of the same pixel and one side, and the remaining three sides are the reflection apertures A of three adjacent pixels. Therefore, each transmission opening B is arranged to be surrounded by the reflection opening A on the four sides. Similarly, the reflection opening A of a certain pixel is arranged so as to be surrounded on four sides by the transmission opening B of the same pixel and the transmission openings B of three adjacent pixels.

  In addition, the boundary between the adjacent transmissive opening B and the reflective opening A is inclined in section with respect to the substrate (see the inclined portion 11a of the insulating layer 11 in FIG. 1). A portion corresponding to between adjacent pixels is arranged so as to partially overlap the signal line S or the gate line G. Accordingly, light leakage at the inclined portion 11 a is blocked by the signal line S or the gate line G in three of the four sides of the transmission opening B.

  Further, as shown in FIG. 2B, the reflective electrode 8 of the reflective opening A is formed so as to cover a part of the inclined portion 11a, and the signal line S or the gate line G and the insulating layer 11 are formed. It is the structure which overlaps through. The transparent electrode 9 of the transmissive opening B is formed up to a marginal position where it partially overlaps or does not overlap the inclined portion 11a at the boundary with the reflective opening A of the adjacent pixel. By adopting such a structure, the area on the signal line S or the gate line G is effectively used as the reflection opening A, and the loss of the aperture ratio due to the signal line S or the gate line G is minimized.

  In the present embodiment, the reflective aperture A of a certain pixel is arranged so as to be surrounded on four sides by the transparent aperture B of the same pixel and the transparent aperture B of three adjacent pixels. The reflective openings are arranged so that only the corners are close to each other. That is, only the corners of the reflective electrodes 8 of the adjacent reflective openings A are close to each other. Therefore, even when the reflective electrode 8 is enlarged to, for example, the signal line S as described above, a short circuit between the reflective electrodes 8 of adjacent pixels is unlikely to occur.

  In the present embodiment, the liquid crystal layer 4 has a homogeneous alignment in which liquid crystal molecules are arranged in substantially the same direction in a state where no voltage is applied, and display is performed in a homogeneous mode. For this reason, here, the orientation film (not shown) formed on the transparent electrode 6, the reflective electrode 8, and the transparent electrode 9 is antiparallel when the liquid crystal display element is manufactured (the opposite directions are parallel to each other). The film was rubbed to give an alignment treatment.

Next, the reason why good display characteristics can be obtained in the liquid crystal display element of this embodiment will be described in comparison with a liquid crystal display element having a conventional structure.
FIG. 3 shows an example of a pixel structure of a conventional transflective liquid crystal display element. In the transflective liquid crystal display element shown in FIG. 3, like the liquid crystal display element of the previous embodiment, a rectangular (rectangular) pixel is divided into two in the longitudinal direction, one being a reflective aperture A and the other being a transmissive aperture. Although it is a portion B, the planar arrangement of each pixel is the same, and the transmission opening B of a certain pixel is close to the transmission opening B of an adjacent pixel at the left and right boundaries. In this pixel arrangement, the area C on the signal line cannot be used for display, resulting in a loss of aperture ratio.

  FIG. 4 shows another example of a pixel structure of a conventional transflective liquid crystal display element. In the transflective liquid crystal display element shown in FIG. 4, a reflective electrode (reflective opening A) is provided on the outer periphery of each pixel in order to compensate for the above-mentioned drawbacks in the transflective liquid crystal display element shown in FIG. A transmission opening B is arranged. Thereby, a part on the signal line S and the gate line G can be covered with the reflective electrode, the aperture ratio is improved, and the light utilization efficiency is increased.

  However, in the transflective liquid crystal display device having the configuration of FIG. 4, the length of the boundary between the transmissive opening B and the reflective opening A in the display area increases. That is, all the four sides around the transmissive opening B become the boundary line with the reflective opening A, and as a result, the ratio of the area occupied by the inclined portion 11a existing along the boundary line in the pixel increases. Moreover, this boundary line cannot overlap the signal line S or the gate line G. In the inclined portion 11a, the liquid crystal layer thickness is intermediate between the optimal liquid crystal layer thickness for transmissive display and the optimal liquid crystal layer thickness for reflective display. That is, when the inclined portion 11a is covered with the transparent electrode 9 to form the transmissive opening B, the contrast particularly during transmissive display is lowered. On the contrary, when the inclined portion 11a is completely covered with the reflective electrode 8 to form the reflective opening A, the contrast particularly in the reflective display is lowered.

  On the other hand, in the transflective liquid crystal display element of this embodiment, unlike the transflective liquid crystal display element of the conventional structure, the transmissive opening B of one pixel has a reflective aperture A of a pixel having three adjacent sides. And close. On the three sides, the boundary line between the transmission opening B and the reflection opening A, that is, the inclined part 11a overlaps with the signal line S or the gate line G, and the above-described contrast reduction is suppressed. Further, by extending the reflective electrode 8 over the signal line S and the gate line G, it is possible to compensate for the aperture ratio loss as described above. As a result, it is possible to realize display with high light utilization efficiency and good contrast.

  As mentioned above, although embodiment of the liquid crystal display element to which this invention was applied was described, it cannot be overemphasized that this invention is not limited to this embodiment. For example, although the homogeneous mode is used in this embodiment, the display mode is not limited to this, and a liquid crystal mode using bend alignment or vertical alignment can be used, or twisted alignment in which nematic liquid crystal is twisted. It is good also as a mode.

  Furthermore, it is desirable to optimize the configuration of the optical film according to the mode to be employed. For example, the λ / 2 plate can be omitted, and a new retardation plate may be added in order to improve CR. Specifically, when a wide viewing angle is required depending on the application of the liquid crystal display element, a plurality of viewing angle compensation films can be newly inserted.

  Further, the shape of the pixel, the shape of the transmission opening, the shape of the reflection opening, the ratio, and the like can be freely selected. In this case, it is desirable to design the pixel structure so that the aperture ratio is as high as possible within a range in which adjacent pixels are not electrically connected to each other. Furthermore, in the present embodiment, the liquid crystal layer is driven by a thin film transistor (TFT) as a switching element, but driving by a TFD (Thin Film Diode) may be used, or simple matrix driving may be used. In this case, the manufacturing yield is improved, the brightness is improved at a low aperture ratio, and the power consumption is also reduced.

It is sectional drawing which shows an example of the structure of a transflective liquid crystal display element. BRIEF DESCRIPTION OF THE DRAWINGS The structure of the transflective liquid crystal display element of embodiment is shown typically, (a) is a top view, (b) is sectional drawing in the xx line | wire of (a). The structural example of the transflective liquid crystal element of the conventional structure is shown typically, (a) is a top view, (b) is sectional drawing in the yy line of (a). The other structural example of the transflective liquid crystal element of a conventional structure is shown typically, (a) is a top view, (b) is sectional drawing in the zz line of (a).

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Transflective liquid crystal display element 2 Upper glass substrate 3 Lower glass substrate 4 Liquid crystal layer 5 Color filter layer 6 Transparent electrode 8 Reflective electrode 9 Transparent electrode 10 Backlight 11 Insulating layer 11a Inclined part 12 TFT (switching element)
A Reflection opening B Transmission opening S Signal line G Gate line

Claims (5)

The pixel has a transmissive aperture for transmitting a part of the light incident from the light source arranged on the back surface, and a reflective aperture for reflecting the external light in the pixel, and corresponds to the transmissive aperture. In the liquid crystal display element in which the thickness of the liquid layer layer and the thickness of the liquid crystal layer corresponding to the reflective opening are different,
A pixel arrangement in which the arrangement of the transmissive opening and the reflective opening in a pixel is different between adjacent pixels;
The reflection opening is formed so as to overlap at least part of a signal line for supplying an electric signal to a pixel or a gate line for driving a switching element disposed in each pixel. Liquid crystal display element. A rectangular pixel is divided into two in the longitudinal direction, one being a transmission opening and the other being a reflection opening,
The three sides of the four sides of the transmissive aperture except for the side in contact with the reflective aperture in the pixel are arranged so as to be close to the reflective aperture of an adjacent pixel. Liquid crystal display element.   3. The liquid crystal display element according to claim 2, wherein the reflection openings of adjacent pixels are arranged so that only the corners are close to each other. In the horizontal pixel line, pixels having different arrangements of transmission openings and reflection openings are alternately arranged,
4. The liquid crystal display element according to claim 3, wherein pixels having the same arrangement of the transmission openings and the reflection openings are arranged in the vertical pixel line.   The liquid crystal display element according to claim 1, wherein the liquid crystal layer has a homogeneous alignment or a vertical alignment.

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