JP2005062387A - Liquid crystal display element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid crystal display element having proper display characteristics in all directions both in transmissive display and in reflective display. <P>SOLUTION: The liquid crystal display element includes in a pixel a transmissive opening part B for performing the display by transmitting a part of an incident light from a light source disposed on the back side and a reflective opening part A for performing the display by reflecting an external light, in which a liquid crystal layer is perpendicularly aligned. The shape of each pixel is approximately square. The transmissive opening part B has the shape approximately point symmetrical with respect to the central point of the pixel, for example square, polygonal, circular, or the like. Further, a projected part or a recessed part for regulating the direction in which the liquid crystal molecule is inclined is formed at the central point of each pixel. <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 eliminating the bias in viewing angle characteristics.

  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.

  Since the reflective liquid crystal display element is basically a display using outside light like paper, the display screen also becomes dark when the use environment itself is dark, making it difficult to visually recognize the display. 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).

  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 homogeneous mode, it is known that the liquid crystal molecules in the vicinity of the interface between the liquid crystal layer and the substrate do not operate sufficiently at the applied voltage (about 4 V) in normal liquid crystal display, and sufficient black display cannot be performed. In order to solve this problem, an applied voltage of 10 V or more is required. However, there are disadvantages that a load is applied to the drive circuit and power consumption increases.

In order to avoid this, it is effective to use the vertical alignment mode instead of the homogeneous mode, and a transflective liquid crystal display element using such a vertical alignment mode has been developed (for example, Patent Document 2 and (See Patent Document 3). In the vertical alignment mode, black display is performed in a state where no voltage is applied (so-called normally black). Therefore, sufficient black display can be realized regardless of the applied voltage, and the contrast is high. In addition, wide viewing angle characteristics can be realized by defining the direction in which the liquid crystal molecules are tilted when a voltage is applied in a plurality of directions within the pixel (so-called MVA: Multi Domain Vertical Alignment Mode).
Japanese Patent Laid-Open No. 11-242226 JP 2002-350853 A JP 2002-287158 A

  However, in the case of a transflective liquid crystal display element using a vertical alignment mode as described in Patent Document 2, since a projection is formed in the transmissive opening, liquid crystal molecules are multiaxially aligned by voltage application, Although the viewing angle becomes wider, the orientation of the liquid crystal molecules is not stable when a voltage is applied at the reflection opening, and at the same time, the orientation is remarkably biased depending on the azimuth angle.

  In order to solve the above problem, for example, as described in Patent Document 3, it is considered that each pixel is provided with a portion having no electrode or a protruding structure in both the transmission opening and the reflection opening. However, it is difficult to form a plurality of protrusions in a fine pixel, and the liquid crystal is divided independently at the transmissive opening and the reflective opening despite the fact that it is within one pixel. There is a risk that bias will occur.

  Further, as described in Patent Document 2 and Patent Document 3, when the vertical alignment mode is used with a normal rectangular pixel shape, there is a disadvantage that the area of the transmissive opening is limited and bright transmissive display cannot be performed. In order to obtain good transmission viewing angle characteristics in all directions, symmetry is required for the shape of the transmissive aperture, and when the symmetric transmissive aperture is arranged in a rectangular pixel, the area of the transmissive aperture is limited. It will be

  The present invention has been proposed in view of such a conventional situation. That is, an object of the present invention is to provide a transflective liquid crystal display element using a vertical alignment mode, which has excellent display characteristics in all directions in both transmissive display and reflective display. . Another object of the present invention is to provide a liquid crystal display element in which the area of the transmissive opening can be freely set and the transmissive / reflective ratio can be optimally set according to the purpose of use. And

  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. A liquid crystal display element. Further, the liquid crystal display element has a vertically aligned liquid crystal layer. In such a liquid crystal display element, each pixel has a substantially square shape, and the transmission opening has a substantially point-symmetric shape with respect to the center point of the pixel.

  In the liquid crystal display element of the present invention, the liquid crystal layer is vertically aligned, and so-called MVA or the like defines the direction in which the liquid crystal molecules tilt when a voltage is applied, thereby realizing a wide viewing angle characteristic. At this time, since the shape of the pixel is substantially square and the transmissive aperture is substantially symmetric with respect to the center point of the pixel, the center of the multiaxial orientation in the transmissive aperture and the pixel (therefore, accordingly) The center of multiaxial orientation in the reflection opening) coincides, and the same viewing angle characteristic is realized in the transmission opening and the reflection opening.

  In addition, the pixel shape is a point-symmetrical square and the transmission opening is substantially point-symmetric with respect to the center point of the pixel, so the size of the transmission opening is the same as the pixel shape. It is no longer limited by the pixel shape as in the case of a rectangle. Therefore, the size of the transmissive opening may be freely set to an arbitrary size in the pixel, and the transmission / reflection ratio is optimally set according to the purpose of use.

  According to the present invention, in the transflective liquid crystal display element in which the liquid crystal layer is vertically aligned, the shape of the pixel is substantially square, and the transmissive opening is substantially symmetric with respect to the center point of the pixel. Therefore, display characteristics can be improved over all directions in both transmissive display and reflective display. In the liquid crystal display element of the present invention, the area of the transmission opening can be freely set, and the transmission / reflection ratio can be optimally set according to the purpose of use.

  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 λ / 4 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. Has been. Similarly, a second polarizing plate 16, a second λ / 2 plate 17, and a second λ / 4 plate 18 are provided on the surface of the lower glass substrate 3 opposite to the surface in contact with the liquid crystal layer 4. Has been placed. The λ / 2 plates 14 and 17 are retardation plates having a retardation value of about 270 nm, and the λ / 4 plates 15 and 18 are retardation plates having a retardation value of around 140 nm. It is not limited. Further, the configuration of the film is not limited to this, and for example, either one or both of the λ / 2 plates 14 and 17 can be removed, and the manufacturing cost can be reduced by doing so. Further, for the sake of simplification, illustration and description of the protective insulating layer, the capacitor electrode, and the like that are not necessary for describing the liquid crystal display element of the present invention are omitted.

  The liquid crystal display element of the present embodiment performs display by applying phase modulation to the liquid crystal layer 4 in which light from the backlight 10 incident on the transparent electrode 9 and external light incident on the reflective electrode 8 are vertically aligned. This is a so-called vertical alignment mode transflective liquid crystal display element.

  Here, as shown in FIG. 1, each pixel electrode is divided into a transmission opening B and a reflection opening A in an area, and the transparent electrode 9 corresponds to the transmission opening and the reflection electrode 8 corresponds to the reflection opening. ing. In the transmissive opening B and the reflective opening A, the thickness of the liquid crystal layer 4 differs depending on the insulating layer 11, but the thickness of the liquid crystal layer 4 in each part can be set to an appropriate value depending on the type of liquid crystal used. it can. For example, in the present embodiment, an n-type nematic liquid crystal having a refractive index anisotropy Δn = 0.09 is used, the liquid crystal layer thickness d1 of the transmission opening B = 4.0 μm, and the liquid crystal layer thickness d2 = 2 of the reflection opening A. 0.0 μm.

  Further, a resin protrusion 19 is provided on the surface of the upper glass substrate 2 in contact with the liquid crystal layer 4 corresponding to the center position of the transmission opening B. The resin protrusion 19 is provided to control the alignment of the liquid crystal molecules of the liquid crystal layer 4 and plays a role of defining the direction in which the liquid crystal molecules are tilted when a voltage is applied by so-called MVA.

  The structure that defines the direction in which the liquid crystal molecules are tilted is not limited to the resin protrusion 19, and may be, for example, a columnar spacer or a recess (hole, slit, or the like) formed in the transparent electrode 6. Further, in the present embodiment, the bottom shape of the resin protrusion 19 is circular, but is not limited to this, and may be an appropriate polygon or the like.

  The positional relationship between the resin protrusion 19 and the transmissive opening B in the pixel is desirably arranged so that the center of the resin protrusion 19 and the transmissive opening B coincides with the center of the pixel as in this embodiment. Furthermore, the viewing angle characteristic becomes more uniform. However, these positional relationships are not necessarily limited to those described above. The positional relationship is appropriately determined depending on the positional relationship of a driving element such as a TFT, the pixel capacitor electrode, or the like, or the shape of the pixel and the shape of the transmission opening B. It is also possible to shift.

  FIG. 2 is a schematic diagram of a planar arrangement of pixels in the liquid crystal display element of the present embodiment. As shown in FIG. 2, in the liquid crystal display element of the present embodiment, one pixel that is partitioned by the signal line S and the gate line G and on which the reflective electrode 8 and the transparent electrode 9 are formed has a shape close to a square. . Here, it is ideal that the shape of each pixel is exactly a square (ratio of long side to short side is 1). However, the shape is not limited to this and may be almost square. For example, in each pixel, the ratio of the long side to the short side can be freely set between 1 and 1.5. In particular, when the ratio of the long side to the short side of a substantially square pixel is 1.5, the same size as a conventional transflective liquid crystal display element can be configured with the same number of pixels.

  3 and 4 show each pixel in an enlarged manner. The shape of each pixel is substantially square, and the transmissive opening B where the transparent electrode 9 faces is also substantially square. The center point of the transmissive aperture B is arranged so as to substantially coincide with the center point of the pixel. Therefore, the reflective opening A corresponding to the reflective electrode 8 is arranged as a square frame-shaped region around the transmissive opening B as shown by the hatched region in FIG.

  The shape of the transmission opening B may be a polygon such as a hexagon or an octagon, or a substantially circular shape, as long as the shape is substantially point-symmetric with respect to the center point of the transmission opening B. FIG. 5 shows an example in which the shape of the transmission opening B is an octagon, and FIG. 6 shows an example in which the transmission opening B is circular. If the shape of the transmissive aperture B is substantially point-symmetric, the liquid crystal alignment is symmetric in both the transmissive aperture B and the reflective aperture A, so that the effect of the present invention can be obtained. In this case, the closer the shape of the transmission opening B is to a circle, the more stable the alignment of the liquid crystal molecules when a voltage is applied, and the same viewing angle characteristics are approached in all directions. If the shape of the transmissive opening B is circular, the same viewing angle characteristic is obtained almost completely in all directions.

  7 and 8 are diagrams for explaining display colors corresponding to the respective pixels. In the example shown in FIG. 7, each pixel is arranged in a matrix, and a color filter is arranged in a pattern corresponding to each pixel, and three pixels R, G, and B surrounded by a line P in the figure are displayed. Collectively, one color information is displayed.

  In the example shown in FIG. 7, the pixels are arranged in a matrix as described above. However, the pixel arrangement and the color arrangement are not limited to this. For example, as shown in FIG. The array may be a so-called Δ array. In this case, display with higher definition can be achieved with the same number of pixels.

  In this embodiment, the color filter layer 5 is uniformly formed over the entire surface of the liquid crystal display element, but a different color filter configuration may be used as necessary. For example, by reducing the color density of the color filter layer 5 corresponding to the reflective aperture A rather than the color filter layer 5 corresponding to the transparent aperture B, it is natural when viewing a display in which both the transmission and reflection modes are combined. Display can be made. This is because the light used for display passes through the color filter layer 5 only once in the transmission opening B and passes twice in the reflection opening A.

  In order to make the color density of the color filter layer 5 corresponding to the reflection opening A smaller than the color filter layer 5 corresponding to the transmission opening B, for example, 1) one of the color filter layers 5 corresponding to the reflection opening A 2) Make the color filter layer 5 corresponding to the transmission opening B thicker than the color filter layer 5 corresponding to the reflection opening A, and 3) Color filter layer 5 corresponding to the transmission opening B. There is a method of making the pigment density higher than that of the color filter layer 5 corresponding to the reflective opening A.

  Next, the principle of obtaining good display characteristics in the liquid crystal display element of this embodiment will be described.

  FIG. 9 shows an example of a pixel structure of a conventional transflective liquid crystal display element. In the liquid crystal display element shown in FIG. 9, one pixel is a vertically long rectangle, and the transmission opening B is an octagon. The protrusion 19 is formed at the center position of the transmissive opening B as in the liquid crystal display element of the embodiment. Therefore, the shape of the transmission opening B with respect to the protrusion 19 is point-symmetrical, and the direction in which the liquid crystal molecules fall when a voltage is applied is radial with respect to the protrusion 19 with respect to the transmission opening B. Yes, showing good viewing angle characteristics.

  However, with respect to the reflective opening A, since there is no strong alignment regulating force, the alignment is not stable, the response speed is slowed down, and the display becomes tailed. Further, when the liquid crystal molecules are settled in a fixed position over a sufficient time, many liquid crystal molecules are tilted in the left-right direction in FIG. 9, so that different viewing angle characteristics are exhibited in the vertical direction and the left-right direction of the liquid crystal display element. Furthermore, in order to make the viewing angle characteristic of the transmissive opening B constant regardless of the azimuth angle, it is necessary to make the upper, lower, left, and right shapes of the transmissive opening B constant, but the pixel shape shown in FIG. The area of the part B cannot be increased beyond a certain value. Therefore, the transmissivity of the transflective liquid crystal display element cannot be made larger than a certain value, and the degree of freedom in design is small.

  On the other hand, in the liquid crystal display element of this embodiment, since the pixel shape is substantially square and the transmissive opening B is also substantially square, the liquid crystal molecules in the pixel are evenly arranged vertically and horizontally around the protrusion 19 when a voltage is applied. . For this reason, both the transmissive display portion and the reflective display portion have substantially the same display characteristics in all directions, and have favorable viewing angle characteristics. Further, since the shape of the pixel and the transmissive opening B is substantially the same, the area of the transmissive opening B can be made large by bringing the area of the transmissive opening B close to the area of the entire pixel. Therefore, it is possible to design a transflective liquid crystal display element having a high degree of freedom in setting the ratio of transmittance / reflectance and having a wide application range.

  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, in this embodiment, the liquid crystal layer is driven by a thin film transistor (TFT) as a switching element. However, 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. It is a schematic diagram of planar arrangement of pixels. It is a top view about 1 pixel. It is sectional drawing in the xx line of FIG. It is a top view which shows the other example of a permeation | transmission opening part. It is a top view which shows the further another example of a permeation | transmission opening part. It is a top view which shows a matrix-like pixel arrangement | sequence. It is a top view which shows the pixel arrangement | sequence made into (DELTA) arrangement | sequence. It is a top view which shows an example of the conventional transflective liquid crystal display element.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Semi-transmissive 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 12 TFT (switching element)
19 Resin protrusion A Reflection opening B Transmission opening S Signal line G Gate line

Claims (11)

The liquid crystal layer has a vertically aligned liquid crystal layer that has a transmissive opening in the pixel that transmits a portion of the light incident from the light source disposed on the back surface and displays the light by reflecting external light. In the liquid crystal display element
Each pixel has a substantially square shape,
The liquid crystal display element, wherein the transmissive opening has a substantially point-symmetric shape with respect to a center point of a pixel.   The liquid crystal display element according to claim 1, wherein a thickness of the liquid layer layer corresponding to the transmission opening and a thickness of the liquid crystal layer corresponding to the reflection opening are different.   The liquid crystal display element according to claim 2, wherein a convex portion or a concave portion that regulates a direction in which the liquid crystal molecules fall is formed at a center point of each pixel. An array substrate on which a pixel electrode and a switching element are formed, and a counter substrate disposed opposite to the array substrate with a liquid crystal layer interposed therebetween,
The liquid crystal display element according to claim 3, wherein the convex portion or the concave portion is formed on the counter substrate.   The liquid crystal display element according to claim 1, wherein the transmission opening is substantially square.   The liquid crystal display element according to claim 1, wherein the transmission opening is substantially polygonal.   The liquid crystal display element according to claim 6, wherein the transmission opening has a substantially hexagonal shape or a substantially octagonal shape.   The liquid crystal display element according to claim 1, wherein the transmission opening is substantially circular.   The liquid crystal display element according to claim 1, wherein each pixel is arranged in a matrix and has a display color different from that of all pixels adjacent to the four sides.   The liquid crystal display element according to claim 1, wherein the pixels are arranged in Δ.   2. The liquid crystal display element according to claim 1, wherein the color density of the color filter layer corresponding to the transmissive opening and the color density of the color filter layer corresponding to the reflective opening are different.

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