JP2009093115A - Liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lateral electric field mode transflective liquid crystal display device in which optical characteristics of the reflective display section is improved without deteriorating those of the transmissive display section. <P>SOLUTION: In the liquid crystal display device which comprises a liquid crystal layer interposed between first and second substrates 1, 2 wherein each of pixels has the reflective display section R and the transmissive display section T, the second substrate 2 has an alignment layer 4 in contact with the liquid crystal layer, and further has a pixel electrode 5 and a common electrode 6 to apply a laterally directed electric field on the liquid crystal layer. In the liquid crystal layer, liquid crystal molecules are oriented in such a way that, in the reflective display section R and with no voltage applied thereto, an orienting direction of a liquid crystal molecule 7 is different from that in the transmissive display section T, and further, a tilt angle of the liquid crystal molecule 7 with respect to the first substrate 1 or the second substrate 2 is different from that in the transmissive display section T. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a transflective liquid crystal display device including a reflective display portion and a transmissive display portion in one pixel.

  Liquid crystal display devices can be broadly classified into voltage application methods. There are a vertical electric field method in which an electric field is applied in the thickness direction (vertical direction) of the liquid crystal and a horizontal electric field method in which an electric field is applied in a horizontal direction parallel to the liquid crystal layer. Since the horizontal electric field method can display a wider viewing angle than the vertical electric field method, it has been actively developed in recent years. PIS (In-Plane Switching) method and FFS (Fringe Field Switching) method are typical modes. It has been developed and is in practical use. Lateral electric field type liquid crystal display devices such as IPS and FFS have begun to spread as displays for portable devices such as mobile phones and digital cameras, in addition to monitors for televisions and personal computers.

  A display device for portable information equipment is used in various environments including outdoors from a sunny day to a dark room, and thus it is desired to be a transflective type. A transflective liquid crystal display device has a reflective display portion and a transmissive display portion in one pixel, and can provide high-contrast display in a wide range of environments including outdoors from a sunny day to a dark room. It has desirable characteristics as a display for information equipment.

  If the display device in the IPS mode or the FFS mode can be made a transflective type, a wide viewing angle transmissive display and a high contrast reflective display can be obtained simultaneously, which is very useful as a display for a portable information device. However, in order to maintain the wide viewing angle characteristic of the transmissive display unit, which is a feature of the IPS and FFS modes, it is not possible to use a film that causes a phase difference when the display is observed from the front. In the ECB mode which is one of the conventional vertical electric field systems, such a retardation film can be used, so that it is easy to provide a reflective display portion in a part of a pixel in a transflective display device.

As a method for realizing an IPS mode transflective display device that avoids the above-described problems, a structure is known in which a retardation layer having a phase difference of one-half wavelength is disposed only on a reflective display portion in a liquid crystal panel. Yes. Patent Document 1 discloses a method for realizing an IPS mode transflective display device without using a retardation plate built in the panel by adjusting the liquid crystal alignment of the transmissive display unit and the reflective display unit in different directions. Proposed. Furthermore, Non-Patent Document 1 proposes a method for realizing a transflective liquid crystal display device using so-called hybrid alignment.
JP 2005-338264 A Y. J. et al. LIM, J.M. J. et al. A. P43 (2004) L972

  In the conventional method in which a retardation layer having a phase difference corresponding to a half wavelength is disposed only on the reflective display portion in the liquid crystal panel, or in the divided alignment method described in Patent Document 1, the liquid crystal layer of the reflective display portion is divided into four. The optical design has a phase difference of one wavelength. In this relationship, the thickness of the liquid crystal layer of the reflective display unit is about half that of the transmissive display unit. In the case of a horizontal electric field method such as IPS or FFS, the distribution of the horizontal electric field intensity in the panel in-plane direction becomes non-uniform at the center of the layer thickness where the degree of switching of the liquid crystal molecules becomes the largest when the thickness of the liquid crystal layer is reduced End up. For this reason, since the switching of the liquid crystal molecules at the time of applying the lateral electric field is locally insufficient, there arises a problem that the reflectance is lowered.

  FIG. 22 is a graph showing electro-optical characteristics of a reflective display portion of a conventional transflective liquid crystal display device. In this graph, the applied voltage is taken on the horizontal axis, and the reflectance Y is taken on the vertical axis. For the sample, an ECB mode, which is representative of a conventional vertical electric field method, and an FFS mode of a horizontal electric field method are selected. In either mode, when the applied voltage is 0V and normally black, the reflectance Y is the lowest and black display is achieved. Here, the retardation of both samples is 140 nm, the phase difference of the λ / 2 phase difference plate is 280 nm, and the axial relationship of the optical members in the respective modes is the same for easy comparison. Λ is the center wavelength of the incident light. . The refractive index anisotropy (birefringence index) Δn of the liquid crystal material was 0.12, and the thickness of the liquid crystal (gap of the liquid crystal cell) was 1.14 μm. As shown in the graph of FIG. 22, when compared with the reflectance Y when the applied voltage is 4 V, the reflection display in the horizontal electric field type FFS mode is only about 60% lower than that in the vertical electric field type ECB mode. I understand that.

  In general, the dependence of the reflectance on the thickness of the liquid crystal is not a problem in the vertical electric field method such as the ECB mode or the VA mode, but is a problem specific to the horizontal electric field method such as the FFS or IPS mode. This is an obstacle to developing the device.

  One way to solve this problem is to reduce the refractive index anisotropy Δn of the liquid crystal and increase the thickness of the liquid crystal in the reflective display portion, so that a uniform lateral electric field is applied to the central portion of the liquid crystal layer. In this way, there is a measure for improving the reflectance. However, in the case of the transflective structure, if Δn is decreased, the liquid crystal thickness of the transmissive display portion is also increased at the same time, and the response speed of the transmissive display portion is reduced.

  In addition, as a method of expanding the liquid crystal thickness of the reflective display part while keeping the liquid crystal thickness of the transmissive display part constant, a so-called hybrid orientation system is adopted in which the orientation of one substrate is homogeneous orientation and the other substrate is homeotropic orientation. Is known and disclosed in Non-Patent Document 1 described above. However, in the method shown in Non-Patent Document 1, it is necessary to use a λ / 2 phase difference plate having a phase difference of ½ wavelength in addition to the polarizing plate normally required in the FFS mode. The viewing angle characteristic of the display unit is significantly deteriorated.

  In view of the above-described problems of the prior art, the present invention is a half of the horizontal electric field method that can improve the optical characteristics (reflectance and contrast) of the reflective display section without degrading the optical characteristics of the transmissive display section. An object is to provide a transmissive liquid crystal display device. In order to achieve this purpose, the following measures were taken. That is, the present invention provides a liquid crystal display device in which a liquid crystal layer is sandwiched between first and second substrates and a pixel has a reflective display portion and a transmissive display portion, and the first substrate is a first polarizing plate. The second substrate has a second polarizing plate, has an alignment layer in contact with the liquid crystal layer, and has an electric field in the liquid crystal layer. The first and second polarizing plates are arranged so that their transmission axes are orthogonal to each other, and the liquid crystal layer is common to the pixel electrode in the transmissive display portion. In a state where no voltage is applied between the electrodes and no voltage is applied, liquid crystal molecules are aligned substantially in parallel with the transmission axis of the first or second polarizing plate. The alignment direction of the molecules is different from the alignment direction of the liquid crystal molecules of the transmissive display portion, and the first group Or tilting angle of the liquid crystal molecules to at least one of the substrate of the second substrate, characterized in that they are oriented differently with tilt angles of liquid crystal molecules in the transmissive display part.

  Preferably, the liquid crystal molecules in the liquid crystal layer of the reflective display portion are twisted with a twisted orientation between the first substrate and the second substrate. The pixel electrode has a stripe shape or a comb shape extending in a predetermined direction, and the liquid crystal layer of the reflective display portion has a tilt angle of liquid crystal molecules with respect to the second substrate of 53 ° or less and the twist. The twist angle of alignment is in the range of 64 ° to 90 °, the retardation given by the product of the thickness of the liquid crystal layer and its refractive index anisotropy is in the range of 194 to 247 nm, and the liquid crystal on the second substrate side The orientation direction of the molecules forms an angle of approximately 0 ° with a predetermined direction in which the stripe shape or the comb shape of the pixel electrode extends. In one embodiment, the pixel electrode has a stripe shape or a comb shape extending in a predetermined direction, and the liquid crystal layer of the reflective display portion has a tilt angle of liquid crystal molecules with respect to the first substrate and the second substrate. Is 40 ° or less, the twist angle of the twisted orientation is in the range of 63 ° to 64 °, and the retardation given by the product of the thickness of the liquid crystal layer and its refractive index anisotropy is in the range of 194 to 200 nm. The alignment direction of the liquid crystal molecules on the second substrate side forms an angle of approximately 20 ° counterclockwise with a predetermined direction in which the stripe shape or comb tooth shape of the pixel electrode extends. In another aspect, the liquid crystal layer of the reflective display unit has a homogeneous alignment in which the alignment directions of liquid crystal molecules are aligned between the first substrate and the second substrate, and has a phase difference of λ / 4 (λ Is the wavelength of light), and the alignment direction of the liquid crystal molecules forms an angle of 40 degrees or more and 50 degrees or less with respect to the transmission axes of the first and second polarizing plates, and with respect to the first and second substrates. In this case, there are regions where the tilt angles of the liquid crystal molecules of the reflective display portion and the transmissive display portion are different, and the pixel electrode has a stripe shape or a comb shape extending in a predetermined direction, and the first electrode The tilt angle of the liquid crystal molecules with respect to both the substrate and the second substrate is 50 ° or less, and the alignment direction of the liquid crystal molecules is approximately 30 ° clockwise with a predetermined direction in which the stripe shape or comb-teeth shape of the pixel electrode extends. Make an angle.

  The present invention also provides a liquid crystal display device having a liquid crystal layer sandwiched between first and second substrates and having a reflective display portion and a transmissive display portion in one pixel, wherein the first substrate is a first polarizing plate. The second substrate has a second polarizing plate, has an alignment layer in contact with the liquid crystal layer, and has an electric field in the liquid crystal layer. The first and second polarizing plates are arranged so that their transmission axes are orthogonal to each other, and the liquid crystal layer is common to the pixel electrode in the transmissive display portion. The liquid crystal layer in which liquid crystal molecules are aligned substantially parallel to the transmission axis of the first or second polarizing plate in a state in which no voltage is applied between the electrodes and no voltage is applied, and light is switched in the reflective display portion An optical layer having a phase difference separately from the first substrate or the second substrate Tilt angle of the liquid crystal molecules to either one of the substrates even without, characterized in that they are oriented differently with tilt angles of liquid crystal molecules in the transmissive display part.

  Preferably, the alignment layer includes a grating layer in which a plurality of grooves are formed in parallel on the first or second substrate. The alignment layer is formed with an alignment film so as to cover the grating layer, and the alignment film has a horizontal alignment ability to align liquid crystal molecules in parallel with the substrate in the absence of voltage. The alignment direction of the liquid crystal molecules is a direction orthogonal to the direction in which the groove extends. In the grating layer, each groove extends along a predetermined direction, and is repeatedly arranged at a given pitch along an orthogonal direction orthogonal to the predetermined direction, and the grating layer extends along the orthogonal direction. By tilting the cross section of the grating layer, a predetermined tilt angle is given to the liquid crystal molecules.

  According to the present invention, the tilt angle of the liquid crystal molecules in the reflective display unit is aligned so as to be different from the tilt angle of the liquid crystal molecules in the transmissive display unit. By adjusting the tilt angle, the refractive index anisotropy Δn of the liquid crystal layer can be adjusted equivalently. The thickness of the liquid crystal layer can be set optimally by adjusting the refractive index anisotropy Δn. By changing the tilt angle between the reflective display unit and the transmissive display unit, the liquid crystal thickness of the reflective display unit can be expanded in an optimal direction while maintaining the optimal liquid crystal thickness of the transmissive display unit. If the liquid crystal thickness of the reflective display portion is increased, a uniform lateral electric field can be applied to the central portion of the thickness of the liquid crystal layer. As described above, it is possible to improve the reflectance of the reflective display unit without reducing the image quality of the transmissive display unit.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic view showing a first embodiment of a liquid crystal display device according to the present invention. (A) is a plan view for one pixel, (b) represents a cross-sectional structure for one pixel, and (c) represents an alignment state of liquid crystal molecules in a reflective display portion and a transmissive display portion in the pixel. . As shown in (a) and (b), in the present liquid crystal display device, a liquid crystal layer is sandwiched between a first substrate 1 and a second substrate 2, and a reflective display portion R and a transmissive display portion T are provided in one pixel. ing. The first substrate 1 has a first polarizing plate and a first alignment film 3 in contact with the liquid crystal layer. The second substrate 2 includes a second polarizing plate, a second alignment film 4 in contact with the liquid crystal layer, and a pixel electrode 5 and a common electrode 6 that apply an electric field to the liquid crystal layer.

  As shown to (c), the 1st and 2nd polarizing plate is arrange | positioned so that the transmission axis may orthogonally cross. In (c), instead of the transmission axis of each polarizing plate, an absorption axis perpendicular thereto is shown.

  As shown in (a), in the transmissive display portion T, the liquid crystal layer has a transmission axis of the first or second polarizing plate in a state in which no voltage is applied between the pixel electrode 5 and the common electrode 6. The liquid crystal molecules 7 are aligned substantially in parallel. On the other hand, in the reflective display portion R, the alignment direction of the liquid crystal molecules 7 is different from the alignment direction of the liquid crystal molecules 7 in the transmissive display portion T when no voltage is applied. Further, as shown in (b), the tilt angle of the liquid crystal molecules 7 with respect to at least one of the first substrate 1 and the second substrate 2 is different between the reflective display portion R and the transmissive display portion T. The orientation is controlled. In the example shown in (b), on the second substrate 2 side, the tilt angle of the liquid crystal molecules 7 of the reflective display portion R is set relatively large, and the tilt angle of the transmissive display portion T is set relatively low. .

  Preferably, as shown in (c), the liquid crystal molecules 7 in the liquid crystal layer of the reflective display portion R have a twisted orientation (twist orientation) in which the orientation is twisted between the first substrate 1 and the second substrate 2. ing. On the other hand, in the transmissive display portion T, the liquid crystal molecules 7 are in a homogeneous alignment in which they are aligned in one direction.

  The pixel electrode 5 has a stripe shape or a comb shape extending in a predetermined direction. In the liquid crystal layer of the reflective display portion R, the tilt angle of the liquid crystal molecules 7 with respect to the second substrate 2 is 53 ° or less, and the twist angle of the twisted orientation is in the range of 64 ° to 90 °. The retardation Δn · d given by the product of the refractive index anisotropy Δn is in the range of 194 to 247 nm, and the alignment direction of the liquid crystal molecules 7 on the second substrate 2 side extends the stripe shape or comb shape of the pixel electrode 5. An angle of approximately 0 ° with the predetermined direction is formed.

  With continued reference to FIG. 1, the manufacturing method and operation of the first embodiment will be described in detail. As described above, the present liquid crystal display device includes the first substrate 1, the liquid crystal layer, and the second substrate 2, and the first substrate 1 and the second substrate 2 sandwich the liquid crystal layer. The first substrate 1 has a color filter 11, a planarizing layer 12, and a first alignment film 3 on the side close to the liquid crystal layer. In order to adjust the liquid crystal thickness of the reflective display portion R and the transmissive display portion T, a step 14 is provided in the reflective display portion R.

  The second substrate 2 has a thin film transistor (TFT) on the side close to the liquid crystal layer as shown in FIG. The source of the TFT is connected to the signal wiring Y. The gate of the TFT is connected to the gate wiring X. The drain of the TFT is connected to the pixel electrode 5 through the first contact hole. In addition, a common wiring C connected to the common electrode 6 through the second contact hole is provided. As shown to (a), the signal wiring Y and the gate wiring X cross | intersect a grid | lattice form, and each pixel respond | corresponds to each grid | lattice. One pixel is a vertically long rectangle, and about one-third of the area is the reflective display portion R, and the remaining two-third area is the transmissive display portion T.

  As shown in (b), the first substrate 1 is made of glass, plastic, or other material. In the color filter 11, red, green, and blue portions are repeatedly arranged in a stripe shape or a delta shape, and unevenness caused by the color filter is flattened by a flattening layer 12. The first alignment film 3 is a polyimide-based film that induces the horizontal alignment of the liquid crystal molecules 7, and the photomolecules in the alignment film are irradiated by electromagnetic waves or charged particles such as a normal rubbing method, a photo-alignment method, or an ion beam alignment method. A process for horizontally aligning the liquid crystal molecules 7 with respect to a predetermined direction is performed by a method using a technique such as breaking bonds or polymerizing.

  The second substrate 2 is made of glass, plastic, or other material. The signal wiring Y is made of aluminum, the gate wiring (scanning wiring) X is made of metal molybdenum, and the pixel electrode 5 and the common electrode 6 are made of a transparent conductive film such as ITO. Similarly to the first alignment film 3, the second alignment film 4 is a polyimide-based film that induces horizontal alignment. In addition to a normal rubbing method, a method such as a photo-alignment method, an ion beam alignment method, or a grating is used. The orientation is controlled in a predetermined direction by an orientation method using the.

  As a method of making the tilt angle of the liquid crystal molecules 7 different between the reflective display portion R and the transmissive display portion T, different types of alignment film materials are applied to the transmissive display portion T and the reflective display portion R, and rubbing or other types are applied. A method of performing an alignment treatment is mentioned. Also, the tilt angle can be differentiated by using a photo-alignment method or an ion beam alignment method. In this case, there is a method of causing the liquid crystal molecules 7 to have different tilt angles by masking the transmissive display portion T and the reflective display portion R, respectively, and changing the irradiation angle of the ultraviolet polarized light or the ion beam to the substrate 2. Alternatively, in the case of adopting the grating orientation, there is a method in which different tilt angles of the liquid crystal molecules 7 are expressed by changing the cross-sectional shape between the transmissive display portion T and the reflective display portion R.

  The pixel electrode 5 has a slit shape or a comb-teeth shape, and the pitch, width, and orientation with respect to the signal wiring Y of the comb teeth are changed between the transmissive display portion T and the reflective display portion R. In some cases, the pitch, width, and orientation of the pixel electrode 5 with respect to the signal wiring Y may be changed for each pixel corresponding to the red, green, and blue color filters 11. As shown in (b), the pixel electrode 5 and the common electrode 6 are separated by an insulating film 21. When a voltage is applied, an electric field is formed between the pixel electrode 5 and the common electrode 6, but the electric field is distorted in an arch shape by the influence of the insulating film 21 and passes through the liquid crystal layer. When the transverse electric field distorted in an arch shape passes just through the central portion of the liquid crystal layer, the alignment change occurs in the liquid crystal layer and switching is performed. By optimizing the thickness of the liquid crystal layer of the reflective display portion R, the most uniform portion of the horizontal electric field generated between the pixel electrode 5 and the common electrode 6 passes through the central portion of the liquid crystal layer. In this case, since the optimal thickness of the liquid crystal layer is different between the transmissive display portion T and the reflective display portion R, a step 14 is generated between them. Further, in order to obtain a black display with high contrast and little color in the reflective display portion R, the thickness of the liquid crystal layer may be further changed for each pixel corresponding to each of the color filters 11 for red, green, and blue.

  In the reflective display portion R, a reflective metal film 22 is disposed below the common electrode 6. The metal film 22 is separated from the second substrate 2 through the first insulating film 23 and the second insulating film 24. By subjecting the surface of the second insulating film 24 in contact with the metal film 22 to an uneven surface, the light diffusive reflecting plate 25 can be formed in the reflective display portion R. Instead of the metal film 22, the diffuse reflection plate 25 can be obtained by forming the common electrode 6 with aluminum, silver, chromium, molybdenum, or other metals in the reflective display portion R. Note that nematic liquid crystal having positive dielectric anisotropy is used for the liquid crystal layer. In some cases, a liquid crystal material having negative dielectric anisotropy may be used.

  FIG. 2 is a schematic diagram showing the basic principle of the present invention. The present invention is a transflective liquid crystal display device characterized by an alignment method in which the tilt angle of the liquid crystal molecules of the reflective display portion is different from the tilt angle of the liquid crystal molecules of the transmissive display portion. An alignment method with a difference in angle is sometimes referred to as hybrid alignment. By adopting the hybrid alignment, the thickness of the liquid crystal layer can be optimally adjusted, and thus the liquid crystal thickness of the reflective display portion can be brought close to the liquid crystal thickness of the transmissive display portion. As shown in the figure, the refractive index anisotropy Δn1 defining the phase difference is maximum when the angle between the incident light beam and the major axis direction of the liquid crystal molecules is a right angle, and the refractive index anisotropy Δn3 is minimum when the angle is parallel. 0. When an intermediate angle between the right angle and the parallel angle is formed, the refractive index anisotropy Δn2 becomes an intermediate value between the two. Therefore, the liquid crystal thickness (cell gap) d can be increased while keeping the retardation Re of the liquid crystal cell constant by orienting the tilt angle of the liquid crystal molecules on one side substrate or both side substrates higher than usual when no voltage is applied. It becomes possible. In this way, by adopting a hybrid orientation in which the tilt angle is changed between the reflective display unit and the transmissive display unit, the gap of the transmissive display unit can be expanded, and the reflectance of the reflective display unit can be increased by the FFS mode or IPS mode horizontal electric field method. It is possible to improve.

  When the liquid crystal molecules are horizontally aligned, the refractive index Δn1 is maximum, and conversely, when the liquid crystal molecules are vertically aligned, the refractive index Δn3 is minimum. When the tilt alignment is performed between the horizontal alignment and the vertical alignment, the refractive index anisotropy Δn2 is between Δn1 and Δn3. As the tilt angle increases from 0 ° to 90 °, the refractive index anisotropy Δn decreases.

  In the optical design of the liquid crystal layer, it is necessary to optimally set the retardation Re = Δn × d. As shown in the figure, even if the liquid crystal thickness (cell gap) is increased from d1 to d2, an appropriate retardation value can be ensured by reducing the refractive index anisotropy Δn accordingly. In order to reduce the refractive index anisotropy Δn, the present invention responds by positively adding a tilt angle to the liquid crystal molecules.

  FIG. 3 is a graph showing the results of measuring the display characteristics of the liquid crystal display device according to the first embodiment of the present invention shown in FIG. The first embodiment is data when the tilt angle of one substrate is changed with an optical design in which the reflective display unit is normally black. In the normally black mode, black is displayed when no voltage is applied. The graph in FIG. 3 shows the relationship between the cell gap and the twist angle at which the black display of the reflective display portion sinks deepest when the tilt angle of one substrate is fixed to 1 degree and the tilt angle of the other substrate is changed and no voltage is applied. It is the result of having investigated about. In this measurement, the liquid crystal molecules on the first substrate side fix the alignment direction parallel or perpendicular to the absorption axis of the polarizing plate, while the alignment direction of the liquid crystal molecules on the second substrate side is changed to be optimal. Searching for conditions. D65 was used as a light source for calculating the luminous reflectance Y.

  As shown in FIG. 3A, it can be seen that as the tilt angle increases, the twist angle of the optimum condition in which black sinks most deeply increases. When the tilt angle is 53 °, the twist angle is 90 °. When the twist angle is 90 ° or more, it is necessary to add a chiral agent in order to define the twist direction of the liquid crystal. For a transmissive display part in which liquid crystal molecules are homogeneously aligned, it is not desirable to add a chiral agent because the liquid crystal molecules induce a shift with respect to the absorption axis of a pair of polarizing plates in which the liquid crystal molecules are arranged in a crossed Nicols state, causing a decrease in contrast. . Therefore, the tilt angle is preferably set to 53 ° or less from the graph (a).

  As shown in (b), with respect to the cell gap (liquid crystal thickness), as predicted, the optimum cell gap where the black level sinks most increases as the tilt angle increases. The optimum gap is 2.95 μm. The optimum gap 2.95 μm in the reflective display portion is almost equal to the cell gap 3.16 μm in the transmissive display portion, and a uniform cell gap can be realized over the entire panel. In this example, a liquid crystal having a refractive index anisotropy Δn of 0.124 at a wavelength λ = 550 nm was used.

  The graph (c) shows the relationship of optimum cell retardation with respect to the tilt angle. When the tilt angle is set to the upper limit of 53 °, the cell retardation is 247 nm. On the other hand, when no tilt angle is given, the cell retardation is 194 nm.

  FIG. 4 is a graph showing the electro-optical characteristics of the first embodiment. The applied voltage is plotted on the vertical axis and the reflectance Y is plotted on the horizontal axis. This graph shows the reflectivity Y when the angle between the liquid crystal molecules on the second substrate side and the slit orientation of the pixel electrode is changed under the condition that the tilt angle is set to 53 ° and the twist angle is set to 90 °. It is the result of examining the voltage dependency. When white display is set at 3.5 to 4 V, compared to the voltage dependency curve of the transmittance Y of the transmissive display portion plotted at the same time, there is no inversion of gradation and an improvement in the reflectance Y is expected. It can be seen that the angle formed between the liquid crystal molecules on the second substrate side and the pixel electrode slit is near 0 °. The reflectance Y that can be obtained at this time is higher than that of the normally black ECB mode shown in FIG. 22, and it can be seen that the reflectance Y is improved by the gap expansion by the hybrid orientation. However, when compared with the voltage dependence of the transmittance Y of the transmissive display portion simultaneously plotted in the graph of FIG. 4, the threshold voltage Vth when the transmittance and the reflectance change are started by voltage application is 1 V in the case of the transmissive display portion. On the other hand, the reflective display portion is 0.5V. Although it is desirable that the threshold voltage characteristics and the γ characteristics of the transmissive display section and the reflective display section are matched, there is no appropriate solution when the tilt angle is 53 °.

  FIG. 5 shows the voltage dependence of the reflectance Y when the angle between the liquid crystal molecules on the second substrate side and the pixel electrode slit is changed under the conditions of a tilt angle of 32 ° and a twist angle of 69 °. Results are shown. Compared with the voltage dependency curve of the transmittance Y of the transmissive display portion plotted at the same time, when white display is set at 3.5 to 4 V, the liquid crystal molecules on the second substrate side and the pixel electrode slits are formed. Most preferably, the angle is 0 °. The reflectance Y is also improved from Y = 36 in the normally black ECB mode shown in FIG. 22, and it can be seen that the reflectance Y is improved by the gap expansion by the hybrid orientation. In addition, the threshold voltage characteristic and the γ characteristic are almost equal between the transmissive display unit and the reflective display unit, so that it can be said that the optical design is desirable compared to when the tilt angle is 53 °.

  From the above results, in the first embodiment, the tilt angle is 53 ° or less, the twist angle is 64 ° to 90 °, the cell retardation is 194 to 247 nm, and the liquid crystal molecules on the second substrate side and the pixel electrode slit are formed. It is desirable that the angle is approximately 0 °.

  FIG. 6 is a schematic view showing a second embodiment of the liquid crystal display device according to the present invention. In order to facilitate understanding, the same notation as in the first embodiment shown in FIG. 1 is adopted. Similar to the first embodiment, the liquid crystal is also twist-aligned in the present embodiment, but is characterized in that the tilt angles of the substrates on both sides are simultaneously made different between the reflective display portion and the transmissive display portion. As shown in the drawing, the pixel electrode 5 has a stripe shape or a comb shape extending in a predetermined direction. In the liquid crystal layer of the reflective display portion R, the tilt angle of the liquid crystal molecules 7 with respect to the first substrate 1 and the second substrate 2 is 40 ° or less, and the twist angle of twist orientation is in the range of 63 ° to 64 °. The retardation Re given by the product of the layer thickness d and its refractive index anisotropy Δn is in the range of Re = Δn × d = 194 to 200 nm, and the orientation direction of the liquid crystal molecules 7 of the second substrate 2 is the pixel electrode 5. An angle of approximately 20 ° is formed counterclockwise with a predetermined direction in which the stripe shape or the comb shape extends.

  FIG. 7 illustrates a first substrate (hereinafter referred to as a CF substrate because a color filter CF is formed) and a second substrate (hereinafter referred to as a TFT substrate because a thin film transistor TFT is formed). The figure shows the results of examining the optimum twist angle and optimum gap at which the black display of the reflective display portion sinks deepest when both the tilt angles of the liquid crystal molecules are changed. In order to facilitate understanding, the same notation as the measurement result of the first embodiment shown in FIG. 3 is adopted. In this measurement, the liquid crystal molecules on the CF substrate side are fixed in parallel or perpendicular to the absorption axis of the polarizing plate on the CF substrate side, while the orientation direction of the liquid crystal molecules on the TFT substrate side is changed, so that the optimum conditions Looking for. As shown in the graph of (a), the optimum twist angle is 63 to 64 °, and it can be seen that there is almost no fluctuation even when the tilt angle is changed. As shown in the graph (b), the optimum gap increases as the tilt angle increases. When the tilt angle is 40 °, the optimum gap becomes 3.1 μm, which is almost equal to the transmissive display portion. A transflective liquid crystal display device with a gap can be realized. The data at this time is a result of using a liquid crystal having a refractive index anisotropy Δn of 0.123 at a wavelength λ = 550 nm, and the cell retardation is about 200 nm as shown in FIG.

  FIG. 8 is a graph showing the results of actual measurement of the electro-optical characteristics of the second embodiment. The reflectance Y of the reflective display unit when the tilt angle with respect to both substrates is 40 °, the twist angle is set to 63 °, and the angle θ between the liquid crystal molecules on the TFT substrate side and the pixel electrode slit is changed. It represents voltage dependency. From the graph of FIG. 8, if the liquid crystal molecules are set in the vicinity of 20 ° counterclockwise from the pixel electrode slit, there is no gradation inversion and the reflectance Y is higher than the ECB mode of the reflectance Y = 36 shown in FIG. Can be obtained.

  From the above results, in the second embodiment, the tilt angle is 40 ° or less, the twist angle is 63 to 64 °, the cell retardation is 194 to 200 nm, and the liquid crystal molecules are 20 ° counterclockwise from the pixel electrode slit. It is desirable to set. The sample of the second embodiment created under these setting conditions has the configuration as shown in FIG. In the embodiment of FIG. 6, the stepped portion 14 is formed on the CF substrate 1 side to absorb a slight difference in level difference between the transmissive display portion T and the reflective display portion R, but the present invention is limited to this. Instead, the stepped portion 14 may be formed on the TFT substrate 2 side.

  FIG. 9 is a schematic view showing a third embodiment of the liquid crystal display device according to the present invention. In order to facilitate understanding, the same notation as in the first embodiment shown in FIG. 1 is adopted. In the first embodiment, the liquid crystal of the reflective display unit is twisted, but in this embodiment, the liquid crystal is homogeneously aligned and the phase difference is just λ / 4. In addition, the tilt angle is different between the reflective display portion and the transmissive display portion on both the substrates.

  As shown in FIG. 9, the liquid crystal layer of the reflective display portion R has a homogeneous alignment in which the alignment directions of the liquid crystal molecules 7 are aligned between the first substrate 1 and the second substrate 2, and a phase difference of λ / 4. The orientation direction of the liquid crystal molecules 7 forms an angle of 40 ° to 50 ° with respect to the transmission axes of the first and second polarizing plates. There are regions where the tilt angles of the liquid crystal molecules 7 of the reflective display portion R and the transmissive display portion T are different from each other with respect to the first and second substrates 1 and 2.

  The pixel electrode 5 has a stripe shape or a comb shape extending in a predetermined direction. The tilt angle of the liquid crystal molecules 7 with respect to both the first substrate 1 and the second substrate 2 is 50 ° or less, and the alignment direction of the liquid crystal molecules 7 is a predetermined direction in which the stripe shape or comb-teeth shape of the pixel electrode 5 extends and a clock. The angle is approximately 30 °.

  FIG. 10 is a graph showing the relationship between the tilt angle and the optimum gap in the third embodiment shown in FIG. In the third embodiment, when the tilt angle with respect to both the TFT substrate and the CF substrate is changed, the result of measuring the optimum gap where the black display of the normally black mode reflective display section sinks deepest is shown. In the third embodiment, as described above, the optimum condition was searched for in an alignment state in which the liquid crystal molecules are homogeneously aligned and at an angle of 45 ° with respect to the absorption axis of the polarizing plate on the CF substrate side. The retardation of the liquid crystal layer was kept constant at 140 nm at λ = 550 nm. As is apparent from the graph of FIG. 10, the optimum gap increases as the tilt angle increases. When the tilt angle is just 50 °, the gap size is about 3 μm, which is the same as that of the transmissive display portion, and a so-called single gap transflective liquid crystal display device can be realized.

  FIG. 11 is a graph showing the electro-optical characteristics of the third embodiment shown in FIGS. 9 and 10. Specifically, the tilt angle of the liquid crystal molecules with respect to the both side substrates is set to 50 °, and the reflectance Y of the reflective display portion when the angle θ formed between the major axis of the liquid crystal molecules and the pixel electrode slit is changed on the TFT substrate side. It is the result of examining the voltage dependency. As shown in the graph of FIG. 11, when the angle θ formed between the major axis of the liquid crystal molecules and the pixel electrode slit is 30 °, there is no gradation inversion and a high reflectance Y characteristic can be obtained.

  FIG. 12 is a schematic cross-sectional view showing a fourth embodiment of the liquid crystal display device according to the present invention. As shown to (a), this liquid crystal display device has the liquid crystal layer between the 1st board | substrate 1 and the 2nd board | substrate 2, and has the reflective display part R and the transmissive display part T in one pixel. The first substrate 1 has a first polarizing plate (not shown) and an alignment layer 3 in contact with the liquid crystal layer. The second substrate 2 includes a second polarizing plate (not shown), an alignment layer 4 in contact with the liquid crystal layer, and a pixel electrode 5 and a common electrode 6 that apply a lateral electric field to the liquid crystal layer. Have The first and second polarizing plates are arranged so that their transmission axes are orthogonal to each other. In other words, the first and second polarizing plates are arranged so that their absorption axes are orthogonal to each other. In the transmissive display portion T, the liquid crystal layer has the liquid crystal molecules 7 substantially parallel to the transmission axis of the first or second polarizing plate in a state where no voltage is applied between the pixel electrode 5 and the common electrode 6. Oriented. On the other hand, the reflective display portion R has an optical layer (retardation layer) 19 having a phase difference separately from the liquid crystal layer for switching light, and at least one of the first substrate 1 and the second substrate 2. The tilt angle of the liquid crystal molecules 7 with respect to the substrates 1 and 2 is aligned so as to be different from the tilt angle of the liquid crystal molecules 7 of the transmissive display portion T. In the example of (a), the liquid crystal molecules 7 in the reflective display portion R are at a high tilt on both sides of the first substrate 1 and the second substrate 2.

  (B) has shown the modification of 4th Embodiment shown to (a). In the embodiment shown in (a), the tilt angle is given to both the substrates, but in the modified example (b), the tilt angle of the liquid crystal molecules is given only to the first substrate side.

  FIG. 13 shows a plan view of one pixel of the fourth embodiment shown in FIG. 12 and the alignment state of the liquid crystal molecules in the reflective display section and transmissive display section included in one pixel. As shown to (a), the area for 1 pixel of the liquid crystal display device of 4th Embodiment is divided | segmented into the reflective display part R and the transmissive display part T similarly to other embodiment. In the present embodiment, the retardation layer 19 having a phase difference of (½) λ is selectively inserted only in the reflective display portion R. Thereby, the optical conditions of the reflective display portion R and the transmissive display portion 7 are made uniform. Therefore, as shown in (b) and (c), there is no difference in the alignment direction of the liquid crystal molecules 7 between the reflective display portion and the transmissive display portion. As shown in (b), in the reflective display section, the λ / 2 retardation layer forms an angle of 22.5 ° with respect to the absorption axis of the first polarizing plate.

  On the other hand, by interposing the retardation layer 19, the thickness of the liquid crystal layer of the reflective display portion R becomes shorter than the thickness of the transmissive display portion T. If no measures are taken, the thickness of the liquid crystal becomes too thin at the reflective display portion R, and it becomes difficult to apply a uniform lateral electric field to the liquid crystal layer. Therefore, according to the present invention, the liquid crystal molecules have a tilt angle on both or one of the first substrate and the second substrate in the reflective display portion R, so that the thickness of the liquid crystal in the reflective display portion R is transmissively displayed as much as possible. The liquid crystal thickness of the portion T is approached.

  FIG. 14 is a schematic cross-sectional view showing a fifth embodiment of the liquid crystal display device according to the present invention. Basically, it is the same as that of the first embodiment shown in FIG. 1, and corresponding reference numerals are assigned to corresponding parts. The feature of this embodiment is that the alignment layer includes a grating layer in which a plurality of grooves are formed in parallel on the first or second substrate. In the example of (a), the alignment layer of the second substrate 2 includes a grating layer. This grating layer is formed on the surface of the fourth insulating film 29 covering the pixel electrode 5. Further, in the alignment layer of this embodiment, the alignment film 4 is formed so as to cover the grating layer. This alignment film 4 has a horizontal alignment ability to align the liquid crystal molecules 7 in parallel with the substrate 2 in the absence of voltage, and the alignment direction of the liquid crystal molecules 7 is a direction perpendicular to the direction in which the grating grooves extend. . In the grating layer, the grooves extend along a predetermined direction, and are repeatedly arranged at a given pitch along an orthogonal direction orthogonal to the predetermined direction, and inclined in the cross section of the grating layer along the orthogonal direction. By attaching a, a predetermined tilt angle can be given to the liquid crystal molecules 7.

  In the modification shown in (b), not only the second substrate 2 side but also the alignment layer on the first substrate 1 side is composed of a combination of a grating layer and an alignment film. The grating layer is formed on the surface of the step 14. The first alignment film 3 covers the grating layer formed on the step 14.

  As is clear from the above description, the present embodiment uses the grating orientation for the divisional orientation of the transmissive display portion T and the reflective display portion R. The grating of the transmissive display portion forms a groove having a symmetrical cross section, and the grating of the reflective display portion forms a grating having an asymmetric cross section. Since the asymmetrical grating has an effect of controlling the tilt angle of the liquid crystal molecules, the tilt angle can be controlled in a region-divided manner in each pixel by using the configuration of this embodiment.

  FIG. 15 is a schematic diagram showing the basic principle of a grating method suitable for divided orientation. As described above, the liquid crystal display device according to the present invention basically includes a pair of substrates bonded to each other through a predetermined gap and the liquid crystal held in the gap. FIG. 15 shows one substrate and liquid crystal molecules existing near the surface. An alignment layer for aligning liquid crystal molecules is formed on at least one of the substrates. Although not shown, an electrode for applying a voltage to the liquid crystal is formed on one of the pair of substrates.

  The alignment layer has a composite structure composed of a base layer in which a plurality of grooves M are formed in parallel, and a film covering these grooves M. However, the plurality of grooves M need not be geometrically strictly parallel, and may be substantially or substantially parallel as long as the effects of the present invention are achieved. Each groove M extends along a predetermined direction and is repeatedly arranged at a given pitch along an orthogonal direction orthogonal to the predetermined direction in which the groove extends. Hereinafter, in the present specification, this predetermined direction may be referred to as a linear direction. However, the groove does not necessarily have a linear shape, and may have a curved shape. The coating is made of, for example, a polymer film such as polyimide resin, and has a horizontal alignment ability for aligning the molecular long axis indicating the longitudinal direction of the liquid crystal molecules in parallel with the substrate in the state where no voltage is applied. When a polymer film is applied to a base layer in which stripe-like grooves (gratings) are formed, polymer chains are aligned along the grating. This aligned polymer chain gives alignment regulating force to the liquid crystal molecules. Therefore, the alignment of liquid crystal molecules can be controlled without rubbing. This is the orientation control by the combined effect of the film and the base layer. Although depending on the processing conditions, the polymer chains are aligned along the linear direction of the groove M in the illustrated example. In some cases, the polymer chains may be aligned in the orthogonal direction of the grating due to the uniaxial stretching effect when the coating is cured on the base layer.

  The alignment layer having a composite structure in which the film and the base layer are stacked performs different alignment control on the liquid crystal molecules according to the aspect ratio of the grating. This aspect ratio represents the ratio of the depth of the grating to the arrangement pitch of the grating. The composite alignment layer according to the present invention has a property that when the aspect ratio is lower than a predetermined lower limit (when the grating groove is shallow), the molecular long axis of the liquid crystal is horizontally aligned in a random direction. This random alignment approximates the alignment state obtained when the polyimide alignment film is not rubbed, and the grooves are too shallow to show the effect of the grating. On the other hand, when the aspect ratio is higher than a predetermined upper limit (when the grating groove is deep), the molecular long axis of the liquid crystal is oriented horizontally (parallel to the groove) in the linear direction of the groove. This parallel alignment is close to the state obtained by the conventional grating alignment, and the alignment regulating force (anchoring force) by the grating dominates the alignment, and the combined effect of the film and the base layer does not appear.

  When the aspect ratio of the grating is between the lower limit value and the upper limit value (when the grating is not too shallow and not too deep and is in an appropriate shape), the molecular long axis of the liquid crystal is oriented horizontally in the direction perpendicular to the groove. Has properties. This orthogonal orientation is just a new orientation state obtained by the combined effect of the grating base layer and the orientation coating, and is excellent in stability and uniformity compared to the parallel orientation obtained by the conventional grating. The alignment layer according to this embodiment is excellent in productivity because the aspect ratio can be suppressed lower than that of the conventional grating alignment layer. In the liquid crystal display device according to the present embodiment, the grating is formed on the base layer so that the aspect ratio is between the lower limit value and the upper limit value, and this is covered with the alignment film. By adopting such a configuration, it is possible to realize a liquid crystal display device that has high productivity and uniform and stable alignment regulation power and can ensure high image quality as compared with the related art.

  FIG. 16 is a schematic diagram showing the alignment state of liquid crystal molecules, where (A) represents orthogonal alignment and (B) represents parallel alignment. (A) and (B) are both cross-sectional views along the orthogonal direction of the grating, and irregularities corresponding to the grating appear in the alignment layer. As shown in (A), in the orthogonal orientation, the liquid crystal molecules are aligned parallel to the orthogonal direction of the grating. As shown in (B), in the parallel alignment, the liquid crystal molecules are aligned in the linear direction of the grating (perpendicular to the paper surface). When the aspect ratio of the grating is appropriately set between the lower limit value and the upper limit value, the liquid crystal molecules are orthogonally oriented as shown in (A) due to the combined effect of the grating base layer and the horizontal alignment film. On the other hand, as shown in (B), when the aspect ratio of the grating exceeds the upper limit and the anchoring effect of the grating alone becomes dominant, the liquid crystal molecules transition to the parallel alignment as in the conventional grating alignment.

  FIG. 17 is a graph showing the relationship between the grating height and the black luminance of the liquid crystal display device. Here, in this liquid crystal display device, the relationship between the upper and lower polarizing plates and the liquid crystal molecule alignment direction is as shown in the schematic diagram of FIG. 19A, which is described later. Aligns liquid crystal molecules by grating alignment. The liquid crystal molecules are homogeneously aligned because the rubbing direction is set in a direction perpendicular to the grating. The black luminance in the graph represents the luminance of the liquid crystal screen when no voltage is applied, and is an index indicating the alignment state of the liquid crystal. The lower the black luminance (the darker the screen), the more uniform and stable the liquid crystal's orthogonal alignment state is.

  In this graph, the pitch of the grating is used as a parameter, and the pitch increases in the order of P1, P2, and P3. The three solid line curves represent the alignment state generated by the elastic strain effect (anchoring force) of the grating itself. As described above, this elastic strain effect basically has the property of aligning liquid crystal molecules in parallel with the grating. As is clear from the graph, the higher the grating (the deeper the groove), the stronger the elastic strain effect of the grating itself, and the liquid crystal transitions from the orthogonal orientation to the parallel orientation, and the whole changes from the homogeneous orientation to the twist orientation. Since the orthogonal orientation is lost in this way, the black luminance increases (the screen goes white).

  On the other hand, the three dotted line curves represent the orientation state due to the effects unique to the present embodiment. The effect unique to the present embodiment is an effect of aligning polymer chains of a polymer film made of polyimide (PI) or the like by the grating of the base layer, whereby the liquid crystal molecules are aligned orthogonally to the grating. As is clear from the graph, when the grating is high (when the grating is deep), the polyimide (PI) film is aligned due to the influence thereof, so that the liquid crystal molecules are orthogonally aligned, and the black luminance is lowered and uniform and stable. An orientation state can be obtained. When the grating is too shallow, the effect of aligning the PI film polymer by the grating does not appear, so that the liquid crystal is in a random alignment state, and the black luminance is increased. Therefore, it is necessary to form the grating in a region where a lower limit value occurs in the aspect ratio of the grating and the polymer alignment effect by the groove appears.

  As described above, in this embodiment, the alignment control of liquid crystal molecules is performed using the range in which the orthogonal alignment ability by the composite alignment layer of the grating base layer and the polymer film is dominant. Theoretically, it is considered that the higher the grating is, the stronger the orthogonal orientation ability is. However, the higher the grating is, the stronger the parallel orientation ability is, and eventually cancels the orthogonal orientation ability and the parallel orientation ability becomes dominant. For this reason, an upper limit value is generated in the aspect ratio of the grating, and it is necessary to form the grating in a region where the parallel alignment ability is not dominant.

  FIG. 18 is a graph showing the relationship between the grating height and anchoring energy. This anchoring energy represents the strength of the elastic strain effect of the grating itself, and the larger this is, the more the parallel alignment state of the liquid crystal is stabilized. In the graph, the anchoring energy obtained by the conventional rubbing orientation is also shown. In this graph, the grating pitch is set to 2 μm, 3 μm, and 4 μm as parameters. As can be seen from the graph, the higher the grating, the stronger the anchoring energy, and the liquid crystal is aligned in parallel and approaches the rubbing alignment state. This embodiment uses the alignment action of the grating with respect to the coating polymer, but it is necessary to suppress the aspect ratio of the grating in a region where the elastic strain effect by the grating itself is not dominant.

  FIG. 19 is a schematic view showing the alignment state of the liquid crystal held on the pair of substrates. As shown in the figure, the molecular long axes of the liquid crystals are aligned horizontally in a certain direction and are horizontally aligned. In this specification, this alignment state may be referred to as homogeneous alignment. In addition, the alignment direction of the molecular long axes of the liquid crystal may be referred to as an alignment direction in this specification. Therefore, the orthogonal orientation unique to this embodiment is a homogeneous alignment in which the alignment direction matches the orthogonal direction of the grating.

  In the liquid crystal display device, the alignment of the liquid crystal is controlled using the alignment layer and the applied voltage is controlled to switch the alignment state, thereby performing a desired image display. The change in the alignment state can be converted into a change in luminance by a pair of upper and lower polarizing plates, for example. (A) represents the crossed Nicols arrangement of a pair of polarizing plates, and the transmission axes of the upper and lower polarizing plates are orthogonal to each other. The transmission axis of the lower polarizing plate on the incident side is parallel to the alignment direction of the liquid crystal. The transmission axis of the polarizing plate on the output side is orthogonal to the alignment direction of the liquid crystal. When the liquid crystal is in an ideal homogeneous orientation, incident light is completely blocked by a pair of polarizing plates, and leakage light becomes zero. Therefore, a black display can be obtained.

  (B) represents the paranicol arrangement of a pair of polarizing plates. Under this Paranicol condition, the transmission axes of the upper and lower polarizing plates are both parallel to the alignment direction of the liquid crystal. In this case, the incident light is emitted as it is without being absorbed. Therefore, white display can be obtained. When the paranicol arrangement is adopted when no voltage is applied, the display is normally white. Conversely, when the crossed Nicols arrangement is adopted, normally black display is obtained when no voltage is applied.

  FIG. 20 is a graph showing the effect of this embodiment, and is a result of measuring the relationship between the grating height and the black luminance with respect to the liquid crystal display device sample produced with the orientation model of FIG. 19A and different grating pitches. Represents. The horizontal axis represents the grating height in μm units, and the vertical axis represents black luminance in nit units. It can be seen that in the sample having the groove arrangement pitch of 5 μm, the black luminance is lowered in the range of the grating height of 0.3 to 0.7 μm, and a stable and uniform orthogonal orientation can be obtained. If the grating height is 0.3 μm or less, the black luminance increases due to random orientation. On the other hand, when the grating height exceeds 0.7 μm, the orthogonal orientation is lost and the parallel orientation is shifted, so that the black luminance increases.

  In a sample having a grating arrangement pitch of 4 μm, a uniform and stable orthogonal orientation state was obtained when the grating height (groove depth) was in the range of 0.2 to 0.7 μm. In addition, in the sample having the grating arrangement pitch of 3 μm, the black luminance is lowered in the range of the grating height of 0.4 to 0.7 μm, and uniform and stable orthogonal orientation is obtained. In addition, in a sample having a grating pitch of 1 μm, black luminance is lowered and a stable orthogonal orientation is obtained in a region where the grating height (groove depth) exceeds 0.1 μm.

  From the results shown in FIG. 20, it can be estimated that, as a general tendency, uniform and stable orthogonal orientation can be obtained when the aspect ratio is in the range of 0.05 to 0.5. Preferably, when the groove pitch is in the range of 1 μm to 5 μm, the depth of the groove is in the range of 0.1 to 0.7 μm so that the molecular long axis of the liquid crystal is oriented in the orthogonal direction of the groove. As a result, horizontal alignment is achieved.

  FIG. 21 shows a structure in which the grating has an asymmetric cross-sectional shape to give a tilt angle to the liquid crystal, which is used for, for example, the orientation control of the reflective display portion of the liquid crystal display device according to the present invention. As shown in FIG. 21, an insulating film 29 is formed on the surface of the substrate 2, and a plurality of grooves M are formed on the surface. As shown in the drawing, a cross-sectional shape in a direction crossing the groove M is formed in an asymmetric shape with the apex of the groove M as a center, and an alignment film 4 having a horizontal alignment ability is formed thereon. With this configuration, in the reflective display portion of the liquid crystal display device, the tilt angle of the liquid crystal molecules on the substrate 2 side is controlled to an angle determined by the asymmetrical grating.

  In the example shown in the figure, a groove M is formed on the substrate 2 on the TFT side so that the cross-sectional shape is a saw-tooth shape, so that the triangular protrusions formed by the pair of inclined surfaces M1 and M2 are sequentially repeated at a predetermined pitch. In addition, a groove M is formed. As a result, the angles θ1 and θ2 formed by the pair of inclined surfaces M1 and M2 with respect to the plane parallel to the surface of the TFT substrate 2 are set to different angles, and the tilt angle of the liquid crystal molecules is controlled. The cross-sectional shape of the groove M is not limited to the sawtooth shape as shown in FIG. 21. For example, when the apex of the groove M is shifted to one side to make an asymmetric shape, the groove is formed in an asymmetric shape. The tilt angle of the liquid crystal molecules can be controlled in various ways.

1 is a schematic diagram showing a first embodiment of a liquid crystal display device according to the present invention. It is a principle explanatory view of the present invention. It is a graph which shows the display characteristic of 1st Embodiment. It is a graph which shows the electro-optical characteristic of 1st Embodiment. It is a graph which similarly shows the electro-optical characteristic of 1st Embodiment. It is a schematic diagram which shows 2nd Embodiment of the liquid crystal display device concerning this invention. It is a graph which shows the display characteristic of 2nd Embodiment. It is a graph which shows the electro-optical characteristic of 2nd Embodiment. It is a schematic diagram which shows 3rd Embodiment of the liquid crystal display device concerning this invention. It is a graph which shows the display characteristic of 3rd Embodiment. It is a graph which shows the electro-optical characteristic of 3rd Embodiment. It is typical sectional drawing which shows 4th Embodiment of the liquid crystal display device concerning this invention. Similarly, it is a schematic plan view of the fourth embodiment and an alignment diagram of liquid crystal molecules. It is sectional drawing which shows 5th Embodiment of the liquid crystal display device concerning this invention. It is a schematic diagram which shows the basic principle of grating orientation. It is a schematic diagram with which it uses for description of grating orientation. It is a graph similarly used for description of grating orientation. It is a graph similarly used for description of grating orientation. It is a schematic diagram for explaining the grating orientation in the same manner. It is a graph which similarly shows the effect of grating orientation. It is a schematic diagram for explaining the grating orientation in the same manner. It is a graph which shows the electro-optical characteristic of the conventional liquid crystal display device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... 1st board | substrate, 2 ... 2nd board | substrate, 3 ... 1st alignment film, 4 ... 2nd alignment film, 5 ... Pixel electrode, 6 ... Common Electrode, 11 ... Color filter, 12 ... Flattening layer, 14 ... Step, 21 ... Third insulating film, 22 ... Metal film, 23 ... First insulating film, 24: second insulating film, R: reflective display unit, T: transmissive display unit

Claims (10)

In a liquid crystal display device having a liquid crystal layer sandwiched between first and second substrates and having a reflective display portion and a transmissive display portion in one pixel,
The first substrate has a first polarizing plate and an alignment layer in contact with the liquid crystal layer,
The second substrate includes a second polarizing plate, an alignment layer in contact with the liquid crystal layer, and a pixel electrode and a common electrode that apply an electric field to the liquid crystal layer,
The first and second polarizing plates are arranged so that their transmission axes are orthogonal to each other,
In the transmissive display portion, the liquid crystal layer has liquid crystal molecules substantially parallel to the transmission axis of the first or second polarizing plate in a state in which no voltage is applied between the pixel electrode and the common electrode. Oriented,
In the reflective display portion, in the state where no voltage is applied, the alignment direction of the liquid crystal molecules is different from the alignment direction of the liquid crystal molecules in the transmissive display portion, and is at least one of the first substrate and the second substrate. A liquid crystal display device, wherein the liquid crystal molecules are aligned such that the tilt angle of the liquid crystal molecules is different from the tilt angle of the liquid crystal molecules of the transmissive display portion.   The liquid crystal display device according to claim 1, wherein the liquid crystal molecules of the liquid crystal layer of the reflective display portion are twisted with a twisted orientation between the first substrate and the second substrate. The pixel electrode has a stripe shape or a comb shape extending in a predetermined direction,
The liquid crystal layer of the reflective display unit has a tilt angle of liquid crystal molecules of 53 ° or less with respect to the second substrate and a twist angle of the twisted orientation in a range of 64 ° to 90 °. The retardation given by the product of the rate anisotropy is in the range of 194 to 247 nm, and the orientation direction of the liquid crystal molecules on the second substrate side is substantially 0 with respect to the predetermined direction in which the stripe shape or comb shape of the pixel electrode extends. The liquid crystal display device according to claim 2, wherein the liquid crystal display device forms an angle of °. The pixel electrode has a stripe shape or a comb shape extending in a predetermined direction,
The liquid crystal layer of the reflective display portion has a tilt angle of liquid crystal molecules of 40 ° or less with respect to the first substrate and the second substrate, and a twist angle of the twisted orientation is in a range of 63 ° to 64 °. The retardation given by the product of the thickness of the film and its refractive index anisotropy is in the range of 194 to 200 nm, and the alignment direction of the liquid crystal molecules on the second substrate side extends the stripe shape or comb tooth shape of the pixel electrode. The liquid crystal display device according to claim 2, wherein the liquid crystal display device forms an angle of approximately 20 ° counterclockwise with respect to a predetermined direction. The liquid crystal layer of the reflective display portion has a homogeneous alignment in which the alignment directions of liquid crystal molecules are aligned between the first substrate and the second substrate, and has a phase difference of λ / 4, and the alignment direction of the liquid crystal molecules Is at an angle of 40 degrees to 50 degrees with respect to the transmission axes of the first and second polarizing plates (λ is the wavelength of light),
2. The liquid crystal display device according to claim 1, wherein regions having different tilt angles of liquid crystal molecules of the reflective display portion and the transmissive display portion exist with respect to the first and second substrates. The pixel electrode has a stripe shape or a comb shape extending in a predetermined direction,
The tilt angle of the liquid crystal molecules with respect to both the first substrate and the second substrate is 50 ° or less,
6. The liquid crystal display device according to claim 5, wherein the alignment direction of the liquid crystal molecules forms an angle of approximately 30 degrees clockwise with respect to a predetermined direction in which the stripe shape or comb shape of the pixel electrode extends. In a liquid crystal display device having a liquid crystal layer sandwiched between first and second substrates and having a reflective display portion and a transmissive display portion in one pixel,
The first substrate has a first polarizing plate and an alignment layer in contact with the liquid crystal layer,
The second substrate includes a second polarizing plate, an alignment layer in contact with the liquid crystal layer, and a pixel electrode and a common electrode that apply an electric field to the liquid crystal layer,
The first and second polarizing plates are arranged so that their transmission axes are orthogonal to each other,
In the transmissive display portion, the liquid crystal layer has liquid crystal molecules substantially parallel to the transmission axis of the first or second polarizing plate in a state in which no voltage is applied between the pixel electrode and the common electrode. Oriented,
The reflective display unit includes an optical layer having a phase difference separately from the liquid crystal layer for switching light, and a tilt angle of liquid crystal molecules with respect to at least one of the first substrate and the second substrate Is oriented so as to be different from the tilt angle of the liquid crystal molecules of the transmissive display portion.   The liquid crystal display device according to claim 1, wherein the alignment layer includes a grating layer in which a plurality of grooves are formed in parallel on the first or second substrate. The alignment layer is formed with an alignment film so as to cover the grating layer,
The alignment film has a horizontal alignment ability to align liquid crystal molecules parallel to the substrate in the absence of a voltage applied,
The liquid crystal display device according to claim 8, wherein the alignment direction of the liquid crystal molecules is a direction orthogonal to a direction in which the groove extends. In the grating layer, each groove extends along a predetermined direction, and is repeatedly arranged at a given pitch along an orthogonal direction orthogonal to the predetermined direction.
10. The liquid crystal display device according to claim 9, wherein a predetermined tilt angle is given to the liquid crystal molecules by inclining a cross section of the grating layer along the orthogonal direction.

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