JP5254477B2 - Liquid crystal display - Google Patents

Description

  The present invention relates to a liquid crystal display device and can be applied to a liquid crystal display device in a liquid crystal mode such as FFS (Fringe Field Switching) and IPS (In-Plane Switching). In the present invention, when no voltage is applied, the reflective display portion and the transmissive display portion are twisted and homogeneously aligned, or in a plurality of color pixels of a color image, twisted and homogeneously aligned when no voltage is applied. By setting as described above, a high-contrast, black-colored display with high color is ensured for the transflective type using the FFS mode or the like.

In recent years, TN (Twisted Nematic) has been used in portable information devices such as mobile phones and electronic still cameras.
), Transflective liquid crystal display panels using various liquid crystal modes such as ECB (Electrically Controlled Birefringence). Here, the transflective liquid crystal display panel is a liquid crystal display panel having a reflective display portion and a transmissive display portion in one pixel, and obtains a high contrast ratio in various environments such as outdoors in a sunny day, dark indoors, and the like. Therefore, it has desirable characteristics as a display device of a portable information device.

  In recent years, liquid crystal display panels having a wide viewing angle such as FFS and IPS have begun to spread to various monitor devices, mobile phones, electronic still cameras, and the like.

  Japanese Patent Application Laid-Open No. 2005-338264 proposes a method of creating a transflective liquid crystal display panel in the IPS mode by changing the alignment direction of the liquid crystal between the transmissive display portion and the reflective display portion. In Japanese Patent Laid-Open No. 2005-338264, specifically, a configuration in which all red, green, and blue pixels are twisted by 45 degrees, and a 1 / 4λ phase difference layer is provided on the reflective display unit to provide red, green, A configuration in which all blue pixels are homogeneously aligned is disclosed.

  By the way, if a transflective liquid crystal display panel is configured in the FFS and IPS liquid crystal modes, a wide viewing angle transmissive display and a reflective display can be obtained at the same time, which is considered useful for portable information devices. However, if a semi-transmission type is to be created with a combination of retardation plates as in the normal ECB and VA modes, there is a problem that the wide viewing angle of transmissive display cannot be maintained, and it is difficult to easily create a semi-transmission type. is there.

  As one method for solving this problem, it is conceivable to apply the method disclosed in Japanese Patent Laid-Open No. 2005-338264, but this method has the following problems. That is, in the configuration disclosed in Japanese Patent Laid-Open No. 2005-338264, in which all the red, green, and blue pixels are twisted at 45 degrees, the optical design is not clearly shown. The liquid crystal layer has a 1 / 4λ retardation layer, and this configuration has a problem that it is difficult in principle to display black. In addition, in a configuration in which a 1 / 4λ retardation layer is provided in the reflective display portion disclosed in Japanese Patent Laid-Open No. 2005-338264 and all pixels of red, green, and blue are homogeneously aligned, the black display exhibits blue. There's a problem.

JP 2005-338264 A

  The present invention has been made in consideration of the above points. In addition to clearly showing a design guideline in the case where the reflective display portion is twist-oriented with respect to the transflective type using the FFS mode or the like, the liquid crystal layer has a 1 / 4λ. The present invention intends to propose a liquid crystal display device capable of ensuring a black display with little coloration when having the above retardation layer.

According to one aspect of the present invention for solving the above problems, 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 on the side opposite to the liquid crystal layer, and the second substrate has a second polarizing plate on the side opposite to the liquid crystal layer, and a substrate surface on the liquid crystal layer side. A pixel electrode for applying an electric field substantially parallel to the first electrode and a common electrode, the first and second polarizing plates are arranged so that the transmission axes are orthogonal to each other, the pixel has a color filter, and a liquid crystal In the transmissive display portion, the liquid crystal molecules are aligned substantially in parallel with the transmission axis of the first or second polarizing plate in a state where no voltage is applied between the pixel electrode and the common electrode in the transmissive display portion. In the state where no voltage is applied between the common electrodes, the red and green pixel regions are homogeneously oriented. Is set, the area of the blue pixel in the liquid crystal display device is set to the twist orientation is provided.

  According to the present invention, a black display with high contrast and little color can be secured for a transflective type using the FFS mode or the like.

It is a top view which shows the structure of 1 pixel of the liquid crystal display panel applied to the liquid crystal display device of Example 1 of this invention. It is sectional drawing which cuts and shows FIG. 1 (A) by the AA line. It is a characteristic curve figure which shows the result of having set cell retardation to 380 [nm] and measuring the optimal twist angle in a reflective display part. It is a characteristic curve figure which shows the analysis result of the reflectance at the time of setting to 37 degrees of twist angles. It is a characteristic curve figure which shows the result of having measured the optimal retardation, hold | maintaining a twist angle at 37 degree | times. It is the characteristic curve figure which measured the change of the reflectance to cell gap. It is sectional drawing which shows the liquid crystal display panel of Example 2 of this invention. It is a characteristic curve figure which shows the measurement result which measured the optimum value of the cell retardation in a green wavelength band. It is a characteristic curve figure which shows the measurement result which measured the optimal value of the twist angle in a green wavelength band. It is a characteristic curve figure which shows the measurement result which measured the optimum value of the cell retardation in a blue wavelength band. It is a characteristic curve figure which shows the measurement result which measured the optimal value of the twist angle in a blue wavelength band. It is a characteristic curve figure which shows the measurement result which measured the optimum value of the cell retardation in a red wavelength band. It is a characteristic curve figure which shows the measurement result which measured the optimal value of the twist angle in a red wavelength band. It is a characteristic curve figure which shows the characteristic of the transmittance | permeability of a color filter. It is sectional drawing which shows the structure of the pixel of the liquid crystal display panel of Example 3 of this invention. It is sectional drawing of the depth direction of FIG. FIG. 16 is a plan view showing red and green pixels of the liquid crystal display panel of FIG. 15. FIG. 16 is a plan view showing blue pixels of the liquid crystal display panel of FIG. 15. FIG. 16 is a characteristic curve diagram for explaining the operation of the liquid crystal display panel of FIG. 15. It is a characteristic curve figure which shows the reflectance of the liquid crystal display panel in the case of only homogeneous orientation. FIG. 16 is a characteristic curve diagram illustrating the reflectance of the liquid crystal display panel of FIG. 15. It is a figure which shows the chromaticity of black in the liquid crystal display panel of FIG. 6 is a diagram for explaining an electrode in a liquid crystal display panel of Example 4. FIG. 6 is a plan view for explaining pixel electrodes of a liquid crystal display panel of Example 4. FIG. It is a graph which shows the change of the reflectance at the time of changing the magnitude | size of an electrode. FIG. 26 is a characteristic curve diagram showing a change in reflectance when a voltage is applied under the optimum condition obtained from FIG. 25. It is a graph with which it uses for description of the electrode in the liquid crystal display panel of Example 5 of this invention. It is a graph which shows the maximum value of the reflectance at the time of changing the magnitude | size of an electrode about the case where cell retardation is 450 [nm] which is a red pixel. It is a top view which shows the structure of the electrode in the case of IPS mode.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings as appropriate.

(1) Configuration and Operation of Embodiment FIG. 1A is a plan view showing the configuration of one pixel of a liquid crystal display panel applied to the liquid crystal display device of Embodiment 1 of the present invention. FIG. It is sectional drawing which cuts and shows FIG. 1 (A) by the AA line. The liquid crystal display device using the liquid crystal display panel 1 is applied to a portable information device such as a mobile phone, and a backlight device is disposed on the back surface of the liquid crystal display panel 1. The liquid crystal display panel 1 is a transflective liquid crystal display panel in which a transmissive display portion and a reflective display portion are provided in one pixel, and a liquid crystal layer 4 is sandwiched between a TFT substrate 3 and a CF substrate 2.

  Here, in the CF substrate 3, the color filter 6, the planarizing layer 7, and the alignment film 8 are sequentially disposed on the side surface of the liquid crystal layer 4 of the transparent insulating substrate 5, and the polarizing plate 9 is disposed on the side surface opposite to the side surface of the liquid crystal layer 4. Be placed. Here, for the transparent insulating substrate 5, various transparent insulating substrate materials such as glass and plastic can be applied. The color filter 6 can employ a stripe arrangement, a delta arrangement, or the like. The flattening layer 7 flattens the step caused by the color filter 6. The alignment film 8 is formed of a polyimide-based polymer material that induces horizontal alignment, and has an alignment ability to align liquid crystal molecules in a predetermined direction by a rubbing method, a photo alignment method, an ion beam alignment method, or the like.

  On the other hand, in the TFT substrate 3, the polarizing plate 11 is disposed on the side surface opposite to the side surface of the liquid crystal layer 4 of the transparent insulating substrate 10. Further, a TFT (Thin Film Transistor) or the like is disposed on the side surface of the liquid crystal layer 4 to form a first insulating film 12, and the common wiring 13, the second insulating film 14, and the common are formed on the first insulating film 12. The electrode 15, the third insulating film 16, the pixel electrode 17, the signal wiring 18, the alignment film 19 and the like are sequentially arranged.

  Here, various transparent insulating substrate materials, such as glass and plastic, can be applied to the transparent insulating substrate 10. The TFT is connected to the scanning wiring, the signal wiring 18, and the pixel electrode 17, and the signal wiring 18 is made of, for example, aluminum. The scanning wiring is made of, for example, molybdenum, and the common electrode 15 and the pixel electrode 17 are made of ITO (Indium Tin Oxide). The common electrode 15 is partially formed of aluminum, silver, chromium, molybdenum, or other metal so as to function as a reflecting plate that reflects incident light in the reflective display portion.

  The pixel electrode 17 is formed in a slit shape, is insulated by the insulating film 16, and is disposed close to the common electrode 15. Thereby, when a voltage is applied between the pixel electrode 17 and the common electrode 15, the liquid crystal display panel 1 generates an electric field between the pixel electrode 17 and the common electrode 15, and this electric field passes through the liquid crystal layer 4 in an arch shape. The orientation of the liquid crystal layer 4 is changed by this electric field. Note that the pixel electrode 17 may have different slit pitches, widths, and directions with respect to the signal lines depending on the color of the transmissive display portion and the reflective display portion or the color filter.

  The alignment film 19 is formed of a polyimide polymer material that induces horizontal alignment in the same manner as the alignment film 8, and is provided with alignment ability by various methods similar to those of the alignment film 8. A nematic liquid crystal having a positive dielectric anisotropy is applied to the liquid crystal layer 4. Alternatively, a liquid crystal having negative dielectric anisotropy may be used.

  In such a configuration, the liquid crystal display panel 1 shows the alignment directions of the liquid crystal molecules when no voltage is applied to the electrodes 15 and 17 in the reflective display portion and the transmissive display portion, respectively, in FIGS. In addition, the alignment direction of the alignment film 8 on the CF substrate 2 side is set to be different between the reflective display portion and the transmissive display portion. In contrast, the alignment film 19 of the TFT substrate 3 is set so that the alignment directions of the reflective display portion and the transmissive display portion are antiparallel to the alignment direction of the alignment film 8 of the CF substrate 2 in the transmissive display portion.

  Thus, in the liquid crystal display panel 1, when no voltage is applied, the transmissive display unit is set to homogeneous alignment, and the reflective display unit is set to twist alignment. Corresponding to the setting of the alignment films 8 and 19, in the liquid crystal display panel 1, the polarizing plate 11 on the TFT substrate 3 side and the polarizing plate 9 on the CF substrate 2 side are arranged so that the absorption axes are orthogonal to each other, and the TFT substrate 3 The alignment direction of the liquid crystal molecules at the side interface is set to be parallel to the absorption axis of the CF substrate 2 side polarizing plate 9.

  Thereby, in this liquid crystal display panel 1, the transmissive display unit is set to a normally black FFS mode, and when no voltage is applied, the transmissive display unit transmits incident light that is transmitted through the polarizing plate 11 on the TFT substrate 3 side from the backlight device. The light is transmitted without giving any phase difference and is completely shielded by the polarizing plate 9 of the CF substrate 2. In addition, when a voltage is applied, liquid crystal molecules are switched in a twisting direction according to the applied voltage, and the polarization state of incident light transmitted through the polarizing plate 11 from the backlight device changes according to the applied voltage between the electrodes 15 and 17. Then, the light enters the polarizing plate 9 of the CF substrate 2 and is emitted from the polarizing plate 9 with a light amount corresponding to the applied voltage between the electrodes 15 and 17. On the other hand, the reflective display unit is set in the twist orientation, and when no voltage is applied, the incident light transmitted through the polarizing plate 9 of the CF substrate 2 is reflected by the reflection unit by the common electrode 15. When returning to the polarizing plate 9, it is set so that the linearly polarized light is orthogonal to the transmission axis of the polarizing plate 9. As a result, the emitted light is shielded by the polarizing plate 9, and the reflective display portion is in a normally black mode display state. On the other hand, when a voltage is applied, by switching of liquid crystal molecules according to the applied voltage, the polarization state in the optical path from passing through the polarizing plate 9 to being reflected by the reflecting portion, from the reflecting portion to reaching the polarizing plate 9 The polarization state in the optical path is changed according to the applied voltage between the electrodes 15 and 17, and the incident light reflected by the reflecting portion is emitted from the polarizing plate 9 with the amount of light according to the applied voltage between the electrodes 15 and 17.

  More specifically, in the liquid crystal display panel 1, the retardation of the transmissive display unit and the reflective display unit when no voltage is applied is set to 380 [nm], and the twist angle on the reflective / transmissive unit side is 37 Set to be degrees. Thereby, in the liquid crystal display panel 1, the retardation value of the liquid crystal layer 4 in the reflective display unit is set to a so-called 3/4 wavelength condition when no voltage is applied.

  As a result, in this liquid crystal display panel 1, the transmissive display unit is configured in the FFS mode, and a simple configuration in which the CF substrate 2 side is divided and oriented without providing a retardation layer ensures high contrast and is colored. Ensure black display with little.

  1 and FIG. 2, the case where the alignment film 8 on the CF substrate 2 side is dividedly aligned has been described. Instead, the alignment film 19 on the TFT substrate 3 side is dividedly aligned so that the transmissive display portion and the reflective film are reflected. The alignment direction of the liquid crystal molecules when no voltage is applied in the display unit may be matched on the CF substrate 2 side.

  Here, FIG. 3 is a characteristic curve diagram showing a result of measuring the optimum twist angle in the reflective display section with the cell retardation at 380 [nm] when no voltage is applied. In this measurement, the alignment direction of the liquid crystal molecules on the TFT substrate 3 side is substantially parallel to the absorption axis of the polarizing plate 9 on the CF substrate 2 side, and the angle formed between the alignment direction of the liquid crystal molecules on the CF substrate 2 side and the absorption axis is It has been changed. Further, a reflector having a reflectance of 100% at all wavelengths was used, and D65 was used as the light source. According to the measurement result of FIG. 3, if the cell retardation when no voltage is applied is set to 380 [nm] and the twist angle is about 37 degrees, the black reflectance is sufficiently reduced and high contrast is secured. I understand that I can do it. When the cell retardation when no voltage is applied is 380 [nm], it can be seen that the twist angle of 37 degrees is the optimum value of the twist angle.

  FIG. 4 is a characteristic curve diagram showing a measurement result obtained by performing a spectrum analysis on the reflectance when the twist angle is set to 37 degrees under the conditions used for the measurement of FIG. As shown in FIG. 4, in the liquid crystal display panel, the reflectance changes according to the wavelength, and as a result, the optimum value of the twist angle also changes depending on the wavelength. In the liquid crystal display panel, the optimum value of the twist angle also varies depending on the color of the polarizing plates 9 and 11, the wavelength dispersion of the birefringence Δn of the liquid crystal, the reflectance spectrum of the metal used for the reflector. As a result, the optimum twist angle is not limited to 37 degrees, and an optimum value can be ensured in the range of 27 to 47 degrees according to the color of the constituent members and color filters constituting the liquid crystal display panel.

  On the other hand, FIG. 5 is a characteristic curve diagram showing the result of measuring the optimum retardation when no voltage is applied while maintaining the twist angle at 37 degrees in comparison with FIG. According to FIG. 5, it can be seen that when the cell retardation when no voltage is applied is 395 [nm], the luminous reflectance is the lowest, and the black reflectance can be sufficiently reduced to ensure high contrast. . In this case as well, as described above with reference to FIG. 4, the optimum retardation value depends on factors such as the wavelength, the color of the polarizing plates 9 and 11, the wavelength dispersion of the birefringence Δn of the liquid crystal, and the reflectance spectrum of the reflector. Since it changes, the optimal value of retardation is securable within the range of 360-430 [nm] according to the component of the liquid crystal display panel 1, and the spectrum of a color filter.

  In this embodiment, since the cell gap is large, the alignment direction of the liquid crystal molecules can be controlled efficiently. That is, FIG. 6 is a characteristic curve diagram obtained by measuring the change in reflectance with respect to the cell gap. The characteristic curve shown in FIG. 6 maintains the retardation of the liquid crystal layer, the elastic constant, and the wavelength dispersion Δε of the dielectric constant at a constant value, and further determines the pitch of the pixel electrode, the thickness of the insulating film 16, and the voltage applied to the electrode. It is the measurement result kept constant.

  According to the measurement result of FIG. 6, it can be seen that the reflectance decreases as the cell gap decreases. This phenomenon occurs when the alignment direction of the liquid crystal molecules is controlled by the horizontal switching mode, and the electric field strength changes depending on the distance from the TFT substrate 3. This is considered to be due to the fact that the horizontal electric field strength that contributes to switching increases when the horizontal electric field strength that contributes to the cell gap increases.

  In the liquid crystal display panel of Example 1, since the retardation when no voltage is applied is 385 [nm] in the reflective display portion and the transmissive display portion, when the liquid crystal of Δn = 0.12 is used, the cell The gap can be set to about 3.2 [μm], whereby sufficient reflectance can be secured without increasing the applied voltage between the electrodes 15 and 17, and the alignment of the liquid crystal molecules can be performed efficiently. The direction can be controlled. In addition, in the retardation of about ¼ wavelength (about 140 [nm]) disclosed in JP-A-2005-338264, the cell gap is about 1.1 [μm]. Need to be increased. As one method for solving this problem, for example, it is conceivable to use a liquid crystal having a small birefringence Δn. In this case, however, it is necessary to increase the gap of the transmissive display unit, and the response speed of the transmissive display is increased. Problems such as lowering occur.

(3) Effects of the Example According to the above configuration, in the transflective liquid crystal display panel, the polarizing plates are arranged so that the transmission axes are orthogonal to each other on the CF substrate side and the TFT substrate side. When no voltage is applied, the liquid crystal molecules are aligned so as to be substantially parallel to the transmission axis of either of the two polarizing plates. In the reflective display portion, the twist angle is 30 to 45 degrees when no voltage is applied, and By aligning the liquid crystal molecules so as to be parallel to the transmission axis of one of the two polarizing plates at the TFT substrate side interface, a transflective type using the FFS mode can be realized.

  By the way, in the liquid crystal display panel 1 of Example 1, as shown in FIG. 4, in a reflective display part, the reflectance of a red wavelength band and a blue wavelength band is still large compared with the reflectance of a green wavelength band, thereby voltage When no voltage is applied, black has a slightly purple reflection color, and the black color is slightly different between the transmissive display portion and the reflective display portion. In this embodiment, this black color difference is prevented.

  That is, FIG. 7 is a cross-sectional view showing a liquid crystal display panel of Example 2 of the present invention in comparison with FIG. In the liquid crystal display panel 21 of this embodiment, the thickness of the liquid crystal layer 4 is optimized in a plurality of color pixels constituting a color image, and the thickness of the liquid crystal layer 4 is different among the plurality of pixels. Except for this, the liquid crystal display panel 1 of the first embodiment has the same configuration. In FIG. 7, illustration of pixel electrodes and the like is omitted.

  More specifically, in this embodiment, in each pixel in which the red, green, and blue color filters 6R, 6G, and 6B are arranged, when no voltage is applied as the transmission wavelength of the color filters 6R, 6G, and 6B decreases. More specifically, in order to reduce the cell retardation, in each pixel in which the red, green, and blue color filters 6R, 6G, and 6B are arranged, the cell retardation when no voltage is applied is 450 nm and 385 nm, respectively. ], 350 [nm].

  Here, FIG. 8 shows the measurement result of measuring the optimum value of cell retardation when no voltage is applied to the reflective display unit with the twist angle fixed at 38 degrees for the green wavelength band, and FIG. 9 shows the green wavelength band. This is a measurement result obtained by measuring the optimum value of the twist angle in the reflective display section while fixing the cell retardation when no voltage is applied to 385 [nm]. According to the measurement results of FIG. 8 and FIG. 9, it can be seen that the cell retardation when no voltage is applied is 385 [nm], the twist angle is 38 degrees, and the reflectivity is the lowest.

  On the other hand, FIG. 10 shows the measurement result of measuring the optimum value of cell retardation when no voltage is applied to the reflective display unit with the twist angle fixed at 38 degrees for the blue wavelength band. It is the measurement result which measured the optimal value of the twist angle in a reflective display part, fixing the cell retardation at the time of no voltage application to 350 [nm] about a zone | band. According to the measurement results of FIGS. 10 and 11, it can be seen that the reflectance decreases most when the cell retardation when no voltage is applied is 350 [nm] and the twist angle is 38 degrees.

  FIG. 12 is a measurement result of measuring the optimum value of cell retardation when no voltage is applied to the reflective display unit with the twist angle fixed at 38 degrees for the red wavelength band, and FIG. It is the measurement result which fixed the cell retardation at the time of no voltage application to 450 [nm], and measured the optimal value of the twist angle in a reflective display part. According to the measurement results of FIGS. 12 and 13, it can be seen that the reflectance decreases most when the cell retardation when no voltage is applied is 450 [nm] and the twist angle is 38 degrees. FIG. 14 is a characteristic curve diagram showing the transmittance characteristics of the color filters used in these measurements. The symbols LR, LG, and LB are the characteristics of the red, green, and blue color filters 6R, 6G, and 6B, respectively. is there.

  Here, according to the measurement results of FIGS. 10 to 13, it can be seen that the reflectance is significantly reduced in the red and blue wavelength bands as compared with the characteristics described above with reference to FIG. 4. As a result, in the liquid crystal display panel 21 of this embodiment, the phenomenon that black is purple in the reflective display section can be more reliably reduced than in the liquid crystal display panel 1 of the first embodiment. It is possible to prevent a difference in black color from the display unit.

  Even in the case of optimizing with different retardation for each color of the color filter as in this embodiment, in the same manner as described in the first embodiment, ± 50 [ Since the optimum value changes in the range of about [nm], the voltage in the range of 400 to 500 [nm], 340 to 440 [nm], and 300 to 400 [nm] in the red, green, and blue pixels, respectively. It is possible to ensure the optimum retardation value when no voltage is applied.

  According to this embodiment, on the premise of the configuration of Embodiment 1, the thickness of the liquid crystal layer in the reflective display unit is set according to the color of the color filter, and the thickness of the liquid crystal layer in the reflective display unit is different between pixels of different colors. By setting differently, it is possible to secure a black display with less color and higher contrast with respect to the transflective type in the FFS mode.

  Specifically, in each of the red, green, and blue pixels, the retardation when no voltage is applied is set to 400 to 500 [nm], 340 to 440 [nm], and 300 to 400 [nm], respectively. As for the transflective type, a black display with much higher contrast and less color can be secured.

  FIG. 15 is a cross-sectional view showing the configuration of the pixels of the liquid crystal display panel according to the third embodiment of the present invention in comparison with FIG. In the liquid crystal display panel 31 of this embodiment, an insulating layer 7A for forming a step is formed on the substrate 5 side of the alignment film 8 in the reflective display portion, and the retardation of the reflective display portion when no voltage is applied by the insulating layer 7A. The value is set to be approximately ¼ wavelength of the transmission wavelength. In this embodiment, the same configurations as those of Embodiments 1 and 2 described above are denoted by the corresponding reference numerals, and redundant description is omitted.

  FIG. 16 is a sectional view showing a section in the depth direction of FIG. As shown in FIG. 16, in this liquid crystal display panel 31, according to the colors of the color filters 6R, 6G, and 6B, the liquid crystal layer 4 of the reflective display portion is selected between twist alignment and homogeneous alignment when no voltage is applied. Is set automatically. That is, in this embodiment, in the red and green pixels, the reflective display portion and the transmissive display portion are set to the homogeneous orientation when no voltage is applied. On the other hand, in the blue pixel, when no voltage is applied, the transmissive display unit is set to the homogeneous orientation, and the reflective display unit is set to the twist orientation.

  17 and 18 are plan views showing these red and green pixels and blue pixels in comparison with FIG. The red and green pixels are set so that the alignment directions in the alignment film 8 of the CF substrate 32 and the alignment film 19 of the TFT substrate 33 are different between the transmissive display unit and the reflective display unit. In the reflection display section, the orientation direction of the liquid crystal molecules is 45 degrees with respect to the absorption axis of the polarizing plate 9 of the CF substrate 32 so that the absorption axis of the polarizing plate 9 of the CF substrate 32 and the orientation direction of the liquid crystal molecules are parallel. The reflective display unit and the transmissive display unit are set in a homogeneous orientation. On the other hand, in the blue pixel, the transmissive display portion is formed in the same manner as the pixel transmissive display portion of the red and green pixels, and is set to a homogeneous orientation when no voltage is applied. In the reflective display portion, the alignment direction of the alignment film 8 of the CF substrate 32 and the alignment film 19 of the TFT substrate 33 is set to be different from that of the transmissive display portion, and the polarizing plate on the TFT substrate 33 side at the interface of the TFT substrate 33. The orientation direction of the liquid crystal molecules is set to be tilted by 13 degrees with respect to the absorption axis of 9, and the twist angle is set to 50 degrees, thereby setting the twist orientation.

  As a result, the liquid crystal display panel 31 is configured such that the liquid crystal layer of the reflective display unit has a ¼ wavelength phase difference, thereby preventing the black coloration in the reflective display unit. Even when the angle of the liquid crystal molecules and the twist angle with respect to the transmission axis and the absorption axis are as described above for the retardation in the first embodiment, the optimum angle varies depending on the elements constituting the liquid crystal display panel. Accordingly, in the homogeneous alignment, the angle formed by the liquid crystal molecules with respect to the absorption axis of the polarizing plate 9 on the CF substrate 32 side is set to 40 to 50 degrees. In this twist alignment, the CF substrate 32 is on the CF substrate 32 side. By setting the angle between the transmission axis of the polarizing plate 9 on the side or the polarizing plate 11 on the TFT substrate 33 side and the liquid crystal molecules to 9 to 18 degrees and setting the twist angle to 44 to 55 degrees, it is a practically sufficient characteristic. Can be secured.

  Here, in FIGS. 19A and 19B, symbols LH and LT indicate when the black color is displayed in the homogeneous alignment and the twist alignment when the liquid crystal layer of the reflective display unit is configured to have a phase difference of ¼ wavelength with respect to the transmissive display unit. Reflectivity. The characteristics of the homogeneous alignment shown in FIG. 19 are when the absorption axis of the polarizing plate 9 on the CF substrate 32 side and the optical axis of the liquid crystal molecules form an angle of 45 degrees, and the characteristic of the reflective display unit described above with reference to FIG. Is the case. The twist orientation shown in FIG. 19 is the case where the absorption axis of the polarizing plate 9 on the CF substrate 32 side and the optical axis of the liquid crystal molecules form an angle of 13 degrees, and the twist angle is 50 degrees. This is the case of the reflective display unit. The twist alignment may be such that the optical axis of the liquid crystal molecules forms an angle of 13 degrees with respect to the absorption axis of the polarizing plate 11 of the TFT substrate 33 instead of the polarizing plate 9 on the CF substrate 32 side.

  According to the measurement result of FIG. 19, in the homogeneous orientation, the reflectance in the blue wavelength band is higher than the reflectance in the red wavelength band and the green wavelength band, so that the black color is displayed away from the achromatic color. It can be seen that On the other hand, in the twist orientation, the reflectance in the blue wavelength band is lower than the reflectance in the red wavelength band and the green wavelength band, so that, contrary to the homogeneous orientation, the black color is displayed away from the achromatic color. I understand that.

  In this embodiment, assuming the wavelength characteristics of the reflectance in the homogeneous orientation and the twist orientation, the homogeneous orientation is applied to the reflective display portion of the red pixel and the green pixel, and the twist orientation is applied to the reflective display portion of the blue pixel. By applying this, the change in reflectance is suppressed in the entire wavelength band.

  That is, FIG. 20 is a characteristic curve diagram showing the reflectance of the liquid crystal display panel in the case of only homogeneous alignment, and FIG. 21 is a characteristic curve diagram showing the reflectance of the liquid crystal display panel 31 of the third embodiment. In FIGS. 20 and 21, symbols LR, LG, and LB are reflectances in red pixels, green pixels, and blue pixels, respectively. Reference sign BLK represents the reflectance during black display by these red, green, and blue pixels. A color filter having the characteristics shown in FIG. 17 was applied to each pixel. FIG. 22 is a diagram in which black display or the like based on the measurement result is plotted on the chromaticity diagram of CIE 1931. Reference numerals P22 and P23 are black displays according to the configurations of FIGS. 20 and 21, respectively. According to FIG. 22, it can be seen that the configuration of this embodiment improves the black chromaticity as indicated by the arrows.

  According to these FIGS. 20 to 22, by mixing a homogeneous orientation and a twist orientation in a plurality of pixels constituting a color image, the reflectance is lowered in the wavelength range corresponding to the display color of the blue pixel, and black display is performed. It can be seen that the chromaticity of the color can be made closer to an achromatic color, and further black coloring can be prevented.

  According to this embodiment, the reflective display portion when no voltage is applied is set to twist orientation or homogeneous orientation according to the color of the color filter, and in a plurality of color pixels of the color image, twist orientation and homogeneous orientation are applied when no voltage is applied. By setting so as to be mixed, it is possible to secure a black display with high contrast and less color.

  More specifically, a homogeneous alignment is applied to the reflective display part of the red pixel and the green pixel so that the optical path length of the reflective display part has a phase difference of about ¼ wavelength with respect to the transmissive display part, and the blue pixel By applying twist orientation to the reflective display portion, it is possible to secure a black display with high contrast and much less color.

  More specifically, this homogeneous alignment is a homogeneous alignment in which liquid crystal molecules form an angle of 40 to 50 degrees with respect to the absorption axis of the polarizing plate 9 on the CF substrate 32 side. This twist alignment is on the CF substrate 32 side. The transmission axis of the polarizing plate 9 on the CF substrate 32 side or the polarizing plate 11 on the TFT substrate 33 side and the liquid crystal molecules form an angle of 9 to 18 degrees, and the orientation has a twist angle of 45 to 55 degrees. It is possible to secure black display with high contrast and less color.

  FIG. 23 is a diagram for explaining electrodes in the liquid crystal display panel according to Embodiment 4 of the present invention. In the liquid crystal display panel of this embodiment, as shown in FIG. 24, the width d1 of the electrode of the pixel electrode 17 and the distance d2 between the electrodes in the transmissive display portion are 3 μm, respectively. ] And 4 [μm]. In FIG. 23, the electrode width d1 and the electrode spacing d2 in the reflective display portion are the same as those in the transmissive display portion, and the optical axis of the liquid crystal molecules at the TFT substrate interface when no voltage is applied is changed in the slit repeat direction. It is a characteristic curve figure which shows the change of a reflectance in the case of. The measurement results in FIG. 23 are measured values when the cell retardation when no voltage is applied is 395 [nm] and a voltage of 4 [V] is applied between the electrodes 15 and 17. 23, in the reflective display portion, when the pixel electrode is arranged so that the optical axis of the liquid crystal molecules at the TFT substrate interface when the voltage is not applied is inclined by 5 degrees with respect to the slit repeating direction, the reflectance when the voltage is applied. It turns out that becomes the maximum.

  Similarly, with respect to the transmissive display portion, the inclination of the liquid crystal molecule optical axis with respect to the repeating direction of the slit that maximizes the transmittance by applying the same voltage as that of the reflective display portion can be obtained.

  Accordingly, in this embodiment, the retardation when no voltage is applied is set to 395 [nm], the liquid crystal layer 4 is formed under the ¼ wavelength condition, and the transmissive display portion and the reflective display portion transmit light when voltage is applied. The repetition direction of the slits is set between the transmissive display unit and the reflective display unit so that the rate and the reflectance are maximized. Thus, in this embodiment, the transmissive display unit and the reflective display unit are set to have different repetition directions.

  In this case, for example, in the case of securing a wide field of view by multi-domain, the repetition direction of the slits may be switched halfway in the reflective display unit and the transmissive display unit. The slit repeat direction is switched between the reflective display unit and the transmissive display unit around the optimum value in the transmissive display unit, and the center value of the repeat direction is set differently between the transmissive display unit and the reflective display unit. The repeat direction can be optimized.

  On the other hand, FIG. 25 is a chart showing the change in reflectance in the reflective display section when a voltage is applied when the size of the electrode is changed. According to the chart of FIG. 25, it can be seen that the reflectivity is maximized when the electrode width d1 is 4 [μm] and the electrode interval d2 is 9 [μm]. FIG. 26 is a characteristic curve diagram showing a change in reflectance when a voltage is applied under the optimum conditions obtained in FIG. Thus, it can be seen that the reflectance changes not only by the slit repeating direction but also by the electrode width d1 and the distance d2 between the electrodes. Thus, in this embodiment, the pixel electrode of the reflective display portion is formed by the electrode width and the electrode spacing at which the reflectance at the time of voltage application increases most. In the transmissive display portion, the pixel electrode is formed with the electrode width d1 = 3 [μm] and the electrode interval d2 = 4 [μm] at which the transmittance is highest when a voltage is applied. As a result, the liquid crystal display panel of this embodiment optimizes the electrode width and the electrode interval in the transmissive display unit and the reflective display unit, and the width and electrode interval of these electrodes are different in the transmissive display unit and the reflective display unit. Set.

  When practically sufficient characteristics can be secured, only one of the slit repeating direction, the electrode width, and the electrode interval is set to be different between the transmissive display unit and the reflective display unit, and the transmittance and The reflectance may be optimized.

  According to this embodiment, by further setting at least one of the slit repeating direction, the electrode width, and the electrode interval to be different between the transmissive display unit and the reflective display unit, the transmittance and reflection in the transmissive display unit are set. It is possible to improve the reflectance in the display unit and improve the luminance during white display.

  FIG. 27 is a chart for explaining electrodes in the liquid crystal display panel according to the fifth embodiment of the present invention. In the liquid crystal display panel of this embodiment, the pixel electrodes are formed in the slit shape described above with reference to FIG. 24 in the liquid crystal display panels of the above embodiments.

  FIG. 27 is a chart showing the maximum reflectivity when the electrode size is changed when the cell retardation of the blue pixel when no voltage is applied is 350 [nm]. In the measurement of the characteristics shown in FIG. 27, the electrode width d1 which is the optimum condition in the cell retardation 395 [nm] described above with reference to FIG. 25 in the fourth embodiment is 4 [μm], and the distance d2 between the electrodes is 9 [μm]. In this condition, the reflectance is maximized by applying a voltage of 3.5 [V], which is lower than 4 [V], and gradation inversion occurs when a voltage of 4 [V] is applied.

  Therefore, in this embodiment, the electrode width d1 is 3.5 [μm], which is a condition that the reflectance is maximized when a voltage of 4 [V] is applied while reliably avoiding such a tone inversion phenomenon. The pixel electrode of the blue pixel is formed with a distance d2 between the electrodes of 5 [μm].

  On the other hand, FIG. 28 is a chart showing the maximum reflectivity when the electrode size is changed when the cell retardation of the red pixel when no voltage is applied is 450 nm. According to this chart, when the electrode width d1 is 4 [μm], which is the optimum condition for the cell retardation 395 [nm] when no voltage is applied, and the distance d2 between the electrodes is 9 [μm], 4 [V]. The reflectance is maximized by the application of voltage, and there is a risk of gradation inversion due to variations in gaps and the like.

  Therefore, in this embodiment, from the chart of FIG. 28, the electrode width d1 is 3.5 [μm] and the distance d2 between the electrodes is a condition that a high transmittance can be obtained by applying a voltage of 4 [V]. The pixel electrode of the red pixel is formed by 10 [μm].

  On the other hand, for the green pixel, the pixel electrode is formed with the electrode width d1 being 4 [μm] and the distance d2 between the electrodes being 9 [μm], which are the conditions described in the fourth embodiment.

  Similarly, for the film thickness of the insulating film 16 between the pixel electrode and the common electrode, an optimum value can be obtained for each color of the color filter. In this embodiment, the film thickness of the insulating film 16 is as follows. This optimum value is set.

  Thereby, in this embodiment, the electrode width, the electrode interval, and the film thickness of the insulating film between the pixel electrode and the common electrode are set according to the color filter, and the electrode width, electrode interval, pixel electrode and The film thickness of the insulating film between the common electrode is set to be different for pixels of different colors.

  When practically sufficient characteristics can be secured, only one of the electrode width, the electrode interval, and the insulating film between the pixel electrode and the common electrode is set according to the color of the color filter. The reflectivity may be optimized.

  According to this embodiment, at least one of the electrode width, the electrode interval, and the insulating film between the pixel electrode and the common electrode is set according to the color of the color filter, whereby the reflectance in the reflective display section is set. Can be increased to increase the brightness level.

  In each of the above-described embodiments, the pixel electrode has a slit shape and the transmissive display unit is set to the FFS mode. However, the present invention is not limited to this, and the pixel electrode and the common electrode are provided as shown in FIG. The present invention can also be widely applied to the case where the transmissive display portion is set to the IPS mode as a slit shape. In the IPS mode, since the common electrode and the pixel electrode are formed in the same plane, the luminance level is increased by optimizing the film thickness of the insulating layer between the common electrode and the pixel electrode described in the fifth embodiment. This technique is difficult to apply.

  Further, in the above-described embodiments, the case where the liquid crystal display device according to the present invention is applied to a portable information device has been described. However, the present invention is not limited to this and is widely applied to various devices such as a stationary information device. be able to.

  The present invention can be applied to liquid crystal display devices of liquid crystal modes such as IPS and FFS.

  1, 21, 31 ... Liquid crystal display panel, 2, 22, 32 ... CF substrate, 3, 23, 33 ... TFT substrate, 4 ... Liquid crystal layer, 5, 10 ... Transparent insulating substrate, 6, 6R, 6G, 6B: Color filter, 9, 11: Polarizing plate, 8, 19: Alignment film, 17: Pixel electrode

Claims (4)

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 on a side opposite to the liquid crystal layer,
The second substrate has a second polarizing plate on the side opposite to the liquid crystal layer, and has a pixel electrode and a common electrode for applying an electric field substantially parallel to the substrate surface on the liquid crystal layer side. ,
The first and second polarizing plates are arranged so that transmission axes are orthogonal to each other,
The pixel has a color filter;
The liquid crystal layer is
In the transmissive display portion, in a state where no voltage is applied between the pixel electrode and the common electrode, liquid crystal molecules are aligned substantially parallel to the transmission axis of the first or second polarizing plate,
In the reflective display unit, a liquid crystal display device in which a red pixel region and a green pixel region are set to homogeneous alignment and a blue pixel region is set to twist alignment in a state where no voltage is applied between the pixel electrode and the common electrode. 2. The liquid crystal display device according to claim 1, wherein in the liquid crystal layer, the retardation of the reflective display unit is approximately ¼ wavelength of the transmission wavelength of the color filter in a state where no voltage is applied between the pixel electrode and the common electrode. . The homogeneous alignment is a homogeneous alignment in which liquid crystal molecules form an angle of 40 to 50 degrees with respect to the absorption axis of the first polarizing plate,
The twist orientation is an orientation in which the transmission axis of the first or second polarizing plate and the liquid crystal molecules form an angle of 9 to 18 degrees and a twist angle of 45 to 55 degrees on the first substrate side. The liquid crystal display device according to claim 2. The pixel electrode is formed of a plurality of first electrodes arranged side by side at a certain interval, and a second electrode connecting the plurality of first electrodes,
At least one of the direction in which the plurality of first electrodes are arranged, the width of the first electrodes, the interval between the first electrodes, and the thickness of the insulating film between the common electrodes is the transmissive display portion and the reflective display portion. The liquid crystal display device according to claim 1, wherein the liquid crystal display device is set differently.

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