JP4816862B2 - Liquid crystal display - Google Patents

Description

  The present invention relates to a liquid crystal display device, and more particularly to a liquid crystal display device capable of transflective display using an in-plane switching mode in a reflective display region.

  In an in-plane switching (IPS) mode liquid crystal display device, liquid crystal molecules are rotationally driven in parallel with the substrate surface by ON / OFF of an electric field applied to a liquid crystal layer sandwiched between two substrates. Thus, image display is performed. In such an IPS mode liquid crystal display device, the polarizing axis is arranged in crossed Nicols outside the substrate, and the alignment axis of the liquid crystal molecules is relative to the transmission axis of one polarizing plate when the electric field is turned off. The liquid crystal molecules are rotationally driven so that the alignment axes of the liquid crystal molecules are 45 ° with respect to the transmission axis of the polarizing plate in a state where they are parallel and the electric field is turned on.

  As a result, in a state where the electric field is turned off, the light incident from the incident side polarizing plate reaches the output side polarizing plate without causing a phase difference in the liquid crystal layer, and is absorbed here to display black. On the other hand, when the electric field is turned on, the alignment direction of the liquid crystal molecules is 45 ° with respect to the transmission axis of the polarizing plate, and a phase difference occurs in the light h passing through the liquid crystal layer. Therefore, the film thickness (cell gap) of the liquid crystal layer is adjusted so that a phase difference of λ / 2 occurs in the light h passing through the liquid crystal layer. As a result, light incident from the incident-side polarizing plate becomes linearly polarized light rotated by 90 ° by passing through the liquid crystal layer, and is transmitted through the outgoing-side polarizing plate to display white.

  The IPS mode liquid crystal display device as described above is known to have a wide viewing angle characteristic. In addition, when the electric field is OFF, black display is performed without causing a phase difference in the liquid crystal layer, so that black floating due to light leakage does not occur, and display with high contrast is possible.

  2. Description of the Related Art In recent years, transflective and semi-reflective liquid crystal display devices with improved visibility under dark conditions and outside light have been widely used as liquid crystal display devices for mobile applications. Since the transflective liquid crystal display device performs display by switching liquid crystal molecules in the vertical direction in the ECB mode, the viewing angle characteristics are not sufficient. Therefore, as described above, it is desired to realize a transflective type using an IPS mode having excellent viewing angle characteristics.

  However, in the IPS mode liquid crystal display device, black display is performed by aligning the alignment axes of one polarizing plate and the liquid crystal molecules arranged in a crossed Nicol state. For this reason, in the configuration of the transmissive IPS mode liquid crystal display device described above, a reflective display region is simply formed by providing a reflective plate between the polarizing plate on the emission side and the liquid crystal layer. The display becomes white and cannot be adjusted to the black display of the transmissive display area.

  Therefore, by providing a λ / 2 retardation layer in the transmissive display region, the transmitted light is absorbed by a polarizing plate arranged in crossed Nicol with the liquid crystal layer functioning as a λ / 2 layer with the electric field turned off. Thus, there has been proposed a configuration in which white display is performed by setting the liquid crystal layer in parallel with the transmission axis of the polarizing plate in a state where the black display is performed and the electric field is turned on (see, for example, Patent Document 1 below).

JP 2003-344837 A

  Incidentally, contrast is one factor that determines the display quality in the display device. In order to obtain high contrast, it is necessary to suppress the brightness of the black display as much as possible. In a transflective liquid crystal display device, a high contrast is particularly required for a transmissive display region.

  However, in the liquid crystal display device disclosed in Patent Document 1, black display is performed using the retardation of the retardation plate or the liquid crystal layer in both the transmissive display area and the reflective display area. For this reason, even in the transmissive display area where the IPS mode original good black display can be obtained, the dispersion of the retardation plate and the thickness of the liquid crystal layer have a great influence on the black display, and the black floating It tends to occur and it is difficult to stably mass-produce.

  Furthermore, since the refractive index of the liquid crystal layer greatly depends on the temperature, a large change in the phase difference of the liquid crystal layer depending on the temperature of the surrounding environment also causes a deterioration in the stability of black display.

  In view of the above, an object of the present invention is to provide a transflective liquid crystal display device which can obtain a good black display in a transmissive display region, and thereby has high contrast and excellent display quality.

In order to achieve such an object, the liquid crystal display device of the present invention is a liquid crystal display device having a transmissive display region and a reflective display region, and a liquid crystal layer is sandwiched between a first substrate and a second substrate. And a liquid crystal panel provided with an electrode for applying an electric field to the liquid crystal layer, and a polarizing plate disposed in crossed Nicols outside the liquid crystal panel. The reflective display area includes a reflective layer and λ / 2.
The first retardation layer is selectively patterned. Among these, the reflective layer is provided on the first substrate side. On the other hand, the retardation layer is provided on the second substrate side with its slow axis maintained at an angle of 20 degrees to 25 degrees with respect to one transmission axis of the polarizing plate. Furthermore, transmission
In the display area, one transparent layer of the polarizing plate is divided by being aligned with the first retardation layer in the reflective display area.
A phase difference pattern in which the overaxis and the slow axis coincide is provided.

  In the transmissive display region, the liquid crystal molecules constituting the liquid crystal layer rotate substantially parallel to the substrate surface of the liquid crystal panel by applying an electric field, and the alignment axis of the liquid crystal molecules is one of the polarizing plates when no electric field is applied. It is configured to display in black by being oriented parallel to the transmission axis. On the other hand, the reflective display region has a phase difference corresponding to λ / 4 because the alignment axis of the liquid crystal molecules constituting the liquid crystal layer is aligned in parallel with one transmission axis of the polarizing plate when no electric field is applied. The liquid crystal layer and the retardation layer are configured to display black due to the retardation.

  The liquid crystal display device having the above configuration is a transflective liquid crystal display device having a transmissive display region and a reflective display region, and a retardation layer is selectively provided only in the reflective display region. ing. The transmissive display area is driven in an IPS mode, in which liquid crystal molecules constituting the liquid crystal layer rotate substantially parallel to the substrate surface of the liquid crystal panel by applying an electric field. Further, when no electric field is applied, the alignment axis of the liquid crystal molecules is aligned in parallel with one transmission axis of the polarizing plate so that black display is obtained. For this reason, in the transmissive display area, the original good black display in the IPS mode is performed without being related to the retardation of the retardation layer or the liquid crystal layer.

  On the other hand, in the reflective display area, when the electric field is not applied, the display state of the transmissive display area and that of the reflective display area coincide with each other because black display is performed due to the phase difference between the phase difference layer and the liquid crystal layer. At this time, since the wavelength dependency of the liquid crystal layer functioning as the λ / 2 retardation layer and the λ / 4 retardation layer cancels each other, black display without color is performed.

  As described above, in the liquid crystal display device of the present invention, the IPS mode original black display is performed in the transmissive display region, and the wavelength dependence of the retardation in the retardation layer and the liquid crystal layer is canceled in the reflective display region. Displayed black with no color. Therefore, it is possible to perform a transflective display with a very good contrast.

Embodiments to which the present invention is applied will be described below with reference to the drawings using reference embodiments .

<First Reference Embodiment>
FIG. 1A is a cross-sectional configuration diagram of a liquid crystal display device according to a first reference embodiment, and FIG. 1B is a plan view illustrating an optical configuration of a main part of the display device. 2 and 3 are schematic views showing an optical configuration in this display device. The liquid crystal display device 1 shown in these drawings is a transflective liquid crystal display device 1 having a transmissive display area A and a reflective display area B in one pixel, and displays black when no voltage is applied. The normally black (NB) mode in which the above is performed is configured as follows.

  That is, the liquid crystal display device 1 is narrowed between the first substrate 10, the second substrate 20 disposed to face the element formation surface of the first substrate 10, and the first substrate 10 and the second substrate 20. A liquid crystal panel including the held liquid crystal layer 30 is provided. Here, it is assumed that the liquid crystal layer 30 is composed of nematic liquid crystal. In this liquid crystal panel, polarizing plates 40 and 50 are provided in close contact with the outer surfaces of the first substrate 10 and the second substrate 20. These polarizing plates 40 are provided in a crossed Nicols state (see FIG. 2). Further, a backlight 60 serving as a light source for performing transmissive display is provided on the outer side of the polarizing plate 40 on the first substrate 10 side.

  Of these, the first substrate 10 is made of a transparent substrate such as a glass substrate. On the surface facing the liquid crystal layer 30, a driving element such as a thin film transistor (Thin Film Transistor) not shown here is connected and connected thereto. Electrodes and wirings are provided, and these are covered with an interlayer insulating film. On the interlayer insulating film, a reflective layer 11 is selectively formed in a pattern so as to cover only the reflective display region B. This reflective layer 11 is covered with an insulating film 12. The insulating film 12 is formed as a convex pattern 12 for adjusting the film thickness (cell gap ga, gb) of a liquid crystal layer 30 described later. Although illustration is omitted here, the reflective layer 11 may be provided in an uneven shape for light scattering on the surface thereof.

  A common electrode 15 is disposed on the interlayer insulating film in the transmissive display area A and on the convex pattern 12 in the reflective display area B together with the pixel electrode 14 connected to the driving element via the electrodes and wirings described above. Has been.

  The pixel electrode 14 and the common electrode 15 are disposed so as to extend in parallel with each other with the transmissive display area A and the reflective display area B interposed therebetween in a direction that forms 45 ° with respect to the transmissive axes of the polarizing plates 40 and 50. (See FIG. 2). Thus, when a voltage is applied between the pixel electrode 14 and the common electrode 15, the voltage is parallel to the substrate surfaces of the first substrate 10 and the second substrate 20 and 45 with respect to the transmission axes of the polarizing plates 40 and 50. An electric field (lateral electric field) in a direction forming an angle is applied to the liquid crystal layer 30. The lateral electric field causes the liquid crystal molecules m constituting the liquid crystal layer 30 to be oriented in a direction of 45 ° with respect to the transmission axes of the polarizing plates 40 and 50. In the case where the reflection layer 11 described above has both reflection characteristics such as aluminum and conductivity, the reflection layer 11 may be used as a relay electrode for the pixel electrode 14 or the common electrode 15. However, the pixel electrode 14 and the common electrode 15 are kept in an insulated state.

  An alignment film 17 is provided on the pixel electrode 14 and the common electrode 15. 2, the alignment film 17 is parallel to the transmission axis of the polarizing plate 40 on the first substrate 10 side and is a polarizing plate on the second substrate 20 side. It is assumed that it has been rubbed or oriented in a direction of 90 ° with respect to 50 transmission axes.

  The alignment direction of the alignment film 17 in the transmissive display area A and the reflective display area B may be 90 ° with respect to the transmission axis of the polarizing plate 40 or the polarizing plate 50, respectively. However, in consideration of obtaining long-term stability and reliability of the alignment state in each of the regions A and B, the alignment directions of the alignment films 17 in the transmissive display region A and the reflective display region B are preferably the same. For this reason, in the following embodiment, the case where the alignment directions of the alignment films 17 in the regions A and B are the same (parallel to the transmission axis of the polarizing plate 40 on the first substrate 10 side) will be described.

  As described above, the alignment axis of the liquid crystal molecules m is parallel to the transmission axis of the polarizing plate 40 in the state of the electric field OFF (black display) in which no voltage is applied to the pixel electrode 14 and the common electrode 15. On the other hand, in the state of electric field ON (white display) in which a lateral electric field is applied to the liquid crystal layer 30 made of nematic liquid crystal by applying a voltage between the electrodes 14-15, the alignment axis of the liquid crystal molecule m and the polarizing plates 40, 50 are used. The angle θ with the transmission axis is θ = 45 °.

  On the other hand, with respect to the configuration on the first substrate 10 side as described above, the second substrate 20 is made of a transparent substrate such as a glass substrate. On the surface of the second substrate 20 facing the liquid crystal layer 30, a retardation layer 21, which will be described in detail later, is formed in a pattern, and a color filter (not shown) is further provided. Is provided. This alignment film 22 has been subjected to a rubbing process or an alignment process in antiparallel to the alignment film 17 provided on the first substrate 10 side.

  Thereby, in the state where the electric field is OFF (black display), the alignment axis of the liquid crystal molecules m is parallel to the transmission axis of the polarizing plate 40 over the film thickness direction of the liquid crystal layer 30. On the other hand, in the state where the electric field is ON (white display), the angle θ between the alignment axis of the liquid crystal molecules m and the transmission axes of the polarizing plates 40 and 50 is 45 ° across the film thickness direction of the liquid crystal layer 30.

  The retardation layer 21 is selectively provided only for the reflective display region B, and is disposed in a state of facing the reflective layer 11. The cell gap gb of the reflective display region B with respect to the cell gap ga of the transmissive display region A is adjusted by the selective arrangement of the retardation layer 21 and the convex pattern 12 described above.

Here, the cell gap ga of the transmissive display area A and the cell gap gb of the reflective display area B are set as follows with reference to FIG. 4 and the following formula (1).

  First, from the above formula (1), in order to realize bright white display in the transmissive display area A when the electric field is ON (white display), the alignment axis mp of the liquid crystal molecules m and the transmission axes 50p of the polarizing plates 40 and 50 are obtained. It can be seen that the phase difference Δnd of the liquid crystal layer 30 in the transmissive display area A may be set to approximately λ / 2 in the above state where the angle θ (θ ′) = 40 ° with 40p is set. For this reason, it is assumed that the cell gap ga in the transmissive display area A is adjusted so as to satisfy the phase difference Δnd (a) = λ / 2 of the liquid crystal layer 30 in the transmissive display area A.

  In contrast to the cell gap ga in the transmissive display region A set as described above, the cell gap gb in the reflective display region B has a phase difference Δnd (b) of the liquid crystal layer 30 of Δnd (b) = Δnd (a). It is assumed that / 2 = λ / 4. For this reason, the cell gap gb in the reflective display region B is adjusted so that the phase difference Δnd (b) = λ / 4 of the liquid crystal layer 30 in the reflective display region B, that is, the cell gap ga = 2gb. And

  Then, based on the phase difference Δnd (b) = λ / 4 in the reflective display region B set as described above, in order to obtain a good contrast in the reflective display region B, light over the entire visible light region is displayed during black display. It is important to suppress reflections. For this purpose, in the reflective display region B, the retardation layer 21 and the liquid crystal layer 30 must be combined to form a broadband λ / 4 (λ / 4 in the wavelength band of visible light). For this reason, the phase difference of the retardation layer 21 provided in the reflective display region B is λ / 2 (for light of 550 nm).

  In the reflective display region B, the balance between the chromatic dispersion of the retardation layer 21 and the chromatic dispersion of the liquid crystal layer 30 is also important in order to obtain a favorable broadband λ / 4 condition between the retardation layer 21 and the liquid crystal layer 30. It becomes. Here, when the wavelength dispersion coefficient A = Δn (400 nm) / Δn (550 nm), preferably 0.8 <A (liquid crystal layer 30) / A (retardation layer 21) <1.3, more preferably 0. Each wavelength dispersion coefficient A is adjusted so that .9 <A (liquid crystal layer 30) / A (retardation layer 21) <1.15.

  The λ / 2 retardation layer 21 is provided so that the angle formed between the slow axis and the transmission axes 40p and 50p of the polarizing plates 40 and 50 is in the range of 20 ° to 25 °. And This value was obtained from the following simulation results.

  FIG. 5 shows a case where the angle θa formed by the slow axis 21p of the retardation layer 21 and the transmission axes 40p and 50p of the polarizing plates 40 and 50 is changed in the liquid crystal display device set as described above. The simulation result of contrast in the transmissive display area is shown. The simulation conditions are: light incident angle 0 °, measurement angle 0 °, polarizing plate polarization degree 99.7%, light source D65, wavelength dispersion coefficient A (liquid crystal layer 30) = 1.03, wavelength dispersion coefficient A (phase difference layer 21) ) = 1.02, and the reflection layer was calculated as a mirror surface. The light source D65 shows a spectrum close to sunlight in the light source standard D.

  From the simulation result shown in FIG. 5, if the angle θa formed by the slow axis 21p of the retardation layer 21 and the transmission axes 40p, 50p of the polarizing plates 40, 50 is in the range of 20 ° to 25 °, the transmission display region It can be seen that a contrast of 20 or more that can be withstood in actual use is obtained. Further, it can be seen that the highest contrast can be obtained at an angle θa = 22.5 °, and it is desirable to adopt this value.

  Further, the λ / 2 retardation layer 21 configured as described above is obtained as follows, for example. First, an alignment treatment film is formed on the second substrate 20 that is the base of the retardation layer 21. The alignment treatment film is subjected to an alignment treatment such as rubbing in accordance with the direction of the slow axis of the retardation layer 21. Then, a photosensitive liquid crystal polymer or a photosensitive nematic liquid crystal monomer is applied to the upper portion of the alignment treatment film, and the photosensitive material layer is subjected to pattern exposure and then developed, thereby delaying a predetermined direction. The photosensitive material layer having the phase axis is left in the reflective display region B, and this is used as the retardation layer 21. The magnitude of the retardation in the retardation layer 21 is adjusted by changing the film thickness and the refractive index anisotropy of the material.

  In the liquid crystal display device 1 configured as described above, the polarizing plate 50 on the second substrate 20 side is included in the light h irradiated from the backlight and the external light h ′ incident from the polarizing plate 50 side serving as an analyzer. Light emitted from here as an analyzer becomes display light.

  Next, the operation of the liquid crystal display device 1 will be described.

  FIG. 2 is a schematic diagram showing an alignment state in a state where no voltage is applied to the pixel electrode 14 and the common electrode 15 (when the electric field is OFF). As shown in this figure, when the electric field is OFF, the liquid crystal molecules m in the liquid crystal layer 30 are parallel to the rubbing direction of the alignment films 17 and 22 and the transmission axis of the polarizing plate 40 on the backlight side, and The polarizing plate 50 is oriented in a direction perpendicular to the transmission axis.

  For this reason, in the transmissive display area A, the backlight light h that has passed through the polarizing plate 40 passes through the liquid crystal layer 30 in which the liquid crystal molecules m are aligned in a direction parallel to the transmission axis of the polarizing plate 40. It passes without causing. For this reason, the light h is absorbed by the polarizing plate 50 as in the normally black display in the normal IPS mode, and becomes black in the transmissive display area A. Therefore, black display without light leakage is possible without being affected by the cell gap ga or the retardation layer.

  On the other hand, in the reflective display region B, the external light h ′ incident from the side of the polarizing plate 50 serving as an analyzer and converted into linearly polarized light has a slow axis θ = 20 with respect to the transmission axis of the polarizing plate 50. By passing through the retardation layer 21 of λ / 2 maintained at ˜25 °, linearly polarized light whose phase is shifted by about 45 ° from 2θ = 40 ° to 50 ° with respect to the transmission axis of the polarizing plate 50. It becomes.

This linearly polarized light (external light h ′) passes through the λ / 4 liquid crystal layer 30 in which the liquid crystal molecules m are aligned at an angle of 45 ° with respect to the transmission axis of the polarizing plate 50 (ie, linearly polarized light). By doing so, it becomes circularly polarized light and reaches the reflective layer 11 . Thereafter, the external light h ′ is reflected by the reflecting layer 11 to become circularly polarized light in the reverse direction, and further passes through the liquid crystal layer 30 to become linearly polarized light having a phase shifted by 135 ° with respect to the transmission axis of the polarizing plate 50. . Further, the external light h ′ passes through the λ / 2 retardation layer 21 and is shifted in phase by 270 degrees (90 degrees) with respect to the transmission axis of the polarizing plate 50. As a result, the external light h ′ is absorbed by the polarizing plate 50 and becomes black in the reflective display region B. Further, since the wavelength dependence of the retardation layer 21 of λ / 2 and the liquid crystal layer 30 of λ / 4 cancel each other, it is possible to obtain black with little color and no wavelength dependence of light.

  FIG. 3 is a schematic diagram showing an alignment state in a state where a voltage is applied to the pixel electrode 14 and the common electrode 15 (when the electric field is ON). As shown in this figure, when the electric field is ON, the liquid crystal molecules m in the liquid crystal layer 30 are parallel to the substrate surface and the rubbing direction and polarization of the alignment films 17 and 22 by the electric field applied to the liquid crystal layer 30. It will be in the state orientated in the direction of 45 degrees with respect to the transmission axis of the plates 40 and 50.

  For this reason, in the transmissive display area A, the liquid crystal layer 30 is a λ / 2 layer with respect to the light h of the backlight that has passed through the polarizing plate 40, as in the case of normally black display in the normal IPS mode. Function. For this reason, the light h that has passed through the polarizing plate 40 passes through the liquid crystal layer 30 to become linearly polarized light that is rotated by 90 °, and is transmitted through the polarizing plate 50 that is arranged in a crossed Nicol state, resulting in white display.

  On the other hand, in the reflective display region B, the external light h ′ incident from the side of the polarizing plate 50 serving as an analyzer passes through the λ / 2 retardation layer 21 in the same manner as when the electric field is turned off, so The linearly polarized light is 45 ° out of phase with the transmission axis. This external light h ′ has a λ / 4 direction in which the liquid crystal molecules m are aligned in a direction that forms 45 ° with respect to the transmission axis of the polarizing plate 50 by application of an electric field, that is, parallel or perpendicular to the polarization direction of the external light h ′. It passes through the liquid crystal layer 30 as it is without causing a phase difference. Then, by passing through the retardation layer 21 of λ / 2, it shifts by 45 °, returns to linearly polarized light parallel to the transmission axis of the polarizing plate 50, passes through the polarizing plate 50, and becomes white display.

As described above, in the liquid crystal display device 1 of this, at the time of electric field at OFF and field ON, it becomes possible to display a similar normally black in a reflective display region B and transmissive display region A. In order to display halftone, the rotation angle of the liquid crystal molecule m is adjusted by the voltage applied to the pixel electrode 14 and the common electrode 15, and the alignment axis mp of the liquid crystal molecule m and the transmission axes 50p of the polarizing plates 40 and 50 are obtained. What is necessary is just to change angle (theta) ((theta ')) which 40p makes in the range of 0 degree-45 degrees.

  In particular, in the transmissive display area, the IPS mode original good black display is performed, and in the reflective display area, the non-colored black display in which the wavelength dependency of the retardation in the retardation layer and the liquid crystal layer is canceled is performed. . Therefore, it is possible to perform a transflective display with a very good contrast.

< Embodiment >
6A is a cross-sectional configuration diagram of a liquid crystal display device according to an embodiment of the present invention , and FIG. 6B is a plan view for explaining an optical configuration of a main part of the display device. The liquid crystal display device 1a shown in these figures, the difference from the liquid crystal display device 1 described with reference to FIG. 1, there is the point that even the transmissive display region A leaving the phase difference layer pattern 21a, the other configurations The same shall apply. In FIG. 6, the same components as those of the liquid crystal display device 1 of FIG. 1 are denoted by the same reference numerals, and detailed description thereof is omitted.

That is, in this liquid crystal display device 1a, the second substrate 20 side in the liquid crystal display device 1 described with reference to FIG. 1, in a state to planarize the step due to the reflective display area retardation layer 21 formed on the B The phase difference pattern 21a is also left in the transmissive display area A. Thereby, the foundation | substrate of the alignment film 22 by the side of the 2nd board | substrate 20 is comprised in the plane.

  The phase difference pattern 21a is provided in a state where the slow axis 21ap is orthogonal to the transmission axis 50p of the polarizing plate 50 (or the transmission axis of the polarizing plate).

  Such a phase difference pattern 21a is formed simultaneously with the phase difference layer 21 by dividing the orientation. That is, first, an alignment treatment layer obtained by dividing the transmissive display area A and the reflective display area B on the second substrate 20 serving as a base of the retardation layer 21 and the retardation pattern 21a so as to have respective alignment directions. Form. Then, a photosensitive liquid crystal polymer or a photosensitive nematic liquid crystal monomer is applied on the alignment treatment layer, and the photosensitive material layer is exposed and developed, whereby the transmissive display area A and A retardation layer 21 and a retardation pattern 21a made of a photosensitive material layer each having a predetermined direction as a slow axis are obtained in the reflective display region B.

The cell gap ga = 2 gb is adjusted by the height of the convex pattern 12 provided in the reflective display region B on the first substrate 10 side, as described in the liquid crystal display device 1 .

In the liquid crystal display device 1 a having such a configuration, the slow axis 21 ap of the phase difference pattern 21 a provided in the transmissive display area A is in the same optical configuration as that of the liquid crystal display device 1. Match. For this reason, in the transmissive display area A, the retardation pattern 21 does not affect the light h of the backlight 60 that has been transmitted through the liquid crystal layer 30 from the first substrate 10 side.

Accordingly, the present be a liquid crystal display device 1a of the implementation mode, similarly to the liquid crystal display device 1, in the transmissive display region A IPS mode inherent good black display is performed, position in the reflective display region B Colorless black display in which the wavelength dependence of the phase difference in the phase difference layer and the liquid crystal layer is canceled is performed, and a transflective display with extremely good contrast can be performed.

< Second Reference Embodiment>
FIG. 7A is a cross-sectional configuration diagram of the liquid crystal display device of the second reference embodiment, and FIG. 7B is a plan view for explaining the optical configuration of the main part of the display device. 8 and 9 are schematic views showing the orientation state in this display device. The liquid crystal display device 1b shown in these drawings is different from the liquid crystal display device 1a described with reference to FIG. 6, in the reflective display area B, further provided second retardation layer 25, the cell of the liquid crystal layer 30 The gap is ga = gb, and the other optical configurations are the same. 7-9, the same code | symbol is attached | subjected about the structure similar to each embodiment mentioned above, and detailed description is abbreviate | omitted.

  Here, the second retardation layer 25 provided in the reflective display region B has a phase difference of λ / 4 which is opposite in phase to the liquid crystal layer 30, and on the liquid crystal layer 30 side of the retardation layer 21 of λ / 2. It shall be provided. The slow axis 25p of the second retardation layer 25 coincides with the direction of the transmission axis of either of the polarizing plates 50 and 40, and the angle formed by the rubbing direction (alignment direction) of the alignment films 17 and 22 is 90. It shall be provided so that The cell gap ga = gb of the liquid crystal layer 30 is assumed to have a phase difference of λ / 2.

  Further, in this case, in order to set the cell gap ga = gb of the liquid crystal layer 30, the transmissive display area A has the second position divided and aligned in the same layer as the second retardation layer 25 together with the retardation pattern 21 a. A phase difference pattern 25a is provided. The second phase difference pattern 25a also does not affect the polarization state of light by making its slow axis 25ap orthogonal to the transmission axis 50p of the polarizing plate 50 (or the transmission axis 40p of the polarizing plate 40). It is assumed that it is configured.

  Next, the operation of the liquid crystal display device 1b will be described.

  FIG. 8 is a schematic diagram showing an alignment state in a state where no voltage is applied to the pixel electrode 14 and the common electrode 15 (when the electric field is OFF). As shown in this figure, when the electric field is OFF, the liquid crystal molecules m in the liquid crystal layer 30 are parallel to the rubbing direction of the alignment films 17 and 22 and the transmission axis of the polarizing plate 40 on the backlight side, and The polarizing plate 50 is oriented in a direction perpendicular to the transmission axis.

In the transmissive display area A, similarly to the liquid crystal display device 1a , the phase difference pattern 21a and the second phase difference pattern 25a having the slow axis aligned with the direction of the transmission axis 50p of the polarizing plate 50 are provided. Yes. For this reason, the phase difference pattern 21a and the second phase difference pattern 25a do not affect the light h of the backlight 60 transmitted through the liquid crystal layer 30 from the first substrate 10 side. Therefore, in the same manner as described above , black display without light leakage is possible without being affected by the cell gap ga or the retardation layer.

  On the other hand, in the reflective display region B, the external light h ′ incident from the side of the polarizing plate 50 serving as an analyzer and converted into linearly polarized light has a slow axis of 20 degrees to the transmission axis of the polarizing plate 50. By passing through the retardation layer 21 of λ / 2 maintained at 25 degrees, linearly polarized light whose phase is shifted by 45 ° with respect to the transmission axis of the polarizing plate 50 is obtained. The linearly polarized light (external light h ′) passes through the second retardation layer 25 of λ / 4, and becomes circularly polarized light and reaches the liquid crystal layer 30.

Thereafter, the circularly polarized light (external light h ′) passes through the liquid crystal layer 30 having a phase λ / 2 opposite to that of the second retardation layer 25 to be circularly polarized in the reverse direction, and is further reflected by the reflective layer 11 . Then, it returns to the original circularly polarized light and passes through the liquid crystal layer 30 again to become the reversely circularly polarized light. Thereafter, the circularly polarized light (external light h ′) passes through the second retardation layer 25 of λ / 4 which has the opposite phase to the liquid crystal layer 30, thereby 135 ° with respect to the transmission axis of the polarizing plate 50. The linearly polarized light is out of phase. Further, the external light h ′ passes through the λ / 2 retardation layer 21 and is shifted in phase by 270 degrees (90 degrees) with respect to the transmission axis of the polarizing plate 50. As a result, the external light h ′ is absorbed by the polarizing plate 50 and becomes black in the reflective display region B.

In addition, the liquid crystal layer 30 having a phase difference of λ / 2 and the second phase difference layer 25 having a phase difference of λ / 4 are composed of a λ / 4 layer. For this reason, the λ / 4 layer and the λ / 2 retardation layer 21 constitute a favorable high-band λ / 4 condition, and it is possible to obtain black with little color without being dependent on the wavelength of light. is there.

  FIG. 9 is a schematic diagram showing an alignment state in a state where a voltage is applied to the pixel electrode 14 and the common electrode 15 (when the electric field is ON). As shown in this figure, when the electric field is ON, the liquid crystal molecules m in the liquid crystal layer 30 are parallel to the substrate surface and the rubbing direction and polarization of the alignment films 17 and 22 by the electric field applied to the liquid crystal layer 30. It will be in the state orientated in the direction of 45 degrees with respect to the transmission axis of the plates 40 and 50.

  For this reason, in the transmissive display area A, the liquid crystal layer 30 is a λ / 2 layer with respect to the light h of the backlight that has passed through the polarizing plate 40, as in the case of normally black display in the normal IPS mode. Function. For this reason, the light h that has passed through the polarizing plate 40 passes through the liquid crystal layer 30 to become linearly polarized light that is rotated by 90 °, and is transmitted through the polarizing plate 50 that is arranged in a crossed Nicol state, resulting in white display.

  On the other hand, in the reflective display region B, the external light h ′ incident from the side of the polarizing plate 50 serving as an analyzer is the same as the phase difference layer 21 of λ / 2 and the second position of λ / 4, as in the case of the electric field OFF. By passing through the phase difference layer 25, it becomes circularly polarized light and reaches the liquid crystal layer 30.

Thereafter, this circularly polarized light (external light h ′) reciprocates in the liquid crystal layer 30 of λ / 2 in which the liquid crystal molecules m are aligned in the direction of 45 ° with respect to the transmission axis of the polarizing plate 50 by applying an electric field. By passing, it becomes circularly polarized light in the same direction. Thereafter, the external light h ′ passes through the second retardation layer 25 of λ / 4 again, and becomes linearly polarized light whose phase is shifted by 45 ° with respect to the transmission axis of the polarizing plate 50. Further, the external light passes through the λ / 2 retardation layer 21 and returns to linearly polarized light parallel to the transmission axis of the polarizing plate 50, and is transmitted through the polarizing plate 50 to display white.

As described above, in this liquid crystal display device 1b, during field OFF time and field ON, it becomes possible to display a similar normally black in the transmissive display region A and the reflective display region B.

  In the transmissive display area A, the IPS mode original good black display is performed, and in the reflective display area B, the wavelength dependency is canceled by the retardation layer 21, the second retardation layer 25, and the liquid crystal layer 30. Therefore, it is possible to perform a transflective display with extremely good contrast.

  Further, since the cell gap ga of the transmissive display area A and the cell gap gb of the reflective display area B can be made the same by providing the second retardation layer 25, an extra step or the like is not provided in the cell. Also good.

< Third Reference Embodiment>
FIG. 10 is a cross-sectional configuration diagram of a liquid crystal display device according to a third reference embodiment, and FIGS. 11 and 12 are schematic views showing an alignment state in the display device. The difference between the liquid crystal display device 1c shown in these drawings and the liquid crystal display device 1 described with reference to FIGS. 1 to 3 is that electrodes are provided so as to generate a vertical electric field in the reflective display region B. The other configurations including the transmissive display area A are the same. 10-12, the same code | symbol is attached | subjected about the structure similar to each embodiment mentioned above, and detailed description is abbreviate | omitted.

That is, in the reflective display region B, the common electrode is not provided on the first substrate 10 side, and the pixel electrode 14b is provided on the upper portion of the convex pattern 12 for adjusting the cell gap gb. Then, an alignment film 17 similar to that of the liquid crystal display device is provided so as to cover the pixel electrode 14b. On the second substrate 20 side, a counter electrode 27 is provided above the retardation layer 21 so as to face the pixel electrode 14b. Then, in a state of covering the opposing electrode 27, provided Oriented film 22. Thereby, when a voltage is applied between the pixel electrode 14 b and the counter electrode 17, an electric field (vertical electric field) perpendicular to the substrate surfaces of the first substrate 10 and the second substrate 20 is applied to the liquid crystal layer 30. It becomes the composition which is done. The vertical electric field causes the liquid crystal molecules m constituting the liquid crystal layer 30 to be aligned in a direction substantially perpendicular to the substrate surface.

The cell gap gb in the reflective display region B is adjusted to a cell gap ga = 2gb as in the liquid crystal display device 1, and the liquid crystal layer 30 in the reflective display region B has a phase difference of λ / 4 when the electric field is ON. It has become.

  Next, the operation of the liquid crystal display device 1c will be described.

FIG. 9 is a schematic diagram showing an alignment state in a state where no voltage is applied to the pixel electrode 14 and the common electrode 15 (when the electric field is OFF). As shown in this figure, when the electric field is OFF, the optical configuration including the alignment state of the liquid crystal molecules m in the liquid crystal layer 30 is the same as that of the liquid crystal display device 1 , and in the transmissive display area A, there is no light leakage. In the reflective display area B, it is possible to obtain black with little coloration.

  FIG. 12 is a schematic diagram showing an alignment state in a state where a voltage is applied to the pixel electrodes 14 and 14b, the common electrode 15, and the counter electrode 27 (when the electric field is ON).

As shown in this figure, in the transmissive display area A, the liquid crystal molecules m in the liquid crystal layer 30 are parallel to the substrate surface and the rubbing direction of the alignment films 17 and 22 by the lateral electric field applied to the liquid crystal layer 30. It will be in the state which orientated in the direction of 45 degrees with respect to the transmission axis of polarizing plate 40,50. For this reason, in the transmissive display area A, white display is performed as in the above embodiment .

  On the other hand, in the reflective display region B, the vertical electric field applied to the liquid crystal layer 30 causes the liquid crystal molecules m in the liquid crystal layer 30 to rise substantially perpendicular to the substrate surface.

  As a result, in the reflective display region B, the external light h ′ incident from the side of the polarizing plate 50 serving as an analyzer passes through the λ / 2 retardation layer 21 in the same manner as when the electric field is turned off, whereby the polarizing plate 50 The linearly polarized light is 45 ° out of phase with respect to the transmission axis. The external light h ′ reciprocates and passes through the liquid crystal layer 30 in which the liquid crystal molecules m rise in the vertical direction by applying an electric field without causing a phase difference. Then, by passing through the retardation layer 21 of λ / 2, it shifts by 45 °, returns to linearly polarized light parallel to the transmission axis of the polarizing plate 50, passes through the polarizing plate 50, and becomes white display.

As described above, this also in the liquid crystal display device 1c, similarly to the above embodiment, it is possible to perform the display of similar normally black in the transmissive display region A and the reflective display region B, also transmissive display region In A, good black display inherent in the IPS mode is performed, and in the reflective display region B, black display without color is performed, and it becomes possible to perform a transflective display with extremely good contrast. .

The embodiment and the reference embodiment of the present invention described above can also be applied to a configuration using a ferroelectric liquid crystal that switches around a cone angle. However, in this case, the liquid crystal layer 30 made of ferroelectric liquid crystal has a configuration in which electrodes are arranged so that a vertical electric field is applied. Even with this configuration, since the ferroelectric liquid crystal by the vertical electric field may be in-plane switching by parallel rotation and the substrate surface, it can be displayed similar to the above-described liquid crystal display device It is.

It is a figure which shows the structure of the liquid crystal display device of 1st reference embodiment. FIG. 2 is a schematic diagram illustrating an alignment state when the electric field is OFF in the liquid crystal display device illustrated in FIG. 1 . It is a schematic diagram which shows the orientation state at the time of the electric field ON in the liquid crystal display device shown in FIG. It is a figure which shows angle (theta) which the transmission axis of a polarizing plate and the orientation direction of a liquid crystal molecule make. It is a graph which shows the relationship between the angle (theta) a which the slow axis of a phase difference layer and the transmission axis of a polarizing plate make, and contrast. It is a figure which shows the structure of the liquid crystal display device of one Embodiment of this invention . It is a figure which shows the structure of the liquid crystal display device of 2nd reference embodiment. It is a schematic diagram which shows the orientation state at the time of the electric field OFF in the liquid crystal display device shown in FIG. It is a schematic diagram which shows the orientation state at the time of the electric field ON in the liquid crystal display device shown in FIG. It is a section lineblock diagram showing the composition of the liquid crystal display of a 3rd reference embodiment. It is a schematic diagram which shows the orientation state at the time of the electric field OFF in the liquid crystal display device shown in FIG. It is a schematic diagram which shows the orientation state at the time of the electric field ON in the liquid crystal display device shown in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1,1a, 1b, 1c ... Liquid crystal display device, 10 ... 1st board | substrate, 11 ... Reflective layer, 12 ... Convex pattern, 14 ... Pixel electrode, 14a ... Pixel electrode, 15 ... Common electrode, 20 ... 2nd board | substrate, 21 ... retardation layer (λ / 2), 21a ... retardation pattern, 30 ... liquid crystal layer, 40, 50 ... polarizing plate, A ... transmission display region, B ... reflection display region, ga ... cell gap, gb ... cell gap, m ... Liquid crystal molecules

Claims (8)

A liquid crystal panel in which a liquid crystal layer is sandwiched between the first substrate and the second substrate in the transmissive display region and the reflective display region, and an electrode for applying an electric field to the liquid crystal layer is provided;
A polarizing plate arranged in crossed Nicols on the outside of the liquid crystal panel;
The reflective display area includes a reflective layer that is selectively patterned on the first substrate side, and a delay that forms an angle of 20 to 25 degrees with respect to one transmission axis of the polarizing plate on the second substrate side. A first retardation layer of λ / 2 that is selectively patterned with a phase axis is provided,
The transmissive display area is provided with a phase difference pattern in which one transmission axis and a slow axis of the polarizing plate are made to coincide with each other by being orientation-divided with the first retardation layer of the reflective display area.
In the transmissive display area, the liquid crystal molecules constituting the liquid crystal layer rotate substantially parallel to the substrate surface of the liquid crystal panel when an electric field is applied, and the alignment axis of the liquid crystal molecules is one of the polarizing plates when no electric field is applied. Oriented parallel to the transmission axis and black display
The reflective display region has a phase difference corresponding to λ / 4 because the alignment axis of liquid crystal molecules constituting the liquid crystal layer is aligned in parallel with one transmission axis of the polarizing plate when no electric field is applied. A liquid crystal display device that displays black due to a phase difference between the liquid crystal layer and the retardation layer. The liquid crystal display device according to claim 1, wherein the liquid crystal layer in the transmissive display region has a phase difference corresponding to λ / 2. The liquid crystal display device according to claim 1, wherein the cell gap in the transmissive display region is configured to be approximately twice the cell gap of the liquid crystal layer in the reflective display region. The liquid crystal display device according to claim 3, wherein the reflective display region is provided with a convex pattern for adjusting a cell gap. The liquid crystal display device according to claim 1, wherein the electrode is provided so as to apply a lateral electric field substantially parallel to a substrate surface of the liquid crystal panel. Electrodes for applying an electric field substantially perpendicular to the substrate surface of the liquid crystal panel to the liquid crystal layer are provided on the first substrate side and the second substrate side in the transmissive display region and the reflective display region. The liquid crystal display device according to claim 1. On the first substrate side in the transmissive display region, an electrode for applying an electric field substantially parallel to the liquid crystal layer on the substrate surface of the liquid crystal panel is provided,
The first substrate side and the second substrate side in the reflective display region are provided with electrodes for applying an electric field substantially perpendicular to the substrate surface of the liquid crystal panel to the liquid crystal layer. 1. A liquid crystal display device according to 1. The liquid crystal display device according to claim 1, wherein the first retardation layer is formed by patterning a photosensitive liquid crystal polymer.

Images