JP3655903B2 - Liquid crystal display - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention combines a reflective liquid crystal display device used in office automation equipment such as a word processor and personal computer, portable information equipment such as an electronic notebook, or a camera-integrated VTR equipped with a liquid crystal monitor, and a reflective type and a transmissive type. The present invention relates to a liquid crystal display device.
[0002]
[Prior art]
Unlike liquid crystal displays (CRTs) and ELs (electroluminescence), liquid crystal displays do not emit light themselves, so a transmissive liquid crystal display device is used in which a backlight is installed behind the liquid crystal display element for illumination.
[0003]
However, since the backlight usually consumes 50% or more of the total power consumption of the liquid crystal display, a portable information device that is frequently used outdoors or always carried is installed with a reflector instead of the backlight. A reflection type liquid crystal display device that performs display only by itself is also realized.
[0004]
As a display mode used in the reflective liquid crystal display device, a polarizing plate is used in addition to a type using a polarizing plate such as a TN (twisted nematic) mode and a STN (super twisted nematic) mode which are widely used at present. In recent years, a phase transition type guest-host mode capable of realizing bright display has been actively developed and disclosed in, for example, Japanese Patent Application Laid-Open No. 4-75022 and Japanese Patent Application No. 7-228365.
[0005]
[Problems to be solved by the invention]
However, since the phase transition type guest-host mode performs display using light absorption of the dye in the liquid crystal layer in which liquid crystal molecules and the dye are dispersed, the contrast is not sufficient, and the TN (twisted nematic) mode and the STN (super twisted nematic). ) The display quality is significantly worse than that of a liquid crystal display device using a polarizing plate such as a mode.
[0006]
In the case of a liquid crystal display device of parallel alignment or twist alignment, liquid crystal molecules near the center of the liquid crystal layer are inclined in a direction perpendicular to the substrate surface when a voltage is applied, but voltage is applied to the liquid crystal molecules near the surface of the alignment film. Even if it is not perpendicular to the substrate, the birefringence of the liquid crystal layer is far from 0. In the display mode in which black display is performed when a voltage is applied, sufficient black cannot be displayed due to the birefringence of the liquid crystal layer. A sufficient contrast cannot be obtained.
[0007]
TN mode and STN mode liquid crystal display devices are also difficult to say at present with sufficient display quality in terms of brightness and contrast, and further improvements in display quality such as higher brightness and improved contrast are required.
[0008]
In addition, the reflection type liquid crystal display device has a drawback that the reflected light used for display is lowered when the ambient light is dark and the visibility is extremely lowered. There was a problem that the visibility under a clear sky or the like where the light was very bright was lowered.
[0009]
[Means for Solving the Problems]
In the present invention, a liquid crystal layer is sandwiched between one substrate and the other substrate, and the first polarizing means provided on the surface of the other substrate opposite to the liquid crystal layer, and the liquid crystal layer of the one substrate are In the liquid crystal display device having the second polarizing means provided on the opposite surface, the one substrate includes a region having a reflective function and a region having a transmissive function, and a reflective display region in one picture element. A transmissive display region, and a first retardation plate provided between the first polarizing means and the liquid crystal layer, and provided between the second polarizing means and the liquid crystal layer. The retardation of the liquid crystal layer of the reflective display region is α when the liquid crystal molecules of the liquid crystal layer are oriented substantially in the direction perpendicular to the substrate surface , for retardation of the liquid crystal layer is beta, wherein the first litter retardation plate Shon in the (λ / 4-α) conditions, a liquid crystal display device characterized by retardation of the second retardation plate is set to (λ / 4- (β-α )) Conditions .
[0012]
The operation according to the present invention will be described below.
[0013]
A liquid crystal display device including a region having a reflection function and a region having a transmission function includes a first polarizing unit, a second polarizing unit, a first retardation plate, and a second retardation plate. In the reflection mode in which the display is performed using the reflected light of the region having the reflection function, the retardation (birefringence) of the liquid crystal layer in the observer direction is 0 (initial alignment state in the vertical alignment mode, and voltage application state in the parallel alignment mode). If so, the linearly polarized light that has passed through the first polarizing means is transmitted through and reflected by the first retardation plate and the liquid crystal layer, and again passes through the liquid crystal layer and the first retardation plate to become the first polarizing means. When incident, since there are many polarization components orthogonal to the transmission axis of the first polarizing means, dark display is possible, and if retardation occurs in the observer direction, linearly polarized light that has passed through the first polarizing means Transmits through the first retardation plate and the liquid crystal layer and reflects again. Since it has a polarization component parallel to the transmission axis of the first polarizing means when passing through the crystal layer and the first retardation plate and entering the first polarizing means, the gradation corresponding to each retardation is obtained. Bright display can be achieved.
[0014]
In the transmission mode in which the display is performed with the transmitted light of the region having the transmission function, if the retardation of the liquid crystal layer in the observer direction is almost zero, the linearly polarized light that has passed through the second polarizing means is converted into the second retardation plate. When the light passes through the liquid crystal layer and the first retardation plate and enters the first polarizing means, dark display is possible because there are many polarization components orthogonal to the transmission axis of the first polarizing means. When the retardation increases in the direction of the person, the linearly polarized light that has passed through the second polarizing means passes through the second retardation plate, the liquid crystal layer, and the first retardation plate and enters the first polarizing means. In addition, since it has a polarization component parallel to the transmission axis of the first polarizing means, a bright display having gradation corresponding to each retardation becomes possible.
[0015]
Therefore, when the reflection mode and the transmission mode are used together, dark display is possible at the same time, and even when both are used together, display with high contrast is possible. Furthermore, gradation display is possible by changing the retardation value according to the voltage.
[0016]
Further, since the retardation of the first retardation plate and the second retardation plate is set to the λ / 4 condition, in the reflection mode in which the display is performed with the reflected light of the region having the reflection function, the observer direction In the state where there is almost no birefringence due to the liquid crystal layer, circularly polarized light enters, becomes circularly polarized light that is reflected by a region having a reflection function and whose rotational direction is reversed, and passes through the first retardation plate, and then the first polarizing means The linearly polarized light is orthogonal to the transmission axis. Since the liquid crystal display device functions as an optical isolator in the reflection region, a dark display with little light leakage is obtained.
[0017]
In addition, in the state where there is birefringence due to the liquid crystal layer in the observer direction, by changing the retardation, when the light incident on the first polarizing means is reflected and is incident on the first polarizing means again, Since a polarization component parallel to the transmission axis of one polarization means is generated and incident, a bright display capable of gradation display is obtained.
[0018]
Next, in the transmission mode in which display is performed using transmitted light from a region having a transmission function, when there is almost no birefringence due to the liquid crystal layer in the observer direction, circularly polarized light is incident on the liquid crystal layer, and the circularly polarized light is preserved when passing through the liquid crystal layer Then, it passes through the first retardation plate and becomes linearly polarized light orthogonal to the transmission axis of the first polarizing means, resulting in dark display with little light leakage. Further, since the retardation changes in a state where there is birefringence due to the liquid crystal layer in the observer direction, when the light incident from the second polarizing means is incident on the first polarizing means, the transmission of the first polarizing means is performed. Since the light is incident as a polarization component parallel to the axis, a bright display capable of gradation display is obtained.
[0019]
Therefore, even when the reflection mode and the transmission mode are used in combination, the liquid crystal molecules are in the same state during dark display, and at the same time, dark display without light leakage is possible. High-contrast display is realized as a transmission type or a dual type.
[0020]
In addition, when the retardation of the liquid crystal layer in the reflective region remains only α, the retardation of the first retardation plate is set to the condition (λ / 4-α), so that the display mode subjected to the parallel alignment treatment Even in the case where the remaining retardation cannot be ignored, such as when the pretilt angle is large even in the vertical alignment process, a high contrast display is realized as a reflective type. In the reflection mode, elliptically polarized light shifted from the circularly polarized light by the remaining retardation is incident on the liquid crystal layer. It passes through the liquid crystal layer and becomes circularly polarized light in a region having a reflection function, and becomes circularly polarized light that is reflected and whose rotation direction is reversed. When the light passes through the liquid crystal layer and is emitted from the liquid crystal layer, it becomes elliptically polarized light deviated from circularly polarized light. The elliptically polarized light at this time is in a state where the phase is shifted by 90 degrees from the time of incidence. For this reason, when it passes through the first retardation plate, it becomes linearly polarized light orthogonal to the transmission axis of the first polarizing means. Since the liquid crystal display device functions as an optical isolator in the reflection region, a dark display with little light leakage is obtained.
[0021]
Therefore, even when the remaining retardation cannot be ignored, a reflective display with high contrast is realized.
[0022]
When the reflective display is main, such as when the area of the reflective electrode is larger than the area of the transmissive electrode, the retardation plate 10 shown in the embodiment may be a λ / 4 plate.
[0023]
Further, when the retardation of the liquid crystal layer in the reflective region remains by α and the retardation of the liquid crystal layer in the transmissive region remains by β, the retardation of the first retardation plate is (λ / 4−α) condition. In addition, when the retardation of the second retardation plate is set to (λ / 4− (β−α)) condition, the pretilt angle is large even in the parallel alignment processing display mode or the vertical alignment processing. Even when the remaining retardation cannot be ignored, a high contrast display is realized as a reflective type, a transmissive type, or a dual type. In the reflection mode, elliptically polarized light shifted from the circularly polarized light by the remaining retardation is incident on the liquid crystal layer. It passes through the liquid crystal layer and becomes circularly polarized light in a region having a reflection function, and becomes circularly polarized light that is reflected and whose rotation direction is reversed. When the light passes through the liquid crystal layer and is emitted from the liquid crystal layer, it becomes elliptically polarized light deviated from circularly polarized light. The elliptically polarized light at this time is in a state where the phase is shifted by 90 degrees from the time of incidence. For this reason, when it passes through the first retardation plate, it becomes linearly polarized light orthogonal to the transmission axis of the first polarizing means. Since the liquid crystal display device functions as an optical isolator in the reflection region, a dark display with little light leakage is obtained.
[0024]
Next, in the transmission mode in which the display is performed with the transmitted light of the region having the transmission function, when there is almost no birefringence due to the liquid crystal layer in the observer direction, the elliptically polarized light in the same state as the output light in the reflection mode when exiting the liquid crystal layer The second phase difference plate is set so that the elliptically polarized light having the phase difference is incident. Therefore, when passing through the first phase difference plate, a straight line orthogonal to the transmission axis of the first polarization means Dark display with little light leakage due to polarized light.
[0025]
Therefore, even when the remaining retardation cannot be ignored, a high-contrast display is realized as a reflective type, a transmissive type, or a dual type.
[0026]
The first retardation plate and the second retardation plate are λ / 4 plates, and the angle formed between the transmission axis of the first polarizing means and the first retardation plate is 45 °, and the second polarization plate. When the angle between the transmission axis of the means and the second retardation plate is 45 °, when the remaining retardation can be ignored, circularly polarized light can be incident on the liquid crystal layer with the simplest configuration.
[0027]
In addition, when a vertically aligned liquid crystal layer using a liquid crystal material exhibiting negative dielectric anisotropy is used, the birefringence of the liquid crystal layer is almost 0 when no voltage is applied to the liquid crystal layer, and a good black color is obtained when no voltage is applied. Level is obtained, and the contrast of the display device is improved.
[0028]
In addition, by providing an optical compensation layer that compensates for the effects caused by the refractive index anisotropy of liquid crystal molecules generated in the light incident direction and viewing angle direction of the liquid crystal layer, the light incident direction and viewing angle direction of the liquid crystal layer are provided. The refractive index anisotropy generated in the above can be compensated for, and a decrease in contrast depending on the incident direction of light and the viewing angle direction can be prevented.
[0029]
In addition, if a chiral material is added to a vertically aligned liquid crystal layer using a liquid crystal material exhibiting negative dielectric anisotropy and the liquid crystal molecules are rotated when a voltage is applied, the rotation of the liquid crystal molecules when a voltage is applied is stabilized. can do. Furthermore, when the rubbing directions of the upper and lower substrates are other than the same direction, the trace of the alignment process is not the same direction, so that the streak is less noticeable.
[0030]
In addition, if the liquid crystal layer is twisted by 90 °, retardation is generated in the tilt direction of the liquid crystal molecules when the liquid crystal layer is oriented with a tilt of several degrees with respect to the substrate in order to prevent disclination when a voltage is applied. Since the directions in which the liquid crystal molecules in the vicinity are inclined at an angle of 90 ° with each other in the vicinity of the upper and lower substrates, the generated retardation can be canceled and a black display with less leakage light can be obtained.
[0031]
DETAILED DESCRIPTION OF THE INVENTION
(Embodiment 1)
Embodiment 1 of the present invention will be described with reference to FIG.
[0032]
A reflective electrode 3 is formed on the substrate 1 with a material having high reflectivity such as Al and Ta, and a counter electrode 4 is formed on the substrate 2, and exhibits a negative dielectric anisotropy between the reflective electrode 3 and the counter electrode 4. A liquid crystal layer 5 made of a liquid crystal material is sandwiched.
[0033]
A vertical alignment film (not shown) is formed on the surfaces of the reflective electrode 3 and the counter electrode 4 that are in contact with the liquid crystal layer 5. After the alignment film is applied, at least one alignment film such as rubbing is aligned. Processing is in progress.
[0034]
The liquid crystal molecules of the liquid crystal layer 5 have a tilt angle of about 0.1 ° to 5 ° with respect to the vertical direction of the substrate surface by an alignment treatment such as rubbing with respect to the vertical alignment film.
[0035]
Since a liquid crystal material exhibiting negative dielectric anisotropy is used for the liquid crystal layer 5, when a voltage is applied between the reflective electrode 3 and the counter electrode 4, the liquid crystal molecules are inclined in a direction parallel to the substrate surface. .
[0036]
Here, the reflective electrode 3 is used as an electrode for applying a voltage to the liquid crystal layer 5, but a film different from the reflective electrode and the electrode, for example, a laminated structure of an Al reflective plate and an ITO transparent electrode may be used.
[0037]
As the liquid crystal material of the liquid crystal layer 5, Ne (refractive index with respect to extraordinary light) = 1.5546, No (refractive index with respect to normal light) = 1.473, ΔN (Ne−No) = 0.0773 A liquid crystal material having
[0038]
A λ / 4 plate 7 is arranged on the opposite surface of the substrate 2 on the side where the counter electrode 4 is formed, and the delay axis of the λ / 4 plate 7 is the long axis of liquid crystal molecules when a voltage is applied to the liquid crystal layer 5. It arrange | positions so that it may incline 45 degrees with respect to a direction.
[0039]
The λ / 4 plate 7 converts linearly polarized light into circularly polarized light and circularly polarized light into linearly polarized light.
[0040]
The λ / 4 plate 7 is formed on the surface of the substrate 2 opposite to the side on which the counter electrode 4 is formed, but may be provided between the reflective electrode 3 and the substrate 2.
[0041]
In addition, the manufacturing cost can be reduced if the λ / 4 plate 7 is attached to the substrate surface or integrated with the polarizing plate 6.
[0042]
Next, a polarizing plate 6 is provided on the surface of the λ / 4 plate 7 opposite to the substrate 2 and is arranged so that the transmission axis of the polarizing plate 6 is inclined by 45 ° with respect to the delay axis of the λ / 4 plate 7. ing.
[0043]
FIG. 7A is a plan view of the active matrix substrate of Embodiment 1, and FIG. 7B is a cross-sectional view taken along the line FF in FIG. 7A.
[0044]
The active matrix substrate includes a gate wiring 21, a data wiring 22, a driving element 23, a drain electrode 24, an auxiliary capacitance electrode 25, a gate insulating film 26, an insulating substrate 27, a contact hole 28, an interlayer insulating film 29, and a reflective electrode 30. I have.
[0045]
The auxiliary capacitance electrode 25 is electrically connected to the drain electrode 24 and overlaps with the auxiliary capacitance wiring 32 via the gate insulating film 26 to form an auxiliary capacitance.
[0046]
The contact hole 28 is provided in the interlayer insulating film 29 in order to connect the reflection 30 and the auxiliary capacitance electrode 25.
[0047]
The light transmission state in the liquid crystal display device of Embodiment 1 will be described with reference to FIG.
[0048]
FIG. 13A shows the case of black display where no voltage is applied to the liquid crystal layer, and FIG. 13B shows the case of white display where voltage is applied to the liquid crystal layer. A reflective electrode 3 is formed on the surface.
[0049]
The black display will be described with reference to FIG.
[0050]
The incident light that enters from the upper surface of the polarizing plate 6 from the upper side of FIG. 13A becomes linearly polarized light that matches the transmission axis of the polarizing plate after passing through the polarizing plate 6 and is incident on the λ / 4 plate 7.
[0051]
The λ / 4 plate 7 is arranged so that the transmission axis direction of the polarizing plate 6 and the delay axis direction of the λ / 4 plate 7 are 45 °, and the light that has passed through the λ / 4 plate 7 becomes circularly polarized light. .
[0052]
When no electric field is applied to the liquid crystal layer 5, the liquid crystal layer 5 using a liquid crystal material exhibiting negative dielectric anisotropy has liquid crystal molecules aligned substantially perpendicular to the substrate surface, and the liquid crystal layer responds to incident light. The refractive index anisotropy of the layer 5 is negligible, and the phase difference caused by the light passing through the liquid crystal layer 5 is almost zero.
[0053]
Therefore, the circularly polarized light that has passed through the λ / 4 plate 7 passes through the liquid crystal layer 5 without breaking the circularly polarized light, and is reflected by the reflective electrode 3 on one substrate 1.
[0054]
The reflected circularly polarized light passes through the liquid crystal layer 5 in the direction of the substrate 2 and enters the λ / 4 plate 7 again as circularly polarized light.
[0055]
After passing through the λ / 4 plate 7, the circularly polarized light incident on the λ / 4 plate 7 becomes linearly polarized light in a direction orthogonal to the transmission axis direction of the polarizing plate 6 and enters the polarizing plate 6.
[0056]
The linearly polarized light that has passed through the λ / 4 plate 7 is linearly polarized light in a direction orthogonal to the transmission axis of the polarizing plate 6 and is absorbed by the polarizing plate 6 and is not transmitted.
[0057]
Thus, when no voltage is applied to the liquid crystal layer 5, black display is obtained.
[0058]
Next, white display will be described with reference to FIG.
[0059]
FIG. 3B shows a case where a voltage is applied to the liquid crystal layer 5, and FIG. 3B is the same as FIG.
[0060]
When a voltage is applied to the liquid crystal layer 5, the liquid crystal molecules aligned in the vertical direction from the substrate surface are inclined in the horizontal direction with respect to the substrate surface, and the circularly polarized light from the λ / 4 plate 7 incident on the liquid crystal layer 5 is It becomes elliptically polarized light due to birefringence, and after being reflected by the reflective electrode 3, the polarization changes further in the liquid crystal layer 5, and even after passing through the λ / 4 plate 7, it becomes linearly polarized light orthogonal to the transmission axis of the polarizing plate 6. Instead, light passes through the polarizing plate 6.
[0061]
By adjusting the voltage applied to the liquid crystal layer at this time, the amount of light that can be transmitted through the polarizing plate 6 after being reflected can be adjusted, and gradation display becomes possible.
[0062]
Further, when a voltage is applied from the reflective electrode 3 and the counter electrode 4 to the liquid crystal layer 5 to change the alignment state of the liquid crystal molecules so that the phase difference of the liquid crystal layer 5 is a ¼ wavelength condition, the λ / 4 plate 7 After passing through the liquid crystal layer 5 and passing through the liquid crystal layer 5, the circularly polarized light becomes linearly polarized light orthogonal to the transmission axis of the polarizing plate 6, and again passes through the liquid crystal layer 5 and becomes circularly polarized light. Later, the light passes through the λ / 4 plate 7 and becomes linearly polarized light parallel to the transmission axis of the polarizing plate 6, and the reflected light transmitted through the polarizing plate 6 is maximized.
[0063]
Accordingly, when no voltage is applied to the liquid crystal layer 5, there is no birefringence in the liquid crystal layer 5, and black display is obtained. When a voltage is applied to the liquid crystal layer 5, the light transmittance varies depending on the applied voltage, and gradation display is performed. Is possible.
[0064]
FIG. 4 shows the vertical incidence vertical light reception of the reflective liquid crystal display device when the cell gap of the liquid crystal layer is d = 3.56 μm and the phase difference of the liquid crystal layer is dΔN = 0.2752. The spectral reflectance characteristics at the time are shown.
[0065]
Here, in FIG. 4, the spectral reflection at the time of vertical incident vertical light reception with respect to the reflector alone is 100.
[0066]
As shown in FIG. 4, in a dark display where no voltage is applied to the liquid crystal layer 5 and a bright display when a voltage of 3.25 V is applied, a sufficient contrast ratio of 50 or more can be obtained over the entire wavelength range from 400 nm to 700 nm. .
[0067]
Further, when the applied voltage of the liquid crystal layer 5 is 3.25 V, a reflectance of about 40% is obtained, which is almost the same as the transmittance of the polarizing plate 6 used, and has high light utilization efficiency and is of a reflective type. Suitable for liquid crystal display devices.
[0068]
FIG. 5 shows the spectral reflectance of the liquid crystal display device in the case of normal incidence and vertical light reception when the cell gap of the liquid crystal layer is d = 4.5 μm and the phase difference of the liquid crystal layer is dΔN = 0.3479 in the first embodiment. Show properties.
[0069]
Therefore, in the reflection type liquid crystal display device in which the cell gap of the liquid crystal showing the spectral reflectance characteristic in FIG. 5 is d = 4.5 μm, a dark display in which no voltage is applied to the liquid crystal layer 5 and a bright display when a voltage of 3 V is applied. In this case, a sufficient contrast ratio of 50 or more can be obtained in the entire wavelength range from 400 nm to 700 nm.
[0070]
Further, when the voltage applied to the liquid crystal layer 5 is 3 V, a reflectance of about 40% can be obtained as in the reflective liquid crystal display device having a cell gap d = 3.56 μm.
[0071]
FIG. 6 shows the relationship between the cell gap and the contrast ratio at a wavelength of 550 nm when the reflection type liquid crystal display device according to the first embodiment is vertically incident and vertically received.
[0072]
FIG. 6 shows the measurement by applying a voltage in which the phase difference dΔn of the liquid crystal satisfies the ¼ wavelength condition.
[0073]
As shown in FIG. 6, in the reflective display device of Embodiment 1, a contrast ratio of 500 or more is maintained regardless of the cell gap of the liquid crystal layer.
[0074]
Therefore, when a voltage is applied to the liquid crystal layer 5, as long as the phase difference dΔn satisfies the ¼ wavelength condition, display can be performed without reducing the contrast ratio, and the cell gap d can be set arbitrarily.
[0075]
FIG. 12 shows the relationship between the deviation of the angle of the delay axis of the λ / 4 plate 7 and the contrast ratio when the delay axis of the λ / 4 plate 7 is inclined by 45 ° with respect to the transmission axis of the polarizing plate 6. Indicates.
[0076]
Here, if the deviation of the angle of the delay axis of the λ / 4 plate 7 is within 3 °, a contrast ratio of 50 or more can be obtained, and a reflective liquid crystal display device with good display characteristics can be produced.
[0077]
Therefore, in the bonding of the polarizing plate and the λ / 4 plate, a high contrast display device can be obtained even if the angle between the delay axis of the λ / 4 plate 7 and the transmission axis of the polarizing plate 6 slightly deviates from the set value.
[0078]
6 and 7 eliminate the influence of the panel surface reflection, but the influence of the panel surface reflection cannot be ignored in actual use, and the contrast ratio in that case is about 20. Is a good value for the contrast of the reflective liquid crystal display device.
[0079]
In the liquid crystal display device using the vertical alignment liquid crystal material used in this embodiment, the retardation of the liquid crystal layer can be almost zero when no voltage is applied. Therefore, in the case of normally black display, the dark state can be made darker. , Can increase the contrast.
[0080]
(Embodiment 2)
A second embodiment of the present invention will be described with reference to FIG.
[0081]
The same reference numerals are given to the same configurations as those in the first embodiment.
[0082]
One substrate 1 is provided with a reflective electrode 3 formed of a material having high reflectivity such as Al and Ta and a transparent electrode 8 formed of a material having high transmittance such as ITO, and the counter electrode 4 is provided on the substrate 2. A liquid crystal layer 5 made of a liquid crystal material having negative dielectric anisotropy is sandwiched between the reflective electrode 3 and the transparent electrode 8 and the counter electrode 4.
[0083]
A vertical alignment film (not shown) is formed on each surface of the reflective electrode 3, the transparent electrode 8, and the counter electrode 4 in contact with the liquid crystal layer 5. After the alignment film is applied, at least one alignment film is formed on the alignment film. Alignment treatment such as rubbing is performed.
[0084]
The liquid crystal molecules of the liquid crystal layer 5 have a tilt angle of about 0.1 ° to 5 ° with respect to the vertical direction of the substrate surface by an alignment treatment such as rubbing on the vertical alignment film.
[0085]
Here, although the reflective electrode 3 is used as an electrode for applying a voltage to the liquid crystal layer, the transparent electrode 8 is extended over the reflective electrode without using the reflective electrode as an electrode, and the voltage is applied to the liquid crystal layer 5 in the reflective region. It is good also as an electrode which applies.
[0086]
As the liquid crystal material of the liquid crystal layer 5, the same liquid crystal material having refractive index anisotropy as Ne = 1.5546 and No = 1.4773 as in the first embodiment was used.
[0087]
A λ / 4 plate 7 is disposed on the opposite surface of the substrate 2 on the side where the counter electrode 4 is formed. The delay axis of the λ / 4 plate 7 is the long axis direction of the liquid crystal molecules when a voltage is applied to the liquid crystal layer 5. It is arrange | positioned so that it may incline 45 degrees with respect to.
[0088]
A λ / 4 plate 10 is disposed on the opposite surface of the substrate 1 on the side where the reflective electrode 3 and the transparent electrode 8 are formed, and the delay axis of the λ / 4 plate 10 is in the same direction as the delay axis of the λ / 4 plate 7. Is set.
[0089]
A polarizing plate 6 is provided on the surface of the λ / 4 plate 7 opposite to the substrate 2, and a polarizing plate 9 is provided on the opposite side of the λ / 4 plate 10 from the substrate 1. The transmission axis is set to be inclined by 45 ° with respect to the delay axes of the λ / 4 plate 7 and the λ / 4 plate 10.
[0090]
FIG. 8A shows a plan view of an active matrix substrate according to Embodiment 2 of the present invention, and FIG. 8B shows a cross-sectional view taken along the line AA of FIG. 8A.
[0091]
The active matrix substrate includes a gate wiring 21, a data wiring 22, a driving element 23, a drain electrode 24, an auxiliary capacitance electrode 25, a gate insulating film 26, an insulating substrate 27, a contact hole 28, an interlayer insulating film 29, and a reflective pixel electrode. 30 and a transmission picture element electrode 31 are provided.
[0092]
The auxiliary capacitance electrode 25 is electrically connected to the drain electrode 24 and overlaps with the gate wiring 21 via the gate insulating film 26 to form an auxiliary capacitance.
[0093]
The contact hole 28 is provided in the interlayer insulating film 29 in order to connect the transmissive pixel electrode 31 and the auxiliary capacitance electrode 25.
[0094]
This active matrix substrate includes a reflective pixel electrode 30 and a transmissive pixel electrode 31 in one picture element, and the reflective picture element electrode 30 that reflects light from the outside in one picture element. A part of the pixel electrode 31 for transmission that transmits the part and the light of the backlight is formed.
[0095]
The light transmission state in the liquid crystal display device of Embodiment 2 will be described with reference to FIG.
[0096]
FIG. 13A shows the case of black display in which no voltage is applied to the liquid crystal layer 5, and FIG. 13B shows the case of white display in which voltage is applied to the liquid crystal layer 5.
[0097]
In FIG. 13, the region having the reflective electrode 3 has the same configuration as that of the reflective liquid crystal display device of the first embodiment, and when used as a reflective display device, the display is performed on the same principle as that of the first reflective liquid crystal display device. Since it is possible, explanation is omitted.
[0098]
The state of light in the region where the transparent electrode 8 which is the right region in FIGS. 13A and 13B is formed will be described.
[0099]
Light emitted from the lower side of FIG. 13A by a light source (not shown) becomes linearly polarized light that matches the transmission axis of the polarizing plate 9 by the polarizing plate 9.
[0100]
The λ / 4 plate 10 is arranged such that the transmission axis direction delay axis direction of the λ / 4 plate 10 and the polarizing plate 9 is 45 °, and the light passing through the λ / 4 plate 10 becomes circularly polarized light. .
[0101]
When an electric field is not generated in the liquid crystal layer 5, the liquid crystal layer 5 using a liquid crystal material exhibiting negative dielectric anisotropy has liquid crystal molecules aligned substantially perpendicular to the substrate surface, and the liquid crystal layer responds to incident light. The refractive index anisotropy of the layer 5 is negligible, and the phase difference generated when light passes through the liquid crystal layer 5 is almost zero.
[0102]
Accordingly, the circularly polarized light emitted from the λ / 4 plate 10 passes through the liquid crystal layer 5 without breaking the circularly polarized light and enters the λ / 4 plate 7.
[0103]
The delay axis direction of the λ / 4 plate 10 and the delay axis direction of the λ / 4 plate 7 coincide, and the circularly polarized light incident on the λ / 4 plate 7 is a straight line in a direction orthogonal to the transmission axis direction of the polarizing plate 9. Polarized light enters the polarizing plate 6.
[0104]
The linearly polarized light emitted from the λ / 4 plate 7 is linearly polarized light in a direction orthogonal to the transmission axis of the polarizing plate 6 and is absorbed by the polarizing plate 6 and does not transmit light.
[0105]
Thus, when no voltage is applied to the liquid crystal layer 5, black display is obtained.
[0106]
Next, white display will be described with reference to FIG.
[0107]
FIG. 13B shows a case where a voltage is applied to the liquid crystal layer, and is the same as FIG. 13A until light passes through the λ / 4 plate 10, and the description thereof is omitted.
[0108]
When a voltage is applied to the liquid crystal layer 5, the liquid crystal molecules of the liquid crystal layer 5 oriented in the vertical direction from the substrate surface are inclined in the horizontal direction with respect to the substrate surface, and the circularly polarized light from the λ / 4 plate 10 incident on the liquid crystal layer is Due to the birefringence of the layer 5, it becomes elliptically polarized light, and even after passing through the λ / 4 plate 7, it does not become linearly polarized light orthogonal to the transmission axis of the polarizing plate 6, but light passes through the polarizing plate 6.
[0109]
By adjusting the voltage applied to the liquid crystal layer 5 at this time, the polarization state of the light incident on the polarizing plate 6 can be changed, and the amount of light transmitted through the polarizing plate 6 can be adjusted to display gradation. .
[0110]
Further, when a voltage is applied to the liquid crystal layer 5 so that the phase difference of the liquid crystal layer 5 is a ½ wavelength condition, the circularly polarized light after passing through the λ / 4 plate 10 is half the cell thickness of the liquid crystal layer 5. It becomes linearly polarized light orthogonal to the transmission axis of the polarizing plate 9 at the point, and becomes circularly polarized light when passing through the remaining liquid crystal layer 5.
[0111]
Since the circularly polarized light emitted from the liquid crystal layer 5 passes through the λ / 4 plate 7 and becomes linearly polarized light parallel to the transmission axis of the polarizing plate 6, most of the light incident on the polarizing plate 6 is transmitted through the polarizing plate 6. Therefore, the light transmitted through the polarizing plate 6 is maximized.
[0112]
Therefore, in the second embodiment, when no voltage is applied to the liquid crystal layer 5 in both the reflective electrode 3 region and the transparent electrode 8 region, the liquid crystal layer 5 has no birefringence and a black display is obtained. By applying a voltage to the light, it is possible to adjust the light transmission amount and display a gradation.
[0113]
In FIG. 9, in the second embodiment, the spectral transmission at the time of normal incidence and vertical light reception in the transmission region of the transflective liquid crystal display device with the cell gap d = 3.56 μm of the liquid crystal layer and the phase difference dΔN = 0.2752 of the liquid crystal layer. The rate characteristic is shown.
[0114]
Here, the spectral reflectance characteristic in the region where the reflective electrode 3 is present is the same as in FIG.
[0115]
In FIG. 9, the spectral transmission at the time of vertical incident vertical light reception with respect to air is set to 100.
[0116]
As shown in FIG. 9, a sufficient contrast ratio can be obtained in the entire wavelength range from 400 nm to 700 nm in black display where no voltage is applied to the liquid crystal layer 5 and bright display when a voltage of 5 V is applied.
[0117]
Further, when the voltage applied to the liquid crystal layer 5 is 5 V, a reflectance of about 30% is obtained, which is about 80% of the transmittance of the polarizing plate 6 used.
[0118]
For this reason as well, this display method has high light utilization efficiency and is suitable for a transflective liquid crystal display device.
[0119]
FIG. 10 shows the transmission of the transflective liquid crystal display device when the cell gap of the liquid crystal layer 5 is d = 4.5 μm and the phase difference of the liquid crystal layer 5 is dΔN = 0.3479 in the liquid crystal display device of the second embodiment. The spectral transmittance characteristic at the time of normal incidence perpendicular light reception in a field is shown.
[0120]
Similar to the transflective liquid crystal display device with a cell gap d = 3.56 μm in FIG. 9, a wavelength of 400 nm to 700 nm in black display in which no voltage is applied to the liquid crystal layer 5 and in bright display when a voltage of 5 V is applied. A sufficient contrast ratio can be obtained over the entire region, and a transmittance of about 40% can be obtained when the voltage applied to the liquid crystal layer is 5V.
[0121]
FIG. 11 shows the relationship between the cell gap and the contrast ratio at a wavelength of 550 nm during normal incidence and vertical light reception in the transmissive region of the transflective liquid crystal display device of the second embodiment.
[0122]
FIG. 11 shows the measurement by applying a voltage satisfying the 1/2 wavelength condition for the phase difference dΔn of the liquid crystal.
[0123]
Thus, regardless of the cell gap, the contrast ratio of 800 or more is maintained when used as a transmissive liquid crystal display device in the transparent electrode 8 region, and the contrast ratio of 500 or more is maintained when used as a reflective liquid crystal display device in the reflective electrode 3 region. Yes.
[0124]
Therefore, when a voltage is applied to the liquid crystal layer 5, as long as the phase difference dΔn satisfies the ½ wavelength condition, display can be performed without a decrease in contrast ratio, and the cell gap d can be set arbitrarily.
[0125]
FIG. 12 shows the relationship between the deviation in the angle of the delay axis of the λ / 4 plate 7 and the contrast ratio when the delay axis of the λ / 4 plate 7 is inclined by 45 ° with respect to the transmission axis of the polarizing plate 6. .
[0126]
Here, if the shift of the angle of the delay axis of the λ / 4 plate 7 is within 3 °, it is used as a transmissive liquid crystal display device in the transmissive region where the transparent electrode 8 is formed, or the reflective electrode 3 is formed. When used as a reflection type liquid crystal display device in the reflection region, a contrast ratio of 50 or more is obtained, and a reflection / transmission type liquid crystal display device with good display characteristics is obtained.
[0127]
Therefore, when the ambient light is dark, it is used as a transmissive liquid crystal display device that displays using light transmitted through the transparent electrode 8 using a backlight. When the ambient light is bright, the light reflectance is relatively low. Display is possible as a reflective liquid crystal display device that displays using the reflected light from the reflective electrode 3 formed of a high film.
[0128]
Therefore, if the ambient light is dark on one panel, use the backlight. If the ambient light is bright, use the ambient light without using the backlight, or use both the backlight and reflected light. Also, it can be used as a transflective liquid crystal display device capable of displaying.
[0129]
Therefore, when the ambient light is brighter than the conventional transmissive liquid crystal display device, it consumes less power because the backlight is not used. When the ambient light is dark, the backlight is used. It is possible to overcome the drawback that a sufficient display cannot be obtained when the ambient light is dark like the device.
[0130]
The liquid crystal display device using the vertical alignment liquid crystal material used in this embodiment can reduce the retardation of the liquid crystal layer to almost zero when no voltage is applied. Therefore, in the case of normally black display, the transmissive display and the reflective display are in a dark state. It can be darker and the contrast can be increased.
[0131]
(Embodiment 3)
Embodiment 3 of the present invention will be described with reference to the schematic cross-sectional view of FIG.
[0132]
The description of the configuration common to Embodiments 1 and 2 is omitted.
[0133]
The liquid crystal display device of Embodiment 3 has a λ / 4 plate 10 and an optical compensation plate 12 between the substrate 1 and the polarizing plate 9, and the λ / 4 plate 7 and the optical compensation plate between the substrate 2 and the polarizing plate 6. 11.
[0134]
When no voltage is applied to the liquid crystal layer 5, the liquid crystal molecules of the liquid crystal layer 5 using a liquid crystal material exhibiting negative dielectric anisotropy are aligned substantially perpendicularly from the substrate surface, and the liquid crystal layer is viewed from the front of the substrate. There is no refractive index anisotropy due to the layer 5.
[0135]
However, when used as a reflective liquid crystal display device, light is used not only in a direction perpendicular to the substrate surface but also from other directions for display. When light enters the liquid crystal layer 5, it is affected by refractive index anisotropy.
[0136]
Further, since the viewing angle direction is not necessarily perpendicular to the substrate surface, the viewing angle direction is affected by the refractive index anisotropy of the liquid crystal molecules of the liquid crystal layer 5 as the viewing angle direction deviates from the vertical direction of the substrate surface. Occur.
[0137]
Therefore, by providing optical compensation layers 11 and 12 that compensate for the effects caused by the refractive index anisotropy of the liquid crystal molecules generated in the light incident direction and viewing angle direction of the liquid crystal layer 5, The refractive index anisotropy generated in the incident direction and the viewing angle direction can be compensated for, and a decrease in contrast depending on the incident direction of light and the viewing angle direction can be prevented.
[0138]
Further, when the prealignment of the liquid crystal molecules is slightly laid from the vertical direction of the substrate surface so that the liquid crystal molecules are inclined in one direction when a voltage is applied in the vertical alignment liquid crystal layer 5, the voltage is not applied to the vertical alignment liquid crystal layer 5. Even in such a case, a slight refractive index anisotropy occurs in the direction perpendicular to the substrate, so that the optical compensation layer is designed so as to compensate for this refractive index anisotropy. The contrast ratio is further improved.
[0139]
In the third embodiment, the λ / 4 plate and the optical compensation layer are described as separate layers, but the same effect can be obtained even if they are formed in the same layer.
[0140]
In the third embodiment, the two optical compensation layers of the optical compensation layer 11 and the optical compensation layer 12 are used. However, only the optical compensation layer 11 may be used.
[0141]
In the third embodiment, a transmission / reflection display device has been described. However, in the reflection liquid crystal display device of the first embodiment, the refractive index anisotropy of liquid crystal molecules in the liquid crystal layer 5 is compensated between the polarizing plate 6 and the reflective electrode 3. Thus, by providing the optical compensation layer, a reduction in contrast ratio can be prevented.
[0142]
In the first to third embodiments, the case of white display and black display has been described. However, it is also possible to perform color display by providing a color filter of each color at a corresponding portion of the reflective region or the transmissive region.
[0143]
By adding a chiral material to the vertically aligned liquid crystal layer 5 using the liquid crystal material exhibiting negative dielectric anisotropy of the first to third embodiments, the liquid crystal molecules are rotated when a voltage is applied, and the liquid crystal when the voltage is applied The rotation of the molecule can be stabilized.
[0144]
At that time, the liquid crystal layer is aligned so that the liquid crystal layer is twisted by 90 °, so that the liquid crystal molecules are aligned at an angle of several degrees with respect to the normal direction of the substrate surface in order to prevent disclination during voltage application. Retardation occurs in the tilt direction of the liquid crystal, but since the tilted directions of the liquid crystal molecules near the substrate form an angle of 90 ° with each other near the upper and lower substrates, the generated retardation can be canceled out, and leakage light is generated. Less black display can be obtained.
[0145]
In Embodiments 1 to 3, vertical alignment liquid crystals having negative dielectric anisotropy are used, but the same display is possible using parallel alignment liquid crystals.
[0146]
That is, when parallel alignment liquid crystal is used instead of vertical alignment liquid crystal, the liquid crystal molecules are arranged in parallel to the substrate surface when no voltage is applied, and the liquid crystal molecules are inclined in the normal direction of the substrate surface when no voltage is applied. A liquid crystal display device can be obtained that displays white when applied and displays black when voltage is applied.
[0147]
In the case of black display using the parallel alignment liquid crystal, the remaining retardation is larger than that in the case of the vertical alignment liquid crystal due to the liquid crystal molecules near the substrate. Therefore, in order to perform a more complete black display, a phase difference plate that compensates for this may be used in combination.
[0148]
When the retardation of α remains in the reflection mode in the liquid crystal layer in which the liquid crystal molecules are substantially oriented in the direction perpendicular to the substrate surface, instead of the λ / 4 plate 7, (λ / 4-α) A retardation plate having retardation may be disposed.
[0149]
In the reflection mode, elliptically polarized light that is shifted from the circularly polarized light by the remaining retardation of the liquid crystal layer is incident on the liquid crystal layer. It passes through the liquid crystal layer and becomes circularly polarized light in a region having a reflection function, and becomes circularly polarized light that is reflected and whose rotation direction is reversed. When the light passes through the liquid crystal layer and exits from the liquid crystal layer, it becomes elliptically polarized light deviated from circularly polarized light. The elliptically polarized light at this time is in a state where the phase at the time of incidence is shifted by 90 degrees. When passing through the retardation plate, it becomes linearly polarized light orthogonal to the transmission axis of the polarizing plate 6.
[0150]
Therefore, even when the retardation remaining in the liquid crystal layer in the state where the liquid crystal molecules are oriented in the direction perpendicular to the substrate surface cannot be ignored, a high contrast display in the reflection mode can be achieved by arranging a retardation plate in consideration of the retardation. Can be realized.
[0151]
Further, when the retardation of α in the reflection mode and β of the transmission mode remains in the liquid crystal layer, a retardation plate having a retardation of (λ / 4−α) instead of the λ / 4 plate 7 λ / Instead of the four plates 10, a retardation plate having a retardation of (λ / 4- (β-α)) may be disposed.
[0152]
In the transmission mode in which the display is performed with the transmitted light of the region having the transmission function, when the liquid crystal molecules are oriented in the vertical direction of the substrate surface, the elliptically polarized light in the same state as the output light in the reflection mode is emitted from the liquid crystal layer. Thus, the retardation plate having the retardation (λ / 4- (β-α)) is set, and the elliptically polarized light having the retardation has the retardation (λ / 4-α). Since the light is incident on the plate, when it passes through the retardation plate having the retardation of (λ / 4−α), it becomes linearly polarized light orthogonal to the transmission axis of the polarizing plate 6 and dark display with little light leakage is obtained.
[0153]
Therefore, even when the retardation remaining in the liquid crystal layer in the state where the liquid crystal molecules are oriented in the direction perpendicular to the substrate surface cannot be ignored, a high contrast display in the reflection mode can be achieved by arranging a retardation plate in consideration of the retardation. Can be realized.
[0154]
【The invention's effect】
A liquid crystal display device including a region having a reflection function and a region having a transmission function includes a first polarizing unit, a second polarizing unit, a first retardation plate, and a second retardation plate. A display device having a reflection mode and a transmission mode can display with high contrast. Further, when the reflection mode and the transmission mode are used in combination, dark display is possible at the same time, and even when both are used together, display with high contrast is possible. Furthermore, gradation display is possible by changing the retardation value according to the voltage.
[0155]
Moreover, when the retardation of the first retardation plate and the second retardation plate is set to the λ / 4 condition, when the liquid crystal molecules of the liquid crystal layer are oriented substantially in the vertical direction of the substrate surface, When there is almost no retardation of the liquid crystal layer, light that passes through the liquid crystal layer and the retardation plate and enters the first polarizing plate in the reflection region and the transmission region is linearly polarized light that is orthogonal to the transmission axis of the polarizing plate. Therefore, a dark display with little light leakage can be obtained.
[0156]
In addition, when the retardation of the liquid crystal layer in the reflective region remains only α, the retardation of the first retardation plate is set to (λ / 4-α) condition, so that the liquid crystal molecules in the liquid crystal layer are almost Even if the retardation of the liquid crystal layer in the reflective region remains only α when facing the vertical direction of the substrate surface, it passes through the liquid crystal layer and the retardation plate in the reflective region and enters the first polarizing plate. Since the light to be converted into linearly polarized light orthogonal to the transmission axis of the polarizing plate, a dark display with little light leakage can be obtained.
[0157]
Further, when the retardation of the liquid crystal layer in the reflective region remains by α and the retardation of the liquid crystal layer in the transmissive region remains by β, the retardation of the first retardation plate is (λ / 4−α) condition. In addition, when the retardation of the second retardation plate is set to (λ / 4− (β−α)) condition, the liquid crystal molecules of the liquid crystal layer are generally oriented in the direction perpendicular to the substrate surface. Even if the retardation of the liquid crystal layer in the reflective region is α and the retardation of the liquid crystal layer in the transmissive region is only β, the first polarized light passes through the liquid crystal layer and the retardation plate in the reflective region and the transmissive region. Since light incident on the plate becomes linearly polarized light orthogonal to the transmission axis of the polarizing plate, dark display with little light leakage can be obtained.
[0158]
The first retardation plate and the second retardation plate are λ / 4 plates, and the angle formed between the transmission axis of the first polarizing means and the first retardation plate is 45 °, and the second polarization plate. Since the angle between the transmission axis of the means and the second retardation plate is 45 °, the state of the liquid crystal molecules in the dark display is the same even when the reflection mode and the transmission mode are used together, and at the same time the light leakage Dark display is possible, and a high contrast display is realized as a reflective type, a transmissive type, or a dual type regardless of the ambient light intensity.
[0159]
Also, if a vertically aligned liquid crystal layer using a liquid crystal material exhibiting negative dielectric anisotropy is used, little light leaks from the polarizing plate when black is displayed when no voltage is applied, and white display and color when voltage is applied. A reflective liquid crystal display device having high light use efficiency and excellent display quality in color display using a filter can be realized.
[0160]
In addition, by providing an optical compensation layer that compensates for the effects caused by the refractive index anisotropy of liquid crystal molecules generated in the light incident direction and viewing angle direction of the liquid crystal layer, it depends on the light incident direction and viewing angle direction. A reduction in contrast can be prevented.
[0161]
In addition, if a chiral material is added to a vertically aligned liquid crystal layer using a liquid crystal material exhibiting negative dielectric anisotropy and the liquid crystal molecules are rotated when a voltage is applied, the rotation of the liquid crystal molecules when a voltage is applied is stabilized. When the upper and lower substrates are rubbed in directions other than the same direction, the trace of the alignment process is not in the same direction, so that the lines are less noticeable.
[0162]
In addition, if the liquid crystal layer is twisted by 90 °, retardation will occur in the tilt direction of the liquid crystal molecules when it is tilted several degrees with respect to the normal direction of the substrate in order to prevent disclination during voltage application. However, since the inclined directions of the liquid crystal molecules in the vicinity of the substrate form an angle of 90 ° with each other in the vicinity of the upper and lower substrates, the generated retardation can be canceled and a black display with less leakage light can be obtained.
[Brief description of the drawings]
FIG. 1 is a cross-sectional configuration diagram of a reflective liquid crystal display device according to a first embodiment of the present invention.
FIG. 2 is a cross-sectional configuration diagram of a transflective liquid crystal display device according to a second embodiment of the present invention.
FIG. 3 is a cross-sectional configuration diagram of a transflective liquid crystal display device according to a third embodiment of the present invention.
FIG. 4 is a spectral reflectance characteristic diagram at the time of vertical incident vertical light reception with a cell gap d = 3.56 μm of the reflective liquid crystal display device according to the first embodiment of the present invention;
FIG. 5 is a spectral reflectance characteristic diagram at the time of normal incidence vertical light reception with a cell gap d = 4.5 μm of the reflective liquid crystal display device according to the first embodiment of the present invention;
FIG. 6 is a relationship diagram between a cell gap and a contrast ratio at a wavelength of 550 nm during normal incidence and vertical light reception of the reflective liquid crystal display device according to the first embodiment of the present invention.
FIG. 7 is a diagram showing an electrode configuration of a reflective liquid crystal display device according to Embodiment 1 of the present invention.
FIG. 8 is a diagram showing an electrode configuration of a reflective liquid crystal display device according to Embodiment 2 of the present invention.
FIG. 9 is a spectral reflectance characteristic diagram at the time of normal incidence vertical light reception in a transmission region of a transmission / reflection liquid crystal display device with a cell gap d = 3.56 μm in Embodiment 2 of the present invention;
FIG. 10 is a spectral reflectance characteristic diagram at the time of normal incidence vertical light reception in a transmission region of a transmission / reflection liquid crystal display device having a cell gap d = 4.5 μm in Embodiment 2 of the present invention;
FIG. 11 is a relationship diagram between a cell gap at a wavelength of 550 nm and a contrast ratio in vertical transmission and vertical light reception in a transmission region of a transflective liquid crystal display device according to Embodiment 2 of the present invention.
FIG. 12 shows a λ in the case where the delay axis of the λ / 4 plate is inclined by 45 ° with respect to the transmission axis of the polarizing plate in the transmission region of the transflective liquid crystal display device according to the second embodiment of the present invention. FIG. 6 is a relationship diagram between a shift in the angle of the delay axis of the / 4 plate and a contrast ratio.
FIG. 13 is a diagram illustrating a light transmission state in the liquid crystal display devices according to the first and second embodiments of the present invention.
[Explanation of symbols]
1, 2 Substrate 3 Reflective electrode 4 Counter electrode 5 Liquid crystal layer (vertical alignment)
6, 9 Polarizing plate 7, 10 λ / 4 plate 8 Transparent electrodes 11, 12 Optical compensation layer

Claims (1)

A liquid crystal layer is sandwiched between one substrate and the other substrate, the first polarizing means provided on the surface of the other substrate opposite to the liquid crystal layer, and the surface of the one substrate opposite to the liquid crystal layer In the liquid crystal display device having the second polarizing means provided,
The one substrate includes a region having a reflective function and a region having a transmissive function, and a reflective display region and a transmissive display region are formed in one picture element,
A first retardation plate provided between the first polarizing means and the liquid crystal layer; and a second retardation plate provided between the second polarizing means and the liquid crystal layer. Have
When the liquid crystal molecules in the liquid crystal layer are oriented substantially in the direction perpendicular to the substrate surface, the retardation of the liquid crystal layer in the reflective display region is α, and the retardation of the liquid crystal layer in the transmissive display region is β. The retardation of the retardation plate is set to (λ / 4-α) condition and the retardation of the second retardation plate is set to (λ / 4- (β-α)) condition. Liquid crystal display device.

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