JP2003131268A - Liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid crystal display device which has excellent mass productivity and which is capable of favorable display without depending on the brightness of the ambient light. SOLUTION: In the liquid crystal display device, each pixel region of a plurality of regions has a reflecting region and a transmitting region and the liquid crystal layer is made of a liquid crystal material having positive dielectric anisotropy. The device has a first polarizing element disposed on the opposite side of a first substrate to the liquid crystal layer, a second polarizing element disposed on the opposite side of a second substrate to the liquid crystal layer, a first phase difference compensating element disposed between the first polarizing element and the liquid crystal layer, and a second phase difference compensating element disposed between the second polarizing element and the liquid crystal layer. The twist angle θt of the liquid crystal layer is in the range of >=0 deg. and <=90 deg.. The retardation of the liquid crystal layer is independently optimized in the reflecting region and in the transmitting region.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device, and more particularly to a reflective / transmissive liquid crystal display device capable of displaying a reflection mode and a transmission mode.

[0002]

2. Description of the Related Art Conventionally, liquid crystal display devices include a reflective display device that uses ambient light, a transmissive display device that uses backlight light, and a transflective display device that includes a half mirror and a backlight. .

The reflection type liquid crystal display device makes it difficult to see the display in a dim environment, and the transmission type liquid crystal display device makes it difficult to see the display in bright sunlight, for example, in the sunlight such as outdoors. There was a flaw. As a liquid crystal display device that uses both of these display modes in combination so that good display can be performed under any environment, Japanese Patent Laid-Open No. 7-3
Japanese Patent No. 33598 discloses a transflective liquid crystal display device.

[0004]

However, the above-mentioned conventional transflective liquid crystal display device has the following problems. In the conventional transflective liquid crystal display device, a half mirror is used instead of the reflective plate in the reflective liquid crystal display device, and a minute transmissive region (for example, a minute hole in the metal thin film) is provided in the reflective region to reflect the reflected light. In addition, the transmitted light is used for display. Since the reflected light and the transmitted light used for display pass through the same liquid crystal layer, the optical path of the reflected light is twice the optical path of the transmitted light, and the retardation of the liquid crystal layer for the reflected light and the transmitted light is greatly different. Couldn't get Moreover, since the display of the reflection mode and the display of the transmission mode are overlapped, the display of the reflection mode and the display of the transmission mode cannot be individually optimized, which causes a problem that it is difficult to display in color or the display becomes blurred. It was

The present invention has been made in order to solve the above problems, and an object of the present invention is to provide a liquid crystal display device which is excellent in mass productivity and is capable of excellent display regardless of the brightness of ambient light. To provide.

[0006]

A liquid crystal display device according to the present invention has first and second substrates and a liquid crystal layer sandwiched between the first and second substrates. A liquid crystal display device having a plurality of picture element regions defined by a pair of electrodes for applying a voltage to, wherein each of the plurality of picture element regions has a reflection region and a transmission region, wherein the liquid crystal layer comprises: A first polarizing element made of a liquid crystal material having a positive dielectric anisotropy and provided on the side of the first substrate opposite to the liquid crystal layer, and provided on the side of the second substrate opposite to the liquid crystal layer. The second polarizing element and the first polarizing element
A first phase difference compensating element provided between the polarizing element and the liquid crystal layer; and a second phase difference compensating element provided between the second polarizing element and the liquid crystal layer. Layer twist angle θ
_t is 0 ° or more and 90 ° or less, and the retardation Rd and the twist angle θ of the visible light region of the liquid crystal layer in the reflection region are
_t is a range surrounded by the curves represented by the formulas (1) and (2), and the formulas (3) and (4), and 0 ° ≦ θ _t ≦ 5
In the range of 4.3 °, the ranges surrounded by the curves represented by the formulas (5) and (6) and the formulas (7) and (8), respectively, and 54.3 ° <θ _t ≦ 90. In the range of °, it is a range surrounded by the curves represented by the formulas (5) and (8), and the retardation Rd and the twist angle θ _t of the visible light region of the liquid crystal layer in the transmission region are: It is the range surrounded by the curves respectively expressed by the formulas (9) and (10) and the formulas (11) and (12), and each of the above formulas is Rd = −0.0043 · θ _t ² −0.065 · θ _t +1011.8 (1) Rd = −0.0089 · θ _t ² + 0.1379 · θ _t +914.68 (2) Rd = −0.0015 · θ _t ² −0.1612 · _{θ t +737.29 (3) Rd =} -0.0064 · θ t 2 -0.0043 · θ t +640.65 (4) R ^{_{= -0.0178 · θ t 2 +0.2219 ·}} θ t +458.92 (5) Rd = -0.0405 · θ t 2 +0.4045 · θ t +364.05 (6) Rd = 0.0347 · θ _t ² −0.4161 · θ _t +1866.53 (7) Rd = 0.0098 · θ _t ² −0.1912 · θ _t +89.873 (8) Rd = −0.0043 · θ _t ² −0. 065 · θ _t +995.66 (9) Rd = −0.0058 · θ _t ² −0.0202 · θ _t +665.8 (10) Rd = −0.0248 · θ _t ² + 0.6307 · θ _t +439 0.58 (11) Rd = 0.0181 · θ _t ² −0.6662 · θ _t +109.51 (12), which achieves the above object.

In the retardation Rd, when the twist angle θ _t of the reflection area is in the range of 0 ° ≦ θ _t ≦ 54.3 °,
In the range surrounded by the curves represented by the formulas (7) and (8), and the retardation Rd, in the range where the twist angle θ _t of the reflection region is 54.3 ° <θ _t ≦ 90 °, In the range surrounded by the curves represented by the above formulas (5) and (8), and in the range where the twist angle θ _{t of the} transmission region is 0 ° or more and 90 ° or less, the retardation is the above formula ( 11) and the range represented by the curve represented by the above formula (12).

It is preferable that the reflective area and the transmissive area have a liquid crystal layer made of the same liquid crystal material, and the thickness of the liquid crystal layer in the reflective area is smaller than the thickness of the liquid crystal layer in the transmissive area. .

The first retardation compensating element has a first retardation plate, the twist angle θ _{t of the} liquid crystal layer is 0 °, and the retardation Rd of the reflection region is 90 nm ≦ Rd ≦ 18.
7 nm and the retardation Rd of the transmission region is 1
10 nm ≦ Rd ≦ 440 nm, and the retardation Rd of the first retardation plate is 30 nm ≦ Rd ≦ 250n.
It may be in the range of m.

The first phase difference compensating element further has a second phase difference plate, and the retardation Rd of the second phase difference plate.
May be in the range of 220 nm ≦ Rd ≦ 330 nm.

The second retardation compensating element has a third retardation plate, and the retardation Rd of the third retardation plate is 1
The range may be 20 nm ≦ Rd ≦ 150 nm.

The second phase difference compensating element further includes a fourth phase difference compensating element.
The retardation Rd of the fourth retardation plate may be in the range of 240 nm ≦ Rd ≦ 310 nm.

The operation of the present invention will be described below. First, the definitions of terms used in this specification will be described. In the reflective / transmissive dual-use liquid crystal display device, a region where display is performed using transmitted light is referred to as a transmissive region, and a region where display is performed using reflected light is referred to as a reflective region. The transmissive region and the reflective region each include a transmissive electrode region and a reflective electrode region formed on the substrate, and a liquid crystal layer sandwiched between the pair of substrates. The transmissive electrode region and the reflective electrode region on the substrate respectively define the two-dimensional spread of the reflective region and the transmissive region. The transparent electrode area is typically defined by a transparent electrode. The reflective electrode region can be defined by the reflective electrode or a combination of transparent and reflective electrodes.

The liquid crystal display device of the present invention has a reflective region and a transmissive region for each picture element region. Therefore, the retardation of the liquid crystal layer can be optimized independently for the reflective area and the transmissive area. Specifically, the retardation of the liquid crystal layer in the reflective region is calculated by the formula (1), the formula (2), and the formula (3).
And equation (4), equation (5) and equation (6), equation (7) and equation (8)
Are set in a range surrounded by the curves respectively represented by (in FIG. 5, the hatched area (including the double-hatched area)), and the retardation of the liquid crystal layer in the transmissive area is expressed by equations (9), (10), and (11). ) And Expression (12), the brightness (reflectance) of the reflective area is 70% or more, and the transmissive area is set to (hatched area (including double hatched area) in FIG. 6). Brightness (transmittance)
Can be 30% or more.

It is preferable that these retardation conditions are satisfied with respect to a wavelength of 550 nm which is the central wavelength of visible light (high visibility). Further, it is more preferable to satisfy all wavelength ranges of visible light (400 nm or more and 800 nm or less).

Further, the twist angle θ _t is 0 ° to 90 °.
Therefore, the rubbing treatment can be performed once to make the twist angles of both the reflective region and the transmissive region having different thicknesses of the liquid crystal layer the same. In order to make the twist angles of the reflective region and the transmissive region different, it is necessary to rub the two regions separately, which causes a problem that the manufacturing process becomes complicated.

Furthermore, the retardation Rd is, in a range twist angle theta _t is 0 ° ≦ θ _t ≦ 54.3 ° in the reflection area, surrounded by a curve represented by the above formula (7) and the formula (8) Range and the retardation Rd
However, the twist angle θ _t of the reflection area is 54.3 ° <θ _t ≦ 90.
In the range of 0 °, the retardation is set to a range surrounded by the curves represented by the formulas (5) and (8) (double hatched region in FIG. 5), and the twist angle θ _t of the transmission region is 0 °. By setting the retardation within the range of 90 ° or less to the range surrounded by the curves represented by the formulas (11) and (12) (double hatching region in FIG. 6), the reflection region and the The retardation of the liquid crystal layer in the transmissive region becomes 0, and if black display is set at this time, good black display can be realized at the same time by applying the same voltage to the reflective region and the transmissive region. Further, the above conditions are the conditions for realizing white display, and the white region where the retardation is closest to 0 (the first peak from the low retardation side in FIGS. 7 and 8).
Corresponding to the selection, the gradation display can be performed well. That is, in the intermediate state in which the white display is changed to the black display, the brightness (reflectance and transmittance) is monotonically decreased, so that good gradation display can be obtained. If a white region is set to the second peak from the low retardation side in FIGS. 7 and 8 as a condition for realizing white display, the first peak exists in the halftone display region, and a good floor is obtained. It cannot be displayed as a key.

When the liquid crystal layers in the transmissive region and the reflective region are made of the same liquid crystal material, the structure and manufacturing method are simpler than the case where the kind of liquid crystal material is changed. In order to set different retardations for the reflective and transmissive areas,
It is effective to change the thickness of the liquid crystal layer in the reflective area and the transmissive area. Further, in order to match the optical path lengths for light contributing to display in the reflective region and the transmissive region, it is effective to make the liquid crystal layer in the transmissive region thicker than the liquid crystal layer in the reflective region. Most preferably, the thickness of the liquid crystal layer in the transmissive region is twice the thickness of the liquid crystal layer in the reflective region.

The first retardation compensating element has the first retardation plate, the twist angle θ _t of the liquid crystal layer is 0 °, and the retardation Rd of the reflection region is 90 nm ≦ Rd ≦ 187 nm,
Retardation Rd in the transmission region is 110 nm ≦ Rd ≦ 4
When the thickness is 40 nm and the retardation Rd of the first retardation plate is in the range of 30 nm ≦ Rd ≦ 250 nm, it is possible to realize bright display of the reflective region and the normally white mode having a high contrast ratio.

The first retardation compensating element has a second retardation plate in addition to the first retardation plate, and if the retardation Rd of the second retardation plate is in the range of 220 nm ≦ Rd ≦ 330 nm. Since the wavelength characteristics of the reflection region are alleviated, it is possible to perform display with higher contrast.

The second retardation compensating element has a third retardation plate, and the retardation Rd of the third retardation plate is 120 nm.
Within the range of ≦ Rd ≦ 150 nm, the dark region is optimized even in the transmissive region, so that display with higher contrast can be performed.

The second retardation compensating element has a fourth retardation plate in addition to the third retardation plate, and the retardation Rd of the fourth retardation plate should be in the range of 240 nm ≦ Rd ≦ 310 nm. In this case, since the wavelength characteristic of the transmission region is relaxed, it is possible to perform display with higher contrast.

[0023]

1A is a partial cross-sectional view of a transflective liquid crystal display device 100 according to Embodiment 1 of the present invention. Further, FIG. 1B shows a top view of the active matrix substrate 70 of the liquid crystal display device 100. Figure 1A is Figure 1B
Corresponds to a cross-sectional view taken along the line AA in FIG.

As shown in FIG. 1A, the liquid crystal display device 10
Reference numeral 0 has an active matrix substrate 70, a counter substrate (color filter substrate) 160, and a liquid crystal layer 140 sandwiched between them. On the surfaces of the active matrix substrate 70 and the counter substrate 160 opposite to the liquid crystal layer 140, retardation compensation elements (retardation plate, retardation film, and a laminated body thereof) 170 and 18 are provided, respectively.
0 is provided. Further, polarizing elements (polarizing plates, polarizing films, etc.) 172 and 182 are provided outside the phase difference compensating elements 170 and 180 so as to sandwich them.

As shown in FIGS. 1A and 1B, a reflective / transmissive active matrix substrate 70 has a plurality of gate bus lines 72 as scanning lines and signal lines as scanning lines on a glass substrate 61 which is an insulating substrate. Source bus lines 74 are alternately provided. In the rectangular region surrounded by each gate bus line 72 and each source bus line 74, a reflective electrode 69 made of a material having high light reflection efficiency (for example, Al, Ag, Ta).
Aside from that, a material with high light transmission efficiency (for example, I
A transparent electrode 68 made of TO) is arranged, and the reflective electrode 69 and the transparent electrode 68 form a pixel electrode. Under the reflective electrode 69, a high-height convex portion 64a, a low-height convex portion 64b, and a polymer resin film 65 formed thereon are formed, and the surface of the reflective electrode 69 is continuous. It is wavy. The height of the convex portion may be one type.

The reflective electrode 69 is connected to the drain electrode 76 of the TFT 71 through a contact hole 79. TFT
71 is formed of a semiconductor layer 77 deposited on the gate insulating film 61a covering the gate electrode 73. The gate electrode 73 and the source electrode 75 of the TFT 71 are formed by branching from the gate bus line 72 and the source bus line 74, respectively.

Opposing substrate (color filter substrate) 160
The color filter layer 164 and the transparent electrode 166 made of ITO or the like are formed on the glass substrate 162 which is an insulating substrate. Liquid crystal layer 140 of both substrates 70 and 160
A horizontal alignment film (not shown) is formed on the side surface.
After applying the alignment film, the alignment treatment is performed by rubbing or the like so as to obtain a desired twist angle. In the liquid crystal layer 140,
A nematic liquid crystal material having a positive dielectric anisotropy is used.
The liquid crystal molecules of the liquid crystal layer 140 are processed to 0.1 with respect to the substrate surface by an alignment treatment such as rubbing on a horizontal alignment film.
It has a tilt angle of about 5 ° to 5 °. The liquid crystal molecules are aligned parallel to the substrate surface when no voltage is applied, and are tilted in the direction normal to the substrate surface when a voltage is applied.

The picture element, which is the minimum display unit of the liquid crystal display device 100, is a reflective area 120R defined by the reflective electrode 69 and a transmissive area 1 defined by the transparent electrode 68.
With 20T. The thickness of the liquid crystal layer 140 is equal to that of the reflective region 1.
It is dr in 20R and d in the transmissive region 120T.
t (dt> dr). This is to make the optical path lengths of the light (reflected light in the reflective region and transmitted light in the transmissive region) that contribute to display substantially equal. dt = 2dr is preferable, but it may be set as appropriate in relation to the display characteristics. It is sufficient that at least dt> dr. Typically, dt is about 4
At ˜6 μm, dr is about 2-3 μm. That is, in the pixel area of the active matrix substrate 70, about 2-3
A step of μm is formed. When the reflective electrode 69 has irregularities as shown in the figure, the average value is dr.
And it is sufficient. As described above, in the reflective / transmissive liquid crystal display device 100, regions having different thicknesses of the liquid crystal layer 140 (a reflective region and a transmissive region) are formed. In this example, the reflective electrode region 120R and the transmissive electrode region 120 having different heights are formed on the surface of the active matrix substrate 70 on the liquid crystal side.
With T and.

When manufacturing a normally black mode liquid crystal display device in the horizontal alignment mode, it is often difficult to control the cell gap. Therefore, in this embodiment,
Normally white is used to ensure a wide process margin.

Details of the display principle in the normally white mode of the liquid crystal display device 100 shown in FIG. 1A are shown in FIGS.
Also, description will be made with reference to FIG. The phase difference compensating elements 170 and 180 are color compensating phase difference plates (1/2
A case will be described in which wave plates) 170a and 180b and phase difference plates (1/4 wave plate) 170b and 180a for converting linearly polarized light into circularly polarized light are provided. 1/2 wave plate 17
0a and 180b are for suppressing the coloring of the display, and may be omitted if the coloring is allowed to some extent, and two sheets may be used for realizing an achromatic display. These may be set appropriately according to the application of the liquid crystal display device. When the liquid crystal is twisted, if the thickness of the liquid crystal layer is different between the transmissive region and the reflective region, disclination is likely to occur at the step portion that is the boundary between these regions. Therefore, horizontal orientation with a twist angle of 0 ° is most preferable.

FIG. 2 shows the polarization state of light in each layer when white is displayed in the reflection area 120R.

The incident light is converted into linearly polarized light by the polarizing plate 172 and is incident on the ½ wavelength plate 170a for color compensation. 1
In the / 2 wave plate 170a, the polarization state of the linearly polarized light changes without changing the polarization state. After that, the linearly polarized light that has entered the quarter-wave plate 170b becomes circularly polarized light, and the liquid crystal layer 14
It is incident on 0. Since the effective phase difference of the liquid crystal layer 140 in the white display state is adjusted to 1/4 wavelength, the incident circularly polarized light becomes linearly polarized light. The linearly polarized light transmitted through the liquid crystal layer 140 is reflected by the reflection plate (reflection electrode 69) while maintaining its polarization state, and is incident on the liquid crystal layer 140 again. Liquid crystal layer 1
The linearly polarized light that has passed through 40 again becomes circularly polarized light, and
It is converted into linearly polarized light by the quarter wave plate 170b. Then, after passing through the half-wave plate 170a, a polarizing plate 172
Is emitted through.

FIG. 3 shows the polarization state of light in each layer when black is displayed in the reflection area 120R.

The incident light is converted into linearly polarized light by the polarizing plate 172 and is incident on the ½ wavelength plate 170a for color compensation. 1
In the / 2 wave plate 170a, the polarization state does not change, but the direction of the polarization axis of linearly polarized light changes. Then 1/4 wave plate 1
The linearly polarized light incident on 70b becomes circularly polarized light and the liquid crystal layer 140
Incident on. Since the voltage for black display is applied, the effective phase difference of the liquid crystal layer 140 is adjusted to 0. Therefore, the incident circularly polarized light passes as it is as circularly polarized light.
The circularly polarized light transmitted through the liquid crystal layer 140 is reflected by the reflection plate 69 while maintaining its polarization state, and is incident on the liquid crystal layer 140 again. Circularly polarized light passes through the liquid crystal layer 140 again while maintaining the polarization state, and is converted into linearly polarized light by the quarter-wave plate 170b. At this time, the polarization direction of the linearly polarized light is rotated by 90 degrees compared with the white display state. 1/2 wave plate 17
The linearly polarized light passing through 0a is absorbed by the polarizing plate 172 and is not emitted from the liquid crystal display device.

FIG. 4 shows the polarization state of light in each layer when white display and black display are performed in the transmissive region 120T. In the design of the reflective / transmissive liquid crystal display device, the arrangement of the polarizing plate 172, the retardation of the phase difference compensation elements 170a and 170b, and the arrangement of the slow axis are determined with respect to the reflective region 120R, and then the transmissive region 120T is determined. On the other hand, the retardation and the arrangement of the slow axes of the phase difference compensation elements 180a and 180b and the arrangement of the polarizing plate 182 are determined. In FIG. 4, the upper polarizing plate 1 provided on the observer side of the liquid crystal display device 100 is reflected by reflecting the procedure of this design.
The polarization state in each layer when light is incident from 72 is shown. Note that the light used for displaying the transmissive region 120T is actually the light from the backlight, and the lower polarizing plate 182 is used.
The change in the polarization state of the light incident from the lower polarizing plate 182 in each layer is equivalent to the change shown in FIG.

The basic structure of the transmissive area 120T is the same as that of the reflective area 120R, and is arranged so as to be a mirror-symmetrical image with respect to the reflection plate 69. The change in the polarization state and polarization direction of each layer is basically the same as that described for the reflective region. The optical retardation of the liquid crystal layer 140 is adjusted to ½ wavelength (twice the retardation of the reflection region 120R).

As described above, in the case where the reflective region 120R and the transmissive region 120T are used together for display, in order to realize the maximum reflective efficiency and transmissive efficiency, the liquid crystal layer 140 is used.
Optical retardation of 1/4 in the reflection area 120R
A wavelength or more, a half wavelength or more in the transmissive region 120T, respectively, and a difference between the retardation when a voltage is applied for black display and the retardation when no voltage is applied, a quarter wavelength or more in the reflective region, It is necessary that the wavelength is ½ wavelength or more in the transmission region.

In order to realize the above-mentioned optical retardation in the reflection area 120R and the transmission area 120T, various forms can be used. For example, a liquid crystal layer with homogeneous alignment, a liquid crystal layer with twist alignment, a liquid crystal layer with hybrid alignment, or the like can be used.

If a liquid crystal display mode in which liquid crystal molecules (at least a part of the liquid crystal molecules) are aligned horizontally with respect to the substrate surface when no voltage is applied, a problem that sufficient black display cannot be realized may occur. is there. This problem will be described below.

When a sufficiently high voltage is applied between the electrodes facing each other across the liquid crystal layer, the liquid crystal molecules rise almost perpendicularly to the surface of the substrate (parallel to the electric field), and the optical retardation of the liquid crystal layer 140 is almost equal. It becomes 0. However, since the applied voltage during black display is finite (typically about 5 V), the orientation of the liquid crystal molecules cannot be changed sufficiently, and the liquid crystal layer 140 is not changed.
A finite optical retardation remains. In particular, liquid crystal molecules in the vicinity of the surface of the alignment film do not vertically align at a voltage applied for driving due to the anchoring effect of the alignment film, and the retardation of the liquid crystal layer 140 does not become zero.
As a result, when a liquid crystal display mode in which liquid crystal molecules (at least some of the liquid crystal molecules) are aligned in the horizontal direction with respect to the substrate surface when no voltage is applied, sufficient black display cannot be realized, and as a result, sufficient contrast cannot be obtained. I can't get it.

In order to solve this problem, the reflection area 1
For 20R, it is effective to adjust the optical retardation of the quarter-wave plate so that black display is possible even in a practical voltage range. Specifically, when the retardation of α remains in the liquid crystal layer 140, 1 /
By making the slow axis of the four-wave plate 170b substantially coincide with the direction of the effective slow axis of the liquid crystal layer 140 and setting the optical retardation of the quarter-wave plate 170b to (λ / 4−α),
Together with the optical retardation that remains in the liquid crystal layer 140 when a voltage is applied, the entire liquid crystal cell is allowed to satisfy the ¼ wavelength condition. As another method, the slow axis of the quarter-wave plate 170b is orthogonal to the direction of the effective slow axis of the liquid crystal layer 140, and the optical retardation of the quarter-wave plate 170b is (λ / 4 + α). By doing so, when the voltage is applied
Cancel the optical retardation remaining at 0, and
It is possible to satisfy the wavelength condition.

Regarding the transmissive region 120T, the reflective region 1
After setting the configuration of 20R as described above, the transparent region 120
1/4 of the major axis or minor axis of the elliptically polarized light emitted from T
The elliptically polarized light is converted into linearly polarized light by aligning it with the optical axis (slow axis) of the wave plate 180b, and the polarization axis of the polarizing plate 182 is set in the direction orthogonal to the polarization axis of this linearly polarized light. Can solve the problem.

Alternatively, when the β retardation remains in the transmission region 120T, the quarter-wave plate 18 is used.
By making the slow axis of 0a substantially coincide with the direction of the effective slow axis of the liquid crystal layer 140 and setting the optical retardation of the quarter-wave plate 180a to (λ / 4- (β-α)). In addition to the optical retardation that remains in the liquid crystal layer 140 when a voltage is applied, the 1/2 wavelength condition can be satisfied. Alternatively, the slow axis of the quarter-wave plate 180a is made orthogonal to the direction of the effective slow axis of the liquid crystal layer 140, and the quarter-wave plate 180a
By setting the optical retardation of (λ / 4 + (β−α)) to cancel the optical retardation remaining in the liquid crystal layer 140 when a voltage is applied, the 1/2 wavelength condition may be satisfied.

Next, the display characteristics of the transflective liquid crystal display device of the present invention will be described. In the liquid crystal display device 100 shown in FIG. 1, the phase difference compensation elements 170 and 1
The relationship between the twist angle θ _t of the liquid crystal layer 140 and the retardation when 80 is a quarter-wave plate is shown in FIG.
FIG. 5 shows 0R and FIG. 6 shows transmissive region 120T.

For the reflection area, the twist angle θ _t is
In the range of 0 ° ≦ θ _t ≦ 90 °, the utilization efficiency of 70% or more can be obtained within the hatched range of FIG. The hatched area in FIG. 5 indicates the retardation Rd (Rd =
Δn · d; birefringence Δn of the liquid crystal layer, thickness d) of the liquid crystal layer in each region are curves represented by equations (1) and (2), and equations (3) and (4), respectively. In the range of 0 ° ≦ θ _t ≦ 54.3 °, the curves are respectively surrounded by the equations (5) and (6) and the equations (7) and (8). Range, and 54.3 ° <
In the range of θ _t ≦ 90 °, it is the range surrounded by the curves represented by the formulas (5) and (8). Rd = −0.0043 · θ _t ² −0.065 · θ _t +1011.8 (1) Rd = −0.0089 · θ _t ² + 0.1379 · θ _t +914.68 (2) Rd = −0. ^{_{0015 · θ t 2 -0.1612 · θ}} t +737.29 (3) Rd = -0.0064 · θ t 2 -0.0043 · θ t +640.65 (4) Rd = -0.0178 · θ t ² + 0.2219 · θ _t +458.92 (5) Rd = −0.0405 · θ _t ² + 0.4045 · θ _t +364.05 (6) Rd = 0.0347 · θ _t ² −0.4161 · θ _t +1866.53 (7) Rd = 0.0098 · θ _t ² −0.1912 · θ _t +89.873 (8) On the other hand, for the transmissive region 120T, the twist angle θ
_{When t} is in the range of 0 ° ≦ θ _t ≦ 90 ° and is in the hatched range of FIG. 6, a utilization efficiency of 30% or more can be obtained. The hatched area in FIG. 6 indicates the retardation Rd.
Is the range surrounded by the curves represented by the equations (9) and (10) and the equations (11) and (12), respectively. Rd = −0.0043 · θ _t ² −0.065 · θ _t +995.66 (9) Rd = −0.0058 · θ _t ² −0.0202 · θ _t +665.8 (10) Rd = −0 0.0248 · θ _t ² + 0.6307 · θ _t +439.58 (11) Rd = 0.0181 · θ _t ² −0.6662 · θ _t +109.51 (12) Sufficient for the liquid crystal layer under the above conditions. By applying voltage, the retardation becomes 0, and dark display with high contrast is realized.

Further, the retardation Rd is the range surrounded by the curves represented by the formulas (7) and (8) in the range where the twist angle θ _t of the reflection region is 0 ° ≦ θ _t ≦ 54.3 °. , And the retardation Rd in the range where the twist angle θ _t of the reflection region is 54.3 ° <θ _t ≦ 90 °,
In the range surrounded by the curves expressed by the formulas (5) and (8) (double hatched region in FIG. 5) and in the range where the twist angle θ _t of the transmission region is 0 ° or more and 90 ° or less By setting the retardation Rd to a range surrounded by the curves expressed by the formulas (11) and (12) (double hatched region in FIG. 6), the liquid crystal layers in the reflective region and the transmissive region are applied when voltage is applied. Retardation becomes 0,
At this time, if black display is set, good black display can be realized at the same time by applying the same voltage to the reflective region and the transmissive region.

The influence of the retardation on the reflectance and the transmittance at each twist angle θ _t is shown in FIGS. 7 and 8, respectively. FIGS. 5 and 6 described above show regions in which the reflectance is 70% or more and the transmittance is 30% or more in FIGS. 7 and 8, respectively.

Furthermore, the above conditions correspond to the selection of the first peak from the low retardation side in FIGS. 7 and 8 as the white region where the retardation is closest to 0, as a condition for realizing white display. Therefore, gradation display can be performed well. That is, the brightness (reflectance and transmittance) in the intermediate state where white display changes to black display
Is monotonically decreased, so that good gradation display can be obtained. If white display is performed by using the second peak from the low retardation side in FIGS. 7 and 8 as a condition for realizing white display, the first peak exists in the halftone display region, and a good floor is obtained. It cannot be displayed as a key.

Similarly, a range where the reflectance is 90% or more (FIG. 9), a region where the transmittance is 50% or more (FIG. 10), and a region where the transmittance is 70% or more (FIG. 11) are 90%. % Or more area (FIG. 12) is obtained. The formulas of the curves that define the respective areas are shown below. Reflectance 90% or more Rd = −0.0043 · θ _t ² −0.065 · θ _t +987.57 (13) Rd = −0.0074 · θ _t ² + 0.049 · θ _t +938.59 (14) Rd = −0.0043 · θ _t ² + 0.0282 · θ _t +712.36 (15) Rd = −0.0061 · θ _t ² + 0.0564 · θ _t +662.94 (16) Rd = −0.0192 ^{_{· θ t 2 +0.1721 · θ t}} +435.68 (17) Rd = -0.0347 · θ t 2 +0.5085 · θ t +387.16 (18) Rd = 0.0217 · θ t 2 -0. 1589 · θ _t +162.09 (19) The intersection of the equations (18) and (19) is the twist angle θ _t 69.5 ° Rd = 0.0167 · θ _t ² −0.4884 · θ _t +115.56 ( 20) Transmittance 50% or more Rd = −0.0046 · θ _t ² −0.0 913 · θ _t +959.69 (21) Rd = −0.0037 · θ _t ² −0.076 · θ _t +692.65 (22) Rd = −0.0308 · θ _t ² + 0.5971 · θ _t +407 .2 (23) Rd = 0.0246 · θ _t ² −0.7079 · θ _t +148.65 (24) The intersection point of the equations (23) and (24) is the twist angle θ _t 81.0 ° and the transmittance 70. % Or more Rd = −0.0074 · θ _t ² + 0.049 · θ _t +922.41 (25) Rd = −0.0043 · θ _t ² + 0.0282 · θ _t +728.54 (26) Rd = −0 .0419 · θ _t ² + 0.5461 · θ _t +371.27 (27) Rd = 0.0347 · θ _t ² −0.5085 · θ _t +179.14 (28) Equations (27) and (28) The intersection point is a twist angle θ _t 57.5 ° and a transmittance of 90% or more Rd = −0.012 7 · θ _t ² + 0.1931 · θ _t +877.69 (29) Rd = 0.0048 · θ _t ² −0.4527 · θ _t +779.34 (30) Rd = −0.0809 · θ _t ² +0 .809 · θ _t +323.6 (31) Rd = 0.0404 · θ _t ² −0.4045 · θ _t +226.52 (32) The intersection of the equations (31) and (32) is the twist angle θ _t 34. 0.0 ° Furthermore, by setting the retardation and twist angle of the liquid crystal layer in the double-hatched areas in FIGS. 9, 10, 11 and 12, the brightness monotonously decreases in the intermediate state where white display changes to black display. Therefore, good gradation display can be obtained.

In the above description, the twist orientation has been explained, but the same can be considered for the hybrid orientation. In the hybrid orientation, one substrate is horizontally oriented and the other substrate is vertically oriented. The optimum retardation at this time may be considered when the twist angle θ _t is 0 ° in FIGS. 5 and 6, and the characteristics at that time are twisted. The characteristics are the same as in the horizontal orientation where the angle θ _t is 0 °.

As the liquid crystal material of the liquid crystal layer 140, a liquid crystal material having a refractive index anisotropy Δn = 0.06 and exhibiting a positive dielectric anisotropy was used.

In the liquid crystal display device 100 shown in FIG. 1, the cell gap d of the liquid crystal layer 140 in the transmissive region 120T.
t = about 5.50 μm, the liquid crystal layer 140 in the reflective region 120R
Cell gap dr = about 3.0 μm, twist angle θ _t =
When a liquid crystal material having a positive dielectric anisotropy having a refractive index anisotropy Δn = 0.06 of the liquid crystal layer 140 of 0 ° is used,
FIG. 13 shows the voltage-transmittance characteristic and the voltage-reflectance characteristic at the time of vertical incidence and vertical light reception.

In FIG. 13, the spectral transmission when vertically incident on the air and at the time of vertical light reception is 1. In this case, the reflection area 1
Since the liquid crystal layer 140 has a residual retardation of about α = 30 nm when the applied voltage is 5 V at 20R, the retardation of the retardation compensation element 170b is set to 110 nm and the slow axis of the retardation compensation element 170b is set to the slow retardation of the liquid crystal layer 140. The phase difference compensating element 17 is arranged so that linearly polarized light is incident in a direction in which it coincides with the phase axis and is rotated 45 ° with respect to this slow axis.
The slow axis of 0a and the polarization axis of the polarizing plate 172 were set. The retardation of the phase difference compensating element 180a is 140 nm, the direction of the optical axis is matched with the long axis of the elliptically polarized light emitted from the liquid crystal layer 140, and the converted linearly polarized light is converted in the polarization direction by the phase difference compensating element 180b. The polarization axis of the polarizing plate 182 was set in the direction orthogonal to the polarization axis of this linearly polarized light.

FIG. 14 shows the spectral brightness (reflectance and transmittance) characteristics of the obtained transflective liquid crystal display device in the white display and black display states. It can be seen from FIG. 14 that a sufficient contrast ratio is obtained in the entire wavelength range of 400 nm to 700 nm in the white display in which no voltage is applied to the liquid crystal layer 140 and the black display in which a voltage of 5 V is applied. From this, it is understood that this display system has high light utilization efficiency and is suitable for a reflective / transmissive liquid crystal display device.

Therefore, when the ambient light is dark, the backlight is used as a transmissive liquid crystal display device which displays by utilizing the light transmitted through the transparent region 120T. When the ambient light is bright, the reflective region 120R is used. It becomes possible to display as a reflection type liquid crystal display device which displays by utilizing the reflected light in. Further, even when the display is performed in the transmissive mode, the reflective region displays the reflective mode, so that it is possible to suppress the phenomenon that the ambient light is reflected on the screen and is difficult to see, which is seen in the conventional transmissive liquid crystal display device. To be done.

Therefore, when the ambient light is dark on one panel, the backlight is used, and when the ambient light is bright, the ambient light is used without using the backlight, or both the backlight and the reflected light are used. It can be used as a reflective / transmissive liquid crystal display device capable of displaying even when used.

Therefore, when ambient light is brighter than the conventional transmissive liquid crystal display device, the power consumption is low because the backlight is not used, and when the ambient light is dark, the backlight is used, so that the conventional reflection is achieved. It is possible to overcome the drawback that a sufficient display cannot be obtained when the ambient light is dark as in the case of a liquid crystal display device.

Although the case of white display and black display has been described, color display can be performed by providing color filters of respective colors at corresponding positions of the reflection area and the transmission area.

It is desirable that the reflectivity and the transmissive part have substantially the same dependency of the applied voltage on the applied voltage (so-called γ characteristic).

Next, the cell gap dr of the liquid crystal layer 140 in the reflection region 120R = about 3.0 μm, the twist angle θ _t = 0 ° of the liquid crystal layer, and the refractive index anisotropy Δn = 0.0 of the liquid crystal layer 140.
1/4 wavelength plate 170b in the reflection region 120R when a liquid crystal material having a positive dielectric constant anisotropy of 6 is used.
FIG. 15 shows the relationship between the retardation Rd and the reflectance in FIG.
Shown in (a) and (b). FIG. 15A shows a case where the slow axis of the quarter-wave plate 170b is provided in a direction parallel to the slow axis of the liquid crystal layer 140, and FIG.
The result when the slow axis of the wave plate 170b is provided in the direction perpendicular to the slow axis of the liquid crystal layer 140 is shown. In addition, this study is performed for a wavelength of 550 nm that maximizes the luminous sensitivity to light.

In a normally white liquid crystal display device, it is said that the brightness when the voltage is OFF is preferably about 50% or more of the ideal reflectance. Therefore, from FIGS. 15A and 15B, the reflection-side retardation plate 1
The retardation Rd of 70b is 30 nm or more and 250 nm.
It is understood that the following range is preferable. The reason for this will be described below.

FIG. 17 shows the relationship between the set angle V of the slow axis of the retardation plate and the slow axis of the liquid crystal phase, and the retardation and brightness (reflectance) of the retardation plate. There is an upward convex curve with an ideal reflectance at the peak (100%) for each set temperature (0 ≦ V ≦ 90), and the curve moves to the right ( Shift in the positive direction of the X-axis). The lower limit of the optimum retardation is determined in the state of being arranged in parallel (V = 0), and the upper limit of the optimum retardation is determined in the state of being arranged vertically (V = 90). The results of detailed examinations for each are shown in FIGS. 15 (a) and 15 (b).

That is, the retardation of the retardation plate is 3
Within the range of 0 nm or more and 250 nm or less, excellent white display and black display are possible by setting the slow axis of the retardation plate and the slow axis of the liquid crystal phase at appropriate angles. In other words, if the retardation of the retardation film is 30 nm or less, or if the retardation of the retardation film is 250 nm or more, good white display cannot be performed no matter how the set angle V is adjusted.

Subsequently, in order to improve the contrast ratio, it is preferable to further provide a retardation plate.
The two-wave plate 170a is used as the retardation plate 170b and the polarizing plate 1 described above.
Insert between 72 and. 1 / in the reflective area
The relationship between the retardation Rd of the two-wave plate 170a and the contrast ratio is shown in FIG. The contrast ratio was examined for wavelengths of 380 nm to 780 nm, the visibility was taken into consideration by multiplying the result by the visibility curve, and the result of FIG. 15C was obtained.

Considering the visibility, it is preferable that the reflective liquid crystal display device has a contrast ratio of about 10 or more. Therefore, it is understood from FIG. 15C that the retardation Rd of the half-wave plate 170a is preferably in the range of 220 nm to 330 nm.

After the reflection area 120R was set preferentially as described above, the display quality of the liquid crystal display device in the transmission area 120T was further examined. Cell gap dt = about 5.5μm of the liquid crystal layer 140 in the transmissive area 120T, a twist angle of the liquid crystal layer θ _t = 0 °, the liquid crystal layer 1
Quarter-wave plate 1 when a liquid crystal material having a positive dielectric anisotropy having a refractive index anisotropy Δn = 0.06 of 40 is used.
The relationship between the retardation Rd and the contrast ratio of 80a (FIG. 4) is shown in FIG. 16 (a). Note that the calculation result of the contrast ratio shown in FIG.
It carried out like 20R.

Considering the visibility, the transmissive liquid crystal display device preferably has a contrast ratio of about 100 or more. Therefore, from FIG. 16A, the phase difference plate 180
It can be seen that the retardation of a is preferably set to 120 nm or more and 150 nm or less.

In order to further improve the contrast ratio in the transmission region 120T, between the quarter wavelength plate 180a and the polarizing plate 182 (the polarization axis of the linearly polarized light emitted from the quarter wavelength plate 180a and the polarizing plate 182). Between the polarization axis of
It is preferable to insert a half-wave plate 180b for color compensation. Retardation Rd of the half-wave plate 180b
From FIG. 16 (b) showing the relationship with the contrast ratio, the retardation of the half-wave plate 180b is 240 nm or more and 310 n or more so that the contrast ratio satisfies about 100 or more.
It can be seen that it is preferable to set m or less.

As described above, when the twist angle of the liquid crystal molecules is 0 °, disclination is unlikely to occur even if there is a difference in cell thickness in the pixel region, and the alignment of the liquid crystal molecules becomes good. In this way, when the twist angle of the liquid crystal layer is 0 °, the retardation of the liquid crystal layer as described above and
By setting the retardations of the four types of retardation films 170a, 170b, 180a, and 180b, it is possible to maximize the respective display characteristics of the reflection mode and the transmission mode of the liquid crystal display device. In addition, the priority order that contributes to the display characteristics of the above-mentioned four types of retardation plates is the retardation plate 170.
b, 170a, 180a, 180b, and the phase difference plate 1
70b is the most important component. As can be seen from the above priority order, it is preferable to preferentially improve the display in the reflection mode.

[0070]

As described above, high contrast display is possible in a display device having a reflection mode and a transmission mode. Further, when the reflection mode and the transmission mode are used together, black display is possible at the same time, and even when both are used together, high contrast display is possible. Further, by changing the applied voltage and changing the retardation value of the liquid crystal layer, gradation display from white display to black display becomes possible.
Further, since the retardations of the liquid crystal layers in the reflective area and the transmissive area can be optimized independently, it becomes possible to drive the liquid crystal layers in the transmissive area and the reflective area at the same voltage at the same time. Therefore, the display in the reflection mode and the display in the transmission mode can be performed by the same drive without being affected by the surrounding environment. Therefore, it is not necessary to switch the display mode according to the surrounding environment.

[Brief description of drawings]

FIG. 1A is a partial cross-sectional view of a reflective / transmissive liquid crystal display device 100 according to a first embodiment.

FIG. 1B is a top view of an active matrix substrate 70 of the liquid crystal display device 100.

FIG. 2 is a diagram showing a polarization state of light in each layer when white is displayed in a reflection area 120R.

FIG. 3 is a diagram showing a polarization state of light in each layer when black is displayed in a reflection area 120R.

FIG. 4 is a diagram showing a polarization state of light in each layer when a display is performed in a transmissive region 120T.

FIG. 5 is a diagram showing a relationship between a twist angle and a retardation of a liquid crystal layer 140 (a region having a reflectance of 70% or more) in a reflective region 120R.

FIG. 6 is a diagram showing a relationship between a twist angle and a retardation of a liquid crystal layer 140 (a region having a transmittance of 30% or more) in a transmissive region 120T.

FIG. 7 is a graph showing the influence of retardation on reflectance at various twist angles.

FIG. 8 is a graph showing the effect of retardation on the transmittance at various twist angles.

FIG. 9 is a diagram showing a relationship between a twist angle and a retardation of a liquid crystal layer 140 (a region where a reflectance is 90% or more) in a reflection region 120R.

FIG. 10 shows the relationship between the twist angle and the retardation of the liquid crystal layer 140 (transmissivity is 50%) for the transmissive region 120T.
It is a figure showing the above-mentioned field.

FIG. 11 shows the relationship between the twist angle and the retardation of the liquid crystal layer 140 in the transmissive region 120T (the transmissivity is 70%).
It is a figure showing the above-mentioned field.

FIG. 12 shows the relationship between the twist angle of the liquid crystal layer 140 and the retardation of the transmissive region 120T (the transmissivity is 90%).
It is a figure showing the above-mentioned field.

FIG. 13 is a diagram showing a voltage-transmittance characteristic and a voltage-reflectance characteristic of the liquid crystal display device according to the embodiment at the time of vertical incidence and vertical light reception.

FIG. 14 is a graph showing the spectral luminance (reflectance and transmittance) characteristics of the liquid crystal display device of the embodiment in white display and black display states.

15 (a) and 15 (b) show 1 in a reflection area.
It is a graph which shows the result of the retardation Rd of / 4 wavelength plate 170b vs. reflectance, (c) is 1 in a reflection area.
It is a graph which shows the relationship of the retardation Rd of 1/2 wavelength plate 170a with respect to a contrast ratio.

FIG. 16A is a quarter wavelength plate 1 in a transmission region.
The relationship between the retardation Rd of 80a and the contrast ratio is shown, (b) shows the half-wave plate 180 in the transmission region.
It is a graph which shows the relationship of the retardation Rd of b to contrast ratio.

FIG. 17 is a graph showing the relationship between the set angle V of the slow axis of the retardation plate and the slow axis of the liquid crystal phase, and the retardation and brightness (reflectance) of the retardation plate.

[Explanation of symbols]

68 Transparent electrode 69 Reflective electrode 70 Active matrix substrate 100 liquid crystal display 120R reflective area 120T transparent area 140 liquid crystal layer 160 Counter substrate (color filter substrate) 170, 180 Phase difference compensating element 172, 182 Polarizing plate

Continued front page    (72) Inventor Masumi Kubo             22-22 Nagaikecho, Abeno-ku, Osaka-shi, Osaka             Inside the company F-term (reference) 2H088 GA02 HA08 HA16 HA17 HA18                       HA21 HA28 JA05 JA11 JA12                       KA07 KA11 KA14 KA26 MA02                       MA06 MA20                 2H089 HA07 QA16 RA05 RA09 SA04                       SA07 SA10 SA16 TA09 TA14                       TA15 TA17 TA18                 2H091 FA08X FA08Z FA11X FA11Z                       FA12X FA12Z FA14Y FA14Z                       FA16Y FA16Z FA31Y FA41Z                       GA13 HA07 JA03 KA02 KA03                       KA05 KA10 LA12 LA17 LA30

Claims (2)

[Claims] 1. A liquid crystal layer having first and second substrates and a liquid crystal layer sandwiched between the first substrate and the second substrate, and defined by a pair of electrodes for applying a voltage to the liquid crystal layer. A liquid crystal display device having a plurality of picture element regions, wherein each of the plurality of picture element regions has a reflective region and a transmissive region,
The liquid crystal layer is made of a liquid crystal material having a positive dielectric anisotropy, a first polarizing element provided on the opposite side of the first substrate from the liquid crystal layer, and a liquid crystal layer of the second substrate. A second polarizing element provided on the opposite side, a first phase difference compensating element provided between the first polarizing element and the liquid crystal layer, and a second polarizing element provided between the second polarizing element and the liquid crystal layer. A second retardation compensation element provided, wherein the twist angle θ _t of the liquid crystal layer is 0 ° or more and 54.3 ° or less, and the retardation R in the visible light region of the liquid crystal layer in the reflection region is
d is represented by Formula (1) and Formula (2), Formula (3) and Formula (4), Formula (5) and Formula (6), or Formula (7) and Formula (8), respectively. Retardation R in the visible region of the liquid crystal layer in the transmission region, which is a range surrounded by a curve
d is equation (9) and equation (10), and equation (11) and equation (12)
Is one of the ranges surrounded by the curves respectively represented by Rd = −0.0043 · θ _t ² −0.065 · θ _t +1011.8 (1) Rd = −0.0089・ Θ _t ² +0.1379 ・ θ _t +914.68 (2) Rd = -0.0015 ・ θ _t ² -0.1612 ・ θ _t +737.29 (3) Rd = -0.0064 ・ θ _t ^2- 0.0043 · θ _t +640.65 (4) Rd = −0.0178 · θ _t ² + 0.2219 · θ _t +458.92 (5) Rd = −0.0405 · θ _t ² + 0.4045 · θ _t +364.05 (6) Rd = 0.0347 · θ _t ² −0.4161 · θ _t +186.53 (7) Rd = 0.0098 · θ _t ² −0.1912 · θ _t +89.873 (8) ^{_{Rd = -0.0043 · θ t 2 -0.065}} · θ t +995.66 (9 ^{_{Rd = -0.0058 · θ t 2 -0.0202}} · θ t +665.8 (10) Rd = -0.0248 · θ t 2 +0.6307 · θ t +439.58 (11) Rd = 0.0181 · theta _t ² is _{-0.6662 · θ t +109.51 (12)} , a liquid crystal display device. 2. The retardation Rd is surrounded by the curves represented by the above formulas (7) and (8) in the range where the twist angle θ _t of the reflection region is 0 ° or more and 54.3 ° or less. In the range where the twist angle θ _{t of the} transmission region is 0 ° or more and 54.3 ° or less, the retardation is represented by the above formula (1).
The liquid crystal display device according to claim 1, wherein the liquid crystal display device is in a range surrounded by a curve represented by 1) and the formula (12).