JP2003043486A - Optical retardation plate compensation and single polarizing plate reflection type two-layer liquid crystal display - Google Patents

Abstract

PROBLEM TO BE SOLVED: To decrease the power consumption of an optical retardation plate compensation and single polarizing plate reflection type two-layer liquid crystal display formed by laminating a liquid crystal cell for compensation on a liquid crystal cell for driving with which a reflection plate in which a pixel electrode in formed integrally with it is assembled and successively laminating an optical retardation plate and one polarizing plate thereon. SOLUTION: The power consumption of the reflection type liquid crystal display is drastically decreased by adjusting the retardation values of the liquid crystal cell for driving and the liquid crystal cell for compensation based on the relation between the driving voltage and the display characteristics of the optical retardation plate compensation single polarizing plate mode reflection type two-layer liquid crystal display to reduce the driving voltage while the excellent display characteristics (luminance, a contrast ratio and achromatic display) is maintained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a two-layer liquid crystal cell structure in which a driving liquid crystal cell whose display is controlled by an information signal and a compensating liquid crystal cell or a compensating liquid crystal polymer film in place of the compensating liquid crystal cell are bonded and laminated. A reflective liquid crystal display in which a retardation plate or a 1/4 wavelength plate instead of the retardation plate and one polarizing plate are sequentially laminated on the compensating liquid crystal cell or compensating liquid crystal polymer film, that is, a retardation plate. Compensation / single-polarizing type reflective two-layer liquid crystal display, and power saving technology for reducing the power consumption of the reflective liquid crystal display based on the relationship between the display characteristics of the reflective liquid crystal display and the liquid crystal drive voltage (ON voltage) Is.

[0002]

2. Description of the Related Art With the rapid spread of high-performance information terminals, the demand for low power consumption, thin, lightweight, and high-quality reflective liquid crystal displays is increasing. Conventionally, various reflective liquid crystal displays have been proposed. Has been done. In the present application, various liquid crystals or liquid crystal displays are represented by the following abbreviations (abbreviations). "TN liquid crystal": Twisted Nematic liquid crystal "STN liquid crystal": Super Twisted Nematic liquid crystal "P liquid crystal": Parallel liquid crystal = liquid crystal "DTN-LCD" with a twist angle of 0 °, that is, parallel alignment: Double-Layered Twisted Nemati
c Liquid Crystal Display = 2-layer TN liquid crystal display “FDTN-LCD” including a driving liquid crystal cell and a compensating liquid crystal cell “FDTN-LCD”: Film Double-Layered Twisted
Nematic Liquid Crystal Display = MDTN-LCD, a two-layer TN liquid crystal display in which the compensating liquid crystal cell having the same molecular orientation as the compensating liquid crystal cell is substituted for the compensating liquid crystal cell "MDTN-LCD": Modified Double-Layered Twis
ted Nematic Liquid Crystal Display = Modified Film Double-Layere "Modified Film Double-Layere", which is a modified two-layer TN liquid crystal display with different retardation sizes of the driving liquid crystal cell and the compensating liquid crystal cell or the compensating liquid crystal polymer film.
d Twisted Nematic Liquid Crystal Display = The compensating liquid crystal polymer film having the same molecular orientation as the compensating liquid crystal cell replaces the compensating liquid crystal cell, and the driving liquid crystal cell and the compensating liquid crystal cell or compensating liquid crystal polymer film Deformed 2-layer TN liquid crystal display "DP-LCD" with different retardation sizes: Double-Layered Parallel Liq
uid Crystal Display = FDP-LCD, a two-layer P liquid crystal display having two liquid crystal cells, a driving liquid crystal cell and a compensating liquid crystal cell using P-liquid crystal in parallel alignment: Film Double-Layered Parallel
Liquid Crystal Display = 2-layer P liquid crystal display in which the compensating liquid crystal cell is replaced with a retardation plate having the same retardation as the compensating liquid crystal cell.

As a reflective liquid crystal display which consumes less power than a transmissive liquid crystal display equipped with a backlight, the number of polarizing plates is reduced to one by incorporating a reflective plate in which pixel electrodes are integrated into a liquid crystal cell. Phase difference plate compensation / single-polarizer type reflection type TN-LC in which an optical element such as a phase difference plate or a quarter wave plate is added to the liquid crystal cell
D and retardation plate compensating / single-polarizing plate type reflective STN-LCDs have been conventionally known. In addition, by the inventors of the present application,
JP-A No. 11-249165, retardation plate compensating / single-polarizing plate reflection type DTN-LCD and retardation plate compensating / single-polarizing plate reflection type FDTN-LCD as disclosed in JP-A No. 11-249165, JP-A No. 2001-91949. Phase difference plate compensation / single-polarizer type reflection type DTN-LCD and phase difference plate compensation / single-polarizer type reflection type F using 1/4 wavelength plate as disclosed in the publication
DTN-LCD, IEICE Technical Report, EID2000-256 (2001-01) pp.7
-12 Retardation plate compensation / single-polarizer type reflective MDTN-LCD and retardation plate compensation / single-polarizer type reflective M
A retardation plate compensating / single polarizing plate type reflective two-layer liquid crystal display such as FDTN-LCD has been proposed. Each of these conventional retardation plate compensating / single-polarizing plate type reflective two-layer liquid crystal displays is operated at a liquid crystal drive voltage of about 5 volts.

[0004]

With the recent widespread use of liquid crystal displays, it is required to further reduce the power consumption of the reflection type liquid crystal display, and the power consumption of the reflection type two-layer liquid crystal display is further reduced. We must seek reduction. One effective means of reducing the power consumption of a reflective liquid crystal display is to keep its drive voltage low. Generally, when the liquid crystal drive voltage is lowered, the display characteristics of the liquid crystal display (brightness of display, that is, reflection of bright state) Ratio, contrast ratio, achromatic color, that is, black and white without coloring, wavelength dependence of spectral reflectance in color display, etc.)
Therefore, there is hesitation in lowering the liquid crystal drive voltage.

In view of such a situation, the present invention simulates the relationship between the driving voltage and the display characteristics in the reflection type two-layer liquid crystal display previously proposed, and then,
By setting the retardation of the driving liquid crystal cell and the retardation of the compensating liquid crystal cell without equal constraint (keeping the same numerical value), the liquid crystal drive voltage can be set significantly lower than before while maintaining good display characteristics. Therefore, it is intended to further reduce the power consumption of the reflective two-layer liquid crystal display.

[0006]

In order to achieve this object, according to the present invention, a driving liquid crystal cell in which a reflecting plate integrally formed with pixel electrodes is incorporated and a compensating liquid crystal cell are laminated, and a retardation film is formed thereon. In a two-layer liquid crystal display consisting of a plate and one polarizing plate additionally laminated, the retardation of the driving liquid crystal cell and the retardation of the compensating liquid crystal cell are adjusted and set without equal constraint, and the liquid crystal driving voltage (ON voltage) is set.
By setting the voltage to 3.5 V or less, the power consumption of the retardation plate compensating / single polarizing plate type reflective two-layer liquid crystal display is reduced.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION One of the basic embodiments of the present invention is to stack a driving liquid crystal cell incorporating a reflecting plate integrally formed with pixel electrodes and a compensating liquid crystal cell on which a retardation film is formed. A two-layer liquid crystal display is constructed by additionally laminating a plate and one polarizing plate, and the retardation of the driving liquid crystal cell and the retardation of the compensating liquid crystal cell are adjusted and set without equal constraint, and the liquid crystal driving voltage (ON voltage ) Is set to 3.5 V or less, and is a retardation plate-compensating / single-polarizing type reflective two-layer liquid crystal display.

Another basic embodiment of the present invention is to provide a driving liquid crystal cell incorporating a reflecting plate integrally formed with pixel electrodes, and a compensating liquid crystal polymer film having the same molecular orientation as the compensating liquid crystal cell. A two-layer liquid crystal display is constructed by laminating and additionally laminating a retardation plate and one polarizing plate on it, and adjusting the retardation of the driving liquid crystal cell and the retardation of the compensating liquid crystal polymer film without equal constraint. It is a reflective two-layer liquid crystal display with retardation plate compensation and single polarization plate set and liquid crystal drive voltage set to 3.5 V or less.

In another basic embodiment of the present invention, a driving liquid crystal cell incorporating a reflection plate integrally formed with pixel electrodes and a compensating liquid crystal cell or a compensating liquid crystal polymer film are laminated. Then, a quarter-wave plate and one polarizing plate are additionally laminated to form a two-layer liquid crystal display, and the retardation of the driving liquid crystal cell and the retardation of the compensating liquid crystal cell or the compensating liquid crystal polymer film, etc. It is a reflective two-layer liquid crystal display with retardation plate compensation and single polarizing plate, which is adjusted and set without restricting the value and the liquid crystal drive voltage is set to 3.5 V or less.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a retardation plate compensation / single polarizing plate type reflection type DTN-.
It is an example of LCD. In FIG. 1, A is a driving liquid crystal cell (abbreviated as “driving cell”) whose display is controlled by an information signal, and B is a compensating liquid crystal cell (abbreviated as “compensation cell”),
The driving liquid crystal cell A and the compensating liquid crystal cell B are joined to be in a laminated state to form a two-layer liquid crystal structure. The driving liquid crystal cell A includes a substrate 5 to which a reflecting plate (specular reflecting plate) 11 integrally formed with pixel electrodes (not shown) is attached, and a transparent substrate 4 to which a common transparent electrode (ITO = Indium Tin Oxide) 3 is attached.
And a driving liquid crystal layer (driving TN liquid crystal layer) 1 enclosed between a reflective plate (pixel electrode) 11 and a common transparent electrode 3 which face each other. The compensating liquid crystal cell B includes a transparent substrate 4a,
A compensation liquid crystal layer (compensation TN liquid crystal layer) 2 is enclosed between 4b. Further, 6 is a retardation plate, 9 is a polarizing plate, 1
Reference numeral 0 denotes a front diffusion plate, which is sequentially laminated on the end surface of the transparent substrate 4b. By incorporating the reflection plate 11 integrated with the pixel electrode in the driving liquid crystal cell A, it is sufficient to add only one polarizing plate 9. Then, a liquid crystal drive voltage (abbreviated as “drive voltage”) e is applied between the pixel electrode integrally formed on the reflector 11 and the common transparent electrode 3. The liquid crystal drive voltage e is 3.5 V (volts) or less, which is a significantly lower voltage of 5 V or 4.5 V which has been conventionally applied. Further, the magnitude of the retardation (Δn · d) A of the driving liquid crystal cell A and the magnitude of the retardation (Δn · d) B of the compensating liquid crystal cell B are equal. Where Δn is the birefringence, d is the cell gap (thickness of the liquid crystal layer)
Alternatively, it is the thickness of the retardation plate.

FIG. 2 shows an embodiment of a retardation plate compensating / single-polarizing plate type reflection type DTN-LCD for color display according to the present invention. As is apparent from FIG. 2, the common transparent electrode of the driving cell A is shown. 3 is the same as the configuration shown in FIG. 1 except that the micro color filter 12 is disposed between the transparent substrate 4 and the transparent substrate 4.

FIG. 3 is a reflection type DTN-L of a single polarizing plate type compensating plate having two retardation plates mounted with two retardation plates according to the present invention.
It is an example of CD. As is clear from comparison between FIG. 1 and FIG. 3, the two phase difference plate compensation / single-polarizing plate reflection type DTN-LCD shown in FIG. 3 has two phase difference plates 6 in order to enhance display characteristics. 7 are arranged side by side, and other configurations are the same as those shown in FIG.

FIG. 4 shows another embodiment of the present invention, which shows a 1/4 wavelength plate compensating single polarizing plate type reflection type DTN-LCD. As is clear from comparing FIG. 1 and FIG.
1/4 wavelength plate compensation / single polarizing plate type reflective DTN-
The LCD has a 1/4 wavelength plate 8 which functions as a kind of retardation plate instead of the retardation plate 6, and the other structure is the same as that shown in FIG.

FIG. 5 shows another embodiment of the present invention, which shows a retardation plate compensating / single polarizing plate type reflection type FDTN-LCD. As is clear from comparison between FIG. 1 and FIG.
Compensation / single polarizing plate type reflection type FDTN-
The LCD has a compensating liquid crystal polymer film 13 corresponding to the compensating cell B disposed between the driving cell A and the retardation plate 6 for the purpose of making the LCD thin and light, and the other structure is shown in FIG. It is the same as that. The compensating liquid crystal polymer film 13 placed in place of the compensating cell B is a liquid crystal polymer film having the same molecular orientation as that of the compensating cell B.

FIG. 6 shows another embodiment of the present invention, which shows a retardation plate compensating / single polarizing plate type reflection type MDTN-LCD. The retardation plate compensating / single polarizing plate type reflective MDTN-LCD shown in FIG.
n · d) A and retardation of compensation cell B (△
The sizes of n · d) B are not equal, and this point is different from the phase difference plate compensating / single-polarizing plate reflection type DTN-LCD in FIG. 1, but other configurations are the same as those shown in FIG.

FIG. 7 shows another embodiment of the present invention, which shows a retardation plate compensating / single polarizing plate type reflection type MFDTN-LCD. The retardation plate compensating / single-polarizing plate type reflective MFDTN-LCD shown in FIG. 7 has a retardation (Δn · d) A of the driving cell A and a retardation (Δn · d) of the compensating liquid crystal polymer film 13. The size of F is different, and in this respect, it is different from the retardation plate compensation / single-polarizing plate type reflection type FDTN-LCD of FIG. 5, but other configurations are as shown in FIG.
It is the same as that shown in.

In all of the above embodiments, the front diffuser plate 10 is added by using the reflector 11 as a specular reflector, but if the diffuser reflector is used as the reflector 11, the front diffuser plate 10 can be omitted. it can.

Further, the retardation plate compensation / single-polarizing plate type reflection type FDTN-LCD shown in FIG.
In both the single polarizing plate type reflection type MDTN-LCD and the retardation plate compensating / single polarizing plate type reflection type MFDTN-LCD shown in FIG. 7, as shown in FIG. Between the micro color filters 12
By providing a phase difference plate compensation / single-polarizing plate reflection type two-layer liquid crystal display for color display, and as necessary, two phase difference plates 6 and 7 can be arranged side by side as shown in FIG. Needless to say.

Further, the already known parallel-aligned liquid crystal is used in place of the TN liquid crystal in each of the above-mentioned embodiments to construct a two-layer P liquid crystal display such as a DP-LCD or FDP-LCD corresponding to the above-mentioned embodiments. You can also DP-L
The CD or FDP-LCD has unique characteristics. That is, the DP-LCD does not require a 1/4 wavelength plate, which is expensive and has not yet realized the ideal characteristic of a 1/4 wavelength plate in the entire visible light range, when configuring a two-layer liquid crystal display, and the parallel arrangement is also possible. The liquid crystal cell using the light P liquid crystal has the excellent feature that it is simple and easy to manufacture. Further, in the single polarizing plate type reflection type DP-LCD, an achromatic display cannot be obtained. Therefore, the retardation plate compensating single polarizing plate type reflection type DP-LCD having the structure in which the achromatic (compensation) phase difference plate is added is It has a unique technical meaning. In addition, the retardation plate compensating / single-polarizing plate reflection type DP-LCD or the retardation plate compensating / single-polarizing plate reflection type FDP-LCD is simple in structure, easy to manufacture and inexpensive, and has retardation of its liquid crystal cell. However, only when the drive voltage (ON voltage) becomes lower than about 2.5V, the retardation value of 0.
Since it has a characteristic of being larger than 2 μm, it has a characteristic of being practically useful only when the driving voltage (ON voltage) is lower than about 2.5V. Since these important features for practical use are recognized in the present invention, the retardation plate compensation / single polarizing plate reflection type DP-LCD and the retardation plate compensation / single polarizing plate reflection type FDP-LCD are novel liquid crystal displays. Can be recognized.

Next, the relationship between the driving voltage (ON voltage) e and the display characteristics in the retardation plate compensating / single-polarizing plate type reflective two-layer liquid crystal display of the present invention including the above-mentioned embodiments will be described. Phase difference plate compensation / single-polarizer type reflection type two-layer liquid crystal display is shown as a representative of the phase difference plate compensation / single-polarizer type reflection type DTN-LCD and phase difference plate compensation shown in FIG.
The analysis is based on a single polarizing plate type reflective FDTN-LCD.

Phase difference plate compensation / single polarizing plate type reflection type DTN-
LCD and retarder compensation, single polarizing plate type reflective FDTN-L
In the CD without the retardation plates 6 and 7 or the quarter-wave plate 8, the following three conditions are established between the compensation cell B (or the compensating liquid crystal polymer film 13) and the driving cell A. Then, it is known that an ideal bright state with a reflectance of 50% is obtained for all visible light when the driving voltage is off, due to the two-layer type compensation principle.

The three conditions are: [1] The twist angle of the compensating liquid crystal layer 2 of the compensating liquid crystal cell B (or the compensating liquid crystal polymer film 13) and the driving liquid crystal layer 1 of the driving liquid crystal cell A. The twist angles must be the same and the twist directions must be opposite. That is, when the twist angle of the compensating liquid crystal layer 2 is φ, the twist angle of the driving liquid crystal layer 1 is (−φ). [2] Adjacent molecules of the compensating liquid crystal cell B and the driving liquid crystal cell A are orthogonal to each other. [3] The retardation of the compensating liquid crystal cell B is equal to that of the driving liquid crystal cell A. Is. The phase difference plate is added to obtain an achromatic display with a high contrast ratio while keeping the ideal bright state when the drive voltage is off as much as possible.

In the analysis, the orientation distribution in the liquid crystal cell is Os.
een-Frank elastic body theory, light propagation characteristics are Stokes parame
It is calculated using ter. The definition of each axis angle used in the analysis is as shown in FIG. That is, P is the transmission axis of the polarizing plate, β is the azimuth angle of the transmission axis, OP is the optical axis (slow axis) of the retardation plate, γ is the azimuth angle of the optical axis, and R1 and R2 are compensation cells B ( Alternatively, the alignment direction of the liquid crystal molecules on the surface of the compensating liquid crystal polymer film 13), R3 and R4 are the rubbing directions of the driving liquid crystal cells (the major axis directions of the liquid crystal molecules), and φ is the twist angle of the liquid crystal and the liquid crystal polymer film. .

Then, the twist angle φ is changed in the range of 10 ° to 63 °, the other design parameters and material parameters are the values shown in Table 1, that is, the typical values in the TN-LCD, and the polarizing plate has the ideal characteristics. Table 2 shows the azimuth angle β of the transmission axis of the polarizing plate, the azimuth angle γ of the optical axis of the retardation plate, the retardation (Δn · d) R of the retardation plate, and the retardation (Δn · d) LC of the liquid crystal layer. The influence on display characteristics in the normal direction of the liquid crystal cell was investigated by changing the range shown, and the driving voltage e was changed within the range of 4.5 V to 1.5 V to obtain the optimum cell condition at each driving voltage e.

The optimum cell condition is a reflectance of 4 in the bright state.
A cell condition of 9% or more, a contrast ratio of 16: 1 or more and an achromatic color is defined as a good cell condition, and the one having the smallest wavelength dependence of the spectral reflectance among those satisfying the good cell condition is the optimum cell. It was a condition. The condition for achromatic display is that the color locus in the cell normal direction drawn on the 1931 CIE-xy chromaticity diagram falls within a circle within 0.05 from the coordinates of the D65 standard light source.

[0026]

[Table 1]

[0027]

[Table 2]

FIG. 9 shows good cell conditions (the reflectance in the bright state is 49 when the driving voltage is 4.5 V and the twist angle of the liquid crystal is 63 °).
%, A contrast ratio of 16: 1 or more, and a cell condition for producing an achromatic color), the retardation of the retardation plate 6 (Δn · d)
The relationship between R and the retardation (Δn · d) LC of the liquid crystal layer is shown in FIG.
V, the good cell condition when the twist angle of the liquid crystal is 63 °, the retardation (Δn · d) R of the retardation plate 6 and the retardation plate 6
It is shown as a relation of the azimuth angle γ of the optical axis.

As is clear from FIGS. 9 and 10, the good cell condition is several cell groups, and the display characteristics in each of the groups A, B, C, and D shown in FIG. As a result, although the contrast ratio of the C group is higher than that of the other cell groups, the wavelength dependence of the spectral reflectance is the smallest and the contrast ratio of about 30: 1 can be obtained.
It was confirmed that the optimum cell condition of the group is most suitable for color display by the color filter method.

Looking at the relationship between the twist angle φ and the display characteristics, the good cell condition is a cell group as shown in FIGS. 9 and 10, and the cell condition varies depending on the twist angle φ, but the twist angle is 63 °. It was confirmed that there is a cell group corresponding to the A group at the time. FIG. 11 shows the retardation (Δn · d) LC of the optimum cell condition of the group corresponding to the group A of FIG. 10 at each twist angle φ. The black circles in FIG. 11 are calculation points, and indicate that the retardation (Δn · d) LC of the liquid crystal layer gradually decreases as the twist angle φ decreases. In terms of display characteristics, there is a cell condition for an achromatic color display that is close to the ultimate display performance of a single polarizing plate type liquid crystal display when the twist angle φ is 60 ° or less. The retardation of the liquid crystal layer suitable for manufacturing (△ n ・ d) is 0.2μ
If it is m or more, it can be said that a twist angle of about 60 ° is a twist angle satisfying the conditions in view of FIG.

Next, the relationship between the drive voltage e and the display characteristics will be described. When the display characteristics were examined by changing the driving voltage e from 4.5 V to 1.5 V with the liquid crystal twist angle φ in the range of 10 ° to 63 °, good cell conditions were obtained for all combinations of the liquid crystal twist angle φ and the driving voltage e. 10 exist, some cell groups are formed as shown in FIG. 10 when the driving voltage e is 4.5 V, and the spectral reflectance corresponding to the group A in FIG. 10 has the smallest wavelength dependence and contrast. It was confirmed that there was a cell group with a sufficiently high ratio.

Then, when attention is paid to the retardation (Δn · d) LC of the liquid crystal layer of the cell group corresponding to the group A,
It was confirmed that the retardation (Δn · d) LC increases as the driving voltage e decreases regardless of the twist angle φ. FIG. 12 shows, as a representative example, the retardation (Δn · d) LC of the liquid crystal layer which is the optimum cell condition in each combination of the twist angle φ and the driving voltage e. As is clear from FIG. 12, the drive voltage e
Is decreased, the retardation (Δn · d) LC increases regardless of the twist angle φ.
Below 3.0V, even if the twist angle φ is 10 °,
It was confirmed that the retardation (Δn · d) LC was larger than 0.20 μm, which is a standard suitable for manufacturing a liquid crystal cell. The retardation (Δn · d) LC under the optimum cell condition when the driving voltage e is 1.5 V is as large as about 1.10 μm regardless of the twist angle φ.
Not shown in.

When the relationship between the display characteristics under the optimum cell condition and the driving voltage e was examined, the following tendency was found. [1] The reflectance in the bright state depends on the driving voltage e and the twist angle φ.
49% or more can be obtained regardless of [2] The wavelength dependence of the spectral reflectance in the bright state does not depend on the drive voltage e as the twist angle φ becomes smaller. [3] With a few exceptions, the reflectance in the bright state decreases with decreasing drive voltage regardless of the twist angle φ, and therefore the contrast ratio increases with decreasing drive voltage e. [4] The wavelength dependence of the spectral reflectance in the dark state does not depend on the drive voltage e as the twist angle φ becomes smaller. [5] The same excellent achromatic display can be obtained regardless of the drive voltage e and the twist angle φ. [6] The reflectance-voltage characteristic draws a valley shape (the valley shape that is the minimum at the driving voltage) when the driving voltage becomes lower than about 3.0V.

As a representative example of the above, FIGS. 13, 14 and 15 show the drive voltage dependence of the display characteristics when the twist angle φ of the liquid crystal is 30 °, and Table 3 shows the cells of FIGS. Liquid crystal layer retardation (Δn · d) LC
And, the reflectance in the bright state and the contrast ratio are shown. Further, in FIGS. 16, 17, and 18, the driving voltage e is 2.0.
The dependence of the display characteristics on the twist angle is shown in Table 4. Table 4 shows the retardation (Δn · d) LC of the liquid crystal layer which is the cell condition of FIGS. 16 to 18, the reflectance in the bright state, and the contrast ratio. Is shown. From Table 3, when the twist angle φ of the liquid crystal is 30 °, the retardation (Δn · d) LC of the liquid crystal layer is 0.20μ when the driving voltage is lower than 3.0V.
16 to FIG. 18 and Table 4, it can be seen from FIG. 16 to FIG. 18 and Table 4 that even if the driving voltage e is 2.0 V, an achromatic display with a display performance close to the limit of a single polarizing plate type can be obtained regardless of the twist angle φ. I understand. The ultimate display performance of the single-polarizer type is display performance satisfying three conditions: the reflectance in the bright state is 50%, the contrast ratio is infinite, and the spectral reflectance does not depend on the wavelength.

[0035]

[Table 3]

[0036]

[Table 4]

As is apparent from FIG. 12, since the retardation (Δn · d) LC of the liquid crystal layer under the optimum cell condition increases with the decrease of the drive voltage e regardless of the twist angle φ, the drive voltage e The phenomenon that an achromatic display with display performance close to the limit of a single-polarizer type liquid crystal display can be obtained even if the voltage is lowered to 2.0 V is basically a 1/4 wavelength plate compensation / single-polarizer type as shown in FIG. Reflective DTN-LCD
It is considered that this is due to the two-layer liquid crystal cell structure including.
Therefore, quarter-wave plate compensation / single-polarizer type reflective DTN-LC
Regarding D, the relationship between the display characteristics and the drive voltage e is examined.

Phase-difference compensating / single-polarizing type reflective DTN-LCD
Then, regardless of the type of the compensating liquid crystal cell sandwiched between the driving liquid crystal cell and the polarizing plate or the compensating polymer film that replaces the compensating liquid crystal cell, there is a difference between the reflectance and the ellipticity of light on the reflector. , There is a relationship as shown in FIG. Therefore,
If all visible light is linearly polarized on the reflector, an ideal achromatic bright state where the reflectance of all visible light is 50% is obtained. Conversely, all visible light is reflected on the reflector. With circularly polarized light, an ideal achromatic dark state where the reflectance of all visible light is 0% can be obtained.

That is, in the 1/4 wavelength plate compensation / single-polarizing plate reflection type DTN-LCD as shown in FIG.
If the retardation of the four-wave plate 8 is 1/4 of each wavelength for all visible light, and the azimuth difference between the polarizing plate 9 and the one-quarter wavelength plate is set to 45 °, this polarizing plate The combination of 9 and the quarter-wave plate 8 becomes a circularly polarizing plate for all visible light, and all visible light transmitted through the polarizing plate 9 becomes circularly polarized light.

Based on this setting, if the following three conditions are established between the compensation cell B and the drive cell A when the drive voltage is off, the quarter-wave plate 8 is formed by the two-layer type compensation principle. The transmitted circularly polarized light reaches the reflector 11 as it is. The three conditions are: [1] The twisting angle of the compensating liquid crystal layer 2 of the compensating cell B (or the compensating liquid crystal polymer film 13) and the twisting angle of the driving liquid crystal layer 1 of the driving cell A are equal to each other. The twist direction should be the opposite direction. That is, when the twist angle of the compensating liquid crystal layer 2 is φ, the twist angle of the driving liquid crystal layer 1 is
Must be (-φ). [2] The retardation of the compensating liquid crystal layer 2 of the compensating cell B and the retardation of the driving liquid crystal layer 1 of the driving cell A are equal. [3] Adjacent molecules of the compensation cell B and the driving cell A are orthogonal to each other. Is. Therefore, when the drive voltage is off, the reflection plate 11
The upper light is circularly polarized light regardless of the wavelength, and an ideal achromatic dark state in which the reflectance of all visible light is 0 is obtained.

On the other hand, since it is not clear whether or not a bright achromatic bright state can be obtained when the drive voltage is turned on, a numerical analysis (simulation) is used to investigate. Therefore, in the analysis, the orientation distribution in the liquid crystal cell was obtained using the Oseen-Frank elastic body theory, and the light propagation characteristics were obtained using the Stokes parameter. The definition of each axis angle used in the analysis is as shown in FIG. That is, P is the transmission axis of the polarizing plate, β is the azimuth angle of the transmission axis, OP is the optical axis (slow axis) of the quarter-wave plate, γ is the azimuth angle of the optical axis, and R1 and R2 are compensation cells. The rubbing direction of B or the long axis direction of the liquid crystal molecules, R3 and R4 are the rubbing directions of the driving cells or the long axis direction of the liquid crystal molecules, and each axial angle is based on the axial direction R1. Note that φ is the twist angle of the liquid crystal and the liquid crystal polymer film.

Then, using typical values in the TN-LCD shown in Table 5 as the values of the design and material parameters, the combination of the polarizing plate 9 and the 1/4 wavelength plate 8 is set to the condition that a circular polarizing plate is set, and the driving voltage is set. (ON voltage) 4.5V to 1.5V TFT
(Thin Film Transistor) The display characteristics in the cell normal direction were examined under the assumption of LCD driving. Since the design method has been clarified, the 1/4 wavelength plate 8 has a retardation of 1/4 of each wavelength with respect to all visible light.

[0043]

[Table 5]

As shown in FIG. 4, a quarter-wave plate compensation / single-polarizing plate type reflection DTN-LCD and a quarter-wave plate compensation / mono-lens unit in which the compensating liquid crystal cell B is replaced with a compensating liquid crystal polymer film 13 are used. As described above, in the polarizing plate type reflection type FDTN-LCD, it is theoretically possible to obtain an ideal achromatic dark state in which the reflectance of all visible light is 0% when the driving voltage is off (0 V). Therefore, it is sufficient to optimize the display characteristics when the drive voltage is on.

In order to obtain the brightest display when the driving voltage is turned on, from the relationship between the reflectance and the ellipticity on the reflection plate shown in FIG.
It suffices that the light of 50 nm becomes linearly polarized on the reflection plate. For that purpose, the 1/4 wavelength plate 8 is excluded from the structure of the 1/4 wavelength plate compensation / single polarizing plate type reflection type DTN-LCD shown in FIG. In the above configuration, it suffices to set the cell condition in which the light having a wavelength of 550 nm is circularly polarized on the reflection plate when the driving voltage is turned on.

Table 6 shows the twist angle φ of the liquid crystal, the azimuth angle β of the polarizing plate 9 and the ratio (Δn · d) D / λ of the retardation (Δn · d) D and the wavelength λ of the driving cell A. The cell condition that the light becomes circularly polarized on the reflection plate 11 is obtained by changing the range, and the 1/4 wavelength plate compensation / single polarization plate type reflection type DTN-
The display characteristics of the LCD were confirmed.

[0047]

[Table 6]

First, the 1/4 wavelength plate compensating / single-polarizing plate type reflection DTN-LCD shown in FIG. 4 is removed from the 1/4 wavelength plate 8 and the circularly polarized light is polarized on the reflecting plate 11 when the driving voltage is turned on. The cell conditions for obtaining an ellipticity of 0.99 or more were obtained. As a result, the ratio of the retardation of the driving cell to the wavelength (Δn ·
d) It was confirmed that there is a relationship as shown in FIG. 21 among _D / λ, the twist angle φ, and the azimuth angle β of the polarizing plate 9. The (a) characteristic of FIG. 21 is the relationship between the retardation of the drive cell and the wavelength (Δn · d) _D / λ with respect to the twist angle φ, and the (b) characteristic of FIG. 21 is the polarizing plate with respect to the twist angle φ. The relationship between the azimuth angles β of 9 is shown, and one set of cell conditions at each drive voltage e is shown by the characteristics (a) and (b) of FIG. Then, when the drive voltage is turned on, the ratio of the retardation of the drive cell that becomes circularly polarized light on the reflection plate 11 and the wavelength (Δn ·
d) It can be seen that _D / λ gradually increases as the driving voltage e decreases. At a drive voltage of 1.5 V, the ratio of the retardation to the wavelength of the drive cell (Δn · d) _D / λ where the light is circularly polarized on the reflection plate 11 becomes about 2.0 regardless of the twist angle β. , Not shown in FIG.

Next, based on the results shown in FIG. 21, the cell conditions under which the light with the wavelength of 550 nm, which has the highest luminosity factor, is circularly polarized on the reflection plate 11 at each drive voltage are obtained, and the cell conditions are obtained.
As a result of examining the display characteristics when the 1/4 wavelength plate 8 is inserted,
The following was confirmed. [1] In all cell conditions obtained from FIG. 21,
Achromatic display with a reflectance in the bright state higher than 49%. [2] Retardation (Δn · d) _{D of the} driving cell is small in the range of driving voltage 4.5V to 2.5V where there are two cell conditions at each twist angle. Smallness. [3] The wavelength dependence of the spectral reflectance tends to gradually increase as the twist angle becomes smaller in the driving voltage range higher than 2.5V, and hardly changes when the driving voltage becomes lower than 2.0V. [4] When the twist angle is larger than 30 °, the wavelength dependence of the spectral reflectance becomes smaller as the drive voltage lowers in the range where the drive voltage drops to 2.5V, and the twist angle becomes smaller than 20 °. In that case, there is almost no change depending on the liquid crystal drive voltage.

As a typical example of such display characteristics, FIG.
2 shows the dependence of the spectral reflectance on the twist angle at a driving voltage of 2.5 V, and FIG. 23 shows the dependence of the spectral reflectance on the driving voltage at a twist angle of 50 °. 24 shows the spectral reflectance characteristic under the cell condition (optimal cell condition) in which the wavelength dependence of the spectral reflectance is the smallest at each driving voltage, FIG. 25 shows its color locus, and FIG. 26 shows its reflectance. −
It shows a voltage characteristic. Table 7 shows the cell conditions and the reflectance in the bright state. From these charts, if the cell conditions are optimized at each drive voltage, it is possible to obtain display characteristics extremely close to the limit of the phase difference compensation / single polarization plate type reflective two-layer liquid crystal display up to a drive voltage of at least 2.5V. It can be seen that even with a driving voltage of 2.0 V, an achromatic color display with a small wavelength dependence of the spectral reflectance can be obtained. At a drive voltage of 1.5 V, the ratio of the retardation of the drive cell that becomes circularly polarized light on the reflection plate 11 to the wavelength (Δn ·
d) _D / λ is about 2.0, and thus the wavelength is 550 nm
Of the driving cell A, which becomes circularly polarized light on the reflector 11, the retardation (Δn · d) _D is about 1.1 μm, which is considerably large. Therefore, the lowering voltage limit is between 2.0V and 1.5V. Becomes

[0051]

[Table 7]

Thus, even if the driving voltage is lowered to 2.0 V, an excellent achromatic display which is almost equal to the driving voltage of 4.5 V can be obtained. With this mechanism, as the drive voltage e decreases, the retardation of the drive cell and the wavelength ratio (Δn · d) _D / λ in the characteristic (a) of FIG. Since the retardation (Δn · d) _{D of the} driving cell A is large, it is considered that it is essentially due to the two-layer type cell structure. That is, the residual birefringence in the drive cell increases as the drive voltage decreases, but the twist angles of the compensation cell and the drive cell are opposite to each other, and thus this residual birefringence has the effect of reducing the retardation of the compensation cell. . Therefore, in order to obtain the spectral reflectance equivalent to that when a high voltage is applied to the driving cell, the retardation of the compensation cell must be set large in advance by the amount that the retardation of the driving cell reduces. However, in order to equalize the retardation of the compensation cell and the driving cell, this correction is repeated, and the retardation (Δn
d) It is necessary to make _D converge to an optimum value. In this way, the retardation of the driving cell A which becomes the optimum cell condition
(Δn · d) _D becomes large, but since it is not a simple phenomenon in practice, in order to optimize the display characteristics, it is necessary to use FIG.
Also, as shown in Table 7, it is necessary to adjust the twist angle φ and the azimuth angle β of the polarizing plate.

As described above, the increase in the retardation (Δn · d) _D of the driving cell under the optimum cell condition as the driving voltage lowers also increases the choice of liquid crystal materials as the driving voltage lowers. Only when the driving voltage is lowered does the cell condition appear such that the retardation (Δn · d) _{D of the} driving cell becomes suitable for manufacturing a liquid crystal display.

In the above description, the birefringence index Δn of the liquid crystal in the compensation cell and the driving cell is constant regardless of the wavelength.
Even when the wavelength dispersion of the birefringence Δn of ZLI-2293 is used for the liquid crystal, the birefringence of the liquid crystal Δn can be optimized by optimizing the cell conditions.
It has been confirmed that an achromatic display that is almost the same as when there is no wavelength dispersion is obtained.

[0055]

As is apparent from the above embodiments, according to the present invention, a driving liquid crystal cell incorporating a reflection plate integrally formed with a pixel electrode, a compensating liquid crystal cell or a compensating liquid crystal polymer. In a two-layer liquid crystal display in which a film is laminated and a retardation plate or a quarter-wave plate and one polarizing plate are not laminated on it, the retardation and compensation of the driving liquid crystal cell are exceeded, beyond the conventional design recognition. By adjusting and setting the retardation of the liquid crystal cell for compensation or the liquid crystal polymer film for compensation without being restricted to the same value,
The liquid crystal drive voltage is set to 3,5 V or less by drastically lowering that of the conventional one. Even if the liquid crystal drive voltage is lowered to 2.0 V, the display performance is almost the same as that of the single-polarizer type liquid crystal display. Colored display is obtained, and the liquid crystal drive voltage is drastically reduced, resulting in good display characteristics (reflectance of about 50%).
%, It is possible to further reduce the power consumption of the reflective liquid crystal display while maintaining high image quality by maintaining an achromatic color display in which the wavelength dependence of the spectral reflectance is small. The present invention has a great effect of reducing the power consumption as compared with an active matrix type reflective liquid crystal display, and in the case of a TFT driven reflective type liquid crystal display with an on-voltage of 5 V which has been widely used conventionally, the power consumption is 1/6. It can be reduced to 1/7.

Further, when the liquid crystal drive voltage is lowered, the retardation of the liquid crystal is increased, so that the drive voltage is lowered, the choice of materials is expanded, and the twist angle of the liquid crystal which can be manufactured is expanded.

[Brief description of drawings]

FIG. 1 is a sectional view of the basic elements of a retardation plate compensating / single polarizing plate type reflective DTN-LCD showing an embodiment of the present invention.

FIG. 2 is a sectional view of the basic elements of a retardation plate compensating / single-polarizing plate reflection type DTN-LCD for color display showing another embodiment of the present invention.

FIG. 3 is a cross-sectional view of a basic element configuration of a retardation plate compensating single polarizing plate type DTN-LCD according to another embodiment of the present invention.

FIG. 4 is a quarter-wave plate compensator according to another embodiment of the present invention.
FIG. 3 is a cross-sectional view of a basic element configuration of a single polarizing plate type reflective DTN-LCD.

FIG. 5 is a cross-sectional view of a basic element configuration of a retardation plate compensating / single-polarizing plate type reflection type FDTN-LCD showing another embodiment of the present invention.

FIG. 6 is a cross-sectional view showing the basic elements of a retardation plate compensating / single-polarizing plate type reflection type MDTN-LCD according to another embodiment of the present invention.

FIG. 7 is a sectional view showing a basic element configuration of a retardation plate compensating / single polarizing plate type reflection type MFDTN-LCD according to another embodiment of the present invention.

FIG. 8 is an explanatory view of the axial angle definition of the retardation plate compensating / single-polarizing plate type reflection type DTN-LCD, FDTN-LCD according to the present invention.

FIG. 9 is a characteristic diagram of a retardation plate compensating / single-polarizing plate type reflective two-layer liquid crystal display according to the present invention [retardation (Δn · d) R of retardation plate and retardation (Δ) of liquid crystal layer]
n ・ d) LC relationship diagram].

FIG. 10 is a characteristic diagram of the same two-layer liquid crystal display [relationship between retardation (Δn · d) R of the retardation plate and azimuth angle γ of the optical axis of the retardation plate].

FIG. 11 is a characteristic diagram of the same two-layer liquid crystal display [a relational diagram between the twist angle φ of the liquid crystal and the retardation (Δn · d) LC of the liquid crystal layer].

FIG. 12 is a characteristic diagram of the same two-layer liquid crystal display [relationship diagram of drive voltage and retardation (Δn · d) LC of the liquid crystal layer].

FIG. 13 is a characteristic diagram of the same two-layer liquid crystal display [relationship diagram of light wavelength and reflectance].

FIG. 14 is a characteristic diagram of the two-layer liquid crystal display [CIE-x
y Chromaticity diagram Color locus].

FIG. 15 is a characteristic diagram of the same two-layer liquid crystal display [relationship diagram between drive voltage and reflectance].

FIG. 16 is a characteristic diagram of the same two-layer liquid crystal display [relationship diagram between light wavelength and reflectance].

FIG. 17 is a characteristic diagram of the two-layer liquid crystal display [CIE-x
y Chromaticity diagram Color locus].

FIG. 18 is a characteristic diagram of the same two-layer liquid crystal display [relationship diagram between drive voltage and reflectance].

FIG. 19 is a relationship diagram between the reflectance of a single polarizing plate type reflective liquid crystal display and the ellipticity of light on a reflector.

FIG. 20 is an explanatory diagram of the axial angle definition of the quarter-wave plate compensation / single-polarizing plate type reflective DTN-LCD according to the present invention.

FIG. 21 is a characteristic diagram of the same two-layer liquid crystal display [relationship between a retardation of a driving cell and a wavelength (Δn · d) _D / λ, a relational diagram of an azimuth angle β of a polarizing plate and a twist angle φ of a liquid crystal].

FIG. 22 is a characteristic diagram of the same two-layer liquid crystal display [relationship diagram between light wavelength and reflectance].

FIG. 23 is a characteristic diagram of the same two-layer liquid crystal display [relationship diagram of light wavelength and reflectance].

FIG. 24 is a characteristic diagram of the same two-layer liquid crystal display [relationship diagram between light wavelength and reflectance].

FIG. 25 is a characteristic diagram of the same two-layer liquid crystal display [CIE-x
y Chromaticity diagram Color locus].

FIG. 26 is a characteristic diagram of the same two-layer liquid crystal display [relationship diagram between drive voltage and reflectance].

[Explanation of symbols]

A: Driving liquid crystal cell (driving cell) B: Compensating liquid crystal cell (compensating cell) 1: Driving liquid crystal layer (driving TN liquid crystal layer) 2: Compensating liquid crystal layer (compensating TN liquid crystal layer) 3: Common transparent Electrodes (ITO) 4, 4a, 4b: Transparent substrate 5: Substrate 6: Phase difference plate 7: Phase difference plate 8: 1/4 wavelength plate 9: Polarizing plate 10: Front diffusion plate 11: Reflection plate (specular reflection plate) (Including pixel electrode) 12: Micro color filter (color filter) 13: Compensation liquid crystal polymer film e: Liquid crystal drive voltage (drive voltage) (ON voltage) P: Transmission axis OP of polarizing plate: Light of retardation plate Axis R1, R2: Alignment direction of liquid crystal molecules on the surface of compensating liquid crystal cell or compensating liquid crystal polymer film R3, R4: Rubbing direction of driving cell (long axis direction of liquid crystal molecule) β: Transmission axis of polarizing plate Azimuth γ: Azimuth of optical axis (slow axis) of retardation plate φ: Twist angle of liquid crystal λ: Light wavelength Δn: Birefringence d: Cell gap (liquid crystal layer thickness) Δn · d: Retardation

Claims (11)

[Claims] 1. A two-layer structure in which a driving liquid crystal cell incorporating a reflecting plate integrally formed with pixel electrodes and a compensating liquid crystal cell are laminated, and a retardation plate and one polarizing plate are additionally laminated thereon. In the liquid crystal display, the retardation of the retardation plate compensation is characterized in that the retardation of the driving liquid crystal cell and the retardation of the compensating liquid crystal cell are adjusted and set without equal constraint, and the liquid crystal driving voltage is set to 3.5 V or less. Single polarizing plate type reflective two-layer liquid crystal display. 2. A driving liquid crystal cell in which a reflecting plate integrally formed with pixel electrodes is incorporated, and a compensating liquid crystal polymer film having the same molecular orientation as that of the compensating liquid crystal cell are laminated, and a retardation plate and 1 In a two-layer liquid crystal display in which a number of polarizing plates are additionally laminated, the retardation of the driving liquid crystal cell and the retardation of the compensating liquid crystal polymer film are adjusted and set without equal constraint, and the liquid crystal driving voltage is 3.5 V. A retardation plate compensating / single polarizing plate type reflective two-layer liquid crystal display characterized by the following settings. 3. A retardation plate compensating / single-polarizing plate type reflective two-layer liquid crystal display according to claim 1, wherein a quarter wave plate is provided in place of the retardation plate. 4. The retardation plate compensating / single-polarizing plate type reflective two-layer liquid crystal display according to claim 1, wherein two retardation plates are arranged in parallel. 5. The retardation plate compensating / single polarizing plate type reflective two-layer liquid crystal display according to claim 1, wherein a color filter is incorporated in the driving liquid crystal cell. 6. The two-layer liquid crystal display is a DTN-LCD.
The retardation plate compensating / single-polarizing plate type reflective two-layer liquid crystal display according to any one of claims 1 to 5. 7. A two-layer liquid crystal display is FDTN-LC.
6. The retardation plate compensating / single polarizing plate type reflection type 2 according to claim 1, wherein the reflection type 2 is D.
Layer liquid crystal display. 8. A two-layer liquid crystal display is MDTN-LC.
6. The retardation plate compensating / single polarizing plate type reflection type 2 according to claim 1, wherein the reflection type 2 is D.
Layer liquid crystal display. 9. The two-layer liquid crystal display is MFDTN-L.
The retardation plate compensating / single-polarizing plate type reflective two-layer liquid crystal display according to any one of claims 1 to 5, which is a CD. 10. A two-layer liquid crystal display is DP-LCD.
The retardation plate compensating / single-polarizing plate type reflective two-layer liquid crystal display according to any one of claims 1 to 5. 11. A two-layer liquid crystal display is FDP-LC.
6. The retardation plate compensating / single polarizing plate type reflection type 2 according to claim 1, wherein the reflection type 2 is D.
Layer liquid crystal display.