KR100562174B1 - Transflective Liquid Crystal Display - Google Patents

Abstract

The present invention relates to a transflective liquid crystal display device using a vertically and horizontally electric field, that is, a Prince electric field, arranged horizontally with respect to a substrate. In the reflection region, a polarizing plate, a λ / 2 retardation plate, a liquid crystal layer, and a reflecting plate are formed. The cell gap of the region is set to twice the reflecting region, and consists of a top polarizer, a top λ / 2 retardation plate, a liquid crystal layer, a bottom λ / 2 retardation plate, and a bottom polarizer. A normal black mode is realized, and a semi-transmissive liquid crystal display device having a high transmittance while showing a high transmittance and uniform reflection and transmittance with respect to an incident wavelength in a reflection and transmission region can be manufactured.

Transflective Liquid Crystal Display, Prince Field Switching, Wide Viewing Angle

Description

Transflective Liquid Crystal Display

1 is a schematic diagram of a transflective liquid crystal display device according to the present invention of Example 1;

FIG. 2 is an optical structure diagram of the reflective liquid crystal display of FIG. 1. FIG.

3 is an optical structural diagram of a transmissive liquid crystal display of FIG.

4 is a graph of reflectance and transmittance according to voltage application of Example 1. FIG.

5A is a graph of light transmittance in a reflection area and a transmission area when no voltage is applied.

5B is a graph of light transmittance in a reflection area and a transmission area when a voltage is applied.

6 is a schematic diagram of a transflective liquid crystal display device according to the invention of Example 2;

FIG. 7 is an optical structure diagram of the reflective liquid crystal display of FIG. 6. FIG.

8 is a parameter space for implementing an optimal transmissive liquid crystal display device.

FIG. 9 is an optical structure diagram of an optimal transmissive liquid crystal display device of FIG. 8; FIG.

10 is a graph of reflectance and transmittance according to voltage application.

Fig. 11A is a graph of light transmittance in a reflection area and a transmission area when no voltage is applied.

11B is a graph of light transmittance in a reflection area and a transmission area when voltage is applied.

Fig. 12A shows the viewing angle dependence for each gray level in the transmission region of the birefringence controlled mode.

12B is a view angle dependency for each gray level in the transmission region of the prince field driven mode.

13A is a view angle characteristic of a reflective region of a transflective liquid crystal display according to the invention of FIG. 6.

FIG. 13B is a view angle of a transmissive region of the transflective liquid crystal display according to the invention of FIG. 6; FIG.

<Description of the symbols for the main parts of the drawings>

1: upper polarizer plate 2: upper substrate

3: alignment film 5: liquid crystal

6: lower polarizer 7: lower substrate

8a: reflective opaque common electrode 8b: transparent common electrode

9: insulating layer 10: transparent pixel electrode

11: color filter 12: upper phase difference plate

13: lower retarder

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semi-transmissive liquid crystal display device in a liquid crystal mode using horizontally arranged liquid crystals using vertical and horizontal electric fields, ie, Prince Field Switching (FFS). A transmissive liquid crystal display device device.

In general, liquid crystal displays are generally classified into two types. It can be divided into a transmissive mode using an internal light source and a reflective mode using an external light source. The transmissive display uses an internal light source, which makes it difficult to apply a mobile information display due to its high power consumption, while the reflective display uses an external light source to consume very little power, and is thin, light, and has excellent outdoor visibility. However, the disadvantage of the reflective mode is that the display image is significantly degraded because the intensity of the ambient light is weak indoors. Therefore, various transflective display modes have been proposed to improve visibility in the outdoors or indoors, and to reduce the power consumption and apply them to mobile information communication displays. In general, liquid crystals that are arranged horizontally or vertically with respect to a substrate in the liquid crystal mode used are rearranged vertically or horizontally by a vertical electric field. The liquid crystal mode has a perfect dark state in front, but has a disadvantage in that the viewing angle is narrow due to a difference in light intensity according to the viewing angle. In addition, in the transflective liquid crystal display using a birefringent control type (hereinafter referred to as ECB) mode in which the liquid crystal directors are arranged horizontally with the rubbing directions of the upper and lower plates opposite to each other, the dark state is not excellent in the reflection region. In addition, since the liquid crystal rises in the electric field direction in the transmission region, the transmittance occurs asymmetrically according to the viewing angle, and the viewing angle is narrow. In order to improve the narrow viewing angle characteristics, an FFS mode has been proposed in which liquid crystals arranged horizontally with respect to the substrate are driven in one direction while being substantially parallel to the substrate by a visible Prince electric field which is an electric field.

On the other hand, in order to improve the narrow viewing angle characteristics, the liquid crystals arranged horizontally with respect to the substrate are driven in one direction while being substantially parallel to the substrate by the electric field of the Prince when the electric field is applied. Field Switching (hereinafter referred to as FFS) mode has been proposed.

Accordingly, an object of the present invention is to fabricate a transflective liquid crystal display using FFS mode having a wide viewing angle and high transmittance.

In order to achieve the above object, the present invention sets the optical cell structure of the optimal reflection type liquid crystal mode, and then sets the cell gap of the transmission area to twice the reflection type liquid crystal cell while maintaining the reflection cell structure in the transmission area. The optical cell structure of the optimal transmissive liquid crystal mode was proposed.

Example 1

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

The present invention uses a method of controlling the thickness of the liquid crystal layer by a first method using only liquid crystal in manufacturing a liquid crystal mode transflective liquid crystal display device using a Prince electric field in which liquid crystals are arranged horizontally with respect to a substrate.

Fig. 1 shows a schematic cross section of a transflective liquid crystal display proposed by the first method of the present invention. The lower substrate has a glass substrate 7 on the lower polarizer 6, and a common electrode 8, which is a planar electrode, on the lower polarizer 6. The common electrode 8 is formed of a reflecting portion and a transmitting portion, the reflecting portion is formed of the reflective electrode 8a, and the transmitting portion is composed of the transparent electrode 8b. An insulator 9 is placed above the common electrode 8 and below the pixel electrode 10 on one plane, and the pixel electrode 10 on the insulator is a lattice-shaped transparent electrode. The width of the pixel electrode 10 is about 1 to 4 µm, and the interval between the pixel electrodes is about 1 to 6 µm. The upper substrate has an upper glass substrate 2 under the upper polarizer 1, and a liquid crystal 5 is positioned between the upper substrate and the lower substrate.

Fig. 2 shows the optical cell structure in the reflective mode, where θ means the angle in the counterclockwise direction with respect to the x axis. Looking at the optical cell structure of the reflecting region, it consists of a polarizing plate, a liquid crystal cell, and a reflecting plate. A reflecting plate exists on the lower substrate, a liquid crystal layer is placed thereon, and the rubbing direction of the liquid crystal is 1 ° to 45 °, and the polarizing plate thereon. It is twisted 45 degrees with respect to this liquid crystal rubbing direction. Looking at the polarization state of light in this optical cell structure, the incident light becomes linearly polarized light by the polarizing plate, and the linearly polarized light is circularly polarized by 45 ° twisted with the liquid crystal director, and the liquid crystal is reflected by the reflecting plate again. Passing through the layer results in light rotated 90 ° to the first linearly polarized light. Therefore, a dark state is realized because it is twisted by 90 ° with the polarizing plate transmission axis and blocked by the polarizing plate absorption axis. Normal black (NB) mode that shows a dark state when no initial voltage is applied.

Figure 3 shows the optical cell structure of the transmission region proposed in the present invention. It consists of the upper plate polarizing plate 1, the liquid crystal cell 5, and the lower plate polarizing plate 6, and 45 degrees and an upper and lower polarizing plate are arranged in parallel with a liquid crystal cell with respect to the polarizing plate transmission axis direction of an upper plate. At this time, when looking at the polarization state of the light, the incident light is a linearly polarized light by the polarizing plate, the linearly polarized light is a linearly polarized light rotated 90 ° the linearly polarized light is twisted 45 ° with the liquid crystal director. Again, the light is rotated by 90 ° with respect to the lower polarizer transmission axis direction, and the light is absorbed by the lower polarizer absorption axis to realize the dark state. Therefore, it adopts NB mode which shows dark state in the transmissive and reflective areas when voltage is not applied.

Figure 4 shows the reflectance and transmittance according to the applied voltage when the incident wavelength in the transflective mode according to the voltage is 550nm. The driving voltage with a light efficiency of 98% in the reflective and transmissive regions is 5.9V in the reflective region and 4.7V in the transmissive region. As shown in the figure, a curve with different reflectance and transmittance according to voltage is shown because the cell gap of the transmissive region and the cell gap of the reflective region are different in the transflective mode.

FIG. 5 shows reflectance and transmittance when voltage is applied and no voltage is applied in the reflection region and the transmission region according to the incident wavelength. 5A shows the degree of light leakage in the transmission region and the reflection region when no voltage is applied. In addition, in the transmission region, the cell structure is the same as the reflection region due to the mirror effect, and thus the reflection and transmittance of the wavelength are almost the same, but the dependence on the wavelength is large. 5B shows the transmittance and reflectance according to the incident wavelength after voltage application. In the low incidence wavelength region, the reflection and transmittance are low, but the overall reflection and transmittance is uniform with the wavelength.

Example 2

The second embodiment of the present invention is more advanced than the case of the first embodiment, and in the transflective mode using only liquid crystal, the dependence on the wavelength is very severe. Therefore, in order to reduce the dependence on the wavelength, an optical phase film was added to the reflecting part and the transmitting part.

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

6 shows a schematic cross-sectional view of a transflective liquid crystal display proposed by the present invention. The same structure as in Example 1, but the lower phase difference plate (1) between the upper polarizing plate 1 and the upper glass substrate 2, the upper retardation plate 12 and the lower polarizing plate 6 and the lower glass substrate (7) 13) One sheet was added.

Fig. 7 shows the optical cell structure in the reflective mode, where θ means the angle in the counterclockwise direction with respect to the x axis. Looking at the optical cell structure of the reflection region was composed of a polarizing plate and a λ / 2 compensation film, 1 sheet, the liquid crystal cell and the reflection plate, the λ / 2 compensation film for a polarizing plate transmission axis 15 ^o, the liquid crystal cell and is 75 ^o twisted. The polarizing plate and the λ / 2 compensation film have a specific angle, making them a broadband λ / 4 compensation film for the electric field and having a perfect dark state. Referring to the dark state, and the light of the incident light is linearly polarized by the polarizer, the linearly polarized been light is λ / 2 compensation films and 15 ^o so turn become a linearly polarized light been 30 ^o rotation with respect to the direction in which the first incoming light, again The light is circularly polarized by 45 ^° twisted liquid crystal director and the light is rotated by 90 ^° to the first linearly polarized light by passing through the liquid crystal layer and λ / 2 compensation film by the reflector. Therefore, a dark state is realized because it is twisted by the polarizing plate 90 ^° and blocked by the polarizing plate.

FIG. 8 illustrates a parameter space for finding an optimal transmission cell structure in an optical cell structure of a reflective mode. The x axis represents the transmission axis of the polarizing plate, and the y axis represents the slow axis of the λ / 2 compensation film. Since the NB mode is adopted in the reflective mode, the transmissive area must have a dark state before voltage application. It can be seen that there are several cases where the dark state can be realized.

FIG. 9 illustrates an optical cell structure of a transmission region proposed in the present invention among conditions having a dark state before voltage application in FIG. 8. It consists of a top polarizer, a top plate λ / 2 compensation film, a liquid crystal cell, a bottom plate λ / 2 compensation film, and a bottom plate polarizing plate, and the top plate λ / 2 compensation film is 15 ^o with respect to the polarizing plate transmission axis direction. Is 75 ^o , 15 ^o is different from the lower plate λ / 2 compensation film, and the upper and lower polarizers are arranged in parallel. Therefore, it adopts NB mode which shows dark state in the transmissive and reflective areas when voltage is not applied.

10 illustrates reflectance and transmittance according to an applied voltage when an incident wavelength in the transflective mode according to voltage is 550 nm. The driving voltage with a light efficiency of 98% in the reflective and transmissive regions is 5.9V in the reflective region and 4.7V in the transmissive region. In addition, the voltage having a light efficiency of 50% is 2.5V in the reflection region R ₅₀ and 2.2V in the transmission region T ₅₀ . As shown in the figure, a curve with different reflectance and transmittance with respect to voltage is shown because in the transflective mode, the cell gap of the transmission region is twice the cell gap of the reflection region.

FIG. 11 shows reflectance and transmittance when voltage is applied in a reflection region and a transmission region according to an incident wavelength and when no voltage is applied. FIG. 11A shows the degree of light leakage in the transmission region and the reflection region when no voltage is applied. Darkness is well maintained at almost all wavelengths in the reflective region. The reason is that the transmission axis of the polarizing plate, the λ / 2 compensation film, and d Δ n become a wideband λ / 4 film with respect to the electric field due to the λ / 2 liquid crystal cell at a specific angle, thereby having a perfect dark state. In addition, in the transmissive region, the cell structure is the same as that of the reflective region due to the mirror effect, thereby having a perfect dark state. 11B shows the transmittance and reflectance according to the incident wavelength after voltage application. Except for the low incidence wavelength region, it shows uniform transmittance and reflectance. It can be seen that the wavelength dependence in the bright state is very low compared to the liquid crystal mode in which the liquid crystal is rotated in one direction when the cell is horizontally aligned with respect to the substrate when applied to the electric field.

12 shows the transmittance as a function of the polar angle with respect to the rubbing direction of the liquid crystal in the transmission type FFS mode and the transmission type ECB mode proposed in the present invention. Figure 12a shows the transmissive ECB mode, where the transmittance is asymmetric in the permeation direction, as mentioned earlier. In the bright state, the front side is best, but the polar angle is large, the luminance uniformity is greatly reduced. It can be seen that in the dark state, light leakage exists in a large polar angle direction, and gray level inversion occurs at -30 ^o . Figure 12b shows the transmission FFS mode proposed in the present invention, and the brightness uniformity of the bright state is very uniform. In the dark state, the gray level reversal occurs over ± 50 ^° .

Fig. 13 shows the viewing angle characteristics of the reflection area and the transmission area of the transflective liquid crystal mode according to the present invention. FIG. 13A illustrates the viewing angle characteristic of the reflective region when the incident wavelength is 550 nm. In the dark state, the region having the reflectances of 7%, 3%, and 1% is represented by an equal reflectance curve according to the incident wavelength. The darkness is perfect up to 30 ^o polar in all directions, and wider in the diagonal. The bright state shows an equal reflectance curve according to the incident wavelength when the driving voltage is applied. Areas of 70%, 50% and 30% of the maximum reflectance at the front face to the incident wavelength are shown. It can be seen that the reflectance for each incident wavelength is uniform according to the azimuth angle, which, unlike other transflective liquid crystal modes, shows that the wavelength dependency is very low in the bright state. In the diagram showing the contrast ratio (hereinafter referred to as CR), an area with a CR of 100 or more is approximately 55 ^o from the front, and is very good between 120 ^o ~ 150 ^o and 300 ^o ~ 330 ^{o in} specific directions. View angle characteristic. Figure 8b shows the viewing angle characteristics of the transmissive region. In the dark state, the transmissive curves of the transmittance range from 7%, 3%, and 1% in the same transmittance curve according to the incident wavelength. As shown in Fig. 13 (a), it is shown that the darkness is perfect up to a polar angle of 30 ^{o in the} direction. The bright state represents an area of 70%, 50%, and 30% of the front maximum transmittance at T ₁₀₀ of the incident wavelength of 550 nm, whereby the transmittance according to the azimuth angle occurs uniformly with respect to the incident wavelength. The area with CR of 5 or more is about 100 ^{o in the} vertical direction from the front and about 110 ^{o in the} horizontal direction. In addition, as in the reflective mode, it has excellent viewing angle characteristics in the specific directions 120 ^o to 170 ^o and 300 ^o to 330 ^o .

Therefore, the transflective liquid crystal display device according to the present invention has an effect of manufacturing a high-quality transflective liquid crystal display device device using the FFS mode showing a wide viewing angle and a high transmittance.

Claims (4)

An upper polarizer; An upper first phase film positioned below the upper polarizing plate and having a phase delay value of λ / 2; An upper substrate positioned below the upper first phase film; A horizontally arranged liquid crystal layer under the upper substrate having a cell gap of a transmissive region twice that of a reflective region, a rubbing direction of the liquid crystal being 1 ° to 45 °, and driven by a Prince electric field; A pixel electrode of the transparent electrode under the liquid crystal layer; An insulating layer under the pixel electrode; A common electrode of a planar shape divided into a reflective region of a reflective opaque electrode and a transparent region of a transparent electrode under the insulating layer; A lower substrate positioned below the common electrode; A lower second phase film positioned below the lower substrate and having a phase delay value of λ / 2 and arranged in parallel with an optical axis of the upper first phase film; A lower polarizing plate positioned under the lower second phase film and having an optical axis parallel to the upper polarizing plate; FFS transflective liquid crystal display device comprising. The method of claim 1, The common electrode is a planar electrode, divided into a reflecting part and a transmitting part, the reflecting part is a reflecting electrode, the transmitting part is a transparent electrode, and the pixel electrode is formed in a lattice form, and the width of the pixel electrode is about 1 to 4 μm. And an interval between the pixel electrodes is about 1 to 6 mu m. The method of claim 1, When the rubbing direction of the liquid crystal is β, the FFS transflective liquid crystal display device in which the optical axis of the vertical polarizing plate transmission axis and the vertical optical compensation film in the transmission region are bent + 60 ° and β + 75 °, respectively. The method of claim 1, In the semi-transmissive LCD which removes the optical compensation film which has a phase delay value of (lambda) / 2 between a board | substrate and a polarizing plate, when the rubbing direction of a liquid crystal is (beta), the polarizing plate transmission axis in a reflection area is (beta) + 45 degrees, FFS transflective liquid crystal display device with 90 ° twisted polarizing plate transmission axis

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