KR100659487B1 - Optically Compensated Splay Liquid Crystal Display - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a liquid crystal display device having a wide viewing angle characteristic, a high transmittance and a high-speed response with a vertically oriented single domain liquid crystal display device, wherein a vertical electric field is applied after liquid crystal molecules are transferred to a splay state by applying a specific voltage. The transmissive and reflective single domain vertically oriented liquid crystal display devices can be fabricated using.

Single domain, splay array, transmissive and reflective liquid crystal display, vertical electric field

Description

Optically Compensated Splay Liquid Crystal Display with Optical Magnetic Compensation Splay Structure

1A shows an arrangement of liquid crystal molecules upon application of voltage before a splay transition.

Figure 1b is a liquid crystal molecular arrangement according to the application of voltage after the splay transition.

Fig. 2 is a sectional view of a transmissive LCD in NW mode according to the first embodiment.

3 is an optical cell structure diagram of FIG.

4 is an initial transmittance curve according to the phase delay value of FIG.

5 is a transmittance curve according to voltage application for each phase delay of FIG. 3.

FIG. 6 is a cross-sectional view of the LCD with the compensation film added thereto. FIG.

7 is an optical cell structure diagram of FIG. 6.

8 is a transmittance curve according to the voltage application of FIG.

9 is a contrast ratio curve of FIG. 7.

FIG. 10 is a wavelength dispersion curve of gray levels of FIG. 7. FIG.

Fig. 11 is a sectional view of a transmissive LCD in NB mode according to the first embodiment.

12 is an optical cell structure diagram of FIG.

13 is an initial transmittance curve according to the phase delay value of FIG. 12.

14 is a transmittance curve according to the voltage application of FIG. 12.

15 is a contrast ratio curve of FIG. 12.

FIG. 16 is a wavelength dispersion curve of gray levels of FIG. 12. FIG.

FIG. 17 is a response time for each gray level of FIG. 12. FIG.

Fig. 18 is a sectional view of a reflective LCD in NW mode according to a second embodiment of the present invention.

19 is an optical cell structure diagram of FIG. 18;

20 is an initial reflectance curve according to the phase delay value of FIG. 19.

21 is a reflectance curve according to the voltage application of FIG.

22 is a contrast ratio curve of FIG. 19.

FIG. 23 is a wavelength dispersion curve of gray levels of FIG. 19. FIG.

Fig. 24 is a sectional view of a reflective LCD in NB mode according to a second embodiment of the present invention.

25 is an optical cell structure diagram of FIG. 24;

FIG. 26 is an initial reflectance curve according to the phase delay value of FIG. 25. FIG.

27 is a reflectance curve according to the application of the voltage of FIG.

FIG. 28 is an equal contrast curve of FIG. 25. FIG.

FIG. 29 is a wavelength dispersion curve of gray levels of FIG. 25. FIG.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display (hereinafter referred to as LCD) having an optically compensated splay (OCS) structure, and more particularly, to a transmissive and reflective single domain LCD. .

In general, TN (vertical nematic) and VA (Vertical Alingment) have a narrow viewing angle problem in a conventional single domain LCD, and in-plane swiching (IPS) mode causes afterimages in video implementation due to slow response speed. have. Therefore, an OCB (optically compensated bend) mode has been developed to overcome the problems of the conventional liquid crystal display.

The OCB (optically compensated bend) mode has a wide viewing angle due to the self-compensation effect of the liquid crystal molecules itself, and the response speed is fast due to the same direction of fluid flow by the liquid crystal molecules before and after voltage application. have. However, there is a disadvantage in that multiple layers of compensation film must be used to compensate for the black state.

Therefore, the existing single domain LCD has a compensation film because there is an image change according to the viewing angle, and the OCB mode having its own compensation structure with a single domain must use multiple layers of compensation film to realize perfect darkness. The use of such compensation films is limited because they only compensate for certain phases.

On the contrary, the objective of the present invention is to manufacture a transmissive type and a reflective type LCD using a vertical electric field in a single domain OCS mode that exhibits a wide viewing angle characteristic due to the self-compensation effect of the display arrangement.

 In order to achieve the above object, the present invention has proposed an optimal optical cell structure of the transmissive and reflective liquid crystal mode.

Example 1

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

Example 1 is a method using a vertical electric field in the production of a single-domain LCD, it is possible to Normally white (NW) mode showing the initial bright state and Normally black (NB) mode showing the dark state Do.
1 illustrates a liquid crystal arrangement state according to an initial stage of an OCS liquid crystal cell and voltage application. FIG. 1 (a) shows that the liquid crystal molecules in the twisted bend state lie in parallel with the substrate while being twisted 180 ° upon application of voltage to the liquid crystal array state before the transition to the initial splay arrangement of the OCS liquid crystal cell. FIG. The arrangement state of the liquid crystal molecules according to the application of voltage in the splay arrangement state is shown.

Fig. 2 shows a schematic cross section of the transmissive LCD proposed by the first method of the first embodiment. The lower substrate has a lower glass substrate 9 on the lower polarizer 10 and a transparent electrode 8 thereon. The vertical alignment layer 7 is coated on the transparent electrode 8. The upper substrate is arranged in the order of the upper polarizing plate 1, the compensation film 2, the glass substrate 3, the transparent electrode 4, and the vertical alignment layer 5. The liquid crystal 6 is positioned between the upper substrate and the lower substrate. When a voltage is applied to the upper and lower substrates, a vertical electric field is generated, and since the liquid crystal has a negative dielectric anisotropy, the liquid crystals are arranged perpendicularly to the direction of the electric field so that the director of the liquid crystal lies horizontally on the substrate. Therefore, the liquid crystal exhibits high-speed response because the up and down fluid flows in the same direction around the center of the cell while driving the splay, and the directors of the upper and lower liquid crystal layers have a symmetry between them. As a result, a wide viewing angle effect is obtained.

FIG. 3 shows the transmissive LCD optical cell structure of FIG. 2, where θ means the angle in the counterclockwise direction with respect to the x-axis. The rubbing direction of the liquid crystal is 45 ^° counterclockwise with respect to the x-axis both up and down, and the transmission axes of the upper and lower polarizing plates 1 and 10 are arranged at 90 ^° and 0 ^° .

FIG. 4 illustrates initial transmittance according to the phase delay value dΔn of the liquid crystal in the transmissive LCD optical cell structure of FIG. 3. When no initial liquid crystal is present (dΔn = 0), no phase delay of light occurs so that the linearly polarized light passing through the lower polarizer coincides with the absorption axis of the upper polarizer and thus no light passes. That is, while showing a dark state between orthogonal polarizers, the transmittance occurs as the phase delay value exists. In a liquid crystal cell in a hybrid arrangement such as OCS, the effective phase delay value dΔneff at the front is (dΔn) / 2. It can be seen that when the incident wavelength λ is 550 nm, the best bright state is shown when dΔn of the initial liquid crystal is near λ, and when the incident wavelength λ is near λ, a good dark state is shown. Therefore, by adjusting dΔn of the liquid crystal, a normally white (NW) mode showing an initial bright state and a normally black (NB) mode showing a dark state are possible.

FIG. 5 is a graph of transmittance variation according to voltage application in the NW mode in which the initial stage is the bright state in the transmissive LCD optical cell structure of FIG. 3. When voltage is applied, the arrangement of the liquid crystals is changed to change the phase delay of light. Because of this, the maximum transmittance is initially shown, and the transmittance decreases with the application of voltage, thereby showing a dark state. The driving voltage is high when dΔn of the liquid crystal cell is near λ, and the driving voltage is low when dΔn is larger than λ. However, when dΔn is near λ, the dark state is uniform and wavelength dispersion is good depending on the application of voltage. However, when dΔn is larger than λ, the dark state is not uniform and wavelength dispersion is also poor. To compensate for this disadvantage, the compensation film may be used to implement the NW mode.

FIG. 6 shows a schematic cross-sectional view of a transmissive LCD using one sheet of compensation film in the first method of Example 1. FIG. The lower substrate has a lower glass substrate 9 on the lower polarizer 10 and a transparent electrode 8 thereon. The vertical alignment film 7 is coated on the transparent electrode 8. The upper substrate is arranged in order of the upper polarizing plate 1, the compensation film 2, the glass substrate 3, the transparent electrode 4, and the vertical alignment layer 5. The liquid crystal 6 is positioned between the upper substrate and the lower substrate.

FIG. 7 shows the transmissive LCD optical cell structure of FIG. 6, where [theta] means an angle counterclockwise with respect to the x-axis. In order to compensate for the viewing angle characteristic and the wavelength dispersion property, a single compensation film 2 was used between the upper polarizing plate 1 and the glass substrate 3. The upper polarizer 1 and the lower polarizer 10 are respectively arranged parallel to the y-axis and the x-axis, and the compensation film 2 is -45 ^o and the rubbing direction of the liquid crystal is 45 ^o , counterclockwise with respect to the x-axis. The direction is distorted. The compensation film 2 at this time was used to compensate for the bright state as a discotic film.

FIG. 8 is a graph illustrating changes in transmittance according to voltage application in the NW mode in the transmissive LCD optical cell structure of FIG. 7. It has a high light efficiency of 94.7%.

FIG. 9 illustrates a contrast ratio (hereinafter referred to as CR) when the incident wavelength is visible light in the NW mode transmissive LCD of FIG. 7. The area where CR is more than 10: 1 is 80 ^{o in the} up, down, left and right, and 50 ^{o in the} diagonal direction.

FIG. 10 shows the transmittance according to the wavelength when divided into six gradations based on the transmittance of the NW mode transmissive LCD of FIG. 7.

FIG. 11 shows a schematic cross section of a transmissive LCD of NB mode proposed by the second method of Example 1. FIG. The lower substrate has a lower glass substrate 9 on the lower polarizer 10 and a transparent electrode 8 thereon. The vertical alignment film 7 is coated on the transparent electrode 8. The upper substrate is arranged in the order of the upper polarizing plate 1, the HWP 2 having a phase value of λ / 2, the glass substrate 3, the transparent electrode 4, and the vertical alignment film 5. The liquid crystal 6 is positioned between the upper substrate and the lower substrate.

FIG. 12 shows the transmissive LCD optical cell structure of FIG. 11, where θ means the angle in the counterclockwise direction with respect to the x-axis. The rubbing direction of the liquid crystal is 45 ^° counterclockwise with respect to the x-axis both up and down. HWP 2 is turned to 135 ^o .

FIG. 13 illustrates the initial transmittance according to the phase delay value dΔn of the liquid crystal in the transmissive LCD optical cell structure of FIG. 12. When there is no initial liquid crystal (dΔn = 0), the linearly polarized light passing through the lower polarizer does not generate phase retardation between the upper and lower glass substrates, and passes through the HWP (2) having a phase value of λ / 2. Since the linearly polarized light is twisted by 90 ° and the light is transmitted in accordance with the transmission axis of the upper polarizing plate, it initially shows a bright state. As the phase delay value of the liquid crystal is present, the light shows the state of bright to dark and bright to dark. The liquid crystal cell initially shows a dark state when dΔn at the front is 550 nm.

FIG. 14 is a graph showing a change in transmittance according to voltage application in an NB mode in which the initial state is a dark state in the transmissive LCD optical cell structure of FIG. 12. The light efficiency at this time is about 91%.

FIG. 15 shows viewing angle characteristics of an NB-mode transmissive LCD, and an area having a CR of 10: 1 or more is about 80 ^{° in the up} , down, left, and right directions, and 55 ^{° in the} diagonal direction.

FIG. 16 shows the transmittance according to the wavelength when divided into six gradations based on the transmittance of the NB mode transmissive LCD of FIG. 12.

FIG. 17 illustrates NB mode cells of the transmissive LCD of FIG. 12 and measures response time for each gray level. In this case, the thickness d of the liquid crystal cell is 3.5 μm. It shows fast response time of less than 5ms in all gradations.

Example 2 (reflective)

The second embodiment of the present invention is a single domain reflective LCD using a vertical electric field, unlike the first embodiment (single domain transmissive LCD).

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

Fig. 18 shows a schematic cross section of the reflective LCD proposed by the first method of the second embodiment. The lower substrate has a reflective electrode 9 on the lower glass substrate 10, and a vertical alignment layer 8 is coated on the reflective electrode 9. The upper substrate includes an upper polarizing plate 1, a half wave plate (HWP) having a lambda / 2 characteristic, a quarter wave plate (QWP) having a lambda / 4 characteristic, a glass substrate ( 4), the transparent electrode 5 and the vertical alignment film 6 are arranged in this order. The liquid crystal 7 is positioned between the upper substrate and the lower substrate.

FIG. 19 shows the reflective LCD optical cell structure of FIG. 18, where [theta] means an angle counterclockwise with respect to the x-axis. Counterclockwise about the liquid crystal rubbing direction are up, down to both the x-axis 55 ^o twisted and the transmission axis 40 ^o twisted and of the upper HWP (2) and QWP (3) of the upper polarizing plate (1) are each 115 ^o, 145 ^{o It is} wrong.

FIG. 20 illustrates the initial reflectance according to the phase delay value dΔn of the liquid crystal in the reflective LCD optical cell structure of FIG. 19. When there is no initial liquid crystal (dΔn = 0), the linearly polarized light passing through the upper polarizer passes through HWP (2) and QWP (3) once (λ / 2 + λ / 4 = 3λ / 4), and the light from the reflector This reflection causes the HWP 2 and the QWP 3 to pass each other again (λ / 2 + λ / 4 = 3λ / 4). That is, light passes 3λ / 2 with a total of 3λ / 4 + 3λ / 4. Therefore the the initial linearly polarized light is passed and the phase difference film again reflected by the reflecting plate after the phase difference film 90 ^o rotation by obtaining a phase difference of 3λ / 2 linearly polarized. As a result, the linearly polarized light passes through the absorption axis of the upper polarizer to absorb light, initially showing a dark state. As the phase delay value of the liquid crystal is present, the light shows the state of bright to dark and bright to dark. When the incident light is 550 nm, the liquid crystal exhibits an initially bright state when dΔn of the liquid crystal is λ / 2, that is, 275 nm.

FIG. 21 shows the reflectance according to the voltage application of the NW mode in which the initial stage is the bright state in the reflective LCD optical cell structure of FIG. 19. The reflectance at this time is about 90%, indicating a high reflectance.

FIG. 22 illustrates a contrast ratio (hereinafter referred to as CR) when the incident wavelength is visible light in the NW mode reflective LCD according to FIG. 19. CR is 5: 80 ^o and, in the diagonal direction of 40 ^o around the one or more areas, down, left, and right.

FIG. 23 shows the reflectance according to the wavelength when divided into six gradations based on the reflectance of the NW mode reflective LCD according to FIG.

Fig. 24 shows a schematic cross section of the reflective LCD proposed in the second method of the second embodiment. The lower substrate has a reflective electrode 8 on the lower glass substrate 9, and a vertical alignment layer 7 is coated on the reflective electrode 8. The upper substrate is arranged in the order of the upper polarizing plate 1, a half wave plate (HWP) 2 having a λ / 2 characteristic, a glass substrate 3, a transparent electrode 4, and a vertical alignment layer 5. . The liquid crystal 6 is positioned between the upper substrate and the lower substrate.

Fig. 25 shows the NB mode reflective LCD optical cell structure of Fig. 24, where θ means the angle in the counterclockwise direction with respect to the x axis. The rubbing direction of the liquid crystal is turned 150 ^° counterclockwise with respect to the x-axis both up and down, the transmission axis of the upper polarizer 1 is shifted by 75 ^° and the upper HWP 2 coincides with the y-axis.

FIG. 26 illustrates initial reflectance according to the phase delay value dΔn of the liquid crystal in the reflective LCD optical cell structure of FIG. 25. When no initial liquid crystal is present (dΔn = 0), the linearly polarized light passes through the upper polarizer and passes through the HWP (2), and the light is reflected from the reflector and passes through the HWP (2) again. That is, the light passes λ with a total of λ / 2 + λ / 2. Therefore, the initial linearly polarized light passes through the retardation film, is reflected by the reflector, and again passes through the retardation film to obtain a retardation of λ so that the polarization state does not change. As a result, the linearly polarized light passes through the transmission axis of the upper polarizing plate to transmit light, thereby initially displaying a bright state. As the phase delay value of the liquid crystal is present, it shows a bright state to a dark state and a bright state to a dark state. When the incident light is 550 nm, the liquid crystal initially exhibits a dark state when dΔn is λ / 2, that is, 275 nm.

FIG. 27 is a graph of reflectance change according to voltage application in an NB mode in which the initial state is a dark state in the reflective LCD optical cell structure of FIG. 25. The light efficiency at this time is about 85%.

Figure 28 is a CR illustrates the viewing angle characteristics of the NB mode reflective LCD 5: the 55 ^o about the one or more regions in the vertical direction 80 ^o, and the left and right diagonal directions.

FIG. 29 shows the reflectance according to the wavelength when divided into six gradations based on the reflectance of the NB mode reflective LCD of FIG.

Therefore, the transmissive and reflective LCD according to the present invention has the effect of eliminating manufacturing complexity by using a single domain and manufacturing a single domain LCD device using a vertical electric field. The LCD of the present invention will greatly contribute to the improvement of image quality and response time compared to the conventional single domain LCD.

Claims (5)

An upper substrate; A liquid crystal layer in which vertically aligned dielectric anisotropy located below the upper substrate is negative; A lower substrate positioned below the upper liquid crystal layer; An array in which liquid crystals vertically arranged on the upper and lower panels are twisted 180 ^° and lying parallel to the upper and lower plates when a voltage below a threshold voltage is applied; A liquid crystal display device showing a splay arrangement in which liquid crystals lie parallel to the upper and lower substrates without kinks when a pulse or a high voltage above a threshold voltage is applied. An upper polarizer; An upper phase film of a discotic shape having a phase difference of 450 to 510 nm positioned under the upper polarizing plate; An upper substrate positioned below the upper phase film; A liquid crystal layer in a splay arrangement positioned below the upper substrate; A lower substrate positioned below the liquid crystal layer; An NW mode transmissive liquid crystal display device using a vertical electric field of a single domain including a lower polarizer plate disposed below the lower substrate. An upper polarizer; An upper phase film using an uniaxil film having a phase difference of 250 nm to 300 nm positioned below the upper polarizer; An upper substrate positioned below the upper phase film; A liquid crystal layer in a splay arrangement positioned below the upper substrate; A lower substrate positioned below the liquid crystal layer; An NB mode transmissive liquid crystal display device which initially displays darkness using a vertical electric field of a single domain including a lower polarizer plate positioned below the lower substrate. An upper polarizer; An HWP located below the upper polarizer; A QWP located below the HWP; An upper substrate positioned below the QWP; A liquid crystal layer in a splay arrangement positioned below the upper substrate; A lower reflective electrode positioned below the liquid crystal layer; An NW mode reflective liquid crystal display device using a vertical electric field of a single domain including a lower substrate positioned below the lower reflective electrode. An upper polarizer; An HWP having a phase value of λ / 2 below the upper polarizer; An upper substrate positioned below the HWP having a phase value of λ / 2; A liquid crystal layer in a splay arrangement positioned below the upper substrate; A lower reflective electrode positioned below the liquid crystal layer; NB mode reflective liquid crystal display device that initially displays the dark using a vertical electric field of a single domain including the lower substrate positioned below the lower reflective electrode.

Images