KR20120073041A - Bistable chiral splay nematic mode liquid crystal display device - Google Patents

Abstract

The present invention provides a display device comprising: first and second substrates facing each other with a display area and a non-display area defined outside thereof; A plate-shaped first electrode formed on an inner side surface of the first substrate; A first insulating layer covering the first electrode; A second electrode and a third electrode spaced apart from each other on the inner side of the first insulating layer and formed side by side in a first direction; A fourth electrode having a plate shape formed on an inner side surface of the second substrate; A BCSN (bistable chiral splay nematic) liquid crystal layer interposed between the first substrate and the second substrate, and having a memory driving mode and a dynamic driving mode, wherein the splay image represents black in the two modes. A bistable chiral splay nematic mode liquid crystal display is provided.

Description

BCS mode liquid crystal display device {Bistable chiral splay nematic mode liquid crystal display device}

The present invention relates to a liquid crystal display, and more particularly, to a bistable chiral splay nematic (BCSN) liquid crystal display capable of switching between a memory mode and a dynamic mode.

Recently, as the information society has developed rapidly, the necessity of a display device having excellent characteristics such as thinning, light weight, and low power consumption has emerged. Accordingly, development of flat panel displays has been actively conducted. In particular, liquid crystal displays are excellent in resolution, color display, image quality, and the like, and are being actively applied to monitors of notebook computers and desktop computers.

In general, a liquid crystal display device arranges two substrates on which electrodes are formed so that the surfaces on which the two electrodes are formed face each other, injects a liquid crystal material between the two substrates, and applies a voltage to the two electrodes to generate an electric field. By moving the liquid crystal molecules, the image is expressed by the transmittance of light that varies accordingly.

In more detail, the structure thereof will be described with reference to FIG. 1, which is an exploded perspective view of a general liquid crystal display. As shown, the liquid crystal display includes an array substrate 10 and a color filter with a liquid crystal layer 30 therebetween. The substrate 20 has a configuration in which the substrates are face-to-face bonded to each other. The array substrate 10 of the lower part of the plurality of gate wirings 14 is vertically and horizontally arranged on the upper surface of the transparent substrate 12 to define a plurality of pixel regions P. And a data line 16, and a thin film transistor T is provided at an intersection point of the two lines 14 and 16 so as to be connected one-to-one with the pixel electrode 18 provided in each pixel region P. FIG.

In addition, the upper color filter substrate 20 facing the array substrate 10 is a rear surface of the transparent substrate 22 and non-display of the gate wiring 14, the data wiring 16, and the thin film transistor Tr. A grid-like black matrix 25 is formed around the pixel region P so as to cover the region, and red (R) and green are sequentially arranged in order to correspond to the pixel region (P) in the grid. A color filter layer 26 including (G) and blue (B) color filter patterns 26a, 26b, and 26c is formed, and is transparent over the entire surface of the black matrix 25 and the color filter layer 26. The common electrode 28 is provided.

Although not shown in the drawings, each of the two substrates 10 and 20 is sealed with a sealant or the like along the edge to prevent leakage of the liquid crystal layer 30 interposed therebetween. 10 and 20 are interposed between the upper and lower alignment layers that provide reliability in the molecular alignment direction of the liquid crystal at the boundary between the liquid crystal layer 30 and the polarization axes perpendicular to each other on the outer surfaces of the substrates 10 and 20. Each of the first and second polarizing plates is provided.

In addition, a back-light is provided on the outer surface of the array substrate 10 to supply light, so that the on / off signal of the thin film transistor Tr is supplied to the gate wiring 14. When the image signal of the data wiring 16 is transferred to the pixel electrode 18 of the selected pixel region P by being sequentially scanned and applied, the liquid crystal molecules are driven by the vertical electric field therebetween, and thus the transmittance of light We can display various images by change

In such a liquid crystal display device, liquid crystals that are frequently used are of the nematic type, smectic type, and cholesteric type. Among the liquid crystals described above, the arrangement of the liquid crystals may be disturbed. In this case, nematic liquid crystals having the property of scattering the light most are used the most.

The electro-optic effect of liquid crystals refers to the phenomenon in which the optical properties of a liquid crystal cell change, resulting in electrical optical modulation, which is caused by the change of liquid crystal molecules from one array state to another by application of an electric field. .

In the liquid crystal display device applying the nematic liquid crystal, the TN (twisted nematic) type and the STN (super twisted nematic) type are most commonly used in view of the fact that molecular arrangement is continuously changed when an electric field is applied to the nematic liquid crystal. do.

In the TN mode type, the panel is configured to have an angle of 90 degrees on each of the transparent electrodes oriented so that the major axis of the liquid crystal molecules are parallel to the electrode surface, and the nematic liquid crystal is interposed therebetween from one electrode. It has an array state twisted 90 degrees continuously in the longitudinal axis direction of the molecule toward the electrode surface of the liquid crystal structure, and the transverse electric field mode type uses a common electric field and a pixel electrode arranged on the same substrate, By rotating the liquid crystal molecules, the viewing angle characteristic is improved compared to the TN mode.

Meanwhile, recently, various types of display devices have been introduced to satisfy rapidly changing consumer demands. In particular, various products are being introduced for light weight, thinness, and energy efficiency due to the advancement and portability of information usage environment. These products are intended to include various functions such as watching video and e-book.

In line with this trend, dual mode-capable liquid crystals can be used to minimize both dynamic mode and power consumption for video viewing, and to use memory modes that act as e-books or e-papers. A display device is needed.

In order to cope with this problem, BCSN (Bistable chiral splay nematic) mode LCDs have been developed.

In the case of the BCSN (Bistable Chiral Splay Nematic) liquid crystal display, the memory mode uses bistable stability between the splay phase and the π-twist phase, and in the dynamic mode, the low bend phase and the high bend phase are high. Switching between phases is used.

However, the conventional BCSN (Bistable chiral splay nematic) liquid crystal display device having such a driving problem is difficult to design a compensation film that satisfies the memory mode and the dynamic mode at the same time because the black state of the memory mode and the dynamic mode is different from each other.

That is, only the optimized black characteristics can be implemented for either the memory mode state or the dynamic mode state. Thus, when the device is operated in an unoptimized mode, the black characteristic is degraded and the contrast ratio is reduced, thereby finally providing excellent display quality. There is a problem that cannot be done.

Accordingly, in order to solve the above-described problem, the present invention has an optimized black state when both driving in the memory mode and the dynamic mode, thereby providing an image having excellent display quality with excellent contrast ratio in either the dynamic mode or the memory mode. It is an object of the present invention to provide a bistable chiral splay nematic (BCSN) mode liquid crystal display.

In order to achieve the above object, a bistable chiral splay nematic (BCSN) mode liquid crystal display according to the present invention includes a first and second substrates facing each other with a display area and a non-display area defined outside thereof; A plate-shaped first electrode formed on an inner side surface of the first substrate; A first insulating layer covering the first electrode; A second electrode and a third electrode spaced apart from each other on the inner side of the first insulating layer and formed side by side in a first direction; A fourth electrode having a plate shape formed on an inner side surface of the second substrate; It includes a bistable chiral splay nematic (BCSN) liquid crystal layer interposed between the first substrate and the second substrate, and has a memory driving mode and a dynamic driving mode, and the splay image represents black in the two modes.

In this case, a first lambda / 4 phase difference film, a second lambda / 4 phase difference film and a polarizing plate are sequentially provided on the outer surface of the second substrate, the light transmission axis of the first lambda / 4 phase difference film is the polarizing plate It is arranged to have an angle of 70 degrees with the light transmission axis of, and the second λ / 4 retardation film is characterized in that the light transmission axis is arranged to have an angle of 35 degrees with the light transmission axis of the polarizing plate.

The first and second alignment layers may include a first alignment layer formed to cover the second and third electrodes, and a second alignment layer formed to cover the fourth electrode, and the first and second alignment layers may have a light transmission axis of the polarizing plate. The second and third electrodes are formed as a reference, and the second and third electrodes are arranged such that their major axes are perpendicular to the alignment direction.

The first substrate may include a first thin film transistor connected to the first electrode and a second thin film transistor connected to the second electrode.

The first substrate may include a gate wiring and first and second data wirings crossing the gate wiring, and the gate wiring and the first data wiring are connected to the first thin film transistor, and the gate wiring and the second data wiring are connected to each other. Is connected to the second thin film transistor, or the first substrate includes first and second gate wires and data wires crossing the first and second gate wires, and the first gate wire and data wires are connected to the first thin film transistor. The second gate line and the data line may be connected to the second thin film transistor.

In addition, a reflector is provided between the first substrate and the first electrode, wherein the reflector is characterized in that the surface of the embossed structure is convex.

In addition, a first auxiliary line is provided in the non-display areas on both sides of the display area of the first substrate, and all of the third electrodes are formed such that one end thereof is connected to the first auxiliary line.

In addition, a color filter layer may be formed on an inner surface of the second substrate, and the fourth electrode may be formed below or above the color filter layer.

 In addition, the bistable chiral splay nematic (BCSN) liquid crystal layer forms a splay state displaying white when no voltage is applied to the first, second, third, and fourth electrodes, and the first and second splay nematic (BCSN) liquid crystal layers. When a voltage is applied to the fourth electrode to generate a vertical electric field, a high band state is formed. When the vertical electric field is removed from the high band state, the fourth electrode forms a π-twist state in which black is displayed. When a voltage is applied to three electrodes and a voltage having a voltage difference greater than a threshold voltage is applied to generate a strong transverse electric field, the splay state is achieved. The threshold voltage difference is applied to the second and third electrodes in the π-twist state, respectively. When a voltage having a smaller voltage difference is applied and a weak transverse electric field is generated, an intermediate twist state representing white and gray is formed, and the bistable chiral splay nemat is used. ic) The liquid crystal layer is characterized in that the free energy is minimum in the splay state and the π-twist state, respectively, so that the liquid crystal layer maintains each state even when an electric field is not continuously applied.

In this case, the memory mode driving is implemented through the splay state, the high band state, and the π-twist state, and the dynamic mode driving is implemented through the π-twist state and the intermediate twist state.

In addition, the threshold voltage difference is characterized in that the 25V to 30V.

As described above, a bistable chiral splay nematic (BCSN) mode liquid crystal display according to an exemplary embodiment of the present invention may be selectively implemented in a memory mode and a dynamic mode, and furthermore, when the two modes are implemented, the same black state is used. As a result, the black characteristics are excellent, the contrast ratio is large, and the display quality is excellent.

The bistable chiral splay nematic (BCSN) mode liquid crystal display according to the embodiment of the present invention forms a reflective display device, and thus does not require a backlight unit, thereby minimizing power consumption and implementing a thin shape.

1 is an exploded perspective view of a general liquid crystal display device.
2 is a plan view of one pixel area of a BCSN mode liquid crystal display according to an embodiment of the present invention;
3 is a cross-sectional view of a portion cut along the cutting line III-III of FIG.
4 is a view showing a state in each mode driving of the bistable chiral splay nematic (BCSN) mode liquid crystal display according to an embodiment of the present invention.
FIG. 5 illustrates a simulation result of arrangement states of liquid crystal molecules according to voltage differences applied to second and third electrodes in a π-twist state in a BCSN (bistable chiral splay nematic) liquid crystal display according to an exemplary embodiment of the present invention. The figure which shows.
FIG. 6 is a view illustrating a layout relationship of each component optimized to have a high contrast ratio and excellent black characteristics in a bistable chiral splay nematic (BCSN) mode liquid crystal display according to an exemplary embodiment of the present invention.

Hereinafter, a BCSN mode liquid crystal display according to the present invention will be described in detail with reference to the accompanying drawings.

 FIG. 2 is a plan view of one pixel area of a BCSN mode liquid crystal display according to an exemplary embodiment of the present invention. The first substrate is mainly illustrated, and FIG. 3 illustrates a portion of FIG. 2 taken along a cutting line III-III. It is a cross section.

FIG. 2 is a plan view of one pixel area of a reflective bistable chiral splay nematic (BCSN) mode liquid crystal display according to a first exemplary embodiment of the present invention, and FIG. 3 is a view taken along line III-III of FIG. Sectional view of the part.

As shown, the reflective bistable chiral splay nematic (BCSN) mode liquid crystal display 100 according to the present invention has a plurality of pixel regions P and a thin film transistor Tr which is a switching element in each pixel region P. As shown in FIG. And a first substrate 101 having first, second, and third electrodes 166, 173, and 175, and a reflecting plate 155 having an embossing structure, and a second having a fourth electrode 185 as a transparent material on the front surface. A substrate 180 and a bistable chiral splay nematic (BCSN) liquid crystal layer 190 interposed between the two substrates 101 and 180 are provided.

First, the configuration of the first substrate 101 including the thin film transistor Tr and the reflecting plate 155 having the embossing structure is made of a transparent plastic material or film having a transparent glass material or flexible characteristics. In the first substrate 101, gate lines 103 and first and second data lines 130 and 131 are formed to cross each other through the gate insulating layer 115 and define a plurality of pixel regions P. Referring to FIG. In this case, the common substrate 106 is formed in the first substrate 101 to pass through the pixel region P in parallel with the gate wiring 103, and a part of the common wiring 106 is another region. The first storage electrode 107 is formed by being thickly formed.

In addition, near the region where the gate line and the first data line cross each other, the gate line and the first data line 103 and 130 are connected to each other, and the first gate electrode 106, the gate insulating layer 112, and the pure amorphous layer are connected to the gate line and the first data line. Switching comprising a first semiconductor layer 120 composed of a first active layer 120a of silicon and a first ohmic contact layer 120b of impurity amorphous silicon, and first source and drain electrodes 133 and 136 spaced apart from each other. A first thin film transistor Tr, which is an element, is formed.

In this case, since the first drain electrode 136 of the first thin film transistor Tr extends to overlap the first storage electrode 107, a portion overlapping with the first storage electrode 107 is formed in the second storage. The electrode 137 is formed. The first and second storage electrodes 107 and 137 overlapping each other and the gate insulating layer 115 interposed between the two electrodes 107 and 137 form a storage capacitor StgC.

In addition, the gate line 103 and the second data line 131 are connected to a region where the gate line 103 and the second data line 131 cross each other, and the second gate electrode 110 and the gate insulating layer are connected to each other. A second semiconductor layer (not shown) consisting of a second active layer (not shown) of pure amorphous silicon and a second ohmic contact layer (not shown) of impurity amorphous silicon, and a second source spaced apart from each other; A second thin film transistor Tr2, which is a switching element composed of the drain electrodes 134 and 138, is formed.

The first protective layer 140 may cover the first and second thin film transistors Tr1 and Tr2, the storage capacitor StgC, and the first and second data lines 130 and 131, and may be an inorganic insulating material. The second protective layer 145 is formed on the entire surface of the first protective layer 140 as an organic insulating material. At this time, the second protective layer 145 is characterized in that the convex irregularities are formed on the surface.

In addition, a third passivation layer 150 is formed on the second passivation layer 145 as an inorganic insulating material, and an example of a metal material having good reflectance on the third passivation layer 150 is aluminum (Al) or As the aluminum alloy, a reflecting plate 155 is formed on the entire surface of each pixel region P, i.e., overlaps the gate and data lines 103 and 130 defining each pixel region P. As shown in FIG.

The third protective layer 150 and the reflecting plate 155 may be embossed with convex surfaces of the second protective layer 145 formed under the influence of the second protective layer 145.

The reflection plate 155 is formed to have an embossing structure in order to suppress the mirror reflection and increase the reflection efficiency so that the reflected light is incident on the user's eyes to improve visibility.

In the exemplary embodiment of the present invention, the surface of the reflector 155 has an embossed structure as an example, but it is apparent that the reflector 155 may be formed to have a flat structure.

Meanwhile, the reflective plate 155 is provided with first and second openings op1 and op2 exposing the third protective layer 150 positioned below the reflective plate 155. The first and second openings op1 and op2 pass through the first and second openings op1 and op2, respectively, and expose drain electrodes 136 and 138 of each of the first and second thin film transistors Tr. This is to provide the first and second drain contact holes 163.

In the exemplary embodiment of the present invention, the first to third protective layers 140, 145, and 150 are formed as an example. However, the first and third protective layers 140 and 150 may be omitted. have.

Since the first protective layer 140 made of an inorganic insulating material is in contact with the active layer 120a, channel contamination and thin film transistors Tr1 and Tr2 that may occur when the organic insulating material is in contact with the active layer 120a. The third protective layer 150 formed of an inorganic insulating material is formed in order to prevent the deterioration of the characteristics of the reflective plate 155 and the reflecting plate 155 made of a metal material in order to solve the problem of weakening the bonding strength between the organic insulating material and the metal material. It is formed between the second protective layer 145 made of an insulating material.

Next, an organic insulating material or an inorganic insulating material is formed on the reflective plate 155 to have a thickness of 1 μm or more, whereby a fourth protective layer 160 having a flat surface is formed without the influence of a step difference thereunder. Is characteristic.

Thus, in the first embodiment of the present invention, forming the fourth protective layer 160 having a flat surface may prevent variation in the thickness of the BCSN liquid crystal layer 190 due to irregularities formed in the reflecting plate 155. For sake. The fourth protective layer 160 may be omitted when the surface of the reflective plate 155 has a flat structure.

On the other hand, when the fourth protective layer 160 is made of an organic insulating material, a fifth protective layer made of an inorganic insulating material to improve the bonding strength between the reflective plate 155 and the fourth protective layer 160 as a modification (Not shown) may be further formed.

Meanwhile, as described above, when the first, second, third, and fourth protective layers 140, 145, 150, and 160 (the fifth protective layer (not shown) are formed), the fifth protective layer (not shown) And a first drain contact hole 163 penetrating through the first opening op1 provided in the reflective plate 155 and exposing the second storage electrode 137.

Next, the fourth protective layer 160 is in contact with the second storage electrode 137 exposed through the first drain contact hole 163 and has a plate shape in each pixel area P, and has a transparent conductivity. The first electrode 166 is formed as a material, for example, indium-tin-oxide (ITO) or indium-zinc-oxide (IZO), which completely overlaps each of the reflecting plates 155.

In this case, the first electrode 166 has a third opening (not shown) that exposes the second drain electrode 138 of the second thin film transistor Tr2.

Next, a sixth passivation layer 170 is formed over the first electrode 166 as an inorganic insulating material over the entire display area. In this case, the sixth passivation layer 170 and the fourth, third, second, and first passivation layers 160, 150, 145, and 140 under the sixth passivation layer 170 are removed to remove the second drain electrode 138 of the second thin film transistor Tr2. ) Is provided with a second drain contact hole 164.

Next, the second protective layer 170 contacts the second drain electrode 138 of the second thin film transistor Tr2 through the second drain contact hole 164 and is parallel to the gate line 103. Thus, the second electrode 173 is formed.

In addition, the first substrate 101 is completed by being spaced apart from each other in parallel with the second electrode 173 and penetrating through the pixel areas P to be spaced apart from each other.

In this case, all of the third electrodes 175 formed in the display area are all connected to first auxiliary wires (not shown) formed at one end of the display area, and through the first auxiliary wires (not shown). At the same time, the first voltage is received.

The second and third electrodes 173 and 175 may be formed of a transparent conductive material such as indium tin oxide (ITO) or indium zinc oxide (IZO).

Although not shown in the drawings, a first alignment layer (not shown) is disposed over the display area over the sixth passivation layer 170 exposed between the second and third electrodes 173 and 175 and the two electrodes 173 and 175. Is being formed.

Meanwhile, in the exemplary embodiment of the present invention, the first and second thin film transistors Tr1 and Tr2 formed in the pixel regions P may include the gate wiring 103 and the first and second data wirings 130 and 131, respectively. Although the first thin film transistor is provided with first and second gate lines spaced apart from each other and a data line crossing the first and second gate lines on the first substrate, the first thin film transistor is connected to the first gate line and the data lines. The second thin film transistor may be configured to be connected to the second gate line and the data line.

The fourth electrode 185 having a structure having a flat surface as a transparent conductive material on the entire surface of the display area of the inner surface of the second substrate 180 facing and corresponding to the first substrate 101 having the above-described configuration. ) Is being formed.

In this case, the red, green, and blue color filter patterns R, G, and the like are sequentially repeated between the inner surface of the second substrate 180 and the fourth electrode 185 in correspondence with each pixel area P. FIG. The color filter layer 183 may be provided.

Furthermore, the black matrix 181 is provided to correspond to the boundary of each pixel region P between the fourth electrode 185 and the second substrate 180, that is, the gate wiring 103 and the data wiring 130. May be

Although not shown, a second alignment layer (not shown) is formed on the entire display area to cover the fourth electrode 185.

Meanwhile, a BCSN liquid crystal composed of a nematic liquid crystal added with a chiral dopant for imparting a property of causing liquid crystal molecules to be twisted between the first substrate 101 and the second substrate 180 each having the aforementioned components. The first and second compensation films 194 and 195 are attached to the outer surface of the second substrate 180 with the layer 190.

In this case, the first and second compensation films 194 and 195 are first and second retardation films each having a phase change of λ / 4. In this case, the light transmission axis of the first compensation film 194 and the second compensation film 195 has a difference of 30 degrees.

In addition, the polarizing plate 197 is provided on the outer surface of the second compensation film 195, thereby completing the BCSN mode liquid crystal display device 100 according to the exemplary embodiment.

Hereinafter, the driving of the BCSN mode liquid crystal display 100 according to the exemplary embodiment of the present invention will be briefly described.

FIG. 4 is a diagram illustrating a state in each mode driving of a bistable chiral splay nematic (BCSN) mode liquid crystal display according to an exemplary embodiment of the present invention, wherein the first and second substrates, the first, second, third and fourth electrodes, and the BCSN liquid crystal are shown in FIG. Only liquid crystal molecules in the layer are briefly shown.

First, the BCSN mode liquid crystal display device 100 according to the exemplary embodiment of the present invention may include a first alignment layer (not shown) provided on the first substrate 101 and a second alignment layer provided on the second substrate 180. (Not shown) has become the same direction.

In this case, an alignment direction of each of the first and second alignment layers (not shown) may be perpendicular to a length direction of the second and third electrodes 173 and 175 spaced apart from each other and parallel to the first substrate 101. It is characterized by being.

Meanwhile, the arrangement state of the liquid crystal molecules 192 in the BCSN liquid crystal layer 190 by the configuration having the initial tilt angles on the first and second substrates 101 and 180 is illustrated in FIG. 4B. As described above, the long axes of the liquid crystal molecules 192 are arranged in the alignment directions of the first and second alignment layers (not shown), and the angles of the liquid crystal molecules 192 are not horizontal to the inner surfaces of the substrates 101 and 180. It is in a splay state of 5 ° tilt.

On the other hand, when the BCSN mode liquid crystal display device 100 according to the embodiment of the present invention operates in the memory mode, the first electrode 166 and the second substrate (provided in the first substrate 101 in the splay state) When different voltages are applied to the fourth electrode 185 provided at 180 to have a voltage difference, the tilt angle of the liquid crystal molecules 192 forming the splay state is changed without changing the azimuth angle as shown in FIG. A high band state is achieved.

When the vertical electric field between the first and fourth electrodes 166 and 185 is turned off with respect to the BCSN liquid crystal layer 190 having the high band state as shown in FIG. 4C, the liquid crystal molecules 192 is gradually rotated 180 degrees between the liquid crystal molecules 192 adjacent to the second alignment layer (not shown) with respect to the liquid crystal molecules 192 adjacent to the first alignment layer (not shown). -A twisted state is achieved. In this case, when the BCSN liquid crystal layer 190 is in a π-twist state, the BCSN liquid crystal layer 190 has a memory characteristic due to liquid crystal characteristics having bistable characteristics.

The nematic liquid crystal to which the chiral dopant is used in the present invention is very stable in the splay state and the π-twist state, and thus has a semi-permanent memory characteristic by being able to maintain this state later.

On the other hand, in the π-twist state to generate a strong transverse electric field by applying a voltage to each of the second and third electrodes 173, 175 formed at regular intervals on the same layer to have a large voltage difference, it is shown in Figure 4b As shown in Fig. 2), the transition to the splay state is achieved. In this case, the voltage difference applied to the second and third electrodes in order to transition from the π-twist state to the splay state is defined as a threshold voltage difference. The threshold voltage difference may be changed by the thickness viscosity of the liquid crystal layer, but is usually 25V. To about 30V.

Since the BCSN liquid crystal layer 190 having such a splay state is also very stable, the BCSN liquid crystal layer 190 splays unless a vertical electric field is applied through the first and fourth electrodes 166 and 185. State is maintained.

Accordingly, the π-twist state is driven in black without any movement in a state in which no electric field is continuously formed in the liquid crystal molecules 192 to operate in a memory mode, and the same image and characters are applied without applying continuous voltage. It can be displayed for a long time, thereby minimizing power consumption.

Accordingly, an example of an application product characterized in that the same characters are displayed for a short time in a few seconds to a long time using the BCSN mode liquid crystal display device 100 according to an embodiment of the present invention for driving such a memory mode. For example, by commercializing an e-book or an e-paper, it is possible to implement characters without power consumption because of the characteristics of maintaining the same state without continuously supplying voltage by the memory function. It has the advantage of being portable without charging.

Meanwhile, when the BCSN mode liquid crystal display device 100 according to the embodiment of the present invention performs the dynamic mode driving, the BCSN mode liquid crystal display device 100 is spaced apart from each other in parallel with each other on the first substrate 180 in a π-twist state in which the above-described black is displayed. When the second and third electrodes 273 and 275 generate different transverse electric fields by applying different voltages so as to have a voltage difference to achieve the splay state, that is, a voltage difference smaller than a threshold voltage difference, the second and third electrodes Rotation of the liquid crystal molecules 192 occurs due to the change in the intensity of the weak transverse electric field expressed by the electrodes 173 and 175 to transition to an intermediate twist state as shown in FIG.

In this case, a difference in the rotation angle of the liquid crystal molecules 192 may occur due to the voltage difference applied between the second and third electrodes 173 and 175, thereby representing white and gray.

Meanwhile, in the embodiment of the present invention, the π-twist state is designed to represent black, and a strong transverse electric field of a specific voltage or more is formed through the second and third electrodes 173 and 175 spaced apart from each other in the π-twist state. When generated, the transition to the splay state, when generating a relative weak electric field below the specific voltage to maintain the intermediate twist state can be implemented in the memory mode and the dynamic mode, respectively.

 As described above, the bistable chiral splay nematic (BCSN) mode liquid crystal display device 100 according to the embodiment of the present invention forms liquid crystal molecules 192 in a π-twist state when operating in a memory driving mode and a dynamic driving mode, respectively. By having the π-twist phase show black, you have one black state in two different modes.

Accordingly, the bistable chiral splay nematic (BCSN) mode liquid crystal display 100 according to the exemplary embodiment of the present invention having one black state regardless of the driving mode is designed by designing a compensation film based on one black state. The display quality is improved because the optimized black and the white with the large contrast ratio can be displayed in any of the modes.

FIG. 5 illustrates a simulation result of arrangement states of liquid crystal molecules according to voltage differences applied to second and third electrodes in a π-twist state in a BCSN (bistable chiral splay nematic) liquid crystal display according to an exemplary embodiment of the present invention. The figure which shows.

As shown, it can be seen that when the OV is applied, the π-twist state is maintained as it is, and when the 5V, 10V, and 20V are applied, the rotation angle of the liquid crystal molecules positioned at the center of the liquid crystal layer is changed.

Accordingly, when applied to have a voltage difference smaller than the threshold voltage transitioning from the π-twist state to the splay state, a difference in the degree of rotation of the liquid crystal molecules is expressed, thereby implementing white and gray.

FIG. 6 is a view schematically illustrating an arrangement relationship of each component optimized to have a high contrast ratio and excellent black characteristics in a bistable chiral splay nematic (BCSN) mode liquid crystal display according to an exemplary embodiment of the present invention. For convenience of description, the transmission axis of the polarizing plate provided on the outer surface of the second substrate is referred to, and the transmission axis of the polarizing plate is referred to as the reference axis.

In the bistable chiral splay nematic (BCSN) mode liquid crystal display according to an exemplary embodiment of the present invention, for example, longitudinal directions of second and third electrodes provided side by side on the inner surface of the first substrate are arranged side by side with respect to the reference axis. An angle of 93 degrees is formed, and an orientation direction (rubbing direction) of the first and second alignment layers formed on the inner surfaces of the first and second substrates is formed to form an angle of 3 degrees with respect to the reference axis.

The compensation film includes two λ / 4 retardation films, and the first λ / 4 retardation film has a light transmission axis of about 70 degrees with respect to the reference axis. It was.

As described above, each component was disposed such that its light transmission axis was at an angle of 35 degrees with respect to the reference axis.

With this arrangement, the optimized black characteristics are implemented in both the memory mode and the dynamic mode.

100 BCSN liquid crystal display 101 101 first substrate
166: first electrode 170: sixth protective layer
173: second electrode 175: third electrode
180: second substrate 185: fourth electrode
190 BCSN liquid crystal layer 192 liquid crystal molecules

Claims (14)

First and second substrates facing each other with a display area and a non-display area defined outside thereof;
A plate-shaped first electrode formed on an inner side surface of the first substrate;
A first insulating layer covering the first electrode;
A second electrode and a third electrode spaced apart from each other on the inner side of the first insulating layer and formed side by side in a first direction;
A fourth electrode having a plate shape formed on an inner side surface of the second substrate;
A bistable chiral splay nematic (BCSN) liquid crystal layer interposed between the first substrate and the second substrate.
And a memory driving mode and a dynamic driving mode, wherein the splay image represents black in the two modes.
The method of claim 1,
A bistable chiral splay nematic (BCSN) mode liquid crystal display, characterized in that the first side lambda / 4 phase difference film, the second lambda / 4 phase difference film and a polarizing plate are sequentially provided on the outer surface of the second substrate.
The method of claim 2,
The first λ / 4 retardation film is disposed such that its light transmission axis has an angle of 70 degrees with the light transmission axis of the polarizing plate,
The second lambda / 4 phase difference film is a bistable chiral splay nematic (BCSN) mode liquid crystal display, characterized in that the light transmission axis is arranged to have an angle of 35 degrees with the light transmission axis of the polarizing plate.
The method of claim 3, wherein
A first alignment layer formed to cover the second and third electrodes, and a second alignment layer formed to cover the fourth electrode, wherein the first and second alignment layers have an orientation direction based on a light transmission axis of the polarizing plate. A bistable chiral splay nematic (BCSN) mode liquid crystal display characterized by three degrees.
The method of claim 4, wherein
And the second and third electrodes are arranged such that their major axes are perpendicular to the alignment direction.
The method of claim 1,
And a first thin film transistor connected to the first electrode, and a second thin film transistor connected to the second electrode, wherein the first substrate has a bistable chiral splay nematic (LCD) mode liquid crystal display.
The method of claim 1,
The first substrate includes a gate line and first and second data lines crossing the gate line, the gate line and the first data line are connected to the first thin film transistor, and the gate line and the second data line are connected to the first substrate. Connected to the second thin film transistor,
Alternatively, the first substrate may include first and second gate wires and data wires crossing the first and second gate wires. The first gate wires and data wires may be connected to the first thin film transistor, and the second gate wires and data wires may be connected to each other. And a bistable chiral splay nematic (BCSN) mode liquid crystal display, connected to the second thin film transistor.
The method of claim 1,
A bistable chiral splay nematic (BCSN) mode liquid crystal display, characterized in that a reflector is provided between the first substrate and the first electrode.
The method of claim 8,
The reflector is a bistable chiral splay nematic (BCSN) mode liquid crystal display, characterized in that the surface of the embossed structure is convex.
The method of claim 1,
A first auxiliary line is provided in the non-display areas on both sides of the display area of the first substrate,
And a bistable chiral splay nematic (BCSN) mode liquid crystal display, wherein the third electrode is formed such that one end thereof is connected to the first auxiliary line.
The method of claim 1,
A color filter layer is formed on an inner surface of the second substrate, and the fourth electrode is a bistable chiral splay nematic (BCSN) mode liquid crystal display, characterized in that formed below or above the color filter layer.
The method of claim 1,
The bistable chiral splay nematic (BCSN) liquid crystal layer has a splay state displaying white when no voltage is applied to the first, second, third and fourth electrodes.
When a voltage is applied to the first and fourth electrodes in the splay state to generate a vertical electric field, a high band state is achieved.
When the vertical electric field is removed in the high band state, a π-twist state indicating black is formed.
When the voltage is applied to the second and third electrodes in the π-twist state and a voltage having a voltage difference greater than a threshold voltage is applied to generate a strong transverse electric field, the splay state is achieved.
In the π-twist state, when a voltage having a voltage difference smaller than the threshold voltage difference is applied to the second and third electrodes, respectively, and a weak transverse electric field is generated, an intermediate twist state representing white and gray is formed.
The bistable chiral splay nematic (BCSN) liquid crystal layer is characterized in that the bistable chiral splay nematic (BCSN) mode maintains each state even when an electric field is not applied continuously because the free energy is minimum in the splay state and the π-twist state, respectively. LCD display device.
The method of claim 12,
The memory mode driving is implemented through the splay state, the high band state, and the π-twist state.
The dynamic mode driving is bistable chiral splay nematic (BCSN) mode liquid crystal display characterized in that is implemented through the π-twist state and the intermediate twist state.
The method of claim 12,
The threshold voltage difference is a bistable chiral splay nematic (BCSN) mode liquid crystal display of 25V to 30V.

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