KR101868541B1 - In-plane switching mode liquid crystal display device - Google Patents

Abstract

The present invention relates to a transverse electric field type liquid crystal display device.
QWPs are formed under the lambda / 4 liquid crystal cell, thin film transistors are formed on the first substrate and the second substrate of the lambda / 4 liquid crystal cell, and liquid crystal molecules of the lambda / 4 liquid crystal cell And a liquid crystal cell of a transverse electric field type which is improved in response time (Falling Time) by reducing a cell gap by replacing a lambda / 2 liquid crystal cell with a lambda / 4 liquid crystal cell will be.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a liquid crystal display (LCD)

[0001] The present invention relates to a transverse electric field type liquid crystal display device with improved response speed, and more particularly to a transverse electric field type liquid crystal display device in which a thin film transistor is formed on each of a first substrate and a second substrate of a quarter wavelength liquid crystal cell, 1/2 liquid crystal cell and QWP in order to realize the orientation of liquid crystal molecules due to the transverse electric field between the first substrate and the second substrate, the cell gap decreases and the response speed of the liquid crystal molecules The liquid crystal display device of the present invention is a liquid crystal display device having a liquid crystal display device.

2. Description of the Related Art [0002] With the development of information society in recent years, demands for the display field have been increasing in various forms. In response to this demand, various flat panel display devices having characteristics such as thinning, light weight and low power consumption have been developed, A liquid crystal display device, a plasma display panel device, and an electro luminescent display device have been studied.

Among these, a liquid crystal display device is one of the most widely used flat panel display devices, and includes two substrates on which pixel electrodes and common electrodes are formed, and a liquid crystal layer between two substrates.

Such a liquid crystal display device determines the orientation of liquid crystal molecules in the liquid crystal layer according to the electric field generated by the voltage applied to the electrodes, and controls the polarization of the incident light to display an image.

The liquid crystal display device is advantageous for moving picture display and has a high contrast ratio. Therefore, the liquid crystal display device can replace a conventional cathode ray tube (CRT) .

The liquid crystal display device does not have a self-luminous element and must have a separate light source. The light source is called a backlight unit (BLU).

The light source of the backlight unit may be a cold cathode fluorescent lamp, an external electrode fluorescent lamp, a light emitting diode (LED), or the like.

In recent years, there has been an increasing demand for high-frequency LCD TVs for 3D TVs with shutter glass, improvement of afterimage, and fast moving images in addition to demands for thinning, lightening, and low power consumption as described above. It is required to improve the response speed.

The liquid crystal display device is classified into a TN (Twisted Nematic) mode in which liquid crystal molecules are aligned so as to twist by 90 degrees and then a voltage is applied to control the liquid crystal molecules according to the arrangement of liquid crystals and the arrangement of electrodes for applying an electric field to the liquid crystal, An IPS (In-Plane Switching) mode in which two electrodes are formed in a plane parallel to the alignment film to change the orientation of the liquid crystal molecules by a horizontal electric field, an initial alignment of the liquid crystal molecules is arranged in parallel to the substrate, And a VA (Vertical Alignment) mode in which a vertical electric field is applied to the liquid crystal.

Among them, the IPS-mode liquid crystal display device generally includes a first substrate and a second substrate which are disposed opposite to each other with a liquid crystal layer therebetween, and the liquid crystal molecules of the liquid crystal layer are horizontally switched by a horizontal electric field, great.

1 is a cross-sectional view of a conventional liquid crystal panel.

1, the liquid crystal panel 100 includes a first polarizer 110, a first substrate 130, a liquid crystal layer 150, a second substrate 170, and a second polarizer 190 .

A plurality of gate wirings (not shown) and a plurality of data wirings (not shown) intersect each other on the inner surface of the first substrate 130 to define pixels. Each thin film transistor Thin Film transistors (not shown) are provided to correspond to the transparent pixel electrodes 134 of the respective pixels in a one-to-one correspondence.

The common electrode 136 is formed so as to be spaced apart in parallel with the pixel electrode 134, and is connected to a common wiring (not shown).

On the inner surface of the second substrate 170, a color filter (not shown) of red (R), green (G), and blue (B) And a black matrix (not shown) for covering non-display elements such as thin film transistors.

A first polarizing plate 110 and a second polarizing plate 190, which selectively transmit only a specific polarized light component of light, are attached to the outer surfaces of the first substrate 130 and the second substrate 170, respectively.

At this time, the first transmission axis of the first polarizer 110 formed on the outer side of the first substrate 130 and the second transmission axis of the second polarizer 190 formed on the outer side of the second substrate 170 are perpendicular to each other .

The liquid crystal molecules 152 (FIG. 2) of the liquid crystal layer 150 formed between the first substrate 130 and the second substrate 170 may be arranged in a predetermined direction through the rubbing process.

In the liquid crystal panel 100, when a thin film transistor selected for each gate line is turned on by an on / off signal of a gate driving circuit to be scanned, a signal voltage of the data driving circuit is transmitted to the corresponding pixel electrode through the data line And the liquid crystal molecules 152 of the liquid crystal layer 150 are changed in direction by the electric field between the pixel electrode 134 and the common electrode 136, the transmittance is different.

The liquid crystal cell includes the first substrate 130 and the second substrate 170 and a liquid crystal layer 150 formed therebetween. The? / 2 retarder characteristic of the liquid crystal cell for display on / A liquid crystal cell of? / 2 is generally used.

FIG. 2A is a cross-sectional view of a conventional liquid crystal array in a black state, and FIG. 2B is a cross-sectional view of a conventional liquid crystal array in a white state.

FIG. 3A is a diagram for explaining a polarization state in a black state in a conventional liquid crystal panel, and FIG. 3B is a diagram for explaining a polarization state in a white state in a conventional liquid crystal panel.

2A and 2B, the common electrode 136 and the pixel electrode 134 formed on the first substrate 130 are arranged in parallel, and the rubbing direction of the alignment film (not shown) And may be formed to have a constant angle with the parallel direction.

Accordingly, the liquid crystal molecules 152 of the liquid crystal layer 150 may also be oriented along the rubbing direction so as to form a constant angle with the parallel direction of the two electrodes.

In this case, the rubbing direction may be determined from a condition for increasing the transmittance of the liquid crystal display device, and may be, for example, a direction rotated clockwise by 20 degrees with respect to a direction parallel to the two electrodes.

Thus, since the liquid crystal molecules 152 are aligned in parallel with the transmission axis of the first polarizer 110, the liquid crystal display device is in a normally black mode.

Accordingly, when no voltage is applied to the two electrodes, the long axis of the liquid crystal molecules 152 is arranged along the rubbing direction (the direction parallel to the transmission axis of the first polarizer 110) The linearly polarized light L1 can not pass through the second polarizer 190 and displays a black state. (Fig. 3A)

On the other hand, when a voltage is applied to the two electrodes, a transverse electric field is formed between the common electrode 136 and the pixel electrode 134, and the liquid crystal molecules 152 are moved clockwise from the initial alignment direction (+45 degrees) and rearranged.

Therefore, the light L1 that is linearly polarized by the first polarizer 110 is phase-delayed by the? / 2 liquid crystal cell and the light L2 whose polarization direction is rotated by the phase retardation is transmitted through the second polarizer 190, To display a white state. (Figure 3b)

4 is a view showing a Poincare sphere for explaining a polarization state in a conventional liquid crystal panel. Here, the Porcocare sphere is a sphere having a radius of 1 represented by orthogonal coordinate points (s1, s2, s3), and can represent polarized light.

All points on the equatorial line of the Poincare sphere correspond to linearly polarized light, the two poles correspond to right circularly polarized light or left circularly polarized light, and the remaining points correspond to elliptically polarized light. The points in the northern hemisphere correspond to right circularly polarized light, The point corresponding to the left elliptical polarization.

The points facing each other with respect to the origin of the Poincare sphere correspond to the mutually orthogonal polarized light.

As shown in FIG. 4, the first point on the S1 axis represents the polarization state of light passing through the first polarizer plate 110, and the second point on the S1 axis represents the polarization state of light that has passed through the liquid crystal cell.

That is, the incident light incident from the backlight unit (not shown) is linearly polarized by the first polarizing plate (horizontal polarizing plate) 110, and the linearly polarized light L1 is located at the first point in the S1 axis, The phase lag occurs, and the light L2 whose polarization direction has been rotated is positioned at the second point.

At this time, L1 and L2 are facing each other with respect to the origin of the Porcocalisphere, and it is understood that they are light perpendicular to each other.

Accordingly, the light L2 in which the phase delay occurs can transmit the second polarizing plate (vertical polarizing plate) 190 perpendicular to the first polarizing plate (horizontal polarizing plate) 110.

In recent years, it has been required to improve the response speed of liquid crystal molecules for realizing fast moving images of LCDs. To improve such a response speed, a method of changing physical properties of a liquid crystal or reducing a cell gap has been proposed.

In the case of the method for improving the response speed by changing the physical properties of the liquid crystal, development of a new liquid crystal having a low viscosity and a high elastic characteristic is required. However, since the range is limited, it is impossible to reduce the cell gap, In the case of the method of reducing the number of display cells, the lambda / 2 retarder characteristic of the liquid crystal cell (LC cell) for the display on / off driving is required and there is a limit of the cell gap.

SUMMARY OF THE INVENTION The present invention has been accomplished in order to solve the above problems, and it is an object of the present invention to provide a liquid crystal display device and a liquid crystal display device in which QWP is applied to an upper portion of a first polarizer, TFTs are formed on a first substrate and a second substrate, 2 liquid crystal display device in which a cell gap is reduced to half of a conventional cell gap to improve a response speed of a liquid crystal.

A liquid crystal cell including a liquid crystal layer sandwiched between the first substrate and the second substrate; a liquid crystal cell including a liquid crystal layer sandwiched between the first substrate and the second substrate; and; A first polarizer disposed on an outer surface of the first substrate and selectively transmitting light; A retardation plate disposed on an inner surface of the first polarizer and configured to retard a phase of light transmitted through the first polarizer; And a second polarizer disposed on an outer surface of the second substrate and selectively transmitting light transmitted through the liquid crystal cell, wherein a first pixel electrode and a first common electrode are formed on the first substrate, And a second pixel electrode and a second common electrode are formed on the substrate.

Here, the liquid crystal cell may have a phase difference of? / 4.

The retardation plate may be a quarter wave plate (QWP) having a phase difference of? / 4.

The first substrate may include a plurality of first gate wirings and a plurality of first data wirings. The first substrate may include a plurality of first gate wirings and a plurality of first data wirings, A plurality of second gate wirings and a plurality of second data wirings are formed on the second substrate, and a plurality of second gate wirings and a plurality of second gate wirings are formed on the second substrate, And a second thin film transistor, which is a switching element, may be formed for each pixel defined by intersection of the data lines.

Here, the first pixel electrode and the first common electrode may be arranged to be rotated by a first angle from a direction parallel to the first data line, and the second pixel electrode and the second common electrode may be arranged in the second And is arranged to be rotated by a second angle from a direction parallel to the data line.

When the first thin film transistor is in the on state and the second thin film transistor is in the off state, the black state can be displayed as the liquid crystal molecules of the liquid crystal cell rotate by the first rotation angle.

On the other hand, when the first thin film transistor is in the off state and the second thin film transistor is in the on state, the white state can be displayed as the liquid crystal molecules of the liquid crystal cell rotate by the second rotation angle.

As described above, in the transverse electric field type liquid crystal display device according to the present invention, since the? / 4 liquid crystal cell and the QWP are used instead of the? / 2 liquid crystal cell, the? / 4 liquid crystal cell of the liquid crystal cell (LC Cell) The cell gap can be reduced to half the cell gap while maintaining the retarder characteristics, and as a result, the response speed and moving image quality of the liquid crystal display device can be improved.

1 is a cross-sectional view of a conventional liquid crystal panel.
Fig. 2A is a diagram showing a cross-sectional view of a liquid crystal array according to a conventional technique in a black state.
FIG. 2B is a diagram showing a cross-sectional view of a liquid crystal array according to the prior art in a white state. FIG.
3A is a diagram for explaining a polarization state of a black state in a conventional liquid crystal panel.
3B is a diagram for explaining the polarization state of the white state in the conventional liquid crystal panel.
Fig. 4 is a diagram showing a porcine curve for explaining a polarization state in a conventional liquid crystal panel. Fig.
5 is a cross-sectional view of a liquid crystal panel according to a preferred embodiment of the present invention.
6 is a plan view of a first substrate according to a preferred embodiment of the present invention.
7 is a plan view of a second substrate according to a preferred embodiment of the present invention.
8 is a view illustrating a liquid crystal array according to a preferred embodiment of the present invention.
9A is a diagram for explaining a polarization state of a black state in a liquid crystal panel according to a preferred embodiment of the present invention.
FIG. 9B is a diagram for explaining the polarization state of the white state in the liquid crystal panel according to the preferred embodiment of the present invention.
FIG. 10 is a view showing a Poincare sphere for explaining a polarization state in a liquid crystal panel according to a preferred embodiment of the present invention.

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

5 is a cross-sectional view of a liquid crystal panel according to a preferred embodiment of the present invention. Will be described with reference to Figs. 7 to 10. Fig.

5, the liquid crystal panel 200 includes a first polarizer 210, a retarder 220, a first substrate 230, a liquid crystal layer 250, a second substrate 270, (290).

A plurality of first gate wirings 231 and a plurality of first data wirings 233 intersect each other on the inner surface of the first substrate 230 to define pixels and a first thin film transistor (Thin Film Transistor) T1, and are connected to the first pixel electrodes 234 of the respective pixels in a one-to-one correspondence manner.

The first common electrode 236 is formed in parallel with the first pixel electrode 234 and is connected to the first common electrode 235.

On the inner surface of the second substrate 270, a color filter (not shown) of red (R), green (G), and blue (B) colors corresponding to each pixel, and a black matrix May be provided.

A plurality of second gate wirings 271 and a plurality of second data wirings 273 intersect each other on the inner surface of the second substrate 270 according to the present invention to define pixels. And a second thin film transistor (T2), which is a switching element, may be provided so as to correspond to the second pixel electrode 274 of each pixel in a one-to-one correspondence.

The second common electrode 276 is formed in parallel with the second pixel electrode 274 and is connected to the second common wiring 275.

In this liquid crystal panel 200, the first and second thin film transistors T1 and T2 selected for each of the first and second gate wirings 231 and 271 are turned on by the on / The signal voltage of the data driving circuit is transmitted to the corresponding first and second pixel electrodes 234 and 274 through the first and second data lines 233 and 273, 234 and 236 and the second and third common electrodes 274 and 276, the liquid crystal molecules 252 of the liquid crystal layer 250 are arranged in different directions to show a difference in transmittance.

The reason why the first and second common electrodes 234 and 236 and the second and common electrodes 274 and 276 are formed on the first and second substrates 230 and 270 according to the present invention is that, (Anticlockwise direction) of the liquid crystal molecules 252 due to the first transverse electric field between the first pixel electrode 234 and the first common electrode 236 and between the second pixel electrode 274 and the second common electrode 276 And the rotation direction (clockwise direction) of the liquid crystal molecules 252 due to the second transverse electric field is different.

Therefore, by applying a voltage to each electrode through the first and second thin film transistors T1 and T2, the display on / off can be realized by rotating the liquid crystal molecules at a predetermined angle.

That is, in order to rotate the liquid crystal molecules 252 clockwise in the initial alignment state, the second thin film transistor T2 must be turned on (here, the first thin film transistor T1 is in the off state) 252 are rotated counterclockwise, the second thin film transistor T2 is first turned off (the liquid crystal molecules are in an initial alignment state at this time), and then the first thin film transistor T1 is turned on (ON).

A first polarizing plate 210 and a second polarizing plate 290, which selectively transmit only a specific polarized light component of light, are attached to the outer sides of the first substrate 230 and the second substrate 270, respectively.

A second polarizing plate (a vertical polarizing plate) 290 is formed on a first transmission axis of the first polarizing plate (horizontal polarizing plate) 210 and a second polarizing plate 290 formed on the outer side of the second substrate 270, And the second transmission axis of the second transmission axis may be perpendicular to each other.

On the other hand, a retardation film 220 having a phase difference of? / 4 may be formed on the first polarizer 210, and the retardation plate 220 serves to retard the phase of light , The polarization state of the light L3 polarized through the first polarizer 210 may be changed as the phase is delayed.

At this time, the retarder 220 may be, for example, a quarter wave plate (QWP).

In other words, the light L3 polarized through the first polarizer 210 may be phase-delayed through the retarder 220 to change its polarization state. For example, if L3 is linearly polarized light, The light L4 in which the phase delay is generated through the light L4 may be left-handed circularly polarized light.

The liquid crystal molecules 252 of the liquid crystal layer 250 formed between the first substrate 230 and the second substrate 270 may be arranged in a certain direction through the rubbing process.

The liquid crystal cell including the first substrate 230 and the second substrate 270 and the liquid crystal layer 250 formed therebetween is referred to as a liquid crystal cell and the liquid crystal cell according to the present invention has a phase difference of? .

When a voltage is applied to the electrode through the first thin film transistor T1, a first transverse electric field is formed between the first pixel electrode 234 and the first common electrode 236, and a first transverse electric field The liquid crystal molecules 252 may be arranged to be rotated by? ₁ (for example, -45 degrees) counterclockwise from the initial alignment direction.

Therefore, the light L4 in which the phase delay occurs through the retarder 220 is phase-delayed by the quarter-wave liquid crystal cell arranged by rotating by? ₁ from the initial alignment direction, and the light L6, Can not transmit the second polarizing plate 290 and can display a black state.

When a voltage is applied to the electrodes through the second thin film transistor T2, a second transverse electric field is formed between the second pixel electrode 274 and the second common electrode 276, and a second transverse electric field The liquid crystal molecules 252 can be arranged to rotate clockwise from the initial alignment direction by? ₂ (for example, +45 degrees).

Therefore, the light L4 in which the phase delay occurs through the retarder 220 is phase-delayed by the quarter-wave liquid crystal cell arranged by rotating by? ₂ from the initial alignment direction, and the light L5, The white state can be displayed as it is transmitted through the second polarizer 290.

The liquid crystal panel according to the present invention is characterized in that a retarder 220 is applied on the first polarizer 210 and the display ON / OFF driving is performed by driving the first and second thin film transistors T1 and T2, respectively, And the first and second transverse electric fields between the common electrodes 234 and 236 and the second pixel and the common electrodes 274 and 276 are formed and the orientation change of the liquid crystal molecules 252 due to the first and second transverse electric fields formed .

Here, the retarder 220 may be formed on the inner surface or the outer surface of the first substrate 230.

Accordingly, the display ON / OFF driving can be expressed not by the conventional LC retarder? / 2 phase difference variation but by the? / 4 phase difference variation of the liquid crystal cell, and the cell gap is reduced to half of the conventional one. The response time (in particular, Falling Time) of the molecules 252 can be improved.

cell Simulation result K11 K22 K33 K r1 CD Δε Vth Vdd ε0 d Tr Tf total 8.5 9.3 19.3 8.7 122 6.0 12.5 1.88 4.2 2.5 4.8 10.0 30.0 40.0 8.5 9.3 19.3 8.7 122 6.0 12.5 1.88 4.2 2.5 4.8 10.0 21.3 31.3 8.5 9.3 19.3 8.7 122 6.0 12.5 1.88 4.2 2.5 4.8 10.0 18.2 28.2 8.5 9.3 19.3 8.7 122 6.0 12.5 1.88 4.2 2.5 4.8 10.0 15.4 25.3 8.5 9.3 19.3 8.7 122 6.0 12.5 1.88 4.2 2.5 4.8 10.0 12.0 21.9 8.5 9.3 19.3 8.7 122 6.0 12.5 1.88 4.2 2.5 4.8 10.0 8.3 18.3

Table 1 is a table showing the simulation result of the change of the falling time (Tf) according to the change of the cell gap.

the liquid crystal molecules (252 in FIG. 7) of the liquid crystal layer 250 are driven by the dual thin film transistors (first and second thin film transistors T1 and T2) even if the? / 2 liquid crystal cell is replaced with the? / 4 liquid crystal cell and the QWP. The characteristics of the liquid crystal cell for display on / off driving can be satisfied through the change of orientation,

In a liquid crystal display device, a liquid crystal cell optically has a? / 2 retarder dynamics. In the present invention, it is replaced with a? / 4 liquid crystal cell and a QWP, The first and second common electrodes 234 and 236 and the second and common electrodes 274 and 276 are formed on the first and second thin film transistors Tl and T2 on / ≪ / RTI >

As a result, the cell gap is reduced to half of the conventional one, so that the response time (in particular, the falling time) of the liquid crystal molecules 252 can be improved.

As shown in Table 1, it can be seen that the Falling Time (Tf) is improved from the existing 30ms to 8.3ms by comparing the cell gap (d) of 4.8 mu m and the case of 2.4 mu m.

FIG. 6 is a plan view of a first substrate according to a preferred embodiment of the present invention, and FIG. 7 is a plan view of a second substrate according to a preferred embodiment of the present invention.

6 and 7, on the first substrate 230 according to the present invention, a first gate wiring 231 arranged in one direction and a first gate wiring 231 arranged in a direction perpendicular to the first gate wiring 231 A data line 233 is formed and a pixel can be defined.

On the first substrate 230, a first thin film transistor T1 for controlling on / off of the voltage by a control signal is formed on the intersection of the first gate wiring 231 and the first data wiring 233 A first common wiring 235 arranged in a pixel so as to be in parallel with the first gate wiring 231 and a plurality of first common electrodes 236 branched from the first common wiring 235 and a first A plurality of first pixel electrodes 234 connected to the thin film transistor T1 and spaced apart from the first common electrode 236 in parallel to the first common electrode 236 are formed.

On the other hand, on the second substrate 270 according to the present invention, a second gate wiring 271 arranged in one direction and a second data wiring 273 arranged in a direction perpendicular to the second gate wiring 271 are formed, A region can be defined.

On the second substrate 270 according to the present invention, the second thin film transistor T2 for controlling on / off of the voltage by a control signal is connected to the second gate wiring 271 and the second data wiring 273 A second common wiring 275 formed in the pixel so as to be in parallel with the second gate wiring 271 and a plurality of second common electrodes 276 branched from the second common wiring 275 and a second A plurality of second pixel electrodes 274 may be formed in parallel with the second common electrode 276 between the second common electrodes 276 connected to the thin film transistor T2.

The first and second common wirings 235 and 275 and the first and second common electrodes 276 are integrally formed and the first and second gate wirings 231 and 271 and the first and second common wirings 231 and 271, The first and second gate electrodes of the transistors T1 and T2 may also be integrally formed.

The first and second pixel electrodes 234 and 274 are formed by using a transparent conductive metal having a relatively high light transmittance such as Indium-Tin-Oxide (ITO) And may be connected to the first and second drain electrodes of the first and second thin film transistors T1 and T2 to receive a voltage.

The first common electrode 236 and the first pixel electrode 234 may be arranged to be rotated by a predetermined angle? _{1 in a} counterclockwise direction with respect to a direction parallel to the first data line 233, The predetermined angle alpha ₁ may be, for example, -15 degrees.

The second common electrode 276 and the second pixel electrode 274 may be arranged to rotate clockwise by a predetermined angle? ₂ with reference to a direction parallel to the second data line 273, angle (α ₂₎ of, for example +15 degrees can.

The first and second polarizers 210 and 290 are disposed outside the first and second substrates 230 and 270 and the orientation of the liquid crystal molecules 252 is determined inside the first substrate 230 (Not shown) may be disposed.

That is, the liquid crystal cell according to the present invention includes first and second substrates 230 and 270 bonded to each other, and a liquid crystal layer interposed between the two substrates, which is phase-delayed by? / 4 serving as a quarter wave plate (QWP) The first common electrode 236 and the second common electrode 240 are formed on the first substrate 230 so as to change the orientation of the liquid crystal molecules 252 of the liquid crystal layer 250 for display on / And a second common electrode 276 and a second pixel electrode 274 may be provided on the second substrate 270.

8 is a view illustrating a liquid crystal array according to a preferred embodiment of the present invention.

FIG. 9A is a diagram for explaining a polarization state of a black state in a liquid crystal panel according to a preferred embodiment of the present invention, and FIG. 9B is a diagram illustrating a state of polarization of a white state in the liquid crystal panel according to a preferred embodiment of the present invention Reference is made to the drawings.

The initial alignment of the liquid crystal molecules 252 of the liquid crystal layer 250 is observed in the vertical direction (rubbing direction) in a state where the first and second thin film transistors T2 are both turned off as shown in Fig. time, the second thin film transistor (T2) is turned off (oFF) and, when the first thin film transistor (T1) is turned on (oN), the liquid crystal molecules 252 in the counterclockwise direction from the vertical direction (rubbing direction) θ ₁ ( -45 degrees).

When the liquid crystal molecules 252 are arranged to rotate counterclockwise from the vertical direction (rubbing direction) by? ₂ (-45 degrees), the left circularly polarized light L4 is phase delayed by the? / 4 liquid crystal cell , And linearly polarized light (horizontal linearly polarized light).

The light L6 in which the phase delay is caused by the lambda / 4 liquid crystal cell is linearly polarized light parallel to L3 and is perpendicular to the second transmission axis of the second polarizing plate (vertical polarizing plate) 290 so that it does not transmit through the second polarizing plate 290 It displays a black state.

On the other hand, when the second thin film transistor T2 is turned on, the first thin film transistor T1 maintains the OFF state, and the liquid crystal molecules 252 move clockwise from the vertical direction (rubbing direction) ₂ (+45 degrees).

The incident light incident from the backlight unit (not shown) is linearly polarized by the first polarizing plate (horizontal polarizing plate) 210 and the linearly polarized light L3 is phase retarded by the retarder 220, have.

When the liquid crystal molecules 252 are rotated by θ ₂ (+45 degrees) in the clockwise direction from the vertical direction (rubbing direction), the left circularly polarized light L 4 is phase delayed by the λ / 4 liquid crystal cell, (Vertical linearly polarized light).

The light L5 having a phase delay due to the? / 4 liquid crystal cell is linearly polarized light perpendicular to L3 and parallel to the second transmission axis of the second polarizing plate (vertical polarizing plate) 290 and thus transmitted through the second polarizing plate 290 White state can be displayed.

FIG. 10 is a view showing a Poincare sphere for explaining a polarization state in a liquid crystal panel according to a preferred embodiment of the present invention.

Here, the Porcocare sphere is a sphere having a radius of 1 represented by orthogonal coordinate points (s1, s2, s3), and can represent polarized light.

All points on the equatorial line of the Poincare sphere correspond to linearly polarized light, the two poles correspond to right circularly polarized light or left circularly polarized light, and the remaining points correspond to elliptically polarized light. The points in the northern hemisphere correspond to right circularly polarized light, The point corresponding to the left elliptical polarization.

The points facing each other with respect to the origin of the Poincare sphere correspond to the mutually orthogonal polarized light.

10, incident light incident from a backlight unit (not shown) is linearly polarized by the first polarizing plate (horizontal polarizing plate) 210, and the light L3 which is linearly polarized is incident on the retarder 220 by a phase retardation And can be left-handed circularly polarized light.

Here, the left circularly polarized light L4 is arranged such that the second thin film transistor T2 is turned on so that the liquid crystal molecules 252 rotate clockwise from the vertical direction (rubbing direction) by? ₂ (+45 degrees) , A phase delay may occur due to the lambda / 4 liquid crystal cell, and thus the polarization state can be changed to vertical linearly polarized light.

The point 1 of the S3 axis represents the light L3 that is linearly polarized by the first polarizer 210 and is phase-delayed through the retarder 220, that is, the left-polarized light L4, Is a horizontal linearly polarized light L6 whose polarization state changes due to a phase delay caused by a lambda / 4 liquid crystal cell and which is in the same polarized state as the linearly polarized light L3 before phase retardation is generated by the retarder 220 .

Therefore, the light L6 in which the phase delay is caused by the? / 4 liquid crystal cell can not transmit the second polarizing plate 290 and can display the black state.

On the other hand, the point 3 in the S1 axis represents the vertical linearly polarized light (L5) in which the polarization state changes due to the phase delay caused by the? / 4 liquid crystal cell.

At this time, the light L5 having a phase delay due to the? / 4 liquid crystal cell is linearly polarized light perpendicular to L3 and parallel to the second transmission axis of the second polarizer 290 (vertical polarizer 290), so that the second polarizer 290 The white state can be displayed.

At this time, it can be seen that L5 and L6 are opposite to each other with respect to the origin, and they are perpendicular to each other.

The embodiments of the present invention as described above are merely illustrative, and those skilled in the art can make modifications without departing from the gist of the present invention. Accordingly, the protection scope of the present invention includes modifications of the present invention within the scope of the appended claims and equivalents thereof.

210: first polarizing plate 220: QWP
230: first substrate 250: liquid crystal layer
270: second substrate 290: second polarizer plate

Claims (7)

A liquid crystal cell including a first substrate and a second substrate facing each other and a liquid crystal layer interposed between the first substrate and the second substrate;
A first polarizer disposed on an outer surface of the first substrate and selectively transmitting light;
A retardation plate disposed on an inner surface of the first polarizer and configured to retard a phase of light transmitted through the first polarizer;
And a second polarizer disposed on an outer surface of the second substrate and selectively transmitting light transmitted through the liquid crystal cell,
A first pixel electrode and a first common electrode are formed on the first substrate, a second pixel electrode and a second common electrode are formed on a second substrate,
Wherein the first pixel electrode and the first common electrode extend in a first direction and the second pixel electrode and the second common electrode extend in a second direction crossing the first direction. Liquid crystal display device.
The method according to claim 1,
In the liquid crystal cell,
lambda] / 4. < / RTI >
The method according to claim 1,
Wherein the retarder comprises:
is a quarter wave plate (QWP) having a phase difference of? / 4.
The method according to claim 1,
Wherein the first substrate is provided with a plurality of first gate wirings and a plurality of first data wirings, and each of the plurality of first gate wirings and the plurality of first data wirings is defined by intersecting the plurality of first data wirings, 1 thin film transistor (Thin Film Transistor) is formed,
Wherein a plurality of second gate wirings and a plurality of second data wirings are formed in the second substrate, and each of the plurality of second gate wirings and each of the plurality of second data wirings is defined as a switching element And a second thin film transistor (TFT) is formed on the second substrate.
5. The method of claim 4,
Wherein the first pixel electrode and the first common electrode are connected to each other,
The first data line and the second data line are arranged to be rotated by a first angle from a direction parallel to the first data line,
The second pixel electrode, and the second common electrode,
And the first electrode is arranged to be rotated by a second angle from a direction parallel to the second data line.
5. The method of claim 4,
When the first thin film transistor is on and the second thin film transistor is off,
And a black state is displayed as the liquid crystal molecules of the liquid crystal cell rotate by a first rotation angle.
5. The method of claim 4,
When the first thin film transistor is in an off state and the second thin film transistor is in an on state,
And a white state is displayed as the liquid crystal molecules of the liquid crystal cell rotate by a second rotation angle.

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