KR101159327B1 - transflective liquid crystal display device - Google Patents

Abstract

A semi-transmissive liquid crystal display device according to an embodiment of the present invention is a transflective liquid crystal display device comprising a lower substrate, an upper substrate spaced apart from the lower substrate by a predetermined distance, and a liquid crystal layer formed between the lower substrate and the upper substrate. First and second phase retardation plates and linear polarizing films are attached to the lower and upper substrates, respectively, and the first and second phase retardation plates are wideband QWPs, respectively, QWP (Quarter Wave Plate) and HWP (Half Wave Plate). ) Are combined to each other, and the characteristics of the QWP and HWP constituting the first and second phase delay plates are different from each other.

According to the present invention, in the phase retardation plate provided in the transflective liquid crystal display device, the upper and lower substrates are provided with phase retardation plates having different characteristics, thereby inclining QWP and HWP constituting the phase retardation plate. There is an advantage that the viewing angle characteristics can be improved by compensating light passing in the direction.

Description

Transflective liquid crystal display device

1 is a cross-sectional view schematically showing the configuration of a conventional transflective liquid crystal display device.

2 is a cross-sectional view schematically showing the configuration of a transflective liquid crystal display device according to a first embodiment of the present invention.

3A or 3B illustrate refractive index anisotropic ellipsoids of QWP or HWP according to an embodiment of the present invention.

4 is a cross-sectional view schematically showing the configuration of a transflective liquid crystal display device according to a second embodiment of the present invention.

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

100: lower substrate 110: first phase delay plate

112, 212: QWP 114, 214: HWP

120, 220: linear polarizer 130: third phase delay plate

200: upper substrate 210: second phase delay plate

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device, and more particularly, to a transflective liquid crystal display device having a phase retardation plate having different characteristics on upper and lower substrates of the liquid crystal display device.

Recently, as the information society has progressed rapidly, a display field for processing and displaying a large amount of information has been developed.

Until recently, cathode ray tubes (CRTs) have been the mainstream of display devices and have been developing.

However, in recent years, the need for a flat panel display has emerged in order to meet the times of miniaturization, light weight, low power consumption, and the like. Accordingly, a thin film transistor-liquid crystal display having excellent color reproducibility has been developed.

Referring to the operation of the liquid crystal display, when an arbitrary pixel is switched by the thin film transistor, the switched arbitrary pixel may adjust the amount of light transmitted from the lower light source.

The liquid crystal display device is generally a backlight type liquid crystal display device that displays a screen by using backlight light, but recently, a reflective liquid crystal display device that does not use the backlight light has been studied. Since it operates using natural light, the power consumption of the backlight can be greatly reduced, and thus it can be used in a portable state for a long time, and the aperture ratio is also superior to that of a conventional backlight type liquid crystal display device, that is, a transmissive liquid crystal display device.

That is, the reflective liquid crystal display device reflects external light by using a material having an opaque reflective characteristic in the pixel portion formed of the transparent electrode in the conventional transmissive liquid crystal display device.

The reflection type liquid crystal display device described above can be used for a long time because it is driven using natural light or an external artificial light source without using an internal light source such as a backlight. In other words, the reflective liquid crystal display device is configured to reflect external natural light to the reflective electrode and use the reflected light. Therefore, only power required for driving the reflective liquid crystal display device is the liquid crystal driving and driving circuit.

However, natural or artificial light sources do not always exist. That is, the reflective liquid crystal display may be used in the daytime where natural light is present or in an office or building where external artificial light exists, but the reflective liquid crystal display may be used in a dark environment in which natural light does not exist. There will be no.

Accordingly, in order to solve the above problem, a transflective liquid crystal display device using the advantages of the reflective liquid crystal display device using natural light and the transmissive liquid crystal display device using backlight light has recently been researched and developed.

The transflective liquid crystal display is free to switch to the reflective or transmissive mode according to the user's will.

1 is a cross-sectional view schematically showing the configuration of a conventional transflective liquid crystal display device.

However, this is a cross-sectional view corresponding to a pixel of one transmissive mode region, in which elements (color filters, first and second electrodes, etc.) that do not affect polarization of light are omitted.

As shown, the conventional transflective liquid crystal display device 9 includes a lower substrate 10 and an upper substrate 20 spaced apart from the lower substrate by a predetermined distance, and between the lower substrate 10 and the upper substrate 20. It consists of the liquid crystal layer 30 formed.

In addition, the lower substrate 10 and the upper substrate 20 are configured by attaching first and second phase retardation plates 12 and 22 and linear polarizing films 14 and 24, respectively.

Here, the first and second phase retardation plates 12 and 22 may use QWP (Quarter Wave Plate) or wideband QWP (QWP + HWP).

In the above-described configuration, the phase delay plates 12 and 22 serve to change the polarization state of light. For example, it functions to convert linearly polarized light incident at a 45 degree angle into circularly polarized light.

In addition, the polarizing films 14 and 24 have a function of converting natural light or backlight light into linear flat light having a predetermined slope, that is, a function of transmitting only linearly polarized light parallel to the polarization axes of the polarizing films 14 and 24. do.

Accordingly, the phase retardation plates 12 and 22 serve to convert light linearly polarized by the polarizing films 14 and 24 into circularly polarized light.

In this case, it is assumed that the liquid crystal layer 30 is a collection of nematic LCs having positive anisotropy in which a long axis is arranged in a direction perpendicular to a vertical electric field direction when a voltage is applied.

In the conventional transflective liquid crystal display device, the first and second phase retardation plates 12 and 22 provided on the upper and lower substrates have the same uniaxiality. There is a disadvantage in that the black luminance is increased in the inclined direction, and thus the viewing angle characteristic of the transflective liquid crystal display device is lower than that of a transmissive liquid crystal display device having only a linear polarizer.

The present invention provides a phase retardation plate provided in a transflective liquid crystal display device, in which upper and lower substrates are provided with phase retardation plates having different characteristics, so that light passing in the oblique directions of QWP and HWP constituting the phase retardation plate is provided. It is an object of the present invention to provide a transflective liquid crystal display device that compensates for and improves viewing angle characteristics.

In order to achieve the above object, the transflective liquid crystal display according to the embodiment of the present invention comprises a transflective liquid crystal layer formed between a lower substrate and an upper substrate spaced apart from the lower substrate by a predetermined distance, and the lower substrate and the upper substrate. In the LCD, first and second phase delay plates and a linear polarizing film are attached to the lower and upper substrates, respectively, and the first and second phase delay plates are QWPs (QWPs) as wideband QWPs, respectively. And a half wave plate (HWP) are coupled to each other, and the characteristics of the QWP and the HWP constituting the first and second phase delay plates are different from each other.

Here, the first and the _{2 n x> n y = n} z is positive A- plate (positive A-plate) in an anisotropic ellipsoid having a uniaxial the QWP and HWP, respectively provided in the phase delay plate or n _x <n _It is characterized by being a negative A-plate with _y = n _z .

In addition, the transflective liquid crystal display device according to another embodiment of the present invention is a transflective liquid crystal display device comprising a lower substrate and an upper substrate spaced apart from the lower substrate by a predetermined distance, and a liquid crystal layer formed between the lower substrate and the upper substrate. The first and second phase delay plates and the linear polarizing film are attached to the lower substrate and the upper substrate, respectively, and a third phase delay plate is provided on the first or second phase delay plate. The two-phase retardation plate is a wideband QWP and is formed by combining a QWP (Quarter Wave Plate) and a HWP (Half Wave Plate), respectively. It is characterized by.

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

2 is a cross-sectional view schematically showing the configuration of a transflective liquid crystal display device according to a first embodiment of the present invention.

However, this is a cross-sectional view corresponding to a pixel of one transmission mode region, in which elements (color filters, first and second electrodes, etc.) that do not affect polarization of light are omitted.

As shown, the transflective liquid crystal display device 90 according to the embodiment of the present invention includes a lower substrate 100 and an upper substrate 200 spaced apart from the lower substrate by a predetermined distance, the lower substrate 100, and the upper substrate. It consists of a liquid crystal layer 300 formed between the (200).

In addition, the lower substrate 100 and the upper substrate 200 are formed by attaching first and second phase retardation plates 110 and 210 and linear polarizing films 120 and 220, respectively.

In the above-described configuration, the phase delay plates 110 and 210 function to change the polarization state of light. For example, it functions to convert linearly polarized light incident at a 45 degree angle into circularly polarized light.

In addition, the polarizing films 120 and 220 convert the natural light or the backlight light into linear flat light having a predetermined inclination, that is, the polarizing films 120 and 220 transmit only linearly polarized light parallel to the polarization axes of the polarizing films 120 and 220. do.

Accordingly, the phase retardation plates 110 and 210 serve to convert light linearly polarized by the polarizing films 120 and 220 into circularly polarized light.

In this case, it is assumed that the liquid crystal layer 300 is a collection of nematic LCs having positive anisotropy in which a long axis is arranged in a direction perpendicular to a vertical electric field direction when a voltage is applied.

Here, the first and second phase delay plates 110 and 210 are wideband QWPs, and QWPs 112 and 212 + HWPs 114 and 214 are combined, respectively, and the first and second phase delay plates 110 and 210 are combined. The characteristics of the QWPs 112 and 212 and the HWPs 114 and 214 constituting 210 are different from each other.

The QWPs 112 and 212 and the HWPs 114 and 214 constituting the phase retardation plate compensate for anisotropy distribution according to a viewing angle of the liquid crystal cell included in the liquid crystal layer 300. By having an anisotropy distribution as opposed to that of a liquid crystal cell, it is manufactured so as to eliminate the retardation difference of light according to the viewing angle when used in combination with the cell.

In general, this causes a change in phase difference with respect to transmitted light by the polymer film, and the film is elongated in a predetermined direction to have birefringence due to anisotropic induction of molecules.

In more detail, when an external magnetic field is applied to a Twistic Nematic (TN) liquid crystal display in a normally black mode, liquid crystal molecules arrange in response to an electric field. Light transmission occurs based on the equation.

I = Io sin ² [θ (1 + u ² ) 1/2] u = -R / θλ, R = Δnd

Here, I is intensity of transmitted light, Io is intensity of incident light, Δn is birefringence, d is liquid crystal cell thickness, λ is wavelength of transmitted light, θ is twist angle of twisted nematic liquid crystal, and R is phase difference.

As shown in the above equation, the phase difference is a value that is closely related to the viewing angle. Therefore, in order to improve the viewing angle, compensation of the phase difference is desirable.

Therefore, uniaxial refractive index anisotropes are mainly used for the QWPs 112 and 212 and the HWPs 114 and 214 constituting the phase retardation plates provided between the liquid crystal substrate and the polarizing plate for retardation compensation.

On the other hand, Figure 3a or 3b is a diagram showing the refractive index anisotropic ellipsoid of QWP or HWP according to an embodiment of the present invention.

As shown in the drawing, when the uniaxiality is nx, ny, and nz in the x, y, and z directions of the Cartesian coordinate system, respectively, the refractive indexes of the two directions are the same and the magnitude is different from the other directions. Say.

The phase retardation plate using the uniaxial refractive index anisotropic body generally used is arrange | positioned so that the long axis of an ellipsoid may be parallel or perpendicular to a film surface.

Also, among the anisotropic ellipsoids having the uniaxiality, n _x > n _y = n _z as shown in FIG. 3A is called a positive A-plate, and n _x as shown in FIG. 3B. The case of <n _y = n _z is called negative A-plate.

Embodiment of the present invention is characterized in that the QWP and HWP provided in the phase retardation plate is a positive A-plate or a negative A-plate, respectively, the first phase retardation plate provided in the lower substrate as shown in FIG. (110) is composed of a positive A-plate QWP 112, a positive A-plate HWP 114, the second phase delay plate 210 provided on the upper substrate is a negative A-plate QWP (212), And a negative A-plate HWP 214.

However, this is only one embodiment. The first phase retardation plate provided on the lower substrate is composed of a negative A-plate QWP and a positive A-plate HWP, and the second phase retardation plate provided on the upper substrate is a positive A-plate. It may be composed of a QWP and a negative A-plate HWP.

As described above, in the phase retardation plate provided in the transflective liquid crystal display device, the phase retardation plate having different characteristics are provided on the upper and lower substrates so that the light passing in the oblique directions of the QWP and HWP constituting the phase retardation plate is prevented. Compensation can improve viewing angle characteristics.

That is, the QWPs 112 and 212 and the HWPs 114 and 214 constituting the phase retardation plate compensate for anisotropy distribution according to the viewing angle of the liquid crystal cell included in the liquid crystal layer 300. It has an anisotropic distribution as opposed to that of the liquid crystal cell, and is manufactured to eliminate the retardation difference of light according to the viewing angle when used in combination with the cell.

The phase retardation plates are configured to have positive and negative properties to each other to compensate for anisotropy between phase delays.

4 is a cross-sectional view schematically showing the configuration of a transflective liquid crystal display device according to a second embodiment of the present invention.

However, this is a cross-sectional view corresponding to a pixel of one transmissive mode region, and the elements (color filters, first and second electrodes, etc.) that do not affect the polarization of light are omitted, and the same components as in FIG. The same reference numerals are used.

As shown, the transflective liquid crystal display device 90 according to the embodiment of the present invention includes a lower substrate 100 and an upper substrate 200 spaced apart from the lower substrate by a predetermined distance, the lower substrate 100, and the upper substrate. It consists of a liquid crystal layer 310 formed between (200).

In addition, the lower substrate and the upper substrate are attached to the first and second phase delay plates 110 and 120 and the linear polarizing films 120 and 220, respectively, and have different properties on the first or second phase delay plates. It is characterized in that the third phase retardation plate 130 having a further provided.

In FIG. 4, although the third phase retardation plate 130 is positioned on the first phase retardation plate 120, this is only an example.

In the above-described configuration, the phase delay plates 110 and 210 function to change the polarization state of light. For example, it functions to convert linearly polarized light incident at a 45 degree angle into circularly polarized light.

In addition, the polarizing films 120 and 220 convert the natural light or the backlight light into linear flat light having a predetermined inclination, that is, the polarizing films 120 and 220 transmit only linearly polarized light parallel to the polarization axes of the polarizing films 120 and 220. do.

Therefore, the phase retardation plates 110 and 210 serve to convert light linearly polarized by the polarizing films 120 and 220 into circularly polarized light.

In this case, the liquid crystal layer 300 is a collection of nematic LCs having positive anisotropy in which a long axis is arranged in a direction perpendicular to a vertical electric field direction when a voltage is applied, which is illustrated in FIG. 4. In the liquid crystal layer 310 is a liquid crystal layer implemented in VA mode.

However, as one embodiment, the liquid crystal display may be implemented in ECB and TN modes using a positive liquid crystal.

Here, the first and second phase delay plates 110 and 210 are wideband QWPs, and QWPs 112 and 212 + HWPs 114 and 214 are combined to form the first and second phase delay plates, respectively. Since the characteristics of the QWP and the HWP are different from each other, the light passing in the oblique directions of the QWP and the HWP constituting the phase retardation plate is compensated for, thereby improving the viewing angle characteristic, and the VA through the third phase retardation plate 130. Compensation for light in the oblique direction passing through the mode liquid crystal layer 310 further improves the viewing angle characteristic.

Here, the QWPs 112 and 212 and the HWPs 114 and 214 constituting the first and second phase delay plates 110 and 210 have anisotropy according to the viewing angle of the liquid crystal cell included in the liquid crystal layer 310. Compensation for the distribution, which has an anisotropic distribution as opposed to that of the liquid crystal cell, is manufactured to eliminate the retardation difference of light according to the viewing angle when used in combination with the cell.

Here, the phase delay plates having positive and negative properties of each other compensate for anisotropy between phase delays.

In general, this causes a change in phase difference with respect to transmitted light by the polymer film, and the film is elongated in a predetermined direction to have birefringence due to anisotropic induction of molecules.

QWP (112, 212) and HWP (114, 214) provided in the phase delay plate is characterized in that the positive A-plate or negative A-plate, respectively, as shown in the embodiment of FIG. As described above, the first phase retardation plate 110 provided on the lower substrate includes the positive A-plate QWP 112 and the positive A-plate HWP 114, and the second phase retardation plate 210 provided on the upper substrate. ) Is composed of a negative A-plate QWP 212 and a negative A-plate HWP 214.

However, this is only one embodiment. The first phase retardation plate provided on the lower substrate is composed of a negative A-plate QWP and a positive A-plate HWP, and the second phase retardation plate provided on the upper substrate is a positive A-plate. Consists of a QWP, a negative A-version HWP,

Alternatively, the first phase delay plate provided on the lower substrate is composed of a negative A-plate QWP and a negative A-plate HWP, and the second phase delay plate provided on the upper substrate is a positive A-plate QWP and a positive A-plate HWP. Or

Alternatively, the first phase retardation plate provided on the lower substrate is composed of a positive A-plate QWP and a negative A-plate HWP, and the second phase retardation plate provided on the upper substrate is a negative A-plate QWP and a positive A-plate HWP. It may be configured as.

In addition, the first phase retardation plate provided on the lower substrate is composed of a positive A-plate QWP and a negative A-plate HWP, and the second phase retardation plate provided on the upper substrate is a positive A-plate QWP and a positive A-plate HWP. It may consist of

The first phase delay plate provided on the lower substrate is composed of a negative A-plate QWP, the negative A-plate HWP, and the second phase delay plate provided on the upper substrate is composed of a negative A-plate QWP and a positive A-plate HWP. May be

As described above, in the phase retardation plate provided in the transflective liquid crystal display device, the phase retardation plate having different characteristics are provided on the upper and lower substrates so that the light passing in the oblique directions of the QWP and HWP constituting the phase retardation plate is prevented. Compensation can improve viewing angle characteristics.

In addition, the second embodiment of the present invention is characterized in that to further improve the viewing angle characteristics by compensating the light in the oblique direction passing through the VA mode liquid crystal layer 310 through the third phase delay plate 130, The third phase retardation plate 130 is composed of a negative C-plate having n _z <n _x = n _y among uniaxial anisotropic ellipsoids.

Here, the third phase retardation plate 130 serves to compensate for the difference in anisotropy according to the viewing angle of the liquid crystal cell.

According to the present invention, in the phase retardation plate provided in the transflective liquid crystal display device, the upper and lower substrates are provided with phase retardation plates having different characteristics, thereby inclining QWP and HWP constituting the phase retardation plate. There is an advantage that the viewing angle characteristics can be improved by compensating light passing in the direction.

Claims (15)

A semi-transmissive liquid crystal display device comprising a lower substrate, an upper substrate spaced apart from the lower substrate by a predetermined distance, and a liquid crystal layer formed between the lower substrate and the upper substrate. The first and second phase retardation plates and the linear polarizing film are attached to the lower substrate and the upper substrate, respectively. The first and second phase retardation plates are wideband QWPs, and are formed by combining QWP (Quarter Wave Plate) and HWP (Half Wave Plate), respectively. The characteristics of the QWP and HWP constituting the first and second phase delay plates are different from each other, A positive A-plate or n _x <n _y = n _x > n _y = n _z among the anisotropic ellipsoids QWP and HWP provided in the first and second phase delay plates are uniaxial, respectively. n _z Where n _x is the refractive index in the x direction of the Cartesian coordinate system, n _y is the refractive index in the y direction of the Cartesian coordinate system, and n _z is the refractive index in the z direction of the Cartesian coordinate system. A transflective liquid crystal display device, characterized in that it is a negative A-plate. delete The method of claim 1, The first phase delay plate provided on the lower substrate is composed of a positive A-plate QWP, a positive A-plate HWP, and the second phase delay plate provided on the upper substrate is a negative A-plate QWP, and a negative A-plate HWP. Transflective liquid crystal display device characterized in that the configuration. The method of claim 1, The first phase delay plate provided on the lower substrate is composed of a negative A-plate QWP and a positive A-plate HWP, and the second phase delay plate provided on the upper substrate is a positive A-plate QWP and a negative A-plate HWP. Transflective liquid crystal display device characterized in that the configuration. A semi-transmissive liquid crystal display device comprising a lower substrate, an upper substrate spaced apart from the lower substrate by a predetermined distance, and a liquid crystal layer formed between the lower substrate and the upper substrate. First and second phase delay plates and linear polarizing films are attached to the lower and upper substrates, respectively, and a third phase delay plate is provided on the first or second phase delay plates. The first and second phase delay plates are wideband QWPs, and are composed of QWP (Quarter Wave Plate) and HWP (Half Wave Plate), respectively, and the characteristics of QWP and HWP constituting the first and second phase delay plates are respectively. Different from each other, A positive A-plate or n _x <n _y = n _x > n _y = n _z among the anisotropic ellipsoids of QWP and HWP provided in the first and second phase retardation plates, respectively. n _z Where n _x is the refractive index in the x direction of the Cartesian coordinate system, n _y is the refractive index in the y direction of the Cartesian coordinate system, and n _z is the refractive index in the z direction of the Cartesian coordinate system. A transflective liquid crystal display device, characterized in that it is a negative A-plate. delete The method of claim 5, The third phase retardation plate is a semi-transmissive liquid crystal display device comprising a negative C-plate (n _z <n _x = n _y of the uniaxial anisotropic ellipsoid). The method of claim 5, The first phase delay plate provided on the lower substrate is composed of a positive A-plate QWP, a positive A-plate HWP, and the second phase delay plate provided on the upper substrate is a negative A-plate QWP, and a negative A-plate HWP. Transflective liquid crystal display device characterized in that the configuration. The method of claim 5, The first phase delay plate provided on the lower substrate is composed of a negative A-plate QWP and a positive A-plate HWP, and the second phase delay plate provided on the upper substrate is a positive A-plate QWP and a negative A-plate HWP. Transflective liquid crystal display device characterized in that the configuration. The method of claim 5, The first phase delay plate provided on the lower substrate is composed of a negative A-plate QWP, the negative A-plate HWP, and the second phase delay plate provided on the upper substrate is a positive A-plate QWP, and a positive A-plate HWP. Transflective liquid crystal display device characterized in that the configuration. The method of claim 5, The first phase delay plate provided on the lower substrate is composed of a positive A-plate QWP and a negative A-plate HWP, and the second phase delay plate provided on the upper substrate is a negative A-plate QWP and a positive A-plate HWP. Transflective liquid crystal display device characterized in that the configuration. The method of claim 5, The first phase retardation plate provided on the lower substrate is composed of a positive A-plate QWP and a negative A-plate HWP, and the second phase retardation plate provided on the upper substrate is a positive A-plate QWP and a positive A-plate HWP. Transflective liquid crystal display device characterized in that the configuration. The method of claim 5, The first phase delay plate provided on the lower substrate is composed of a negative A-plate QWP, the negative A-plate HWP, and the second phase delay plate provided on the upper substrate is a negative A-plate QWP, and the positive A-plate HWP. Transflective liquid crystal display device characterized in that the configuration. The method of claim 5, The liquid crystal layer is a transflective liquid crystal market value, characterized in that the liquid crystal layer implemented in VA mode. The method of claim 5, The liquid crystal display device is a transflective liquid crystal display device, characterized in that implemented in ECB, TN mode using a positive liquid crystal.

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