Liquid crystal display and the fabricating method of the same

A transflective liquid crystal display (LCD) includes: a first substrate formed with a thin film transistor and a pixel electrode connected to the thin film transistor; a second substrate formed with a common electrode and a color filter and facing the first substrate; a liquid crystal layer formed between the first substrate and the second substrate; a first polarizing plate disposed at one side of the first substrate that does not face the second substrate; a second polarizing plate disposed at one side of the second substrate that does not face the first substrate; a cholesteric film formed on the first substrate; and a backlight unit disposed at one side of the first polarizing plate that does not face the first substrate.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to and the benefit of Korean Patent Application No. 10-2010-0125723, filed in the Korean Intellectual Property Office on Dec. 9, 2010, the entire content of which is incorporated herein by reference.

BACKGROUND

The described technology relates generally to a liquid crystal display (LCD). More particularly, the described technology relates generally to a transflective liquid crystal display (LCD).

2. Description of Related Art

A liquid crystal display (LCD) is slimmer, lighter, and consumes less power than a comparable cathode ray tube (CRT). As a result, the liquid crystal display (LCD) has been prevalently used for midsize and large products such as a monitor and a TV, and small-sized products such as mobile phones, personal digital assistants (Pads), and portable multimedia players (PMPs).

The LCD is a display device that includes a liquid crystal display panel displaying image data using an optical characteristic of liquid crystal. The liquid crystal display panel includes an array panel formed with a thin film transistor (TFT), a color filter panel formed with a color filter (CF), and a liquid crystal interposed therebetween, and the image is displayed by driving and controlling the liquid crystal by an electric field difference between the array panel and the color filter panel.

The liquid crystal display (LCD) may be divided into a transmissive type using light incident from its backlight unit disposed at one side of its liquid crystal display panel, and a reflective type using external light such as solar light.

The reflective type liquid crystal display (LCD) uses only external light incident through the LCD such that power consumption thereof is relatively small compared to the transmissive type liquid crystal display (LCD) using only internal light incident from its backlight unit. Also, when the transmissive type liquid crystal display (LCD) is used outdoors, visibility may be remarkably deteriorated due to external (outer) light such as the solar light. However, in the case of a reflective liquid crystal display (LCD), the outer light is used as the light source such that the reflective liquid crystal display (LCD) may not be used when the outer light is not present.

Therefore, a transflective liquid crystal display (LCD) including both the transmissive type and the reflective type has been proposed. The transflective liquid crystal display (LCD) includes a transmissive part and a reflective part inside the liquid crystal display panel such that the transmissive mode and the reflective mode may be selectively realized. Generally, the transflective liquid crystal display (LCD) includes a step inside the liquid crystal display panel, and thereby a difference of an interval, that is, a cell gap between two substrates of the liquid crystal display panel is generated, and the transmissive mode and the reflective mode are realized by the difference of the cell gap.

However, the transflective liquid crystal display (LCD) generates light leakage due to the step such that light loss is increased, and when a light blocking layer at the step is formed to block the light leakage, the aperture ratio is decreased. Also, the cell gap is not uniform such that an internal structure is complicated, and resultantly the manufacturing process thereof is complicated.

SUMMARY

The described technology provides a transflective liquid crystal display (LCD) having a uniform cell gap, and a manufacturing method thereof.

A liquid crystal display (LCD) according to an exemplary embodiment includes: a first substrate formed (arranged) with a thin film transistor and a pixel electrode connected to the thin film transistor; a second substrate formed (arranged) with a common electrode and a color filter and facing the first substrate; a liquid crystal layer between the first substrate and the second substrate; a first polarizing plate disposed (located) at one side of the first substrate facing away (e.g., that does not face) the second substrate; a second polarizing plate disposed (located) at one side of the second substrate that does not face the first substrate; a cholesteric film formed on the first substrate; and a backlight unit disposed at one side of the first polarizing plate that does not face the first substrate.

The cholesteric film may include a reflective layer and a transmissive layer, and the reflective layer and the transmissive layer are located at an entire area in (of) one pixel.

The reflectance of the reflective layer of the cholesteric film may be 100%.

The reflectance of the cholesteric film may be 50%.

The first polarizing plate and the second polarizing plate may respectively change incident light into different circular polarization directions.

The cholesteric film may be disposed between the thin film transistor and the pixel electrode, and the cholesteric film may have a hole to connect the thin film transistor and the pixel electrode.

The liquid crystal display (LCD) may further include a ¼ wavelength plate and a cholesteric reflective plate disposed between the first polarizing plate and the backlight unit.

The reflectance of the cholesteric reflective plate may be 100%.

The liquid crystal display (LCD) may further include a protective layer formed on the thin film transistor, and an organic layer formed on the protective layer.

The liquid crystal display (LCD) may further include a diffusion layer formed between the second substrate and the second polarizing plate.

The color filter may include light diffusion particles.

The liquid crystal layer may be an electrically controlled birefringence (ECB) mode liquid crystal layer, a vertical alignment (VA) mode liquid crystal layer, an optically compensated birefringence (OCB) mode liquid crystal layer, or a hybrid aligned nematic (HAN) mode liquid crystal layer.

A method for manufacturing a liquid crystal display (LCD) according to an exemplary embodiment includes: forming a thin film transistor on a first substrate; forming a cholesteric film on the thin film transistor; forming a hole in the cholesteric film; forming a pixel electrode connected to the thin film transistor through the hole; forming a color filter and a common electrode on a second substrate; injecting a liquid crystal contacting the first substrate and the second substrate and between the first substrate and the second substrate; disposing a first polarizing plate at one side of the first substrate facing away (e.g., that does not face) the second substrate; disposing a second polarizing plate at one side of the second substrate that does not face the first substrate; and disposing a backlight unit at one side of the first polarizing plate that does not face the first substrate.

The cholesteric film may be formed by irradiating ultraviolet (UV) light to a reactive mesogen and by heat-treating it.

The ultraviolet (UV) light may be selectively irradiated to the reactive mesogen to form a reflective layer and a transmissive layer.

The reflective layer and the transmissive layer may be formed at entire area in (of) one pixel.

A ¼ wavelength plate and a cholesteric reflective plate may be disposed between the first polarizing plate and the backlight unit.

The reflectance of the reflective layer may be 100%.

The reflectance of the cholesteric film may be 50%.

A protective layer may be formed on the thin film transistor, and an organic layer may be formed on the protective layer.

A diffusion layer may be formed between the second substrate and the second polarizing plate.

Light diffusion particles may be formed in the color filter.

According to an exemplary embodiment, the liquid crystal display (LCD) has a uniform cell gap such that the aperture ratio may be increased.

Also, the opening area is increased such that the luminance may be improved.

Further, the transflective liquid crystal display (LCD) may be manufactured through a simple method.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The present invention will be described more fully hereinafter with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown.

The drawings and description are to be regarded as illustrative in nature and not restrictive. Like reference numerals designate like elements throughout the specification. In addition, the size and thickness of each component shown in the drawings are arbitrarily shown for better understanding and ease of description, but the present invention is not limited thereto.

FIG. 1is a schematic diagram of a liquid crystal display (LCD) according to a first exemplary embodiment, andFIG. 2is an enlarged cross-sectional view of a liquid crystal display (LCD) according to the first exemplary embodiment. A liquid crystal display (LCD) according to the present exemplary embodiment will be described with reference to them.

Referring toFIG. 1andFIG. 2, a liquid crystal display (LCD)100includes a liquid crystal display panel and a backlight unit90. The liquid crystal display panel includes a first substrate11, a second substrate12facing the first substrate11, and a liquid crystal layer50formed between the first substrate11and the second substrate12, and the backlight unit90is disposed under the first substrate11.

The first substrate11and the second substrate12may be formed of transparent glass for internal light emitted from the backlight unit90and outer (external) light such as a natural light (e.g., solar or sun light) to be transmitted, and they are mutually combined by a sealing member15that is formed according to an outer perimeter thereof. A thin film transistor20and a pixel electrode40, connected to the thin film transistor20, are formed on the first substrate11and a common electrode65is formed on the second substrate12, and when voltages are applied to the pixel electrode40and the common electrode65, an electric field is formed therebetween such that the liquid crystal layer50is driven.

In more detail, also referring toFIG. 2, a gate electrode21, a gate insulating layer22, a semiconductor layer23, and an ohmic contact layer24are sequentially formed on the first substrate11. Also, a source electrode25and a drain electrode26are formed on the ohmic contact layer24and on the gate insulating layer22, and a protective layer35is formed on the thin film transistor20.

A cholesteric film30is formed on the thin film transistor20and the protective layer35. The cholesteric film30includes a reflective layer31and a transmissive layer32, having a function selectively reflecting one of either left circular polarized light or right circular polarized light, and the cholesteric film30will be described in more detail later.

In the present specification, light that is rotated in a clockwise direction is referred to as left circular polarized light, and a light that is rotated in a counterclockwise direction is referred to as a right circular polarized light.

A pixel electrode40is formed on the cholesteric film30. The pixel electrode40is connected to the drain electrode26of the thin film transistor20through a via hole41formed in the cholesteric film30and the protective layer35, thereby receiving an electrical signal.

The common electrode65facing the pixel electrode40is formed on the second substrate12, and when voltages are applied to the pixel electrode40on the first substrate11and the common electrode65on the second substrate12, an electric field is formed and the liquid crystal layer50, formed between the first substrate11and the second substrate12, is accordingly driven.

In one embodiment, the pixel electrode40and the common electrode65are formed of a transparent material such as indium tin oxide (ITO) or indium zinc oxide (IZO) for light to be transmitted.

In the present exemplary embodiment, liquid crystal molecules of the liquid crystal layer50maintain a horizontal state when the electric field is not formed, and are vertically aligned, thereby being operated as an electrically controlled birefringence (ECB) mode when the electric field is formed. However, the present invention is not limited thereto, and the liquid crystal layer50may be formed with a vertically aligned (VA) mode wherein it maintains a vertical state when the electric field is not formed, and is vertically aligned when the electric field is formed. Also, various other modes such as an optically compensated birefringence (OCB) mode or a hybrid aligned nematic (HAN) mode may be formed.

A color filter60is formed on the second substrate12. The color filter60for filtering light from white color light that is transmitting through the liquid crystal layer50, to a desired color light, uses three primary color filters of red (R), green (G), and blue (B) for one pixel. A uniform color is realized through an additive color mixture while either the internal light that is emitted from the backlight unit90and transmitted through the cholesteric film30, or the outer light that is incident from the outside and reflected by the cholesteric film30, is passed through the color filter60. Here, the color filter60in the present exemplary embodiment may be formed by using a color photoresist.

A polarizing plate70is formed to have a first polarizing plate71at one side of the first substrate11and a second polarizing plate72at one side of the second substrate12. The polarizing plate70formed at one side of the first substrate11and the second substrate12as the circular polarizing plate may be formed by a combination of a linear polarizing plate and a ¼ wavelength plate. The light passing through the polarizing plate70is rotated in the clockwise direction or in the counterclockwise direction. That is, the polarizing plate70changes the incident light into the left circular polarized light or the right circular polarized light.

In the present exemplary embodiment, the polarizing plate70includes the first polarizing plate71and the second polarizing plate72. The first polarizing plate71and the second polarizing plate72are respectively positioned under the first substrate11and on the second substrate12, thereby changing the incident light into circular polarized light of different directions. That is, if the first polarizing plate71changes the incident light into the left circular polarized light, then the second polarizing plate72changes the incident light into the right circular polarized light, and if the first polarizing plate71changes the incident light into the right circular polarized light, then the second polarizing plate72changes the incident light into the left circular polarized light.

A diffusion layer80to improve the viewing angle is formed between the second substrate12and the second polarizing plate72in the present exemplary embodiment. The light incident to the side of the second substrate12generates a mirror reflection in the cholesteric film30such that the light is not diffused in all directions, and the viewing angle may become narrow. However, in the present exemplary embodiment, the light reflected from the cholesteric film30is passed through the diffusion layer80such that the problem due to the mirror reflection may be solved and the viewing angle may be improved.

The backlight unit90includes a light source and a light guide plate. As the light source, a light emitting diode (LED) may be used, and this may be mounted to a printed circuit film and may be disposed at one side of the light guide plate. Here, the number of light sources used may be variously changed according to a usage and a size of the liquid crystal display (LCD)100, and the light source may be disposed under a guide plate if necessary. The light emitted from the light source is incident to the light guide plate, and the light guide plate guides the light to uniformly diffuse the light onto the entire surface of the light guide plate.

Also, an optical sheet may be disposed between the liquid crystal display panel and the backlight unit90. The optical sheet may include a diffusion sheet, a prism sheet, a protection sheet, etc., and thereby the light passing through the light guide plate of the backlight unit is incident in the direction vertical to the liquid crystal display panel. Also, a reflection sheet may be further disposed under the backlight unit90. When the reflection sheet is disposed, the reflection sheet reflects the light emitted to the lower surface of the light guide plate toward the optical sheet, and thereby the light loss may be reduced or minimized.

FIG. 3AtoFIG. 3Care views schematically showing a process of forming a cholesteric film of a liquid crystal display (LCD) according to the first exemplary embodiment. Hereafter, a manufacturing method of a cholesteric film and a characteristic thereof according to the present exemplary embodiment will be described with reference to these.

Referring toFIG. 3A, a reactive mesogen30′ having a nematic phase is coated on a substrate S. In the present exemplary embodiment, the reactive mesogen30′ used to form the cholesteric film30includes a mesogen that is capable of exhibiting liquid crystal properties and an end group that is capable of being polymerized, meaning a monomer molecule having a liquid crystal phase.

Referring toFIG. 3B, ultraviolet (UV) light is irradiated to the reactive mesogen30′ coated on the substrate S. When the ultraviolet (UV) light is irradiated, an irradiation region of the ultraviolet (UV) light may be selected by using a mask M. The reactive mesogen is hardened in the region where the ultraviolet (UV) light is irradiated to form a hardening region31′, and the reactive mesogen is not hardened in the region where the ultraviolet (UV) light is not irradiated to form a non-hardening region32′.

Referring toFIG. 3C, heat is applied to the entire hardening region31′ and non-hardening region32′, thereby completing the cholesteric film30. As described above, the cholesteric film30includes a reflective layer31and a transmissive layer32, and referring toFIG. 3C, a reflective layer31(having refractive index anisotropy) is formed at the region where the ultraviolet (UV) light is irradiated to the reactive mesogen, and the transmissive layer32(having a refractive index isotropy ultraviolet (UV) light) is formed at the region where the ultraviolet (UV) light is not irradiated.

The reflective layer31of the cholesteric film30has a characteristic of reflecting the incident light of a special polarization state by the refractive index anisotropy. In more detail, the reflective layer31of the cholesteric film30has the right circular or left circular polarization direction. Here, when the polarization direction of the incident light accords (corresponds and matches) with the polarization direction of the reflective layer31, the reflective layer31reflects the incident light, but when the polarization directions do not accord, the incident light is passed as it is. Here, the thickness of the reflective layer31is controlled to control reflectance, and in the present exemplary embodiment, the reflective layer31is formed to reflect the incident light according to the polarization direction of the reflective layer31at 100%.

Differently from the reflective layer31, the transmissive layer32of the cholesteric film30does not have the refractive index anisotropy and the special polarization direction, thereby having a function of transmitting the incident light as it is.

A manufacturing process of the cholesteric film30is similar to a manufacturing process of an organic layer formed on a protective layer such that a transflective mode of the liquid crystal display (LCD)100may be realized by using the manufacturing process of the organic layer formed on the protective layer.

FIG. 4AandFIG. 4Bare cross-sectional views schematically showing a reflective mode and a transmissive mode of a liquid crystal display (LCD) according to the first exemplary embodiment. An operation of a transflective mode of a liquid crystal display (LCD) according to the present exemplary embodiment will be described with reference to these.

In the present exemplary embodiment, the first polarizing plate71and the second polarizing plate72respectively change the incident light into the left circular polarized light and the right circular polarized light, and the reflective layer31of the cholesteric film has the characteristic of reflecting the left circular polarized light. However, the present invention is not limited thereto, and the first polarizing plate and the second polarizing plate may respectively change the incident light into the right circular polarized light and the left circular polarized light, and the reflective layer of the cholesteric film may have the characteristic of reflecting the right circular polarized light.

FIG. 4Ashows a white state in which a liquid crystal layer50ais horizontally aligned, wherein the left side shows a path of external light incident from the outside of the liquid crystal display (LCD), and the right side shows a path of internal light emitted from the inside the liquid crystal display (LCD).

Firstly, referring to the path of the external light, a portion of the external light is changed into the right circular polarized light while passing through the second polarizing plate72positioned on the second substrate. The liquid crystal layer50athat is horizontally aligned between the two substrates functions as a phase retardation plate such that the right circular polarized light incident to the liquid crystal layer50ais changed into the left circular polarized light while passing through it. As described above, the external light that is changed into the left circular polarized light while passing through the second polarizing plate72and the liquid crystal layer50ais reflected by the reflective layer31of the cholesteric film30. In the present exemplary embodiment, the reflectance of the reflective layer31is 100%, all the external light incident to the internal of the liquid crystal display (LCD) is reflected by the reflective layer31.

When the external light is reflected by the reflective layer31, phase retardation is not generated and the external light that is reflected as left circular polarized light is changed into the right circular polarized light while passing through the liquid crystal layer50a. The external light that is changed into the right circular polarized light, is passed through the color filter and the second substrate, and is then emitted through the second polarizing plate72to the outside.

Referring to the path of the internal light, the internal light that is emitted from the backlight unit90disposed under the first substrate, is changed into the left circular polarized light while the portion thereof is passed through the first polarizing plate71. The internal light that is changed into the left circular polarized light is passed through the transmissive layer32of the cholesteric film30as it is, and is changed into the right circular polarized light while passing through the liquid crystal layer50athat is horizontally aligned. In this way, the internal light that is changed into the right circular polarized light through the first polarizing plate71and the liquid crystal layer50a, is passed through the color filter and the second substrate, and is then emitted outside through the second polarizing plate72.

As described above, in the white state in which the liquid crystal layer50ais horizontally aligned, the external light is passed through the second polarizing plate72and is reflected by the reflective layer31of the cholesteric film30; and the internal light is passed through the first polarizing plate71and the transmissive layer32of the cholesteric film30; and both the external light and the internal light are then emitted to the side of the second substrate such that the external light that is reflected and the internal light that is passed in one pixel may all be used.

FIG. 4Bshows a black state in which the liquid crystal layer50bis vertically aligned, wherein the path of the external light incident from the outside of the liquid crystal display (LCD) is shown at the left side, and the path of the internal light emitted from the inside of the liquid crystal display (LCD) is shown at the right side.

Firstly, referring to the path of the external light, a portion of the external light is changed into the right circular polarized light while passing though the second polarizing plate72positioned on the second substrate, and the external light (changed into the right circular polarized light) is passed through the liquid crystal layer50bthat is vertically aligned between the two substrates as it is. Here, the phase retardation is not generated for the external light passing through the liquid crystal layer50b. As described above, the external light that is changed into the right circular polarized light while passing through the second polarizing plate72and the liquid crystal layer50b, does not accord (not correspond and match) with the polarization direction of the reflective layer31of the cholesteric film30, such that it is passed through the reflective layer31as it is. Also, the external light is passed through the reflective layer31(changed into the right circular polarized light), and it is not passed through the first polarizing plate71.

Referring to the internal light, a portion of the internal light that is emitted from the backlight unit90positioned under the first substrate, is changed into the left circular polarized light while passing through the first polarizing plate71. The internal light of the left circular polarization is transmitted through the transmissive layer32of the cholesteric film30as it is, and is passed through the liquid crystal layer50bthat is vertically aligned as it is without the phase retardation. In this way, the internal light that is changed into the left circular polarized light through the first polarizing plate71and the liquid crystal layer50b, is not passed through the second polarizing plate72such that it is not emitted outside the second substrate.

As described above, in the black state in which the liquid crystal layer50bis vertically aligned, all external and internal light is not emitted toward the second substrate such that the image is not realized.

Also, in the present exemplary embodiment, the liquid crystal layer may be operated with an ECB mode, that is the white state in the off state when the electric field is not formed between the two substrates, or may be operated with a VA mode, that is the white state in the on state when the electric field is formed between the two substrates.

In the present exemplary embodiment, the cholesteric film30including the reflective layer31and the transmissive layer32are formed (located) at (on or in) the entire area (and, e.g., as part of a same layer) of (in) each pixel of the liquid crystal display (LCD)100, and thereby the external light such as the solar light may be reflected by the reflective layer31and the internal light emitted from the backlight unit90may be transmitted through the transmissive layer32. That is, the liquid crystal display (LCD)100according to the present exemplary embodiment may be operated with the transflective mode in which the reflection and the transmission are simultaneously or concurrently realized.

Also, the reflection portion and the transmission portion are formed without the step such that a uniform interval, that is, a uniform cell gap, may be maintained between the two substrates. Resultantly the light leakage may be prevented, the light loss may be reduced, and the additional light block layer is not necessary such that the reduction of the aperture ratio may be prevented.

Hereinafter, a liquid crystal display (LCD) according to other exemplary embodiments will be described with reference toFIG. 5toFIG. 14. For the description of other exemplary embodiments, descriptions of the same configurations as in the first exemplary embodiment are simplified or omitted.

FIG. 5is an enlarged cross-sectional view of a liquid crystal display (LCD) according to a second exemplary embodiment.

Referring toFIG. 5, a liquid crystal display (LCD)101has the same structure as the liquid crystal display (LCD)100of the first exemplary embodiment except for a ¼ wavelength plate173and a cholesteric reflective plate133disposed under the first substrate11.

The ¼ wavelength plate173that changes the polarization direction of the incident light by 90 degrees is disposed under the first polarizing plate71, and the cholesteric reflective plate133is disposed between the ¼ wavelength plate173and the backlight unit90.

The cholesteric reflective plate133may be manufactured through a similar method to the cholesteric film30. In more detail, to reflect the incident light of a set or predetermined polarization direction throughout the entire region of the cholesteric reflective plate133, the cholesteric reflective plate133is formed to have refractive index anisotropy like the reflective layer31of the cholesteric film30. Also, the thickness of the cholesteric reflective plate133is controlled to realize the reflectance of 100%.

The light efficiency of the incident light passing through the transmissive layer32of the cholesteric film30may be improved through the configuration further including the ¼ wavelength plate173and the cholesteric reflective plate133, and this will be described in more detail.

FIG. 6is a cross-sectional view schematically showing a reflective mode and a transmissive mode of a liquid crystal display (LCD) according to the second exemplary embodiment. An operation of a transflective mode of a liquid crystal display (LCD) according to the present exemplary embodiment will be described with reference to these.

In the present exemplary embodiment, like the first exemplary embodiment, the first polarizing plate71and the second polarizing plate72respectively change the incident light into the left circular polarized light and the right circular polarized light, and the reflective layer31of the cholesteric film has the characteristic of reflecting the left circular polarized light.

FIG. 6shows a white state in which the liquid crystal layer50ais horizontally aligned, wherein the path of external light incident from the outside of the liquid crystal display (LCD) is shown at the left side, and the path of internal light emitted from the inside of the liquid crystal display (LCD) is shown at the right side.

In the present exemplary embodiment, the configuration of the second polarizing plate72and the cholesteric film30is the same as that of the first exemplary embodiment such that the path of the external light incident from the outside is also the same as the path of the external light in the first exemplary embodiment.

Referring to the internal light in the present exemplary embodiment, the internal light emitted from the backlight unit90is emitted toward the cholesteric reflective plate133. The cholesteric reflective plate133in the present exemplary embodiment has the characteristic of reflecting the incident light of the set or predetermined polarization direction, and in more detail, the left circular polarized light. Accordingly, the left circular polarized light among the internal light incident from the backlight unit90is again reflected to the backlight unit90and the rest of the internal light is transmitted through the cholesteric reflective plate133as it is.

The portion of the left circular polarized light reflected by the cholesteric reflective plate133among the internal light is reflected by the optical sheet disposed on the backlight unit90or by the backlight unit90itself, and then is again progressed toward the cholesteric reflective plate133. In this process, the phase of the left circular polarized light is changed, and therefore the internal light reflected by the backlight unit90or the optical sheet is transmitted through the cholesteric reflective plate133. At this time, the light that is reflected by the backlight unit90and is transmitted through the cholesteric reflective plate133, is in the range of 30-50% of the left circular polarized light reflected by the cholesteric reflective plate133.

The internal light transmitting through the cholesteric reflective plate133is changed into the linear polarized light of the same direction as the transmissive axis of the first polarizing plate71while passing through the ¼ wavelength plate173, and then is again changed into the left circular polarized light while passing through the first polarizing plate71. When the light passing through the cholesteric reflective plate133is directly passed through the first polarizing plate71(without the cholesteric reflective plate133and the ¼ wavelength plate173), the luminance of the light is decreased by half by the first polarizing plate71, however the ¼ wavelength plate173of the present exemplary embodiment has the function of passing the light, passing through the cholesteric reflective plate133, through the polarizing plate71without the luminance loss.

The internal light passing through the ¼ wavelength plate173and the first polarizing plate71is transmitted through the transmissive layer32of the cholesteric film, as it is. The internal light passing through the transmissive layer32is changed into the right circular polarized light while passing through the liquid crystal layer50athat is horizontally aligned, and is emitted outside through the second polarizing plate72, the color filter, and the second substrate.

Like the first exemplary embodiment, in the structure in which the cholesteric reflective plate133and the ¼ wavelength plate173are removed, and in the process in which the internal light emitted from the backlight unit90is changed into the left circular polarized light through the first polarizing plate71, light loss of about 50% is generated. However the internal light of the set or predetermined polarization state may be reused by adding the cholesteric reflective plate133and the ¼ wavelength plate173, thereby improving the light efficiency.

FIG. 7is an enlarged cross-sectional view of a liquid crystal display (LCD) according to a third exemplary embodiment.

Referring toFIG. 7, a liquid crystal display (LCD)102has a similar structure to the liquid crystal display (LCD)100of the first exemplary embodiment. However, in the present exemplary embodiment, the diffusion plate is not additionally formed on the second substrate12; but the present exemplary embodiment does include a color filter260formed with a first color filter261including light diffusion particles and a second color filter262where the light diffusion particles are not included.

As described above, when the external light is reflected by the reflective layer31of the cholesteric film30, mirror reflection is generated such that the viewing angle may be decreased in the reflection of the external light. In the present exemplary embodiment, to compensate the viewing angle that is decreased by the mirror reflection, the first color filter261including the light diffusion particles is formed as a portion of the color filter.

A haze of the first color filter261is increased by this configuration, and accordingly the light passing through it is diffused at a wide angle such that the viewing angle is increased.

In the present exemplary embodiment, when considering the improvement of the viewing angle related to the external light reflected by the reflective layer31of the cholesteric film30, the first color filter261including the light diffusion particles is formed corresponding to the reflective layer31of the cholesteric film30, and the second color filter262without the light diffusion particles is formed corresponding to the transmissive layer32of the cholesteric film30. However, the present invention is not limited thereto, and the size and position of both the first color filter261including the light diffusion particles and the second color filter262without the light diffusion particles may be variously changed. Also, when considering the efficiency of the light diffusion and a stable process, the second color filter, may be omitted and the color filter may include the light diffusion particles on the whole region.

FIG. 8is an enlarged cross-sectional view of a liquid crystal display (LCD) according to a fourth exemplary embodiment.

Referring toFIG. 8, a liquid crystal display (LCD)103has a similar structure to the liquid crystal display (LCD)100according to the first exemplary embodiment. However, in the present exemplary embodiment, a protective layer that is formed on the gate insulating layer22in the liquid crystal display (LCD)100of the first exemplary embodiment is not additionally formed, and a cholesteric film330has the function of the protective layer.

That is, the cholesteric film330, including a reflective layer331and a transmissive layer332, is directly formed on the gate insulating layer22by the manufacturing process described throughFIG. 3AtoFIG. 3C.

As described above, the protective layer is not separately formed, and the cholesteric film330has the function of the protective layer, and thereby the manufacturing process to form the transflective mode may be further simplified.

FIG. 9is an enlarged cross-sectional view of a liquid crystal display (LCD) according to a fifth exemplary embodiment.

Referring toFIG. 9, a liquid crystal display (LCD)104has a similar structure to the liquid crystal display (LCD)100according to the first exemplary embodiment. However, an organic layer437is formed between the protective layer35and the cholesteric film30in the present exemplary embodiment.

That is, the present exemplary embodiment additionally forms the cholesteric film30to the conventional deposition structure of the protective layer35and the organic layer437, and thereby a similar manufacturing process of the cholesteric film30to the manufacturing process of the organic layer437(without dramatically changing the manufacturing process of the organic layer437) is used to realize the transflective mode of the liquid crystal display (LCD)104.

FIG. 10is an enlarged cross-sectional view of a liquid crystal display (LCD) according to a sixth exemplary embodiment.

Referring toFIG. 10, the liquid crystal display (LCD)105has a similar structure to the liquid crystal display (LCD)100according to the first exemplary embodiment. However, in the present exemplary embodiment, a cholesteric film530only includes the reflective layer having the refractive index anisotropy, which is different from the first exemplary embodiment.

In the present exemplary embodiment, the ultraviolet (UV) light is irradiated and heat treatment is executed to the entire region of the reactive mesogen to form the cholesteric film530, and thereby a reflective layer having refractive index anisotropy is formed on the entire region of the cholesteric film530. Also, in the present exemplary embodiment, the cholesteric film530has reflectance of about 50%, as described above, and this reflectance of the cholesteric film530may be controlled by controlling the thickness of the cholesteric film530.

As described above, the cholesteric film530in the present exemplary embodiment is different from the first exemplary embodiment such that the shape for realizing the transflective mode is changed, and this will be described hereafter.

FIG. 11AandFIG. 11Bare cross-sectional views schematically showing a reflective mode and a transmissive mode of a liquid crystal display (LCD) according to the sixth exemplary embodiment, and the operation of the transflective mode of the liquid crystal display (LCD) according to the present exemplary embodiment will be described.

In the present exemplary embodiment, like the first exemplary embodiment, the first polarizing plate71and the second polarizing plate72respectively change the incident light into the left circular polarized light and the right circular polarized light, and the reflective layer31of the cholesteric film reflects the left circular polarized light.

FIG. 11Ashows the white state in which the liquid crystal layer50ais horizontally aligned, wherein the left side is the path of the external light and the right side is the path of the internal light.

Firstly, referring to the path of the external light, a portion of the external light is changed into the right circular polarized light while passing through the second polarizing plate72positioned on the second substrate, and then is again changed into the left circular polarized light while passing through the liquid crystal layer50athat is horizontally aligned between two substrates. As above described, the external light that is changed into the left circular polarized light while passing through the second polarizing plate72and the liquid crystal layer50aaccords the polarized light direction of the cholesteric film530such that it is reflected. In the present exemplary embodiment, it is set up that the reflectance of the reflective layer31is 50%. Thus, about 50% of the external light incident to the interior of the liquid crystal display (LCD) is reflected by the reflective layer31, and the rest is passed through the cholesteric film530.

When the external light is reflected by the reflective layer31, the phase retardation is not generated and the external light that is reflected as the left circular polarized light is changed into the right circular polarized light while passing through the liquid crystal layer50a. The external light that is changed into the right circular polarized light is passed through the color filter and the second substrate, and is emitted through the second polarizing plate72to the outside.

Referring to the path of the internal light, the internal light emitted from the backlight unit90disposed under the first substrate is changed into the left circular polarized light while a portion thereof is passed through the first polarizing plate71. As described above, in the present exemplary embodiment, the reflectance of the cholesteric film530is about 50%, such that about 50% of the internal light arriving at the cholesteric film530is reflected from the cholesteric film530in the direction of the first polarizing plate71, and the remainder of about 50% is transmitted through the cholesteric film530.

The internal light transmitted through the cholesteric film530is changed into the right circular polarized light while passing through the liquid crystal layer50athat is horizontally aligned, is then passed through the color filter and the second substrate, and is then emitted through the second polarizing plate72to the outside.

As described above, in the white state in which the liquid crystal layer50ais horizontally aligned, the external light and the internal light pass through the second polarizing plate72and the first polarizing plate71, and are reflected and transmitted through the cholesteric film530having reflectance of about 50% such that the external light and the internal light are both used in one pixel.

FIG. 11Bis the black state in which the liquid crystal layer50bis vertically aligned, wherein the left side is the path of the external light and the right side is the path of the internal light.

Referring to the path of the external light of the black state, a portion of the external light is changed into the right circular polarized light while passing through the second polarizing plate72positioned on the second substrate, and is passed as it is through the liquid crystal layer50bthat is vertically aligned between the two substrates without the phase retardation. As described above, the external light that is changed into the right circular polarized light while passing through the second polarizing plate72and the liquid crystal layer50b, does not accord (correspond) with the polarization direction of the cholesteric film530such that it is transmitted as it is. On the other hand, the external light that is transmitted through the cholesteric film530as it is, is changed into the right circular polarized light such that it is not passed through the first polarizing plate71.

Referring to the path of the internal light, the internal light from the backlight unit90positioned under the first substrate is changed into the left circular polarized light while a portion thereof is passed through the first polarizing plate71. The internal light of the left circular polarized light is transmitted through the cholesteric film530as it is, and is also transmitted as it is through the liquid crystal layer50bthat is vertically aligned without the phase retardation. As described above, the internal light that is changed into the left circular polarized light while passing through the first polarizing plate71and the liquid crystal layer50b, is not transmitted through the second polarizing plate72such that it is not emitted outside the second substrate.

In this way, the external light and the internal light are both not emitted to the side of the second substrate in the black state in which the liquid crystal layer50bis vertically aligned such that the image is not realized.

As described above, differently from the cholesteric film30in which the reflective layer31and the transmissive layer32are additionally formed in the firsts exemplary embodiment, the single cholesteric film530that is capable of progressing both the reflection and the transmissions, is formed by controlling the reflectance such that the transflective mode may be realized while simplifying the internal structure. Therefore, the uniform cell gap may be maintained such that the light loss may be reduced and the reduction of the aperture ratio may be prevented.

FIG. 12is an enlarged cross-sectional view of a liquid crystal display (LCD) according to a seventh exemplary embodiment.

Referring toFIG. 12, a liquid crystal display (LCD)106has the same structure as the liquid crystal display (LCD)105according to the sixth exemplary embodiment except for a ¼ wavelength plate673and a cholesteric reflective plate633disposed under the first substrate11. A cholesteric film630according to the present exemplary embodiment has the same configuration as that of the cholesteric film530according to the sixth exemplary embodiment.

The ¼ wavelength plate673and the cholesteric reflective plate633are disposed between the first polarizing plate71and the backlight unit90, and the cholesteric reflective plate633is formed to have refractive index anisotropy throughout the entire region, like the cholesteric film630. However, differently from the cholesteric film630, the cholesteric reflective plate633has reflectance of 100%.

The light efficiency with which the incident light is transmitted through the cholesteric film630may be improved by the configuration further including the ¼ wavelength plate673and the cholesteric reflective plate633, and this will be described in more detail.

FIG. 13is a cross-sectional view schematically showing a reflective mode and a transmissive mode of a liquid crystal display (LCD) according to the seventh exemplary embodiment, and the operation of the transflective mode of the liquid crystal display (LCD) according to the present exemplary embodiment will be described.

In the present exemplary embodiment, like the sixth exemplary embodiment, the first polarizing plate71and the second polarizing plate72respectively change the incident light into the left circular polarized light and the right circular polarized light, and the cholesteric film630reflects the left circular polarized light with reflectance of about 50%.

FIG. 13shows the white state in which the liquid crystal layer50ais horizontally aligned, wherein the left side is the path of the external light, and the right side is the path of the internal light.

In the present exemplary embodiment, the second polarizing plate72and the cholesteric film630are the same as those of the sixth exemplary embodiment such that the path of the external light is the same as the path of the external light in the sixth exemplary embodiment.

In the present exemplary embodiment, referring to the path of the internal light, the internal light emitted from the backlight unit90is progressed toward the cholesteric reflective plate633. In the present exemplary embodiment, the cholesteric reflective plate633has the characteristic of reflecting the left circular polarized light. Accordingly, the left circular polarized light among the internal light incident from the backlight unit90is again reflected to the backlight unit90, and the remainder of the internal light is passed through the cholesteric reflective plate633as it is.

The portion of the left circular polarized light that is reflected by the cholesteric reflective plate633among the internal light, is reflected by the optical sheet disposed on the backlight unit90or by the backlight unit90itself such that it is again progressed toward the cholesteric reflective plate633. In this process, the phase of the left circular polarized light is changed such that the internal light reflected by the backlight unit90or the optical sheet is transmitted through the cholesteric reflective plate633. Here, the light that is reflected by the backlight unit90and is transmitted through the cholesteric reflective plate633is at a degree of about 30-50% of the left circular polarized light reflected by the cholesteric reflective plate633.

The internal light that is passed through the cholesteric reflective plate633is changed into the linear polarized light of the same direction as the transmissive axis of the first polarizing plate71, through the ¼ wavelength plate673, and then is again changed into the left circular polarized light, through the first polarizing plate71. As described above, ¼ the wavelength plate673allows the circular polymerized light that is transmitted through the cholesteric reflective plate633, to be passed through the first polarizing plate71without the luminance loss.

In the present exemplary embodiment, the reflectance of the cholesteric film630is about 50% such that 50% of the internal light that arrives at the cholesteric film630is reflected by the cholesteric film530in the direction of the first polarizing plate71, and the remaining about 50% is transmitted through the cholesteric film630. For convenience, the internal light that is reflected from the cholesteric film630to the first polarizing plate71is not shown.

The internal light passing through the ¼ wavelength plate173and the first polarizing plate71is transmitted through the cholesteric film630as it is. The internal light passing through the cholesteric film630is changed into the right circular polarized light through the vertical aligned liquid crystal layer50a, and is then emitted to the outside through the second polarizing plate72after passing through the color filter and the second substrate.

As shown in the present exemplary embodiment, the cholesteric reflective plate633and the ¼ wavelength plate673are added such that the internal light of the set or predetermined polarization state may be reused, and thereby the light efficiency may be improved.

FIG. 14is an enlarged cross-sectional view of a liquid crystal display (LCD) according to an eighth exemplary embodiment.

Referring toFIG. 14, a liquid crystal display (LCD)107is similar to the liquid crystal display (LCD)105of the sixth exemplary embodiment. However, in the present exemplary embodiment, the protective layer formed on the gate insulating layer22in the liquid crystal display (LCD)105of the sixth exemplary embodiment is not additionally formed, and the cholesteric film730has a function as the protective layer.

That is, the protective layer is not additionally formed and a cholesteric film730is formed directly on the gate insulating layer22to function as the protective layer, and thereby the manufacturing process to form the transflective mode may be further simplified.

As described above, the described technology has been described in connection with some exemplary embodiments. However, the present invention is not limited to the exemplary embodiments. The scope of the present invention is defined by the appended claims, and those having ordinary skill in the art will easily understand that the present invention may be modified in various ways without departing from the concept and scope of the claims.