WO2012053756A2

WO2012053756A2 - Liquid crystal display

Info

Publication number: WO2012053756A2
Application number: PCT/KR2011/007349
Authority: WO
Inventors: Young-Jae Lee; Jin Su Kim; Jun Lee; Kyoung Jong Yoo
Original assignee: Lg Innotek Co., Ltd.
Priority date: 2010-10-20
Filing date: 2011-10-05
Publication date: 2012-04-26
Also published as: TWI507779B; KR20120040868A; TW201222085A; KR101319444B1; WO2012053756A3

Abstract

An LCD including a wire grid polarizer is provided. The wire grid polarizer includes a plurality of grid patterns formed directly on the top or bottom surface of a bottom substrate of a liquid crystal panel. The wire grid polarizer is formed directly on a bottom glass substrate where TFTs and liquid crystals are formed, making it possible to reduce production costs due to the removal of an existing polarizing film, to reduce a total thickness of the LCD, and to achieve brightness enhancement.

Description

LIQUID CRYSTAL DISPLAY

The present invention relates to a structure of a liquid crystal display including a wire grid polarizer.

A liquid crystal display (LCD) is a flat panel display that is widely used in a variety of applications, including portable phones, notebook computers, monitors, and TVs. An LCD is a device that transmits or blocks light by a change in alignment of liquid crystal when an electric signal is applied to each pixel in a liquid crystal panel disposed between two polarizing plates. Therefore, a separate light source is required for operating an LCD. A backlight unit is provided as the light source.

FIG. 1 is a conceptual diagram illustrating a structure of a conventional LCD. Referring to FIG. 1, the LCD includes a liquid crystal panel A and a backlight unit B disposed under the liquid crystal panel A. The liquid crystal panel A includes a top substrate 9, a bottom substrate 6, a liquid crystal LC between the top substrate 9 and the bottom substrate 6, and

ITOs

7 and 8 for driving the liquid crystal panel. In particular, a color filter is arranged at an upper portion of the liquid crystal panel A, and a thin film transistor (TFT) array is arranged at a lower portion of the liquid crystal panel A. The backlight unit B is disposed under the liquid crystal panel A and includes a light guide plate 2 for guiding light emitted from a light source upwards, a reflection sheet 1, a diffusion plate 3, and a brightness enhancement film (BEF) 4.

To increase transmittance of light, a polarizing film 5 is provided on the bottom surface of the bottom substrate 6 constituting the TFT array of the liquid crystal panel A, and a polarizing film 10 is provided on the top surface of the top surface of the top substrate 9 constituting the TFT array.

However, since a conventional LCD uses an expensive polarizing film, manufacturing costs thereof increase and a thick polarizing film makes it difficult to manufacture a slim LCD. In addition, since a polarizing film is inferior in durability and heat resistance, the applicability of an LCD manufacturing process is extremely limited. The use of an absorptive polarizing film deteriorates brightness enhancement.

An aspect of the present invention is to provide an LCD in which a wire grid polarizer is formed directly on a bottom glass substrate where TFTs and liquid crystals are formed, making it possible to reduce production costs due to the removal of an existing polarizing film, to reduce a total thickness of the LCD, and to achieve brightness enhancement.

According to an embodiment of the present invention, an LCD includes a liquid crystal panel, and a wire grid polarizer with a plurality of grid patterns formed directly on the top or bottom surface of a bottom substrate of the liquid crystal panel.

Specifically, the wire grid polarizer may further include a second grid pattern on a first grid pattern formed on the bottom substrate.

According to the embodiments of the present invention, the wire grid polarizer is formed directly on the bottom glass substrate where TFTs and liquid crystals are formed, making it possible to reduce production costs due to the removal of an existing polarizing film, to reduce a total thickness of the LCD, and to achieve brightness enhancement.

The above and other aspects, features and advantages of certain exemplary embodiments of the present invention will be more apparent from the following description taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a cross-sectional view illustrating structure and function of a conventional LCD;

FIG. 2 is a cross-sectional conceptual diagram illustrating a structure of an LCD including a wire grid polarizer according to an embodiment of the present invention;

FIG. 3 is a conceptual diagram illustrating a main part of a wire grid polarizer according to an embodiment of the present invention;

FIGS. 4A to 4C are cross-sectional conceptual diagrams illustrating a blackening layer formed in the wire grid polarizer according to an embodiment of the present invention;

FIG. 5 is a conceptual diagram illustrating a structure of a wire grid polarizer according to another embodiment of the present invention;

FIG. 6 is a conceptual diagram illustrating a structure of a wire grid polarizer according to another embodiment of the present invention;

FIG. 7 is a cross-sectional conceptual diagram illustrating a structure of a wire grid polarizer according to an embodiment of the present invention; and

FIGS. 8 to 12 are cross-sectional conceptual diagrams illustrating a structure of a wire grid polarizer according to another embodiment of the present invention.

Exemplary embodiments of the present invention are directed to provide a technique that makes an entire liquid crystal panel slim, such that a wire grid polarizer is formed directly on a bottom glass substrate constituting an LCD and a TFT is formed thereon, thereby achieving brightness enhancement and reducing production costs.

To this end, exemplary embodiments of the present invention are directed to provide a wire grid polarizer that includes a liquid crystal panel and a plurality of grid patterns formed directly on the top or bottom surface of a bottom substrate of the liquid crystal panel. In particular, polarization efficiency can be improved by adjusting the period, height and width of the grid patterns. Moreover, the reliability of the LCD can be improved by various surface treatments or protective layers.

Exemplary embodiments of the present invention will be described below in detail with reference to the accompanying drawings. Wherever possible, the same reference numerals will be used to refer to the same elements throughout the specification, and a duplicated description thereof will be omitted. It will be understood that although the terms first , second , etc. are used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another element.

FIG. 2 is a cross-sectional conceptual diagram illustrating a structure of an LCD including a wire grid polarizer according to an embodiment of the present invention.

Referring to FIG. 2, an LCD according to an embodiment of the present invention may include a liquid crystal panel A and a wire grid polarizer 100. The wire grid polarizer 100 includes a plurality of grid patterns formed directly on one surface of a bottom substrate of the liquid crystal panel A or on the other surface opposite to the surface of the bottom substrate. The LCD further includes a backlight unit B for radiating light emitted from a light source upwards.

That is, the essential point of the liquid crystal panel A according to the embodiment of the present invention is that the wire grid polarizer is implemented by forming a plurality of grid patterns directly on a bottom glass substrate. A TFT array 7 including ITO may be disposed on the wire grid polarizer. A color filter 8 and a liquid crystal LC are disposed under a top glass substrate 9. A polarizing film may be further provided on the top glass substrate 9. The term directly means that the grid patterns are formed in close contact with the surface of the bottom glass substrate.

In addition, the backlight unit B disposed under the liquid crystal panel A may be provided with a general backlight unit that includes a light guide plate 2 for guiding light emitted from the light source upwards, a diffusion plate 3, and a variety of enhancement films 4.

FIG. 3 illustrates the structure of the wire grid polarizer 100 that is provided directly on the bottom glass substrate 110 of the liquid crystal panel A.

Referring to FIG. 3, the wire grid polarizer 100 according to the embodiment of the present invention may include a first grid layer 120 with at least one first grid pattern 121 formed directly on the bottom substrate 110 of the liquid crystal panel A, and at least one second grid pattern 130 formed using a metal on the first grid pattern 121.

The wire grid polarizer 100 may further include a protective layer C on the second grid pattern 130. The protective layer C may be formed to cover the side and top surface of the second grid pattern 130.

In case where the protective layer C is provided, a TFT array 7 may be provided on the protective layer C.

The substrate 110 may be a glass substrate for an LCD. The first grid layer 120 stacked on the top surface of the substrate 110 is formed using a polymer. It is preferable that first grid patterns 121, which are protrusion patterns having a constant period, are formed on the surface of the first grid layer 120 formed using a polymer.

That is, the first grid layer 120 is defined as a layer that includes a plurality of first grid patterns 121 which are protrusion patterns formed at a constant period on the surface of a resin layer formed of a polymer. In particular, it is more preferable that the first grid layer 120 according to the embodiment of the present invention is formed using a material having a refractive index equal to that of the substrate 110. If necessary, the first grid layer 120 may be formed using a material having a refractive index lower or higher than that of the substrate 110.

In addition, a width to height ratio of the first grid pattern 121 according to the embodiment of the present invention may range from 1:0.2 to 1:5. It is preferable that the width (w) of the first grid pattern 121 ranges from 10 nm to 200 nm and the height (h1) of the first grid pattern 121 ranges from 10 nm to 500 nm. In addition, the period of the first grid pattern may range from 100 nm to 250 nm.

The second grid pattern 130 includes fine metallic protrusion patterns arranged at a constant period. Specifically, the second grid pattern 130 is a protrusion structure formed on the top surface of the first grid pattern 121 by a deposition process or the like. The second grid pattern 130 may be formed using any one metal selected from aluminum (Al), chromium (Cr), silver (Ag), copper (Cu), nickel (Ni), and cobalt (Co), or an alloy thereof. The term period means a distance between one metal grid pattern (e.g., the second grid pattern) and an adjacent metal grid pattern (e.g., the second grid pattern).

In addition, the cross section of the second grid pattern 130 may have various shapes, e.g., rectangle, triangle, semicircle, etc, and may have a metal wire shape that is partially formed on a substrate patterned in a triangular, rectangular or sinusoidal shape. That is, the second grid pattern 130 may be formed using any metal wire grids arranged at a constant period in a single direction, without regard to the cross-section structure.

In this case, the period of the second grid pattern 130 may be equal to or less than half the wavelength of light used. Accordingly, the period of the second grid pattern 130 may range from 100 nm to 250 nm, which ensures a balance of a visible light region and maintains white balance. If the period of the second grid pattern 130 exceeds 250 nm, red light, green light, and white light are unbalanced.

Furthermore, the wire grid polarizer according to the embodiment of the present invention can adjust transmittance according to the height and width of the two grids (the first grid pattern and the second grid pattern). If the grid width is widened in the same pitch, the transmittance is reduced and the polarization extinction ratio is increased. Therefore, in order for ensuring the maximum polarization efficiency, polarization characteristic is improved as the pitch is reduced. If the grid patterns are formed at the same inter-grid distance and the same grid width, polarization characteristic is improved as the grid height is increased. If the grid patterns are formed at the same inter-grid distance and with the same grid height, polarization characteristic is improved as the grid width is increased. Therefore, it is preferable that the width of the first grid pattern is adjusted to 0.2-1.5 times the width of the second grid pattern. Furthermore, the width to height ratio of the second grid pattern 130 may range from 1:0.5 to 1:1.5. In particular, the ratio of the width of the first grid pattern to the width of the second grid pattern may range from 1:0.2 to 1:1.5. Specifically, the width of the second grid pattern may range from 2 nm to 300 nm. In this manner, polarization characteristic can be maximized.

In the above-described wire grid polarizer according to the embodiment of the present invention, the structure of the special wire grid polarizer is implemented directly on the bottom glass substrate of the liquid crystal panel constituting the LCD, thereby reducing the production cost of the LCD due to the removal of the existing polarizing film. In addition, since the grid pattern is implemented directly on the bottom substrate of the liquid crystal panel, the total thickness of the LCD is reduced and brightness is enhanced as compared to the existing polarizing film.

Various modifications of the above-described wire grid polarizer formed on the bottom glass substrate according to the present invention will be described below.

(1) Structure of Blackening Layer

A wire grid polarizer according to another embodiment of the present invention will be described below with reference to FIGS. 4A to 4C. The wire grid polarizer includes a second grid pattern 130, which is a metal grid pattern formed on one surface or both surfaces of a bottom glass substrate 110, and a blackening layer E formed at a partial or entire portion of the second grid pattern 130. The blackening layer E remarkably reduces a surface re-reflection ratio of light incident from the exterior, which further improves a contrast ratio and readability. In addition, the wire grid polarizer according to the embodiment of the present invention may further include a polymer layer 120 between the substrate 110 and the second grid pattern 130. The polymer layer 120 is formed using a polymer and functions to increase a bonding strength between the substrate 110 and the metal grid pattern 130, leading to improvement of durability.

As illustrated in FIG. 4C, the blackening layer E according to the embodiment of the present invention can also be applied to the structure of FIG. 3 in which the first grid pattern 121 is formed on the polymer layer and the second grid pattern 130 is formed on the first grid pattern 121.

The blackening layer E may be formed by blackening a partial or entire portion of the second grid pattern 130 using an organic material or an inorganic material. That is, the blackening according to a preferred embodiment of the present invention refers to a formation of a cover layer that covers the surface of the second grid pattern 130 using an organic material or an inorganic material. More preferably, the surface reflectivity of the substrate may be set to be equal to or less than 40% due to the blackening layer E.

Examples of the organic material for the blackening include a chromium oxide or a carbon-containing material, and the inorganic material may be treated by an oxidizing process on copper. That is, in the case of the inorganic material, copper is deposited on the above-described metal grid pattern and is etched so that only copper is formed partially or entirely on the metal grid pattern. Then, a wet or dry metal oxidation (blackening) process is performed for blackening copper. Alternatively, the blackening layer E may be formed by depositing chromium on the metal grid pattern and etching the deposited chromium so that chromium is formed partially or entirely on the metal grid pattern.

(2) Structure of Nano Optical Pattern under Substrate

FIG. 5 illustrates a wire grid polarizer according to another embodiment of the present invention. The wire grid polarizer includes a first grid layer 120 with at least one first grid pattern 121 on a substrate 110, and at least one second grid pattern 130 formed on the first grid pattern 121. In particular, the wire grid polarizer may further include a polymer layer 140 with a plurality of optical patterns 141 formed on the rear surface of the bottom glass substrate 110. The term rear surface indicates a surface opposite to the surface on which the first grid pattern and the second grid pattern are formed. The polymer layer 140 includes the plurality of optical patterns 141 on the opposite surface of the substrate where the metal grid pattern is formed. Thus, the presence of the polymer layer 140 reduces loss of light when light is incident. Therefore, an amount of transmitted light is increased, leading to the stabilization of color coordinates.

In this case, it is preferable that the polymer layer 140 formed on the opposite surface of the substrate where the second grid pattern 130 is formed includes a plurality of nano-sized optical patterns 141. In this case, the polymer layer may use a UV resin or a thermosetting resin, but the present invention is not limited thereto. A polymer resin having high light transmittance may also be used.

As for the optical patterns 141 formed on the surface of the polymer layer 140, protrusion patterns protruding upward from the surface of the polymer layer may be arranged regularly or irregularly. The width of the protrusion pattern may range from 10 nm to 200 nm. The optical patterns which are protrusion patterns may have a variety of 3D shapes. For example, the vertical section of the optical patterns may have various shapes, e.g., rectangle, triangle, semicircle, etc. for a conical type, a cylindrical type, a prism type, and a grating type.

In addition, in case where the polymer layer is formed on the substrate, the optical patterns may be formed by pressurization using a mold in which patterns are formed. Furthermore, it is more preferable that the polymer layer according to the embodiment of the present invention is formed using a material having a refractive index lower than that of the substrate. Therefore, a critical angle of incident light L1 is increased and thus the surface reflection on the plane of incidence is reduced, thereby increasing transmittance. The presence of the nano-scale optical patterns on the plane of incidence increases the light incidence area and thus increases transmittance. Furthermore, the polymer layer 140 also serves as a protective layer for protecting the substrate 110, which increases resistance to scratches on the substrate.

(3) Structure of Protective Layer

In another manner, as illustrated in FIG. 6, a surface treatment layer Y may be formed on the first grid pattern 121 or the second grid pattern 130.

The surface treatment layer Y may be formed on the first grid pattern or the second grid pattern. The structure of the surface treatment layer Y may be formed by surface treatment using any one of an atmospheric plasma treatment, a vacuum plasma treatment, an oxygenated water treatment, a pro-oxidant treatment, an anticorrosive treatment, and a self-assembly monolayer (SAM) coating.

In particular, as illustrated in FIG. 6, in case where the surface treatment layer Y is formed to surround the entire second grid pattern and the close contact region Z of the first grid pattern 121 and the second grid pattern 130, an oxide film or a similar surface treatment film is provided which is capable of increasing durability without deformation on the surface of each grid pattern. Therefore, physical properties that improve the close contact between the first and second grid patterns and the polymer layer can be obtained, without degrading optical characteristics.

(4) Multi-Layer Structure of Light Absorbing Layer

The wire grid polarizer according to the embodiment of the present invention includes a first grid layer 120 with at least one first grid pattern 121 on a substrate 110, a second grid pattern 130 formed using a metal on the first grid pattern 121, and a light absorbing layer Q stacked on the second grid pattern 130 to absorb light incident from the exterior.

The second grid pattern 130 is formed using a metal having high reflectivity and therefore increases light reflection efficiency, making it possible to reuse the light. The light absorbing layer Q functions to absorb light incident from the exterior, leading to brightness enhancement.

The light absorbing layer Q is formed on the second grid pattern 130 and functions to absorb light incident from the exterior, and it may be formed in various shapes.

As illustrated in FIG. 7, the light absorbing layer Q may be formed in a stack structure that includes a first absorptive grid pattern 151 formed on the second grid pattern 130, a third grid pattern 152 formed using a metal on the first absorptive grid pattern 151, and a second absorptive grid pattern 153 formed on the third grid pattern 152. Through such a structure, the light absorbing layer Q can absorb light incident from the exterior. In particular, the first and second

absorptive grid patterns

151 and 153 may be formed using a transparent metal oxide, e.g., SiO₂, MgO₂, CeO₂, ZrO₂, ZnO, indium tin oxide (ITO), etc. To increase light absorption efficiency, the second grid pattern 153 may be formed using a metal. The third grid pattern 152 may be formed using any one metal selected from aluminum (Al), chromium (Cr), silver (Ag), copper (Cu), nickel (Ni), cobalt (Co), and molybdenum (Mo), or an alloy thereof. In this case, the thickness h1 of the first absorptive grid pattern 151 ranges from 50 nm to 300 nm, the thickness of the third grid pattern 152 ranges from 1 nm to 20 nm, and the thickness h2 of the second absorptive grid pattern 153 ranges from 50 nm to 500 nm.

The structure of the light absorbing layer Q may also be modified in various shapes as illustrated in FIGS. 8 to 12.

As illustrated in FIG. 8, the light absorbing layer Q may be modified in such a manner that a second absorptive grid layer 154 is formed on the second grid pattern 130 not in a pattern structure but in a single layer structure. Instead of the second absorptive grid pattern 153 that is individually disposed, the second absorptive grid layer 154 is formed by deposition to entirely cover the third grid pattern 152. The second absorptive grid layer 154 can function to absorb light and also serve as a protective layer for protecting the whole wire grid polarizer.

As illustrated in FIG. 9, a functional film 160 may be further provided on the second absorptive grid pattern 153 of the wire grid polarizer illustrated in FIG. 7. As illustrated in FIG. 10, a functional film 160 may be further provided on the second absorptive grid layer 154 of the wire grid polarizer illustrated in FIG. 8. The functional film 160 is disposed on the light absorbing layer Q to compensate a viewing angle or stabilize special color coordinates. To this end, a compensation film (COP, TAC, PC substrate) may be formed by a lamination process.

Also, the wire grid polarizer may be formed to have structures of FIGS. 11 and 12.

Referring to FIG. 11, the wire grid polarizer may include a first grid layer 120 with at least one first grid pattern 121 on a substrate 110, and a light absorbing layer Q with an absorptive grid pattern on the first grid pattern 121. In addition, the wire grid polarizer may further include a second grid pattern 130 with at least one second grid pattern formed using a metal on the light absorbing layer Q. That is, the structure of the second grid pattern 130 illustrated in FIG. 7 or 8 may be disposed at the uppermost portion of the wire grid polarizer.

The light absorbing layer Q may be formed in a stack structure that includes a first absorptive grid pattern 151 formed on the first grid pattern 121, a third grid pattern 152 formed using a metal on the first absorptive grid pattern 151, and a second absorptive grid pattern 153 formed on the third grid pattern 152. Through such a structure, the light absorbing layer Q can absorb light incident from the exterior. In particular, the first and second

absorptive grid patterns

151 and 153 may be formed using a transparent metal oxide, e.g., SiO₂. To increase light absorption efficiency, the third grid pattern 152 may be formed using a metal.

That is, the third grid pattern 152 may be formed using any one metal selected from aluminum (Al), chromium (Cr), silver (Ag), copper (Cu), nickel (Ni), cobalt (Co), and molybdenum (Mo), or an alloy thereof. In this case, as described above, the thickness of the first absorptive grid pattern 151 ranges from 50 nm to 300 nm, the thickness of the third grid pattern 152 ranges from 1 nm to 20 nm, and the thickness of the second absorptive grid pattern 153 ranges from 50 nm to 500 nm. It is apparent that the same materials and dimensions as those described above with reference to FIG. 2 can also be applied to the other construction, including the adjustment of the dimensions of the first and second grid patterns.

As illustrated in FIG. 12, a protective layer 170 may be further provided in the structure of FIG. 10 to protect the second grid pattern 130 that is a metal pattern. Specifically, the protective layer 170 may be formed using an oxide or a polymer resin on the second grid pattern 130.

While the invention has been shown and described with reference to exemplary embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. Therefore, the scope of the invention is defined not by the detailed description of the invention but by the appended claims, and all differences within the scope will be construed as being included in the present invention.

Claims

A liquid crystal display comprising:

a liquid crystal panel; and

a wire grid polarizer including a plurality of grid patterns formed on one surface of a bottom substrate of the liquid crystal panel or the other surface opposite to the surface of the bottom substrate.
The liquid crystal display of claim 1, wherein the wire grid polarizer further includes a second grid pattern on the first grid pattern formed on the bottom substrate.
The liquid crystal display of claim 2, further comprising a protective layer that covers the second grid pattern.
The liquid crystal display of claim 3, wherein the protective layer is formed to cover the side and top surface of the second grid pattern.
The liquid crystal display of claim 2, wherein the first grid pattern is formed using a polymer having a refractive index equal to that of the substrate.
The liquid crystal display of claim 5, wherein the second grid pattern is formed using any one metal selected from aluminum, chromium, silver, copper, nickel, and cobalt, or an alloy thereof.
The liquid crystal display of claim 5, wherein a width to height ratio of the first grid pattern ranges from 1:0.2 to 1:5.
The liquid crystal display of claim 7, wherein a ratio of the height of the first grid pattern to the height of the second grid pattern ranges from 1:0.2 to 1:1.5.
The liquid crystal display of claim 7, wherein the width of the first grid pattern ranges from 10 nm to 200 nm, and the height of the first grid pattern ranges from 10 nm to 500 nm.
The liquid crystal display of claim 9, wherein the width of the second grid pattern ranges from 2 nm to 300 nm.
The liquid crystal display of claim 1, further comprising a polymer layer with a plurality of optical patterns formed on the opposite surface of the bottom substrate where the first and second grid patterns are formed.
The liquid crystal display of claim 2, further comprising a surface treatment layer on the first grid pattern or the second grid pattern of the wire grid polarizer.
The liquid crystal display of claim 2, further comprising a blackening layer on a partial or entire portion of the first grid pattern of the wire grid polarizer.
The liquid crystal display of claim 13, wherein the blackening layer is blackened with an organic material or an inorganic material, and surface reflectivity of the blackened substrate is equal to or less than 40%.
The liquid crystal display of claim 2, wherein the wire grid polarizer further includes a light absorbing layer stacked on the second grid pattern to absorb light incident from the exterior.
The liquid crystal display of claim 15, wherein the light absorbing layer includes:

a first absorptive grid pattern formed on the second grid pattern;

a third grid pattern formed using a metal on the first absorptive grid pattern; and

a second absorptive grid pattern formed on the third grid pattern.
The liquid crystal display of claim 15, wherein the light absorbing layer includes:

a first absorptive grid pattern formed on the second grid pattern;

a third grid pattern formed using a metal on the first absorptive grid pattern; and

a second absorptive grid layer formed on the third grid pattern.
The liquid crystal display of claim 1, wherein the wire grid polarizer includes:

a first grid layer with at least one first grid pattern on the bottom substrate;

a light absorbing layer with an absorptive grid pattern on the first grid pattern;

at least one second grid pattern formed using a metal on the absorptive grid pattern.