Patent Publication Number: US-2016223869-A1

Title: Liquid crystal display and manufacturing method thereof

Description:
CLAIM OF PRIORITY 
     This application claims priority to and the benefit accruing under 35 U.S.C. §119 from Korean Patent Application No. 10-2015-00′1.4347 filed in the Korean Intellectual Property Office on Jan. 29, 2015, the entire contents of which are incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a liquid crystal display including quantum dots and a manufacturing method thereof the display having an improved backlight with improved white color purity while having a slimmer design by eliminating the need for two separate. substrates. 
     2. Description of the Related Art 
     A liquid crystal display (LCD) is a non-emissive display that is incapable of emitting light by itself and thus incident light from the outside is required to display an image. Accordingly, a backlight unit (BLU) for emitting light is positioned at a rear side of an LCD. 
     Recently, a BLU using three color light emitting diodes (LEDs) has been developed, and the BLU using these three color LEDs as a light source can implement high color purity, thereby being applicable to high quality display devices. Particularly, a white LED is being developed in which light emitting out of a single color LED chip is convened into white light. 
     However, while the white LED is economically feasible, it has a problem that color purity and color reproducibility are low, and thus efforts for using a semiconductor nanocrystal as the BLU have recently been made to improve the color reproducibility and the color purity and to ensure price competitiveness. 
     In addition, two sheets of display panels of which the LCD consists may include a thin film transistor array panel and an opposing display panel. That is, in the conventional LCD, two substrates are indispensably used and constituent elements are separately formed on the two substrates, thereby requiring a long processing time while causing the display to be heavy, thick, and costly. 
     The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention, and therefore it may contain information that does not constitute prior an as per 35 U.S.C. 102, taken either prior to or after the AIA. 
     SUMMARY OF THE INVENTION 
     The present invention has been made in an effort to provide a liquid crystal display and a manufacturing method thereof that may reduce weight, thickness, cost, and processing time by using only one substrate while including quantum dots within a capping layer. 
     According to one aspect of the present invention, there is provided a liquid crystal display device, including a substrate, a pixel electrode arranged on the substrate, a liquid crystal layer arranged in a microcavity on the pixel electrode, a roof layer supporting the microcavity and a capping layer arranged on the roof layer and having a thickness in the range of 50 to 100 microns, wherein the capping layer includes a color conversion portion that includes a plurality of quantum dots distributed within a polymer layer. 
     The quantum dots may include a plurality of red quantum dots and a plurality of green quantum dots. The polymer layer may include a plastic resin that transmits light. The capping layer may also include a barrier portion arranged on at least one surface of the color conversion portion. The barrier portion may include at least one of polyethylene terephthalate (PET) film, a polycarbonate (PC) film, and a co-polyethylene terephthalate (CoPET) film. Each of the quantum dots and the barrier portion include at least one of silica, alumina, titania, zirconia, and a combination thereof. The liquid crystal display device may also include a first alignment layer arranged on the pixel electrode, a second alignment layer facing the first alignment layer with the microcavity therebetween and a common electrode arranged on the second alignment layer. The display device may also include a planar LED light source that emits either blue visible light or ultraviolet light, the light source may he arranged on an opposite side of the capping layer than the liquid crystal layer. 
     According to another aspect of the present invention, there is included a liquid crystal display, including a substrate, a pixel electrode arranged on the substrate, a liquid crystal layer arranged on the pixel electrode, a common electrode arranged on the liquid crystal layer and forming a microcavity with the pixel electrode, a roof layer supporting the microcavity, a first capping layer arranged on the roof layer, a polarizer arranged on the first capping layer and a second capping layer and a third capping layer sequentially arranged on the polarizer, wherein the second capping layer having a thickness within a range of 50 to 100 microns and includes a plurality of quantum dots dispersed within a polymer layer. 
     The quantum dots may include a plurality of red quantum dots and a plurality of green quantum dots. The first capping layer and the third capping layer may include a polymer layer that is absent of any quantum dots. The polymer layer of each of the first, second and third capping layers may include a plastic resin that transmits light. The quantum dots may include at least one of silica, alumina, titania, zirconia, and a combination thereof. The display device may also include a first alignment layer arranged on the pixel electrode, a second alignment layer facing the first alignment layer with the microcavity therebetween and a common electrode arranged on the second alignment layer. The third capping layer may include a reflecting film. The reflecting film may transmit blue light while reflecting both green light and red light. The reflecting film may include at least one layer including silicon oxide and at least one layer including titanium oxide. The display device may also include a reflecting film arranged on the third capping layer. The reflecting film may transmit blue light while reflecting both green light and red light. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more complete appreciation of the invention, and many of the attendant advantages thereof, will be readily apparent as the same becomes better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings, in which like reference symbols indicate the same or similar components, wherein: 
         FIG. 1  is a cross-sectional view of a liquid crystal display according to a first exemplary embodiment of the present invention; 
         FIG. 2  is an enlarged cross-sectional view of a capping layer shown in  FIG. 1 ; 
         FIG. 3  a cross-sectional view of a liquid crystal display according to a second exemplary embodiment of the present invention; 
         FIG. 4  is a cross-sectional view of a liquid crystal display according to a third exemplary embodiment of the present invention; and 
         FIG. 5  is a cross-sectional view of a liquid crystal display according to a fourth exemplary embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention will be described more fully hereinafter with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention. 
     In the drawings, the thickness of layers, films, panels, regions, etc., are exaggerated for clarity. Like reference numerals designate like elements throughout the specification. It will be understood that when an element such as a layer, film, region, or substrate is referred to as being “on” another element, it can be directly on the other element or intervening elements may also be present. In contrast, when an element is referred to as being “directly on” another element, there are no intervening elements present. 
     A liquid crystal display according to a first exemplary embodiment of the present invention will be now described in detail with reference to  FIG. 1 . Turning now to  FIG. 1 ,  FIG. 1  is a cross-sectional view of a liquid crystal display according to a first exemplary embodiment of the present invention. Referring now to FIG,  1 , a liquid crystal panel  1000  includes a substrate  110 , a plurality of gate lines (not shown), a gate insulation layer  140 , a plurality of semiconductors  154 , a plurality of data lines  171 , and a passivation layer  180 . 
     A plurality of light blocking members  220  and a first insulating layer  240  are disposed on the passivation layer  180 . The light blocking members  220  respectively overlap the data lines  171 . The first insulating layer  240  covers the light blocking member  220  while producing a flat upper surface. 
     A pixel electrodes  191  are formed on the first insulating layer  240 , a first alignment layer  11  is formed on the pixel electrodes  191 , a second alignment layer  21  is arranged to face the first alignment layer  11 , and a microcavity  305  is formed between the first alignment layer  11  and the second alignment layer  21 . 
     A liquid crystal material including liquid crystal molecules is injected into the microcavity  305 , and a liquid crystal injection hole (not shown) for injecting the liquid crystal material is formed in the microcavity  305 . The liquid crystal injection hole (not shown) may be arranged at a lateral surface of the microcavity  305 . 
     A common electrode  270  is disposed on the second alignment layer  21 . The common electrode  270  is applied with the common voltage to generate an electric field along with the pixel electrodes  191  to which the data voltage is applied, thereby determining tilt directions of the liquid crystal molecules  310  disposed within the microcavity  305  between the two electrodes. The common electrode  270  forms a capacitor along with the pixel electrodes  191  to maintain an applied voltage even after the thin film transistor is turned off. 
     In the first exemplary embodiment, the common electrode  270  has been described to be arranged on the microcavity  305 , but in another exemplary embodiment, the common electrode  270  may be arranged under the microcavity  305 , thereby allowing liquid crystals to be driven according to a coplanar electrode (CE) mode. 
     A roof layer  360  is arranged on the common electrode  270 . The roof layer  360  serves as a structure for supporting the microcavity  305  such that the microcavity  305  arranged between the pixel electrode  191  and the common electrode  270  can maintain its shape. The roof layer  360  may he made out of a photoresist or an organic material. 
     A second insulating layer  370  made of silicon nitride (SiNx) or silicon oxide (SiOx) is arranged on the roof layer  360 , and a capping layer  390  is arranged on the second insulating layer  370 . The capping layer  390  covers a liquid crystal injection hole of the exposed microcavity  305  while filling a portion where the liquid crystal injection hole (not shown) is arranged. The capping layer  390  according to the first exemplary embodiment may be filled with a base material which may be an organic material or an inorganic material, and may further include a plurality of quantum dots  13  and  15  dispersed within the base material. The quantum dots  13  and  15  include red quantum dots  13  and green quantum dots  15 , and may be distributed within in the capping layer  390 . Herein, the capping layer  390  including the quantum dots  13  and  15  may be formed to have a thickness of about 50-100 μm. 
     A light source  700  emitting light, from an upper portion of the liquid crystal panel  1000  to a lower portion thereof may be arranged within the liquid crystal display. The light source  700  may include a light emitting diode (LED). The light emitting diode (LED) may be a blue color LED or an ultraviolet LED. Further, the light emitting diode (LED) may be a diode for emitting light of a blue wavelength, but it is not limited thereto. 
     As described above, the reason why the light source  700  for emitting light of a specific wavelength may be used is that the quantum dots  13  and  15  arranged within the capping layer  390  may amplify or generate light of different wavelengths that can also be supplied to the liquid crystal panel  1000 . That is, while being positioned to be spaced apart by a predetermined distance from the light source  700 , the capping layer  390  that includes the quantum dots  13  and  15  functions as a light converting layer that converts the light emitted from the light source  700  into the white light and allows the produced white light to emit towards the liquid crystal panel  1000 . 
     When the light emitted from the light source  700  passes through the capping layer  390  containing the quantum dots  13  and  15 , the white light in which blue, green, and red light are mixed can be produced. In this case, when compositions and sizes of the quantum dots  13  and  15  arranged within the capping layer  390  are varied such that desired ratios of the blue, green, red light can be controlled, white light with excellent color reproducibility and purity may be produced. 
     The capping layer  390  containing quantum dots  13  and  15  according to the first exemplary embodiment of the present invention will be now described more fully with reference to  FIG. 2 . Turning now to  FIG. 2 ,  FIG. 2  is an enlarged cross-sectional view of a capping layer shown in  FIG. 1 . Referring to  FIG. 2 , the capping layer  390  includes a color conversion portion  12  including a polymer layer  19  in which red quantum dots  13  and green quantum dots  15  are distributed. The polymer layer  19  is made out of a plastic resin. The plastic resin may include various materials that form a polymer or film, and kinds of the materials are not particularly limited. In the exemplary embodiment of the present invention, the plastic resin transmits light, even if it is hardened, and light transmittance is not limited thereto. 
     The quantum dots  13  and  15  are distributed in the polymer layer  19  of the color conversion portion  12  to implement color reproducibility and color purity. The quantum dots  13  and  15  may be selected from a group II-VI compound, a group IV-VI compound, a group IV element, a group IV compound, and a combination thereof. 
     The group II-VI compound may be selected from: a group of two-element compounds selected from CdSe, CdTe, ZnS, ZnSe, ZnTe, ZnO, HgS, HgSe, HgTe, MgSe, MgS, and a mixture thereof; a group of three-element compounds selected from CdSeS, CdSeTe, CdSTe, ZnSeS, ZnSeTe, ZnSTe, HgSeS, HgSeTe, HgSTe, CdZnS, CdZnSe, CdZnTe, CdHgS, CdHgSe, CdHgTe, HgZnS, HgZnSe, HgZnTe, MgZnSe, MgZnS, and a mixture thereof; and a group of four-element compounds selected from HgZnTeS, CdZnSeS, CdZnSeTe, CdZnSTe, CdHgSeS, CdHgSeTe, CdHgSTe, HgZnSeS, HgnSeTe, HgZnSTe, and a mixture thereof. A group III-V compound may be selected from: a group of two-element compounds selected from GaN, GaP, GaAs, GaSb, AlN, AlP, AlAs, AlSb, InN, InP, InAs, InSb, and a mixture thereof; a group of three-element compounds selected from GaNP, GaNAs, GaNSb, GaPAs, GaPSb, AlNP, AlNAs, AlNSb, AlPAs, AlPSb, InNP, InNAs, InNSb, InPAs, InPSb, GaAlNP, and a mixture thereof; and a group of four-element compounds selected from GaAlNAs, GaAlNSb, GaAlPAs, GaAlPSb, GalnNP, GalnNAs, GalnNSb, GalnPAs, GalnPSb, InAlNP, InAlNAs, InAlNSb, InAlPAs, InAlPSb, and a mixture thereof. The group IV-VI compound may be selected from: a group of two-element compounds selected from SnS, SnSe, SnTe, PbS, PbSe, PbTe, and a mixture thereof; a group of three-element compounds selected from SnSeS, SnSeTe, SnSTe, PbSeS, PbSeTe, PbSTe, SnPbS, SnPbSe, SnPbTe, and a mixture thereof and a group of four-element compounds selected from SnPbSSe, SnPbSeTe, SnPbSTe, and a mixture thereof. The group IV element may be selected from a group of Si, Ge, and a mixture thereof. The group IV compound may be a two-element compound selected from a group of SiC, SiGe, and a mixture thereof. 
     In this case, the binary compound, the tertiary compound, or the quaternary compound may be present in particles in uniform concentrations, or may have partially different concentrations in the same particle, respectively. In addition, a core/shell structure in which some quantum dots  13  and  15  enclose some other quantum dots  13  and  15  may be possible. An interfacing surface between the core and the shell may have a concentration gradient in which a concentration of an element decreases closer to its center. 
     The quantum dots  13  and  15  may have a full width at half maximum (FWHM) of a light-emitting wavelength spectrum of about 45 nm or less, preferably about 40 nm or less, and more preferably about 30 nm or less. In the quantum dots  13  and  15  having the FWHM, the color purity or color reproducibility may be improved. 
     In addition, shapes of the quantum dots  13  and  15  are not specifically limited to shapes that are generally used in the related art, but specifically, it is desirable that a nanoparticle having a spherical, pyramidal, multi-arm, or cubic shape, and a nanotube, a nanowire, a nanofiber, and a planar nanoparticle are used. 
     In  FIG. 2 , the color conversion portion  12  is illustrated to include a mixture of the red quantum dots  13  and the green quantum dots  15  in a same layer, but instead may consist of a first layer including the red quantum dots  13  and a second layer including the green quantum dots  15 . 
     The color conversion portion  12  may further include an inorganic oxide, and the inorganic oxide may be selected from silica, alumina, titania, zirconia, and a combination thereof. The inorganic oxide may act as a light-diffusing material. 
     The capping layer  390  containing the quantum dots  13  and  15  may further include barrier portions  17   a  and  17   b  arranged on opposite surfaces of the color conversion portion  12 . However, the barrier portions  17   a  and  17   b  may instead be arranged on just one surface thereof. 
     The barrier portions  17   a  and  17   b  may be made out of at least one of a polyethylene terephthalate (PET) film, a polycarbonate (PC) film, and a co-polyethylene terephthalate (CoPET) film. The barrier portions  17   a  and  17   b  may further include an inorganic oxide. The inorganic oxide may be selected from silica, alumina, titania, zirconia, and a combination thereof. 
     In addition, the barrier portions  17   a  and  17   b  may have protrusions and depressions on a surface that does not contact the color conversion portion  12 . These protrusions and depressions may serve to diffuse light that is emitted from an LED light source. 
     The barrier portions  17   a  and  17   b  may have oxygen permeability of about 0.01 cm 3 .mm 2 .day.atm to about 0.5 cm 3 .mm/m 2 .day.atm, and moisture permeability of about 0.001 g/mm 2 .day to 0.01 g/m 2 .day. When within these ranges for the oxygen permeability and for moisture permeability, the quantum dots  13  and  15  may be stably protected from an external environment. 
     Although not illustrated in  FIG. 2 , adhesive layers may be further included between the color conversion portion  12  and the barrier portions  17   a  and  17   b.  When the barrier portions  17   a  and  17   b  serve as a base material, no adhesive layer is required. 
     In addition, protective films (not shown) may be further included on an external surface of the capping layer  390 , that is, on respective surfaces of the barrier portions  17   a  and  17   b  that do not contact the color conversion portion  12 . The protective film, as a release film, may be made of a polyester such as polyethylene terephthalate. 
     Next, a liquid crystal display according to a second exemplary embodiment of the present invention will be described in detail with reference to  FIG. 3 . Turning now to  FIG. 3 ,  FIG. 3  a cross-sectional view of the liquid crystal display according to the second exemplary embodiment of the present invention. 
     The liquid crystal display according to the second exemplary embodiment shown in  FIG. 3  is substantially the same as the first exemplary embodiment shown in  FIG. 1  except that the display of the second embodiment includes a polarizer  22  and a plurality of capping layers, and thus a repeated description will be omitted. 
     As shown in  FIG. 3 , a liquid crystal display according to the second exemplary embodiment of the present invention includes a first capping layer  390   a  arranged on a roof layer  360 , a polarizer  22  arranged on the first capping layer  390   a,  and a second capping layer  390   b  and a third capping layer  390   c  sequentially arranged on the polarizer  22 . The second capping layer  390   b  includes quantum dots  13  and  15 , and the first capping layer  390   a  and the third capping layer  390   c  do not include the quantum dots  13  and  15 . 
     Since the first capping layer  390   a  and the third capping layer  390   c  of the second exemplary embodiment may be substituted for the barrier portions  17   a  and  17   b  shown in  FIG. 2 , barrier portions of the second capping layer  390   b  containing the quantum dots  13  and  15  may be removed. 
     The polarizer  22  may be a coated-type polarizer or a wire grid polarizer, but it is not limited thereto. In addition, another polarizer may be further disposed below a substrate  110 . 
     Liquid crystal displays according to the third and fourth exemplary embodiments will now be described with reference to  FIGS. 4 and 5  respectively. Turning now to  FIGS. 4 and 5 ,  FIGS. 4 and 5  are cross-sectional views of the liquid crystal displays according to the third and fourth exemplary embodiments of the present invention, respectively. 
     The liquid crystal display of the third exemplary embodiment shown in  FIG. 4  is substantially the same as the second exemplary embodiment shown in  FIG. 3 , except for a reflection film  400  being substituted for the third capping layer  390   c,  and thus a repeated description will be omitted. 
     As shown in  FIG. 4 , the liquid crystal display of the third exemplary embodiment includes the reflection film  400  formed on a top surface of the second capping layer  390   b.  The reflection film  400  forwardly reflects light emitted from lateral and rear sides of the second capping layer  390   b  containing quantum dots  13  and  15  to prevent loss of light emitted from the lateral and rear sides of the second capping layer  390   b.    
     The reflection film  400  is a dielectric multilayer of a silicon oxide and a titanium oxide, allowing light, of the blue wavelength range to be transmitted while allowing light of the green and red wavelength ranges to be reflected. The reflection film  400  may be formed to have a thickness of less than 1.5 μm, and preferably has a thickness of 0.1 μm to 1.5 μm. 
     The reflection film  400  reflects the red and green light of the red and green fluorescent dots, which are redirected from the surfaces other than the front surface, such that they travel towards the front surface and towards the liquid crystal panel  1000 , thereby improving the light efficiency. Simultaneously, since the blue light emitted by the light source  700  emitting the blue light is not reflected by the reflection film  400  but is transmitted through the front surface, the overall efficiency of the light emitted toward the front surface from the second capping layer  390   b  containing quantum dots  13  and  15  may be improved. 
     Next, referring to  FIG. 5 , a liquid crystal display according to the fourth exemplary embodiment shown in  FIG. 5  is substantially the same as the second exemplary embodiment shown in  FIG. 3 , except for a reflection film  400  being formed on a capping layer  390   c,  and thus a repeated description will be omitted. 
     As shown in  FIG. 5 , the liquid crystal display of the fourth exemplary embodiment includes the reflection film  400  formed on a top surface of the third capping layer  390   c.  The reflection film  400  forwardly reflects light emitted from lateral and rear sides of the second capping layer  390   b  containing quantum dots  13  and  15  to prevent loss of light emitted from the lateral and rear sides of the second capping layer  390   b.    
     The reflection film  400  is the same as that described with reference to  FIG. 4 , and thus a repeated description will be omitted. 
     As described above, according to the exemplary embodiment of the present invention, it is possible to reduce weight, thickness, cost, and processing time thereof by using one substrate and integrally including quantum dots in a capping layer. As a result, a second substrate may be omitted, thereby reducing the thickness, weight and complexity of the display. 
     Unlike earlier attempts to use quantum dots Q in an LCD display device as in  FIG. 3  of KR 2013-0123718 to Kim et al, the present invention includes an LCD display device that has a macro-cavity structure that is different from conventional LCD display devices. In conventional LCD display devices, there is only one cell for the entire filled liquid crystal layer. However, an LCD display device having a micro-cavity structure includes a plurality of separated micro-cavities that correspond to the pixels. An example of a micro-cavity LCD display device can be found in US 2015/0015825 to Chae et al. 
     A conventional LCD that uses quantum dots includes a separate quantum dot sheet with display panels and the backlight unit. However, in the present invention where there are a plurality of micro-cavities that correspond to the pixels, the display can include quantum dots in the capping layer, instead of including a separate quantum dot sheet. By including the quantum dots in the capping layer as opposed to having to include a separate quantum dot sheet, the design for the LCD display device is simplified as a separate quantum dot sheets are not required. 
     While this invention has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims. 
     DESCRIPTION OF SYMBOLS 
       110 : substrate 
       140 : gate insulating layer 
       154 : semiconductor 
       171 : data line 
       180 : passivation layer 
       220 : light blocking member 
       240 : first insulating layer 
       191 : pixel electrode 
       11 ,  21 : first, second alignment layer 
       270 : common electrode 
       305 : microcavity 
       360 : root layer 
       370 : second insulating layer 
       390 : capping layer 
       22 : polarizer 
       12 : color conversion portion 
       13 ,  15 : quantum dots 
       19 : polymer layer 
       17   a,    17   b : barrier portion 
       700 : light, source 
       1000 : liquid crystal panel 
       400 : reflection film