WO2009078515A1

WO2009078515A1 - The color filter layer including rare-earth element in display device and method for manufacturing the same

Info

Publication number: WO2009078515A1
Application number: PCT/KR2008/003222
Authority: WO
Inventors: Sang-Ho Sohn; Jin-Gu Jeong
Original assignee: Kyungpook National University Industry-Academic Cooperation Foundation
Priority date: 2007-12-17
Filing date: 2008-06-10
Publication date: 2009-06-25
Also published as: KR20090064786A

Abstract

A color filter layer formed on a display element used for a flexible display. The color filter layer is an oxide thin film in which at least one rare-earth oxide containing at least one rare-earth element that selectively absorbs visible light and at least one ordinary oxide are mixed and fired. A refractive index of the color filter layer ranges from that of a front substrate to that of each transparent electrode. Thus, the color filter layer has a good filter function in a visible light region, and thus provides high optical transmittance. Further, the color filter layer prevents penetration of external gas or moisture and diffusion of ions.

Description

THE COLOR FILTER LAYER INCLUDING RARE-EARTH ELEMENT IN DISPLAY DEVICE AND METHOD FOR MANUFACTURING THE SAME

Technical Field

[1] The present invention relates to a color filter layer formed on a display element used for a flexible display, and more particularly, to a color filter layer for a display device and a method of manufacturing the same, in which the color filter layer is an oxide thin film in which at least one rare-earth element such as neodymium (Nd) and praseodymium (Pr), which selectively absorbs visible light is mixed and fired with at least one ordinary oxide.

[2]

Background Art

[3] In general, display devices, such as an organic light emitting device (OLED), a liquid crystal display (LCD), etc., which are known as flat panel displays, are somewhat different in structure from each other, but have the following basic structure. Referring to FIG. 1, the display device is designed so that transparent electrodes 30, a metal electrode 50, and a light emitting layer 40 are arranged between a front substrate 10 and a back substrate 60. The transparent electrodes 30 and the light emitting layer 40 are formed by vacuum deposition or thick film printing.

[4] An ion diffusion barrier layer 20 is formed between the front substrate 10 and the back substrate 60 at a thickness of several nanometers. The ion diffusion barrier layer 20 prevents electrical properties of the transparent electrodes 30 from being changed by the diffusion of mobile ions such as alkali ions (Na, K, Cl, etc.) or radicals from the front substrate 10 to the transparent electrodes.

[5] The light emitting layer 40 is fundamentally made up of a red phosphor 41, a green phosphor 42, and a blue phosphor 43. The light emitting layer 40 can represent image or data information in a manner such that, when direct or alternate current is applied to the transparent electrodes 30 and the metal electrode 50 by a driving circuit 70, the red phosphor 41, the green phosphor 42 and the blue phosphor 43 are excited to emit visible light.

[6] This light emission is slightly different from that of the LCD, because the LCD uses three colors of light emitted from a backlight instead of three colors of light emitted from the light emitting layer. Such a driving circuit is formed below the backlight, and is an electronic circuit that applies a pulse signal between two electrodes of the flat panel display device, i.e., the LCD in order to display information. Further, the three colors of light are produced from a phosphor layer of the display device, and then are converted into visible light (red, blue and green colors of light and a mixture thereof) coming out of the display device.

[7] However, a technical level of the phosphor for the current display device does not cover perfect reproduction of the red, blue and green colors of light. Furthermore, the OLED has a very wide spectral width of the light emitted from the red, green and blue phosphors, and thus deteriorates color purity (or color saturation). For this reason, there is a need for drastic improvement of the color purities of the phosphors. Further, since the LCD produces the three colors of light from a backlight by exciting a fluorescent layer, it has a fundamental problem with the color purity.

[8] In this manner, the phosphors for the OLED have a problem with the color purity in itself. Further, in the case of the LCD, the fluorescent substance for the backlight involves the fundamental problem. Thus, a study for improving this problem is started.

[9] In order to improve the color purity to increase display quality, a color filter is proposed. In the case of the conventional flat panel display device using a glass as a substrate, a red color filter, a green color filter and a blue color filter are formed between a front glass substrate and transparent electrodes at a thick thickness by screen printing or electrophoresis, and are followed by firing. Then, a black dielectric is filled between the color filters.

[10] In general, a material for the red color filter includes an iron oxide inorganic pigment, while materials for the green and blue color filters include a cobalt oxide inorganic pigment. In the case of the screen printing, this inorganic pigment is mixed with a low-temperature degradable resin such as ethylcellulose and an organic solvent such as butylcarbitolacetate to thereby obtain a paste, and then the red, green and blue color filters are sequentially formed by three steps of thick film firing.

[11] Since the color filters for the display device formed by this conventional method makes use of the glass as the substrate, they can be fabricated through high- temperature thermal processing called three steps of thick film firing. In contrast, in the case of a flexible display using a polymer film as a matrix, the polymer matrix used for a front substrate or the transparent electrodes are subjected to a change in thermal, electrical properties during the thermal processing. Further, the polymer film and the transparent electrodes cause a chemical reaction, thereby reducing a lifespan of the display device. Thus, a method capable of obtaining the color filter layer on the polymer matrix using the low-temperature (room temperature) processing if possible has been studied.

[12] Meanwhile, many related arts including Korean Patent Application Publication No.

10-2001-0026838 have developed a color filter for a plasma display panel (PDP), which can be fabricated by coating a polymer matrix with resin ink that is obtained by resolving an organic dye instead of an inorganic pigment into a solvent together with a polymer binder. The conventional color filter is fabricated by resolving at least two dyes into a single solvent together with a polymer binder such as gelatin. The color filter layer, in which the resolved dyes are coated into a thick film on a transparent support made of polymer such as polymethylmethacrylate or polycarbonate, is disposed on an outer surface of the display device. The color filters fabricated by the related art can eliminate orange light and near infrared. However, the dyes used for the color filters are vulnerable to heat or external light, and thus deteriorate reliability of the color filters.

[13] Referring to FIG. 1, a next- generation flat panel display such as a plastic LCD or a flexible OLED uses polymer, which is vulnerable to penetration of external oxygen or moisture, as a substrate material, so that a separate gas barrier layer must be installed between the front substrate 10 and the ion diffusion barrier layer 20. The gas barrier layer includes a plurality of layers made of an organic or inorganic compound at a thickness from tens of nanometers to hundreds of nanometers, and thus brightness of the display is degraded. Moreover, this gas barrier layer inevitably increases the cost of fabrication. In addition, when the color filter layer is formed for the displays including a touch screen, the brightness of each display is reduced by at least 40%, which leads to reduction in definition.

[14]

Disclosure of Invention

Technical Problem

[15] The present invention has been made to solve the foregoing problems with the prior art, and therefore the present invention is directed to provide a color filter layer, which is an oxide thin film in which at least one rare-earth oxide containing at least one rare- earth element that selectively absorbs visible light and at least one ordinary oxide are mixed and fired, thereby having a good filter function in a visible light region, serving as an ion diffusion barrier layer as well as a gas barrier layer, and minimizing reduction in brightness, and a method of fabricating the same. Technical Solution

[16] According to an aspect of the present invention, there is provided a color filter layer formed on a display element used for a flexible display, in which the color filter layer is an oxide thin film in which at least one rare-earth oxide containing at least one rare- earth element that selectively absorbs visible light and at least one ordinary oxide are mixed and fired.

[17] Here, the rare-earth oxide may include at least one of neodymium oxide (Nd O ) and praseodymium oxide (Pr O ). [18] Further, the rare-earth oxide may include neodymium oxide (Nd O ) and

2 3 praseodymium oxide (Pr O ) having a ratio of 40 wt% through 60 wt% to 60 wt% through 40 wt%.

[19] Also, the rare-earth oxide may range from 10 wt% to 90 wt%.

[20] Further, the ordinary oxide may include at least one of aluminum oxide (Al O ) or silicon oxide (SiO ). [21] According to another aspect of the present invention, there is provided a method of fabricating a color filter layer formed on a display element used for a flexible display, which includes: mixing at least one rare-earth oxide containing at least one rare-earth element that selectively absorbs visible light with at least one ordinary oxide, firing the mixture, and forming a melt; forming the melt into a thin film on a front substrate; and vacuum-depositing the thin film onto transparent electrodes. [22] Here, the rare-earth oxide may include at least one of neodymium oxide (Nd O ) and praseodymium oxide (Pr O ). [23] Further, the rare-earth oxide may include neodymium oxide (Nd O ) and praseodymium oxide (Pr O ) having a ratio of 40 wt% through 60 wt% to 60 wt% through 40 wt%. [24] Further, the rare-earth oxide may be mixed and fired with the ordinary oxide at an amount from 10 wt% to 90 wt%. [25] Also, the vacuum-depositing of the thin film onto each transparent electrode may be performed by one of e-beam evaporation, sputtering evaporation, and ion plating evaporation. [26] Meanwhile, the ordinary oxide may include at least one of aluminum oxide (Al O ) or silicon oxide (SiO ). Further, the color filter layer may have a refractive index between that of the front substrate and that of each transparent electrode. [27] Further, each transparent electrode may include one of indium tin oxide (In O :Sn) and indium zinc oxide (In O :ZnO), and have a thickness from 100 nm to 300 nm.

Further, the refractive index of the color filter layer may range from 1.7 to 1.9. [28] Further, the forming of the fired melt may include mixing the rare-earth oxide with the ordinary oxide, and firing the mixture within a range from 800⁰C to 1500⁰C. [29] In addition, the front substrate may be made of glass or polymer, and the polymer may include one of polyethersulfone (PES) and polyethylene terephthalate (PET).

Advantageous Effects

[30] As set forth above, according to the present invention, the color filter layer is an oxide thin film in which at least one rare-earth oxide containing at least one rare-earth element that selectively absorbs visible light and at least one ordinary oxide are mixed and fired. The refractive index of the color filter layer ranges from that of the front substrate to that of each transparent electrode. Thus, the color filter layer has a good filter function in a visible light region, and thus provides high optical transmittance to improve definition of the flexible display. Further, the color filter layer prevents penetration of external gas or moisture and diffusion of ions to increase a lifespan of the flexible display.

[31]

Brief Description of the Drawings

[32] FIG. 1 is a cross-sectional view illustrating the typical structure of a conventional flat panel display.

[33] FIG. 2 is a cross-sectional view illustrating the structure of a flat panel display having a color filter layer according to the present invention.

[34] FIG. 3 is a graph showing the optical transmission characteristic of a flat panel display having a color filter layer according to the present invention.

[35] <Major Reference Numerals and Symbols of the Drawings>

[36] 10: front substrate

[37] 11: displayed light

[38] 20: ion diffusion barrier layer

[39] 30: transparent electrode

[40] 40: light emitting layer

[41] 41: red phosphor

[42] 42: green phosphor

[43] 43: blue phosphor

[44] 50: metal electrode

[45] 60: back substrate

[46] 70: driving circuit

[47] 102: color filter layer

[48]

Best Mode for Carrying Out the Invention

[49] The invention will now be described more fully with reference to the accompanying drawings, in which exemplary embodiments thereof are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

[50] Hereinafter, the exemplary embodiments of the invention will be described with reference to the accompanying drawings. Among the drawings, FIG. 1 is a cross- sectional view illustrating the typical structure of a conventional flat panel display. FIG. 2 is a cross-sectional view illustrating the structure of a flat panel display having a color filter layer according to the present invention. FIG. 3 is a graph showing the optical transmission characteristic of a flat panel display having a color filter layer according to the present invention.

[51] The present invention is directed to a color filter layer formed on a display element used for a flexible display. The flexible display refers to a device which can be folded or rolled because it is made of a flexible material, and to which thin film transistor liquid crystal display (TFT LCD) technology, organic electroluminance (EL) technology (or a organic light emitting diode (OLED) technology), electrophoretic technology, laser induced thermal image (LITI) technology, etc. are applied. In order to improve color purity of the flexible display to increase its display quality, a color filter layer is formed between a front substrate and transparent electrodes.

[52] The color filter layer of the present invention includes rare-earth elements that selectively absorb visible light. The rare-earth elements are a collection of 17 chemical elements that include scandium (Sc) yttrium (Y), and fifteen (15) Lanthanides having atomic numbers 57 through 71, all of which belong to Group 3 of the periodic table. The rare-earth elements having the odd atomic numbers have an amount less than that of those having the even atomic numbers. Further, the rare-earth elements generally are silvery- white or gray metals.

[53] The rare-earth elements are gradually oxidized in air. Further, the rare-earth elements are resolved in acid solution or hot water, but not in alkali solution. The metals known as the rare-earth elements have very similar chemical properties, and all usually make trivalent (+3) compounds. Some of them, cerium (Ce), terbium (Tb) and praseodymium (Pr) make tetravalent (+4) compounds, and ytterbium (Yb), europium (Eu) and samarium (Sm) make divalent (+2) compounds. The rare-earth elements are positive next to alkali metals and alkaline earth metals, and hydroxides thereof are basic ones.

[54] Among the rare-earth elements, neodymium (Nd) and praseodymium (Pr) are adopted as components of the present invention. The rare-earth elements of neodymium (Nd) and praseodymium (Pr) selectively transmit three primary colors of light among the visible light. The rare-earth elements of neodymium (Nd) and praseodymium (Pr) are oxidized to yield neodymium oxide (Nd O ) and praseodymium oxide (Pr O ).

[55] The color filter layer is formed by mixing at least one rare-earth oxide containing the rare-earth element with at least one ordinary oxide containing no rare-earth element and then firing the mixture. The neodymium oxide (Nd O ) and the praseodymium oxide (Pr O ), each of which is the rare-earth oxide containing the earth element, are added alone or in mixture. In the case in which the neodymium oxide (Nd O ) and the praseodymium oxide (Pr O ) are added in mixture, they are added at a ratio of 40 wt% through 60 wt% to 60 wt% through 40 wt%. The rare-earth oxides such as neodymium oxide (Nd O ) and praseodymium oxide (Pr O ) containing the rare-earth elements range from 10 wt% to 90 wt%. If the rare-earth oxides are added at an amount of 10 wt% or less, characteristics of the filter are not expected. If the rare-earth oxides are added at an amount of 90 wt% or more, characteristics of the filter are improved, but brightness of the display is reduced. Thus, the rare-earth oxides are preferably added within the above defined range of weight ratio.

[56] The ordinary oxides include aluminum oxide (Al O ) and silicon dioxide (SiO ). The aluminum oxide (Al O ) exists as an oxide film covered on aluminum in the natural world. This aluminum oxide film has high corrosion resistance. The silicon dioxide (SiO ) is silicic acid anhydride, and is generally called silica. The silica refers to silicon dioxide as an ingredient in various silicates existing in nature. Since the silicon dioxide (SiO ) is resistant to high temperature, has very low expansion, and is resistant to rapid thermal change, it is used as heat resistant glass. Further, since the silicon dioxide (SiO ) well transmits ultraviolet, it is used for various optical devices.

[57] Any ordinary oxide can be used as the oxide for the color filter layer. However, from the viewpoint of optical transmittance, it is proper that a refractive index of the color filter layer ranges from that of the front substrate to that of the transparent electrode. Assuming that the refractive indices of two media forming an interface be n and n , the optical transmittance T is expressed by the following Equation 1.

[58] [Equation 1]

[59] ₂

_T= \ . . ^{( 77 l "} " ^{2 )}

O i+ « ₂)

[60] Since a material, which is used for the transparent electrode above a polymer matrix

(having a refractive index from 1.5 to 1.6) such as glass, polyethersulfone (PES), or the like, is indium tin oxide (In O :Sn) or indium zinc oxide (In O :ZnO), the color filter

2 3 2 3 layer formed between them preferably has a refractive index from about 1.7 to about 1.9, and most preferably about 1.8. [61] Thus, any oxide can be used for the color filter layer. However, Al O , which is known with a refractive index of about 1.76 in a visible light range, is most suitable for the color filter layer. Although SiO seems to be unsuitable because the refractive index thereof is about 1.4, the refractive index of SiO is increased up to about 1.7 when Nd 2 O3 or Pr2 O3 is added to SiO 2 Thus, SiO 2 also serves for the purpose. The color filter layer of the present invention, which adjusts the refractive index difference using the optical transmittance formula, can minimize the reduction in brightness. [62] Each transparent electrode is made of indium tin oxide (In O :Sn) or indium zinc oxide (In O :ZnO) at a thickness from 100 nm to 300 nm. If the thickness of the transparent electrode is less than 100 nm, resistance of the transparent electrode is increased. In contrast, if the thickness of the transparent electrode is more than 300 nm, the transmittance of the light generated from the interior of the display is reduced. Thus, the thickness of the transparent electrode preferably falls within the numerical range.

[63] A method of fabricating the color filter layer used for the flexible display includes the step of mixing at least one rare-earth oxide containing at least one rare-earth element that selectively absorbs visible light with at least one ordinary oxide, firing the mixture, and thereby forming a melt, the step of forming the melt into a thin film on a front substrate, and the step of depositing the thin film onto transparent electrodes under vacuum.

[64] As described above, the rare-earth oxide containing at least one rare-earth element is obtained in a manner such that neodymium oxide (Nd O ) or praseodymium oxide (Pr O ) is mixed with the ordinary oxide, or that neodymium oxide (Nd O ) and praseodymium oxide (Pr O ) are mixed with each other, and then are again mixed with the ordinary oxide. In the case in which the mixture of the neodymium oxide (Nd O ) and the praseodymium oxide (Pr O ) is added, they have an added ratio of 40 wt% through 60 wt% to 60 wt% through 40 wt%. The rare-earth oxide(s) is mixed with the ordinary oxide within a range from 10 wt% to 90 wt%, and then the mixture is fired. The ordinary oxide includes aluminum oxide (Al O ) or silicon dioxide (SiO ), which is intended to minimize the reduction in brightness as described above.

[65] The mixed oxide is fired within a range from 800⁰C to 1500⁰C. If the firing temperature is less than 800⁰C, the mixed oxide is not melted well, and thus the rare- earth oxide containing the rare-earth element is not physically and chemically mixed with the ordinary oxide. In contrast, if the firing temperature is more than 1500⁰C, the process undergoes low efficiency. Thus, the firing temperature preferably falls within this range.

[66] The vacuum deposition is performed by one selected from e-beam evaporation, sputtering evaporation and ion plating evaporation, by which the transparent electrodes are vacuum-deposited with the oxide thin film. This method belongs to vapor dep osition, particularly physical vapor deposition (PVD) requiring vacuum environment. The deposition called PVD includes sputtering evaporation, e-beam evaporation, thermal evaporation, laser molecular beam epitaxy (LMBE), pulsed laser deposition (PLD), and so on. The deposition called PVD is based on a physical change in which a gaseous state is converted into a solid state when matters to be deposited are deposited onto a substrate. Among the PVDs, one is performed by previously sintering or melting a compound to yield a solid target, and evaporating the solid target using heat or electron beams, and depositing the evaporated target onto a substrate.

[67] Further, another slightly complicated deposition is performed by putting raw materials into respective (effusion) cells, evaporating the raw materials into gases using heat, laser beams or electron beams when doors of the cells are open and closed, and converting the evaporated raw materials into a solid state when the evaporated raw materials come into contact with a substrate. The PVDs are used to obtain a high- quality thin film or nano-structure, and thus can obtain a high-quality deposited surface.

[68] The e-beam evaporation is adapted to rapidly evaporate oxide melted through electron beams and to deposit the evaporated oxide onto a substrate. The sputtering evaporation is adapted to fabricate a thin film by bombarding the surface of a solid material with high-energy particles and ejecting atoms or molecules from the solid material surface. The ion plating evaporation is adapted to inject gas such as argon into a vacuum chamber, cause plasma under high vacuum of about 10 torr to ionize the gas together with a material to be deposited, and deposit the ionized particles onto a target to be deposited.

[69] The front substrate is made of glass or polymer. The polymer may include polyethersulfone (PES) or polyethylene terephthalate (PET). Polymer resins, which are presently used for a display substrate, include polyethylene terephthalate (PET), polycarbonate (PC), polyethersulfone (PES), etc., all of which have high transparency and are used together with a solvent resistant layer and a gas barrier layer coated through secondary processing.

[70] The polyethersulfone (PES) is an amorphous aromatic thermoplastic resin, has high heat resistance, high thermal oxidation stability, and high mechanical strength, all of which are shown at a glass transition temperature from 18O⁰C to 25O⁰C depending on a chemical structure, and transparency and a low coefficient of thermal expansion (CTE: 60 ppm/°C). Due to these characteristics, the PES is variously used as a material for cards, mobile phones, LCD substrates for electronic pocket notebooks.

[71] The polyethylene terephthalate (PET) is saturated polyester that can be obtained by polycondensation of terephthalic acid and ethylene glycol. The PET has good rigidity, electrical properties, weather resistance, and heat resistance, and undergoes very low r eduction in tensile strength despite long-term exposure under high temperature. Due to these characteristics, the PET is variously used similar to the PES.

[72] Hereinafter, among the exemplary embodiments of the present invention, a first embodiment will be described with reference to the accompanying drawings, and then a second embodiment will be described regarding characteristics of a color filter layer fabricated according to the first embodiment. However, the following embodiments are merely described for the illustrative purposes, but not intended to limit the scope of the present invention.

[73]

[74] First Embodiment

[75] A method of fabricating a color filter layer used for a flexible display of the present invention includes the step of mixing at least one rare-earth oxide containing at least one rare-earth element that selectively absorbs visible light with at least one ordinary oxide, firing the mixture, and thereby forming a melt, the step of forming the melt into a thin film on a front substrate, and the step of depositing the thin film onto transparent electrodes under vacuum.

[76] Referring to FIG. 2, there are various rare-earth elements, which can be added in an oxide form in order to selectively transmit light within a visible light range. Neodymium (Nd) and praseodymium (Pr), each of which transmit three primary colors (red, green and blue) of light, can be added to oxide such as SiO , Al O , etc. alone or in mixture. Neodymium oxide (Nd O ) and praseodymium oxide (Pr O ) used for the present invention showed similar effects when they were formed into a thin film together with oxide other than silicon dioxide (SiO ) or aluminum oxide (Al O ) used for the present invention, because the light absorption of the rare-earth elements, namely, the neodymium (Nd) and the praseodymium (Pr) took place by transition of inner shell electrons, which are electrostatically shielded and are hardly changed with respect to any oxide.

[77] The ordinary oxide makes use of aluminum oxide (Al O ) or silicon dioxide (SiO ).

As described above, the ordinary oxide is not limited to this oxide, but a refractive index of the color filter layer must range from that of the front substrate 10 and that of each transparent electrode 30. In the case in which each transparent electrode 30 uses indium tin oxide (In O :Sn) or indium zinc oxide (In O :ZnO), the refractive index of

2 3 2 3 the color filter layer must range from about 1.7 to about 1.9, and most preferably about 1.8. The refractive index of the color filter layer can be varied depending on a kind of the transparent electrode 30, but it is not limited to the transparent electrode 30. Depending on the selected transparent electrode 30, the ordinary oxide for the color filter layer can be selected. [78] The materials of Nd 2 O 3 and Pr 2 O 3 were added to the oxides of SiO 2 and Al 2 O 3 within a range from 10 wt% to 90 wt%, and then were fired in an electric furnace at a temperature from 800⁰C to 1500⁰C. The fired materials, namely, SiO -Nd O -Pr O and Al 2 O 3 -Nd 2 O 3 -Pr 2 O 3 were formed into materials for deposition, and the materials for deposition were evaporated onto soda lime glass or PES polymer at a thickness from 1 to 50 at room temperature using sputtering. Thereby, the color filter layer 102 was formed. [79] The materials, namely, SiO -Nd O -Pr O and Al O -Nd O -Pr O were evaporated in

2 2 3 2 3 2 3 2 3 2 3 vacuum using well-known vacuum deposition equipment such as e-beam equipment or sputtering equipment. These oxide materials were bombarded with electrons or ions, and thus are evaporated in an atomic or molecular state. Thereby, the color filter layer was formed on the front substrate 10.

[80] Further, referring to FIG. 2, the color filter layer 102 can be formed on an outer surface of the front substrate 10. Even in this case, the color filter layer shows a similar function when formed on an inner surface of the front substrate. Each transparent electrode 30 is formed of oxide such as indium tin oxide (In O :Sn) or indium zinc

2 3 oxide (In O :ZnO) at a thickness from 100 to 300 nm using typical low-temperature (room temperature) vacuum deposition such as sputtering deposition or e-beam deposition.

[81] [82] Second Embodiment [83] In the first embodiment of the exemplary embodiments, the color filter layer for the display which is formed into the thin film on the PES film matrix improved an optical transmission characteristic in a visible light range.

[84] Referring to FIG. 3, it can be found that the color filter layer for the display has good optical transmission characteristics of red (600 nm or more), green (500 nm to 550 nm), and blue (470 nm or less) in a visible light range. In other words, one color filter layer 102 serves to selectively transmit only three primary colors of light.

[85] Table 1 shows results of measuring color coordinates of an OLED, and Table 2 shows results of measuring color coordinates of an LCD. Referring to Tables 1 and 2, all of the red (R), the green (G) and the blue (B) are remarkably improved in the OLED and LCD employing the color filter layer of the present invention.

[86] [87] Table 1 [Table 1] [Table ]

[88] [89] Table 2 [Table 2] [Table ]

[90] Further, gas barrier degrees (moisture permeability and oxygen permeability) of the color filter layer for the display according to the exemplary embodiment of the present invention shown 1x10 g/m /day, 1x10 cm /m /day, which were measured using two types of equipment available from the MOCON company (PERMATRAN-W MODEL 2/21 and OX-TRAN MODEL 3/33). These gas barrier degrees result from a dense thin film of oxide having a thickness of tens of nanometers. As a result, it was found that the color filter layer of the present invention remarkably improved the gas barrier function. These numerical values can be applied to the LCD as well as the OLED using the polymer substrate.

[91] The color filter layer 102 of the present invention is the oxide thin film similar to the ion diffusion barrier layer 20 of a conventional substrate, and thus can have the same function as the ion diffusion barrier layer 20. Furthermore, the color filter layer has a thickness from 1 to 50, which is thicker than the ion diffusion barrier layer 20 having a thickness of hundreds of nanometers, and thus shows a better diffusion barrier effect.

[92] Meanwhile, the color filter layer for a display of the present invention is formed into the thin film using at least one rare-earth oxide containing at least one rare-earth element, thereby improving reduction of the color purity, which is the problem of a conventional flexible display. Further, the color filter layer prevents a change in the thermal, electrical properties of the transparent electrodes, which are generated when the polymer film is used, using the oxide. Furthermore, the color filter layer of the present invention does not cause chemical reaction with the transparent electrodes, thereby improving reduction of a lifespan of the display.

[93] The color filter layer of the present invention has a single layer, thereby preventing the costs of fabrication from being increased. Further, the color filter layer of the present invention minimizes the reduction in brightness, thereby improving to the maximum extent the transmission characteristic of light, which is the most important function in the display. In addition, the color filter layer serves to prevent the ions from being diffused. As described above, the present invention is a useful invention having various functions in the flexible display, and is considered to be an essential invention in the telecommunication society that has been gradually developed.

Claims

[I] A color filter layer formed on a display element used for a flexible display, characterized in that the color filter layer is an oxide thin film in which at least one rare-earth oxide containing at least one rare-earth element that selectively absorbs visible light and at least one ordinary oxide are mixed and fired.

[2] The color filter layer as set forth in claim 1, wherein the rare-earth oxide includes at least one of neodymium oxide (Nd O ) and praseodymium oxide (Pr O ). [3] The color filter layer as set forth in claim 2, wherein the rare-earth oxide includes neodymium oxide (Nd O ) and praseodymium oxide (Pr O ) having a ratio of 40 wt% through 60 wt% to 60 wt% through 40 wt%. [4] The color filter layer as set forth in claim 1, wherein the rare-earth oxide ranges from 10 wt% to 90 wt%. [5] The color filter layer as set forth in claim 1, wherein the ordinary oxide includes at least one of aluminum oxide (Al O ) or silicon oxide (SiO ). [6] A method of fabricating a color filter layer formed on a display element used for a flexible display, comprising: mixing at least one rare-earth oxide containing at least one rare-earth element that selectively absorbs visible light with at least one ordinary oxide, firing the mixture, and forming a melt; forming the melt into a thin film on a front substrate; and vacuum-depositing the thin film onto transparent electrodes. [7] The method as set forth in claim 6, wherein the rare-earth oxide includes at least one of neodymium oxide (Nd O ) and praseodymium oxide (Pr O ). [8] The method as set forth in claim 6, wherein the rare-earth oxide includes neodymium oxide (Nd O ) and praseodymium oxide (Pr O ) having a ratio of 40 wt% through 60 wt% to 60 wt% through 40 wt%. [9] The method as set forth in claim 6, wherein the rare-earth oxide ranges from 10 wt% to 90 wt%. [10] The method as set forth in claim 6, wherein the ordinary oxide includes at least one of aluminum oxide (Al O ) or silicon oxide (SiO ).

[I I] The method as set forth in claim 6, wherein the color filter layer has a refractive index from a refractive index of the front substrate and a refractive index of each transparent electrode.

[12] The method as set forth in claim 6, wherein each transparent electrode includes one of indium tin oxide (In O :Sn) and indium zinc oxide (In O :ZnO), and has a

2 3 2 3 thickness from 100 nm to 300 nm. [13] The method as set forth in claim 11, wherein the refractive index of the color filter layer ranges from 1.7 to 1.9. [14] The method as set forth in claim 6, wherein the forming of the fired melt includes mixing the rare-earth oxide with the ordinary oxide, and firing the mixture within a range from 800⁰C to 1500⁰C. [15] The method as set forth in claim 6, wherein the vacuum-depositing is performed by one of e-beam evaporation, sputtering evaporation, and ion plating evaporation. [16] The method as set forth in claim 6, wherein the front substrate is made of glass or polymer, and the polymer includes one of polyethersulfone (PES) and polyethylene terephthalate (PET).