Abstract:
An organic electro-luminescence display apparatus and an organic thin film transistor for the same include: a first electrode-layer supplying holes; a second electrode layer supplying electrons; an organic thin film layer disposed between the first electrode layer and the second electrode layer, the organic thin film layer emits light through the recombination of the holes and the electrons; and a sealing protection layer insulating at least the second electrode layer and the organic thin film layer from an external gas, wherein the sealing protection layer includes at least a LaF 3  layer. Since the penetration of harmful materials such as moisture or oxygen is prevented, the organic electro-luminescence display apparatus can provide constant performance. In addition, since an additional sealing structure is not required, the organic electro-luminescence display apparatus is lighter, thinner, and less costly to manufacture.

Description:
[0001]     This application claims priority to Korean Patent Application No. 10-2005-0078041, filed on Aug. 24, 2005, and all the benefits accruing therefrom under 35 U.S.C. §119, the contents of which in its entirety are herein incorporated by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to an organic electro-luminescence display apparatus and an organic thin film transistor for the same, and more particularly, to an organic electro-luminescence display apparatus providing constant performance by using a structure that prevents the penetration of harmful materials such as moisture or oxygen, and an organic thin film transistor for the same.  
         [0004]     2. Description of the Related Art  
         [0005]     Flat panel display apparatuses such as organic electro-luminescence display apparatuses, liquid crystal display apparatuses, or inorganic electro-luminescence display apparatuses are classified as either a passive driving type flat panel display apparatus or an active driving type flat panel display apparatus, dependent on their driving types. The active driving type flat panel display apparatuses control input signals for each pixel using thin film transistors (“TFTs”) that can process many signals, and thus, are frequently used for realizing a moving picture. However, an organic thin film transistor, including organic materials for forming a semiconductor active layer, malfunctions when oxygen and moisture penetrate into a thin film structure and react with a layer structure of the organic thin film transistor.  
         [0006]      FIG. 1  is a cross-sectional view of a conventional organic electro-luminescence display apparatus. Referring to  FIG. 1 , a first electrode layer  21  which is formed of, for example, indium tin oxide (ITO), and supplies holes, a hole transport layer  23 , a light emitting layer  25  which emits light through the recombination of the holes and the electrons, an electron transport layer  27 , a second electrode layer  29 , which is formed of a metal electrode supplying electrons, all of which are sequentially formed on a glass substrate  10 . In the light emitting layer  25 , light is generated through recombining holes inserted from the first electrode layer  21  and electrons inserted from the second electrode layer  29 . For the recombination, the first electrode layer  21  may be made of a material having a high work function, and the second electrode layer  29  may be made of a material having a low work function such as a metal. Since the second electrode layer  29  has characteristics of high activity and chemical instability, the second electrode layer  29  easily reacts with external moisture or oxygen. Thus the metal second electrode layer  29  is easily oxidized or corroded. When moisture or oxygen penetrates into an organic thin film layer  22  including the light emitting layer  25 , the structure of the organic thin film layer  22  changes, thereby degrading a light emitting characteristic of the apparatus. Conventionally, the organic thin film layer  22  and the second electrode layer  29  are sealed with a capping element  30  made of metal or plastic to isolate the organic thin film layer  22  and the second electrode layer  29  from external harmful materials. The capping element  30  is attached to the first electrode layer  21  using an adhesive agent  35 , for example, an ultraviolet (“UV”) adhesive, and moisture absorbents  40  are disposed in the capping element  30 . Specifically, an inlet to a cavity is prepared in the upper side of the capping element  30 , and the moisture absorbent  40  are inserted through the inlet and fixed using tapes having pores.  
         [0007]     However, as described above, the capping element  30  isolating the layers from external gas such as moisture or oxygen, increases the weight and volume of the apparatus, thereby making it difficult to manufacture a lightweight, thin, simple and small display apparatus. In addition, since additional processes such as a process of attaching the capping element  30  or a process of mounting the moisture absorbents  40  are required, the manufacturing time becomes longer and the manufacturing yield becomes lower. Furthermore, the reliability of products is degraded due to the additional elements.  
       BRIEF SUMMARY OF THE INVENTION  
       [0008]     An aspect of the present invention provides constant performance of an organic electro-luminescence display apparatus by using a structure that prevents the penetration of impurities such as moisture or oxygen, and an organic thin film transistor for the same.  
         [0009]     An aspect of the present invention also provides an organic electro-luminescence display apparatus having a simple structure, thereby reducing manufacturing processes and costs.  
         [0010]     According to an exemplary embodiment of the present invention, there is provided an organic electro-luminescence display apparatus including: a first electrode layer supplying holes; a second electrode layer supplying electrons; an organic thin film layer disposed between the first electrode layer and the second electrode layer, and the organic thin film layer emits light through the recombination of the holes and the electrons; and a sealing protection layer insulating at least the second electrode layer and the organic thin film layer from an external gas, wherein the sealing protection layer includes at least a LaF 3  layer.  
         [0011]     The apparatus may further include an insulation substrate acting also as a supporting structure, wherein the first electrode layer, organic thin film layer, and second electrode layer are sequentially stacked on the insulation substrate, wherein the sealing protection layer seals an outer region ranging from the lateral sides of the organic thin film layer and the second electrode layer to the upper sides of the second electrode layer.  
         [0012]     The sealing protection layer may have a monolayer structure of the LaF 3  layer, a multilayer structure including at least two layers of the LaF 3  layer and one of an organic layer and an inorganic layer, or a multilayer structure including at least three layers of the LaF 3  layer, an organic layer and an inorganic layer. The inorganic layer may be formed of one of silicon nitride and silicon oxide.  
         [0013]     The LaF 3  layer may have a thickness of at least 30 nm. The LaF 3  layer may be formed using one deposition method selected from the group consisting of physical vapor deposition (PVD) including ion beam deposition and chemical vapor deposition (CVD) including low pressure CVD (LPCVD) and plasma enhanced CVD (PECVD).  
         [0014]     According to another exemplary embodiment of the present invention, there is provided an organic thin film transistor which includes a gate electrode formed on an insulation substrate, an organic insulation layer covering the gate electrode, a source electrode and a drain electrode formed on the upper surface of the organic insulation layer, and an organic semiconductor layer formed on the source and drain electrodes. The organic thin film transistor includes: a passivation layer which includes at least a LaF 3  layer and is formed on the upper surface of the organic insulation layer or on the upper surface of the organic semiconductor.  
         [0015]     The passivation layer may have a monolayer structure of the LaF 3  layer, a multilayer structure including at least two layers of the LaF 3  layer and one of an organic layer and an inorganic layer, or a multilayer structure including at least three layers of the LaF 3  layer, the organic layer and the inorganic layer. The inorganic layer may be formed of one of silicon nitride and silicon oxide.  
         [0016]     The passivation layer may cover the source and drain electrodes the organic semiconductor layer formed between the source and drain electrodes. The LaF 3  layer may have a thickness of at least 30 nm.  
         [0017]     The LaF 3  layer may be formed using one deposition method selected from the group consisting of physical vapor deposition (PVD) including ion beam deposition and chemical vapor deposition (CVD) including low pressure CVD (LPCVD) and plasma enhanced CVD (PECVD). 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0018]     The above and other aspects, features and advantages of the present invention will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings in which:  
         [0019]      FIG. 1  is a cross-sectional view of a conventional organic electro-luminescence display apparatus;  
         [0020]      FIG. 2  is a cross-sectional view of an organic electro-luminescence display apparatus according to an exemplary embodiment of the present invention;  
         [0021]      FIG. 3  is a graph illustrating the degree of protection against moisture of LaF 3  layers;  
         [0022]      FIG. 4  is a cross-sectional view of an organic electro-luminescence display apparatus according to another exemplary embodiment of the present invention; and  
         [0023]      FIG. 5  is a cross-sectional view of an organic thin film transistor according to an exemplary embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0024]     Hereinafter, the present invention will be described more fully with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown.  
         [0025]      FIG. 2  is a cross-sectional view of an organic electro-luminescence display apparatus according to an exemplary embodiment of the present invention. The organic electro-luminescence display apparatus includes an insulation substrate  110 , which is formed of glass or plastic and acts as a supporter, and an organic light emitting device  120  formed on the insulation substrate  110 . The insulation substrate  110  may be formed of transparent or translucent glass, or flexible plastic such as polyethylene terephthalate (PET) or polycarbonate.  
         [0026]     The organic light emitting device  120  emits red, green or blue light according to a current flow to display predetermined image information, and includes a first electrode layer  121  supplying holes, (e.g., an anode), a second electrode layer  129  supplying electrons, (e.g., a cathode, and an organic thin film layer  122  which is disposed between the first electrode layer  121  and the second electrode layer  129  and has a light emitting region. The first electrode layer  121  may be formed of a material having a high work function, for example, indium-tin oxide (ITO) that is usually used for a transparent electrode.  
         [0027]     The organic thin film layer  122  formed on the first electrode layer  121  may be formed of a plurality of low molecular organic layers or a plurality of high molecular organic layers. When using the low molecular organic layers, an organic thin film layer may have a stacked structure of a hole injection layer, a hole transport layer, an organic light emitting layer, an electron transport layer and an electron injection layer. The organic thin film layer  122  in the  FIG. 2  has a hole transport layer  123 , an organic light emitting layer  125  and an electron transport layer  127 . When using high molecular organic layers, the organic thin film layer  122  may typically have a structure of a hole transport layer and a light emission layer. However, the organic thin film layer  122  is not limited thereto, but may have a monolayer structure of the organic light emission layer  122 , a double layer structure of the hole transport layer  123  and the organic light emission layer  125 , a double layer structure of the organic light emitting layer  125  and the electron transport layer  127 . The second electrode layer  129 , that is the cathode electrode, may be formed by depositing materials having a low work function such as a metal, for example Mg/Ag, Mg, Al or alloys thereof.  
         [0028]     When a voltage is applied to the organic light emitting device  120  to bias the first electrode layer  121  as an anode and the second electrode layer  129  as a cathode, holes inserted from the first electrode layer  121  and electrons inserted from the second electrode layer  129  are recombined in the organic light emitting layer  125 , and thus the energy level in the organic light emitting layer  125  decreases from an excited state to a ground state. Thus, the organic light emitting layer  125  emits light having a specific wavelength corresponding to the energy difference between the excited state and the ground state.  
         [0029]     A sealing protection layer  130  is formed to cover lateral and upper sides of the organic light emitting device  120 . Specifically, the sealing protection layer  130  isolates the organic thin film layer  122  and the second electrode layer  129  formed on the first electrode layer  121  from external gases. The sealing protection layer  130  may be formed by depositing LaF 3  along the outer surface of the organic light emitting device  120  to have a predetermined thin film thickness. The LaF 3  is not dissolved in moisture, and prevents impurities such as moisture or oxygen from penetrating into and reacting with the organic light emitting device  120 , thereby increasing durability of the organic light emitting device  120  against moisture and oxygen.  
         [0030]     In  FIG. 2 , the edges of the first electrode layer  121  are not covered by the sealing protection layer  130 , however, the present invention is not limited thereto. For example, the sealing protection layer  130  may cover the entire structure of the organic light emitting device  120  including the entire major surface area of first electrode layer  121  that is opposite a major surface area attached to the insulation substrate  110 .  
         [0031]      FIG. 3  is a graph illustrating the degree of protection against moisture of LaF 3  layers. Fourier transform infrared spectroscopy (“FT-IR”) was employed to obtain the results illustrated in  FIG. 3 . In the FT-IR, infrared rays with various wavelengths are radiated on a sample and then an absorption peak is detected, thereby detecting whether or not a specific material exists in the sample.  
         [0032]     An MgO layer having a thickness of 500 nm was formed on a silicon substrate, and a LaF 3  layer is formed on the MgO layer as a protecting layer against moisture. The degree of moisture absorbtion of the MgO layer is measured by the FT-IR. MgO is not resistant to moisture and reacts with moisture to form Mg(OH) 2 . The LaF 3  layer formed on the MgO layer can prevent the reaction between the MgO layer and the moisture.  
         [0033]      FIG. 3  illustrates transmittance profiles of a conventional MgO layer on which a LaF 3  layer is not formed (e.g., LaF 3  layer is absent), and LaF 3  coated on MgO layers having a LaF 3  layer thickness of 5 nm, 15 nm, and 30 nm. In the conventional MgO layer, an absorption peak appears at about a wavenumber of 3700 cm −1  when the transmittance rapidly drops. The absorption peak is caused by the inherent vibration mode of an OH-group, and indicates the reaction between the MgO layer and moisture. The absorption peak decreases as the thickness of the LaF 3  layer increases, as illustrated in  FIG. 3 . When the thickness of the LaF 3  layer is equal to 30 nm, the absorption peak disappears such that the LaF 3  layer is thick enough to completely prevent the penetration of moisture. Thus, the results can be used to determine a standard thickness of the LaF 3  layer. The LaF 3  layer may have a thickness of at least 30 nm as a protecting layer, for example, about 50 nm to about 1000 nm.  
         [0034]      FIG. 4  is a cross-sectional view of an organic electro-luminescence display apparatus according to another exemplary embodiment of the present invention. The organic electro-luminescence display apparatus includes an organic light emitting device  220  formed on an insulation substrate  210 , a sealing protection layer  230  covering and sealing the organic light emitting device  220 . The organic light emitting device  220  includes a first electrode layer  221  supplying holes, a second electrode layer  229  supplying electrons, and an organic thin film layer  222 , which is disposed between the first electrode layer  221  and the second electrode layer  229 . The organic light emitting device  220  emits light through the recombination of the inserted holes and the inserted electrons.  
         [0035]     In the current exemplary embodiment, the sealing protection layer  230  has a stacked structure including two or more different layers, one layer including a LaF 3  layer. Specifically, the sealing protection layer  230  in  FIG. 4  includes an inner interlayer  235  and an outer LaF 3  layer  231 . The LaF 3  layer  231  prevents the penetration of moisture or oxygen that can react with the organic light emitting device  220 , as described in the previous exemplary embodiment of  FIG. 2 , thereby preventing corrosion or oxidation of the organic light emitting device  220  and the formation of dark spots not having a display function.  
         [0036]     The interlayer  235  is formed between the organic light emitting device  220  emitting light and the LaF 3  layer  231  functioning as a protection layer and increasing the bonding attachment between the organic light emitting device  220  and the LaF 3  layer  231 . If the LaF 3  layer  231  is formed directly on the organic light emitting device  220  as in the prior art, the LaF 3  layer may not completely seal the outside of the organic light emitting device  220  because of the material characteristic differences between the LaF 3  layer  231  and the material in the organic light emitting device  220 , thereby generating a gap therebetween. The interlayer  235  is formed to prevent the generation of the gap between the LaF 3  layer  231  and the organic light emitting device  220 . The interlayer  235  is formed of an organic material or an inorganic material, and may be formed of a material which has similar material characteristics to LaF 3  and is easily attached to LaF 3 .  
         [0037]     When the interlayer  235  covering the organic light emitting device  220  with the LaF 3  layer  231  is an inorganic layer, the interlayer  235  may be formed of silicon oxide or silicon nitride, for example, SiO 2  or Si 3 N 4 . When the interlayer  235  is an organic layer, the interlayer  235  may be formed of a high molecular organic material, for example, polythiophene (PTh), polyfluorene (PF), polyarylenevinylene (PAV), or a precursor thereof, or a low molecular organic material, for example, copper(ll) pthalocyanine (CUPc), tris(8-quinolinolato)aluminum (Alq3), or a precursor thereof, but the present invention is not limited thereto.  
         [0038]     The LaF 3  layer  231  may be formed of a thick film having a predetermined thickness to prevent the penetration of an external gas such as oxygen or moisture. However, a single process may not form the thick film for the LaF 3  layer  231  because of process factors or material characteristics of the LaF 3 . A sealing protection layer having a stacked structure may solve this problem. That is, an interlayer, which is easily attached to the LaF 3  layer, is formed between LaF 3  layers, and thus a sealing protection layer having a desired thickness can be provided.  
         [0039]     The sealing protection layer according to exemplary embodiments of the present invention includes a LaF 3  layer, and has a stacked structure of the LaF 3  layer and an organic layer, a stacked structure of the LaF 3  layer and an inorganic layer, or a stacked structure of the LaF 3  layer, the organic layer and the inorganic layer. That is, the sealing protection layer  230  in  FIG. 4  includes an interlayer  235 , which is an organic layer or an inorganic layer and formed on the organic light emitting device  220 , and a LaF 3  layer  231  formed on the interlayer  235 . However, the present invention is not limited thereto. For example, an organic layer is formed on the light emitting device  220 , and then a LaF 3  layer and an inorganic layer are sequentially formed on the organic layer. Alternatively, for example, an inorganic layer is formed on the light emitting device  220 , and then a LaF 3  layer and an organic layer are sequentially formed on the organic layer. For both cases, the LaF 3  protects the light emitting device  220  from penetration of external moisture and oxygen. The inorganic layer may be formed of silicon oxide or silicon nitride, and the organic layer may be a high molecular organic layer or a low molecular organic layer.  
         [0040]     The LaF 3  layer may be formed using one deposition method selected from the group consisting of physical vapor deposition (“PVD”) including ion beam deposition and chemical vapor deposition (“CVD”) including low pressure CVD (“LPCVD”) and plasma enhanced CVD (“PECVD”). To optimize conditions for forming the LaF 3  layer, an inorganic layer or an organic layer is formed and then the LaF 3  layer is formed thereon.  
         [0041]      FIG. 5  is a cross-sectional view of an organic thin film transistor according to yet another exemplary embodiment of the present invention. The organic thin film transistor includes a gate electrode  311  formed on a predetermined region of an insulation substrate  310 , an organic insulation layer  313  covering and insulating the gate electrode  311 , a source electrode  315  and a drain electrode  317  formed on the organic insulation layer  313 , an organic semiconductor layer  320  formed on the organic insulation layer  313  to connect the source electrode  315  and the drain electrode  317 , and a passivation layer  330  formed on the organic semiconductor layer  320 .  
         [0042]     The insulation substrate  310 , whereon the organic thin film transistor is formed, supports an organic thin film structure. The insulation substrate  310  is formed of glass, silicon, or flexible plastic. The gate electrode  311  formed on the insulation substrate  310  can be formed of a typical metal electrode material, for example, Au, Ag, Al, Cu, Ni, or an alloy thereof. The gate electrode  311  may be formed by vacuum depositing an electrode material onto a predetermined region of the insulation substrate  310 . The organic insulation layer  313 , covering and insulating the gate electrode  311 , is formed on the insulation substrate  310 . The organic insulation layer  313  may be formed of polyimide, benzocyclobutene (BCB), or photoacryl.  
         [0043]     The source electrode  315  and the drain electrode  317  each are formed on a predetermined region of the organic insulation layer  313 . The source electrode  315  and the drain electrode  317  may be conductive layers which are vacuum deposited onto the organic insulation layer  313  as a predetermined pattern and may be formed of typical metal electrode materials like the above-described gate electrode  311 . The organic semiconductor layer  320  is formed on the organic insulation layer  313  and forms a conduction pathway between the source electrode  315  and the drain electrode  317 . The organic semiconductor layer  320  may be formed of a commonly used material, for example, pentacene, polyacetylene, polyaniline, or a precursor thereof.  
         [0044]     The passivation layer  330  covers and seals the inner thin films to prevent the metallic electrodes from oxidation or corrosion and reaction of the organic material layer with oxygen and moisture, such that the characteristics of the organic thin film transistor are not degraded. The passivation layer  330  is formed by depositing LaF 3  to a predetermined thickness on upper regions of the source electrode  315 , the drain electrode  317  and the organic semiconductor layer  320 . The LaF 3  is not dissolved in moisture, and prevents impurities such as moisture or oxygen from penetrating into and reacting with the inner thin films, thereby increasing durability of the organic thin film transistor.  
         [0045]     The passivation layer of the present invention includes a LaF 3  layer. The passivation layer may be a LaF 3  monolayer layer, as illustrated in  FIG. 5 , or a multi-layer in which a LaF 3  layer and an organic layer and/or an inorganic layer are stacked. When the passivation layer is a multi-layer, one of or both of the organic layer and the inorganic layer are formed on the upper side or lower side of the LaF 3  layer. For example, an organic layer having similar material characteristics to an organic semiconductor is formed on the organic semiconductor layer  320 , and then a passivation layer in which LaF 3  layers are stacked is formed on the organic layer. In this case, since the organic material layers have similar material characteristics, they are better attached to each other. The organic or inorganic layer forming the passivation layer  330  with the LaF 3  layer can be formed of the same materials as the sealing protection layer  230  described above with respect to  FIG. 4 . That is, the inorganic layer may be formed of silicon oxide or silicon nitride, for example, SiO 2  or Si 3 N 4 . The organic layer may be formed of a high molecular organic material, for example, polythiophene (PTh), polyfluorene (PF), polyarylenevinylene (PAV), or a precursor thereof, or a low molecular organic material, for example, copper(II) pthalocyanine (CUPc), tris(8-quinolinolato)aluminum (Alq3), or a precursor thereof, but the present invention is not limited thereto.  
         [0046]     Based on the results in  FIG. 3 , to effectively prevent the penetration of impurities such as oxygen and moisture, the passivation layer  330  of the present invention may have a thickness of at least 30 nm or more, for example, about 50 nm to about 1000 nm. In the exemplary embodiment of  FIG. 5 , the passivation layer  330  is formed on the organic semiconductor layer  320 , but the present invention is not limited thereto. That is, if the passivation layer  330  includes a LaF 3  layer as an external gas protection layer, the passivation layer  330  can be formed on any portion of the organic thin film structure, for example, on the organic insulation layer  313 .  
         [0047]     In the organic electro-luminescence display apparatus and the organic thin film transistor for the same according to the present invention, a vulnerable inner thin film structure is sealed with a LaF 3  layer having high resistivity against the penetration of moisture or oxygen, thereby preventing the degradation of the display device characteristics such as the generation of dark spots, which substantially reduce a display function and light luminance of the display device.  
         [0048]     The organic electro-luminescence display apparatus according to the present invention does not require any additional protecting structure for sealing the organic light emitting device and any additional processes for sealing the device and preparing moisture absorbents, thereby reducing the manufacturing costs thereof.  
         [0049]     While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims.