Patent Document

CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of Korean Patent Application No.10-2004-0088878, filed on Nov. 3, 2004, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present embodiments relate to a method of manufacturing a substrate having a thin film transistor (TFT), a TFT manufactured according to the same, a method of manufacturing a flat panel display device, and a flat display device manufactured according to the same, and more particularly, to a method of manufacturing a substrate having a TFT that can be applied to flexible devices having a plastic substrate, a substrate having the TFT manufactured according to the same, a method of manufacturing a flat panel display device, and a flat display device manufactured according to the same. 
     2. Description of the Related Art 
     Thin film transistors (TFTs) used in a flat panel display device, such as liquid crystal display (LCD) devices, organic light emitting display (OLED) devices, or inorganic light emitting display devices, are used as a switching device that controls the operation of each pixel, and as a driving device for driving each pixel. 
     The TFT includes a semiconductor layer, a gate electrode, and source and drain electrodes. The semiconductor layer includes source and drain regions doped at high concentration and a channel region formed between the source and drain regions. The gate electrode is insulated from the semiconductor layer and located in a region corresponding to the channel region. The source and drain electrodes are respectively connected to source and drain regions. 
     Recently, flat display devices have been required to have the characteristics of slimness and flexibility. 
     In order to obtain flexibility of a flat display device, attempts have been made using a plastic substrate instead of the conventional glass substrate. 
     However, in the case of the plastic substrate, an additional barrier layer must be formed, since the plastic substrate is less waterproof and less resistant to oxygen penetration than the glass substrate. The barrier layer is coated on the surface of the plastic substrate to block the penetration of oxygen or moisture through the substrate. The barrier layer is expensive and requires an additional process. 
     To obtain a flexible flat display device, an organic semiconductor thin film transistor is used instead of a conventional silicon thin film transistor. When the organic semiconductor is used, an inexpensive thin film transistor can be manufactured, since the organic semiconductor can be formed at a low temperature, and can easily be applied to the plastic substrate, which cannot be used at a high temperature. 
     However, when a TFT is manufactured using the organic semiconductor, and a light emitting device is subsequently formed by a conventional process, the organic semiconductor is easily deformed. Particularly, in the case of the OLED device, forming a pixel electrode connected to the TFT and forming an aperture for a light emitting device on a pixel defining film may both cause problems. 
     Therefore, to manufacture a flexible flat display device, a new method is needed. 
     SUMMARY OF THE INVENTION 
     The present embodiments can be applied to a flexible device, and provide a method of manufacturing a substrate having a thin film transistor (TFT) included on a plastic substrate, a substrate manufactured thereby, a method of manufacturing a flat panel display device, and a flat panel display device manufactured thereby. 
     According to an aspect of the present embodiments, there is provided a method of manufacturing a substrate having a thin film transistor (TFT), the method comprising: preparing a film in which a plurality of conductive patterns are included on a base; bonding the film to a substrate; forming the TFT in a manner such that it is electrically connected to the conductive pattern on the film; and forming an insulating layer covering the TFT on the film. 
     According to another aspect of the present embodiments, there is provided a substrate having a TFT manufactured according to the method described above. 
     According to still another aspect of the present embodiments, there is provided a method of manufacturing a flat panel display device, the method comprising: preparing a film in which a plurality of conductive patterns are included on a base; bonding the film to a substrate; forming the TFT in a manner such that it is electrically connected to the conductive pattern on the film; forming an insulating film covering the TFT on the film; forming an opening in the insulating film to expose a region of the conductive pattern; and forming a display device on the conductive pattern exposed through the opening. 
     According to one embodiment, there is provided a flat panel display device comprising: a film bonded to a substrate in which a plurality of conductive patterns are included on a base, a TFT that it is electrically connected to the conductive pattern on the film, an insulating film covering the TFT on the film, and an opening in the insulating film that exposes a region of the conductive pattern. 
     In one aspect, the TFT comprises: at least one of source and drain electrodes connected to the conductive pattern, wherein the source and drain electrodes are formed on the film, a semiconductor layer contacting each of the source and drain electrodes, a gate insulating film on the semiconductor layer and a gate electrode on the gate insulating film. 
     In another aspect, the gate insulating film is patterned to at least a region corresponding to the semiconductor layer. In yet another aspect, the semiconductor layer is formed of an organic material. 
     In still another aspect, the organic material comprises at least one from the group consisting of pentacene, tetracene, naphthalene, alpha-4-thiophene, alpha-6-thiophene, perylene and its derivatives, rubrene and its derivatives, coronene and its derivatives, perylene tetracarboxylic diimide and its derivatives, perylene tetracarboxylic dianhydride and its derivatives, oligonaphthalene and its derivatives, alpha-5-thiophene oligothiophene and its derivatives, phthalocyanine that does or does not include a metal and its derivatives, pyromelitic dianhydride and its derivatives, and pyromelitic diimide and its derivatives. 
     In another aspect, the TFT comprises: at least one source electrode and at least one drain electrode connected to the conductive pattern, wherein the source and drain electrodes are formed on the semiconductor layer, a gate insulating film on the semiconductor layer and the source and drain electrodes and a gate electrode on the gate insulating film. 
     In another aspect, the gate insulating film is patterned to at least a region corresponding to the semiconductor layer. 
     In another aspect, the semiconductor layer is formed of an organic material. 
     In another aspect, the organic material comprises at least one from the group consisting of pentacene, tetracene, naphthalene, alpha-4-thiophene, alpha-6-thiophene, perylene and its derivatives, rubrene and its derivatives, coronene and its derivatives, perylene tetracarboxylic diimide and its derivatives, perylene tetracarboxylic dianhydride and its derivatives, oligonaphthalene and its derivatives, alpha-5-thiophene oligothiophene and its derivatives, phthalocyanine that does or does not include a metal and its derivatives, pyromelitic dianhydride and its derivatives, and pyromelitic diimide and its derivatives. 
     In still another aspect, at least one of the surfaces of the film does not expose the conductive pattern, and wherein the surface of the film on which the conductive pattern is not exposed faces the outside. 
     In another aspect, the substrate comprises plastic. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other features and advantages of the present embodiments will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings in which: 
         FIGS. 1 through 7  are cross-sectional views illustrating a method of manufacturing a thin film transistor on a plastic substrate according to one embodiment; 
         FIG. 8  is a cross-sectional view illustrating a method of manufacturing an organic light emitting display device using the substrate manufactured according to the method depicted in  FIGS. 1 through 7 ; and 
         FIG. 9  is a cross-sectional view illustrating an organic light emitting display device manufactured according to another embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present embodiments will now be described more fully with reference to the accompanying drawings, in which exemplary embodiments are shown. 
       FIGS. 1 through 7  are cross-sectional views illustrating the sequence of a method of manufacturing a substrate having a thin film transistor according to an embodiment, and  FIG. 8  is a cross-sectional view illustrating a method of manufacturing an organic light emitting display device using the substrate manufactured according to the method illustrated in  FIGS. 1 through 7 . 
     Referring to  FIG. 1 , a film  30  is lamination bonded using a lamination roller R on a substrate  10 . The film  30  is made such that a conductive pattern  32  is included in a base  31  formed of a resin. Referring to  FIG. 2 , the conductive pattern  32  is formed in a regular pattern. 
     The conductive pattern  32  will become a pixel electrode and can be formed in a single layer or multiple layers of a conductive material, which will be described later. 
     The conductive pattern  32  can be formed of, for example, ITO, IZO, or ZnO when the pixel electrode is used as a transparent electrode, and can be formed of, for example, Ag, Mg, Al, Pt, Pd, Au, Ni, Nd, Ir, Cr, or a compound of these metals when the pixel electrode is used as a reflective electrode. When the pixel electrode is used as a transparent electrode, the pixel electrode is an anode electrode, and when the pixel electrode is used as a reflective electrode, the pixel electrode is a cathode electrode. However, the present embodiments are not limited thereto, and even if the pixel electrode is used as a reflective electrode, after forming a reflection film formed of, for example, Ag, Mg, Al, Pt, Pd, Au, Ni, Nd, Ir, Cr, or an alloy of these metals, an ITO film, an IZO film, a ZnO film, or an In 2 O 3  film, etc. can be formed on the reflective film, and the pixel electrode can be an anode. 
     In at least one surface of the film  30 , the conductive pattern  32  is not exposed to the outside. As depicted in  FIG. 1 , when the film  30  is laminated on the substrate  10 , the lamination is performed so that the surface of the conductive pattern  32  which is not exposed faces the outside. In  FIGS. 1 through 8 , the conductive pattern  32  of the film  30  is shown with the side facing the substrate  10  exposed, but the present embodiments are not limited thereto, and the conductive pattern  32  might not be exposed on either side of the film  30 . 
     The film  30  can be bonded in various ways. As depicted in  FIG. 1 , the film  30  can be laminated, or can be attached to the substrate  10  using an adhesive. 
     In one embodiment, the substrate  10  can be a plastic substrate. In this embodiment, a barrier layer  20  may be coated on the opposite surface to that which the film  30  is attached. The barrier layer  20  blocks the penetration of moisture and/or oxygen through the substrate  10 . The barrier layer may be coated on the surface on which the film  30  is attached. 
     The barrier layer  20  can be, for example, a composite layer of an inorganic material layer and a polymer layer. 
     The inorganic material layer can be formed of, for example, metal oxides, metal nitrides, metal carbides, metal oxynitrides, or a compound of these metals. The metal oxides can be, for example, silica, alumina, titania, indium oxide, tin oxide, indium tin oxide, or a compound of these oxides. The metal nitride can be, for example, aluminum nitride, silicon nitride, or a compound of these nitrides. The metal carbide can be, for example, silicon carbide, and the metal oxynitride can be, for example, silicon oxynitride. The inorganic material layer can be formed of any inorganic material that can block the penetration of moisture or oxygen, such as silicon. 
     The inorganic material layer can be formed by deposition or other methods. When the inorganic material layer is formed by evaporation, pores can form in the inorganic material layer. In some embodiments, in order to prevent the pores from continuously growing on the same spot, a polymer layer can be further included in addition to the inorganic material layer. The polymer layer can be formed of, for example, organic polymer, inorganic polymer, organometallic polymer, or hybrid organic/inorganic polymer. 
     The barrier layer  20  is not necessarily included, and may be omitted. 
     The substrate  10  is not limited to plastic, but can also be formed of glass or metal. 
     Referring to  FIG. 3 , a first opening  31   a  and a second opening  31   b  are formed by patterning the film  30  after the film  30  is attached to the substrate  10 . 
     The first opening  31   a,  as will be described later, allows the drain electrode to contact the conductive pattern  32 , and the second opening  31   b,  as will be described later, is to form a light emitting device. 
     Referring to  FIG. 4 , a source electrode  41  and a drain electrode  42  are formed on the base  31  after patterning the film  30 . 
     At this time, as described above, the drain electrode  42  is connected to the conductive pattern  32  through the first opening  31   a.    
     After the source and drain electrodes  41  and  42  are formed, as depicted in  FIG. 5 , a semiconductor layer  43  is formed covering the source and drain electrodes  41  and  42 . 
     The semiconductor layer  43  can be, for example an organic semiconductor. 
     An organic semiconductor can be formed of a semiconductive organic material, such as a polymer or a low molecular weight organic compound. The semiconductive organic material includes at least one from the group consisting of pentacene, tetracene, naphthalene, alpha-4-thiophene, alpha-6-thiophene, perylene and its derivatives, rubrene and its derivatives, coronene and its derivatives, perylene tetracarboxylic diimide and its derivatives, perylene tetracarboxylic dianhydride and its derivatives, oligonaphthalene and its derivatives, alpha-5-thiophene oligothiophene and its derivatives, phthalocyanine that does or does not include a metal and its derivatives, pyromelitic dianhydride and its derivatives, and pyromelitic diimide and its derivatives. 
     At this time, referring to  FIG. 5 , after forming the organic semiconductor layer  43  covering the source and drain electrodes  41  and  42 , the semiconductor layer  43  is patterned to have regions as depicted in  FIG. 5 , using a laser etching method, such as a laser ablation method. Besides this method, other patterning methods which are used for patterning organic semiconductors can also be applied, and the regions are not necessarily patterned as shown in  FIG. 5 . 
     The semiconductor layer  43  can be an inorganic semiconductor layer formed of, for example, CdS, GaS, ZnS, CdSe, CaSe, ZnSe, CdTe, SiC, or Si. 
     Referring to  FIG. 6 , after forming the semiconductor layer  43 , a gate insulating film  44  is formed on the semiconductor layer  43 , and a gate electrode  45  is formed on the gate insulating film  44 . 
     The gate insulating film  44  can be formed of organic or inorganic materials. Examples of suitable inorganic material include SiO 2 , SiNx, Al 2 O 3 , TiO 2 , Ta 2 O 5 , HfO 2 , ZrO 2 , BST, and PZT, and examples of suitable organic material include general polymer, polymethyl methacrylate (PMMA), polystyrene (PS), polymer derivatives having a phenol group, acrylic polymer, imide polymer, aryl ether polymer, amide polymer, fluoride polymer, p- xylylene polymer, vinyl alcohol polymer, and a blend of these materials. Also, inorganic-organic stack layer films can be used. 
     The gate insulating film  44  can be patterned to an island type as depicted in  FIG. 6  so that it receives less stress when the substrate  10  is bent. The gate insulating film  44  can be patterned at least to cover a region corresponding to the semiconductor layer  43 . 
     However, the present embodiments are not limited thereto, and the gate insulating film  44  can be formed to cover any part of the entire region but the region on which the light emitting device is formed. 
     The gate electrode  45  is formed to correspond to the channel region of the semiconductor layer  43 . 
     Referring to  FIG. 7 , after forming the gate electrode  45 , an insulating film  46  can be further formed to cover the TFT. The insulating film  46  protects the TFT and, as will be described later, has openings which allow it to act as a pixel defining layer. 
     The insulating film  46  can be a single layer or multiple layers of inorganic or organic materials. Examples of suitable inorganic material includes SiO 2 , SiN x , Al2O 3 , TiO 2 , Ta2O 5 , HfO 2 , ZrO 2 , BST, and PZT, and examples of the organic material includes general polymer, polymethyl methacrylate (PMMA), polystyrene (PS), polymer derivatives having phenol group, acrylic polymer, imide polymer, arylether polymer, amide polymer, fluoride polymer, p-xylylene polymer, vinyl alcohol polymer, and a blend of these materials. However, the present embodiments are not limited thereto, and various insulating materials can be used. 
     After forming the substrate  10  having the TFT formed by the method described above, referring to  FIG. 8 , a third opening  46   a  is formed to expose a portion of the conductive pattern  32  by etching the insulating film  46 . 
     In the present embodiments, the second opening  31   b  described above can be formed at the same time as the third opening  46   a.    
     An organic light emitting diode (OLED) is formed by forming an organic layer  33  that includes an emission layer (not shown) and a facing electrode  34  covering the organic layer  33  in the third opening  46   a.    
     The organic layer  33  can be, for example, a low molecular weight organic layer or a polymer organic layer. 
     If the organic layer  33  is a low molecular weight organic layer, the organic layer  33  can be formed in a single or a composite structure by stacking a Hole Injection Layer (HIL), a Hole Transport Layer (HTL), an Emission Layer (EML), an Electron Transport Layer (ETL), and an Electron Injection Layer (EIL). Examples of organic materials that can be used for forming the organic layer  33  include copper phthalocyanine (CuPc), N,N′-di(naphthalene-1-yl)-N,N′-diphenyl-benzidine (NPB), and tris-8-hydroxyquinoline aluminum (Alq3). The low molecular weight organic layer can be formed by an evaporation method. 
     If the organic layer  33  is a polymer organic layer, the organic layer  33  can have a structure having a HTL and an EML. At this time, the polymer HTL is formed of poly-(2,4)-ethylene-dihydroxy thiophene (PEDOT) and the EML is formed of a polyphenylenevinylene (PPV) or polyfluorene group polymer organic material using an inkjet printing or spin coating method. 
     The facing electrode  34  can be used as a transparent electrode or a reflective electrode. When the facing electrode  34  is used as a transparent electrode, the facing electrode  34  can be formed of, for example, ITO, IZO, ZnO or In 2 O 3 , and when the facing electrode  34  is used as a reflection electrode, the facing electrode  34  can be formed of, for example, Li, Ca, LiF/Ca, LiF/Al, Al, Mg, or a compound of these metals. ITO, IZO, ZnO or In 2 O 3  form on the reflection film after forming the reflection film using, for example, Ag, Mg, Al, Pt, Pd, Au, Ni, Nd, Ir, Cr, or a compound of these metals. However, the present embodiments are not limited thereto, and even if the facing electrode  34  is used as a transparent electrode, after depositing a material layer formed of a metal having a low work function, such as for example, Li, Ca, LiF/Ca, LiF/Al, Al, Ag, Mg, or a compound of these metals facing the organic layer  33 , an auxiliary electrode layer or a bus electrode line formed of a material for forming the transparent electrode, such as for example, ITO, IZO, ZnO or In 2 O 3 , can be included on the material layer. 
     According to the present embodiments, a flat display device can be manufactured by bonding the film  30  on which the conductive pattern  32  is formed, allowing the conductive pattern  32  to serve as the pixel electrode, particularly if the substrate is formed of plastic. 
     Also, since the conductive pattern  32  acts as a barrier against moisture or oxygen, the air tightness of the device can further be improved. 
       FIG. 9  is a cross-sectional view illustrating a flat display device according to another embodiment. Referring to  FIG. 9 , after forming a semiconductor layer  43  on a film  30 , a source electrode  41  and a drain electrode  42  are formed to contact the semiconductor layer  43 . At this time, a first opening  31   a  is formed on the outside of the semiconductor layer  43  to put the drain electrode  42  in contact with the conductive pattern  32 , but the present embodiments are not limited thereto. That is, the drain electrode  42  can be formed after forming the first opening passing through a base  31  and the semiconductor layer  43  on which a film  30  is formed. 
     The rest of the flat display device in  FIG. 9  is identical to that described with reference to  FIG. 8 . The descriptions thereof will not be repeated. 
     The structure of the TFT and the light emitting device according to the present embodiments are not limited, and can be varied as needed. 
     In the aforementioned present embodiments, an active matrix type light emitting display device has been described. However, as described above, the present embodiments can also be applied to any display device having a TFT, such as TFT LCD device. 
     Also, the TFT formed on a plastic substrate according to the present embodiments can be applied to any device having a flexible TFT, such as an electronic sheet or a smart card, besides the above mentioned display device. 
     While the present embodiments have 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 embodiments as defined by the following claims.

Technology Category: 5