Abstract:
A Thin Film Transistor (TFT) includes: a gate electrode; a source electrode and a drain electrode each insulated from the gate electrode; and an organic semiconductor layer adapted to contact each of the source and drain electrodes, the organic semiconductor layer being insulated from the gate electrode; wherein the organic semiconductor layer includes a boundary region having a smaller grain size than other portions of the organic semiconductor layer, the boundary region being arranged around at least a channel region and a source and drain region of the organic semiconductor layer.

Description:
CLAIM OF PRIORITY  
       [0001]     This application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C. §119 from an application for THIN FILM TRANSISTOR AND FLAT DISPLAY PANEL HAVING THE SAME earlier filed in the Korean Intellectual Property Office on Jun. 8, 2004 and there duly assigned Serial No. 10-2004-0041975.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to a Thin Film Transistor (TFT) and a flat display panel having the TFT, and more particularly, to a TFT that can simply provide a patterning effect on a semiconductor layer and a flat display panel having the same.  
         [0004]     2. Description of the Related Art  
         [0005]     Thin Film Transistors (TFTs) used in Liquid Crystal Display (LCD) devices, Organic Electro Luminescence Display (OELD) devices, or Inorganic Electro Luminescent Display (IELD) devices are used as switching devices that control the operation of pixels and driving devices for driving the pixels in display devices.  
         [0006]     The TFT includes a semiconductor layer having source/drain regions doped with a high concentration of a dopant and a channel region formed between the source/drain region, a gate electrode disposed on a region corresponding to the channel region and insulated from the semiconductor layer, and source/drain electrodes contacting each of the source/drain regions.  
         [0007]     A recent flat display device should be flexible as well as thin. To obtain a flexible display device, many attempts have been made to use plastic substrates instead of conventional glass substrates. When a plastic substrate is used, a low temperature process must be used. Therefore, there is a drawback in that a conventional polysilicon thin film cannot be used.  
         [0008]     To solve this problem, recently, the use of organic semiconductors have been introduced. Therefore, a low price TFT can be manufactured since organic semiconductors can be formed by a low temperature process.  
         [0009]     However, organic semiconductors cannot be patterned by a conventional photolithography method. That is, patterning is required for forming an active channel. However, when the patterning is performed by a conventional wet or dry etching process, the organic semiconductor can be damaged by the etching process.  
         [0010]     Therefore, a new patterning method for patterning a semiconductor layer is required.  
       SUMMARY OF THE INVENTION  
       [0011]     The present invention provides a TFT that includes patterning on a semiconductor layer and a flat display panel having the TFT.  
         [0012]     According to one aspect of the present invention, a Thin Film Transistor (TFT) is provided, the TFT comprising: a gate electrode; a source electrode and a drain electrode each insulated from the gate electrode; and an organic semiconductor layer adapted to contact each of the source and drain electrodes, the organic semiconductor layer being insulated from the gate electrode; wherein the organic semiconductor layer includes a boundary region having a smaller grain size than other portions of the organic semiconductor layer, the boundary region being arranged around at least a channel region and a source and drain region of the organic semiconductor layer.  
         [0013]     The roughness of a lower part of the organic semiconductor layer contacting the boundary region of the organic semiconductor layer is preferably greater than roughness of other lower parts of the organic semiconductor layer contacting other portions of the organic semiconductor layer.  
         [0014]     The TFT preferably further comprises an insulating film adapted to cover the gate electrode, the organic semiconductor layer being arranged on the insulating film; wherein roughness of the insulating film corresponding to the boundary region of the organic semiconductor layer is greater than roughness of other portions of the insulating film corresponding to other portions of the organic semiconductor layer.  
         [0015]     The TFT preferably further comprises: an insulating film adapted to cover the gate electrode, the source and drain electrodes being arranged on the insulating film; a protection film having an opening corresponding to the gate electrode and adapted to cover the insulating film and source and drain electrodes; wherein the organic semiconductor layer is arranged on the protection film; and wherein roughness of the protection film corresponding to the boundary region of the organic semiconductor layer is greater than roughness of other portions of the protection film corresponding to other portions of the organic semiconductor layer.  
         [0016]     The TFT preferably further comprises an organic light emitting film; wherein the source and drain electrodes are arranged on the substrate; wherein the organic light emitting film is arranged on the substrate to cover the source and drain electrodes; and wherein a portion of the substrate corresponding to the boundary region of the organic semiconductor layer has a greater surface roughness than other portions of the substrate corresponding to other portions of the organic semiconductor layer.  
         [0017]     The organic semiconductor layer preferably includes at least a material consisting of pentacene, tetracene, anthracene, naphthalene, a-6-thiophene, a-4-thiophene, perylene and their derivatives, rubrene and its derivatives, coronene and its derivatives, perylene tetracarboxylic diimide and its derivatives, perylene tetracarboxylic dianhydride and its derivatives, oligoacene of naphthalene and its derivatives, a-5-oligothiophene of thiophene and its derivatives, phthalocianin and its derivatives, pyromellitic dianhydride and its derivatives, and pyromellitic diimide and its derivatives.  
         [0018]     According to another aspect of the present invention, a flat display device including a Thin Film Transistor (TFT) is provided, the TFT comprising: a gate electrode; a source electrode and a drain electrode each insulated from the gate electrode; and an organic semiconductor layer adapted to contact each of the source and drain electrodes, the organic semiconductor layer being insulated from the gate electrode; wherein the organic semiconductor layer includes a boundary region having a smaller grain size than other portions of the organic semiconductor layer, the boundary region being arranged around at least a channel region and a source and drain region of the organic semiconductor layer.  
         [0019]     According to yet another aspect of the present invention, a Thin Film Transistor (TFT) is provided, the TFT comprising: a gate electrode; a source electrode and a drain electrode each insulated from the gate electrode; an organic semiconductor layer adapted to contact each of the source and drain electrodes, the organic semiconductor layer being insulated from the gate electrode; and a surface-treated portion having a greater surface roughness than other portions on a same plane, the surface-treated portion being arranged at least peripherally of a channel region of the organic semiconductor layer to contact a lower portion of the organic semiconductor layer.  
         [0020]     The TFT preferably further comprises an insulating film arranged to cover the gate electrode; the organic semiconductor layer being arranged on the insulating film, and the surface-treated portion being arranged on the insulating film.  
         [0021]     The TFT preferably further comprises: an insulating film arranged to cover the gate electrode, the source and drain electrodes being arranged on the insulating film; and a protection film having an opening corresponding to the gate electrode, the protection film being arranged to cover the insulating film and the source and drain electrodes, the organic semiconductor layer being arranged on the protection film; wherein the surface-treated portion is arranged on the protection film.  
         [0022]     The source and drain electrodes are preferably arranged on the substrate, the organic semiconductor layer are arranged to cover the source and drain electrodes on the substrate, and the surface-treated portion is arranged on the substrate.  
         [0023]     A grain size of the organic semiconductor layer contacting the surface-treated portion is preferably less than that of the organic semiconductor layer not contacting the surface-treated portion.  
         [0024]     The surface-treated portion preferably comprises a metal.  
         [0025]     The organic semiconductor layer preferably includes at least a material consisting of pentacene, tetracene, anthracene, naphthalene, a-6-thiophene, a-4-thiophene, perylene and their derivatives, rubrene and its derivatives, coronene and its derivatives, perylene tetracarboxylic diimide and its derivatives, perylene tetracarboxylic dianhydride and its derivatives, oligoacene of naphthalene and its derivatives, a-5-oligothiophene of thiophene and its derivatives, phthalocianin and its derivatives, pyromellitic dianhydride and its derivatives, and pyromellitic diimide and its derivatives.  
         [0026]     According to still another aspect of the present invention, a flat display device that includes a Thin Film Transistor (TFT) comprising: a gate electrode; a source electrode and a drain electrode each insulated from the gate electrode; an organic semiconductor layer adapted to contact each of the source and drain electrodes, the organic semiconductor layer being insulated from the gate electrode; and a surface-treated portion having a greater surface roughness than other portions on a same plane, the surface-treated portion being arranged at least peripherally of a channel region of the organic semiconductor layer to contact a lower portion of the organic semiconductor layer.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0027]     A more complete appreciation of the present invention, and many of the attendant advantages thereof, will be readily apparent as the present invention 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:  
         [0028]      FIG. 1  is a cross-sectional view of a structure of a TFT according to an embodiment of the present invention;  
         [0029]      FIG. 2  is a photograph of grains of a pentacene organic layer grown on a Pd film having a low surface roughness;  
         [0030]      FIG. 3  is a photograph of grains of a pentacene organic layer grown on a Pd film having a high surface roughness;  
         [0031]      FIG. 4  is a cross-sectional view of a structure of a TFT according to another embodiment of the present invention;  
         [0032]      FIG. 5  is a cross-sectional view of a structure of a TFT according to still another embodiment of the present invention;  
         [0033]      FIGS. 6 and 7  are cross-sectional views of a structure of a TFT using a metal pattern according to another embodiment of the present invention; and  
         [0034]      FIG. 8  is a cross-sectional view of an OELD device to which the TFT of  FIG. 1  is applied.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0035]     The present invention will now be described more fully with reference to the accompanying drawings in which exemplary embodiments of the present invention are shown.  
         [0036]      FIG. 1  is a cross-sectional view of a structure of a TFT according to an embodiment of the present invention.  
         [0037]     Referring to  FIG. 1 , the TFTs  10  and  10 ′ according to the present invention are included on a substrate  11 . The substrate  11  can be formed of glass, plastic or a metal, a surface of which is processed with an insulator. The TFTs  10  and  10 ′ formed on the substrate  11  are formed close to each other and have an identical structure. First, the TFT  10  will now be described.  
         [0038]     A gate electrode  12  having a predetermined pattern is formed on the substrate  11 , and a gate insulating film  13  is formed to cover the gate electrode  12 . Each of the source/drain electrodes  14  are formed on the gate insulating film  13 . The source/drain electrodes  14 , as depicted in  FIG. 1 , a predetermined portion can be formed to overlap the gate electrode  12 , but it is not limited thereto. An organic semiconductor layer  15  is formed on an entire upper part of the source/drain electrodes  14 .  
         [0039]     The organic semiconductor layer  15  includes source/drain regions  15   b  and a channel region  15   a  that connects the source and drain regions  15   b . The organic semiconductor layer  15  can be formed of an n-type or p-type organic semiconductor and the source/drain regions  15   b  can be doped only with an n-type or p-type dopant.  
         [0040]     The organic semiconductor layer  15  can be formed of a material selected from the group consisting of pentacene, tetracene, anthracene, naphthalene, a-6-thiophene, a-4-thiophene, perylene and their derivatives, rubrene and its derivatives, coronene and its derivatives, perylene tetracarboxylic diimide and its derivatives, perylene tetracarboxylic dianhydride and its derivatives, oligoacene of naphthalene and its derivatives, a-5-oligothiophene of thiophene and its derivatives, phthalocianin that can or can not contain a metal and its derivatives, pyromellitic dianhydride and its derivatives, and pyromellitic diimide and its derivatives.  
         [0041]     As depicted in  FIG. 1 , since the organic semiconductor layer  15  is deposited on the entire surface of the source/drain electrodes  14 , if the organic semiconductor layer  15  is not patterned additionally, cross-talk can occur between the adjacent TFTs  10  and  10 ′.  
         [0042]     To prevent cross-talk between the adjacent TFTs  10  and  10 ′, a boundary region  15   c  having a smaller grain size than other portion is interposed between the adjacent TFTs  10  and  10 ′.  
         [0043]     Thus, the boundary region  15   c  raises the patterning effect of the organic semiconductor layer  15  since the boundary region  15   c  is disposed around the channel region  15   a . Therefore, the boundary region  15   c  can be formed as a closed loop that surrounds the TFT  10  or can be formed in a plurality of straight lines that are not connected to each other.  
         [0044]     The boundary region  15   c  having a smaller grain size than other regions is formed in the organic semiconductor layer  15  to prevent the migration of carriers through the boundary region  15   c  by increasing its resistance compared with the resistance of the other regions.  
         [0045]     In the organic semiconductor layer  15 , if the grain size is small, the grain boundary becomes larger, and then, the resistance increases by increasing the trap site. That is, as the grain size decreases in the boundary region  15   c , the boundary region  15   c  forms a barrier. Accordingly, the patterning effect between the adjacent TFTs can be obtained.  
         [0046]     The boundary region  15   c  having a smaller grain size can be obtained in many ways. According to an embodiment of the present invention, a boundary region  15   c  having a smaller grain size can be formed in the organic semiconductor layer  15  by forming a surface-treated portion  16  under a lower part of the organic semiconductor layer  15  corresponding to the boundary region  15   c.    
         [0047]     In the organic semiconductor layer  15 , the size of the grain can vary according to the morphology of material, such as a surface roughness, which contacts the lower part of the organic semiconductor layer  15 . That is, the greater the roughness of the material contacting the lower part of the organic semiconductor layer  15 , the larger the number of small grains formed, because a large number of seeds are formed when depositing the organic semiconductor layer  15  and the seeds can not grow to large size grains.  
         [0048]      FIGS. 2 and 3  are photographs showing grains of a pentacene organic layer grown on a Pd film which has a low surface roughness and a high surface roughness, respectively. The surface roughness of the Pd film in  FIG. 2  is 11 Å/s, and that of the Pd film in  FIG. 3  is 48 Å/s. As shown in  FIGS. 2 and 3 , the grain size of the organic semiconductor layer  15  grown on the high roughness Pd film is smaller than that of the organic semiconductor layer  15  grown on the low roughness of Pd film.  
         [0049]     This result has been disclosed by Knipp et al. in Journal of Applied Physics. vol.93, No.1, Jan. 1, 2003.  
         [0050]     An aspect of the present invention is to form the boundary region  15   c  in the organic semiconductor layer  15  using the above characteristic of the organic semiconductor layer  15 . According to the formation of the boundary region  15   c , a patterning effect that separates the adjacent TFTs from each other without performing an additional patterning can be obtained.  
         [0051]     As depicted in  FIG. 1 , when forming a multiple number of TFTs  10  and  10 ′ for constructing a particular circuit, the boundary region  15   c  is formed on the surface-treated portion  16  by forming a predetermined surface-treated portion  16  on a region for forming the boundary region  15   c  among surfaces of the gate insulating film  13  on which the organic semiconductor layer  15  is formed.  
         [0052]     The surface-treated portion  16  has a rougher surface than other portions by plasma processing a surface of an insulating film, such as the gate insulating film  13 . The magnitude of surface roughness difference can be determined by considering the resistance in the boundary region  15   c  and can be in a range of 2-50 times greater than that of the channel region  15   a.    
         [0053]     In this manner, the boundary region  15   c  having a smaller grain size than other portions can be formed in the organic semiconductor layer  15  by forming the surface-treated portion  16  directly under the organic semiconductor layer  15  around the channel regions  15   a  and  15   a′  of the TFTs  10  and  10 ′, and eventually, a patterning effect between the adjacent TFTs can be obtained.  
         [0054]     As shown in  FIG. 1 , in the case of the channel region  15   a , large size grains are formed since the channel region  15   a  is located close to a portion of the gate insulating film  13  having less surface roughness than that of the surface-treated portion  16 , thereby obtaining a high mobility characteristic.  
         [0055]     The surface-treated portion  16  for forming the boundary region  15   c  is not necessarily formed on the gate insulating film  13 , but can be formed anywhere as long as it contacts the lower part of the organic semiconductor layer  15 .  
         [0056]      FIG. 4  is a cross-sectional view illustrating a structure of a TFT according to another embodiment of the present invention, in which the surface-treated portion  16  is formed on an upper part of an additional protection film  17 . In  FIG. 4 , the protection film  17  is formed to cover the source/drain electrodes  14  and  14 ′ and the channel regions  15   a  and  15   a′  can be formed in predetermined openings  17   a  and  17   a′  in the protection film  17 . At this time, the organic semiconductor layer  15  is formed on the protection film  17 .  
         [0057]     Inorganic materials that can be used for forming the gate insulating film  13  or the protection film  17 , on which the surface-treated portion  16  can be formed, can be selected form the group consisting of SiO 2 , SiNx, Al 2 O 3 , TiO 2 , Ta 2 O 5 , HfO 2 , ZrO 2 , BST, or PZT, and organic materials can be a ordinary polymer, such as PMMA or PS, polymer derivatives having phenol group, acryl polymers, imid polymers, arylester polymers, amide polymers, fluoride polymers, p-xylene polymers, vinyl alcohol polymers, and a blend of these materials. An inorganic-organic stacking film can also be used.  
         [0058]     SAM, such as OTS or HMDS, or coating a super thin film of fluoride polymer or ordinary polymer can be processed on the uppermost part of the gate insulating film  13  or the protection film  17  adjacent to the organic semiconductor layer  15 .  
         [0059]      FIG. 5  is a cross-sectional view illustrating a structure of a TFT according to still another embodiment of the present invention, in which the surface-treated portion  16  is formed on the substrate  11 . This is a case when the surface-treated portion  16  is applied to a staggered structure TFT.  
         [0060]     That is, the source/drain electrodes  14  and  14 ′ are formed on the substrate  11  and the organic semiconductor layer  15  is formed to cover the source/drain electrodes  14  and  14 ′. The gate insulating film  13  is formed to cover the organic semiconductor layer  15 , and the gate electrodes  12  and  12 ′ are formed on regions corresponding to the channel regions  15   a  and  15   a′  of the organic semiconductor layer  15 .  
         [0061]     At this time, the boundary region  15   c  between the TFTs  10  and  10 ′ can be formed by interposing the surface-treated portion  16  between the TFTs  10  and  10 ′.  
         [0062]     The uppermost part of the substrate  11  adjacent to the organic semiconductor layer  15  can be SAM processed, such as OTS or HMDS, or can be coated with a super thin film of a fluoride polymer or an ordinary polymer.  
         [0063]     The surface-treated portion  16  can also be applied to a variety of TFT structures.  
         [0064]     The boundary region  15   c  of the present invention cannot only be obtained by the surface-treated portion  16  formed in the gate insulating film  13  or the protection film  17 .  
         [0065]     That is, as depicted in  FIGS. 6 and 7 , the boundary region  15   c  is formed on a metal pattern  18  by forming the metal pattern  18  around the channel region  15   a . The metal pattern  18  has a greater roughness than the gate insulating film  13  or the protection film  17 , thereby forming the boundary region  15   c  by the aforementioned principle.  
         [0066]     Accordingly, the patterning effect of the organic semiconductor layer  15  can be obtained by forming the boundary region  15   c  between the adjacent TFTs  10  and  10 ′ by the metal pattern  18 .  
         [0067]     At this time, as depicted in  FIG. 6  and  7 , the metal pattern  18  can also be formed on the gate insulating film  13  and on the additional protection film  17 , respectively.  
         [0068]     The metal pattern  18  can also be formed by depositing an additional metal film or a metal film like the source/drain electrodes or wirings.  
         [0069]     The metal pattern  18  can also be applied to a staggered TFT structure as depicted in  FIG. 5 . That is, in the staggered TFT structure in  FIG. 5 , the boundary region  15   c  can be formed by forming the metal pattern  18  on the substrate  11 .  
         [0070]     The TFT according to the present invention can be formed not only on a stacking structure as described above but also on a variety of stacking structures.  
         [0071]     The structure of the TFT as described above can be applied to flat display devices, such as LCDs or OELD display devices.  
         [0072]     As an example,  FIG. 8  is a cross-sectional view illustrating an OELD device to which the TFT of  FIG. 1  is applied.  
         [0073]     In  FIG. 8 , one sub-pixel of the OELD is depicted. Each sub-pixel includes the OELD (hereinafter, EL device) as a self-luminant device and at least more than one TFT. The sub-pixel also includes an additional capacitor (not shown).  
         [0074]     The OELD can have a variety of pixel patterns according to the color of the EL device (OLED). The OELD preferably includes sub-pixels of red, green, and blue.  
         [0075]     Each of the sub-pixels of red R, green G, and blue B hasa TFT structure as depicted in  FIG. 8 , an EL device (OLED) as a self-luminant, and a TFT. The TFT can be the TFT according to the aforementioned embodiments of the present invention. However, the TFT is not limited thereto, but it can include a variety of structures.  
         [0076]     As shown in  FIG. 8 , the aforementioned TFT is disposed on an insulating substrate  21 .  
         [0077]     As depicted in  FIG. 8 , the TFT  20  includes a gate electrode  22  having a predetermined pattern on a substrate  21 , a gate insulating film  23  formed to cover the gate electrode  22 , and source/drain electrodes  24  on the gate insulating film  23 . At this time, as described above, a surface-treated portion  26  (not shown) is formed on the gate insulating film  23 . The detailed descriptions of the surface-treated portion  26  will be omitted since the embodiments are the same as in the above descriptions.  
         [0078]     Upper parts of the source/drain electrodes  24  and the surface-treated portion  26  are covered by an organic semiconductor layer  25 .  
         [0079]     The organic semiconductor layer  25  includes source/drain regions  25   b  and a channel region  25   a  that connects the source/drain regions  25   b . A boundary region  25   c  is formed on the surface-treated portion  26  in the organic semiconductor layer  25 .  
         [0080]     A passivation film  28  is formed to cover the TFT  20  after forming the organic semiconductor layer  25 . The passivation film  28  is formed in a single or a multiple layer, and can be formed of an organic material, an inorganic material, or a composite of organic/inorganic materials.  
         [0081]     A pixel electrode  31  as one electrode of an EL device  30  is formed on the passivation film  28  and a defining layer  29  is formed on the pixel electrode  31 . Afterward, an organic light emitting film  32  of the EL device  30  is formed after forming a predetermined opening  29   a  in the defining layer  29 .  
         [0082]     The EL device  30  displays a predetermined image information by emitting red, green, or blue light according to the current flow, and comprises the pixel electrode  31  connected to one of the source/drain electrodes  24  of the TFT  20 , a opposing electrode  33  formed to cover the entire pixels, and the organic light emitting film  32  that emits light and is disposed between the pixel electrode  31  and the opposing electrode  33 .  
         [0083]     The pixel electrode  31  and the opposing electrode  33  are insulated from each other by the organic light emitting film  32 , and light is emitted form the organic light emitting film  32  by applying a voltage having different polarities to the organic light emitting film  32 .  
         [0084]     The organic light emitting film  32  can be formed of a low molecule organic or a polymer organic film. When it is formed of a low molecule organic film, 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) can be stacked in a single or a multiple layer structure. The organic light emitting film  32  can be formed of an organic material selected from the group consisting of copper phthalocyanine (CuPc), (N,N′-Di(naphthalene-1-yl)-N,N′-diphenyl-benzidine (NPB), or tris-8-hydroxyquinoline aluminum)(Alq3). The low molecule organic film is formed by a vacuum deposition method.  
         [0085]     In the case of the polymer organic film, the organic light emitting film  32  can have a structure that includes a HTL and an EML. At this time, a PEDOT is used as the HTL and an organic polymer, such as Poly-Phenylenevinylene (PPV) and Polyfluorene group, can be used as the EML, and the poltmer organic film can be formed by a screen printing method or an ink jet printing method.  
         [0086]     The organic films are not limited thereto, but they can be applied to a variety of embodiments.  
         [0087]     The pixel electrode  31  can function as an anode and the opposing electrode  33  can function as a cathode, but the polarity of the pixel electrode  31  and the facing electrode  33  can be reversed.  
         [0088]     The present invention is not limited to the above structure, but a variety of structures of the OELD can be applied.  
         [0089]     However, in the case of an LCD, the manufacturing of a lower substrate of the LCD device is completed by forming a lower orientation film (not shown) that covers the pixel electrode  31 .  
         [0090]     As described above, the TFT according to the present invention can be mounted on each of the pixels as depicted in  FIG. 8  or can be mounted on a driver circuit (not shown) that does not implement an image.  
         [0091]     A flexible plastic substrate is suitable for the substrate  21  of the OELD device.  
         [0092]     According to the present invention, the following effects can be obtained.  
         [0093]     First, a patterning effect that separates TFTs adjacent to each other can be obtained by the grain size difference without performing an additional patterning process on an organic semiconductor layer. Therefore, a complicated patterning process can be omitted.  
         [0094]     Second, the reduction of characteristics of an active channel can be minimized since a dry or wet etching process is not performed.  
         [0095]     Third, the processing time can be reduced and the efficiency of process can be increased since it is unnecessary to etch the entire surface of the organic semiconductor layer except the active channel region. Also, since a wet etching process accompanied by the patterning process is not performed, the process can be simplified and the efficiency thereof can be increased.  
         [0096]     Fourth, a leakage current can be reduced by separating the channel region from the adjacent TFTs.  
         [0097]     Fifth, the mobility characteristic can be improved by increasing the grain size of the channel region.  
         [0098]     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 can be made therein without departing from the spirit and scope of the present invention as defined by the following claims.