Abstract:
An organic semiconductor device is provided. A conductive gate layer and a gate dielectric layer are formed on a substrate. Patterned metal layers are formed on the gate dielectric layer beside the conductive gate layer. An electrode modified layer is formed on a top surface and sidewall of each of the patterned metal layer. The patterned metal layers and the electrode modified layers formed thereon serve a source and a drain. An organic semiconductor layer is formed on the source and the drain.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the priority benefit of Taiwan application serial no. 95127931, filed Jul. 31, 2006. All disclosure of the Taiwan application is incorporated herein by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to an integrated circuit and a method of fabricating the same, and more particularly, to an organic semiconductor device and a method of fabricating the same. 
         [0004]    2. Description of Related Art 
         [0005]    An organic thin film transistor (OTFT) is fabricated by the material comprising organic conjugate polymer or oligomer. Compared with the traditional inorganic transistor, the OTFT can be fabricated under a relative low temperature, thus the lighter, thinner, and cheaper plastic can be used as the material of the substrate to replace glass. In addition, the fabricating process of an OTFT is comparatively simple and has development potential. 
         [0006]    Though OTFT has the above described advantages, some drawbacks such as slow carrier mobility and high driving voltage are needed to be solved. The main reason that the carrier mobility is very slow is: the grain size of the organic semiconductor of the active layer is varied along with the material property and the surface roughness of the underneath layer; boundaries exist between small grains, and these boundaries hinder the transition of the carriers. Thus, the carrier mobility is slowed down, and electrical characteristics of devices are affected, thereby restricting the development and applications of the OTFT. 
         [0007]    Currently, major researches are focused on how to have the organic semiconductor of the active layer exist in the form of single crystal or grain having larger size. One of the remarkable methods is to modify the property of the surface where the organic semiconductor is deposited; that is, the dielectric layer is covered by a middle layer which is capable of improving the crystal phase of the organic semiconductor. However, the grains formed on the surface and the boundaries of the metal electrodes are still small. Therefore, some researches involving forming a single layer of self-align material (SAM) on the surface of the metal layer or modifying the semiconductor material to help the semiconductor grain arrangement are developed. However, the single layer of self-align material has disadvantages of easily vaporizing and unstable quality. The method of modifying the semiconductor material has a drawback of affecting the semiconductor material property. 
       SUMMARY OF THE INVENTION 
       [0008]    The present invention is directed to an organic semiconductor device and a method for fabricating the same having higher carrier mobility to reduce power consuming. 
         [0009]    The present invention is also directed to an organic semiconductor device and a method for fabricating the same which can change the arrangement of the organic semiconductor grains on the surface and the boundaries of the metal electrode and increase the grain size. 
         [0010]    The present invention provides a method of fabricating an organic semiconductor device. A gate conductive layer is formed on a substrate, and then a gate dielectric layer is formed. Next, patterned metal layers are formed on the gate dielectric layer beside the gate conductive layer. Then, an electrode modified layer is formed on the surface and the sidewall of each patterned metal layer, and the patterned metal layers and the electrode modified layers formed thereon serve a source and a drain. Thereafter, an organic semiconductor layer is formed on the source and the drain to be an active layer. 
         [0011]    The present invention provides an organic semiconductor device comprising a gate conductive layer, a gate dielectric layer, a source and a drain, and an active layer. The gate conductive layer is disposed on the substrate. The gate dielectric layer covers the substrate and the gate conductive layer. The source and the drain are disposed on the gate dielectric layer beside the gate conductive layer, and the source and the drain are formed of the patterned metal layers and the electrode modified layers covering on the surface and the sidewall of the patterned metal layers. The active layer covers a portion of the source and the drain and fills a gap between the source and the drain. 
         [0012]    The present invention provides an organic semiconductor device comprising two electrodes and an organic semiconductor layer. Each electrode includes a patterned metal layer and an electrode modified layer covering on the surface and the sidewall of the patterned metal layer. The organic semiconductor layer is disposed between the two electrodes and extends to cover a portion of the electrode modified layers. 
         [0013]    In the present invention, an organic conductive layer is added between the metal electrode and the organic semiconductor active layer, thereby the grains of the organic semiconductor active layer on the metal electrode become larger, such that the carrier mobility of the device can be improved. 
         [0014]    The electrode is formed of the organic conductive layer and the metal layer, and therefore its work function can match the semiconductor material more, and it also can compensate the insufficient conductivity problem when only the conductive polymer is used as the material of the electrode. 
         [0015]    The method for forming the organic conductive layer can be coating a conductive polymer electrode material with a fully coating process and then patterning the conductive polymer electrode material by laser, thereby its surface is more planar compared with that of layers formed with inkjet printing or screen printing. 
         [0016]    Various specific embodiments of the present invention are disclosed below, illustrating examples of various possible implementations of the concepts of the present invention. The following description is made for the purpose of illustrating the general principles of the invention and should not be taken in a limiting sense. The scope of the invention is best determined by reference to the appended claims. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]      FIGS. 1A to 1D  are cross-sectional views illustrating a method for fabricating an organic semiconductor device according to an embodiment of the present invention. 
           [0018]      FIGS. 2A to 2C  are cross-sectional views illustrating a method for fabricating an organic semiconductor device according to another embodiment of the present invention. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0019]    In the present invention, an organic conductive layer is added between the metal electrode and the organic semiconductor active layer, and it has a work function matching with the semiconductor material. In addition, the present invention can also help the arrangement of the organic semiconductor grains and make the grains of the organic semiconductor active layer on the metal electrode become larger, so as to improve the carrier mobility of the device. The present invention can be applied to the organic semiconductor devices, and is described as follows. 
         [0020]      FIGS. 1A to 1D  are cross-sectional views illustrating a method for fabricating an organic semiconductor device according to an embodiment of the present invention. 
         [0021]    Please refer to  FIG. 1A , a gate conductive layer  102  is formed on a substrate  100 . The substrate  100  can be a flexible substrate or a rigid substrate, wherein the material of the flexible substrate is plastic, for example, and the material of the rigid substrate is silicon, glass or quartz, for example. The gate conductive layer  102  is formed by forming a conductive layer, such as a polysilicon layer or a metal layer, on the substrate  100 , and then patterning the conductive layer by a photolithography and etching process. 
         [0022]    Next, a gate dielectric layer  104  is formed over the substrate  100 , and the material of the gate dielectric layer  104  is an inorganic material or a polymer material having a dielectric constant larger than 3, or a high dielectric constant material having a higher dielectric constant. The gate dielectric layer  104  can be formed by spin coating or spin-slide coating. 
         [0023]    Thereafter, metal layers  106  and  108  are formed on the gate dielectric layer  104 . The metal layers  106 ,  108  can be formed of a single metal material, such as gold or silver, or an alloy composed of two or more metal materials, such as Ti—Al—Ti. The metal layers  106  and  108  can be formed by depositing process with a shallow mask. 
         [0024]    Next, please refer to  FIG. 1B , an electrode modified material layer  110  is formed over the substrate  100 . The material of the electrode modified material layer  110  is, for example, a conductive polymer material, such as poly(3,4-ethylenedioxythiophene), poly(styrenesulfonate)(PEDOT:PSS), polyaniline or polypyrrole, and its thickness is, for example, from 500 angstrom to 1500 angstrom. The electrode modified material layer  110  can be coated on the metal electrodes  106 ,  108  and on the gate dielectric layer  104  between the metal electrodes  106 , 108  by spin coating. 
         [0025]    Then, please refer to  FIG. 1C , the electrode modified material layer  110  is patterned to form electrode modified layers  110   a  and  110   b  covering the top surface and the sidewall of the metal layers  106 ,  108 , such that the electrode modified layer  110   a  and the metal electrode  106  form a source  120 , and the electrode modified layer  110   b  and the metal electrode  108  form a drain  130 . The electrode modified material layer  110  is patterned by, for example, laser  112 , screen printing or inkjet printing, to remove a portion of the electrode modified material layer  110  positioned between the metal layers  106  and  108  and remain the electrode modified layers  110   a ,  110   b  on the top surface and the sidewall of the metal electrodes  106 ,  108 . 
         [0026]    Please refer to  FIG. 1D , an active layer  114  is formed over the substrate  100  to cover a portion of the source  120  and the drain  130  and fill the gap  113  between the source  120  and the drain  130 . The material of the active layer  114  is, for example, an organic semiconductor material, such as pentacene or poly(3-hexylthiophene) (P3HT). The active layer  114  is formed by, for example, thermal evaporation or solution process which is a coating process, such as a spin coating process, to form a film layer, and then patterning the film layer by photolithography and etching process. In addition, the active layer  114  can also be formed with a direct deposition patterning process, such as an inkjet printing process, a contact printing process or the like. 
         [0027]      FIGS. 2A to 2C  are cross-sectional views illustrating a method for fabricating an organic semiconductor device according to another embodiment of the present invention. 
         [0028]    Please refer to  FIG. 2A , in another embodiment, a gate conductive layer  102 , a gate dielectric layer  104  and metal layers  106 ,  108  are formed over the substrate  100  according to the method described in the foregoing embodiment. 
         [0029]    Please refer to  FIG. 2B , before forming the electrode modified material layer  110 , a middle layer  116  is formed on the gate dielectric layer  104  between the metal layers  106 ,  108 . The material of the middle layer  116  is, for example, octadecyltrichlorosilane (OTS) monolayer, polyimide or polymethyl methacrylate, and its thickness is between 500 angstrom and 1500 angstrom. The middle layer  116  is formed, by forming a film layer with a spin coating process, and then patterning the film layer with a photolithography and etching process. In addition, the middle layer  116  can also be formed with a direct deposition patterning process, such as an inkjet printing process, a contact printing process or the like. The middle layer  116  would change the arrangement of the organic semiconductor grains of the active layer subsequently formed covering the gate dielectric layer  104 . After forming the middle layer  116 , an electrode modified material layer  110  is formed with the method described above. 
         [0030]    After that, please refer to  FIG. 2C , the electrode modified material layer  110  is patterned with the method described above to form an electrode modified layer  110   a  and an electrode modified layer  110   b , wherein the electrode modified layer  110   a  and the metal electrode  106  form a source  120  and the electrode modified layer  110   b  and the metal electrode  108  form a drain  130 . Next, an active layer  114  is formed with the method described above. 
         [0031]    Generally, the grain size of the organic semiconductor on the silicon oxide layer is about 0.2-0.5 μm, however, it would be reduced significantly if the organic semiconductor is formed on the metal electrode, such as Au, such that the electron mobility of the bottom contact device is about equal or less than 0.16 cm2V-1s −1 . In the present invention, an organic conductive layer is added between the metal layer and the organic semiconductor layer, such that the grains of the organic semiconductor of the active layer become larger, and the work function of the organic conductive layer matches with that of the semiconductor material. Hence, the electron mobility can achieve about 0.48 cm2V-1s −1  or more. That is, the electron mobility can be increased by 3 times. In addition, the conductive polymer material used as the electrode modified layer can be formed by coating a film layer on the metal electrode by spin coating or printing, and then patterning the film layer with laser, and therefore the formed electrode modified layer has a planar surface. In addition, the method for forming the electrode modified layer is simple and the electrode modified layer does not have the disadvantages of easily vaporizing and unstable quality. 
         [0032]    The above description provides a full and complete description of the preferred embodiments of the present invention. Various modifications, alternate construction, and equivalent may be made by those skilled in the art without changing the scope or spirit of the invention. Accordingly, the above description and illustrations should not be construed as limiting the scope of the invention which is defined by the following claims.