BRIEF DESCRIPTION OF THE DRAWINGS
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.
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
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.
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.
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.
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.
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.
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.
Then, please refer to FIG. 1C, the electrode modified material layer 110 is patterned to form electrode modified layers 110a and 110b covering the top surface and the sidewall of the metal layers 106, 108, such that the electrode modified layer 110a and the metal electrode 106 form a source 120, and the electrode modified layer 110b 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 110a, 110b on the top surface and the sidewall of the metal electrodes 106, 108.
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.
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.
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.
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.
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 110a and an electrode modified layer 110b, wherein the electrode modified layer 110a and the metal electrode 106 form a source 120 and the electrode modified layer 110b and the metal electrode 108 form a drain 130. Next, an active layer 114 is formed with the method described above.
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.
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.
Patent Application
20080032440
