Patent Document

CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This is a continuation application of U.S. patent application Ser. No. 11/352,181, filed Feb. 10, 2006, which application claims the benefit of Korean Patent Application No.2005-0011575, filed on Feb. 11, 2005, in the Korean Intellectual Property Office, the disclosures of which are incorporated herein by their references. 
     
    
     BACKGROUND 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a TFT substrate for a display apparatus and a manufacturing method of the same. 
         [0004]    2. Description of the Related Art 
         [0005]    Since an LCD is thinner, lighter, and consumes less power than a CRT, the LCD has been generally used for a flat panel display. The LCD typically comprises an upper substrate on which a common electrode and color filters are formed, a lower substrate on which pixel electrodes and thin film transistors (TFTs) are formed, and liquid crystals injected between the upper and lower substrates. 
         [0006]    A driving circuit drives the TFT corresponding to each pixel, thereby causing liquid crystal molecules to change their orientation. Such change in the orientation of the liquid crystal molecules controls the amount of light transmitted from a backlight to the color filters. 
         [0007]    The TFT comprises a gate electrode, a source electrode, a drain electrode, and a semiconductor layer forming a channel area. Amorphous silicon or polysilicon are used for the semiconductor layer, and the amorphous silicon has low off current. However, the amorphous silicon has a disadvantage in that it generates a leakage current when it is irradiated by light. The leakage current prohibits a storage capacitor from maintaining required potential, thereby generating a flickering or an afterimage. 
         [0008]    To prevent the amorphous silicon from being exposed to light of the backlight, a full island structure has been introduced which is designed to form the amorphous silicon within a gate electrode area (i.e., formed only in an area overlapping the gate electrode). However, such a structure disadvantageously has a low aperture ratio since the aperture ratio decreases as the size of the gate electrode becomes large, and such a structure also causes RC delay since RC delay increases as an area where data wiring and the gate electrode overlap becomes large. 
       SUMMARY 
       [0009]    Accordingly, it is an aspect of the present invention to provide a TFT substrate for a display apparatus having a high aperture ratio and causing less afterimages, and a manufacturing method of the same. 
         [0010]    The foregoing and/or other aspects of the present invention are also achieved by providing a TFT substrate for a display apparatus comprising a gate wiring comprising a gate electrode, a data wiring comprising a data line, a source electrode connected to the data line and a drain electrode connected to a pixel electrode, and a semiconductor layer disposed between the gate wiring and the data wiring, wherein the semiconductor layer under the drain electrode is disposed within an area of the gate electrode and the semiconductor layer under the source electrode extends outward from the gate electrode. 
         [0011]    According to an embodiment of the present invention, the semiconductor layer comprises amorphous silicon. 
         [0012]    According to another embodiment of the present invention, the TFT further comprises an ohmic contact layer disposed between the semiconductor layer and the data wiring and having the same pattern as the semiconductor layer. 
         [0013]    The foregoing and/or other aspects of the present invention are also achieved by providing a TFT substrate for a display apparatus comprising a gate wiring comprising a gate electrode, a data wiring comprising a data line, a source electrode connected to the data line and a drain electrode connected to a pixel electrode, and a semiconductor layer disposed between the gate wiring and the data wiring and forming a channel area between the source electrode and the drain electrode, wherein the semiconductor layer overlapped by the drain electrode is disposed within an area of the gate electrode, and the semiconductor layer overlapped by the source electrode extends outward from the gate electrode. 
         [0014]    The foregoing and/or other aspects of the present invention are also achieved by providing a manufacturing method for a TFT substrate for a display apparatus comprising 
         [0000]    forming a gate wiring comprising a gate electrode by depositing gate wiring material and patterning,
 
forming on the gate wiring a semiconductor layer overlapping the gate electrode partly, and
 
forming a source electrode and a drain electrode by depositing data wiring material and patterning, the semiconductor layer under the source electrode extending outward from the gate electrode and the semiconductor layer under the drain electrode being disposed within an area of the gate electrode.
 
         [0015]    According to an embodiment of the present invention, a part of the source electrode may extend outward from the gate electrode (i.e., into an area not overlapping the gate electrode) in the aforementioned embodiments. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]    The above and/or other aspects and advantages of the present invention will become apparent and more readily appreciated from the following description of the exemplary embodiments, taken in conjunction with the accompanying drawings of which: 
           [0017]      FIG. 1  is a layout view of a TFT substrate according to a first embodiment of the present invention; 
           [0018]      FIG. 2  is a sectional view taken along the II-II line of  FIG. 1 ; 
           [0019]      FIG. 3  is a layout view of a gate wiring and a semiconductor layer according to the first embodiment of the present invention; 
           [0020]      FIG. 4  is a layout view of a semiconductor layer and a data wiring according to the first embodiment of the present invention; 
           [0021]      FIG. 5  is a layout view of a gate wiring and a data wiring according to the first embodiment of the present invention; 
           [0022]      FIGS. 6A to 8B  are diagrams illustrating a manufacturing process of a TFT substrate according to the first embodiment of the present invention; 
           [0023]      FIG. 9  is a layout view of a TFT substrate according to a second embodiment of the present invention; 
           [0024]      FIG. 10  is a sectional view taken along the X-X line of  FIG. 9 ; 
           [0025]      FIG. 11  is a layout view of a TFT substrate according to a third embodiment of the present invention; and 
           [0026]      FIG. 12  is a sectional view taken along the XII-XII line of  FIG. 11 . 
       
    
    
     DETAILED DESCRIPTION 
       [0027]    Reference will now be made in detail to exemplary embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout. The embodiments are described below in order to explain the present invention by referring to the figures. 
         [0028]    A TFT substrate  1  according to a first embodiment will be described below by referring to  FIGS. 1 to 5 . 
         [0029]    Referring now to  FIGS. 1 to 4 , a gate wiring  21  and  22  is formed on an insulating substrate  11 . The gate wiring  21  and  22  comprises a gate line  21  extending in a transverse direction and a gate electrode  22  connected to the gate line  21 . 
         [0030]    A gate insulation layer  31  made of, for example, silicon nitride (SiNx), is formed on the insulating substrate  11  and covers the gate wiring  21  and  22 . 
         [0031]    A semiconductor layer  32  made of, for example, amorphous silicon, is formed on the gate insulation layer  31  of the gate electrode  22 . An ohmic contact layer  33  made of, for example, silicide or n+ hydrogenated amorphous silicon heavily doped with n-type impurity, is formed on the semiconductor layer  32 . 
         [0032]    A data wiring  41 ,  42 , and  43  is formed on the ohmic contact layer  33  and the gate insulation layer  31 . The data wiring  41 ,  42 , and  43  may have a Mo single-layered structure or a Mo/Al/Mo triple-layered structure in one example. 
         [0033]    The data wiring  41 ,  42 , and  43  is disposed in a longitudinal direction. The data wiring  41 ,  42 , and  43  comprises a data line  41  intersecting the gate line  21  and defining a pixel, a source electrode  42  branched out from the data line  41  extended to an upper part of the ohmic contact layer  33 , and a drain electrode  43  separated from the source electrode  42  and disposed on an upper part of the ohmic contact layer  33  opposite the source electrode  42 . The source electrode  42  has a U shape in one example. 
         [0034]    A passivation layer  51  is formed on the data wiring  41 ,  42 , and  43  and the semiconductor layer  32  uncovered by the data wiring  41 ,  42  and  43 . The passivation layer  51  is preferably made of silicon nitride (SiNx), a-Si:C:O or a-Si:O:F deposited by a plasma enhanced chemical vapor deposition (PECVD) process, and/or acryl-containing organic insulating material. The a-Si:C:O layer and the a-Si:O:F layer deposited by the PECVD process each have low dielectric constants, in one example being lower than 4. Therefore, such layers have little parasitic capacitance even though they are thin in thickness. Also, such layers have good adhesive properties when compared to other layers and high step coverage. Further, since such layers are made of inorganic material, they have a higher thermostability than organic insulating layers. 
         [0035]    The passivation layer  51  has a contact hole  71  exposing the drain electrode  43 . A pixel electrode  61  is formed on the passivation layer  51  and is electrically connected to the drain electrode  43  through the contact hole  71  and disposed in a pixel area. The pixel electrode  61  is made of transparent conducting material such as indium tin oxide (ITO) or indium zinc oxide (IZO). Here, the pixel electrode  61  overlaps the gate line  21 , thereby composing a storage capacitor. A storage capacitance wiring may be added in the same layer where the gate wiring  21  and  22  is disposed to increase the storage capacitance. 
         [0036]    A layout of the gate wiring  21  and  22 , the semiconductor layer  32 , and the data wiring  41 ,  42 , and  43  in the TFT substrate  1  will be further described below. 
         [0037]    Referring to  FIG. 3 , a layout of the gate wiring  21  and  22  and the semiconductor layer  32  will be described first. A large portion of the semiconductor layer  32  overlaps the gate electrode  22 , but some portions A and B of the semiconductor layer  32  do not overlap the gate electrode  22 . In such a structure, the size of the gate electrode  22  can be smaller because the gate electrode  22  does not need to cover the entire semiconductor layer  32 . The drain electrode  43  is formed on an area where the semiconductor layer  32  overlaps the gate electrode  22  entirely, and the source electrode  42  is formed on an area where the semiconductor layer  32  extends outward from the gate electrode  22  (see, e.g.,  FIG. 2 ) into an area which does not overlap the gate electrode  22 . 
         [0038]    Referring to  FIG. 4 , a layout of the semiconductor layer  32  and the data wiring  41 ,  42 , and  43  will be described. The whole source electrode  42  overlaps the semiconductor layer  32 , but only a portion of the drain electrode  43  overlaps the semiconductor layer  32 . Some portions C and D of the semiconductor layer  32  are not covered with the data wiring  41 ,  42 , and  43 , and some of such portions are not covered with the gate wiring  21  and  22 , either. The areas E and F ( FIG. 1 ) that are not covered by the gate wiring  21  and  22  or the data wiring  41 ,  42 , and  43  are exposed to the light emitted from the backlight. 
         [0039]    Referring to  FIG. 5 , a layout of the gate wiring  21  and  22  and the data wiring  41 ,  42 , and  43  will be described. A portion of the drain electrode  43  overlaps the gate electrode  22 , and a portion G of the source electrode  42  does not overlap the gate electrode  22 . 
         [0040]    Such a TFT substrate has the following advantages. 
         [0041]    First, since the semiconductor layer  32  formed under the source electrode  42  is not entirely covered by the gate electrode  22 , the size of the gate electrode  22  can be smaller than previously possible in the full island structure. Accordingly, the size of the gate electrode  22  is smaller than in a full island structure, and thus an aperture ratio is higher. 
         [0042]    Second, the RC delay between the wirings is decreased. As shown in  FIG. 5 , a portion G of the source electrode  42  is extended outward from the gate electrode  22 . Thus, the area where the source electrode  42  and the gate electrode  22  overlap becomes reduced, thereby decreasing the RC delay. 
         [0043]    Third, the afterimaging caused by a leakage current occurs less. The semiconductor layer  32  formed under the drain electrode  43  is entirely covered by the gate electrode  22  (refer to H in  FIG. 2 ) so that the leakage current from the drain electrode  43  to the source electrode  42  is not generated. On the other hand, the areas E and F ( FIG. 1 ) that are not covered by the gate electrode  22  or the source electrode  42  are exposed to the light emitted from the backlight. Accordingly, the leakage current from the source electrode  42  to the drain electrode  43  is generated, because a hole current is initially generated from the area E and F of the semiconductor layer  42  exposed to the light from the backlight. However, the leakage current from the source electrode  42  to the drain electrode  43  does not induce afterimaging because afterimages are caused by the leakage current from the drain electrode  43  to the source electrode  42 . 
         [0044]    The above embodiments can be modified in various ways. For example, the area E of the semiconductor layer  32  may overlap the gate line  21  or the data line  41  so that the area E is not exposed to the light emitted from the backlight. 
         [0045]    Referring now to  FIGS. 6A to 8B , a fabricating process of a TFT according to the first embodiment will be described.  FIG. 6B ,  FIG. 7B , and  FIG. 8B  are sectional views of the  FIG. 6A ,  FIG. 7A , and  FIG. 8A  along lines VIB-VIB, VIIB-BIIB, and VIIIB-VIIIB, respectively. 
         [0046]    First, as shown in  FIGS. 6A and 6B , the gate wiring  21  and  22  comprising the gate line  21  and the gate electrode  22  is formed on the insulating substrate  11  by depositing gate wiring material and then patterning by photolithography using a mask. The gate electrode  22  is formed smaller than in the full island structure, thereby enhancing the aperture ratio. 
         [0047]    Next, as shown in  FIGS. 7A and 7B , layer  31  made of silicon nitride, layer  32  made of amorphous silicon, and layer  33  made of amorphous silicon are deposited sequentially. Then, as shown in  FIGS. 8A and 8B , the semiconductor layer  32  and the ohmic contact layer  33  are formed on the gate insulation layer  31  over the gate electrode  22  by photolithography of layer  32  and layer  33 . A portion of the semiconductor layer  32 , on which the drain electrode  43  is to be formed, is formed within the area of the gate electrode  22 . Another portion of the semiconductor layer  32 , on which the source electrode  42  is to be formed, extends outward from the gate electrode  22 . Accordingly, the semiconductor layer  32  partially overlaps the gate electrode  22 . 
         [0048]    Afterwards, as further shown in  FIGS. 8A and 8B , the data wiring  41 ,  42 , and  43  is formed by depositing data wiring material and then patterning by photolithography using a mask. The data wiring  41 ,  42 , and  43  comprises the data line  41  intersecting the gate line  21 , the source electrode  42  connected to the data line  41  and extending over the gate electrode  22 , and the drain electrode  43  separated from and opposing the source electrode  42 . Subsequently, the doped amorphous silicon layer  33  which is not covered by the data wiring  41 ,  42 , and  43  is etched thereby dividing the doped amorphous silicon layer  33  into two parts and exposing the semiconductor layer  32  between the two divided, doped amorphous silicon layers  33 . Then, an oxygen plasma treatment is preferably performed on the exposed semiconductor layer  32  to stabilize the exposed surface. 
         [0049]    In one example, the data wiring  41 ,  42 , and  43  may have a Mo single-layered structure or a Mo/Al/Mo triple-layered structure. 
         [0050]    The source electrode  42  has a U shape, and some portions of the source electrode  42  do not overlap the gate electrode  22 . The drain electrode  43  overlaps the gate electrode  22  partly, and the semiconductor layer  32  under the drain electrode  43  is disposed within the area of the gate electrode  22 . 
         [0051]    Afterwards, as shown in  FIGS. 1 and 2 , a passivation layer  51  is formed by growing silicon nitride, a-Si:C:O, or a-Si:O:F using a chemical vapor deposition (CVD) process or coating an organic insulation layer. Next, the contact hole  71  exposing the drain electrode  33  is formed by a photolithographic process. 
         [0052]    Finally, an ITO or IZO layer is deposited and then patterned by photolithography to form the pixel electrode  61  connected to the drain electrode  33  through the contact hole  71 , resulting in accomplishing the TFT substrate  1 . 
         [0053]    A TFT substrate according to a second embodiment will be described below with reference to  FIGS. 9 and 10 . 
         [0054]    Unlike the first embodiment, a whole source electrode  42  overlaps a gate electrode  22 . Like the first embodiment, the whole semiconductor layer  32  under a drain electrode  43  overlaps the gate electrode  22 , and a semiconductor layer  32  under the source electrode  42  extends outward from the gate electrode  22 . 
         [0055]    According to the second embodiment, an area where the source electrode  42  and the gate electrode  22  overlap becomes larger, thereby increasing RC delay. However, the size of the gate electrode  22  becomes smaller than in a full island structure, thereby enhancing the aperture ratio. Moreover, a leakage current directed from the drain electrode  43  to the source electrode  42  is not generated, thereby reducing afterimaging. 
         [0056]    A TFT substrate according to a third embodiment will be described below with reference to  FIGS. 11 and 12 . 
         [0057]    Unlike the first embodiment, a channel area has a straight shape. Like the first embodiment, a whole semiconductor layer  32  under a drain electrode  43  overlaps the gate electrode  22 , and a semiconductor layer  32  under a source electrode  42  extends outward from the gate electrode  22 . 
         [0058]    According to the third embodiment, the size of the gate electrode  22  becomes smaller than in a full island structure, thereby enhancing the aperture ratio. Also, there is no leakage current directed from the drain electrode  43  to the source electrode  42 , thereby reducing afterimaging. 
         [0059]    The TFT and the TFT substrate according to the embodiment of the present invention can be employed in not only LCDs but also in organic light emitting diodes (OLEDs). 
         [0060]    Here, the OLED uses an organic material that emits light by itself when it receives an electric signal. Such an OLED having a layered structure comprises a cathode layer (pixel electrode), a hole injecting layer, a hole transporting layer, a light-emitting layer, an electron transportation layer, an electron implantation layer, and an anode layer (counter electrode). According to the embodiments of the present invention, the drain contact part of the TFT substrate is electrically connected with the cathode layer, thereby transmitting a data signal. On the other hand, the drain contact part of the TFT substrate can be electrically connected with the anode layer. 
         [0061]    Although a few embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that changes may be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims and their equivalents.

Technology Category: h