Abstract:
A system for displaying images including a display panel and a fabrication method thereof are provided. The display panel includes a substrate having a first, second and third areas, a first patterned semiconductor layer disposed over the first area of the substrate, a first insulating layer covering the first patterned semiconductor layer and the first, the second and the third areas of the substrate, a second patterned semiconductor layer disposed on the first insulating layer of the first and the third areas respectively, a second insulating layer covering the second patterned semiconductor layer and the first insulating layer, and a patterned conductive layer disposed on the second insulating layer to form a first thin-film transistor at the first area and a second thin-film transistor at the third area.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This Application claims priority of Taiwan Patent Application No. 98113283, filed on Apr. 22, 2009, the entirety of which is incorporated by reference herein. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The invention relates to a system for displaying images including a display panel, and more particularly to a capacitor layout design for an organic light emitting diode display panel and a fabrication method thereof. 
         [0004]    2. Description of the Related Art 
         [0005]    Recently, organic light emitting diode (OLED) displays have been applied widely to display elements of various products. Of OLED displays, an active matrix organic light emitting diode (AMOLED) display usually utilizes thin film transistors (TFTs) for a switching element of a pixel area and for a driving element of a light emitting element. 
         [0006]    Referring to  FIG. 1 , a schematic circuit of a pixel unit  100  of a conventional active matrix organic light emitting diode (AMOLED) display is shown. The pixel unit  100  has a driving TFT  112  for driving a light emitting element  116  such as an organic light emitting diode (OLED). In addition, a switching TFT  106  is applied to switch the states of the pixel unit  100  and a storage capacitor  108  is to store image data. A gate of the switching TFT  106  is coupled to a scanning line  102 , a drain of the switching TFT  106  is coupled to a data line  104  and a source of the switching TFT  106  is coupled to one terminal of the storage capacitor  108  and a gate of the driving TFT  112 . In addition, another terminal of the storage capacitor  108  is coupled to a power line  114  through a capacitor line  110  and coupled to a source of the driving TFT  112 . Two terminals of the light emitting element  116  are coupled to an anode  118  and a cathode  120  respectively. A drain of the driving TFT  112  is coupled to the anode  118  of the light emitting element  116 . 
         [0007]    In general, an active layer of a thin film transistor of an AMOLED display is formed by a low temperature polysilicon process to satisfy with a heat-resistant temperature of a glass substrate of the AMOLED display. The active layer formed by the low temperature polysilicon process has several advantages such as high carrier mobility, high integrated driving circuit capability and low electric charge leakage. However, in addition to the above mentioned advantages, AMOLED displays need to have high storage capacitance and high aperture ratio. 
         [0008]    Therefore, a layout design for a capacitor of an OLED display panel that satisfies the requirements for high storage capacitance and high aperture ratio is desirable. 
       BRIEF SUMMARY OF THE INVENTION 
       [0009]    The invention provides a system for displaying images including a display panel. The display panel comprises a substrate having a first area, a second area and a third area. A first patterned semiconductor layer is disposed over the first area of the substrate. A first insulating layer is disposed to cover the first patterned semiconductor layer and the first, the second and the third areas of the substrate. A second patterned semiconductor layer is disposed on the first insulating layer of the first and the third areas respectively. A second insulating layer is disposed to cover the second patterned semiconductor layer and the first insulating layer and a patterned conductive layer is disposed on the second insulating layer. A first thin-film transistor comprises the first patterned semiconductor layer, the first insulating layer and the second patterned semiconductor layer at the first area, and a second thin-film transistor comprises the second patterned semiconductor layer, the second insulating layer and the patterned conductive layer at the third area. 
         [0010]    The invention further provides a method for fabricating a system for displaying images, including forming a display panel. The method for forming the display panel comprises providing a substrate having a first area, a second area and a third area. A first patterned semiconductor layer is formed over the first area of the substrate. A first insulating layer is formed to cover the first patterned semiconductor layer and the substrate. A second patterned semiconductor layer is formed on the first insulating layer of the first and the third areas. A second insulating layer is formed to cover the second patterned semiconductor layer and a patterned conductive layer is formed on the second insulating layer of the first and the third areas. A first thin-film transistor comprises the first patterned semiconductor layer, the first insulating layer and the second patterned semiconductor layer of the first area, and a second thin-film transistor comprises the second patterned semiconductor layer, the second insulating layer and the patterned conductive layer of the third area. 
         [0011]    A detailed description is given in the following embodiments with reference to the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    The invention can be more fully understood by reading the subsequent detailed description and examples with reference to the accompanying drawings, wherein: 
           [0013]      FIG. 1  is a schematic circuit of a pixel unit  100  of a conventional active matrix organic light emitting diode (AMOLED) display; 
           [0014]      FIG. 2  is a schematic plane view of a sub-pixel area of an organic light emitting diode display panel according to an embodiment of the invention; 
           [0015]      FIG. 3  is a schematic cross section along the line  3 - 3 ′ of the display panel of  FIG. 2  according to an embodiment of the invention; 
           [0016]      FIGS. 4A-4F  are schematic cross sections of a method for fabricating the organic light emitting diode display panel of  FIG. 3  according to an embodiment of the invention; 
           [0017]      FIG. 5  is a schematic plane view of a sub-pixel area of an organic light emitting diode display panel according to another embodiment of the invention; 
           [0018]      FIG. 6  is a schematic cross section along the line  5 - 5 ′ of the display panel of  FIG. 5  according to an embodiment of the invention; and 
           [0019]      FIG. 7  schematically shows a system for displaying images including the display panel according to an embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0020]    The following description is of the best-contemplated mode of carrying out the invention. The description is provided for illustrating the general principles of the invention and is not meant to be limiting. The scope of the invention is best determined by reference to the appended claims. 
         [0021]    In an embodiment of the invention, a layout design for a capacitor of an organic light emitting diode display panel is improved to increase the storage capacitance and enhance aperture ration of the organic light emitting diode display panel. 
         [0022]    Referring to  FIG. 2 , a plane view of a sub-pixel area  400  of an organic light emitting diode display panel according to an embodiment of the invention is shown. The sub-pixel area  400  can be divided into a first area  410 , a second area  420  and a third area  430  along a cross section line  3 - 3 ′. In this embodiment, a driving TFT is disposed at the first area  410 , a capacitor is disposed at the second area  420  and a switching TFT is disposed at the third area  430 . A patterned conductive layer  402   a  of the first area  410 , a patterned conductive layer  402   b  of the second area  420  and the patterned conductive layer  402   b  of the third area  430  are used for an upper electrode layer of the capacitor. A plane view layout of the upper electrode layer is shown in  402   a  and  402   b  of  FIG. 2 . According to the capacitor layout design of this embodiment, the storage capacitance and the aperture ratio of the organic light emitting diode display panels of the invention can be enhanced. 
         [0023]    Referring to  FIG. 3 , a schematic cross section along the cross section line  3 - 3 ′ of the display panel of  FIG. 2  according to an embodiment of the invention is shown. First dielectric layers  502  and  504  are formed to cover a substrate  500 . First patterned semiconductor layers  506  and  506   a  are disposed on the first dielectric layers  502  and  504  of the first area  410 . A first insulating layer  508  is formed to cover the first patterned semiconductor layers  506  and  506   a  and the first dielectric layers  502  and  504 . Second patterned semiconductor layers  510 ,  512 ,  514 ,  514   a,    514   b  and  514   c  are formed on the first insulating layer  508  at the first area  410 , the second area  420  and the third area  430  respectively. Second insulating layers  516  and  518  are formed on the second patterned semiconductor layers  510 ,  512 ,  514 ,  514   a,    514   b  and  514   c.  Then, patterned conductive layers  402   a,    402   b  and  402   c  are formed on the second insulating layers  516  and  518  of the first area  410 , the second area  420  and the third area  430 , respectively, such that the driving TFT at the first area  410 , the capacitor at the second area  420  and the switching TFT at the third area  430  are formed. 
         [0024]    It is appreciated that in the display panel of  FIG. 3 , the patterned conductive layer  402   a  is disposed over a gate  510  of the driving TFT at the first area  410 , such that an additional capacitor is formed at the first area  410 . In addition, in this embodiment, the second patterned semiconductor layer  512  of the second area  420  and the second patterned semiconductor layer  514   a  of the third area  430  have the same first-typed conductance, for example an N-typed heavy doping polysilicon layer, and the second patterned semiconductor layers  512  and  514   a  are connected to each other. 
         [0025]    Referring to  FIGS. 4A-4F , cross sections of a method for fabricating the display panel of  FIG. 3  according to an embodiment of the invention are shown. Referring to  FIG. 4A , the substrate  500  is provided first, for example a glass substrate or the other flexible plastic substrates. Two layers of the first dielectric layers  502  and  504  are formed on the substrate  500 . Then, a first patterned intrinsic semiconductor layer  505  is formed on the first dielectric layer  504  at the first area  410 . 
         [0026]    Referring to  FIG. 4B , the first insulating layer  508  is formed to cover the first patterned intrinsic semiconductor layer  505  and the first dielectric layer  504 . A patterning process is performed to the first insulating layer  508  at the first area  410 , the second area  420  and the third area  430  to form a second patterned intrinsic semiconductor layer  509 . Then, a mask  541  is disposed on the second patterned intrinsic semiconductor layer  509  and a heavy doping process  542  is performed to the first patterned intrinsic semiconductor layer  505 . The heavy doping process  542  can be a P-typed heavy doping process or an N-typed heavy doping process. 
         [0027]    Referring to  FIGS. 4B and 4C , after a heavily doped source/drain  506   a  and a polysilicon channel  506  are formed, the mask  541  is removed. Then, a mask  544  is disposed at the first area  410  and the third area  430  for performing a first-typed conductance lightly doping process  546  to the second patterned intrinsic semiconductor layer  509 , wherein the first-typed conductance can be N-type conductance or P-type conductance. Next, referring to  FIG. 4D , a second patterned semiconductor layer  514   b  with the first-typed lightly doped conductance is formed at the first area  410 , the second area  420  and the third area  430 . Then, a mask  548  is disposed on the second patterned semiconductor layer  514   b  at the third area  430  for performing a first-typed conductance heavily doping process  550 , wherein the first-typed conductance can be N-type conductance or P-type conductance. 
         [0028]    Referring to  FIG. 4E , the mask  548  of  FIG. 4D  is removed, and the second patterned semiconductor layer  510  with the first-typed conductance is formed at the first area  410  as the gate of the driving TFT at the first area  410 . The second patterned semiconductor layer  512  with the first-typed conductance is formed at the second area  420  as the lower electrode layer of the capacitor at the second area  420 . The second patterned semiconductor layers  514   a  and  514   c  with the first-typed heavily doped conductance and the second patterned semiconductor layer  514   b  with the first-typed lightly doped conductance are formed at the third area  430  as the source/drain of the switching TFT at the third area  430 , and an undoped polysilicom channel  514  is also formed. Then, two layers of the second insulating layers  516  and  518  are formed to cover the second patterned semiconductor layers  510 ,  512 ,  514 ,  514   a,    514   b  and  514   c.    
         [0029]    Referring to  FIG. 4F , the patterned conductive layers  402   a,    402   b  and  402   c,  for example a metal layer, are formed on the second insulating layer  518  respectively. Then, an additional capacitor is formed from the patterned conductive layers  402   a  and the second patterned semiconductor layer  510  of the driving TFT at the first area  410  to increase capacitance. The patterned conductive layer  402   b  at the second area  420  is used for the upper electrode layer of the capacitor. The patterned conductive layer  402   c  at the third area  430  is used for the gate of the switching TFT. In the embodiment, the switching TFT is a double gate TFT. 
         [0030]    Referring to  FIG. 3  again, a first contact hole is formed in the first insulating layer  508 , the second insulating layers  516  and  518 , and the second dielectric layers  520  and  530 . A second contact hole  534  is formed in the second dielectric layers  520  and  530 . A third contact hole  536  is formed in the second insulating layers  516  and  518 , and the second dielectric layers  520  and  530 . Then, patterned electrode layers  560   a  and  560   b,  for example a metal layer are formed on the second dielectric layers  520  and  530 . The patterned electrode layer  560   a  is electrically connected to the second patterned semiconductor layer  514   a  at the third area  430  through the third contact hole  536 . The patterned electrode layer  560   b  is electrically connected to the source  506   a  at the first area  410 , the patterned electrode layer  402   b  at the second area  420  and the second patterned semiconductor layer  514   a  (source/drain) at the third area  430  through the first contact hole  532  and the second contact hole  534 . In the embodiment, the two TFTs at the third area  430  both have first-typed (N-typed) conductance TFTs and the second patterned semiconductor layer  512  has a first-typed heavily doped conductance, such that the second patterned semiconductor layers  512 ,  514   a,    514   b  and  514   c  at the second area  420  and the third area  430  are connected. Accordingly, the switching TFT at the third area  430  can be driven by the patterned electrode layer  560   b  and an additional electrode is not required. Therefore, the aperture ratio of the pixel can be effectively enhanced. 
         [0031]    Referring to  FIG. 5 , a plane view of a sub-pixel area  600  of an organic light emitting diode display panel according to another embodiment of the invention is shown. The difference between the capacitor plane layouts of  FIG. 5  and  FIG. 2  is that the metal layer of the capacitor of  FIG. 5  includes a protruding portion  402   d  extending to the third area  430 . 
         [0032]    Referring to  FIG. 6 , a cross section along the cross section line  5 - 5 ′ of the display panel of  FIG. 5  according to an embodiment of the invention is shown. The difference between  FIG. 6  and  FIG. 3  is that the gate  710  of the driving TFT at the first area  410  and the lower electrode layer  712  of the capacitor at the second area  420  both are the second patterned semiconductor layers of the same first-typed conductance, for example a P-typed heavily doped conductance. In addition, the second patterned semiconductor layer  514   a  at the third area  430  is a polysilicon layer of a second-typed conductance, for example an N-typed heavily doped conductance, which is not connected with the second patterned semiconductor layer  712  of the first-typed conductance, for example a P-typed heavily doped conductance, at the second area  420 . Accordingly, a fourth contact hole  538  formed in the second insulating layers  516  and  518  and the second dielectric layers  520  and  530  at the third area  430  is required to expose the second patterned semiconductor layer  514   a  of the switching TFT at the third area  430 . Then, the fourth contact hole  538  is filled with a patterned electrode layer  560   c  to electrically connect the capacitor at the second area  420  with the switching TFT at the third area  430 . Referring to  FIG. 5  again, a contact hole  540  is further formed on the second dielectric layer  530  at the second area  420  and the patterned electrode layer (not shown in  FIG. 5 ) is electrically connected to the patterned electrode layer  560   c  through the contact hole  540 . 
         [0033]    The above mentioned dielectric layers  502 ,  504 ,  520  and  530  and the insulating layers  508 ,  516  and  518  can be silicon oxide, silicon nitride or the combinations thereof. The above mentioned first patterned semiconductor layers  506  and  506   a  and the second patterned semiconductor layers  510 ,  710 ,  512 ,  712 ,  514 ,  514   a,    514   b  and  514   c  are formed by different crystallization processes. The first patterned semiconductor layers can be formed by a non-laser crystallization process, for example a solid state crystallization process, a metal-induced crystallization process, a metal-induced lateral crystallization process, an electric field enhanced metal-induced lateral crystallization process or an electric field enhanced rapid thermal annealing process. The second patterned semiconductor layers can be formed by a laser crystallization process, for example an excimer laser annealing process. 
         [0034]    Although the above mentioned embodiments are illustrated with P-typed driving TFTs and N-typed switching TFTs to explain the invention, one skilled in the art can appreciate that N-typed driving TFTs and P-typed switching TFTs also can be used in the organic light emitting diode display panel of the invention. The combinations of N-typed or P-typed doping of each polysilicon layer are not limited to the above mentioned embodiments, and can be selected and combined according to requirements. 
         [0035]    The organic light emitting diode display panel of the invention utilizes a polysilicon layer as the gate of the driving TFT and forms a metal layer over the gate of the driving TFT to form an additional capacitor. In addition, the layout design of the upper electrode layer of the capacitor can increase the storage capacitance and the aperture ratio of the display panels. Meanwhile, the organic light emitting diode display panel of the invention further utilizes non-laser crystallization processes to form the active layer of the driving TFT and utilizes laser crystallization processes to form the active layer of the switching TFT, such that light emitting uniformity of the display panels can be improved. 
         [0036]    Referring to  FIG. 7 , a system for displaying images including the display panel according to an embodiment of the invention is shown. The system for displaying images is such as an electronic device  50  or a display device  30 . The display device  30  comprises a display panel  20  and the display device  30  is for example an organic light emitting diode display and the display panel  20  is for example an organic light emitting diode display panel. In general, the display device  30  can be a part of the electronic device  50  and the electronic device  50  further comprises an input unit  40  coupled to the display device  30 , wherein the input unit  40  is operative to provide input to the display panel  20  such that the display panel  20  displays images. The system  50  for displaying images can be a mobile phone, digital camera, personal data assistant (PDA), notebook computer, desktop computer, television, car display or portable DVD player. 
         [0037]    While the invention has been described by way of example and in terms of preferred embodiment, it is to be understood that the invention is not limited thereto. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.