Abstract:
An LTPS-LCD structure and a method for manufacturing the structure are provided. The structure comprises a substrate where a plurality of pixels are formed thereon. Each of these pixels comprises a control area, a capacitance area, and a display area. The structure is initially formed with a transparent electrode on the substrate, followed by a control device, a capacitance storage device. The display unit is then formed on the control area, the capacitance area, and the display area, respectively. As a result, the capacitance of the structure can be enhanced and the manufacturing processes of masks can be reduced.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
       [0001]    Not applicable. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to an LCD structure and a method for manufacturing the structure. In particular, the invention relates to an LTPS-TFT LCD structure and a method for manufacturing the structure to reduce photolithography processes with masks and simultaneously enhance pixel capacitance. 
         [0004]    2. Descriptions of the Related Art 
         [0005]    Liquid crystal displays (LCDs) are mainstream products on the display market. Not only do LCDs save power and emit low radiation, they are also lightweight and portable. Technologies of thin-film-transistor LCD (TFT-LCD) can be classified into two groups: amorphous silicon (α-Si) and poly-silicon (Poly-Si). The technology and techniques of α-Si are fully developed and frequently used in TFT-LCDs on the display market. 
         [0006]    However, low temperature poly silicon (LTPS) is a recent and novel technology for manufacturing Poly-Si LCDs. In comparison with conventional α-Si LCDs, carrier mobility on the LTPS TFT is at least two hundred times higher than that on the α-Si TFT due to its characteristics. The displays which utilize LTPS technology also have higher performance, with shorter response time and greater brightness, resolution, and color saturation. Therefore, LTPS-LCD can present images with higher display quality. Moreover, the physical structure and elements in the LTPS-LCDs can be minimized, so the TFT module area is at least 50% smaller. Thus, LTPS-LCDs can be thinner and lighter to reduce power exhausting. The size advantage of the TFT modules also reduces manufacturing costs of the LTPS-LCDs as well. Because of the many advantages present by LTPS technology, LTPS-LCDs attract lots of attentions on the LCD market. 
         [0007]    In the conventional LTPS photolithography manufacturing processes, six masks are usually involved. These processes for manufacturing an LPTS display structure  10  are outlined in  FIGS. 1A˜1F . For illustration, a TFT  11  and a capacitance storage device  13  are merely shown in the figures. Firstly,  FIG. 1A  shows the photolithography process with the first mask. Poly-silicon islands  110 ,  130  are formed onto a substrate  100  to function as fundamental materials for the TFT  11  and the capacitance storage device  13 . 
         [0008]    Referring to  FIG. 1B , the photolithography process with the second mask is illustrated. A lower insulator layer  12  is formed to cover the aforesaid poly-silicon islands  110 ,  130 . Then, first conductive layers  113 ,  133  are respectively formed on the lower insulator layer  12 . Subsequently, as shown the arrows in  FIG. 1B , the poly-silicon islands  110  are doped with P+ and P− ions to turn into a source/drain structure. 
         [0009]    After that, as shown in  FIG. 1C , an upper insulator layer  14  covers the aforesaid first conductive layer  113 ,  133  and the lower insulator layer  12 . Two contact holes  141  are then formed by the photolithography process with the third mask. The contact holes  141  are utilized to expose the source/drain structure for following electrical conduction. 
         [0010]    The photolithography process with the fourth mask is shown in  FIG. 1D . Second conductive layers  115 ,  135  are formed, in which the second conductive layer  115  connects the source/drain structure within the contact hole  141 . The other second conductive layer  135  is correspondingly formed above the first conductive layer  133 . As a result, a MIM (metal-insulator-metal) capacitance is formed between the first conductive layer  133  and the second conductive layer  135 . 
         [0011]    Referring to  FIG. 1E , a passivation layer  16  is formed to cover the above mentioned elements. Then, the photolithography process with the fifth mask can be proceeded to form a contact hole  161  for partially exposing the second conductive layer  115  which is connecting with the drain structure. 
         [0012]    Finally, a transparent electrode  17  is formed by the photolithography process with the sixth mask. The transparent electrode  17  electrically connects with the second conductive layer  115  at the contact hole  161  and further connects to a display area (not shown) of the pixel for providing the required electric fields. 
         [0013]    However, the conventional LTPS display structure  10  still has disadvantageous limitations. As shown in  FIG. 1B , the poly-silicon island  130  that is sheltered from the first conductive layer  133  cannot be doped during the doping process. Consequently, the final product would not have any effective capacitance between the first conductive layer  133  and the poly-silicon island  130 . As a result, the capacitance provided from the display structure  10  is substantially reduced. Furthermore, because of the complicated manufacturing processes of the conventional structure, more photolithography processes with masks are required, raising the cost of manufacturing. 
         [0014]    Given the above, an LTPS-LCD structure which can be made from simplified photolithography processes and promote capacitances needs to be developed in this field. 
       SUMMARY OF THE INVENTION 
       [0015]    The primary objective of this invention is to provide an LTPS-LCD structure. By previously disposing a transparent electrode on the bottom of the display structure, an effective capacitance can be generated within the un-doped poly-silicon area. Thus, the capacitance of the final product can be promoted to benefit effective operation of the display structure. 
         [0016]    Another objective of this invention is to provide a method for manufacturing the LTPS-LCD structure. By disposing the transparent electrode during the previous photolithography process, the processes for manufacturing the entire TFT and capacitance storage device can be simplified to effectively economize costs and shorten manufacturing periods. 
         [0017]    To achieve the aforementioned objectives, an LTPS-LCD structure is provided in the present invention. The structure comprises a substrate, a transparent electrode, a lower insulator layer, a control device, a first conductive layer, an upper insulator layer, and a second conductive layer. The substrate is formed with a plurality of pixel areas each including a control area, a capacitance area, and a display area. The transparent electrode is formed on the substrate that corresponds to the display area, the control area, and the capacitance area. The lower insulator layer is formed on the transparent electrode that corresponds to the control area. The control device is formed on the lower insulator layer that corresponds to the control area. The first conductive layer is partially formed on the control device and the transparent electrode that corresponds to the control area and the capacitance area respectively. The upper insulator layer at least partially covers the control device and the first conductive layer. The second conductive layer at least partially covers the upper insulator layer for forming a capacitance storage device with the first conductive layer on the capacitance area, whereby it electrically connects the control device to the transparent electrode disposed on the display area. 
         [0018]    A method for manufacturing the aforementioned LTPS-LCD structure is also provided in the present invention. The method comprises the following steps: forming the transparent electrode on the display area, the control area, and the capacitance area of the substrate; forming a silicon-oxide insulator layer that corresponds to the control area; locally forming a first conductive layer on the silicon-oxide insulator layer and the transparent electrode that corresponds to the control area and the capacitance area, and forming the control device on the control area; forming an upper insulator layer which at least partially covering the control device and the first conductive layer; and forming a second conductive layer which at least partially covering the upper insulator layer to form a capacitance storage device with the first conductive layer. 
         [0019]    The detailed technology and preferred embodiments implemented for the subject invention are described in the following paragraphs accompanying the appended figures for people skilled in this field to well appreciate the features of the claimed invention. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]      FIGS. 1A to 1F  are schematic views illustrating the manufacturing processes of the conventional LTPS display structure; 
           [0021]      FIGS. 2A and 2B  are schematic views illustrating the photolithography process with the first mask of a preferred embodiment of the present invention; 
           [0022]      FIG. 3  is a schematic view illustrating the photolithography process with the second mask of the preferred embodiment of the present invention; 
           [0023]      FIG. 4  is a schematic view illustrating the photolithography process with the third mask of the preferred embodiment of the present invention; 
           [0024]      FIG. 5  is a schematic view illustrating the photolithography process with the fourth mask of the preferred embodiment of the present invention; and 
           [0025]      FIG. 6  is a schematic view illustrating the photolithography process with the fifth mask of the preferred embodiment of the present invention. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0026]    A preferred embodiment of the LTPS-LCD structure of the present invention is shown in  FIG. 6 , and preferred processes for manufacturing the structure are shown from  FIG. 2A  through  FIG. 6 . 
         [0027]    The LTPS-LCD structure  20  of the present invention comprises a control device  51 , a capacitance storage device  53 , and a pixel unit  55 . Referring to  FIGS. 2A and 2B , the structure  20  comprises a substrate  200  which is formed with a plurality of pixel areas. To specifically disclose the present invention, only a pixel area  30  is representatively shown in the figures. Each pixel area  30  includes a control area  31 , a capacitance area  33 , and a display area  35 . 
         [0028]    As shown in  FIG. 2B , a transparent electrode  21  is previously formed on the control area  31 , the capacitance area  33 , and the display area  35  of the substrate  200 . Preferably, the transparent electrode  21  is made of Indium Tin Oxide (ITO). Then, a silicon-oxide insulator layer  22  (or namely a lower insulator layer) is formed on the transparent electrode  21  that corresponds to the control area  31 . A poly-silicon layer  23  is then formed on the silicon-oxide insulator layer  22 , wherein the silicon-oxide insulator layer  22  and the poly-silicon layer  23  are formed with a predetermined pattern. 
         [0029]    In  FIG. 2A , the above-mentioned manufacturing process is illustrated more specifically. The transparent electrode  21 , the silicon-oxide insulator layer  22 , and the poly-silicon layer  23  are successively formed on the substrate  200 , and a photolithography (etching) process is subsequently performed. That is to say, the silicon-oxide insulator layer  22  is also formed on the transparent electrode  21  that corresponds to the capacitance area  33  and the display area  35 . Similarly, the poly-silicon layer  23  is also formed on the silicon-oxide insulator layer  22  that corresponds to the control area  31 , the capacitance area  33 , and the display area  35 . Subsequently, photo-resist layers  41 ,  43 ,  45  are respectively disposed onto the poly-silicon layer  23  corresponding to the control area  31 , the capacitance area  33 , and the display area  35 . Preferably, the photo-resist layers  41 ,  43 ,  45  are made from a half-tone mask. It is further noted that the photo-resist layers  41 ,  43 ,  45  have different predetermined thicknesses due to the half-tone mask process. For example, a photolithography process with the first mask of the present invention is provided by etching the photo-resist layer  41  which has a greater thickness. Because the photo-resist layers  43  and  45  are thinner, the poly-silicon layer  23  and the silicon-oxide insulator layer  22  on the display area  35  can be removed with etching, leaving only the transparent electrode  21 . Similarly, the poly-silicon layer  23  on the capacitance area  33  can be removed as well. Preferably, due to the specific thickness of the photo-resist layer  43 , the silicon-oxide insulator layer  22  on the capacitance area  22  can be removed completely after etching. As a result of these processes, the capacitance storage device  53  of the final product can have a higher capacitance. 
         [0030]    With reference to  FIG. 3 , first conductive layers  25 ,  25 ′ are partially formed on the transparent electrode  21  that corresponds to the control area  31  and the capacitance area  33 . In this case, the first conductive layer  25  is formed as a gate structure on the control area  31 . More specifically, a mid-insulator layer  24  is previously formed that corresponds to the control area  31 , the capacitance area  33 , and the display area  35 . Then, the photolithography process with the second mask of the present invention is performed. The first conductive layers  25 ,  25 ′ are respectively formed that corresponds to the control area  31  and the capacitance area  33 . Finally, the control device  51  is doped into a source electrode  231  and a drain electrode  232  on the control area  31 . Preferably, the control device  51  is partially performed with a lightly doped drain (LDD) process to form an LDD structure for higher conductivity. 
         [0031]    Following the aforesaid processes, an upper insulator layer  26  is formed as shown in  FIG. 4 . The upper insulator layer  26  at least partially covers the control device  51  and the first conductive layers  25 ,  25 ′. Furthermore, the upper insulator layer  26  is formed to cover the aforesaid elements. Then, two contact holes  261 ,  262  are formed by a photolithography process with the third mask. The source electrode  231  and the drain electrode  232  can be exposed from the upper insulator layer  26  and the mid-insulator layer  24  for electrical connection. 
         [0032]    The photolithography process with the fourth mask of the present invention is shown in  FIG. 5 . According to the above-mentioned structure, second conductive layers  271 ,  272  are formed to at least partially cover the upper insulator layer  26 . Accordingly, the capacitance storage device  53  is formed between the second conductive layer  272  and the first conductive layer  25 ′, and the control device  51  is electrically connected to the transparent electrode  21  on the display area  35  to form the required electric fields. More specifically, the second conductive layers  271 ,  272  connect onto the source electrode  231  and the drain electrode  232  of the control device  51  through the contact holes  261 ,  262  in the upper insulator layer  26  and the mid-insulator layer  24 . 
         [0033]    Finally, as shown in  FIG. 6 , the photolithography process with the fifth mask of the present invention forms a passivation layer  28  to cover the LTPS-LCD structure  20  on the second conductive layer  271 ,  272 . 
         [0034]    In accordance with the aforesaid manufacturing processes, the LTPS-LCD structure  20  of the present invention is obtained. On the control area  31 , the structure  20  successively comprises the substrate  200 , the transparent electrode  21 , the lower insulator layer  22 , the control device  51 , the mid-insulator layer  24 , the first conductive layer  25 , the upper insulator layer  26 , the second conductive layer  271 , and the passivation layer  28 . On the capacitance area  33 , preferably, the structure  20  successively comprises the substrate  200 , the transparent electrode  21 , the mid-insulator layer  24 , the first conductive layer  25 ′, the upper insulator layer  26 , the second conductive layer  272 , and the passivation layer  28 . However, on the display area, only the substrate  200  and the transparent electrode  21  remain. 
         [0035]    Specifically, the lower insulator layer  22  is formed on the transparent electrode  21  to correspond to the control area  31  and the capacitance area  33 . Alternatively, the lower insulator layer  22  can simply be formed on the control area  31  to generate a higher capacitance without the lower insulator layer  22  on the capacitance area  33 . Corresponding to the control area  31 , the control device  51  is formed on the lower insulator layer  22 . Preferably, the mid-insulator layer  24  is disposed under the first conductive layers  271 ,  272 . That is to say, the first conductive layer  271 ,  272  are partially formed on the control device  51  and the transparent electrode  21  that corresponds to the control area  31  and the capacitance area  33 , respectively. The upper insulator layer  26  at least partially covers the control device  51  and the first conductive layers  25 ,  25 ′. The second conductive layers  271 ,  272  at least partially cover the upper insulator layer  26 , to form the capacitance storage device  53  with the first conductive layer  25 ′ and electrically connect the control device  51  to the transparent electrode  21  on the display area  55 . 
         [0036]    Preferably, the control device  51  is a thin-film-transistor (TFT) and the lower insulator layer  22  can be the silicon-oxide insulator layer  22 . The passivation layer  28  completely covers the second conductive layer  271 ,  272 . 
         [0037]    According to the above-mentioned LTPS-LCD structure  20  of the present invention, the transparent electrode  21  is previously formed on the substrate  200 . This structure can not only enhance the efficiency of the capacitance storage device, but can also diminish the number of steps within the photolithography processes or etching processes with masks from six to five. This can substantially reduce costs and shorten manufacturing processes. 
         [0038]    The above disclosure is related to the detailed technical contents and inventive features thereof. People skilled in this field may proceed with a variety of modifications and replacements based on the disclosures and suggestions of the invention as described without departing from the characteristics thereof. Although such modifications and replacements are not fully disclosed in the above descriptions, they have substantially been covered in the following claims as appended.