Patent Publication Number: US-8115215-B2

Title: Array substrate and method for manufacturing the same

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an array substrate and a method for manufacturing the same, and more particularly, to an array substrate and a method for manufacturing the same in order to reduce flickers of frames. 
     2. Description of Related Art 
     Cathode ray tube televisions are now virtually obsolete due to their bulkiness and have been replaced by thin and light display devices, such as liquid crystal displays (LCDs). Among LCDs, thin film transistor liquid crystal displays (TFT-LCDs) are of particular interest to R&amp;D in this field. 
     In TFT-LCDs, the response rate of liquid crystal (LC) is one of directions for study. In this kind of LCDs, each pixel is electrically connected with a TFT as a switch element. In a determined period, the TFT inputs electricity required for the pixel, and the input electricity is maintained until the next input of electricity required for the next scanning. Generally, the capacitance of the LC is not large. It is difficult to maintain original input electricity only by the capacitance of the LC until the next input of electricity required for the next scanning. Hence, a storage capacitor (Cs) is required to connect with the TFT of the pixel in parallel so as to increase the capacitance maintaining the electricity. In general, the Cs is disposed on the gate or on the common electrode. 
     However, the above-mentioned parallel disposition of the storage capacitor line and the gate electrode line results in a crosstalk effect generated by the data line due to the storage capacitor line. Therefore, there is a layout of the storage capacitor line and the data line disposed in parallel to reduce the crosstalk effect. As shown in  FIG. 1 , a pixel  10  is enclosed by two neighbor data lines  11  and two neighbor scan lines  12 , and has a TFT  13  serving as a switch element. Near the switch element, the data line  11  is interlaced with the scan line  12 . A storage capacitor line  14  is disposed in parallel to the data line  11 , and is used for formation and connection of storage capacitance of every pixel  10 . A pixel electrode  15  crosses over two data lines  11  and two scan lines  12 . However, in the LCDs having the storage capacitor lines  14  in parallel to the data lines  11 , while the TFT  13  is turned off, a kickback voltage (ΔVp) toward the pixel electrode  15  is generated by the scan line  12  due to a parasitic capacitance. An equation is as follows: 
               Δ   ⁢           ⁢   Vp     =       (     Vgh   -   Vgl     ⁢           )     ⁢           ⁢     Cgd     Clc   +   Ccs   +   Cgd               
wherein Vgh is a voltage of turning on the gate; Vgl is a voltage of turning off the gate; Clc is a capacitance of the LC; Ccs is a storage capacitance; and Cgd is a parasitic capacitance. If the parasitic capacitance is large, the kickback voltage (ΔVp) is large. Due to the kickback voltage (ΔVp), a feedthrough voltage under polar changes of the pixel electrode results in the flickers of a frame.
 
     SUMMARY OF THE INVENTION 
     In view of the above-mentioned shortcomings, one aspect of the present invention is directed to an array substrate comprising a substrate, a gate metal layer, a gate insulation layer, a semiconductor layer, a patterned metal layer, a flat layer, and a pixel electrode. In the array substrate, the gate metal layer is disposed on the surface of the substrate, and serves as a gate and a scan line. The gate insulation layer is disposed on the substrate, and covers the gate metal layer. In addition, the semiconductor layer is disposed on the surface of the gate insulation layer and over the gate. The patterned metal layer is disposed on the surface of the semiconductor layer comprising a source and a drain, and on the surface of the gate insulation layer comprising a storage capacitor line and a data line. The storage capacitor line is parallel to the data line, and the storage capacitor line has an extending portion parallel to the scan line. Furthermore, the flat layer covers over the substrate. The pixel electrode is disposed on the surface of the flat layer, which conducted with the drain, and overlapping parts of the scan line, parts of the data line, parts of the storage capacitor line, and parts of the extending portion. 
     The array substrate may comprise an ohmic contact layer corresponding to two sides of the gate. The ohmic contact layer is disposed between the semiconductor layer and the patterned metal layer. Additionally, the ohmic contact layer may be made of materials such as N + —Si. 
     The array substrate may comprise a protection layer disposed on the surfaces of the gate insulation layer and the patterned metal layer. 
     In the array substrate, the pixel electrode may cover the storage capacitor line. The extending portion of the storage capacitor line may substantially align with the border of the pixel electrode, or may overlap the pixel electrode. The pixel electrode may be an indium tin oxide (ITO) electrode or an indium zinc oxide (IZO) electrode. The array substrate may comprise a transparent electrode layer disposed between the ohmic contact layer and the metal layer. The transparent electrode layer is connected with the pixel electrode. The transparent electrode layer may be made of ITO or IZO. 
     Another aspect of the present invention is directed to a method for manufacturing an array substrate. The method comprises providing a substrate; forming a gate metal layer on the substrate, and the gate metal layer serving as a gate and a scan line; forming a gate insulation layer to cover the gate metal layer; forming a semiconductor layer on the surface of the gate insulation layer corresponding to the gate; forming a patterned metal layer on the surface of the semiconductor layer comprising a source and a drain separated from each other, and on the surface of the gate insulation layer comprising a storage capacitor line and a data line; forming a patterned flat layer over the substrate to cover the patterned metal layer, the gate insulation layer, and the semiconductor layer; and forming a pixel electrode on the surface of the flat layer to overlap parts of the scan line, parts of the data line, parts of the storage capacitor line, and parts of the extending portion. The storage capacitor line is parallel to the data line, and has an extending portion parallel to the scan line. The pixel electrode is conducted with the drain. 
     Hence, the storage capacitor line, applied in the present invention, extends to the overlap region of the pixel electrode and the scan line, so that the storage capacitance produced thereby may cover part of a parasitic capacitance. While the TFT is turned off, a generated kickback voltage toward the pixel electrode is reduced due to the above. Therefore, when the pixel electrode is performed with polar changes in the same gray-scale frame, the present invention can provide a solution to reduce flickers of the frame resulting from a feedthrough voltage in prior arts. 
     Other objects, advantages, and novel features of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a top view of a pixel according to a conventional liquid crystal display panel; 
         FIG. 2  is a top view of an array substrate pixel in a preferred embodiment of the present invention; 
         FIGS. 3A to 3G  show sectional views taken along line AA′ as shown in  FIG. 2  for manufacturing an array substrate pixel according to one embodiment of the present invention; 
         FIGS. 4A to 4F  show sectional views taken along line BB′ as shown in  FIG. 2  for manufacturing an array substrate pixel according to one embodiment of the present invention; 
         FIG. 5  is a top view of an enlargement of part of an array substrate pixel according to an embodiment of the present invention; 
         FIGS. 6A to 6C  show sectional views taken along line AA′ as shown in  FIG. 2  for manufacturing an array substrate pixel according to another preferred embodiment of the present invention; 
         FIG. 7A  shows a sectional view taken along line AA′ as shown in  FIG. 2  for manufacturing an array substrate pixel according to another preferred embodiment of the present invention; 
         FIG. 7B  shows a sectional view taken along line BB′ as shown in  FIG. 2 ; and 
         FIG. 8  shows a sectional view taken along line AA′ as shown in  FIG. 2  for manufacturing an array substrate pixel according to another preferred embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     By the following specific embodiment, the present invention is put into practice. One skilled in the art can easily understand other advantages and efficiency of the present invention through the disclosed content of the specification. Through other different embodiments, the present invention can be carried out or applied. According to different observations and applications, all details of the specification can be modified and changed as not going against the spirit of the present invention. 
     Embodiment 1 
       FIG. 2  is a top view of a partial array substrate of the first embodiment of the invention. The array substrate comprises a pixel electrode  29 , a TFT  30 , and a storage capacitor line  31 . The pixel electrode  29  is disposed over a pixel enclosed by two neighbor scan lines  32  and two neighbor data lines  33 . Besides, the TFT  30  comprises a source  26   a , a drain  26   b , and a gate  21   a . The source  26   a , the drain  26   b , and the gate  21   a  are respectively connected with the data line  33 , the pixel electrode  29 , and the scan line  32 . The storage capacitor line  31  is disposed in parallel with the data line  33 . Additionally, the storage capacitor line  31  has an extending portion between the scan line  32  and the pixel electrode  29 , i.e. the extending portion is parallel to the scan line  32 . The storage capacitor line  31  and the data line  33  are simultaneously formed by being patterned. 
     Illustrating the present embodiment in more detail, as shown in  FIGS. 3A to 3G , there is a flow chart of the AA′ line in the  FIG. 2  for manufacturing an array substrate pixel. Besides, as shown in  FIGS. 4A to 4F , there is a flow chart of the BB′ line in the  FIG. 2  for manufacturing an array substrate pixel. 
     With reference to  FIGS. 3A and 4A , a glass substrate  20  is provided. Then, a gate metal layer  21  is formed by photolithography and etching on the surface of the glass substrate  20 . The gate metal layer  21  is formed as the gate  21   a  in the TFT  30  and the scan line  32  in  FIG. 4A . As shown in  FIG. 2 , the TFT  30  mainly serves as a switch element. 
     With reference to  FIGS. 3B and 4B , a gate insulation layer  22  is formed on the surface of the glass substrate  20  having the gate metal layer  21  thereon. Then, a semiconductor layer  23  and an ohmic contact layer  24  are in sequence deposited and then patterned on the region corresponding to the gate  21   a.    
     Subsequently, as shown in  FIG. 3C , a transparent electrode layer  25  is formed by being patterned. The transparent electrode layer  25  may be made of ITO or IZO, but the invention is not limited the above materials and can be revised based on practical requirements. Then, patterned metal layers  26   a ,  26   b , and  26   c  are formed on the surface of the structure shown in  FIGS. 3C and 4C . The patterned metal layers  26   a  and  26   b  are separated by a gap corresponding to the gate  21   a , and they respectively serve as a source  26   a  and a drain  26   b . In addition, the source  26   a  is connected with the data line  33  (in  FIG. 2 ); the drain  26   b  is connected with the pixel electrode  29  (in  FIG. 2 ); the metal layer  26   c  is disposed on the surface of the gate insulation layer  22 , and serves as the storage capacitor line  31  and the data line  33  (in  FIG. 2 ). Moreover, the metal layer  26   c  serving as the storage capacitor line  31  extends to a region over the scan line  32 , and the extending part of the metal layer  26   c  is the extending portion of the storage capacitor line  31 . 
     In  FIG. 3D , the ohmic contact layer  24  and the transparent electrode layer  25  revealed by the gap between the source  26   a  and the drain  26   b  are etched. The formed transparent electrode layers  25   a  and  25   b  can serve as connective channels, and the formed ohmic contact layers  24   a  and  24   b  are mainly used as interface layers to enhance adhesion and conductivity of the source  26   a  and the drain  26   b.    
     As shown in  FIGS. 3E and 4D , a protection layer  27  is formed on the surface of the structure, and then the protection layer  27  is patterned to expose part of the transparent electrode layer  25   b  (in  FIG. 3E ). The protection layer  27  can be used to protect the semiconductor layer  23 . 
     With reference to  FIG. 3F , a flat layer  28  is formed on the surface of the structure, and then the flat layer  28  is patterned to form a first contact window  28   a  and a second contact window  28   b  respectively on a region exposing part of the transparent electrode layer  25   b  and on another region corresponding to part of the storage capacitor line  31  (in  FIG. 2 ). The flat layer  28  of the present embodiment may be made of any material such as organic materials, inorganic materials, or multilayer structures. As long as a material has enough thickness for planarization effect, it may serve as the flat layer. The thickness of the flat layer  28  in the present embodiment is about 25000 to 35000 Å. After patterning the flat layer  28 , the first contact window  28   a  is formed to correspond to the exposed part of the transparent electrode layer  25   b , and is mainly used to be a connector between the drain  26   b  and the pixel electrode  29  produced by the subsequent step. The second contact window  28   b  is used for formation a storage capacitor. Furthermore, as shown in  FIG. 4E , the flat layer  28  is also disposed over the scan line  32  corresponding to the BB′ line. 
     Finally, with reference to  FIGS. 3G and 4F , the pixel electrode  29  is formed on the surface of the above-mentioned structure. The pixel electrode  29  is a transparent electrode, and may be made of ITO or IZO, but the invention is not limited the above materials and can be revised based on practical requirements. As shown in  FIG. 2 , parts of the scan line  32  and the data line  33  are covered by the pixel electrode  29 . The pixel electrode  29  deposited on the revealed transparent electrode layer  25   b  (i.e. the first contact window  28   a ) is conducted with the drain  26   b . Besides, the metal layer  26   c , the protection layer  27 , and the pixel electrode  29  in the second contact window  28   b  can be formed as a capacitor to store capacitance. The metal layer  26   c  is parallel to the data line  33 , and extends to a region between the scan line  32  and the pixel electrode  29 . Consequently, the array substrate of the present invention is completed. 
     Furthermore, when the gate  21   a  is applied with a high voltage, the electricity is perceived by the semiconductor layer  23 , and turns on the TFT in a broken circuit. Then, the drain  26   b  is applied with a low voltage so that more and more electrons are attracted into a channel. Since the electrons produced from the source  26   a  are pushed by the voltage and flow to the drain  26   b  (i.e. the corresponding current from the drain  26   b  flows to the source  26   a ). If the gate  21   a  is applied with a negative voltage, the electron flow and the current are in contrast to the above. Therefore, the TFT can be used as a switch element. The semiconductor layer  23  can preferably be made of amorphous silicon, and the ohmic contact layer  24  can preferably be made of materials such as N + —Si, but not limited thereto. 
     Embodiment 2 
     With reference to  FIG. 5 , there is shown a top view of partial enlargement of an array substrate in the present embodiment. The method for manufacturing the array substrate in the present embodiment is similar to Embodiment 1. The extending portion of storage capacitor line  31  in Embodiment 1 is over part of the scan line  32 , but does not extend over the border of the pixel electrode  29 . However, in the present embodiment, when forming the metal layers  26   a ,  26   b , and  26   c  (in  FIG. 3C ), the extending portion of the storage capacitor line  31  is formed to have a fillister overlapping the pixel electrode  29  in the C region of  FIG. 5 . Except for the above, other steps in the present embodiment are all the same with those in Embodiment 1. The reason for forming the fillister of the storage capacitor line  31  to overlap the pixel electrode  29  is illustrated as follows. When manufacturing the array substrate, alignment deviations come into existence between layers. The capacitance variation is resulted from the pixel electrode  29  (i.e. the ITO electrode) shifting upwards or downwards while the pixel electrode  29  is exposed. Therefore, the fillister of the storage capacitor line  31  can cause the capacitance variation to be limited therein, so as to reduce the capacitance variation, i.e. to decrease the effect of exposure. Finally, the array substrate of the present embodiment is completed. In other words, the capacitance variation is resulted from the pixel electrode shifting while the pixel electrode is exposed. If the area of the capacitance variation is limited in the fillister, so as to reduce the capacitance variation, and also can increases the stability. 
     Embodiment 3 
     With reference to  FIGS. 6A to 6C , another method for manufacturing an array substrate of the present embodiment is provided. The method in the present embodiment is similar to Embodiment 1. However, as shown in  FIG. 6A , the array substrate of the present embodiment does not comprise the transparent electrode layer  25  ( FIG. 3C ). 
     Subsequently, as shown in  FIG. 6B , the ohmic contact layer  24  is etched. The following steps of the present embodiment are the same with those of Embodiment 1. Finally, the array substrate structure as shown in  FIG. 6C  is formed, in which the pixel electrode  29  is connected with the metal layer  26   b.    
     Embodiment 4 
     With reference to  FIGS. 7A to 7B , there are sectional views respectively in the AA′ line of  FIG. 2  and in the BB′ line of  FIG. 2 . Another method for manufacturing an array substrate is provided. The method in the present embodiment is similar to Embodiment 1. However, in the present embodiment, the protection layer  27  in  FIG. 3E  is not formed. Except for the above, other steps of the present embodiment are the same with those in Embodiment 1. Besides, the second contact window  28   b  is formed as a ditch by halftone process and the flat layer  28  still covers the metal layer  26   c . Finally, the array substrate is completed as shown in  FIGS. 7A and 7B . 
     Embodiment 5 
     With reference to  FIG. 8 , another method for manufacturing an array substrate is also provided. The method in the present embodiment is similar to Embodiment 3. However, in the present embodiment, the array substrate of the present embodiment does not comprise the protection layer  27  in  FIG. 6C . Besides, the second contact window  28   b  is formed as a ditch by halftone process and the flat layer  28  still covers the metal layer  26   c . Moreover, in the embodiment, the sectional view in the BB′ line of  FIG. 2  is as shown in  FIG. 7B  (i.e. Embodiment 4). Finally, the array substrate is completed as shown in  FIG. 8 . 
     Consequently, in the present invention, the storage capacitor line is parallel to the data line, and the storage capacitor line has the extending portion corresponding to the region between the scan line and the pixel electrode on the array substrate. In other words, the extending portion is parallel to the scan line. Therefore, the generated kickback voltage toward the pixel electrode due to the parasitic capacitance is decreased so as to reduce flickers of the frame. 
     Although the present invention has been explained in relation to its preferred embodiments, it is to be understood that many other possible modifications and variations can be made without departing from the scope of the invention as hereinafter claimed.