Patent Publication Number: US-2011074662-A1

Title: Panel for liquid crystal display device

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a panel or a substrate of a liquid crystal display device and, more particularly, to a panel or a substrate of an active matrix liquid crystal display device and the repairing method of the same. 
     2. Description of Related Art 
     The improvement of the yield of the process for manufacturing a panel of a liquid crystal display device (LCD) is very important. For improving the yield, it is necessary to repeatedly inspect in all the steps of the manufacturing process for screening out the unqualified products. However, particles exist inside and/or outside the apparatuses for manufacturing processes. The particles usually result in defects on the substrate for the liquid crystal display devices. For example, as a particle  90  falls on the surface of the switch  21  of the substrate  1  (see  FIG. 1 ), the particle  90  results in shorting between the data line (source line)  35  and the drain  36 . This shorting causes source-drain leakage and will further make the liquid crystal display device generate dark dots or bright dots (i.e. point defects) as the display device displays. 
     Since dumping the liquid crystal display device with point defects directly costs money, the manufacturers of LCD devices do many efforts on improving the manufacturing process and environment for manufacturing. For example, the LCD makers increase the frequency for cleaning the environment, enhancing the monitoring for the cleanness of the manufacturing environment, and improving the maintenance of the manufacturing apparatuses. On the other hand, the LCD manufacturers also develop method for repairing the LCD panel or the substrate of the LCD devices for saving costs. The yield can be improved effectively if the defected LCD device or the substrate of the LCD device can be well repaired. Of course, the cost can be reduced when the defected LCD device or the substrate of the LCD device can be well repaired. 
     The conventional method for repairing the defects on the LCD is shown in  FIG. 1 . A particle  90  falls on the surface of a switch (thin film transistor)  21  of a normally black liquid crystal display device and further results in a TFT defect such as source-drain leakage or TFT weak. When a voltage is applied on the LCD, a bright dot (i.e. a point defect) generates. The conventional method for repairing the defects illustrated above is achieved by welding the capacitor conductive lines  47  and the capacitor top lead  471  together and further cutting the drain  36 , wherein the capacitor top lead  471  contact the pixel electrode  52  through contact holes  45 , and the pixel electrode  52  electrically connected to the switch  21  through the drain  36 . The cross of  FIG. 1  marks  500  is the position of cutting. After repairing, the repaired pixel of the LCD acts as a permanent dark dots. Since human eyes are not sensitive to the dark dots, the consumer can also accept the LCDs with limited dark dots. Even though the tolerance value for the dark dots is higher than that of the bright dots, the permanent dark dots are not actually recovered through the conventional repairing method. In other words, the permanent dark dots are still abnormal pixels. 
     In addition, the defects caused by other factors decrease greatly since the process for manufacturing LCDs improves a lot in recent years. Hence, the point defects resulted from source-drain leakage become major defects relatively. Moreover, the tolerable requirement for the point defects becomes strict as the size of the LCD increases. Therefore, it is desirable to provide an improved method to mitigate the aforementioned problems of the source-drain leakage. 
     SUMMARY OF THE INVENTION 
     The present invention provides a panel of the liquid crystal display device. The substrate of the panel includes a plurality of pixels. Each pixel comprises: a switch, a pixel electrode, and a floating conductive line. The switch includes a gate, a source, and two drains. The pixel electrode is electrically connected to the switch by the assistance of the drain. The floating conductive line crosses the two drains without electrical connection. Hence, when source-drain leakage generates, the switch can be repaired by cutting the drains, and selectively welding the drain, and the floating conductive line. For example, when a particle falls on the location between the drain and the source, TFT source-drain leakage may happen because the short between the source and the drain generates. 
     Moreover, in the present invention, the source of the switch refers to the branch of the data line, which extends to overlap the switch. The source of the switch is connected to the data line. 
     In this kind of condition, the pixel with defects can be repaired into a normal pixel for displaying if the circuit of the defected pixel has the dual drain circuit of the pixel of the present invention. The repairing steps of the method of the present invention can be of following steps: (A) providing a substrate of a liquid crystal display device having a plurality of pixels, wherein each pixel includes: a switch having a gate, a source, and two drains; a pixel electrode; and a floating conductive line; wherein the pixel electrode electrically connects to the switch through the drain, and the floating conductive line crosses the two drains without electrical connection; (B) cutting one of the two drains, wherein the location of the cut on the drain is not between “the crossed position of the drain and the floating conductive line” and “the switch”; and (C) checking the pixel through charging the source and the gate on the substrate. 
     If the repaired pixel displays normally, the repairing is completed and can be stopped. In contrary, if the laser-repaired pixel doesn&#39;t display normally, it means that perhaps the particle falls on the uncut drain. In this situation, the defected pixel can be subsequently repaired by the following steps: (D) cutting the uncut drain, wherein the location of the cut on the conductive line is between “the crossed position of the drain and the floating conductive line” and “the switch”; and; (E) welding the two drains and the floating conductive line together to make the two drains electrically connected to the floating conductive line. 
     Hence, if the defect of a pixel is TFT source-drain leakage or TFT weak, the defect can be repaired through the laser-welding of the connection of dual drain and the floating conductive line design of the substrate of the present invention. 
     In addition, the present invention also provides a substrate having dual-source circuit in the TFT area. The substrate includes a plurality of pixels. Each pixel comprises: a switch, a pixel electrode, and a floating conductive line. The switch includes a gate, two sources, and a drain. The pixel electrode is electrically connected to the switch by the assistance of the drain. The floating conductive line crosses the two sources without electrical connection. 
     In this invention, the source refers to the branch of the data line, which extends to overlap the switch. The source of the switch is connected to the data line. 
     Likewise, the pixel with TFT source-drain leakage defect (or TFT weak) can be repaired into a normal pixel for displaying if the circuit of the defected pixel has the dual source circuit of the pixel of the present invention. The repairing steps of the method of the present invention can be a method of following steps: (A) providing a substrate of a liquid crystal display device having a plurality of pixels, wherein each pixel includes: a switch having a gate, a drain, and two sources; a pixel electrode; and a floating conductive line; wherein the pixel electrode electrically connects to the switch through the drain, and the floating conductive line crosses the two sources without electrical connection; (B) cutting one of the two source s, wherein the location of the cut on the source is not between “the crossed position of the source and the floating conductive line” and “the switch”; and (C) checking the pixel through charging the source and the gate on the substrate. 
     If the repaired pixel displays normally, the repairing is completed and can be stopped. In contrary, if the laser-repaired pixel doesn&#39;t display normally, it means that perhaps the particle falls on the uncut source. In this situation, the defected pixel can be subsequently repaired by the following steps: (D) cutting the uncut source, wherein the location of the cut on the source is between “the crossed position of the source and the floating conductive line” and “the switch”; and (E) welding the two sources and the floating conductive line together to make the two sources electrically connect to the floating conductive line. 
     The sources (or the drains) of the present invention can be cut with any cutting steps. Preferably, the source s (or the drains) are cut by laser. The laser of the present invention can be any laser. Preferably, the laser of the present invention is YAG laser, ruby laser, or CO 2  laser. The sources (or the drains) and the floating conductive line of the present invention can be welded with any laser. Preferably, the sources (or the drains) and the floating conductive line of the present invention are welded by YAG laser, ruby laser, or CO 2  laser. 
     In addition, each pixel of the substrate of the liquid crystal display device can further include a gate conductive line that is electrically connected to the gate. Each pixel of the substrate of the liquid crystal display device can optionally further include capacitor conductive line that is electrically connected to the drain, and the drain can be electrically connected to the pixel electrode through the capacitor conductive line, and the drain can electrically connected with the pixel electrode through the capacitor conductive line. The capacitor conductive line can be in any form. Preferably, the capacitor conductive line includes a top capacitor lead, and a bottom capacitor lead, wherein the top capacitor lead overlaps the bottom capacitor lead without electrical connection. In addition, the top capacitor lead can have at least one contact hole for electrically connecting the pixel electrode and the top capacitor lead. The pixel electrode of the substrate of the present invention can be made of any conductive material. Preferably, the pixel electrode of the substrate of the present invention is made of transparent conductive materials. More preferably, the pixel electrode is made of indium tin oxide or indium zirconium oxide (IZO). The floating conductive line can be made of any conductive material. Preferably, the floating conductive line and the gate conductive line are made of the same material. 
     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 the TFT switch of the substrate of a prior art. 
         FIG. 2  is a top view of the TFT switch of the substrate of the first embodiment of the present invention. 
         FIG. 3  is a top view of the TFT switch of the substrate of the embodiments of the present invention. 
         FIG. 4  is a cross section view of AA′ dash line in  FIG. 2   
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       FIG. 2  and  FIG. 3  are the top view of the TFT switch of the substrate of a LCD panel in the embodiments of the present invention. By way of repairing the structure of the circuit in the TFT area of the substrate of a LCD panel, the LCD panel with source-drain leakage can be repaired and transferred into a normal LCD panel. 
     Embodiment 1 
     A top view of the TFT switch of the substrate of a panel in the present embodiment of the present invention is shown in  FIG. 2 . The substrate  1  of the present embodiment comprises a plurality of pixels. Each pixel has a pixel electrode  52 , a gate conductive line  38 , a capacitor conductive line  47 , a data line (source line)  35 , a floating conductive line  33 , and a switch  21 . 
     The switch of the present invention can be a thin film transistor. In the present embodiment, the switch  21  is a filed-effect transistor (FET). The switch  21  of the present embodiment includes a gate (not shown), a source  350 , and two drains  36 ,  361  for providing high charging rate to the LCD, especially the large-sized LCD. 
     The LCD of the present embodiment is a normally black LCD. In other words, the LCD of the present embodiment display dark as no voltage is applied thereon. As shown in  FIG. 2 , the source  350  is a branch of the data line  35 , and is extended to overlap the switch  21 . The data lines  35  perpendicularly cross the gate conductive lines  38  without electrical connection. A dielectric layer (not shown in figures) is located between the data lines  35  and gate conductive lines  38  for preventing electrical contact. Moreover, capacitor conductive lines  47  are located between the locations of the two gate conductive lines  38 . Preferably, the capacitor conductive lines  47  are parallel to the gate conductive lines  38  to avoid electrical contact with the gate conductive lines  38 . Furthermore, the capacitor conductive lines  47  also cross the data lines  35  without electrical connection. Similarly, a dielectric layer (not shown in the figures) is arranged between the capacitor conductive lines  47  and the data lines  35  to avoid electrical contact there between. 
     The data lines  35  are electrically connected to the electric power sources (not shown) and the source  350 . The gate conductive lines  38  are electrically connected to the electric power sources (not shown) and the gate of the switch  21 . Through these connections, the source  350  and the gate conductive lines  38  can provide enough voltage to drive the switch  21  when the LCD displays. In addition, the drains  36 ,  361  are electrically connected to the capacitor conductive lines  47  and the drain of the switch  21 . Owing to the circuit of the drains  36 ,  361 , and the capacitor conductive lines  47 , the applied voltage can be passed to the capacitor conductive lines  47  and the pixel electrode  52 . Hence, the pixel electrode  52  can be electrically connected with the switch  21  by way of the drain  36 ,  361 . Furthermore, part of the capacitor conductive lines  47  is made of top capacitor lead  471  and bottom capacitor lead  472 . A dielectric layer is arranged between the top capacitor lead  471  and bottom capacitor lead  472 . The top capacitor lead  471 , the dielectric layer, and the bottom capacitor lead  472  form a storage capacitor for a pixel. The drain  36 ,  361  can be electrically connected to the top capacitor lead  471  or the bottom capacitor lead  472 . In the present embodiment, the drains  36 ,  361  are electrically connected to the top capacitor lead  471 . In addition, two contact holes  45  are made on each capacitor conductive line  47  to contact the pixel electrode  52 . 
     The repairing method of the substrate of the present embodiment can be illustrated following. As a particle  90  falls on the surface of the location of the source  350  and the drain  36 , the source  350  and the drain  36  short by way of the particle  90  (i.e. the source-drain leakage). Therefore, the pixel electrode  52  corresponding to the abnormally charged switch  21  displays a bright dot on the screen. 
     The following explanation is referred to  FIG. 2  and  FIG. 4 . As shown in  FIG. 2 , the switch  21  of the present embodiment has two drains  36 ,  361 . The floating conductive line  33  crosses the drains  36 ,  361  without electrical connection.  FIG. 4  is a cross-section view of the AA′ line. On the surface of the substrate  1  (the glass substrate), there are floating conductive line  33 , two drains  36 ,  361 , and a dielectric layer  54  (see  FIG. 4 ). Since the dielectric layer  54  is located between the floating conductive line  33  and the drains  36 ,  361 , the floating conductive line  33  and the drains  36 ,  361  are not electrically connected. In addition, there is a flatting layer  93  covered the drains  36 ,  361 . Furthermore, a pixel electrode  52  is located on the flatting layer  93  and covers the flatting layer  93 . The substrate  1  and another opposite substrate  2  are assembled to form a panel of a liquid crystal display device when liquid crystal  3  is injected. 
     It is hard to observe the position of the particle fallen on the surface of the substrate after the panel is assembled. However, the defect caused by the source-drain leakage on the LCD of the present embodiment can be repaired through the following steps: (1) First, one of the two drains  36 ,  361  is cut by laser. The cutting position on the drains  36 ,  361  cannot be arranged between “the crossed position of the drains  36 ,  361  and the floating conductive line  33 ” and “the switch  21 ”. In the present embodiment, the drain  361  is cut first and the position of cutting is marked as a cross  100 . (2) The panel is applied with a voltage for checking. If the bright dot recovers normal display condition after the laser cut illustrated above is done, the repairing is achieved. In contrary, if the bright dot does not recover to normal condition for display, it means that the particle  90  perhaps falls on the other uncut drain line  36 . In the present embodiment, the laser-processed pixel of the LCD still displays a bright dot when the voltage is applied. (3) The uncut drain  36  is then cut by laser. The position of the cut is located on the drain  36  between “the crossed position of the drain  36  and the floating conductive line  33 ” and “the switch  21 ”. In the present embodiment, the drain  36  is cut second and the position of cutting is marked as a cross  200 . (4) The floating conductive line  33  and drains  36 ,  361  are welded through a laser to make the floating conductive line  33 , and drains  36 ,  361  electrically connected. In the present embodiment, the circles  300 ,  400  mark the locations of the laser welding. Through the laser welding illustrated above, the electrically opened drains  36 ,  361  can be transferred as a new drain by the assistance of the floating conductive line  33 . Besides, the new drain is electrically insulated from the particle  90 . The pixel electrode  52  can be electrically connected to the switch  21  through the new drain. Of course, the pixel electrode  52  displays normally after the repairing is finished. 
     Embodiment 2 
       FIG. 3  is a top view of another embodiment of the present invention. In the present embodiment, the switch  21  of each pixel of the substrate of the liquid crystal display device includes a gate (not shown), a drain  36 , and two sources  351 ,  352 . The sources  351 ,  352  of the switch  21  are electrically connected to the data line  35 . Besides, the sources  351 ,  352  are the branches of the data line  35 , and are extended to overlap the switch  21 . The floating conductive line  33  crosses the two sources  351 ,  352  without electrical connection. The other part of the pixel of the present embodiment is the same as that of the embodiment 1 illustrated above. 
     Similarly, the repairing of the source-drain leakage of the pixel of the panel of the liquid crystal display device is achieved by cutting sources and laser welding. As shown in  FIG. 3 , assuming the source  351  of a pixel of an assembled LCD panel is short, the source  351  is cut on the position marked cross  600  to make the source  351  electrically disconnected. The repaired panel is then applied with a voltage for testing. If the pixel proceeded with laser cutting is still a bright dot, it means that the repairing is not finished yet. In other words, the particle perhaps falls around the other source  352 . The source  352  is then cut with laser. The location of the laser cut on the source  352  is marked by a cross  700 . Finally, the two sources  351 ,  352 , and the floating conductive line  33  are electrically connected by laser welding. In other words, a laser-welding-repaired electrical path or a new source forms. The pixel electrode  52  can be electrically connected to the switch  21  through the new source. 
     The laser used in the present invention can be any laser. In the present embodiment, the laser is YAG laser, ruby laser, or CO 2  laser. The wavelength and the power of the laser can be adjusted according to the real demand for the sources or drains treated by laser cutting or laser welding. 
     Although the present invention has been explained in relation to its preferred embodiment, it is to be understood that many other possible modifications and variations can be made without departing from the spirit and scope of the invention as hereinafter claimed.