Abstract:
Display systems and related methods involving bus lines with low capacitance cross-over structures are provided. A representative display system includes: a first structure comprising: a plurality of scan lines extending in a first direction; and a plurality of data lines extending in a second direction and crossing over the scan lines at respective cross-over locations, each of the plurality of data lines having a pair of side walls spaced apart from each other at each of the cross-over locations, with each of the side walls exhibiting a height higher than portions of the data lines not located at the cross-over locations.

Description:
BACKGROUND 
     Technical Field 
       [0001]    The disclosure generally relates to signal lines of display panels. 
       Description of the Related Art 
       [0002]    Displays, such as liquid crystal displays (LCDs), are widely used in electronic devices, such as laptops, smart phones, digital cameras, billboard-type displays, and high-definition televisions. In addition, electroluminescent displays such as OLEDs are also gaining in public attention. 
         [0003]    LCD panels may be configured as disclosed, for example, in Wu et al., U.S. Pat. No. 6,956,631, which is assigned to AU Optronics Corp., the parent company of the assignee of the current application, and hereby incorporated by reference in its entirety. As disclosed in Wu et al.  FIG. 1 , the LCD panel may comprise a top polarizer, a lower polarizer, a liquid crystal cell, and a back light. Light from the back light passes through the lower polarizer, through the liquid crystal cell, and then through the top polarizer. As further disclosed in Wu et al.  FIG. 1 , the liquid crystal cell may comprise a lower glass substrate and an upper substrate containing color filters. A plurality of pixels comprising thin film transistor (TFT) devices may be formed in an array on the glass substrate, and a liquid crystal compound may be filled into the space between the glass substrate and the color filter forming a layer of liquid crystal material. 
         [0004]    Still, the structure of TFTs in displays may be various. For instance, The TFTs, gate and data lines, and pixel electrodes may be formed in a multilayer structure such as that shown in  FIGS. 1 and 2E  of Lai et al., U.S. Pat. No. 7,170,092 and in its division U.S. Pat. No. 7,507,612, both of which are assigned to AU Optronics Corp., the parent company of the assignee of the current application, and both of which are hereby incorporated by reference in their entireties. The multilayer structure may comprise a first conducting layer, a first insulating layer, a semiconductor layer, a doped semiconductor layer, and a second conducting layer disposed in sequence on the substrate. It may further comprise a second insulating layer and a pixel electrode disposed on the second insulating layer. The first conducting layer may comprise at least one of a gate line or a gate electrode. The doped semiconductor layer may comprise a source and a drain. The second conducting layer may comprise a source electrode and a drain electrode. The multilayer structure may be formed using a series of wet and dry etching processes, for example as disclosed in Lai et al.  FIGS. 2A-2D . 
         [0005]    Additional techniques for forming TFTs are disclosed in Chen, U.S. Pat. No. 7,652,285, which is assigned to AU Optronics Corp., the parent company of the assignee of the current application, and hereby incorporated by reference in its entirety. As disclosed in Chen, to form the channel of the TFT, the second metal layer is etched in order to open a portion of the second metal layer over the gate electrode and to separate the source region and drain region. This etching can be performed in multiple ways, including the back-channel etching process disclosed for example in Chen  FIGS. 2A-2E  and the etch stop process disclosed for example in Chen  FIGS. 5A-5D and 6 . Chen discloses that TFT leakage currents may be reduced by adding a spacer layer formed at the sidewalls of the conductive doped amorphous silicon layer, isolating the conductive amorphous silicon layer from the insulating layer. Chen discloses that this spacer layer can be formed by oxidizing the exposed surface of the conductive amorphous silicon layer after the etch of the second metal layer is performed. Chen discloses that this surface may be oxidized by a number of different techniques, including oxygen plasma ashing, or the use of ozone plasma in the presence of carbon tetrafluoride and sulfur hexafluoride gases 
         [0006]    As explained in Sawasaki et al., U.S. Pat. No. 7,557,895, which is assigned to AU Optronics Corp., the parent company of the assignee of the current application, and hereby incorporated by reference in its entirety, the thickness of the liquid crystal layer typically must be uniformly controlled, in order to avoid unevenness in brightness across the LCD panel. As disclosed in Sawasaki et al., the required uniformity may be achieved by disposing a plurality of pillar spacers between the TFT substrate and the color filter substrate. As further disclosed in Sawasaki et al., the pillar spacers may be formed with different heights, such that some spacers have a height that is greater than the gap between the substrates and other spacers have a height that is less than the gap between the substrates. This configuration may permit the spacing between the substrates to vary with temperature changes but also prevent excessive deformation when forces are applied to the panel. 
         [0007]    Sawasaki et al. further discloses a method for assembling the substrates with the liquid crystal material between them. This method comprises steps of preparing the two substrates, coating a sealing material on the circumference of the outer periphery of one of the pair of substrates, dropping an appropriate volume of liquid crystal on one of the pair of substrates, and filling in the liquid crystal between the pair of substrates by attaching the pair of substrates in a vacuum followed by returning the attached pair of substrates to atmospheric pressure. 
         [0008]    In LCD panels, the semiconductor material making up the TFT channel may be amorphous silicon. However, as disclosed in Chen, U.S. Pat. No. 6,818,967, which is assigned to AU Optronics Corp., the parent company of the assignee of the current application, and hereby incorporated by reference in its entirety, poly-silicon channel TFTs offer advantages over amorphous silicon TFTs, including lower power and greater electron migration rates. Poly-silicon may be formed by converting amorphous silicon to poly-silicon via a laser crystallization or laser annealing technique. Use of the laser permits fabrication to occur at temperatures below 600° C., and the fabricating technique is thus called low temperature poly-silicon (LTPS). As disclosed in Chen, the re-crystallization process of LTPS results in the formation of mounds on the surface of the poly-silicon layer, and these mounds impact the current characteristics of the LTPS TFT. Chen discloses a method to reduce the size of the LTPS surface mounds, by performing a first anneal treatment, then performing a surface etching treatment, for example using a solution of hydrofluoric acid, and then performing a second anneal treatment. The resulting LTPS surface has mounds with a height/width ratio of less than 0.2. A gate isolation layer, gate, dielectric layer, and source and drain metal layers can then be deposited above the LTPS layer to form a complete LTPS TFT. 
         [0009]    As disclosed in Sun et al., U.S. Pat. No. 8,115,209, which is assigned to AU Optronics Corp., the parent company of the assignee of the current application, and hereby incorporated by reference in its entirety, a disadvantage of LTPS TFTs compared to amorphous silicon TFTs is a relatively large leakage current during TFT turn off. Use of multiple gates reduces leakage current, and Sun et al. discloses a number of different multi-gate structures for a polycrystalline silicon TFT, including those shown in Sun et al.  FIGS. 2A-2B and 3-6 . 
         [0010]    An alternative to LCD devices is the active matrix organic light-emitting device (OLED), as disclosed for example in Huang, U.S. Pat. No. 6,831,410, which is assigned to AU Optronics Corp., the parent company of the assignee of the current application, and hereby incorporated by reference in its entirety. As disclosed in Huang, a TFT is formed over a substrate. An insulating layer is formed, covering the TFT. A contact opening is formed in the insulating layer, exposing the drain terminal of the TFT, and an anode layer is formed over the insulating layer and the exposed opening, forming a contact between the anode layer and the TFT drain terminal. A light-emitting layer is formed over the anode layer, and a cathode layer is formed over the light-emitting layer. As explained in Huang, there is a risk that the cathode layer will form a short circuit with the anode layer via the contact opening. To prevent such short circuits, Huang discloses depositing a planarization layer that fills the space above the contact. The light-emitting and cathode layers are then formed over the planarization layer. 
         [0011]    As display size is increased, various problems may become evident. For instance, as line resistance and line capacitance increase due to the increased line lengths, capacitive and loading effects on scan and data lines of a display may implicate scan line delay. In particular, rise time of a scan line driving signal may be slowed or delayed to such an extent (e.g., greater than 0.1 T scan ) that luminance non-uniformity, flicker, cross-talk and/or image retention problems are exhibited. 
       SUMMARY 
       [0012]    Display systems and related methods involving bus lines with low capacitance cross-over structures are provided. In one embodiment, a display system comprises: a first structure comprising: a plurality of scan lines extending in a first direction; and a plurality of data lines extending in a second direction and crossing over the scan lines at respective cross-over locations, each of the data lines having a pair of side walls spaced apart from each other at each of the cross-over locations, with each of the side walls exhibiting a height higher than portions of the data lines not located at the cross-over locations. 
         [0013]    Another embodiment of a display system comprises: a substrate; a scan line supported by the substrate and extending in a first direction; a data line supported by the substrate and extending in a second direction such that the data line crosses over the scan line at a cross-over location; and gate insulation disposed between the scan line and the data line; wherein the data line has a first section, a second section and an interconnect section electrically interconnecting the first section and the second section, the interconnect section being disposed at the cross-over location, the interconnect section having side walls defining an aperture, the side walls extending higher than heights exhibited by the first section and the second section. 
         [0014]    In another embodiment, a method for manufacturing a display system comprises: providing a substrate; supporting a first metal layer with the substrate to form a plurality of scan lines extending in a first direction; providing a bump over each of the scan lines; and providing a second metal layer with a portion of the layer extending partially over an exterior of each of the bumps to form a plurality of data lines extending in a second direction and crossing over the scan lines at respective cross-over locations such that the second metal layer forms side walls spaced apart from each other by a corresponding one of the bumps for each of the data lines. 
         [0015]    Other objects, features, and/or advantages will become apparent from the following detailed description of the preferred but non-limiting embodiments. The following description is made with reference to the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]      FIG. 1  is a schematic diagram of an embodiment of an LCD system. 
           [0017]      FIG. 2  is a schematic diagram of the embodiment of  FIG. 1  showing detail of a bus cross-over location. 
           [0018]      FIGS. 3A-3B through 9A-9B  are schematic, cross-sections (as viewed along section lines similar to section line  3 - 3  of  FIG. 2 ) showing representative process steps for manufacturing an embodiment. 
           [0019]      FIG. 10  is a flowchart depicting an embodiment of a method for manufacturing a display system. 
       
    
    
     DETAILED DESCRIPTION 
       [0020]    For ease in explanation, the following discussion describes embodiments of the present disclosure in the context of a display system, such as a liquid crystal display (LCD) system or organic light emitting diode (OLED) display system. It is to be understood that the invention is not limited in its application to the details of the particular arrangements shown since the invention is capable of other embodiments. Also, the terminology used herein is for the purpose of description and not of limitation. 
         [0021]    In this regard, display systems and related methods involving bus lines with low capacitance cross-over structures are provided. In some embodiments, the bus lines may incorporate side walls that interconnect segments of bus lines at cross-over locations. So configured, capacitance of the lines at the cross-over locations may be reduced without significantly increasing resistance. Exemplary embodiments will now be described with reference to the drawings. 
         [0022]    With reference to  FIG. 1 , an embodiment of a display system  100  configured as an LCD panel is depicted. Fundamentally, display system  100  includes an LCD panel  110  with a plurality of pixels, data control circuitry  120  and gate control circuitry  130 . The circuits and functions can be implements by hardware, software or a combination of hardware and software such as microcontrollers, application-specific integrated circuits (ASIC) and programmable microcontrollers. 
         [0023]    LCD panel  110  incorporates a plurality of pixels (typically thousands of pixels, e.g., pixels  140 ,  150 ), which are arranged in a two-dimensional array comprising a plurality of rows and columns. For ease of illustration, only a few pixels are shown. As is known, in a thin film transistor (TFT) LCD panel, a pixel is typically formed from three pixel elements (PEs): one red, one green, and one blue, although various configurations may be used. For instance, pixel  150  is depicted as including three PEs-PE(R), PE(G) and PE(B). One or more transistors and one or more storage capacitors are typically coupled to each pixel element, thereby forming driving circuitry for the associated pixel element. 
         [0024]    The transistors of all pixels in a given row typically are connected to bus lines—their gate electrodes are connected to a gate (scan) line (e.g., line  154 ), and their source electrodes are connected to a source (data) line (e.g., line  152 ). The gate control circuitry  130  and data control circuitry  120  control the voltage applied to the respective gate and data bus lines to individually address each pixel element in the LCD panel. By controllably pulsing the respective pixel element driving transistors, the driving circuits can control the transmissivity of each PE, and thereby control the color of each pixel. The storage capacitors assist in maintaining the charge across each pixel between successive pulses (which are delivered in successive frames). Common lines (not shown) provide reference (common) signals for the electrodes. 
         [0025]    A portion of the embodiment of  FIG. 1  is depicted schematically in  FIG. 2 , in which detail of a bus cross-over location  160  is presented. In particular, as shown in  FIG. 2 , gate line  154  extends in a first direction and is provided as a strip of material that exhibits generally uniform rectangular cross-sections along its length. Gate line  154  includes top and bottom (generally planar) surfaces  162  and  164 , respectively, and opposing side surfaces  166  and  168  that are substantially parallel to each other. Gate line  154  exhibits a width W g . 
         [0026]    As shown in  FIG. 2 , data line  152  extends in a second direction that is generally perpendicular to the first direction of gate line  154 , although other configurations may be used in other embodiments. Data line  152  includes top and bottom (generally planar) surfaces  172  and  174 , respectively, and opposing side surfaces  176  and  178  that are substantially parallel to each other. Data line  152  exhibits a width W d . 
         [0027]    Data line  152  incorporates first and second segments ( 182  and  184 , respectively) each of which exhibits generally uniform rectangular cross-sections along its length. A cross-over segment  186  interconnects segments  182 ,  184 , with cross-over segment  186  being positioned at cross-over location  160  (i.e., the location at which data line  152  crosses over gate line  154 ). It should be noted that although not depicted for ease of illustration, one or more of various other materials and/or features may be provided at a cross-over location, such as a gate insulating material disposed between lines  152  and  154 , for example. 
         [0028]    Cross-over segment  186  includes an aperture  188  that defines a void  190  (which may be at least partially filled in some embodiments) that is positioned over gate line  154 . In this embodiment, aperture  188  is generally rectangular in plan view and incorporates inner surfaces of side walls  191 ,  192 ,  193  and  194 . Specifically, side walls  191  and  193  are aligned with the second direction and form the interconnecting structure of cross-over segment  186  as side walls  191  and  193  span the width of gate line  154  to electrically connect segments  182  and  184 . Side walls  192  and  194  are aligned with the first direction and are positioned outboard of gate line  154 . 
         [0029]    Each of the side walls  191 - 194  protrudes upwardly from surface  172  and exhibits a height (H s ) (not including the thickness of data line  154 ) of between approximately 1 μm and approximately 5 μm (e.g., approximately 3.0 μm), and a width (W s ) of between approximately 0.1 μm and approximately 0.7 μm (e.g., approximately 0.3 μm). By providing the sidewalls, line resistance of the cross-over segment may be controlled (e.g., reduced) while improving the mechanical stability of line  152  in the vicinity of vid  190 . 
         [0030]    In contrast to conventional bus cross-overs that exhibit a capacitance (C) of ε(S/d), where ε is the dielectric constant between the lines, S is the overlapping surface area of the lines and d is the distance separating the lines, thus ε((w d ·w g )/d), the embodiment of  FIG. 2  exhibits a capacitance of ε((2·w s ·w g )/d), where 2·w s &lt;w d . In some embodiments, the reduction in surface area of the cross-over segment when compared to a conventional line of uniform area (a relationship of 2·w s  to w d ) can result in a reduction in capacitance of between approximately 20% and approximately 60% (e.g., approximately 40%). Of significance, this may be accomplished without significantly increasing (and in some cases maintaining) line resistance owing to the increase in conductive line material used (e.g., the material used in forming the extended height of the side walls  191  and  193 ). 
         [0031]      FIGS. 3A-3B through 9A-9B  are schematic, cross-sections showing representative process steps for manufacturing an embodiment of a display system. Each cross-section shown in  FIGS. 3B-9B  is respectively observed from the cross-section lines  3 B- 3 B through  9 B- 9 B marked in  FIGS. 3A-9A . As shown in  FIGS. 3A and 3B , a representative first step in the process involves providing a substrate  202  and forming a first metal layer  204  on an upper surface of the substrate. Metal layer  204 , which may comprise Al, Cu, Mo or metal alloy, for example, may be deposited by sputtering or thermal evaporation. Metal layer  204  is used to form a gate line. 
         [0032]    In  FIGS. 4A-4B , a gate insulation layer  206  is deposited on a top surface of metal layer  204 . Additionally, a semiconductor device  207  (for example, an active layer configured as a channel of a switching device such as a thin film transistor (TFT)) also is formed. The material of the semiconductor device  207  may be, for example, amorphous Silicon, low temperature poly-Silicon or Indium Gallium Zinc oxide. 
         [0033]    In  FIGS. 5A-5B , a bump  208  is formed over the gate insulation layer  206 . The bump  208  is made of an organic layer. The organic layer is formed over the gate insulation layer  206 . The organic layer, which may be acrylate, epoxy or siloxane, for example, is formed by spin coating or slit coating. The organic layer is configured in the form of a bump  208  with a height of approximately 2-3 μm. Also depicted in  FIG. 3C  is a layer of photoresist  210  deposited on top of bump  208 . Notably, the photoresist applied to the bump exhibits an overhang portion. 
         [0034]    As shown in  FIGS. 6A-6B , a second metal layer  212  is deposited. By way of example, the metal may be Al, Cu or metal alloy, for example. Notably, metal layer  212  adheres to the side walls (e.g., side walls  214 ,  216 ) of bump  208 , and forms a cap  218  about the exposed upper surfaces of photoresist  210 . 
         [0035]    In  FIGS. 7A-7B , photoresist  220  is applied to facilitate formation of a data line, a source electrode  221  and a drain electrode  223  of a TFT, which are formed after metal etching is performed as depicted in  FIGS. 8A-8B , which removes material down to the gate insulation layer in areas not covered by the photoresist. The photoresist is subsequently removed by stripper as shown in  FIGS. 9A-9B . 
         [0036]    As shown in  FIGS. 9A-9B , in addition to the photoresist  210  and  220  being removed, the cap  218  is removed along with the photoresist (this removal technique is known as the lift-off method). Thus, the remaining structure incorporates substrate  202 , metal layer  204  (configured as a gate line), gate insulation layer  206 , bump  208  and metal layer  212  (configured as a data line). 
         [0037]    The data line formed from metal layer  212  incorporates a cross-over segment  230  that includes side walls (e.g., side walls  232  and  234 ). Cross-over segment  230  electrically interconnects segments  236  and  238  of the data line using side walls similar to side walls  232  and  234  (although the interconnecting side walls are not illustrated in  FIG. 3F  due to the cross-sectional perspective. The side walls extend outwardly from the generally planar top surface of the data line and may be inclined inwardly toward each other, such that each exhibits an angle (θ) of between approximately 45 and approximately 90 degrees, preferably between approximately 70 and approximately 90 degrees. The angle of inclination of the side walls is determined, at least in part, by the angle of the exterior surface of the bump that is in contact with the metal layer  212 . 
         [0038]    A flowchart depicting an embodiment of a method for manufacturing a display system is depicted in  FIG. 10 . As shown in  FIG. 10 , the process may be construed as beginning at block  250 , in which a substrate is provided. In block  252 , a first metal layer is provided on the substrate for forming a gate line. Then, in block  254 , a gate insulation layer is provided on the first metal layer. The metal layer and the gate insulation layer can be provided through a process such as Physical Vapor Deposition, Chemical Vapor Deposition or printing. 
         [0039]    In block  256 , a bump (e.g., a bump of organic material) is provided on the gate insulation layer. The bump can be provided through a process such as Physical Vapor Deposition, Chemical Vapor Deposition or printing. Then, as shown in block  258 , a second metal layer is provided. The second metal layer can be provided through a process such as Physical Vapor Deposition, Chemical Vapor Deposition or printing. In particular, the second metal layer is configured as a data line that includes side walls extending partially over the exterior of the bump (e.g., up the sides of the bump) to form a cross-over segment. In some embodiments, formation of the side walls may be accomplished by one or more of various process steps, such as by performing a lift-off method to remove a cap formed over the top of the bump. This may involve selectively applying photoresist, upon which a portion of the second metal layer is deposited. In particular, the photoresist is located over the bump. Additional photoresist is then applied for forming various features, such as may be provided by performing a metal etch. Thereafter, all the photoresist is removed, which also lifts off the portion of the second metal layer that was formed on top of photoresist, thereby forming an aperture in the second metal layer and exposing the bump (see,  FIGS. 6A-6B to 9A-9B , for example). The lift-off method may be performed through dissolving the photoresist by solvent. 
         [0040]    By reducing capacitive and loading effects on scan and data lines of a display with a cross-over segment, scan line delay may be correspondingly reduced. As such, the desire for increased display size may be accommodated without the conventional drawbacks of luminance non-uniformity, flicker, cross-talk and/or image retention problems. 
         [0041]    The embodiments described above are illustrative of the invention and it will be appreciated that various permutations of these embodiments may be implemented consistent with the scope and spirit of the invention.