Patent Publication Number: US-9905582-B2

Title: Display device

Description:
This application is a continuation of copending application Ser. No. 14/708,613 filed on May 11, 2015 which is a continuation of application Ser. No. 14/298,292 filed on Jun. 6, 2014 (now U.S. Pat. No. 9,030,389 issued May 12, 2015) which is a continuation of application Ser. No. 13/894,722 filed on May 15, 2013 (now U.S. Pat. No. 8,749,461 issued Jun. 10, 2014) which is a continuation of application Ser. No. 13/543,110 filed on Jul. 6, 2012 (now U.S. Pat. No. 8,446,348 issued May 21, 2013) which is a continuation of application Ser. No. 12/496,206 filed on Jul. 1, 2009 (now U.S. Pat. No. 8,217,864 issued Jul. 10, 2012) which is a continuation of application Ser. No. 10/863,877 filed on Jun. 8, 2004 (now U.S. Pat. No. 7,557,779 issued Jul. 7, 2009), which are all incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an active matrix display device, and more particularly, relates to a wiring structure of an active matrix display device comprising a light emitting element. 
     2. Description of the Related Art 
     In recent years, a large sized electro luminescence (abbreviated as EL hereinafter) display device has been developed with a view to entry into the television market. 
     As the length of a wiring is increased with enlargement of a display device, voltage drop occurs. The voltage drop becomes a problem particularly in a current supply line for supplying a current to a light emitting element. 
     This is because the voltage drop causes display variations since a voltage applied to an EL element varies among each region. 
     SUMMARY OF THE INVENTION 
     The invention provides a display device in which display variations due to voltage drop are suppressed by distributing the current load of wirings. 
     A display device of the invention is an active matrix display device comprising a first current input terminal, a second current input terminal and a plurality of current supply lines which extend parallel to each other. Each of the current supply lines is connected to a plurality of driving transistors arranged in a line. One end of each of the current supply lines is connected to the first current input terminal via a first wiring which extends in a direction intersecting with the current supply lines. The other end of each of the current supply lines is connected to the second current input terminal via a second wiring which extends in a direction intersecting with the current supply lines. Accordingly, a current is supplied to each of the current supply lines from both the first current input terminal and the second current input terminal. It is to be noted that the first current input terminal and the second current terminal are provided separately from each other. 
     The current supply line in this specification is a wiring connected to a transistor (driving transistor) for supplying a current to a light emitting element in a light emitting display device in particular. Current supply to the light emitting element from the current supply line is controlled by turning the driving transistor ON or OFF. 
     Note that, the first wiring may be connected to a plurality of the first current input terminals. Similarly, the second wiring may be connected to a plurality of the second current input terminals. 
     According to the display device having the aforementioned structure, the current load can be distributed to a node between the first wiring and a wiring directly connected to the first current input terminal and to a node between the second wiring and a wiring directly connected to the second current input terminal, thereby suppressing voltage drop at the current supply lines. 
     A display device of the invention is an active matrix display device comprising a plurality of current supply lines which extend parallel to each other and a plurality wirings which extend in a direction intersecting with the current supply lines. The current supply lines are electrically connected to the wirings at each intersection of the current supply lines and the wirings. It is to be noted that the current supply lines and the wirings are formed on different layers with an insulating layer interposed therebetween. Further, a connecting portion provided in the insulating layer allows the current supply lines to be electrically connected to the wirings. 
     According to the display device having the aforementioned structure, a current can be supplied to each light emitting element via a plurality of current paths, thereby distributing the current load. As a result, voltage drop at a current supply line can be suppressed. 
     In the case of a display device comprising a plurality of light emitting elements which emit different color light, the aforementioned structure may be adopted for each group of current supply lines which supply a current to light emitting elements emitting the same color light. 
     Drop in voltage can be suppressed in such a manner, and thus a display device in which display variations due to voltage drop are suppressed can be achieved. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1A and 1B  are diagrams showing the invention. 
         FIG. 2  is a diagram showing the invention. 
         FIG. 3  is a diagram showing the invention. 
         FIG. 4  is a top plan view of a pixel portion of a display device according to the invention. 
         FIG. 5  is a cross sectional view of a pixel portion of the display device according to the invention. 
         FIG. 6  is a cross sectional view of a pixel portion of the display device according to the invention. 
         FIG. 7  is a diagram showing the invention. 
         FIG. 8  is a diagram showing the display device using the invention. 
         FIGS. 9A to 9F  are views showing electronic apparatuses using the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Embodiment Mode 1 
     An embodiment mode of the invention is described with reference to  FIGS. 1A and 1B . 
       FIG. 1A  is a pattern diagram showing current supply lines which are led out, among a plurality of wirings provided in the active matrix display device of the invention. 
     A pixel portion  71  formed on a substrate  70  comprises a plurality of pixels each having a switching transistor  82 , a driving transistor  83  and a light emitting element  84  as shown in  FIG. 1B . Further, reference numeral  81  denotes a source line and  76  denotes a current supply line in  FIG. 1B . It is assumed in this embodiment mode that the light emitting element  84  in each pixel emits the same color light. 
     A plurality of current supply lines  76   a  to  76   i  provided on the substrate  70  extend in one direction and parallel to each other. The current supply lines  76   a  to  76   i  are connected to a wiring  85  which extends substantially perpendicular to the current supply lines  76   a  to  76   i , and connected to a first current input terminal  72  or  74  via a node  77  or  79  which is provided at the ends of the wiring  85 . It is to be noted that the first current input terminals  72  and  74  are provided separately from each other. 
     The opposite ends of the current supply lines  76   a  to  76   i  connected to the wiring  85  are connected to a wiring  86  which extends substantially perpendicular to the current supply lines  76   a  to  76   i , and connected to a second current input terminal  73  or  75  via a node  78  or  80  which is provided at the ends of the wiring  86 . It is to be noted that the second current input terminals  73  and  75  are provided separately from each other. 
     In the display device having the aforementioned structure, an electrical signal is transmitted to each of the current supply lines  76   a  to  76   i  from the first current input terminals  72  and  74  and the second current input terminals  73  and  75  which are provided separately from each other. 
     In such a manner, a current is inputted to a current supply line from first and second current input terminals provided separately. According to this, the current load of the nodes  77  and  79  are distributed to the nodes  78  and  80 , and significant voltage drop can thus be prevented from occurring locally. 
     Although the display device of monochrome light emission is shown in this embodiment mode, the invention may be applied to a display device of three color emission of RGB. In the latter case, the structure shown in this embodiment mode may be adopted for each color emission. Further, a circuit configuration of the pixel portion for driving the light emitting element is not especially limited. 
     Embodiment Mode 2 
     An embodiment mode of the invention is described with reference to  FIGS. 2 and 3 . 
       FIG. 2  is a pattern diagram showing current supply lines which are led out, among a plurality of wirings provided in the active matrix display device of the invention.  FIG. 3  is a diagram showing a circuit configuration of the pixel portion of the display device shown in  FIG. 2 . 
     In  FIG. 2 , a pixel portion  11  formed on a substrate  10  comprises current supply lines  12   a  to  12   i  arranged in columns. Wirings  13   a  to  13   f  are arranged so as to intersect with the current supply lines  12   a  to  12   i  arranged in columns, and the wirings  13   a  to  13   f  are connected to the current supply lines  12   a  to  12   i  at intersections of the wirings  13   a  to  13   f  and the current supply lines  12   a  to  12   i . Further, the current supply lines  12   a  to  12   i  are connected to current input terminals  14 . 
     In  FIG. 3 , the pixel portion  11  of the display device comprises a plurality of current supply lines  90   a  to  90   i  arranged in a longitudinal direction and a plurality of wirings  91   a  to  91   c  arranged in a lateral direction. An area surrounded by two longitudinally adjacent current supply lines and two laterally adjacent wirings corresponds to one pixel. 
     A pixel  92  comprises a switching transistor, a driving transistor and a light emitting element. The driving transistor provided in each pixel is connected to each of the current supply lines  90   a  to  90   i . It is to be noted that all the light emitting elements emit the same color light in this embodiment mode. 
     Via the wirings  91   a  to  91   c  which extend substantially perpendicular to the current supply lines  90   a  to  90   i , each of the current supply lines  90   a  to  90   i  is electrically connected to the adjacent current supply line, for example, such that the current supply lines  90   a  and  90   b  are connected to each other, the current supply lines  90   b  and  90   c  are connected each other, and the like. 
     As set forth above, the current supply lines are electrically connected to each other both in the longitudinal and the lateral directions per pixel. Therefore, the number of current paths is increased to distribute the current load, which prevents significant voltage drop from occurring locally. 
     Although the display device of monochrome light emission is shown in this embodiment mode, the invention may be applied to a display device of three color emission of RGB. In the latter case, the structure shown in this embodiment mode may be adopted for each color emission. Further, a circuit configuration of the pixel portion for driving the light emitting element is not especially limited. 
     The circuit configuration shown in this embodiment mode can be implemented in combination with that shown in Embodiment Mode 1 in order to still suppress the current load. 
     EMBODIMENT 
     Embodiment 1 
     A display device using the invention is described with reference to  FIGS. 4 to 7 . Note that, the display device shown in this embodiment adopts the structures described in both Embodiment Modes 1 and 2.  FIG. 7  is a diagram showing a circuit configuration of a pixel portion of the display device according to this embodiment. 
       FIG. 4  is a top plan view showing a part of a pixel portion of the display device according to the invention.  FIG. 5  is a cross sectional view taken by cutting along a line A-A′ of  FIG. 4 , whereas  FIG. 6  is a cross sectional view taken by cutting along a line B-B′ of  FIG. 4 . 
     A display device of this embodiment comprises a plurality of pixels using as a unit light emitting elements each of which emits red, green or blue light. Each of the pixels comprises a driving transistor  22  for driving the light emitting element, a switching transistor  20 , an erasing transistor  21 , a current supply line  28 , source lines  25   a  and  25   b , a first scan line (erasing line)  23 , and a second scan line (gate line)  24 . In the display device, the pixels are arranged in matrix. 
     Electrodes  30  and  61  ( 61   a  and  61   b ) of a light emitting element are electrodes of a light emitting element which emits red light, electrodes  31  and  62  ( 62   a  and  62   b ) of a light emitting element are electrodes of a light emitting element which emits green light, and electrodes  32  and  63  ( 63   a  and  63   b ) of a light emitting element are electrodes of a light emitting element which emits blue light. An electrode  69  of a light emitting element is provided so as to face the electrodes  61 ,  62  and  63  of the light emitting elements with light emitting layers  66 ,  67  and  68  respectively interposed therebetween. 
     The light emitting element which emits red light is connected to a current supply line  28  via the driving transistor  22   b , the light emitting element which emits green light is connected to a current supply line  29  via the driving transistor  22   c , and the light emitting element which emits blue light is connected to current supply lines  60   a  and  60   b  via the driving transistor  22   a  and  22   d , respectively. The current supply lines  28 ,  29 ,  60   a , and  60   b  extend parallel to each other. The current supply lines  60   a  and  60   b  are provided in different pixels and electrically connected to each other via third wirings  57  ( 57   a  and  57   b ). It is to be noted that the current supply lines  60   a  and  60   b , and the third wirings  57  ( 57   a  and  57   b ) are formed on different layers with first interlayer insulating layers  58  and  59  interposed therebetween, and electrically connected to each other via a connecting portion provided in the first interlayer insulating layers  58  and  59 . 
     Via first wirings  55  ( 55   a  and  55   b ), the current supply line  28  is electrically connected to a current supply line which is included in a pixel unit laterally adjacent to a pixel unit including the current supply line  28  and which is connected to the light emitting element emitting red light via the driving transistor. Similarly, via second wirings  56  ( 56   a  and  56   b ), the current supply line  29  is electrically connected to a current supply line which is included in a pixel unit laterally adjacent to a pixel unit including the current supply line  29  and which is connected to the light emitting element emitting green light via the driving transistor. 
     Reference numeral  50  denotes a substrate,  52  denotes a semiconductor layer,  25   a ,  25   b ,  26 , and  27  denote source lines,  23  denotes a first scan line,  24  denotes a second scan line,  53  denotes a gate insulating layer, and  64  and  65  denote banks. 
     In  FIG. 7 , current supply lines  101   a  to  101   c ,  102   a  to  102   c  and  103   a  to  103   c  intersect with wirings  110   a  to  110   c ,  111   a  to  111   c  and  112   a  to  112   c . The current supply lines  101   a  to  101   c  are electrically connected to the wirings  110   a  to  110   c , and  102   a  to  102   c  are electrically connected to  111   a  to  111   c , further,  103   a  to  103   c  are electrically connected to  112   a  to  112   c . Reference numerals  120   a  to  120   c  denote areas including light emitting elements which emit red light,  121   a  to  121   c  denote areas including light emitting elements which emit green light, and  122   a  to  122   c  denote areas including light emitting elements which emit blue light. 
     As set forth above, in the display device according to the invention, current supply lines which are connected to light emitting elements emitting the same color light (via a driving transistor) are electrically connected to each other both in the longitudinal and the lateral directions. 
     Therefore, the number of current paths through which a current from a current input terminal flows is increased, thereby distributing the current load. Further, significant voltage drop can be prevented from occurring locally. 
     Embodiment 2 
     A display device using the invention is described with reference to  FIGS. 8 and 9A to 9F . 
     As shown in  FIG. 8 , an active matrix display device comprises an external circuit  3004  and a panel  3010 . The external circuit  3004  includes an A/D converter unit  3001 , a power supply unit  3002  and a signal generation unit  3003 . A video data signal inputted in an analog manner is converted to a digital signal in the A/D converter unit  3001 , and supplied to a signal line driver circuit  3006 . The power supply unit  3002  generates power having a desired voltage value from power of battery and outlet, and supplies the generated power to the signal line driver circuit  3006 , a scan line driver circuit  3007 , a light emitting element  3011 , the signal generation unit  3003  and the like. The signal generation unit  3003  converts various inputted signals such as a power supply, a video signal and a synchronizing signal, as well as generating a clock signal and the like for driving the signal line driver circuit  3006  and the scan line driver-circuit  3007 . 
     Signals and power supplies from the external circuit  3004  are inputted to an internal circuit and the like via an FPC and an FPC connecting portion  3005  provided in the panel  3010 . 
     A glass substrate  3008  is provided on the panel  3010 , and on the glass substrate  3008 , the FPC connecting portion  3005 , the internal circuit and the light emitting element  3011  are formed. The internal circuit includes the signal line driver circuit  3006 , the scan line driver circuit  3007  and a pixel portion  3009 . The pixel configuration described in Embodiment Mode 1 is adopted as an example in  FIG. 8 , however, any one of the pixel configurations described in embodiment modes of the invention can be applied to the pixel portion  3009 . 
     The pixel portion  3009  is arranged at the center of the substrate  3008 , and the signal line driver circuit  3006  and the scan line driver circuit  3007  are arranged at the periphery thereof. The light emitting element  3011  and a counter electrode of the light emitting element  3011  are formed over the whole surface of the pixel portion  3009 . 
       FIGS. 9A to 9F  show examples of electronic apparatuses including the display device shown in  FIG. 8 . 
       FIG. 9A  shows a display device which includes a housing  5501 , a supporting base  5502 , a display portion  5503  and the like. The display device of the invention can be applied to the display portion  5503 . 
       FIG. 9B  shows a video camera which includes a main body  5511 , a display portion  5512 , an audio input portion  5513 , operating switches  5514 , a battery  5515 , an image receiving portion  5516  and the like. 
       FIG. 9C  shows a notebook personal computer using the invention, which includes a main body  5521 , a housing  5522 , a display portion  5523 , a keyboard  5524  and the like. 
       FIG. 9D  shows a portable information terminal (PDA) using the invention, which includes a main body  5531  having a display portion  5533 , an external interface  5535 , operating switches  5534  and the like. Further, a stylus  5532  is provided as an attachment for operation. 
       FIG. 9E  shows a digital camera which includes a main body  5551 , a display portion A  5552 , an eye contacting portion  5553 , operating switches  5554 , a display portion B  5555 , a battery  5556  and the like. 
       FIG. 9F  shows a mobile phone using the invention, which includes a main body  5561  having a display portion  5564 , an audio output portion  5562 , operating switches  5565 , an antenna  5566  and the like. 
     According to the display device described above, display variations due to voltage drop are suppressed, leading to improved image quality. Further, image quality of electronic apparatuses including such a display device can also be enhanced. 
     According to the invention, the current load of wirings for transmitting an electrical signal to each pixel of a display device can be distributed, thereby preventing significant voltage drop from occurring locally. Further, display variations due to voltage drop are suppressed. 
     This application is based on Japanese Patent Application serial no. 2003-170090 filed in Japan Patent Office on 13 Jun. 2003, the contents of which are hereby incorporated by reference. 
     Although the present invention has been fully described by way of Embodiment Modes and Embodiments with reference to the accompanying drawings, it is to be understood that various changes and modifications will be apparent to those skilled in the art. Therefore, unless such changes and modifications depart from the scope of the present invention hereinafter defined, they should be constructed as being included therein.