Abstract:
A display panel has a display area with a matrix of individual display pixels. The display panel also includes an electrode that is arranged to cover at least substantially the entirety of the display area. A common electrode is generally frame-shaped and is arranged exclusively around the perimeter of the display area. The common electrode has a notched portion that is located at a power supply lead pattern having a potential that is different from the potential that is applied to the common electrode. The notched portion advantageously substantially reduces the surface area of the common electrode overlapping the power supply lead.

Description:
CROSS REFERENCES TO RELATED APPLICATIONS 
     The present invention contains subject matter related to Japanese Patent Application JP 2007-064417 filed in the Japanese Patent Office on Mar. 14, 2007, the entire contents of which are incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a technique of reducing the probability of occurrence of a short circuit between power supplies in a display panel having a display area with a matrix array of display elements. 
     The present invention relates to a display panel, an electronic device, and a method of making the display panel. 
     2. Description of the Related Art 
     Recently, flat panel displays (FPDs) have remarkably become widespread. Displays of various types are proposed along with the widespread use of FPDs. In the current FPD field, liquid crystal displays (LCDs) are predominantly used. 
     LCDs, which are not self-light-emitting devices, need additional components, such as a backlight and a polarizer. Accordingly, the LCDs have disadvantages in that it is difficult to reduce the thickness and the brightness tends to degrade. 
     In contrast, organic electroluminescent (EL) displays, which are self-light-emitting devices, need no additional components, such as a backlight, in principle. Advantageously, a reduction in thickness and an increase in brightness of the organic EL displays are easier than those of the LCDs. 
     In particular, active-matrix organic EL displays in which a drive circuit (switching element) is provided for each display pixel have advantages in that low current consumption can be achieved because each display pixel can hold light emission. 
     The active-matrix organic EL displays further have advantages in that the displays having a large screen and those having a high-definition screen can be relatively easily realized. Accordingly, the active-matrix organic EL displays are expected to enter the mainstream of next-generation FPDs. 
       FIG. 1  illustrates the structure of a panel of an organic EL display. 
     The organic EL display, indicated at  1 , includes a glass substrate  3  as a base substrate. The upper surface of the glass substrate  3  has a display area  5  with a matrix array of display pixels. The display pixels are driven by active matrix driving. 
     Scan-signal supply TABs  7 , video-signal supply TABS  9 , and power supply TCPs  11  are connected to the glass substrate  3  so as to surround the display area  5 . The scan-signal supply TABS  7  are used to supply signals for controlling a video-signal write operation and a light emission operation on the display pixels. 
     The video-signal supply TABs  9  are used to supply video signals for the display pixels. The power supply TCPs  11  are used to supply drive power. 
     In addition, a cathode layer is arranged on the upper surface of the display area  5  so as to cover the whole of the display area  5  (or an organic-layer deposition area  13 ). The organic-layer deposition area  13 , serving as a range where an organic material for a luminous layer is deposited, is slightly larger than the display area  5 . 
     A cathode-layer deposition area  15 , which provides a maximum area for cathode layer formation, is larger than the organic-layer deposition area  13  by approximately 1 to 2 mm in each side. The cathode layer is held at 0 V by a cathode common electrode  17 , indicated by a hatched portion in  FIG. 1 , electrically connected to the cathode layer in the periphery of the cathode-layer deposition area  15 . 
     Those deposited layers are coated with a sealing compound (not shown) and the sealing compound is then overlaid with a sealing glass, thus constructing the organic EL display  1 . 
       FIG. 2  is an enlarged view of related-art arrangement in the vicinity of the power supply TCP in the organic EL display  1 . A cathode power supply pad supplies-cathode power to a cathode power supply lead pattern  21 . 
     The cathode power supply lead pattern  21  is connected to the cathode common electrode  17  via a contact  23 . The cathode common electrode  17  is frame-shaped so as to be arranged along the periphery of the display area  5  and is electrically connected to the cathode layer deposited in the cathode-layer deposition area  15 . 
     An anode power supply lead pattern  25  is connected to an anode power supply pad. The anode power supply lead pattern  25  is a metallization pattern underlying the cathode common electrode  17  and is connected to the display pixels in the display area. 
       FIG. 3  illustrates the cross section of part where the cathode common electrode  17  overlaps the anode power supply lead pattern  25 . In other words,  FIG. 3  is a cross-sectional view taken along the line A-A in  FIG. 2 . 
     The anode power supply lead pattern  25  is arranged on the upper surface of the glass substrate  3  and is covered with a protective layer  31 . 
     The protective layer  31  is overlaid with a planarizing layer  33 , which is covered with the cathode common electrode  17 . 
     The cathode common electrode  17  is coated with the sealing compound indicated at  35 . The sealing compound  35  is covered with the sealing glass indicated at  37 . The above-described layered structure is of a general type. 
     Related-art organic EL displays are disclosed in Japanese Unexamined Patent Application Publication Nos. 2005-164679, 2005-19151, and 2003-100447. 
     SUMMARY OF THE INVENTION 
     Related-art layered structures have the following disadvantages: Generally, the anode power supply lead pattern  25  arranged below the cathode common electrode  17  needs an enough width (for example, approximately 3 to 5 mm) to alleviate a reduction in potential upon driving. 
     This leads to an increase in the area of overlap between the cathode common electrode  17  and the anode power supply lead pattern  25 . 
     Unfortunately, the large area of overlap therebetween means increasing the probability of occurrence of a short circuit between power supplies due to poor resistance to pressure which may be caused by a pin hole, formed by dust, in the protective layer  31  or the planarizing layer  33  between the cathode common electrode  17  and the anode power supply lead pattern  25 . 
     Such a phenomenon tends to occur especially in large panels and becomes a serious problem for products. In many cases, the large panels use amorphous silicon transistors as driving elements. The use of amorphous silicon transistors also contributes to the above-described phenomenon. 
     The amorphous silicon transistors have advantages in that they are easier to make than polycrystalline silicon transistors and variations in characteristics in the substrate are relatively small. Unfortunately, the amorphous silicon transistors have disadvantages in that its drive capability is small. In order to compensate for the small drive capability, a relatively large voltage of approximately 25 V is needed as a voltage applied between anode and cathode. 
     Since organic EL elements are current-driven type luminescent elements that emit light by current flowing therethrough, the capacity of anode power supply and that of cathode power supply have to increase as increasing the number of pixels and the panel size. 
     Therefore, the occurrence of a short circuit between the power supplies may be a fatal defect. Increasing the thickness of an interlayer insulating layer is effective in reducing the probability of occurrence of a short circuit therebetween. However, this approach is not practical because changing the thickness of the interlayer insulating layer involves changing a process of making the display panel. 
     It is desirable to provide a display panel in that the probability of occurrence of a short circuit between power supplies can be reduced without changing a process of making the display panel and a method of making the display panel. 
     An embodiment of the present invention provides a display panel having a display area with a matrix array of display pixels, the display panel including a common electrode having a notch arranged in a particular portion. 
     In this embodiment, the common electrode is electrically connected to an electrode arranged so as to cover the whole of the display area. The common electrode is frame-shaped and is arranged along the periphery of the display area. 
     In the common electrode, the notch is arranged over a power supply lead pattern to which a potential different from that applied to the common electrode is applied. 
     According to this embodiment of the present invention, the area of overlap between the common electrode and the power supply lead pattern, to which a potential different to that applied to the common electrode is applied, can be minimized. 
     Minimizing the overlap area enables sufficient resistance to pressure to be held even when a pin hole caused by dust occurs, thus reducing the probability of occurrence of a short circuit between power supplies. As the area of the notch increases (i.e., the overlap area decreases), the probability of occurrence of a short circuit between power supplies generally decreases. Advantageously, the yield of the display panel can be increased by the decrease in the probability of occurrence. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram illustrating a general panel structure of an organic EL display; 
         FIG. 2  is a plan view of related-art arrangement in the vicinity of power supply pads; 
         FIG. 3  is a cross-sectional view of part, where a cathode common electrode overlaps an anode power supply lead pattern, in the related art arrangement; 
         FIG. 4  is a plan view of arrangement in the vicinity of power supply pads according to an embodiment of the present invention; 
         FIG. 5  is a cross-sectional view of part, where a cathode common electrode is removed above an anode power supply lead pattern, in the embodiment of the present invention; 
         FIGS. 6A to 6C  are diagrams explaining a process of making a display panel,  FIGS. 6A to 6C  including the cross sections of parts near the power supply pads; 
         FIGS. 7A to 7C  are diagrams explaining the process of making the display panel,  FIGS. 7A to 7C  including the cross sections of the parts near the power supply pads; 
         FIGS. 8A and 8B  are diagrams explaining the process of making the display panel,  FIGS. 8A and 8B  including the cross sections of the parts near the power supply pads; 
         FIGS. 9A and 9B  are diagrams explaining the process of making the display panel,  FIGS. 9A and 9B  including the cross sections of the parts near the power supply pads; 
         FIG. 10  explains the process of making the display panel and includes the cross sections of the parts near the power supply pads; 
         FIG. 11  explains the process of making the display panel and includes the cross sections of the parts near the power supply pads; 
         FIG. 12  is a plan view of another arrangement in the vicinity of power supply pads; 
         FIG. 13  is a plan view of another arrangement in the vicinity of power supply pads; 
         FIG. 14  is a plan view of another arrangement in the vicinity of power supply pads; 
         FIG. 15  is a plan view of another arrangement in the vicinity of power supply pads; 
         FIG. 16  is a plan view of another arrangement in the vicinity of power supply pads; 
         FIG. 17  is a diagram illustrating the conceptual structure of an electronic device; 
         FIG. 18  is a perspective view of a television receiver; 
         FIGS. 19A and 19B  are perspective views of a digital camera; 
         FIG. 20  is a perspective view of a video camera; 
         FIGS. 21A and 21B  are external views of a mobile phone; and 
         FIG. 22  is a perspective view of a computer. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A display panel according to an embodiment of the present invention will be described below. 
     In the following description, components which are not illustrated or described in the present specification are those to which a known or well-known technique in the art is applied. 
     Embodiments which will be described below are implementations of the present invention. The present invention is not restricted to the embodiments. 
     (A) Organic EL Display 
     (A-1) Panel Structure 
     The fundamental structure of an organic EL display according to the present embodiment is the same as that shown in  FIG. 1 , except for the arrangement in the vicinity of the power supply TCPs  11 . Accordingly, a difference will now be described below. 
       FIG. 4  is a plan view of arrangement specific to the present embodiment. In  FIG. 4 , the same components as those in  FIG. 2  are designated by the same reference numerals. 
     In the present embodiment, a cathode common electrode  17  has a rectangular notch  41  that is opposed to an anode power supply lead pattern  25 . 
     The width of the notch  41  is larger than that of the anode power supply lead pattern  25 . The depth of the notch  41  is set such that the bottom of the notch  41  reaches the periphery of a cathode-layer deposition area  15 . Accordingly, the width of the cathode common electrode  17  in the notch  41  is substantially the same as that of the area of overlap between the cathode common electrode  17  and the cathode layer. 
       FIG. 5  illustrates the cross section of part where the cathode common electrode  17  is removed above the anode power supply lead pattern  25 . In other words,  FIG. 5  is a cross-sectional view taken along the line C-C in  FIG. 4 . In  FIG. 5 , the same components as those in  FIG. 3  are designated by the same reference numerals. 
     Referring to  FIG. 5 , in the part where-the notch  41  is arranged, there is no cathode common electrode  17  above the anode power supply lead pattern  25 . The cross section of this part is common to another part where the anode power supply lead pattern  25  is arranged in the vicinity of the cathode-layer deposition area  15 . 
     In the present embodiment, therefore, the area of overlap between the anode power supply lead pattern  25  and the cathode common electrode  17  with interlayer insulating layers therebetween can be remarkably reduced. 
     Advantageously, if a pin hole occurs in an interlayer, a short circuit between the power supplies can be remarkably minimized. 
     (A-2) Method of Making Display Panel 
     A method of making the display panel with the above-described structure will be explained below with reference to  FIGS. 6A to 11 .  FIGS. 6A to 11  illustrate the cross sections (taken along the line B-B of  FIG. 4 ) of part where a cathode power supply lead pattern  21  is arranged and the cross sections (taken along the line C-C of  FIG. 4 ) of part where the anode power supply lead pattern  25  is arranged. 
     First, a metallic layer  51  for lead patterning is formed on the upper surface of a glass substrate  3  ( FIG. 6A ). 
     Subsequently, the metallic layer  51  is coated with a resist  53  and the resist  53  is then patterned for formation of lead patterns ( FIG. 6B ). 
     After that, the resist  53  and part of the metallic layer  51  are removed by etching. Consequently, only the metallic layer  51  underlying the resist  53  is remained on the glass substrate  3 , thus forming the cathode power supply lead pattern  21  and the anode power supply lead pattern  25  ( FIG. 6C ). 
     A protective layer  31  is then arranged so as to cover the lead patterns and the glass substrate  3  ( FIG. 7A ). 
     After that, the protective layer  31  is coated with the resist  53  and the resist  53  is then patterned for formation of a contact  23  ( FIG. 7B ). Since the contact  23  is provided for the cathode power supply lead pattern  21 , an opening  55  is arranged only in a region including the line B-B in  FIG. 4 . 
     After that, the resist  53  and part of the protective layer  31  are removed by etching. Consequently, only the protective layer  31  under the opening  55  is removed, thus forming an opening  57  for the contact  23  ( FIG. 7C ). 
     Subsequently, a planarizing layer  33  is arranged so as to cover the protective layer  31  and the cathode power supply lead pattern  21  ( FIG. 8A ). 
     After that, the planarizing layer  33  is coated with the resist  53  and the resist  53  is patterned for formation of the contact  23  ( FIG. 8B ). Since the contact  23  is provided for the cathode power supply lead pattern  21 , an opening  59  is arranged in a region including the line B-B in  FIG. 4 . 
     After that, the planarizing layer  33  and the protective layer  31  under the opening  59  are removed by etching. Consequently, a hole  61  that reaches the cathode power supply lead pattern  21  is formed so as to downwardly extend from the opening  59  ( FIG. 9A ). 
     Subsequently, the cathode common electrode  17  is formed by vapor deposition ( FIG. 9B ). The cathode common electrode  17  is arranged in the periphery of the display area  5  so as to be frame-shaped. The cathode common electrode  17  is arranged uniformly on the surface including side walls of the hole  61 . The hole  61  corresponds to the contact  23 . 
     After that, the cathode common electrode  17  is coated with the resist  53  and the resist  53  is patterned for formation of the notch  41  ( FIG. 10 ). Since the notch  41  is arranged only above the anode power supply lead pattern  25 , an opening  63  is arranged only in a region including the line C-C in  FIG. 4 . 
     After that, the cathode common electrode  17  under the opening  63  is removed by etching. Consequently, the notch  41  is formed so as to downwardly extend from the opening  63  ( FIG. 11 ). 
     (A-3) Advantages 
     The notches  41  are arranged in the cathode common electrode  17  in part where the cathode common electrode  17  overlaps the anode power supply lead pattern  25 , thus reducing the probability of occurrence of a short circuit between the power supplies, the short circuit being a fatal defect caused upon occurrence of a pin hole. Advantageously, the yield of the organic EL display can be improved, thus reducing the manufacturing cost. 
     As for the process of making the organic EL display, it is unnecessary to change the fundamental processing steps. A step of forming the notch  41  may be added to the fundamental processing steps. Advantageously, the organic EL display can be efficiently made in terms of the making process. 
     (B) Modifications 
     (B-1) Shape of Notch 
     The foregoing embodiment relates to the arrangement of the rectangular notches  41 . 
     The notch  41  is not necessarily limited to the rectangular one. 
     For example, the notch  41  may be rounded as shown in  FIG. 12 . In  FIG. 12 , the corners of the bottom of the notch  41  are rounded. The corners thereof at the open end may be rounded. Alternatively, all of the corners may be rounded. 
     The notch  41  may be V-shaped as shown in  FIG. 13 . In this case, the area of overlap between the cathode common electrode  17  and the anode power supply lead pattern  25  is larger than that in  FIG. 4  or that in  FIG. 12  but is remarkably smaller than that in  FIG. 2 . Although the probability of occurrence of a short circuit between the power supplies is higher than that in the foregoing embodiment, the probability can be lower than that in the related art. 
     As shown in  FIG. 14 , a hole, also indicated at  41 , may be formed by cutting a part out of the cathode common electrode  17  instead of the notch  41 . In this case, the area of overlap between the cathode common electrode  17  and the anode power supply lead pattern  25  is larger than that in  FIG. 4  or that in  FIG. 12  but is remarkably smaller than that in  FIG. 2 . Although the probability of occurrence of a short circuit between the power supplies is higher than that in the foregoing embodiment, the probability can be lower than that in the related art. 
     The notch  41  may be arranged so as not to reach the cathode-layer deposition area  15  as shown in  FIG. 15 . In this case, the area of overlap between the cathode common electrode  17  and the anode power supply lead pattern  25  is larger than that in  FIG. 4  or that in  FIG. 12  but is remarkably smaller than that in  FIG. 2 . Although the probability of occurrence of a short circuit between the power supplies is higher than that in the foregoing embodiment, the probability can be lower than that in the related art. 
     The width of the notch  41  may be narrower than that of the anode power supply lead pattern  25  as shown in  FIG. 16 . In this case, the area of overlap between the cathode common electrode  17  and the anode power supply lead pattern  25  is larger than that in  FIG. 4  or that in  FIG. 12  but is remarkably smaller than that in  FIG. 2 . Although the probability of occurrence of a short circuit between the power supplies is higher than that in the foregoing embodiment, the probability can be lower than that in the related art. 
     (B-2) Position for Formation of Notch 
     In the foregoing embodiment, the notch  41  is arranged in each part where the cathode common electrode  17  overlaps the anode power supply lead pattern  25  to which an anode potential is applied. 
     The notch  41  may be disposed in part where the cathode common electrode  17  overlaps another lead pattern to which a potential different from that applied to the cathode common electrode  17  is applied. 
     (B-3) Position of Layer for Common Electrode 
     In the foregoing embodiment, the cathode common electrode  17  is arranged over the cathode layer. 
     The present invention is applicable to a case where the cathode common electrode  17  is disposed under the cathode layer. 
     (B-4) Type of Common Electrode 
     In the foregoing embodiment, the common electrode is the cathode common electrode. 
     The present invention is applicable to a case where the common electrode is used for application of another potential. 
     (B-5) Applications 
     The foregoing embodiment relates to the organic EL display serving as a display panel module. 
     The organic EL display may be mounted on an electronic device and be distributed as another type of product. 
       FIG. 17  illustrates the conceptual structure of an electronic device  71 . The electronic device  71  includes an organic EL display  73  having the above-described panel structure and a system controller  75 . A process executed by the system controller  75  depends on the type of the electronic device  71 . 
     The electronic device  71  has a function of displaying an image or a video image that is generated therein or externally supplied and is not limited to a specific field device. 
     Applications of this type of electronic device  71  include, for example, a television receiver.  FIG. 18  is a perspective view of a television receiver  81 . 
     The front surface of a housing of the television receiver  81  has a display screen  87  including a front panel  83  and a filter glass  85 . The display screen  87  corresponds to the organic EL display described in the foregoing embodiment. 
     Applications of this type of electronic device  71  include, for example, a digital camera.  FIGS. 19A and 19B  illustrate a digital camera  91 .  FIG. 19A  is a perspective view of the digital camera  91  viewed from the front (i.e., the side of an object).  FIG. 19B  is a perspective view of the digital camera  91  viewed from the rear (i.e., the side of a user or photographer). 
     The digital camera  91  includes an imaging lens (disposed behind a protective cover  93  since the protective cover  93  is closed in  FIG. 19A ), a light emitting unit  95  for flash shooting, a display screen  97 , a control switch  99 , and a shutter release  101 . The display screen  97  corresponds to the organic EL display described in the foregoing embodiment. 
     Applications of this type of electronic device  71  include, for example, a video camera.  FIG. 20  is a perspective view of a video camera  111 . 
     The video camera  111  includes a body  113 , an imaging lens  115  that is disposed in the front of the body  113  and captures an image of an object, a start and stop switch  117 , and a display screen  119 . The display screen  119  corresponds to the organic EL display described in the foregoing embodiment. 
     Applications of this type of electronic device  71  include, for example, a portable terminal.  FIGS. 21A and 21B  are external views of a foldable mobile phone  121 , serving as a portable terminal.  FIG. 21A  illustrates the mobile phone  121  in an unfolded state.  FIG. 21B  illustrates the mobile phone  121  in a folded state. 
     The mobile phone  121  includes an upper housing  123 , a lower housing  125 , a connecting member (a hinge in this case)  127 , a main display screen  129 , a sub-display screen  131 , a picture light  133 , and an imaging lens  135 . The main display screen  129  and the sub-display screen  131  each correspond to the organic EL display described in the foregoing embodiment. 
     Applications of this type of electronic device  71  include, for example, a computer.  FIG. 22  is a perspective view of a notebook-sized personal computer  141 . 
     The notebook-sized personal computer  141  includes a lower housing  143 , an upper housing  145 , a keyboard  147 , and a display screen  149 . The display screen  149  corresponds to the organic EL display described in the foregoing embodiment. 
     Other applications of this type of electronic device  71  include, for example, an audio player, a game console, an electronic book, and an electronic dictionary. 
     (B-6) Other Displays 
     The foregoing embodiment has been described with respect to the organic EL display, serving as a display device. 
     The present invention can be applied to other self-light-emitting displays, such as an inorganic EL display and an LED display. 
     It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and alterations may occur depending on design requirements and other factors insofar as they are within the scope of the appended claims or the equivalents thereof.