Abstract:
The present invention provides a light-emitting display device to improve the throughput efficiency of light transmitting from the light-projecting surface. The light-emitting display device is provided with a plurality of anodes isolated from each other by isolating films in the shape of islands, cathodes arranged opposite to the anodes and a plurality of pixels disposed in the form of a matrix. The pixels are held between the anodes and the cathodes. Each of the pixels has at least a thin film layer including a luminous layer which emits light when a predetermined voltage is applied between the anode and the cathode. The anode defines the light-projecting surface to transmit light from the organic thin film. The cathode is provided with a declined surface between adjacent ones of the pixels. The declined surface defines an acute angle with respect to the light-projecting surface.

Description:
BACKGROUND OF THE INVENTION  
       Field of the Invention  
         [0001]    This invention relates to a light-emitting display device.  
           [0002]    Display devices using light-emitting diodes, liquid crystal display devices, or organic EL (electro luminescence) devices as a light modulation layer of a pixel are apt to expand their application ranges in addition to display devices such as business machines and computers primarily because the display units can be thinned. Among these display devices, a light-emitting display device using organic EL devices has the following advantages compared with a liquid crystal display device (LCD).  
           [0003]    (a) Since the organic light-emitting display device is of a self-emission type, a clear display and a wide viewing angle can be obtained. Further, low power consumption, lightweight, and thin thickness can be realized because no rear light source is necessary.  
           [0004]    (b) The response speed is fast. The response speed of organic light-emitting display device is on the order of microsecond (ps) while that of an LCD is on the order of millisecond (ms).  
           [0005]    (c) Since a solid luminous layer is used, there is the possibility that the working temperature range may be wider.  
           [0006]    On the basis of these advantages, research and development of an organic light-emitting display devices have been promoted actively. Particularly, there have been carried out those of a polycrystalline silicon thin film transistor (p-Si TFT) type organic self-emission display system. Pixels of this display system are disposed in a matrix form and each connected p-Si TFTs for driving the display device so that such a display system can realize high resolution.  
           [0007]    [0007]FIG. 10 shows schematically a cross sectional view of an array substrate in a conventional organic light-emitting display device. An organic thin film layer including at least an organic luminous layer  113  is held between an anode  109  and a cathode  115 . When an energizing voltage is supplied between the anode and the cathode, electrons and holes are injected into the organic thin layer where they are recombined. Thus, exciters are generated in the organic thin layer. Light is emitted from the organic thin layer when the exciters lose energy by transferring from a higher energy level to a lower one.  
           [0008]    The organic light-emitting display device, as shown in FIG. 10, has an opening above the anode  109  connected to a driving TFT. The driving TFT includes a p-Si layer  103 , a gate insulating film  104 , a gate electrode  105 , and source and drain electrodes  107 . A passivation film  110  and a partition insulating film  111  are formed over the p-Si layer  103 , gate insulating film  104 , gate electrode  105  and source and drain electrodes  107 .  
           [0009]    The luminous intensity of such a conventional organic light-emitting display device is about a half of the luminous intensity (100 to 150 nt) of the LCD. Further, cross talk occurs between neighboring pixels. Where, in particular, the color of red (R), green (G), or blue (B) is emitted from the pixel, colors from neighboring pixels are mixed so that the contrast of the organic light-emitting display device is considerably lowered.  
         SUMMARY OF THE INVENTION  
         [0010]    An object of the present invention is to provide a solution for the aforementioned problem.  
           [0011]    An object of the present invention is to provide a light-emitting display device with improvement of the output efficiency of light from the light-projecting surface.  
           [0012]    Another object of the present invention is to suppress the occurrence of cross talk between neighboring pixels.  
           [0013]    A first aspect of a light-emitting display device in accordance with the present invention includes a plurality of first electrodes electrically isolated from each other; second electrodes provided opposite to the first electrodes; a plurality of pixels held between the first and second electrodes; and a light reflecting surface disposed between adjacent ones of said pixel electrodes.  
           [0014]    The pixels are disposed in a matrix form and each have at least a light-emitting layer. One of the first and second electrode defines a light-projecting surface. The light-reflecting surface transmits light traveling from one of the adjacent pixels toward the other thereof to the light-projecting surface.  
           [0015]    A second aspect of a light-emitting display device in accordance with the present invention further includes partition insulation films to electrically isolate the first electrodes from each other. The partition insulation films define openings between the adjacent pixels. The other of the first and second electrodes provides opposite to the light-projecting surface via the luminous layer includes inclined surfaces provided along the partition insulation films. The inclined surfaces are used for the light-reflecting surfaces and define an acute angle with respect to the light-projecting surface.  
           [0016]    A third aspect of a light-emitting display device in accordance with the present invention is characterized in that the second electrodes are continuously formed on the pixels.  
           [0017]    A fourth aspect of a light-emitting display device in accordance with the present invention is characterized in that the inclined surfaces are formed around the pixels.  
           [0018]    A fifth aspect of a light-emitting display device in accordance with the present invention further includes partition insulation films to electrically isolate the first electrodes from each other. The partition insulation films define openings around the pixels. The second electrodes are provided to cover the partition insulation films and include inclined surfaces at the openings which define an acute angle with respect to the light-projecting surface.  
           [0019]    The above-stated and other objects and advantages of the invention will become apparent from the following description when taken with the accompanying drawings. It will be understood, however, that the drawings are for purposes of illustration and are not to be construed as defining the scope or limit of the invention, reference being had for the latter purpose to the claims appended hereto. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0020]    [0020]FIG. 1 is a plan view of an array substrate of a light-emitting display device in accordance with the present invention;  
         [0021]    [0021]FIG. 2 is a longitudinal cross section of the organic light-emitting display device shown in FIG. 1;  
         [0022]    [0022]FIG. 3( a ) is a plan view of pixels of a light-emitting display device;  
         [0023]    [0023]FIG. 3( b ) shows schematically a partial cross section of one pixel of the present invention;  
         [0024]    [0024]FIG. 4( a ) shows a longitudinal cross section of a pixel in accordance with the present invention;  
         [0025]    [0025]FIG. 4( b ) shows an enlarged part of the pixel set forth in FIG. 4( a );  
         [0026]    [0026]FIG. 5 is a circuit diagram of a plurality of pixels used in an organic light-emitting display device in accordance with the present invention;  
         [0027]    [0027]FIG. 6 shows a longitudinal cross section of a pixel in accordance with the second embodiment of the present invention;  
         [0028]    [0028]FIG. 7 is a longitudinal cross section of a pixel of a light-emitting display device in accordance with the present invention;  
         [0029]    [0029]FIG. 8 is a longitudinal cross section of a pixel of a light-emitting display device in accordance with the present invention;  
         [0030]    [0030]FIG. 9 is a circuit diagram of panel array elements in a light emitting display device in accordance with the present invention; and  
         [0031]    [0031]FIG. 10 is a longitudinal cross section of a pixel of a conventional organic light-emitting display device. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0032]    The preferred embodiments of the present invention will be explained in detail hereinafter with reference to the accompanying drawings. The first embodiment of the present invention is shown in FIG. 1 which is a schematic plan view of an array substrate  100  for an organic light-emitting display device. The array substrate  100  includes a display area  120  in which pixels  1  are disposed in a matrix form (not shown). Two sides of the display area  120  are provided with an X-direction driving circuit  121  and a Y-direction driving circuit  123 . The X-direction driving circuit  121  is disposed on the right side of the drawing and connected to wires  122  led from the respective pixels. The Y-direction driving circuit  123  is disposed on the lower side of the drawing and connected to wires  123  led from the respective pixels.  
         [0033]    [0033]FIG. 2 shows schematically a longitudinal cross section of an organic light-emitting display device  200 . The array substrate  100  shown in FIG. 1 is incorporated into the organic light-emitting display device  200 . Sealing members  131  are provided at the edges of the light-emitting display device. An opposite substrate  133 , for example a glass substrate, is mounted on the sealing members  131 . On the inner surfaces of the glass substrate  133  is coated with a desiccant  132  such as zeolite or BaO Coated. Further, drying nitrogen is filled inside the organic light-emitting display device  200 . A display surface of the organic light-emitting display device  200  is on the array substrate.  
         [0034]    As shown in FIG. 3( a ), the display area of the light-emitting display device includes a plurality of pixels  1  to be disposed in a matrix form (not shown). The pixels  1  are composed of red, green and blue color elements  11 ,  12  and  13 . FIG. 3( b ) is a schematic plan view of one pixel  11 . The pixel  11  has openings M and S to be explained later.  
         [0035]    [0035]FIG. 4( a ) shows a cross sectional view of a pixel along a cutting line IV(a)-IV(a) of the pixel shown in FIG. 3( b ). The TFT shown in the drawing is a driving TFT.  
         [0036]    As shown in FIG. 5, a pixel switching TFT  44  has the source connected to a signal line  41 , and the gate connected to a gate line  43 . When the pixel switching TFT  44  is selected by applying a scanning signal to the gate from the gate line  43  and an image signal to the source from the signal line  41 , a driving TFT  45  turns on, a display element  46  is energized and a current is supplied from a current supply line  42  to the source of the driving TFT 45 . The supplied current passes through the drain and enables the display element  46  to emit light.  
         [0037]    As shown in FIG. 4( a ), an undercoat layer  102  is laminated on a light transmissible substrate  101  and a p-Si layer  103  is formed on the undercoat layer  102  in an island shape. The p-Si layer  103  is divided into a source region  103   a , a channel region  103   b , and a drain region  103   c . A gate insulating film  104  is coated on the undercoat layer  102  and the p-Si layer  103 . A gate electrode  105  is formed in the region corresponding to the channel region  103   b  of the p-Si layer  103  via the gate insulating film  104 . Further, the source and drain electrodes  107   a  and  107   b  connected to the source and drain regions of the p-Si layer  103 , respectively, are electrically insulated from the gate electrode  105  by an interlayer insulating film  106 . In a predetermined pixel area on the interlayer insulating film  106 , the anode  109  made of a transparent material, for example, ITO (indium tin oxide) is formed in an island shape and electrically connected to the drain electrode  107   b.    
         [0038]    An opening is defined over the anode  109  by an organic partition insulating film  111  formed on an inorganic passivation film  110 . An organic thin layer including at least an organic luminous layer  113  is laminated on the anode  109 . A cathode  115  is continuously formed over a plurality of pixels opposite to the anode  109  via the organic thin layer. Such an organic thin layer is composed of, for example, the organic luminous layer  113 , an anode buffer layer  112 , and a cathode buffer layer  114 . The anode buffer layer  112  and the cathode buffer layer  114  may be, however, made of an inorganic or organic material laminated film.  
         [0039]    The partition insulating film  111  has an opening or recess S defined between the neighboring pixels as shown in FIGS.  4 ( a ) and  4 ( b ). Thus, the partition insulating film  111  is formed overall the periphery inside the edge of each pixel. Such an opening S is also schematically shown in FIG. 3( b ). There are provided at the portion of the opening S inclined walls laminated with the partition insulating film  111 , anode buffer layer  112  and cathode  115  on the side of the anode  109  (reference number  21  in FIG. 3( b )). Such an inclination is a an acute angle (θ&lt;90°), preferably, more than 45 degrees with respect to the light-projecting surface, the anode  109  or the substrate  101 . With this structure, light advancing in the horizontal direction, i.e., light components P 2  and P 3  shown in FIGS.  4 ( a ) and  4 ( b ) are reflected on the surface of the cathode  115  made of a metallic film and advance toward the display surface. As a result, there is increased the luminous intensity of the display panel.  
         [0040]    The inclined angle may be, however, smaller than 90 degrees from the viewpoint of increasing the luminous intensity.  
         [0041]    A manufacturing method for an organic light-emitting display device relating to this embodiment will be explained hereunder.  
         [0042]    Firstly, a light transmissible substrate  101  such as the glass substrate is prepared. The undercoat layer  102  made of a lamination layer of a SiNx film with a thickness of 50 nm and a SiOx film with a thickness of 100 nm is formed on a main surface of the glass substrate  101 . The p-Si layer  103  with a thickness of 50 nm is then deposited on the undercoat layer  102  in an island shape.  
         [0043]    Next, the gate insulating film  104  made of SiOx, for example, with a film thickness of 140 nm is formed on the undercoat layer  102  and the p-Si layer  103 . Further, the gate electrode  105  made of a MoW film with a thickness of 300 nm is deposited on the gate insulating film  104 .  
         [0044]    Ions are implanted into the p-Si layer  103  through the gate electrode  105  used as a mask. Thus, the region of the p-Si layer  103  positioned under the gate electrode  105  becomes a channel region  103   b , the source region  103   a  and drain region  103   c  are formed on both sides thereof.  
         [0045]    Next, the interlayer insulating film  106  made of SiOx, for example, with a thickness of 660 nm is formed on the gate insulating film  104  and the gate electrode  105 . Then, an ITO (indium tin oxide) film is formed on the interlayer insulating film  106  and a patterning process is applied to the ITO film to make the anode  109  as a first electrode in an island shape which covers a predetermined region.  
         [0046]    A connecting hole is bored to reach the source and drain regions  103   a  and  103   b  through the interlayer insulating film  106  and the gate insulating film  104 . A metallic film, such as, a laminated film of an Mo film with a thickness of 50 nm, an Al film with a thickness of 450 nm, and an Mo film with a thickness of 100 nm is embedded in this hole. Thus, the source and drain electrodes  107   a  and  107   b  are formed and the anode  109  is connected to the drain electrode  107   b  of the driving TFT.  
         [0047]    Next, the passivation film  110  made of a SiNx film, for example, with a thickness of 450 nm is formed on the interlayer insulating film  106  and the surface of the anode  109 . An opening is formed to make the outer surface of the anode  109  exposed. Further, the partition insulating film  111  is coated on the exposed surface of the anode  109  and the passivation film  110 . The partition insulating film  111  is formed so as to cover the end of the anode  109 . The first opening through which the surface of the anode  109  is exposed is formed at the area indicated by the arrow M. Also, the second opening is formed inside the edge of the pixel at the area indicated by the arrow S. This opening is defined to prevent a short circuit with the cathode  115  as described later. Further, a wall surface  111 F of the partition insulating film  111  is made in the opening indicated by the arrow S, as shown in FIG. 4( b ). The surface on the side of the anode  109  is inclined at an acute angle, for example, θ=45° with respect to the light-projecting surface or the substrate  101 .  
         [0048]    Next, the anode buffer layer  112  made of laminated layers of hole transportation, injection and the like is deposited on an upper surface of the partition insulating film  111  and the anode  109 . The total thickness of the laminated layers is 110 nm, for instance. Then, the organic luminous layer  113  and the cathode buffer layer  114  composed of an electron injection layer and the like are deposited in order. The organic luminous layer  113  and the cathode buffer layer  114  each are 30 nm in thickness. Finally, the cathode  115  is formed on the overall surface.  
         [0049]    As a result, the light component P 1  among the light components P 1 , P 2 , P 3  radiated from the organic luminous layer  113  advances directly toward the display surface. The light components P 2  and P 3  advance in the horizontal direction via the partition insulating film  111  and are reflected toward the display surface by the cathode  115  on the wall surface at the opening, indicated by the arrow S, of the partition insulating film  111  on the side of the anode  109 . Thus, the luminous intensity of the display device increases significantly.  
         [0050]    A wire  108  may be laid as shown in the drawing between the pixels. It is desirable to define an inclined plane at the end portion of the wire  108  so that the inclined plane reflects the light components P 2  and P 3  inside the device.  
         [0051]    At the portion indicated by the arrow S shown in FIG. 4( a ) or ( b ) in the aforementioned embodiment, the light component P 3  passes through the partition insulating film  111 , is reflected by the cathode  115  via the anode buffer layer  112 , and then advances toward the display surface. The light component P 3  is attenuated twice according to the absorption coefficient (absorptive coefficient) of the anode buffer layer  112  and advances toward the light-projecting surface. As a result, the efficiency is lowered. In order to prevent it, where the cathode  115  is directly attached to the inclined wall surface  111 F of the opening of the partition insulating film  111 , attenuation of the light component P 3  can be substantially avoided.  
         [0052]    [0052]FIG. 5 is a longitudinal cross section of the pixel of the second embodiment of an organic light-emitting display device in accordance with the present invention. The same numerals in FIG. 6 denote substantially the same or corresponding elements as those in FIG. 4( a ) and  4 ( b ) and the explanation thereof will be omitted.  
         [0053]    A reference numeral  11 A generally designates a pixel. In the same way as with the first embodiment, an opening is provided at the area indicated by arrow S and the wall surface  111 F on the side of the anode  109  is inclined, for example, at about 45 degrees with respect to the light-projecting surface. The anode buffer layer  112 , the organic luminous layer  113 , and the cathode buffer layer  114  are respectively formed on the anode  109  in the region surrounded by the partition insulating film  111 , and the cathode  115  is formed on the pixel  11 A. The cathode  115  is directly attached to the wall surface  111 F of the partition insulating film  111  inclined at about 45 degrees with respect to the light-projecting at the portion indicated by the arrow S.  
         [0054]    The light components P 3  (and P 2 ) advancing in the horizontal direction from the organic luminous layer  113  is directly reflected by the cathode  115  on the inclined surface of the partition insulating film  111 . Thus, the light components P 3  is not attenuated by the anode buffer layer  112  as mentioned above. The luminous intensity of the display device can be increased more than that set forth in the embodiment shown in FIGS.  4 ( a ) and  4 ( b ).  
         [0055]    As mentioned above, an opening is provided between the neighboring pixels of the organic light-emitting display device and the wall surface of the opening of the partition insulating film is made at an acute angle with respect to the light-projecting surface, the anode  109  or the substrate  101  so that light leaking in the direction parallel to the light-projecting surface can be taken out efficiently from the pixel.  
         [0056]    Namely, the electrode on the side opposite to the light-projecting surface is made of a material with a high reflection factor and the electrode is configured to make an acute angle with respect to the light-projecting surface at the end portion of each pixel, so that light emitted from the organic luminous layer can be taken out efficiently from the light-projecting surface.  
         [0057]    Further, where the opening is provided around the entire internal surface of the edge portion of each pixel, that structure can prevent light from leaking and suppress cross-talk between the neighboring pixels. As a result, the contrast of the light-emitting display device is improved and color mixture between the neighboring pixels can be significantly avoided in the case of a color display.  
         [0058]    The organic luminous layer set forth ion the first and second embodiment is made by applying vapor deposition of small molecular materials, e.g., Alg3 or the like.  
         [0059]    Now referring to FIG. 7, there is shown a longitudinal cross section of an array substrate in an organic light-emitting display device as a third embodiment of the present invention. An organic luminous layer  113  is made of a highly polymerized compound, e.g., polyfluorene. The luminous layer  113  is formed by using a method of jetting an ink corresponding to a color of red (R), green (G) or blue (B). Namely, the highly polymerized system organic luminous material is sequentially jetted out toward an opening defined by a partition insulation film  111  and an anode buffer layer  112  so that the organic luminous layer  113  is formed. The thickness of the anode buffer layer  112  maybe 30 nm while that of the luminous layer  113  may be 80 nm this embodiment.  
         [0060]    Since the luminous layer  113  is formed in such a way as set forth above by using the highly polymerized system luminous material, this embodiment is easily adaptive to changes in design of various sizes of the array substrate. Further, an appropriate quantity of the luminous material is selectively jetted out toward a necessary portion, the luminous material may be efficiently used.  
         [0061]    Next, a fourth embodiment of the present invention will be described with reference to FIG. 8 which shows a cross-sectional view of an organic light-emitting display device. In this embodiment, a driving TFT (driving element)  45  is connected to a first electrode, i.e., an anode  109 . As shown, the anode  109  is connected to a drain electrode  107   b  of the driving TFT  45  through an insulation film  116 . A signal line  41  is formed on an interlayer insulation layer  106 . the insulation layer  116  is also provided to cover the signal line  41  and the interlayer insulation layer  106 .  
         [0062]    According to this embodiment, since the insulation layer  116  is provided between the first electrode  109  and the signal line  41 , the first electrode  109  of this embodiment has more degree of freedom for disposition than that of the first, second or third embodiment in which the first electrode  109  is disposed on the same plane as the signal line  41 . In addition, this embodiment is capable of increasing a luminous area.  
         [0063]    It should be noted that the present that the present invention is not limited to the embodiments set forth above but has various variations. As shown in FIG. 9, for example, a pixel 1 includes a pixel switch  44  to select a pixel to which a video signal is supplied from a Y-direction driving circuit  123  in response to a scanning signal supplied from an X-direction driving circuit  121 , a first capacitor  47  to hold during one horizontal scanning period the video signal supplied from a signal line  41  through the pixel switch  44 , a driving element  45  to supply a driving current to a display element  46  in accordance with the video signal, and a reset circuit  48 .  
         [0064]    The pixel switch  44  and the driving element  45  are composed of an n-type TFT and a p-type TFT, respectively. The reset circuit  48  includes a second capacitor  48   a  disposed between the drain electrode of the pixel switch  44  and the gate of driving element  45 , a first switch  48   b  connected between the gate and drain electrode of the driving element  45  and a second switch the drain electrode of the driving element  45  and the first electrode of the display element  46 .  
         [0065]    Meanwhile, the display element set forth hereinabove means a laminated layer device which includes a first electrode and a second electrode provided opposite to the first electrode and a light-emitting device held between the first and second electrode. Further, the light-emitting device (organic thin layer) may be composed of an anode buffer layer commonly formed for each color, a cathode buffer layer and a luminous layer provided for each color. The light-emitting device may be also functionally composite double layer or a single layer.  
         [0066]    In the embodiment explained above, the anode is made transparent and disposed on the side of light-projecting surface and the cathode is provided as a light-reflecting electrode disposed on the side opposite to the light-projecting surface. However, there may be other structures. The cathode, for instance, which is made of an optically transparent and electrically conductive film may be disposed on the side of light-projecting surface while the anode which is a laminated film of an electrically conductive file and a metal layer may be disposed on the side opposite to the light-projecting surface.  
         [0067]    In addition, a light-transmitting display device in the embodiments described above projects light to the outer through the array substrate on which TFTs and other elements are disposed. As one of its alternatives, the second electrode is made of a transparent conductive film so that light can be projected to the outer through the second electrode. In any case, it is important to dispose a light-projecting surface between neighboring pixels in order for light traveling from one pixel toward the other of the neighboring pixels to pass through the light-projecting surface.  
         [0068]    By way of example, the opening defined by the anode buffer layer  112  and the partition insulation film  111  is provided at the entire surrounding of the pixel in the embodiments described above. The opening may be formed in a stripe shape along the raw of a pixel. In the case of color display, a mixture of colors between neighboring pixels can be suppressed significantly if each color of red, green or blue is formed in such a stripe.  
         [0069]    A light-emitting display device is not only an organic luminous display device such as an electro-luminescence device, but also other display devices may be applied.  
         [0070]    As set forth above, according to the present invention, there can be provided a light-emitting display device capable of improving throughput efficiency of light to the light-projecting surface. Further, a light-emitting display device of the present invention has the advantage of substantial suppression or reduction on cross talk between neighboring pixels.