Abstract:
An actual concrete pixel structure of a top emission type display comprises a plurality of pixels arranged in a matrix on a substrate. Each of the pixels includes a light emission device prepared by forming a transparent pixel electrode and a metal pixel electrode on both surfaces of a light emitting layer and a driving circuits for controlling the driving current of the light emission device. The driving circuit is formed on the substrate, and the light emission device is formed in a layer manner above the driving circuit with an intermediate layer made of an insulation material interposed therebetween. The transparent pixel electrode is situated on the side opposite to the substrate. The metal pixel electrode of the light emission device is connected with the driving circuit through a conduction portion which extends through the intermediate layer. Thus, light emitted from the light emission device can be prevented from reaching transistors by locating the transistors constituting the driving circuit below the metal pixel electrode, and leak current by the light of the transistor in the off state can be suppressed to prevent degradation in the image quality.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention relates to an active matrix type display, for example, a display using light emission devices that emit light by themselves, such as organic LEDs.  
           [0002]    Demands for personal computers, portable information terminals, information communication equipment or composite products thereof have been increased with the coming of high information society. For the products described above, displays of reduced thickness and weight and having high-speed response are demanded.  
           [0003]    As a display suitable to such demands, displays using light emission devices capable of saving electric power have been proposed. Generally, an active matrix type display is formed by arranging rectangular pixel regions in a matrix on a substrate. For example, an organic LED as one of light emission devices is formed by putting an organic LED device comprising a hole transportation layer, a charge injection layer and an organic light emission layer between a transparent pixel electrode (anode) and a metal pixel electrode (cathode) in such a manner that both surfaces of the organic LED device are in contact with the transparent pixel electrode and the metal pixel electrode, respectively. Then, existent active matrix type organic LED displays are formed by disposing a transparent pixel electrode of the organic LED device on the side of the transparent substrate such as glass and disposing the metal pixel electrode on the side opposite to the substrate.  
           [0004]    In the driving circuit for the organic LED device in each pixel, a first thin layer transistor (TFT 1 ) is disposed at a position near the intersection between each of scanning lines and signal lines arranged in a lattice, TFT 1  is driven by scanning signals and pixel signals to store date in a capacitor (holding capacitor), a second thin layer transistor (TFT 2 ) is driven in accordance with the voltage of the capacitor and the current flowing to the organic light emitting layer by way of the transparent pixel electrode as the anode connected with TFT 2  is controlled to emit light. Then, light emitted from the organic light-emitting layer is taken out through the transparent pixel electrode on the side of the substrate.  
           [0005]    By the way, in the case of a bottom emission type display in which emission light is taken out from the substrate, since the area of the driving circuit comprising TFT 1 , TFT 2 , capacitor and lines arranged for each of the pixels hinders light transmission, an improvement in the so-called aperture ratio is limited.  
           [0006]    In view of the above, to improve the aperture ratio without effect of the driving circuits such as TFT, the so-called top emission type display that takes out light from the side opposite to the substrate has been proposed so far (Document: SID2001 Digest-24-4L). In the top emission type, an improvement in the aperture ratio can be expected as compared with the bottom emission type.  
           [0007]    In the top emission type, light is taken out by using a transparent electrode layer on the upper side of the organic LED device, but the document described above discloses no actual structure of the organic LED device and the driving circuit.  
           [0008]    Further, the dielectric constant of the transparent pixel electrode layer is generally greater by about one digit or more as compared with that of the metal pixel electrode layer. Accordingly, current consumption increases as the size of the display panel enlarges, which poses a problem that a loss of current supply line to the organic LED device-increases.  
           [0009]    Further, the organic LED device degrades rapidly due to heat or humidity. Accordingly, the method of forming a transparent pixel electrode layer in the upper portion or a method of patterning the transparent pixel electrode layer becomes significant. In particular, to realize multi-color display organic LED devices of plural colors are necessary. However, since light emission characteristics of devices are different from one color to another color at present, it is preferred to separate for each color lines for current supply in order to effectively control display colors. However, this involves a problem that it is difficult to form the transparent pixel electrode layer into an optional shape.  
           [0010]    A first object of the present invention is to provide a specific pixel structure in the top emission type display using light emission devices.  
           [0011]    A second object of the present invention is to provide a current supply structure to a transparent pixel electrode capable of coping with enlarging scale in the top emission type display using light emission devices.  
           [0012]    A third object of the present invention is to provide a pixel structure suitable to coloration of a panel in the top emission type display using organic LED devices.  
         SUMMARY OF THE INVENTION  
         [0013]    According to a first aspect of the present invention, there is provided an active matrix type display comprising a substrate and a plurality of pixels arranged in a matrix on the substrate, wherein each of the pixels includes a light emission device prepared by forming a transparent pixel electrode and a metal pixel electrode on both surfaces of a light emitting layer, and a driving circuit for controlling a driving current of the light emission device, the driving circuit is formed on the substrate, the light emission device is formed in a layer manner above the driving circuit with an intermediate layer made of an insulation material interposed, the transparent pixel electrode being situated on the side opposite to the substrate, and the metal pixel electrode of the light emission device is connected with the driving circuit through a conduction portion which extends through the intermediate layer.  
           [0014]    With this configuration, since an aperture ratio of the light emission device is free from the effect of the driving circuit in the lower layer, for example, a scanning signal line, a pixel signal lines, a current line allowing a driving current of the light emission devices to flow therethrough and a transistor, the aperture ratio can be increased. In particular, since the aperture ratio is determined only by the conduction portion for connecting the lower layer portion and the upper layer portion, extremely high aperture ratio can be obtained.  
           [0015]    In the case described above, the transistors for controlling a driving current of the light emission devices are preferably disposed below the metal pixel electrode of the light emission device. With this configuration, the light emitted from the light emission device can be shielded by the metal pixel electrode and occurrence of leak current due to the light in the off state of the transistor can be suppressed. As a result, the potential change of the capacitor to which image data is written by the transistors can be suppressed to reduce the degradation in the image quality.  
           [0016]    In particular, the metal pixel electrode covering transistors is preferably a metal pixel electrode of the light emission device at the preceding stage in the scanning direction. That is, when a pixel signal is written to a corresponding capacitor by the transistor, since the metal pixel electrode in the upper layer has already been selected, it is in a constant potential state. Accordingly, the effect on the writing operation can be decreased. In addition, since current flows through the metal pixel electrode in this case, effect caused by the peripheral electric fluctuations can also be shielded.  
           [0017]    According to a second aspect of the present invention, there is provided an active matrix type display comprising a substrate; and a plurality of pixel elements arranged in a matrix on the substrate, wherein each of the pixels includes a lower layer having a driving circuit formed thereon, an intermediate layer made of an insulator material formed on the lower layer, and an upper layer having a light emission device formed on the intermediate layer, the driving circuit includes scanning signal lines and image signal lines disposed to cross to each other along the arrangement of the pixels, a first current line for allowing a driving current of the light emission device to flow therethrough, and a transistor circuit connected with the scanning signal line and the image signal line to control the driving current of the light emission device by way of the first current line in response to a scanning signal and a pixel signal, the light emission device includes a light emitting layer, and a transparent pixel electrode and a metal pixel electrode that interpose the light emitting layer therebetween, the transparent pixel electrode being situated on the side opposite to the substrate, the transistor circuit is connected with the metal pixel electrode of the light emission device through a conductor which extends through the intermediate layer, and disposed below a metal pixel electrode of a pixel at the preceding stage in the scanning direction of the pixels, and a second current line is disposed in the upper layer so as to allow a driving current of the light emission device to flow therethrough, and the second current line is connected with the transparent pixel electrode of the light emission device.  
           [0018]    While the transparent pixel electrode of high light permeability generally has a high sheet resistance, formation of the second current line can reduce the loss due to lines and can provide the light emission devices with more pixel current. In particularly, as the size of the display panel enlarges, the amount of current per line increases, and the length of the lines also increase to result in more current loss in the current lines. Then, it is difficult to apply a sufficient voltage to light emission devices remote from a power source because of the voltage drop along the lines; however, provision of the second current line with low resistance enables to obtain a large sized panel.  
           [0019]    In this case, the second current line formed in the upper layer can be extended to a portion overlapping the first current line. Further, when the capacitor for controlling the transistor that defines the driving current of the light emission device is disposed below the first and second current lines at constant potential, the voltage held in the capacitor can be held more stably to attain display of high quality. Further, the pixel signal line and the first current line are preferably extended in one identical direction and disposed substantially at an equal interval. This can minimize the wiring capacitance between the pixel signal line and the first current line to reduce the load capacitance of the transistor that writes pixel data into the capacitor and enable high-speed operation.  
           [0020]    Further, the second current lines are preferably disposed in a lattice-like configuration along the arrangement of the pixels. This can decrease the voltage drop caused by the second current lines, which is applicable to large sized panels.  
           [0021]    According to a third aspect of the present invention, there is provided an active matrix type display comprising a substrate; and a plurality of pixels arranged in a matrix on the substrate, wherein each of the pixels includes a light emission device prepared by forming a transparent pixel electrode and a metal pixel electrode on both surfaces of a light emitting layer and a driving circuit for controlling a driving current of the light emission device, the driving circuit is formed on the substrate, the light emission device is formed in a layer manner above the driving circuit with an intermediate layer made of an insulation material interposed therebetween, the transparent pixel electrode being situated on the side opposite to the substrate, the metal pixel electrode of the light emission device is connected with the driving circuit through a conduction portion which extended through the intermediate layer, and an insulative partition wall having a height higher than the height of the transparent pixel electrode is formed at the boundary region between the plurality of respective pixels.  
           [0022]    With this configuration, the light emission device can be prepared by forming a mask (for example an interlayer insulative layer) for an aperture that defines the light emission device, and vapor depositing light emitting materials of different emission colors or dissolving such light emission materials into a solvent and printing them by means of an ink jet printer or the like, to the apertures defined on a color basis, thereby making it possible to cope with coloration. That is, by arranging light emission devices emitting different colors, for example, red, green and blue for each row of pixel successively, and connecting the second current lines separately on a color basis to a power source, bias voltage for light emission devices having different characteristics of respective colors can be adjusted and, as a result, color images of high quality can be obtained.  
           [0023]    According to a fourth aspect of the present invention, there is provide an active matrix type display comprising: a substrate; and a plurality of pixels arranged in a matrix on the substrate, wherein each of the pixels includes a lower layer having a driving circuit formed thereon, an intermediate layer made of an insulator material formed on the lower layer, and an upper layer having a light emission device formed on the intermediate layer, the driving circuit includes a transistor circuit that controls a driving current of the light emission device in response to a scanning signal and a pixel signal, the light emission device includes a light emission layer, and a transparent pixel electrode and a metal pixel electrode that interpose the light emission layer therebetween, the transparent pixel electrode being situated on the side opposite to the substrate, and the transistor circuit is connected with the metal pixel electrode of the light emission device through a conductor which extends through the intermediate layer, and disposed below the metal pixel electrode of a pixel of the preceding stage in a scanning direction of the pixels.  
           [0024]    The light emitted obliquely from the light emission device is reflected at a transparent protective layer formed on the surface and intrudes into other pixels to possibly lower the contrast. In this regard, when the second current line of the constitution described above is provided, since the light emitted obliquely from the light emission device is reflected on the surface of the second current line and emitted to the outside as an emission light of that pixel, the light taking-out efficiency can be improved as a whole. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0025]    Other objects and advantages of the invention will become apparent from the following description of embodiments with reference to the accompanying drawings in which:  
         [0026]    [0026]FIG. 1 is a plan view showing a portion of a pixel region in a display according to a first embodiment of the invention;  
         [0027]    [0027]FIG. 2 is a cross sectional view of the display taken along line II-II in FIG. 1;  
         [0028]    [0028]FIG. 3 is a cross sectional view of the display taken along line III-III in FIG. 1;  
         [0029]    [0029]FIG. 4 is a driving circuit diagram for a pixel in a preferred embodiment according to this invention;  
         [0030]    [0030]FIG. 5 is a plan view showing a portion of a pixel region in a display according to a second embodiment of this invention;  
         [0031]    [0031]FIG. 6 is a cross sectional view of the display taken along line VI-VI in FIG. 5;  
         [0032]    [0032]FIG. 7 is a cross sectional view of the display taken along line VII-VII in FIG. 5;  
         [0033]    [0033]FIG. 8 is a plan view showing a portion of a pixel region in a display of a third embodiment according to this invention;  
         [0034]    [0034]FIG. 9 is a cross sectional view of the display taken along line IX-IX in FIG. 8;  
         [0035]    [0035]FIG. 10 is a cross sectional view of the display taken along line X-X in FIG. 8;  
         [0036]    [0036]FIG. 11 is a plan view showing a portion of a pixel region in a display according to a fourth embodiment of the invention;  
         [0037]    [0037]FIG. 12 is a cross sectional view of the display taken along line XII-XII in FIG. 11;  
         [0038]    [0038]FIG. 13 is a plan view showing a portion of a pixel region in a display according to a fifth embodiment of the invention;  
         [0039]    [0039]FIG. 14 is a cross sectional view of the display taken along line XIV-XIV in FIG. 12;  
         [0040]    [0040]FIG. 15 is a cross sectional view of a display according to a sixth embodiment of the invention, which is a cross sectional view at a position identical with line XIV-XIV shown in FIG. 13;  
         [0041]    [0041]FIG. 16 is a cross sectional view of a display according to a seventh embodiment of the invention, which is a cross sectional view at a position identical with line XIV-XIV shown in FIG. 13; and  
         [0042]    [0042]FIG. 17 is an explanatory view for explaining the effect of the display of the seventh embodiment. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0043]    Preferred embodiments of this invention will be described with reference to the drawings.  
         [0044]    [Embodiment 1] 
         [0045]    FIGS.  1  to  4  show constitutional views of an active matrix type display of a first embodiment. FIG. 1 is a plan view showing a portion of a pixel region in the display; FIG. 2 is a cross sectional view taken along line II-II in FIG. 1; FIG. 3 is a sectional view taken along line III-III in FIG. 1; and FIG. 4 is a circuit diagram of a driving circuit for a pixel. As shown in FIG. 4, a first thin film transistor Tsw  16  is disposed correspondingly to each intersection between a scanning signal line  11  and a pixel signal line  12  wired in a matrix, in which a gate electrode of the Tsw  16  is connected to the scanning signal line  11 , a source electrode is connected to the pixel signal line  12  and a drain electrode is connected to a first current line  13 . Further, the first current line  13  is connected by way of a source-drain circuit of a second thin film transistor Tdr  17  to an anode (metal pixel electrode  18 ) of an organic LED device  25  as a light emission device. A cathode (transparent pixel electrode  19 ) of an organic LED device  25  is grounded to the earth. Further, a gate electrode of the Tdr  17  is connected by way of a line  10  to a capacitor (holding capacitance) Cs  15 , and the other end of the capacitor  15  is connected with a drain of the Tsw  16 . Then, when the scanning signal is H, the Tsw  16  turns on to hold a pixel signal in the capacitor Cs  15 , which drives the Tdr  17  as an active device in accordance with the voltage of the capacitor Cs  15  to control the current flowing to the organic LED device  25 . Thus, the organic LED device  18  emits light in response to the pixel signal.  
         [0046]    The display having the driving circuits and the organic LED devices described above is constituted as shown in FIGS.  1  to  3 . The display is divided, as shown in the cross sectional view of FIG. 2, into a lower layer having a driving circuit formed on a substrate  26 , an insulative layer  22  as an intermediate layer formed on the lower layer and an upper layer having the organic LED device  25  formed on the insulative layer  22 . FIG. 1 shows a plan as viewed on the side of the lower layer in which a driving circuit for a portion of the pixel region is formed; to show the relative positional relationship with the upper layer, the metal pixel electrode  18  is shown by a dotted chain.  
         [0047]    As shown in FIG. 1 to FIG. 3, scanning signal lines  11  ( 11 - 1 ,  11 - 2 ) and pixel signal lines  12  are disposed as a lattice and each pixel corresponds to a region surrounded with the signal lines. As described later, rectangular metal pixel electrodes  18  constituting the pixels are arranged such that each of the electrodes is displaced downward (in the direction of row) in the drawing by about one-half pitch of a rectangular region surrounded with the scanning signal lines  11  and the pixel signal lines  12 . Further, the first current lines  13  are disposed such that each of them extends in the direction of row parallel with the pixel signal lines  12 . Each first thin film transistor Tsw  16  is disposed at a position near each intersection between the scanning signal line  11  and the pixel signal line  12 . The gate electrode and the source electrode of Tsw  16  are connected to the scanning signal line  11  and the pixel signal line  12 , respectively, while the drain electrode thereof is connected by way of the line  10  to the capacitor  15  for accumulating pixel data. Each second thin film transistor Tdr  17  for controlling the current flowing to the organic LED device  18  is disposed at a position near the Tsw  16  in which the source electrode is connected to the first current line  13 , the drain electrode is connected through a contact area  20  opened in the insulative layer  22  to the metal pixel electrode  18  of the LED device  25  by way of a line  28 . The upper surface of the insulative layer  22  is flattened on the side where the metal pixel electrode  18  is formed.  
         [0048]    As described previously, the metal pixel electrodes  18  are positioned while being displaced each in the direction of the row so as to cover the circuit including Tsw  16  and Tdr  17  of a pixel selected subsequent to the pixel of its own in the sequence of scanning. In other words, the circuit including the Tsw  16  and Tdr  17  is covered by the metal pixel electrode  18  selected before the pixel of its own in the sequence of scanning. For example, in FIG. 1, in the sequence of scanning the scanning signal line  11 - 2  subsequent to the scanning signal line  11 - 1 , Tsw  16 - 2  and Tdr  17 - 2  of the driving circuit for the pixel connected to the scanning signal line  11 - 2  are covered at the upper portion thereof with a metal pixel electrode  18 - 1  connected with Tdr  17 - 1  for the pixel driven by the scanning signal line  11 - 1  in the preceding stage.  
         [0049]    The cross sectional structure of the pixel region having thus been constituted will be described with reference to FIGS. 2 and 3. FIG. 2 is a cross sectional view taken along line II-II in FIG. 1 and FIG. 3 is a cross sectional view taken along line III-III in FIG. 1. As shown in the figures, for the thin film transistors Tsw  16  and Tdr  17 , a gate electrode  16   g  is patterned on a gate insulative layer  21  formed by stacking SiO 2  on a polycrystalline silicon thin film layer  28  formed on the upper surface of the substrate  26 , and an interlayer insulative layer  23  is further patterned, on which the pixel signal line  12  and the line  10  are connected while being in contact with the source electrode and the drain electrode. The gate electrode  16   g  can be formed, for example, of a metal such as chromium (Cr) or aluminum (Al), or an alloy material thereof. The interlayer insulative layer  23  can be formed of a single layer of SiO 2  or SiN, or a laminate thereof. Contact with the source electrode and the drain electrode can be established by a metal such as Al or an alloy thereof. Further, the capacitor Cs  15  is constituted by using, as a dielectric member, the gate insulative layer  21  interposed between the polycrystalline silicon thin film  28  and an electrode  15   a  formed of the same material as the gate electrode  16   g.    
         [0050]    As shown in FIGS. 2 and 3, in the pixel driving circuit, a portion containing the Tsw  16 , Tdr  17 , capacitor  15  and first current line  13  is formed in the lower layer portion below the insulative layer  22  as the intermediate layer portion. Then, in the upper layer portion above the insulative layer  22 , the metal pixel electrode  18  is patterned on the insulative layer  22 . In this step, by forming an opening in the insulative layer  22  at a position corresponding to the line  28  connected to the drain electrode of the Tdr  17  in the layer portion connected with the metal pixel electrode  18 , a contact area  20  for connecting the metal pixel electrode  18  with the line  28  is formed at the position of the opening. Then, after covering the portion above the contact area  20  with an interlayer insulative layer  24  and forming an opening area in the upper surface of the metal pixel electrode  18 , the organic LED device  25  is formed by using a mask by the method such as patterning vapor deposition and, further, a transparent pixel electrode  19  is stacked on the organic LED device  25 . Then, they are sealed with a transparent substrate or layer such as glass or plastic with no gaps, or sealed in a state being filled with an inert gas. The transparent pixel electrode  19  is formed in common over the entire display and connected with a grounding line at a periphery, not shown, of the display.  
         [0051]    According to the first embodiment having the constitution as described above, since the aperture ratio of the organic LED device  25  is determined only by the contact area  20  for connecting the lower layer portion and the upper layer portion, free from the effects, for example, of the thin film transistors  16 ,  17 , the scanning signal line  11 , pixel signal line  12  and the first current line  13  in the lower layer portion, an extremely high aperture ratio can be obtained.  
         [0052]    Further, since the thin film transistors Tsw  16  and Tdr  17  are covered with the metal pixel electrode  18 , they are free from the effect of light emitted from the organic LED device  25  containing a light-emitting layer. As a result, since occurrence of leak current caused by the light in the off state of the transistors can be suppressed, the potential change of the capacitor  15  can be suppressed to reduce the degradation in image quality.  
         [0053]    In particular, by covering the thin film transistors Tsw  16  and Tdr  17  by the metal pixel electrode  18  of the pixel at the preceding stage in the scanning direction, since the metal pixel electrode  18  in the upper layer has already been selected and at a constant potential state when a pixel signal is written to the thin film transistor Tsw  16  by the pixel signal of the pixel signal line  12 , the effect thereof on the writing operation can be reduced. In addition, since current flows in the metal pixel electrode  18  in this case, it has also an effect of shielding the effect of periphery electrical fluctuations.  
         [0054]    [Embodiment 2] 
         [0055]    FIGS.  5  to  7  are constitutional views of an active matrix type display of a second embodiment. FIG. 5 is a plan view showing a portion of a pixel region in the same manner as in FIG. 1; FIG. 6 is a cross sectional view taken along line VI-VI in FIG. 5; and FIG. 7 is a cross sectional view taken along line VII-VII in FIG. 5. This embodiment is different from the first embodiment in that when the metal electrode  18  is patterned on the insulative layer  22  with aluminum Al or an alloy material thereof, second current lines  14  are formed simultaneously. The second current lines  14  are formed each at a position substantially equal with that of the first current line  13  in the lower layer portion in each of the pixels. The second current line  14  is connected through a contact area  27  with the transparent pixel electrode  19 .  
         [0056]    In this case, a material of high light permeability such as ITO is preferably used for the transparent pixel electrode  19 . Generally, since the sheet resistance of ITO is higher by one digit or more than that of Al, when the transparent pixel electrode  19  itself is used for the current line as in the first embodiment, the current supplied to the organic LED device  25  is sometimes restricted due to voltage drop in the transparent pixel electrode  19 . In this regard, according to this embodiment, since the second current line  14  is formed, larger pixel current can be supplied to each of the organic LED devices  25  by reducing the loss due to the transparent pixel electrode  19 .  
         [0057]    In other words, as a display panel becomes larger in size, the amount of current flowing to the transparent pixel electrode  19  increases while the distance along which the current flows also increases; therefore, resistance is increased to increase the current loss. Because of the voltage drop, it is difficult to apply a sufficient voltage to organic LED devices  25  remote from a power source. Accordingly, provision of the second current lines of low resistance makes it possible to realize a large sized display panel.  
         [0058]    Further, since the capacitor  15  for controlling the thin film transistor  17  that defines the driving current for the organic LED device  25  is disposed below the current lines  13 ,  14  at a constant potential, voltage held in the capacitor  15  can be held more stably to provide high quality display.  
         [0059]    [Embodiment 3] 
         [0060]    FIGS.  8  to  10  show constitutional views of an active matrix type display of a third embodiment. FIG. 8 is a plan view showing a portion of a pixel region in the same manner as in FIG. 1; FIG. 9 is a cross sectional view taken along line IX-IX in FIG. 9; and FIG. 10 is a cross sectional view taken along line X-X in FIG. 8. This embodiment is different from the second embodiment in that second current lines  14  formed on the insulative layer  22  are disposed each in parallel with a shorter side of the metal pixel electrode  18 . The metal pixel electrode  18  is connected by way of a contact area  20  with the second thin film transistor Tdr  17  controlling the driving current and the second current line  14  is connected with a transparent pixel electrode  19  by way of a contact area  27 .  
         [0061]    Since the second current lines  14  are disposed in parallel with the shorter side of the metal pixel electrode  18 , the aperture area that contributes to the light emission of the organic LED device  25  can be made closer to a square shape and the aperture ratio can be increased as compared with the second embodiment shown in FIG. 5. Accordingly, when a comparison is made on the basis of identical pixel brightness, since the current density in each of the organic LED devices  25  can be reduced, the device life can be improved.  
         [0062]    [Embodiment 4] 
         [0063]    [0063]FIGS. 11 and 12 are constitutional views of an active matrix type display of a fourth embodiment. FIG. 11 is a plan view showing a portion of a pixel region in the same manner as in FIG. 1; and FIG. 12 is a cross sectional view taken along line XI-XI in FIG. 11. This embodiment is different from the second or third embodiment in that the second current lines  14  are arranged as a mesh to surround the metal pixel electrode  18 . The metal pixel electrode  18  is connected by way of the contact area  20  with the second thin film transistor Tdr  17  that controls the driving current, and the second current line  14  is connected by way of a contact area  27  with the transparent pixel electrode  19 .  
         [0064]    In the second or third embodiment, the second current lines are formed independently on every direction of row or direction of column of pixels. Accordingly, since the voltage drop increases in the second current line in the line in which the amount of current supply increases even when the width of the line is increased as compared with the line in which the amount of current supply is small, this tends to appear as the difference of display. For example, consideration is to be made on the case of attaining a maximum brightness 500 cd/m 2  at an efficiency of 7 cd/A of the organic LED device  25  in a display panel having a diagonal size of 20 inch or more.  
         [0065]    In this case, when the current lines  13 ,  14  are formed by using Al having a sheet resistance of 0.1 Ω/□ in a pixel sized 108×320 μm, the width of the line has to be made about 60 μm to suppress the voltage drop to 3 V or less. Aside from the first current line  13 , since the second current line  14  gives a direct effect on the aperture ratio, it is preferred that the line width is narrowed. In view of the above, in this embodiment, the aperture ratio is improved by disposing the second current line  14  as a mesh, thereby decreasing the width of the lines.  
         [0066]    [Embodiment 5] 
         [0067]    [0067]FIGS. 13 and 14 show constitutional views of an active matrix type display of a fifth embodiment. FIG. 13 is a plan view showing a portion of a pixel region in the same manner as in FIG. 1; and FIG. 14 is a cross sectional view taken along line XIV-XIV in FIG. 13. This embodiment is different from the second embodiment in that the pixel signal line  12  formed in the lower layer portion is positioned substantially at the center between the adjacent first current lines  13 - 1  and  13 - 2 . The voltage of the pixel signal transmitted by the pixel signal line  12  is stored in the capacitor Cs  15  by the thin film transistor Tsw  16  selected by the scanning signal line  11 . Then, when the thin film transistor Tsw  16  turns off, the current controlled by the thin film transistor Tdr  17  in accordance with the voltage stored in the capacitor Cs  15  is supplied through the contact  20  to the organic LED device  25 .  
         [0068]    As described above, by disposing the pixel signal line  12  at a position most remote from the adjacent first current line  13 , the interline capacitance of the lines can be minimized. The interline capacitance is in proportion with the length of the line and in inverse proportion with the distance between the lines. Since the distance between the first current lines  13  is determined by the pixel pitch, the sum of the interline capacitance between two adjacent current lines  13  and the pixel signal line  12  is minimized when the pixel signal line  12  is situated at the center of the two adjacent current lines. When the panel size and definition of the display are increased to necessitate high speed driving, an increase in the load capacitance lowers the writing speed and deteriorates the image quality. Accordingly, positioning of the pixel signal line  12  at the center of the adjacent current lines  13  is optimal also so as to reduce the wiring load capacitance.  
         [0069]    [Embodiment 6] 
         [0070]    [0070]FIG. 15 is a constitutional view of an active matrix type display of a sixth embodiment. This is a cross sectional view showing a portion at a position equal with that for the line XIV-XIV of the fifth embodiment shown in FIG. 13. This embodiment is different from the fifth embodiment in adding a process of forming a partition wall  30  made of an insulator after forming the line  14  in the lower layer portion; the partition wall  30  has a width equal with or less than the second line  14  and is higher than the layer thickness of the transparent pixel electrode  19 .  
         [0071]    After forming the partition wall  30 , an interlayer insulative layer  24  provided with an aperture that defines a light emitting portion is formed, an organic LED material is vapor deposited by using a mask for organic LED devices  25  of different emitting colors while taking care, for example, that they cover the opening defined on every color and the organic LED material is not deposited to the contact area  27 . Alternatively, the organic LED device  25  may be formed also by dissolving a light emitting material in a solvent and printed by an ink jet printer or the like. Such a stacking method of the organic LED device  25  is merely an example that does not limit the invention. After stacking the organic LED device  25  as described above, a transparent conductive layer as a transparent pixel electrode  19  is further stacked over the entire surface. The stacked transparent conductive layer is connected on a row of pixel basis by the partition walls  30  formed on the second current lines  14  to separate second current lines  14 , respectively, through contact areas  27 .  
         [0072]    With the manufacturing method as described above, when organic LED devices emitting light of different colors, for example, red, green and blue on a row of pixel basis are arranged successively, bias for the organic LED devices can be controlled in accordance with the respective colors by connecting the second current lines  14  separately on a color basis to the power source at the periphery of the display region. Since the light emission characteristics, such as the current and the life, of the organic LED devices are different from each other on a color basis, determination of the optimal bias voltage on a color basis in view of the color display on a display is important to displaying color images at high quality.  
         [0073]    [Embodiment 7] 
         [0074]    [0074]FIG. 16 is a constitutional view of an active matrix type display of a seventh embodiment. This is a cross sectional view showing a portion at a position identical with that taken along line XIV-XIV of the fifth embodiment shown in FIG. 13. This embodiment is different from the second embodiment in view of the cross sectional structure of the second current line  14 . That is, as shown in the figure, the second current lines  14  are formed covering the outer surface of protruded ridges  31  formed on the intermediate layer of an insulative layer  22 . The protruded ridge  31  is formed with a width narrower than that of the second current line  14  and a height from ½ times to twice the thickness of the second current line. In short, the second current line  14  is formed covering the outer surface of the protruded ridge  31  such that the height of the line  14  is higher than the height of the transparent pixel electrode  19  at a portion opposing to the metal pixel electrode  18 .  
         [0075]    According to this constitution, it can cope with colored display by the same effect as that of the partition wall  30  of the sixth embodiment as well as can provide an effect of increasing the amount of light that can be taken out of the organic LED device  25  and suppressing mixing of emission light with that from other adjacent pixels.  
         [0076]    That is, as shown in FIG. 17, in a case where the metal pixel electrode  18  and the flat second current lines  14  are formed on the flat insulative layer  22  having a surface unevenness of 100 nm or less, light emitted from the organic LED device  25  transmits a surface protective layer  32  to the outside as an emission light. However, the light emitting in an oblique direction as shown by an arrow  33  in the figure is reflected at the boundary of the surface protective layer  32  and propagates in the lateral direction through the inside. As a result, this lowers not only the emission efficiency but also the contrast when the light is reflected at the electrode of another pixel and emitted externally to cause degradation of the image quality.  
         [0077]    In view of the above, to decrease the light propagating the inside as described above, the second current line  14  is constituted as shown in FIG. 16. That is, among the light beams emitted obliquely from the organic LED device  25 , an light beam having a small incident angle relative to the surface protective layer  32  is reflected on the surface of the second current line  14  having a convex cross section and is taken out to the outside as the emission light of the pixel. Accordingly, the light taking-out efficiency can be improved as a whole.  
         [0078]    When the display in each of the embodiments according to this invention described above is constituted as the top emission type, a display of high brightness and high image quality can be attained by realizing pixels of high aperture ratio and suppressing the factors of degradation in the image quality due to light emission or electric signals.  
         [0079]    In the embodiments described above, while each of the thin film transistors  16 ,  17  is constituted as a top gate type, it will be apparent that an identical effect can also be obtained by constituting each of them as the bottom gate type.  
         [0080]    Further, the thin film transistors  16 ,  17  are not restricted only to polycrystalline silicon but may be formed also with amorphous silicon or single crystal silicon without changing the effects of the invention.  
         [0081]    Further, the number of the thin film transistors in the pixel is not restricted only two but more two thin film transistors can be used in accordance with the constitution of the driving circuit.  
         [0082]    While the descriptions have been made of the example using ITO as the transparent electrode  19 , other conductive layer of high light permeability such as made of IZO may be used. Furthermore, the current lines  13 ,  14  are not restricted only to Al but a metal such as copper Cu of lower resistance can be used.  
         [0083]    As has been described above, this invention can provide a concrete pixel structure of a top emission type display using a light emission device.  
         [0084]    Further, this invention can provide a current supply structure to a transparent pixel electrode capable of coping with enlarging size of a top emission type display using a light emission device.  
         [0085]    Further, this invention can provide a pixel structure suitable to coloration of panel in a top emission type display using organic LED devices.  
         [0086]    While the invention has been described in its preferred embodiments, it is to be understood that the words which have been used are words of description rather than limitation and that changes within the purview of the appended claims may be made without departing from the true scope and spirit of the invention in its broader aspects.