Patent Abstract:
An electroluminescent device including a substrate, a transistor disposed above the substrate, the transistor including a gate electrode, a silicon film opposing the gate electrode, and a gate insulating film between the gate electrode and the silicon film. The electroluminescent device including a first interlayer insulation film covering the transistor, a second interlayer insulation film disposed above the first interlayer insulation film, and a pixel electrode disposed above the second interlayer insulation film and electrically connected to the transistor. The electroluminescent device including an organic EL layer disposed between the pixel electrode and a counter electrode, and a capacitor including a first electrode formed by the same material as the silicon film and a second electrode formed by the same material as the gate electrode.

Full Description:
[0001]    This is a Continuation of application Ser. No. 12/289,243, filed Oct. 23, 2008, which in turn is a Continuation of application Ser. No. 10/465,878, filed Jun. 20, 2003, which in turn is a Division of application Ser. No. 10/224,412, filed Aug. 21, 2002, which in turn is a Division of application Ser. No. 09/155,644, filed Oct. 2, 1998, which in turn us the U.S. National Phase of PCT/JP98/00655, filed Feb. 17, 1998, which in turn claims priority of Japanese Application No. 09-032474, filed Feb. 17, 1997, and Japanese Application No. 09-066046, filed Mar. 19, 1997. The disclosure of the prior applications is hereby incorporated by reference herein in its entirety. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of Invention 
         [0003]    The invention relates to a display apparatus in which a current-driven light-emitting device, such as an organic electro luminescence (hereinafter referred to as “EL”) display device, are driven by using thin-film transistors. More particularly, the invention relates to a current-driven light-emitting display apparatus driven by thin-film-transistors, which realizes the suppression of deterioration with time, and to a method of producing the same. 
         [0004]    2. Description of Related Art 
         [0005]    The inventor of this invention carefully examined organic EL display devices driven by thin-film transistors, and ascertained the following facts. 
         [0006]    (1) In an organic EL display device driven by thin-film transistors, since the organic EL display device is a direct-current device, direct current also runs through thin-film transistors, which are connected in series to the EL device, for the purpose of controlling it. 
         [0007]    (2) Thin-film transistors are classified into an n-channel type and a p-channel type. These types differ extremely in the manner in which deterioration with time occurs. 
         [0008]    Accordingly, an object of the present invention is to suppress the deterioration with time of thin-film transistors in a current luminescent device driven by the thin-film transistors. 
       SUMMARY OF THE INVENTION 
       [0009]    (1) In the present invention, there is provided a current-driven light-emitting display apparatus comprising a plurality of scanning lines and a plurality of data lines, thin-film transistors and current luminescent devices being formed in positions corresponding to each of the intersections of the scanning lines and the data lines, wherein at least one of the thin-film transistors is a p-channel type thin-film transistor. 
         [0010]    It is possible to suppress the deterioration with time of a thin-film transistor with this apparatus. 
         [0011]    (2) In the present invention, there is provided a current-driven light-emitting display apparatus in which a plurality of scanning lines a plurality of data lines, common electrodes, and opposite electrodes are formed, with first thin-film transistors being formed in positions corresponding to the intersections of the scanning lines and the data lines, second thin-film transistors, holding capacitors, pixel electrodes, and current luminescent elements, the first thin-film transistors controlling conductivity between the data lines and the holding capacitors by the potentials of the scanning lines, the second thin-film transistors controlling conductivity between the common electrodes and the pixel electrodes by the potentials of the holding capacitors, to thereby control the current which flows through the current luminescent elements provided between the pixel electrodes and the opposite electrodes wherein the second thin-film transistors are p-channel type thin-film transistors. 
         [0012]    (3) In the present invention, there is provided a current-driven light-emitting display apparatus according to (1) or (2), further comprising a driving circuit for driving the current luminescent element, the driving circuit is comprised of the plurality of scanning lines, the plurality of data lines, the thin-film transistors, and the current luminescent elements, which are disposed on the substrate, wherein the p-channel type thin-film transistors are formed in the same step as the thin-film transistors in the driving circuits. 
         [0013]    (4) In the current-driven light-emitting display apparatus according to any of (1) or (3), the thin-film transistors are polysilicon thin-film transistors. 
         [0014]    (5) The invention provides a current-driven light-emitting display apparatus according to (3), wherein the drive circuits comprise complementary type thin-film transistors, the first thin-film transistors are formed in the same step as n-channel type thin-film transistors in the driving circuits, and the second thin-film transistors are formed in the same step as the p-channel type thin-film transistors in the driving circuits. 
         [0015]    According to (5), it is possible to provide a current-driven light-emitting display apparatus, which exhibits high performance with no deterioration with time, without increasing the number of steps for producing the apparatus. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]      FIG. 1  is a block diagram of the basic structure of a display to which the present invention is applied; 
           [0017]      FIG. 2  is an equivalent circuit diagram of a display device equipped with thin-film transistors according to a first embodiment of the present invention; 
           [0018]      FIG. 3  is a drive voltage diagram of the display device equipped with thin-film transistors according to the first embodiment of the present invention; 
           [0019]      FIG. 4  is a current-voltage characteristic chart of a current-thin-film transistor according to the first embodiment of the present invention; 
           [0020]      FIG. 5  is a current-voltage characteristic chart of an organic EL display device according to the first embodiment of the present invention; 
           [0021]      FIG. 6(   a ) is a sectional view of an organic display EL device equipped with thin-film transistors according to the first embodiment of the invention, and  FIG. 6(   b ) is a plan view of an organic display EL device according to the first embodiment of the present invention; 
           [0022]      FIG. 7  is an equivalent circuit diagram of an organic EL display device equipped with thin-film transistors used in a second embodiment of the present invention; 
           [0023]      FIG. 8  is a drive-voltage diagram of an organic EL display device equipped with thin-film transistors according to the second embodiment of the present invention; 
           [0024]      FIG. 9  is a current-voltage characteristic chart of a current-thin-film transistor according to the second embodiment of the present invention; 
           [0025]      FIG. 10  is a current-voltage characteristic chart of an organic EL display device according to the second embodiment of the present invention; 
           [0026]      FIG. 11(   a ) is a sectional view of an organic EL display device equipped with thin-film transistors according to the second embodiment of the present invention, and  FIG. 11(   b ) is a plan view of an organic EL display device equipped with thin-film transistors according to the second embodiment of the present invention; 
           [0027]      FIG. 12  is a chart showing the deterioration with time of an n-channel type thin-film transistor; 
           [0028]      FIG. 13  is a chart showing the deterioration with time of a p-channel type thin-film transistor; and 
           [0029]      FIG. 14(   a )-( d ) are flow diagrams of the process for producing a thin-film-transistor-drive organic EL display device according to the present invention. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     The General Structure of an Organic El Display Device 
       [0030]    Referring to the drawings, the preferred embodiments of the present invention will be described. 
         [0031]    As shown in  FIG. 1 , the center region of a substrate  1  constitutes a display part. In the outer periphery of the transparent substrate  1 , at the top side of the drawing, a data-side drive circuit  3 , which outputs image signals to data lines  112 , is arranged, and at the left side of the drawing, a scanning-side drive circuit  4 , which outputs scanning signals to scanning lines  111 , is arranged. In these drive circuits  3  and  4 , n-type thin-film transistors and p-type thin-film transistors form complementary type TFTs. These complementary type thin-film transistors are included in shift register circuits, level shift circuits, analog switch circuits, etc. 
         [0032]    Arranged on the transparent substrate  1  are a plurality of scanning lines  111 , and a plurality of data lines  112  extending in a direction perpendicular to the direction in which the scanning lines extend. The intersections of these data lines  112  and scanning lines  111  constitute pixels  7  in the form of a matrix. 
         [0033]    Formed in each of these pixels  7  is a first thin-film transistor (hereinafter referred to as “a switching thin-film transistor”)  121 , in which scanning signals are supplied to a gate electrode  21  (a first gate electrode) through the scanning line  111 . One end of the source/drain region of the switching thin-film transistor  121  is electrically connected to a data line  112 , while the other end of the source/drain region is electrically connected to a potential holding electrode  113 . In addition, a common line  114  is disposed in parallel to the scanning line  111 . Holding capacitor  123  is formed between the common line  114  and the potential holding electrode  113 . The common line is maintained at a controlled potential. Accordingly, when the switching thin-film transistor  121  is turned ON through the selection by a scanning signal, the image signal from the data line  112  is written to the holding capacitor  123  through the switching thin-film transistor. 
         [0034]    The potential holding electrode  113  is electrically connected to the gate electrode of second thin-film transistor  122  (hereinafter referred to as “a current-thin-film transistor”). The one end of the source/drain region of the current-thin-film transistor  122  is electrically connected to a common line  114 , while, the other end of the source/drain region is electrically connected to one electrode  115  of a luminescent element  131 . When the current-thin-film transistor  122  is turned ON, the current of the common line  114  flows to the luminescent element  131  of such as an organic EL display device through the current-thin-film transistor  122 , so that the luminescent element  131  emits light. Further, although one electrode of the holding capacitor is connected to a common line  114  in this arrangement, it is also possible for it to be connected to a capacitance line being provided separately, instead of being connected to the common line  114 . Alternatively, one electrode of the holding capacitor may be connected to an adjacent gate line. 
       First Embodiment 
       [0035]      FIG. 2  is a block diagram of an organic EL display device equipped with thin-film transistors, according to a first embodiment of the present invention.  FIG. 3  is a drive voltage diagram of an organic EL display device with thin-film transistors according to the first embodiment of the present invention.  FIG. 4  is a current-voltage characteristic diagram of a current-thin-film transistor according to the first embodiment of the present invention.  FIG. 5  is a current-voltage characteristic chart of an organic EL display device, according to the first embodiment of the present invention. 
         [0036]    In  FIG. 2 , there are shown a scanning line  111 , a data line  112 , a holding electrode  113 , a common line  114 , a pixel electrode formed of Al  115 , an opposite electrode formed of ITO  116 , a switching thin-film transistor  121 , an n-channel type current-thin-film transistor  122 , a holding capacitor  123 , an organic EL display element  131  (hereinafter referred to as “a forward oriented organic EL display device”) which is caused to emit light by the current flowing to the pixel electrode  115  from the opposite electrode  116 , and the current directions of the organic EL display device  131  and  141 . 
         [0037]    In  FIG. 3 , there are shown a scanning potential  211 , a signal potential  212 , a holding potential  213 , a common potential  214 , a pixel potential  215 , and a counter potential  216 .  FIG. 3 , only a part of each potential is shown to illustrate the respective potential relationships. The potential of the scanning line  111  corresponds to the scanning potential  211 ; the potential of the data line  112  corresponds to the signal potential  212 ; the potential of the holding electrode  113  corresponds to the holding potential  213 ; the potential of the common line  114  corresponds to the common potential  214 ; the potential of the pixel electrode  115  formed of Al corresponds to the pixel potential  215 ; and the potential of the opposite electrode  116  formed of ITO (Indium Tin oxide) corresponds to the counter potential  216 .  FIG. 3  shows each signal potential schematically and partially. 
         [0038]    Numeral  221  indicates a period in which a pixel is in the display-state, wherein current flows into the forward oriented organic EL display element  131 , so that it emits light, and numeral  222  indicates a period in which the pixel is in the non-display state, wherein current does not flow into the forward oriented organic EL display element  131 , so that it does not emit light. 
         [0039]    Referring to  FIG. 4 , a curve  31  indicates the current-voltage characteristic of the n-channel type current-thin-film transistor  122  as observed when the drain voltage is 4V, and a curve  32  indicates the current-voltage characteristic of the n-channel type current-thin-film transistor  122  as observed when the drain voltage is 8V. Regarding either drain voltage, the following facts can been seen. When the gate voltage is low, the n-channel type current-thin-film transistor  122  is turned OFF and a small amount of drain current flows demonstrating a high source/drain resistance. When the gate voltage is high, the n-channel type current-thin-film transistor  122  is turned ON and a large amount of drain current flows demonstrating a low source/drain resistance. 
         [0040]    In  FIG. 5 , numeral  4  indicates the current-voltage characteristic of the forward oriented organic EL display element  131 . Here, the voltage represents the counter potential  216  against the pixel potential  215 , and the current represents the current which flows to the pixel electrode  115  from the opposite electrode  116 . The forward oriented organic EL display element  131  is OFF when the voltage is not higher than a certain threshold voltage; the resistance is high and allows no current to flow, so that the device does not emit light. The device is ON when the voltage is over a certain threshold voltage, and the resistance is low and allows current to flow, so that the device emits light. In this case, the threshold voltage is approximately 2V. 
         [0041]    The operation of an organic EL display device equipped with the thin-film transistors of this embodiment will be described with reference to  FIG. 2 ,  FIG. 3 ,  FIG. 4 , and  FIG. 5 . 
         [0042]    The switching thin-film transistor  121  controls the conductivity between the data line  112  and the holding electrode  113  by means of the potential of the scanning line  111 . In other words, the scanning potential  211  controls the conductivity between the signal potential  212  and the holding potential  213 . While in this example, the switching thin-film transistor  121  is an n-channel type thin-film transistor, a p-channel type thin-film transistor is also applicable. 
         [0043]    For the period  221  in which the pixel is in the display-state, the signal potential  212  is high, and the holding potential  213  is retained at a high level. For the period  222  in which the pixel is in the non-display state, the signal potential  212  is low, and the holding potential  213  is retained at a low level. 
         [0044]    The n-channel type current-thin-film transistor  122  has the characteristic as shown in  FIG. 3  and controls the conductivity between the common line  114  and the pixel electrode  115  by means of the potential of the holding electrode  113 . In other words, the holding potential  213  controls the conductivity between the common potential  214  and the pixel potential  222 . For the period  221  in which the pixel is in the display-state, the holding potential  213  is high, so that the common line  114  is electrically connected to the pixel electrode  115 . For the period  222  in which the pixel is in the non-display state, the holding potential  213  is low, so that the common line  114  is disconnected from the pixel electrode  115 . 
         [0045]    The organic EL display element  131  has the characteristic as shown in  FIG. 5 . For the period  221  in which the pixel is in the display-state, the current flows between the pixel electrode  115  and the opposite electrode  116 , so that the organic EL display element  131  emits light. For the period  222  in which the pixel is in the non-display state, no current flows, so that the device does not emit light. 
         [0046]      FIG. 6(   a ) is a sectional view of a thin-film transistor organic EL display device (1 pixel) according to an embodiment of the present invention.  FIG. 6(   b ) is a plan view of a thin-film transistor organic EL display device (1 pixel) according to an embodiment of the present invention. The section taken along the line A-A′ of  FIG. 6(   a ) corresponds to the section taken along the line A-A′ of  FIG. 6(   b ). 
         [0047]    In  FIG. 6(   a ), numeral  132  indicates a hole injection layer, numeral  133  indicates an organic EL layer, and numeral  151  indicates a resist. 
         [0048]    In this example, the switching thin-film transistor  121  and the n-channel type current-thin-film transistor  122  adopt the structure and the process ordinarily used for a low-temperature polysilicon thin-film transistor, which are used for thin-film transistor liquid crystal display devices, i.e., a top-gate structure and a process conducted in the condition that the maximum temperature is 600° C. or less. However, other structures and processes are also applicable. 
         [0049]    The forward oriented organic EL display element  131  is formed by the pixel electrode  115  formed of Al, the opposite electrode  116  formed of ITO, the hole injection layer  132 , and the organic EL layer  133 . In the forward oriented organic EL display element  131 , the direction of current of the organic EL display device, indicated at  141 , can be set from the opposite electrode  116  formed of ITO to the pixel electrode  115  formed of Al. Further, the structure of the organic EL display device is not restricted to the one used here. Other structures are also applicable, as long as the direction of current of the organic EL display device, indicated at  141 , can be set to the direction from the opposite electrode to pixel electrode. 
         [0050]    Here, the hole injection layer  132  and the organic EL layer  133  are formed by an ink-jet printing method, employing the resist  151  as a separating structure between the pixels, and the opposite electrode  116  formed of ITO is formed by a sputtering method, yet other methods are also applicable. 
         [0051]    In this embodiment, the common potential  214  is lower than the counter potential  216 , and the current-thin-film transistor is the n-channel type current-thin-film transistor  122 . 
         [0052]    In the period  221  in which the pixel is in the display-state, the n-channel type current-thin-film transistor  122  is ON. The current which flows through the forward oriented organic EL display element  131 , i.e., the ON-current of the n-channel type current-thin-film transistor  122  depends on the gate voltage, as shown in  FIG. 4 . Here, the term “gate voltage” means the potential difference between the holding potential  213  and the lower one of the common potential  214  and the pixel potential  215 . In this embodiment, the common potential  214  is lower than the pixel potential  215 , so that the gate voltage indicates the potential difference between the holding potential  213  and the common potential  214 . The potential difference can be sufficiently large, so that a sufficiently large amount of ON-current is obtainable. The ON-current of the n-channel type current-thin-film transistor  122  also depends on the drain voltage. However, this does not affect the above situation. 
         [0053]    Conversely, in order to obtain a necessary amount of ON-current, the holding potential  213  can be made lower, and the amplitude of the signal potential  212  and therefore the amplitude of the scanning potential  211  can be decreased. In other words, in the switching thin-film transistor  121  and the n-channel type current-thin-film transistor  122 , a decrease in drive voltage can be achieved without entailing any loss in image quality, abnormal operations, or a decrease in the frequency enabling them to operate. 
         [0054]    Further, in the embodiment of the present invention, the signal potential  212  for the pixel to be in the display-state is lower than the counter potential  216 . 
         [0055]    As stated above, in the period  221  in which the pixel is in the display-state, the ON-current of the n-channel type current-thin-film transistor  122  depends on the potential difference between the holding potential  213  and the common potential  214 , but not directly on the potential difference between the holding potential  213  and the counter potential  216 . Thus, the holding potential  213 , i.e., the signal potential  212  for the pixel to be in the display-state, can be made lower than the counter potential  216 , and therefore, the amplitude of the signal potential  212  and the amplitude of the scanning potential  211  can be decreased, while retaining a sufficiently large ON-current in the n-channel type current-thin-film transistor  122 . That is, in the switching thin-film transistor  121  and the n-channel type current-thin-film transistor  122 , a decrease in drive voltage can be accomplished without entailing any loss in image quality, abnormal operations, and a decrease in the frequency enabling them to operate. 
         [0056]    Moreover, in this embodiment, the signal potential  212  for the pixel to be in the non-display-state is higher than the common potential  214 . 
         [0057]    In the period  222  in which the pixel is in the non-display-state, when the signal potential  212  becomes slightly higher than the common potential  214 , the n-channel type current-thin-film transistor  122  is not completely turned OFF. However, the source/drain resistance of the n-channel type current-thin-film transistor  122  becomes considerably higher, as shown in  FIG. 4 . Thus, the pixel potential  215 , which is determined by dividing the common potential  214  and the counter potential  216  by the values of the resistance of the n-channel type current-thin-film transistor  122  and the resistance of the forward oriented organic EL display element  131 , becomes a potential close to the counter potential  216 . 
         [0058]    The voltage which is applied to the forward oriented organic EL display element  131  is the potential difference between the pixel potential  215  and the counter potential  216 . As shown in  FIG. 5 , the forward oriented organic EL display element  131  is turned OFF when the voltage is not higher than a certain threshold voltage, when no current flows, so that the display device does not emit light. Namely, the utilization of a threshold potential of the forward oriented organic EL display element  131  makes it possible for the forward oriented organic EL display element  131  not to emit light, even if the signal potential  212  is slightly higher than the common potential  214 , and the n-channel type current-thin-film transistor  122  is not completely turned OFF. 
         [0059]    Here, the amplitude of the signal potential  212 , and therefore the amplitude of the scanning potential  211  can be decreased by making the signal potential  212  for the pixel to be in the non-display state to be higher than the common potential  214 . In other words, with regard to the switching thin-film transistor  121  and the n-channel type current-thin-film transistor  122 , a decrease in drive potential can be accomplished without entailing any loss of image quality, abnormal operations , or a decrease in the frequency enabling them to operate. 
         [0060]    The operation of an organic EL display device equipped with the thin-film transistors of this embodiment is not as simple as described above; it operates under a more complicated relationship between voltage and current. However, the description above holds true approximately and qualitatively. 
       Second Embodiment 
       [0061]      FIG. 7  is an equivalent circuit diagram of an organic EL display device equipped with thin-film transistors, according to the second embodiment of the present invention.  FIG. 8  is a drive voltage diagram of the organic EL display device with thin-film transistors, according to the second embodiment of the present invention.  FIG. 9  is a current-voltage characteristic chart of the organic EL display device according to the second embodiment of the present invention. 
         [0062]    In  FIG. 7 , there are shown a pixel electrode formed of ITO  615 , an opposite electrode formed of Al  616 , a p-channel type current-thin-film transistor  622 , and an organic EL display device  631  (hereinafter referred to as “a reverse oriented organic EL display device”), which is caused to emit light by the current flowing to the Opposite electrode  616  from the pixel electrode  615 . Numeral  641  indicates the direction of the current of the organic EL display device. This direction is the reverse of that shown in  FIG. 2 . Except for this, this embodiment is the same as the above first embodiment shown in  FIG. 2 . 
         [0063]      FIG. 8  is the same as  FIG. 3  except that the level of each potential is different from that of  FIG. 3 . 
         [0064]    In  FIG. 9 , a curve  81  indicates a current-voltage characteristic of a p-channel type current-thin-film transistor  622  as observed when the drain voltage is 4V. A curve  82  indicates a current-voltage characteristic of the p-channel type current-thin-film transistor  622  as observed when the drain voltage is 8V. 
         [0065]    In  FIG. 10 , a curve  9  indicates a current-voltage characteristic of a reverse oriented organic EL display device  631 . 
         [0066]    The organic EL display device equipped with the thin-film transistors of this embodiment operates in the same way as that of the first embodiment, except that the potential relationship regarding the current-thin-film transistor is reversed due to the fact that the current-thin-film transistor is the p-channel type thin-film transistor  622 . 
         [0067]      FIG. 11(   a ) is a sectional view of an organic EL display device (1 pixel) equipped with the thin-film transistors, according to the second embodiment of the present invention.  FIG. 11(   b ) is a plan view of a thin-film transistor organic EL display device (1 pixel), according to the second embodiment of the present invention. The section taken along the line A-A′ of  FIG. 11(   a ) corresponds to the section taken along the line A-A′ of  FIG. 11(   b ). 
         [0068]      FIG. 11(   a ) is the same as  FIG. 6(   a ), except that it shows a hole injection layer  632  and an organic EL layer  633 . 
         [0069]    The reverse oriented organic EL display device  631  is formed by means of the pixel electrode  615  formed of ITO, the opposite electrode  616  formed of Al, the hole injection layer  632 , and the organic EL layer  633 . In the reverse oriented organic EL display device  631 , the direction of current of the organic EL display device, indicated at  641 , can be set to the direction from the pixel electrode  615  formed of ITO to the opposite electrode  616  formed of Al. 
         [0070]    In this embodiment, a common potential  714  is higher than a counter potential  716 . Further, the current-thin-film transistor is the p-channel type current-thin-film transistor  622 . 
         [0071]    In this embodiment, a signal potential  712  for the pixel to be in the display-state is higher than the counter potential  716 . 
         [0072]    Furthermore, in this embodiment, the signal potential  712  for the pixel to be in the non-display-state is lower than the common potential  714 . 
         [0073]    All of the effects of the thin-film transistor organic EL display device of this embodiment are also the same as those of the first embodiment, except that the potential relationship regarding the current-thin-film transistor is reversed due to the fact that the current-thin-film transistor is the p-channel type thin-film transistor  622 . 
         [0074]    In this embodiment, the current-thin-film transistor  122  is a p-channel type thin-film transistor. This arrangement enables the deterioration with time of the current-thin-film transistor  122  to significantly decrease. Furthermore, the arrangement adopting a p-channel type polysilicon thin-film transistor enables the deterioration with time of the current-thin-film transistor  122  to decrease even further. 
         [0075]      FIG. 14  is a diagram of a process of producing the current-driven light-emitting display apparatus equipped with the thin-film transistors, according to the embodiment of the present invention described above. 
         [0076]    As shown in  FIG. 14(   a ), an amorphous silicon layer with a thickness of 200 to 600 angstroms is deposited all over a substrate  1 , and the amorphous silicon layer is polycrystallized by laser annealing etc., to form a polycrystalline silicon layer. After this, patterning is performed on the polycrystalline silicon layer to form a silicon thin-film  421 , which serves as a source/drain channel region of the switching thin-film transistor  121 , a first electrode  423  of the storage capacitor  123 , and a silicon thin-film  422 , which serves as a source/drain channel region of the current-thin-film transistor  122 . Next, an insulation film  424 , which serves as a gate insulation film, is formed over the silicon thin-films  421 ,  422 , and the first electrode  423 . Then, implantation of phosphorous (P) ions is selectively effected on the first electrode  423  to lower the resistance thereof. Next, as shown in  FIG. 14(   b ), gate electrodes  111  and  111 ′, which consist of TaN layers, are formed on the silicon thin-films  421  and  422  through the intermediation of the gate insulation film. Next, a resist mask  42  is formed on the silicon layer  422  serving as a current-thin-film transistor, and phosphorous (P) ions are implanted through self-alignment using the gate electrode as a mask to form an n-type source/drain region in the silicon layer  421 . Subsequently, as shown in  FIG. 14(   c ), a resist mask  412 ′ is formed on the first silicon layer  421  and the first electrode, and boron (B) is ion-implanted in the silicon layer  422  through self-alignment using the gate electrode  111 ′ as a mask to form a p-type source/drain region in the silicon layer  422 . In this way, an n-channel type impurity doping  411  allows the switching thin-film transistor  121  to be formed. At this time, the current-thin-film transistor  122  is protected by the resist mask  42 , so that the n-channel type impurity doping  411  is not performed. Then, a p-channel type impurity doping  412  allows the current-thin-film transistor  122  to be formed. 
         [0077]    Further, though not illustrated, in a case in which a shift register of a drive circuit section which drives the switching transistor  121 , and a thin-film transistor constituting a sample hold circuit etc., are to be formed on the same substrate, it is possible to form them simultaneously in the same step of process as has been described above. 
         [0078]    A second electrode  425  of the storage capacitor may be formed together with the gate electrodes  111  and  111 ′ simultaneously, either of the same or different materials. 
         [0079]    As shown in  FIG. 14(   d ), after the formation of an inter-layer insulation film  43  and, then, contact holes, electrode layers  426 ,  427 ,  428  and  429  formed of aluminum, ITO or the like are formed. 
         [0080]    Next, after an inter-layer insulation film  44  is formed and flattened, contact holes are formed; then, ITO  45  is formed with a thickness of 1000 to 2000 angstroms, preferably about 1600 angstroms, in such a manner that one electrode of the current-thin-film transistor is connected thereto. For each pixel region, bank layers  46  and  47 , which are not less than 2.0 μm in width, are defined. Next, an organic EL layer  48  is formed by an ink-jet method etc., in the region surrounded by the bank layers  46  and  47 . After the organic EL layer  48  is formed, an aluminum-lithium layer with a thickness of 6000 to 8000 angstroms is deposited as an opposite electrode  49  on the organic EL layer  48 . Between the organic EL layer  48  and the opposite electrode  49 , a hole injection layer may be disposed, as shown in  FIG. 6(   a ). 
         [0081]    The process mentioned above enables an organic EL display device driven by means of a high-performance thin-film transistor to be formed. Since polysilicon is much higher in the mobility of carriers than amorphous-silicon, a rapid operation is possible. 
         [0082]    In particular, in this embodiment, when the p-type current-thin-film transistor  122  and the n-type switching thin-film transistor  121  are formed, it is possible to form both of n-type and p-type thin-film transistors, which are complementary type thin-film transistors constituting a shift register of a drive circuit, a sample hold circuit and the like, being simultaneously formed in the above mentioned embodiment. The arrangement makes it possible to realize a construction capable of decreasing the deterioration with time of the current-thin-film transistor  122 , without increasing the number of production steps. 
         [0083]    As described above, in the first embodiment, an n-channel type current-thin-film transistor is used, and, in the second embodiment, a p-channel type current-thin-film transistor is used. Here, the deterioration with time of p-channel and n-channel type thin-film transistors will be examined. 
         [0084]      FIG. 12  and  FIG. 13  are charts showing respectively the deterioration with time of n-channel type and p-channel type thin-film transistors, especially of polysilicon thin-film transistors, under equivalent voltage application conditions. Numerals  511  and  512  of  FIG. 12  indicate the conductivity characteristics of an n-channel type thin-film transistor, in the cases in which Vd=4V and in which Vd=8V, respectively, before voltage application. Numerals  521  and  522  indicate the conductivity characteristics of an n-channel type thin-film transistor, in the cases in which Vg=0V and Vd=15V and in which Vd=4V and Vd=8V, respectively, after voltage application of approximately 1000 seconds. Numerals  811  and  812  of  FIG. 13  indicate the conductivity characteristics of a p-channel type thin-film transistor in the cases in which Vd=4V, and in which Vd=8V, respectively, before voltage application. Numerals  821  and  822  indicate the conductivity characteristics of a p-channel type thin-film transistor in the cases in which Vg=0V and Vd=15V, and in which Vd=4V and Vd=8V, respectively, after voltage application for approximately 1000 seconds. It can be seen that in the p-channel type thin-film transistor, the decrease of ON-current and the increase of OFF-current are smaller than in the n-channel type. 
         [0085]    Taking into consideration the difference in the deterioration-with-time characteristic between the p-type and the n-type thin-film transistors as shown in  FIG. 12  and  FIG. 13  respectively, at least either a switching thin-film transistor or a current-thin-film transistor is formed of a p-channel type thin-film transistor, especially a p-type polysilicon thin-film transistor, whereby the deterioration with time can be suppressed. Further, by forming the switching thin-film transistor as well as the current-thin-film transistor of a p-type thin-film transistor, it is possible to maintain the characteristics of the display device. 
         [0086]    While an organic EL display device is used as the luminescent device in the embodiment described above, this should not be construed restrictively, yet, it is needless to say that an inorganic EL display device or other current-driven luminescent devices are also applicable. 
       INDUSTRIAL APPLICABILITY 
       [0087]    The display apparatus according to the present invention can be used as a display apparatus equipped with a current-driven luminescent device such as an organic EL display device or an inorganic EL display device, and a switching device to drive the luminescent device, such as a thin-film transistor.

Technology Classification (CPC): 7