Abstract:
Provided is an organic light-emitting display apparatus including a substrate; and a plurality of pixels on the substrate, wherein each of the pixels comprise: an organic light-emitting device comprising a first electrode, a second electrode, and an intermediate layer between the first electrode and the second electrode, wherein the intermediate layer comprises an organic emission layer; a driving transistor configured to drive the organic light-emitting device; and a switching transistor electrically coupled to the driving transistor, wherein the gate electrode of the driving transistor comprises a first conductive layer, and a second conductive layer between the first conductive layer and the active layer of the driving transistor and has a smaller size than the first conductive layer, and the gate electrode of the switching transistor comprises a same material as the first conductive layer.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to and the benefit of Korean Patent Application No. 10-2013-0033087, filed in the Korean Intellectual Property Office on Mar. 27, 2013, the entire content of which is incorporated herein by reference. 
       BACKGROUND 
       [0002]    1. Field 
         [0003]    Aspects of the present invention relate to an organic light-emitting display apparatus. 
         [0004]    2. Description of the Related Art 
         [0005]    Recently, thin film-type portable flat panel display apparatuses have become more popular as display apparatuses. From among flat panel display apparatuses, an organic light-emitting display apparatus is a self-emission display apparatus that has a relatively wide viewing angle, a relatively high contrast ratio, and a relatively high response speed compared to other display apparatus technologies. Due to these characteristics, the organic light-emitting display apparatus is getting attention as a next-generation display apparatus. 
         [0006]    An organic light-emitting display apparatus includes an intermediate layer, a first electrode, and a second electrode. The intermediate layer includes an organic emission layer, and when a voltage is applied to the first electrode and the second electrode, the organic emission layer generates visible light. 
         [0007]    Also, the organic light-emitting display apparatus may further include one or more transistors (TR) that drive the organic light-emitting display apparatus, and in particular, one pixel may include a switching TR and a driving TR. 
         [0008]    In this regard, because characteristics of a switching TR and a driving TR included in one pixel largely affect driving of an organic light-emitting display apparatus, there is a need to effectively control the switching TR and the driving TR. 
         [0009]    However, it is difficult to control the switching TR and the driving PR included in one pixel without an additional process, thereby limiting an improvement in image-quality characteristics of an organic light-emitting display apparatus. 
       SUMMARY 
       [0010]    Embodiments of the present invention provide an organic light-emitting display apparatus for improving an image quality and a method of manufacturing an organic light-emitting display apparatus. 
         [0011]    According to an aspect of the present invention, there is provided an organic light-emitting display apparatus including a plurality of pixels on the substrate, wherein each of the pixels includes: an organic light-emitting device comprising a first electrode, a second electrode, and an intermediate layer between the first electrode and the second electrode, wherein the intermediate layer comprises an organic emission layer; a driving transistor configured to drive the organic light-emitting device and comprising an active layer, a gate electrode, a source electrode, and a drain electrode; and a switching transistor electrically coupled to the driving transistor and comprising an active layer, a gate electrode, a source electrode, and a drain electrode, wherein the gate electrode of the driving transistor comprises a first conductive layer, and a second conductive layer between the first conductive layer and the active layer of the driving transistor and has a smaller size than the first conductive layer, and the gate electrode of the switching transistor comprises a same material as the first conductive layer. 
         [0012]    The first conductive layer may protrude over opposite sides of the second conductive layer. 
         [0013]    An overlapping region of the second conductive layer and the active layer of the driving transistor may be smaller than an overlapping region of the first conductive layer and the active layer of the driving transistor. 
         [0014]    The second conductive layer may include a transmissive conductive material. 
         [0015]    The transmissive conductive material may include ITO, IZO, ZnO, In 2 O 3 , IGO, or AZO. 
         [0016]    An electrical resistance of the first conductive layer may be smaller than an electric resistance of the second conductive layer. 
         [0017]    Each of the pixels may further include a capacitor. 
         [0018]    The capacitor may include a first capacitor electrode and a second capacitor electrode, and the first capacitor electrode may be include the same material as the first conductive layer, and the second capacitor electrode may include a same material as the source electrode and drain electrode of the driving transistor or the source electrode and drain electrode of the switching transistor. 
         [0019]    The first electrode and the second conductive layer of the driving transistor may be formed on a same layer. 
         [0020]    The first electrode may be formed of a same material as in the second conductive layer of the driving transistor. 
         [0021]    A portion of the active layer of the driving transistor that corresponds to the first conductive layer and does not correspond to the second conductive layer may be a non-doped portion. 
         [0022]    According to another aspect of the present invention, there is provided a method of manufacturing an organic light-emitting display apparatus, the organic light-emitting display apparatus including a plurality of pixels on a substrate, the method including: forming one of the pixels, the forming of one of the pixels includes: forming an organic light-emitting device including a first electrode, a second electrode, and an intermediate layer between the first electrode and the second electrode, the intermediate layer including an organic emission layer; forming a driving transistor configured to drive the organic light-emitting device, the driving transistor including an active layer, a gate electrode, a source electrode, and a drain electrode; and forming a switching transistor electrically coupled to the driving transistor, the switching transistor including an active layer, a gate electrode, a source electrode, and a drain electrode, wherein the gate electrode of the driving transistor includes a first conductive layer, and a second conductive layer between the first conductive layer and the active layer of the driving transistor, wherein the second conductive layer has a smaller size than the first conductive layer, and the gate electrode of the switching transistor includes a same material as the first conductive layer. 
         [0023]    Forming the gate electrode of the driving transistor may further include, after the first conductive layer is formed, forming the second conductive layer by using the first conductive layer as an etch mask. 
         [0024]    Forming the second conductive layer may include using a wet etching process. 
         [0025]    Forming the second conductive layer may include forming the first conductive layer and a preliminary second conductive layer between the first conductive layer and the active layer, and then etching the preliminary second conductive layer. 
         [0026]    The preliminary second conductive layer may be larger than the first conductive layer. 
         [0027]    The method may further include performing a doping process on the active layer of the driving transistor, wherein the doping process may include using the first conductive layer of the gate electrode of the driving transistor as a doping mask. 
         [0028]    During the doping process, a conduction portion may be formed on the first electrode and may include the same material as the first conductive layer, wherein the conduction portion may be configured to be used as a doping blocking member. 
         [0029]    The first electrode and the second conductive layer of the driving transistor may include a same material and may be on a same layer. 
         [0030]    The method may further include forming a capacitor in each of the pixels, wherein the capacitor may include a first capacitor electrode and a second capacitor electrode, the first capacitor electrode may include the same material as the first conductive layer and may be formed concurrently with the first conductive layer, and the second capacitor electrode may include a same material as the source electrode and drain electrode of the driving transistor or the source electrode and drain electrode of the switching transistor, and the second capacitor electrode may be formed concurrently with the source electrode and drain electrode of the driving transistor or the source electrode and drain electrode of the switching transistor. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0031]    The above and other features and aspects of the present invention will become more apparent by describing in some detail example embodiments thereof with reference to the attached drawings in which: 
           [0032]      FIG. 1  is a schematic cross-sectional view of an organic light-emitting display apparatus according to an embodiment of the present invention; 
           [0033]      FIG. 2  is a circuit diagram schematically illustrating a pixel of the organic light-emitting display apparatus of  FIG. 1 ; 
           [0034]      FIG. 3  illustrates a driving TR and a switching transistor (TR) illustrated in  FIG. 1 ; 
           [0035]      FIG. 4  is a diagram illustrating characteristics of the driving TR illustrated in  FIG. 1 ; 
           [0036]      FIG. 5  is a diagram illustrating characteristics of the switching TR illustrated in  FIG. 1 ; 
           [0037]      FIG. 6  is a schematic cross-sectional view of an organic light-emitting display apparatus according to another embodiment of the present invention; and 
           [0038]      FIGS. 7A to 7E  are diagrams illustrating a method of manufacturing the organic light-emitting display apparatus of  FIG. 6 . 
       
    
    
     DETAILED DESCRIPTION 
       [0039]    The structure and operation of the present invention are described in more detail by referring to embodiments of the present invention. 
         [0040]      FIG. 1  is a schematic cross-sectional view of an organic light-emitting display apparatus  100  according to an embodiment of the present invention, and  FIG. 2  is a circuit diagram schematically illustrating a pixel of the organic light-emitting display apparatus  100  of  FIG. 1 . 
         [0041]    The organic light-emitting display apparatus  100  includes a plurality of pixels (not shown) on a substrate  101 . For convenience of explanation, only one pixel is illustrated in  FIGS. 1 and 2 . 
         [0042]    Referring to  FIGS. 1 and 2 , a pixel of the organic light-emitting display apparatus  100  includes a driving transistor (TR) TR 1 , a switching TR TR 2 , a capacitor Cst, and an organic light-emitting device EL. 
         [0043]    The driving TR TR 1  includes an active layer  103   a , a gate electrode  105   a , a source electrode  109   a , and a drain electrode  110   a . The switching TR TR 2  includes an active layer  103   b , a gate electrode  105   b , a source electrode  109   b , and a drain electrode  110   b . The capacitor Cst includes a first capacitor electrode  141  and a second capacitor electrode  142 . The organic light-emitting device EL includes a first electrode  121 , a second electrode  122 , and an intermediate layer  123 . 
         [0044]    As illustrated in  FIG. 2 , one pixel is coupled to a scan line S extending in a first direction, and a data line D extending in a second direction crossing the first direction. The data line D allows a data signal provided by a data driving unit (not shown) to be applied to the switching TR TR 2 . Also, the scan line S allows a scan signal provided by a scan driving unit (not shown) to be applied the switching TR TR 2 . Also, a power supply line V allows a voltage provided by the power driving unit (not shown) to be applied to the organic light-emitting device EL. 
         [0045]    Data signals are transmitted to the driving TR TR 1  through the switching TR TR 2 , and the driving TR TR 1  drives the organic light-emitting device EL in correspondence to the data signals. In this regard, the capacitor Cst may maintain data voltage constant for a period of time (e.g., a predetermined period of time). 
         [0046]    However, the structure illustrated in  FIG. 2  is only an example, and the organic light-emitting display apparatus  100  may additionally include a TR (not shown) other than the switching TR TR 2  and the driving TR TR 1  to compensate for a threshold voltage of the driving TR TR 1 , and a capacitor (not shown) other than the capacitor Cst. 
         [0047]    Structures of the respective members are described in more detail below. 
         [0048]    The substrate  101  may be formed of a transparent glass material including SiO 2  as a major component. However, a material for forming the substrate  101  is not limited thereto, and for example, a transparent plastic material may also be used. In this regard, a plastic material that forms the substrate  101  may be at least one selected from various suitable organic materials. 
         [0049]    A buffer film  102  is formed on the substrate  101 . The buffer film  102  may prevent or substantially prevent permeation of impurity elements through the substrate  101  and provides a relatively flat or planar surface on the substrate  101 , and may be formed of any one of various suitable materials that provide such properties. For example, the buffer film  102  may include an inorganic material, such as silicon oxide, silicon nitride, silicon oxynitride, aluminum oxide, aluminum nitride, titanium oxide, or titanium nitride, or an organic material, such as polyimide, polyester, or acryl, and these materials may be formed as a plurality of stacks or layers for use as the buffer film  102 . 
         [0050]    In one embodiment, the buffer film  102  may be omitted according to process conditions. 
         [0051]    The active layer  103   a  of the driving TR TR 1  and the active layer  103   b  of the switching TR TR 2  may be formed on the buffer film  102 . The active layer  103   a  and the active layer  103   b  may be formed of an identical or substantially similar material, for example, an inorganic material, such as silicon material, an organic semiconductor material, or oxide semiconductor material. 
         [0052]    A gate insulating film  104  covering the active layer  103   a  and the active layer  103   b  is formed on the buffer film  102 . The gate insulating film  104  may be formed of various suitable insulating materials, for example, an oxide or a nitride. 
         [0053]    The gate electrode  105   a  of the driving TR TR 1 , the gate electrode  105   b  of the switching TR TR 2 , and the first capacitor electrode  141  are formed on the gate insulating film  104 . 
         [0054]    The gate electrode  105   a  of the driving TR TR 1  includes a first conductive layer  106  and a second conductive layer  107 . The first conductive layer  106  is formed on the second conductive layer  107 . That is, the second conductive layer  107  is formed on the gate insulating film  104 , and the first conductive layer  106  is formed on the second conductive layer  107 . 
         [0055]    Also, the second conductive layer  107  may have a smaller width than the first conductive layer  106 . In more detail, the first conductive layer  106  may protrude over opposite sides of the second conductive layer  107 . That is, an overlapping region of the second conductive layer  107  and the active layer  103   a  is smaller than an overlapping region of the first conductive layer  106  and the active layer  103   a.    
         [0056]    The second conductive layer  107  includes a transmissive conductive material, and in more detail, the second conductive layer  107  may be formed of ITO, IZO, ZnO, In 2 O 3 , IGO, or AZO. 
         [0057]    The first conductive layer  106  may be formed of a material with a lower electric resistance than the second conductive layer  107 . Also, the first conductive layer  106  may include metal or an alloy thereof, such as Mo, MoW, or Al-based alloy, but a material for forming first conductive layer  106  is not limited thereto. Also, the first conductive layer  106  may have a single-layer structure or a stack (e.g., multiple layer) structure of Mo/Al/Mo. 
         [0058]    The gate electrode  105   b  of the switching TR TR 2  may be formed on the gate insulating film  104 . The gate electrode  105   b  may be formed of the same material as used in forming the first conductive layer  106  of the gate electrode  105   a  of the driving TR TR 1 . Also, like the first conductive layer  106 , the gate electrode  105   b  may have a single-layer structure or a stack structure of Mo/Al/Mo. 
         [0059]    The first capacitor electrode  141  may be formed on the gate insulating film  104 . The first capacitor electrode  141  may be formed of the same material as used in forming the first conductive layer  106  of the gate electrode  105   a  of the driving TR TR 1 . 
         [0060]    An interlayer insulating film  108  is formed on the gate electrode  105   a , the gate electrode  105   b , and the first capacitor electrode  141 . The interlayer insulating film  108  may be formed of various insulating materials. 
         [0061]    The source electrode  109   a  of the driving TR TR 1 , the drain electrode  110   a  of the driving TR TR 1 , the source electrode  109   b  of the switching TR TR 2 , the drain electrode  110   b  of the switching TR TR 2 , and the second capacitor electrode  142  are formed on the interlayer insulating film  108 . 
         [0062]    The source electrode  109   a  of the driving TR TR 1  and the drain electrode  110   a  of the driving TR TR 1  may be coupled to the active layer  103   a  of the driving TR TR 1 . The source electrode  109   a  of the driving TR TR 1  and the drain electrode  110   a  of the driving TR TR 1  may be formed of various suitable conductive materials, and may be formed of metal, such as Au, Pd, Pt, Ni, Rh, Ru, Ir, Os, Al, Mo, Nd, Mo, W, or an alloy of at least two of these, but a material for forming the source electrode  109   a  and the drain electrode  110   a  is not limited thereto. 
         [0063]    The source electrode  109   b  of the switching TR TR 2  and the drain electrode  110   b  of the switching TR TR 2  may be coupled to the active layer  103   b  of the switching TR TR 2 . The source electrode  109   b  of the switching TR TR 2  and the drain electrode  110   b  of the switching TR TR 2  may be formed of various materials, and may be formed of metal, such as Au, Pd, Pt, Ni, Rh, Ru, Ir, Os, Al, Mo, Nd, Mo, W, or an alloy of at least two of these, but a material for forming the source electrode  109   b  and the drain electrode  110   b  is not limited thereto. 
         [0064]    The second capacitor electrode  142  may be formed to overlap with the first capacitor electrode  141  by using Au, Pd, Pt, Ni, Rh, Ru, Ir, Os, Al, Mo, Nd, Mo, W, or an alloy of two or more of these, but a material for forming the second capacitor electrode  142  is not limited thereto. 
         [0065]    A passivation layer  111  is formed on the capacitor Cst, the driving TR TR 1 , and the switching TR TR 2 . The passivation layer  111  may be formed of an insulating material. 
         [0066]    The first electrode  121  of the organic light-emitting device EL is formed on the passivation layer  111 . In more detail, the first electrode  121  is coupled to the drain electrode  110   a  of the driving TR TR 1 . Also, when the first electrode  121  acts as an anode, a material for forming the first electrode  121  may include a material with high work function, such as ITO, IZO, ZnO, or In 2 O 3 . Also, depending on the purpose or design, the first electrode  121  may further include a reflective film formed of Ag, Mg, Al, Pt, Pd, Au, Ni, Nd, Ir, Cr, Li, Yb, or Ca. 
         [0067]    A pixel define film  119  is formed on the first electrode  121 . In more detail, the pixel define film  119  has an opening corresponding to a top surface of the first electrode  121 , and the intermediate layer  123  is formed in the opening to contact the top surface of the first electrode  121 . 
         [0068]    The intermediate layer  123  includes an organic emission layer to emit visible light. Also, optionally, the intermediate layer  123  may further include at least one layer selected from a hole transport layer, a hole injection layer, an electron transport layer, and an electron injection layer. 
         [0069]    The second electrode  122  is formed on the intermediate layer  123 . When the second electrode  122  acts as a cathode, the second electrode  122  may be formed of metal, such as Ag, Mg, Al, Pt, Pd, Au, Ni, Nd, Ir, Cr, Li, or Ca. Also, the second electrode  122  may include ITO, IZO, ZnO, or In 2 O 3  to enable transmission of light. 
         [0070]    Also, although not illustrated herein, an encapsulation member (not shown) may be further positioned on the second electrode  122  to protect, for example, the organic light-emitting device EL, and the encapsulation member (not shown) may be formed of an organic material or an inorganic material, and may have a single-layer structure or a multi-layer structure, or a stack structure including an organic material and an inorganic material. 
         [0071]    In the present embodiment, the first electrode  121  is an anode and the second electrode  122  is a cathode. However, the present invention is not limited thereto, and for example, the first electrode  121  may act as a cathode and the second electrode  122  may act as an anode, and materials for forming the first electrode  121  and the second electrode  122  may vary correspondingly. 
         [0072]    In the organic light-emitting display apparatus  100  according to the present embodiment, the gate electrode  105   a  of the driving TR TR 1  is different from the gate electrode  105   b  of the switching TR TR 2  in terms of shape. The organic light-emitting display apparatus  100  will be described in more detail with reference to  FIG. 3 . 
         [0073]      FIG. 3  illustrates a driving TR and a switching TR illustrated in  FIG. 1 . 
         [0074]    First, regarding the switching TR TR 2 , the active layer  103   b  includes a channel region C corresponding to (e.g., at least partially vertically aligned with) the gate electrode  105   b , a source region S corresponding to (e.g., at least partially vertically aligned with) the source electrode  109   b , and a drain region D corresponding to (e.g., at least partially vertically aligned with) the drain electrode  110   b.    
         [0075]    Then, regarding the driving TR TR 1 , the active layer  103   a  includes a channel region C corresponding to (e.g., at least partially vertically aligned with) the second conductive layer  107  of the gate electrode  105   a , a source region S corresponding to (e.g., at least partially vertically aligned with) the source electrode  109   a , and a drain region D corresponding to (e.g., at least partially vertically aligned with) the drain electrode  110   a . Also, the active layer  103   a  includes intermediate regions G 1  and G 2 , respectively corresponding to width differences W 1  and W 2  of the first conductive layer  106  and the second conductive layer  107  in a direction. The intermediate regions G 1  and G 2  of the active layer  103   a  may act as a resistor of the driving TR TR 1 . In particular, when a doping process is performed on the active layer  103   a , the first conductive layer  106  may act as a doping mask so that the intermediate regions G 1  and G 2  may not be doped. 
         [0076]    Thus, a voltage applied to the channel region C of the active layer  103   a  is lower than a voltage Vgs applied between the gate electrode  105   a  and the source electrode  109   a . Accordingly, compared to a case in which the intermediate regions G 1  and G 2  are not formed, a current Ids flowing between the source electrode  109   a  and the drain electrode  110   a  of the driving TR TR 1  is reduced. 
         [0077]    Therefore, S.S (sub-threshold swing) value of the driving TR TR 1  increases. That is, when the voltage is a threshold voltage or lower, the slope of the IV curve decreases. On the other hand, a S.S value of the switching TR TR 2  is smaller than that of the driving TR TR 1 . That is, when the voltage is a threshold voltage or lower, the slope of the IV curve increases. 
         [0078]    This will be described in more detail in connection with  FIGS. 4 and 5 . 
         [0079]      FIG. 4  is a diagram to explain characteristics of the driving TR illustrated in  FIG. 1 .  FIG. 4  shows a IV curve, and  FIG. 4(   a ) corresponds to a case in which the driving TR TR 1  has a low S.S value, and  FIG. 4(   b ) corresponds to a case in which the driving TR TR 1  has a high S.S value. That is, the driving TR TR 1  according to the present embodiment corresponds to  FIG. 4(   b ). 
         [0080]    Referring to  FIG. 4 , if the current range for driving the organic light-emitting display apparatus  100  is assumed to be in a range of about 1e −12  A to 5e −7  A, ΔVgs 2  of  FIG. 4(   b ) is greater than ΔVgs 1  of  FIG. 4(   a ). When the driving TR TR 1  has a high S.S value as illustrated in  FIG. 4(   b ), that is, when a IV curve has a gentle slope before a threshold voltage, a voltage margin for the expression of gradation of the organic light-emitting display apparatus  100  is high. That is, the driving TR TR 1  according to the present embodiment has a high S.S value so that the organic light-emitting display apparatus  100  may relatively easily express gradation. 
         [0081]      FIG. 5  is a diagram to explain characteristics of the switching TR illustrated in  FIG. 1 .  FIG. 5  shows a IV curve, and  FIG. 5(   a ) corresponds to a case in which the switching TR TR 2  has a low S.S value, and  FIG. 5(   b ) corresponds to a case in which the switching TR TR 2  has a high S.S value. That is, the switching TR TR 2  according to the present embodiment corresponds to  FIG. 5(   a ). 
         [0082]    Referring to  FIG. 5 , regarding the organic light-emitting display apparatus  100 , ΔVgs 1  of  FIG. 5(   a ) is the same as ΔVgs 2  of  FIG. 5(   b ), which corresponds to a case in which the S.S value is high, has a current difference of ΔI compared to  FIG. 5(   a ) due to the increase in resistance. That is, the switching TR TR 2  of  FIG. 5(   b ) may experience a voltage drop and thus, characteristics of the switching TR TR 2  decreases. In particular, to additionally compensate for the voltage drop, the swing range of the switching TR TR 2  may need to be widened or the driving time may be increased, and additionally, voltage drop may occur due to a kickback phenomenon. The switching TR TR 2  of the organic light-emitting display apparatus  100  according to the present embodiment, unlike the driving TR TR 1 , may have a low S.S value due to the relative absence of the resistance occurring due to the intermediate regions G 1  and G 2 . By doing so, characteristics of the switching TR TR 2  may be improved. 
         [0083]    Also, the organic light-emitting display apparatus  100  according to the present embodiment, the second conductive layer  107  of the gate electrode  105   a  of the driving TR TR 1  is formed of a transmissive conductive material with a greater resistance than the first conductive layer  106 , and thus, due to the increase in resistance, a S.S value thereof is increased. Also, because the gate electrode  105   b  of the switching TR TR 2  is formed of the same material as used to form the first conductive layer  106  instead of the transmissive conductive material, the resistance thereof is decreased and thus, a S.S value thereof is decreased. 
         [0084]    The driving TR TR 1  and the switching TR TR 2  organic light-emitting display apparatus  100  according to the present embodiment have different shapes. Due to the difference in shape, characteristics of the driving TR TR 1  and the switching TR TR 2  may be differently controlled. That is, without a decrease in characteristics of the switching TR TR 2 , characteristics of the driving TR TR 1  may be improved. That is, without a decrease in data signal characteristics of the switching TR TR 1 , a voltage margin for the expression of gradation is increased and thus, image-quality characteristics of an organic light-emitting display apparatus may be relatively easily improved. 
         [0085]      FIG. 6  is a schematic cross-sectional view of an organic light-emitting display apparatus  200  according to another embodiment of the present invention. 
         [0086]    The organic light-emitting display apparatus  200  includes a plurality of pixels (not shown) on a substrate  201 . For the convenience of explanation, only one pixel is illustrated in  FIG. 6 . 
         [0087]    Referring to  FIG. 6 , a pixel of the organic light-emitting display apparatus  200  includes a driving transistor TR 1 , a switching TR TR 2 , a capacitor Cst, and an organic light-emitting device EL. For convenience of explanation,  FIG. 6  illustrates only one pixel. 
         [0088]    The driving TR TR 1  includes an active layer  203   a , a gate electrode  205   a , a source electrode  209   a , and a drain electrode  210   a . The switching TR TR 2  includes an active layer  203   b , a gate electrode  205   b , a source electrode  209   b , and a drain electrode  210   b . The capacitor Cst includes a first capacitor electrode  241  and a second capacitor electrode  242 . The organic light-emitting device EL includes a first electrode  221 , a second electrode  222 , and an intermediate layer  223 . 
         [0089]    The data signal is transmitted to the driving TR TR 1  through the switching TR TR 2 , and the driving TR TR 1  drives the organic light-emitting device EL according to the data signal. In this regard, the capacitor Cst may maintain the data voltage constant for a period of time (e.g., a predetermined period of time). 
         [0090]    A buffer film  202  is formed on the substrate  201 . In one embodiment, the buffer film  102  may be omitted according to process conditions. 
         [0091]    The active layer  203   a  of the driving TR TR 1  and the active layer  203   b  of the switching TR TR 2  may be formed on the buffer film  202 . The active layer  203   a  and the active layer  203   b  may be formed of an identical (or substantially similar) material. 
         [0092]    A gate insulating film  204  covering the active layer  203   a  and the active layer  203   b  is formed on the buffer film  202 . 
         [0093]    The gate electrode  205   a  of the driving TR TR 1 , the gate electrode  205   b  of the switching TR TR 2 , and the first capacitor electrode  241  are formed on the gate insulating film  204 . 
         [0094]    The gate electrode  205   a  of the driving TR TR 1  includes a first conductive layer  206  and a second conductive layer  207 . The first conductive layer  206  is formed on the second conductive layer  207 . That is, the second conductive layer  207  is formed on the gate insulating film  204 , and the first conductive layer  206  is formed on the second conductive layer  207 . 
         [0095]    Also, the second conductive layer  207  may have a smaller width than the first conductive layer  206 . That is, the first conductive layer  206  may protrude over opposite sides of the second conductive layer  207 . That is, an overlapping region of the second conductive layer  207  and the active layer  203   a  is smaller than an overlapping region of the first conductive layer  206  and the active layer  203   a.    
         [0096]    The second conductive layer  207  includes a transmissive conductive material, and in more detail, the second conductive layer  207  may be formed of ITO, IZO, ZnO, In 2 O 3 , IGO, or AZO. 
         [0097]    The first conductive layer  206  may include metal or an alloy thereof, such as Mo, MoW, or Al-based alloy, but a material for forming first conductive layer  106  is not limited thereto. Also, the first conductive layer  206  may have a single-layer structure or a stack (e.g., multiple layer) structure of Mo/Al/Mo. 
         [0098]    The gate electrode  205   b  of the switching TR TR 2  may be formed on the gate insulating film  204 . The gate electrode  205   b  may be formed of the same material as used in forming the first conductive layer  206  of the gate electrode  205   a  of the driving TR TR 1 . Also, like the first conductive layer  206 , the gate electrode  105   b  may have a single-layer structure or a stack (e.g., multiple layer) structure of Mo/Al/Mo. 
         [0099]    The first capacitor electrode  241  may be formed on the gate insulating film  204 . The first capacitor electrode  241  may be formed of the same material as used in forming the first conductive layer  206  of the gate electrode  205   a  of the driving TR TR 1 . 
         [0100]    The first electrode  221  may be formed on the gate insulating film  204 . The first electrode  221  may include a transmissive conductive material, and may be formed of the same material as used in the second conductive layer  207 . 
         [0101]    An interlayer insulating film  208  is formed on the gate electrode  205   a , the gate electrode  205   b , the first electrode  221 , and the first capacitor electrode  241 . 
         [0102]    The source electrode  209   a  of the driving TR TR 1 , the drain electrode  210   a  of the driving TR TR 1 , the source electrode  209   b  of the switching TR TR 2 , the drain electrode  210   b  of the switching TR TR 2 , and the second capacitor electrode  242  are formed on the interlayer insulating film  208 . 
         [0103]    The source electrode  209   a  of the driving TR TR 1  and the drain electrode  210   a  of the driving TR TR 1  may be coupled to the active layer  203   a  of the driving TR TR 1 . Also, the driving TR TR 1  is electrically coupled to the first electrode  221 , and for example, the drain electrode  210   a  is electrically coupled to the first electrode  221 . 
         [0104]    The source electrode  209   b  of the switching TR TR 2  and the drain electrode  210   b  of the switching TR TR 2  may be coupled to the active layer  203   b  of the switching TR TR 2 . 
         [0105]    A second capacitor electrode  242  overlaps a first capacitor electrode  241 . 
         [0106]    A pixel define layer  211  is formed on the capacitor Cst, the driving TR TR 1 , and the switching TR TR 2 . The pixel define layer  211  may be formed of an insulating material. The pixel define film  211  exposes a predetermined portion of a top surface of the first electrode  221 , and the exposed portion of the first electrode  221  contacts the intermediate layer  223 . 
         [0107]    The intermediate layer  223  includes an organic emission layer configured to emit visible light. 
         [0108]    The second electrode  222  is formed on the intermediate layer  223 . 
         [0109]    Also, although not illustrated herein, an encapsulation member (not shown) may be further positioned on the second electrode  222  to protect, for example, the organic light-emitting device EL, and the encapsulation member (not shown) may be formed of an organic material or an inorganic material, and may have a single-layer structure or a multi-layer structure, or a stack structure including an organic material and an inorganic material. 
         [0110]    In the organic light-emitting display apparatus  200  according to the present embodiment, the gate electrode  205   a  of the driving TR TR 1  is different from the gate electrode  205   b  of the switching TR TR 2  in terms of shape. 
         [0111]    That is, regarding the driving TR TR 1 , the active layer  203   a  has intermediate regions corresponding to width differences of the conductive layer  206  and the second conductive layer  207  in opposite directions. The intermediate regions of the driving TR TR 1  of the active layer  203   a  act as a resistor. Thus, a voltage applied to the channel region C of the active layer  203   a  is lower than a voltage Vgs applied between the gate electrode  205   a  and the source electrode  209   a . Accordingly, compared to a case in which the intermediate regions are not formed, a current Ids flowing between the source electrode  209   a  and the drain electrode  210   a  of the driving TR TR 1  reduces. 
         [0112]    Therefore, a S.S value of the driving TR TR 1  increases. That is, when the voltage is a threshold voltage or lower, the slope of the IV curve decreases. On the other hand, a S.S value of the switching TR TR 2  is smaller than that of the driving TR TR 1 . That is, when the voltage is a threshold voltage or lower, the slope of the IV curve increases. By doing so, a voltage margin for expression of gradation of the organic light-emitting display apparatus  200  may be relatively easily improved. 
         [0113]    However, the switching TR TR 2 , unlike the driving TR TR 1 , has a low S.S value, due to the absence of resistance caused by the intermediate regions. By doing so, characteristics of the switching TR TR 2  may be improved. 
         [0114]    The driving TR TR 1  and the switching TR TR 2  organic light-emitting display apparatus  200  according to the present embodiment have different shapes. Due to the difference in shape, characteristics of the driving TR TR 1  and the switching TR TR 2  may be differently controlled. That is, without a decrease in characteristics of the switching TR TR 2 , characteristics of the driving TR TR 1  may be improved. That is, without a decrease in data signal characteristics of the switching TR TR 1 , a voltage margin for the expression of gradation is increased and thus, image-quality characteristics of an organic light-emitting display apparatus may be relatively easily improved. 
         [0115]      FIGS. 7A to 7E  are diagrams illustrating a method of manufacturing the organic light-emitting display apparatus  200  of  FIG. 6   
         [0116]    First, referring to  FIG. 7A , the buffer film  202  is formed on the substrate  201 . The active layer  203   a  of the driving TR TR 1  and the active layer  203   b  of the switching TR TR 2  are formed on the buffer film  202 . The active layer  203   a  and the active layer  203   b  may be formed of an identical material. A gate insulating film  204  covering the active layer  203   a  and the active layer  203   b  is formed on the buffer film  202 . 
         [0117]    Then, referring to  FIG. 7B , the first conductive layer  206  of the gate electrode  205   a  of the driving TR TR 1  is formed on the gate insulating film  204 . In more detail, a preliminary second conductive layer  207 ′ and the first conductive layer  206  of the gate electrode  205   a  of the driving TR TR 1  are formed. The preliminary second conductive layer  207 ′ may have a greater width than the first conductive layer  206 . 
         [0118]    Also, the gate electrode  205   b  of the switching TR TR 2 , the first electrode  221 , and the first capacitor electrode  241  are formed on the gate insulating film  204 . Also, a conduction portion BP is formed on the first electrode  221 , and the conduction portion BP and the first conductive layer  206  may be formed of an identical (or substantially similar) material. The conduction portion BP may act as a doping blocking member for the first electrode  221  when a doping process is performed on the active layer  203   a  and the active layer  203   b . In a subsequent process, the conduction portion BP may be completely or partially removed to expose at least a top surface of the first electrode  221 . 
         [0119]    Also, when a doping process is performed on the active layer  203   a  and the active layer  203   b , the first conductive layer  206  and the gate electrode  205   b  may act as a doping mask. Therefore, intermediate regions (see G 1  and G 2  of  FIG. 3 ) of the active layer  203   a  of the driving TR TR 1  may not be doped to increase the resistance of the intermediate regions. 
         [0120]    Thereafter, referring to  FIG. 7C , an etching process, for example, a wet etching process, may be performed on the resultant structure by using the first conductive layer  206  as a mask without use of a separate mask, so as to etch the preliminary second conductive layer  207 ′ until a desired portion thereof is removed, thereby forming the second conductive layer  207 . By doing this, the gate electrode  205   a  of the driving TR TR 1  is formed. 
         [0121]    A time for the etching process is controlled such that the second conductive layer  207  has a smaller width than the first conductive layer  206 . That is, the first conductive layer  206  may protrude over opposite sides of the second conductive layer  207 . That is, an overlapping region of the second conductive layer  207  and the active layer  203   a  is smaller than an overlapping region of the first conductive layer  206  and the active layer  203   a.    
         [0122]    Thereafter, referring to  FIG. 7D , an interlayer insulating film  208  is formed on the gate electrode  205   a , the gate electrode  205   b , the first electrode  221 , and the first capacitor electrode  241 . 
         [0123]    The source electrode  209   a  of the driving TR TR 1 , the drain electrode  210   a  of the driving TR TR 1 , the source electrode  209   b  of the switching TR TR 2 , the drain electrode  210   b  of the switching TR TR 2 , and the second capacitor electrode  242  are formed on the interlayer insulating film  208 . 
         [0124]    The source electrode  209   a  of the driving TR TR 1  and the drain electrode  210   a  of the driving TR TR 1  may be coupled to the active layer  203   a  of the driving TR TR 1 . Also, the driving TR TR 1  is electrically coupled to the first electrode  221 , and for example, the drain electrode  210   a  is electrically coupled to the first electrode  221 . 
         [0125]    The source electrode  209   b  of the switching TR TR 2  and the drain electrode  210   b  of the switching TR TR 2  may be coupled to the active layer  203   b  of the switching TR TR 2 . 
         [0126]    A second capacitor electrode  242  overlaps a first capacitor electrode  241 . 
         [0127]    A pixel define layer  211  is formed on the capacitor Cst, the driving TR TR 1 , and the switching TR TR 2 . The pixel define layer  211  may be formed of an insulating material. Also, the pixel define film  211  is formed to expose a portion (e.g., a predetermined portion) of a top surface of the first electrode  221 . 
         [0128]    Referring to  FIG. 7E , the intermediate layer  223  is formed to contact the top surface of the first electrode  221 . The second electrode  222  is formed on the intermediate layer  223  to complete the manufacturing of the organic light-emitting display apparatus  200 . 
         [0129]    In the organic light-emitting display apparatus  200  according to the present embodiment, the gate electrode  205   a  of the driving TR TR 1  is different from the gate electrode  205   b  of the switching TR TR 2  in terms of shape. That is, without a separate mask, the first conductive layer  106  of the gate electrode  105   a  is used as an etch mask, and the etching time is controlled to relatively easily form the second conductive layer  107  to have a smaller size than the first conductive layer  106 . By doing this, the SS value of the driving TR TR 1  is relatively easily increased, thereby improving expression of gradation of the organic light-emitting display apparatus  200 . 
         [0130]    That is, according to the method according to the present embodiment, the driving TR TR 1  and the switching TR TR 2  included in the organic light-emitting display apparatus  200  have different shapes and characteristics of the driving TR TR 1  and the switching TR TR 2  are differently controlled. That is, without a decrease in characteristics of the switching TR TR 2 , characteristics of the driving TR TR 1  may be improved. That is, without a decrease in data signal characteristics of the switching TR TR 1 , a voltage margin for the expression of gradation is increased and thus, image-quality characteristics of an organic light-emitting display apparatus may be relatively easily improved. 
         [0131]    While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims, and their equivalents.