Patent Publication Number: US-11663978-B1

Title: Driving circuit and display including the same

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to and the benefit of Korean Patent Application No. 10-2022-0035527 filed in the Korean Intellectual Property Office on Mar. 22, 2022, the entire contents of which are incorporated herein by reference. 
     BACKGROUND 
     (a) Field of the Invention 
     The present disclosure relates to a driving circuit and a display including the same. 
     (b) Description of the Related Art 
     To reduce cost of driver ICs such as a gate driver or a light emitting driver of a display and down-size the display, a driver integrated on an array may be applied to the display. High performance such as high operation rates, high reliability, or low power consumption is needed for the integrated driver. 
     The a-Si TFT has lower mobility than the poly-Si and the oxide TFT so the a-Si TFT is inappropriate for the high-performance display. 
     The LTPS TFT has been generally used to the TFT backplane technology for small displays such as mobile displays, and it has high mobility and excellent stability. However, it is difficult to reduce power consumption of the display because of high Off-state currents of the LTPS TFT. 
     On the contrary, the oxide TFT has a very low Off current but has lower current driving performance than the LTPS TFT so it may cause high power consumption. The oxide TFT is easily operated in the depletion mode having a negative threshold voltage (VTH), which generates a malfunction of the gate driver because of a leakage current path. Many TFTs and capacitors must be used to prevent the leakage current path so it is inappropriate in the use of high-resolution displays. Most of the gate drivers configured with the LTPS or the oxide TFT use the bootstrapping method, and the bootstrapping generates a gate bias stress to the TFT. 
     The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention, and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art. 
     SUMMARY OF THE INVENTION 
     The present invention has been made in an effort to provide a driving circuit that is appropriate for a high-resolution display. 
     An embodiment of the present invention provides a driving circuit including a plurality of stages for supplying a plurality of signals, wherein the respective stages include: a first LTPO transistor including a first transistor that is a low-temperature polycrystalline silicon thin film transistor (LTPS TFT) and a second transistor that is an oxide TFT; and a second LTPO transistor including a third transistor that is an LTPS TFT and a fourth transistor that is an oxide TFT. A first end of the first LTPO transistor may be connected to a gate of the second LTPO transistor, and voltages of signals corresponding to the respective stages from among the signals may be a voltage at a first end of the second LTPO transistor. 
     The respective stages may further include: a fifth transistor operable by a previous signal output from a previous stage of the respective stages; and a sixth transistor operable by a next signal output from a next stage of the respective stages, and the previous signal may be supplied to a gate and a first end of the fifth transistor, the next signal may be supplied to a gate of the sixth transistor, and a second end of the fifth transistor and a first end of the sixth transistor may be connected to a gate of the first LTPO transistor. The previous signal may be supplied to a gate and a first end of the fifth transistor, the next signal may be supplied to a gate of the sixth transistor, and a second end of the fifth transistor and a first end of the sixth transistor may be connected to a gate of the first LTPO transistor. 
     A first end of the third transistor and a first end of the fourth transistor may be connected to a first end of the second LTPO transistor, and a first voltage may be supplied to a second end of the third transistor, and a clock signal may be supplied to a second end of the fourth transistor. 
     A first end of the first transistor and a first end of the second transistor may be connected to a first end of the first LTPO transistor, and a second voltage may be supplied to a second end of the first transistor, and a third voltage may be supplied to a second end of the second transistor. 
     The respective stages further include: a control circuit including a third LTPO transistor including a fifth transistor that is an LTPS TFT and a sixth transistor that is an oxide TFT; and a fourth LTPO transistor including a seventh transistor that is an LTPS TFT and an eighth transistor that is an oxide TFT. A first end of the third LTPO transistor may be connected to a gate of the fourth LTPO transistor, a voltage at a first end of the fourth LTPO may be a voltage of a control signal that is an output of the control circuit, and the first LTPO transistor may be operated according to the control signal. 
     The control circuit of the respective stages may further include: a ninth transistor operable by a previous control signal output from a control circuit of a previous stage of the respective stages; and a tenth transistor operable by a next control signal output from a control circuit of a next stage of the respective stages. The previous control signal may be supplied to a gate and a first end of the ninth transistor, the next control signal may be supplied to a gate of the tenth transistor, and a second end of the ninth transistor and a first end of the tenth transistor may be connected to a gate of the third LTPO transistor. 
     A first end of the seventh transistor and a first end of the eighth transistor may be connected to a first end of the fourth LTPO transistor, and a first voltage may be supplied to a second end of the seventh transistor, while a clock signal may be supplied to a second end of the eighth transistor. 
     A first end of the fifth transistor and a first end of the sixth transistor may be connected to the first end of the third LTPO transistor, and a second voltage may be supplied to a second end of the fifth transistor, while a third voltage may be supplied to a second end of the sixth transistor. 
     The respective stages may further include: a ninth transistor operable by a corresponding one of a plurality of other signals corresponding to the signals; and a tenth transistor operable by the control signal. The corresponding other signal may be supplied to a gate and a first end of the ninth transistor, the control signal may be supplied to a gate of the tenth transistor, and a second end of the ninth transistor and a first end of the tenth transistor may be connected to a gate of the first LTPO transistor. 
     A first end of the seventh transistor and a first end of the eighth transistor may be connected to a first end of the second LTPO transistor, and a first voltage may be supplied to a second end of the seventh transistor, while a second voltage may be supplied to a second end of the eighth transistor. 
     A first end of the fifth transistor and a first end of the sixth transistor may be connected to a first end of the first LTPO transistor, and a third voltage may be supplied to a second end of the fifth transistor, while the second voltage may be supplied to a second end of the sixth transistor. 
     A gate of the first transistor and a bottom gate of the second transistor may extend from one line, and a top gate of the second transistor may be connected to the bottom gate through a via contact. 
     A gate of the third transistor and a bottom gate of the fourth transistor may be branched from one line, and a top gate of the second transistor may be connected to the bottom gate through a via contact. 
     Another embodiment of the present invention provides a display including: a plurality of pixel rows including a plurality of pixels; and a gate driver including a plurality of stages for generating a plurality of gate signals and supplying the same to the pixel rows, wherein the respective stages may include a first LTPO transistor realized with a first transistor that is a low-temperature polycrystalline silicon thin film transistor (LTPS TFT) and a second transistor that is an oxide TFT, the second transistor may be synchronized with an On-pulse of a corresponding previous gate signal and may output a corresponding clock signal as the gate signal, and the first transistor may be synchronized with an On-pulse of a corresponding next gate signal and may output an Off-level gate signal. 
     The respective stages may further include a second LTPO transistor realized with a third transistor that is an LTPS TFT and a fourth transistor that is an oxide TFT, the third transistor may be synchronized with an On-pulse of the previous gate signal and may turn on the second transistor, and the fourth transistor may be synchronized with an On-pulse of the corresponding next gate signal and may turn on the first transistor. 
     The display may further include a light emitting driver including a plurality of light emitting stages for generating a plurality of light emitting signals and supplying the same to the pixel rows, wherein the respective light emitting stages may include a second LTPO transistor realized with a third transistor that is an LTPS TFT and a fourth transistor that is an oxide TFT, the fourth transistor may be synchronized with an On-pulse of a corresponding gate signal and may output an On-level light emitting signal, and the third transistor may be synchronized with an On-pulse of a light emitting control signal and may output an Off-level light emitting signal. 
     The respective light emitting stages may further include a third LTPO transistor realized with a fifth transistor that is an LTPS TFT and a sixth transistor that is an oxide TFT, the fifth transistor may be synchronized with an On-pulse of the corresponding gate signal and may turn on the fourth transistor, and the sixth transistor may be synchronized with an On-pulse of the light emitting control signal and may turn on the third transistor. 
     The respective light emitting stages may further include: a light emitting control circuit for generating the light emitting control signal, the light emitting control circuit may include a fourth LTPO transistor including a fifth transistor that is an LTPS TFT and a sixth transistor that is an oxide TFT; and a fifth LTPO transistor including a seventh transistor that is an LTPS TFT and an eighth transistor that is an oxide TFT, and a first end of the fourth LTPO transistor may be connected to a gate of the fifth LTPO transistor, while a voltage at a first end of the fifth LTPO may be a voltage of the control signal. 
     The present invention provides the driving circuit that is appropriate for the high-resolution display. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    shows a circuit diagram of a complementary transistor according to an embodiment. 
         FIG.  2    shows a cross-sectional view of a structure of a complementary transistor according to an embodiment. 
         FIG.  3 A  shows a curved line of a transmission characteristic of a first transistor according to an embodiment. 
         FIG.  3 B  shows a curved line of an output characteristic of a first transistor according to an embodiment. 
         FIG.  4 A  shows a curved line of a transmission characteristic of a second transistor according to an embodiment. 
         FIG.  4 B  shows a curved line of an output characteristic of a second transistor according to an embodiment. 
         FIG.  5    shows a display according to an embodiment. 
         FIG.  6    shows a circuit diagram of a pixel circuit according to an embodiment. 
         FIG.  7    shows a block diagram of a gate driver according to an embodiment. 
         FIG.  8    shows a circuit diagram of two adjacent stages from among a plurality of stages according to an embodiment. 
         FIG.  9    shows a waveform diagram of clock signals, gate signals, and voltages at nodes according to an embodiment. 
         FIG.  10    shows a waveform diagram of an example of stage outputs and voltages at nodes acquired by a first simulation. 
         FIG.  11    shows a waveform diagram of an example of stage outputs and voltages at nodes acquired by a second simulation. 
         FIG.  12    shows a waveform diagram of an example of stage outputs and voltages at nodes acquired by a third simulation. 
         FIG.  13    shows a top plan view of a layout of some stages from among a gate driver according to an embodiment. 
         FIG.  14    and  FIG.  15    show gate signal waveform diagrams of a first stage and a 32-nd stage according to simulations. 
         FIG.  16    shows a top plan view of a layout of an i-th stage shown in  FIG.  8   . 
         FIG.  17    shows a cross-sectional view with respect to a line I-I′ in  FIG.  16   . 
         FIG.  18    shows a cross-sectional view with respect to a line II-II′ in  FIG.  16   . 
         FIG.  19    shows a block diagram of a light emitting driver according to an embodiment. 
         FIG.  20    shows a circuit diagram of two adjacent light emitting stages from among a plurality of light emitting stages according to an embodiment. 
         FIG.  21    shows a waveform diagram of clock signals, light emitting control signals, gate signals, and voltages at nodes, and light emitting signals according to an embodiment. 
         FIG.  22 A  shows a top plan view of a layout of an i-th light emitting stage shown in  FIG.  20   . 
         FIG.  22 B  shows a top plan view of a layout of a light emitting control circuit portion shown in  FIG.  22 A . 
         FIG.  22 C  shows a top plan view of a layout of a remaining portion excluding a portion shown in  FIG.  22 B  from  FIG.  22 A . 
         FIG.  23    shows a cross-sectional view with respect to a line III-III′ in  FIG.  22 C . 
         FIG.  24    shows a cross-sectional view with respect to a line IV-IV′ in  FIG.  22 C . 
         FIG.  25    shows a waveform diagram of signals generated when an operation of a light emitting driver according to an embodiment is simulated. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Embodiments disclosed in the present specification will be described in detail with reference to the accompanying drawings. In the present specification, the same or similar components will be denoted by the same or similar reference numerals, and an overlapped description thereof will be omitted. 
     In describing embodiments of the present specification, when it is determined that a detailed description of the well-known art associated with the present invention may obscure the gist of the present invention, it will be omitted. The accompanying drawings are provided only in order to allow embodiments disclosed in the present specification to be easily understood and are not to be interpreted as limiting the spirit disclosed in the present specification, and it is to be understood that the present invention includes all modifications, equivalents, and substitutions without departing from the scope and spirit of the present invention. 
     Terms including ordinal numbers such as first, second, and the like will be used only to describe various components, and are not interpreted as limiting these components. The terms are only used to differentiate one component from other components. 
     It is to be understood that when one component is referred to as being “connected” or “coupled” to another component, it may be connected or coupled directly to another component or be connected or coupled to another component with the other component intervening therebetween. On the other hand, it is to be understood that when one component is referred to as being “connected or coupled directly” to another component, it may be connected or coupled to another component without the other component intervening therebetween. 
     It is to be understood that terms such as “including,” “having,” etc. are intended to indicate the existence of features, numbers, steps, actions, components, parts, or combinations thereof disclosed in the specification, and are not intended to preclude the possibility that one or more other features, numbers, steps, actions, components, parts, or combinations thereof may exist or may be added. 
     In the drawings, the thickness of layers, films, panels, regions, etc., are exaggerated for clarity. Like reference numerals designate like elements throughout the specification. It will be understood that when an element such as a layer, film, region, or substrate is referred to as being “on” another element, it can be directly on the other element or intervening elements may also be present. In contrast, when an element is referred to as being “directly on” another element, there are no intervening elements present. 
     A complementary transistor according to an embodiment will now be described. 
       FIG.  1    shows a circuit diagram of a complementary transistor according to an embodiment. 
       FIG.  2    shows a cross-sectional view of a structure of a complementary transistor according to an embodiment. 
     The complementary transistor  100  includes a first transistor  200  and a second transistor  300 . 
     A voltage V 1  is supplied to a source of the first transistor  200 , a voltage V 2  is supplied to a source of the second transistor  200 , and a drain of the first transistor  200  is connected to a drain of the second transistor  200 . A node where the two drains are connected to each other may be an output end of the transistor  100 . A gate voltage VG 1  is supplied to a gate of the first transistor  200  to thus control conduction of the first transistor  200 , and a gate voltage VG 2  is supplied to a gate of the second transistor  300  to thus control conduction of the second transistor  300 . 
     When the gates of the first transistor  200  and the second transistor  300  are connected to each other, the transistor  100  may be operated as an inverter. That is, one of the first transistor  200  and the second transistor  300  is turned on and the other is turned off by the gate voltage VG 1  or VG 2 , so one of the voltage V 1  and the voltage V 2  is output as an output voltage VOUT. 
     The first transistor  200  may be realized with a low-temperature polycrystalline silicon and oxide thin-film transistor LTPO TFT. The transistor  100  may be a self-aligned coplanar p-type low-temperature polycrystalline silicon (LTPS) TFT. The second transistor  300  may be realized with an oxide TFT. For example, the second transistor  300  may be realized with an amorphous-indium-gallium-zinc-oxide (a-IGZO) TFT, an example of the oxide TFT. However, the example of the first and second transistors is given to describe an embodiment, and the present invention is not limited thereto. 
     Blue laser annealing (BLA) may be used in a process for crystallizing a-Si of the first transistor  200 . High mobility caused by a grain size that is greater than that of excimer laser annealing (ELA) may be provided. The second transistor  300  may be a dual gate (DG) n-type TFT. The second transistor  300  may be formed by a back channel etching (BCE). A top gate (TG) and a bottom gate (BG) of the second transistor  300  are electrically connected to each other so an On state current of the second transistor  300  may be high and a threshold voltage may be 0 V which is uniform. A detailed process for manufacturing the first and second transistors  200  and  300  may refer to two known theses given below. No detailed description on the manufacturing process will be provided. That the second transistor  300  has a dual gate structure is an example for describing an embodiment, and the second transistor  300  according to the present invention may be realized with the oxide TFT with a single gate structure. 
     1) A. Rahaman, H. Jeong and J. Jang, “A High-Gain CMOS Operational Amplifier Using Low-Temperature Poly-Si Oxide TFTs,” IEEE Transactions on Electron Devices, vol. 67, no. 2, pp. 524-528, February 2020. 
     2) Y. Chen, S. Lee, H. Kim, J. Lee, D. Geng, and J. Jang, “In-pixel temperature sensor for high-luminance active matrix micro-light-emitting diode display using low-temperature polycrystalline silicon and oxide thin-film-transistors,” J. Soc. Inf. Display, vol. 28, no. 6, pp. 528-534, May 2020. 
     Referring to  FIG.  2   , a buffer layer  120  is positioned on the substrate  110 . The buffer layer  120  may have a single-layer or multilayer structure. The buffer layer  120  is shown to be a single layer in  FIG.  1   , and it may be a multilayer depending on embodiments. The buffer layer  120  may include an organic insulating material or an inorganic insulating material. For example, the buffer layer  120  may include at least one of a silicon nitride (SiNx), a silicon oxide (SiOx), and a silicon oxynitride (SiOxNy). 
     A first semiconductor layer  130  including a first region  131 , a second region  132 , and a third region  133  is positioned on the buffer layer  120 . 
     The semiconductor layer  130  may include polysilicon, for example, it may include low temperature poly silicon (LTPS). 
     The first region  131  of the semiconductor layer  130  may be a channel region, and the second region  132  and the third region  133  of the first semiconductor layers  131 ,  132 , and  133  may respectively be a source region and a drain region. 
     Sheet resistance of the first region  131  that is the channel region of the first semiconductor layers  131 ,  132 , and  133  is greater than sheet resistance of the second region  132  and the third region  133  that are the source region and the drain region of the first semiconductor layers  131 ,  132 , and  133 , and a carrier concentration of the first region  131  that is the channel region of the first semiconductor layers  131 ,  132 , and  133  is lower than carrier concentration of the second region  132  and the third region  133  that are the source region and the drain region of the first semiconductor layers  131 ,  132 , and  133 . 
     No impurity may be included in the first region  131  that is the channel region of the first semiconductor layers  131 ,  132 , and  133 . The concentration of the impurities of the second region  132  and the third region  133  of the first semiconductor layers  131 ,  132 , and  133  may be higher than the concentration of the impurities of the first region  131  of the first semiconductor layers  131 ,  132 , and  133 . 
     Impurities, for example, n-type impurities or p-type impurities, may be included in the second region  132  and the third region  133  of the first semiconductor layers  131 ,  132 , and  133 . For example, the n-type impurities may be P (phosphorus), As (arsenic), and Sb (antimony), and the p-type impurities may be B (boron), Al (aluminum), and In (indium). 
     A gate insulating film (GI)  141  is positioned in the first region  131  of the first semiconductor layers  131 ,  132 , and  133 . The gate insulating film  141  may include an organic insulating material or an inorganic insulating material, for example, the gate insulating film  141  may include at least one of a silicon nitride, a silicon oxide, a silicon oxynitride, and a tetra ethyl ortho silicate (TEOS). A first gate electrode  151  is positioned on the gate insulating film  141 . 
     The first gate electrode  151  is disposed to overlap the first region  131  of the first semiconductor layers  131 ,  132 , and  133 , and the gate insulating film  141  is positioned between the first region  131  and the gate electrode  151  of the first semiconductor layers  131 ,  132 , and  133 . 
     The first gate electrode  151  may be a multilayer on which metal films including one of copper (Cu), a copper alloy, aluminum (Al), an aluminum alloy, molybdenum (Mo), and a molybdenum alloy are stacked. 
     An insulation pattern  142  may be positioned on the buffer layer  120 . A bottom gate (BG) electrode  152  may be positioned on the insulation pattern  142 . The insulation pattern  142  and the gate insulating film  141  may be formed in a same process stage, and the bottom gate electrode  152  and the first gate electrode  151  may be formed in a same process stage. 
     A passivation layer  160  is positioned on the first semiconductor layers  131 ,  132 , and  133 , the first gate electrode  151 , and the bottom gate electrode  152 . The passivation layer  160  may include at least one of a silicon nitride, a silicon oxide, a silicon oxynitride, and a tetra ethyl ortho silicate (TEOS), and may be made of an organic material such as a polyacrylate resin or a polyimide resin, or a stacked film of organic materials and inorganic materials. 
     The passivation layer  160  includes a first contact hole  162  overlapping the second region  132  of the first semiconductor layers  131 ,  132 , and  133  and a second contact hole  163  overlapping the third region  133  of the first semiconductor layers  131 ,  132 , and  133 . 
     Second semiconductor layers  171 ,  172 , and  173  overlapping the bottom gate electrode  152  and including a first region  171 , a second region  172 , and a third region  173  are positioned on the passivation layer  160 . The second semiconductor layers  171 ,  172 , and  173  may include oxide semiconductors. 
     The oxide semiconductor may include at least one of unary metal oxides such as an indium (In)-based oxide, a tin (Sn)-based oxide, or a zinc (Zn)-based oxide; binary metal oxides such as an In—Zn-based oxide, an Sn—Zn-based oxide, an Al—Zn-based oxide, a Zn—Mg-based oxide, an-Sn—Mg based oxide, an In—Mg-based oxide, or an In—Ga-based oxide; ternary metal oxides such as an In—Ga—Zn-based oxide, an In—Al—Zn-based oxide, an In—Sn—Zn-based oxide, an Sn—Ga—Zn-based oxide, an Al—Ga—Zn-based oxide, an Sn—Al—Zn-based oxide, an In—Hf—Zn-based oxide, an In—La—Zn-based oxide, an In—Ce—Zn-based oxide, an In—Pr—Zn-based oxide, an In—Nd—Zn-based oxide, an In—Sm—Zn-based oxide, an In—Eu—Zn-based oxide, an In—Gd—Zn based oxide, an In—Tb—Zn-based oxide, an In—Dy—Zn-based oxide, an In—Ho—Zn based-oxide, an In—Er—Zn-based oxide, an In—Tm—Zn-based oxide, an In—Yb—Zn-based oxide, or an In—Lu—Zn-based oxide; and quaternary metal oxides such as an In—Sn—Ga—Zn-based oxide, an In—Hf—Ga—Zn-based oxide, an In—Al—Ga—Zn-based oxide, an In—Sn—Al—Zn-based oxide, an In—Sn—Hf—Zn-based oxide, or an In—Hf—Al—Zn-based oxide. For example, the second semiconductor layer  130   a  may include the indium-gallium-zinc oxide (IGZO) from among the In—Ga—Zn-based oxides. 
     The second semiconductor layers  171 ,  172 , and  173  may include at least one of IGZO (Indium-Gallium-Zinc Oxide), IZTO (Indium-Zinc-Tin Oxide), IGZTO (Indium-Gallium-Zinc-Tin Oxide), and IGO (Indium-Gallium Oxide). 
     The first region  171  of the second semiconductor layers  171 ,  172 , and  173  may be the channel region, and the second region  172  and the third region  173  of the semiconductor layers  171 ,  172 , and  173  may be the source region and the drain region. 
     A first source electrode  71  and a first drain electrode  72  are positioned on the passivation layer  160 , and a second source electrode  73  and a second drain electrode  74  are positioned on the passivation layer  160  and the second semiconductor layers  171 ,  172 , and  173 . 
     The first source electrode  71  and the first drain electrode  72  are connected to the second region  132  that is the source regions of the first semiconductor layers  131 ,  132 , and  133  and the third region  133  that is the drain regions of the first semiconductor layers  131 ,  132 , and  133  through the first contact hole  162  and the second contact hole  163  of the passivation layer  160 . 
     The second source electrode  73  and the second drain electrode  74  may be positioned on the second region  172  that is the source regions of the second semiconductor layers  171 ,  172 , and  173  and the third region  173  that is the drain regions of the second semiconductor layers  171 ,  172 , and  173 . 
     The first source electrode  71 , the first drain electrode  72 , the second source electrode  73 , and the second drain electrode  74  may include an aluminum-based metal, a silver-based metal, and a copper-based metal with low resistivity, for example, they may have a triple-layered structure including a lower layer including a refractory metal such as titanium, molybdenum, chromium, and tantalum, or an alloy thereof, an intermediate layer including an aluminum-based metal, a silver-based metal, and a copper-based metal with low resistivity, and an upper layer including a refractory metal such as titanium, molybdenum, chromium, and tantalum. 
     A second gate insulating film  180  may be positioned on the first source electrode  71 , the first drain electrode  72 , the second source electrode  73 , and the second drain electrode  74 , and a top gate (TG) electrode  153  may be positioned on the second gate insulating film  180 . 
     The top gate electrode  153  and the bottom gate electrode  152  may overlap the first region  171  that is the channel regions of the second semiconductor layers  171 ,  172 , and  173 . 
     A second protection layer  190  may be positioned on the second gate electrode  153 . 
     The first semiconductor layers  131 ,  132 , and  133  may form a first transistor  200  together with the first gate electrode  151 , the first source electrode  71 , and the first drain electrode  72 . A channel region of the first transistor  200  is formed in the first region  131  between the second region  132  and the third region  133  of the first semiconductor layers  131 ,  132 , and  133 . 
     Similarly, the second semiconductor layers  171 ,  172 , and  173  may form a second transistor  300  together with the bottom gate electrode  152 , the top gate electrode  153 , the second source electrode  73 , and the second drain electrode  74 . A channel region of the second transistor  300  is formed in the first region  171  between the second region  172  and the third region  173  of the second semiconductor layers  171 ,  172 , and  173 . 
     Although not shown in  FIG.  2   , a contact hole to be connected to a line (not shown) for the first source electrode  71  and the second source electrode  73  to supply a predetermined voltage may be positioned on at least one of the second gate insulating film  180  and the second protection layer  190 . A contact hole for connecting the first drain electrode  72  and the second drain electrode  74  to each other may be positioned on at least one of the second gate insulating film  180  and the second protection layer  190 . 
       FIG.  3 A  shows a curved line of a transmission characteristic of a first transistor according to an embodiment. 
       FIG.  3 B  shows a curved line of an output characteristic of a first transistor according to an embodiment. 
     The first transistor  200  shows field effect mobility (μ FE ) of ˜130 cm 2 /Vs, subthreshold swing (SS) of ˜0.3 V/dec, and a threshold voltage (V TH ) of ˜4.2 V. 
       FIG.  4 A  shows a curved line of a transmission characteristic of a second transistor according to an embodiment. 
       FIG.  4 B  shows a curved line of an output characteristic of a second transistor according to an embodiment. 
     The second transistor  300  shows the field effect mobility (μ FE ) of −13 cm 2 /Vs, the subthreshold swing (SS) of −0.1 V/dec, and the threshold voltage (V TH ) of 0.5 V. 
       FIG.  5    shows a display according to an embodiment. 
     As shown in  FIG.  5   , the display  1  includes a display unit  10  including a plurality of pixels PX, a gate driver  20 , a data driver  30 , a light emitting driver  40 , a power supply  50 , and a controller  60 . 
     The pixels PX are respectively connected to a corresponding gate line from among a plurality of gate lines S 1  to Sn connected to the display unit  10 , a corresponding light emitting control line from among a plurality of light emitting control lines EM 1  to EMn, and a corresponding data line from among a plurality of data lines D 1  to Dm. Although not directly shown in the display unit  10  of  FIG.  5   , the pixels PX may respectively be connected to two power supply lines connected to the display unit  10  and may receive a first power voltage ELVDD and a second power voltage ELVSS. Although not directly shown in  FIG.  5   , an initialization voltage for initializing the pixel circuit may be supplied to the pixel circuit through an additional line before the data signal is applied to the pixel circuit. 
     The display unit  10  includes a plurality of pixels PX substantially arranged in a matrix form. Although not specifically limited, the gate lines S 1  to Sn and the light emitting control lines EM 1  to EMn face each other, extend in a row direction, and are substantially parallel to each other in an arranged form of pixels, and a plurality of data lines D 1  to Dm substantially extend in a column direction and are substantially parallel to each other. 
     A plurality of pixels PX of the display unit  10  are connected to the corresponding gate lines. One corresponding gate line may be connected to a pixel row configured with a plurality of pixels PX. However, the present invention is not limited thereto, and a number of gate lines connected to the pixel row may be two depending on the pixel circuit. The pixels PX emit light with predetermined luminance by a driving current supplied to an organic light emitting diode according to the corresponding data signal transmitted to the data lines D 1  to Dm. 
     The gate driver  20  generates gate signals corresponding to the respective pixels and transmits them through the gate lines S 1  to Sn. That is, the gate driver  20  may transmit the gate signals through the gate lines corresponding to the pixels included in the respective pixel rows. 
     The gate driver  20  may receive a gate driving control signal GCS from the controller  60 , may generate gate signals, and may sequentially supply the gate signals to the gate lines S 1  to Sn connected to the respective pixel rows. 
     The data driver  30  may transmit data signals to the respective pixels through the data lines D 1  to Dm. The data driver  30  receives a data driving control signal DCS from the controller  60  and supplies the data signals corresponding to the data lines D 1  to Dm connected to the pixels included in the respective pixel rows. 
     The light emitting driver  40  is connected to the light emitting control lines EM 1  to EMn. That is, the light emitting control lines EM 1  to EMn substantially facing the pixels in the row direction and extending in parallel to each other connect the respective pixels and the light emitting driver  40 . 
     The light emitting driver  40  generates light emitting control signals corresponding to the respective pixels and transmits them through the light emitting control lines EM 1  to EMn. When receiving the light emitting control signals, the respective pixels are controlled to emit light of images corresponding to the image data signal in response to a control of the light emitting control signal. That is, operations of the light emitting control transistors included in the respective pixels are controlled in response to the light emitting control signal transmitted through the corresponding light emitting control line, and the organic light emitting diode connected to the light emitting control transistor may or may not emit light with luminance caused by a driving current corresponding to the data signal. 
     The power supply  50  supplies the first power voltage ELVDD and the second power voltage ELVSS to the pixels PX of the display unit  10 . The first power voltage ELVDD may be a predetermined high-level voltage, and the second power voltage ELVSS may be lower than the first power voltage ELVDD. Voltage values of the first power voltage ELVDD and the second power voltage ELVSS are not limited, and may be set or controlled by control of the power control signal PCS transmitted from the controller  60 . 
     The controller  60  converts a plurality of image signals transmitted from an outside into a plurality of image data signals DATA and transmits them to the data driver  30 . The controller  60  receives a vertical synchronization signal Vsync, a horizontal synchronizing signal Hsync, and a clock signal MCLK (not shown), generates control signals for controlling driving of the gate driver  20 , the light emitting driver  40 , and the data driver  30 , and transmits the control signals to the same. That is, the controller  60  generates a gate driving control signal GCS for controlling the gate driver  20 , a light emitting driving control signal ECS for controlling operations of the light emitting driver  40 , and a data driving control signal DCS for controlling the data driver  30 , and transmits them. 
     The controller  60  generates a power control signal PCS for controlling driving of the power supply  50  and transmits the same to the power supply  50 . 
       FIG.  6    shows a circuit diagram of a pixel circuit according to an embodiment. 
     As shown in  FIG.  6   , the pixels PX may respectively include a driving transistor DTR, a switching transistor STR, a light emitting control transistor ETR, a capacitor CST, and an organic light emitting diode OLED. The pixel circuit shown in  FIG.  6    represents an example for describing one of various pixel circuits, and the present invention is not limited thereto. Various types of pixel circuits known to a person of ordinary skill in the art may be applied to the present invention. 
     The first power voltage ELVDD is supplied to a source of the driving transistor DTR, a first end of the switching transistor STR is connected to a gate of the driving transistor DTR, and the capacitor CST is connected between the gate and the source of the driving transistor DTR. A data line Dj (j is one of natural numbers of 1 to m) is connected to a second end of the switching transistor STR, and the gate line Si (i is one of natural numbers of 1 to n) is connected to a gate of the switching transistor STR. A first end of the light emitting control transistor ETR is connected to a drain of the driving transistor DTR, a second end of the light emitting control transistor ETR is connected to an anode of the organic light emitting diode OLED, and a gate of the light emitting control transistor ETR is connected to the corresponding light emitting control line EMi. A second power voltage ELVSS is supplied to a cathode of the organic light emitting diode OLED. 
     When the switching transistor STR is turned on, the data signal transmitted through the data line Dj is written in the capacitor CST, and while the light emitting control transistor ETR is in an On state, the driving transistor DTR supplies a current corresponding to the voltage written in the capacitor CST to the organic light emitting diode OLED. 
     A capacitor for compensating a threshold voltage of the driving transistor and a switching transistor for supplying an initialization voltage may be additionally positioned on the pixel circuit shown in  FIG.  6   . Various types of known pixel circuits that are different from the pixel circuit shown in  FIG.  6    may be applied to the present invention. 
       FIG.  7    shows a block diagram of a gate driver according to an embodiment. 
     As shown in  FIG.  7   , the gate driver  20  includes a plurality of stages SR_ 1  to SR_n, and the respective stages SR_ 1  to SR_n may receive a previous gate signal and a next gate signal that are outputs of a previous stage and a next stage, and a clock signal, and may generate a gate signal. A start signal STR instead of the previous gate signal may be input to the first stage SR_ 1  from among the stages SR_ 1  to SR_n. To supply a next gate signal to the last stage SR_n from among the stages SR_ 1  to SR_n, the gate driver  20  may further include a stage SR_d as a dummy. Two clock signals CLK 1  and CLK 2  may sequentially and alternately correspond to the first stage SR_ 1  to the last stage SR_n of the stages SR_ 1  to SR_n, and the corresponding clock signal may be input to the corresponding stage. 
     The stages SR_ 1  to SR_n may be respectively synchronized with the corresponding previous gate signals and output a gate signal with an On-level gate pulse (referred to as an On-pulse) based on the corresponding clock signal, and may be synchronized with the corresponding next gate signal and may output an Off-level gate signal. 
       FIG.  8    shows a circuit diagram of two adjacent stages from among a plurality of stages according to an embodiment. 
     To describe an operation of the gate driver according to an embodiment,  FIG.  8    shows a circuit diagram of two adjacent stages SR_i and SR_i+1 from among the stages SR_ 1  to SR_n. 
     The stage SR_i includes six transistors T 1  to T 6 . Respective two transistors T 3  and T 4  and the two transistors T 5  and T 6  from among the six transistors T 1  to T 6  are realized with the above-described complementary transistor  100 , and may function as an inverter. The transistors T 1  and T 2  are LTPS TFTs, and may be p-type transistors. 
     The stage SR_i+1 may also be realized with a same circuit structure as the stage SR_i. The stage SR_i+1 includes six transistors T 11  to T 16 . Respective two transistors T 13  and T 14  and two transistors T 15  and T 16  from among the six transistors T 11  to T 16  are realized with the above-described complementary transistor  100 , and may function as an inverter. The transistors T 11  and T 12  are LTPS TFT, and may be p-type transistors. 
     On the stage SR_i, a previous gate signal S[i−1] that is an output of a previous stage SR_i−1 is supplied to the drain of the transistor T 1 , and the gate and the drain of the transistor T 1  are connected to each other. That is, the transistor T 1  is diode-connected. A source of the transistor T 1  is connected to a drain of the transistor T 2 , and a node N 1  on which the transistors T 1  and T 2  are connected to each other is connected to gates of the transistors T 3  and T 4 . A next gate signal S[i+1] that is an output of the next stage SR_i+1 is supplied to a gate of the transistor T 2 , and the voltage VSS is supplied to the source of the transistor T 2 . A voltage VBH is supplied to a source of the transistor T 3 , a drain of the transistor T 3  is connected to the drain of the transistor T 4 , and a voltage VBL is supplied to a source of the transistor T 4 . A node N 2  on which two transistors T 3  and T 4  are connected to each other is connected to gates of the two transistors T 5  and T 6 . The voltage VSS is supplied to a source of the transistor T 5 , a drain of the transistor T 5  is connected to a drain of the transistor T 6 , and a clock signal CLK 1  is supply to a source of the transistor T 6 . A node NOUT_i on which two transistors T 5  and T 6  are connected to each other is connected to the gate line Si. The gate signal S[i] may be supplied to a plurality of pixels PX of the corresponding pixel row through the gate line S[i]. A voltage at the node NOUT_i may be a voltage at the gate signal S[i]. 
     On the stage SR_i+1, the previous gate signal S[i] that is an output of the previous stage SR_i is supplied to a drain of the transistor T 11 , and the gate and the drain of the transistor T 1  are connected to each other. That is, the transistor T 11  is diode connected. The source of the transistor T 11  is connected to a drain of the transistor T 12 , and a node N 3  on which two transistors T 11  and T 12  are connected to each other is connected to gates of the two transistors T 13  and T 14 . A next gate signal S[i+2] that is an output of the next stage SR_i+2 is supplied to a gate of the transistor T 12 , and the voltage VSS is supplied to a source of the transistor T 12 . The voltage VBH is supplied to a source of the transistor T 13 , a drain of the transistor T 13  is connected to a drain of the transistor T 14 , and the voltage VBL is supplied to a source of the transistor T 14 . A node N 4  on which the two transistors T 13  and T 14  are connected to each other is connected to gates of the transistors T 15  and T 16 . The voltage VSS is supplied to a source of the transistor T 15 , a drain of the transistor T 15  is connected to a drain of the transistor T 16 , and a clock signal CLK 2  is supplied to a source of the transistor T 16 . A node NOUT_i+1 on which the two transistors T 15  and T 16  are connected to each other is connected to the gate line Si+1. The gate signal S[i+1] may be supplied to a plurality of pixels PX of the corresponding pixel row through the gate line Si+1. 
     The voltage VSS is an Off-level voltage of the gate signals S[i] and S[i+1], and it may be a high-level voltage depending on embodiments. The voltage VBH may be an Off-level for the transistors T 5  and T 15  and may be an On-level for the transistors T 6  and T 16 , and the voltage VBL may be an On-level for the transistors T 5  and T 15  and may be an Off-level for the transistors T 6  and T 16 . 
     An operation of a stage according to an embodiment will now be described with reference to  FIG.  9   . 
       FIG.  9    shows a waveform diagram of clock signals, gate signals, and voltages at nodes according to an embodiment. 
     The clock signals CLK 1  and CLK 2  periodically and alternately have the high-level voltage VSS and the low-level voltage VL, and may have phases that are opposite to each other. A threshold voltage VTH of the transistors T 1  and T 11  may be a negative voltage. 
     For a period P 1 , the gate signal S[i−1] has an On-level. The transistor T 1  is turned on, and the voltage at the node N 1  becomes a voltage VL-VTH of VL 1  that is a subtraction of the threshold voltage VTH of the transistor T 1  from the voltage VL of the gate signal S[i−1]. The voltage VL 1  may be a low-level voltage for turning on the transistor T 3 . The transistor T 3  is tuned on by the voltage VL 1 , and the transistor T 4  is turned off, so the voltage at the node N 2  is charged with the voltage VBH. By the voltage VBH, the transistor T 6  is turned on and the transistor T 5  is turned off. The clock signal CLK 1  is supplied as a gate signal S[i] to the gate line (Si) through the transistor T 6  that is turned on. As the clock signal CLK 1  is the voltage VSS for the period P 1 , the gate signal S[i] is maintained at the voltage VSS. 
     When the period P 1  ends, the gate signal S[i−1] becomes the high-level voltage VSS, and the transistor T 1  is blocked. For a period P 2 , without bootstrapping, the voltage at the node N 1  is maintained at the voltage VL 1 , the voltage at the node N 2  is maintained at the voltage VBH, and the transistors T 3  to T 6  maintain the state of the period P 1 . For the period P 2 , as the clock signal CLK 1  is the low-level voltage VL, the gate signal S[i] is charged with the On-level voltage VL. 
     For the period P 2 , as the gate signal  0  is On-level, the transistor T 11  is turned on and the voltage at the node N 3  becomes a voltage VL-VTH of VL 1  that is a subtraction of the threshold voltage VTH of the transistor T 11  from the voltage VL of the gate signal  0 . The voltage VL 1  may be a low-level voltage for turning on the transistor T 13 . By the voltage VL 1 , the transistor T 13  is turned on, the transistor T 14  is turned off, and the voltage at the node N 4  is changed with the voltage VBH. By the voltage VBH, the transistor T 16  is turned on and the transistor T 15  is turned off. The clock signal CLK 2  is supplied as the gate signal S[i+1] to the gate line Si+1 through the transistor T 16  that is in the On state. For the period P 2 , as the clock signal CLK 2  is the voltage VSS, the gate signal S[i+1] is maintained at the voltage VSS. 
     When the period P 2  ends, the gate signal  0  becomes a high-level voltage VSS and the transistor T 11  is blocked. For a period P 3 , without bootstrapping, the voltage at the node N 3  is maintained at the voltage VL 1 , the voltage at the node N 4  is maintained at the voltage VBH, and the transistors T 13  to T 16  maintain the state of the period P 2 . For the period P 3 , as the clock signal CLK 2  has the low-level voltage VL, the gate signal S[i+1] is changed with the On-level voltage VL. 
     For the period P 3 , as the gate signal S[i+1] is On-level, the transistor T 2  is in the On state. The voltage at the node N 1  becomes the voltage VSS, and by the voltage VSS, the transistor T 4  is turned on and the transistor T 3  is turned off. The voltage at the node N 2  is pulled down to the voltage VBL through the transistor T 4  that is in the On state. By the voltage VBL, the transistor T 5  is turned on and the transistor T 6  is turned off. The gate signal S[i] is discharged to be the voltage VSS through the transistor T 5  that is in the On state. 
     For a period P 4 , as the gate signal S[i+2] is On-level, the transistor T 12  is in the On state. The voltage at the node N 3  becomes voltage VSS, and by the voltage VSS, the transistor T 14  is tuned on and the transistor T 13  is turned off. The voltage at the node N 4  is pulled down to the voltage VBL through the transistor T 14  that is in the On state. By the voltage VBL, the transistor T 15  is turned on and the transistor T 16  is turned off. The gate signal S[i+1] is discharged to be the voltage VSS through the transistor T 15  that is in the On state. 
     According to the above-described operation, the stages SR_ 1  to SR_n may sequentially supply a plurality of On-level gate signals S[ 1 ] to S[n] to the gate lines S 1  to Sn. 
     When the resolution of the display  1  is 4K (3840×2160), an operational frequency of the gate driver  20  may be 120 Hz. The clock signals CLK 1  and CLK 2  and the gate signals S[ 1 ] to S[n] may swing between the voltage VSS and the voltage VL. Table 1 expresses parameters of the six transistors T 1  to T 6  configuring the respective stages when a simulation on the operation of the gate driver according to an embodiment is performed. 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                   
                 Parameters (W/L) 
               
               
                   
                   
               
             
            
               
                   
                 T1 (μm/μm) 
                 10/6 
               
               
                   
                 T2 (μm/μm) 
                 20/6 
               
               
                   
                 T3 (μm/μm) 
                 10/6 
               
               
                   
                 T4 (μm/μm) 
                 50/6 
               
               
                   
                 T5 (μm/μm) 
                 40/6 
               
               
                   
                 T6 (μm/μm) 
                 100/6  
               
               
                   
                   
               
            
           
         
       
     
       FIG.  10    shows a waveform diagram of an example of stage outputs and voltages at nodes acquired by a first simulation. 
       FIG.  10    shows the simulation on the 32-th one of a plurality of stages configuring the gate driver  20 , the threshold voltage of the a-IGZO TFTs (e.g., T 4  and T 6 ) is 0.5 V, the voltage VBL is −15 V, the voltage VBH is 0 V, the voltage VL is −15 V, and the voltage VSS is 0 V. Transmission characteristics and output characteristics of the a-IGZO TFT used to the simulation may follow the waveforms shown in  FIG.  4 A  and  FIG.  4 B . 
       FIG.  11    shows a waveform diagram of an example of stage outputs and voltages at nodes acquired by a second simulation. 
     The waveform shows simulation results for an operation in the depletion mode, and the threshold voltage of the a-IGZO TFTs (e.g., T 4  and T 6 ) may be −7.5 V as a simulation condition. Other conditions are identical with the conditions of the simulation of  FIG.  10   . 
     As shown in  FIG.  10   , when the threshold voltage VTH of the a-IGZO TFT is 0.5 V, outputs may be generated with the gate signal according to the voltage VBH of 0 V and the voltage VBL of −15 V. That is, the outputs may be generated as the level for turning the switching transistor (STR of  FIG.  6   ) of the pixel PX on/off. 
     However, as shown in  FIG.  11   , when the threshold voltage VTH of the a-IGZO TFT is −7.5 V that is a negative voltage, the output has a waveform from which a peak component is removed and which has a ripple component. This is because the a-IGZO TFT is operated in a severe depletion mode. The depletion mode may be easily generated in the process for manufacturing the a-IGZO TFT, and in the case of long driving, the threshold voltage may be moved to a negative voltage because of a bias stress. Therefore, to check whether the gate driver including the a-IGZO TFT is normally operated, it must be considered whether an output is normally generated when the a-IGZO TFT is operated in the depletion mode. 
       FIG.  12    shows a waveform diagram of an example of stage outputs and voltages at nodes acquired by a third simulation. 
     The simulation condition for acquiring the waveform shown in  FIG.  12    is: the threshold voltage of the a-IGZO TFTs T 4  and T 6  is −7.5 V, the voltage VBL is −17 V, and the voltage VBH is 2 V. The transmission characteristic of the a-IGZO TFT used to the simulation may follow the waveform shown in  FIG.  13   . Other conditions are identical with the conditions of the simulation of  FIG.  10   . 
     As shown in  FIG.  12   , when the a-IGZO TFT is operated in the depletion mode, the output may be generated to be a gate signal that has the Off-level of about 0 V and the On-level of about −14.5 V by the voltage VBH of 2 V and the voltage VBL of −17 V. That is, the output may be generated to be a level that may turn the switching transistor (STR of  FIG.  6   ) of the pixel PX on/off. 
       FIG.  13    shows a top plan view of a layout of some stages from among a gate driver according to an embodiment. 
     A width w 1  of the stage is equal to or less than 300 um, and it is found that the width is reduced compared to prior art. This is because there is no need to use a capacitor for a bootstrapping by using the inverter realized with the a-IGZO transistor in the gate driver  20 . A size of the conventional gate driver needing the capacitor is increased because of the capacitor. 
       FIG.  14    and  FIG.  15    show gate signal waveform diagrams of a first stage and a 32-nd stage according to simulations. 
     The width of the On-level pulse of the gate signal shown in  FIG.  14    is 10 us, and the width of the On-level pulse of the gate signal shown in  FIG.  15    is 1 us. For the purpose of a simulation, resistance and capacitance that are output loads of the first and 32-nd stages are set to be 6 kΩ and 12 pF. 
     It is found that a rising time and a falling time of the gate signal with the width of 10 us are equal to or less than 230 ns and equal to or less than 900 ns, and the rising time and the falling time of the gate signal with the width of 1 us are equal to or less than 230 ns and equal to or less than 250 ns. When the rising time and the falling time are considered, the gate driver according to an embodiment may be applied to the display with the driving frequency of 240 Hz and the resolution of 8K (7680×4320). 
       FIG.  16    shows a top plan view of a layout of an i-th stage shown in  FIG.  8   . 
       FIG.  17    shows a cross-sectional view with respect to a line A-A′. 
       FIG.  18    shows a cross-sectional view with respect to a line B-B′ in  FIG.  17   . 
       FIG.  16    shows one BL 1  of five bus lines shown in  FIG.  13   . The line may be made of a conductive material in the following description. When a description on a predetermined layer is needed, a layout in which a certain layer covering the predetermined layer is removed may be shown. A semiconductor layer  401  realized with low-temperature polysilicon and a semiconductor layer  601  realized with the a-IGZO are marked with thick solid lines so as to be distinguished from other layers. 
     As shown in  FIG.  16   , the drain of the transistor T 1  is connected to the line L 1  for transmitting the gate signal S[i−1], and the gate of the transistor T 1  extends from the line L 1 . The source of the transistor T 1  and the drain of the transistor T 2  are connected to a line L 2 , the gate of the transistor T 2  extends from the line L 3  for transmitting the gate signal S[i+1], and the source of the transistor T 2  is connected to the bus line BL 1  for supplying the voltage VSS. 
     The line L 2  may correspond to the node N 1 . The gate of the transistor T 3  and the bottom gate BG 1  of the transistor T 4  extend from the line L 2 . The top gate TG 1  and the bottom gate BG 1  of the transistor T 4  are connected to each other through a via contact CT 1 . The drain of the transistor T 3  and the drain of the transistor T 4  may be connected to a line L 51 , and the line L 51  may be connected to a line L 41  through a via contact CT 2 . The line L 41  and the line L 42  may be connected to each other through a via contact CT 31 , and the line L 42  and the line L 9  may be connected to each other through via contact CT 32 . The source of the transistor T 3  is connected to the line L 5 , and the voltage VBH may be supplied through the line L 5 . Two lines L 61  and L 62  are connected to the source of the transistor T 4 , and may be branched from the line L 6  and may extend. The voltage VBL may be supplied through the line L 6 . 
     The bottom gate BG 2  of the transistor T 6  is branched from the line L 9  and extends. The bottom gate BG 2  and the top gate TG 2  are connected to each other through a via contact CT 4 , and the gate of the transistor T 5  extends from the line L 9 . 
     The source of the transistor T 6  is connected to two lines L 71  and L 72 , and the lines L 71  and L 72  may be branched from a line L 7  and may extend. The clock signal CLK 1  may be supplied to the line L 7 . The drain of the transistor T 6  may be connected to three lines L 81 , L 82 , and L 83 , and the lines L 81 , L 82 , and L 83  may be branched from the line L 8  and may extend. The line L 8  is connected to the gate line Si through a via contact CT 5 . The drain of the transistor T 5  is connected to the line L 83 , and the source of the transistor T 5  is connected to a line L 10 . The line L 10  is connected to the bus line BL 1 , and the voltage VSS is supplied to the source of the transistor T 5 . 
     The line L 11  is connected to the drains of the transistor T 5  and the transistor T 6  through a via contact CT 5  so the gate signal S[i] may be supplied to the previous stage through the line L 11 . The gate signal S[i] may be supplied to the next stage through the line L 8 . 
     A cross-sectional structure of the transistors T 3  and T 4  configuring an inverter will now be described with reference to  FIG.  17   . The same portions as the cross-sectional structure described with reference to  FIG.  2    will be omitted. 
     As shown in  FIG.  17   , the source and the drain (P+ region) of the transistor T 3  are connected to the line L 5  and the line L 51 , and the gate of the transistor T 3  extends from the line L 2 . 
     Regarding the semiconductor layer of the transistor T 4 , the a-IGZO layer  401  is formed to have a single layer, and it may be realized into two a-IGZO layers as distinguished with dotted lines. Here, an insulating layer  180  may be positioned in a region between two dotted lines. 
     The source region T 4 S 1  of the a-IGZO layer  401  is connected to the line L 61 , the source region T 4 S 2  of the a-IGZO layer  401  is connected to the line L 62 , and the drain region T 4 D of the a-IGZO layer  401  is connected to the line L 51 . 
     From among two bottom gates BG 11  and BG 12 , the bottom gate BG 11  is positioned on an insulation pattern  411  to correspond to a channel region CH 11  of the a-IGZO layer  401 , and the other bottom gate BG 12  is positioned on an insulation pattern  412  to correspond to a channel region CH 12  of the a-IGZO layer  401 . A passivation layer  160  may be positioned between the a-IGZO layer  401  and the two bottom gates BG 11  and BG 12 . 
     From among two top gates TG 11  and TG 12 , the top gate TG 1  may be positioned on an insulating layer  180  to correspond to a channel region CH 11  of the a-IGZO layer  401 , and the other top gate TG 12  may be positioned on an insulating layer  180  to correspond to a channel region CH 12  of the a-IGZO layer  401 . 
     A cross-sectional structure of the transistors T 5  and T 6  configuring an inverter will now be described with reference to  FIG.  18   . The same portions as the cross-sectional structure described with reference to  FIG.  2    will be omitted. 
     As shown in  FIG.  18   , the source and the drain (P+ region) of the transistor T 5  are connected to the line L 10  and the line L 83 , and the gate of the transistor T 5  extends from the line L 9 . 
     Regarding the semiconductor layer of the transistor T 6 , the a-IGZO layer  601  is formed to have a single layer, and it may be realized into four a-IGZO layers as distinguished with dotted lines. Here, an insulating layer  180  may be positioned in a region between two adjacent dotted lines. 
     A drain region T 6 D 1  of the a-IGZO layer  601  is connected to the line L 83 , a source region T 6 S 1  of the a-IGZO layer  601  is connected to the line L 71 , a drain region T 6 D 2  of the a-IGZO layer  601  is connected to the line L 82 , a source region T 6 S 2  of the a-IGZO layer  601  is connected to the line L 72 , and a drain region T 6 D 3  of the a-IGZO layer  601  is connected to the line L 81 . 
     From among four bottom gates BG 21 , BG 22 , BG 23 , and BG 24 , the bottom gate BG 21  may be positioned on an insulation pattern  611  to correspond to a channel region CH 21  of the a-IGZO layer  601 , the bottom gate BG 22  may be positioned on an insulation pattern  612  to correspond to a channel region CH 22  of the a-IGZO layer  601 , the bottom gate BG 23  may be positioned on an insulation pattern  613  to correspond to a channel region CH 23  of the a-IGZO layer  601 , and the bottom gate BG 24  may be positioned on an insulation pattern  614  to correspond to a channel region CH 24  of the a-IGZO layer  601 . A passivation layer  160  may be positioned between the a-IGZO layer  601  and the four bottom gates BG 21 , BG 22 , BG 23 , and BG 24 . 
     From among four top gates TG 21 , TG 22 , TG 23 , and TG 24 , the top gate TG 21  may be positioned on the insulating layer  180  to correspond to a channel region CH 21  of the a-IGZO layer  601 , the top gate TG 22  may be positioned on the insulating layer  180  to correspond to a channel region CH 22  of the a-IGZO layer  601 , the top gate TG 23  may be positioned on the insulating layer  180  to correspond to a channel region CH 23  of the a-IGZO layer  601 , and the top gate TG 24  may be positioned on the insulating layer  180  to correspond to a channel region CH 24  of the a-IGZO layer  601 . 
     The LTPO TFT may be applied to the gate driver and the light emitting driver. 
     A light emitting driver according to an embodiment will now be described with reference to  FIG.  19    to  FIG.  25   . 
       FIG.  19    shows a block diagram of a light emitting driver according to an embodiment. 
     As shown in  FIG.  19   , the light emitting driver  40  includes a plurality of light emitting stages ESR_ 1  to ESR_n, and the respective light emitting stages ESR_ 1  to ESR_n may receive a previous light emitting control signal (e.g., EC[i−1]) and a next light emitting control signal (e.g., EC[i+1]) generated by a corresponding previous light emitting stage and a next light emitting stage, a corresponding gate signal (e.g., S[i]), and a corresponding clock signal (e.g., CLK 3 ) and may generate a corresponding light emitting signal (e.g., E[i]). From among the light emitting stages ESR_ 1  to ESR_n, a light emitting control start signal ECSTR and not a previous light emitting control signal may be input to the first light emitting stage ESR_ 1 . To supply a next light emitting control signal to the last stage ESR_n from among the light emitting stages ESR_ 1  to ESR_n, the light emitting driver  40  may further include a stage ESR_d as a dummy. Two clock signals CLK 3  and CLK 4  sequentially and alternately correspond to the first light emitting stage ESR_ 1  to the last light emitting stage ESR_n of the light emitting stages ESR_ 1  to ESR_n, and the corresponding clock signals may be input to the corresponding light emitting stages. 
     The light emitting stages ESR_ 1  to ESR_n may be synchronized with the corresponding gate signal and may output a corresponding light emitting signal as On-level, may generate a corresponding light emitting control signal according to the corresponding clock signal for a period from a time when the previous light emitting control signal becomes On-level to a time when the next light emitting control signal becomes On-level, and may be synchronized with the time when the corresponding light emitting control signal becomes On-level and may output the corresponding light emitting signal as Off-level. 
       FIG.  20    shows a circuit diagram of two adjacent light emitting stages from among a plurality of light emitting stages according to an embodiment. 
       FIG.  20    shows a circuit diagram of two adjacent light emitting stages ESR_i and ESR_i+1 from among a plurality of light emitting stages ESR_ 1  to ESR_n, for the purpose of describing an operation of the light emitting driver according to an embodiment. 
     The light emitting stage ESR_i includes twelve transistors T 21  to T 32 . From among the transistors T 21  to T 32 , the two transistors T 23  and T 24 , the two transistors T 25  and T 26 , the two transistors T 29  and T 30 , and the two transistors T 31  and T 32  may be respectively realized with the above-described complementary transistor  100 , and may be operable as an inverter. The four transistors T 21 , T 22 , T 27 , and T 28  are LTPS TFTs and may be p-type transistors. 
     The light emitting stage ESR_i+1 may be realized with the same circuit structure as the light emitting stage ESR_i. The light emitting stage ESR_i+1 includes twelve transistors T 33  to T 44 . From among the twelve transistors T 33  to T 44 , the two transistors T 35  and T 36 , the two transistors T 37  and T 38 , the two transistors T 41  and T 42 , and the two transistors T 43  and T 44  may be respectively realized with the above-described complementary transistor  100 , and may be operable as an inverter. The four transistors T 33 , T 34 ,  39 , and  40  are LTPS TFTs and may be p-type transistors. 
     On the light emitting stage ESR_i, the corresponding gate signal S[i] is supplied to a source of the transistor T 21 , and a gate and the source of the transistor T 21  are connected to each other. That is, the transistor T 21  is diode-connected. A drain of the transistor T 21  is connected to a drain of the transistor T 22 , and a node N 5  on which the two transistors T 21  and T 22  are connected to each other is connected to gates of the transistors T 23  and T 24 . A light emitting control signal EC[i] is supplied to a gate of the transistor T 22 , and the voltage VSS is supplied to the source of the transistor T 22 . The voltage VBH is supplied to a source of the transistor T 23 , a drain of the transistor T 23  is connected to a drain of the transistor T 24 , and the voltage VL is supplied to a source of the transistor T 24 . A node N 6  on which the two transistors T 23  and T 24  are connected to each other is connected to gates of the two transistors T 25  and T 26 . The voltage VSS is supplied to a source of the transistor T 25 , a drain of the transistor T 25  is connected to a drain of the transistor T 26 , and the voltage VL is supplied to a source of the transistor T 26 . A node EOUT_i on which the two transistors T 25  and T 26  are connected to each other is connected to the corresponding light emitting control line EMi. A light emitting signal E[i] may be supplied to a plurality of pixels PX of the corresponding pixel row through the light emitting control line EMi. 
     On the light emitting stage ESR_i, a pulse width of the light emitting signal E[i] may be controlled by the corresponding gate signal S[i] and the light emitting control signal EC[i]. The light emitting stage ESR_i may include a light emitting control circuit EC_i including six transistors T 27  to T 32  for generating the light emitting control signal EC[i]. 
     On the light emitting control circuit EC_i, a previous light emitting control signal EC[i−1] generated by a previous light emitting stage ECR_i−1 is supplied to a source of the transistor T 27 , and a gate and the source of the transistor T 27  are connected to each other. That is, the transistor T 27  is diode-connected. A drain of the transistor T 27  is connected to a drain of the transistor T 28 , and a node N 7  on which the two transistors T 27  and T 28  are connected to each other is connected to gates of the transistors T 29  and T 30 . A next light emitting control signal EC[i+1] generated by the next light emitting stage ECR_i+1 is supplied to a gate of the transistor T 28 , and the voltage VSS is supplied to a source of the transistor T 28 . The voltage VBH is supplied to a source of the transistor T 29 , a drain of the transistor T 29  is connected to a drain of the transistor T 30 , and the voltage VL is supplied to a source of the transistor T 30 . A node N 8  on which the transistors T 29  and T 30  are connected to each other is connected to gates of the transistors T 31  and T 32 . The voltage VSS is supplied to a source of the transistor T 31 , a drain of the transistor T 31  is connected to a drain of the transistor T 32 , and the corresponding clock signal CLK 3  is supplied to a source of the transistor T 32 . A voltage at the node ECOUT_i on which the transistors T 31  and T 32  are connected to each other may be the light emitting control signal EC[i]. The light emitting control signal EC[i] may be supplied to the gate of the transistor T 22 , the gate of the transistor corresponding to the transistor T 28  on the previous light emitting stage ESR_i−1, and the gate of the transistor T 39  on the next light emitting stage ESR_i+1. 
     On the light emitting stage ESR_i+1, the corresponding gate signal S[i+1] is supplied to a source of the transistor T 33 , and a gate and the source of the transistor T 33  are connected to each other. That is, the transistor T 33  is diode-connected. A drain of the transistor T 33  is connected to a drain of the transistor T 34 , and a node N 9  on which the two transistors T 33  and T 34  are connected to each other is connected to gates of the two transistors T 35  and T 36 . The light emitting control signal EC[i+1] is supplied to the gate of the transistor T 36 , and the voltage VSS is supplied to a source of the transistor T 34 . The voltage VBH is supplied to a source of the transistor T 35 , a drain of the transistor T 35  is connected to a drain of the transistor T 36 , and the voltage VL is supplied to a source of the transistor T 36 . A node N 10  on which the two transistors T 35  and T 36  are connected to each other is connected to gates of the two transistors T 37  and T 38 . The voltage VSS is supplied to a source of the transistor T 37 , a drain of the transistor T 37  is connected to a drain of the transistor T 38 , and the voltage VL is supplied to a source of the transistor T 38 . A node EOUT_i+1 on which the two transistors T 37  and T 38  are connected to each other is connected to the corresponding light emitting control line EMi+1. The light emitting signal E[i+1] may be supplied to a plurality of pixels PX of the corresponding pixel row through the light emitting control line EMi+1. 
     On the light emitting stage ESR_i+1, the pulse width of the light emitting signal E[i+1] may be controlled by the corresponding gate signal S[i+1] and the light emitting control signal EC[i+1]. The light emitting stage ESR_i+1 may include a light emitting control circuit EC_i+1 including six transistors T 39  to T 44  for generating the light emitting control signal EC[i+1]. 
     On the light emitting control circuit EC_i+1, the previous light emitting control signal EC[i] generated by the previous light emitting stage ECR_i is supplied to a source of the transistor T 39 , and a gate and the source of the transistor T 39  are connected to each other. That is, the transistor T 39  is diode-connected. A drain of the transistor T 39  is connected to a drain of the transistor T 40 , and a node N 11  on which the two transistors T 39  and T 40  are connected to each other is connected to gates of the transistors T 41  and T 42 . The next light emitting control signal EC[i+2] generated by the next light emitting stage ECR_i+2 is supplied to a gate of the transistor T 40 , and the voltage VSS is supplied to a source of the transistor T 40 . The voltage VBH is supplied to a source of the transistor T 41 , a drain of the transistor T 41  is connected to a drain of the transistor T 42 , and the voltage VL is supplied to a source of the transistor T 42 . A node N 12  on which the two transistors T 41  and T 42  are connected to each other is connected to gates of the two transistors T 43  and T 44 . The voltage VSS is supplied to a source of the transistor T 43 , a drain of the transistor T 43  is connected to a drain of the transistor T 44 , and the corresponding clock signal CLK 4  is supplied to a source of the transistor T 44 . A voltage at a node on which the two transistors T 43  and T 44  are connected to each other may be the light emitting control signal EC[i+1]. The light emitting control signal EC[i+1] may be supplied to the gate of the transistor T 34 , the gate of the transistor T 28  on the previous light emitting stage ESR_i, and a gate of a transistor corresponding to the transistor T 39  on the next light emitting stage ESR_i+2. 
     An operation of the light emitting stage according to an embodiment will be described with reference to  FIG.  21   . 
       FIG.  21    shows a waveform diagram of clock signals, light emitting control signals, gate signals, and voltages at nodes, and light emitting signals according to an embodiment. 
     The clock signals CLK 3  and CLK 4  alternately have high-level voltages VSS and low-level voltages VL of which phases may be inverted from each other. The threshold voltages VTH of the transistors T 21 , T 27 , T 33 , and T 39  may be negative voltages. 
     For a period P 11 , the gate signal S[i] is On-level. The transistor T 21  is then turned on, and the voltage at the node N 5  becomes the voltage VL-VTH of VL 2  that is a subtraction of the threshold voltage VTH of the transistor T 21  from the voltage VL of the gate signal S[i]. The voltage VL 2  may be a low-level voltage for turning on the transistor T 23 . By the voltage VL 2 , the transistor T 23  is turned on and the transistor T 24  is turned off, and the voltage at the node N 6  is charged with the voltage VBH. By the voltage VBH, the transistor T 26  is turned on and the transistor T 25  is turned off. The voltage VL is supplied as a light emitting signal E[i] to the light emitting control line Emi through the transistor T 26  that is in the On state. 
     When the period P 11  ends, the gate signal S[i] becomes the high-level voltage VSS and the transistor T 21  is blocked. For a period P 12 , without bootstrapping, the voltage at the node N 5  is maintained at the voltage VL 2 , the voltage at the node N 6  is maintained at the voltage VBH, and the transistors T 23  to T 26  maintain the state of the period P 11 . For a period P 12 , the light emitting signal E[i] is maintained at the On-level voltage VL. 
     For a period P 13 , as the light emitting control signal EC[i−1] is On-level, the transistor T 27  is turned on, and the voltage at the node N 7  becomes the voltage VL-VTH of VL 2  that is a subtraction of the threshold voltage VTH of the transistor T 27  from the voltage VL of the light emitting control signal EC[i−1]. The voltage VL 2  may be a low-level voltage for turning on the transistor T 29 . By the voltage VL 2 , the transistor T 29  is turned on and the transistor T 30  is turned off so the voltage at a node N 8  is charged with the voltage VBH. By the voltage VBH, the transistor T 32  is turned on and the transistor T 31  is turned off. The clock signal CLK 3  is supplied as the light emitting control signal EC[i] through the transistor T 32  that is in the On state. For the period P 13 , as the clock signal CLK 3  is the voltage VSS, the light emitting control signal EC[i] is maintained at the voltage VSS. As the transistor T 22  is still in the Off state, for the period P 13 , the voltages at the node N 5  and the node N 6  and the light emitting signal E[i] maintain the state of the period P 12 . 
     When the period P 13  ends, the light emitting control signal EC[i−1] becomes the high-level voltage VSS and the transistor T 27  is blocked. For a period P 14 , without bootstrapping, the voltage at the node N 7  is maintained at the voltage VL 2 , and the voltage at the node N 8  is maintained at the voltage VBH so the transistors T 29  to T 32  maintain the state of the period P 13 . For the period P 14 , as the clock signal CLK 3  is the low-level voltage VL, the light emitting control signal EC[i] is charged with the On-level voltage VL. 
     For the period P 14 , as the light emitting control signal EC[i] is On-level, the transistor T 22  is in the On state. The voltage at the node N 5  becomes the voltage VSS, and by the voltage VSS, the transistor T 24  is turned on and the transistor T 23  is turned off. The voltage at the node N 6  is pulled down to the voltage VL through the transistor T 24  that is in the On state. By the voltage VL, the transistor T 25  is turned on and the transistor T 26  is turned off. The light emitting signal E[i] is discharged to the voltage VSS through the transistor T 25  that is in the On state. 
     For a period P 15 , as the light emitting control signal EC[i+1] is On-level, the transistor T 28  is in the On state. The voltage at the node N 7  becomes the voltage VSS, and by the voltage VSS, the transistor T 30  is turned on and the transistor T 29  is turned off. The voltage at the node N 8  is pulled down to the voltage VL by the transistor T 30  that is in the On state. By the voltage VL, the transistor T 31  is turned on and the transistor T 32  is turned off. The light emitting control signal EC[i] is discharged to the voltage VSS through the transistor T 31  that is in the On state. 
     For a period P 21 , the gate signal S[i+1] is On-level. The transistor T 33  is turned on, and the voltage at the node N 9  becomes the voltage VL-VTH of VL 2  that is a subtraction of the threshold voltage VTH of the transistor T 33  from the voltage VL of the gate signal S[i+1]. The voltage VL 2  may be a low-level voltage for turning on the transistor T 35 . By the voltage VL 2 , the transistor T 35  is turned on and the transistor T 36  is turned off so the voltage at the node N 10  is charged with the voltage VBH. By the voltage VBH, the transistor T 38  is turned on and the transistor T 37  is turned off. The voltage VL is supplied as the light emitting signal E[i+1] to the light emitting control line EMi+1 through the transistor T 38  that is in the On state. 
     When the period P 21  ends, the gate signal S[i+1] becomes the high-level voltage VSS, and the transistor T 33  is blocked. For a period P 22 , without bootstrapping, the voltage at the node N 9  is maintained at the voltage VL 2 , and the voltage at the node N 10  is maintained at the voltage VBH so the transistors T 35  to T 38  maintain the state of the period P 21 . For the period P 22 , the light emitting signal E[i+1] is maintained at the On-level voltage VL. 
     For the period P 14 , as the light emitting control signal EC[i] is On-level, the transistor T 39  is turned on, and the voltage at the node N 11  becomes the voltage VL-VTH of VL 2  that is a subtraction of the threshold voltage VTH of the transistor T 39  from the voltage VL of the light emitting control signal EC[i]. The voltage VL 2  may be a low-level voltage for turning on the transistor T 41 . By the voltage VL 2 , the transistor T 41  is turned on and the transistor T 42  is turned off so the voltage at the node N 12  is charged with the voltage VBH. By the voltage VBH, the transistor T 44  is turned on and the transistor T 43  is turned off. The clock signal CLK 4  is supplied to the light emitting control signal EC[i+1] through the transistor T 44  that is in the On state. For the period P 14 , as the clock signal CLK 4  is the voltage VSS, the light emitting control signal EC[i+1] is maintained at the voltage VSS. As the transistor T 34  is still in the Off state, for the period P 14 , the voltage at the nodes N 9  and N 10  and the light emitting signal E[i+1] maintain the period P 22 . 
     When the period P 14  ends, the light emitting control signal EC[i] becomes the high-level voltage VSS and the transistor T 39  is blocked. For the period P 15 , without bootstrapping, the voltage at the node N 11  is maintained at the voltage VL 2 , and a voltage at a node N 12  is maintained at the voltage VBH, so the transistors T 41  to T 44  maintain the state of the period P 14 . For the period P 15 , as the clock signal CLK 4  is the low-level voltage VL, the light emitting control signal EC[i+1] is charged with the On-level voltage VL. 
     For the period P 15 , as the light emitting control signal EC[i+1] is On-level, the transistor T 34  is in the On state. The voltage at the node N 9  becomes the voltage VSS, and by the voltage VSS, the transistor T 36  is turned on and the transistor T 35  is turned off. The voltage at the node N 10  is pulled down to the voltage VL through the transistor T 36  that is in the On state. By the voltage VL, the transistor T 37  is turned on and the transistor T 38  is turned off. The light emitting signal E[i+1] is charged to the voltage VSS through the transistor T 37  that is in the On state. 
     For a period P 16 , as the light emitting control signal EC[i+2] is On-level, the transistor T 40  is in the On state. The voltage at the node N 11  becomes the voltage VSS, and by the voltage VSS, the transistor T 42  is turned on and the transistor T 41  is turned off. The voltage at the node N 12  is pulled down to the voltage VL through the transistor T 42  that is in the On state. By the voltage VL, the transistor T 43  is turned on and the transistor T 44  is turned off. The light emitting control signal EC[i+1] is discharged to the voltage VSS through the transistor T 43  that is in the On state. 
     Each time the gate signal S[i] becomes On-level in a next frame and the gate signal S[i+1] becomes On-level, the above-described operation may be repeated. According to the above-noted operation, for each frame, the light emitting stages ESR_ 1  to ESR_n may sequentially supply a plurality of On-level light emitting control signals E[ 1 ] to E[n] to the light emitting control lines EM 1  to EMn. 
     As can be known from the waveform diagram shown in  FIG.  21   , On duties of the light emitting signals E[ 1 ] to E[n] are determined by an On pulse of the corresponding light emitting control signal. Therefore, the On duties of the light emitting signal may be adjusted without changing the pulse widths of the signals that are input to the light emitting driver  40 . In detail, in one frame, the On duty of the light emitting signal E[ 1 ] may be determined according to the period between the On pulse of the gate signal S[ 1 ] and the On pulse of the light emitting control start signal ECSTR input to the light emitting stage ESR_ 1 . 
     The effect described above with regard to the gate driver may be equivalently applied to the light emitting driver. This is because the light emitting driver  40  is realized with the LTPO TFT and no additional capacitor for bootstrapping is needed. 
       FIG.  22 A  shows a top plan view of a layout of an i-th light emitting stage shown in  FIG.  20   . 
     Referring to  FIG.  22 A , the light emitting control circuit EC_i may be positioned in a region  22   b , and other components may be positioned in a region  22   c.    
       FIG.  22 B  shows a top plan view of a layout of a light emitting control circuit portion shown in  FIG.  22 A . 
       FIG.  22 C  shows a top plan view of a layout of a remaining portion excluding a portion shown in  FIG.  22 B  from  FIG.  22 A . 
       FIG.  23    shows a cross-sectional view with respect to a line III-III′ in  FIG.  22 C . 
       FIG.  24    shows a cross-sectional view with respect to a line IV-IV′ in  FIG.  22 C . 
     Referring to  FIG.  22 A to  22 C , when a description on a predetermined layer is needed, a layout in which a certain layer covering the predetermined layer is removed may be shown. Referring to  FIG.  22   , semiconductor layers  402  and  403  realized with low-temperature polysilicon and semiconductor layers  602  and  603  realized with a-IGZO are marked with thick solid lines to be distinguished from other layers. 
     As shown in  FIG.  22 B , a drain of the transistor T 27  is connected to a line L 12  for transmitting the light emitting control signal EC[i−1], and a gate of the transistor T 27  extends from the line L 12 . A source of the transistor T 27  and a drain of the transistor T 28  is connected to a line L 13 , a gate of the transistor T 28  extends from a line L 27  for transmitting the light emitting control signal EC[i+1], and a source of the transistor T 28  is connected to a bus line BL 2  for supplying the voltage VSS. 
     The line L 13  is connected to the line L 14  through a via contact. A gate of the transistor T 29  and a bottom gate BG 3  of the transistor T 30  extend from the line L 14 . A top gate TG 3  and the bottom gate BG 3  of the transistor T 30  are connected to each other through a via contact CT 6 . Drains of the transistor T 29  and the transistor T 30  are connected to a line L 15 . The voltage VL may be supplied to a source of the transistor T 30 , and the voltage VBH may be supplied to a source of the transistor T 29 . 
     A bottom gate BG 4  of the transistor T 32  includes a portion extending from the line L 15  and a portion branched and extending, the bottom gate BG 4  and a top gate TG 4  of the transistor T 32  are connected to each other through a via contact CT 7 , and a gate of the transistor T 31  extends from the line L 15 . A source of the transistor T 32  is connected to two lines L 161  and L 162 , and the lines L 161  and L 162  may be branched from a line L 16  and may extend. The clock signal CLK 3  may be supplied to the line L 16 . A drain of the transistor T 32  and a drain of the transistor T 31  are connected to a line L 17 , and the line L 17  is connected to a line L 18  through a via contact CT 8 . The source of the transistor T 31  is connected to the bus line BL 2 , and the voltage VSS is supplied to a source of the transistor T 31 . 
     The line L 18  may extend to a gate of the transistor T 22 , and may be connected to a drain of the transistor T 39  of the light emitting control circuit EC_i+1 on the next light emitting stage ESR_i+1. 
     As shown in  FIG.  22 C , the drain of the transistor T 21  is connected to a line L 19  for transmitting the corresponding gate signal S[i], and the gate of the transistor T 21  extends from the line L 19 . A source of the transistor T 21  and a drain of the transistor T 22  are connected to a line L 20 , a gate of the transistor T 22  extends from the line L 18  for transmitting the light emitting control signal EC[i], and a source of the transistor T 22  is connected to the bus line BL 2  for supplying the voltage VSS. 
     The line L 20  is connected to a line L 21  through a via contact. A gate of the transistor T 23  and a bottom gate BG 5  of the transistor T 24  extend from the line L 21 . A top gate TG 5  and a bottom gate BG 5  of the transistor T 24  are connected to each other through a via contact CT 9 . Drains of the transistor T 23  and the transistor T 24  are connected to a line L 22 . The voltage VBH may be supplied to a source of the transistor T 23 . A source of the transistor T 24  may be connected to a line L 231 , the line L 231  may be branched from a line L 23 , and the voltage VL may be supplied to the line L 23 . 
     The line L 24  is connected to the line L 22  through a via contact. A bottom gate BG 6  of the transistor T 26  includes a portion extending from a line L 24  and a portion branched and extending, the bottom gate BG 6  is connected to the top gate TG 6  of the transistor T 26  through a via contact CT 10 , and the gate of the transistor T 25  extends from the line L 24 . A source of the transistor T 26  may be connected to the lines L 231  and L 232 , and the lines L 231  and L 232  may be branched from the line L 23  and may extend. A drain of the transistor T 26  and a drain of the transistor T 25  are connected to a line L 25 , and the line L 25  is connected to a line L 26  through a via contact CT 11 . A source of the transistor T 25  is connected to the bus line BL 2 , and the voltage VSS is supplied to the source of the transistor T 25 . The line L 26  may be connected to the light emitting control line EMi, and may extend as the light emitting control line EMi. 
     Cross-sectional structures of the transistors T 29  and T 30  may be similar to those of the transistors T 23  and T 24 , and cross-sectional structures of the transistors  31  and  32  may be similar to those of the transistors T 25  and T 26 .  FIG.  23    shows cross-sectional structures of the transistors T 23  and  24 , and  FIG.  24    shows cross-sectional structures of the transistors T 25  and T 26 . 
     A cross-sectional structure of the transistors T 23  and T 44  configuring an inverter will now be described with reference to  FIG.  24   . The same portions as the cross-sectional structure described with reference to  FIG.  2    will be omitted. 
     As shown in  FIG.  23   , the source and the drain (P+ region) of the transistor T 23  are connected to the line L 22  and the line L 221 , and the gate of the transistor T 23  extends from the line L 21 . The voltage VBH may be supplied to the line L 221 . 
     A source region T 24 S of the a-IGZO layer  403  is connected to the line L 61 , and a drain region T 24 D of the a-IGZO layer  403  is connected to the line L 22 . 
     The bottom gate BG 5  may be positioned on an insulation pattern  421  to correspond to a channel region CH 31  of the a-IGZO layer  403 , and the top gate TG 5  may be positioned on an insulating layer  180  to correspond to the channel region CH 31  of the a-IGZO layer  403 . 
     A cross-sectional structure of the transistors T 25  and T 26  configuring an inverter will now be described with reference to  FIG.  24   . The same portions as the cross-sectional structure described with reference to  FIG.  2    will be omitted. 
     As shown in  FIG.  24   , the source and the drain (P+ region) of the transistor T 25  are connected to the bus line BL 2  and the line L 25 , and the gate of the transistor T 25  extends from the line L 24 . 
     Regarding the semiconductor layer of the transistor T 26 , the a-IGZO layer  603  is formed to have a single layer, and it may be realized into two a-IGZO layers as distinguished with dotted lines. Here, an insulating layer  180  may be positioned in a region between two adjacent dotted lines. 
     A source region T 26 S 1  of the a-IGZO layer  603  may be connected to the line L 231 , a source region T 26 S 2  of the a-IGZO layer  603  may be connected to the line L 232 , and a drain region T 26 D of the a-IGZO layer  603  may be connected to the line L 25 . The line L 25  may be connected to the line L 26  through the via contact CT 11 . 
     From among the two bottom gates BG 61  and BG 62 , the bottom gate BG 61  may be positioned on an insulation pattern  621  to correspond to a channel region CH 41  of the a-IGZO layer  603 , and the bottom gate BG 62  may be positioned on an insulation pattern  622  to correspond to a channel region CH 42  of the a-IGZO layer  603 . A passivation layer  160  may be positioned between the a-IGZO layer  603  and the two bottom gates BG 61  and BG 62 . 
     From among two top gates TG 61  and TG 62 , the top gate TG 61  may be positioned on the insulating layer  180  to correspond to the channel region CH 41  of the a-IGZO layer  603 , and the top gate TG 62  may be positioned on the insulating layer  180  to correspond to the channel region CH 42  of the a-IGZO layer  603 . 
       FIG.  25    shows a waveform diagram of signals generated when an operation of a light emitting driver according to an embodiment is simulated. 
     In this instance, widths of the transistors T 23  and T 29 , the transistors T 21  and T 27 , the transistors T 22 , T 28 , and T 31 , the transistor T 25 , the transistors T 24  and T 30 , the transistor T 26 , and the transistor T 32  may be 10 μm, 20 μm, 40 μm, 50 μm, 100 μm, 200 μm, and 400 μm. The clock signal CLK 3  may swing between 0 V and −15 V, the VSS may be 0 V, and the threshold voltage Vth of the a-IGZO TFT may be −5.5 V, VL may be −15 V, and VBH may be 6 V. When the threshold voltage of the a-IGZO TFT is a negative voltage, so when the voltage at the node N 8  is the voltage VL, the transistor T 32  may not be completely turned off. The light emitting control signal EC[i] has ripples according to an incomplete Off state of the transistor T 32 . However, as a ripple voltage of the light emitting control signal EC[i] is insufficient in turning on the transistors T 21  and T 22 , the transistor T 21  is turned on by the gate signal S[i], and the voltages at the node N 5  and the node N 6  are not influenced by the ripples. Accordingly, the light emitting signal E[i] may have an excellent waveform without degradation. That is, when the threshold voltage Vth of the a-IGZO TFT is a negative voltage, the light emitting driver  40  may generate a light emitting signal having a waveform that is appropriate to drive the display without ripples. 
     While this invention has been described in connection with what is presently considered to be practical embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims. 
     DESCRIPTION OF SYMBOLS 
     
         
         
           
               1 : display 
               10 : display unit 
               20 : gate driver 
               30 : data driver 
               40 : light emitting driver 
               50 : power supply 
               60 : controller 
               100 : complementary transistor 
               200 : first transistor 
               300 : second transistor