Organic light emitting display device and method for driving the same

Abstract

An organic light emitting display device and a method for driving the organic light emitting display device are provided. The organic light emitting display device may include a display panel, a source driving circuit and a voltage generator. The display panel may include a pixel circuit including a driving transistor for driving an organic light emitting diode. The driving transistor may have four independent terminals including a first gate electrode and a second gate electrode. The source driving circuit may provide a data voltage to the pixel circuit. The voltage generator may apply an independent bias voltage to the second gate electrode of the driving transistor to control a driving voltage range of the driving transistor.

Description

Technical Field

[0001] The exemplary embodiments relate to an organic light emitting display device and a method of driving the organic light emitting display device. More particularly, the exemplary embodiments relate to an organic light emitting display device having improved display quality and a method of driving the organic light emitting display device having improved display quality. Background Art

[0002] Organic light emitting display devices have attracted much attention as next-generation display devices because of their thin thickness, light weight, low power consumption, and short response time.

[0003] The organic light emitting display device may include a plurality of pixels. Each pixel may include an organic light emitting diode and a pixel circuit for driving the organic light emitting diode. The pixel circuit may include a plurality of transistors and a plurality of capacitors. The plurality of transistors may drive the organic light emitting diode. The organic light emitting diode may emit light having a brightness corresponding to a driving voltage.

[0004] Recently, as organic light emitting display devices have higher resolutions and larger sizes, the area of ​​pixel circuits has been reduced and minimized. Therefore, due to area limitations, multiple transistors in the area of ​​pixel circuits may have reduced sizes and poor driving capabilities. Therefore, due to transistor degradation, the display quality of the organic light emitting display device may be degraded. Summary of the invention

[0005] An embodiment relates to an organic light-emitting display device, which includes: a display panel, including a plurality of pixel circuits, each pixel circuit including a driving transistor having four independent terminals and an organic light-emitting diode for emitting light according to a driving current generated by the driving transistor, the four independent terminals including a first gate electrode and a second gate electrode; a source driving circuit, for providing a data voltage to the plurality of pixel circuits so that a gate voltage corresponding to the data voltage is applied to the first gate electrode of the driving transistor; and a voltage generator, for applying an independent bias voltage to the second gate electrode of the driving transistor, the independent bias voltage being used to control a driving voltage range of the driving transistor, wherein: a channel length of the driving transistor is approximately 3 μm or less, and a voltage level of the independent bias voltage is approximately -7V to approximately 6V.

[0006] The driving transistor may further include a drain electrode for receiving the first emission power supply voltage and a source electrode connected to the organic light emitting diode.

[0007] The driving voltage range of the driving transistor may be a range of gate voltages corresponding to data voltages corresponding to middle grayscales and higher grayscales.

[0008] The driving voltage of the driving transistor may range from about 2V or more to about 5V or less.

[0009] The threshold voltage of the driving transistor may be about -5V to about 5V.

[0010] The subthreshold voltage slope of the driving transistor may be about 0.11 V / dec to about 0.21 V / dec.

[0011] Each pixel circuit may further include a switching transistor and a capacitor, and wherein: the switching transistor includes a gate electrode connected to the scan line, a drain electrode connected to the data line, and a source electrode connected to the first gate electrode of the driving transistor, and the capacitor includes a first electrode connected to the first gate electrode of the driving transistor and a second electrode for receiving a first emission power supply voltage.

[0012] The display panel may include a base substrate, an active pattern of a driving transistor, and a voltage line for transmitting an independent bias voltage, wherein: a first gate electrode overlaps a channel region of the active pattern and is located on the active pattern, a second gate electrode is located on the base substrate, is located below the channel region, and is connected to the voltage line, and the active pattern includes an oxide semiconductor, overlaps the second gate electrode, and is located on the second gate electrode, and wherein the active pattern is located between the first gate electrode and the second gate electrode.

[0013] An embodiment relates to a method for driving an organic light emitting display device, the organic light emitting display device comprising: a plurality of pixel circuits, each pixel circuit comprising an organic light emitting diode and a driving transistor having four independent terminals for driving the organic light emitting diode, the four independent terminals comprising a first gate electrode and a second gate electrode, the method comprising: applying a gate voltage corresponding to a data voltage to the first gate electrode of the driving transistor; applying an independent bias voltage to the second gate electrode of the driving transistor to control a driving voltage range of the driving transistor; and applying a driving current to the organic light emitting diode based on the gate voltage, wherein: a channel length of the driving transistor is approximately 3 μm or less, and a voltage level of the independent bias voltage is approximately -7V to approximately 6V.

[0014] The driving transistor may further include a drain electrode for receiving the first emission power supply voltage and a source electrode connected to the organic light emitting diode.

[0015] The driving voltage of the driving transistor may range from about 2V or more to about 5V or less.

[0016] The threshold voltage of the driving transistor may be about -5V to about 5V.

[0017] The subthreshold voltage slope of the driving transistor is about 0.11 V / dec to about 0.21 V / dec.

[0018] The method of driving an organic light-emitting display device may also include: applying a gate voltage corresponding to a data voltage to a first gate electrode of a driving transistor in response to a scan signal; storing the gate voltage of the first gate electrode in a capacitor; and applying a driving current to the organic light-emitting diode through the driving transistor based on the voltage stored in the capacitor.

[0019] The independent bias voltage may be applied through a voltage line connected to the second gate electrode of the driving transistor.

[0020] An embodiment relates to a pixel unit, which includes: an organic light emitting diode for emitting light corresponding to a grayscale data voltage; and a pixel circuit for driving the organic light emitting diode according to the grayscale data voltage, the pixel circuit including a driving transistor having four independent terminals, the four independent terminals including a first gate electrode and a second gate electrode, wherein: the driving transistor generates a driving current according to a first gate voltage of the first gate electrode of the driving transistor corresponding to the grayscale data voltage and supplies the driving current to the organic light emitting diode, and the driving voltage range of the driving transistor is controlled by a second gate voltage of the second gate electrode of the driving transistor, and the second gate voltage of the second gate electrode of the driving transistor is charged using an independent bias voltage.

[0021] The driving voltage range of the driving transistor may be a range of a first gate voltage of the driving transistor corresponding to data voltages of intermediate grayscales and higher grayscales.

[0022] The driving voltage of the driving transistor may range from about 2V or more to about 5V or less.

[0023] The threshold voltage of the driving transistor may be about -5V to about 5V.

[0024] The subthreshold voltage slope of the driving transistor may be about 0.11 V / dec to about 0.21 V / dec. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Features will become apparent to those skilled in the art by describing in detail exemplary embodiments with reference to the accompanying drawings, in which:

[0026] Figure 1 An organic light emitting display device according to an exemplary embodiment is shown;

[0027] Figure 2A and Figure 2B shows a volt-ampere (IV) characteristic curve showing a driving voltage range of a driving transistor;

[0028] Figure 3A pixel circuit according to an exemplary embodiment is shown;

[0029] Figure 4 shows a cross-sectional view of a display panel including a four-terminal transistor according to an exemplary embodiment;

[0030] Figure 5 shows a volt-ampere (IV) characteristic curve of a four-terminal transistor according to an exemplary embodiment; and

[0031] Figure 6 Experimental data showing independent bias voltage and drive voltage ranges for a four-terminal transistor according to an exemplary embodiment are shown. DETAILED DESCRIPTION

[0032] Figure 1 An organic light emitting display device 1000 according to an exemplary embodiment is shown. Figure 1 The organic light emitting display device 1000 may include a display panel 100 , a main driver circuit 200 , a source driver circuit 300 , a scan driver circuit 400 , and an emission driver circuit 500 .

[0033] The display panel 100 may include a display portion DA and a peripheral portion. The peripheral portion may include a plurality of peripheral areas PA1, PA2, PA3, and PA4 surrounding the display portion DA.

[0034] The display part DA may include a plurality of data lines DL, a plurality of scan lines SL, a plurality of voltage lines VL1 and VL2, and a plurality of pixel units PU. The plurality of data lines DL may be connected to the source driver circuit 300, and a plurality of data voltages may be provided to the plurality of pixel units PU. The plurality of scan lines SL may be connected to the scan driver circuit 400, and a plurality of scan signals may be provided to the plurality of pixel units PU. The first voltage line VL1 may provide a first emission power supply voltage ELVDD to the plurality of pixel units PU. The second voltage line VL2 may provide an independent bias voltage Vb to the plurality of pixel units PU.

[0035] Each pixel unit PU may include a pixel circuit PC. The pixel circuit PC may be connected to a corresponding data line DL, a corresponding scan line SL, and a corresponding first voltage line VL1 and a second voltage line VL2. In addition, the pixel circuit PC may include a plurality of transistors and at least one capacitor. The plurality of transistors may include a driving transistor TD for driving the organic light emitting diode OLED. The driving transistor TD may be connected to an anode electrode of the organic light emitting diode OLED, and may supply a driving current corresponding to a data voltage to the anode electrode of the organic light emitting diode OLED.

[0036] According to an exemplary embodiment, the driving transistor TD may include a channel and four independent terminals. The four independent terminals of the driving transistor TD may include a source electrode, a drain electrode, a first gate electrode, and a second gate electrode. The first gate electrode may be disposed above the channel. The second gate electrode may be disposed below the channel. The channel may be between the first gate electrode and the second gate electrode.

[0037] The channel may include an oxide semiconductor. The length of the channel of the driving transistor may be less than or equal to about 3 μm. The channel length may be changed according to the resolution and size of the display panel 100.

[0038] The main driver circuit 200 may include a timing controller 230 and a voltage generator 250 mounted on a main printed circuit board 210 .

[0039] The timing controller 230 may receive an image signal and a control signal from an external device. The image signal may include a red image signal, a green image signal, and a blue image signal. The control signal may include a horizontal synchronization signal, a vertical synchronization signal, and a main clock signal. The timing controller 230 may output image data converted from the image signal according to specifications (e.g., the pixel structure and resolution of the display unit DA). The timing controller 230 may generate a first control signal for driving the source driver circuit 300 and a second control signal for driving the scan driver circuit 400 based on the control signal.

[0040] The voltage generator 250 may generate a plurality of driving voltages. The plurality of driving voltages may include a source driving voltage supplied to the source driver circuit 300, a scan driving voltage supplied to the scan driver circuit 400, and a panel driving voltage supplied to the display panel 100.

[0041] The panel driving voltage may include a first emission power supply voltage ELVDD, a second emission power supply voltage ELVSS, and an independent bias voltage Vb. The panel driving voltage may be provided to the pixel circuit PC. The first emission power supply voltage ELVDD may be applied to the anode electrode of the organic light emitting diode OLED. The second emission power supply voltage ELVSS may be applied to the cathode electrode E2 of the organic light emitting diode OLED. The first emission power supply voltage ELVDD may be greater than the second emission power supply voltage ELVSS. The independent bias voltage Vb may be applied to the fourth terminal (e.g., the second gate electrode) of the driving transistor TD. The independent bias voltage Vb may be about -7V to about 6V.

[0042] The source driver circuit 300 may include a plurality of source driver units 330 mounted on a source printed circuit board 310. The plurality of source driver units 330 may include a flexible circuit film and a source driver chip mounted on the flexible circuit film. The source driver circuit 300 may be connected to the first peripheral area PA1 of the display panel 100. The source driver circuit 300 may convert image data supplied from the timing controller 230 into a data voltage using a gamma voltage. The data voltage may be provided to the pixel unit PU of the display panel 100.

[0043] The first emission power voltage ELVDD, the second emission power voltage ELVSS, and the independent bias voltage Vb may be provided to the display panel 100 through the source printed circuit board 310 without passing through the plurality of source driving units 330 .

[0044] The scan driver circuit 400 may be disposed in the second peripheral area PA2 of the display panel 100. The scan driver circuit 400 may include a plurality of transistors directly formed in the second peripheral area PA2 by the same process as that of manufacturing transistors in the pixel circuit PC included in the display portion DA. The scan driver circuit 400 may generate a plurality of scan signals based on a control signal provided by the timing controller 230, and may provide the plurality of scan signals to a plurality of scan lines SL.

[0045] Figure 2A and Figure 2B The volt-ampere (IV) characteristic curve showing the driving voltage range of the driving transistor is shown. Figure 2A According to a comparative exemplary embodiment, the driving transistor may have three terminals, which may include a gate electrode for receiving a data voltage, a drain electrode for receiving a first emission power supply voltage, and a source electrode connected to an anode electrode of the organic light emitting diode OLED.

[0046] According to a comparative exemplary embodiment, the driving transistor having the three terminals may have a gate voltage V corresponding to the data voltage based on the gate electrode. G The driving current I flowing from the drain electrode to the source electrode D The driving current I of the driving transistor D can be applied to the organic light emitting diode OLED. The organic light emitting diode OLED can be driven by a current I D To generate light. The driving current I of the driving transistor D According to the gate voltage V G The brightness of light emitted from the organic light emitting diode OLED can be changed and controlled.

[0047] Generally, a pixel can display about 256 grayscales from black grayscale to white grayscale. Therefore, the brightness of light emitted from the organic light emitting diode OLED can display 256 grayscales. The data voltage supplied to the driving transistor may include 256 grayscale voltages corresponding to the 256 grayscales.

[0048] Figure 2A The volt-ampere (IV) characteristic curve of the driving transistor having the first driving voltage range VD_range_1, the second driving voltage range VD_range_2, the first driving current range ID_range_1 and the second driving current range ID_range_2 is shown. G When the gate voltage VD_range_1 of the driving transistor is within the first driving voltage range VD_range_1, the driving transistor may flow with a first current within the first driving current range ID_range_1. G When within the second driving voltage range VD_range_2, the driving transistor may flow with a second current of the second driving current range ID_range_2.

[0049] The first driving voltage range VD_range_1 may correspond to a data voltage range corresponding to middle gray (eg, 128 gray) or higher gray. For example, when a middle gray or high gray data voltage is applied to the driving transistor, the first driving voltage range VD_range_1 may represent a gate voltage range of the driving transistor.

[0050] The second driving voltage range VD_range_2 may correspond to a data voltage range of low grayscale. For example, when a data voltage of low grayscale (e.g., less than 128 grayscale) is applied to the driving transistor, the second driving voltage range VD_range_2 may represent a gate voltage range of the driving transistor. The second driving voltage range VD_range_2 may be narrower than the first driving voltage range VD_range_1.

[0051] As the driving current of the driving transistor decreases, the driving voltage range VD_range of the driving transistor decreases. In addition, since the organic light-emitting display device has a higher resolution and a larger size, the size of the driving transistor is reduced, thereby reducing the driving current of the driving transistor (reduced to, for example, about 1nA or less). Therefore, due to the reduced driving current of the driving transistor, the driving voltage range VD_range of the driving transistor is reduced (reduced to, for example, about 0.3V). Therefore, the reduction in the driving voltage range VD_range of the driving transistor deteriorates the display quality of the organic light-emitting display device.

[0052] [surface]

[0053] length 2.5μm 3.5μm 4.5μm VD_range 1.45V 1.75V 2.07V

[0054] Referring to the above table, when the channel length of the driving transistor is about 4.5 μm, the driving voltage range VD_range of the driving transistor may be about 2.07 V (e.g., the difference between the minimum gate voltage and the maximum gate voltage of the driving transistor when a data voltage corresponding to an intermediate grayscale or higher grayscale is applied to the driving transistor). When the channel length of the driving transistor is about 3.5 μm, the driving voltage range VD_range of the driving transistor may be about 1.75 V. When the channel length of the driving transistor is about 2.5 μm, the driving voltage range VD_range of the driving transistor may be about 1.45 V.

[0055] According to an exemplary embodiment, Figure 2B A volt-ampere (IV) characteristic curve showing a driving voltage range VD_range of a driving transistor having four independent terminals is shown. The four independent terminals may include a source electrode, a drain electrode, a first gate electrode above a channel, and a second gate electrode below the channel. For example, the four independent terminals may operate independently of each other.

[0056] The subthreshold slope (SS) may refer to the slope of a curve below the threshold voltage of a transistor in a volt-ampere (IV) characteristic curve. Figure 2A and Figure 2B As shown in Figure 2A The subthreshold slope (SS) ratio of the driving transistor with three terminals in Figure 2B The subthreshold slope (SS) of the driving transistor having four terminals is steep.

[0057] According to an exemplary embodiment, a driving transistor having four terminals with a channel length of about 3 μm or less can obtain a driving voltage range VD_range of about 3 V or more by gently adjusting a subthreshold slope (SS) (the slope of a curve below a threshold voltage in a volt-ampere (IV) characteristic curve). For example, in order to smooth the subthreshold voltage slope (SS), an independent bias voltage Vb may be applied to a second gate electrode corresponding to a fourth terminal of the driving transistor.

[0058] For example, a driving transistor having four independent terminals may have a channel length of about 3 μm or less, and a voltage level of the independent bias voltage Vb may be about −7V to about 6V.

[0059] Figure 3 A pixel circuit PC according to an exemplary embodiment is shown. Figure 4 A cross-sectional view of a display panel 100 including a driving transistor TD having four independent terminals according to an exemplary embodiment is shown.

[0060] Reference Figure 1 and Figure 3 , the pixel circuit PC may include an organic light emitting diode OLED, a driving transistor TD, a capacitor CST and a switching transistor TS.

[0061] The driving transistor TD may include four independent terminals. The four independent terminals may operate independently of each other. The driving transistor TD may include a first gate electrode GE11 connected to the switching transistor TS, a drain electrode DE1 for receiving a first emission power supply voltage ELVDD, a source electrode SE1 connected to an anode electrode of the organic light emitting diode OLED, and a second gate electrode GE12 for receiving an independent bias voltage Vb. The first emission power supply voltage ELVDD may be a power supply voltage having a high level.

[0062] The capacitor CST may include a first electrode CE1 for receiving the first transmission power voltage ELVDD and a second electrode CE2 connected to the first gate electrode GE11 of the driving transistor TD.

[0063] The switching transistor TS may include a gate electrode GE2 connected to the scan line SL and receiving the scan signal S, a drain electrode DE2 connected to the data line DL and for receiving the data voltage Vdata, and a source electrode SE2 connected to the first gate electrode GE11 of the driving transistor TD. The switching transistor TS may have three independent terminals (e.g., the gate electrode GE2, the source electrode SE2, and the drain electrode DE2). In other words, the switching transistor TS and the driving transistor TD may be different types of transistors.

[0064] The organic light emitting diode OLED may include an anode electrode connected to the source electrode SE1 of the driving transistor TD and a cathode electrode for receiving the second emission power voltage ELVSS. The second emission power voltage ELVSS may be a power voltage having a low level.

[0065] According to an exemplary embodiment, a driving method of the pixel circuit PC is as follows. The second gate electrode GE12 of the driving transistor TD may receive an independent bias voltage Vb through a second voltage line VL2. The driving voltage range VD_range of the driving transistor TD may be controlled according to the level of the independent bias voltage Vb. In addition, the threshold voltage (Vth) of the driving transistor TD may be controlled by the independent bias voltage Vb.

[0066] For example, during a period in which the pixel circuit PC operates, the independent bias voltage Vb may be always applied to the second gate electrode GE12 of the driving transistor TD. Alternatively, when the pixel circuit PC operates, the independent bias voltage Vb may be selectively applied to the second gate electrode GE12 of the driving transistor TD. When a data voltage corresponding to an intermediate grayscale or higher grayscale is applied to the first gate electrode GE11 of the driving transistor TD, the driving voltage range VD_range of the driving transistor TD may be the voltage range of the first gate electrode GE11 (e.g., the gate voltage range of the driving transistor TD). In other words, when the gate voltage V G When the driving voltage range VD_range of the driving transistor TD is within, the driving transistor TD can generate a driving current corresponding to the intermediate grayscale and higher grayscale. For example, the driving transistor TD can have a channel including an oxide semiconductor, and the length of the channel can be about 3 μm or less. The voltage level of the independent bias voltage Vb can be about -7V to about 6V.

[0067] For example, when the scan signal S is supplied through the scan line SL, the switching transistor TS may be turned on. The data voltage Vdata received through the data line DL may be applied to the capacitor CST through the turned-on switching transistor TS. The data voltage Vdata applied to the capacitor CST may be applied to the first gate electrode GE11 of the driving transistor TD. The driving current I corresponding to the data voltage Vdata stored in the capacitor CST may be D To drive the driving transistor TD. The driving current I D can be applied to the organic light emitting diode OLED. The organic light emitting diode OLED can be driven by a current I D To emit light. By driving current I D The generated light may have brightness corresponding to the data voltage Vdata.

[0068] For example, when the pixel circuit PC is driven, the independent bias voltage Vb may be always applied to the second gate electrode GE12 of the driving transistor TD. Alternatively, when the pixel circuit PC is driven, the independent bias voltage Vb may be selectively applied to the second gate electrode GE12 of the driving transistor TD. For example, the first gate electrode GE11 and the second gate electrode GE12 of the driving transistor TD may receive different voltages and may operate independently of each other. The driving transistor TD may have a channel including an oxide semiconductor and have a channel length of about 3 μm or less.

[0069] Reference Figure 4, the display panel 100 may include a base substrate 110 according to an exemplary embodiment, a driving transistor TD, a second voltage line VL2 , a storage capacitor CST, and an organic light emitting diode OLED.

[0070] The base substrate 110 may be an insulating substrate including glass, polymer, etc. The base substrate 110 may include a first plastic layer, a first barrier layer, a second plastic layer, and a second barrier layer sequentially stacked. For example, the first plastic layer and the second plastic layer may be formed of a material selected from the group consisting of polyimide (PI), polyethylene naphthalate (PEN), polyethylene terephthalate (PET), polyarylate (PAR), polycarbonate (PC), polyetherimide (PEI), polyethersulfone (PS), etc. The first barrier layer and the second barrier layer may include amorphous silicon (a-Si), silicon oxide (SiO x ), Silicon Nitride (SiN x ) and other silicon-containing materials.

[0071] The driving transistor TD may be disposed on the base substrate 110. The driving transistor TD may include an active pattern A, a first gate electrode GE11, a source electrode SE1, a drain electrode DE1, and a second gate electrode GE12. For example, the first insulating layer 120 may be between the active pattern A and the second gate electrode GE12, and may overlap the active pattern A, the source electrode SE1, and the drain electrode DE1. The gate insulating layer 130 may be between the active pattern A and the first gate electrode GE11.

[0072] The active pattern A may be formed of a polysilicon semiconductor or an oxide semiconductor. The oxide semiconductor may be at least one selected from the group consisting of titanium (Ti), hafnium (Hf), zirconium (Zr), aluminum (Al), tantalum (Ta), germanium (Ge), zinc (Zn), and indium (In)-based oxides and / or indium (In)-based composite oxides. The composite oxide may be at least one selected from the group consisting of indium gallium zinc oxide (In-Ga-Zn-O), indium zinc oxide (Zn-In-O), indium gallium oxide (In-Ga-O), indium tin oxide (In-Sn-O), indium zirconium gallium oxide (In-Zr-Ga-O), indium zirconium tin oxide (In-Zr-Sn-O), indium zinc aluminum oxide (In-Zn-Al-O), indium tin aluminum oxide (In-Sn-Al-O), indium aluminum gallium oxide (In-Al-Ga-O), indium tantalum zinc oxide (In-Ta-Zn-O), indium tantalum gallium oxide (In-Ta-Ga-O), indium germanium gallium oxide (In-Ge-Ga-O), indium germanium zinc oxide (In-Ge-Zn-O), indium germanium tin oxide (In-Ge-Sn-O), titanium indium zinc oxide (Ti-In-Zn-O), and hafnium indium zinc oxide (Hf-In-Zn-O).

[0073] The active pattern A may include a source region AS, a channel region AC, and a drain region AD. The active pattern A may be doped with N-type impurities or P-type impurities. The source region AS and the drain region AD may be separated by the channel region AC and may be doped with impurities of an opposite type to the impurities doped in the channel region AC.

[0074] A channel of the driving transistor TD may be defined by the channel region AC. When the display panel has a high resolution, the channel length of the driving transistor TD may be designed to be about 3 μm or less.

[0075] The source electrode SE1 may be connected to the source region AS through a first contact hole formed in the second insulating layer 140. The drain electrode DE1 may be connected to the drain region AD through a second contact hole formed in the second insulating layer 140. The second gate electrode GE12 may overlap the active pattern A and may be disposed thereunder.

[0076] The second voltage line VL2 may be connected to the second gate electrode GE12 as the fourth terminal of the drive transistor TD through a third contact hole formed in the first insulating layer 120 and the second insulating layer 140. The second voltage line VL2 may be applied with an independent bias voltage Vb. The independent bias voltage Vb may be applied to the second gate electrode GE12. According to the voltage level of the independent bias voltage Vb, the threshold voltage (Vth), the subthreshold voltage slope (SS), and the mobility (Mob) of the drive transistor TD may be controlled or adjusted.

[0077] According to an exemplary embodiment, the driving voltage range VD_range of the driving transistor TD may be about 3V, and the threshold voltage (Vth) may be about -5V to about 5V, so that the independent bias voltage Vb may be about -7V to about 6V.

[0078] The capacitor CST may include a first electrode CE1, a second electrode CE2 overlapping the first electrode CE1, and a second insulating layer 140 disposed between the first electrode CE1 and the second electrode CE2. For example, the first electrode CE1 of the capacitor CST may be formed of the same metal layer as the first gate electrode GE11 of the driving transistor TD. The second electrode CE2 of the capacitor CST may be formed of the same metal layer as the source electrode CE1 and the drain electrode DE1 of the driving transistor TD.

[0079] The organic light emitting diode OLED may include an anode electrode E1, an organic light emitting layer OL, and a cathode electrode E2. For example, the anode electrode E1 may be connected to the source electrode SE1 of the driving transistor TD through a fourth contact hole. At least one of the anode electrode E1 and the cathode electrode E2 of the organic light emitting diode OLED may be any one of a light-transmitting electrode, a light-reflecting electrode, and a semi-light-transmitting electrode. Light emitted from the organic light emitting layer OLED may be transmitted through the anode electrode E1 or toward the cathode electrode E2.

[0080] Figure 5 A volt-ampere (IV) characteristic curve of a four-terminal transistor according to an exemplary embodiment is shown. Figure 6 Experimental data showing independent bias voltage and drive voltage ranges for a four-terminal transistor according to an exemplary embodiment.

[0081] Reference Figure 3 , Figure 5 and Figure 6 According to an exemplary embodiment, a driving transistor TD having four independent terminals may include a channel including an oxide semiconductor (e.g., indium germanium zinc oxide (In-Ge-Zn-O)), a first gate electrode GE11 on the channel, a source electrode SE1, a drain electrode DE1, and a second gate electrode GE12 below the channel. The driving transistor TD may have a channel length of about 2.5 μm.

[0082] According to the first emission power voltage ELVDD, the drain electrode DE1 of the driving transistor TD may receive a drain voltage Vd of about 5.1 V. An independent bias voltage Vb may be applied to the second gate electrode GE12 of the driving transistor TD.

[0083] For example, refer to Figure 6 Under the first condition, when the independent bias voltage Vb of about -7V is applied to the second gate electrode GE12 of the driving transistor TD, the on-current Ion of the driving transistor TD may be about 2.20E-06A (i.e., about 2.2μA), the threshold voltage Vth may be about 4.71V, the driving voltage range VD_range may be about 4.69V, the subthreshold voltage slope SS may be about 0.20V / dec, and the mobility Mob may be about 1.73cm 2 / V·s.

[0084] Under the second condition, when the independent bias voltage Vb of about -5V is applied to the second gate electrode GE12 of the driving transistor TD, the on-current Ion of the driving transistor TD may be about 2.98E-06A (i.e., about 2.98μA), the threshold voltage Vth may be about 3.51V, the driving voltage range VD_range may be about 4.21V, the subthreshold voltage slope SS may be about 0.16V / dec, and the mobility Mob may be about 2.04cm 2 / V·s.

[0085] Under the third condition, when the independent bias voltage Vb of about 1V is applied to the second gate electrode GE12 of the driving transistor TD, the on-current Ion of the driving transistor TD may be about 5.65E-06A (i.e., about 5.65μA), the threshold voltage Vth may be about 0.11V, the driving voltage range VD_range may be about 3.08V, the subthreshold voltage slope SS may be about 0.15V / dec, and the mobility Mob may be about 3.85cm 2 / V·s.

[0086] Under the fourth condition, when the independent bias voltage Vb of about 6V is applied to the second gate electrode GE12 of the driving transistor TD, the on-current Ion of the driving transistor TD may be about 7.91E-06A, the threshold voltage Vth may be about -2.67V, the driving voltage range VD_range may be about 2.63V, the subthreshold voltage slope SS may be about 0.14V / dec, and the mobility Mob may be about 5.23cm 2 / V·s.

[0087] like Figure 6 As shown in , the driving voltage range VD_range of the driving transistor TD can increase as the voltage level of the independent bias voltage Vb decreases. For example, when the independent bias voltage Vb is about -15 V, the driving voltage range VD_range can be fully expanded to about 7.37 V. On the contrary, when the voltage level of the independent bias voltage Vb is low, the threshold voltage Vth of the driving transistor TD has a high voltage level.

[0088] like Figure 5 As shown in , as the independent bias voltage Vb of the driving transistor TD decreases toward the negative polarity (-), the threshold voltage Vth of the driving transistor TD can increase toward the positive polarity (+). As the independent bias voltage Vb increases toward the positive polarity (+), the threshold voltage Vth can decrease toward the negative polarity (-). As the independent bias voltage Vb decreases, the driving voltage range VD_range can increase.

[0089] When the driving transistor TD is driven for a long time, the threshold voltage Vth of the driving transistor TD may drift. The drifted threshold voltage Vth may be compensated by various compensation algorithms. When the threshold voltage Vth of the driving transistor TD is preset to a too high voltage level or preset to a too low voltage level, the threshold voltage compensation may be difficult. Therefore, considering the threshold voltage compensation, the voltage level of the threshold voltage Vth may be preset to about +5V to about -5V.

[0090] As described above, the voltage level of the independent bias voltage Vb may be preset to about 3V in consideration of the voltage level of the threshold voltage Vth within the range of the driving voltage range VD_range may be obtained.

[0091] According to an exemplary embodiment, considering the threshold voltage Vth and the driving voltage range VD_range, the voltage level of the independent bias voltage Vb may be preset to about -7 V to about 6 V. When the voltage level of the independent bias voltage Vb is about -7 V to about 6 V, the driving voltage range VD_range may be about 4.69 V to about 2.63 V, and the voltage level of the threshold voltage Vth may be about 4.71 V to about -2.67 V.

[0092] According to an exemplary embodiment, the driving voltage range of the driving transistor may be about 2 V or more to about 5 V or less. The threshold voltage of the driving transistor may be about -5 V to about 5 V. The subthreshold voltage slope of the driving transistor may be about 0.11 V / dec to about 0.21 V / dec.

[0093] According to an exemplary embodiment of the present invention, a driving transistor having a channel length of less than 3 μm may include four independent terminals, and a driving voltage range VD_range of about 3 V may be achieved by applying an independent bias voltage Vb of about -7 V to about 6 V to a fourth terminal (e.g., a second gate terminal) of the driving transistor. Therefore, when the channel length of the driving transistor is short in an organic light-emitting display device with high resolution, an appropriate driving voltage range may be obtained by the independent bias voltage Vb to improve display quality. Therefore, although the channel length of the driving transistor is short in an organic light-emitting display device with high resolution, a sufficient driving voltage range may be obtained to improve display quality.

[0094] The exemplary embodiments may be applied to display devices and electronic devices having display devices. For example, the exemplary embodiments may be applied to computer monitors, laptop computers, digital cameras, cellular phones, smart phones, smart tablet computers, televisions, personal digital assistants (PDAs), portable multimedia players (PMPs), MP3 players, navigation systems, game controllers, video phones, etc.

[0095] Example embodiments have been disclosed herein, and although specific terms are employed, they are used and will be interpreted only in a general and descriptive sense, and not for purposes of limitation. In some cases, as will be apparent to one of ordinary skill in the art as of the time of filing this application, features, characteristics, and / or elements described in conjunction with a specific embodiment may be used alone or in combination with features, characteristics, and / or elements described in conjunction with other embodiments, unless otherwise specifically stated. Therefore, it will be understood by those skilled in the art that various changes in form and detail may be made without departing from the spirit and scope of the invention as set forth in the claims.

Claims

1. An organic light-emitting display device, comprising: A display panel including a plurality of pixel circuits, each pixel circuit including a driving transistor having four independent terminals including a first gate electrode and a second gate electrode, and an organic light emitting diode for emitting light according to a driving current generated by the driving transistor; a source driving circuit for providing a data voltage to the plurality of pixel circuits so that a gate voltage corresponding to the data voltage is applied to the first gate electrode of the driving transistor; as well as a voltage generator, for applying an independent bias voltage to the second gate electrode of the driving transistor, wherein the independent bias voltage is used to control a driving voltage range of the driving transistor, wherein: The channel length of the driving transistor is 3 μm or less, and The voltage level of the independent bias voltage is -7V to 6V, The display panel includes a base substrate, an active pattern of the driving transistor and a voltage line for transmitting the independent bias voltage. The first gate electrode overlaps the channel region of the active pattern and is located on the active pattern, The second gate electrode is located on the base substrate, below the channel region, and connected to the voltage line, and The active pattern includes an oxide semiconductor, overlaps the second gate electrode, and is located on the second gate electrode, and Wherein, the active pattern is located between the first gate electrode and the second gate electrode.

2. The organic light emitting display device according to claim 1, wherein: The driving transistor further includes a drain electrode for receiving a first emission power supply voltage and a source electrode connected to the organic light emitting diode.

3. The organic light emitting display device according to claim 1, wherein: The driving voltage range of the driving transistor is a range of gate voltages corresponding to data voltages corresponding to middle grayscales and higher grayscales.

4. The organic light emitting display device according to claim 1, wherein: The driving voltage range of the driving transistor is 2V or more to 5V or less.

5. The organic light emitting display device according to claim 1, wherein: The threshold voltage of the driving transistor is -5V to 5V.

6. The organic light emitting display device according to claim 1, wherein: The subthreshold voltage slope of the driving transistor is 0.11 V / dec to 0.21 V / dec.

7. The organic light emitting display device according to claim 1, wherein: Each pixel circuit also includes a switching transistor and a capacitor. The switching transistor includes a gate electrode connected to a scan line, a drain electrode connected to a data line, and a source electrode connected to the first gate electrode of the driving transistor, and The capacitor includes a first electrode connected to the first gate electrode of the driving transistor and a second electrode for receiving a first transmission power supply voltage.

8. A method for driving an organic light emitting display device, the organic light emitting display device comprising: A display panel comprising a plurality of pixel circuits, each pixel circuit comprising an organic light emitting diode and a driving transistor having four independent terminals for driving the organic light emitting diode, the four independent terminals comprising a first gate electrode and a second gate electrode, the method comprising: applying a gate voltage corresponding to a data voltage to the first gate electrode of the driving transistor; applying an independent bias voltage to the second gate electrode of the driving transistor to control a driving voltage range of the driving transistor; and applying a driving current to the organic light emitting diode based on the gate voltage, wherein: The channel length of the driving transistor is 3 μm or less, and The voltage level of the independent bias voltage is -7V to 6V, The display panel includes a base substrate, an active pattern of the driving transistor and a voltage line for transmitting the independent bias voltage. The first gate electrode overlaps the channel region of the active pattern and is located on the active pattern, The second gate electrode is located on the base substrate, below the channel region, and connected to the voltage line, and The active pattern includes an oxide semiconductor, overlaps the second gate electrode, and is located on the second gate electrode, and Wherein, the active pattern is located between the first gate electrode and the second gate electrode.

9. The method of claim 8, wherein: The driving transistor further includes a drain electrode for receiving a first emission power supply voltage and a source electrode connected to the organic light emitting diode.

10. The method of claim 8, wherein: The driving voltage range of the driving transistor is 2V or more to 5V or less.

11. The method of claim 8, wherein: The threshold voltage of the driving transistor is -5V to 5V.

12. The method of claim 8, wherein: The subthreshold voltage slope of the driving transistor is 0.11 V / dec to 0.21 V / dec.

13. The method of claim 8, further comprising: applying the gate voltage corresponding to the data voltage to the first gate electrode of the driving transistor in response to a scan signal; storing the gate voltage of the first gate electrode in a capacitor; as well as A driving current is applied to the organic light emitting diode through the driving transistor based on the voltage stored in the capacitor.

14. The method of claim 8, wherein: The independent bias voltage is applied through a voltage line connected to the second gate electrode of the driving transistor.

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