KR100897902B1 - Organic light emitting diode display - Google Patents

Abstract

The present invention relates to an organic light emitting display device capable of preventing the occurrence of the left and right luminance difference due to the distortion of the gate signal, the present invention comprises: a gate line; A data line formed in a direction orthogonal to the gate line; A power line perpendicular to the gate line in a direction parallel to the data line; A switching transistor comprising a plurality of transistors connected in series to transfer a signal applied to the data line; A driving transistor for driving a signal output from the switching transistor; The organic light emitting diode which emits light by the signal output from the driving transistor and a storage capacitor connected to a gate electrode of the driving transistor and the other side connected to the power line, the storage capacitor is the switching transistor is turned on ( In the On state, a charging operation is performed in response to a signal output from the switching transistor and a signal transmitted through the power line, and when the switching transistor is Off, the driving operation is performed by performing a discharge operation. According to the present invention, a switching transistor is formed of a plurality of transistors connected in series, thereby preventing the occurrence of left and right luminance difference of the organic light emitting display device due to gate signal distortion. At the same time, before the leakage of the switching transistor It reduces the effect to improve the image quality of the OLED display.

Organic light emission, luminance, distortion, gate signal

Description

Organic light emitting display device {ORGANIC LIGHT EMITTING DIODE DISPLAY}

The present invention relates to a manufacturing technology of a semiconductor device, and more particularly, to an organic light emitting display device.

BACKGROUND OF THE INVENTION A display is gradually shifting from a cathode ray tube (CRT) device using a cathode ray tube to a flat panel display device including a liquid crystal display. Liquid crystal displays have the advantages of light weight and low power consumption, and are currently used as flat panel displays. However, since LCDs are light-receiving devices rather than self-light emitting devices, there are technical limitations in brightness, contrast ratio, viewing angle, and large area. It is developing. One of such new flat panel display devices is an organic light emitting display device having advantages of low voltage driving, self-luminous, light weight, wide viewing angle, and fast response speed.

1 is an equivalent circuit diagram of a unit pixel of an active matrix organic light emitting display device according to the related art.

As shown in FIG. 1, the unit pixel of the active matrix organic light emitting display device according to the related art is a switching transistor (ST), a storage capacitor (C), a driving transistor (DT), and an organic light emitting diode. (OLED).

Here, in order to drive the organic light emitting diode OLED, the data signal transferred from the data line DL is switched when the switching transistor ST is turned on by the gate signal transmitted from the gate line GL. The data is stored in the storage capacitor C through ST. The data signal is transmitted to the gate electrode of the driving transistor DT to operate the driving transistor DT to output light through the organic light emitting diode OLED.

However, in the prior art, a large number of pixels exist in one panel, all of which are connected to the gate line GL. The gate signal flows along the gate line GL. Since the resistance gradually increases along the gate line GL, the square wave of the gate signal applied to the pixel connected to the first end of the gate line GL and the pixel connected to the last end thereof. Was the same initially, but distorted toward the last stage. The distortion of the gate signal affects the voltage charged in the storage capacitor C, causing a difference in left and right luminance of the organic light emitting display device. Specifically, the gate signal distortion reduces the voltage charged in the storage capacitor C while the switching transistor ST is on. When the voltage charged in the storage capacitor C decreases, the organic light emitting diode ( The current flowing through the OLED decreases, thereby lowering the luminance of the organic light emitting diode OLED. As a result, a difference between the voltages charged in the storage capacitor C occurs in the pixel connected to the first end of the gate line GL and the pixel connected to the last end, thereby causing a left and right luminance difference.

In addition, in the related art, crosstalk, flicker, and the like occur due to leakage current of the switching transistor ST, thereby degrading the luminous efficiency of the organic light emitting display device. This is because the leakage current of the switching transistor ST acts as a discharge path of the storage capacitor C, and thus the data signal stored in the storage capacitor C cannot be kept constant for a predetermined time.

In order to solve the above problems, a method of adding a compensation circuit including a plurality of transistors to a pixel has been proposed. However, in the case where the compensation circuit is added to the above-described pixel structure, since a plurality of transistors are added, the driving method is relatively complicated, there is a concern that the non-emission area in the pixel structure is increased and the aperture ratio is reduced. In addition, since the possibility of occurrence of leakage current through the added transistor is relatively high, the voltage holding capability of the storage capacitor C is relatively low, and even if a compensation circuit is added, the image quality of the organic light emitting display device may be degraded. There is a problem.

The present invention has been proposed to solve the above-mentioned problems of the prior art, and an object thereof is to provide an organic light emitting display device capable of preventing the occurrence of a left and right luminance difference due to distortion of a gate signal.

Another object of the present invention is to provide an organic light emitting display device capable of reducing leakage current of a switching transistor.

In addition, another object of the present invention is to provide an organic light emitting device capable of preventing left and right luminance differences due to gate signal distortion and reducing leakage current of a switching transistor without a separate compensation circuit.

The present invention according to an aspect for achieving the above object, a gate line; A data line formed in a direction orthogonal to the gate line; A power line perpendicular to the gate line in a direction parallel to the data line; A switching transistor comprising a plurality of transistors connected in series to transfer a signal applied to the data line; A driving transistor for driving a signal output from the switching transistor; The organic light emitting diode which emits light by the signal output from the driving transistor and a storage capacitor connected to the gate electrode of the driving transistor, one side is connected to the power line, the storage capacitor is the switching transistor is In the on state, the charging operation is performed in response to a signal output from the switching transistor and a signal transmitted through the power line, and the discharge operation is performed when the switching transistor is in the off state. An organic light emitting display device for maintaining an operation of the driving transistor is provided.

The switching transistor may be composed of a plurality of transistors having the same channel area or a plurality of transistors having different channel areas. At this time, in the switching transistor, the transistor having the smallest channel area may be electrically connected to the gate electrode of the driving transistor.

In addition, the switching transistor may include a plurality of transistors having the same conductivity type channel and having the same channel area, or having the same conductivity type channel and having different channel areas.

The switching transistor and the driving transistor may have a channel having the same conductivity type, and may be an NMOS or a PMOS.

According to the present invention, the switching transistor is formed of a plurality of transistors connected in series, thereby preventing the occurrence of the left and right luminance difference of the organic light emitting diode display due to the distortion of the gate signal and reducing the leakage current of the switching transistor.

In addition, the present invention forms a switching transistor with a plurality of transistors connected in series, but by forming a channel area of each transistor different from each other, more effectively prevent the left and right luminance difference of the organic light emitting display device due to the distortion of the gate signal. There is an effect that can be prevented.

In addition, the present invention is to form a switching transistor of a plurality of transistors connected in series, the channel area of the transistor connected to the gate electrode of the driving transistor among the plurality of transistors by forming a smaller than the channel area of the remaining transistors, It has the effect of reducing the kickback voltage and reducing leakage current.

In addition, the present invention has the effect of preventing the lowering of the aperture ratio of the organic light emitting display device by forming the compensation circuit by reducing the left and right luminance difference and the leakage current of the switching transistor without a separate compensation circuit.

Thus, the present invention has the effect of improving the image quality of the organic light emitting display device.

Hereinafter, the most preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art may easily implement the technical idea of the present invention.

According to the present invention to be described later, the left and right luminance difference due to the difference in the voltage charged in the storage capacitor in the pixel connected to the first end of the gate line and the pixel connected to the last end due to the gate signal distortion and crosstalk caused by the leakage current of the switching transistor An organic light emitting display device capable of preventing crosstalk and flicker is provided.

To this end, in the embodiments of the present invention described below, the switching transistor is formed of a plurality of transistors connected in series, thereby reducing the leakage current of the switching transistor while simultaneously responding to the gate signal distortion.

2A and 2B are equivalent circuit diagrams of unit pixels of an active matrix organic light emitting display device according to an exemplary embodiment of the present invention. 2A illustrates a case in which both the switching transistor ST and the driving transistor DT are configured as PMOS, and FIG. 2B illustrates a case where both the switching transistor ST and the driving transistor DT are configured as NMOS. Drawing.

As shown in FIGS. 2A and 2B, the unit pixel of the active matrix organic light emitting display device according to the exemplary embodiment of the present invention may include a gate line GL and a data line DL formed in a direction orthogonal to the gate line GL. ), A power line PL orthogonal to the gate line GL in a direction parallel to the data line DL, and a switching transistor ST including a plurality of transistors connected in series to transfer a signal applied to the data line GL. ), A driving transistor DT for driving a signal output from the switching transistor ST, an organic light emitting diode OLED which emits light by a signal output from the driving transistor DT, and one side of the driving transistor DT And a storage capacitor C connected to the gate electrode of the second side and connected to the power line PL. At this time, the storage capacitor C performs a charging operation in response to a signal output from the switching transistor ST and a signal transmitted through the power line PL when the switching transistor ST is on. When the switching transistor ST is in an off state, the discharge transistor performs a discharge operation to maintain the operation of the driving transistor DT.

In the exemplary embodiment of the present invention illustrated in FIGS. 2A to 2B, the switching transistor ST includes a first transistor T1 and a second transistor T2 connected in series. This is for convenience of description, and the switching transistor ST of the present invention may be formed of two or more transistors. In this case, the plurality of transistors constituting the switching transistor ST may be transistors having channels of the same conductivity type. In addition, the switching transistor ST and the driving transistor DT may be transistors having channels of the same conductivity type as each other. For example, both the first transistor T1, the second transistor T2, and the driving transistor DT constituting the switching transistor ST may be PMOS or NMOS.

In the organic light emitting display device of the present invention having the above-described structure, in order to drive the organic light emitting diode OLED, a gate signal is applied to the gate line GL to turn the switching transistor ST on. The data signal is stored in the storage capacitor C in response to the data signal transmitted from the data line DL through the switching transistor ST and the power signal transmitted through the power line PL. The data signal stored in the storage capacitor C is transmitted to the gate electrode of the driving transistor DT to turn the driving transistor DT on for a predetermined time to emit light through the organic light emitting diode OLED. Output it.

According to the present invention, the switching transistor ST is formed of a plurality of transistors connected in series, so that the storage capacitor C in the pixel connected to the first end of the gate line GL and the pixel connected to the last end due to the distortion of the gate signal. It is possible to prevent the occurrence of the left and right luminance difference of the organic light emitting display device due to the difference in the voltage charged in the. This will be described in more detail with reference to FIG. 3.

3 illustrates a relationship between gate signal distortion and a charging voltage of a storage capacitor.

As shown in FIG. 3, in general, an organic light emitting display device has many pixels in one panel, and many of these pixels are connected to the gate line GL. At this time, the gate signal for turning on / off the switching transistor ST moves along the gate line GL, because the resistance of the gate line GL gradually increases along the gate line GL. As shown in FIG. 3A, a square wave of a gate signal applied to a pixel connected to the first end of the gate line GL and a pixel connected to the last end is initially the same, but gate signal distortion occurs at the last end.

In the related art, the voltage charged in the storage capacitor C, that is, the data signal charged in the storage capacitor C is reduced while the switching transistor ST is on due to the above-described gate signal distortion. When the voltage charged in the storage capacitor C decreases, the amount of current flowing through the organic light emitting diode OLED is reduced, thereby lowering the luminance of light emitted by the organic light emitting diode OLED. As a result, a difference in voltage charged in the storage capacitor C occurs between the pixel connected to the first end of the gate line GL and the pixel connected to the last end, thereby causing a left and right luminance difference.

In contrast, in the present invention, the switching transistor ST is formed of a plurality of transistors connected in series, so that the voltage charged in the storage capacitor C is reduced even if the gate signal distortion as shown in FIG. Can be suppressed. This is because the effective channel length can be increased compared to a single transistor by connecting a plurality of transistors in series within the same area.

Here, the plurality of transistors constituting the switching transistor ST of the present invention have transistors having the same conductive channel and having the same channel area, or transistors having the same conductive channel and having different channel areas. Can be heard. In this case, in order to more effectively prevent the left and right luminance difference from occurring in the organic light emitting display device, it is preferable to form the transistors having different channel areas than the transistors having the same channel area. . When the switching transistor ST is composed of transistors having the same channel area, the voltage charged in the storage capacitor C according to the gate signal distortion shows the relationship as shown in V2 of FIG. This is because the transistors having the area have the same relationship as that of V1 in FIG. 3. This will be described in detail with reference to FIG. 4.

4 is a plan view illustrating a switching transistor according to an exemplary embodiment of the present invention.

As shown in FIG. 4, the switching transistor ST according to the exemplary embodiment of the present invention is formed on the substrate (not shown) and spaced apart from each other to have a predetermined distance with the first electrode 11 and the second electrode 12. An active layer 13 formed at both ends of the substrate to contact the first electrode 11 and the second electrode 12, a first gate electrode 14 formed on the active layer, and connected to the gate line GL; A second gate electrode 15, a first gate electrode 14, and a gate insulating film (not shown) formed between the second gate electrode 15 and the active layer 13 are included. In this case, the first electrode 11 may be connected to the data line DL, and may be connected to the gate electrode of the second electrode 12 driving transistor DT.

Here, the region where the first gate electrode 14 and the active layer 13 overlap each other serves as a channel region of the first transistor T1, and the second gate electrode 15 and the active layer 13 overlap each other. The region serves as a channel region of the second transistor T2. In this case, the channel area A1 of the first transistor T1 may be the same as the channel area A2 of the second transistor T2 (A1 = A2) or may be different from each other (A1> A2 or A1 <A2).

 As mentioned above, in order to more effectively prevent the occurrence of the left and right luminance difference in the organic light emitting display device, the transistors having different channel areas are formed with the transistors having different channel areas than the transistors having the same channel area. It is desirable to.

For example, when the gate signal distortion occurs in the pixel connected to the last end of the gate line GL as shown in FIG. 3A, the channel area of the first transistor T1 and the second transistor T2 is the same. (A1 = A2), the first transistor T1 and the second transistor T2 are turned on at the same time by the gate signal. In this case, the resistance components of the first transistor T1 and the second transistor T2 are stored in the storage capacitor. The voltage charged in (C), that is, the data signal charged in the storage capacitor C is influenced, which is smaller than the conventional switching transistor ST, but the voltage charged in the storage capacitor C may decrease due to gate signal distortion. There is a concern ('V2' in Fig. 3).

However, when the channel areas of the first transistor T1 and the second transistor T2 are formed differently (A1> A2 or A1 <A2), the resistance value of the first transistor T1 and the second transistor T2 are different. The resistance values of have different values. As a result, the first transistor T1 and the second transistor T2 may be prevented from being turned on at the same time due to the difference in resistance between the first transistor T1 and the second transistor T2. As a result, the reduction of the charging voltage of the storage capacitor C due to the gate signal distortion can be effectively suppressed by minimizing the influence of the resistance component of the switching transistor ST on the voltage charged in the storage capacitor C. 'V1' of FIG. 3)

Here, the plurality of transistors having different channel areas may be implemented by forming different line widths of the gate electrodes of the transistors or different widths of the active layers contacting the gate electrodes.

In addition, the organic light emitting display device of the present invention can reduce the leakage current of the switching transistor ST by configuring the switching transistor ST as a plurality of transistors connected in series. Through this, crosstalk, flicker, and the like caused by leakage current of the switching transistor ST may be prevented, thereby improving image quality of the organic light emitting display device.

Particularly, the switching transistor ST is composed of a plurality of transistors having different channel areas, but the channel area A2 of the transistor connected to the driving transistor DT, that is, the second transistor T2 is left over. When the transistor is formed smaller than the channel area A1 of the first transistor T1, the leakage current of the switching transistor ST may be reduced and the kick back voltage may be reduced. For reference, the kickback voltage is a voltage generated by the storage capacitor C due to a phenomenon in which the applied data signal of the driving transistor DT decreases instantly due to the gate signal erasing when the gate signal is applied and then erased. It means descent. Since the kickback voltage is affected by the area of the region where the active layer 13 and the gate electrodes 14 and 15 overlap, that is, the channel area, the channel area A2 of the transistor contacting the terminal causing the kickback, for example, the second transistor T2. You can reduce the kickback voltage by decreasing

As described above, according to the present invention, the switching transistor ST is formed of a plurality of transistors connected in series, thereby preventing the occurrence of the left and right luminance difference of the organic light emitting display device due to the distortion of the gate signal, and at the same time, the leakage current of the switching transistor ST. Can be reduced.

In addition, the present invention is composed of a plurality of transistors connected in series with the switching transistor (ST), by forming a channel area of each transistor different from each other, more effectively the left and right luminance difference of the organic light emitting display device according to the distortion of the gate signal Can be prevented.

In addition, the present invention is composed of a plurality of transistors connected in series with the switching transistor (ST), the channel area of the transistor connected to the gate electrode of the driving transistor (DT) of the plurality of transistors smaller than the channel area of the other transistors By forming, the kickback voltage can be reduced while reducing the leakage current of the switching transistor ST.

In addition, the present invention can prevent the lowering of the aperture ratio of the organic light emitting diode display by forming the compensation circuit by reducing the left and right luminance difference and reducing the leakage current of the switching transistor ST without a separate compensation circuit.

Thus, the present invention has the effect of improving the image quality of the organic light emitting display device.

Although the technical spirit of the present invention has been described in detail according to the above preferred embodiment, it should be noted that the above embodiment is for the purpose of description and not of limitation. In addition, those skilled in the art will appreciate that various embodiments within the scope of the technical idea of the present invention are possible.

1 is an equivalent circuit diagram of a unit pixel of an active matrix organic light emitting display device according to the related art.

2A and 2B are equivalent circuit diagrams of a unit pixel of an active matrix organic light emitting display device according to an exemplary embodiment of the present invention.

3 illustrates a relationship between gate signal distortion and a charge voltage of a storage capacitor.

4 is a plan view showing a switching transistor according to an embodiment of the present invention.

* Description of symbols on the main parts of the drawings *

GL: Gate Line DL: Data Line

PL: Power Line ST: Switching Transistor

DT: Driving Transistor T1: First Transistor

T2: second transistor 11: first electrode

12 second electrode 13 active layer

14: first gate electrode 15: second gate electrode

Claims (8)

Gate line; A data line formed in a direction orthogonal to the gate line; A power line perpendicular to the gate line in a direction parallel to the data line; A switching transistor comprising a plurality of transistors connected in series and having different channel areas and transferring a signal applied to the data line in response to the gate line; A driving transistor for driving a signal output from the switching transistor; An organic light emitting diode which emits light by a signal output from the driving transistor; And One side is connected to the gate electrode of the driving transistor, the other side includes a storage capacitor connected to the power line, The storage capacitor performs a charging operation in response to a signal output from the switching transistor and a signal transmitted through the power line when the switching transistor is in an on state, and the switching transistor is in an off state. The organic light emitting display device maintains an operation of the driving transistor by performing a discharge operation. delete delete The method of claim 1, In the switching transistor, An organic light emitting display device having a transistor having a smallest channel area electrically connected to a gate electrode of the driving transistor. delete The method of claim 1, The switching transistor includes a plurality of transistors having the same conductive channel and different channel areas. The method of claim 1, The switching transistor and the driving transistor have the same conductivity type channel. The method of claim 1, And the switching transistor and the driving transistor are NMOS or PMOS.

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