KR102122543B1 - Organic Light Emitting Display - Google Patents

Abstract

An organic light emitting display device according to the present invention includes a display panel that displays an image including a plurality of pixels; And a data driving circuit that outputs the compensation voltage differently according to a sensing value for the driving current; Each of the pixels includes an organic light emitting diode; A driving TFT made of a double gate type having a main gate electrode and a sub gate electrode; A switch TFT that applies a data voltage for determining the driving current to the main gate electrode of the driving TFT; And a compensation TFT that applies the compensation voltage for compensating the threshold voltage shift of the driving TFT to the sub gate electrode of the driving TFT.

Description

Organic light emitting display device

The present invention relates to an active matrix type organic light emitting display device, and more particularly, to an organic light emitting display device capable of compensating for deterioration of a driving TFT.

The active matrix type organic light emitting display device includes an organic light emitting diode (hereinafter referred to as “OLED”) that emits light by itself, and has a fast response speed, high light emission efficiency, high brightness, and a wide viewing angle.

The self-luminous device OLED includes an anode electrode and a cathode electrode, and an organic compound layer (HIL, HTL, EML, ETL, EIL) formed therebetween. The organic compound layer includes a hole injection layer (HIL), a hole transport layer (HTL), an emission layer (EML), an electron transport layer (ETL), and an electron injection layer (Electron Injection layer, EIL). When a driving voltage is applied to the anode electrode and the cathode electrode, holes passing through the hole transport layer (HTL) and electrons passing through the electron transport layer (ETL) are moved to the emission layer (EML) to form excitons, and as a result, the emission layer (EML) Visible light is generated.

The organic light emitting display device arranges pixels including OLEDs in a matrix form and adjusts the luminance of the pixels according to the gradation of video data. Each of the pixels is a driving thin film transistor (TFT) that controls the driving current flowing through the OLED according to the voltage between the gate and the source, a capacitor that maintains the gate potential of the driving TFT constant for one frame, and a data voltage in response to the gate signal. It includes a switch TFT to store in a capacitor. The luminance of the pixel is proportional to the magnitude of the driving current flowing through the OLED.

In such an organic light emitting display device, the threshold voltage of the driving TFT between pixels varies depending on the formation position for reasons of process variation or the like, or the electrical power of the driving TFT due to gate-bias stress as the driving time elapses. There is a disadvantage that the characteristics are deteriorated. When the electrical characteristics of the driving TFT are deteriorated, the current characteristic curve of the driving TFT is shifted, so it is difficult to realize the desired luminance and the life is shortened.

In order to solve such a problem, in the prior art, as shown in FIG. 1, the electrical characteristic deviation of the driving TFT between pixels P, that is, the threshold voltage deviation of the driving TFT is sensed in the driver IC (DIC), and then internal calculation is performed. By adjusting the size of pixel data for image realization, luminance differences due to threshold voltage variations are compensated.

For example, as shown in FIG. 2, a positive stress is applied to the gate electrode of the driving TFT for a long time so that the threshold voltage of the driving TFT rises by'φ' from'Vth1' to'Vth2' and the current characteristic curve of the driving TFT is'A'. When shifted to the right from'B', the current flowing between the drain and source of the driving TFT under the same condition is lowered by'ΔI' from'I1' to'I2'. In FIG. 2,'Vgs' indicates the gate-source voltage of the driving TFT. In order to compensate for this current reduction, the prior art modulates the data voltage applied to the gate electrode of the driving TFT to be greater than the threshold voltage increase (φ) while maintaining the current characteristic curve of the driving TFT in the deteriorated'B' state. Take the way. The positive stress felt by the gate electrode of the driving TFT is proportional not only to the length of the applied time but also to the magnitude of the applied voltage. According to the prior art, the deterioration of the driving TFT is accelerated in the compensation process as shown in FIG. 3 because an increasingly larger data voltage (Vth2+φ) is applied to the driving TFT to compensate for degradation.

In addition, since the voltage range that can be output from the driver IC is pre-determined according to the purpose as shown in FIG. 4, the deterioration of the driving TFT becomes so severe that the size of the desired compensation voltage is the compensation voltage range of the driver IC (16V-12V=4V) If it exceeds, compensation becomes impossible. This problem is attributable to the fact that the deterioration characteristics of the driving TFT do not saturate at any point, but continue, and also the limitation of the magnitude of the compensation voltage capable of compensating the deterioration of the driving TFT.

In the conventional compensation method, since the range for compensation is narrow and limited, it is difficult to solve luminance unevenness due to deterioration of the driving TFT and shortening the life of the product.

Accordingly, an object of the present invention is to provide an organic light emitting display device capable of efficiently compensating for deterioration of a driving TFT.

In order to achieve the above object, an organic light emitting display device according to an embodiment of the present invention includes a display panel for displaying an image including a plurality of pixels; And a data driving circuit that outputs the compensation voltage differently according to a sensing value for the driving current; Each of the pixels includes an organic light emitting diode; A driving TFT made of a double gate type having a main gate electrode and a sub gate electrode; A switch TFT that applies a data voltage for determining the driving current to the main gate electrode of the driving TFT; And a compensation TFT that applies the compensation voltage for compensating the threshold voltage shift of the driving TFT to the sub gate electrode of the driving TFT.

The present invention includes a double gate type driving TFT having two gate electrodes, and a compensation voltage corresponding to a threshold voltage change of the driving TFT is applied to the sub electrode of the driving TFT to restore the threshold voltage shift. Accordingly, the present invention solves a conventional problem in which deterioration is accelerated in the compensation process and the compensation range is limited. The present invention can effectively compensate for the threshold voltage deterioration, prevent driving failure due to long-term driving, improve reliability, and increase the uniformity of luminance to significantly extend the life of the product.

1 is a view schematically showing a connection relationship between a drive IC and a display panel.
Figure 2 is a view showing a conventional deterioration compensation scheme.
3 is a view showing that deterioration is accelerated by compensation in a conventional deterioration compensation scheme.
4 is a diagram exemplarily showing a voltage range that can be output from a driver IC.
5 is a view showing an organic light emitting display device according to an exemplary embodiment of the present invention.
6 is a view showing a compensation method of the present invention compared to a conventional compensation method.
7A to 8B are diagrams showing a principle in which a threshold voltage is compensated in a driving TFT.
9 is a view showing electrical characteristics of a double gate type driving TFT.
10 and 11 are diagrams showing types of double gate type driving TFTs capable of bidirectional control.
12A to 12C are views sequentially showing a threshold voltage compensation process according to the present invention.

Hereinafter, preferred embodiments of the present invention will be described with reference to FIGS. 5 to 12C.

5 shows an organic light emitting display device according to an exemplary embodiment of the present invention.

Referring to FIG. 5, an organic light emitting display device according to an exemplary embodiment of the present invention includes a display panel 10 in which pixels P are arranged in a matrix form, and a data driving circuit 12 for driving the data lines 14 And a gate driving circuit 13 for driving the gate lines 15 and a timing controller 11 for controlling the driving timing of the data driving circuit 12 and the gate driving circuit 13.

A plurality of data lines 14 and a plurality of gate lines 15 are intersected on the display panel 10, and pixels P are arranged in a matrix form for each intersection area. The display panel 10 includes sensing current supply lines (SL in FIG. 6) for sensing the driving current flowing through the pixels P, and compensation voltage supply lines (for applying the compensation voltage to the pixels P) ( CL of FIG. 6 is further formed. The gate line 15 includes a scan signal supply line for supplying a scan signal (SCAN in FIG. 6), a sensing control signal supply line for supplying a sensing control signal (SEN in FIG. 6), and a compensation control signal (FIG. 6). It includes a compensation control signal supply line for supplying CP.

Each pixel P has a compensation TFT T2 and a second storage in addition to an OLED, a driving TFT DT including two gate electrodes, a switch TFT ST, and a first storage capacitor Cst1 as shown in FIG. 6. A capacitor Cst2 may be further provided. Further, at least one of the pixels P may further include the sensing TFT T1 of FIG. 6. The driving TFT DT has a double gate type structure, and includes a main gate electrode to which a data voltage for determining a driving current is applied, and a sub-gate electrode to which a compensation voltage for threshold voltage compensation is applied. The sensing TFT (T1) is for sensing the threshold voltage shift of the driving TFT (DT) by sensing the current flowing through the driving TFT (DT). One may be formed for each pixel group including the above pixels P, or may be formed only in one of the pixels P. The compensation TFT T2 is for restoring the threshold voltage shift by applying a compensation voltage φ to the driving TFT DT, and may be formed one for each pixel P. The second storage capacitor Cst2 is for maintaining the compensation voltage φ for a predetermined period. The structure of the pixel P including the sensing TFT T1 and the compensation TFT T2 is not limited to that illustrated in FIG. 6 and may be variously changed. However, for convenience, the following description illustrates that the structure of the pixel P is implemented as shown in FIG. 6. Each pixel P is connected to the data line 14, the gate line 15, and the compensation voltage supply line CL, and in some cases, may be additionally connected to the sensing current supply line SL. Each pixel P is supplied with high and low potential cell driving voltages VDD and VSS from a power generation unit (not shown).

The timing controller 11 rearranges digital video data (RGB) input from the outside according to the resolution of the display panel 10 and supplies it to the data driving circuit 12. In addition, the timing controller 11 is based on timing signals such as a vertical synchronization signal (Vsync), a horizontal synchronization signal (Hsync), a dot clock signal (DCLK), and a data enable signal DE, and the data driving circuit 12 A data control signal DDC for controlling the operation timing of and a gate control signal GDC for controlling the operation timing of the gate driving circuit 13 are generated.

The data driving circuit 12 converts digital video data RGB input from the timing controller 11 into an analog data voltage based on the data control signal DDC and supplies it to the data lines 14. The data driving circuit 12 generates the compensation voltage φ differently according to the sensing current input from the display panel 10, and compensates the compensation voltage φ under the control of the timing controller 11 to the compensation voltage supply line CL To supply. The compensation voltage φ is for compensating for a change in the threshold voltage of the driving TFT DT, and depends on the threshold voltage of the driving TFT DT sensed through the sensing current. The data driving circuit may output a compensation voltage φ suitable for the threshold voltage of the current driving TFT DT by referring to a first look-up table previously set (compensation voltage according to the threshold voltage is stored). The compensation voltage φ may gradually increase as the threshold voltage of the driving TFT DT is shifted to the right (+), and conversely, decrease as the threshold voltage of the driving TFT DT is shifted to the left (-). . Due to the compensation voltage φ, the threshold voltage shift of the driving TFTs is recovered, and the reduction of the driving current due to the threshold voltage shift is compensated.

On the other hand, in the present invention, in order to additionally compensate for the driving current flowing through each pixel P, each pixel measured in the display panel with reference to a preset second lookup table (current compensation data according to the driving current is stored) ( The digital video data RGB supplied to the data driving circuit 12 may be additionally modulated by the timing controller 11 according to the driving current amount of P).

The gate driving circuit 13 generates a scan signal based on the gate control signal GDC. The gate driving circuit 13 supplies the scan signal to the scan signal supply line in a line sequential manner. The gate driving circuit 13 may be directly formed on the display panel 10 according to a gate-driver in panel (GIP) method. The gate driving circuit 13 is a sensing control signal SEN to be supplied to the gate electrode of the sensing TFT T1 under the control of the timing controller 11 and a compensation control signal CP to be supplied to the gate electrode of the compensation TFT T2. Can cause more. The gate driving circuit 13 may supply the sensing control signal SEN to the sensing control signal supply line and the compensation control signal CP to the compensation control signal supply line.

Figure 6 shows the compensation method of the present invention compared to the conventional compensation method.

Referring to FIG. 6, the conventional compensation method senses a threshold voltage shift of the driving TFT DT by sensing a current Ids flowing through the driving TFT DT, and compensates for a compensation voltage corresponding to the threshold voltage increase φ. After greatly modulating the data voltage Vdata, the modulation voltage Vdata+φ was applied to the gate electrode of the driving TFT DT. That is, in the conventional compensation method, when the current characteristic curve of the driving TFT DT is shifted to the right due to an increase in the threshold voltage of the driving TFT DT, the gate-source of the driving TFT DT is maintained while maintaining the shift state. Only the magnitude of the liver voltage was increased. According to the prior art, there is a problem that the threshold voltage of the driving TFT is deteriorated rather quickly due to deterioration compensation.

On the other hand, the compensation method of the present invention senses the threshold voltage shift of the driving TFT DT by sensing the current Ids flowing in the driving TFT DT and drives the compensation voltage φ corresponding to the threshold voltage increase. The threshold voltage shift is restored to the original state by applying to the sub gate electrode of (DT). That is, the compensation method of the present invention, when the current characteristic curve of the driving TFT (DT) is shifted to the right due to the threshold voltage increase of the driving TFT (DT) as shown in FIGS. 8A and 8B, the driving TFT (DT) Is to move the current characteristic curve back to its original position.

To this end, the pixel P of the present invention is a driving TFT (DT) having a double gate type structure to control the current (Ids) flowing through the OLED, and is switched according to the scan signal (SCAN) to drive the TFT (DT) Switch TFT (ST) for applying a data voltage (Vdata) to the main gate electrode of the first storage capacitor (Cst1) is connected between the main gate electrode and the source electrode of the driving TFT (DT) to store the data voltage (Vdata) , A compensation TFT (T2) that is switched according to the compensation control signal (CP) to apply a compensation voltage (φ) to the sub gate electrode of the driving TFT (DT), and between the sub gate electrode and the source electrode of the driving TFT (DT). The second storage capacitor Cst2 may be connected to store the compensation voltage φ. Further, the pixel P of the present invention further includes a sensing TFT T1 that is switched according to the sensing control signal SEN to sense the current flowing in the driving TFT DT and applies the sensing current to the data driving circuit. can do.

The OLED is connected between the high potential cell driving voltage (VDD) and the low potential cell driving voltage (VSS). The main gate electrode of the driving TFT DT is at the first node N1, the sub gate electrode of the driving TFT DT is at the third node N3, the drain electrode is at the high potential cell driving voltage VDD, and The source electrode is connected to the anode electrode of the OLED. The gate electrode of the switch TFT ST is connected to the scan signal supply line, the drain electrode to the data line 14, and the source electrode to the first node N1. The gate electrode of the compensation TFT T2 is connected to the compensation control signal supply line, the drain electrode is connected to the compensation voltage supply line CL, and the source electrode is connected to the third node N3. The gate electrode of the sensing TFT T1 is connected to the sensing control signal supply line, the drain electrode is connected to the second node N2, and the source electrode is connected to the sensing current supply line SL.

7A to 8B show the principle in which the threshold voltage is compensated in the driving TFT (DT).

7A and 7B, the driving TFT DT of the present invention includes a main gate electrode GE1 and a sub-gate electrode GE2 positioned above and below an active layer for forming a current channel, and an active layer. It includes a source electrode (SE) and a drain electrode (DE) that are electrically connected to each other through. The data voltage Vdata is applied to the main gate electrode GE1, and a driving current flowing through the channel is determined according to a potential difference between the main gate electrode GE and the source electrode SE.

When a positive data voltage Vdata is applied to the main gate electrode GE1 for a long time as in FIG. 7A, electrons (-) are concentrated in the channel due to the positive stress accumulated in the main gate electrode GE1 to increase channel resistance. Accordingly, as shown in FIG. 8A, the threshold voltage of the driving TFT DT is shifted from'Vth1' to'Vth2' by'φ', and the current characteristic curve of the driving TFT DT is from'A' to'B' to the right. Shift. As a result, the current flowing between the drain and the source of the driving TFT DT under the same condition is lowered from'I1' to'I2' by'ΔI'.

In this state, when a compensation voltage corresponding to'φ' is applied to the sub-gate electrode GE2 as shown in FIG. 7B, electrons (-) are dispersed in the channel and channel resistance is reduced. Accordingly, as shown in FIG. 8B, the threshold voltage of the driving TFT DT is recovered from'Vth2' to'Vth1' and the current characteristic curve of the driving TFT DT is shifted from'B' to'C' to the left. As a result, the current flowing between the drain and source of the driving TFT DT under the same conditions is compensated by'ΔI' from'I2' to'I1'.

9 shows the electrical characteristics of the double gate type driving TFT (DT).

Referring to FIG. 9, it is shown that as the bias voltage applied to the sub-gate electrode in the double gate type driving TFT (DT) is increased, electrical characteristics of the driving TFT (DT) are changing. When bias voltages applied to the sub-gate electrodes are respectively applied to -30V, -20V, -10V, 0V, 10V, 20V, and 30V, the threshold voltage and current characteristic curve of the driving TFT (DT) are determined by the magnitude of the bias voltage. It shifts to the left in proportion.

10 and 11 show the types of the double gate type driving TFT (DT) capable of bidirectional control.

In the double gate type driving TFT (DT) of the present invention, a coplanar structure (Coplanar) in which the main gate electrode GE1, the source electrode SE, and the drain electrode DE are all positioned on the active layer ACT as shown in FIG. type), including the sub gate electrode GE2 formed under the active layer ACT. Looking specifically at the double gate type driving TFT (DT) made of a coplanar structure, a sub gate electrode GE2 is formed on the substrate GLS, and a buffer layer (a) is formed between the sub gate electrode GE2 and the active layer ACT. BUF) is formed. In addition, the gate insulating film GI, the main gate electrode GE1, and the interlayer insulating film IL are sequentially formed on the active layer ACT layer, and penetrate the interlayer insulating film IL and the gate insulating film GI to pass through the active layer. A source electrode and a drain electrode connected to (ACT) are formed.

In the double gate type driving TFT (DT) of the present invention, as shown in FIG. 11, the main gate electrode GE1, the source electrode SE, and the drain electrode DE are all located under the active layer ACT. Inverted coplanar type) includes a sub gate electrode GE2 formed on the active layer ACT. Looking specifically at the double gate type driving TFT (DT) made of an inverted coplanar structure, the main gate electrode GE1 and the gate insulating layer GI are sequentially formed on the substrate GLS, and are active on the gate insulating layer GI. The layer ACT and the source electrode SE and the drain electrode DE are formed at the same time. Then, a protective layer PASI covering the active layer ACT, the source electrode SE, and the drain electrode DE is formed, and an auxiliary gate electrode GE2 is formed thereon.

12A to 12C sequentially show a threshold voltage compensation process according to the present invention. 12A to 12C, an operation of a pixel in which the sensing TFT T1 is further formed will be described as an example. In the pixel on which the sensing TFT T1 is not formed, only the driving current sensing operation described below is excluded, and the remaining operations are applied as it is.

In the present invention, the switch TFT (ST) is turned on as shown in FIG. 12A to apply and store the data voltage (Vdata) to the first storage capacitor (Cst1) connected to the main gate electrode of the driving TFT (DT). The driving current Ids as shown in FIG. 12B flows between the drain-source of the driving TFT DT due to the voltage across the first storage capacitor Cst1, that is, the gate-source voltage of the driving TFT DT. In this state, the present invention turns on the sensing TFT T1 to sense the driving current Ids flowing in the driving TFT DT and supplies it to the data driving circuit.

The present invention generates a compensation voltage corresponding to the driving current (Ids) in the data driving circuit. Then, the present invention turns on the compensation TFT (T2) to apply and store the compensation voltage to the second storage capacitor (Cst2) connected to the sub-gate electrode of the driving TFT (DT). The threshold voltage shift due to the gate bias stress applied to the main gate electrode is recovered by the compensation voltage applied to the sub gate electrode.

As described above, the present invention includes a double gate type driving TFT having two gate electrodes, and a compensation voltage corresponding to a change in threshold voltage of the driving TFT is applied to the sub electrode of the driving TFT to restore the threshold voltage shift. Order. Accordingly, the present invention solves a conventional problem in which deterioration is accelerated in the compensation process and the compensation range is limited. The present invention can effectively compensate for the threshold voltage deterioration, prevent driving failure due to long-term driving, improve reliability, and increase the uniformity of luminance to significantly extend the life of the product.

Through the above description, those skilled in the art will appreciate that various changes and modifications are possible without departing from the technical idea of the present invention. Therefore, the technical scope of the present invention should not be limited to the contents described in the detailed description of the specification, but should be determined by the scope of the claims.

10: display panel 11: timing controller
12: data driving circuit 13: gate driving circuit
14: data line 15: gate line

Claims (4)

A display panel that displays an image including a plurality of pixels; And
And a data driving circuit that generates a compensation voltage and supplies it to the display panel;
Each of the pixels,
Organic light emitting diodes;
A driving TFT formed of a double gate type having a main gate electrode connected to a first node and a sub gate electrode connected to a third node, and generating a driving current;
A switch TFT connected between a data line and the first node to apply a data voltage for determining the driving current to the main gate electrode of the driving TFT;
A storage capacitor connected to the second node and the third node between the source electrode of the driving TFT and the organic light emitting diode to store the compensation voltage;
A compensation TFT connected to the sub gate electrode of the driving TFT and applying the compensation voltage for compensating the threshold voltage shift of the driving TFT to the sub gate electrode of the driving TFT; And
And a sensing TFT connected between the second node and a sensing current supply line,
The storage capacitor has a first terminal connected to the sub-gate electrode of the driving TFT and the compensation TFT to maintain the compensation voltage, and a second terminal directly connected to the sensing TFT and the organic light emitting diode,
During the first period, the switch TFT is turned on and the sensing TFT and the compensation TFT are turned off, so that the driving current flows through the driving TFT,
During the second period following the first period, the sensing TFT is turned on and the switch TFT and the compensation TFT are turned off, so that the data driving circuit is a part of the driving current through the sensing TFT and the sensing current supply line. The first voltage is sensed to generate the compensation voltage,
During the third period following the second period, the compensation TFT is turned on and the switch TFT and the sensing TFT are turned off, so that the data driving circuit supplies the compensation voltage to the sub of the driving TFT through a compensation voltage supply line. Applied to a gate electrode to restore the threshold voltage shift of the driving TFT to its original state,
The magnitude of the compensation voltage is determined according to the threshold voltage shift amount of the driving TFT,
The driving current flowing through the driving TFT during the second period is
The first current applied from the second node to the sensing TFT and the second current applied from the second node to the organic light emitting diode are distributed.
The amount of threshold voltage shift of the driving TFT is an organic light emitting display device reflected in the first current. delete delete According to claim 1,
The first current is a part of the driving current flowing between the drain-source of the driving TFT.

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