KR100623919B1 - Oled - Google Patents

Abstract

The present invention provides an organic light emitting diode that emits light by an output current, a storage capacitor that stores a specific voltage proportional to an increase in a data signal and a threshold voltage applied through a data line, and is connected between a power supply voltage and an organic light emitting diode. A driving thin film transistor which supplies an output current with a threshold voltage compensated to the organic light emitting diode by using a data signal stored in the storage capacitor and a specific voltage proportional to the rise of the threshold voltage, and between the gate and the data line of the driving thin film transistor. An organic light emitting display device including an input switching unit connected to a gate and connected to a first scan line to transfer a data signal applied through a data line by a first scan signal applied through the first scan line. do.

Organic electroluminescence, threshold voltage, storage capacitor

Description

Organic electroluminescent device {OLED}

1 is an equivalent circuit diagram of a conventional active matrix organic light emitting display device.

2 is a graph showing changes in voltage-current characteristics due to deterioration of a driving thin film transistor of an active matrix organic light emitting display device according to the related art.

3 is a driving timing diagram illustrating a kickback phenomenon of a conventional active matrix organic light emitting display device.

4 is an equivalent circuit diagram of an organic light emitting display device according to a first embodiment of the present invention.

5 is a driving timing diagram of the organic light emitting display device of FIG. 4.

6 is an equivalent circuit diagram of an organic light emitting display device according to a second embodiment of the present invention.

The present invention relates to an organic electroluminescent device.

Organic light emitting diodes (OLEDs) were self-luminous devices that emit fluorescent materials by recombination of electrons and holes. The organic light emitting display device including the organic light emitting display device is wall-mounted or portable because the response speed is faster, the DC driving voltage is lower, and the ultra thin film is possible than the passive light emitting device which requires a separate light source like the liquid crystal display device. Application was possible.

Such an organic light emitting display device implements color using pixels in which red, blue, and green subpixels represent one color. At this time, the organic light emitting diode is an active matrix organic light emitting diode (active matrix) which is a method of driving using a simple matrix type organic light emitting diode (PMOLED) and a thin film transistor (TFT) as a method of driving a subpixel. OLED, AMOLED).

As the driving method of the active matrix organic light emitting diode (AMOLED), there are a current driving method, a voltage driving method, and a digital driving method.

1 is an equivalent circuit diagram of a conventional active matrix type organic electroluminescent device of a current driving method.

Conventional current drive type active matrix organic light emitting display device 10 is a 2T1C (two TFT and one capacitor) pixel composed of driving thin film transistor DT, switching thin film transistor ST, and storage capacitor Cst. Or pixel structure. At this time, the driving and switching thin film transistors DT and ST were n-type MOS transistors.

In addition, the conventional organic light emitting display device 10 includes an organic light emitting diode (OLED) of an organic light emitting layer formed between the charge transport layer. The organic light emitting diode OLED was formed between the power supply voltage VDD and the driving thin film transistor DT. The organic light emitting diode OLED emits light corresponding to the amount of the output current I _OLED applied from the driving thin film transistor DT.

The driving thin film transistor DT was formed between the organic light emitting diode OLED and the ground power supply GND, and a gate thereof was connected to one end of the storage capacitor Cst. The driving thin film transistor DT is a driving thin film transistor (Driving Transistor) for supplying an output current I _OLED to the organic light emitting diode OLED.

The switching thin film transistor ST is connected between the driving thin film transistor DT and the data line 12, and a gate thereof is connected to the scan line 14. Therefore, when the scan signal is applied to the gate of the switching thin film transistor ST through the scan line 14, the switching thin film transistor ST is turned on to apply and store a data signal to the gate of the driving thin film transistor DT. The data signal is stored in the capacitor Cst.

The storage capacitor Cst stores the data signal switched by the switching thin film transistor ST, but the scan signal is erased so that the driving thin film transistor DT is stored by the stored data signal even when the switching thin film transistor ST is turned off. Was turned on.

As a result, the conventional organic light emitting display device 10 stores the data signal in the storage capacitor Cst and drives the driving thin film transistor DT with the stored data signal, thereby emitting organic light with an output current I _OLED corresponding to the data signal. The diode OLED was emitted.

However, as the conventional organic light emitting device 10 uses the driving thin film transistor DT, deterioration occurs due to various causes. Thus, as shown in FIG. 2, the driving thin film transistor DT has a problem in that the voltage-current characteristic curve is shifted to the right to increase the threshold voltage Vth. For example, the threshold voltage (Vth) increased from 2V to 2.5V.

Accordingly, in the conventional organic light emitting diode 10, as the threshold voltage Vth increases, the output current I _OLED of the driving thin film transistor DT decreases as shown in Equation 1, thereby decreasing the luminance of the organic light emitting diode OLED. Dropped.

Here, I _OLED is the output current of the driving thin film transistor DT, β is the constant of the driving thin film transistor DT, Vgs is the source-gate voltage of the driving thin film transistor DT, and Vth is the driving thin film transistor ( The threshold voltage of DT) is shown.

Therefore, since the organic light emitting diode 10 reduces the luminance of the organic light emitting diode OLED due to an increase in the threshold voltage Vth, the lifespan of the organic light emitting display device composed of the conventional organic light emitting diodes 10 is reduced. It has caused a fatal problem of reducing.

3 is a driving timing diagram illustrating a kickback phenomenon of a conventional active matrix organic light emitting display device.

Referring to FIG. 3, in the conventional organic light emitting display device 10, when a scan signal is applied to the switching thin film transistor ST through the scan line 14, the data signal switched to the switching thin film transistor DT is erased. There was a problem in that a kickback phenomenon in which the magnitude is instantaneously reduced due to the cancellation of the scan signal. As shown in FIG. 3, when the scan signal is erased, the data signal drops instantaneously, and as a result, the amount of the output current I _OLED of the driving thin film transistor DT output to the organic light emitting diode OLED is dropped. It caused a problem of lowering the luminance.

As a result, the conventional organic light emitting display device 10 has a fatal problem in that its lifespan is low due to deterioration and kickback of the driving thin film transistor DT.

The present invention has been made to solve the above problems, and an object of the present invention is to provide an organic light emitting diode that does not degrade luminance even when the driving thin film transistor is deteriorated by compensating the threshold voltage of the driving thin film transistor.

Another object of the present invention is to provide an organic light emitting display device capable of reducing kickback in which a data signal is shaken by erasing a scan signal.

In order to achieve the above technical problem, the present invention, an organic light emitting diode that emits light by an output current, a storage capacitor unit for storing a specific voltage in proportion to the rise of the data signal and the threshold voltage applied through the data line, and a power supply A driving thin film transistor connected between the voltage and the organic light emitting diode and supplying the output current compensated with the threshold voltage to the organic light emitting diode by using a specific voltage proportional to the increase in the threshold voltage and the data signal stored in the storage capacitor. An input switching part connected between the gate and the data line of the thin film transistor and having a gate connected to the first scan line to transfer a data signal applied through the data line by a first scan signal applied through the first scan line. It provides an organic electroluminescent device comprising.

In this case, the driving thin film transistor, the input switch unit, and the threshold voltage compensator may be an n-type MOS transistor.

In still another aspect, the present invention provides an organic light emitting diode that emits light by an output current, a storage capacitor unit for storing a specific voltage proportional to an increase in a data signal and a threshold voltage applied through a data line, a ground voltage and an organic light source. A driving thin film transistor which is connected between the light emitting diodes and supplies an output current of which the threshold voltage is compensated to the organic light emitting diode by using a data signal stored in the storage capacitor and a specific voltage proportional to the increase of the threshold voltage. And an input switching unit connected between the gate and the data line, the gate being connected to the first scan line to transfer the data signal applied through the data line by the first scan signal applied through the first scan line. An organic electroluminescent device is included.

In this case, the driving thin film transistor, the input switch unit, and the threshold voltage compensator may be a p-type MOS transistor.

Meanwhile, the storage capacitor unit includes a first storage capacitor formed between the source and the gate of the driving thin film transistor and a second storage capacitor formed between the drain and the gate of the driving thin film transistor, and between the second storage capacitor and the drain of the driving thin film transistor. The display device may further include a second switching thin film transistor unit connected to the second scan line and activated by a second scan signal applied through the second scan line.

In addition, the first scan line and the second scan line may be the same line, and the first scan signal and the second scan signal may be the same signal.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

Example 1

4 is an equivalent circuit diagram of an organic light emitting display device according to a first embodiment of the present invention.

Referring to FIG. 4, the active matrix type organic light emitting display device 20 according to the first embodiment of the present invention may include a driving thin film transistor DT, first and second switching thin film transistors ST1 and ST2, and first and second thin film transistors. Second storage capacitors Cst1 and Cst2 and an organic light emitting diode OLED are included. At this time, the driving and first and second switching thin film transistors DT, ST1 and ST2 were n-type MOS transistors. The driving and first and second switching thin film transistors DT, ST1 and ST2 are amorphous silicon thin film transistors (a-Si TFTs).

The organic light emitting diode OLED includes an organic light emitting layer formed between the charge transport layers and emits light by recombination of electrons and holes. The organic light emitting diode OLED is formed between the power supply voltage VDD and the driving thin film transistor DT. The organic light emitting diode OLED emits light corresponding to the amount of the output current I _OLED applied from the driving thin film transistor DT. The organic light emitting diode OLED may be formed of various stacked structures and light emitting materials, but a detailed description thereof will be omitted.

The driving thin film transistor DT is formed between the organic light emitting diode OLED and the ground power supply GND, and a gate thereof is connected to one end of the first storage capacitor Cst2 and the second storage capacitor Cst2. The driving thin film transistor DT is a driving thin film transistor which supplies an output current I _OLED to the organic light emitting diode OLED.

In particular, in the driving thin film transistor DT, the second switching thin film transistor ST2 and the second storage capacitor Cst2 are formed in series between the drain and the gate, and the first storage capacitor Cst1 is formed between the gate and the source. Formed. As a result, when the drain voltage of the driving thin film transistor DT increases, the gate voltage of the driving thin film transistor DT also increases when the second switching thin film transistor ST2 is turned on.

The first switching thin film transistor ST1 is connected between the gate of the driving thin film transistor DT and the data line 22, and the gate is connected to the scan line 24. Therefore, when a scan signal is applied to the gate of the first switching thin film transistor ST1 through the scan line 24, the first switching thin film transistor ST1 is turned on to provide a data signal to the gate of the driving thin film transistor DT. Is applied to store the data signal in the first storage capacitor Cst.

As described above, the second switching thin film transistor ST2 is formed between the drain of the driving thin film transistor DT and the other end of the second storage capacitor, and a gate thereof is connected to the scan line 24. When the scan signal is applied through the scan line 24 to turn on the second switching thin film transistor ST2, the second switching thin film transistor ST2 stores the drain voltage of the driving thin film transistor DT by the first storage capacitor. Distributes between (Cst1) and the second storage capacitor (Cst2).

The first storage capacitor Cst1 stores the data signal switched by the first switching thin film transistor ST1, but the scan signal is erased so that the first and second switching thin film transistors ST1 and ST2 are stored even when the first and second switching thin film transistors ST1 and ST2 are turned off. The driving thin film transistor DT is driven by the data signal.

In this case, the driving thin film transistor DT supplies the output current I _OLED corresponding to the data signal stored in the first storage capacitor Cst to the organic light emitting diode OLED.

The second storage capacitor Cst2 is connected to the gate of the driving thin film transistor DT and the second switching thin film transistor Cst2.

5 is a driving timing diagram of the organic light emitting display device of FIG. 4. A deterioration compensation principle of the organic light emitting display device 20 according to the first embodiment of the present invention will be described with reference to FIGS. 4 and 5.

4 and 5, when the driving thin film transistor DT is deteriorated, the threshold voltage Vth of the driving thin film transistor DT is increased. When the threshold voltage Vth rises, the output current I _OLED decreases as can be seen from Equation 1. Reduction of the output current I _OLED decreases the voltage across the organic light emitting diode OLED, so that one end of the organic light emitting diode OLED and one end of the second thin film transistor ST2 and the driving thin film transistor DT are reduced. The voltage of node A, which is a common node of the drain, is increased.

When the scan signal is applied to the gates of the first and second switching thin film transistors ST1 and ST2, the data signal is applied to the gate of the driving thin film transistor DT and the voltage of the node A is simultaneously applied to the first storage capacitor Cst1 and the first storage capacitor CST1. 2 is distributed to the storage capacitor Cst2. Therefore, the gate voltage of the driving thin film transistor DT or the voltage of the node B becomes the voltage of the node A distributed as shown in Equation 2 to the data voltage.

In Equation 2, V _B is the gate voltage or the voltage of the node B of the driving thin film transistor, V _D is the data signal or data voltage, Cst1 and Cst2 is the capacitance of the first and second storage capacitors, V _A Denotes the voltage of node A.

As can be seen from Equations 1 and 2, deterioration of the driving thin film transistor DT increases the threshold voltage Vth to reduce the output current I _OLED , but decreases the gate voltage of the driving thin film transistor DT. As a result, the threshold voltage Vth is compensated for.

In particular, it is preferable that Cst1 and Cst2 are set so that the capacitance of the first and second storage capacitors can compensate for the output current I _OLED which decreases due to the increase of the threshold voltage Vth.

Therefore, even if the driving thin film transistor DT is deteriorated and the threshold voltage Vth is increased, the output current I _OLED may be maintained at a constant amount to maintain a constant luminance of the organic light emitting diode OLED.

In addition, since the gate voltage of the driving thin film transistor DT increases, a kickback phenomenon in which the data voltage fluctuates when the scan signal is erased may compensate for an increase in the gate voltage of the driving thin film transistor DT.

Example 2

6 is an equivalent circuit diagram of an organic light emitting display device according to a second exemplary embodiment of the present invention.

Referring to FIG. 6, the organic light emitting display device 30 according to the second exemplary embodiment of the present invention includes a driving thin film transistor DT, first and second switching thin film transistors ST1 and ST2, and first and second storages. Capacitors Cst1 and Cst2 and organic light emitting diodes OLED are the same as the organic light emitting diode 20 according to the first embodiment, but are driven and first and second switching thin film transistors DT and ST1. , ST2) are different in that they are p-type MOS transistors. However, the driving and first and second switching thin film transistors DT, ST1 and ST2 are amorphous silicon thin film transistors (a-Si TFTs).

Meanwhile, the driving thin film transistor DT, the first and second switching thin film transistors ST1 and ST2, and the first and second storage capacitors Cst1 and Cst2 have the same role.

At this time, the organic light emitting diode 30 according to the second embodiment of the present invention, in order to perform the same operation as the organic light emitting diode 20 according to the first embodiment consisting of n-type MOS transistors, organic light emitting diode The OLED is formed between the driving thin film transistor DT and the ground power supply GND, and the first storage capacitor Cst is between the source and the gate of the driving thin film transistor DT, and the second storage capacitor Cst2 is formed. Is formed between the gate and the drain of the driving thin film transistor DT, and the second switching thin film transistor ST2 is formed between the second storage capacitor Cst2 and the drain of the driving thin film transistor DT.

Similarly to the organic light emitting diode 20 according to the first exemplary embodiment of the present invention, when the driving thin film transistor DT is deteriorated and the threshold voltage Vth is increased, the gate voltage of the driving thin film transistor DT is equal to the equation (2). It rises together to compensate for the threshold voltage (Vth).

Embodiments of the present invention have been described above with reference to the drawings, but the present invention is not limited thereto.

In the above embodiments, the gates of the first and second switching thin film transistors ST1 and ST2 are connected to the same scan line, so that the same scan signal is applied to the gates of the first and second switching thin film transistors ST1 and ST2. However, gates of the first and second switching thin film transistors ST1 and ST2 are connected to different scan lines, respectively, so that different scan signals may be applied.

In the above embodiments, the driving and the first and second switching thin film transistors DT, ST1 and ST2 are described as amorphous silicon thin film transistors (a-Si TFTs), but these are hot or low temperature polysilicon crystallized by a laser excimer or the like. It may be a thin film transistor (LTPS, HTPS).

In the above embodiments, the driving and the first and second switching thin film transistors DT, ST1, and ST2 are described as one each, but may be configured as a plurality of thin film transistors to perform the same function.

In the above embodiments, the driving and first and second switching thin film transistors DT, ST1, and ST2 are respectively described as mode p-type or n-type MOS thin-film transistors, but they may be a mixture of p-type and n-type. .

Although the embodiments of the present invention have been described above with reference to the accompanying drawings, those skilled in the art to which the present invention pertains may be embodied in other specific forms without changing the technical spirit or essential features of the present invention. I can understand that. Therefore, since the embodiments described above are provided to fully inform the scope of the invention to those skilled in the art, it should be understood that they are exemplary in all respects and not limited. The invention is only defined by the scope of the claims.

By such a configuration, the present invention has the effect of compensating the threshold voltage of the driving thin film transistor so that the luminance does not decrease even when the driving thin film transistor is deteriorated.

In addition, the present invention also has the effect of reducing the kickback shake of the data signal by the erase of the scan signal.

Accordingly, the lifetime of the device, which is a key factor of the organic light emitting device, can be improved.

Claims (6)

An organic light emitting diode emitting light by an output current; A storage capacitor unit configured to store a specific voltage proportional to an increase in a threshold voltage and a data signal applied through the data line; A driving voltage is connected between a power supply voltage and the organic light emitting diode and supplies an output current of which the threshold voltage is compensated to the organic light emitting diode by using a data signal stored in the storage capacitor and a specific voltage proportional to the increase of the threshold voltage. A thin film transistor; A data signal applied through the data line by a first scan signal connected between the gate of the driving thin film transistor and the data line, and the gate is connected to the first scan line. An organic light emitting device comprising an input switching unit for transmitting. An organic light emitting diode emitting light by an output current; A storage capacitor unit configured to store a specific voltage proportional to an increase in a threshold voltage and a data signal applied through the data line; A drive connected to a ground voltage and the organic light emitting diode and supplying the organic light emitting diode to an output current compensated with the threshold voltage using a specific voltage proportional to a rise of the data signal stored in the storage capacitor and the threshold voltage. Thin film transistor; A data signal applied through the data line by a first scan signal connected between the gate of the driving thin film transistor and the data line, and the gate is connected to the first scan line. An organic light emitting device comprising an input switching unit for transmitting. The method of claim 1, The driving thin film transistor, the input switch unit, and the threshold voltage compensating unit are n-type MOS transistors. The method of claim 2, The driving thin film transistor, the input switch unit, and the threshold voltage compensating unit are p-type MOS transistors. The method according to claim 3 or 4, The storage capacitor unit includes a first storage capacitor formed between the source and the gate of the driving thin film transistor, and a second storage capacitor formed between the drain and the gate of the driving thin film transistor, A second switching thin film transistor portion connected between the second storage capacitor and the drain of the driving thin film transistor and having a gate connected to the second scan line and activated by a second scan signal applied through the second scan line; Organic electroluminescent device comprising a. The method of claim 5, And the first scan line and the second scan line are the same line, and the first scan signal and the second scan signal are the same signal.

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