KR20080061823A - Bias-aging method and the circuit structure for amoled - Google Patents

Abstract

A bias-aging method and a circuit structure for an AMOLED(Active Matrix Organic Light Emitting Diode) are provided to stabilize characteristics of a display device using an organic light emitting device by accurately forming off-stress in a source electrode of the device for bias-aging. A bias-aging method of a display device using an AMOLED includes the steps of: applying a first signal to a gate electrode of a switching transistor(S-TFT); applying a second signal for forming off-stress between a gate and a source to a source electrode of the switching transistor in response to the first signal; and applying a third signal for forming off-stress between a drain and a source to a drain electrode of the switching transistor in response to the first signal.

Description

Bias aging method and aging circuit structure of display device using active organic light emitting display device

1 is an equivalent circuit diagram of one pixel of a typical AMOLED implemented as a PMOS device.

FIG. 2 is a graph illustrating the drain-source current Ids according to the gate-source voltage Vgs of the above-described transistor.

3 is a waveform diagram and an equivalent circuit diagram of one pixel for explaining a method of forming off-stress of a display device using an AMOLED according to an exemplary embodiment of the present invention.

4 is a block diagram schematically illustrating a part of a display panel in a display apparatus using an organic light emitting display device according to an exemplary embodiment of the present invention.

5A is an equivalent circuit diagram illustrating an equivalent circuit structure for performing bias aging for pixels in a display device using an AMOLED according to the present invention.

5B is a waveform diagram illustrating waveforms of an operation signal of FIG. 5A.

6 is a current-voltage curve graph of a switching transistor changed according to a preferred embodiment of the present invention.

7 is an equivalent circuit diagram illustrating an example in which technical matters of the present invention can be applied to other types of PMOS devices.

<Description of the symbols for the main parts of the drawings>

GL1 to GLn: gate line DL1 to DLm: data line

P1 to P8: Pixel area S-TFT: Switching transistor

D-TFT: Driving Transistor Cst: Storage Capacitor

N1: N1 node OLED: light emitting diode

VDD: Power Supply Voltage

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a display device using AMOLED, and more particularly, to a bias aging method and a circuit structure of a switching device and an organic light emitting device included in a circuit using AMOLED.

Recently, as the information society has progressed rapidly, a display field for processing and displaying a large amount of information has been developed.

Until recently, cathode ray tube (CRT) has become the mainstream of display devices, and has been continuously developing, but recently, the necessity of flat panel display is required to meet the times of miniaturization, light weight and low power consumption. It has emerged. As a result, a thin film transistor-liquid crystal display device (hereinafter referred to as TFT-LCD) having excellent color reproducibility, an electron injection electrode and a hole injection electrode Injects electrons and holes from the anode into the light emitting layer, respectively, and emits light when the exciton of the injected electrons and holes falls from the excited state to the ground state. An organic light emitting display device using an electroluminescent device (OLED) has been developed.

The thin film transistor type liquid crystal display device and the organic light emitting display device use a thin film transistor as a switching element or a driving element for its operation, and the thin film transistor is formed at a low temperature on a large insulating substrate such as a low cost glass substrate. Amorphous Silicon Thin Film Transistors (a-Si: H TFTs), in which semiconductor layers are formed of amorphous silicon, have become mainstream, but in recent years, high-resolution displays can be realized. The use of poly-silicon thin-film transistors with relatively low prices is increasing.

As described above, the thin film transistor and the organic light emitting diode (hereinafter referred to as the organic light emitting diode) used in the display device are driven by the leakage current (I _off ) generated by the moving electrons in the PN junction part when driven at room temperature for a long time. Afterimages occur on an image surface of a display device panel using TFT-LCDs and OLEDs, and continuous afterimages cause pixel defects.

1 is an equivalent circuit diagram of one pixel of a typical AMOLED implemented as a PMOS device.

As shown, one pixel of a typical AMOLED includes a switching transistor (S-TFT), a driving transistor (D-TFT), a storage capacitor (Cst), and light emission provided at intersections of gate lines and data lines. It is composed of a diode (OLED).

Referring to the operation of the AMOLED schematically, when the low-level gate driving signal Vg is applied through the gate line, the switching transistor S-TFT connected thereto is turned on. After that, a data signal in the form of a voltage is input to the data line, and a voltage corresponding to the data signal is charged in the storage capacitor Cst, and a current corresponding to the data signal is emitted through the driving transistor D-TFT. It flows through the diode OLED to display an image.

Subsequently, when a high-level gate driving signal Vg is applied through the gate line, the switching transistor S-TFT is turned off and the data is stored in the storage capacitor Cst. The voltage corresponding to the signal is discharged to maintain the current flowing through the light emitting diode OLED for one frame.

However, the above-described switching transistor S-TFT causes a predetermined amount of current to flow due to leakage-current generated during turn-off, and thus is applied to the gate electrode of the driving transistor D-TFT. As a result, the gate-source voltage Vgs of the driving transistor D-TFT changes.

Accordingly, the amount of current flowing through the light emitting diode OLED, which is determined by the gate-source voltage Vgs, is changed, which is a major cause of various image quality defects of the display panel.

FIG. 2 is a graph illustrating the drain-source current Ids according to the gate-source voltage Vgs of the above-described transistor.

As shown, the amount of drain-source current Ids is determined according to the gate-source voltage Vgs, especially when the gate-source voltage Vgs is 0 or less, that is, the thin film transistor is turned-on. In the off state, the magnitude (a) of the leakage current flowing through the thin film transistor is large enough to affect the quality of the image.

Therefore, in order to reduce the leakage current, a bias aging for reducing leakage current and improving mobility of the PMOS device by applying off stress to a plurality of input terminals of a cell in a polysilicon TFT-LCD. Aging process is performed.

In the conventional bias aging process, a separate aging circuit is used to apply a predetermined voltage corresponding to a stress condition to the gate electrode and the drain electrode of the thin film transistor, but the source electrode is in a floating state. The exact gate-source voltage (Vgs) and drain-source voltage (Vds) could not be known, and thus the desired result was not obtained.

As described above, the present invention has been made to maximize the efficiency of the bias aging process for improving image quality defects caused by leakage current generated in an off-state thin film transistor in a display panel to which an AMOLED device is applied. No additional circuit configuration is needed on the circuit, and a method for applying off stress to a PMOS device is proposed.

In order to achieve the above object, the bias aging method of the display device using the AMOLED according to a preferred embodiment of the present invention, a plurality of pixel areas defining a plurality of gate lines and data lines cross each other; A switching transistor having a gate electrode connected to the gate line, a source electrode connected to the data line, and a drain electrode connected to a power supply voltage terminal; An AAMOLED is defined as one pixel including a driving transistor having a gate electrode interposed therebetween, a driving transistor connected to a drain electrode of the switching transistor, a source electrode connected to a source electrode, and a light emitting diode disposed on the drain electrode. A bias aging method of a display device, comprising: applying a first signal to a gate electrode of the switching transistor; Applying a second signal to a source electrode of the switching transistor to form a gate-source off-stress in response to the first signal; And applying a third signal to form a drain-source off-stress in response to the first signal to the drain electrode of the switching transistor.

The switching and driving transistor is characterized in that the PMOS.

The applying of the first signal to the gate electrode of the switching transistor may include applying the first signal through the gate line; Turn-on the switching transistor (Turn-On) is characterized in that it comprises.

The first signal is a voltage signal having a level of -15V.

The second signal is a voltage signal having a level of + 10V.

Applying a third signal forming a drain-source off-stress in response to the first signal to a drain electrode of the switching transistor; Turning off the switching transistor; And applying the third signal through the data line.

The third signal has the same frequency and different phases as the second signal.

The fourth signal is a voltage signal having a level of + 20V.

In order to achieve the above object, a display device using an AMOLED according to a preferred embodiment of the present invention, a plurality of pixel areas defining a plurality of gate lines and data lines cross each other; A switching transistor having a gate electrode connected to the gate line, a source electrode connected to the data line, and a drain electrode connected to a power supply voltage terminal; AMOLED is defined as one pixel including a driving transistor having a gate electrode interposed between the storage capacitor, a drain electrode of the switching transistor, a source electrode connected to a source electrode, and a light emitting diode disposed at the drain electrode. A display device comprising: a gate driver connected to the gate line to turn on / off the switching transistor; And a data driver connected to the data line to adjust a magnitude of a current flowing through the light emitting diode.

Hereinafter, a bias aging method of a display apparatus using an AMOLED according to an embodiment of the present invention will be described with reference to the accompanying drawings.

3 is a waveform diagram and an equivalent circuit diagram of one pixel for explaining a method of forming off-stress of a display device using an AMOLED according to an exemplary embodiment of the present invention.

As shown, first, by using a gate driver (not shown), the gate driving signal Vgn of the low signal is applied to the gate electrode of the switching transistor S-TFT through the gate line GLn, thereby turning the gate electrode. Turn-On and apply a data signal Vdata of a predetermined voltage to the drain electrode of the switching transistor S-TFT through the data line DLm. At this time, the voltage level of the gate driving signal Vgn should apply a voltage signal having a level capable of forming off-stress between the data signal of the predetermined voltage and the gate-source Vgs.

 Thereafter, a gate driving signal Vgn of a high signal is applied to the switching transistor S-TFT, turned off, and applied to the drain electrode through a data line DLm. The reverse phase voltage of the voltage is applied to form an off-stress condition between the drain and the source Vds.

Such driving is realized by the control of the gate and data drivers 20 and 30, and of course, the bias aging process equipment may be used before mounting the gate and data drivers 20 and 30 as in the related art.

4 is a block diagram schematically illustrating a part of a display panel in a display apparatus using an organic light emitting display device according to an exemplary embodiment of the present invention.

As shown in the drawing, the display panel 10 includes a plurality of gate lines GL1 to GL4, gate drivers 20 driving the plurality of data, and a plurality of data. The pixel portion P, which is formed separately in a matrix type region defined by crossing the lines DL1 to DL4 and the data driver 30 driving the lines DL1 to DL4 and the gate lines GL1 to GL4 and the data lines DL1 to DL4. It is composed of

In general, in order to perform the bias aging process, before the gate and the data drivers 20 and 30 are mounted, aging process equipment is connected to turn off a predetermined voltage through the gate line GL and the data line DL. -The method of applying the stress (Off stress) is used, but in the present invention, after mounting the gate and the data drivers (20, 30), the driving and applying the off-stress (Off stress) is the biggest feature.

Hereinafter, the bias aging method of the display device using the AMOLED according to a preferred embodiment of the present invention through the specific drawings as follows.

FIG. 5A is an equivalent circuit diagram illustrating an equivalent circuit structure for performing bias aging for pixels in a display device using an AMOLED according to the present invention, and FIG. 5B is a waveform diagram illustrating waveforms of an operation signal of FIG. 5A.

In the following description, for the sake of convenience, operations of the pixels connected to the four gate lines GL1 to GL4 and the data lines DL1 to DL4 enabled in synchronization with the first to fourth clock signals CLK1 to CLK4 are performed. Describe the bias aging method.

First, each pixel P1 to P8 has a gate electrode connected to the gate lines GL1 to GLn, a source electrode connected to the data lines DL1 to DLm, and a drain electrode connected to the N1 node N1. A driving transistor (D-) having a switching transistor (S-TFT), a gate electrode connected to the N1 node (N1), a source electrode connected to a power supply voltage (VDD) terminal, and a drain electrode connected to a diode (OLED). TFT and a storage capacitor Cst provided between the switching transistor S-TFT and the source electrode of the driving transistor D-TFT.

First, the first to fourth clock signals CLK1 to CLK4 having a low voltage are sequentially applied to the gate driver 20 of FIG. 3, so that the gate driver 20 of FIG. 3 synchronizes the gate driving. The signals Vg1 to Vg4 are applied to the pixels P1 to P4 through the gate lines GL1 to GL4.

This operation is similar to the general four clock CLK4 driving gate driver, except that the voltage level of the supplied gate driving signal is a specific level of voltage for off-stress.

In this case, the voltage level of the gate driving signals Vg1 to Vg4 is + 20V when the high signal is high, and -15V when the low signal is low.

In addition, the data driver 30 of FIG. 3 transmits the data signal odd / even Vdata to each pixel pixel P1 to P8 through the data lines DL1 to DLm in synchronization with the gate driving signals Vg1 to Vg4. Is authorized.

This operation is also similar to a general data driver, except that the voltage level of the supplied data signal is not a voltage level corresponding to gray scale, but a voltage of a specific level for off-stress, which is a high signal. In the case of + 10V, and in the case of a low signal, it is preferably -10V. The data signal is divided into odd and even according to corresponding data lines DL1 to DLm. These odd / even data signals each have the same frequency and different phases.

Referring to the form of the signal waveform applied to each pixel in more detail, first and second pixels P1 and P2 connected to the first gate line GL1 in synchronization with the first clock signal CLK1. A low signal of -15V is applied to the gate electrode of the switching transistor S-TFT, and the switching transistor S-TFT is turned on. Subsequently, when an odd / even Vdata of + 10V / -10V is input through the data lines DL1 to DLm, the source of the switching transistor S-TFT of the first pixel P1 is input. A voltage of +10 V is applied to the drain electrode, and a voltage of -10 V is applied to the source and drain electrodes of the switching transistor S-TFT of the second pixel P2.

Subsequently, in synchronization with the second clock signal CLK2, the gate electrode of the switching transistor S-TFT of the third and fourth pixels P3 and P4 connected to the second gate line GL1 may be -15V. A low signal is applied and the switching transistor S-TFT is turned on.

At the same time, a + 20V high signal is applied to the gate electrodes of the switching transistors S-TFT of the first and second pixels P1 and P2 connected to the first gate line GL1. The switching transistor S-TFT is turned off.

Subsequently, when an odd / even Vdata of -10V / + 10V is input through the data lines DL1 to DLm, the source of the switching transistor S-TFT of the third pixel P3 is input. And a -10V voltage is applied to the drain electrode, and a + 10V voltage is applied to the source and drain electrodes of the switching transistor S-TFT of the fourth pixel P4.

In addition, a + 10V voltage applied to the drain electrode of the switching transistor S-TFT of the first pixel P1 is stored in the storage capacitor Cst, and a -10V voltage is applied to the source electrode. In addition, a pre-applied -10V voltage is stored in the storage capacitor Cst to the drain electrode of the switching transistor S-TFT of the second pixel P2, and a + 10V voltage is applied to the source electrode.

Accordingly, the switching transistors S-TFT of the first and second pixels P1 through P2 may have the aforementioned gate-source (Vgs) stress conditions (Vgs = 10V) and drain-source (Vds) stress conditions ( Vds = -20V) is satisfied to form off-stress.

Thereafter, in synchronization with the third clock signal CLK3, the switching transistors S-TFT of the third and fourth pixels P3 and P4 are turned off in the same manner as the first and second pixels of the previous clock CLK2. -The off-stress is formed, and in the case of the clock CLK4, the off-stress is formed in the same manner as described above.

Accordingly, the gate and data drivers may be controlled without the need for a separate bias-aging process, thereby forming a more accurate off-stress.

Although the equivalent circuit diagram described above uses a P-type transistor, the equivalent circuit structure is not very different from that of using an N-type transistor, and it is applied to a kind of device capable of obtaining a bias aging effect in only one process. There is only a relationship.

FIG. 6 is a current-voltage curve graph of a switching transistor that is changed according to a preferred embodiment of the present invention. As shown in FIG. 6, when the voltage difference between the gate and source Vgs is 0, a leakage current having a predetermined magnitude is shown. When the voltage difference between the gate and the source Vgs is 0, the current-voltage curve of the switching transistor S-TFT having the first curve characteristic is hardly present.

7 is an equivalent circuit diagram illustrating an example in which technical matters of the present invention can be applied to other types of PMOS devices.

As shown in the figure, since the liquid crystal display device (a) has a voltage driving type similar to the pixel of the AMOLED in the embodiment of the present invention, the off-stress between the gate and the source Vgs is considered. As a result, the first thin film transistor T1 may be turned on, and a drain-source-off-stress may be applied, and the technical matters of the present invention may be applied.

In addition, the present invention can be applied to the case of the display device (b) using the current programming AMOLED. Referring to the drawings, a general current programming scheme includes a structure in which one pixel includes first and second switching transistors S1-TFT and S2-TFT, a sampling transistor SP-TFT, and a driving transistor D-TFT. to be.

In this current programming method, each of the first and second switching transistors S1 -TFT and S2 -TFT turns on each other in consideration of off-stress between gates and sources Vgs, thereby Drain-source off-stress may be applied.

Although the above has been described with reference to a preferred embodiment of the present invention, the potential level described is an example, and the combination of various potentials can be applied according to the needs and applications since the variation in the size and process time of the bias aging effect depends on the magnitude of the applied potential. Do. That is, those skilled in the art will understand that various modifications and changes can be made without departing from the spirit and scope of the invention as set forth in the claims below.

In the bias aging method of the AMOLED according to the present invention as described above, the application of the off-stress to the device by applying a gate and a data driver mounted on the display panel as it is, as a separate device Do not use aging process equipment.

In addition, the off-stress of the accurate off-stress determined by the designer's intention is also formed on the source electrode of the device to be bias aged, which is more effective in stabilizing device characteristics of the display device using the organic light emitting display device. There is an advantage.

Claims (9)

A plurality of pixel regions in which a plurality of gate lines and data lines cross each other; A switching transistor having a gate electrode connected to the gate line, a source electrode connected to the data line, and a drain electrode connected to a power supply voltage terminal; An AAMOLED is defined as one pixel including a driving transistor having a gate electrode interposed therebetween, a driving transistor connected to a drain electrode of the switching transistor, a source electrode connected to a source electrode, and a light emitting diode disposed on the drain electrode. In the bias aging method of the display device used, Applying a first signal to a gate electrode of the switching transistor; Applying a second signal to a source electrode of the switching transistor to form a gate-source off-stress in response to the first signal; Applying a third signal forming a drain-source off-stress in response to the first signal to a drain electrode of the switching transistor; Bias aging method of the display device using the AMOLED comprising a. The method of claim 1, The switching and driving transistor is a PMOS bias biasing method for a display device using an AMOLED. The method of claim 1, Applying the first signal to the gate electrode of the switching transistor, Applying the first signal through the gate line; Turning on the switching transistor; Bias aging method of the display device using the AMOLED comprising a. The method of claim 3, wherein The first signal is a voltage signal having a level of -15V, bias aging method of the display device using the AMOLED. The method of claim 1, And the second signal is a voltage signal having a level of +10 V. A bias aging method of a display apparatus using an AMOLED. The method of claim 1, Applying a third signal forming a drain-source off-stress in response to the first signal to a drain electrode of the switching transistor; Turning off the switching transistor; Applying the third signal through the data line; Bias aging method of the display device using the AMOLED comprising a. The method of claim 6, And the third signal has a frequency and a phase different from that of the second signal, respectively. The method of claim 6, And the fourth signal is a voltage signal having a level of +20 V. A bias aging method of a display apparatus using an AMOLED. A plurality of pixel regions in which a plurality of gate lines and data lines cross each other; A switching transistor having a gate electrode connected to the gate line, a source electrode connected to the data line, and a drain electrode connected to a power supply voltage terminal; AMOLED is defined as one pixel including a driving transistor having a gate electrode interposed between the storage capacitor, a drain electrode of the switching transistor, a source electrode connected to a source electrode, and a light emitting diode disposed at the drain electrode. In the display device used, A gate driver connected to the gate line to turn on / off the switching transistor; A data driver connected to the data line to adjust a magnitude of a current flowing through the light emitting diode; Bias aging circuit structure of the display device using the AMOLED comprising a.

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