KR100642264B1 - Picture element structure of organic light emitting diode - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an organic light emitting display device, and more particularly, to a pixel structure of an organic light emitting device that prevents degradation of an organic light emitting device due to a decrease in aperture ratio due to an area occupied by a power supply wiring. The pixel structure of the organic light emitting device according to the present invention is formed in a first direction, the data line for transmitting a data voltage; A plurality of scan lines formed in a second direction crossing the first direction and transferring scan signals; A respective switching transistor configured to select each pixel defined by the data line and the plurality of scan lines; Each capacitor configured to store a corresponding charge according to a voltage applied to the data line; Each driving transistor connected to the scan line to receive a power supply voltage through the scan line; And an organic light emitting diode emitting light by the current flowing through the driving transistor.

Active matrix OLED, pixel, aperture ratio, current density

Description

Pixel Structure of Organic Light Emitting Device {PICTURE ELEMENT STRUCTURE OF ORGANIC LIGHT EMITTING DIODE}             

1 is a conventional pixel circuit diagram for driving an organic EL device using a thin film transistor;

2 is a layout of a pixel circuit for driving the conventional organic EL device shown in FIG. 1;

3 is a view showing a light emission rate of an organic EL device according to a driving time in the pixel structure of FIG. 1;

4 is a pixel circuit and an operation timing diagram for driving an organic EL device according to an embodiment of the present invention;

5 is an operation timing diagram according to an operation region of a gate select signal in the pixel circuit of FIG. 4;

FIG. 6 is a diagram illustrating a case in which a gate selection signal SCAN.n-1 of a previous stage is used as a V _DD power supply according to an embodiment of the present invention; FIG.

7 is a diagram illustrating a case where a next gate selection signal SCAN.n-1 is used as a V _DD power supply according to an embodiment of the present invention;

8 is a diagram illustrating an example in which gate selection signals SCAN.2n-1 and SCAN.2n of adjacent pixels are used as a V _DD power supply according to an embodiment of the present invention;

9 is a diagram illustrating an example in which a gate selection signal SCAN.n of a current stage is used as a V _DD power supply for each pixel;

10 is a cross-sectional view illustrating a pixel structure of an organic light emitting diode according to an embodiment of the present invention;

11 is a layout of a 2-TFT organic EL pixel circuit,

12 is an organic EL pixel circuit diagram according to another embodiment of the present invention;

13 is the layout of FIG.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an organic light emitting display device, and more particularly, to a pixel structure of an organic light emitting device that prevents degradation of an organic light emitting device due to a decrease in aperture ratio due to an area occupied by a power supply wiring.

At present, there is a great demand for thinner, lighter, lower power consumption, and the like of the display device, and one of the attentions as the next-generation display device is an organic light emitting device. The organic light emitting device uses an electroluminescence (EL) phenomenon of certain organic materials or polymers, and does not require a backlight, so that the organic light emitting device can be thinner than a liquid crystal display device, and can be manufactured more inexpensively and easily, while providing a wide viewing angle and bright light. There is an advantage.

The organic light emitting diodes may be classified into a passive-matrix type and an active-matrix type according to the presence of a switching element included in the unit pixel of the organic light emitting display panel.

In the passive-matrix method, the anode and cathode are orthogonal and the line is selected. The active-matrix method connects a driving thin film transistor (TFT) and a capacitor to each indium tin oxide (ITO) pixel electrode to provide capacitance It is a drive system to maintain the voltage by.

FIG. 1 is a conventional pixel circuit for driving an organic EL element using a thin film transistor, and shows one of NxM pixels.

Referring to FIG. 1, a driving thin film transistor DR TFT is connected to an organic EL element OLED to supply a current for emitting light. The current amount of the driving thin film transistor DR TFT is configured to be controlled by a data voltage applied through the switching thin film transistor SW TFT. At this time, a capacitor C _ST for maintaining the applied voltage for a predetermined time is connected between the source and the gate of the driving transistor. The scan line SCAN is connected to the gate of the switching transistor SW TFT, and the data line DATA is connected to the source.

Referring to the operation of the pixel circuit having the above structure, when the switching TFT is turned on by a scan signal applied to the gate of the switching TFT, the data voltage is driven through the data line. DR TFT). In response to the data voltage applied to the gate, current flows through the driving thin film transistor (DR TFT) to the organic EL device OLED to emit light, and the organic EL device emits light in proportion to the injected current density. do.

As described above, an organic light emitting display that emits light by passing a current through an organic EL device has a problem in that a light emitting area ratio (aperture ratio) at which light is output is significantly lower than that of a liquid crystal display. The aperture ratio refers to the ratio of the area of actual light emission to the total area of the sub-pixel.

FIG. 2 is a diagram showing a layout of a pixel circuit for driving the conventional organic EL element shown in FIG.

Referring to FIG. 2, a conventional organic EL device includes a switching transistor and a driving transistor, and basically includes a data line 21, a scan line 22, and a V _DD power supply line 23 for supplying current. Since it is provided with, the aperture ratio becomes very low. In particular, V _DD power supply line 23, so the thin film transistor for driving is and the current source acts that can flow a current to the organic EL device, such V _DD power is the same for all the individual pixels supplied also be open to the pixel panel ( It should be wired in the direction of column). In this case, the V _DD power supply line 23 usually has a wiring width of about 6 to 8 μm and a wiring margin of about 2 μm between adjacent wirings, and thus occupies a considerable area in terms of the total area of individual pixels. do. For example, in the case of a 2.4-inch QVGA (240xBRGx320) panel, the pitch of each pixel is 51 μm, and thus the area occupied by the V _DD power supply line is about 15%. As a result, the opening ratio is reduced by the area occupied by the power supply line.

The low aperture ratio directly affects the life-time of the organic EL element. The amount of light emitted is determined by the amount of current injected into the organic EL element, and the amount of light increases as the amount of current increases. However, current driving for a long time causes degradation of the organic EL device, and the degradation of the organic EL device may include an increase in the threshold voltage at which the organic EL device emits light and a decrease in luminous efficiency. have. When the luminous efficiency is lowered, it means that the previous luminous amount cannot be secured even by the same amount of current.

3 is a view showing the light emission rate of the organic EL device according to the driving time in the pixel structure of FIG. 1, and it can be seen that the light emission rate of the organic EL device is greatly reduced with long driving. As described above, when the output characteristics of the organic EL device are deteriorated, the light emission control capability of each pixel is also lowered, resulting in a deterioration of the image quality of the organic light emitting display.

On the other hand, deterioration of the organic EL element is closely related to the current density flowing through the organic EL element. That is, the factor directly affecting the deterioration of the organic EL device is known as the current density flowing per unit area rather than the amount of current. Therefore, the technology to reduce the current density may be an effective way to suppress the degradation of the organic light emitting device. In this case, a method of lowering the current density by increasing the aperture ratio in injecting a predetermined amount of current may be performed.

However, increasing the aperture ratio in the organic light emitting pixel may be very limited. The organic light emitting display is composed of pixel circuits for controlling the amount of current, typically two to six transistors, control lines for operating these transistors, and data voltages during the frame. Storage capacitors for storage, and the like. Therefore, the area ratio of these circuits in the individual pixels is very large, about 50 to 80%, and therefore the aperture ratio is relatively low, which is about 20 to 50%.

Accordingly, an object of the present invention is to provide a pixel structure of an organic light emitting device that can significantly increase the emission area of an organic EL device. .

Another object of the present invention is to provide a pixel structure of an organic light emitting device which can fundamentally suppress deterioration of the organic light emitting device by reducing the current density flowing to the organic light emitting device.

Another object of the present invention is to provide a pixel structure of an organic light emitting device that can obtain sufficient capacitance without occupying a separate area when implementing a pixel circuit of an organic light emitting display device.

In order to achieve the above object, a pixel structure of an organic light emitting diode according to the present invention is formed in a first direction and includes a data line transferring a data voltage; A plurality of scan lines formed in a second direction crossing the first direction and transferring scan signals; A respective switching transistor configured to select each pixel defined by the data line and the plurality of scan lines; Each capacitor configured to store a corresponding charge according to a voltage applied to the data line; Each driving transistor connected to the scan line to receive a power supply voltage through the scan line; And an organic light emitting diode emitting light by the current flowing through the driving transistor.

In addition, the present invention provides a circuit region including a driving transistor and a data line to achieve the above object; A pixel structure of an organic light emitting device including a light emitting region having a transparent conductive material layer, a light emitting layer, and a cathode layer, the pixel structure being formed in the circuit region of the same layer as the transparent conductive material layer of the light emitting region to be connected to the data line. A transparent conductive material layer serving as a first electrode of the capacitor; A BANK layer formed over an entire surface of the transparent conductive material layer in the circuit region and the light emitting region to serve as a dielectric layer of the capacitor in the circuit region; An organic light emitting layer formed on the BANK layer and formed to contact the transparent conductive material layer in the emission region; And an electrode layer formed on the organic light emitting layer and serving as a second electrode of the capacitor in the circuit region, and acting as a cathode electrode in the emitting region.

Preferably, the gate electrode of the driving transistor is connected to the data line such that input data is applied to the transparent conductive material layer of the circuit area via the gate electrode and the data line.

More preferably, the drain electrode of the driving transistor is connected to the transparent conductive material layer of the light emitting region.

Hereinafter, with reference to the accompanying drawings will be described an embodiment of the present invention; Note that the same components in the drawings are represented by the same reference numerals and symbols as much as possible even though they are shown in different drawings. In addition, in describing the present invention, when it is determined that a detailed description of a related known function or configuration may unnecessarily obscure the subject matter of the present invention, the detailed description thereof will be omitted.

4 is a pixel circuit and an operation timing diagram for driving an organic EL device according to an embodiment of the present invention.

Referring to FIG. 4, the pixel circuit is applied to the organic EL element 41, a driving transistor 42 for supplying current to the organic EL element 41, and the driving transistor 42. A switching transistor 43 for controlling the data voltage and a capacitor 44 connected between the source and the gate of the driving transistor 42 to maintain the applied voltage for a predetermined period of time. In addition, a data line DATA and scan lines SCAN and SCAN 'are included. The gate of the switching transistor 43 is connected to the scan line SCAN, and the source is connected to the data line DATA. In this case, the V _DD power is configured to be supplied through the scan line SCAN 'without being supplied by a separate external power source.

The operation of the pixel circuit having the above configuration is as follows. Referring to FIG. 4, when the gate selection signal is applied, the switching transistor 43 is turned on to apply data to the pixel. FIG. 5 illustrates an operation timing diagram according to an operation region of a gate selection signal in the pixel circuit of FIG. 4. In FIG. 5, the gate selection signal is switched (V _SS ) only when input data is applied to a pixel. One frame time will have a V _DD voltage. Therefore, it serves to supply the V _DD power during the time of actual light emission.

6 to 8 illustrate examples of using the gate selection signal according to an embodiment of the present invention and layout thereof.

FIG. 6 illustrates a case in which the gate selection signal SCAN.n-1 of the previous stage is used as the V _DD supply power, and the gate selection signal of the previous stage is supplied as the V _DD voltage of the current stage. FIG. 7 illustrates a case where the next stage gate selection signal SCAN.n-1 is used as the V _DD power supply, and the next stage gate selection signal is supplied as the current stage V _DD voltage. When the gate selection signal of the previous (n-1) stage or the next (n + 1) stage is switched, the voltage of the gate node of the driving transistor of the current stage is fluctuated by coupling. This causes distortion of the stored data value and changes the current value of the programmed organic EL device. However, when the scanning by the gate selection signal is completed and the voltage is returned to the V _DD voltage, the gate node voltage of the driving transistor is returned to the original voltage value, and the current value of the organic EL element OLED is also restored.

8 shows an example in which the gate selection signals SCAN.2n-1 and SCAN.2n of pixels adjacent to each other are used as the V _DD power supply. As shown in FIGS. 6 and 7, the gate selection signal of the previous stage or the next stage needs to pass through the wiring line in order to be applied to the current stage. Therefore, as shown in FIG. 8, when the gate selection signal of the relative pixel is utilized between adjacent pixels, the wiring line is reduced, thereby increasing the aperture ratio.

9 shows an example in which the gate selection signal SCAN.n of the current stage is used as the V _DD supply power for each pixel. Since the gate selection signal of the current stage is used, the gain on the wiring is maximized and the aperture ratio is increased as much as possible. It can be seen that.

Meanwhile, as shown in FIG. 9, when the gate selection signal of the current stage is used as the V _DD power supply, the applied data must be preserved even when the gate selection signal is switched. In other words, the storage capacitor should be connected to a node with a fixed voltage. In the conventional pixel circuit, the storage capacitor is connected to the V _DD line, and in the case of FIGS. 6 to 8, the storage capacitor is connected to the neighboring scan line. However, in the circuit of Figure 9 it is not possible to connect the storage capacitor to the current scan line. This is because when the storage capacitor is connected to the scan line, the data stored in the capacitor is distorted by coupling when the scan line is turned off. Therefore, in this embodiment, the storage capacitor 91 is connected to the cathode electrode of the organic EL element 92, as shown in FIG. This is to ensure that the applied data voltage is preserved even when the scan selection signal is switched.

10 is a cross-sectional view illustrating a pixel structure of an organic light emitting diode according to an exemplary embodiment of the present invention. FIG. 10 is a view illustrating a structure of a capacitor according to the present invention as a structure including a driving thin film transistor connected to the organic EL device and the capacitor of FIG. 9.

Referring to FIG. 10, a pixel structure of an organic light emitting diode includes an insulating substrate 101 in which a light emitting region E and a circuit region C are defined, and a semiconductor layer 102 formed on the insulating substrate in a circuit region C. Referring to FIG. ), A gate insulating film 103 formed on the semiconductor layer 102, a gate electrode 104 formed on the gate insulating film 103, and a gate electrode 104 formed on the gate electrode 104. A data line 105 formed to be connected, a source electrode 106 and a drain electrode 107 formed to be spaced apart from the data line 105 at a predetermined interval, and connected to the semiconductor layer 102, and the data line. (104) Indium Tin Oxide (ITO) layers 108C and 108E formed in the circuit region C and the light emitting region E thereon, and a BANK layer formed to surround the entire surface of the ITO layer 108 ( 109 and the organic layer formed to be in contact with the BANK layer 109 in the circuit region C and the ITO layer 108 in the emission region E. An EL light emitting layer 110 and metal layers 111C and 111E formed on the organic EL light emitting layer 110 are included.

In FIG. 10, the ITO layer 108C in the circuit region C is connected with the data line 105, and the ITO layer 108E in the light emitting region E is connected with the drain electrode 107. In addition, the metal layer 111C in the circuit region C forms a capacitor electrode together with the ITO layer 108C, and the metal layer 111E in the light emitting region E serves as a cathode electrode of the organic EL element. That is, when the ITO layer 108E is formed in the light emitting region E, the ITO layer 108C is formed in the circuit region to be used as one electrode of the capacitor, and the cathode layer of the organic EL element is used as the other electrode of the capacitor. . In addition, the BANK layer is made of a dielectric including an inorganic dielectric or an organic dielectric such as SiO ₂ or SiN _X , and may play a sufficient role as a dielectric of the capacitor in this embodiment. Therefore, according to the present invention, a capacitor having sufficient capacitance can be formed without occupying a separate area in the pixel. In addition, the ITO layer can be processed simultaneously when the anode electrode of the organic EL device is stacked and patterned, so no additional process is required, and since the BANK and cathode layers are also made at the same time during the organic EL device process, a separate mask patterning or process is required. It doesn't work.

11 is a layout of a 2-TFT organic EL pixel circuit, where (a) is a layout of a conventional pixel circuit in which a V _DD supply line is separately present, and (b) is a layout according to the present invention. In FIG. 11 (b), an ITO layer (ITO for C _ST ) for designing a storage capacitor in the TFT circuit portion is designed, so that the opening ratio is 54% from the conventional 34% (see FIG. 11 (a)). It can be seen that the increase.

FIG. 12 illustrates another embodiment of the present invention. FIG. 12A illustrates a circuit compensating threshold voltages of a driving transistor (SH Jung, SID 2002, pp. 622-625), and FIG. 12B. According to the present invention, in the pixel circuit of FIG. 12A, a separate V _DD supply line is removed and replaced with a gate select signal.

FIG. 13 is a layout of FIG. 12. Referring to FIG. 13A, it can be seen that the number of transistors is large and the aperture ratio is reduced to about 25% by the gate selection line, the data input signal line, and the V _DD supply line. On the other hand, referring to FIG. 13 (b), it can be seen that the ITO layer for the storage capacitor design is partitioned and the opening ratio is increased by 44%.

Meanwhile, in the detailed description of the present invention, specific embodiments have been described, but various modifications may be made without departing from the scope of the present invention. Therefore, the scope of the present invention should not be limited to the described embodiments, but should be determined not only by the scope of the following claims, but also by the equivalents of the claims.

As described above, the pixel structure of the organic EL device according to the present invention can significantly increase the emission area of the organic EL device by eliminating the V _DD supply line and reducing the area occupied by the wiring. Accordingly, it is possible to fundamentally suppress deterioration of the organic EL device by reducing the current density flowing to the organic EL device. As a result, the lifespan of the organic EL device is increased and the image quality of the organic light emitting display is improved. Therefore, the present invention can directly contribute to the improvement of the reliability of driving the organic EL device when combined with the research for the physical properties improvement of the organic EL device.

In addition, the present invention proposes a new storage capacitor structure consisting of ITO / BANK / cathode, it is possible to obtain a sufficient capacitance that exceeds the capacitance of the existing storage capacitor without occupying a separate area when implementing the pixel circuit. Moreover, the capacitor structure according to the present invention has an advantage in terms of process efficiency and cost since no additional process is required.

Claims (9)

A data line formed in a first direction and transferring a data voltage; A plurality of scan lines formed in a second direction crossing the first direction and transferring scan signals; A respective switching transistor configured to select each pixel defined by the data line and the plurality of scan lines; Each capacitor configured to store a corresponding charge according to a voltage applied to the data line; Each driving transistor connected to the scan line to receive a power supply voltage through the scan line; And a respective organic light emitting diode (LED) which emits light by a current flowing through the driving transistor. The driving transistor of claim 1, wherein the driving transistor of each pixel The pixel structure of the organic light emitting device, characterized in that connected to the scan line of the current stage of the plurality of scan lines. The method of claim 2, wherein the capacitor And a node having a fixed voltage so that the applied data is preserved even when the scan signal is switched. The driving transistor of claim 1, wherein the driving transistor of each pixel The pixel structure of the organic light emitting device, characterized in that connected to the scan line of the adjacent stage of the plurality of scan lines cross each other. A circuit region having a driving transistor and a data line; In the pixel structure of an organic light emitting device comprising a light emitting region comprising a transparent conductive material layer, a light emitting layer, a cathode layer, A transparent conductive material layer formed in the circuit region of the same layer as the transparent conductive material layer of the light emitting region so as to be connected to the data line and serving as a first electrode of the capacitor; A bank layer formed over the transparent conductive material layer in the circuit region and the light emitting region and serving as a dielectric layer of the capacitor in the circuit region; An organic light emitting layer formed on the bank layer and formed to be in contact with the transparent conductive material layer in the emission region; And an electrode layer formed on the organic light emitting layer and acting as a second electrode of the capacitor in the circuit region, and acting as a cathode electrode in the light emitting region. The organic light emitting diode of claim 5, wherein the gate electrode of the driving transistor is connected to the data line such that input data is applied to the transparent conductive material layer of the circuit region via the gate electrode and the data line. Pixel Structure of Light-Emitting Element. 7. The pixel structure of claim 6, wherein the drain electrode of the driving transistor is connected to the transparent conductive material layer of the light emitting region. The method of claim 5 or 6, wherein the transparent conductive material layer A pixel structure of an organic light emitting device, characterized in that the ITO (Indium Tin Oxide) layer. The method of claim 5, wherein the bank BANK layer is A pixel structure of an organic light emitting device, characterized in that it comprises an inorganic dielectric or an organic dielectric, such as SiO ₂ or SiN _X.

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