KR100759558B1 - Organic light emitting display - Google Patents

Abstract

An object of the present invention is to provide an organic light emitting display device that can solve the problem of dark spots caused by particles.

To this end, the present invention provides a substrate, a thin film transistor formed on the substrate and having a source / drain electrode and a gate electrode, a reflective film formed on the substrate and electrically insulated from the thin film transistor, An organic light emitting display device includes at least one insulating layer covering a thin film transistor and a reflective layer, and an organic light emitting element formed on the insulating layer and positioned on the reflective layer and electrically connected to the thin film transistor.

Description

Organic light emitting display device

1 is a cross-sectional photograph showing the generation of dark spots due to the conventional reflective film particles,

FIG. 2 is a circuit diagram schematically illustrating a pixel circuit of one unit pixel of an organic light emitting diode display of the present invention; FIG.

3 is a circuit diagram illustrating a more specific example of FIG. 2;

4 is a cross-sectional view of an organic light emitting diode display according to an exemplary embodiment of the present invention;

5 is a cross-sectional view of an organic light emitting diode display according to another exemplary embodiment of the present invention;

6 is a cross-sectional view of an organic light emitting diode display according to another exemplary embodiment of the present invention.

The present invention relates to an organic light emitting diode display, and more particularly, to an organic light emitting diode display capable of solving an electrical short circuit problem of an organic light emitting diode due to particles of a reflective film.

The active matrix type organic light emitting diode display (AM) has a pixel circuit for each pixel, which is electrically connected to the scan line, the data line, and the power supply line. Include.

The active matrix organic light emitting diode display may further include a separate reflective film under the ITO, which is an anode, in a top-emission structure for realizing an image in the direction of the sealing member. However, the reflective film positioned below the ITO in contact with the ITO is made of a metal which is easy to oxidize, such as Al, Mg, Ag, etc., so that an oxide film is easily formed between the ITO and the ITO when forming a hole for contact between the driving thin film transistor and the ITO. Such an oxide film results in increasing the resistance of ITO and degrades contact characteristics with the driving thin film transistor.

In addition, such a reflective film generates a large amount of process particles during its manufacturing process, and thus an electrical short circuit between the anode and the cathode in the anode / organic film / cathode structure of the organic light emitting device to be manufactured. electrical short.

1 is a cross-sectional photograph of a portion in which such a short occurs, and the second white portion at the bottom is a reflecting film and an anode composite structure made of ITO / Ag / ITO, and an organic film having a black layer thereon is EL, The thin part formed on white is transflective cathode. As shown in FIG. 1, particles are present on the reflective film and the anode composite structure made of ITO / Ag / ITO, and the particles show that the cathode and anode composite structures are shorted. As a result of component analysis on this particle, it was found that it was an Ag film. Therefore, this particle is generated during the formation of the reflective film.

The short caused by the particles acts as the main cause of the dark spots, which causes the pixel to be defective. Here, since the thickness of the anode is less than 1/10 of the thickness of the organic film, the thickness of the reflecting film is the thickness of the organic film, and thus, the dark spot expression rate due to the reflector particles is 100 times higher than the dark spot expression rate due to the anode particles on the reflecting film.

On the other hand, in the top emitting structure, a method of improving the light efficiency by adjusting the distance between the reflective film and the transflective cathode to a distance capable of causing optical resonance is used. In the conventional top emitting structure, the EL is thin to control this distance. Since it was possible only with a layer, that is, an organic film, it was limited in setting the resonance distance.

Although a structure in which a reflective film is formed using the same material as the Vdd line is disclosed in Korean Patent Laid-Open Publication No. 2005-21718 by the present applicant, this is also limited to match optical resonance.

The present invention has been made to solve the above problems, and an object thereof is to provide an organic light emitting display device that can solve the problem of dark spots caused by particles.

In order to achieve the above object, the present invention provides a substrate, a thin film transistor formed on the substrate and having a source / drain electrode and a gate electrode, and formed on the substrate and electrically connected to the thin film transistor. An organic light emitting display including an insulated reflective film, at least one insulating layer covering the thin film transistor and the reflective film, and an organic light emitting element formed on the insulating layer and positioned on the reflective film and electrically connected to the thin film transistor Provide the device.

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

FIG. 2 schematically illustrates a pixel circuit PC of one unit pixel of the organic light emitting diode display of the present invention.

As shown in FIG. 2, each pixel includes a Vdd power line Vdd in which a data line Data and a scan line serve as one driving power of an organic light emitting diode (OLED).

The pixel circuit PC of each pixel is electrically connected to the data line Data, the scan line, and the Vdd power line Vdd, and controls the light emission of the OLED.

3 illustrates a more specific example of FIG. 2, wherein the pixel circuit PC of each pixel includes two thin film transistors M1 and M2 and one capacitor unit Cst.

Referring to FIG. 3, each pixel of the organic light emitting diode display according to the exemplary embodiment of the present invention may include a switching TFT M2, at least two thin film transistors of the driving TFT M1, and a capacitor unit Cst. And an organic electroluminescent element (OLED).

The switching TFT M2 is turned on / off by a scan signal applied to the scan line Scan to transfer a data signal applied to the data line Data to the storage capacitor Cst and the driving TFT M1. The switching element is not necessarily limited to the switching TFT M2 as shown in FIG. 3, and may include a switching circuit including a plurality of thin film transistors and capacitors, and a circuit that compensates for the Vth value of the driving TFT M1. Alternatively, a circuit for compensating for the voltage drop of the driving power source Vdd may be further provided.

The driving TFT M1 determines the amount of current flowing into the organic light emitting element OLED according to the data signal transmitted through the switching TFT M2.

The capacitor unit Cst stores a data signal transmitted through the switching TFT M2 for one frame.

In the circuit diagram according to FIG. 3, the driving TFT M1 and the switching TFT M2 are illustrated as PMOS TFTs, but the present invention is not limited thereto, and at least one of the driving TFT M1 and the switching TFT M2 is not limited thereto. Can be formed of an NMOS TFT, of course. In addition, the number of the thin film transistors and capacitors as described above is not necessarily limited thereto, and of course, a larger number of thin film transistors and capacitors may be provided.

4 is a cross-sectional view of an organic light emitting diode display according to an exemplary embodiment of the present invention.

According to the embodiment according to FIG. 4, the driving thin film transistor M1 and the reflective film 120 are provided on the substrate 100, and a passivation film 108 is formed to cover them, and the passivation film 108 is formed on the substrate 100. An organic light emitting diode OLED is formed.

The substrate 100 may use a glass material, but is not limited thereto, and may also use a plastic material, and may use a metal material such as SUS and Ti.

A buffer layer 101 made of an organic compound and / or an inorganic compound is further formed on the upper surface of the substrate 100. Preferably, the substrate 100 is formed of SiOx (x ≧ 1) or SiNx (x ≧ 1).

After the semiconductor active layer 102 arranged in a predetermined pattern is formed on the buffer layer 101, the semiconductor active layer 102 is embedded by the gate insulating layer 103. The semiconductor active layer 102 has a source region 102b and a drain region 102c, and further includes a channel region 102a therebetween. The semiconductor active layer 102 may be formed by forming an amorphous silicon film on the buffer layer 101 and then crystallizing it to form a polycrystalline silicon film, and then patterning the polycrystalline silicon film. The source and drain regions 102b and 102c of the semiconductor active layer 102 are doped with impurities in accordance with the type of the TFT such as the driving TFT M1 and the switching TFT M2. 3 and 4 illustrate a PMOS type driving TFT M1, but the present invention is not limited thereto, and may be formed of an NMOS type.

A gate electrode 104 corresponding to the semiconductor active layer 102 and an interlayer insulating layer 105 embedded therein are formed on the top surface of the gate insulating layer 103.

After contact holes are formed in the interlayer insulating layer 105 and the gate insulating layer 103, the source electrode 106 and the drain electrode 107 are respectively formed on the interlayer insulating layer 105 and the source region 102b. And the drain region 102c.

In this case, the reflective film 120 is formed of the same material as the source / drain electrodes 106 and 107 separately from the source / drain electrodes 106 and 107. The reflective film 120 is electrically shorted with the source / drain electrodes 106 and 107.

Since the reflective film 120 is formed at the same time as the source / drain electrodes 106 and 107 in the present invention, the source / drain electrodes 106 and 107 and the reflective film 120 are light reflective with a material having good electrical conductivity. It is preferably formed in thickness. It is preferable to be provided with metal materials such as Ag, Mg, Al, Pt, Pd, Au, Ni, Nd, Ir, Cr, Li, Ca, and compounds thereof.

The passivation film 108 is formed on the driving thin film transistor M1 and the reflective film 120, and the pixel electrode 111 of the organic light emitting diode OLED is formed on the passivation film 108. The pixel electrode 111 contacts the drain electrode 107 of the driving TFT M1 by the via hole formed in the passivation film 108. The passivation film 108 may be formed of an inorganic material and / or an organic material. As shown in FIG. 4, the passivation film 108 may be formed as a flattening film so that the top surface is flat regardless of the curvature of the lower film. It may be formed to go along the bend. The passivation film 108 is preferably formed of a transparent insulator so that a resonance effect can be achieved.

After the pixel electrode 111 is formed on the passivation film 108, the pixel defining layer 109 is formed of an organic material and / or an inorganic material so as to cover the pixel electrode 111 and the passivation film 108. The electrode 111 is opened so as to be exposed.

The organic emission layer 112 and the counter electrode 113 are formed on at least the pixel electrode 111.

The pixel electrode 111 functions as an anode electrode, and the counter electrode 113 functions as a cathode electrode. Of course, the polarities of the pixel electrode 111 and the counter electrode 113 may be reversed. It's okay.

The pixel electrode 111 may be formed of a material having a high work function, and may be formed of a transparent conductor such as ITO, IZO, In2O3, and ZnO.

The counter electrode 113 may be formed of a metal material such as Ag, Mg, Al, Pt, Pd, Au, Ni, Nd, Ir, Cr, Li, Ca, and a compound thereof having a low work function. , Al, or the like to form a semi-transmissive reflective film so as to transmit light after optical resonance.

The pixel electrode 111 and the opposite electrode 113 are insulated from each other by the organic layer 112, and light is emitted from the organic layer 112 by applying voltages having different polarities to the organic layer 112.

The organic layer 112 may be a low molecular or high molecular organic film. When using a low molecular organic film, a hole injection layer (HIL), a hole transport layer (HTL), an emission layer (EML), an electron transport layer (ETL), an electron injection layer (EIL) : Electron Injection Layer) can be formed by stacking single or complex structure, and usable organic materials are copper phthalocyanine (CuPc), N, N-di (naphthalen-1-yl) -N, N '-Diphenyl-benzidine (N, N'-Di (naphthalene-1-yl) -N, N'-diphenyl-benzidine: NPB), tris-8-hydroxyquinoline aluminum ( Alq3) can be used in various ways. These low molecular weight organic films are formed by the vacuum deposition method. In this case, the hole injection layer, the hole transport layer, the electron transport layer, the electron injection layer and the like can be commonly applied to red, green, and blue pixels as a common layer. Therefore, unlike FIG. 4, these common layers may be formed to cover all pixels, such as the counter electrode 113.

In the case of the polymer organic film, the structure may include a hole transporting layer (HTL) and a light emitting layer (EML). In this case, PEDOT is used as the hole transporting layer, and polyvinylvinylene (PPV) and polyfluorene are used as the light emitting layer. Polymer organic materials such as (Polyfluorene) are used and can be formed by screen printing or inkjet printing.

The organic layer as described above is not necessarily limited thereto, and various embodiments may be applied.

After the organic light emitting diode OLED is formed, the organic light emitting diode OLED is sealed and shielded from outside air.

Meanwhile, in the present invention, the reflective film 120 and the pixel electrode 111 are arrayed to have a structure overlapping each other as shown in FIG. 3. In this case, when the distance R between the reflective film 120 and the counter electrode 113 is adjusted to adjust the resonance distance, the light emitted from the organic layer 112 is between the reflective film 120 and the counter electrode 113. After the light resonance is generated in the direction of the counter electrode 113 can be further improved light extraction efficiency. Since the optical resonance distance R can be adjusted by the passivation film 108, it is easy to have a different thickness for each of the red, green, and blue pixels, and thus can be designed to have an optimal thickness for each color. .

As described above, in the present invention, since the passivation film 108 is formed on the reflective film 120, even if particles are generated during the formation of the reflective film 120, the passivation film 108 opposes the pixel electrode 111 formed by the particles. It is possible to prevent the short of the electrode 113, it is possible to reduce the dark spot failure.

Meanwhile, in the present invention, the reflective film 120 may be formed separately from the source / drain electrodes 106 and 107 of the driving TFT M1. That is, as shown in FIG. 5, the first passivation film 108a is formed to cover the driving TFT M1, and the reflective film 120 is formed on the first passivation film 108a, and then covered again. After the second passivation film 108b is formed, the pixel electrode 111 is formed on the second passivation film 108b. In this case, the reflective film 120 is less affected by the array structure of the driving TFT M1.

6 shows that the reflective film 120 is formed at the same time as the gate electrode 204. In this case, the interlayer insulating film 105 is preferably formed of a transparent insulator.

Although the above embodiments have been described with respect to an organic light emitting display, the present invention can be applied to various kinds of flat panel displays such as a liquid crystal display in addition to the organic light emitting display.

According to the present invention as described above, it is possible to prevent the short generation of the pixel electrode and the counter electrode caused by the particles generated during the reflective film forming process, and in the front emission structure, it is possible to easily apply the optical resonance structure.

Although the present invention has been described with reference to one embodiment shown in the accompanying drawings, this is merely exemplary, and various modifications and equivalent other embodiments are possible to those skilled in the art. I can understand. Therefore, the true scope of protection of the present invention should be defined only by the appended claims.

Claims (6)

Board; A thin film transistor formed on the substrate and having a source / drain electrode and a gate electrode; A reflective film formed on the substrate and electrically insulated from the thin film transistor; At least one insulating layer covering the thin film transistor and the reflective film; And An organic light emitting display device comprising: an organic light emitting element formed on the insulating layer and positioned on the reflective layer and electrically connected to the thin film transistor. The reflective layer is formed under the insulating layer covering the reflective layer. The method of claim 1, The reflective layer is formed of the same material as the source / drain electrodes. delete The method according to any one of claims 1 to 2, The organic light emitting diode includes a pixel electrode, an organic emission layer, and an opposite electrode, and the reflective layer overlaps the pixel electrode. The method of claim 4, wherein The pixel electrode and the opposite electrode are light transmissive electrode bodies. The method according to any one of claims 1 to 2, And the insulating layer is a transparent insulator.

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