KR100834341B1 - an active matrix organic electroluminescence display device - Google Patents

Abstract

The present invention relates to an active matrix organic electroluminescent device.

In a conventional active matrix organic electroluminescent device, a protective layer made of an organic film is formed on a thin film transistor. The organic film has a fixed charge therein, thereby degrading the characteristics of the thin film transistor.

In the active matrix organic electroluminescent device according to the present invention, only a protective layer made of an inorganic insulating layer is present on the thin film transistor, and the organic layer is removed from the upper portion of the thin film transistor, thereby preventing deterioration of the characteristics of the thin film transistor.

Organic electroluminescent device, organic film

Description

Active matrix organic electroluminescence display device             

1 is a band diagram showing the structure of a general organic electroluminescent device.

2 is a circuit diagram of one pixel of a conventional active matrix organic electroluminescent device.

3 is a cross-sectional view of a conventional active matrix organic electroluminescent device.

4 is a cross-sectional view of an active matrix organic electroluminescent device according to a first embodiment of the present invention.

5 is a cross-sectional view of an active matrix organic electroluminescent device according to a second embodiment of the present invention.

<Description of Symbols for Main Parts of Drawings>

110 substrate 121 gate electrode

122: source electrode 123: drain electrode

131: active layer 140: first protective layer

150: second protective layer 160: first electrode                 

171, 172, 173: organic light emitting layer 180: second electrode

T1: thin film transistor

The present invention relates to an organic electroluminescent device, and more particularly, to an active matrix organic electroluminescent device including a thin film transistor.

Currently, a cathode ray tube (CRT) is used as a main device in a display device such as a television or a monitor, but this has a problem of weight and volume and high driving voltage. Accordingly, there is a need for a flat panel display having excellent characteristics such as thinness, light weight, and low power consumption, and has emerged, such as a liquid crystal display, a plasma display panel, and an electric field emission. Various flat panel display devices such as a field emission display and an electroluminescent display (or electroluminescence display (ELD)) have been researched and developed.

The dual electroluminescent device is a display device using an electroluminescence (EL) phenomenon in which light is generated when a certain electric field is applied to a phosphor, and an inorganic electroluminescent device and an organic electroluminescent device depending on a source causing excitation of carriers. (organic electroluminescence display: OELD or organic ELD).

Among them, the organic electroluminescent device is attracting attention as a natural color display device because it emits light in all regions of visible light including blue, and has high luminance and low operating voltage characteristics. In addition, because of self-luminous, the contrast ratio is high, the ultra-thin display can be realized, and the process is simple, so that environmental pollution is relatively low. On the other hand, the response time is easy to implement a moving picture with a few microseconds, there is no restriction on the viewing angle, it is stable even at low temperatures, it is easy to manufacture and design a drive circuit because it is driven at a low voltage of DC 5V to 15V.

The organic electroluminescent device has a structure similar to that of an inorganic electroluminescent device, but the light emitting principle is called organic light emitting diode (OLED) because the light emission is achieved by recombination of electrons and holes.

A structure of a general organic electroluminescent device is shown in FIG. 1 as a band diagram. As shown, an organic electroluminescent device includes a hole transport layer between an anode electrode 1 and a cathode electrode 7. (hole transporting layer) 3, an emission layer (4), and an electron transporting layer (electron transporting layer) (5) is located. In this case, a hole injection layer 2 between the anode electrode 1 and the hole transport layer 3 and between the electron transport layer 5 and the cathode electrode 7 to inject holes and electrons more efficiently. And an electron injection layer 6 may be further included.

Here, holes injected from the anode electrode 1 into the light emitting layer 4 through the hole injection layer 2 and the hole transport layer 3, and the electron injection layer 6 and the electron transport layer 5 from the cathode electrode 7 Electrons injected into the light emitting layer 4 through) form an exciton 8, from which the light corresponding to the energy between the holes and the electrons is emitted. In this case, the anode 1 has a high work function, such as transparent indium-tin-oxide (hereinafter referred to as ITO) or indium-zinc-oxide (hereinafter referred to as IZO). Made of a material, light is emitted toward the anode electrode 1. On the other hand, the cathode electrode 7 is preferably made of a material such as aluminum (Al), calcium (Ca), aluminum alloy which has a low work function and is chemically stable.

Recently, an active matrix form in which a plurality of pixels are arranged in a matrix form and thin film transistors are connected to each pixel is widely used in a flat panel display device, and an active matrix organic electroluminescent device applied to the organic electroluminescent device is used. It demonstrates with reference to attached drawing.

FIG. 2 illustrates a circuit structure of one pixel of an active matrix organic electroluminescent device, and as illustrated, one pixel of the active matrix organic electroluminescent device includes a switching thin film transistor 14 and a driving thin film. And a transistor 15, a storage capacitor 16, and a light emitting diode 17.

Here, the gate electrode of the switching thin film transistor 14 is connected to the gate wiring 11, and the source electrode is connected to the data wiring 12. The drain electrode of the switching thin film transistor 14 is connected to the gate electrode of the driving thin film transistor 15, and the drain electrode of the driving thin film transistor 15 is connected to the anode electrode of the light emitting diode 17. The source electrode of the driving thin film transistor 15 is connected to the power line 13, and the cathode electrode of the light emitting diode 17 is grounded. Next, the storage capacitor 16 is connected to the gate electrode and the source electrode of the driving thin film transistor 15.

Therefore, when a signal is applied through the gate line 11, the switching thin film transistor 14 is turned on, and an image signal from the data line 12 is transferred to the storage capacitor 16 through the switching thin film transistor 14. Stored. The image signal is transmitted to the gate electrode of the driving thin film transistor 15 to operate the driving thin film transistor 15 to output light through the light emitting diode 17. In this case, the luminance is controlled by controlling the current flowing through the light emitting diode 17. Adjust Here, since the driving thin film transistor 15 is driven by the voltage value stored in the storage capacitor 16 even when the switching thin film transistor 14 is turned off, the current is continuously emitted until the image signal of the next screen is input. It flows into the diode 17 to emit light.

3 is a cross-sectional view of the active matrix organic electroluminescent device. As illustrated, a thin film transistor T is formed on the substrate 20, and a protective layer 50 is formed thereon to cover the thin film transistor T. The thin film transistor T includes a gate electrode 31 and source and drain electrodes 32 and 33, and includes an active layer 41.

An anode electrode 60, which is made of a transparent conductive material and is a hole supply layer, is formed on the passivation layer 50, and the anode electrode 60 is connected to the drain electrode 33 of the thin film transistor T. Subsequently, organic light emitting layers 71, 72, and 73 that emit red, green, and blue colors are formed on the anode electrode 60, respectively. The cathode electrode 80 is formed of an opaque conductive material and supplies electrons thereon. ) Is formed.

In the active matrix organic electroluminescent device, since the lower anode electrode 60 is made of a transparent conductive material and the upper cathode electrode 80 is made of an opaque conductive material, light is emitted from the organic light emitting layers 71, 72, and 73. Light is emitted downward through the anode electrode 60. Therefore, it is preferable that the board | substrate 20 consists of a transparent board | substrate.

On the other hand, the protective layer 50 is formed of an organic layer to protect the thin film transistor (T), eliminate the step caused by the thin film transistor (T), reduce the signal interference between the cathode electrode 80 and the wiring, or an inorganic film It is used in the form of laminating an organic film on the top.

However, when the organic layer is used as the protective layer 50, there is a fixed charge having a positive property inside the organic layer. In general, the thin film transistor in the organic electroluminescent device is stable and driven. Since the p-type thin film transistor excellent in aspect is used, there is a problem in that the thin film transistor T is degraded, such as a pinning effect, due to the influence of the charge present in the organic film.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems, and an object of the present invention is to provide an active matrix organic electroluminescent device which can prevent the characteristics of a thin film transistor from deteriorating.

In the active matrix organic electroluminescent device according to the present invention for achieving the above object, a thin film transistor is formed on an insulating substrate, and a first protective layer made of an inorganic insulating film is formed on the thin film transistor. Subsequently, a second passivation layer is formed on the first passivation layer, and the second passivation layer is removed. The first electrode connected to the thin film transistor is formed on the second passivation layer. Next, an organic light emitting layer is formed on the first electrode, and a second electrode is formed thereon.

In another active matrix organic electroluminescent device of the present invention, a thin film transistor is formed on an insulating substrate, and a first protective layer made of an inorganic insulating film is formed on the thin film transistor. Subsequently, a second passivation layer is formed on the first passivation layer, and a portion of the second passivation layer is removed, and red, green, and blue color filters are formed thereon. Next, red and green color conversion layers are formed on the red and green color filters, respectively, and first electrodes connected to the thin film transistors are formed on the color conversion layer and the blue color filter. Next, an organic light emitting light emitting blue light is formed on the first electrode, and a second electrode is formed thereon.

The first protective layer may be formed of any one of a silicon nitride film and a silicon oxide film.

On the other hand, the second protective layer may be made of an organic insulating film, it may be made of any one of benzocyclobutene and photo acrylic.

In the present invention, the organic light emitting layer may cover the thin film transistor.

As described above, in the present invention, since only the protective layer made of the inorganic insulating film or the protective layer made of the inorganic insulating film and the organic light emitting layer are present on the thin film transistor, and the organic layer does not exist, deterioration of the characteristics of the thin film transistor can be prevented.

Hereinafter, an active matrix organic electroluminescent device according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

4 is a cross-sectional view of an active matrix organic electroluminescent device according to a first embodiment of the present invention. As illustrated, a plurality of thin film transistors T1 are formed on the insulating substrate 110. The thin film transistors T1 are formed of a gate electrode 121 and source and drain electrodes 122 and 123, and are polycrystalline. It includes an active layer 131 made of silicon. Here, the substrate 110 may be made of a transparent substrate such as a glass substrate.

Next, a first protective layer 140 is formed on the thin film transistor T1 to cover the thin film transistor T1 and has a contact hole exposing the drain electrode 123. It is preferable that it consists of an insulating film. Here, the first protective layer 140 may be formed of a silicon nitride film or a silicon oxide film.                     

Next, a second passivation layer 150 is formed on the first passivation layer 140. The second passivation layer 150 is formed of an organic layer and removed from the top of the thin film transistor T1. In this case, the second protective layer 150 may be made of a material such as benzocyclobutene (hereinafter referred to as BCB) or photo-acryl.

Next, a first electrode 160 is formed on the second protective layer 150, and the first electrode 160 is connected to the drain electrode 123. The first electrode 160 may be made of a transparent conductive material such as ITO or IZO, and the first electrode 160 may serve as an anode electrode.

Subsequently, organic emission layers 171, 172, and 173 that emit red, green, and blue light are formed on the first electrode 160.

Next, a second electrode 180 is formed on the entire surface of the substrate 110 on the organic light emitting layers 171, 172, and 173, and the second electrode 180 is formed of an opaque conductive material such as metal to serve as a cathode. can do.

As described above, in the exemplary embodiment of the present invention, since only the first protective layer 140 made of the inorganic insulating layer is present on the thin film transistor T1, and the organic layer does not exist, the characteristic of the thin film transistor T1 is prevented from deteriorating. can do.

However, since the organic light emitting layers of red, green, and blue have different lifetimes in the organic electroluminescent device, it is difficult to maintain color when driving for a long time. Recently, in order to solve this problem, a method in which each pixel has the same organic emission layer and color is implemented using a color changing medium has been proposed.                     

An active matrix organic electroluminescent device according to a second embodiment of the present invention is illustrated in FIG. 5.

As illustrated, a plurality of thin film transistors T2 including the gate electrode 221 and the source and drain electrodes 222 and 223 are formed on the insulating substrate 210, and the thin film transistors T2 are made of polycrystalline silicon. The active layer 231 is formed.

Next, a first passivation layer 240 covering the thin film transistor T2 and having a contact hole exposing the drain electrode 223 is formed on the thin film transistor T2. The first protective layer 240 is preferably made of an inorganic insulating film, and may be made of a silicon nitride film or a silicon oxide film.

Next, a second passivation layer 250 is formed on the first passivation layer 240. The second passivation layer 250 is formed of an organic layer and removed from the top of the thin film transistor T2. In this case, the second protective layer 250 may be made of a material such as BCB or photo acryl.

Next, red, green, and blue color filters 263a, 262a, and 261 are formed on the second passivation layer 250, respectively, and green and red on the green color filter 262a and the red color filter 263a, respectively. Color conversion layers 262b and 263b are formed.

Next, a first electrode 270 is formed on the blue color filter 261 and the green and red color conversion layers 262b and 263b, and the first electrode 270 is connected to the drain electrode 223.

Next, an organic emission layer 280 that emits blue light is formed on the first electrode 270. In this case, the organic light emitting layer 280 is formed over the entire surface of the substrate 210 to cover the thin film transistor T2. Since the organic light emitting layer 280 has a small amount of electric charge present therein, the organic light emitting layer 280 is disposed on the thin film transistor T2. Positioning does not significantly affect the characteristics.

Next, a second electrode 290 is formed over the entire surface of the substrate 210 on the organic emission layer 280.

The present invention is not limited to the above embodiments, and various changes and modifications can be made without departing from the spirit of the present invention.

In the active matrix organic electroluminescent device according to the present invention, since only a protective layer made of an inorganic insulating film is present on the thin film transistor and no organic film is present, the characteristics of the thin film transistor can be prevented from being lowered.

On the other hand, when the color conversion layer is used to make the life of the device the same, the organic light emitting layer is positioned above the thin film transistor, but the organic light emitting layer has little influence on the characteristics of the thin film transistor because the amount of charge is small inside.

Claims (6)

Insulating substrate; A thin film transistor formed on the substrate; A first protective layer covering the thin film transistor and formed of an inorganic insulating film; A second passivation layer formed on the first passivation layer and having a portion located above the thin film transistor; A first electrode formed on the second passivation layer and connected to the thin film transistor; An organic light emitting layer on the first electrode; A second electrode formed on the organic emission layer Active matrix organic electroluminescent device comprising a. Insulating substrate; A thin film transistor formed on the substrate; A first protective layer covering the thin film transistor and formed of an inorganic insulating film; A second passivation layer formed on the first passivation layer and having a portion located above the thin film transistor; Red, green, and blue color filters formed on the second passivation layer; A red and green color conversion layer formed on the red and green color filters, respectively; A first electrode formed on the red and green color conversion layers and the blue color filter and connected to the thin film transistor; An organic emission layer formed on the first electrode and emitting blue light; A second electrode formed on the organic emission layer Active matrix organic electroluminescent device comprising a. The method according to claim 1 or 2, The first protective layer is an active matrix organic electroluminescent device comprising any one of a silicon nitride film and a silicon oxide film. The method of claim 3, wherein The second protective layer is an active matrix organic electroluminescent device comprising an organic insulating film. The method of claim 4, wherein The second protective layer is an active matrix organic electroluminescent device comprising any one of benzocyclobutene and photo acryl. The method of claim 2, The organic light emitting layer is an active matrix organic electroluminescent device covering the thin film transistor.

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