KR20050089236A - Organic light emitting diode and method of forming passivation layer for organic light emitting diode - Google Patents

Abstract

Disclosed are a method of forming an OLED and a protective film for an OLED.

In the method of the present invention, a protective film is formed on the second electrode of the top-emitting organic light-emitting device comprising a first electrode, an organic film including a light emitting layer, and a second electrode including a transparent conductive film, on the substrate. And a low speed deposition step of forming a seed layer at a relatively low speed, and a high speed deposition step of forming a body layer at a relatively high deposition rate on the seed layer.

According to the present invention, it is possible to form a protective film having good humidity and oxygen barrier properties having a high overall density and high efficiency, and to protect the lower films already formed from damage by plasma.

Description

Organic light emitting diode and method of forming passivation layer for organic light emitting diode

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an organic light emitting device used in an organic light emitting display device and a method of forming the same, and more particularly, to a protective film structure of an organic light emitting device (OLED) and a method of manufacturing the protective film.

The organic light emitting display device, which has recently attracted attention as a next-generation flat panel display device, has excellent characteristics such as self-luminous, wide viewing angle, and fast response characteristics. An organic light emitting diode (OLED) used in such an organic light emitting diode display is generally provided with a first electrode, an organic layer including a hole transport layer, a light emitting layer, an electron transport layer, and a second electrode on a glass substrate.

When a voltage of about several volts V is applied between the first and second electrodes, holes are generated in the first electrode, and electrons separated in the second electrode are generated. The generated holes and electrons are combined in the light emitting layer via the hole transport layer or the electron transport layer, respectively, to generate excitons of high energy state. As the excitons return to the ground state, light with energy corresponding to the energy difference between the two states is generated. Typically, light passes through the substrate through the first electrode having transparency. In addition, the organic light emitting device may be variously configured in the display device, in which the electron and hole generation and transport layers may be formed separately, or the electroluminescent layer may serve as the generation layer or transport layer.

BACKGROUND ART A display device using an organic light emitting element for a pixel includes a simple matrix organic electroluminescent display and an active matrix organic electroluminescent display. The simple matrix organic light emitting display device includes an organic film made of a hole transporting layer, a light emitting layer, an electron transporting layer, and the like at a position where a plurality of anode lines and a cathode line cross each other, and each pixel lights only a selection time during one frame period. . The selection time is a time width obtained by dividing one frame period by the number of anode lines. The simple matrix organic electroluminescent display has the advantage that the structure is simple.

However, when the number of pixels increases, the selection time becomes short. Therefore, it is necessary to increase the driving voltage, increase the instantaneous luminance during the selection time, and set the average luminance in one frame period to a predetermined value. Therefore, there is a problem that the lifespan of the organic light emitting element is shortened. In addition, since the organic light emitting element is a current drive, especially in the case of a large screen, a voltage drop due to wiring resistance occurs, and voltage cannot be uniformly applied to each pixel, resulting in luminance fluctuations in the display device. Therefore, the simple matrix organic electroluminescent display has limitations in resolution and large screen.

In an active matrix organic light emitting display device, each pixel includes an organic layer constituting an organic light emitting element and a driving element including several thin film transistors such as a switching transistor. Therefore, it is possible to continue lighting in the selected pixel of the display device during one frame period, and it is not necessary to increase the maximum luminance, so that the life of the organic light emitting element can be long. Therefore, in view of resolution and large screen, an active matrix organic electroluminescent display is advantageous.

In the case where the organic light emitting display emits light toward the substrate on the rear side as usual, the aperture ratio is limited in the active matrix organic electroluminescent display device in which a thin film transistor for driving element is provided between the substrate and the organic light emitting element. In order to solve this problem, attempts at front emission to make the upper second electrode transparent and emit light from the upper electrode side are increasing. For example, a method of forming an organic light emitting display device using a second upper electrode as a two-layer structure, using an electron injection layer such as an alkaline metal layer as a first layer, and a transparent electrode such as indium tin oxide (ITO) as a second layer Known.

On the other hand, in order not to damage the lower organic light emitting layer, a low temperature film forming process is required to form the second electrode and the protective film positioned thereon. In place of the protective film, a separate substrate may be placed on the second electrode and sealed to the lower substrate. In particular, in the front emission type and the flexible screen type, the light efficiency, the deformation flexibility of the formed screen, the convenience of the process, In consideration of cost, it is more preferable to form a protective film instead of a substrate. 1 is a cross-sectional view illustrating a film formation structure of a pixel portion of an organic light emitting display device in which a passivation layer 110 is formed on a second electrode 100.

When oxygen or moisture flows into the organic layer 90 or the second electrode 100 including the light emitting layer, there is a problem that the electrode is oxidized and corroded while the electroluminescence is performed. When the electrode is oxidized, there is a problem that current leakage and short circuit occur, and pixel defects occur, which in turn shortens the life of the display device itself. In the case of the top emission type organic light emitting display device, since the light emitted from the light emitting layer is emitted to the outside through the second electrode 100 and the passivation layer 110, the passivation layer 110 and the related luminous efficiency should be considered.

Therefore, the adoption of an excellent water resistant low temperature forming protective film that can protect the internal organic light emitting layer from moisture or oxygen is essential for manufacturing an organic light emitting device. Moreover, in the front emission type or the flexible screen type, the adoption of a protective film having the above-described characteristics while having excellent transmittance and refractive index is essential for manufacturing an organic light emitting device.

Conventional protective film materials include inorganic materials such as SiO ₂ , SiNx, SiON, and Al ₂ O ₃ , which are used as protective film layers of semiconductor devices, and organic materials such as polyethylene terephthalate, polyvinylidene fluoride, polymethyl methacrylate, and polyimide. The material was used. In general, the method of forming the protective film is used a lot of CVD methods such as a thin film PECVD (Plasma Enhanced Chemical Vapor Deposition), such as SiO _2, SiNx, SiON. However, CVD has a problem of deteriorating organic film characteristics of the organic light emitting device, even at low temperature CVD, mostly made at a temperature of 200 ℃ to 400 ℃ to improve the properties of the film.

In this regard, Huang recently formed a low temperature silicon nitride film (SiN _X ) using PECVD to visualize its use as a protective film (Materials Science & Engineering B, Vol. 98, p248, 2003). In addition, Japan's ULVAC and ANELVA have also reported the formation of silicon nitride films using CAT-CVD (Catalytic CVD) through the development of low-temperature growth SiN _X film forming equipment on large-area substrates (Thin Solid Films Vol. 430, p58). , p165, 2003).

However, HDP CVD (High Density Plasma CVD) using a high density plasma or CAT-CVD using a high temperature susceptor deteriorates the organic layer as the temperature is raised by exposing the lower layers already formed while using the high density plasma and the temperature is increased. An interfacial reaction between each layer of the underlying membrane takes place. Among the interfacial reactions, in particular, a reaction between the electron injection layer and the transparent electrode of the second electrode, the electron injection layer, and the organic light emitting layer may cause leakage of current.

In addition, when the protective film is grown at a low temperature through the CVD process, the growth rate of the film may be slow, which may cause a decrease in process productivity, and the growth of a thin film having a dense structure is difficult, and thus the film properties are easily deteriorated. When the low temperature forming thin film is thick, there is also a problem in that cracks are likely to occur due to tension generation in the film, and thus it cannot serve as a protective film.

An object of the present invention is to provide an OLED having a protective film and a method for forming a protective film for OLED, which can solve the conventional problems as described above.

An object of the present invention is to provide a method for forming a protective film for an OLED having a growth rate that can prevent a decrease in productivity in the overall process.

An object of the present invention is to provide an OLED and a protective film forming method for the OLED having a protective film that can prevent the lower organic light emitting layer degradation and current leakage.

In addition, it is an object of the present invention to provide an OLED having a protective film having excellent transmittance, refractive index and external air blocking ability, and a method for forming a protective film for such an OLED.

In the organic light emitting device (OLED) of the present invention for achieving the above object in the organic light emitting device is provided with a first electrode, an organic film including a light emitting layer, a second electrode and a protective film in order on the substrate,

The protective film is made of the same material, but characterized in that it comprises a relatively thin low-speed deposition seed layer having a dense crystal density and a relatively thick high-speed deposition body layer.

In particular, the present invention is preferably used for an organic light emitting device of a top emission type or flexible screen type organic light emitting display device in which the second electrode includes a transparent conductive film.

In the present invention, a material of the protective film may be a silicon-based compound such as SiO ₂ , SiNx, SiON, or a transition metal oxide such as ZrO, HfO, TaO, RuO, ZnO, WO, CoO, or the like.

The method for forming a protective film for an OLED of the present invention for achieving the above object,

In forming a protective film on the second electrode of the top-emitting organic light emitting device comprising a first electrode, an organic film including a light emitting layer, and a second electrode including a transparent conductive film in order on the substrate,

And a low speed deposition step of forming a seed layer at a relatively low deposition rate and a high speed deposition step of forming a body layer at a relatively high deposition rate on the seed layer.

In the present invention, the forming of the seed layer may be performed at a temperature of 100 ° C. or lower, more preferably 80 ° C. or lower, using an inductively coupled plasma (ICP) CVD apparatus.

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

2A and 2B are cross-sectional views illustrating important steps of a low temperature multi-stage protective film deposition process according to an embodiment of the present invention, and FIG. 3 is a passivation rate of a protective film deposition process over time in a low-temperature multistage protective film deposition process according to an embodiment of the present invention. It is a graph represented by the change relationship of.

Referring to FIGS. 2A and 2B, a process of forming a passivation layer on a substrate is briefly described. First, a thin film transistor is formed on the substrate 10. The thin film transistor typically includes one thin film transistor serving as a switch for each pixel and one or more driving thin film transistors.

As an example of a method of forming a thin film transistor, a buffer film (not shown) is first formed on a substrate 10 using a silicon oxide film or the like. The gate electrode 20 and the gate line are formed on the buffer film, and the gate insulating film 30 is stacked thereon. A source / drain region and a channel formed of the amorphous silicon layer 40 are formed on the gate insulating layer 30. Contact holes are formed with the interlayer insulating film 45, and data lines and source / drain electrodes 51 and 53 are formed. A contact hole exposing the interlayer insulating film 60 and the drain (source) electrode 53, which also serves as a thin film transistor protective film, is formed.

Next, a method of forming an organic light emitting diode connected to the drain electrode 53 of the thin film transistor will be described. A first electrode 70 corresponding to the pixel electrode or the anode is formed so as to be connected to the drain (source) electrode 53 through the contact hole already formed in each pixel portion. A barrier rib 80 pattern is formed to distinguish each pixel, and an organic layer 90 including a light emitting layer is formed on the first electrode 70 of each pixel portion that is divided into the barrier rib 80 pattern. In general, the organic layer 90 has a structure including organic layers having a differentiated function such as a hole transporting layer, a light emitting layer, an electron transporting layer, and an electron injection layer in more detail.

The second electrode 100 corresponding to the common electrode or the cathode is formed on the organic layer 90. The first electrode 70 and the second electrode 100 may be regarded as constituting a capacitor. However, when the organic layer 90 has the same characteristics as a diode, each pixel includes a plurality of thin film transistors and one diode. It may be said that it is configured. The second electrode 100 may also have a differentiated detailed layer structure. In the organic light emitting device of the top emission type, a transparent conductive film such as indium tin oxide (ITO) is the central part of the organic light emitting device so that most of the light is transmitted. Is done.

The passivation layer is formed on the second electrode 100. The protective film is preferably formed using an ICP CVD apparatus that can reduce the underlying film damage by the plasma while applying a high density plasma. As a protective film, a silicon nitride film such as Si ₃ N ₄ is most commonly used, but other silicon compounds such as SiO ₂ , SiNx, SiON, and transition metal oxides such as ZrO, HfO, TaO, RuO, ZnO, WO, CoO, and the like may be used. have.

First, as shown in FIG. 2A, a low temperature seed layer 210 having a dense crystal density is formed on a substrate on which the second electrode 100 is formed while controlling process variables. Process variables may include the frequency of RF power applied to the substrate table on which the substrate is placed, the distance between the substrate and the ICP source, the flow rate of the source gases forming the film, and the like. The temperature of the substrate is maintained at 80 ° C. or lower using cooling water of the substrate table or substrate chuck and back side helium (helium supplied between the substrate and the substrate chuck). In this configuration, it is possible to exclude the heater device usually provided on the substrate in the CVD process has the advantage of lowering the manufacturing cost of the equipment.

In such a low temperature substrate environment, source gases such as silane (SiH ₄ ), ammonia (NH ₃ ) and nitrogen (N ₂ ) gas are supplied to the CVD chamber through an injector. Activated radicals past the ICP region in the chamber are deposited at a low growth rate with a small critical nuclear growth size at the substrate surface over the second electrode to form a seed layer 210. The seed layer may act as a buffer between the lower layer and the lower layer when forming the main body layer growing at a high speed, induces the state of the protective film main body layer to a high crystal density state such as the seed layer, and the plasma impact It serves to protect the lower film such as an electrode from the.

In a more specific example, in the seed layer forming step, for example, a distance between a substrate table or a substrate and an ICP source is 15 to 20 cm based on a large substrate having a length of 2M, and a process pressure of a CVD chamber is 5 mTorr to 10 mTorr, and a substrate temperature. When the temperature is 80 ° C. or less, a high frequency power of 0 to 100 W can be applied to the magnetic field forming coil through the substrate chuck so as to form an ICP. At this time, the high frequency electric field generated through the substrate chuck causes the high frequency of the megahertz band to be applied so that ion acceleration having high kinetic energy among plasma particles is weakened.

In addition, the injection amount of the source gas or the precursor gas is lowered to maintain a low deposition rate so as to have a dense crystal structure. For example, the gas input amount and the gas input ratio are silane: nitrogen: argon = 5 sccm: 15 sccm: 20 sccm, silane: nitrogen: ammonia: argon = 5 sccm: 15 sccm: 15 sccm: 20 sccm, silane: ammonia: Argon = 5sccm: 15sccm: 20sccm is mentioned. Argon is used for forming plasma, not as a source gas.

Since the seed layer formation rate is low, the thickness of the seed layer may be formed so that the seed layer 210 covering the second electrode 100 is suitable for preventing plasma damage to the second electrode in an environment in which the body layer 220 is formed. It is preferable to set the minimum thickness at.

Once the seed layer 210 is formed, the body layer 220 is formed on the seed layer 210 by changing the protective film deposition environment as shown in FIG. 2B. In relation to the CVD process conditions at this time, high power is input to the magnetic field forming coil and the high frequency application electrode for forming the ICP. However, in order to accelerate the plasma particles to have a high kinetic energy through the high frequency application electrode, a relatively low frequency of the kilohertz band is applied. In order to maintain a high deposition rate, the injection amount of the source gas or the precursor gas is increased.

For example, high frequency power of 100 to 1000 W may be applied to a magnetic field forming coil through a substrate chuck to power the magnetic field forming coil to form an ICP under the same conditions. At this time, the high frequency electric field generated through the substrate chuck causes a relatively low frequency of the kilohertz band to be applied to enhance ion acceleration having high kinetic energy among the plasma particles.

In addition, in order to have a high deposition rate, the injection amount of source gas or precursor gas is increased to 10 to 100 sccm of silane, 200 to 500 sccm of ammonia, 50 to 200 sccm of nitrogen, and 10 to 50 sccm of argon, and the main speed control is silane. Use gas. For example, the gas input amount and the gas input ratio are silane: nitrogen: argon = 20 sccm: 50 sccm: 20 sccm, silane: nitrogen: ammonia: argon = 20 sccm: 50 sccm: 30 sccm: 20 sccm, silane: ammonia: Argon = 20sccm: 50sccm: 20sccm is mentioned.

Although the film is formed at a high rate when forming the body layer, a protective film having a relatively dense crystal density may be formed because the crystal structure of the lower seed layer serves to induce the crystal structure of the body layer. As a result, the protective film having the necessary characteristics can be formed with high overall efficiency through the multi-stage process.

 3 is an exemplary graph of protective film growth rate over time of an OLED formed in one process chamber in accordance with the present invention. Since the inclined portion between the seed layer forming step and the main body layer forming step is transient, the first inclined part and the first inclined part may not be set if a separate transition step is set between the seed layer forming step and the main body layer forming step of the protective film. Along with the last inclined portion, it may appear naturally in the film forming process.

FIG. 4 is a graph showing Mocon test (moisture permeability test) results of a protective film made of silicon nitride film grown on a polyethersulfone (PES) film. As shown in the results, a low water vapor transmission rate of 5 × 10 ⁻² mg / m ² -day was observed for the silicon nitride film formed by the two-step protective film forming process using the low temperature seed layer on the basis of 24 hours after the experiment.

On the other hand, the above embodiment is made by way of illustration for explaining the present invention. Therefore, the OLED can be implemented in various forms within the limits described in the claims in the detailed configuration, and the organic electroluminescent display device in which the OLED is used also forms the polysilicon layer on the substrate in the number and form of the thin film transistor. And an upper gate type to form a gate thereon.

According to the present invention, a protective film having an overall dense crystal density can be formed with high efficiency. A protective film having a dense crystal density formed through such a process has good barrier property against humidity and oxygen, and in the formation process, the seed layer protects the lower films already formed on the substrate from damage due to plasma and thus leakage current through the organic film. It is possible to provide OLEDs with high characteristics by suppressing generation.

1 is a cross-sectional view illustrating a film formation structure of an organic light emitting display pixel portion including an organic light emitting element and a thin film transistor having a passivation layer formed thereon.

2A and 2B are cross-sectional views illustrating important steps of a low temperature multi-stage protective film deposition process according to an embodiment of the present invention.

3 is a graph showing a low temperature multi-step protective film deposition process according to an embodiment of the present invention as a change in the protective film deposition rate over time;

FIG. 4 is a graph showing Mocon test (moisture permeability test) results of a protective film made of silicon nitride film grown on a polyethersulfone (PES) film.

* Explanation of symbols for the main parts of the drawings

10 substrate 20 gate electrode

30: gate insulating film 40: silicon layer

45,60: interlayer insulating film 51,53: source / drain electrodes

70: first electrode 80: partition

90: organic film 100: second electrode

110: protective film 210: protective film seed layer

220: protective film body layer

Claims (7)

In an organic light emitting device (OLED) formed of a first electrode, an organic film including a light emitting layer, a second electrode and a protective film in order on the substrate, An organic light emitting diode (OLED), characterized in that the protective film has a dense crystal density of the same material but has a relatively thin slow deposition seed layer and a relatively thick fast deposition body layer. The method of claim 1, The organic light emitting device (OLED), characterized in that the second electrode comprises a transparent conductive film. The organic light emitting device of claim 1, wherein the protective layer is formed of one of silicon-based compounds such as SiO ₂ , SiNx, and SiON and transition metal-based oxides such as ZrO, HfO, TaO, RuO, ZnO, WO, and CoO. ). In the step of forming a protective film on the second electrode of the top-emitting organic light emitting diode (OLED) comprising a first electrode, an organic film including a light emitting layer, and a second electrode including a transparent conductive film in order on the substrate, A slow deposition step of forming a seed layer at a relatively low deposition rate, A method of forming a protective film for an organic light emitting device (OLED), characterized in that the high-speed deposition step of forming a body layer on the seed layer by relatively high deposition rate is provided. The method of claim 4, wherein The low-speed deposition step is a method for forming a protective film for an organic light emitting device (OLED), characterized in that at a temperature below 100 ℃ using an inductively coupled plasma (ICP) CVD equipment. The method of claim 5, Process pressure 5-10 mTorr, The low-speed deposition step is a high frequency power of 0 ~ 100Watt applied to the substrate chuck, 100 ~ 500Watt of the magnetic field forming power for ICP, the supply rate range of 5 ± 3sccm of xylene gas The high-speed deposition step is a high-frequency power 100 to 1000 Watts applied to the substrate chuck, 500 to 3000 Watts of magnetic field formation power for ICP, 10 to 100 sccm of the supply rate of xylene gas, characterized in that the protective film forming method for an organic light emitting device (OLED). The method of claim 4, wherein In the deposition step, a protective film for an organic light emitting diode (OLED), characterized in that the characteristics of the deposited film are controlled through the high frequency power applied to the chuck on which the substrate is placed, the distance between the magnetic field forming coil for ICP and the substrate, and the supply rate of the deposition source gas. Forming method.