JP2007123174A - Organic electroluminescent element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an organic EL element having a barrier layer capable of preventing intrusion of moisture or oxygen into an organic compound layer and effectively taking out the light emitted therefrom. <P>SOLUTION: The organic EL element is composed of an opaque electrode 2, the organic compound layer 6, a transparent electrode 7 and the barrier layer 8 covering those elements laminated on a glass substrate 1. The barrier layer 8 formed on the transparent electrode 7 is made to contain at least silicon, nitrogen, and hydrogen as main component, and oxygen as additive element, made to contain an area where density of nitrogen against that of silicon is 30 atomic% or higher and 70 atomic% or lower, and gradient of oxygen density is made to periodically change in film thickness direction. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an organic electroluminescence (EL) element used for a flat panel display or the like.

  Conventionally, a liquid crystal element has been most widely used as a flat panel display, but the response speed to an electric field is as slow as several tens of msec, and this response speed is a problem for displaying moving images. Come. There is also a problem that viewing angle dependency is large.

  In order to solve the above problems, an organic EL element, which is a self-luminous device compatible with a flat panel, has recently attracted attention. However, the organic EL element causes deterioration in characteristics due to moisture and oxygen, and an organic compound layer and The electrode layer is peeled off, causing dark spots. Therefore, in order to realize a space-saving flat panel display using an organic EL element, a highly functional barrier layer for preventing infiltration of moisture and oxygen into the organic compound layer is required.

Conventionally, the barrier layer having a high transmittance is formed by vapor deposition, sputtering, or CVD using silicon dioxide (SiO ₂ ) or silicon nitride (Si ₃ N ₄ ).

  However, the organic compound layer constituting the organic EL element is crystallized at a temperature exceeding 100 ° C., resulting in deterioration of the characteristics of the organic EL element. Therefore, at least an opaque electrode, an organic compound layer, and a transparent electrode are laminated, and the barrier layer formed thereon is required to be formed at a low temperature of 80 ° C. or lower.

  A silicon dioxide film or a silicon nitride film using sputtering formed on a laminated film including an organic compound layer does not have a performance of sufficiently preventing moisture from deteriorating the characteristics of the organic EL element. That is, these films formed by sputtering are hard and have poor coverage, and are not sufficiently covered by the influence of the surface roughness of the electrode on which the film is formed. Furthermore, cracks and defects are generated due to the internal stress of the film.

  In addition, a silicon dioxide film using plasma CVD is formed at a high temperature exceeding 300 ° C. to obtain a barrier layer having a high moisture resistance, but a sufficient moisture resistance cannot be obtained at a temperature of 100 ° C. or less. . Furthermore, when the thickness of the silicon nitride film formed by plasma CVD is increased, the light transmittance is greatly reduced. Further, the film stress causes cracks and a decrease in coverage, and it is not suitable as a barrier layer on the light extraction surface side. It is enough.

  Patent Document 1 discloses an organic EL element in which a polycarbonate substrate is coated with a resin layer, planarized, and a moisture barrier film made of silicon oxynitride is formed by sputtering. Patent Document 2 discloses a semiconductor device using a semiconductor insulating film such as a TFT and a manufacturing method thereof. However, in the method of heating the substrate temperature to 350 ° C. or higher, the organic compound layer is denatured and denatured by heat, causing deterioration of the characteristics of the organic EL element. In addition, the moisture proof performance of the silicon oxynitride film decreases due to an increase in the amount of oxygen in the film, and the silicon oxynitride film in which the oxygen concentration with respect to the total number of silicon, nitrogen, and oxygen exceeds 50 atomic% is the moisture proof performance of the organic EL element. It is insufficient.

JP 2002-1000046 A JP 2001-53286 A

  Thus, even in the methods disclosed in Patent Documents 1 and 2, it is difficult to form a barrier layer of an organic EL element that is weak against plasma ion bombardment and heat.

  The problem to be solved by the present invention is to provide an organic EL device having a barrier layer that prevents moisture and oxygen from entering the organic compound layer and can efficiently extract light emitted from the organic compound layer. is there.

The present invention relates to an organic EL device comprising at least an opaque electrode, an organic compound layer, a transparent electrode and a barrier layer covering them laminated on a substrate.
The barrier layer formed on the transparent electrode includes at least silicon, nitrogen, and hydrogen as main components, oxygen as an additive element, a region having a nitrogen concentration of 30 to 70 atomic% with respect to silicon, and in a film thickness direction. The organic EL device is characterized in that a nitrogen concentration gradient is periodically formed.

  In the present invention, the barrier layer is preferably formed by a VHF plasma CVD method.

  The organic EL device of the present invention can be composed of a barrier layer having a high light transmittance from the organic compound layer and a high moisture-proof performance, and can prevent device deterioration and occurrence of dark spots.

  The present invention is described in detail below.

  1 and 2 are conceptual diagrams of an example of the organic EL element of the present invention.

  In the organic EL device shown in FIG. 1, a hole injection electrode 2 which is an opaque electrode is formed on a glass substrate 1, and an organic compound of a hole injection transport layer 3, a light emitting layer 4 and an electron injection transport layer 5 is formed thereon. Layer 6 is formed. Further, an electron injection electrode 7 which is a transparent electrode is formed thereon, and a barrier layer 8 is formed so as to cover them. In addition, the lower layer of the opaque electrode 2 often forms a TFT.

  ITO and IZO are preferably used for the transparent electrode 7 of the organic EL element of the present invention, but ITO may contain tungsten or Zn.

  The barrier layer 8 is formed on the transparent electrode 7 on the light extraction surface side of the light emitted from the light emitting layer 4 by a plasma CVD method so as to substantially cover the opaque electrode 2, the organic compound layer 6, and the transparent electrode 7. By using a VHF band with an excitation frequency of plasma CVD of 30 MHz or more and 100 MHz or less, plasma ion bombardment can be weakened and thermal damage to the element can be suppressed, and a dense and defect-free silicon oxynitride film and silicon nitride film can be formed. it can.

  Since the organic EL element has poor adhesion between the organic compound layer 6 and the electrodes 2 and 7, the barrier layer 8 is required to have high uneven coverage on the surface of the transparent electrode 7, moisture resistance, and low stress film quality.

  From the results shown in Table 1 to be described later, it was found that the coverage and moisture resistance can be improved by reducing the nitrogen concentration of the silicon nitride film to a range of 30 to 70 atomic%. This is considered to be that by reducing the nitrogen concentration with respect to silicon, the nitride film is close to the nature of metal, and the flexibility and coverage are improved.

  However, in order to obtain a high light transmittance with a low stress, a silicon nitride layer having a low nitrogen concentration cannot satisfy the light transmittance. Therefore, a low nitrogen concentration silicon nitride layer and a barrier film in which a nitrogen concentration gradient is periodically formed by increasing or decreasing the nitrogen concentration of the silicon nitride layer or the silicon oxynitride layer are effective.

  In the organic EL device of the present invention, the internal stress in the barrier film 8 is reduced by forming a nitrogen concentration gradient periodically in the film thickness direction, including a region where the nitrogen concentration relative to silicon is 30 or more and 70 atomic% or less. In addition, a film having high moisture resistance and high light transmittance was formed.

  The following two patterns are shown as specific representative examples.

  The barrier layer 8 of the organic EL element 1 forms a silicon nitride layer in which the nitrogen concentration with respect to silicon is gradually increased to 50 or more and 110 atomic% or less in the range of about 500 mm from the surface of ITO. Thereafter, the thickness of 5000 mm is formed constant at a nitrogen concentration of 110 atomic%. Thereafter, in the film thickness range of about 500 mm, the nitrogen concentration is gradually reduced to 50 atomic%, and then 1000 mm is made constant. Thereafter, for 500%, only the nitrogen concentration is gradually increased to 110 atomic%, and thereafter, a film thickness range of about 5000% is formed while maintaining the nitrogen concentration at 110 atomic%.

  In the organic EL element 2, the barrier layer 8 has an oxygen concentration of 30 atomic% with respect to silicon and a nitrogen concentration of 110 atomic% with respect to silicon within a range of about 5000 mm from the surface of ITO. In the subsequent film thickness range of about 500 mm, the oxygen concentration is 0 atomic% and the nitrogen concentration is gradually reduced to 70 atomic%. Thereafter, for 1000 liters, the oxygen concentration is maintained at 0 atomic% and the nitrogen concentration is maintained at 70 atomic%. Thereafter, in the film thickness range of about 500 mm, the oxygen concentration is increased to 30 atomic% and the nitrogen concentration is increased to 110 atomic%. This is repeated again, and thereafter, a film thickness range of about 3000 mm is maintained and formed.

  The nitrogen concentration gradient at this time was formed by changing the flow rate of ammonia. It is also possible to change the silane gas flow rate or control the plasma power.

  An organic EL element in which a part of the barrier layer 8 includes a region having a nitrogen concentration of 30 to 70 atomic% with respect to silicon and has a nitrogen concentration gradient periodically in the film thickness direction has the following effects. That is, this organic EL element has not only high moisture proof performance, but also can suppress light reflection caused by lamination of films having different refractive indexes and improve light transmittance.

  The barrier layer used in the organic EL device of the present invention is also effective in the bottom emission device.

  Examples of the present invention will be described below.

[Example 1]
The moisture permeability including the coverage of the barrier layer of the present invention was measured as follows.

1000 calcium films were formed on a silicon wafer on which slits having a width of 1 μm, a depth of 1 μm, and a slope angle of 55 ° were formed. Using this silicon wafer, a barrier film was formed thereon, and an acceleration test was performed by a pressure cooker under the conditions of 121 ° C., 2 × 10 ⁵ Pa, and 100% RH. Then, the ring illumination was irradiated, it observed with the optical microscope, and the number of defects which looked at a black spot was counted.

The conditions of the silicon nitride film were varied such that the silane flow rate was 50 sccm and the ammonia flow rate was 0 or more and 1000 sccm or less. The deposited film forming device is composed of a high-frequency electrode and a substrate holder / ground electrode facing it, and the silicon wafer substrate on which calcium is deposited is set in the substrate holder, and further, nitrogen gas is flowed to discharge the pressure of the discharge furnace. Was maintained at 100 Pa. Thereafter, the vacuum vessel was once evacuated to 1 × 10 ⁻⁵ Pa, and then monosilane gas and ammonia gas were flowed to control the reaction space pressure to 100 Pa. Then, 60 MHz high frequency power having a power density of 150 mW / cm ² was supplied to the high frequency electrode, and a silicon nitride film having a thickness of about 6000 mm was deposited.

The sample was allowed to stand for 20 hours in a pressure cooker apparatus having an environment of 2 × 10 ⁵ Pa, 121 ° C., and RH 100%, and the moisture permeability was evaluated by the change in the reflectance of calcium formed on the silicon wafer.

  As a result, as shown in Table 1, the number of defects that appear as black spots is 6 when the nitrogen concentration relative to silicon is 0 atomic%, 0 when 30 or more and 70 atomic% or less, 5 when 90 atomic%, or 14 when 110 atomic%. It has occurred. From this, when the nitrogen concentration is 30 or more and 70 atomic% or less, the results are high in coverage and moisture resistance.

[Example 2]
In Example 2, the barrier layer having the nitrogen concentration gradient shown in FIG. 2 is formed on the transparent electrode of the organic EL element using the nitrogen concentration of 30 to 70 atomic%, which is a good result from the result of Example 1. After forming, the characteristics of the device were evaluated.

  First, a chromium electrode is formed on a glass substrate, an organic compound layer is formed thereon by vapor deposition, and a transparent electrode of the upper layer is formed by sputtering ITO to a thickness of 150 nm, and further covers the organic compound layer and the transparent electrode. Thus, the barrier layer was formed by plasma CVD as follows.

The discharge furnace of the deposited film forming apparatus was kept at 80 ° C. An organic EL element was set on the substrate holder of the discharge furnace, and further nitrogen gas was flowed to maintain the pressure of the discharge furnace at 100 Pa and heated at 80 ° C. for 10 minutes. After that, the vacuum vessel is once evacuated to 1 × 10 ⁻⁵ Pa, and then flows by changing the monosilane gas in the range of 50 sccm, ammonia in the range of 20 to 500 sccm, and dinitrogen monoxide gas in the range of 0 to 80 sccm. The pressure was controlled at 100 Pa. Then, 60 MHz high frequency power having a power density of 150 mW / cm ² was supplied to the high frequency electrode, and a silicon nitride film was deposited on the organic EL element.

The plasma excitation frequency is preferably in the VHF band of 30 MHz to 100 MHz, but may be 27 MHz or 105 MHz. The power density is preferably 500 mW / cm ² or less.

  The barrier layer was formed as follows so that the nitrogen concentration gradient shown in FIG.

  The barrier layer of the organic EL element 1 increases the nitrogen concentration with respect to silicon from 50 atomic% to 110 atomic% in the range of about 1000 mm from the surface of ITO. Thereafter, a film thickness range of about 5000 mm is formed with an oxygen concentration of 30 atomic% and a nitrogen concentration of 110 atomic%. Thereafter, the oxygen concentration is reduced to 0 atomic% and the nitrogen concentration is reduced to 50 atomic% in a film thickness range of about 1000 mm, and thereafter the film thickness range of about 6000 mm is maintained. Thereafter, the film thickness range of about 500 mm increases the nitrogen concentration to 110 atomic%, and thereafter, the film thickness range of about 5000 mm maintains and forms this.

  The organic EL element 1 was left in an environment with a temperature of 60 ° C. and a relative humidity of 95%. The VI characteristics and luminance characteristics after 100 hours, 240 hours and 500 hours were measured. At the same time, an organic EL element sealed with a glass substrate and having calcium oxide inserted therein was produced, and compared with being left indoors. The results are shown in FIGS. As a result, there were almost no fluctuations in driving voltage and luminance, and no deterioration was observed. Furthermore, dark spots with a diameter of Φ1 μm or more were not generated.

[Example 3]
Next, in Example 3, the organic EL element 2 of the barrier layer having the nitrogen concentration gradient shown in FIG. 3 was formed in the same manner as in Example 2, and the VI characteristics and luminance after the acceleration test were measured. Furthermore, the situation of the dark spot was confirmed.

  In the organic EL element 2, the barrier layer was formed with an oxygen concentration of about 30 atomic% and a nitrogen concentration of 110 atomic% with respect to silicon in a range of about 5000 mm from the surface of ITO. Thereafter, in the film thickness range of about 500 mm, the oxygen concentration was gradually decreased to 0 atomic% and the nitrogen concentration was decreased to 70 atomic%, and the film thickness range of 6000 mm was maintained. Thereafter, a film thickness range of about 500 mm was formed by increasing the nitrogen concentration to 110 atomic%.

  The organic EL element 2 was left in an environment with a temperature of 60 ° C. and a relative humidity of 95%. The VI characteristics after 100 hours, 240 hours and 500 hours were measured. The results are shown in FIGS. As a result, there was no significant difference in VI characteristics and luminance characteristics. In addition, dark spots of Φ1 μm or more were not generated.

  Thus, when the film thickness range of the nitrogen concentration of 30 or more and 70 atomic% or less is about 0.6 μm or more, moisture resistance can be improved, and the nitrogen concentration gradient is continuously combined with the barrier layer of nitrogen concentration of 70 atomic% or more. By changing it periodically, the transmittance can be improved.

  4 to 6 are schematic diagrams in which the nitrogen concentration is continuously and periodically changed. The barrier layer is configured by providing approximately 0.6 μm of a region having a nitrogen concentration of 30 to 70 atomic%. These barrier layers are also effective for the moisture-proof effect and light transmittance.

It is typical sectional drawing of one Embodiment in which the barrier layer of the organic EL element of this invention was formed. It is a schematic diagram of one Embodiment showing the nitrogen concentration gradient in the barrier layer of the organic EL element of this invention. It is a schematic diagram of one Embodiment showing the nitrogen concentration gradient in the barrier layer of the organic EL element of this invention. It is a schematic diagram showing the nitrogen concentration gradient in the barrier layer of the organic EL element of this invention. It is a schematic diagram showing the nitrogen concentration gradient in the barrier layer of the organic EL element of this invention. It is a schematic diagram showing the nitrogen concentration gradient in the barrier layer of the organic EL element of this invention. It is a graph of the drive voltage fluctuation | variation in the durability test of the organic EL element of this invention. It is a graph of the brightness | luminance change in the durability test of the organic EL element of this invention.

Explanation of symbols

1 Glass substrate 2 Opaque electrode (hole injection electrode)
3 hole injection transport layer 4 light emitting layer 5 electron transport layer 6 organic compound layer 7 transparent electrode (electron injection electrode)
8 Barrier layer 9 Protective glass 10 Adhesive (thing)

Claims (2)

In an organic electroluminescence device comprising at least an opaque electrode, an organic compound layer, a transparent electrode and a barrier layer covering them laminated on a substrate,
The barrier layer formed on the transparent electrode includes at least silicon, nitrogen, and hydrogen as main components, oxygen as an additive element, a region having a nitrogen concentration of 30 to 70 atomic% with respect to silicon, and in a film thickness direction. An organic electroluminescence device characterized in that a nitrogen concentration gradient is periodically formed.   2. The organic electroluminescence device according to claim 1, wherein the barrier layer is formed by a VHF plasma CVD method.

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