JP2004111201A - Substrate for light-emitting element, substrate with transparent conductive film for light-emitting element, and light-emitting element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a substrate suitable for a light-emitting element anda substrate having a transparent conductive film prevented from the generation of short circuits and dark spots, capable of preventing increase of a leak current. <P>SOLUTION: The substrate for an organic EL element is made to have a maximum surface roughness of 20 nm or less, and an average surface roughness of 1.0 nm or less. The substrate with the transparent conductive film for the organic EL element has a transparent conductive film formed on the substrate with a maximum surface roughness of the transparent conductive film of 20 nm or less, and average surface roughness of 1.0 nm or less. <P>COPYRIGHT: (C)2004,JPO

Description

【００４３】
【表２】

【００４４】
表１および２より、ガラス基板およびＩＴＯ膜の最大表面粗さを２０ｎｍ以下にすると、ダークスポットやショートの発生が少なくなり、リーク電流を抑制できることが確認された。また、ガラス基板およびＩＴＯ膜の最大平均粗さを２０ｎｍ以下とし、さらに、平均表面粗さを１．０ｎｍ以下ですると、さらにダークスポットやショートの発生が少なくなり、さらにリーク電流を抑制できることが確認された。
【００４５】
【発明の効果】
本発明の最大表面粗さおよび平均表面粗さを低減した基板や透明導電膜付き基板を用いることにより、ショートやダークスポットの発生を抑制し、リーク電流の増大を防止できる。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a substrate used as an electrode of a light emitting element such as an organic EL element and an inorganic EL element, a substrate with a transparent conductive film, and a light emitting element using the substrate with a transparent conductive film.
[0002]
[Prior art]
Flat panel displays are increasingly in demand with the advancement of information technology in recent years. Recently, an organic EL display that is self-luminous and can be driven at a low voltage has attracted attention as a light-emitting element of a next-generation flat panel display. Similarly, inorganic EL displays are also attracting attention as light-emitting elements for next-generation flat panel displays. An organic EL element used for an organic EL display basically includes an electrode (anode) made of a substrate with a transparent conductive film, an organic layer such as an electron transport layer, a light emitting layer, and a hole transport layer, a metal electrode (cathode), and the like. Have a laminated structure. An inorganic EL element used for an inorganic EL display basically has a structure in which an electrode, an insulating layer, a light emitting layer, an insulating layer, a back electrode, and the like made of a substrate with a transparent conductive film are stacked on a substrate. ing.
[0003]
The organic EL element includes an active organic EL element and a passive organic EL element having different driving methods. Active-type organic EL elements mainly use alkali-free glass substrates, while passive-type organic EL elements mainly use soda lime glass substrates.
[0004]
In particular, a soda-lime glass substrate for STN-LCD manufactured by a float process is often used for passive organic EL elements because it is inexpensive. A soda-lime glass substrate for STN-LCD needs to reduce the waviness of the glass substrate for the purpose of suppressing cell gap unevenness. Therefore, although the glass surface is polished, it is necessary to control the unevenness of a finer glass substrate in order to use it for applications of passive organic EL elements (see, for example, Patent Document 1). .
[0005]
When fine irregularities exist on the glass substrate, it is difficult to reduce the fine irregularities on the transparent conductive film even if a transparent conductive film is formed thereon, and the irregularities on the transparent conductive film also increase.
[0006]
In the case of an organic EL element, it is necessary to apply a higher current to the organic EL element in order to ensure luminance with an increase in definition and size. When a substrate with a transparent conductive film with large irregularities on a glass substrate or transparent conductive film is used, there is a problem that such irregularities cause short circuit, dark spot, or increased leakage current. there were.
[0007]
[Patent Document 1]
Japanese Patent Laid-Open No. 11-191487
[Problems to be solved by the invention]
An object of the present invention is to provide a substrate suitable for a light-emitting element and a substrate with a transparent conductive film, which can suppress the occurrence of short circuits and dark spots and prevent an increase in leakage current.
[0009]
[Means for Solving the Problems]
The present invention provides a substrate for a light emitting device, wherein the substrate has a maximum surface roughness of 20 nm or less. In the present invention, the average surface roughness of the substrate is preferably 1.0 nm or less.
[0010]
In addition, the present invention is a substrate with a transparent conductive film for a light-emitting element in which a transparent conductive film is formed on the light-emitting element substrate, wherein the maximum surface roughness of the transparent conductive film is 20 nm or less. Provided is a substrate with a transparent conductive film for a light-emitting element. In the present invention, the average surface roughness of the transparent conductive film is preferably 1.0 nm or less.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
The inventors of the present invention have made extensive studies in order to suppress the occurrence of short circuits and dark spots in the organic EL element and prevent an increase in leakage current. As a result, the inventors have focused on the following points.
[0012]
The short circuit means that current is intensively flown in the portion when the organic EL element is formed or driven, and local destruction occurs. The cause is said to be mainly due to the presence of irregularities including foreign substances and pinholes in the substrate, transparent conductive film, organic layer, metal film for metal electrodes, and the like.
[0013]
The dark spot means a non-light emitting portion existing on the organic EL element that is already present when the organic EL element is formed, and when the organic EL element is driven or stored in the atmosphere. In the worst case, the entire surface of the organic EL element may not emit light. One of the causes is that the organic layer is crystallized, and there are irregularities including foreign substances such as substrates, transparent conductive films, organic layers and metal films for metal electrodes, and pinholes. It is said that moisture, oxygen, etc. permeate and the organic layer or the metal film for the metal electrode peels off.
[0014]
The leakage current means a current that flows when a reverse bias is applied, and is said to increase when a large voltage is applied locally. If minute irregularities exist on the substrate, transparent conductive film, organic layer, etc., the film thickness near the irregularities becomes thinner than the film thickness of other parts, and a large local voltage is applied near the irregularities. It is said that this is one of the causes.
[0015]
That is, if the unevenness of the glass substrate or the transparent conductive film is eliminated, an organic EL element with no short circuit or dark spot and with little leakage current can be produced. Details of the present invention will be described below.
[0016]
When the substrate used in the present invention is used as a substrate for a light emitting device, a glass substrate or a film substrate is preferably used. Moreover, it is preferable that the thickness of the said glass substrate is 0.2-1.5 mm from a viewpoint of intensity | strength and the transmittance | permeability. Further, it is not necessarily flat and plate-like, and may be curved or atypical.
[0017]
Examples of the glass substrate include a soda lime glass substrate, a quartz glass substrate, a non-alkali glass substrate, and a borosilicate glass substrate. In particular, in the case of a passive organic EL element, it is preferable to use an inexpensive soda lime glass substrate or borosilicate glass substrate.
[0018]
The maximum surface roughness of the substrate is required to be 20 nm or less, and preferably 10 nm or less in order to produce an organic EL device with little occurrence of shorts and dark spots and low leakage current. The average surface roughness of the substrate is preferably 1.0 nm or less for the same reason.
[0019]
In order to set the maximum surface roughness and the average surface roughness of the substrate within the above ranges, it is preferable to polish the glass substrate under appropriate conditions. Specifically, a polishing method such as wet polishing or dry polishing using an abrasive can be used. By setting the maximum surface roughness and average surface roughness of the substrate within the above ranges, it is possible to suppress the occurrence and growth of dark spots, which are practical problems, to suppress the occurrence of short circuits, and to further reduce the leakage current. Therefore, a stable organic EL element can be produced.
[0020]
When glass containing an alkali component such as soda lime glass is used as the substrate, a barrier layer made of silica may be provided on the substrate in order to suppress elution of the alkali component from the glass substrate. In order to suppress dark spots, short-circuits, or leakage currents that are problematic in practice, it is preferable to suppress irregularities such as foreign matter and pinholes in the silica film. A barrier layer made of silica is produced by sputtering, CVD, coating, ion plating, etc., but if a flat film with a small amount of foreign matter and a small maximum surface roughness and average surface roughness can be obtained, There is no limit. The thickness of the silica film is preferably 10 nm or more from the viewpoint of suppressing the elution of alkali components from the substrate.
[0021]
In order to produce an organic EL device with no short circuit or dark spot, which is a practical problem, and with low leakage current, it is not sufficient to set the maximum surface roughness and average surface roughness of the substrate within the preferred ranges. It is necessary to suppress the unevenness of the transparent conductive film. Specifically, it is necessary that the maximum surface roughness of the transparent conductive film be 20 nm or less, and preferably 10 nm or less. Moreover, it is preferable that the average surface roughness of a transparent conductive film is 1.0 nm or less. As a material for the transparent conductive film, indium oxide containing tin (hereinafter referred to as ITO), zinc oxide containing gallium, oxide containing indium and zinc, and the like are preferably used.
[0022]
Examples of the method for forming the transparent conductive film include a vacuum deposition method, a sputtering method, an ion plating method, and a coating method. However, if a flat film with a small maximum surface roughness and a small average surface roughness is obtained, the production method is limited. There is no.
[0023]
In addition, since the surface state of the transparent conductive film varies greatly depending on the film forming conditions and the film forming method, an appropriate film forming condition and film forming method can be selected in order to suppress unevenness on the transparent conductive film. is important.
[0024]
When the film is formed by sputtering as the film formation condition, if the film is formed under a condition where the oxygen partial pressure in the chamber is low, abnormal protrusions are easily formed, and convex defects are likely to occur on the transparent conductive film. On the other hand, when the film is formed under a high oxygen partial pressure, the surface roughness of the transparent conductive film increases. The oxygen partial pressure in the sputtering gas in the chamber is preferably 0.1 to 5% by volume.
[0025]
Moreover, in order to reduce the unevenness | corrugation of a transparent conductive film, you may process the surface of a transparent conductive film. Examples of the surface treatment method include physical polishing, chemical polishing, and etching.
[0026]
Examples of the light emitting element in the present invention include an organic EL element and an inorganic EL element.
[0027]
The organic EL device of the present invention is basically formed by laminating an electrode (anode) composed of a substrate with a transparent conductive film, an organic material layer such as an electron transport layer, a light emitting layer, and a hole transport layer, a metal electrode (cathode), and the like. Have a structure. By using the substrate with a transparent conductive film of the present invention as the anode, it is possible to obtain an organic EL element with a small leakage current and a small number of dark spots and shorts.
[0028]
Examples of the material for the electron transport layer include phthalocyanines such as copper phthalocyanine (CuPc), 4,4 ′, 4 ″ -tris (N- (3-methylphenyl) -N-phenylamino) triphenylamine, 4 , 4 ′, 4 ″ -tris (N, N-diphenylamino) triphenylamine and other starburst amines can be used. In particular, copper phthalocyanine is preferably used as the material for the hole injection layer in terms of device reliability and adhesion to the ITO film.
[0029]
The material of the light emitting layer is not particularly limited as long as it is a material exhibiting light emitting ability, and examples thereof include tris (8-quinolinol) aluminum (Alq). When Alq is used as the light emitting layer, the light emitting layer also functions as an electron transport layer. For the purpose of improving luminous efficiency and device lifetime, the light emitting layer may be doped with various dyes.
[0030]
The material of the hole transport layer is not particularly limited as long as it is a material having hole injection or electron barrier properties. For example, N, N′-diphenyl- (3-methylphenyl) -1,1 ′ -Biphenyl-4,4'diamine (TPD), 4,4'-bis (N- (1-naphthyl) -N-phenylamino) biphenyl (α-NPD), N, N'-di (phenanthrene-9- Yl) -N, N′-diphenyl-1,1′-biphenyl-4,4′-diamine (PPD) and one or more selected from the group consisting of triphenyldiamine.
[0031]
As the material of the cathode, a metal or alloy having a small work function is preferably used, and Al, AlLi, MgAg, etc. are exemplified, and the film is formed by a vapor deposition method or the like.
[0032]
【Example】
Hereinafter, the present invention will be described in detail using Examples (Examples 1 to 3) and Comparative Examples (Examples 4 and 5). However, the present invention is not limited to this.
[0033]
(Example 1)
A soda-lime glass substrate (ASA manufactured by Asahi Glass Co., Ltd., plate thickness: 0.7 mm) having a maximum surface roughness of 8.9 nm and an average surface roughness of 0.6 nm was prepared.
[0034]
Here, the maximum surface roughness refers to a measurement region in which the glass substrate is washed with pure water, and then the surface roughness of the glass substrate is measured using an atomic force microscope (Digital Instruments, Inc .: NanoScope 3 multimode AFM). The largest unevenness difference was taken. The measurement area was 5 μm × 5 μm. In addition, the average surface roughness means that after the glass substrate is washed with pure water, the surface roughness of the glass substrate is measured using an atomic force microscope (Digital Instruments, NanoScope 3 multimode AFM). The average surface roughness. The measurement area was 5 μm × 5 μm.
[0035]
After cleaning the glass substrate, it was set in a sputtering apparatus, and a silica film having a thickness of about 20 nm was formed on the glass substrate by RF sputtering. At this time, a silica target was used as the target. Next, an ITO film having a thickness of 170 nm was formed on the silica film by DC magnetron sputtering to obtain a substrate with an ITO film. In this case, the target, SnO ₂ was used ITO target was added 10% by mass of the total amount of _In 2 _{O 3} and SnO _2. As the sputtering gas, a mixed gas of oxygen gas (1.0% by volume in the sputtering gas) and argon gas was used.
[0036]
The maximum surface roughness and average surface roughness of the produced ITO film were measured. The results are shown in Table 1. The method for measuring the maximum surface roughness and the average surface roughness of the ITO film is the same as the method for measuring the maximum surface roughness and the average surface roughness of the glass substrate.
[0037]
The substrate with the ITO film was taken out of the sputtering apparatus, and the ITO film was patterned into a predetermined shape by wet etching using a photolithographic method.
[0038]
Further, on the ITO layer to be the anode, CuPc of about 20 nm, Alq of about 50 nm, α-NPD of about 100 nm, and Al film of about 200 nm were formed to produce a 5 mm × 5 mm square organic EL device. CuPc, α-NPD, and Alq were all formed by vacuum deposition.
[0039]
Table 2 shows the results of the leakage current, the number of dark spots generated, and the number of shorts generated of the organic EL element manufactured as described above. Moreover, the evaluation methods of the leakage current, the number of dark spots and the number of shorts are as follows.
[0040]
1. Leakage current / voltage characteristics were measured, and leakage current was measured.
◎ means less than 10 ^-4 when x is 1, ◯ means 10 ^-4 or more and less than 10 ^-3 when x is 1, and △ means x Means that it is 10 ⁻³ or more and less than 1 when. It is practically preferable that they are ◎ and ○.
2. The number of dark spots generated The organic EL element obtained was driven at a constant current of 100 cd / m ² for 24 hours, and the number of dark spots generated visually was counted. It is practically preferable that the number is 10 or less.
3. The number of occurrences of short circuit The organic EL element obtained was driven at a constant current of 100 cd / m 2 for 24 hours, and then the number of occurrences of short circuit confirmed visually was counted. It is practically preferable that the number is zero.
[0041]
(Examples 2 to 5)
An organic EL device was obtained in the same manner as in Example 1 except that the maximum surface roughness and the average surface roughness of the glass substrate were set to the values described in Table 1. Table 1 shows the results of the maximum surface roughness and the average surface roughness of the produced ITO film, and Table 2 shows the evaluation results of the organic EL elements.
[0042]
[Table 1]

[0043]
[Table 2]

[0044]
From Tables 1 and 2, it was confirmed that when the maximum surface roughness of the glass substrate and the ITO film was 20 nm or less, the occurrence of dark spots and shorts was reduced, and the leakage current could be suppressed. In addition, when the maximum average roughness of the glass substrate and the ITO film is 20 nm or less and the average surface roughness is 1.0 nm or less, the occurrence of dark spots and shorts is further reduced, and it is confirmed that the leakage current can be further suppressed. It was done.
[0045]
【The invention's effect】
By using a substrate with a reduced maximum surface roughness and average surface roughness or a substrate with a transparent conductive film according to the present invention, the occurrence of short circuits and dark spots can be suppressed, and an increase in leakage current can be prevented.

Claims (6)

A substrate for a light emitting element, wherein the maximum surface roughness of the substrate is 20 nm or less. The substrate for light emitting device according to claim 1, wherein the average surface roughness of the substrate is 1.0 nm or less. The light emitting element substrate according to claim 1, wherein the substrate is a glass substrate. It is a board | substrate with the transparent conductive film for light emitting elements formed by forming a transparent conductive film on the light emitting element substrate of Claim 1, 2, or 3, Comprising: The maximum surface roughness of the said transparent conductive film is 20 nm or less A substrate with a transparent conductive film for a light-emitting element. 5. The substrate with a transparent conductive film for a light-emitting element according to claim 4, wherein the transparent conductive film has an average surface roughness of 1.0 nm or less. The light emitting element formed using the board | substrate with a transparent conductive film for light emitting elements of Claim 4 or 5.