JP2001237075A - Thin film el element and manufacturing method of the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To mask the polychromatic patterning of a thin film EL element easy and improve the heat resistance. SOLUTION: A painting type thin film EL element is made polychromatic with long life by using a thermosetting resin with high heat resistance for a light emitting layer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a display element used as a light emitting display or a backlight for a liquid crystal display.

[0002]

2. Description of the Related Art Electroluminescent (EL) panels have high visibility, excellent display capability, and high-speed response. In recent years, there have been reports on thin-film EL devices using organic compounds as constituent materials (for example, see the related paper Applied Physics Letters, No. 51).
Volume 913, 1987 (Applied Physics Letters, 51, 19)
87, P.913.))). In this report, a low-voltage, low-voltage,
A high-luminance thin-film EL device has been realized. As a light-emitting material, a tris (8-quinolinolato) aluminum complex (hereinafter, Alq) is used, which is an excellent light-emitting substance having both high luminous efficiency and electron transport.

Further, Journal of Applied Physics, Vol. 65, p. 3610, 1989 (Journal
f Applied Physics, 65, 1989, p. 3610.) created a device in which Alq forming an organic light emitting layer was doped with a fluorescent dye such as a coumarin derivative or DCM1, and the emission color could be changed by appropriate selection of the dye. Was found. Furthermore, it was clarified that the luminous efficiency was increased as compared with the undoped one.

On the other hand, a thin film EL element made of an organic polymer has also been receiving attention because of the inherent possibility that the manufacturing method for the thin film EL element may lead to a reduction in cost such as coating and printing and an increase in size. Polymer thin-film EL elements are roughly divided into two types: those composed of a luminescent polymer having a luminescent group in the main chain or side chain of the polymer, and those in which a luminescent material is dispersed in the polymer. .

When an application to a display or the like is attempted, colorization is indispensable, and it is necessary to divide and arrange each color. In a low-molecular-weight system, a first emission color material is deposited using a mask cut into a desired pattern at the time of evaporation, and a mask or a substrate is moved so as not to overlap with the first emission color material, so that the second emission color is removed. A plurality of luminescent color materials can be arranged on the same plane such that a color material is deposited and a third luminescent color material is deposited so as not to overlap the first and second luminescent color materials.

[0006] In the polymer system, since it is formed by coating,
As a means of colorization, there is a method of attaching a color filter to a white light emitting device in which a dye of each color is mixed in one light emitting layer. However, the white light emitting device has a disadvantage that the efficiency of the device is reduced because light is absorbed by the color filter. Therefore, Japanese Patent Application Laid-Open
In JP-A-105894, a method is employed in which a photosensitive compound is used for a light emitting layer to perform patterning by a photo process.

[0007]

However, the photosensitive compound has low heat resistance and is easily deteriorated by Joule heat generated during operation. In addition, purification is said to be the key to the improvement of properties such as efficiency and long life in polymer systems. Therefore, the step of including a photosensitive compound in the light-emitting layer is not preferable because it contains ions as a reaction initiator or a reactant, and acts as an impurity, causing deterioration of characteristics during long-term operation. Furthermore, when the light-emitting layer is exposed to light, ultraviolet rays are directly irradiated to a portion acting as a light-emitting group, thereby causing deterioration. Particularly, when a negative resist is used, a portion to be left as a light-emitting layer is irradiated with ultraviolet light. There has been a problem that the luminescent group is deteriorated due to decomposition, isomerization and the like.

[0008]

Accordingly, we have been able to achieve a longer life of a thin film EL device by using a thermosetting resin having excellent heat resistance for the light emitting layer. Reached.

Specifically, according to the first aspect of the present invention, in a thin film EL device having at least a light emitting layer between an anode and a cathode, the light emitting layer is made of a plurality of light emitting materials containing a thermosetting resin. A thin-film EL device comprising a first light-emitting material applied, patterned, and then heat-cured alternately to obtain a multicolored thin-film EL device.

According to a second aspect of the present invention, a light-emitting group is contained in the main chain or the side chain of the thermosetting resin according to the first aspect.

According to a third aspect of the present invention, the thermosetting resin according to the first aspect is made of polyimide.

According to the invention of claim 4 of the present application, in a thin film EL device having at least a hole transport layer and a light emitting layer between an anode and a cathode, the hole transport layer comprises a thermosetting resin and a hole transport material; In addition, the light emitting layer is a thin film EL element made of a plurality of light emitting materials including a thermosetting resin, and the first light emitting material is applied, patterned, and heat cured after the hole transport layer is applied and cured by heating. Is alternately repeated to provide a multi-colored thin film EL device.

According to a fifth aspect of the present invention, the thermosetting resin contained in the hole transport layer according to the fourth aspect is made of polyimide.

According to a sixth aspect of the present invention, a light-emitting group is contained in a main chain or a side chain of the thermosetting resin contained in the light-emitting layer according to the fourth aspect.

According to a seventh aspect of the present invention, the thermosetting resin contained in the optical layer according to the fourth aspect is made of polyimide.

According to the invention of claim 8 of the present application, in the method of manufacturing a thin film EL device having at least a light emitting layer between an anode and a cathode, the light emitting layer is formed of a plurality of light emitting materials including a thermosetting resin. A method of applying a first light-emitting material, and then alternately repeating a patterning step and a heat-curing step at least two times. You.

According to a ninth aspect of the present invention, a luminescent group is contained in the main chain or the side chain of the thermosetting resin according to the eighth aspect.

According to a tenth aspect of the present invention, the thermosetting resin according to the eighth aspect is made of polyimide.

According to a eleventh aspect of the present invention, in the patterning step of the eighth aspect, a dry etching method is applied.

According to a twelfth aspect of the present invention, the light emitting layer according to the eighth aspect is formed after forming the hole transport layer.

According to a thirteenth aspect of the present invention, an electron transport layer is further formed after forming the light emitting layer according to the eighth aspect.

[0022]

Embodiments of the present invention will be described below.

FIG. 1 is a sectional view showing an example of a technique for forming a light emitting layer of a thin film EL device of the present invention. In FIG. 1, a shows a light emitting layer material application step, b shows a resist pattern formation, c shows a dry etching step, and d shows a resist removal step and a thermosetting step of a resin contained in the light emitting layer. 1
a to 1d, forming a first light emitting layer pattern,
After being insolubilized by thermal curing, a second light emitting layer pattern is applied and formed. By repeating the series of operations a to d n times, it is possible to form a light emitting layer in which n light emitting colors are arranged on the same plane. Since the resist pattern can be finely patterned to several tens of μm, a series of steps including a step of forming the resist pattern enables a display having fine pixels to be manufactured.

The step b shown in FIG. 1B or 2B can be replaced with a metal mask bonding step. In this case, the pitch of the mask pattern is 100 μm
Although it is in an order, the operation can be easily performed because it is merely attached to the surface of the light emitting layer on which the mask is applied.

As the polymer contained in the light emitting layer, a thermosetting resin such as a melamine resin, a urethane resin, and a urea resin, or a heat-resistant polymer such as polyimide, polyamide, and polybenzimidazole is preferable. In particular, polyimide having almost no hygroscopicity is preferable. Polyimide is synthesized by heating a polyamic acid produced by alternate copolymerization of a carboxylic acid dianhydride and a diamine compound into an imidized compound. Examples of anhydrides of carboxylic acids include biphenyltetracarboxylic dianhydride, benzophenonetetracarboxylic dianhydride, bicyclo [2,2,2] oct-7-en-
2,3,5,6-tetracarboxylic dianhydride and the like. Examples of diamine compounds include 1,4-bis (4
-Aminophenylthio) benzene, 1,4-bis (4-
Aminophenylthio) naphthalene, 9,10-bis (4
Sulfur-containing compounds such as -aminophenylthio) anthracene and 1,6-bis (4-aminophenylthio) pyrene, and sulfur atoms substituted with oxygen atoms such as 1,4-bis (4-aminophenoxy) benzene Those are also preferred.

As the light emitting material contained in the light emitting layer, a dye having a quantum efficiency close to 1 such as a laser dye such as coumarin 6, DCM, and phenoxazone 9 is preferable. In addition, condensed rings such as naphthalene, anthracene, pyrene, and naphthacene and derivatives thereof are also preferable. For example, rubrene is also a light emitting material having a quantum efficiency close to 1. These luminescent materials may be included as a luminescent group in the main chain or side chain of the polymer, or the luminescent material may be dispersed in a polymer matrix. For example, when the polyimide contains a light-emitting group in the main chain, the polyimide may be substituted with a benzene ring of the diamine compound, and is preferably connected by an oxygen atom or a sulfur atom. Particularly preferably, the form linked to the central part of the diamine compound, such as the above-mentioned naphthalene compound and anthracene compound, is preferable because there is no fear of concentration quenching.

In the form of the thin-film EL device, a hole transport layer is provided between the light emitting layer and the anode, and between the light emitting layer and the cathode, respectively.
Preferably, an electron transport layer is formed. Generally, since the hole transport layer is sequentially formed on the transparent substrate on which the transparent electrode is formed, it is necessary to select a material that does not dissolve when the light emitting layer is formed by coating. Therefore, a derivative having triphenylamine having excellent hole transport properties as a basic skeleton is dispersed in the above-mentioned thermosetting resin or heat-resistant polymer, and cured after coating to form a hole transport layer having excellent insolubilization or solvent resistance. Good to do. Examples of the triphenylamine derivative include tetraphenylbenzidine compounds described in JP-A-7-126615, triphenylamine trimer and benzidine dimer, various triphenyldiamine derivatives described in JP-A-8-48656, JP-A-7-65958
MTPD (commonly known as TPD), tristriamine, and the like described in Japanese Patent Application Laid-Open No. H10-260, 1988 are preferable. Alternatively, since a vapor-deposited film of a phthalocyanine compound such as copper phthalocyanine, titanyl phthalocyanine, or metal-free phthalocyanine, which is a hole injecting material, is an insoluble film, a hole transport layer may be formed therefrom. In forming the electron transport layer, since the light emitting layer is insolubilized, a polymer layer may be applied and formed, or a low molecule may be deposited. Examples of the polymer electron transport material include polyfluorene and a polymer having oxadiazole in a main chain or a side chain.
q, metal complexes such as tris (4-methyl-8-quinolinolato) aluminum, and 4,4,8,8-tetrakis (1H
-Pyrazol-1-yl) pyrazabole and the like, 3- (2'-benzothiazolyl) -7-diethylaminocoumarin and the like. Also, materials having a hole blocking function such as bathocuproine and triazole derivatives, or dilithium phthalocyanine, disodium phthalocyanine, magnesium porphine, 4,4,8,8-tetrakis (1H-pyrazole) described in Japanese Patent Application No. 11-214712. An electron injection material such as 1-yl) pyraza ball is also preferable.

The light emitting layer preferably has a thickness of 10 to 1000 nm. The hole transport layer and the electron transport layer each preferably have a thickness of 1 to 100 nm.

Next, a dry etching method will be described.
Reactive ion etching (R
IE) and the like. A general-purpose type such as a barrel type or a parallel plate type may be used.
r gas or the like may be introduced at the same time. When performing patterning using a resist pattern, it is necessary to perform etching in a soft state before curing. After curing by heat treatment, the thermosetting resin, heat-resistant polymer, and the like contained in the light emitting layer have a lower etching rate than the resist. Therefore, since the resist is etched earlier than the light emitting layer is etched, a pattern cannot be obtained. When a metal mask is used, it may be cured, but it is not preferable because the power of etching needs to be increased, so that the light emitting layer is particularly damaged by the light emitting group and leads to a decrease in efficiency.

The thin-film EL element can emit surface light by making at least one electrode transparent or translucent. Usually, an ITO (indium tin oxide) film is often used for an anode serving as a hole injection electrode. Other examples include tin oxide, Ni, Au, Pt, and Pd. For the purpose of improving the transparency or reducing the resistivity of the ITO film, a film forming method such as sputtering, electron beam evaporation, or ion plating is employed. The film thickness is determined from the required sheet resistance value and the visible light transmittance. However, since the driving current density is relatively high in the thin-film EL element, the film thickness is reduced by 1 to reduce the sheet resistance value.
It is often used with a thickness of 00 nm or more.

The cathode serving as an electron injection electrode has Tang.
The proposed MgAg alloy or AlLi alloy,
In many cases, an alloy of a metal having a low work function and a low electron injection barrier and a metal having a relatively large work function and being stable is used. Further, a metal having a low work function may be formed on the organic layer side, and a metal having a large work function may be thickly laminated for the purpose of protecting the metal having a low work function, such as Li / Al or LiF / Al.
Such a laminated electrode can be used. For forming these cathodes, a vapor deposition method or a sputtering method is preferable. When an electron injecting material such as dilithium phthalocyanine, disodium phthalocyanine, magnesium porphine, 4,4,8,8-tetrakis (1H-pyrazol-1-yl) pyrazaball is used, a metal having a large work function and a stable metal function is used. Since the electrode can be constituted only by the electrode, the electrode is hardly subjected to a reaction such as oxidation and the life characteristics can be improved.

The substrate is a thin film EL obtained by laminating the above thin films.
Any material can be used as long as it can support the element, and a transparent or translucent material can be used so as to extract light emitted in the organic layer. Glass such as Corning 1737, a resin film of polycarbonate or the like is used.
However, the softening point needs to be higher than the curing temperature of the thermosetting resin and the heat-resistant resin used for the light emitting layer.

Next, the present invention will be described in more detail based on specific embodiments.

(Example 1) (Synthesis of polyimide precursor polyamic acid used for light emitting layer and hole transport layer) Benzophenonetetracarboxylic dianhydride and 1,4-bis (4
-Aminophenylthio) benzene was stirred in N, N-dimethylformamide at room temperature for 1 hour to obtain a polyamic acid (PA1). Similarly, benzophenonetetracarboxylic dianhydride and 9,10-bis (4-aminophenylthio) anthracene are used to convert (PA2) from benzophenonetetracarboxylic dianhydride and 1,6-bis (4-aminophenylthio) pyrene. From (PA3).

(Formation of Hole Transport Layer) A solution in which PA1 and tristriamine were mixed at a weight ratio of 6: 4 was spin-coated on a glass substrate on which an ITO transparent electrode was formed.
By heating at 200 ° C., a hole transport layer made of polyimide with a temperature of 500 ° was obtained.

(FIG. 1-1a: Formation of First Light-Emitting Layer) As a first light-emitting layer, PA2 was spin-coated on the hole transport layer and dried by heating at 90 ° C. for 30 minutes.

(FIG. 1-1b: Formation of resist pattern) On the first light emitting layer, a positive resist (MP1400: manufactured by Shipley Far East) was applied to a thickness of 2.5 μm by a spinner, and the pixel pitch was 40 μm / 100 μm. 3 with mask
After exposure for 0 second and development with a developer (MF312: Shipley Far East), post-baking was performed at 90 ° C. for 15 minutes.

(FIG. 1-1c: Dry Etching Step) Dry etching was performed with an oxygen plasma asher at a high frequency output of 400 W, a set temperature of 100 ° C., a vacuum of 1 Torr when oxygen was introduced, and a processing time of 10 minutes.

(FIG. 1-1d: resist removal + resin curing step) The resist was prepared by immersing the substrate in fuming nitric acid (Kanto Chemical).
After immersion and removal for 30 minutes, washing with running water was performed for 30 minutes.
Subsequently, the mixture was heated at 200 ° C. for 1 hour to perform imidation, thereby obtaining a 500 ° first light-emitting layer made of polyimide.

(FIG. 1-2a: Formation of Second Light Emitting Layer) PA2 was spin-coated as a second light emitting layer on the patterned first light emitting layer, and dried by heating at 90 ° C. for 30 minutes.

(FIG. 1-2b: Formation of resist pattern) The process was performed in the same manner as in the above-described step of FIG. 1-1b, except that the mask at the time of exposure was aligned so as not to overlap the portion where the first light emitting layer was formed.

(FIG. 1-2c: Dry Etching Step) The etching was performed in the same manner as in the step of FIG. 1-1c.

(FIG. 1-2d: resist removal + resin curing step) The same procedure as in FIG. 1-1d was performed to obtain a second light emitting layer made of polyimide.

(Formation of Electron Transport Layer)
4,4,8,8-tetrakis (1H-pyrazole-1-
(I) An electron transport layer made of pyraza balls was formed at a thickness of 100 °.

(Formation of Electrode) Subsequently, an electron injection electrode made of Li was formed at 10 ° by a vacuum evaporation method, and Al was deposited at 1000 ° as a protective cathode.

Through the above steps, a thin film EL device having a light emitting layer with a pixel size of 40 μm and a pixel pitch of 50 μm was obtained. By applying the voltage, white light emission is obtained in the entire lighting,
When a single color display was performed by matrix driving, blue-green light emission from polyimide using PA2 as a precursor and orange light emission from polyimide using PA3 as a precursor were observed. Further 15
When the device was continuously driven in a high temperature environment of 0 ° C., it continued to emit light stably without a decrease in luminance.

The present invention can take various embodiments.

A thin-film EL device according to one embodiment of the present invention has at least a light-emitting layer between an anode and a cathode, and the light-emitting layer is made of a plurality of light-emitting materials containing a thermosetting resin. The method is characterized in that a light-emitting material is applied, patterned, and then heat-cured alternately and alternately, resulting in multicoloring. It is preferable that the main chain or the side chain of the thermosetting resin contains a light emitting group. Preferably, the thermosetting resin is polyimide.

A thin film EL device of another embodiment has at least a hole transport layer and a light emitting layer between an anode and a cathode, wherein the hole transport layer is made of a thermosetting resin and a hole transport material,
The light-emitting layer is composed of a plurality of light-emitting materials including a thermosetting resin, and after applying a hole transport layer and heat-curing, the first light-emitting material is alternately applied, patterned, and heat-cured alternately. It is characterized by being colored. In addition,
The thermosetting resin contained in the hole transport layer is preferably polyimide. Further, it is preferable that the main chain or the side chain of the thermosetting resin contained in the light emitting layer contains a light emitting group, and the thermosetting resin contained in the light emitting layer is preferably polyimide.

The method of manufacturing a thin film EL device according to one embodiment of the present invention is a method of manufacturing a thin film EL device having at least a light emitting layer between an anode and a cathode, wherein the light emitting layer is made of a thermosetting resin. And a step of patterning and a step of heating and curing after applying the first luminescent material at least twice alternately. Note that it is preferable to apply a dry etching method in the patterning step.

[0051]

As described above, according to the present invention, by using a thermosetting resin having excellent heat resistance for the light emitting layer, it is possible to achieve both multicolor and long life in a coating type thin film EL device. it can.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of forming a light emitting layer.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Substrate 11 First light emitting layer 12 Second light emitting layer 20 Resist

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification code FI Theme coat ゛ (Reference) H05B 33/12 H05B 33/12 B (72) Inventor Tetsuya Sato 1006 Kazuma, Kazuma, Kazuma, Osaka Matsushita Electric Industrial Co., Ltd. (72) Inventor Hitoshi Hisada 1006 Kazuma Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.F-term (reference)

Claims (13)

[Claims] 1. A thin film EL device having at least a light emitting layer between an anode and a cathode, wherein the light emitting layer is made of a plurality of light emitting materials containing a thermosetting resin, wherein the first light emitting material is A thin-film EL device characterized by multi-coloring by alternately repeating coating, patterning, and heat curing. 2. The thin-film EL device according to claim 1, wherein a light-emitting group is contained in a main chain or a side chain of the thermosetting resin. 3. The thin film EL device according to claim 1, wherein said thermosetting resin is polyimide. 4. A thin film EL device having at least a hole transport layer and a light emitting layer between an anode and a cathode, wherein the hole transport layer is made of a thermosetting resin and a hole transport material,
In addition, the light emitting layer is a thin film EL element made of a plurality of light emitting materials including a thermosetting resin, and the first light emitting material is applied, patterned, and heat cured after the hole transport layer is applied and cured by heating. The thin film EL device is characterized in that the process is alternately repeated to obtain a multicolor. 5. The thin film EL device according to claim 4, wherein the thermosetting resin contained in the hole transport layer is polyimide. 6. The thin-film EL device according to claim 4, wherein a light-emitting group is contained in a main chain or a side chain of the thermosetting resin contained in the light-emitting layer. 7. The thin film EL according to claim 4, wherein the thermosetting resin contained in the light emitting layer is polyimide.
element. 8. A method of manufacturing a thin film EL device having at least a light emitting layer between an anode and a cathode, the method comprising a step of forming the light emitting layer from a plurality of light emitting materials including a thermosetting resin. A method of manufacturing a thin film EL device, comprising: repeating a step of patterning and a step of heating and curing after applying a first luminescent material at least twice alternately. 9. The method according to claim 8, wherein a light-emitting group is contained in a main chain or a side chain of the thermosetting resin. 10. The method according to claim 8, wherein said thermosetting resin is polyimide. 11. The method according to claim 8, wherein a dry etching method is applied in the patterning step. 12. The method according to claim 8, wherein the light emitting layer is formed after forming the hole transport layer. 13. The thin film E according to claim 8, wherein an electron transport layer is further formed after forming said light emitting layer.
Manufacturing method of L element.