JPH07240278A - Thin film el element - Google Patents

Abstract

PURPOSE:To obtain a thin film EL element which can improve the luminance of a full color, and a multicolor thin film EL elements. CONSTITUTION:In a thin film EL element using strontium sulfide as the mother body of a luminous layer 4, the iron content in the film forming member of the luminous layer 4 is suppressed less than 10ppm, the cobalt content less 10ppm, the calcium content less than 100ppm, the barium content less than 100ppm, the carbon content less than one atomic%, and the nickel content is suppressed less than 10ppm.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to full-color and multi-color thin film EL devices, and more particularly to a thin film EL device for improving brightness.

[0002]

2. Description of the Related Art A thin film EL element can be used as a flat display panel having a large area and is thin. Therefore, it is expected to have a wide range of applications such as character display, graphic display and image display, and has been in the limelight in recent years. Especially development of double insulation type EL element (SID 74 Dige
st of Technical Papers 19
74, Journal of Electrochem
ical society, 114, 1066, 196
By 7), the brightness and life are dramatically improved, and thin film EL
The device has come to be applied to displays, and even monochrome displays with yellow-orange emission have come to the market.

The emission color of the thin film EL element is determined by the combination of a semiconductor matrix such as ZnS or SrS forming the emission layer and an emission center added. For example, yellow-orange emission is ZnS.
It is obtained by adding Mn as a luminescent center to the host. As a method for forming the light emitting layer, a resistance heating vapor deposition method, an electron beam vapor deposition method, a sputtering method, a MOCVD method, an ALE method, or the like is used. When applying a thin film EL device to a full-color or multi-color thin display, a thin film EL device that emits the three primary colors of red, green and blue, or a thin film E that emits white light
A combination of an L element and a color filter is required. Therefore, much efforts have been made to develop a thin film EL element that emits each color with high brightness. For example, regarding the red thin film EL device, Japanese Patent Laid-Open No. 63-299094 and Japanese Patent Laid-Open No. 225589/1990 disclose blue thin film E.
Regarding the L element, JP-A-63-274091, JP-A-64-2298, JP-A-1-217885, JP-A-1-280795, and JP-A-2-56.
896, JP-A-3-11591, JP-A-4
Japanese Patent Application Laid-Open No. 196088 and Japanese Patent Application Laid-Open No. 5-65478 disclose white thin film EL elements in Japanese Patent Application Laid-Open No. 62-749.
No. 86, No. 6-95182, No. 2-
66872, JP-A-2-98092, JP-A-2-242548, JP-A-3-167783, JP-A-4-202285, etc. are proposed. In developing such a color thin film EL device, SrS is a promising base material, and is blue green when Ce is added as an emission center, red when Eu is added, and white when Ce and Eu are added at the same time. It is known to emit light.

[0004]

According to the method described above,
ZnS: Mn is the one that has reached the practical level of brightness.
However, there is a problem in that high luminance cannot be obtained with the SrS-based material. The present invention has been made in view of the above problems, and an object thereof is to provide a thin-film EL element that improves the brightness of full-color and multi-color thin-film EL elements.

[0005]

According to the present invention, the aforementioned object is to provide a thin film E containing strontium sulfide as a light emitting layer matrix.
In the L element, the iron content of the film forming material of the light emitting layer is 10 p
pm or less, cobalt content of the light emitting layer film forming material is 10p
pm or less, the calcium content of the film forming material of the light emitting layer is 10
0 ppm or less, the barium content of the light emitting layer film forming material is 1
This is achieved by setting the carbon content of the light-emitting layer film forming material to 1 ppm or less, and the nickel content of the light-emitting layer film forming material to 10 ppm or less.

[0006]

Although the details of the light emission mechanism of the thin film EL device are not clear, the process in which electrons accelerated by the electric field applied to the light emitting layer excite the emission center and the emission center returns to the ground state Is a popular theory. That is, the thin film EL having SrS as the light emitting layer matrix according to the constitution of the present invention.
In the device, if impurities are mixed in the light emitting layer, it becomes a film with many defects and the electron acceleration is hindered, so that the electron acceleration in the light emitting layer cannot be performed efficiently, and it is considered that the brightness of the thin film EL device is reduced. To be

The inventors of the present invention have made extensive studies on the degree of influence of these impurities. Iron, cobalt, calcium, barium, carbon and nickel generate crystal defects in the light emitting layer crystal, and electrons accelerated by the electric field It was found that they were scattered by the crystal defects of and deteriorated the efficiency of acceleration and hindered the luminescence transition process of the luminescence center. Various experimental research results, iron content 10ppm or less, cobalt content 10ppm or less,
By suppressing the calcium content to 100 ppm or less, the barium content to 100 ppm or less, the carbon content to 1 atomic percent or less, and the nickel content to 10 ppm or less, it is possible to efficiently accelerate electrons in the light emitting layer and improve the brightness. It was possible to do.

[0008]

EXAMPLE An explanation will be given with reference to FIG. FIG. 1 is a cross-sectional configuration diagram showing a thin film EL element of an embodiment of the present invention. SrS
Ce as a luminescent center with a system material as a base, and 0.2 mol% of Ce
SrS pellets of Experiments 1 to 5 having the compositions shown in Table 1 were prepared for each element of iron, cobalt, calcium, barium, carbon, and nickel.

[0009]

[Table 1]

Further, these are thin film ELs having the structure shown in FIG.
A device was manufactured by the following procedure. First, on the transparent substrate 1 (glass substrate) by the reactive sputtering method [HOYA Co., Ltd.
Manufactured: NA-40] and a transparent electrode 2 of ITO having a thickness of 170 nm
Was formed. 20% oxygen by using Si target
-Introducing a mixed gas of 80% argon and by reactive sputtering, a SiO _{2 of} 30 nm in thickness and a mixed gas of 30% of nitrogen and 70% of argon are introduced, and Si ₃ N _{4 of} 170 nm in thickness. The first insulating layers 3 and 3a were sequentially formed.

Subsequently, the temperature of the glass substrate 1 was set to 55 for each element by electron beam evaporation using the SrS pellets of Experiments 1 to 5 having the compositions shown in Table 1.
A light emitting layer 4 having a thickness of 700 nm was formed at 0 ° C. The film thus obtained was heated in vacuum at 700 ° C. for 2 hours. Next, again by reactive sputtering, Si ₃ N ₄ having a thickness of 170 nm and SiO ₂ having a thickness of 30 nm were sequentially formed to form the second insulating layers 5a and 5. Next, Al was vapor-deposited by the electron beam vapor deposition method to form the upper electrode 6. The insulating layer used in the thin film EL element of the present invention is not limited to this embodiment. For example, SiO ₂ · Y ₂ O ₃ · T
iO ₂ · Al ₂ O ₃ · HfO ₂ · Ta ₂ O ₅ · BaTa
₂ O ₅ · SrTiO ₃ · PbTiO ₃ · Si ₃ N ₄ · Z
Examples thereof include rO _{2 and the} like, and mixed films or laminated films of these.

FIGS. 2 to 7 show the thin film EL elements thus obtained, which were measured for their respective element contents and emission luminances. It should be noted that the emission brightness uses an arbitrary unit (a relative value, not an absolute value of brightness). Fig. 2 is a characteristic diagram for iron, Fig. 3 is a characteristic diagram for cobalt, Fig. 4 is a characteristic diagram for calcium, Fig. 5 is a characteristic diagram for barium, and Fig. 6 is a characteristic diagram for carbon.
FIG. 7 is a characteristic diagram in the case of nickel. According to these characteristic diagrams, the iron content is 10 ppm or less, the cobalt content is 10 ppm or less, the calcium content is 100 ppm or less, the barium content is 100 ppm or less, the carbon content is 1 atomic percent or less, and the nickel content is 10 ppm or less. It has been shown that by suppressing the amount to be 0, the acceleration of electrons in the light emitting layer can be efficiently performed, and the brightness is improved.

[0013]

According to the present invention, in a thin film EL device using SrS as a base material of a light emitting layer, the kind and maximum content of an impurity which becomes a film having many crystal defects in the light emitting layer and inhibits electron acceleration are found. As a result, electrons in the light emitting layer can be efficiently accelerated, the brightness is improved, and the full-color and multi-color thin film EL elements can be obtained with the effects as shown in the examples.

[Brief description of drawings]

FIG. 1 is a cross-sectional configuration diagram showing a thin film EL element according to an embodiment of the present invention.

FIG. 2 is a characteristic diagram when the element of the present invention is iron.

FIG. 3 is a characteristic diagram when the element of the present invention is cobalt.

FIG. 4 is a characteristic diagram when the element of the present invention is calcium.

FIG. 5 is a characteristic diagram when the element of the present invention is barium.

FIG. 6 is a characteristic diagram when the element of the present invention is carbon.

FIG. 7 is a characteristic diagram when the element of the present invention is nickel.

[Explanation of symbols]

1 Transparent Substrate 2 Transparent Electrode 3 First Insulating Layer (SiO ₂ ) 3a First Insulating Layer (Si ₃ N ₄ ) 4 Light Emitting Layer 5 Second Insulating Layer (SiO ₂ ) 5a Second Insulating Layer (Si ₃ N ₄ ) 6 Upper electrode

Claims (6)

[Claims] 1. A transparent substrate, a transparent electrode, a first insulating layer, and a light emitting layer are sequentially laminated, a light emitting layer is covered with a second insulating layer, and an upper electrode is formed on the second insulating layer, and strontium sulfide is used as the light emitting layer. In a thin film EL device as a base material, the iron content of a film forming material of a light emitting layer is 10 ppm or less, a thin film EL device. 2. The thin film EL element according to claim 1, wherein the film forming material of the light emitting layer has a cobalt content of 10 ppm or less. 3. The thin film EL element according to claim 1, wherein the film forming material of the light emitting layer has a calcium content of 100 ppm or less. 4. The thin film EL element according to claim 1, wherein the film forming material for the light emitting layer has a barium content of 100 ppm or less. 5. The thin film EL device according to claim 1, wherein the film forming material of the light emitting layer has a carbon content of 1 atomic% or less. 6. The thin-film EL element according to claim 1, wherein the film-forming material for the light-emitting layer has a nickel content of 10 ppm or less.