JPH0562778A - Thin film electroluminescence element - Google Patents

Abstract

PURPOSE:To increase the crystal grain size of a light emitting layer and provide high-intensity luminescence by forming an amorphous thin film, then heat- treating it. CONSTITUTION:A transparent electrode 2 is formed on a glass base 1, and an insulating layer 5 is formed on it. A light emitting layer 4 is deposited by sputtering on it, an insulating layer 6 is formed on it, then a back electrode 3 is formed. The amorphous light emitting layer 4 formed at the base temperature of l5O0 deg.C or below is heat-treated in the sulfide gas atmosphere such as hydrogen sulfide at 650 deg.C or above for crystallization.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thin film electroluminescence device (hereinafter referred to as EL device) which emits light in response to an applied electric field.
It is abbreviated as an element. ).

[0002]

2. Description of the Related Art M is used for compound semiconductors such as ZnS and ZnSe.
The phenomenon of electroluminescence, which emits light when a high voltage is applied to a material doped with an emission center such as n, has been known for a long time. In recent years, due to the development of the double insulating layer type EL element, the brightness and the life have been dramatically improved, and the thin film EL element has been applied to a thin display, and has come to the present market.

The emission color of the EL element is determined by the combination of the semiconductor matrix forming the light emitting layer and the doped emission center.
For example, electroluminescence emission of yellow-orange color is obtained by doping Mn as a luminescence center into the ZnS matrix and edge color electroluminescence emission (hereinafter abbreviated as EL emission) by addition of Tb. Further, when the SrS matrix is doped with Ce as the emission center, blue-colored EL emission is obtained, and when the CaS matrix is doped with Eu as the emission center, red emission is obtained.

However, only the yellow-orange system in which the ZnS matrix is doped with Mn has reached the brightness of the practical level at present. EL full-color thin film display
In the case of manufacturing using an element, an EL element that emits the three primary colors of blue, green, and red is necessary, and E that emits each color with high brightness is required.
The development of the L element is being actively pursued. As the method for forming the light emitting layer, resistance heating vapor deposition method, electron beam heating vapor deposition method, sputter vapor deposition method, MOCVD method (metal organic chemical vapor deposition method), MBE method (molecular beam epitaxial method), ALE method (atomic method) Layer epitaxial method) and the like are used. Regarding the relationship between the crystallinity of the light emitting layer formed by these methods and the brightness of the EL element, it is known that the EL element having a highly crystallized light emitting layer has high brightness.
It is presumed that this is because the electrons accelerated by the electric field applied to the light emitting layer efficiently excite the luminescence center. A highly crystalline thin film can be obtained from the ZnS: Mn light emitting layer formed by using the MOCVD method, the ALE method, and the MBE method.
An EL element that emits light with high brightness has been manufactured. But,
In a system using a compound semiconductor other than ZnS as a base material, for example, a SrS: Ce light emitting layer that emits blue light, an element that emits light with high brightness has not been obtained.

The MOCVD method, the ALE method, and the MBE method are promising methods for forming a highly crystalline thin film, but it is difficult to uniformly disperse the emission centers, and a large-area EL emission layer is used. There is also a problem that it is inferior to the electron beam heating vapor deposition method and the sputter vapor deposition method in terms of difficulty in economical production. In order to increase the crystallization of the light-emitting layer, which is one of the promising conditions for manufacturing an EL device exhibiting high-luminance light emission, the substrate temperature at the time of forming the light-emitting layer is increased, or in a vacuum or after the light-emitting layer is formed. Methods such as high temperature heat treatment in an active gas atmosphere have been taken. However, in many cases, thin film EL elements use glass as a substrate, and therefore, when heat treatment is performed at a high temperature of 850 ° C. or higher, distortion of glass or the like has been a problem. Further, when a sulfide such as ZnS, SrS, CaS, CdS is used as the base material of the light emitting layer, the amount of S in the film is reduced by the high temperature heat treatment and deviates from the stoichiometric composition, resulting in a defect due to the escape of S. It was also a big problem that a crystallized light emitting layer could not be formed.

Japanese Examined Patent Publication No. 63-461117, JP-A-1
-272093 and British Patent No. 2230382
After the light emitting layer is formed,₂Heat treatment in S
Is listed. In particular, British Patent No. 2230382
In the detailed document, H of 650 ° C or more and 1 hour or more₂For S heat treatment
From SrS: Ce system, the maximum brightness is 12000 cd / m ²
Has been obtained.

[0007]

SUMMARY OF THE INVENTION The present invention is an EL device which emits light with high brightness by further improving the crystallinity of the light emitting layer.
The purpose is to provide a device.

[0008]

[Means for Solving the Problems] Under such circumstances,
As a result of earnest studies on a method of manufacturing an EL device exhibiting high-luminance light emission, the present inventors have found that after forming an amorphous thin film, the light emitting layer is heat-treated at a temperature of 650 ° C. or higher in a sulfide gas atmosphere. The inventors of the present invention have found that the crystal grains of (3) greatly grow, and thereby the brightness of the EL element is significantly improved, and thus the present invention has been completed.

That is, the present invention is a thin film electroluminescent device having a structure in which both sides of a light emitting layer doped with an emission center are sandwiched by insulating layers and at least one of both sides is sandwiched by a light transmissive electrode. The thin-film electroluminescent element is characterized in that the light-emitting layer is amorphous after the light-emitting layer is formed and before heat treatment.

The present invention will be described in detail below. Figure 1
It is a thin film EL element having a double insulation structure showing one specific example of the present invention. In the figure, 1 is a transparent substrate such as a glass plate, 2
Is a transparent electrode made of an ITO thin film having a thickness of about 100 to 300 nm, and 3 is a back electrode made of an Al thin film or an ITO thin film having a thickness of about 100 to 500 nm, which is patterned into a shape corresponding to a display pattern. 4 is Zn
Group IIb sulfides such as S, CdS, Zn _x Cd _1-x S, and S
rS, alkaline earth metal sulfides such as CaS, Zn _x S
A semiconductor matrix made of a mixed composition such as r _{1 -x} S doped with a small amount of a rare earth element or an emission center such as Mn, for example, SrS: Ce, SrS: Ce, Eu, Ca.
A light emitting layer made of S: Eu or the like. The thickness of the light-emitting layer is not particularly limited, but if it is too thin, the emission brightness will be low, and if it is too thick, the light emission starting voltage will be high.
It is in the range of 000 nm, more preferably 100 to 15
The range is 00 nm. Reference numerals 5 and 6 denote insulating layers adjacent to the front surface and the back surface of the light emitting layer 4. The insulating layer used in the EL device of the present invention is not particularly limited. For example, S
iO ₂ , Y ₂ O ₃ , TiO ₂ , Al ₂ O ₃ , HfO ₂ ,
Ta ₂ O ₅ , BaTa ₂ O ₅ , PbTiO ₃ , Si ₃ N
₄ , ZrO ₂ or the like, a mixed film thereof, or a laminated film of two or more kinds can be used.

A film is formed between the insulating layer and the light emitting layer during film formation.
It is preferable to use a buffer layer to prevent a reaction between the two during the heat treatment. The buffer layer is not particularly limited, but metal sulfides, especially ZnS, CdS, Sr
S, CaS, BaS, CuS, etc. are mentioned. The thickness of the buffer layer is not particularly limited, but is in the range of 10 to 1000 nm, and more preferably 50 to 300 nm.

As the method for forming the light emitting layer, many methods such as electron beam heating vapor deposition, sputter vapor deposition, MBE, MOCVD and ALE can be selected. In order to obtain an amorphous thin film, the substrate at the time of film formation A temperature of 150 ° C. or lower is suitable. Further, among various film forming methods, the sputter vapor deposition method is preferable because an element exhibiting high brightness can be obtained. It is important to carry out the heat treatment of the light emitting layer in a sulfide gas atmosphere. Examples of the sulfide gas include hydrogen sulfide, carbon disulfide, sulfur vapor, ethyl mercaptan, methyl mercaptan, dimethyl sulfur, diethyl sulfur, and the like. Among them, hydrogen sulfide gas is preferable because it has a large effect of improving luminance. The concentration of the sulfurizing gas is not particularly limited, but is 0.01 to 100%,
It is more preferably 0.1 to 30%. An inert gas such as Ar or He is used as the diluent gas. Further, in order for the effect of the sulfide gas to appear remarkably, the heat treatment temperature must be 650 ° C. or higher and the time must be 1 hour or longer. Also,
Performing heat treatment at a temperature of 800 ° C. or higher is not realistic because of problems such as high resistance of ITO used as a strained transparent electrode of the substrate glass and use of an expensive quartz glass substrate.

A feature of the present invention is that the light emitting layer immediately after film formation is an amorphous thin film, and by heat treatment in a sulfide gas atmosphere, crystal grains grow drastically to form a highly crystallized light emitting layer. It is possible. If the light emitting layer is crystallized before the heat treatment, the effect of grain growth due to the heat treatment tends to be suppressed rather, and rather, the grain size is large due to remarkable grain growth when the heat treatment is applied to the amorphous thin film. A light emitting layer can be formed, and the brightness of the EL element is further increased.

[0014]

EXAMPLES Examples of the present invention will be specifically described below.

[0015]

[Example 1] On a glass substrate [Hoya Co., Ltd., NA-4
0], an ITO electrode having a thickness of about 100 nm was formed by the reactive sputtering method. Then, a Ta target and a SiO ₂ target are used to form a Ta ₂ film having a thickness of 400 nm.
O ₅ and SiO ₂ having a thickness of 100 nm were sequentially formed by a sputter deposition method to form an insulating layer. Subsequently, as a buffer layer, a ZnS thin film having a thickness of about 100 nm was formed by sputter vapor deposition in an argon gas using a ZnS target. Next, as a light emitting layer, SrS and 0.
Using a target in which ₃ mol% CeF ₃ and KCl were mixed, the substrate was water-cooled and sputter deposition was performed while the temperature was kept at 100 ° C. or lower to form a thin film having a thickness of about 800 nm. Then, heat treatment was performed at 700 ° C. for 4 hours in an argon gas atmosphere containing 2 mol% hydrogen sulfide. Further, a laminated film was formed on the light emitting layer in the order of ZnS, SiO ₂ , and Ta ₂ O ₅ by the above method to construct a double insulating structure. Finally, Al electrodes were formed in a stripe shape by a resistance heating vapor deposition method using a metal mask. As the lower electrode, a part of the light emitting layer and the insulating layer was peeled off to leak the ITO electrode, and this was used.

FIG. 2 is an X-ray diffraction spectrum of the light emitting layer before heat treatment. In the figure, the peaks derived from SrS are minute and extremely broad, and it can be seen that an amorphous light emitting layer was formed. Further, FIG. 3 shows an X-ray diffraction spectrum of the light emitting layer after the heat treatment.
Strong and sharp peaks appear at the positions corresponding to the (200) plane and the (220) plane of S.
It can be confirmed that the crystallinity of the light emitting layer is remarkably improved and grain growth occurs. In addition, SrS (20 obtained by measuring the width of a point having an intensity half the maximum value of the peak)
The full width at half maximum of the peaks of the (0) plane and the (220) plane is 0.
They are 12 degrees and 0.16 degrees, which are smaller than the peak half width in Comparative Example 1 which is a conventional technique.

The maximum brightness of the EL device manufactured from this light emitting layer is 16500 cd / m ^{2 when} driven by a 5 kHz sin wave.
Met.

[0018]

Comparative Example 1 An element was produced in the same manner as in Example 1 except that the substrate temperature when forming the light emitting layer by sputtering vapor deposition was 250 ° C. The X-ray diffraction spectra of this device before and after heat treatment are shown in FIGS. 4 and 5, respectively. A relatively sharp peak appears before the heat treatment. The half-value widths of the peaks of the SrS (200) plane and the (220) plane after heat treatment obtained by the same method as described above are 0.17 degrees,
It was 0.24 degrees. In addition, E produced from this light emitting layer
The maximum brightness of L element is 120 by 5kHz sin wave drive.
It was 00 cd / m ² .

[0019]

Example 2 When forming a light emitting layer by sputter deposition,
0.3 mol% CeF ₃ and K for SrS and SrS
Sr was used in the same manner as in Example 1 except that a target mixed with CI and 0.02 mol% EuF ₃ was used.
An S: Ce, Eu white EL device was produced. As a result of measuring the X-ray diffraction spectrum, the light emitting layer before heat treatment was amorphous. The maximum brightness of this device is 5 kHz si
It was 8000 cd / m ^{2 when} driven by n-wave.

[0020]

Example 3 When forming a light emitting layer by sputtering deposition,
0.3 mol% EuF ₃ and K relative to CaS and CaS
A CaS: Eu red EL device was produced in the same manner as in Example 1 except that a target mixed with Cl was used.
As a result of measuring the X-ray diffraction spectrum, the light emitting layer before heat treatment was amorphous. The maximum brightness of this device is 5
It was 2500 cd / m ^{2 when} driven by a kHz sin wave.

[0021]

Example 4 When forming a light emitting layer by sputtering deposition,
SrS and ZnS were mixed at a molar ratio of 9: 1, and further mixed with 0.
3 mol% CeF₃And KCl mixed target
In the same manner as in Example 1 except that (Sr; Z
n) An S: CeEL device was produced. X-ray diffraction spectrum
As a result, the light emitting layer before heat treatment was amorphous.
there were. The maximum brightness of this device is 5kHz sin wave drive.
8000 cd / m in motion ²Met.

[0022]

According to the present invention, a highly crystallized light emitting layer having a large crystal grain size can be obtained, and as a result, an EL element which emits light with high brightness can be manufactured.

[Brief description of drawings]

FIG. 1 is a partial cross-sectional view showing an EL element which is a specific example of the present invention.

FIG. 2 is an X-ray diffraction spectrum diagram of the light emitting layer before heat treatment in a sulfide gas atmosphere in Example 1.

3 is an X-ray diffraction spectrum diagram of the light emitting layer after heat treatment in a sulfurizing gas atmosphere in Example 1. FIG.

FIG. 4 is an X-ray diffraction spectrum diagram of a light emitting layer before heat treatment in a sulfurizing gas atmosphere in Comparative Example 1.

5 is an X-ray diffraction spectrum diagram of the light emitting layer after a heat treatment in a sulfurizing gas atmosphere in Comparative Example 1. FIG.

[Explanation of symbols]

 1 glass substrate 2 transparent electrode 3 back electrode 4 light emitting layer 5, 6 insulating layer

Claims (1)

[Claims] 1. A thin-film electroluminescent device having a structure in which both sides of a light-emitting layer doped with a light-emitting center are sandwiched by insulating thin films, and at least one of both sides is sandwiched by a light-transmissive electrode, and a light-emitting layer is formed. A thin-film electroluminescent device, characterized in that the light-emitting layer after film formation and before heat treatment is amorphous.