JPH09134784A - El element and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the occurrence of a by-product so as to improve the crystallinity of a luminous layer, and enhance color purity by forming a non- dope layer, to which no luminescence center is added, between the luminous layer and an insulation layer using same base material as that of the luminous layer. SOLUTION: In an EL element having a luminous layer which is formed by adding Ce as a luminescence center to base material, calcium thio gallate CaGa2S4, a non-dope layer 4 of the CaGa2S4 is formed on an insulation layer 3 luminous layer by a sputtering method, and thereon a luminous layer 5 is formed by a predetermined method. Since no luminescence center as impurity exists by providing the non-dope layer like this, no by-product taking the impurity as cores is produced in the non-dope layer 4, and in the early stage of the crystal growth of a compound on the non-dope layer, the occurrence of the by-product taking a luminescence center element as a growth core is suppressed so as to facilitate crystallizing the compound. Accordingly, the crystallinity of the luminous layer is improved, and the diffusion of carriers running in the luminous layer is reduced so that the luminescence brightness of the EL element is significantly improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an EL (electroluminescence) element used for a self-luminous segment display or matrix display of instruments, a display of various information terminal devices, etc., and a manufacturing method thereof.

[0002]

2. Description of the Related Art Conventionally, an EL element is formed by sequentially laminating a first electrode, a first insulating layer, a light emitting layer, a second insulating layer and a second electrode on a glass substrate which is an insulating substrate. At least the light extraction side from the light emitting layer is made of an optically transparent material. Here, the light emitting layer is formed by adding a light emitting center to a base material, and various materials have been proposed as those materials. Among them, alkaline earth metal thiogallates (MGa ₂ S ₄ , M = Ca, Sr, B
An EL device having a light emitting layer (hereinafter, simply referred to as an alkaline earth metal thiogallate light emitting layer) in which a) is used as a base material and Ce (cerium) is added as a light emitting center element is attracting attention as a device that emits blue light.

[0003]

Generally, the crystallization temperature of alkaline earth metal thiogallate is high, and when it is used as a light emitting layer of an EL device, a heat treatment at 600 to 650 ° C. is performed. The upper limit of the heat treatment temperature is 650 ° C., because heat treatment at a temperature higher than this causes a remarkable distortion in the glass substrate.

However, at present, even if the heat treatment is performed at these temperatures, the crystallinity of the alkaline earth metal thiogallate light emitting layer is such that ZnS (zinc sulfide) or SrS (strontium sulfide) is used as a base material for light emission. It was significantly lower than the layer. Therefore, it has been extremely difficult to realize an EL device having practically sufficient brightness by using the alkaline earth metal thiogallate light emitting layer.

For high brightness, it is important to improve the crystallinity of the alkaline earth metal thiogallate light emitting layer. But,
Alkaline earth metal thiogallate is a ternary compound of alkaline earth metals (Ca, Sr, Ba), gallium (Ga) and sulfur (S). The crystallization mechanism is very complex.

In general, the initial growth process has a great influence on the crystallinity of the light emitting layer thereafter. In particular, in the alkaline earth metal thiogallate light emitting layer, by-products such as alkaline earth metal sulfides (CaS, SrS, BaS) that crystallize at low temperature are likely to be formed in the initial stage of growth. Once these by-products are formed, the growth of the by-products continues to occur, so that the entire light-emitting layer is a mixture of the alkaline earth metal thiogallate and the by-products. Therefore, the crystallinity of the intended alkaline earth metal thiogallate light emitting layer is significantly reduced.

Further, among the by-products, when alkaline earth metal sulfides (CaS, SrS, BaS) are formed,
Since the emission wavelength of Ce, which is the emission center, is longer than that of alkaline earth metal thiogallate, the blue purity of EL emission is also reduced. Therefore, in order to improve the crystallinity of the alkaline earth metal thiogallate light-emitting layer and prevent the deterioration of blue purity, it is important to suppress the formation of by-products in the initial stage of growth.

The present invention has been made in view of the above problems, and in the one having a light emitting layer to which a light emitting center is added, which is made of a IIa-IIIb-VIb group (excluding O) compound such as an alkaline earth metal thiogallate as a base material. The purpose of the present invention is to suppress the formation of by-products, improve crystallinity, and improve color purity.

[0009]

According to a first aspect of the present invention, there is provided a light-emitting layer (5) comprising a IIa-IIIb-VIb group (excluding O) compound as a base material and an emission center added thereto. A feature of the present invention is that a non-doped layer (4) made of the same base material as that of the light emitting layer and having no luminescent center added is formed between the insulating layers (3).

Therefore, by providing the non-doped layer, the emission center as an impurity does not exist, so that the by-product (IIa-VIb) having the impurity as a nucleus is not generated in the non-doped layer. Then, when a IIa-IIIb-VIb group (excluding O) compound is formed on the non-doped layer in which the by-product is not formed, the IIa group sulfide having the luminescent center element as a growth nucleus is formed at the initial stage of crystal growth of the compound. IIa-IIIb-V that can suppress the generation of by-products such as substances (affected by the fact that no by-products are generated in the non-doped layer as the base)
Crystallization of Ib group compounds (excluding O) becomes very easy,
The crystallinity of the light emitting layer can be significantly improved. As a result, scattering of carriers traveling in the light emitting layer is reduced, so that the carriers can be easily accelerated to high energy, and the EL emission brightness is significantly improved.

In particular, when an alkaline earth metal thiogallate light-emitting layer is used as in the second aspect of the invention, alkaline earth metal sulfides (CaS, Sr) that crystallize at low temperatures are used.
By-products such as (S, BaS) are likely to be formed in the initial stage of growth, and therefore the effect of providing the non-doped layer is great. Further, as in the invention according to claim 3, by setting the film thickness of the non-doped layer to 5 nm or more and 200 nm or less, generation of alkaline earth metal sulfide can be suppressed, and particularly, claim 4 When the film thickness is set to 8 nm or more and 100 nm or less as in the above invention, the suppressing effect can be greatly enhanced.

Further, according to the invention of claim 5, the composition ratio of Ga to the alkaline earth metal is 2.0 or more.2.
Even when it is 4 or less, the generation of alkaline earth metal sulfide can be effectively suppressed. The invention according to claim 6 is characterized by a method for manufacturing an EL element in which the non-doped layer (4) and the light emitting layer (5) are sequentially formed. At this time, as in the invention according to claim 7, by continuously forming the non-doped layer (4) and the light emitting layer (5) in a vacuum, an oxide layer is formed at the interface between these layers. Can be prevented and the crystallinity of the light emitting layer can be further improved.

The sputtering method or the vapor phase epitaxy method can be used to form each layer. However, when the vapor phase epitaxy method is used, the non-doping is performed as in the invention of claim 7. When the Group IIIb source gas is first supplied when forming the layer (4), the initial stage of crystal growth can be improved.
Generation of by-products such as IIa group sulfides can be eliminated,
The crystallinity of the light emitting layer can be further improved.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION

(First Embodiment) FIG. 1 shows an EL element 10 according to the present invention.
FIG. 3 is a schematic view showing a cross section of FIG. The EL element 1 shown in FIG.
At 0, light is extracted in the direction of the arrow. EL element 10
Is formed by sequentially laminating the following thin films on the glass substrate 1 which is an insulating substrate. That is, a first transparent electrode (first electrode) 2 made of optically transparent ZnO (zinc oxide) is formed on a glass substrate 1, and an optically transparent Ta ₂ O ₅ (tantalum pentoxide) is formed on the upper surface thereof. ) Consisting of
Insulating layer 3, CaGa ₂ S ₄ (calcium thiogallate)
A non-doped layer 4 consisting of, a CaGa ₂ S ₄ : Ce (calcium thiogallate: cerium) light emitting layer 5 containing Ce as an emission center, a second insulating layer 6 consisting of Ta ₂ O ₅ ,
And a second transparent electrode (second electrode) 7 made of ZnO is formed.

The thickness of each of the above layers is 300 nm for the first and second transparent electrodes 2 and 6, and 30 for the first and second insulating layers 3 and 5.
0 nm, the non-doped layer 4 is 20 nm, and the light emitting layer 5 is 600 nm.
nm. The thickness of each of these layers is the same as that of the glass substrate 1.
It is based on the central part of. Next, a method of manufacturing the above-mentioned thin film EL element 10 will be described.

First, the first transparent electrode 2 was formed on the glass substrate 1. As the vapor deposition material, ZnO powder and Ga ₂ O _{3 are used.}
(Gallium oxide) was added and mixed, and pelletized was used. An ion plating apparatus was used as a film forming apparatus. Specifically, the inside of the ion plating apparatus was evacuated while keeping the temperature of the glass substrate 1 constant. Then, Ar (argon) gas was introduced to keep the pressure constant, and the beam power and the high frequency power were adjusted so that the film formation rate was in the range of 6 to 18 nm / min.

Next, the first insulating layer 3 made of Ta ₂ O ₅ was formed on the first transparent electrode 2 by the sputtering method. Specifically, the temperature of the glass substrate 1 is kept constant, a mixed gas of Ar and O ₂ (oxygen) is introduced into the sputtering apparatus, and 1K
The film was formed with a high frequency power of W. Next, a non-doped layer 4 containing CaGa ₂ S ₄ as a base material was formed on the first insulating layer 3 by a sputtering method. Specifically, the glass substrate 1 was kept at a constant temperature of 300 ° C., a gas containing H ₂ S (hydrogen sulfide) mixed with Ar at a ratio of 5 mol% was introduced into the film forming chamber, and high frequency power of 300 W was applied. A film was formed. A CaGa ₂ S ₄ sintered body was used as the sputtering target.

Next, CaGa ₂ S is formed on the non-doped layer 4.
CaG with ₄ as a base material and Ce added as a luminescent center
The a ₂ S ₄ : Ce light emitting layer 5 was formed by the sputtering method. At this time, the substrate on which the non-doped layer 4 was formed was transferred to another film forming chamber having a sputter target to which an emission center was added while keeping it in vacuum, and then CaGa ₂ S ₄ : C
e The light emitting layer 5 was formed. In the case where a plurality of film forming chambers are not provided, the same effect can be obtained by providing two kinds of sputtering targets (non-doped and Ce-doped) in the same film forming chamber.

Specifically, the glass substrate 1 is kept at a constant temperature of 300 ° C., a gas containing Ar mixed with H ₂ S at a ratio of 5 mol% is introduced into the film forming chamber, and CaGa is supplied at a high frequency power of 300 W. _{The 2} S ₄ : Ce light emitting layer 5 was formed. As the sputtering target, a CaGa ₂ S ₄ : Ce sintered body to which Ce was added as a light emission center was used. When the X-ray diffraction pattern was examined for the CaGa ₂ S ₄ : Ce light emitting layer 5 immediately after the sputter film formation, no diffraction peak was observed,
It was confirmed to be amorphous.

Next, sputter-deposited CaGa ₂ S ₄ :
The Ce light emitting layer 5 was heat-treated at 650 ° C. for 1 minute in an Ar atmosphere containing 20% of H ₂ S. As a result, C, which was amorphous and did not emit light immediately after the sputtering film formation,
The aGa ₂ S ₄ : Ce light emitting layer 5 was crystallized and started to emit light. Next, the second insulating layer 6 made of Ta ₂ O ₅ was formed on the light emitting layer 5 by the same method as the above-mentioned first insulating layer 3. Then, the second transparent electrode 7 made of a ZnO film was formed on the second insulating layer 6 by the same method as the above-mentioned first transparent electrode 2.

CaGa ₂ S formed as described above
_{When the} X-ray diffraction pattern of the ₄ : Ce light emitting layer 5 was examined, as shown in FIG. 2, only the diffraction peak corresponding to CaGa ₂ S ₄ was observed, and CaS (calcium sulfide) and other by-products were observed. No related diffraction peaks were found. On the other hand, in the comparative example manufactured by the same process as above without providing the non-doped layer 4, as shown in FIG.
In addition to the diffraction peak corresponding to aGa ₂ S ₄ , a diffraction peak corresponding to CaS was observed. In addition, CaGa ₂ S ₄
The orientation and the half-value width of the diffraction peak are also deteriorated as compared with the above embodiment, and the crystallinity of the light emitting layer of the comparative example is significantly decreased as compared with the above embodiment.

Next, when the EL emission characteristics were evaluated, it was found that this embodiment has a remarkably higher blue purity (CIE) than the comparative example.
Chromaticity coordinates: X = 0.15, Y = 0.19) and blue emission luminance were obtained. On the other hand, in the comparative example, as can be seen from the results of the above X-ray diffraction peak, the emission spectrum was a mixture of EL emission from CaGa ₂ S ₄ : Ce and CaS: Ce. However, the green emission from CaS: Ce has higher visibility, so the actual emission color is green (CIE
Chromaticity coordinates: X = 0.27, Y = 0.52). Further, in the comparative example, the crystallinity thereof was lower than that of the above-described embodiment, and thus the obtained green light emission was also weak.

Although not described in the above description of the manufacturing process, after the light emitting layer 5 was formed, cleaning was performed using water to remove particles. Then, while the cleaning effect was sufficiently obtained in the above-described embodiment, CaS was eluted in the comparative example because it was water-soluble, and a large number of non-light emitting portions were generated due to peeling of the light emitting layer. Next, in the above-described embodiment, the thickness of the non-doped layer 4 was changed and its dependence was examined. The film thickness of the non-doped layer 4 was controlled by changing the sputtering time in the above embodiment.

As a result, as shown in FIG. 4, when the thickness of the non-doped layer 4 was 5 nm or more, the generation of CaS could be suppressed as compared with the case where the non-doped layer 4 was not provided. In particular, the thickness of the non-doped layer 4 is 8 nm or more and 100 n
When it was less than m, the production of CaS could be suppressed very greatly. The thickness of the non-doped layer 4 is 200 n
When the thickness becomes m or more, the threshold value of EL emission increases by 20 V or more. Therefore, the thickness of the non-doped layer 4 is 2
It is desirable that the thickness is 00 nm or less. (Second Embodiment) In the second embodiment, in addition to the first embodiment, the first and second insulating layers 3 and 6 are formed of optically transparent Al ₂ O ₃ (aluminum oxide), and
The non-doped layer 4 and the CaGa ₂ S ₄ : Ce light emitting layer 5 are formed by a metal organic chemical vapor deposition (MOCVD) method.

A method of manufacturing this product will be described below. Similar to the first embodiment, the first transparent electrode 2 is formed on the glass substrate 1, and Al ₂ O _{3 is formed} on the first transparent electrode 2.
The first insulating layer 3 made of metal is formed by metal organic chemical vapor deposition (MOCV).
It was formed by the D) method. Specifically, the glass substrate 1 is 4
After keeping the temperature at a constant temperature of 00 ° C. and making the inside of the film forming chamber under a reduced pressure atmosphere, using an Ar carrier gas, Al (CH ₃ )
₃ (Trimethylaluminum) and O ₂ were introduced into the film forming chamber. Then, by reacting and pyrolysis of these raw material gases, thereby forming a first insulating layer 3 made of Al ₂ O _3.

Next, CaGa ₂ S ₄ is formed on the first insulating layer 3.
The non-doped layer 4 using as a base material was formed by the MOCVD method. Specifically, the glass substrate 1 is kept at a constant temperature of 590 ° C., the inside of the film forming chamber is placed under a reduced pressure atmosphere, and then Ar
Ca (C ₁₁ H ₁₉ O ₂ ) ₂ (calcium dipivaloylmethanate) was used using a carrier gas, and Ga (C ₂ H ₅ ) ₃ (triethylgallium) was also used using an Ar carrier gas.
And H ₂ S diluted with Ar gas were introduced into the film forming chamber. Then, by reacting and thermally decomposing these source gases, the non-doped layer 4 made of CaGa ₂ S _{4 is} formed.
Was formed.

Next, CaGa ₂ S is formed on the non-doped layer 4.
CaG with ₄ as a base material and Ce added as a luminescent center
The a ₂ S ₄ : Ce light emitting layer 5 was formed by the MOCVD method. Specifically, the glass substrate 1 is kept at a constant temperature of 590 ° C., the inside of the film forming chamber is put under a reduced pressure atmosphere, and then Ca (C ₁₁ H ₁₉ O ₂ ) ₂ is added by using an Ar carrier gas.
Ga (C ₂ H ₅ ) ₃ and Ar using carrier gas
H ₂ S diluted with gas was introduced into the film forming chamber. Furthermore, in order to add the luminescence center element, C in Ar carrier gas is added.
e (C ₁₁ H ₂₀ O ₂ ) ₃ (cerium dipivaloyl methanide) was evaporated at 148 ° C., and this was supplied to the film forming chamber.
Then, by reacting and thermally decomposing these raw material gases, CaGa ₂ S added with Ce as a luminescence center
₄ : A Ce light emitting layer 5 was formed.

CaGa _{2 formed} by MOCVD method
The X-ray diffraction pattern of the S ₄ : Ce light emitting layer 5 was examined. As a result, a diffraction peak corresponding to the (400) plane of CaGa ₂ S ₄ was observed, and it was confirmed that it was crystallized. Next, the second insulating layer 6 made of Al ₂ O ₃ was formed on the light emitting layer 5 in the same manner as the above-described first insulating layer 3.
Then, the second transparent electrode 7 made of a ZnO film was formed.
The film thickness of each layer described above is the same as that shown in the first embodiment.

When the EL emission characteristics in the second embodiment were evaluated, as in the first embodiment, as compared with the comparative example,
High blue purity and blue emission brightness were obtained. Also, CaG
An X-ray diffraction pattern of the a ₂ S ₄ : Ce light emitting layer 5 was examined. As a result, CaGa ₂ S ₄ was found to be the same as that shown in FIG.
Only the diffraction peak corresponding to was observed.

Next, in the non-doped layer 4 and the light emitting layer 5 made of CaGa ₂ S ₄ , the Ga / Ca composition ratio was changed, and the influence of the Ga / Ca composition ratio on the insertion of the non-doped layer 4 was examined. In the second embodiment, the Ga / Ca composition ratio was controlled by changing the supply ratio of the Ca raw material and the Ga raw material. In addition, the Ga / Ca composition ratio is the electron probe X
Line Micro Analysis (EPMA: Electron Probe Mic)
ro Analysis) method was used for analysis.

The results are shown in FIG. The formation of CaS could be suppressed by inserting the non-doped layer 4 in the region where the Ga / Ca composition ratio was 2.0 to 2.4. In particular, the Ga / Ca composition ratio is stoichiometry (2.
The effect is large in the region close to 0). Also, Ga /
In the region where the Ca composition ratio is 2.5 or more, CaGa ₂ S ₄ does not grow, and in the region where the Ga / Ca composition ratio is less than 2.0,
Even if the non-doped layer 4 is inserted, the generation of CaS is remarkable. Therefore, the Ga / Ca composition ratio of the CaGa ₂ S ₄ light emitting layer is set to 2.
It is desirable to set it to 0 to 2.4.

When the non-doped layer 4 is formed by MOCVD, Ga (C ₂ H ₅ ) which is a IIIb group source gas is used.
It is desirable to supply ₃ first. This is because CaS, which is an alkaline earth metal sulfide, is not formed at the initial stage of crystal growth due to the film formation by the raw material gas, and the crystallinity is further improved. In addition to CaGa ₂ S ₄ shown in the above-described embodiment, SrGa ₂
S ₄ (Strontium thiogallate), BaGa ₂ S ₄
(Barium thiogallate) or alkaline earth metal selenogallate (MGa ₂ Se ₄ , M = Ca, Sr, Ba) and other IIa-IIIb-VIb group compounds (excluding O) were used as the light-emitting base material in the light-emitting layer. Also in this case, the same effect as described above can be obtained.

Regarding the luminescence center element to be added,
In addition to Ce, rare earth elements such as Tb (terbium), Eu (europium) and Sm (samarium), or Mn
(Manganese), Pb (lead), or the like can be used.

[Brief description of the drawings]

FIG. 1 is a schematic view showing a vertical cross section of an EL element according to a first embodiment of the present invention.

FIG. 2 is an X-ray diffraction spectrum according to the first embodiment of the present invention.

FIG. 3 is an X-ray diffraction spectrum of a comparative example in which a non-doped layer is not provided.

FIG. 4 is a characteristic diagram showing the relationship between the film thickness of the non-doped layer and the generation of CaS according to the first embodiment of the present invention.

FIG. 5 is a Ga / C of a light emitting layer according to a second embodiment of the present invention.
a Composition ratio and CaS and CaGa _TwoS_FourThe relationship with
It is a characteristic view to show.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Glass substrate (insulating substrate), 2 ... 1st transparent electrode (1st electrode), 3 ... 1st insulating layer, 4 ... Undoped layer, 5 ... Light emitting layer, 6 ... 2nd insulating layer, 7 ... 2nd Transparent electrode (second electrode), 10 ... EL element.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor, Masaru Hattori, 1-1, Showa-cho, Kariya city, Aichi prefecture, Nihondenso Co., Ltd.

Claims (8)

[Claims] 1. A first electrode (2) on a substrate (1).
An insulating layer (3), a light emitting layer (5), a second insulating layer (6) and a second electrode (7) are laminated and formed, and at least the light extraction side from the light emitting layer (5) is optically transparent. In the EL device described above, the light emitting layer (5) is a compound in which a IIa-IIIb-VIb group (excluding O) compound is used as a base material and an emission center is added,
Between the light emitting layer (5) and the first insulating layer (3), a non-doped layer (4) made of the same host material as that of the light emitting layer (5) and containing no emission center is formed. Characteristic EL element. 2. The EL device according to claim 1, wherein the IIa element is an alkaline earth metal and the IIIb group element is Ga. 3. The thickness of the non-doped layer (4) is 5 n.
3. The thickness is not less than m and not more than 200 nm.
The EL device according to 1. 4. The film thickness of the non-doped layer (4) is 8 n.
3. The thickness is not less than m and not more than 100 nm.
The EL device according to 1. 5. The EL device according to claim 2, wherein the composition ratio of Ga to the alkaline earth metal is 2.0 or more and 2.4 or less. 6. A first electrode (2) and a first electrode (2) on a substrate (1).
An insulating layer (3), a light emitting layer (5), a second insulating layer (6) and a second electrode (7) are laminated and formed, and at least the light extraction side from the light emitting layer (5) is optically transparent. In the method for manufacturing an EL device described above, a step of forming a non-doped layer (4) containing a IIa-IIIb-VIb group (excluding O) compound as a host material and not adding an emission center on the first insulating layer (3). And on the non-doped layer (4), the group IIa-IIIb-VIb (O
And a step of forming the light emitting layer (5) using a compound as a host material and adding an emission center. 7. The method of manufacturing an EL device according to claim 6, wherein the non-doped layer (4) and the light emitting layer (5) are continuously formed in a vacuum. 8. The step of forming the non-doped layer (4) is characterized in that the non-doped layer (4) is formed by first supplying the Group IIIb source gas using a vapor phase growth method. The method for manufacturing an EL element according to claim 6.