JP4125108B2 - Thin film electroluminescent device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a thin-film electroluminescent element used for an electroluminescent display having features of being thin and excellent in flatness, having a long life and high contrast.
[0002]
[Prior art]
2. Description of the Related Art It is widely known that an electroluminescent element (hereinafter referred to as an EL element) using electroluminescence, which is one of light emission phenomena, is used for a flat display.
[0003]
As a light-emitting layer constituting such an EL element, a layer using a sulfide phosphor thin film such as ZnS: Mn has been conventionally known. On the other hand, an attempt has been made to use an oxide phosphor thin film excellent in handling and stability in the atmosphere as the light emitting layer. For example, Zn ₂ SiO ₄ : Mn and ZnGa ₂ O ₄ : Mn that emit green light, CaO: Mn that emits red light, and CaO: Pb that emits blue light are known as oxide phosphor thin films (non-patent literature). 1).
[0004]
[Non-Patent Document 1]
"Flat Panel Display Dictionary", supervised by Uchida, Uchiike, Industrial Research Committee [0005]
[Problems to be solved by the invention]
By the way, although the above-described oxide phosphor thin film, particularly the phosphor thin film having Mn ions as the emission center, various luminescences such as green, red, and yellow as described above are obtained, but blue luminescence is obtained. Not. For this reason, it has been difficult to make the emission center material for each color light the same material in producing a full color panel that emits each color light of R, G, and B. As a result, when forming phosphor thin films for light emission of each color, problems such as complicated panel manufacturing process and insufficient light emission characteristics occur due to different film forming conditions such as heat treatment temperature. It was.
[0006]
Of course, the blue component can be extracted from the emitted blue-green component using a color filter, but the emission luminance of the blue component obtained in this way is somewhat different depending on the color purity and the characteristics of the color filter, It becomes about 1/10 of the light emission luminance of the original blue-green component.
[0007]
It is also conceivable to produce a full-color panel by combining the above-described oxide phosphor thin film with a sulfide-based thin film. For example, when CaGa ₂ S ₄ or SrGa ₂ S ₄ which is a ternary compound thiogallate is used as a base material and Ce ³⁺ ions are activated as a luminescent center, BaAl ₂ S ₄ which is a thioaluminate is further used as a base material. When Eu ²⁺ ions are activated, practical blue light emission can be obtained.
[0008]
However, the formation of oxide phosphor thin films requires high-temperature heat treatment in the air or in an oxygen atmosphere, which oxidizes sulfide phosphor thin films and exhibits their original light-emitting performance. Difficult to do.
[0009]
Therefore, it is desired to produce a full color panel that can emit light of three primary colors of R, G, and B using only an oxide phosphor thin film.
In particular, considering the formation process of the oxide phosphor thin film by high-temperature heat treatment, it is desired to use the same series of materials as possible for the base material as well as the luminescent center element.
[0010]
The present invention has been made in view of such circumstances, and provides a thin-film EL element composed of a novel host material in which a light-emitting layer is formed of an oxide phosphor thin film and can emit various colored lights including blue. It is for the purpose.
[0011]
In addition, the present invention includes a light emitting layer made of an oxide phosphor thin film that can generate light of three primary colors of R, G, and B using the same luminescent center element and / or a base material of a light emitting layer of the same series. Another object of the present invention is to provide a thin film EL element.
[0012]
[Means for Solving the Problems]
Thin film electroluminescent element according to the present invention (thin-film EL element) is provided with two electrode layers, a luminescent layer made of phosphor thin film for emitting disposed fluorescence between these two electrode layers, the light emitting layer Is characterized in that the base material is formed of SrSb ₂ O _X (where X = 4, 5, 6) and the base material is activated with Mn ions as the emission center .
As described above, when SrSb ₂ O _X is used as the base material of the light emitting layer, various color lights including blue can be emitted by appropriately changing the light emission center element.
[0013]
The present invention of using SrSb ₂ O _X as the base material of the light emitting layer has a wide interval between the Sr ions that replace the ions of the luminescent center element and the oxygen ions in the crystal structure of SrSb ₂ O _X. This has been achieved for the first time by the inventor's idea that the influence of oxygen ions on the ions of the luminescent central element will be small and the subsequent experiments.
[0014]
In addition, activation of Mr ions as a luminescent center in SrSb ₂ O _X which is the base material enables blue EL emission which has been conventionally required.
Further, according to the thin film EL element configured as described above, SrSb ₂ O _X : Mn (X = 4, 5, 6) is used as the blue light emitting phosphor thin film, and the green light emitting phosphor thin film is described above. By using Zn ₂ SiO ₄ : Mn or ZnGa ₂ O ₄ : Mn, at least the luminescent center element is the same, and the process can be simplified.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, a thin film electroluminescent (EL) device according to an embodiment of the present invention will be described with reference to the drawings.
[0018]
Hereinafter, the thin film EL element according to the embodiment of the present invention will be specifically described.
The thin film EL device according to an embodiment of the present invention uses Mn ²⁺ ions as the emission center and uses the ternary compound SrSb ₂ O _X (X = 4, 5, 6) in the light emitting layer.
This thin film EL element is of a double insulation structure type having a cross-sectional structure as shown in FIG.
[0019]
As shown in FIG. 1, in the thin film EL device according to the present embodiment, a lower electrode layer 2, a lower insulating layer 3, a light emitting layer 4, an upper insulating layer 5 and an upper electrode layer 6 are sequentially stacked on a glass substrate 1. The EL light emission 7 of the light emitting layer 4 is output through the glass substrate 1. Note that a buffer layer may be provided at at least one of the upper and lower adjacent positions of the light emitting layer 4.
[0020]
The lower electrode layer 2 is a transparent electrode layer made of, for example, ITO (tin-added indium oxide), ZnO or the like, while the upper (back) electrode layer 6 is an opaque electrode layer made of Al or the like. Each of the electrode layers 2 and 6 has a thickness of about 200 nm, for example. The upper electrode layer 6 can be a transparent electrode layer.
The upper and lower insulating layers 3 and 5 are made of, for example, Ta ₂ O ₅ and have a thickness of about 500 nm, for example.
[0021]
Further, the light emitting layer 4 is an oxide phosphor thin film, and is formed of SrSb ₂ O _X : Mn (X = 4, 5, 6) as described above. The layer thickness is about 0.8 μm, for example.
[0022]
By the way, although Mn ^<2+> ion is light-emitted by the forbidden transition of 3d electron, the light emission color is determined strongly received by the influence by a ligand. However, so far the oxide phosphor thin film which is known, the influence of oxygen ions is a ligand surrounding the Mn ²⁺ ion is strongly affects Mn ²⁺ ions, from red to green (blue-green) In the meantime, color light emission was obtained, but blue light emission was not obtained.
[0023]
Therefore, the present inventor paid attention to SrSb ₂ O _X crystals whose crystal structure has been reported by Janin et al. (J. Janin and R. Bernard: Compt. Rend. 240 614 (1953)) and M. l. Y. Allusalu
(Tr. Inst. Fiz. Astron. Akad. Nauk. Est. SSR. 8 58 (1958)). That is, according to this report, in the Sr (Ca) Sb ₂ O _X crystal, the distance between Sr ions and oxygen ions is as large as 2.5 mm.
[0024]
The inventor of the present application uses the SrSb ₂ O _X as a base material and uses Mn ions as the emission center, so that the distance between Sr ions substituted for Mn ions and oxygen ions is as large as 2.5 mm, so Mn ions Was considered to be able to emit blue light without being bound by oxygen ions.
Thus, it was confirmed that blue light emission was obtained from the light emitting layer 4 formed of SrSb ₂ O _X : Mn (X = 4, 5, 6).
[0025]
Hereinafter, a method for forming the layers 1 to 6 will be described.
[0026]
The lower electrode layer 2 and the upper electrode layer 6 are formed by electron beam evaporation, but other film formation methods such as other evaporation methods, sputtering methods, ion plating methods, CVD methods, etc. It is also possible to form.
[0027]
The insulating layers 3 and 5 are formed by high frequency magnetron sputtering, but can be formed by, for example, vapor deposition, ion plating, or CVD.
[0028]
The light emitting layer 4 is formed by electron beam evaporation, but is formed by other film forming methods such as co-evaporation, sputtering, ion plating, sol-gel, or CVD. It is also possible.
[0029]
Hereinafter, a method for forming the light emitting layer 4 will be described.
The film formation method of the light emitting layer 4 includes the following two manufacturing steps.
[0030]
That is, first, the glass substrate 1 is heated to a temperature of about 200 ° C., each material of SrO, Sb ₂ O ₅ , and MnO is mixed, and the hardened pellet is irradiated with an electron beam to evaporate the material. Then, a thin film of SrSb ₂ O _X : Mn (X = 4, 5, 6) is formed on the insulating layer 3 (first step).
[0031]
Subsequently, heat treatment at about 500 ° C. is performed in the atmosphere for about 1 hour to promote crystallization (second step).
[0032]
【Example】
The light emitting layer 4 was formed by the film forming method described in the above embodiment.
The light emitting layer 4 was formed twice.
[0033]
FIG. 2 shows an X-ray diffraction pattern of the light emitting layer 4 of this example formed in this way. (A) shows the X-ray diffraction pattern for the light-emitting layer 4 formed in the first time, and (B) shows the X-ray diffraction pattern for the light-emitting layer 4 formed in the second time. The film formation conditions such as the heat treatment temperature are slightly different between the first time and the second time.
[0034]
As is clear from FIGS. 2A and 2B, according to the present example, although the composition ratios are slightly different from each other, both of them contain a large amount of SrSb ₂ O _X : Mn (X = 4, 5, 6). It was confirmed that a crystalline thin film was formed.
[0035]
In addition, FIG. 3 shows an EL emission spectrum when a thin film EL element having a light emitting layer formed by the above example is driven. In FIG. 3, the peak located at around 450 nm shows blue light emission by Mn ²⁺ ions. In addition, the peak located in the vicinity of 400 nm close to the ultraviolet region indicates light emission due to Sb ⁵⁺ , and if light emission due to Mn ²⁺ increases, it decreases accordingly.
[0036]
In the above-described embodiment, SrSb ₂ O _X : Mn (X = 4, 5, 6) is used as the phosphor thin film, but ions such as Cu, Cr, Pb, and Bi are used instead of Mn ions. It is considered that a similar result can be obtained even if is used as the emission center. Also, if rare earth element ions are used as the emission center instead of Mn ions, various colored lights (for example, R, G, and B color lights) can be emitted according to the type of rare earth element used as the emission center. In addition, since the full color panel can be manufactured while sharing the base material of the light emitting layer for each color light, the temperature process in the manufacturing process can be made common, and the manufacturing cost can be reduced.
[0037]
Further, in the phosphor thin film SrSb ₂ O _X : Mn (X = 4, 5, 6) described above, the Sr of the base material is changed to another element, particularly, other 2A group such as Mg, Ca, Ba, etc. By forming a thin film, various colored lights can be emitted. For example, it has been confirmed that green light emission having a peak near 510 nm can be obtained from a phosphor thin film CaSb ₂ O _X : Mn (X = 4, 5, 6) obtained by replacing Sr with Ca. By adopting such a configuration, it is possible to manufacture full-color panels using the same series of base materials and the same luminescent center element, thereby further standardizing the temperature process and further promoting cost reduction. can do. In addition, various light emission colors can be obtained by combining the same series of base material and light emission center material, which facilitates the production of a multi-color panel.
[0038]
In addition, when the Sr of the base material of the fluorescent material SrSb ₂ O _X : Mn (X = 4, 5, 6) described above is replaced with another element, for example, the elements that replace Sr are, for example, Sr, Mg, Ca, By selecting two or more elements selected from Group 2A elements such as Ba and adjusting the mixing ratio of the two or more selected elements, the wavelength of the emitted colored light can be set to an arbitrary value. is there.
[0039]
The thin film EL element according to the above-described embodiment is formed by sequentially laminating the lower electrode layer 2, the lower insulating layer 3, the light emitting layer 4, the upper insulating layer 5 and the upper electrode layer 6 on the glass substrate 1. However, it is possible to use a ceramic substrate instead of the glass substrate 1. In particular, by using a ceramic substrate made of a ceramic material having a high dielectric constant, it is possible to have a function as an insulating layer in addition to a function as a substrate. Thereby, the insulating layers 3 and 5 described above can be omitted. As a specific example of the ceramic substrate having a high dielectric constant, for example, a 0.2 mm-thick barium titanate plate (BaTiO ₃ ) is used. A light-emitting layer made of a SrSb ₂ O _X : Mn (X = 4, 5, 6) thin film is directly formed on this substrate by using the film forming method described above. Thereafter, in order to promote crystallization, heat treatment is performed at about 500 ° C. in the atmosphere for about 1 hour.
[0040]
In this case, the upper electrode layer is directly formed on the light emitting layer, and the lower electrode layer is directly formed on the surface of the ceramic substrate opposite to the light emitting layer arrangement side.
[0041]
In addition, as embodiment of this invention, it is not restricted to what was mentioned above, The change of another various aspect is possible.
For example, the layer configuration of the thin film EL element of the present invention is not limited to that of the above-described embodiment, and may be a layer configuration in which other layers such as a buffer layer are interposed between the above-described layers, A layer structure in which only one insulating layer is present is also possible.
[0042]
Of course, the constituent material, thickness, and film forming method of each layer are not limited to those described above.
[0043]
【The invention's effect】
According to the thin film EL element of the present invention, the base material of the light emitting layer disposed between the two electrode layers is formed of SrSb ₂ O _X (where X = 4, 5, 6). The light emitting layer can emit light of various colors including blue. In particular, when Mn ions are activated as the emission center for this base material, blue light emission that cannot be obtained with a conventional oxide phosphor thin film having Mn ions as the emission center can be obtained.
[0045]
In this case, if a light emitting layer capable of generating three primary colors of R, G, and B is formed using the same luminescent center element, for example, Mn, not only the same series of base materials but also the same light emission. Since a thin film EL element having a light emitting layer capable of generating three primary colors of R, G, and B using a central element can be obtained, the temperature process in the manufacturing process can be further shared, and a full color The manufacturing cost of the display for performing display can be further reduced.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing a layer structure of a thin film EL device according to an embodiment of the present invention. FIG. 2 is a diagram showing an X-ray diffraction pattern of a light emitting layer of a thin film EL device according to an embodiment of the present invention. The figure which shows EL emission spectrum of the thin film EL element based on the Example of this invention
DESCRIPTION OF SYMBOLS 1 Glass substrate 2 Lower electrode layer 3 Lower insulating layer 4 Light emitting layer 5 Upper insulating layer 6 Upper electrode layer 7 EL light emission

Claims (2)

And two electrode layers, they are disposed between two electrode layers were fluoresce with a luminescent layer made of phosphor thin film, the light emitting layer is SrSb 2 _O X _(provided that the base material, X = 4, 5, A thin-film electroluminescent element formed by 6) and activated by using Mn ions as a light emission center in the base material . Thin film electroluminescent device as claimed in claim 1, characterized in that disposed a ceramic plate obtained by laminating the light-emitting layer on the two electrode layers.

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