JP2605570B2 - Inorganic thin film EL device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inorganic thin-film electroluminescence device (hereinafter referred to as an EL device) using an inorganic phosphor, and more particularly, to an inorganic phosphor used for a flat light source or a display. Inorganic thin film EL
Related to the element.

[0002]

2. Description of the Related Art Inorganic thin-film EL elements have attracted attention as flat panel displays or flat light sources. Until now, at least one of ZnS, CaS, SrS and the like has been used as a base material, and Mn, Tb, Sn, Ce, Eu, and Eu have been used. An inorganic phosphor doped with at least one of Sm, Tm and the like as an emission center in an amount of 5 wt% or less is used. Of these, ZnS: Mn has been studied as an orange phosphor, and is used as a flat panel display because of its excellent properties such as brightness and life. As for the green light emitting phosphor, research on zinc sulfide such as ZnS: Tb has been widely conducted. Other base materials include SrS: Ce as a blue light-emitting phosphor and Ca as a red light-emitting phosphor.
S: Eu, green light emitting phosphor such as CaS: Ce,
Phosphors composed of alkaline earth metal sulfides have also been actively studied.

[0003] Regarding the light emission mechanism of a phosphor, transition metal (Mn) emits light by direct collision of a parent electron, whereas the energy corresponding to the band gap of the parent element is rare earth element. The ratio of light emission after transition increases. Alkaline earth metal sulfides have a band gap energy of 4.3 to 4.4 eV, a small amount of ZnS of 3.6 eV, and have a band gap in order to obtain blue to ultraviolet light that requires high energy. The gap energy is small. Therefore, in order to obtain blue to ultraviolet light emission, Zn having a high band gap energy
F ₂ : Gd (7 to 8 eV) as a base material (JJ.
A. P. vol. 10B. (1991) pp. L181
5-11816), with CaF ₂ : Eu as the parent (Ap
pl. Phys. Lett. 41.1982. P. 46
2) is being studied.

[0004]

By the way, ZnS: M
Except for n, inorganic phosphors using these sulfides have insufficient luminous brightness, efficiency, and lifetime to be used as flat panel displays or flat light sources, and currently practical color flat panel displays are formed. Not. The present invention has been made in view of the above-described conventional circumstances, and an object of the present invention is to provide an inorganic thin film EL device capable of performing full-color display at a practical level.

[0005]

Means for Solving the Problems The present inventor has found that when a rare earth element is added to a fluoride of a Group IIb metal, light emission in the range from ultraviolet to infrared can be obtained. The invention has been completed. The inorganic thin film EL device of the present invention has a light emitting layer formed from a composition obtained by adding a rare earth element or a compound thereof to a fluoride of a group II metal, and a fluoride of the group II metal in the light emitting layer is used. ,formula:
M _1-x F _{2 + y} (where M represents a Group II metal, x represents 0.001 to 0.9, and y represents 0.001 to 1.8
Represents ).

Hereinafter, the inorganic thin film EL device of the present invention will be described in detail. In the present invention, the light-emitting layer is formed from a composition obtained by adding a rare earth element or a compound thereof to a fluoride of a group II metal as an inorganic phosphor, and in the formed light-emitting layer, fluorine of a group II metal is used. The monsters
As shown in the above formula, the fluorine content is increased from the stoichiometric composition ratio. As a result, it becomes possible to increase the concentration of hole carriers in the light emitting layer, so that an electron injection layer can be provided. In the present invention, the composition ratio between Group II metal and fluorine, that is, the preferable ranges of x and y in the above formula, are respectively x = 0.2 to 0.6 and y = 0.4 to 1.x.
2.

In the present invention, the Group II metals include cadmium, zinc, strontium, calcium, barium and beryllium, and at least one fluoride of these metals can be used.

The rare earth element added to the fluoride of the Group II metal includes cerium, praseodymium, neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium and ytterbium. At least one of a rare earth element and a rare earth compound is added. As the rare earth compound, a compound containing at least one of fluorine, chlorine, bromine, iodine and oxygen is used. Specific examples of the rare earth compound that can be used in the present invention include gadolinium fluoride, erbium fluoride, neodymium oxide, and the like.

In the inorganic thin film EL device of the present invention, in order to form a light emitting layer using the above materials, a pressure sintering method, a co-activator, for example, using a low melting point metal such as gold or zinc. It can be formed by a gas phase method such as a vacuum evaporation method, a sputtering method, a CVD method, and an MOCVD method using the pellets fixed by pressure. In the present invention, when forming the light emitting layer, the content of the Group II metal and fluorine in the light emitting layer can be shifted from the stoichiometric composition ratio by controlling the substrate temperature, the film formation atmosphere, and the like. . For example, the content of F can be increased by introducing CF ₄ in a film forming atmosphere.

The layer structure of the inorganic thin film element of the present invention is not particularly limited as long as it has the above-mentioned light emitting layer. For example, an element having a structure shown in FIGS. Can be. 1 has a structure in which a back electrode 2, an insulating layer 3, a light emitting layer 4, an insulating layer 3, and a transparent electrode 5 are sequentially provided on an insulating substrate 1. In FIG. A transparent electrode 5, an insulating layer 3, a light emitting layer 4, an insulating layer 3, and a back electrode 2 are sequentially provided. Further, a structure may be employed in which a back electrode, an insulating layer, a semiconductor layer, a light emitting layer, a semiconductor layer, an insulating layer, and a transparent electrode are sequentially provided on an insulating substrate.

As the insulating layer, ZnF ₂ , CaF ₂ , M
gF ₂ , SiN _x , TaO _x , Al ₂ O ₃ , Y ₂ O ₃ ,
PbTiO ₃ or the like can be used, and these may be used in duplicate. Further, the semiconductor layer functions as a carrier injection layer for improving luminance of light emission. These semiconductors include hydrogenated amorphous silicon, Ca
I-VII compound semiconductors such as S and MgS; II-VI compound semiconductors such as HgI _2;
Examples thereof include V compound semiconductors, IV-VI compound semiconductors such as TiO ₂ and SnO ₂ , V-VI compound semiconductors such as As ₂ O ₃ and Bi ₂ O _3, and organic semiconductors such as polyvinyl carbazole.

Since the inorganic thin film EL device of the present invention has a high carrier concentration, a direct current or a low frequency alternating current can be used as a driving voltage. Particularly, a direct current is preferable, and there is an advantage that circuit design becomes easy. .

In the inorganic thin-film EL device of the present invention, the light-emitting layer composed of an inorganic phosphor exhibits a high EL light-emitting intensity, and the light emission varies variously depending on the type of the rare-earth element added. For example, adding gadolinium gives purple light, adding praseodymium gives blue light, adding terbium gives green light, and adding europium gives orange light. Therefore, various emission colors can be obtained by changing the rare earth element or the rare earth compound to be added, and full color can be obtained.

[0014]

【Example】

Example 1 Gadolinium fluoride (10 wt%) was mixed with zinc fluoride (89 wt%), and Au was added as a coactivator to 800 kg / cm ^2.
And fixed to form pellets for vapor deposition. Using the pellets, an inorganic thin film EL device having a layer configuration shown in FIG. 1 was produced. That is, on an Al electrode 2 formed on an insulating substrate 1, Ta ₂ O ₅ is vapor-deposited with an electron beam to a thickness of 2000 angstroms to form an insulating layer 3, and then the pellet obtained by the above procedure is formed. Was deposited with an electron beam to form a light-emitting layer 4 composed of an inorganic fluorescent layer having a thickness of 7000 angstroms. In this case, at a substrate temperature of 200 ° C., CF
_{When a} film was formed in _four gases, the ratio of Zn to F was 0.8: 2.3 by SEMEPMA measurement. When the conductivity of the film was measured, it was increased by one digit as compared with the case where no CF ₄ gas was introduced. On top of that, Ta ₂ O ₅ was vapor-deposited with an electron beam to a thickness of 2000 Å to form an insulating layer 3, and a transparent electrode film 5 made of ITO was vapor-deposited to a thickness of 1000 Å. When the emission characteristics of the inorganic thin film EL device obtained as described above were examined, ultraviolet emission having a peak at around 312 nm was obtained at an intensity of 0.01 mW / cm ² .

Example 2 Erbium fluoride 10% by weight and cadmium fluoride 90% by weight
And sintered under pressure at 800 kg / cm ^{2 to} obtain pellets for vapor deposition. Using the pellets, an inorganic thin film EL device having a layer configuration shown in FIG. 2 was produced. That is, on a transparent conductive material 5 made of ITO formed on a transparent substrate 6 made of glass, CaF ₂ is vapor-deposited by an electron beam to form an insulating layer 3 having a thickness of 2000 angstroms. Using pellets obtained, substrate temperature 2
The light emitting layer 4 composed of an inorganic fluorescent layer having a thickness of 7000 angstroms was formed by electron beam evaporation in a CF ₄ gas at 00 ° C. By SEMEPMA measurement,
In the light emitting layer 4, the ratio between Cd and F was 0.9: 2.2. Also, when the conductivity of the light emitting layer was measured,
This was an order of magnitude higher than that without introduction of CF ₄ gas. On top of that, CaF ₂ was deposited by electron beam to a thickness of 2
Forming an insulating layer 3 of 2,000 Å;
A back electrode 2 made of Al was deposited to a thickness of 1000 Å. The inorganic thin film E obtained as described above
When the light emission characteristics of the L element were examined, the green light emission was 0.0
It was obtained at an intensity of 1 mW / cm ² .

[0016]

The inorganic thin-film EL device of the present invention has a light-emitting layer composed of the inorganic phosphor having the above-described structure, and can emit light in a wide wavelength range with higher luminance and longer life than the conventional device. Things. Therefore, the inorganic thin film EL element of the present invention is extremely useful as a flat light source for a display or the like, and its practical value is high.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of an example of an inorganic thin film EL device of the present invention.

FIG. 2 is a schematic sectional view of another example of the inorganic thin film EL device of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Insulating substrate, 2 ... Back electrode, 3 ... Insulating layer, 4 ... Light emitting layer, 5 ... Transparent electrode, 6 ... Transparent substrate.

Claims (4)

(57) [Claims] 1. A light-emitting layer formed from a composition obtained by adding a rare earth element or a compound thereof to a fluoride of a group II metal, wherein the fluoride of the group II metal in the light-emitting layer has a formula:
M _1-x F _{2 + y} (where M represents a Group II metal, x represents 0.001 to 0.9, and y represents 0.001 to 1.8
Represents Inorganic thin film EL characterized by the following:
element. 2. The inorganic thin-film EL device according to claim 1, wherein the Group II metal comprises at least one element selected from the group consisting of cadmium, zinc, strontium, calcium, barium, and beryllium. 3. The method according to claim 1, wherein the rare earth element added is cerium, praseodymium, neodymium, samarium, europium, gadolinium, terbium, dysprosium,
2. The inorganic thin film EL device according to claim 1, wherein the device is at least one selected from the group consisting of holmium, erbium, thulium, and ytterbium. 4. The inorganic thin film E according to claim 1, wherein the rare earth compound to be added contains at least one element selected from the group consisting of fluorine, chlorine, bromine, iodine and oxygen.
L element.