JPH06203960A - Inorganic thin film el element - Google Patents

Abstract

PURPOSE:To provide an inorganic thin film EL element extremely useful as a flat light source for display and capable of full color display in practical level. CONSTITUTION:An inorganic thin film EL element has a light emitting layer formed from a composite in which a rare earth element or its compound is added to a fluoride of a metal of the group II, and the fluoride of the metal of the group II in the light emitting layer is represented by the formula: M1-xF2+y (wherein M represents a metal of the group II, x represents 0.001-0.9, and y represents 0.001-1.8). The metal of the group II is selected from cadmium, zinc, strontium, calcium, barium and beryllium, and the rare earth element is selected from cerium, praseodymium, neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium and yttrium.

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 electroluminescent device (hereinafter referred to as an EL device) using an inorganic phosphor, more specifically, an inorganic phosphor used for a flat light source, a display or the like. Inorganic thin film EL
Regarding the device.

[0002]

2. Description of the Related Art Inorganic thin film EL devices have been attracting attention as flat panel displays or flat light sources, and have hitherto been prepared by using at least one of ZnS, CaS, SrS, etc. as a base material and Mn, Tb, Sn, Ce, Eu, An inorganic phosphor doped with 5 wt% or less of at least one of Sm and Tm as an emission center 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 characteristics such as brightness and life. Further, zinc sulfides such as ZnS: Tb have been widely studied for green light emitting phosphors. Other base materials include SrS: Ce as a blue light emitting phosphor and Ca as a red light emitting phosphor.
S: Eu, CaS: Ce, etc. as the green light emitting phosphor,
Phosphors composed of alkaline earth metal sulfides have also been actively studied.

Regarding the light emission mechanism of the phosphor, the transition metal (Mn) emits light directly by collision with the electrons of the host, whereas the rare earth element has an energy corresponding to the band gap of the host. The ratio of transition and light emission increases. The band gap energy of alkaline earth metal sulfides is 4.3 to 4.4 eV, ZnS is also small at 3.6 eV, and in order to obtain blue-to-ultraviolet light emission that requires high energy, The gap energy is small. Therefore, in order to obtain blue to ultraviolet emission, Zn having a high band gap energy is used.
F _2: Gd (7~8eV) a or a mother (J.J.
A. P. vol. 10B. (1991) pp. L181
5-l1816) and CaF ₂ : Eu as a matrix (Ap
pl. Phys. Lett. 41.1982. P. 46
2) is being studied.

[0004]

By the way, ZnS: M
Except for n, the inorganic phosphors using these sulfides are not sufficient in terms of light emission brightness, efficiency, and lifetime for use as flat panel displays or flat light sources, and currently practical color flat panel displays are formed. Not not. The present invention has been made in view of the conventional circumstances described above, and an object thereof is to provide an inorganic thin film EL element capable of 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 Group IIb metal fluoride, light emission in the range from ultraviolet to infrared can be obtained. The invention was completed. The inorganic thin film EL device of the present invention has a light emitting layer formed of a composition obtained by adding a rare earth element or a compound thereof to a fluoride of a Group II metal, and the fluoride of the Group II metal in the light emitting layer is ,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 ) Is indicated by.

The inorganic thin film EL element of the present invention will be described in detail below. In the present invention, the light emitting layer is formed as an inorganic phosphor from a composition obtained by adding a rare earth element or a compound thereof to a fluoride of a Group II metal, and in the formed light emitting layer, a fluorine of a Group II metal is contained. Compound
As shown by the above formula, the content of fluorine increases with a deviation from the stoichiometric composition ratio. As a result, it is possible to increase the concentration of hole carriers in the light emitting layer, and thus it is possible to provide an electron injection layer. In the present invention, the composition ratio of the Group II metal and fluorine, that is, the preferable ranges of x and y in the above formula are x = 0.2 to 0.6 and y = 0.4 to 1.
It is 2.

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

Examples of the rare earth element added to the fluoride of the Group II metal include 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 coactivator, for example, a low melting point metal such as gold or zinc is used. It can be formed by a vapor phase method such as a vacuum vapor deposition method, a sputtering method, a CVD method, or a MOCVD method using the pellets that are pressure-fixed. In the present invention, when the light emitting layer is formed, the contents of Group II metal and fluorine in the light emitting layer can be deviated from the stoichiometric composition ratio by controlling the substrate temperature, the film forming atmosphere and the like. . For example, the content of F can be increased by introducing CF ₄ in the film forming atmosphere.

The inorganic thin film element of the present invention is not particularly limited in its layer structure as long as it has the above-mentioned light emitting layer, and examples thereof include those having the structures shown in FIGS. 1 and 2. You can 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, and in FIG. In addition, the transparent electrode 5, the insulating layer 3, the light emitting layer 4, the insulating layer 3 and the back electrode 2 are sequentially provided. Further, it may have a structure 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 acts as a carrier injection layer for improving the luminance of light emission. As these semiconductors, hydrogenated amorphous silicon, Ca
I-VII compound semiconductors such as S and MgS, II-VI compound semiconductors such as HgI ₂ , and III- such as AlAs and GaN
V compound semiconductor, TiO _2, IV-VI compound semiconductors such as _{SnO 2, As 2 O 3,} Bi 2 O 3 V-VI compound semiconductor such as an organic semiconductor such as polyvinylcarbazole and the like.

Since the inorganic thin film EL element of the present invention has a high carrier concentration, it is possible to use direct current or low frequency alternating current as a driving voltage, and direct current is particularly 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 made of an inorganic phosphor exhibits a strong EL light emission intensity, and its light emission changes variously depending on the kind of the rare earth element added. For example, the addition of gadolinium gives purple light, the addition of praseodymium gives blue light, the addition of terbium gives green light, and the addition of europium gives orange light. Therefore, various emission colors can be obtained by changing the rare earth element or rare earth compound to be added, and full color can be realized.

[0014]

【Example】

Example 1 Gadolinium fluoride 10 wt% was mixed with zinc fluoride 89 wt% and Au was added as a co-activator to obtain 800 kg / cm ^2.
Then, it was pressure-fixed to obtain pellets for vapor deposition. Using this pellet, an inorganic thin film EL device having the layer structure shown in FIG. 1 was produced. That is, Ta ₂ O ₅ was vapor-deposited with an electron beam to a thickness of 2000 angstroms on an Al electrode 2 formed on an insulating substrate 1 to form an insulating layer 3, and then the pellets obtained by the above procedure. Was evaporated by an electron beam to form a light emitting layer 4 made of an inorganic fluorescent layer having a thickness of 7,000 Å. In this case, CF at the substrate temperature of 200 ° C
_{When the} film was formed in ₄ gases, the ratio of Zn and F was 0.8: 2.3 by SEMEPMA measurement. Further, when the film conductivity was measured, it increased by one digit as compared with the case where CF ₄ gas was not introduced. Then, 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 element obtained as described above were examined, ultraviolet emission having a peak near 312 nm was obtained at an intensity of 0.01 mW / cm ² .

Example 2 10 wt% erbium fluoride and 90 wt% cadmium fluoride
And pelletized under pressure at 800 kg / cm ^{2 to} obtain pellets for vapor deposition. Using this pellet, an inorganic thin film EL device having the layer structure shown in FIG. 2 was produced. That is, CaF ₂ is vapor-deposited by electron beam on the transparent conductive material 5 made of ITO formed on the transparent substrate 6 made of glass to form the insulating layer 3 having a thickness of 2000 angstrom, and then obtained by the above procedure. Using the pellets, the substrate temperature 2
By evaporating with an electron beam in CF ₄ gas at 00 ° C., a light emitting layer 4 made of an inorganic fluorescent layer having a thickness of 7,000 Å was formed. By SEMEPMA measurement,
In this light emitting layer 4, the ratio of Cd and F was 0.9: 2.2. Further, when the conductivity of this light emitting layer was measured,
It increased by an order of magnitude compared to the case where CF ₄ gas was not introduced. CaF ₂ is vapor-deposited on it by electron beam to a thickness of 2
000 angstrom insulating layer 3 is formed, and further,
A back electrode 2 made of Al was deposited to a thickness of 1000 angstrom. Inorganic thin film E obtained as described above
When the emission characteristics of the L element were examined, green emission was 0.0
It was obtained at an intensity of 1 mW / cm ² .

[0016]

Since the inorganic thin film EL element of the present invention has the light emitting layer made of the inorganic phosphor having the above-mentioned constitution, it can emit light in a wide wavelength range with higher brightness and longer life than the conventional one. Can be one. Therefore, the inorganic thin film EL element of the present invention is extremely useful as a flat light source for displays and the like, and has high practical value.

[Brief description of drawings]

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

FIG. 2 is a schematic cross-sectional view of another example of the inorganic thin film EL element 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)

[Claims] 1. A fluorinated compound of Group II metal having a light emitting layer formed of a composition obtained by adding a rare earth element or a compound thereof to a fluorinated compound of Group II metal.
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
element. 2. The inorganic thin film EL element 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 rare earth element added is cerium, praseodymium, neodymium, samarium, europium, gadolinium, terbium, dysprosium,
2. The inorganic thin film EL element according to claim 1, wherein the inorganic thin film EL element 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 added contains at least one element selected from the group consisting of fluorine, chlorine, bromine, iodine and oxygen.
L element.