Electric lamp and discharge devices – With luminescent solid or liquid material – Solid-state type
Patent
1984-10-05
1988-03-22
Moore, David K.
Electric lamp and discharge devices
With luminescent solid or liquid material
Solid-state type
2523016P, H05B 3314, H05B 3318
Patent
active
047331283
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to an electroluminescence (EL) display device and a process for producing the same, particularly to an EL display device using a novel EL material which permits improvement of brightness and a process for producing the same.
BACKGROUND ART
It has heretofore been known from old times that zinc sulfide containing a rare earth element, a fluoride of rare earth elements, manganese or the like as an activator emits light having a color determined by the activator when a high electric field is applied thereto. For example, there have been formed thin film EL elements having a structure in which an insulator layer, an emission layer (e.g., a zinc sulfide layer containing an activator), an insulator layer and a rear electrode are successively laminated, for example, on a glass substrate equipped with a transparent electrode, and there have been obtained EL elements which are various in colors of light emitted by them depending on the kind of activator. When manganese-activated zinc sulfide is used as the emission layer, the brightness is about 5,000 cd/m.sup.2 at an applied electric field of 5 KHz and is almost on the practical use level, but is insufficient in reproducibility. For example, when a manganese-activated zinc sulfide emission layer is formed by a sputtering method suitable for forming a thin film having a large area and a good film thickness distribution, the reproducibility of brightness is particularly poor. By use of a fluoride of rare earth element, there has been attained a brightness which is higher than when a rare earth element alone is used, but this brightness does not attain the practical use level. As the causes of these facts, there are considered the imperfectness of crystallinity of zinc sulfide, imperfect introduction of activator to a substitutional site of zinc sulfide crystal lattice, etc. An EL element having a high brightness is desired to be developed by removing these causes.
SUMMARY OF THE INVENTION
This invention provides an EL display device which has a high brightness and can be produced with good reproducibility and a process for producing the same, by using, as an EL emission layer, zinc sulfide containing an activator and phosphorus as a coactivator.
The EL emission layer can be formed by using as the activator at least one member selected from the group consisting of rare earth elements such as Pr, Sm, Eu, Tb, Dy, Ho, Er, Tm, and halides thereof.
As a method for adding the above-mentioned coactivator to zinc sulfide, although the above-mentioned activator and the above-mentioned coactivator may individually be added, it is also advisable to add them in the form of a compound thereof.
As to a process for producing the EL emission layer in this invention, the EL emission layer is formed by a sputtering method by using, as a target, zinc sulfide containing an activator and phosphorus as a coactivator. Thereby, an EL emission layer having a high brightness can be formed with very good reproducibility.
The percentages of the number of atoms of the activator and the coactivator to the number of atoms of zinc are preferably 0.1% or more and 10% or less .
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a partially sectioned perspective view showing one example of the electroluminescence display device according to this invention, and
FIG. 2 is a set of curves showing the voltage-brightness characteristics of the device of the present example and a conventional device in comparison with each other.
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 1 shows one embodiment of the EL display device according to this invention. In this device, on one side of a transparent insulating substrate, for example, a glass substrate 1 is provided a plurality of transparent electrode layers 2 aligned in stripes in parallel with one another. The transparent electrode layers 2 are made of tin-containing indium oxide (ITO) and have a thickness of 200 nm. On the one side of the glass substrate 1 are successively formed an insulator layer 3, an EL emission
REFERENCES:
patent: 4171501 (1979-10-01), Tanimizu et al.
patent: 4381474 (1983-04-01), Cusano
patent: 4551397 (1985-11-01), Yaguchi et al.
Abe Atsushi
Fujita Yosuke
Matsuoka Tomizo
Nishikawa Masahiro
Nitta Tsuneharu
Matsushita Electric - Industrial Co., Ltd.
Moore David K.
Wieder K.
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