Electric lamp and discharge devices: systems – Plural power supplies – Plural cathode and/or anode load device
Patent
1984-01-18
1987-01-06
Dixon, Harold
Electric lamp and discharge devices: systems
Plural power supplies
Plural cathode and/or anode load device
2504841, 313503, H05B 3700
Patent
active
046349340
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to electroluminescent display devices and more particularly to an electroluminescent display device having a novel construction which ensures an improved luminescent brightness and low voltage driving.
BACKGROUND ART
In the past, electroluminescent display devices (hereinafter simply referred to as EL display devices) have been known including EL display devices of a double insulating layer type in which the sides of an electroluminescent light-emitting layer (hereinafter simply referred to as an EL layer) are held between insulating layers which are in turn held externally between a transparent electrode made essentially of indium oxide (In.sub.2 O.sub.3) or tin oxide (SnO.sub.2) and a metal electrode made of aluminium (Al) or the like and EL display devices of a single insulating layer type in which an EL layer is directly formed on a transparent electrode mass essentially of indium oxide or tin oxide and then an insulating layer and a metal electrode are successively provided on the EL layer. If these two types of EL display devices are constructed so that they have the same total insulating layer thickness and the same EL emitting thickness and an ac voltage or pulse voltage is applied to cause light emission, the EL display device of the single insulating layer type is lower than the EL display device of the double insulating layer type in terms of luminescent threshold voltage and also the EL display device of the double insulating layer type is higher than the EL display device of the single insulating layer type in terms of luminescent brightness. Thus, the known EL display devices have had their own merits and demerits and therefore there has been a demand for an EL display device which has a lower luminescence threshold voltage or is adapted to be driven at a lower voltage and which also has a higher luminescent brightness.
SUMMARY OF THE INVENTION
The present invention provides an EL display device of the type in which energizing means apply signal voltages corresponding to information to an assembly of an EL layer, including zinc sulfide containing a luminescently active material, and an insulating layer thereby displaying the information in the form of an image, wherein one of the energizing means arranged on the side of the EL layer includes a plurality of semiconductive electrodes containing at least one compound selected from the group consisting of the chemical compounds of Groups II-VI or at least one compound selected from the group of chemical compounds of Groups II-VI and tin oxide thus ensuring a reduced luminescent threshold voltage and an increased luminescent brightness.
As regards the Group II-VI chemical compound constituting the semiconductive electrodes which form one of the energizing means, at least one of zinc oxide (ZnO), zinc selenide (ZnSe), zinc telluride (ZnTe), zinc sulfide (ZnS), cadmium sulfide (CdS) and cadmium selenide (CdSe) is preferred and particularly zinc oxide is preferred most. Also, it is needless to say that the semiconductive electrodes may be made of at least one of these chemical compounds and tin oxide.
Any one of the heretofore known materials may be used as the luminescingly active material added to the zinc sulfide of the EL layer and it is only necessary to make the selection in accordance with the desired luminescent color. Manganese (Mn), copper (Cu), silver (Ag), aluminum (Al), terbium (Tb), dysprosium (Dy), erbium (Er), praseodymium (Pr), samarium (Sm), holmium (Ho), thulium (Tm) and their halides may be cited as examples of the luminescingly active material.
BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 is a partly cutaway perspective view showing an example of an EL display device according to the invention,
FIG. 2 is a graph showing applied voltage-luminescent brightness characteristic curves for the EL display device shown in FIG. 1 in comparison with the applied voltage-luminescent brightness characteristic curve of a conventional single insulating layer type EL display device and a double ins
REFERENCES:
patent: 2925532 (1960-02-01), Larach
patent: 3133222 (1964-05-01), Cerull'i
patent: 3564260 (1971-02-01), Tanaka et al.
patent: 3590253 (1971-06-01), Novice
patent: 4137481 (1979-01-01), Hilsum
patent: 4486499 (1984-12-01), Morimoto
Sasakura et al., "The Dependency of Electroluminescent Characteristics of ZnS:Mn Thin Films Upon Their Device Parameters", J. Appl. Phys., vol. 52, No. 11, Nov. 19, 1981.
Direct Current Thim Film Electroluminescence Device by Marrello et al., IBM Tech. Disc. Bull., vol. 22, No. 4, Sep. 79, p. 1636.
Abe Atsushi
Fujita Yosuke
Matsuoka Tomizo
Nitta Tsuneharu
Tohda Takao
Dixon Harold
Matsushita Electric - Industrial Co., Ltd.
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