Active solid-state devices (e.g. – transistors – solid-state diode – Incoherent light emitter structure
Patent
1993-04-28
1995-08-22
Limanek, Robert P.
Active solid-state devices (e.g., transistors, solid-state diode
Incoherent light emitter structure
257103, 313503, H01L 310296, H05B 3314
Patent
active
054442680
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a modification of a thin film EL device for performing an EL emission according to an electric field being applied, and in particular, to a thin film EL device for providing a stable luminance for a long time and for improving the luminance of a blue color display.
RELATED ART
So far, various studies have been conducted for multi-color thin film EL devices. As basic materials for light emission layers, strontium sulfide (SrS) and calcium sulfide (CaS), which are sulfides of alkaline earth metals, are used. To cause such thin film EL devices to stably emit visible light, a suitable interface should be formed between a light emission layer and the insulation layers which sandwich the light emission layer. To do that, a device having insulation layers composed of a nitride such as Si.sub.3 N.sub.4, AIN, or BN has been proposed as disclosed in, for example, Japanese Published Unexamined Patent Application (A) 62-5596.
However, even if the above-mentioned thin film EL device, which has insulation layers composed of a nitride, is used, the SrS or CaS as the basic material of the light emission layer reacts with moisture, CO.sub.2, and so forth contained in the air. Thus, a partial conversion to an oxide (such as SrO and CaO) or a carbonate (such as SrCO.sub.3 and CaCO.sub.3) takes place, which results in aged deterioration of the light emission layer of the device. Thus, the luminance of the EL device diminishes in a short time.
In addition, SrS:Ce or ZnS:TmF.sub.3 has been used as a light emission layer for a conventional blue color display thin film EL device.
However, although the light emission layer which is composed of SrS:Ce has the highest luminance in blue color display thin film EL devices, the luminance thereof is at most 1000 cd/m.sup.2 when a sine wave of 5 kHz is applied to the light emission layer. When this device is used for a dot matrix display which is driven at 60 Hz, a luminance of 20 to 30 cd/m.sup.2 is required, while for this use the maximum luminance of the device which is composed of SrS:Ce is at most 10 cd/m.sup.2, which is 1/2 to 1/3 times that of the required luminance.
The present invention is made from the above-mentioned point of view. An object of the present invention is to provide a thin film EL device for continuously furnishing stable luminanee for a long time and for enhancing the luminance of a blue color display at least two to three times that of the conventional devices.
SUMMARY OF THE INVENTION
The present invention is a thin film EL device, comprising a pair of opposed electrodes and a laminate composed of a light emission layer and an insulation layer, wherein the light emission layer is composed of a sulfide of an alkaline earth metal as a basic material, and wherein at least the insulation layer disposed adjacent to the light emission layer is either a sulfate or a carbonate of an alkaline earth metal.
Between the insulation layer and the electrodes, another insulation layer composed of Ta.sub.2 O.sub.5, SION, or SiN:H can be disposed.
The light emission layer is composed of Ce as a basic material and a Pb dopant of 1 at% (atomic %) or less as a coactivator.
According to the above mentioned construction, since insulation layers are composed of a sulfate or a carbonate of an alkaline earth metal, which is a stable compound, they are not adversely affected by moisture, CO.sub.2, and so forth contained in air. In addition, since the insulation layers contain the same alkaline earth metal as the light emission layer, whose basic material is a sulfide of the alkaline earth metal, a suitable interface can be formed, thereby preventing aged deterioration of the light emission layer.
Moreover, according to the present invention, Ce as a light emission substance is used and Pb of 1 at% as a coactivator is added thereto along with SrS as the basic material, thereby SrS:Ce, Pb is formed. Thus, besides the conventional excitation of Cs, there is another excitation due to an energy transmission from excited Pb to Ce. Theref
REFERENCES:
patent: 4717858 (1988-01-01), Tanaka et al.
patent: 4900584 (1990-02-01), Tuenge et al.
patent: 5101288 (1992-03-01), Ohta et al.
Matsuno Akira
Miyakoshi Atsushi
Kabushiki Kaisha Komatsu Seisakusho
Limanek Robert P.
Williams Alexander Oscar
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