JPS598040B2 - Thin film EL element - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention utilizes EL (Ele-ctr) by applying an alternating electric field.
This invention relates to a thin film EL element that emits light (oluminescene).

Conventionally, for AC-operated thin-film EL elements, a high electric field (about 106V, /(about 72V)) is regularly applied to the light emitting layer.
In order to improve the dielectric strength, luminous efficiency, and stability of operation, 0.1 to 2.0 w was added with % Mn (or Cu, Aι,
ZnS Mn (or ZnSe:Mn)E is a three-layer structure in which a semiconductor light emitting layer such as ZnS or Zn-Be doped with Br (Br, etc.) is sandwiched between dielectric thin films such as Y203 or TiO2.
L elements have been developed, and improvements in various light emitting characteristics have been confirmed.

This thin film EL element emits light with high brightness when an alternating current electric field of several kilohertz is applied, and is characterized by a long life. In addition, regarding the light emission of this thin film EL element, there are two processes: increasing the applied voltage and decreasing it from the high voltage side.
It was discovered that the thin-film EL element has a hysteresis characteristic in which the luminance differs for the same applied voltage, and in the process of increasing the applied voltage to a thin-film EL element with this hysteresis characteristic, light, electric field, and heat When the light, electric field, heat, etc. are removed and the element returns to its original state, the thin film EL element is excited to a state of luminance corresponding to the intensity, and the luminance remains high even if the light, electric field, heat, etc. are removed and the element returns to its original state. The so-called memory phenomenon has opened up new fields of use for display technology.
FIG. 1 shows the basic structure of a ZnS:Mn thin film EL device as an example of a thin film EL device.

The structure of the thin film FL element will be explained in detail based on FIG.
A first dielectric layer 3 made of Aι203, Si3N4, SiO2, etc. is formed in an overlapping manner by sputtering, electron beam evaporation, or the like.

A ZnS light emitting layer 4 is formed on the first dielectric layer 3 by electron beam evaporation of a ZnS:Mn sintered beret. At this time, the ZnS:Mn sintered pellets used for vapor deposition are pellets in which the concentration of Mn, which is an active substance, is set to suit the purpose. On the ZnS light emitting layer 4, a first
A second dielectric layer 5 made of the same material as the dielectric layer 3 is laminated, and a back electrode made of At or the like is formed by vapor deposition thereon. The transparent electrode 2 and the back electrode 6 are connected to an AC power source 7, and the thin film EL element is driven. electrodes 2, 6
When an AC voltage is applied between them, the AC voltage is induced between the dielectric layers 3 and 5 on both sides of the ZnS light emitting layer 4, and therefore the electric field generated within the ZnS light emitting layer 4 causes conduction. Electrons that are excited and accelerated by the band and have obtained sufficient energy directly excite the Mn emission center, and the excited Mn
When the luminescent center returns to its ground state, it emits yellow light.

That is, when electrons accelerated in a high electric field excite the electrons of Mn atoms that enter the Zn site, which is the luminescent center in the ZnS luminescent layer 4, and fall to the ground state, strong luminescence occurs in a wide wavelength range, sometimes peaking at 5850λ. exhibits. The thin film EL element having the above structure can be used as a flat thin display device that takes advantage of the space factor, and can be used for computer output display terminal equipment and various other display devices containing characters and figures. It can be used as a display means for still images, moving images, etc.

Thin-film EL panels as flat flat display devices have a lower operating voltage than conventional cathode ray tubes (CRTs), and are superior in terms of weight and strength compared to plasma display panels (PDPs), which are also flat display devices. The operable vorticity range is wider than that of a liquid crystal display (LCD).
It has many advantages such as fast response speed. In addition, since it can be used as a pure fixed matrix type panel, it has a long operating life, and its address accuracy makes it very effective as an input/output display means for computers and the like. The conventional thin film EL device described above emits yellow light, but
Attempts are also being made to develop technologies to obtain luminescent colors other than yellow luminescence.

However, it has been extremely difficult to introduce a plurality of luminescent centers into the same luminescent layer, to obtain the unique luminescence of each luminescent center, and to mix these luminescent lights to obtain mixed color luminescence. Therefore, there has been a long desire to develop a technology that can realize a thin film EL element that emits light of any desired color, particularly white light, with a simple structure. The present invention emits white light by using a two-layer structure of a light emitting layer in which a light emitting layer doped with the rare earth element dysprosium(4)y) as a light emitting center and a light emitting layer doped with thulium (Tm) as a light emitting center are laminated. The object of the present invention is to provide a new and useful thin-film EL device in which the color temperature can be controlled by changing the film thickness ratio between each light-emitting layer. Hereinafter, the present invention will be explained in detail in the order of manufacturing steps according to Examples.

FIG. 2 is a cross-sectional view of a thin film EL device showing one embodiment of the present invention.

In FIG. 2, a transparent electrode 2 made of Tn2O3 or the like is formed on a glass substrate 1, and SiO2, Si3N4 or the like is formed on the transparent electrode 2.
A dielectric layer 3 is formed to have a thickness of about 2000×.

Furthermore, ZnS:Dy is formed on the dielectric layer 3 as a first light emitting layer 4a.
F3 is deposited to a thickness of about 0 to 10,000 λ and laminated on the first light emitting layer 4a, and a second light emitting layer 4b made of ZnS:TmF3 is deposited to a thickness of about 1,000 to 10,000.

Next, on the second light emitting layer 4b, Sl3N4, At2O3? A conductor layer 5 having a thickness of approximately 2000λ is formed, and At is further formed as a back electrode 6 by vapor deposition. The thin film light emitting device manufactured through the above steps emits white light when an alternating current voltage is applied from the power source 7.

The color of this emitted light is shown on color coordinates as shown in FIG. FIG. 3 is an international standard chromaticity diagram, showing the positions of the emitted light colors of the thin film light emitting device of the above example and the thin film E where the light emitting layer is composed of three layers of ZnS:TmF and three layers of ZnS:DyF.
The position of the emitted light color of the L element is also shown at the same time. In the above embodiment, when the film thickness ratio of the first light emitting layer 4a and the second light emitting layer 4b is changed, the emitted light color moves on a straight line connecting the point Tm and the point Dy in FIG. 3.

That is, when the thickness of the second light emitting layer 4b (ZnS:TmF3) is increased relative to the first light emitting layer 4a (ZnS:DyF3), the emitted light color moves toward the point Tm as shown by the arrow in the figure. By the way, the points on the color coordinates corresponding to the temperature of a perfect black body, that is, the color temperature, are shown as a curve in FIG. 3. As is clear from this, the color temperature curve is similar to the locus of the change in luminescent color corresponding to the change in the film thickness of the first light emitting layer 4a and the second light emitting layer 4b. Therefore, the first light emitting layer 4a and the second light emitting layer 4b
The color temperature of the emitted light color of the obtained thin film EL element can be controlled by changing the film thickness ratio of , and the unique EL emitted color of the thin film EL element is determined. As explained in detail above, according to the present invention, white light emission can be easily obtained,
It is also possible to control the color temperature of the emitted light.

[Brief explanation of the drawing]

FIG. 1 is a block diagram illustrating the structure of a conventional thin film EL element. FIG. 2 is a configuration diagram of a thin film EL device showing one embodiment of the present invention. FIG. 3 is an international standard chromaticity diagram illustrating the emission color of a thin film EL device according to one embodiment of the present invention. 3,5...
- Dielectric layer, 4a...first light emitting layer, 4b...second light emitting layer.

Claims (1)

[Claims] 1. In a thin film EL element that has a light emitting layer interposed between a transparent electrode and a back electrode and emits EL light upon application of a voltage,
The color temperature of the EL emitted light color is composed of at least a two-layer structure in which a layer containing dysprosium and a layer containing thulium are superimposed with the light-emitting layer as a light-emitting center, and the color temperature of the EL emission color is mixed in accordance with the layer thickness of each layer of the two-layer structure. A thin film EL device characterized by controlling and setting the following.