JPS6143839B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a thin film EL device, and particularly to a thin film structure for improving the contrast of a display using EL light emission (electroluminescence).

As an example of a thin film EL device, the basic structure of a ZnS:Mn thin film EL device is shown in FIG.

The structure of the thin film EL element will be explained in detail based on FIG. 1. A transparent electrode 2 made of In ₂ O ₃ , SnO ₂ , etc. is placed on a glass substrate 1, and Y ₂ O ₃ , etc.
A first dielectric layer 3 made of TiO ₂ , Al ₂ O ₃ , Si ₃ N ₄ , SiO ₂ or the like is formed in an overlapping manner by sputtering or electron beam evaporation. A ZnS light emitting layer 4 is formed on the first dielectric layer 3 by electron beam evaporation of ZnS:Mn sintered pellets. At this time, the ZnS:Mn sintered pellets used for deposition are pellets in which the concentration of Mn, which is an active substance, is set to suit the purpose. A second dielectric layer 5 made of the same material as the first dielectric layer 3 is laminated on the ZnS light emitting layer 4, and a back electrode 6 made of Al or the like is further deposited thereon. The transparent electrode 2 and the back electrode 6 are connected to an AC power source 7, and the thin film
The EL element is driven.

When an AC voltage is applied between the electrodes 2 and 6 from the AC power source 7, the above AC voltage is induced between the dielectric layers 3 and 5 on both sides of the ZnS light emitting layer 4, and therefore,
Electrons that are excited and accelerated into the conduction band by the electric field generated in the ZnS luminescent layer 4 and have obtained sufficient energy directly excite the Mn luminescent center, and when the excited Mn luminescent center returns to the ground state. emits yellow light. In other words, electrons accelerated in a high electric field
When the electrons of the Mn atoms that have entered the Zn site, which is the luminescence center in the ZnS luminescent layer 4, are excited and fall to the ground state, the electrons are emitted in a wide wavelength range with a peak of approximately 5850 Å.
Exhibits strong luminescence.

The thin film EL element having the structure described above can be used as a flat thin display device that takes advantage of the space factor, and can be used to display characters, symbols, still images, moving images, etc. on computer output display terminal equipment and various display panels that contain characters and figures. It can be used as a display means for images, etc.

The back electrode 6 used in the thin film EL panel is preferably made of a material that is easy to manufacture, has good adhesion to the dielectric layer 5, and has high conductivity, and aluminum thin film is generally used. However, aluminum thin film has an extremely high light reflectance among metals (reflectance of 90% or more), and therefore, under bright ambient light, the back electrode 6 made of aluminum thin film does not pass through the glass substrate 1 into the EL panel. The problem is that the intruding external light is reflected at the interface, resulting in a decrease in contrast and display quality. That is, each thin film layer that makes up the thin film EL panel has extremely high transparency, and external light incident from the glass substrate 1 passes through each thin film layer and reaches the back electrode 6.
Since the EL light emitted from the ZnS light-emitting layer 4 and the reflected light reflected from the back electrode 6 cause mutual interference, the contrast ratio between the light-emitting and non-light-emitting pixels decreases. If the ambient light is extremely bright, the brightness of the EL emission and the reflected light will be about the same, and the display performance will deteriorate significantly. As a means to solve this problem, a blackened electrode structure has been developed in which a plurality of layers of oxide films are interposed at the interface of the back electrode, and the oxide films absorb light irradiated onto the back electrode surface. However, even with this structure, it is difficult to sufficiently reduce the amount of light reflected from the back electrode, and light that enters through the arrangement gap of the back electrode is not absorbed.
It is also insufficient to achieve an improvement in contrast.

In view of the above-mentioned problems, the present invention utilizes a blackened film as a constituent film on the back side of a thin-film EL element, thereby forming a light absorption function and forming a black background in display, thereby improving contrast and display quality. The purpose is to provide a new and useful thin film EL device that has been dramatically improved.

Hereinafter, the present invention will be explained in detail according to embodiments with reference to the drawings.

a-Si _x C _1-x :H film (hydrogenated amorphous silicon carbide film) known as an insulating film
The film composition (x value) can be arbitrarily controlled by film manufacturing conditions. When the value of x is in the range of 0 to 0.5, that is, when the film composition has more C than Si, the color of the film is dark brown to black, and the resistivity is as high as 10 ⁹ to 10 ¹¹ [Ωcm], indicating that the black insulating film is can get. In this example, by using this C-rich a-Si _x C _1-x :H film as all or a part of the dielectric layer provided on the back side of the thin film EL element, the reflection around the back metal electrode is reduced. Reduce light.

FIGS. 2A, B, C, D, and E are schematic structural diagrams of thin film EL devices showing embodiments of the present invention, respectively.

Similar to FIG. 1, a transparent electrode 2 and a first
dielectric layer 3, NnS light emitting layer 4, second dielectric layer 5
are sequentially laminated, and a back electrode 6 made of an aluminum metal film is formed on the second dielectric layer 5. Further, the transparent electrode 2 and the back electrode 6 are connected to an AC power source 7 to drive the thin film EL element. In FIG. 2A, all of the second dielectric layer 5 provided on the back side is a-
It is a thin film EL element composed of Si _x C _1-x :H(x0.5)8. Figure 2B shows the a-Si _x C _1-x :H film 8.
It is interposed at the interface between the ZnS light emitting layer 4 and the second dielectric layer 5. FIG. 2C shows an a-Si _x C _1-x :H film 8 interposed inside the second dielectric layer 5 in the form of a layer parallel to the layer interface. Figure 2 D is a-Si _x C _1-x :H
A film 8 is layered on the surface layer region of the second dielectric layer 5 on the back electrode 6 side. Figure 2 E is a-
A Si _x C _1-x :H film 8 is interposed at the interface between the back electrode 6 and the second dielectric layer 5 .

There are various methods for producing the a- _Six C _1-x :H film 8, but in this example, a reactive sputtering method will be described below. A Si target is sputtered with a mixed gas of Ar gas and hydrocarbon gas, and a-
Si _x C _1-x :H film is produced, but at this time Ar gas is replaced with hydrocarbon gas (e.g. CH ₄ gas, C ₃ T ₈ gas, etc.)
By controlling the mutual gas pressures, an a-Si _x C _1-x :H film 8 having an arbitrary film composition can be produced. a-Si _x C _1-x : a-SiC film in which the x value of the H film 8 is in the range of 0 to 0.5 (C is a composition ratio of Si or more) or a
In the case of -C film (when x = 0), the color of the film is blackish brown to black as described above, and the specific resistance of the film is 3
As shown in the figure, even when CH ₄ gas or C ₃ H ₈ gas is used, a high resistance value of 10 ⁹ to 10 ¹¹ [Ωcm] is exhibited. The solid line in the figure is a characteristic curve using CH ₄ gas, and the broken line is a characteristic curve using C ₃ H ₈ .

Dielectric layer 5 superimposed on the back side of ZnS light emitting layer 4
Black-based a-Si _x C _1-x :H in all or part of
By using the film 8, the hydrogenated amorphous silicon carbide film 8 can significantly absorb the light irradiated onto the back electrode 6, and the contrast of the display can be dramatically improved. Therefore, the display quality is good and the technology is very effective as a light emitting display device.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the basic structure of a conventional thin film EL element. FIGS. 2A, B, C, D, and E are each a schematic diagram of a thin film EL element illustrating an embodiment of the present invention. Figure 3 is a-Si _x C _1-x :H
FIG. 2 is a characteristic diagram illustrating the relationship between the composition ratio of a film and specific resistance. 3...First dielectric layer, 4...ZnS light emitting layer, 5
...Second dielectric layer, 8...a-Si _x C _1-x :H
film.

Claims (1)

[Claims] 1. In a thin film EL element in which both main surfaces of a light emitting layer that emit EL light in response to an applied voltage are covered with dielectric layers, all or part of the dielectric layer located on the back side of the light emitting layer is The part is a-Si _x C _1-x :H(x
0.5) A thin film EL device characterized by being composed of a film.