JPS62202492A - Thin film el device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention has a structure in which both the upper and lower principal surfaces of a light emitting layer are sandwiched between insulating films, and in response to the application of an alternating current electric field, E L (E
The present invention relates to a so-called three-layer thin film EL element that emits light (electroluminescence), and particularly relates to an element (1η structure) for improving the contrast of a display that utilizes all EL light emission.

<Prior art and its problems> The basic structure of a conventionally known thin film EL element is shown in FIG. A plurality of transparent electrodes 2 are arranged in parallel in strips on a transparent substrate 1 made of glass or the like, and a first insulating layer M3, ZnS
A light emitting layer 4 doped with an active substance and a second insulating layer 5 are sequentially stacked to form a 3M structure in which the light emitting layer 4 is sandwiched between upper and lower insulators M3 and M5. On the second insulating layer 5, strip-shaped back electrodes 6 made of Ae are arranged in parallel in a direction perpendicular to the transparent electrode 2, and the back electrodes 6 and the length of the transparent electrodes are connected to an AC power source 7 to form a thin film EL element. Driven.

As the back electrode 6 used in the thin film EL element, it is desirable to use a material that is easy to manufacture, has good adhesion to the second insulating layer 5, and has high conductivity, and aluminum thin film is generally used. . However, the aluminum thin film has an extremely high luminous emissivity among metals (reflectance of 90% or more), and therefore, when the back electrode 6 using the aluminum thin film is exposed to the E L through the glass substrate 1 under bright ambient light,
External light that has entered the panel is reflected at the interface, resulting in a problem of deterioration of contrast and display quality. That is, each thin film layer constituting the thin film EL element has extremely high transparency, and external light incident on the Galanu substrate 1 is completely transmitted through each thin film layer and reaches the back electrode 6.
′=! reaches the rear surface (reflected at j6 and emitted to the outside again, the EL all-emissive back electrode 6
The reflected light caused by mutual interference occurs, and the contrast ratio between the light-emitting picture element and the non-light-emitting picture element +7) decreases significantly. Furthermore, if the ambient light is extremely bright, the luminance of the EL total emitted reflected light will be about the same9, and the display performance will be significantly deteriorated.

<Means for Solving the Problems> In view of the above problems, the present invention provides a thin film exhibiting photochromism (for example, a PLZT thin film doped with Fe) that serves both as a substrate and a first insulating layer of a three-layer thin film EL element. @
) is deposited on the surface of the PLZT ceramic plate,
The object of the present invention is to provide a new and useful thin-film EL device in which a thin film exhibiting photochromism has a light-absorbing function, forms a black background in a display, and dramatically improves contrast and display quality.

When the light-emitting layer fully emits EL, the thin film exhibiting photochromism deposited on the PLZT ceramic plate changes color to black in response to the light. As a result, a black background is formed on the back surface of the light emitting layer during the period when the light emitting layer emits all EL light, and light is absorbed in this portion.

<Example> FIG. 1 is a schematic diagram of a thin film EL device showing one example of the present invention. A plurality of Al electrodes 8 are arranged in parallel on one side of a PLZT ceramic plate 9 which serves both as a substrate and a first insulating layer. On the other side of the PLZT ceramic plate 9 is a thin film 10 exhibiting photochromism in a region corresponding to the position where the light emitting layer is formed.
Deposit.

This thin film 10 may be formed on the entire surface of the wide PLZT ceramic plate 9. A light emitting layer 11 made of Zn5e or CaS doped with Mn or rare earth ions as an active substance is formed, and this is covered with a second insulating layer 12. 8 on top of that
The Al second insulating layer 12 is Y203, Ti0
An oxide or nitride such as 2 + S i02 , S i3N<, etc. is selected as appropriate. A plurality of strip-shaped transparent electrodes 13 are formed in a direction perpendicular to the electrode 8 on top of the pattern A.
A thin film EL device is produced. Transparent electrode 13 and Al electrode 8
is connected to an AC power source 14 to drive the thin film EL element. In this case, the EL light is transmitted to the upper part of FIG.
It is emitted to the side.

PLZT ((Pb, La) (Zr, Ti)03) ceramic plate is famous as a translucent ceramic,
The one doped with Fe is 3.200~5JOO
It is known that when irradiated with light of wavelength A, it exhibits photochromism, which causes it to turn black.

On the other hand, active substances such as thulium (Tm) or T
The ZnS light emitting layer doped with the m compound has a wavelength of 4,770
Emit blue EL light near A. Therefore, in order to take advantage of these characteristics, in this embodiment, the light-emitting layer 11 is an EL light-emitting layer that emits blue light (for example, TmF as an active material).
A thin film 10 exhibiting photochromism is made of Fe deposited on a PLZT ceramic plate 9 by a thin film forming method such as sputtering or plasma CVD.
A doped PLZT thin film is selected, and the structure is such that the EL light from the light emitting layer 11 is irradiated onto the thin film 10 exhibiting photochromism.

When an alternating current electric field is applied to the light-emitting layer 11 via the Al electrode 8 and the transparent electrode 13, and the blue EL light with a wavelength of around 4.770A is emitted, the thin film 1 made of Fe-doped PLZT is formed.
0 is colored black. Due to the light absorption effect of this blackened thin film 10, the external light and EL light irradiated to the Al electrode 8 can be significantly reduced, and the contrast of display by EL light obtained in the direction of the transparent heavy state 13 is dramatically increased. improve.

The thin film 10 is blackened only while the EL light is being irradiated to form a black background for display, and returns to its original transparent state when the EL light irradiation is stopped.

In the above embodiment, since the PLZT ceramic plate 9 has a very large relative dielectric constant (ε=900 to 5.000), if the thickness of the PLZT ceramic plate 9 is 0.1 or less, the driving voltage can be lower than the conventional one. It is possible to reduce the voltage considerably. In addition, a PLZT-based thin film ((Pb.

La) (Zr, Ti)03. Pb(Zr, Ti)
03, (Pb, La)Ti03, PbTiO3.

If PbZrO3, etc.) are used, even lower voltage driving becomes possible since these materials also have a large dielectric constant.

Furthermore, since this PLZT thin film and the PLZT ceramic plate 9 are made of similar materials, their adhesion is also improved.

Note that various materials other than Fe-doped PLZT can be used as the thin film 10 exhibiting photochromism.

Furthermore, any material can be used for the light emitting layer 11 as long as it emits EL light having a wavelength component that causes the thin film 10 to undergo a coloring reaction.

<Effects of the Invention> In the thin film EL device using the substrate of the present invention and the PLZT ceramic plate on which a thin film exhibiting photochromism is deposited on the surface as the first green layer, a blackened layer is formed on the back surface during full EL emission, and the external Since a large amount of light is absorbed, the contrast of the display is improved, and therefore the display quality is improved, which is a very effective effect when used as a light emitting display device. Further, the driving voltage of the EL element can also be reduced.

[Brief explanation of drawings]

FIG. 1 is a schematic configuration diagram of a thin EL element illustrating one embodiment of the present invention. FIG. 2 is a block diagram showing the basic structure of a conventional thin film EL element.

Claims (1)

[Claims] 1. In a thin film EL element comprising a light emitting layer that generates EL light emission in response to the application of an electric field and an insulating layer covering the light emitting layer interposed between a pair of electrodes, the light emitting layer is a thin film exhibiting photochromism. 1. A thin film EL device characterized in that it is formed so as to overlap a PLZT ceramic plate on which is deposited.