JPS62200681A - 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 upper and lower main surfaces of a light emitting layer are sandwiched between insulating films, and responds to application of an alternating current electric field to produce an EL (E
The present invention relates to a so-called three-layer thin film EL element that emits light (electroluminescence), and particularly relates to thin film drawing 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 such as Galanu, and a lower dielectric layer 3 and a Zn
A light emitting layer 4 and an upper dielectric layer 5 in which S is doped with an active material.
are sequentially laminated to cover the light emitting layer 4 from the top and bottom of the dielectric layer 3.
A three-layer structure sandwiched by 5 is constructed. On the upper dielectric layer 5, a band-shaped Al layer is formed in a direction perpendicular to the transparent electrode 2.
The back electrodes 6 and the transparent type 1M2 are connected to an AC power source 7 to form a thin film EL.

The element is being driven.

For the back electrode 6 used in thin film EL elements, it is desirable to use a material that is easy to manufacture, has good adhesion to the upper dielectric layer 5, and has high conductivity, and aluminum thin film is generally used. . However, the aluminum thin film has an extremely high light reflectance among metals (reflectance of 90 or higher), so the back electrode 6 using the aluminum thin film will not penetrate into the EL element through the glass substrate 1 under bright ambient light. This causes a problem in that the external light that is generated is reflected at the interface, resulting in a decrease in contrast and display quality. That is, each thin film layer constituting the thin film EL element 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 it is reflected by the back electrode 6 and emitted to the outside again, Z
The reflected light reflected by the EL all-emissive back electrode 6 of the nS light-emitting layer 4 causes mutual interference, and the contrast ratio between the light-emitting picture element and the non-light-emitting picture element decreases significantly. Further, when the ambient light is extremely bright, the luminance of all EL light-emitting devices becomes approximately the same, and the display performance is significantly deteriorated.

Means for Solving the Problems> In view of the above problems, the present invention provides a thin film exhibiting photochromism (for example, Fet-doped The purpose of the present invention is to provide a new and useful thin film EL device that has a light absorption function by inserting a PLZT thin film (PLZT thin film) to form a black background in display and dramatically improve contrast and display quality. . When the light emitting layer emits all EL light, the inserted thin film turns black due to the photochromic effect in response to the light. As a result, a black background is formed during the period when the light-emitting layer emits all EL light.

<Example> FIG. 1 is a block diagram of a thin film EL device showing one example of the present invention. Similar to FIG. 2, a transparent electrode 2, Y
3. A lower dielectric layer consisting of 2O3, TiOz, SiO2 or Si3N4, etc. ZnS.

A light emitting layer 4 made of Zn5e or CaS doped with Mn or rare earth ions as an active substance is sequentially laminated. In this embodiment, a thin film 8 exhibiting photochromism is provided on the light emitting layer 4.
are superimposed. Furthermore, an upper dielectric layer 5 made of metal oxide or nitride and a back electrode 6 made of an aluminum metal film are laminated thereon to form a thin film EL element. The back electrode 6 and the transparent electrode 2 form a matrix electrode structure which is orthogonal to each other as in FIG. 2, and both electrodes 2.6 are connected to an AC power source 7 to drive the thin film EL element.

PLZT ((Pb,
It is known that Fe-doped La) (Zr, Ti) Os) exhibits photochromism, which causes the material to turn black when irradiated with light having a wavelength of 3,200 to 5,100 A. On the other hand, as an active substance added to the light emitting layer 4, for example, thulium (Tm) or a Tm compound (e.g., T
The ZnS light-emitting layer doped with mF3) has a wavelength of 4,770
All blue EL light near A is emitted. Therefore, in order to take advantage of these characteristics, in this example, a blue-emitting aged EL light-emitting layer (for example, the above-mentioned TmT3-doped ZnS layer) is selected as the light-emitting layer 4, and a thin film 8 exhibiting photochromism is formed by sputtering or plasma. The light is formed of an Fe-doped PLZT thin film formed by CVD or the like, and the EL light is emitted from the light emitting layer 4 toward the back surface of the EL thin film 8.

When an alternating current electric field is applied to the light-emitting layer 4 and all blue EL light with a wavelength of around 4,770A is emitted, the Fe-doped PLZ
The T thin film 8 is colored black by irradiation with this light. This blackened thin film 8 can significantly absorb external light irradiated onto the back electrode 6, thereby reducing the amount of scenery reflected on the back electrode 6 and dramatically improving the contrast of the display. The thin film 8 becomes black only while irradiated with the EL light, and returns to its original transparent state when the EL light is turned off.

Note that the upper dielectric layer 5 is a PLZT-based thin film ((Pb,
La)(Zr, Ti)Os, Pb(Zr, Ti)
03, (Pb, La)Ti03, PbT
iO3, PbZr0a, etc.), light emission/! At the same time, the adhesion with the Fe-doped PLZT thin film 8 inserted at the interface with the PLZT film 14 is improved, and at the same time, since the dielectric constant of the PLZT-based thin film is large, it also has the effect of lowering the driving voltage of the thin film EL element.

In addition to the above-mentioned ZnS:Tm, four films 8 may be used as the light-emitting layer 4.
Any device that emits EL light having a wavelength component within the range that governs the photochromic effect can be applied. Furthermore, the thin film 8 exhibiting photochromism is not limited to Fe-doped PLZT.

<Effects of the invention> Thin film E in which a thin film exhibiting photochromism of the present invention is inserted
Since a W cornea is formed on the back surface of the L element during full EL emission, external light is largely absorbed, improving display contrast. Therefore, the display quality is good and it is very effective as a light emitting display device.

[Brief explanation of drawings]

FIG. 1 is a schematic configuration diagram of a thin film EL device illustrating one embodiment of the present invention. FIG. 2 is a basic configuration diagram of a conventional thin film EL element. 1...Glass substrate 2...Transparent electrode 3...
Lower dielectric layer 4... Light emitting layer 5... Upper dielectric layer 6... Back electrode 7... AC power supply 8...
・Thin film agent Patent attorney Takeshi Sugiyama (and 1 other person) Figure 2

Claims (1)

[Claims] 1. 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 a dielectric layer covering the light emitting layer, which is interposed between a pair of electrodes, the light emitting layer and the dielectric layer A thin film EL device characterized by having a thin film exhibiting photochromism inserted between the two. 2. The thin film EL device according to claim 1, wherein the thin film is made of Fe-doped PLZT.