JPH0416917B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Technical Field The present invention relates to a thin film EL element having a back electrode structure with excellent display efficiency and high withstand voltage.

(b) Background art The thin film EL device previously proposed by the applicant is the first
As shown in the figure, a transparent electrode 2 is placed on a glass substrate 1,
A first dielectric layer 3 made of Y ₂ O ₃ or Si ₃ N ₄ ,
A light emitting layer 4 made of ZnS containing a small amount of Mn etc. and a second dielectric layer 5 made of the same material as the first dielectric layer 3 are sequentially laminated by electron beam evaporation or sputtering, and then 50 as black back electrode
~300 Å Mo layer 6 and 50-300 Å Al ₂ O ₃ layer 7 and Al
A three-layer film consisting of layer 8 is laminated by electron beam evaporation or sputtering (for example, Japanese Patent Application No. 19128-1982).

When such a black back electrode is used, reflection of external light is reduced, display contrast is improved, and high visibility can be obtained.

Incidentally, a thin film EL element having such a black electrode structure is considered to have an electrically equivalent circuit as shown in FIG. As you can see from the figure,
An EL element is equivalently thought to consist of series-connected capacitors C ₁ to C ₄ formed by each thin film and an electrode, and the AC voltage E for driving the EL element is divided according to the capacitance of each capacitor. applied.
However, in the case of a thin film EL element having a black electrode structure, as described above, there is a layer between the second dielectric layer 5 and the Al electrode layer 8, which is a Mo layer 6 with a relatively small dielectric constant.
Since the structure is such that the Al ₂ O ₃ layer 7 is inserted,
The voltage portion of the driving AC voltage E that is applied to the capacitor C ₄ increases, and the voltage portion that is applied to the capacitor C ₂ to which the largest voltage is to be applied, that is, the light emitting layer 4, becomes smaller, resulting in poor display efficiency. In addition, although a relatively large voltage is applied to the capacitor C ₄ formed by the Mo layer ₆ , the Al ₂ O ₃ layer 7, and the Al layer 8, the withstand voltage is unstable because the Al ₂ O ₃ layer 7 is thin. Therefore, it is conceivable that the element itself will be destroyed in a chain reaction due to the voltage breakdown in this part.

(c) Object and structure of the invention The present invention has been made in view of the above points, and an object thereof is to provide a thin film EL element having a back electrode structure with excellent display efficiency and high withstand voltage.
In order to achieve this purpose, the dielectric layer constituting the back electrode and two of the two metal layers are electrically short-circuited.

(d) Examples The present invention will be explained below based on the drawings.

FIG. 3 shows an embodiment of a thin film EL device according to the present invention, in which the same reference numerals as in FIG. 1 indicate the same components.

In this embodiment, after forming a Mo layer 6 on the second dielectric layer 5, an Al ₂ O ₃ layer 7 is formed in a region several mm inside the area where the Mo layer 6 is formed.
Thereafter, an Al layer 8 is formed in an area that is the same as or larger than the area in which the Mo layer 6 is formed. The formation area of each of these layers can be regulated to a predetermined area by vapor deposition or sputtering by closely adhering a stainless thin plate (mask) with holes of predetermined dimensions to the substrate. Further, after the black electrode is formed, patterning into a matrix, seven segments, or the like can be freely performed by etching or the like.

In this way, the Al ₂ O ₃ layer 7 forming the black electrode is
By forming the Mo layer 6 and the Al layer 8 in a narrower region, the Mo layer 6 and the Al layer 8 come into contact with each other at the periphery of the thin film forming region and are electrically short-circuited. As a result, the Mo layer 6 and the Al layer 8, which sandwich the Al ₂ O ₃ layer 7 from both sides and serve as capacitor electrodes, become at the same potential, and the capacitor C ₄ (see Figure ₂ ) is no _longer formed. The film thickness of 7 no longer affects the drive AC voltage E of the element. In other words, part of the driving AC voltage E is
No more voltage is applied to the Al ₂ O ₃ layer 7. Therefore, the voltage applied to the light emitting layer 4 can be increased by that much, the display efficiency can be improved, and there is no problem with the breakdown voltage of the Al ₂ O ₃ layer 7.
If the voltage applied to the light-emitting layer 4 remains the same as before, it is natural that the drive AC voltage applied to the EL element can be reduced, and experiments have shown that this reduction can be as much as about 10%. Become.

(e) Effects of the Invention As explained above, according to the present invention, a transparent electrode is selectively formed on a light-transmitting substrate, a light-emitting layer is formed on the transparent electrode, and a first layer is formed on the light-emitting layer. forming a metal layer on the first metal layer, forming an insulating layer inside the formation area of the first metal layer, and forming a second metal layer on the insulating layer and the first metal layer; The first metal layer and the second metal layer were brought into contact with each other on a region where a transparent electrode was not formed.

Therefore, the drive voltage can be lowered without impairing high visibility, and drive circuit elements with low breakdown voltage can be used. As a result, the cost of the circuit can be reduced. In addition, since there is no voltage applied to dielectric layers such as the Al ₂ O ₃ layer, which has a relatively unstable breakdown voltage due to its thin film thickness, there is no need to worry about breakdown voltage breakdown, significantly improving the yield and reliability of EL devices. I can do it.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view showing the structure of a conventional thin film EL device, FIG. 2 is an equivalent circuit of the conventional thin film EL device shown in FIG. 1, and FIG. 3 is an embodiment of the thin film EL device according to the present invention. FIG. DESCRIPTION OF SYMBOLS 1... Glass substrate, 2... Transparent electrode, 3, 5... Dielectric layer, 4... Light emitting layer, 6... Mo layer, 7... Al ₂ O ₃ layer,
8...Al layer.

Claims (1)

[Scope of Claims] 1. A transparent electrode selectively disposed on a light-transmitting substrate; a light-emitting layer formed on the substrate and the transparent electrode; and a light-emitting layer formed on the light-emitting layer. a dielectric layer formed on the first metal layer in a region inside the formation range of the first metal layer; and a dielectric layer formed on the first metal layer and on the dielectric layer. and a second metal layer that is in contact with the first metal layer on a region where the transparent electrode is not formed, the first metal layer, the dielectric layer, and the second metal layer. A thin film EL device characterized by forming a black back electrode.