JPS6366898A - Thin film el device - Google Patents

Abstract

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

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention relates to a thin film EL element used for displaying characters, graphics, etc., and more specifically to the configuration of a back electrode of a thin film EL element.

2. Description of the Related Art An X-Y matrix display device has been known as a solid-state image display device using an electroluminescent phosphor. In this device, a group of horizontal parallel electrodes and a group of vertical parallel electrodes are arranged perpendicularly to each other on both sides of an electroluminescent layer, and a signal is applied through a switching device by a feeder line connected to each electrode group, and a signal is applied to the intersection of both electrodes. Partial electroluminescent layers (hereinafter abbreviated as EL emitter layers) are made to emit light (the light emitting part surfaces at these intersections are called pixels), and characters, symbols, figures, etc. are displayed by the combination of the emitted pixels.

The display board of the solid-state image display device used here is:
Usually, a transparent parallel electrode group is formed on a transparent substrate such as glass, and an EL light emitting layer is sequentially laminated on one or both sides with a dielectric layer or resistor layer interposed therebetween. A '1\ plane parallel electrode group is formed as an end layer in an arrangement perpendicular to the lower layer transparent parallel electrode group. Generally, transparent parallel electrodes are formed by depositing tin oxide on a smooth glass substrate. Aluminum is formed by vacuum evaporation or the like as a back electrode which is perpendicular to this and faces oppositely.

Problems to be Solved by the Invention Incidentally, various dielectric films are used as the dielectric layer, but when the EL light emitting layer emits light, the electric field strength in the dielectric film or resistor film is 105 V/cI11 or more. Often high electric fields. A dielectric film or a resistor film is manufactured by a method such as vapor deposition, sputtering, or CVD, but defects such as pinholes and dust occur in the film. At these defects, the film is more likely to undergo dielectric breakdown at lower electric field strengths than at locations without defects. The dielectric breakdown in the constituent films of thin IIIEL elements is large (particularly in the 2Ni type).

One type is called self-healing dielectric breakdown, and as shown in FIG. 2, the upper electrode 12 around the dielectric breakdown point 11
This is a type in which the particles are scattered within a range of several tens of micrometers due to the discharge energy, and the upper electrode 12 and lower electrode 13 become electrically open. Here, 14 is a substrate, 15 and 16 are dielectric layers or resistor layers, and 17 is an EL light emitting layer. The other type is a self-healing type that does not have dielectric breakdown, and as shown in Figure 3, the upper electrode 12 is not sufficiently scattered and the upper electrode 12 and lower electrode 13 are electrically shorted through the dielectric breakdown point 18. Become. If voltage is further applied in this state, dielectric breakdown may spread throughout the dielectric film or resistor film, and if this type of dielectric breakdown occurs, the upper and lower electrodes will be disconnected, and this thin film EL element becomes unusable and fatal. This type of dielectric breakdown occurs as the film thickness of the upper electrode 12 becomes thinner (for this reason, in a thin film EL element, the upper electrode, that is, the back electrode, is made as thin as possible to prevent the resistance from becoming too mossy and becoming undesirable as an electrode). Or, the material of the dielectric layer or resistor layer itself is made to exhibit self-healing dielectric breakdown.

However, even thin film EL elements that undergo self-healing dielectric breakdown are not completely free from problems. In other words, as the display area of a thin-film EL element is made finer and denser, the pitch of the back electrode becomes smaller and the width of the back electrode becomes narrower. The back electrode around the broken part is scattered in a range of several tens of micrometers due to the discharge energy.Therefore, the width of the back electrode is 10 μm.
When the thickness is about 0 μm, when self-healing dielectric breakdown occurs and the scattering of the back electrode is larger than the width of the back electrode, disconnection of the back electrode occurs. Further, even when the scattering of the back electrode is smaller than the width of the back electrode, if dielectric breakdown occurs at a plurality of adjacent locations on the back electrode, the scattered portions of the back electrode will join together, resulting in disconnection. Even if disconnection does not occur, if the scattering area of the back electrode due to dielectric breakdown is large, part of the pixel becomes a non-light-emitting part, which increases the quality of the thin-film EL element as a display element.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to solve the above-mentioned technical problems and provide a stable thin-film EL device that is less prone to dielectric breakdown than conventional thin-film EL devices.

Means for Solving the Problems The present invention provides a structure in which a plurality of striped transparent electrodes arranged in a seven-trix pattern in directions orthogonal to each other on a light-transmitting substrate and a back electrode have a small number of In a thin film EL element in which an EL light emitter layer is provided on the electrode side via a dielectric layer or a resistor layer, the back electrode is made of one of gold, platinum, and palladium and has a thickness of 10 nm to 110 nm.
A laminated film is formed of a 0n metal vapor deposited film and an aluminum vapor deposited film, and the metal vapor deposited film is provided in contact with the dielectric layer or the resistor layer.

Effect With the above configuration, gold, which has a high dielectric breakdown electric field strength of the dielectric film or resistor film, can be used as the back electrode of the thin film EL element.
By using a thick layer of a metal vapor-deposited film consisting of one of platinum or palladium and an aluminum vapor-deposited film, the withstand voltage of the dielectric layer or resistor layer of a thin-film EL element can be increased (and dielectric breakdown of the element may occur). difficult (can be done)

Embodiment FIG. 1 is a diagram for explaining an embodiment of the thin film EL device of the present invention. In the figure, a transparent electrode 2 is formed on an insulating substrate 1, and a first dielectric layer 3, an EL light emitting layer 4, and a second dielectric layer 5 are sequentially laminated thereon. Furthermore, there are two types of back electrodes, namely, a back electrode A8 formed by laminating a first back electrode 6 and a second back electrode 7, and a back electrode B9 consisting of only the second back electrode 7. It has been established that Here, the first back electrode 6 and the second back electrode 7 play an important role in the present invention, and the first back electrode 6 is selected from vapor deposited films of gold, platinum, and palladium. As the second back electrode 7, an aluminum vapor-deposited film is used. The thickness of the first back electrode 6 is desirably 10 nm or more and 1100 nm or less. If the film thickness is less than 10 nm, it will be difficult to form a uniform film over the entire surface and the effect will be small, and if it is thicker than 1100 nm, the cost of the evaporation material will increase and it will be uneconomical. The film thickness of the second back electrode 7 is desirably 10 nn or more and 500 n111 or less, and if it is thinner than 10 n11, the film will not be uniform over the entire surface and the electrical resistance will be large. Also, J
'X, the element becomes less prone to self-healing dielectric breakdown.

The transparent electrode 2 of the thin film EL device produced in this way,
An AC voltage is applied between the back electrode A8 and the back electrode B9 to drive the element, and when the device emits light and the dielectric breakdown occurs on the back electrode 8 and on the back electrode Be compared, it is found that under the same driving voltage. The number of dielectric breakdowns that occurred was much smaller and more stable in the configuration with 8 on the back electrode. For example, it is conceivable to form the back electrode entirely with a vapor-deposited film of gold, platinum, or palladium, but the resistivity of platinum or palladium is four times that of aluminum, so in that case, the electrical resistance of the electrode would be In order to reduce the dielectric loss, the film thickness must be increased, and as a result, the device will not suffer from self-healing dielectric breakdown.

Also, the resistivity of gold is only slightly lower than that of aluminum, which is disadvantageous in terms of cost.

Here, as the insulating substrate 1, a normal thin film substrate such as glass, alumina, or fosterlite can be used.

As the transparent electrode 2, tin oxide (Sno2), indium oxide (In20s), or indium tin oxide (IT
It is formed from a transparent conductive film such as O).

The first dielectric layer 3 and the second dielectric layer 5 are not particularly limited, but include Be, Mg, Y, .Ti, Zr,
Sr, Hf, Nb, Ta, Cr, Mo,
W, Zn, A1. Oxides and nitrides, fluorides, etc. of Ga, Si or the lanthanide elements are suitable, as well as mixtures or compounds thereof. In particular, a dielectric layer with a high dielectric constant can be obtained with an oxide having a perovskite structure.

The EL emitter layer 4 is made of, for example, zinc sulfide (Z) containing an active substance.
nS) can be used. The active substance is Mn,
Cu, Ag+Au, TbFs, SmFs, ErF
s + TmF3. DYF3, PrFs, EuF3
etc. are appropriate. The EL light emitter layer 4 may be made of materials other than zinc sulfide, for example, materials that exhibit electroluminescence such as SrS or CaS containing an active substance may be used.

Next, a specific example of the present invention will be explained using FIG. 4. What is shown in FIG. 4 is a thin film EL device according to the present invention, which was manufactured by the following procedure. A commercially available transparent glass plate 31 is used as a substrate, and an ITO film with a thickness of 200τ1 m is formed on the entire surface by electron beam evaporation at a temperature of 300° C., and a desired stripe shape is formed by photolithography. A transparent electrode 32 is obtained. Next, the substrate temperature is 400
Indium titanium oxide (SrT) to a thickness of 600 nm at ℃
ies) film was formed by a sputtering method to form the first dielectric layer 33. Next, while maintaining the substrate temperature at 250° C., manganese-activated zinc sulfide (ZnS:Mn) was deposited by electron beam to a thickness of 400n+u with a manganese concentration of 1 mol% to form the EL light emitting layer 34. Formed. After the deposition, a heat treatment was subsequently performed in a vacuum chamber at a temperature of 550° C. for 1 hour to improve the properties of the EL emitter layer 34. Then, by electron beam evaporating yttrium oxide (Y203) to a thickness of 50 nm,
A second dielectric layer 35 was formed. Note that the substrate temperature at this time was 200°C. Furthermore, on top of that, 5Qnm of gold,
A back electrode 36 was formed by successively forming aluminum layers to a thickness of 150 nm by electron beam evaporation, and the device was completed.

An AC pulse voltage (frequency 6011z, pulse width 30 us) was applied between the transparent electrode 32 and the back electrode 36 to drive this element to emit light. In an element with the same configuration as this element, the back electrode began to break due to dielectric breakdown at a driving voltage of 250V, whereas in the element according to the present invention, the back electrode did not completely break at the same driving voltage. There wasn't.

In this example, an AC drive type was explained, but similar results were obtained with a DC drive type in which the dielectric layer was replaced with a resistor layer.

Effects of the Invention As described above, according to the present invention, the back electrode of a thin film EL element is formed with a layer of a vapor-deposited gold film made of one of gold, platinum, and palladium and a vapor-deposited aluminum film. , with a simple configuration! It is possible to provide a stable thin film E-L element with little dielectric breakdown and no increase in driving voltage.
Great effect.

[Brief explanation of the drawing]

FIG. 1 is a thin 11 mm E
2(a) and 3(a), which are cross-sectional views showing the structure of the L element, are diagrams of a thin film EL element for explaining a more specific embodiment of the present invention using a dielectric film or a resistor film. FIG. 3 is a sectional view showing the configuration. l...Insulating substrate, 2...Transparent electrode, 3...
1st dielectric layer, 4... EL light emitter layer, 5... second
Dielectric layer, 6... First back electrode, 7... Second back electrode, 8... Back electrode B19... To back electrode 〇 Name of agent Patent attorney Toshio Nakao and 1 other famous person 1 3rd = 1219th electrode
4 U2

Claims (2)

[Claims] (1) A dielectric layer or a resistor layer is interposed at least on the back electrode side between a plurality of striped transparent electrodes arranged in a matrix in directions orthogonal to each other on a transparent substrate and a back electrode. In a thin film EL device comprising an EL light emitter layer, the back electrode is made of one of gold, platinum, and palladium and has a thickness of 10 nm to 100 nm.
A thin film E comprising a laminated film of a metal vapor-deposited film and an aluminum vapor-deposited film, and the metal vapor-deposit film is provided so as to be in contact with the dielectric layer or the resistor layer.
L element. (2) The thickness of the aluminum vapor deposited film is from 10 nm to 50 nm.
The thin film EL device according to claim 1, characterized in that the thickness of the thin film EL device is 0 nm.