JPH02256192A - Thin film el element and manufacture thereof - Google Patents

Abstract

PURPOSE:To melt one electrode and stop the melting of a luminous layer when the luminous layer and an insulating layer have a defect and the portion is melted by the voltage application by using a member with the melting point lower than that of the portion consisting of the luminous layer and the insulating layer for one electrode. CONSTITUTION:The first electrode 2 is made of an oxide (ITO) of indium and tin, the second electrode 6 is made of Al, and the voltage is applied and gradually increased. When a defect exists on a film, the Al electrode, insulating layers 3 and 5, and a luminous layer 4 are broken by the voltage lower than the insulation withstanding value of an insulating material into the conductive state and locally melted, and Al (portion shown by A) with the melting point lower than that of the insulating layers 3 and 5 and the ITO are first melted and evaporated. The insulating layers 3 and 5 are left and Al (portion shown by A) is melted on them. The insulation state of the portion is immediately recovered. The melting of the insulating layers 3 and 5 is not continued, and it is locally stopped and is not spread over the whole picture elements.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a thin film electroluminescent (EL) device that emits light upon application of an alternating current electric field.

The present invention relates to a thin film EL device in which the dielectric breakdown voltage and yield of the device are improved by improving electrode materials.

<Prior art> Figure 8 shows a thin film E with a double insulation structure formed with a light-emitting layer sandwiched in between.
FIG. 3 is a cross-sectional view showing an example of an L element. In the figure, 1 is a glass substrate, 2 is a transparent first electrode made of indium oxide (In203) or an oxide of indium and tin (T i'O), and 3 is S i 02 or Al 20
The first insulating layer is made of 3 or the like. ITO is widely used as an electrode for EL devices because it is superior to other materials in terms of transparency, specific resistance, spectral absorption, and ease of pattern formation. 4 is a ZnS light emitting layer doped with Mn or a rare earth compound, 5 is a second insulating layer made of the same material as the first insulating layer, and 6 is a second electrode made of AI or the like.

When an AC electric field is applied between the first electrode 2 and the second electrode 6 by the AC power source 15, the EL element with the above configuration is 1 to 2×1
Light is emitted by an electric field of about 0'V/cm.

<Problem to be solved by the invention> In recent years, for use in aircraft flat panels, the second electrode shown in FIG. 8 is formed of a transparent electrode made of I T' 0 similar to the first electrode, and Attempts have been made to realize a multicolor EL panel in which light emitting layers of different colors are laminated.

However, when voltage is applied to the electrodes to make one light-emitting layer emit light, dielectric breakdown occurs locally around pinholes, dust, defects, etc. in the film, and the breakdown spreads to the entire EL pixel (propagating breakdown). There was a problem in that the display quality of the panel was significantly deteriorated due to pixel loss (also called pixel loss).

The present invention has been made in view of the above-mentioned conventional problems, and by studying the mechanism of dielectric breakdown and selecting appropriate electrode materials, it is possible to create a highly reliable transparent EL device with high dielectric strength.
The purpose is to realize panels and multicolor EL panels.

Means for Solving the Problems> In claim 1, the structure of the present invention for solving the problems of the prior art is as follows:
Consists of laminated electrodes with a light-emitting layer and an insulating layer in between,
In a thin film EL device in which the light emitting layer is made to emit light by applying an alternating current voltage to the electrode, at least one layer of the electrode is transparent and has a melting point lower than that of the portion consisting of the light emitting layer and the insulating layer. It is characterized by using a member with a melting point.

In claim 2, in the thin film EL element according to claim 1, the low melting point member is CTO, and the CTO is 5n0.
It is characterized by being sandwiched between thin films containing 2 or 5n02 and an additive.

In a third aspect of the present invention, in the thin film EL device according to the first aspect, the nine light emitting layers are 2N, and the electrodes from the substrate side are the first and second electrodes. Second.
When the third electrode is used, at least the first electrode. According to a fourth aspect of the present invention, in the thin film EL device according to claim 1, one light-emitting layer is made of two layers, and the electrode from the substrate side is made of C'l'O. Second.
When the third electrode is used, at least the second electrode is CTO.
After the EL element is completed, a negative potential is applied to the second electrode, a positive DC voltage is applied to the other electrodes, and then an AC voltage is applied.

In a fifth aspect of the present invention, in the thin film El element according to the first aspect, one light emitting layer is made of two layers, an upper light emitting layer and a lower light emitting layer, and the electrodes from the substrate side are arranged as the first and second light emitting layers. Second. When the third electrode is used, at least the first electrode is CTO.

The second electrode is I'f"O, and after the EL element is completed, a positive potential is applied to the second electrode, a negative DC voltage is applied to the other electrodes, and then an AC voltage is applied. It is something to do.

In claim 6, in the thin film EL device according to claim 1, when at least two light emitting layers are formed, a light emitting test is performed once the first layer is manufactured to a state where it can emit light, and then thereafter. It is characterized by carrying out the manufacturing process of.

Effect> In claim 1.3, if a member having a melting point lower than the melting point of the portion consisting of the light-emitting layer and the insulating layer is used for one of the electrodes, 1.
Even if there is a defect in the emissive layer or insulating layer and that part melts when a voltage is applied, one electrode will melt and the emissive layer will stop melting (9) If both electrodes are below the melting point of the emissive layer and insulating layer, If a material with a high melting point is used, the melting will spread throughout, making it impossible to emit light.)

In claim 2, the resistance of the CTO increases due to the influence of oxygen from the insulating layer. Although it is difficult to form a low-resistance product with SnO2 or additives added thereto, it has strong resistance to oxygen and water, so by sandwiching CTO with this, it is possible to prevent an increase in resistance.

In claim 4, if local destruction is caused in advance by applying a negative voltage to the second electrode, CTO, and a positive voltage to the other electrodes, the destruction will not spread to the entire area.

In claim 5, if local destruction is caused in advance by applying a positive potential to the ITO, which is the second electrode, and a negative DC voltage to the other electrodes, the destruction will not spread to the whole.

In claim 6, if a destructive inspection is performed at the time when the lower light emitting layer is manufactured, the influence of destruction of the lower light emitting layer does not extend to the upper light emitting layer.

<Example> An embodiment of the present invention will be described below with reference to one drawing.

First, the causes of dielectric breakdown in the cases where ITO is used as the first electrode and AI is used as the second electrode, and when ITO is used as the second electrode will be explained. The thin film EL element is mounted on a glass substrate.
TO electrode, insulating layer 9 light emitting layer.

When the insulating layer and the Aj7 electrode are formed by a thin film forming method such as sputtering or vapor deposition, or when a voltage is applied to the electrodes sandwiching the light-emitting layer in order to cause it to emit light.

If there is dust or defects in any of the layers, dielectric breakdown occurs locally, and the first electrode, the insulating layer 1, the light-emitting layer, and the second electrode melt (in this melted state, the insulation of the insulating layer and the light-emitting layer conductivity decreases and becomes conductive).

FIG. 9 is an enlarged sectional view showing the state of destruction when a voltage is applied using ITO as the first electrode and AI as the second electrode.

When the voltage is gradually increased, if there is a defect in the film, AI will be removed at a voltage lower than the dielectric strength value originally possessed by the insulating material.
The electrode, insulating layer, and light-emitting layer are destroyed and become conductive, melting locally, but AI, which has a lower melting point than the insulating layer and I'f'O, melts and evaporates first (that is, the insulating layer is left behind). The AI above it (the part indicated by A) will melt. Therefore, the insulation state of that part will recover quickly.

The melting of the insulating layer does not last, stops locally, and does not spread to the entire pixel. Therefore, the function as an EL display is maintained.

Figure 10 shows 1. FIG. 7 is an enlarged cross-sectional view showing a state of destruction when the second electrode is made of ITO. In this case as well, the insulating layer including ITO and the light-emitting layer melts due to dust and defects existing in the insulating layer, but since the melting temperature of I'l'0 is equal to or higher than that of the insulating layer, its melting and The rate of evaporation will be slower than that of the insulating layer. As a result, the insulating layer continues to melt and break down in the direction of the arrow while maintaining its conductive state due to the high temperature, and finally the pixel is destroyed. ．． ITo is used as the electrode, and Si02, Ta205, and insulating layer are used.
The results show the results of testing the electric field strength leading to propagation type breakdown by forming each insulating layer of Al2oz to a thickness of about 0.3 to 0.5 μm and using AI or ITO as the second electrode.

According to the figure, when SiO2 is used as the insulating layer and AI is used as the second electrode, the withstand voltage is about 7.6 x 10'V/cm, and when ITO is used, the breakdown voltage is about 2. lX10'
The withstand voltage is only about V/cm. In addition, as an insulating layer, Ta
If you use 205, if you use AI, IXl 06V/
cm, 0 for ITo, 5 x 10' V/
cm, and when A11203 is used as the insulating layer, 4.8X10' V/cm for AI, I
In the case of TO, the withstand voltage is only about 08×10'V/cm. As mentioned earlier, in order to make the light emitting layer emit light, the
Since an electric field of approximately IQ'V/cm is required, a sufficient margin is required for the dielectric strength voltage of the insulating layer. Therefore, if the second electrode is made of ITO, propagation type breakdown will occur no matter which insulating layer is used.

Here A1. Looking at the melting points of ITO, the light emitting layer, and the insulating layer, the melting point of AI is 660°C, and the melting point of ITO is 16
00 to 2000°C, and the sublimation point of the light-emitting layer mainly composed of ZnS (since ZnS is a sublimable substance) is about 1180°C. The melting point of 5i02 in the insulating layer is 1610-171
0℃, Ta205 is 1470℃, Al2O3 is 2050℃
It is ℃.

From the above, the first point. It can be seen that when both the second electrodes are made of ITO, the melting point of the electrodes is higher than that of the part consisting of the light emitting layer and the insulating layer, so propagation-type breakdown progresses.

The present applicant confirmed the above fact through experiments, and found that the melting point is lower than that of the part consisting of the light-emitting layer and the insulating layer.

In addition, various studies were conducted on materials that are transparent, have low resistivity, have low spectral absorption, and are easy to pattern. As a result, a mixture containing CdO and 5n02 as main components (Cd2Sn04, Cd5n03...hereinafter,
We discovered that it is superior as a transparent EL electrode (both referred to as CTO).

FIG. 1 shows an EL device according to an embodiment of claim 1 of the present invention.
8 is a sectional view of a main part of a light emitting element, which is the same as the conventional example shown in FIG. 8, except that CTO is used as the second electrode.

The melting point of CTO is about 1130°C, and when we conducted experiments using CTO as the second electrode and the three types of insulating layers shown in Figure 11 above, the propagation was 2 to 3 times that of ITO. We were able to obtain the electric field strength that would break the mold, and we were able to realize a transparent flat panel.

Note that the second electrode is not limited to the above-mentioned c'ro, and for example, 100% CdO (sublimated at 700°C) or SnO2 (melted at 1127°C) as an oxide film is also possible, and additives may be added to 5n02. Additions are also possible. For example, those with Sb added (ATo) and those with F added (FTo).
TO) and also Pmanah Te as an additive to 5n02.
Or, it is the one in which C1 is added. Other CuI, Cu
2 Sχ etc. can also be used, and the key is transparency.

Any member may be used as long as it has a low specific resistance and a melting point lower than that of the portion consisting of the light emitting layer and the insulating layer.

FIG. 2 shows another embodiment of claim 1, and is a sectional view in which the present invention is applied to an EL element having two light emitting layers. In the figure, 1 is a glass substrate, 2 is a first electrode (C
TO), 3, 5, 7.9 are insulating layers, 4 is a lower light emitting layer, 6
is a second electrode (ITO), 8 is an upper light emitting layer, and 10 is a third electrode (CTO). Here, the upper light emitting layer 8 is made of, for example, Zn.
A green EL element such as S:TbF3 is used, and the lower light emitting layer 4 is a red EL element such as ZnS:SmF3.

According to the above configuration, CT is performed across the second electrode made of ITO.
1st consisting of O. Since the third electrode is formed, even if dielectric breakdown occurs, the breakdown can be suppressed locally, making it possible to emit light from multicolored light emitting elements on a transparent panel.

FIG. 3 shows an embodiment according to claim 2. According to the applicant's experiments, CTO is either superior as an electrode with a low melting point, or is susceptible to the influence of oxygen from insulating layers (absorbing and releasing oxygen), resulting in an increase in resistance and a decrease in transparency. There's a problem. while 5n02 or SnO
A material made by adding additives to No. 2 (hereinafter referred to as ATO) has a melting point similar to that of CTO, and has the advantage of being highly resistant to oxygen and water, but has the problem of being difficult to form into a material with low resistance. Therefore, in one aspect of the present invention, the CTO is set to about 2000A, which is sandwiched between ATOs of about 500A.

According to the above configuration, since the CTO, which is easy to obtain low resistance, is protected by A'I"0, which is difficult to obtain low resistance but has strong resistance to oxygen and water, it is possible to obtain an electrode without an increase in resistance value or a decrease in transparency. I can do it.

FIG. 4 shows an embodiment according to claim 3, and shows the second embodiment.
In the two-layer EL element shown in the figure, the first electrode and the second electrode are CTO.

-1- According to the configuration described above, dielectric breakdown becomes more localized than in the example shown in FIG.

FIG. 5 shows an embodiment according to claim 4, and shows the second embodiment.
In the two-layer EL element shown in the figure, the second electrode is CTO, and the first electrode is CTO. The third electrode is an ITO electrode. 1. In the present invention, after the EL element is completed, by applying a negative voltage to the second electrode and a positive voltage to the other electrodes, even if dielectric breakdown occurs, the breakdown can be localized. It was designed to remain at .

FIG. 6 shows an embodiment according to claim 5, and shows the second embodiment.
In the two-layer EL element shown in the figure, the second electrode is TO and the first electrode is TO. The third electrode is a CTO electrode, and in the present invention, after the EL element is completed, by applying a positive voltage to the second electrode and a negative voltage to the other electrodes, even if dielectric breakdown occurs, the breakdown can be localized. It was designed to remain at .

The relationship between the electrode combination and the applied voltage in claim 4.5 has been confirmed by the applicant through experiments, but has not yet been theoretically elucidated.

FIG. 7 is a diagram used to explain claim 6, and here, the first electrode is TTO, the second electrode is CTO, and at the time of manufacturing up to this point, a distance is applied to the first electrode, and a negative voltage is applied to the second electrode. Apply the voltage and perform a destructive test. Through the destructive test, parts with dust or defects are locally destroyed (numeral 12 indicates a hole caused by destruction of the lower light emitting layer). Then the second electrode (CTO
), an insulating layer is applied to the entire area to fill in the broken portion and to form an isolation planarization layer 13. After that, the insulating layer 7.9 and the second electrode 6a are sandwiched between the light emitting layer 8 of node 2 and the second electrode 6a as in the conventional case.
, a third t'Fi 110 is formed. In that case, the second electrode 2
It is preferable to use CTO for either a or the third electrode 10. According to the manufacturing method described above, since the influence of destruction of the first light emitting layer does not extend to the second light emitting layer and destroying it, it is possible to improve the display quality.

Note that even when the nine light-emitting layers are made up of three layers, dielectric breakdown can be locally suppressed by making all the electrodes CTO. Furthermore, if the two light-emitting layers are two or three layers, or transparency is not required, an AI electrode may be used as the outermost electrode (back type @l).

<Effects of the Invention> As specifically explained above in conjunction with the embodiments, according to the present invention, at least one layer of the electrodes sandwiching one light-emitting layer is transparent,
In addition, since a member having a melting point lower than that of one light-emitting layer and an insulating layer is used, it is possible to realize a transparent panel in which dielectric breakdown does not spread over the entire flat panel. Also, CT
A highly reliable EL light emitting device can be realized by arranging O, applying a DC voltage in advance, and providing a test step in the middle of the process.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing one embodiment of a thin film EL element related to claim 1 of the present invention, FIG. 2 is a sectional view showing another embodiment related to claim 1, and FIG. 3 is a sectional view showing another embodiment of the thin film EL element related to claim 1 of the present invention. FIG. 4 is a sectional view showing an embodiment of a thin film EL element according to claim 3 of the present invention, and FIG. A cross-sectional view showing one embodiment of the EI-element, FIG. 6 is a fifth aspect of the present invention.
7 is a sectional view showing an embodiment of a thin film EL element according to claim 6 of the present invention, and FIG. 8 is a sectional view showing a conventional EI thin film element. 9 and 10 are cross-sectional views showing a state in which local melting occurs due to voltage application, and FIG. 11 is a diagram showing the relationship between the material of the insulating layer and the electric field strength of propagation type breakdown.

Claims (1)

[Scope of Claims] 1) Consisting of an electrode laminated on an insulating substrate with at least one EL light emitting layer and an insulating layer sandwiched therebetween, the light emitting layer is made to emit light by applying an alternating current voltage to the electrode. 1. A thin film EL device characterized in that at least one of the electrodes is transparent and has a melting point lower than that of the light emitting layer and the insulating layer. 2) In the thin film EL device according to claim 1, the low melting point member is CTO, and the CTO is SnO_2 or Sn
A thin film EL device characterized by being sandwiched between thin films containing O_2 and additives. 3) In the thin film EL device according to claim 1, when the light emitting layer has two layers, an upper light emitting layer and a lower light emitting layer, and the electrodes from the substrate side are first, second, and third electrodes, at least the first, second, and third light emitting layers are provided.
A thin film EL device characterized in that the second electrode is CTO. 4) In the thin film EL device according to claim 1, when the light-emitting layer has two layers, an upper light-emitting layer and a lower light-emitting layer, and the electrodes from the substrate side are the first, second, and third electrodes, at least the second electrode A method for manufacturing a thin film EL device, characterized in that after completion of the EL device, a negative potential is applied to the second electrode, a positive DC voltage is applied to the other electrodes, and then an AC voltage is applied. . 5) In the thin film EL device according to claim 1, when the light-emitting layer has two layers, an upper light-emitting layer and a lower light-emitting layer, and the electrodes from the substrate side are first, second, and third electrodes, at least the first electrode is CTO, the second electrode is ITO, and after the EL element is completed, a positive potential is applied to the second electrode, a negative DC voltage is applied to the other electrodes, and then an AC voltage is applied. A method for manufacturing a thin film EL element. 6) In the thin film EL device according to claim 1, when at least two light emitting layers are formed, a light emitting test is performed once the first layer is manufactured to a state where it can emit light, and then the subsequent manufacturing steps are performed. A method for manufacturing a thin film EL device, characterized by carrying out the following steps.