JPS5910033B2 - Method for manufacturing thin film electroluminescent devices - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a thin film electroluminescent device (
The present invention relates to a method of manufacturing a thin film EL device (hereinafter referred to as a thin film EL device).

A thin film made of a ■-■ group compound semiconductor, such as zinc sulfide (ZnS), to which manganese (Mn) and rare earth compounds, etc. are added to form a luminescent center, is insulated with yttrium oxide (Y2O3) on both sides or one side. A thin-film EL device is well known, in which a thin film layer is provided and sandwiched between opposing electrodes, and it emits light with high brightness by applying an alternating current voltage between the opposing electrodes. It is known that they have a longer lifespan than electroluminescent devices.

Figure 1 is a cross-sectional configuration diagram of a conventional thin film EL element, in which 1 is a glass substrate, 2 is an indium oxide (In2O3)
Or a transparent electrode layer made of tin oxide (SnO2), etc.
3 is a first insulating layer made of yttrium oxide (Y2O3) or silicon nitride (Si3N4), 4 is a ZnS light emitting layer doped with Mn or a rare earth compound, and 5 is a second insulating layer.
An insulator layer, 6 a back electrode made of aluminum or the like, and 7 an AC power source. As is clear from Figure 1, this E
The L element has a transparent electrode layer 2, a first insulator layer 3, a ZnS light emitting layer 4, and a second insulator layer 5 laminated in this order on a glass substrate 1.
It is formed by a vacuum evaporation method or a sputtering method, and a back electrode 6 is further provided thereon.

An AC power source T is connected between the transparent electrode layer 2 and the back electrode 6. A thin film EL element with such a structure emits light by connecting an AC power source 7 between the transparent electrode layer 2 and the back electrode 6 and applying an AC electric field, but in order to obtain high luminance light emission, a considerably high Since an electric field (approximately 106 V/cm) is required, the insulating layers 3 and 5 are required to have good insulation properties and high breakdown voltage.

Conventionally, the insulator layers 3 and 5 are made of a thin film of an oxide of a group I or group element such as Y2O3, samarium oxide (Sm2O3), zirconium oxide (ZrO2), or tantalum oxide (Ta2O5) or a nitride such as Si3N4. It is formed and used by a vacuum evaporation method or a sputtering method.

However, when an oxide is formed by vapor deposition, the crystallinity of the film is poor if it is formed at a low substrate temperature, and when the light emitting layer 4 is formed by laminating layers, the insulator layer 3 On the other hand, if it is formed at a high substrate temperature, a film with good crystallinity can be obtained, but on the other hand, an oxide film with oxygen deficiency and a misaligned composition is produced, resulting in only a thin film layer with poor insulation properties. There was a drawback. Furthermore, when the insulator layers 3 and 5 are formed by sputtering, the degree of vacuum during formation is low and the ZnS light emitting layer 4 is formed by vacuum evaporation, so the insulator layers 3 and 5 and the light emitting layer are 4 cannot be manufactured using the same vacuum equipment, and the vacuum must be broken each time each layer is manufactured.
Since it is necessary to change the device, impurities are likely to be adsorbed at the interface between the insulating layer and the light-emitting layer, resulting in the formation of interface levels that have a negative effect on the light-emitting characteristics. The present invention aims to obviate the aforementioned drawbacks.

Specifically, it is an object of the present invention to provide a method for manufacturing an EL element in which an insulating layer has good crystallinity, is free from the risk of cracking due to thermal distortion, etc., and does not form an oxide layer with a different composition due to oxygen vacancy. That is, an object of the present invention is to provide a method for manufacturing a thin film EL device that can easily manufacture a high-brightness EL device with good light emission characteristics and durability. Therefore, the method for manufacturing a thin film EL device according to the present invention is a thin film electroluminescent device in which an insulating layer is provided on both sides of a light emitting layer, and electrode means for applying an electric field to the light emitting layer via the insulating layer is formed. In the method for manufacturing a luminescent device, the insulating layer is formed by forming a group I, group, or group oxide layer by vacuum deposition, and then depositing the insulating layer at a temperature of 400 to
It is characterized by performing heat treatment at a temperature of 600° C. for 1 to 2.5 hours.

According to the method for manufacturing a thin film EL device according to the present invention, since heat treatment is performed in a low vacuum atmosphere after forming the insulating layer, the oxygen deficiency state of the insulating layer is compensated for.

Therefore, an excellent insulating layer with good crystallinity and no oxygen vacancies can be manufactured. Furthermore, since layer formation is performed using a vacuum evaporation method, the light-emitting layer can also be manufactured in the same device. Therefore, impurities are not adsorbed at the interface between the insulating layer and the light-emitting layer, and the interface states that adversely affect the light-emitting characteristics are prevented. is not formed, and
It has the advantage of being easy to manufacture. To explain the present invention in more detail, the method for manufacturing a thin film EL device according to the present invention involves first forming a transparent electrode layer on a substrate by a method such as vacuum evaporation, and then laminating an insulating layer on the substrate by vacuum evaporation. urge

The insulator layer is an oxide layer of group I, group oxide, or group oxide because these oxides have good performance as an insulator layer of an EL light emitting device. As this insulating layer, for example, yttrium oxide (Y2O3), samarium oxide (Sm2
O3), zirconium oxide (ZrO2), tantalum oxide (Ta2O5), and the like can be suitably used. When forming these insulating layers, the substrate temperature is preferably 400 to 600°C.

This is because if the temperature is less than 400°C, the crystallinity of the insulating layer will be poor, and if it exceeds 600°C, there is a risk that the glass substrate will soften.

Further, the degree of vacuum at this time is preferably about 10<-6> to 5*10<-6>.

The insulator layer formed in this way is heated to a vacuum degree of 10-4 to 5×1.
Heat treatment is performed for 1 to 2.5 hours in 0-6T0rr.

If the degree of vacuum is less than 10-4T0rr, it may cause operational difficulties such as defects in the device, and there is a risk that the light-emitting layer may change in quality.If it exceeds 5x10-6T0rr, oxygen may dissociate. This is because this results in the drawback that the oxygen deficiency becomes more intense and it becomes difficult to compensate for the oxygen deficiency state. Furthermore, if the heat treatment time is less than 1 hour, the effect of the heat treatment will not be apparent, and if it exceeds 2.5 hours, oxygen will begin to dissociate, and there is a risk that the heat treatment to compensate for oxygen vacancies will be wasted. . The temperature of the heat treatment is 400 to 600°C.

If the temperature is less than 400°C, the effect of heat treatment will not be so great that 60°C
This is because if the temperature exceeds 0° C., there is a risk that the glass substrate will become soft.

Next, a light emitting layer is formed on this insulating layer, and the degree of vacuum at this time is 10-6 to 5 x 10-6 T.
Approximately 0rr is preferable.

According to the method for manufacturing a thin film EL device according to the present invention, a back electrode may be formed directly on this light emitting layer, and an insulating layer is further formed on this light emitting layer, preferably by the method described above, and then heat treated. Alternatively, a back electrode may be formed on this second insulating layer.

Next, embodiments according to the present invention will be described. Example FIG. 2 is a schematic cross-sectional view of a thin film EL device manufactured by the method according to the present invention, in which 8 is a glass substrate, 9 is a transparent electrode layer, 10 is a first insulator layer, 11 is a light emitting layer, 12 is a second insulator layer, 13 is a back electrode, and 14 is an AC power source.

As is clear from FIG. 2, this thin-film EL device has almost the same structure as the EL device shown in FIG.

In manufacturing this thin film EL element, first, a transparent electrode layer 9 of indium oxide (In2O3) is formed on a glass substrate 8 by vacuum evaporation, and then a transparent electrode layer 9 of samarium oxide (Sm2O3) is formed on the glass substrate 8.
3) at a substrate temperature of 300°C;
Lamination was carried out by electron beam evaporation under conditions of a degree of vacuum of about 10 -6 to 5 x 10 -6 T0rr. After that, Sm2O
3. In order to compensate for the oxygen deficiency state of the insulator layer 10, 10-5T
Heat treatment was performed at 450° C. for about 1 to 2 hours in a low vacuum of about 0 rr. Next, ZnS powder to which approximately 0.3 to 0.5 wt% of Mn was added was formed into a pellet shape, and then fired (
Z fabricated at 1100°C for 2 hours in an argon atmosphere
Using an nS:Mn sintered beret, a ZnS:Mn light-emitting layer 11 was formed by electron beam evaporation in a vacuum of about 10-6T0rr, and further, the crystallinity of the light-emitting layer 11 was improved and M
In order to diffuse n, 10-6 to 5×10-6T0rr
Heat treatment was carried out at 400 to 500° C. for about 1 hour in a vacuum of about 100°C. Thereafter, a second insulating layer 12 is formed on the ZnS:Mn light emitting layer 11 using the same method as when the first insulating layer 10 was formed and heat-treated, and a back electrode 1 made of Al is further formed on the ZnS:Mn light emitting layer 11.
3 was formed by a vacuum evaporation method. In this way, by performing heat treatment in a low vacuum after the insulating layer deposition, the light transmittance of the insulating layers 10 and 12, which had turned brown immediately after the thin film was formed and had a composition of Sm2O3- due to oxygen loss, was improved. The film was improved and became the original Sm2O3 thin film.

In addition, since the first insulating layer 10 was formed at a higher substrate temperature than conventionally, no cracks occurred when the ZnS:Mn light emitting layer 11 was laminated. Furthermore, in the manufacturing method of the present invention, since the first insulating layer 10, the light emitting layer 11, and the second insulating layer 12 are all formed by electron beam evaporation, the manufacturing process including the heat treatment process can be performed continuously in the same apparatus. ,
Since the interface is not exposed to the atmosphere, the generation of interface states that adversely affect device characteristics can be significantly suppressed.

FIG. 3 is a luminance-voltage characteristic diagram of a thin film EL device having the structure shown in FIG. 2 manufactured by the method according to the present invention, in which curve A shows the characteristics of the thin film EL device manufactured by the method according to the present invention, Curve B is the characteristic of a thin film EL device manufactured by a conventional method.

Although the film thicknesses of the insulating layer and the light emitting layer of both EL devices are almost the same, the EL device manufactured by the method of the present invention has improved brightness and breakdown voltage compared to the EL device of the conventional method. Was. FIG. 4 is a diagram showing the temporal change in the emission intensity of a thin film EL element with a three-layer structure (first insulator layer, light emitting layer, second insulator layer), and the curve C is E.
When an AC power source is connected to the L element, the voltage waveform is applied to the back electrode. Curve D is the emission waveform of the EL element manufactured by the method of the present invention, and curve E is the waveform of the light emission of the EL element manufactured by the conventional method. This is the light emission waveform of the EL element.

As is clear from FIG. 4, the conventional EL element hardly emits light when the potential of the back electrode is negative, and the emitted light waveform is asymmetrical with respect to the polarity of the applied voltage, whereas the method of the present invention The EL device manufactured by E. et al. emits light with the same intensity every half cycle of the applied electric field, regardless of the polarity of the voltage, and the emitted light waveform is symmetrical. Therefore, in the luminance-voltage characteristics shown in FIG. 3, the large difference in maximum luminance between the EL element manufactured by the method of the present invention and the conventional EL element is due to the emission waveforms of both EL elements. It is clear that this arises from differences. FIG. 5 is a schematic cross-sectional view of a thin film EL device with a two-layer structure (first insulating layer - light emitting layer) covered with a second insulating layer 12, and the same reference numerals as in FIG. 2 refer to the same elements. shall be indicated.

FIG. 6 is a diagram showing the emission waveform of the EL element of FIG. 5, in which curve C is the AC voltage waveform applied to the back electrode 13, and curve F is the emission waveform of the thin film EL element.

As is clear from FIG. 6, the emission waveform is asymmetrical with respect to the voltage polarity, and is similar to the emission waveform of the conventional thin film EL element shown by curve E shown in FIG. Therefore, from this, when a thin film EL element with a three-layer structure is manufactured by the conventional method, the second insulating layer 5 has poor insulation properties and does not function as an insulator. It is clear that the insulating properties of the insulating layer will improve if the device is manufactured.It should be noted that even when using the conventional method, the first insulating layer 3 has quite good insulating properties. 4
After forming the first insulating layer 3, heat treatment is performed in vacuum mainly for the purpose of improving the film quality of the light emitting layer, and the oxygen deficiency state of the first insulating layer 3 is also compensated for at the same time during this heat treatment. As explained above, if a thin film EL device is manufactured by the method of the present invention,
It is possible to obtain an EL element with high brightness and high breakdown voltage, and since a series of manufacturing steps of the element can be carried out continuously using the same vapor deposition apparatus, the interface between the insulating layer and the light emitting layer becomes clean. The method is to use high-brightness thin film EL with stable luminescent properties and long life.
This is a useful method for manufacturing devices.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional configuration diagram of a conventional thin film EL device, FIG. 2 is a schematic cross-sectional diagram of a thin film EL device manufactured according to an embodiment of the present invention, and FIG. 3 is a luminance-voltage characteristic diagram of the thin film EL device. , 4th
The figure shows the emission waveform of a thin film EL element with a three-layer structure.
The figure is a schematic cross-sectional view of a thin film EL element with a two-layer structure, and FIG. 6 is a diagram showing the light emission waveform of the element of FIG. 5. 1, 8... Glass substrate, 2, 9... Transparent electrode layer, 3, 10... First insulator layer, 4, 1
1... Light emitting layer, 5, 12... Second insulating layer, 6, 13... Back electrode, 14...
AC source.

Claims (1)

[Claims] 1. A method for manufacturing a thin film electroluminescent device, in which an insulating layer is provided on both sides of a light emitting layer, and electrode means for applying an electric field to the light emitting layer via the insulating layer is formed, wherein the insulating layer is Group, IV or V oxide layer is formed by vacuum evaporation and then 10^-^4-5x
A method for manufacturing a thin film electroluminescent device, characterized by performing heat treatment at a temperature of 400 to 600° C. for 1 to 2.5 hours in a vacuum of 10^-^6 Torr.