JPH11126690A - Manufacture of thin film electroluminescent element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the manufacturing method of an EL element using an alkali earth metal sulfide as a luminescent layer, with high luminescent brightness and high life characteristics in spite of using a non-alkali glass substrate. SOLUTION: In the manufacturing method of a thin EL element formed by laminating a first electrode 2a, a first insulating layer 3a, a luminescent layer 4, a second insulating layer 3b, and a second electrode 2b on a non-alkali glass substrate 1a in order, at least after the luminescent layer 4 is formed, the non-alkali glass substrate 1a is held at a temperature which is a deformation limit temperature or lower in a single heat treatment method and a first holding temperature near to the deformation limit temperature, then heat treated at a second holding temperature higher than the first holding temperature.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a thin film EL device used for a thin display device.

[0002]

2. Description of the Related Art Thin-film EL devices exhibiting electroluminescence (hereinafter referred to as EL) by applying a voltage to a light-emitting layer have many excellent properties such as high-brightness light emission, high-speed response, wide viewing angle, thin and light weight, and high resolution. Because of its features, it has attracted attention as a thin display device.

FIG. 5 is a sectional view of a typical thin film EL device. A thin film EL element is formed on a glass substrate 1a by a first electrode layer 2
a, a first insulating layer 3a, a light emitting layer 4, a second insulating layer 3b, and a second electrode layer 2b are laminated. In order to protect the light emitting layer 4, another counter glass substrate 1b is covered via a support member 6, and a silicone oil 5 is filled between the two substrates for moisture proof. In the power supply E, the light emitting layer 4 emits light by a voltage applied from the power supply E connected to the first electrode layer 2a and the second electrode layer 2b, and the light emission passes through the glass substrate 1a or the opposite glass substrate 1b. And emitted outside the EL element.

The luminescent color of an EL element is determined by a combination of a semiconductor base such as zinc sulfide (ZnS) or strontium sulfide (SrS) constituting a luminescent layer and a luminescent center to be added. It is obtained by adding manganese (Mn) as a luminescent center to a (ZnS) matrix. However, the one that has reached the practical level of luminance at present is ZnS: Mn in which manganese (Mn) is doped into zinc sulfide (ZnS).
Only a monochromatic display that emits yellow-orange light. Therefore, the thin film E for multi-color or full color
The development of L elements is strongly desired. Alkaline earth metal sulfides, especially strontium sulfide (SrS) and calcium sulfide (CaS), are promising as base materials, and cerium (Ce), europium (E
u), praseodymium (Pr), blue-green (SrS: Ce), red (CaS: Eu), white (SrS: Ce, E
u), it is known to emit light in white (SrS: Pr).

It is known that the above-mentioned light-emitting layer is improved in luminance and life characteristics by a heat treatment which is heated and held at a high temperature after film formation. On the other hand, as the substrate on which the light emitting layer is formed, the transmittance of light emission, impurities that affect the light emission efficiency, the flatness for assembling the display, and the heat resistance of the light emitting layer to the heat treatment temperature are glass. Among them, quartz glass is the best, but is not practical at all in terms of cost. For this reason, non-alkali glass, which is intermediate between soda glass and quartz glass, which is thermally inferior to impurities, is generally used.

[0006]

It is known that the above heat treatment for improving the luminance and life characteristics of the light emitting layer is more effective at a high temperature, while the luminance uniformity of the EL device is different from that of the glass substrate. It depends on the parallelism with the opposing glass substrate (which has not been heat-treated and has good flatness), and this depends on the deformation (warpage) of the glass substrate. In the case of the conventional method in which the temperature is simply raised to the set temperature and maintained, the deformation limit temperature is about 590 ° C. due to deformation of the non-alkali glass used for the substrate. At such a temperature, the characteristics of the EL light-emitting layer, particularly the blue-green (SrS: Ce) light-emitting layer, have not yet been sufficiently improved, which is an obstacle to realizing a multi-color and full-color thin-film EL element.

In view of the above problems, an object of the present invention is to provide a method of manufacturing an EL device using an alkaline earth metal sulfide as a light emitting layer, which is excellent in light emission luminance and lifespan, using a non-alkali glass substrate. It is in.

[0008]

In order to achieve the above object, a first electrode, a first insulating layer, a light emitting layer, a second insulating layer and a second electrode formed on a non-alkali glass substrate are provided. In a method of manufacturing a thin film EL element in which electrodes are sequentially laminated, at least after forming a light emitting layer, a first temperature near or below a deformation limit temperature of a non-alkali glass substrate when the light emitting layer is heat-treated at a single temperature. Then, heat treatment is performed at a second holding temperature higher than the first holding temperature.

The first holding temperature is 570 ° C. to 59 ° C.
The temperature is preferably 0 ° C. The second holding temperature is preferably 590 ° C. to 650 ° C. The second holding temperature can be equal to or higher than a deformation limit temperature of the non-alkali glass substrate.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION

Example 1 Strain point (temperature at which viscosity becomes 4 × 10 ¹⁴ poise) 660 ° C.
Using a non-alkali glass as a substrate, the relationship between the warpage of the substrate before and after the heat treatment and the heat treatment method was examined. The substrate has an area of 150 × 220 cm and a thickness of 1.1 mm.

FIG. 4 is a cross-sectional view of a heat treatment apparatus for performing a heat treatment according to the present invention. Inside the heat treatment tube 6 whose outside is covered with a heater 7, a substrate holder 5 having a flat surface and containing a heater is installed. The gas can be replaced by evacuating from the exhaust port 6v and introducing an arbitrary gas from the gas inlet 6i, and the gas can be discharged from the outlet 6o while introducing the gas. Heat treatment with an arbitrary temperature profile can be performed in an arbitrary atmosphere.

The two-step heat treatment according to the present invention is as follows. The substrate 1 is placed in the heat treatment apparatus described above, evacuated to 4 Pa, and purged with 10% H ₂ S / Ar gas. Then, the first holding is performed at a heating rate of 60 ° C./min while flowing gas at atmospheric pressure. After the temperature was raised to a temperature (590 ° C.) and held for 30 minutes, the temperature was raised to a second holding temperature at 60 ° C./min and held for 60 minutes, and then the temperature was lowered to room temperature at a rate of 30 ° C./min. The H ₂ S gas is necessary for the heat treatment of the light emitting layer, and has no effect on the heat treatment of the glass substrate alone.

For comparison, a conventional heat treatment was also performed. The same non-alkali glass substrate was heated at 60 ° C./m
In, the temperature was raised to the conventional temperature for holding, and after holding for 1 hour and 30 minutes, the temperature was lowered to room temperature at 30 ° C./min. The amount of deformation of the substrate after the heat treatment was measured by measuring the maximum gap (warpage) generated at that time by overlapping the flat surface plate. In this experiment, a substrate which was confirmed to have no deformation before heat treatment was used.

FIG. 1 is a graph showing the heat treatment temperature dependency of the deformation amount of the non-alkali glass substrate according to the present invention after the heat treatment. The polygonal line a indicates the case of the two-step heat treatment according to the present invention, the polygonal line b indicates the case of the conventional heat treatment, and the horizontal axis indicates the second holding temperature and the conventional holding temperature. From this graph, it can be seen that the deformation increases with the holding temperature at 590 ° C. or higher in the conventional heat treatment, but the deformation increases with the holding temperature only at 650 ° C. or higher in the two-step heat treatment. Note that the deformation of the non-alkali glass substrate was not affected by the multilayer film from the first electrode layer to the light emitting layer and the second insulating layer.

In the case of a non-alkali glass substrate having a strain point of 600 ° C. and the same size as that described above, the deformation limit temperature in the conventional heat treatment was 570 ° C., but the first holding temperature was 5 ° C.
Deformation could be suppressed by setting the second holding temperature to 630 ° C. at 70 ° C. From the above facts, the effect of the difference in heat treatment on the difference in deformation of the non-alkali glass could not be clarified. However, according to the present invention, since the heat treatment up to the deformation limit temperature, which was the limit in the conventional heat treatment at one holding temperature (single temperature), can be performed without deformation, the non-alkali glass substrate has hitherto been used. The heat treatment of the light-emitting layer, which was not possible due to deformation, can be performed at a higher temperature than in the past, and it can be expected that higher luminance than in the past can be obtained.

The above-described two-step heat treatment was performed on the non-alkali glass substrate (strain point: 660 ° C.) on which the light emitting layer was formed.
An EL device having the above configuration was manufactured as a prototype, and it was confirmed that the luminance and the life of the luminance were improved. First, an ITO layer having a thickness of about 200 nm was formed on a non-alkali glass substrate to form a first electrode layer. Next, a first insulating layer was formed by sequentially laminating an SiO ₂ layer having a thickness of 30 nm and a SiON layer having a thickness of 180 nm by sputtering. Next, using a strontium sulfide (SrS) pellet obtained by doping a strontium sulfide (SrS) matrix with 0.2 mol% of cerium (Ce) as a luminescent center as a raw material, a light emitting layer was formed by electron beam evaporation. A light emitting layer having a thickness of 1200 nm was formed at a substrate temperature of 500 ° C. Next, a 180-nm-thick SiN layer and a 30-nm-thick SiO ₂ layer were sequentially laminated again by sputtering to form a second insulating layer. Here, after performing the above heat treatment, Al was deposited by electron beam evaporation to form a second electrode layer, and the luminance and the life thereof were measured. For comparison, a conventional heat treatment was performed for the heat treatment, and the other EL elements were not changed.

FIG. 2 is a view showing E subjected to a two-step heat treatment according to the present invention.
4 is a graph showing the applied voltage dependence of the luminance of the L element. Curve c is the EL element that has undergone the heat treatment according to the present invention, and curve d is the EL element that has undergone the conventional heat treatment. FIG.
FIG. 5 is a graph showing a change over time in luminance during continuous light emission of an EL element subjected to a two-step heat treatment according to the present invention. Curve e is the EL element that has undergone the heat treatment according to the present invention, and curve f is the EL element that has undergone the conventional heat treatment.

The light-emitting layer base material to which the method for manufacturing an EL device according to the present invention can be applied is not limited to the examples. For example, as the light-emitting layer, SrS, CaS, BaS, MgS, or the like, a mixture thereof, or a film in which these are stacked with ZnS or the like can be used. Further, the rare earth element as the luminescent center is not limited to the above-described embodiment, and for example, a compound such as Ce, Eu, Pr or a mixture thereof can be used.

The insulating layer is not limited to the above embodiment. For example _{SiO 2, SiON, Y 2 O} 3, TiO 2, Al 2 O 3, HfO 2,
Ta ₂ O ₅ , BaTa ₂ O ₅ , SrTiO ₃ , PbTiO _3, ZrO _2, or the like, or a mixed film or a stacked film thereof can be used.

[0020]

According to the present invention, a first electrode, a first insulating layer, a light emitting layer,
In a method for manufacturing a thin-film electroluminescence (hereinafter, referred to as EL) element in which a second insulating layer and a second electrode are sequentially laminated, at least after the formation of the light-emitting layer, the light-emitting layer is heat-treated at a single temperature. After holding at a first holding temperature close to or below the deformation limit temperature of the alkali glass substrate, and then performing a heat treatment at a second holding temperature higher than the first holding temperature, it does not deform at a higher temperature than before. Heat treatment can be performed, improving crystallinity and Ce
It is possible to prevent a change in a crystal field around a light emission center of (cerium) or the like, and to obtain an EL element with improved luminance and life characteristics.

[Brief description of the drawings]

FIG. 1 is a graph showing the heat treatment temperature dependence of the deformation amount of a non-alkali glass substrate according to the present invention after the heat treatment.

FIG. 2 is a graph showing the applied voltage dependence of the luminance of an EL element subjected to a two-step heat treatment according to the present invention.

FIG. 3 is a graph showing a temporal change in luminance during continuous light emission of an EL element subjected to a two-step heat treatment according to the present invention.

FIG. 4 is a cross-sectional view of a heat treatment apparatus that has performed a heat treatment according to the present invention.

FIG. 5 is a cross-sectional view of a typical thin-film EL device.

[Explanation of symbols]

 1a Non-alkali glass substrate 1b Opposite glass substrate 2a First electrode layer 2b Second electrode layer 3a First insulating layer 3b Second insulating layer 4 Light emitting layer 5 Silicone oil 6 Supporting material 7 Furnace 7i Gas inlet 7o Gas outlet 7v Vacuum exhaust port 8 Hot plate 9 External heater

Claims (4)

[Claims] 1. A thin-film electroluminescence (hereinafter referred to as EL) in which a first electrode, a first insulating layer, a light emitting layer, a second insulating layer and a second electrode formed on a non-alkali glass substrate are sequentially laminated. The device manufacturing method)
At least after the formation of the light-emitting layer, after the light-emitting layer is kept at a first holding temperature that is equal to or lower than the deformation limit temperature of the non-alkali glass substrate when the heat treatment is performed at a single temperature, and
Then, a heat treatment is performed at a second holding temperature higher than the first holding temperature. 2. The first holding temperature is from 570 ° C. to 59 ° C.
The thin film EL according to claim 1, wherein the temperature is 0 ° C.
Device manufacturing method. 3. The second holding temperature is from 590 ° C. to 65 ° C.
The method according to claim 1, wherein the temperature is 0 ° C. 4. 4. The method according to claim 1, wherein the second holding temperature is equal to or higher than a deformation limit temperature of the non-alkali glass substrate.