JPH1050476A - Manufacture of thin-film el element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve and stabilize the brightness and the life properties of a thin-film EL element produced by forming a first electrode, a first insulating layer, an electroluminescent layer of a group II metal sulfide, a second insulating film, and a second electrode on an insulating substrate. SOLUTION: After an electroluminescent layer 4 is formed on an insulating substrate 1 by an electron beam evaporation method, the resultant substrate is inserted in a thermally treating apparatus, the apparatus is evacuated to 4 Pa or lower, a gas exchange is carried out, and heating treatment is carried out in an atmosphere containing sulfur. After that, a second insulating layer 5 and a second electrode 6 are successively formed. By the evacuation, harmful molecules absorbed on the surface of the electroluminescent layer are desorbed and the surface is stabilized by the treatment in the sulfur-containing atmosphere. Moreover, oxygen intake from adsorptive molecules is lessened, and the brightness property and the life property are improved. It is more preferable that the vacuum-evacuation and the gas exchange be repeated and that preheating of the treatment apparatus and a substrate holder be carried out.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thin film electroluminescent element (hereinafter referred to as a thin film EL) used for a thin display device.
(Hereinafter referred to as an element), and in particular, a heat treatment method after forming the light emitting layer.

[0002]

2. Description of the Related Art A thin-film EL element exhibiting electroluminescence by applying a voltage has high luminance emission, high-speed response,
Because of its excellent features such as a wide viewing angle, thinness and light weight, and high resolution, it has attracted attention as a thin display device. The luminescent color of the thin-film EL element is zinc sulfide (Zn) constituting the luminescent layer.
S) or a semiconductor base material of a group II metal sulfide such as strontium sulfide (SrS) and a luminescent center to be added can be combined. For example, yellow-orange emission is obtained by adding manganese (Mn) as a luminescent center to a ZnS base material. Is obtained.

[0003] However, the one which has reached a practical level of luminance at present is ZnS: M, in which ZnS is doped with Mn.
n is a monocolor display that emits yellow-orange light. Therefore, thin-film EL for multi-color and full-color
The development of devices is strongly desired. Alkaline earth metal sulfides, especially strontium sulfide (SrS) and calcium sulfide (CaS), are promising base materials, and cerium (Ce), europium (Eu), and praseodymium (Pr), which are rare earths, are added as emission centers. By doing, respectively, blue-green (SrS: Ce) and red (CaS:
Eu), white (SrS: Ce, Eu), white (SrS:
It is known to emit light in Pr).

[0004]

The EL light emitting layer including the alkaline earth metal sulfide is generally subjected to a heat treatment in a sulfur atmosphere as a post-treatment after the film formation in order to improve the luminance and the life characteristics. I have. At this time, the substrate (element substrate) is taken out to the atmosphere in order to transfer the substrate from the light emitting layer film forming apparatus to the heat treatment apparatus and from the heat treatment apparatus to the subsequent insulating film forming apparatus.

[0005] However, the alkaline earth metal sulfide EL light emitting layer is composed of carbon monoxide gas (CO) and carbon dioxide gas (CO ₂ ).
It reacts very well with water and water vapor (H ₂ O) to cause a change in composition, and even when heat treatment is performed in a sulfur atmosphere, stable light emission characteristics may not be obtained. Further, when a small amount of oxygen such as water vapor or carbon dioxide gas is adsorbed on the surface of the light emitting layer, oxygen atoms on the surface of the light emitting layer move by applying a voltage, and the crystal field around the light emission center such as cerium (Ce) changes. Changes in device characteristics (color display, etc.),
The problem is that the threshold voltage rises and the life characteristics deteriorate.

There is a method of using an in-line manufacturing apparatus in which the substrate is not taken out of the apparatus in order to prevent adsorbed gas such as water vapor from adhering when the element substrate is moved between apparatuses, but expensive equipment is required. Product costs are higher. The present invention has been made in view of the above-described problems, and a thin-film EL device having a light emitting layer of a Group II metal sulfide having excellent emission luminance and life characteristics and having stable characteristics does not require expensive equipment. An object of the present invention is to provide a manufacturing method which can be easily obtained.

[0007]

In order to solve these problems, the present invention provides at least a first electrode, a first insulating layer, a light emitting layer made of a Group II metal sulfide, and a second insulating layer on an insulating substrate. In the method for manufacturing a thin-film EL element in which a layer and a second electrode are stacked, a substrate on which a light-emitting layer is formed by electron beam evaporation is inserted into a heat treatment apparatus, the inside of the heat treatment apparatus is evacuated, and then a gas containing sulfur. And heat-treats the light-emitting layer.

In this case, carbon dioxide and water vapor adsorbed when the substrate is exposed to the atmosphere are released by vacuum evacuation, and then heat-treated in an atmosphere containing sulfur, whereby the sulfur reacts and the device The surface is stabilized and sulfur is incorporated into the crystals. In particular, if the ultimate vacuum in the heat treatment apparatus during evacuation is set to 4 Pa or less, the residual air in the heat treatment apparatus becomes 1 ppm or less, and heat treatment in a sulfur atmosphere is not hindered.

The evacuation and gas replacement may be repeated twice or more. By doing so, the adsorbed carbon dioxide and water vapor are further desorbed by vacuum evacuation, the residual atmospheric concentration in the heat treatment apparatus is further reduced, and the sulfur atmosphere treatment is completely performed. Further, gas replacement before evacuation may be performed with a rare gas.

[0010] A rare gas is easier to handle than a toxic hydrogen sulfide gas or the like. When inserting and removing the substrate, the apparatus components such as the substrate holder in the heat treatment apparatus and the inner wall of the apparatus are preheated in a temperature range of 60 to 200 ° C. If you do that,
The amount of adsorbed gas brought into the heat treatment apparatus can be reduced, and the amount of oxygen taken into the EL element can be reduced.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention provides a method of manufacturing a thin film EL device having a group II metal sulfide light-emitting layer, which comprises removing harmful molecules adsorbed by vacuum evacuation and then treating the atmosphere with sulfur. Excellent luminous brightness and life characteristics,
Moreover, the present invention provides a manufacturing method in which a thin-film EL element having stable characteristics can be easily obtained. This will be described below with reference to the drawings. [Example 1] An EL device using strontium sulfide (SrS) doped with cerium (Ce) as a light emitting layer was manufactured.

FIG. 3 shows a thin film EL according to an embodiment of the present invention.
It is sectional drawing of an element. Transparent ITO (indium tin oxide) serving as a first electrode 2 on a glass substrate 1, a first insulating layer 3
A silicon oxide (SiO ₂ ) film, a silicon oxynitride (SiON) film, a light emitting layer 4, a silicon oxide (SiO ₂ ) film as a second insulating layer, and a silicon oxynitride (SiON) film are sequentially laminated, and the surface thereof is formed. In addition, an aluminum electrode serving as the second electrode 6 is provided. First electrode 2 and second electrode 6
An AC voltage is applied from the drive power supply 7 during the period to emit light.

First, a glass substrate having a film thickness of about 2
A 00 nm ITO (indium tin oxide) film is formed,
One electrode. Subsequently, a 30 nm-thick S
iO _TwoAnd 180 nm thick Si_ThreeN_FourAre formed in order,
The first insulating layer was used. Next, cerium (Ce) was
l% doped strontium sulfide (SrS) pellets
At a substrate temperature of 500 ° C. by electron beam evaporation.
A light emitting layer with a thickness of 1000 nm was formed. Next, the light emitting layer
Is subjected to a heat treatment.

FIG. 4 shows a heat treatment apparatus used for heat treatment of the light emitting layer.
Shown in Quartz tube heat treatment furnace 1 heated by infrared heater
The thin-film EL element 8 formed up to the light-emitting layer is placed on the substrate holder 9 and inserted from an insertion opening (not shown) of the substrate 0. The gas introduction valve 11a and the exhaust valve 11b are closed, the evacuation valve 11c is opened, and the heat treatment furnace 10 is
The inside is evacuated to 4 Pa. Vacuum evacuation valve 11c
Is closed, the gas introduction valve 11a is opened, and the gas is replaced with 10% hydrogen sulfide (H ₂ S) / argon (Ar) gas.
Heat treatment was performed at 630 ° C. for 30 minutes at an atmospheric pressure (1 × 10 ⁵ Pa).

Thereafter, the thickness 18 is again formed by the sputtering method.
0 nm Si ₃ N ₄ and 30 nm thick SiO ₂ were sequentially formed to form a second insulating layer, and aluminum was further deposited by electron beam evaporation to form a second electrode. FIG. 1 shows the luminance characteristics of the EL element of Example 1 having undergone such a manufacturing process and of a comparative example in which vacuum evacuation was not performed before heat treatment. The horizontal axis is the driving voltage, and the vertical axis is the light emission luminance.

In the EL element of Example 1, the voltage for obtaining the same luminance is lower than that of the comparative example by about 25 V. Also,
When compared at the same drive voltage, the luminance is improved by orders of magnitude. FIG. 2 shows the life characteristics. Since the acceleration test can be performed by increasing the frequency of the applied voltage, the abscissa indicates the aging time expressed in relative time, and the ordinate indicates the light emission luminance. The test was actually performed at 500 Hz.

In the EL device of Example 1, a decrease in the luminance level is small, and a remarkable extension of the life is recognized. In this case as well, the substrate after the formation of the light emitting layer is taken out into the air, heat-treated, and taken out into the air to form the second insulating film. However, according to the method of the present invention,
Carbon dioxide gas and water vapor adsorbed by evacuation are released,
Thereafter, by performing a heat treatment in an atmosphere containing sulfur, the sulfur reacts to stabilize the element characteristics.

Oxygen adsorbed on the surface of the light-emitting layer is also replaced by sulfur to prevent a change in the crystal field around the light-emitting center such as Ce, thereby lowering the threshold voltage and improving the life characteristics. It is considered to have been realized. The evacuation during the heat treatment is preferably 4 Pa or less. With this degree of vacuum evacuation, when the pressure is reduced to 1 atm by introduction of an inert gas or the like, the residual air becomes 1 ppm or less, and the heat treatment in the sulfur atmosphere is not adversely affected. Further, it is important that the atmosphere of the heat treatment contains sulfur vapor. In addition to the addition of hydrogen sulfide, the sulfur may be heated and the vapor may be sent. [Embodiment 2] Under the same conditions and procedures as in Embodiment 1, vacuum evacuation up to ⁴ Pa and substitution of 10% H ₂ S / Ar gas were performed twice at the time of heat treatment of the light emitting layer, and at atmospheric pressure (1 × 10 ⁵ Pa). A gas flow was performed, and a heat treatment was performed at 630 ° C.
This was designated as Example 2. The luminance characteristics at this time are shown in FIG. 1, and the life characteristics are shown in FIG.

In the EL element of Example 2, the voltage at which the same luminance is obtained is lower than that of the EL element of Example 1, and the luminance is improved when compared with the same driving voltage. In FIG. 2 as well, the EL element of Example 2 has a smaller decrease in luminance level than the EL element of Example 1 and has an extended life. It is understood that the characteristics are further improved by repeating the evacuation and the gas replacement. Further, it was found that the atmosphere during the final heat treatment needs to contain sulfur, but the gas replacement before vacuuming may be a rare gas such as argon. Example 3 After forming a light emitting layer in the same procedure as in Example 1, the substrate was taken out at 120 ° C.
It is inserted into a heat treatment apparatus heated to the same temperature using a substrate holder or the like heated to 0 ° C., and after performing evacuation and gas replacement as in Example 1, heat treatment is performed.
The substrate was taken out at a temperature of 100 ° C., and attached to an insulating film forming apparatus heated to 120 ° C. in advance to form a film.

FIG. 1 also shows the luminance characteristics of the EL device of the third embodiment. In the EL element of Example 3, the voltage at which the same luminance is obtained is lower than that of the EL element of Example 1, and the luminance is improved when compared with the same driving voltage. Although the results of the aging test of the EL element of Example 3 are not shown in FIG. 2 to avoid complicating the drawing, the decrease in the luminance level is smaller than that of the EL element of Example 1 and the life is prolonged. Was observed.

As described above, when the substrate is inserted and removed, the substrate of the light emitting layer film forming apparatus, the heat treating apparatus, the substrate of the insulating film forming apparatus, the substrate holder, the inner wall of the apparatus, and the accessory parts are pre-heated to be brought into the heat treating apparatus. Adsorbed gas can be reduced and its adverse effects can be avoided. The preheating temperature is preferably in the range of 60 to 200C. At a temperature lower than 60 ° C., almost no desorption of water occurs, and the effect of preheating is not seen. At a high temperature exceeding 200 ° C., it is difficult to take out and insert the substrate.

In the above embodiment, an example of SrS has been given.
The light emitting layer used in the EL device of the present invention is not limited to the above embodiment. For example, the light-emitting layer can also be CaS, BaS, MgS, or the like, a mixed film thereof, or a film in which ZnS or the like is stacked therewith. Further, the rare earth metal as the luminescent center is not limited to Ce in the above embodiment. For example, Eu,
Examples include compounds such as Pr and mixtures thereof.

The method of forming the light emitting layer is not limited to the electron beam evaporation method, but may be a sputtering method or an atomic layer epitaxial method (ALE). Further, the insulating layer is not limited to the above embodiment. For example, Si
O ₂ , SiON, Y ₂ O ₃ , TiO ₂ , Al ₂ O ₃ , H
fO ₂ , Ta ₂ O ₅ , BaTa ₂ O ₅ , SrTiO ₃ ,
Examples include PbTiO ₃ , ZrO ₂ , and a mixed film or a laminated film thereof.

[0024]

As described above, according to the method for manufacturing a thin-film EL device of the present invention, the substrate on which the light emitting layer is formed is inserted into the heat treatment apparatus, and the inside of the heat treatment apparatus is evacuated. By performing gas replacement with a gas containing and heat-treating the light-emitting layer, the adsorbed gas is desorbed, and the incorporation of oxygen atoms into the EL element is reduced, improving characteristics such as threshold voltage and lifetime, and stabilizing A thin-film EL element can be obtained.

[Brief description of the drawings]

FIG. 1 is a diagram showing light emission luminance characteristics of thin film EL devices of Examples 1, 2, and 3 of the present invention and a comparative example.

FIG. 2 is a luminescence lifetime characteristic diagram of the thin film EL devices of Examples 1 and 2 of the present invention and a comparative example.

FIG. 3 is a sectional view of a thin film EL element.

FIG. 4 is a configuration diagram of a heat treatment apparatus that implements the manufacturing method of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Glass substrate 2 First electrode 3 First insulating layer 4 Light emitting layer 5 Second insulating layer 6 Second electrode 7 Drive power supply 8 Thin film EL element 9 Substrate holder 10 Heating furnace 11a, b, c Valve 12 Vacuum pump 13 Replacement gas Or atmosphere gas 14 Exhaust

Claims (5)

[Claims] 1. A method of manufacturing a thin-film EL device in which at least a first electrode, a first insulating layer, a light emitting layer made of a Group II metal sulfide, a second insulating layer and a second electrode are laminated on an insulating substrate. In the method, the substrate on which the light-emitting layer is formed by electron beam evaporation is inserted into a heat treatment apparatus, the inside of the heat treatment apparatus is evacuated, and then the gas is replaced with a gas containing sulfur, and the heat treatment of the light-emitting layer is performed. Of manufacturing a thin-film EL element. 2. The method according to claim 1, wherein the ultimate degree of vacuum in the heat treatment apparatus during evacuation is set to 4 Pa or less so that the residual air in the heat treatment apparatus is 1 ppm or less. Method. 3. The method according to claim 1, wherein the evacuation and the gas replacement are repeated at least twice. 4. The method according to claim 3, wherein gas replacement before evacuation is performed with a rare gas. 5. A thin film wherein a device part such as a substrate holder in a heat treatment device and an inner wall of the device are preheated in a temperature range of 60 to 200 ° C. when inserting and removing a substrate. Manufacturing method of EL element.