JP2905657B2 - Method for manufacturing electroluminescent element - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing an electroluminescence (EL) device used for, for example, a display of a terminal of various information devices.

[0002]

2. Description of the Related Art Heretofore, an EL element has attracted attention as a device which makes use of a phenomenon of emitting light when an electric field is applied to a phosphor such as zinc sulfide (ZnS) and which constitutes a self-luminous type flat display. In a typical cross-sectional structure of an EL element, a first electrode, a first insulating layer, a light-emitting layer, a second insulating layer, and a second electrode are sequentially stacked and formed on a glass substrate. First
A transparent electrode such as ITO is formed as an electrode, and SiN, Ta ₂ O ₅ or the like is formed as a first insulating layer and a second insulating layer by a sputtering method or the like. As a light emitting layer, ZnS is used as a base material, and Mn, Tb,
Sm or the like is added as a luminescent center element, and formed by vacuum evaporation or sputtering. Depending on the type of the luminescent center, a desired luminescent color can be obtained for the above-described Mn, yellow-orange, Tb, green, and Sm, red. A second insulating layer, a second
Electrodes are formed by forming electrodes.

[0003]

SUMMARY OF THE INVENTION
In the L element, it is necessary to perform a high-temperature heat treatment after forming the light emitting layer to increase the luminance. For example, in a yellow-orange light emitting EL element to which Mn is added, high luminance can be obtained by heat treatment, whereby Mn, which is a luminescence center element, is uniformly diffused into ZnS and substituted at the Zn position, and the crystallinity of ZnS is improved. It is well known. On the other hand, when a luminescent center compound such as a rare earth fluoride such as TbF ₃ is added to ZnS, it is difficult to diffuse the luminescent center compound by heat treatment after forming the luminescent layer.

[0004] Here, a method disclosed in Japanese Patent Publication No. 61-41111, entitled "Method of forming EL thin film" is known. In this method, the luminescent center is uniformly dispersed in the light emitting layer by forming a film in advance by a sputtering method, and after forming the film, heat treatment is performed in a vacuum to recover sputtering damage, improve the crystallinity of the light emitting layer, and improve the crystallinity. The brightness has been increased. In this case, the Ar gas taken in during the sputtering is released from the film and a defect is generated in the film to become a non-radiative coupling center. Therefore, the heat treatment temperature must be suppressed to 500 ° C. or less.
However, when a high-luminance sample that has been heat-treated in a vacuum is continuously emitted, the applied voltage-emission luminance characteristic changes significantly.

On the other hand, for example, Japanese Patent Publication No. 62-137
Japanese Unexamined Patent Publication No. 98, “Method for Manufacturing Thin Film EL Element” is known. In this method, the heat treatment temperature is set to 580 ° C. or higher in vacuum deposited ZnS: Mn, and the unbonded Z
Attempts have been made to reduce n and reduce the change in applied voltage-emission luminance characteristics. However, also in this method, the change rate of the applied voltage with respect to time in the light emission starting voltage is 250 m.
It is as large as V / hr, for example, it changes as much as 20 V when the durability time is 100 hours. As described above, the EL element has a problem to be solved in terms of increasing the luminance and extending the life. The inventors have
As a result of intensive experimental research on the above-mentioned problems, it has been found that the cause of the decrease in light emission luminance and the deterioration of durability is a decrease in the S / Zn ratio in the light-emitting layer having zinc sulfide (ZnS) as a base material due to high-temperature heat treatment in vacuum. As a result, they have provided a novel method for manufacturing an EL element as described below.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a method for manufacturing an EL device having high luminance stability and excellent durability characteristics. It is.

[0007]

Means for Solving the Problems To solve the above-mentioned problems, the present invention comprises an EL in which a luminescent layer is formed on an insulating substrate by using a sulfide as a base material and adding a luminescent center element or compound.
A method of manufacturing a device, wherein after forming the light emitting layer, in a non-oxidizing gas atmosphere containing a sulfide gas, a partial pressure of the sulfide gas is set to 0.02 Torr to 0.6 Torr, and a temperature range is set to 500 ° C. to 65 ° C.
The heat treatment is performed at 0 ° C. The grounds for defining the range of the partial pressure of the sulfide gas and the heat treatment temperature are described below. If the partial pressure of the sulfide gas is less than 0.02 Torr, the supply of the S element is not sufficient. On the other hand, if the partial pressure of the sulfide gas exceeds 0.6 Torr, the supply of the S element becomes excessive and the luminance degradation is large, and the durability is increased. Inferior. When the heat treatment temperature is lower than 500 ° C, the degree of thermal decomposition of the sulfide gas is small and the supply of S element is not sufficient, and the initial luminance decreases. On the other hand, when the heat treatment temperature exceeds 650 ° C, the initial luminance decreases and the breakdown voltage decreases. The margin is also reduced, resulting in poor high luminance stability and durability characteristics.

[0008]

According to the above-mentioned means, the luminescent layer containing sulfide as a base material can be used in the atmosphere even when the S element having a high vapor pressure evaporates due to the high-temperature heat treatment and the unbound Zn element increases. For example, by introducing a gas containing a sulfide gas such as H2 S gas, the S element can be replenished and combined with the unbound Zn element. In addition, damage in the film of the light emitting layer is recovered by the high temperature heat treatment, and the crystallinity is improved. As a result,
Since the occurrence of unstable localized levels due to the S element deficiency can be suppressed, the durability deterioration of the EL element is reduced, and the initial luminance can be improved by improving the crystallinity.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to specific embodiments. FIG. 1 is a schematic diagram showing a cross-sectional structure of an EL device according to the present invention. The EL element 10 is formed by sequentially laminating a first electrode 2, a first insulating layer 3, a light emitting layer 4, a second insulating layer 5, and a second electrode 6 on a glass substrate 1, which is an insulating substrate. . In the EL element 10, light is extracted in the direction of the arrow. In the following, the thickness of each layer is described with reference to the central portion.

Next, a method of manufacturing the above-described EL element 10 will be described below. Glass substrate 1 (thickness 1.1
mm: Non-alkali glass, strain point 650 ° C) on ITO (In
A first electrode 2 was formed by forming a transparent electrode of dium Tin Oxide (indium tin oxide) by a vacuum evaporation method and then processing the electrode into a desired pattern shape by wet etching. Using silicon as a target on top of it, argon,
Using SiON (silicon oxynitride) or Ta ₂ O ₅ (tantalum pentoxide) and Al ₂ O ₃ (aluminum oxide) as a mixed target by high frequency sputtering in a mixed gas atmosphere of nitrogen and oxygen, argon and oxygen Formed by high frequency sputtering in a mixed gas atmosphere of SiON / Ta ₂ O ₅ .Al ₂ O ₃
The first insulating layer 3 consisting of two layers is formed.

Further, a luminescent layer 4 is formed by a high-frequency sputtering method in a mixed gas atmosphere of argon and helium using ZnS containing TbOF at a predetermined ratio as a luminescent center as a target. The luminescent center element or compound is manganese (Mn) or a rare earth and its compound. Thereafter, the inside of the quartz chamber in which the EL element 10 is set is sufficiently evacuated, and H ₂ S (hydrogen sulfide) gas diluted to 20% with Ar (argon), which is a non-oxidizing gas, is introduced. The pressure in the chamber was adjusted to 2 Torr by adjustment, heated to 550 ° C. at a temperature rising time of 10 ° C./min, held for 3 hours, and then gradually cooled to perform heat treatment (annealing). On top of that, the same SiON / Ta ₂ O ₅ .Al
_{A second} insulating layer 5 made of ₂ O ₃ is formed. On top of that, Ga ₂
Using ZnO (zinc oxide) to which O ₃ (gallium oxide) is added as a vapor deposition material, forming a film by ion plating,
Thereafter, the second electrode 6 was formed by processing into a desired shape by wet etching. The thickness of each layer is 200
nm, the first insulating layer 3 and the second insulating layer 5 are 100 nm
The thickness of the light emitting layer 4 is 800 nm, and the thickness of the second electrode 6 is 400 nm in a two-layer structure of 400 nm of Ta ₂ O ₅ .Al ₂ O ₃ .

The EL element 10 manufactured as described above
FIG. 2 shows the change of the light emission luminance characteristic (cd / m ² ) and the light emission start voltage (V) with respect to the durability time (hr) when the device was continuously emitted as the product of the invention. FIG. 2 also shows a change in an EL element manufactured by heat treatment in a vacuum without introducing H ₂ S as a conventional EL element. The driving condition for continuous light emission is frequency 1
KHz, pulse width 40 μsec, and applied voltage were set to an initial light emission start voltage +60 V in a dry nitrogen atmosphere. Looking at the change in the light emission starting voltage, the conventional product sharply changes after 100 hours of the endurance time and decreases by about 40 V after 300 hours, whereas the product of the present invention hardly changes and keeps it at 5 V or less. Have been. Also, regarding the change of the light emission luminance, it can be seen that the product of the present invention has a smaller decrease and has excellent durability characteristics.

In order to obtain the effect as in this embodiment,
As a condition of the heat treatment in H ₂ S, the temperature range is 500 ° C. to 650 ° C.
Need to be controlled. Fig. 3 shows the atmospheric gas pressure as 20%
Initial luminance (cd / m ² ) or withstand voltage (V), which is the initial characteristic when the heat treatment temperature is changed at a diluted H ₂ S gas pressure of 2 Torr.
The relationship was shown. FIG. 4 shows that the atmospheric gas pressure is 20%.
The relationship between the luminance degradation (%) and the emission start voltage change (V), which are the durability characteristics when the heat treatment temperature is changed at a diluted H ₂ S gas pressure of 2 Torr, is shown. It should be noted that the luminance degradation or the change in the light emission start voltage is the same as that described above under the continuous light emission driving condition, and the durability time is 3 hours.
This is a ratio in emission luminance or a deviation in emission start voltage between the EL element and the EL element immediately after manufacture at 00 hours.
Here, if the heat treatment temperature is lower than 500 ° C., the degree of thermal decomposition of H ₂ S is small and the supply of S element is not sufficient, so that the crystallinity of the light emitting layer is not improved and the light emission luminance is not improved.
On the other hand, if the heat treatment temperature is higher than 650 ° C., it is not desirable because the light emission luminance is reduced, the withstand voltage tolerance is reduced, and the durability is deteriorated.

Further, the partial pressure of the sulfide gas is 0.02 Torr to 0.6 To
It is necessary to control the range of the atmospheric gas pressure of the non-oxidizing gas containing the sulfide gas to 0.1 Torr to 3 Torr so that the pressure becomes rr. Figure 5 shows the heat treatment temperature at 550 ° C and the atmospheric gas pressure.
The relationship with the initial luminance (cd / m ² ) or the withstand voltage (V), which is the initial characteristic when the H ₂ S gas pressure was changed by 20% dilution, was shown. FIG. 6 shows that the heat treatment temperature is 550 ° C. and the atmospheric gas pressure is
The relationship between the luminance degradation (%) and the light emission starting voltage (V), which are the durability characteristics when the H ₂ S gas pressure was changed by 20% dilution, was shown. Here, the partial pressure of the sulfide gas is less than 0.02 Torr, that is,
If the atmospheric gas pressure is lower than 0.1 Torr, the supply of S element is not sufficient, and the improvement of the initial luminance is hardly observed. On the other hand, when the partial pressure of the sulfide gas exceeds 0.6 Torr, that is, when the atmospheric gas pressure exceeds 3 Torr, the supply of the S element becomes excessive and the luminance deteriorates. By processing within this temperature range and gas pressure range and controlling the S / Zn ratio of the ZnS light emitting layer to a range of 0.9 to 1.1 near the stoichiometric value, it is possible to obtain an EL device with little deterioration in durability. still,
The stoichiometric value of the ZnS light emitting layer is 1.0, and the S / Zn ratio is EPMA (Electron Probe Micro Analysi
s: electron beam microanalysis).

In the EL element 10 of the above embodiment, H ₂
If the temperature during the heat treatment in S exceeds 550 ° C., the first electrode 2 made of ITO, which is exposed for taking out the electrode, is sulfided, so that the resistance increases. According to our experiments,
The sheet resistance of about 10Ω / □ is 100kΩ at 200nm thickness.
/ □. According to X-ray diffraction, it was confirmed that In ₂ O ₃ was sulfided and In ₂ S ₃ was generated. This sulfidation reaction proceeds not only to the surface of the first electrode 2 made of ITO but also deep inside the exposed portion 2a. Therefore, it is impossible to conduct conduction by etching such a sulfide layer.

In the case of such an oxide film transparent conductive film such as ITO, sulfuration in high-temperature hydrogen sulfide is inevitable. Therefore, a method for preventing the first electrode 2 from having a high resistance will be described below. The first method is, as shown in FIG.
Before the heat treatment in H ₂ S, a ZnO film is formed as a sacrificial layer 7 on the exposed portion 2a of the first electrode 2 made of GaAs. In this method, ZnO is heat-treated in H ₂ S.
Is sulfurized to generate ZnS, but sulfuration of the first electrode 2 made of ITO is prevented. After the heat treatment in H ₂ S and the formation of the second insulating layer 5, the sacrificial layer 7 is etched with dilute acid, so that ITO appears at the exposed portion 2 a of the first electrode 2, thereby avoiding an increase in resistance. In the second method, as shown in FIG. 8, the exposed portion 2a of the first electrode 2 made of ITO is previously formed as a sulfur-resistant metal film before heat treatment in H ₂ S.
For example, the land electrode 8 is formed of Au / Ni. That is, it is necessary to finally form a land electrode 8 for soldering on the exposed portion 2a of the first electrode 2, but before the heat treatment in H ₂ S, the Au / Ni land electrode 8 is formed.
Is a method of preventing sulfidation by forming in advance. or,
A third method is to form the first electrode 2 itself from a metal electrode (for example, Cr, Mo, Ta, Au, etc.) which is originally hardly sulfided. In this method, light emission cannot be taken out from the light emitting layer 4 to the electrode side as in the case where the first electrode 2 made of ITO is used. However, by forming the second electrode 6 with a transparent conductive film, one-sided light emission can be taken out. EL element can be formed, and panel light emission luminance can be improved.

In the above embodiment, the H ₂ S gas diluted to 20% was used, but the partial pressure of the sulfide gas during the heat treatment was set to 0.02 Torr.
It is sufficient that the pressure can be controlled to 0.6 Torr, and it is not limited to 20% diluted H ₂ S gas. That is, the dilution concentration may be arbitrarily selected, and the atmospheric gas pressure may be controlled so that the partial pressure of the sulfide gas is in a desired range. The non-oxidizing gas for dilution is Ar
Other inert gases (He, Ne, Xe,
The same effect can be obtained by using N ₂ ).

[Brief description of the drawings]

FIG. 1 is a schematic view showing a basic structure of an EL device according to a specific example of the present invention.

FIG. 2 is a characteristic diagram showing a relationship between light emission luminance and light emission start voltage with respect to a durability time in an EL element according to the present invention and a conventional EL element.

FIG. 3 is a characteristic diagram showing initial characteristics (initial luminance and breakdown voltage margin) when the heat treatment temperature is changed while the atmospheric gas pressure is constant in the manufacture of the EL device according to the example.

FIG. 4 is a characteristic diagram showing durability characteristics (luminance degradation and light emission start voltage) when the heat treatment temperature is changed while the atmospheric gas pressure is constant in the manufacture of the EL device according to the example.

FIG. 5 is a characteristic diagram showing initial characteristics (initial luminance and withstand voltage tolerance) when the heat treatment temperature is constant and the atmospheric gas pressure is changed in the manufacture of the EL device according to the example.

FIG. 6 is a characteristic diagram showing durability characteristics (luminance degradation and light emission starting voltage) when the heat treatment temperature is constant and the atmospheric gas pressure is changed in the manufacture of the EL device according to the example.

FIG. 7 is a plan view showing a state in which a sacrificial layer is formed on a first electrode during a process in a method for manufacturing an EL element according to the present invention.

FIG. 8 is a plan view showing a state in which a land electrode is formed on a first electrode during a process in a method for manufacturing an EL element according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Glass substrate (insulating substrate) 2 ... 1st electrode 3 ... 1st insulating layer 4 ... Light emitting layer 5 ... 2nd insulating layer 6 ... 2nd electrode

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Yoshiyasu Ando 1-1-1, Showa-cho, Kariya-shi, Aichi Japan Inside Denso Co., Ltd. (72) Inventor Nobue Ito 1-1-1, Showa-cho, Kariya-shi, Aichi Japan Nihon Denso (56) References JP-A-2-306585 (JP, A) JP-A-57-124883 (JP, A) JP-A-4-332494 (JP, A) JP-A-4-121992 (JP, A) A) (58) Field surveyed (Int. Cl. ⁶ , DB name) H05B 33/10

Claims (1)

(57) [Claims] 1. A method for manufacturing an electroluminescent element in which a light-emitting layer in which a sulfide is used as a base material and a light-emitting central element or a compound is added is formed on an insulating substrate, the method including a sulfide gas after the light-emitting layer is formed. In a non-oxidizing gas atmosphere, the partial pressure of the sulfide gas is set to 0.02 Torr to 0.6 Torr,
A method for producing an electroluminescent device, wherein the heat treatment is performed at a temperature in a range of 500 ° C. to 650 ° C.