JP2837359B2 - Method for manufacturing thin film EL 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 a thin-film EL device in which a change in emission luminance-applied voltage characteristic with a lapse of driving time is small and a light emission starting voltage is relatively low, and more particularly to a method of manufacturing an EL light emitting layer. About the method.

[0002]

2. Description of the Related Art A thin-film EL (electroluminescent) element is a light-emitting element having excellent performance such as a self-luminous type, a high response speed, and a long life.
(Factory Automation) It has been put to practical use as information display means for equipment. The EL light-emitting layer of the thin-film EL element in which the EL light-emitting layer is disposed between two electrodes, at least one of which has a light-transmitting property, is made of an EL light-emitting layer material in which a light-emitting center is added to a base material. The emission color is determined by the layer material. For example, in order to obtain yellow-orange light emission, an EL light emitting layer material in which Mn is added as a light emission center to ZnS as a base material is used.

The EL light emitting layer is generally formed by a vapor deposition method, for example, EB.
(Electron beam) It is created by an evaporation method. Specifically, first, a pellet made of an EL light emitting layer material is prepared, and the pellet and a substrate on which the EL light emitting layer is to be formed are arranged in a vacuum chamber. Next, the inside of the vacuum chamber is depressurized to heat the pellets, and the evaporated EL light emitting layer material is adhered to the substrate and deposited to a desired thickness. In the case of the EB evaporation method, the heating of the pellet is performed by an electron beam.

[0004] Heat treatment is applied to the EL light emitting layer formed by the vapor deposition method. This heat treatment is performed to improve the crystallinity of the EL light emitting layer and improve the light emitting characteristics. For example, it is performed in order to increase the luminance, lower the light emission start voltage, and reduce the luminance degradation during long-time driving. Since the higher the heat treatment temperature, the better the effect is obtained, a substrate on which an EL light emitting layer and two electrodes interposing the EL light emitting layer are formed, for example, a glass substrate,
Those with a high strain point temperature are selected.

[0005] The above-mentioned strain point temperature means that the viscosity is 10 ¹³ pois.
This is the temperature at the time of e, which is the upper limit temperature during the heat treatment for removing the strain in the glass. When the glass is heat-treated at a temperature lower than the strain point temperature, no viscous flow occurs and no warpage occurs. Conversely, when heat treatment is performed at a temperature higher than the strain point temperature, deformation occurs.

The heat treatment performed after forming the EL light emitting layer is performed at a temperature of 10 ° C. to 50 ° C. higher than the strain point temperature of the glass substrate used.
Only done at lower temperatures. For example, the heat treatment is performed at 630 ° C. when non-alkali glass (strain point temperature 640 ° C.) is used, and at 450 ° C. when soda lime glass (strain point temperature 490 ° C.) is used.

[0007] By performing the heat treatment as described above, the above-described light emitting characteristics are improved. However, in order to reduce the manufacturing cost, when soda lime glass, which is less expensive than non-alkali glass, is used. Since the strain point temperature is low, the heat treatment is performed at a relatively low temperature. For this reason,
The following inconvenience occurs.

FIG. 6 is a graph showing the relationship between the light emission luminance and the applied voltage of a conventional thin film EL device. The vertical axis indicates the light emission luminance, and the horizontal axis indicates the applied voltage. The solid line S3 indicates the characteristics before long-time driving, and the broken line S4 indicates the characteristics after long-time driving. .

A thin-film EL element having an EL light-emitting layer that has been heat-treated at a relatively low temperature is applied with a voltage having an asymmetrical pulse waveform, which is close to actual driving conditions and is caused by variations in characteristics of a driver IC (Integrated Circuit). If driving is performed for a long time in such a state, the emission luminance-applied voltage curve changes from the state shown by the solid line S3 to the state shown by the broken line S4, that is, the rise of the emission luminance accompanying the voltage application shifts to a lower voltage side. . Hereinafter, such a phenomenon is referred to as “N-shift phenomenon”. Therefore, before performing the long-time driving, the voltage Vth is applied after the long-time driving is performed, even though the voltage at which the desired luminance L1 during non-light emission is obtained is determined as the light-emission starting voltage Vth. Then, when the light emission state is not performed, the luminance becomes L2 (> L1), the displayed image is not completely erased, and the image remains unerased. Hereinafter, such a phenomenon is referred to as a “burn-in phenomenon”.

A method for eliminating such a seizure phenomenon caused by the N-shift phenomenon is disclosed in JP-A-61-42893, JP-A-61-68892, and JP-A-61-68892.
No. 232597. In each of these disclosed examples, H ₂ S is introduced during the entire period in which the EL light-emitting layer is formed by a vapor deposition method. It is disclosed that this eliminates the N-shift phenomenon and the seizure phenomenon.

[0011]

According to the disclosures of the above three publications, when an EL light emitting layer is formed in an H ₂ S atmosphere, the N-shift phenomenon is eliminated and the burning phenomenon is eliminated. It was confirmed that the voltage Vth increased. In order not to apply a large load to a driver IC used as a driving circuit of the thin film EL element, the light emission starting voltage V
Although it is preferable that th be 200 V or less, according to the disclosed example of the above publication, the light emission starting voltage Vth exceeds 200 V, and a high withstand voltage driver IC is required, and the manufacturing cost of the thin film EL element is high. Become.

An object of the present invention is to provide a method of manufacturing a thin film EL device in which a change in emission luminance-applied voltage characteristic due to long-time driving is small and a light emission start voltage is relatively low.

[0013]

According to the present invention, an EL light emitting layer made of an EL light emitting layer material containing Mn or ZnS to which a rare earth element is added is disposed between two electrodes, at least one of which has translucency. In the method for manufacturing a thin-film EL device, the EL light-emitting layer is formed by depositing an EL light-emitting layer material by a vapor deposition method, and has a predetermined thickness D selected from the total thickness of the EL light-emitting layers. A method for manufacturing a thin film EL device, wherein the method is formed in a gas atmosphere containing: Further, according to the present invention, the predetermined thickness D is 0
<D ≦ 200 nm is selected.
Further, according to the present invention, the predetermined thickness D is 0 <D ≦ 5 nm.
It is characterized by being selected in the range of. Further, the present invention is characterized in that the gas containing the S element is H ₂ S gas.

[0014]

According to the present invention, there is provided a thin film EL device in which an EL light emitting layer made of an EL light emitting layer material containing ZnS to which Mn or a rare earth element is added is disposed between two electrodes, at least one of which has translucency. The EL light emitting layer is formed by heating the EL light emitting layer material, depositing the EL light emitting layer material evaporated by the heating on a substrate on which the EL light emitting layer is to be formed, and depositing the EL light emitting layer material to a desired thickness. Up to a predetermined thickness D selected to be smaller than the total thickness of the light emitting layer, it is formed in a gas atmosphere containing an S element, preferably in an H ₂ S gas atmosphere.

By performing the deposition in a gas atmosphere containing the S element, the N-shift phenomenon in which the light emission luminance-applied voltage curve shifts to a lower voltage side with time is eliminated, thereby driving for a long time. Later, it was confirmed that the displayed image was completely erased even with the light emission start voltage Vth set before performing the long-time driving, and the burning phenomenon in which the image disappears was eliminated. In addition, by setting the period for introducing the gas containing the S element to the period for forming the thickness D selected to be smaller than the total thickness of the EL light emitting layer, the burning phenomenon caused by the N-shift phenomenon can be eliminated. It was confirmed that the light emission start voltage Vth could be reduced.

Preferably, the thickness D is 0 <D ≦
The light emission start voltage Vth can be set to 200 V or less, so that it is not necessary to use a driver IC having a high withstand voltage.

Preferably, the thickness D is 0 <D ≦
The light emission start voltage Vth is selected to be in the range of 5 nm, whereby the emission start voltage Vth can be set to be substantially the same as the case where the deposition is performed in a vacuum atmosphere containing no S element.

Therefore, there is little change in the light emission luminance-applied voltage characteristic due to long-time driving, and the light emission starting voltage Vt
A thin-film EL element having a relatively low h is obtained. The total thickness of the EL light emitting layer is selected so as to obtain sufficient EL light emitting characteristics, and is generally formed to a thickness of about 500 nm to 1000 nm.

[0019]

FIG. 1 is a sectional view showing the structure of a thin film EL device 1 manufactured by a method for manufacturing a thin film EL device according to one embodiment of the present invention. The thin-film EL element 1 includes a light-transmitting substrate 2, a transparent electrode 3, a first insulating layer 4, an EL light-emitting layer 5, a second insulating layer 6, and a metal electrode 7. The translucent substrate 2 is realized by, for example, soda lime glass, and a transparent electrode 3 is formed on one surface 2a. Transparent electrode 3
Is formed of, for example, an ITO (indium tin oxide) film, has a thickness of 150 nm, and is formed in a plurality of parallel belt shapes. The first insulating layer 4 is formed on the surface 2a of the translucent substrate 2 and the transparent electrode 3, and is formed of, for example, SiO
₂ film and a Si ₃ N ₄ film. SiO ₂ film on the one surface 2a and the transparent electrode 3 of the light-transmitting substrate 2, the SiO ₂
Si ₃ N ₄ films are respectively formed on the films, and
nm, having a thickness of 200 nm.

The EL light emitting layer 5 is formed on the first insulating layer 4 and is realized by an EL light emitting layer material in which ZnS is used as a base material and Mn is added to ZnS as a light emission center. The EL light emitting layer 5 is generally formed to a thickness of about 500 nm to 1000 nm. In this example, the EL light emitting layer 5 was formed to a thickness of 850 nm as described later.

The second insulating layer 6 is formed on the EL light-emitting layer 5 and comprises, for example, a Si ₃ N ₄ film and a SiO ₂ film.
An Si ₃ N ₄ film is provided on the EL light emitting layer 5 and an S ₃ N ₄ film is provided on the Si ₃ N ₄ film.
An SiO ₂ film is formed, each having a thickness of 100 nm, 3
It has a thickness of 5 nm. The metal electrode 7 is formed on the second insulating layer 6 and is realized by, for example, an Al film to have a thickness of 600 nm.
m, and is formed in a plurality of strips in a direction orthogonal to the transparent electrode 3.

FIG. 2 is a process chart showing a method of manufacturing the thin-film EL element 1. FIG. 3 is a side view showing the vapor deposition device 11 used when forming the EL light emitting layer 5. In step a1, a transparent electrode 3 is formed on one surface 2a of the light transmitting substrate 2. In step a2, the first insulating layer 4 is formed on the one surface 2a of the translucent substrate 2 and the transparent electrode 3.
This is because the SiO ₂ film first targets Si, and A
formed by a reactive sputtering method using r: O ₂ = 50: 50 (molar ratio) as a sputtering gas;
_{On the two} films, a Si ₃ N ₄ film is formed by a reactive sputtering method using Si as a target and N ₂ as a sputtering gas.

In step a3, an EL light emitting layer 5 is formed on the first insulating layer 4. First, 0.4 wt% of Mn is added to ZnS.
A mixed pellet 13 is prepared. The substrate 13 on which the pellet 13 and the EL light-emitting layer 5 are to be formed, that is, the substrate on which the steps up to the step a2 have been completed, is arranged at a predetermined position in the bell jar 12 of the vapor deposition apparatus 11. The pellet 13 is disposed below the bell jar 12, and the substrate 14 is disposed above. The bell jar 12 is an outer wall of a tank in which vapor deposition is performed.
Inside the bell jar 12, gas inside is exhausted from an exhaust port 18 and H ₂ S gas is introduced from an insertion port 17. For example, the partial pressure is 3.3 × 10 ⁻⁴ Pa or 8.6 × 1.
It is set to 0 ^-4 Pa. In such a state, when the substrate 14 is heated by the heater 15 and the pellet 13 is heated by the EB gun 16, the EL light emitting layer material constituting the pellet 13 evaporates by heating and adheres to the surface of the substrate 14. Thus, by depositing to a desired thickness, the EL
The light emitting layer 5 is formed. The vapor deposition in the H ₂ S atmosphere is performed up to a predetermined thickness D selected to be smaller than 850 nm, which is the total thickness of the EL light emitting layer 5. That is, film thickness 0
To a film thickness D in an H ₂ S atmosphere,
Deposition is performed in a vacuum atmosphere containing no H ₂ S up to 50 nm.

[0024] As a comparative example, 850 nm to H ₂
An example performed in an S atmosphere and an example performed in a vacuum atmosphere containing no H ₂ S were also performed.

In step a4, a second insulating layer 6 is formed on the EL light emitting layer 5. First, the Si ₃ N ₄ film is formed on the first insulating layer 4.
It is formed in the same manner as the Si ₃ N ₄ film of, SiO ₂ film to the the Si ₃ N ₄ film on are formed in the same manner as the SiO ₂ film of the first insulating layer 4. Further, after forming the second insulating layer 6, 450
The heat treatment is performed in a vacuum atmosphere of ° C. This is performed to improve the crystallinity of the EL light emitting layer 5 to improve the light emitting characteristics. In step a5, a metal electrode 7 is formed on the second insulating layer 6.
Is formed.

FIG. 4 shows that the total thickness of the EL light emitting layer 5 is 850 nm.
, H was deposited in an H ₂ S atmosphere.
₅ is a graph showing a relationship between a 2S-introduced film thickness D and a light emission start voltage Vth of the thin film EL element 1 formed at that time.
The solid line S1 indicates the case where the partial pressure of H ₂ S is 3.3 × 10 ⁻⁴ Pa, and the broken line S2 indicates the case where the partial pressure of H ₂ S is 8.6 × 10 ⁻⁴ Pa. It can be seen that in any case of the partial pressure, the light emission starting voltage Vth tends to increase as the film thickness D increases. When the light emission start voltage Vth increases, a driver IC that drives the thin-film EL element 1 needs to have a high withstand voltage, and the manufacturing cost of the thin-film EL element 1 increases.

In order to avoid such inconvenience, 85
It is preferable to perform vapor deposition in a H ₂ S atmosphere to a thickness D selected to be smaller than 0 nm, and to perform vapor deposition in a vacuum atmosphere containing no H ₂ S from the thickness D to 850 nm.

In order to reduce the increase in manufacturing cost due to the use of a driver IC having a high withstand voltage, the light emission starting voltage Vth is preferably set to 200 V or less as described above. It is preferable to select the range of ≦ 200 nm.

Still more preferably, the thickness D is 0 <
It is selected in the range of D ≦ 5 nm. As a result, a light emission start voltage Vth substantially equal to that obtained when vapor deposition is performed in a vacuum atmosphere containing no H ₂ S can be obtained.

FIG. 5 shows an H ₂ S-introduced film thickness D and an accelerated test in which the thin film EL element 1 produced at that time is subjected to an acceleration test in which substantially the same luminescence characteristics as when driven for a long time are obtained. 5 is a graph showing a relationship between a light emission luminance L and a light emission start voltage Vth.

In the acceleration test, a pulse drive having a frequency of 30 Hz is performed on the assumption that a voltage having an asymmetrical pulse waveform is actually applied.
A voltage was applied to any one of the electrodes so as to have an amplitude of (Vth + 40) V, and a voltage was applied to the other electrode such that the amplitude was also (Vth + 10) V at a frequency of 30 Hz. In addition, driving was performed at an environmental temperature of 55 ° C. for 40 hours. Note that the light emission start voltage Vth was an applied voltage value at which the light emission luminance was 3.4 cd / m ² before the acceleration test was performed.

Symbols 21 and 22 indicate a partial pressure of H ₂ S of 3.3.
× The case of a 10 ^-4 Pa, reference numeral 23 indicates a case of a partial pressure of 8.6 × 10 ^-4 Pa of H ₂ S, respectively,
Reference numerals 21 and 23 indicate the case where (Vth + 40) V is applied to the transparent electrode 3 and a pulse voltage of (Vth + 10) V is applied to the metal electrode 7 (A). Reference numerals 22 and 24 indicate (Vth + 10) V to the transparent electrode 3. And (Vth + 4)
(B) shows a case where a pulse voltage of 0) V is applied. If the light emission luminance L at the light emission start voltage Vth after the acceleration test is 5 cd / m ² or less, there is no problem in use, that is, since the seizure phenomenon due to the N-shift phenomenon does not occur, the thickness D is 5,200. , 400, 650 and 85
It can be seen that there is no problem in any case of 0 nm. That is, 3.4 cd /, which is the luminance L before the acceleration test is performed.
A light emission luminance substantially equal to m ² is obtained. When the thickness D is 0, the light emission luminance L is increased, which indicates that the image sticking phenomenon occurs. Table 1 below
Shows the emission luminance L when the thickness D is 0 and when the thickness D is 5 nm.

[0033]

[Table 1]

From the above, it can be seen that ZnS: Mn
In the thin-film EL device 1 having the L light emitting layer 5, in order to eliminate the seizure phenomenon caused by the N-shift phenomenon, it is preferable that the EL light emitting layer 5 is formed by vapor deposition in an H ₂ S atmosphere. It can be seen that in order to reduce the voltage Vth, it is preferable to vapor-deposit in an H ₂ S atmosphere to a thickness D which is smaller than the total thickness of the EL light-emitting layer 5.

In order to suppress the emission start voltage Vth from increasing, the thickness D is preferably set to 0 <D ≦ 200 nm, and more preferably, the thickness D is set to 0 <D.
By setting ≦ 5 nm, a light-emission starting voltage Vth similar to that obtained when vapor deposition is performed in a vacuum atmosphere can be obtained.

Therefore, it is possible to produce a thin-film EL element having stable emission luminance-applied voltage characteristics even after long-time driving without increasing the manufacturing cost by using a driver IC having a high withstand voltage. Further, even if the light-transmitting substrate is realized by an inexpensive glass substrate having a low strain point temperature, the thin-film EL element 1 having excellent characteristics can be obtained, and the manufacturing cost can be reduced.

The N-shift phenomenon is considered to be caused by poor crystallinity of the EL light-emitting layer, particularly poor crystallinity in the initial stage of crystal growth during vapor deposition. The poor crystallinity of the layer
When a symmetrical AC pulse waveform voltage is applied,
It is inferred from the fact that when the polarity of the AC pulse differs, the EL emission intensity differs.

By depositing in an H ₂ S atmosphere, N-
The reason why the shift phenomenon is eliminated may be as follows, for example. When deposited in vacuum, Z
A part of nS is dissociated, and the E
The L light emitting layer 5 has a shortage of the S component. That is,
There will be Zn atoms not bonded to S. This is because the vapor pressure of S is higher than that of Zn,
This occurs because S in nS is re-evaporated. When a voltage is applied to such an EL light-emitting layer 5, Zn atoms precipitate and an N-shift phenomenon occurs in which the emission luminance-applied voltage characteristic changes. When the vapor deposition is performed in an H ₂ S atmosphere, the partial pressure of S increases, the re-evaporation of S decreases, and Z which is not bonded to S is increased.
The number of n atoms is reduced. Therefore, precipitation of Zn atoms is reduced, and the N-shift phenomenon is eliminated.

The EL light emitting layer 5 is deposited on the first insulating layer 4, that is, on the Si ₃ N ₄ film in this embodiment.
This Si ₃ N ₄ film is amorphous, and when vapor deposition is performed on such a film surface, the direction of crystal growth is not determined, and a film having low crystallinity is formed in an initial stage of growth. When the EL light emitting layer 5 having a portion with low crystallinity (dead layer layer) is formed, an intermediate level due to a lattice defect or the like is formed near the dead layer layer. For this reason, as the driving time becomes longer, electrons are emitted in the vicinity of the dead layer, the emission luminance increases, and an N-shift phenomenon occurs. According to this example, it is considered that the introduction of H ₂ S during the vapor deposition suppressed the formation of the dead layer, thereby eliminating the N-shift phenomenon.

In this embodiment, the EL light emitting layer 5 is made of Zn.
Although the case of S: Mn has been described,
Since H ₂ S is introduced at the time of vapor deposition in order to supplement S of S, an example in which a rare earth element is used instead of Mn also belongs to the scope of the present invention, and the same effect as that of the present embodiment can be obtained. .

It is also possible to use a gas capable of supplying S instead of H ₂ S.

[0042]

As described above, according to the present invention, the EL light-emitting layer is formed of a gas containing an S element up to a predetermined thickness D which is smaller than the total thickness of the EL light-emitting layer, preferably an H ₂ S gas atmosphere. Is formed. Therefore, a change in the emission luminance-applied voltage characteristic due to long-time driving is reduced, and it is possible to eliminate an unerased image left when an displayed image is erased. Further, the light emission start voltage Vth becomes relatively low,
It is not necessary to use a driver IC having a high withstand voltage, and the manufacturing cost is reduced.

According to the invention, the thickness D is set to 0 <
By selecting the range of D ≦ 200 nm, the light emission start voltage Vth becomes 200 V or less.

By selecting the thickness D in the range of 0 <D ≦ 5 nm, the light emission starting voltage Vth can be reduced to substantially the same level as when vapor deposition is performed in a vacuum atmosphere.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a configuration of a thin-film EL device 1 manufactured by a method for manufacturing a thin-film EL device according to one embodiment of the present invention.

FIG. 2 is a process chart showing a method for manufacturing the thin-film EL element 1.

FIG. 3 is a side view showing a vapor deposition device 11 used when forming the EL light emitting layer 5.

FIG. 4 is a graph showing a relationship between an H ₂ S introduction film thickness D and a light emission start voltage Vth of the thin film EL element 1.

FIG. 5 is a graph showing the relationship between the H ₂ S-introduced film thickness D and the light emission luminance L of the thin-film EL element 1 after performing an acceleration test.

FIG. 6 is a graph showing the relationship between light emission luminance and applied voltage of a conventional thin film EL element.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Thin-film EL element 3 Transparent electrode 5 EL light emitting layer 7 Metal electrode

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Akihiro Kitabatake 1-8-27 Kusune, Higashi-Osaka-shi, Osaka Sanyo Vacuum Industry Co., Ltd. No. 27 Sanyo Vacuum Industry Co., Ltd. (56) References JP-A-1-235189 (JP, A) JP-A-5-6792 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , (DB name) H05B 33/14 H05B 33/10

Claims (4)

(57) [Claims] 1. A method in which Mn or a rare earth element is added between two electrodes, at least one of which has translucency.
A method for manufacturing a thin-film EL device having an EL light-emitting layer made of an EL light-emitting layer material containing S, wherein the EL light-emitting layer is formed by depositing an EL light-emitting layer material by a vapor deposition method, and has a total thickness of the EL light-emitting layer. A method of manufacturing a thin-film EL device, wherein a predetermined thickness D, which is smaller than the thickness, is formed in a gas atmosphere containing an S element. 2. The predetermined thickness D is 0 <D ≦ 200n.
2. The method according to claim 1, wherein the thickness is selected from the range of m. 3. The thin film E according to claim 2, wherein the predetermined thickness D is selected in a range of 0 <D ≦ 5 nm.
Manufacturing method of L element. 4. The method according to claim 1, wherein the gas containing the S element is an H ₂ S gas.