JPH05326151A - Thin film el element and its manufacture - Google Patents

Abstract

PURPOSE:To improve luminance and dielectric characteristic by containing an oxide tantalum film in at least one of first and second insulating layers nipping a light emitting layer. CONSTITUTION:On a base glass 1, a metal Ta film is sputtered and evaporated as the material of a first electrode 2, and worked into a determined stripe pattern by photolithography. Then, the surface of the electrode 2 is oxidized by anode oxidation to form a Ta2O5 film 3a forming a part of a first insulating layer 3. The thickness of the Ta2O5 film can be precisely controlled by the voltage to be applied to the anode. A SiO2 film 3b and a Si3N4 film 3a are successively accumulated by sputtering, and the formation of the insulating layer 3 is completed. A light emitting layer 4 is then formed by electron beam evaporation, and a Si3N4 film 5a and an Al2O3 film 5b are accumulated by spattering to form a second insulating layer 5. Finally, an ITO film is sputtered and evaporated, and a stripe second electrode 6 crossing at a right-angled to the electrode 2 is formed by photolithography.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thin film electroluminescence (EL) device and a method for manufacturing the same.

[0002]

2. Description of the Related Art A conventional thin film EL element is shown in FIG. This thin film EL element is a substrate glass 1
1, a first electrode 12 made of a metal Ta film, a first insulating layer 13, a light emitting layer 14, a second insulating layer 15, and I
Second electrode 16 made of TO (tin-doped indium oxide) film
And the light emitting layer 14 are sandwiched between the insulating layers 13 and 15 from both sides to form a double insulating structure. The light emitting layer 14 is formed of a ZnS: Mn film having a thickness of about 1 μm in which the base material ZnS is doped with Mn as an emission center. The first insulating layer 13 is made of SiO ₂ film 13a having a thickness of 400Å to 500Å and Si ₃ N ₄ having a thickness of 2200Å to 2400Å.
The second insulating layer 15 has a thickness of 12
00 Å ~ 1300 Å Si ₃ N ₄ film 15a and thickness 300 Å ~
It is composed of 600 Å Al ₂ O ₃ film 15b. During operation, a voltage is applied to the first and second electrodes 12 and 16. Then, when the electric field applied to the light emitting layer 14 exceeds a threshold value, light emission starts, and the light emission luminance is set to the first and second insulating layers 13 and 15.
Is approximately proportional to the accumulated charge amount Q of.

[0003]

By the way, in addition to the emission brightness, the insulating layers 13 and 15 are important performances of the thin film EL element.
It has dielectric breakdown characteristics. When the applied voltage between the first and second electrodes 12 and 16 is gradually increased, as shown in FIG.
(Represented by Co), a current rapid increase region appears following the Ohm's law region seen in the low electric field (inflection point D ₁ ), and further, the heat generated by the current flowing through the insulating layers 13 and 15 causes dielectric breakdown. (Inflection point D ₂ ). This is the mechanism of dielectric breakdown. Therefore, in order to improve the dielectric breakdown characteristics, the insulating properties of the insulating layers 13 and 15 are improved to suppress the absolute value of the current to a low value, and the inflection points D ₁ and D ₂ in the IV characteristics are set to a high electric field. I should go.

Here, if the thickness of the insulating layer 13 or 15 is simply increased in order to improve the insulating property, the capacitance of the insulating layers 13 and 15 is reduced and the amount of accumulated charge is reduced to cause light emission. The brightness will decrease.

Therefore, an object of the present invention is to provide a thin film EL element capable of improving the emission luminance and dielectric breakdown characteristics by devising the material of the insulating layer, and a manufacturing method thereof.

[0006]

In order to achieve the above object, a thin film EL device of the present invention comprises a light emitting layer, first and second insulating layers sandwiching the light emitting layer, and outsides of both insulating layers. In the thin film EL element having the first and second electrodes provided in, the tantalum oxide film is included in at least one of the insulating layers.

The method of manufacturing a thin film EL element according to the present invention comprises: a first electrode made of a metal tantalum film on a substrate;
A method for manufacturing a thin-film EL element, in which a first insulating layer including a tantalum oxide film, a light emitting layer, a second insulating layer, and a second electrode are sequentially stacked, wherein the tantalum oxide film is the first It is characterized in that it is formed by oxidizing the surface of the electrode.

[0008]

The current flowing through the first and second insulating layers of the thin film EL element is rate-controlled by the conduction characteristic of the material having the highest insulating property among the materials forming the insulating layer. Therefore, as a material forming the insulating layer, the conventional insulating layer material SiO ₂ ,
Tantalum oxide (T which has better insulation than Si ₃ N ₄ and Al ₂ O ₃
By including the a ₂ O ₅ ) film, the dielectric breakdown characteristics of the entire insulating layer are improved. Also, the relative permittivity εr of Ta ₂ O ₅ above
As shown in Table 1, εr = 24, which is much larger than the conventional insulating layer material. Therefore, the capacitance of the insulating layer is increased, the amount of accumulated charge is increased, and the emission brightness is improved.

[Table 1]

The Ta ₂ O ₅ film is metal tantalum (Ta).
When the first electrode consisting of
The a ₂ O ₅ film is easily manufactured with high film thickness accuracy by, for example, the anodic oxidation method. Therefore, this thin film EL element can be easily manufactured with almost no difference from the conventional process.

[0010]

EXAMPLES Hereinafter, the thin film EL device of the present invention and the manufacturing method thereof will be described in detail with reference to examples.

FIG. 1 shows a cross-sectional structure of a thin film EL element of one embodiment. This thin film EL element is provided on a substrate glass 1, a light emitting layer 4, a first insulating layer 3 and a second insulating layer 5 that sandwich the light emitting layer 4, and outside these both insulating layers 3, 5. It also comprises a first electrode 2 and a second electrode 6. The light emitting layer 4 has a matrix material ZnS with Mn as an emission center.
And a ZnS: Mn film having a thickness of about 1 μm. The first insulating layer 3 comprises a Ta ₂ O ₅ film 3a having a thickness of 2000Å to 3000Å and a SiO ₂ film 3 having a thickness of 400Å to 500Å.
b and a Si ₃ N ₄ film 3c having a thickness of 2200Å to 2400Å. On the other hand, the second insulating layer 5 has a thickness of 1200.
Å ~ 1300 Å Si ₃ N ₄ film 5a and thickness 300 Å ~ 60
It consists of 0Å Al ₂ O ₃ film 5b. The first and second electrodes 2 and 6 are made of a metal Ta film and an ITO (tin-doped indium oxide) film, respectively.

The thin film EL device is manufactured as follows. First, a metal Ta film as a material of the first electrode 2 is sputter-deposited on the substrate glass 1 and processed into a predetermined stripe pattern by photolithography. next,
The surface of the processed first electrode 2 is oxidized by an anodic oxidation method to form a Ta ₂ O ₅ film 3a forming a part of the first insulating layer 3. The film thickness of the Ta ₂ O ₅ film 3a can be accurately controlled by the voltage applied to the anode. Then, the SiO ₂ film 3b and the Si ₃ N ₄ film 3c are deposited by the sputtering method or the CVD method to complete the formation of the first insulating layer 3. Next, after forming the light emitting layer 4 by the electron beam evaporation method or the sputter evaporation method, the Si ₃ N ₄ film 5a and the Al ₂ O ₃ film 5b are deposited by the sputtering method or the CVD method to form the second insulating layer 5. Form. Finally, an ITO film is sputter-deposited and a stripe-shaped second electrode 6 which intersects the first electrode 2 perpendicularly is formed by photolithography. Above T
Since the a ₂ O ₅ film 3a can be easily formed, according to this manufacturing method, a thin film EL element can be easily manufactured with almost no difference from the conventional process.

In order to confirm the effect of providing the Ta ₂ O ₅ film 3a, the inventors of the present invention have described the thin film EL device (of the present invention).
Then, the dielectric breakdown voltage and the maximum accumulated charge amount of the thin film EL element (conventional example) shown in FIG. 5 were measured. As shown in Table 2, the breakdown voltage of the conventional example is 160.7 V, whereas that of the present invention is 250.7 V, which is about 1.6.
I was able to improve it twice. Further, the maximum accumulated charge amount (which is approximately proportional to the light emission luminance) is 3.36 μC / cm ² in the conventional example, whereas it is 4.48 μC / cm ² in the present invention,
It was possible to improve it about 1.3 times. The reason why the dielectric breakdown characteristics can be improved can be explained by the current density-electric field characteristics shown in FIG. As shown in FIG. 2, the current density of the present invention (C ₁ ) is smaller than that of the conventional example (C ₂ ) under the same electric field. Also, the inflection point (indicated by arrow ↓ in the figure) between the Ohm's law region and the current rapid increase region is on the higher electric field side than the conventional example,
As a result, the breakdown voltage could be improved. Therefore, the electric field during actual operation (usually 2.0 to 2.5 MV / cm)
And the breakdown voltage can be increased, and the reliability of the device can be improved.

[Table 2]

FIG. 3 shows the resistance value in the thickness direction of the insulating layer (when an electric field of 2 MV / cm is applied) and the insulating layer 3 under various conditions.
5 shows the correlation with the breakdown electric field of No. 5. Insulation layer 3,
The breakdown electric field of 5 is 5M with a margin to the electric field during operation.
Since it is necessary to have V / cm or more, it has been found that the resistance value of the Ta ₂ O ₅ film must be 10 ¹³ Ω · cm or more.

[0015]

As is apparent from the above, the thin-film EL device of the present invention includes the tantalum oxide film in at least one of the first and second insulating layers sandwiching the light emitting layer, and therefore, the light emitting property and the dielectric breakdown. The characteristics can be improved. Therefore, reliability can be improved.

Further, according to the method of manufacturing a thin film EL element of the present invention, since the tantalum oxide film is formed by oxidizing the surface of the first electrode made of metal tantalum, the conventional process is almost unchanged and simple. A thin film EL device can be manufactured.

[Brief description of drawings]

FIG. 1 is a diagram showing a cross-sectional structure of a thin film EL element according to an embodiment of the present invention.

FIG. 2 is a diagram showing electric field-current density characteristics of a tantalum oxide film forming a part of an insulating layer of the thin film EL element.

FIG. 3 is a diagram showing a correlation between a resistance value in the thickness direction of the insulating layer and a breakdown electric field.

FIG. 4 is a diagram showing voltage-current characteristics of an insulating layer of a conventional thin film EL element.

FIG. 5 is a diagram showing a cross-sectional structure of a conventional thin film EL element.

[Explanation of symbols]

1 substrate glass 2 first electrode (metal Ta film) 3 first insulating layer 3a Ta ₂ O ₅ film 3b SiO ₂ film 3c, 5a Si ₃ N ₄ film 4 light emitting layer 5 second insulating layer 5b Al ₂ O ₃ film 6 Second electrode (ITO film)

Continued front page (72) Inventor Masaru Yoshida 22-22 Nagaike-cho, Abeno-ku, Osaka, Osaka

Claims (2)

[Claims] 1. A thin film EL device comprising a light emitting layer, first and second insulating layers sandwiching the light emitting layer, and first and second electrodes provided outside the both insulating layers, wherein A thin-film EL device comprising a tantalum oxide film on at least one of the insulating layers. 2. A first electrode made of a metal tantalum film, a first insulating layer containing a tantalum oxide film, a light emitting layer, a second insulating layer, and a second electrode are sequentially laminated on a substrate. A method of manufacturing a thin film EL element, wherein the tantalum oxide film is formed by oxidizing the surface of the first electrode.