JPH07130470A - Thin film el element and its manufacture - Google Patents

Abstract

PURPOSE:To enhance the reliability of a thin film EL element by reducing the drive voltage and heightening the dielectric breakdown voltage. CONSTITUTION:A transparent electrode 3, first dielectric substance layer 4, EL light emitting layer 5, second dielectric substance layer 6, and metal electrode 7 are laid one over another on the surface 2a of a photo-transmissive base board 2 in the sequence as named so that a thin film EL element 1 is produced. The first and the second dielectric substance layer 4, 6 are formed by a sputtering method in which the target consists of a hybrid sintered body of StO and TiN, wherein SrTiON is produced as the major constituent. The drive voltage is thus reduced, and resultant thin film EL element 1 is equipped with an enhanced dielectric breakdown voltage and with excellent reliability.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thin film EL (electroluminescent) element and a method for manufacturing the same, and more particularly to a dielectric layer constituting the thin film EL element and a method for forming the dielectric layer.

[0002]

2. Description of the Related Art Generally, a thin film EL device has an EL light emitting layer disposed between a pair of electrodes, at least one of which has a light transmitting property, and between the EL light emitting layer and at least one of the electrodes. It is configured by arranging dielectric layers. Since the thin film EL element is a self-luminous type, has high brightness and has a long life, it is expected to be used as a display means for electronic devices and the like. As the dielectric layer material, Y ₂ O ₃ ,
Although SiO ₂ , Si ₃ N ₄ , Al ₂ O ₃ and Ta ₂ O ₅ are typical, recently, a material having a higher dielectric constant ε, such as PbTiO ₃ , for the purpose of reducing the driving voltage, is used. BaTiO ₃ , SrTiO ₃ and CaTiO ₃ are used.

In the thin film EL element, the capacitance of the EL light emitting layer and the capacitance of the dielectric layer are connected in series, and it is considered that the driving voltage is divided by the capacitance and applied to each layer. Therefore, in order to efficiently apply a voltage to the EL light emitting layer and reduce the driving voltage, it is desirable to use a material having a permittivity as high as possible. For example, EL
Assuming that the light emitting layer and the dielectric layer have almost the same film thickness, and the materials having the dielectric constants ε of about the same are used as the materials of the both, the electric capacities of the both become equal, and about the applied voltage Only half is applied to the EL emitting layer. However, if, for example, a material having a dielectric constant ε one digit higher than that of the EL light emitting layer material is used as the dielectric layer material, about 90% of the applied voltage will be applied to the EL light emitting layer. Therefore, the driving voltage can be reduced, and the power consumption for driving the thin film EL element can be reduced. For example, the dielectric constant ε of Y ₂ O ₃ is 1
2 and the dielectric constant ε of Al ₂ O ₃ is 8,
The dielectric constant ε of PbTiO ₃ is 150, and SrTi
The dielectric constant ε of O ₃ is 140.

[0004]

Although the above-mentioned high dielectric constant material is effective for reducing the driving voltage of the thin film EL element, the use of the material causes the following disadvantages. That is, although the material has a high dielectric constant, it has a low withstand voltage. For example, the dielectric breakdown voltage of PbTiO ₃ is 0.5 MV / cm, and the dielectric breakdown voltage of SrTiO ₃ is 1.5 MV / cm to 2 MV / cm. Meanwhile, the breakdown voltage of Y ₂ O ₃ is 3 MV / cm to 5 MV / c.
m, Al ₂ O _{3 has} a breakdown voltage of 5 MV / cm, Si ₃ N
The dielectric breakdown voltage of ₄ is 6 MV / cm to 8 MV / cm. In order to stably apply a voltage without causing dielectric breakdown in the EL light emitting layer, it is desirable that the dielectric layer material has a dielectric breakdown voltage as high as possible. However, since the above-mentioned high dielectric constant material has a relatively low dielectric breakdown voltage, dielectric breakdown easily occurs, and there is a problem that the reliability of the thin film EL element is lowered.

It is an object of the present invention to provide a thin film EL element having a low driving voltage, little dielectric breakdown, and excellent reliability, and a manufacturing method thereof.

[0006]

According to the present invention, an EL light emitting layer is disposed between a pair of electrodes, at least one of which has a light transmitting property, and a dielectric layer containing oxynitride of a perovskite type compound as a main component. Is a thin film EL element characterized by being disposed between the EL light emitting layer and at least one of the electrodes.

Further, according to the present invention, an EL light emitting layer is arranged between a pair of electrodes, at least one of which is transparent, and a dielectric layer is arranged between the EL light emitting layer and at least one of the electrodes. In the method of manufacturing a thin film EL element,
A method of manufacturing a thin film EL element, characterized in that the dielectric layer is formed by a sputtering method using a mixed sintered body of an oxide and a nitride as a target.

[0008]

According to the present invention, in a thin film EL device, an EL light emitting layer is disposed between a pair of electrodes, at least one of which has translucency, and the EL light emitting layer is disposed between the EL light emitting layer and at least one of the electrodes. And a dielectric layer whose main component is an oxynitride of a perovskite type compound. The dielectric layer is formed by a sputtering method using a mixed sintered body of oxide and nitride as a target. It was confirmed that the driving voltage can be reduced by using a film containing an oxynitride of a perovskite type compound as a main component formed by the method as a dielectric layer of a thin film EL element. It was also confirmed that the dielectric breakdown voltage was improved. Therefore, it is possible to provide a thin film EL element that has low power consumption, little occurrence of dielectric breakdown, and excellent reliability.

[0009]

1 is a cross-sectional view showing the structure of a thin film EL element 1 which is an embodiment of the present invention. The thin film EL device 1
Is a so-called double-insulating thin-film EL element, and includes a transparent substrate 2, a transparent electrode 3, a first dielectric layer 4, an EL light emitting layer 5, a second dielectric layer 6, and a metal electrode 7 stacked in this order. Configured.

FIG. 2 is a process chart showing the procedure for manufacturing the thin film EL element 1. In step a1, one surface 2 of translucent substrate 2 made of, for example, glass or plastic is used.
A transparent electrode 3 having a film thickness of, for example, about 1500 Å is formed on a. The transparent electrode 3 is realized by, for example, ITO (indium tin oxide) or SnO ₂ , and ITO is used in this embodiment. The ITO is formed on the entire surface 2a and then patterned into a plurality of parallel strips to form the transparent electrode 3.

In step a2, the first dielectric layer 4 is formed on the surface 2a on which the transparent electrode 3 is formed. The first dielectric layer 4 is formed by a sputtering method targeting a mixed sintered body of oxide and nitride. As the oxide, an oxide of an element selected from Group IIa and Group IVb of the periodic table, for example, an oxide of an element selected from Sr, Ca, Ba and Pb is used.
Specifically, SrO, CaO, BaO, BaO ₂ , Pb
O, Pb ₃ O ₄ , PbO ₂ or the like is used. The nitride is a nitride of an element selected from the IVa group and the IVb group, such as Ti, Zr, Hf and S.
A nitride of an element selected from n is used. Specifically, TiN, ZrN, HfN, SnN or the like is used. In this example, SrO was used as the oxide, TiN was used as the nitride, and the mixing ratio of SrO and TiN was 1: 1. The mixed powdered SrO and TiN are
Heat and pressure are applied by a so-called hot pressing method to obtain a mixed sintered body. At the time of sputtering, the mixed sintered body is used as a target. Further, Ar was used as the sputtering gas at the time of sputtering, the gas pressure was set to 1.5 Pa, the substrate temperature for attaching the dielectric layer was set to 350 ° C., and the RF (high frequency) power was set to 150 W.
By such a so-called RF sputtering method,
A first dielectric layer 4 having a film thickness of about 5000Å was formed. The formed first dielectric layer 4 is mainly composed of an oxynitride of a perovskite type compound (general formula ABX ₃ ),
In this embodiment, SrTiON is the main component.

In step a3, on the first dielectric layer 4,
For example, the EL light emitting layer 5 is formed by using ZnS as a base material and containing a slight amount of Mn as a light emitting center. The EL light emitting layer 5 is formed to have a film thickness of about 5000Å, for example, by an electron beam evaporation method.

In step a4, a second layer is formed on the EL light emitting layer 5.
The dielectric layer 6 is formed. The second dielectric layer 6 has the first
It is formed in the same manner as the dielectric layer 4, and in this embodiment,
The film thickness is about 5000 by the same RF sputtering method.
A second dielectric layer 6 containing Å SrTiON as a main component was formed.

In step a5, on the second dielectric layer 6,
For example, a metal electrode 7 made of Al is formed. After the metal electrode 7 is formed on the entire surface of the second dielectric layer 6,
A plurality of strips are patterned in a direction orthogonal to the transparent electrode 3.

In this embodiment, the sputtering gas is A
Although the example using r has been described, the first and second dielectric layers 4 can be formed by using only Ar, or by using a mixed gas in which a gas selected from O ₂ , N ₂ and N ₂ O is mixed. , 6 can be formed. The gas mixing ratio is appropriately selected so that the formed dielectric layers 4 and 6 have a desired composition ratio. However, if the Ar ratio is low, the film formation rate may be slowed down, and the production efficiency may be reduced. From this point, it is preferable that the Ar ratio is large.

In this embodiment, the target Sr
Although the example in which the mixing ratio of O and TiN is set to 1: 1 has been described, the mixing ratio of the target material can be selected at an arbitrary ratio. However, since the films formed in all the ratios are not suitable as the dielectric layer of the thin film EL element, the ratios are appropriately selected so that good characteristics can be obtained. In addition to the mixed sintered body of SrO and TiN, for example, the mixed sintered body of SrO—TiN—TiO ₂ can be used as a target to form the dielectric layers 4 and 6. The mixing ratio in this case is also appropriately selected so that good characteristics can be obtained.

FIG. 3 is a graph showing the relationship between the applied voltage to the thin film EL element 1 and the brightness. The vertical axis represents luminance (ft-L), and the horizontal axis represents applied voltage (V). The curve L1 shows the result of the thin film EL element 1 according to the present example using the film containing SrTiON as the main component as the first and second dielectric layers 4 and 6, and the curve L2 shows the results of the first and second dielectric layers. 2 shows the results of a comparative example using SrTiO ₃ films as the dielectric layers 4 and 6.

Since almost the same brightness is obtained with almost the same applied voltage in both the curves L1 and L2, the conventional Y ₂ O ₃
It can be seen that the driving voltage can be reduced more than when a material having a relatively low dielectric constant such as SiO ₂ or SiO ₂ is used for the dielectric layers 4 and 6. Also, the curves L1 and L2
The upper points P1 and P2 indicate the points where the element caused dielectric breakdown due to the voltage application. In the case of using the SrTiO ₃ film (P2), dielectric breakdown occurs when the applied voltage becomes about 170V, but in the present embodiment (P1), it occurs when the applied voltage becomes about 210V. . From this, it is understood that the use of the film containing SrTiON as a main component increases the dielectric breakdown voltage and improves the reliability of the thin film EL element 1.

Further, according to the method of forming the dielectric layers 4 and 6 of the present embodiment, a single layer film containing SrTiON as a main component is formed, and a DC voltage is applied to the film when a ramp voltage whose voltage increases at a constant speed is applied. When the (DC) withstand voltage was measured, it was about 4 MV / cm. On the other hand, SrTiO 3 which is a comparative example
_{For the three} films, it was about 2 MV / cm. From this, too
It can be seen that this example is a dielectric layer having a high withstand voltage, and a dielectric layer having a high withstand voltage can be formed.

As another embodiment of the present invention, when a film containing CaTiON as a main component is used for the first and second dielectric layers 4 and 6, the same result as the above embodiment can be obtained. confirmed. The film containing CaTiON as a main component can be formed by the same method as in the above-described example except that CaO is used as the oxide, and the film other than the first and second dielectric layers 4 and 6 of the thin film EL element 1 is formed. The components were formed in the same manner.

In the above-mentioned embodiment, an example in which the dielectric layers 4 and 6 are formed by the sputtering method has been described. However, other than the sputtering method, for example, Sr (OCH ₃ ) ₂ and Ti containing an alkoxide in which an alkyl group is bonded to oxygen and Ti are used. Pyrolysis CVD (chemical vapor deposition) method or plasma CVD method using (OCH ₃ ) ₄ as a raw material and O ₂ , N ₂ and NH ₃ as a carrier gas, or Sr (OCH ₃ ) ₂
And Ti (N (C ₂ H ₅ ) ₂ ) ₄ as raw materials.

In the above embodiment, both the first and second dielectric layers 4 and 6 of the thin film EL element 1 having the double insulation structure are S.
Although an example of using a film containing rTiON or CaTiON as a main component has been described, an example of using only one of the dielectric layers as the film is also within the scope of the present invention. In addition to the double insulation structure, the dielectric layer of the thin film EL element in which the dielectric layer is provided only between the EL light emitting layer 5 and any one of the electrodes 3 and 7 is used as the film. Such examples also belong to the scope of the present invention.

Target materials (oxides and nitrides) used in forming dielectric layers according to the present invention
Is not necessarily 100% pure. Impurities are also contained in the above-mentioned SrO, TiN, and CaO. Although it is possible to reduce the concentration of these impurities, it is difficult to achieve a purity of 100% due to the manufacturing method.
Moreover, in order to achieve high purity, the manufacturing cost increases.
Therefore, at least several tens of ppm to several hundreds of ppm of impurities are mixed in the dielectric layer formed according to the present invention. Although the dielectric layer of the present invention has an oxynitride of a perovskite type compound as a main component, the main component means that 50% or more of the perovskite type compound is contained in the entire dielectric layer material. Means Other than the perovskite type compound of 50% or more, the above-mentioned impurities or substances mixed in other than these, for example, materials having a relatively low dielectric constant. By mixing in a material having a relatively low dielectric constant, the dielectric layer is adjusted to have a desired dielectric constant and withstand voltage. As the low dielectric constant material mixed for such a purpose, for example, SiO
₂ , Si ₃ N ₄ , Al ₂ O ₃ , Y ₂ O ₃ and Ta ₂ O ₅ may be mentioned.

In JP-A-61-269894, a dielectric layer of a thin film EL element is formed by a sputtering method using a perovskite type oxide sintered body as a target and a sputtering gas containing nitrogen. Although an example using a film is disclosed, there is no description that the film formed by this method is based on the perovskite type oxynitride according to the present invention. In general, the composition and characteristics of the formed film greatly differ depending on the forming method and forming conditions. The dielectric layer of the present invention is formed by using a mixed sintered body of an oxide and a nitride as a target, and the forming method is different from that of the above publication.

Further, in the forming method according to the present invention, the composition ratio of the formed film can be easily adjusted and controlled by the mixing ratio of the target material and the mixing ratio of the sputtering gas. In addition, the range in which the composition ratio can be adjusted is widened. For example, when the above-mentioned SrO and TiN are used as the target material, the Sr and T of the film formed by adjusting the mixing ratio of SrO and TiN.
The composition ratio with i can be changed. For example, when Ar is used as the sputtering gas, a film having a composition ratio substantially equal to the mixing ratio of the target material is formed. on the other hand,
Based on the above publication, for example, when SrTiO ₃ is used as a target material and a film is formed by using N ₂ gas, in order to change the composition ratio of Sr and Ti of the formed film, SrT
The composition ratio of iO ₃ must be changed, and the target material must be changed.

[0026]

As described above, according to the present invention, the thin film EL
The dielectric layer of the device is formed by a sputtering method targeting a mixed sintered body of oxide and nitride.
The dielectric layer formed by the above method contains oxynitride of a perovskite type compound as a main component, and a thin film EL element using the dielectric layer has a reduced driving voltage and an improved breakdown voltage. To do. Therefore, the power consumption is low,
It is possible to provide a thin film EL element having excellent reliability.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a configuration of a thin film EL element 1 which is an embodiment of the present invention.

FIG. 2 is a process drawing showing a procedure for manufacturing the thin film EL element 1.

FIG. 3 is a graph showing the relationship between the brightness of the thin film EL element 1 and the applied voltage.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 thin film EL element 2 translucent substrate 3 transparent electrode 4 first dielectric layer 5 EL light emitting layer 6 second dielectric layer 7 metal electrode

Claims (2)

[Claims] 1. An EL light emitting layer is disposed between a pair of electrodes, at least one of which has translucency, and a dielectric layer containing oxynitride of a perovskite type compound as a main component is at least the EL light emitting layer. A thin-film EL device, characterized in that it is arranged between one of the electrodes. 2. A thin film EL in which an EL light emitting layer is disposed between a pair of electrodes, at least one of which has translucency, and a dielectric layer is disposed between the EL light emitting layer and at least one of the electrodes. A method of manufacturing a thin film EL element, characterized in that the dielectric layer is formed by a sputtering method using a mixed sintered body of an oxide and a nitride as a target.