JP2837007B2 - EL display element - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an EL (Electroluminescence) used for a display of various information terminal equipment.
The present invention relates to a display element, and more particularly to an EL display element structure which has a high withstand voltage and is hardly broken to improve reliability.

[0002]

2. Description of the Related Art Conventionally, a thin-film EL display element has a luminescent base material such as zinc sulfide (ZnS) or alkaline earth sulfide (CaS, SrS), and manganese (Mn) or manganese (Mn) as a luminescent center.
It utilizes the phenomenon of emitting light when an electric field is applied to a light emitting layer formed by doping a small amount of terbium (Tb), samarium (Sm), or the like, and is attracting attention as a self-luminous type flat display element. It can be said that the thin-film EL display element is a display element particularly suitable for applications requiring high display quality, such as an in-vehicle display device. FIG. 8 is a schematic diagram showing a typical sectional structure of a thin film EL display element. The thin-film EL display element 10 includes a lower electrode (transparent electrode) 2, a lower insulating layer 3, a light-emitting layer 4, an upper insulating layer 5, and an upper electrode (metal electrode or transparent electrode) 6 on a glass substrate 1, which is an insulating substrate. Are sequentially laminated. Among these, the lower insulating layer 3 and the upper insulating layer 5 formed so as to cover the light emitting layer 4 from above and below are major factors that determine the reliability of the thin-film EL display element 10. As the material of the lower insulating layer 3 and the upper insulating layer 5, oxides such as Al ₂ O _3, SiO _2, Ta ₂ O ₅ , and Si ₃ N ₄
There have been proposed nitrides such as AlN, and composite oxides such as PbTiO ₃ and PZT. Further, an insulating layer having a laminated structure in which a plurality of them are combined has been proposed.

[0003]

Here, since the thin film EL display element is driven under a high voltage, it is required that the insulating layer has a high withstand voltage and a high dielectric constant.
Furthermore, in order to complete a thin-film EL display element, the insulating layer must have the following performance. First,
Adhesion with a light emitting layer containing zinc sulfide (ZnS) as a base material must be good not only for a completed thin film EL display element but also throughout the entire process of forming the element. That is, even in a wet etching step when the electrode is finely processed into a desired shape during the process, film peeling often occurs between the light emitting layer and the insulating layer. Secondly, in the case of dielectric breakdown, a self-healing type breakdown mode in which the breakdown portion is pinpointed and the breakdown does not spread further is desirable, rather than a breakdown mode in which the breakdown propagates one after another to cause a large breakdown. .
In other words, in this self-healing destruction mode,
Even if a dielectric breakdown occurs, only a small invisible breakdown point remains, which leads to an improvement in the yield of the thin film EL display element. Here, it is known to use a nitride for the insulating layer. This is because zinc sulfide in the light-emitting layer is oxidized when an oxide-based insulating film is formed on the light-emitting layer using oxygen plasma, the number of recombination centers increases, and the light-emitting efficiency decreases. However, conventionally, there has been no proposal that comprehensively considers the improvement of the adhesion and the destruction mode with respect to the light emitting layer described above, and the type of the insulating layer has been empirically determined.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems. It is an object of the present invention to improve the adhesion between an insulating layer and a light emitting layer and to improve the mode of destruction of the insulating layer. An object of the present invention is to provide a self-healing EL display element in which dielectric breakdown does not progress.

[0005]

According to an aspect of the present invention for solving the above-mentioned problems, there is provided a light emitting device having an electrode sandwiched between electrodes on an insulating substrate.
A light layer, and insulated between the light emitting layer and any of the electrodes;
An EL display device having a layer disposed therein, wherein the lower insulating layer or the upper insulating layer adjacent to the light emitting layer is formed of a nitride insulating film, and at least the light emitting layer in a thickness direction of the nitride insulating film. And a nitride or an oxide containing oxygen at a portion at least farthest from the light-emitting layer in a thickness direction of the nitride-based insulating film.

[0006]

[Operation and Effect] The insulating layer adjacent to the light emitting layer of the EL display element is composed of a nitride-based insulating film. And
At least a portion of the nitride-based insulating film that is in contact with the light-emitting layer in the thickness direction is a nitride containing no oxygen, and at least a portion of the nitride-based insulating film that is farthest from the light-emitting layer in the thickness direction contains oxygen. Nitride or oxide.
That is, a nitride-based insulating film is used for the insulating layer of the EL display element of the present invention, and oxygen contained in the nitride-based insulating film is controlled in the thickness direction. Thereby, zinc sulfide (ZnS)
In addition, it is possible to improve the adhesion between the light emitting layer and the nitride-based insulating film typified by the above, and to set the breakdown mode of the nitride-based insulating film to a self-recovery type in which the initial dielectric breakdown does not propagate.

The inventors have found the following as a major cause of a film peeling phenomenon that often occurs between a light emitting layer and an insulating layer of an EL display element. As a method for forming an insulating layer of an EL display element, a sputtering method, in particular, a reactive sputtering method is often used because a dense and high-quality film layer can be obtained. In this method, for example, when an oxide-based insulating film is to be formed as an insulating layer, oxygen is present in a chamber at the time of forming the insulating layer, and oxygen plasma thereby oxidizes the surface of the light emitting layer made of zinc sulfide (ZnS). I do. Oxidation of the surface of the light emitting layer causes zinc oxide (
The concept that ZnO) occurs directly was a general concept. In contrast, the inventors have found that zinc sulfate (Zn SO4) is formed near the surface of the light emitting layer by the above-described oxidation of the surface of the light emitting layer by oxygen plasma. As shown in FIG. 7, zinc sulfate is a substance which is about 100,000 times more soluble in water than zinc sulfide or zinc oxide. The zinc sulfate formed during the process melts out and causes film peeling from that part.

In order to prevent film peeling due to the above reasons, it is necessary to prevent oxygen plasma from being present in the initial stage of forming the insulating layer. The most typical nitride film as a non-oxide insulating film is a silicon nitride (SiN _x ) film. Further, the inventors have conducted intensive experimental research on the fracture mode and found the following phenomena. That is,
In the silicon nitride film, a state without oxygen (SiN _x )
In this film, the dielectric breakdown became a propagation mode, and once breakdown occurred, the breakdown spread to a large area. On the other hand, the film containing oxygen (SiO _x N _y ) exhibited a self-recovery breakdown mode in which the initial breakdown did not propagate. From the results described above, the inventors have found that the insulating layer for preventing the peeling of the film between the light emitting layer and the insulating layer and for setting the destruction mode to the self-healing type may have the structure of the present invention. I understood. That is, the film peeling phenomenon of the insulating film is dominated by the state of the contact portion with the light emitting layer, and the breakdown mode of the insulating film is dominated by the state of the portion farthest from the light emitting layer.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to specific embodiments. FIG. 1 is a schematic view showing a longitudinal section of a thin film EL display element according to the present invention. The thin-film EL display element 100 has a glass substrate 1 (thickness) which is an insulating substrate.
1.1mm, HOYA NA40: non-alkali glass)
The following thin films are formed and configured. On the glass substrate 1, ITO (Indium TinOxide: indium oxide-
(Tin) a lower electrode (transparent electrode) 2 made of a transparent conductive film, a lower insulating layer 3 made of a nitride-based insulating film, a light-emitting layer 4, an upper insulating layer 5 made of a nitride-based insulating film, and an upper electrode 5 made of an Al thin film. Are formed. The light emitting layer 4 was made of ZnS: Mn, which emits orange light by adding zinc sulfide (ZnS) as a base material and adding a small amount of manganese (Mn). Portions of the lower insulating layer 3 and the upper insulating layer 5 made of a nitride insulating film adjacent to the light emitting layer 4 are oxygen-free layers 3a and 5a containing no oxygen. These oxygen-free layers 3a and 5a are made of a nitride containing no oxygen. Further, portions of the lower insulating layer 3 and the upper insulating layer 5 made of a nitride-based insulating film farthest from the light emitting layer 4 are oxygen-containing layers 3b and 5b containing oxygen. These oxygen layers 3b and 5b are made of nitride or oxide containing oxygen.

FIG. 2 is an explanatory diagram showing the distribution of the nitrogen concentration and the oxygen concentration in the thickness direction of the nitride insulating film of the lower insulating layer 3 and the upper insulating layer 5. The nitride insulating film was based on SiN _x . The nitride-based insulating film is in the form of SiN _x at a contact portion adjacent to the light emitting layer, is in the form of SiO _x N _y as it is separated from the light emitting layer, and is in the form of SiO _{x at} a portion (surface) farthest from the light emitting layer. And That is, the oxygen-free layers 3a and 5a are made of SiN _x and the oxygen-containing layers 3b and 5a are
b is made of SiO _x .

Next, the above-mentioned thin-film EL display element 1
00 is described below. IT on glass substrate 1
O is sputtered in a mixed gas atmosphere of argon (Ar) and oxygen (O ₂ ) by high frequency sputtering to form a film having a thickness of 2000 mm, and a transparent lower electrode is formed by wet etching in a stripe shape in the X direction, which is the horizontal direction of the drawing. 2 was formed. Next, using a sputtering apparatus capable of supplying a mixed gas of argon, oxygen and nitrogen (N ₂ ) into the chamber with a target of Si metal, high-frequency sputtering is performed in the mixed gas atmosphere to form a nitride-based material on the lower electrode 2. A lower insulating layer 3 as an insulating film was formed. At the start of the film formation, only the argon gas and the oxygen gas were supplied into the chamber. During the film formation, the supplied oxygen amount was gradually decreased, and instead, a nitrogen gas was supplied, and the supplied nitrogen amount was gradually increased. And immediately before the end of film formation,
The supply of oxygen gas was stopped, and only argon gas and nitrogen gas were supplied. This film thickness was 2000 mm. The light emitting layer 4 on the lower insulating layer 3 was formed by ZnS: Mn pellets and formed by electron beam evaporation. The Mn concentration is 1 wt% and the film thickness is 6000 °. Next, an upper insulating layer 5 which was a nitride-based insulating film was formed on the light emitting layer 4. The upper insulating layer 5 has a structure opposite to that of the lower insulating layer 3. That is, at the start of film formation, only the argon gas and the nitrogen gas are supplied into the chamber of the sputtering apparatus, the nitrogen gas is gradually reduced, the oxygen gas is increased, and finally the nitrogen gas is set to 0, and only the argon gas and the oxygen gas are used. A film was formed. This film thickness is the same as that of the lower insulating layer 3.
00Å. Finally, Al was deposited by electron beam evaporation for 200 hours.
A film was formed to a thickness of 0 °, and a stripe-shaped upper electrode 6 was formed by a photoetching method in the Y direction perpendicular to the drawing. Incidentally, the elements of the above-described configuration SiN _x -SiO _x N _y -Si
_Ox product.

For comparison with the above-mentioned SiN _x -SiO _x N _y -SiO _x product, each of the lower insulating layer 3 and the upper insulating layer 5 is made of S
An element formed of only iN _x is a SiN _x product. An element in which each of the lower insulating layer 3 and the upper insulating layer 5 is formed of only SiO _x is referred to as a SiO _x product. That is, the lower insulating layer 3 of the SiN _x product
The upper insulating layer 5 is sputtered on a Si target in a mixed gas atmosphere of only argon gas and nitrogen gas, and the lower insulating layer 3 and the upper insulating layer 5 of SiO _x are formed in a mixed gas atmosphere of only argon gas and oxygen gas. It was produced by sputtering. The thicknesses of the lower insulating layer 3 and the upper insulating layer 5 are all 2000 Å
And

The SiN _x -SiO _x N _y -SiO _x product and the SiN _x product of the present invention did not have any problem even in the photoetching step of the upper electrode 6 without causing film peeling. However, SiO _x
The product was delaminated in the wet etching process of the cleaning process and the photo etching process, and a satisfactory thin-film EL display element could not be produced. In this case, the film peeling occurred between the light emitting layer 4 and the upper insulating layer 5. The cause was analyzed by X-ray photoelectron spectroscopy. As a result, the Si
O _x article luminescent layer: It has been found that ZnSO the outermost surface portion of the (ZnS Mn) ₄ is formed. As can be seen from FIG. 7, ZnSO ₄ is 100,000 times more soluble in water than ZnS and ZnO, and ZnSO ₄ formed between the light emitting layer and the insulating layer.
It is considered that the layer was dissolved in water in the cleaning step or the wet etching step of the photo etching step, and the film was peeled therefrom. It is considered that ZnSO ₄ was formed by oxidizing ZnS, which is the base material of the light emitting layer, by oxygen plasma generated by sputtering when forming the insulating film (SiO _x ). Here, it has been generally accepted that ZnS is directly converted to ZnO by oxidation. It is considered that in the SiN _x -SiO _x N _y -SiO _x product and the SiN _x product of the present invention, ZnS 4 in the light emitting layer was not directly exposed to oxygen plasma, so that ZnSO ₄ was not formed and no film peeling occurred.

Next, the completed SiN _x -SiO _x N _{y of} the present invention.
Increasing the driving voltage until breakdown against the -SiO _x article and SiN _x article compared the state after the dielectric breakdown. Although there was not much difference between the voltage values at which the two breakdown occurred, the breakdown modes of the two were greatly different. That is, SiN _x -SiO _x N _y -Si
O _x article did not proceed further with only breakdown is formed a hole having a diameter of about 0.1 mm to 0.5 mm (self-healing). In contrast, SiN _x article is instantaneously propagated when the first small dielectric breakdown occurs, the entire light-emitting pixel is broken quickly emerging (propagating). Although the cause of this difference in the breakdown mode is unknown, an experimental result showing a self-healing type failure mode when oxygen is present on the outermost surface portion of the nitride-based insulating film opposite to the surface in contact with the light emitting layer has been reported. Have been obtained.

FIG. 3 is a schematic view showing a longitudinal section of another embodiment of the thin film EL display element according to the present invention. In this figure, the configuration above the light emitting layer 4 is shown, but the configuration is also directed to the lower side of the light emitting layer 4. An upper insulating layer 5 is formed on the light emitting layer 4. This upper insulating layer 5 has the same SiN _x -SiO _x N _y as in the above embodiment.
-SiO _x configuration. In the present embodiment, an insulating layer 7 of tantalum pentoxide (Ta ₂ O ₅ ) having a film thickness of 4000 ° is formed on the upper insulating layer 5. The insulating layer 7 is formed in order to further improve the withstand voltage from the case where only the upper insulating layer 5 is used. As described above, even if another type of insulating layer is formed by being stacked on the upper insulating layer 5, the effect is the same as described above.

FIGS. 4 to 6 are explanatory diagrams showing the distributions of the nitrogen concentration and the oxygen concentration in another example of the thickness direction of the nitride insulating film according to the present invention. In FIG. 4, only the portion of the nitride-based insulating film that is in contact with the light-emitting layer is formed of a SiN _x layer,
When it is away from the light emitting layer, it has a structure of SiO _x N _y layer.
In this case, there is no SiO _x layer. In FIG. 5, the nitride insulating film is followed by a SiN _x layer from the contact portion with the light emitting layer,
The surface of the outermost shell, which is the farthest part from the light emitting layer, is made of SiO _x N
_This is one in which a _y layer is formed. In FIG. 6, in the nitride-based insulating film, the SiN _x layer continues from the contact portion with the light emitting layer, and the SiO _x layer is formed on the outermost shell surface which is the portion farthest from the light emitting layer. All of the structures of the nitride-based insulating films shown in FIGS. 4 to 6 are effective in improving the film peeling and the breakdown mode as in the above-described embodiment. The light emitting layer in the above-described embodiment is Z
nS: Mn, but ZnS: Tb (green emission) and Zn
The same applies when other additives such as S: Sm (red emission) are added. Was used SiN _x based on the nitride-based insulating film may be composed of other nitrides such as AlN system in the present invention.
In the present embodiment, the lower insulating layer and the upper insulating layer are configured symmetrically. However, the improvement of the dielectric breakdown mode and the effect of preventing film peeling are dominated by the upper insulating layer. It may be configured.

[Brief description of the drawings]

FIG. 1 is a schematic view showing a longitudinal section of a thin-film EL display device according to a specific example of the present invention.

FIG. 2 is an explanatory diagram showing distributions of a nitrogen concentration and an oxygen concentration in a thickness direction of a nitride-based insulating film according to the example.

FIG. 3 is a schematic view showing a longitudinal section in another embodiment of the thin-film EL display element according to the present invention.

FIG. 4 is an explanatory view showing distributions of a nitrogen concentration and an oxygen concentration in another example of the thickness direction of the nitride-based insulating film according to the present invention.

FIG. 5 is an explanatory diagram showing distributions of a nitrogen concentration and an oxygen concentration in another example of the thickness direction of the nitride-based insulating film according to the present invention.

FIG. 6 is an explanatory diagram showing distributions of a nitrogen concentration and an oxygen concentration in another example of the thickness direction of the nitride-based insulating film according to the present invention.

FIG. 7 is a table showing the solubility of zinc sulfide and its oxide in water.

FIG. 8 is a schematic view showing a longitudinal section of a conventional thin film EL display element.

[Explanation of symbols]

 1—Glass substrate (insulating substrate) 2—Lower electrode 3—Lower insulating layer (nitride-based insulating film) 3a—Oxygen-free layer (nitride containing no oxygen) 3b—Oxygenated layer (nitride containing oxygen or Oxide) 4-light-emitting layer 5-upper insulating layer (nitride-based insulating film) 5a-oxygen-free layer (nitride containing no oxygen) 5b-oxic layer (nitride or oxide containing oxygen) 6-top electrode

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Yoshiyasu Ando 1-1-1, Showa-cho, Kariya-shi, Aichi Japan Inside Denso Corporation (72) Inventor Masayuki Suzuki 1-1-1, Showa-cho, Kariya-shi, Aichi Japan Japan Denso Stock In-company (56) References JP-A-2-148596 (JP, A) JP-A-2-306658 (JP, A) JP-A-2-306588 (JP, A) JP-A-3-4483 (JP, A) JP-A-4-36994 (JP, A) JP-A-2-117096 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) H05B 33/22

Claims (1)

(57) [Claims] 1. A light-emitting device sandwiched between electrodes on an insulating substrate.
An insulating layer between the light emitting layer and any of the electrodes.
A EL display elements were arranged, oxygen in the contact portion between the light-emitting layer and the insulating layer formed of a nitride insulating film adjacent and at least the light emitting layer in the thickness direction of the nitride-based insulating film An EL display element comprising: a nitride containing no oxygen; and a nitride or an oxide containing oxygen at least at a portion farthest from the light emitting layer in a thickness direction of the nitride-based insulating film.