JPH05121170A - Thin film el display element - Google Patents

Abstract

PURPOSE:To provide a thin film EL display element having the improved adhesion between an insulating layer and a luminescent layer and the self-recovery type breakdown mode of the insulating layer. CONSTITUTION:A lower electrode 2, a lower insulating layer 3 made of a nitride insulating film, a luminescent layer 4, an upper insulating layer 5 made of the nitride insulating film, and an upper electrode 6 are laminated in sequence on a glass base 1 to form a thin film EL display element 100. Portions adjacent to the lower insulating layer 3 made of the nitride insulating film and the luminescent layer 4 of the upper insulating layer 5 are oxygen-free layers 3a, 5a made of a nitride containing no oxygen. Portions most apart from the luminescent layer 4 of the lower insulating layer 3 and the upper insulating layer 5 made of the nitrate insulating film are oxygen-containing layers 3b, 5b made of a nitride or an oxide containing oxygen. The adhesion between the insulating layer and the luminescent layer of the thin film EL display element 100 is improved, and the breakdown mode of the insulating layers can be made the self-recovery type in which no dielectric breakdown proceeds.

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 (Electroluminescen) used for displays of various information terminal devices.
ce) The present invention relates to a display element, and more particularly to a thin film EL display element structure having a high withstand voltage and being hard to break and improving reliability.

[0002]

2. Description of the Related Art Conventionally, a thin film EL display element has zinc sulfide (ZnS), alkaline earth sulfide (CaS, SrS), etc. as a luminescent base, and manganese (Mn),
It utilizes a 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), etc., and is attracting attention as a self-luminous 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 a vehicle-mounted display device. FIG. 8 is a schematic diagram showing a typical cross-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, which are 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,
A nitride such as AlN and a complex oxide such as PbTiO ₃ and PZT have been proposed. Further, an insulating layer having a laminated structure in which a plurality of them are combined has also been proposed.

[0003]

Since the thin film EL display device is driven under a high voltage, it is required that the insulating layer has a high withstand voltage and a large dielectric constant.
Further, in order to complete the thin film EL display device, the insulating layer must have the following properties. First,
Adhesion to the light emitting layer using zinc sulfide (ZnS) as a base material must be good not only for the finished thin film EL display device but also for the whole process of forming the device. In other words, film peeling often occurs between the light emitting layer and the insulating layer even in a wet etching process or the like when the electrode is finely processed into a desired shape during the process. Secondly, in the case of dielectric breakdown, a self-healing breakdown mode in which the breakdown is pinpointed and the breakdown does not expand further is preferred, rather than a breakdown mode in which the breakdown propagates one after another and becomes a large breakdown. ..
In other words, if this self-healing destruction mode,
Even if dielectric breakdown occurs, only small invisible breaking points remain, which also leads to an improvement in the yield of thin film EL display elements. Here, it is known to use nitride for the insulating layer. This is because when an oxide-based insulating film is formed on the light emitting layer by using oxygen plasma, zinc sulfide in the light emitting layer is oxidized, the number of recombination centers increases, and the light emission efficiency decreases. However, conventionally, there is no proposal that comprehensively considers the improvement of the adhesiveness and the destruction mode for the above-mentioned light emitting layer, and the type of the insulating layer has been empirically determined.

The present invention has been made to solve the above problems, and an object of the present invention is to improve the adhesiveness between an insulating layer and a light emitting layer and to prevent the destruction mode of the insulating layer. Self-healing thin film E in which insulation breakdown does not progress
It is to provide an L display device.

[0005]

The structure of the invention for solving the above-mentioned problems is a thin film EL in which a lower electrode, a lower insulating layer, a light emitting layer, an upper insulating layer and an upper electrode are sequentially laminated on an insulating substrate. In the display element, the lower insulating layer or the upper insulating layer adjacent to the light emitting layer is composed of a nitride insulating film, and at least a contact portion with the light emitting layer in a thickness direction of the nitride insulating film. It is characterized in that the nitride does not contain oxygen, and the nitride or oxide containing oxygen is used at least in a portion farthest from the light emitting layer in a thickness direction of the nitride insulating film.

[0006]

[Operation and effect] The lower insulating layer and the upper insulating layer adjacent to the light emitting layer of the thin film EL display device are composed of a nitride insulating film. Then, a nitride containing no oxygen is used in at least a portion in contact with the light emitting layer in the thickness direction of the nitride insulating film, and oxygen is used in at least a portion farthest from the light emitting layer in the thickness direction of the nitride insulating film. A nitride or an oxide containing That is, a nitride insulating film is used for the lower insulating layer and the upper insulating layer of the thin film EL display element of the present invention, and oxygen contained in the nitride insulating film is controlled in the film thickness direction. This improves the adhesiveness between the light emitting layer typified by zinc sulfide (ZnS) and the nitride-based insulating film, and self-recovers the breakdown mode of the nitride-based insulating film so that the initial breakdown does not propagate. It can be a mold.

The inventors have found the following as a major cause of the film peeling phenomenon that often occurs between the light emitting layer and the insulating layer of a thin film EL display device. A sputtering method, in particular, a reactive sputtering method is often used as a method for forming an insulating layer of a thin film EL display element because a dense and high-quality film layer can be obtained. In this method, for example, when an oxide-based insulating film is formed as the insulating layer, oxygen exists in the chamber when the insulating layer is formed,
The resulting oxygen plasma oxidizes the surface of the light emitting layer made of zinc sulfide (ZnS). The general concept is that zinc oxide (ZnO) is directly produced by the oxidation of the surface of the light emitting layer. On the other hand, the inventors have found that zinc sulfate (ZnSO ₄ ) is formed in the vicinity of the surface of the light emitting layer by the oxidation of the surface of the light emitting layer by oxygen plasma. Compared to zinc sulfide or zinc oxide, this zinc sulfate is a substance that is about 100,000 times more soluble in water as shown in FIG. 7, and when water is present in the surroundings such as in a cleaning process or a wet etching process, The zinc sulfate formed during the process dissolves out and film peeling occurs from that part.

In order to prevent the peeling of the film due to the above reasons, it is necessary to prevent oxygen plasma from existing at the initial stage when the insulating layer is formed. A silicon nitride (SiN _x ) film is a most typical nitride film as a non-oxide insulating film. In addition, the inventors of the present invention have found the following phenomenon as a result of earnest experimental research on the destruction mode. That is,
Silicon nitride film containing no oxygen (SiN _x )
In the film, the dielectric breakdown became a propagation mode, and once the 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 dielectric breakdown did not propagate. From the above-mentioned results, the inventors should provide the insulating layer for preventing the peeling of the film between the light emitting layer and the insulating layer and for making the breakdown mode self-recovering, to have the constitution of the present invention. I understood. That is, the film peeling phenomenon of the insulating film is controlled by the state of the contact portion with the light emitting layer, and the breakdown mode of the insulating film is conversely controlled by the state of the portion farthest from the light emitting layer.

[0009]

EXAMPLES The present invention will be described below based on specific examples. FIG. 1 is a schematic view showing a vertical section of a thin film EL display device according to the present invention. The thin film EL display device 100 includes a glass substrate 1 (thickness:
1.1mm, HOYA NA40: non-alkali glass)
The following thin films are formed and configured. ITO (Indium Tin Oxide) is formed on the glass substrate 1.
Tin) lower electrode (transparent electrode) 2 made of a transparent conductive film, lower insulating layer 3 made of a nitride insulating film, light emitting layer 4, upper insulating layer 5 made of a nitride insulating film, and upper electrode 5 made of an Al thin film. Are formed. As the light emitting layer 4, ZnS: Mn was used, which was a zinc sulfide (ZnS) base material and a small amount of manganese (Mn) was added to emit orange light. The 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 nitride containing no oxygen. Further, the most distant parts of the lower insulating layer 3 and the upper insulating layer 5 made of a nitride insulating film from the light emitting layer 4 are the aerobic layers 3b and 5b containing oxygen. These aerobic layers 3b and 5b are made of a nitride or oxide containing oxygen.

FIG. 2 is an explanatory view showing the distribution of nitrogen concentration and oxygen concentration in the film 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 has a shape of SiN _x in a contact portion adjacent to the light emitting layer, and has a shape of SiO _x N _y as the distance from the light emitting layer increases, and a shape of SiO _{x in} a portion (front surface) farthest from the light emitting layer. And That is, the oxygen-free layers 3a and 5a are made of SiN _x , and the aerobic layers 3b and 5a.
b consists of SiO _x .

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

[0012] For comparison experiment with the SiN _x -SiO _x N _y -SiO _x products, each of the lower insulating layer 3 and the upper insulating layer 5 S
An element formed of only iN _x is a SiN _x product. Further, 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
And the upper insulating layer 5 sputters 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 the SiO _x product are 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 cause film peeling even in the photoetching process of the upper electrode 6 and had no problem. However, SiO _x
The product peeled off in the cleaning process and the wet etching process such as the photo-etching process, and a satisfactory thin film EL display device could not be manufactured. Film peeling in this case 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 peeled Si
It was found that ZnSO ₄ was formed on the outermost surface of the light emitting layer (ZnS: Mn) in the O _x product. 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 is formed.
It is considered that the layer was dissolved in water during the wet etching process such as the cleaning process and the photoetching process, and the film peeling occurred from there. It is considered that this ZnSO ₄ was formed by oxidizing ZnS, which is the base material of the light emitting layer, by the oxygen plasma generated by sputtering during the formation of the insulating film (SiO _x ). Here, conventionally, it has been generally accepted that ZnS is directly converted into ZnO by oxidation. It is considered that the ZnS 4 of the light-emitting layer of the SiN _x -SiO _x N _y -SiO _x product and the SiN _x product of the present invention were not directly exposed to oxygen plasma, and thus ZnSO ₄ was not formed and film peeling did not occur.

Next, the completed SiN _x -SiO _x N _{y of} the present invention.
-The drive voltage was increased until the dielectric breakdown occurred for the SiO _x product and the SiN _x product, and the states after the dielectric breakdown were compared. Although there was not much difference in the voltage value at which the dielectric breakdown occurred, the breakdown modes of the two were significantly different. That is, SiN _x -SiO _x N _y -Si
With respect to the O _x product, the dielectric breakdown only formed a hole with a diameter of about 0.1 mm to 0.5 mm and did not proceed any further (self-recovery type). On the other hand, in the case of the SiN _x product, when a small dielectric breakdown occurs at first, it propagates instantly, and the entire light emitting pixel is broken in a blink (propagation type). The cause of this difference in breakdown mode is unknown, but experimental results showing a self-recovery breakdown mode when oxygen is present at the outermost surface of the nitride-based insulating film opposite to the surface in contact with the light emitting layer Has been obtained.

FIG. 3 is a schematic view showing a vertical section in another embodiment of the thin film EL display element according to the present invention. It should be noted that although the configuration above the light emitting layer 4 is shown in this figure, the configuration below the light emitting layer 4 is also symmetrical. An upper insulating layer 5 is formed on the light emitting layer 4. The upper insulating layer 5 is similar SiN _x -SiO the above-described examples _x N _y
It is a configuration of -SiO _x. In this embodiment, an insulating layer 7 made of tantalum pentoxide (Ta ₂ O ₅ ) having a film thickness of 4000 Å is formed on the upper insulating layer 5. The insulating layer 7 is formed to further improve the withstand voltage compared with the case of only the upper insulating layer 5. In this way, the effect is the same as that described above even if another type of insulating layer is stacked and formed on the upper insulating layer 5.

4 to 6 are explanatory views showing distributions of nitrogen concentration and oxygen concentration in another embodiment of the nitride type insulating film according to the present invention in the film thickness direction. In FIG. 4, only the contact portion of the nitride-based insulating film with the light emitting layer is composed of the SiN _x layer,
When it is separated from the light emitting layer, it has a structure of a SiO _x N _y layer.
In this one, there is no SiO _x layer. In FIG. 5, the nitride-based insulating film has a SiN _x layer continuing from the contact portion with the light emitting layer,
SiO _x N on the outermost shell surface, which is the part farthest from the light emitting layer
_{The y} layer is formed. In FIG. 6, the nitride insulating film has a SiN _x layer continuing from the contact portion with the light emitting layer, and the SiO _x layer is formed on the outermost shell surface that is the farthest portion from the light emitting layer. The structures of the nitride-based insulating films shown in FIGS. 4 to 6 are all effective in improving the film peeling and the breakdown mode as in the above-mentioned embodiments. As the light emitting layer in the above embodiment, Z
As explained with nS: Mn, ZnS: Tb (green emission) and Zn
The same applies when other additives such as S: Sm (red emission) are added. In the present invention, the nitride-based insulating film is made of SiN _x series, but may be made of other nitrides such as AlN series.
In this example, the lower insulating layer and the upper insulating layer were symmetrically configured, but the improvement of the dielectric breakdown mode and the effect of preventing film peeling are dominated by the upper insulating layer, and only the upper insulating layer is provided by the present invention. You can configure it.

[Brief description of drawings]

FIG. 1 is a schematic view showing a vertical 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 nitrogen concentration and oxygen concentration in a film thickness direction of a nitride insulating film according to the example.

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

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

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

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

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

FIG. 8 is a schematic view showing a vertical section of a conventional thin film EL display device.

[Explanation of symbols]

 1-Glass Substrate (Insulating Substrate) 2-Lower Electrode 3-Lower Insulating Layer (Nitride Insulating Film) 3a-Oxygen-Free Layer (Nitride Not Containing Oxygen) 3b-Aerobic Layer (Nitride Containing Oxygen or Oxide) 4-Emitting layer 5-Upper insulating layer (nitride-based insulating film) 5a-Oxygen-free layer (nitride that does not contain oxygen) 5b-Aerobic layer (nitride or oxide that contains oxygen) 6-Upper part electrode

Front page continuation (72) Inventor Yoshiyasu Ando 1-1, Showa-cho, Kariya city, Aichi Prefecture Nihon Denso Co., Ltd. (72) Inventor Masayuki Suzuki 1-1-cho, Showa-cho, Kariya city, Aichi prefecture Within

Claims (1)

[Claims] 1. A lower electrode, a lower insulating layer, and
A thin film EL display device comprising a light emitting layer, an upper insulating layer and an upper electrode, which are sequentially laminated, wherein the lower insulating layer or the upper insulating layer adjacent to the light emitting layer is composed of a nitride-based insulating film, A nitride containing no oxygen in at least a contact portion with the light emitting layer in the thickness direction of the physical insulating film, and a nitride containing oxygen in at least a portion farthest from the light emitting layer in the thickness direction of the nitride insulating film. Alternatively, a thin film EL display device characterized by using an oxide.