JPH0613185A - Thin film el display element - Google Patents

Abstract

PURPOSE:To provide a thin film EL display element by which high brightness emission becomes possible by low voltage impression. CONSTITUTION:A thin film EL display element 100 is formed by laminating a transparent electrode 12, the first emission layer 13, the first and the second insulating layers 14a and 14b, the second emission layer 15 and a back plate 16 in order on a glass substrate 11. In the thin film EL display element 100, The insulating layers are formed substantially as a single layer of the first and the second insulating layers 14a and 14b, so that a voltage drop can be reduced in the insulating layers. That is, since an electric field applied to the thin film EL display element 100 is impressed effectively on the first and the second emission layers 13 and 15, partial pressure of impressed voltage to the emission layers is increased, so that emission brightness to the impressed voltage can be heightened.

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 (Electroluminescence) display element used as a surface emitting light source for, for example, a dot matrix of instruments, a character display display or backlight illumination.

[0002]

2. Description of the Related Art Thin-film EL display elements are made of zinc sulfide.
It takes advantage of the phenomenon of light emission when a fluorescent substance such as (ZnS) is applied with an electric field, and is attracting attention as a constituent of a self-luminous flat display. FIG. 5 shows a conventional thin film E
3 is a schematic diagram showing a typical cross-sectional structure of the L display element 10. FIG. The thin film EL display element 10 is formed by sequentially stacking a transparent electrode 2, a first insulating layer 3, a light emitting layer 4, a second insulating layer 5 and a back electrode 6 on a glass substrate 1. The glass substrate 1 which is an insulating substrate is generally N
Non-alkali glass that does not contain alkali ions such as a is used. As the transparent electrode 2 and the back electrode 6, ITO in which indium oxide (In ₂ O ₃ ) is doped with tin (Sn) is used.
An (Indium Tin Oxide) film or zinc oxide (ZnO) doped with gallium (Ga), aluminum (Al), or the like is used. The ITO film is an optically transparent conductive film,
Since it has a low resistivity, it has been widely used for transparent electrodes. As the first insulating layer 3 and the second insulating layer 5 which are insulating films, tantalum pentoxide (Ta ₂ O ₅ ), silicon nitride (Si ₃ N ₄ ), SiO ₂ , Al ₂ O ₃ or a mixture thereof or those The composite membrane of is used. As the light emitting layer 4, for example, a material in which zinc sulfide (ZnS) is used as a base material and manganese (Mn), terbium (Tb), oxygen (O), fluorine (F) or the like is added as an emission center is used. An electric field of 10 ⁶ V / cm or more is applied to the light emitting layer 4. The emission color of the thin film EL display device depends on the type of additive in zinc sulfide (ZnS). For example, when manganese (Mn) is added as the emission center, it is yellow-orange, and when Tb, O, F is added. Gives a green emission.

[0003]

The thin film EL having the above structure.
A display element 10 was prepared, and a voltage was applied to make it emit light. As shown in FIG. 2 as a conventional product, the thin film EL display device 10 starts to emit light (luminance of 10 ⁰ = 1 cd / m ² or more) when a voltage of 200 V or more is applied, and when the applied voltage is 364 V. The emission brightness was about 2000 cd / m ² (1 KHz drive). Here, the inventors conducted extensive research into a method of obtaining high brightness at a voltage lower than that of the conventional product,
We reached the following conclusions. Since the insulating layers for limiting the current flowing through the light emitting layer without contributing to light emission are present on both sides of the light emitting layer, the voltage drop in the insulating layer portion becomes large and the driving voltage becomes high. That is, the voltage applied to the thin film EL display element is not effectively applied to the light emitting layer. In the conventional thin film EL display device, it is possible to reduce the film thickness in order to suppress the voltage drop in the insulating layer. However, if the insulating layer does not have a predetermined thickness per layer, the breakdown voltage will be exceeded and dielectric breakdown will occur. Further, if the insulating film is thinner than a predetermined thickness, pinholes and the like are likely to occur in the manufacturing process, and reliability is lost.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a thin film EL display device capable of emitting high brightness light by applying a low voltage. is there.

[0005]

The structure of the invention for solving the above-mentioned problems is a thin film E in which a laminated structure is formed on an insulating substrate and at least the material on the light extraction side is optically transparent.
In the L display device, the laminated structure has at least one insulating layer and one layer on each side of the insulating layer.
It is characterized by comprising at least two light emitting layers and electrodes facing both outermost layers with the light emitting layers sandwiched therebetween.

[0006]

According to the above means, since the insulating layer forming the thin film EL display element can be made substantially single (one layer), the voltage drop in the insulating layer is reduced. Further, since the insulating layer can have a predetermined thickness, it is possible to prevent dielectric breakdown beyond the breakdown voltage. Thereby, the electric field applied to the thin film EL display element is effectively applied to the light emitting layer, the partial voltage of the voltage applied to the light emitting layer is increased, and the emission brightness with respect to the applied voltage can be increased.

[0007]

EXAMPLES The present invention will be described below based on specific examples. FIG. 1 is a schematic diagram showing a cross-sectional structure of a thin film EL display device 100 according to the present invention. The thin film EL display device 100 includes a glass substrate 1 which is an insulating substrate.
The following thin films are sequentially laminated and formed on the substrate 1. On the glass substrate 11, a transparent electrode 1 made of an ITO transparent conductive film which is an oxide transparent electrode transparent to visible light.
2 is formed, and on the upper surface thereof, a first light emitting layer 13 made of zinc sulfide (ZnS) doped with Tb, O, F, and made of an optically transparent silicon nitride represented by the chemical formula of SiN _x. The first insulating layer 14a and the second insulating layer 14b made of tantalum pentoxide (Ta ₂ O ₅ ), terbium (Tb), oxygen (O),
Fluorine (F) -added zinc sulfide (ZnS) second light emitting layer 15 and aluminum (Al) back electrode 1
6 is formed.

Next, the above-mentioned thin film EL display device 1
The manufacturing method of 00 is described below. First, the glass substrate 11
The transparent electrode 12 was formed on the top by the vacuum evaporation method. As a specific vapor deposition material, tin oxide (SnO ₂ ) is mixed in indium oxide (In ₂ O ₃ ) so that Sn atoms are 5% with respect to In atoms, and the mixture is fired to form a pellet. What was done was used. The glass substrate 11 and the vapor deposition material were set in an electron beam vapor deposition apparatus, and the vacuum chamber was evacuated to 3 × 10 ⁻⁴ Pa while keeping the glass substrate 11 at 250 ° C. Next, oxygen was introduced up to 6.7 × 10 ^-2 Pa and the deposition rate was 0.1-
An ITO transparent conductive film was formed to a thickness of 200 nm while adjusting the output of the electron beam so as to be 0.3 nm / sec. This ITO transparent conductive film was patterned by using a photolithography method to form the transparent electrode 12.

A first light emitting layer 13 in which ZnS is used as a base material and Tb, O, F is added as a light emitting center on the transparent electrode 12 is formed.
Was formed by sputtering. Specifically, the glass substrate 11 on which the above-mentioned layers were formed was set in a sputtering apparatus, the glass substrate 11 was kept at 400 ° C., and the vacuum chamber was evacuated to 1 × 10 ⁻³ Pa or less. After that, Ar gas was introduced at a rate of 30 cc / min and He gas was introduced at a rate of 20 cc / min into the vacuum chamber while adjusting the exhaust valve to adjust the pressure in the vacuum chamber to 2.4 Pa.
Set to. Using a sintering target in which Tb, O, F was added to ZnS, 1.86 W / cm ^{2 was} added per unit area, pre-sputtering was performed for 15 minutes, and then film formation was performed at a deposition rate of 50 nm / min. One light emitting layer 13 was deposited to a thickness of 800 nm. This first
After forming the light emitting layer 13, the glass substrate 11 is heated at 550 ° C. for 3 hours.
Heat treatment was performed for an hour.

Next, on the first light emitting layer 13, RF (Rad
io Frequency: S by the magnetron sputtering method
A first insulating layer 14a made of iN _x and a second insulating layer 14b made of Ta ₂ O ₅ were formed. First, the first insulating layer 14a of the first layer was formed as follows. The glass substrate 11 on which the transparent electrode 12 is formed is set in the sputtering device 2
After holding at 00 ℃ for 30 minutes, the inside of the vacuum chamber is 3.5 × 10 ^-3 P
Exhausted to a. After that, while introducing Ar gas at a rate of 60 cc / min and N ₂ gas at a rate of 140 cc / min into the vacuum chamber, the exhaust valve was adjusted to set the pressure in the vacuum chamber to 0.75 Pa. Using Si as a target, applying high-frequency power of 1.55 W / cm ² per unit area of the target, performing pre-sputtering for 10 minutes, and then forming a film at a deposition rate of 7.63 nm / min.
The insulating layer 14a was deposited to 100 nm.

Next, the second insulating layer 14b as the second layer was formed as follows. The glass substrate 11 on which the above layers were formed was set in a sputtering apparatus and kept at 200 ° C. for 30 minutes, and then the vacuum chamber was evacuated to 3 × 10 ^-2 Pa. Then, while introducing Ar gas at a rate of 180 cc / min and O ₂ gas at a rate of 20 cc / min into the vacuum chamber, the exhaust valve was adjusted to set the pressure in the vacuum chamber to 1 Pa. Ta ₂ O as a target
Using a sintered target consisting of ₅ and applying high frequency power of 2.07 W / cm ² per unit area of the target and performing pre-sputtering for 10 minutes, film formation was performed under the conditions of a deposition rate of 5.76 nm / min and the second insulating layer 14b was deposited to a thickness of 500 nm.

Next, a second layer is formed on the insulating layers 14a and 14b.
The light emitting layer 15 was formed. The second light emitting layer 15 was formed by the same method as the first light emitting layer 13 and was deposited to 800 nm. Furthermore,
A back electrode 16 was formed on the second light emitting layer 15 by an electron beam evaporation method using Al. High-purity metallic aluminum was used as the vapor deposition material. The second insulating layer 14b
The glass substrate 11 and the vapor deposition material formed up to this point are set in an electron beam vapor deposition apparatus, and the inside of the vacuum chamber is 6.7 × 10 ⁻⁴ P.
After evacuation to a or less, the electron beam output was adjusted so that the film forming rate was 3 nm / sec or more, and an Al film was deposited to 300 nm. This Al film was patterned by a photolithography method to form the back electrode 16.

In the thin film EL display device 100 according to this embodiment, the insulating layer has a two-layer structure of 14a and 14b. This is for the following reason. An insulating layer film made of Ta ₂ O ₅ is directly formed on the light emitting layer made of ZnS by a sputtering method. At this time, a trace amount of zinc sulfate (ZnSO ₄ ) is generated at the interface between the light emitting layer and the insulating layer by converting the O ₂ gas introduced into the vacuum chamber into plasma. Since the generated ZnSO ₄ has a high solubility in water, peeling occurs at the interface between the light emitting layer and the insulating layer when the back electrode is patterned in the subsequent step. In order to prevent this peeling, the thin film E
In the L display element 100, a first insulating layer made of SiN _x that does not generate ZnSO ₄ is formed immediately above a light emitting layer made of ZnS, and Ta having a large relative dielectric constant is formed thereon. The second insulating layer made of ₂ O ₅ is formed. Therefore, if an insulating layer that does not generate ZnSO ₄ at the interface with the light emitting layer, such as silicon nitride or tantalum sulfide, is used, there is no problem even if only one insulating layer is used. Further, in a process which does not use water in a subsequent step, for example, in a process of forming a back electrode only by sputtering or vapor deposition in a specific region using a mask such as stainless steel, an insulating layer made of Ta ₂ O _{5 is used.} It may be a single layer. When the thin film EL display device 100 thus obtained was energized to emit light by passing between the transparent electrode 12 and the back electrode 16, stable light emission could be observed without dielectric breakdown or uneven brightness. Since the thin film EL display device of the present invention has a vertically symmetrical layered structure on the insulating substrate as in the conventional laminated structure, the current-voltage characteristics are the same in both upper and lower directions. Therefore, the driving circuit for driving the thin film EL display element may be a simple one as in the past.

FIG. 2 is a characteristic diagram showing the relationship between the applied voltage and the emission luminance of the thin film EL display device of the present invention and the conventional thin film EL display device. Since the thin film EL display device of the present invention has only one insulating layer, high luminance is obtained with a low driving voltage from the time when the electric field strength in the light emitting layer exceeds the light emission starting electric field strength. Therefore, in the saturated luminance region (the region where the characteristic curves of the product of the present invention and the conventional product intersect, which is equal to or higher than the emission luminance), the product of the present invention can obtain a high emission luminance at the same drive voltage as compared with the conventional product. There is.

FIG. 3 is a schematic view showing the cross-sectional structure of the second embodiment of the thin film EL display device according to the present invention. Thin film EL display element 200 according to the present embodiment
Is an example in which the emission color of the first light emitting layer and the emission color of the second light emitting layer in the thin film EL display element 100 of the first embodiment are changed. The layers having the same structure as the thin film EL display element 100 of the first embodiment are designated by the same reference numerals and the description thereof will be omitted. ITO on the glass substrate 11
A transparent electrode 12 made of a transparent conductive film is formed. A first light emitting layer 13 made of ZnS doped with Tb, O, F, a first insulating layer 14a made of silicon nitride represented by SiN _x chemical formula, and a Ta ₂ doped with Al ₂ O ₃ are formed thereon. O ₅
A second insulating layer 14b made of Mn, a second light emitting layer 15 'made of ZnS to which Mn is added, and a back electrode 16 made of Al are sequentially formed.

Next, the above-mentioned thin film EL display element 2
The manufacturing method of 00 is described below. The basic layer structure of the thin film EL display element 200 is the same as that of the above-described thin film EL display element 100, and the transparent electrode 12, the first light emitting layer 13, the first insulating layer 14a, and the second insulating layer 14a are provided on the glass substrate 11.
The insulating layer 14b, the second light emitting layer 15 ', and the back electrode 16 are formed. Among these, the transparent electrode 12 and the first light emitting layer 1
3, the first insulating layer 14a and the second insulating layer 14b were formed by the same method as in the first embodiment. Second light emitting layer 1
5'was formed by electron beam evaporation and deposited to a thickness of 600 nm. Specifically, 0.5 to 1 mol% of Mn powder was mixed into ZnS powder and mixed well, and then pellets molded and sintered were used as an evaporation material. The glass substrate 11 on which the second insulating layer 14b was formed was kept at 200 ° C. in a vacuum deposition tank, and the inside of the vacuum tank was evacuated to a pressure of 1.3 × 10 ⁻³ Pa or less. After that, electron beam evaporation was performed under the conditions of a deposition rate of 0.1 to 0.5 nm / sec. Next, the back electrode 16 is formed on the second light emitting layer 15 '.
Was formed. This back electrode 16 was formed by the same method as in the first embodiment. The thickness of each layer other than the second light emitting layer 15 'was formed to be the same as that of the first embodiment.

By applying a voltage to the thin film EL display element 200, a green emission color is obtained from the first emission layer 13 and a yellow-orange emission color is obtained from the second emission layer 15 '. For this reason, these colors appear yellow to the human eye. This yellow tint is determined by the ratio of the green light emission brightness to the yellow-orange light emission brightness. That is, when the film thickness of the first light emitting layer 13 for green light emission and the film thickness of the second light emitting layer 15 'for yellow orange light emission are changed, as shown in FIG.
It is possible to obtain an arbitrary emission color on a line connecting green and yellow-orange on the coordinates of the CIE (International Commission on Illumination) xy chromaticity diagram. Incidentally, the change of the color tone can be performed not only by changing the film thickness described above but also by adjusting the condition of the applied voltage.

[Brief description of drawings]

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

FIG. 2 is a characteristic diagram showing a relationship between an applied voltage and a light emission luminance in the thin film EL display element according to the example and a conventional thin film EL display element.

FIG. 3 is a schematic view showing another embodiment of the cross-sectional structure of the thin film EL display device according to the present invention.

FIG. 4 is an explanatory diagram in which an emission spectrum when light is emitted from the thin film EL display device having the layer structure of FIG. 3 is plotted on the coordinates of the CIExy chromaticity diagram.

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

[Explanation of symbols]

 11 ... Glass substrate (insulating substrate) 12 ... Transparent electrode 13 ... First light emitting layer 14a ... First insulating layer 14b ... Second insulating layer 15 ... Second light emitting layer 16 ... Back electrode

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor, Masaru Hattori, 1-1, Showa-cho, Kariya city, Aichi prefecture, Nihondenso Co., Ltd.

Claims (1)

[Claims] 1. A thin film EL having a laminated structure on an insulating substrate and at least a material on a light extraction side is optically transparent.
In the display device, the laminated structure includes at least one insulating layer, one or more light emitting layers on both sides of the insulating layer, and electrodes facing both outermost layers of the light emitting layer. A thin film EL display device characterized by the above.