JPH05326145A - Thin film el display element - Google Patents

Abstract

PURPOSE:To provide a red light emitting thin film EL display element having a high luminance and a satisfactory color purity. CONSTITUTION:A thin film EL display element 100 is formed of a first transparent electrode 12, transparent first insulating layer 13, light emitting layer 14 consisting of zinc sulfide (ZnS) to which samarium (Sm) is added in the form of simple substance, transparent second insulating layer 15, and second transparent electrode 16 successively laminated on a glass base 11. This thin film EL display element has no unnecessary energy loss of colliding electrons and a high luminance since the samarium (Sm) is present in the form of simple substance as the luminous center of the light emitting layer. Further, the peak on the shorter wave side from red of emission spectrum is minimized to provide red emission with a satisfactory color purity.

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 (Electrical Electrification) used for, for example, a surface emitting source for a backlight of instruments.
roluminescence) Display element.

[0002]

2. Description of the Related Art Conventionally, a thin film EL display element has been noted as a self-luminous flat display by utilizing a phenomenon of emitting light when an electric field is applied to a phosphor such as zinc sulfide (ZnS). There is. As a typical layer structure of a thin film EL display device, a first layer formed of an optically transparent ITO film on a glass substrate which is an insulating substrate.
It is known that an electrode, a first insulating layer made of tantalum pentoxide (Ta ₂ O ₅ ) and the like, a light emitting layer, a second insulating layer and a second electrode made of an ITO film are sequentially laminated. ITO (In
The dium tin oxide film is a transparent conductive film obtained by doping indium oxide (In ₂ O ₃ ) with tin (Sn), and has been widely used for transparent electrodes since it has a low resistivity.
As the light emitting layer, for example, zinc sulfide is used as a base material, and manganese (Mn) or terbium trifluoride (Tb) is used as a light emitting center.
The one to which F ₃ ) is added is used. The emission color of the thin film EL display device is determined by the type of additive in zinc sulfide. For example, when manganese (Mn) is added as the emission center, it is yellow-orange, and when terbium trifluoride (TbF ₃ ) is added. Gives a green emission.

[0003]

In the thin film EL display device having the above-mentioned layer structure, zinc sulfide added with samarium trifluoride (SmF ₃ ) has been studied as a constituent material of the light emitting layer for obtaining red light emission. .. A thin film EL display device having a light emitting layer made of this constituent material has a low emission brightness of 1000 cd / m ² (5 KHz drive) at the maximum, and has a poor color purity because the emission spectrum includes a component on the shorter wavelength side than red. Then, it is not practical as a display device such as an EL panel.

Therefore, in recent years, samarium trichloride (SmC
A thin film EL display device using zinc sulfide added with l ₃ ) as another constituent material of a light emitting layer for obtaining red light emission has been studied. This thin film EL display element has less components on the shorter wavelength side than red in the emission spectrum, and compared with the thin film EL display element using zinc sulfide added with samarium trifluoride (SmF ₃ ) as the constituent material of the light emitting layer. ,
An improvement in color purity can be seen. However, at present, the causal relationship as to why the color purity is improved by using zinc sulfide added with samarium trichloride (SmCl ₃ ) as a constituent material of the light emitting layer has not been clarified at present. For this reason,
There was no definite guideline for the constituent material of the light emitting layer for obtaining a red light emitting thin film EL display element having high brightness and good color purity.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a red-emitting thin-film EL display device having high brightness and good color purity. ..

[0006]

The structure of the invention for solving the above-mentioned problems comprises a first electrode, a first insulating layer, a light emitting layer using zinc sulfide (ZnS) as a base material, and a second electrode on an insulating substrate. A thin-film EL display device in which an insulating layer and a second electrode are sequentially laminated with at least a material on the light extraction side using an optically transparent material, and samarium (Sm) is a single substance as the emission center of the emission layer. It is characterized in that it is added in the form.

[0007]

[Operation and effect] Samarium (Sm) in the form of a single film is a thin film E
Zinc sulfide (ZnS) of the L display element is added as a luminescent center of a luminescent layer having a base material. Here, samarium trifluoride (SmF ₃ ) or samarium trichloride (SmCl ₃ ) was added as the emission center of the light emitting layer of the conventional red light emitting thin film EL display element. In the light emitting layer to which these light emitting centers are added, energy loss of collision electrons occurs due to fluorine and chlorine existing in combination with samarium (Sm). Therefore, the red-emitting thin film EL
The emission efficiency of the display element was lowered, and the emission spectrum of the display element contained more wavelengths on the short wavelength side than red. That is, in the thin film EL display device of the present invention, since samarium (Sm) exists as a simple substance as the light emission center of the light emitting layer, there is no unnecessary energy loss of collision electrons and the light emission brightness is high. Further, in the thin film EL display device of the present invention, the emission spectrum has a smaller peak on the short wavelength side than red, and the color purity of red emission is improved.

[0008]

EXAMPLES The present invention will be described below based on specific examples. FIG. 1 is a schematic view 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 laminated and formed on the 1 in sequence. On the glass substrate 11, optically transparent zinc oxide
A first transparent electrode (first electrode) 12 made of (ZnO) is formed, and an optically transparent first insulating layer 13 made of tantalum pentoxide (Ta ₂ O ₅ ) and samarium (Sm) are formed on the upper surface thereof.
Is added as a simple substance in the form of a zinc sulfide (ZnS) light emitting layer 14, an optically transparent tantalum pentoxide (Ta ₂ O ₅ ) second insulating layer 15, and an optically transparent zinc oxide (ZnO). )
A second transparent electrode (second electrode) 16 composed of 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
A first transparent electrode 12 was formed on top. As a vapor deposition material,
Gallium oxide (Ga ₂ O ₃ ) was added to zinc oxide (ZnO) powder and mixed, and the mixture was molded into pellets. An ion plating device was used as a film forming device. Specifically, while maintaining the temperature of the glass substrate 11 at 150 ° C., the inside of the ion plating apparatus was evacuated to 5 × 10 ⁻³ Pa. After that, introduce argon (Ar) gas to 6.5 × 10 ^-1
The beam power and the high frequency power were adjusted so that the deposition rate was in the range of 1.0 to 3.0 Å / sec while maintaining the pressure Pa.

Next, a first insulating layer 13 made of tantalum pentoxide (Ta ₂ O ₅ ) was formed on the first transparent electrode 12 by sputtering. Specifically, the temperature of the glass substrate 11 is set to 200 ° C.
And maintain the inside of the sputtering system at 1.0 Pa, and introduce a mixed gas of argon (Ar) and oxygen (O ₂ ) into the sputtering system (200c
c / min) and the deposition rate was 2Å / sec with a high frequency power of 1 kW.

Zinc sulfide (ZnS) is formed on the first insulating layer 13.
With samarium as the base material and metal samarium (Sm) as the emission center
Sulfide: Samarium (ZnS: S) directly doped with
The light emitting layer 14 made of m) was formed by sputtering. By this method, the structure of the light emitting layer 14 of the present invention can be directly formed. Specifically, the temperature of the glass substrate 11 is maintained at 250 ° C., the inside of the sputtering apparatus is maintained at 4 Pa, a mixed gas of argon (Ar) and helium (He) is introduced into the apparatus, and high frequency power of 150 W is applied. The deposition rate was 40Å / sec.

After the above layers are formed on the glass substrate 11,
Heat treatment was performed at 400 to 600 ° C. for 2 hours in a vacuum of 5 × 10 ⁻⁴ Pa. After the heat treatment, the second insulating layer 15 made of tantalum pentoxide (Ta ₂ O ₅ ) was formed on the light emitting layer 14 by the same method as the first insulating layer 13. After that, the second transparent electrode 16 made of zinc oxide (ZnO) was formed by the same method as the first transparent electrode 12. The thickness of each layer is the same as the first and second transparent electrodes 1.
2 and 16 are 3000 Å, 1st and 2nd insulating layers 13 and 15 are 4000
Å, the light emitting layer 14 is 8000Å.

FIG. 2 shows a red light emitting thin film EL display device having the structure of the above-described embodiment and a red light emitting thin film EL display device to which samarium trifluoride (SmF ₃ ) is added as a light emitting center of a conventional light emitting layer. Applied voltage V
_This is a comparison of the relationship between _OP (V) and light emission luminance L (cd / m ² ). Further, FIG. 3 shows a red light emitting thin film EL in which samarium (Sm) having the structure of the above-described embodiment is added in a single form.
Red-emitting thin-film EL with samarium trifluoride (SmF ₃ ) added as the emission center of the display element and conventional emission layer
It is a comparison of the emission spectrum (wavelength-spectral intensity) in the display device. As is clear from FIG. 2 and FIG. 3, in the red light emitting thin film EL display device 100 having the light emitting layer structure of the present invention, red having a high luminance and a small emission spectrum peak on the shorter wavelength side than red, and having a good color purity. It was found that light emission was obtained.

FIG. 4 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 device 500 according to the present embodiment
Is a laminated thin film E obtained by combining the red light emitting thin film EL display device 100 of the first embodiment and the second thin film EL display device 200 having the second light emitting layer 24.
It constitutes an L display element. The layers of the thin film EL display device 100 of the first embodiment are designated by the same reference numerals and the description thereof is omitted. On the glass substrate 21 of the second thin film EL display element 20, zinc oxide (Zn
O) of the third transparent electrode 22 and tantalum pentoxide (T
The third insulating layer 23 made of a ₂ O ₅ ) was formed by the same method as in the previous embodiment. Next, the second light emitting layer 24 was formed thereon by the sputtering method. The second light emitting layer 24 is zinc sulfide.
Using (ZnS) as a base material and terbium as the emission center:
Oxygen: Fluorine (TbOF) is added to emit green light. On the second light emitting layer 24, tantalum pentoxide (Ta ₂ O
The fourth insulating layer 25 composed of ₅ ) and the fourth transparent electrode 26 were formed by the same method as in the above-mentioned embodiment. Third and fourth insulating layer 2
The film thickness of 3,25 is 4500Å, the second light emitting layer 24 is 8000Å,
The third and fourth transparent electrodes 22 and 26 were set to 3000 Å.

In the thin film EL display device 500 having the above structure, the first light emitting layer 14 or the second light emitting layer 2 is used.
By applying a voltage to No. 4, red and green emission colors are obtained. Furthermore, the first and second light emitting layers 14, 2
By causing 4 to emit light at the same time, amber emission, which is a mixture of these colors, can be obtained. Therefore, by combining these, multi-coloring can be realized.

The glass substrates 11 and 21 are assembled by vacuum injection of silicon oil in order to prevent moisture absorption. Then, the red color, the green color, and the intermediate color thereof are the emission colors from the glass substrate 11 side. Further, in the above structure, the second transparent electrode 16 and the fourth transparent electrode 26 may be shared. That is, after forming the second transparent electrode 16, the fourth insulating layer 25, the second light emitting layer 24, and the third insulating layer 2 are directly formed thereon.
3 and the third transparent electrode 22 are laminated in this order to form the glass substrate 21.
Can also be used as a dummy glass for assembling by injecting silicon oil under vacuum.

The present invention is not limited to the above embodiment, but various modifications such as the following are possible. (1) First, second, third and fourth insulating layers 13, 15, 23,
25 was composed of tantalum pentoxide (Ta ₂ O ₅ ), but Al ₂ O
It may be composed of ₃ , Si ₃ N ₄ , PbTiO ₃ , Y ₂ O ₃ and a laminate thereof. (2) The light emitting layer includes one layer, two layers, and three or more layers, for example, R
Thin-film EL with three light-emitting layers that emit GB respectively
A full color display is possible for the display device. (3) The light emitting layer was formed by the sputtering method.
ron Beam) It may be formed by a vapor deposition method or a CVD method. (4) The red light-emitting thin film EL display device of this example was formed by directly doping zinc sulfide (ZnS) with metal samarium (Sm) as a base material of the light emitting layer. A forming method is also conceivable. Samarium (Sm) halide as the emission center, for example, samarium trifluoride (SmF ₃ ), samarium trichloride
After forming the light emitting layer to which (SmCl ₃ ) is added, a high temperature annealing process is performed to remove the halogen. As the emission center, for example, samarium trifluoride (SmF)
₃ ), When forming a light emitting layer to which samarium trichloride (SmCl ₃ ) is added, a reducing gas is introduced so that samarium (Sm) becomes a single form. (5) In the above embodiment, light is emitted from both sides of the thin film EL display element, but light can be emitted from one side by appropriately changing the materials of the electrodes and the insulating layers.

[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 showing a relationship between an applied voltage and a light emission luminance in the thin film EL display device of the same example and a conventional thin film EL display device including a light emitting layer having samarium trifluoride (SmF ₃ ) as an emission center. It is a figure.

FIG. 3 is a characteristic diagram showing wavelengths and spectral intensities of a thin film EL display device of the same example and a conventional thin film EL display device including a light emitting layer having samarium trifluoride (SmF ₃ ) as an emission center. ..

FIG. 4 is a schematic view showing a cross-sectional structure of another embodiment of the thin film EL display device according to the present invention.

[Explanation of symbols]

 11-Glass substrate (insulating substrate) 12-First transparent electrode (first electrode) 13-First insulating layer 14-Light emitting layer 15-Second insulating layer 16-Second transparent electrode (second electrode) 100-Thin film EL display element

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yui Hattori 1-1-1, Showa-cho, Kariya city, Aichi prefecture

Claims (1)

[Claims] 1. A first electrode, a first insulating layer, and
What is claimed is: 1. A thin-film EL display device comprising a light-emitting layer containing zinc sulfide (ZnS) as a base material, a second insulating layer, and a second electrode, which are sequentially laminated at least with a material on the light extraction side being optically transparent. A thin film EL display device, wherein samarium (Sm) is added as a single substance as a light emission center of the light emitting layer.