JPH03222287A - Thin film el element - Google Patents

Abstract

PURPOSE:To cut the reflection from external lights without any reduction in luminous strength from an EL(electroluminescent) element and improve the visibility as a display panel by providing a multilayered reflection preventing film on the glass base surface on the opposite side to the EL element. CONSTITUTION:A thin film EL element is formed by successively laminating a transparent glass base 1, a transparent electrode 2, a first insulating layer 3, an EL luminescent layer 4, a second insulating layer 5 and a back plate 6, and a multilayered reflection preventing layer 7 is provided on the opposition to the glass base plate 1. The multilayered reflection preventing film 7 is constituted in a five-layer structure having a first layer 71, a second layer 72, a third layer 73, a forth layer 74 and a fifth layer 75 in the order from the air side. Namely, the multilayered reflection preventing film 7 is formed by repeating a low refractive index material and a high refractive index material from the air side. As the low refractive index material, either of MgF2 or SiO2 may be used, and as the high refractive index material, one of ZrO2, Ti2O5, TiO2 or CeO2, or a mixture consisting of the combinations thereof may be used. Hence, the reflection from external lights can be cut without any reduction in luminous strength from the thin film EL element, and an improvement in visibility as a display panel can be enhanced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a thin film EL element that can obtain EL light emission by applying an alternating current.

[Conventional technology]

In recent years, with the progress of the information society, the need for flat displays has been increasing more and more, and thin film EL devices, as one of them, have come into practical use in the past few years.

The structure of a typical conventional thin film EL element is, for example, disclosed in Japanese Unexamined Patent Publication No. 6
2-150690, and as shown in FIG. 5, a transparent electrode 2. is disposed on a transparent glass substrate 1. First insulating layer 3. EL light emitting layer 4. It is constructed by sequentially laminating a second insulating layer 5 and a back electrode 6. Here, as the transparent electrode 2, a transparent conductive film such as ITO is formed by weeding, and the first insulating layer 3 and the second insulating layer 5 have a high dielectric strength and a high dielectric constant in order to improve the light emission characteristics. YzO1A7 as a well-balanced material! zos.

TazOs+SiJ'n or the like is used and is mainly formed by sputtering. The EL light-emitting layer 4 is formed by vapor deposition of Mn-doped ZnS or the like as a light-emitting center, and the back electrode 6 is a 1st grade vapor deposited film.

Regarding such FR film EL elements, how to achieve high brightness will give them an advantage over other flat display systems such as plasma displays and liquid crystal displays, which will lead to their widespread practical use. Intensive research is being conducted based on this judgment.

On the other hand, with regard to thin-film EL elements, the aim is to improve visibility as a display panel from a different perspective than high-brightness light emission, and in this regard, a layer with high light absorption rate is placed behind the light-emitting layer. There is a method of increasing the contrast between the light-emitting part and the non-light-emitting part by providing such a light-emitting part, and this method is being put into practical use.

[Problem to be solved by the invention]

However, in general, there are very few materials that have both light absorbing properties and electrical insulating properties, and an optimal material has not yet been found in consideration of long-term stability and productivity.

In addition, a method of improving visibility is generally used for display panels by installing a polarizing filter on the front of the glass substrate to cant the reflection from outside light, but for thin-film EL elements, it is desirable to improve visibility as much as possible. This is not an optimal method because it reduces the luminescence intensity.

The present invention has been made in view of such conventional problems, and has an object to improve visibility as a display panel by canting reflection from external light without reducing the intensity of light emitted from a thin film EL element. The purpose of the present invention is to provide a thin EL element that can be used.

[Means and effects for solving the problems] In order to achieve the above object, the present invention provides a transparent glass substrate with a transparent electrode, a first insulating layer, and an EL light emitting layer.

Thin film EL formed by sequentially laminating a second insulating layer and a back electrode
In the device, a multilayer antireflection coating was provided on the opposite side of the glass substrate.

Further, in the present invention, the multilayer antireflection film is constituted by repeating a low refractive index material and a high refractive index material from the air side, and the low refractive index material is MgPz or SiO.
Either of □ is used as high refractive index material Zr0z+Taz
It is preferable to use either Os+ TiOz or CeOt or a mixture thereof.

By forming the multilayer antireflection film on the opposite side of the glass substrate in this way, it is possible to significantly reduce reflected light from outside light over the entire visible light range.

Specifically, about 4% of external light incident on the surface of a conventional glass substrate without an antireflection film is reflected.

This results in uniformly reflected light regardless of whether it is a light-emitting part or a non-light-emitting part, which causes a significant loss of visibility in an environment with strong external light. On the other hand, in the case of the present invention provided with an anti-reflection film, the reflection from the glass substrate surface is at most 1%.
As a result, visibility will be greatly improved.

(Example) (First Example) As shown in FIG. 1, ITO transparent conductive material M1000λ was formed by vapor deposition on a transparent glass substrate +7i 1, and was patterned into a stripe shape to form a transparent electrode 2.

Next, on the transparent electrode 2, a first insulating layer 3 is formed of Y! 0
After forming 33,000 layers by sputtering, EL
A light-emitting layer 4 of 5000 Å of Mn-doped ZnS was formed by electron beam evaporation, and a second insulating layer 5 of 3000 Å of hOs was formed by sputtering. After that, in order to improve the brightness of the light emitting layer, annealing was performed in vacuum for 55 minutes.
The test was carried out at 0°C for 30 minutes. Then, 12,000 layers of A were formed as the back electrode 6 by vapor deposition, and patterned into stripes so as to be orthogonal to the transparent electrode 2.

A multilayer antireflection film 7 was formed by electron beam evaporation on the opposite side of the glass substrate Fi1 to the conventional type thin film EL device thus produced. This multilayer antireflection coating is shown in Table 1.
As shown in the membrane structure, the first layer 71. Second layer 72. Third layer 73 Fourth layer 74. and a fifth layer 75.

(The following is a blank space) Table 1 The reflectance characteristics of the multilayer antireflection film 70 obtained in this manner are shown in FIG. The reflectance in the visible range (400 to 700 r+m) is at a low level of 0.5% or less, which indicates that it is sufficiently effective in improving visibility.

(Second Embodiment) As shown in FIG. 3, as a first step, a multilayer antireflection film 8 is formed by electron beam evaporation on a transparent glass substrate Fi,l.
It took shape. The film structure of this multilayer antireflection film 8 is as shown in Table 2, in which the first layer 81. 2nd layer 8
2. It has a four-layer structure including a third layer 83 and a fourth layer 84.

Table 2 The reflectance characteristics of the multilayer antireflection film 8 thus obtained are shown in FIG. It can be seen that the reflectance in the visible range (400-b) is 1% or less, which is sufficient to improve visibility.

In the multilayer antireflection film 8 here, MgF is used as a low refractive index material, and SiO□, which has higher resistance, is used in consideration of the influence of etching liquid in the subsequent process and the thermal influence of vacuum annealing.

After forming the multilayer antireflection film 8 in this manner, a 1000 ITO transparent conductive film was formed by vapor deposition on the opposite side of the transparent glass substrate 1, and was patterned into stripes to form the transparent electrode 2. Next, Y! is formed as a first wA edge layer 3 on the transparent electrode 2! After forming 033,000 layers by sputtering, ZnS50 doped with Mn was used as the EL light emitting layer 4.
00 Å was formed by electron beam evaporation, and a second insulating layer 5 of hOJOOOO was formed by sputtering.

After this, in order to improve the brightness of the light emitting layer, annealing was performed in vacuum for 5 minutes.
The test was carried out at 50°C for 30 minutes. Finally, AQ2000 was formed as a back electrode 6 by vapor deposition, and patterned into stripes perpendicular to the transparent electrode 2 to obtain a thin film EL element.

In this embodiment, the multilayer anti-reflection film 8 is formed first, but it is not limited to this, and can be arbitrarily set depending on the previous and subsequent steps.

Furthermore, in both Examples, the case was described in which Zns was used as the light emitting material and Mn was used as the dopant, but the present invention is applicable to other combinations, that is, in the former case, SrS, CaS, etc. were used, and in the latter case, Tb, Eu, Ce, etc. were used. may also be used.

〔Effect of the invention〕

As described above, according to the thin film EL element of the present invention, since the multilayer antireflection film is provided on the glass substrate surface opposite to the EL element, external light can be absorbed without reducing the intensity of light emitted from the EL element. It is possible to improve visibility as a display panel by cutting reflections from the screen. Furthermore, the multilayer antireflection film of the present invention is made of inexpensive and stable materials, and there is no fear of damaging the EL element during vapor deposition, so it has high productivity.

[Brief explanation of drawings]

FIG. 1 is a vertical cross-sectional view showing a first embodiment of the thin film EL device of the present invention, FIG. 2 is a graph showing the reflectance characteristics of the multilayer antireflection coating in the thin film EL device shown in FIG. 1, and FIG. FIG. 4 is a graph showing the reflectance characteristics of the multilayer anti-reflection coating in the thin film EL device shown in FIG. 3. FIG. 5 is a longitudinal cross section showing the conventional thin film EL device. It is a front view. 1...Glass substrate 2...Transparent electrode 3...First insulating layer 4...EL light emitting layer 5...Second insulating layer 6...Back electrode 7.8...Multilayer antireflection film

Claims (2)

[Claims] (1) Transparent electrode, first insulating layer, E on a transparent glass substrate
1. A thin film EL device comprising an L light-emitting layer, a second anti-green layer, and a back electrode stacked one after another, characterized in that a multilayer antireflection film is provided on the opposite side of the glass substrate. (2) The multilayer anti-reflection film is composed of a low refractive index material and a high refractive index material repeated from the air side, and the low refractive index material is either MgF_2 or SiO_2, and the high refractive index material is ZrO_2, Ta_2O_
5. The thin film EL device according to claim 1, characterized in that a mixture consisting of either TiO_2 or CeO_2 or a combination thereof is used.